Impaired Structural and Functional Development of Cerebellum Following Gestational Exposure of Deltamethrin in Rats: Role of Reelin

ORIGINAL RESEARCH

Impaired Structural and Functional Development of CerebellumFollowing Gestational Exposure of Deltamethrin in Rats: Roleof Reelin

Kamendra Kumar • Nisha Patro • Ishan Patro

Received: 23 October 2012 / Accepted: 27 April 2013 / Published online: 17 May 2013

� Springer Science+Business Media New York 2013

Abstract Reelin is an extracellular matrix molecule that

is involved in the normal development of the cerebellar

lamination, Bergmann glial fibres alignment, Purkinje cell

monolayer arrangement and granule cell migration. In this

study, we have examined the effects of maternal exposure

of deltamethrin (DLT), a type II pyrethroid insecticide, on

the structural and functional development of rat cerebellum

during postnatal life. DLT (0.75 mg/kg body weight,

intraperitoneally dissolved in dimethylsulphoxide) was

administered in timed pregnant rats during two different

gestational time periods, i.e. gestational days of 7–10 and

11–14, respectively. In DLT exposed rats, a significant

overexpression of reelin was observed in the cells of the

external granule cell layer (EGL) and internal granule cell

layer along with an ectopic expression of reelin in the EGL

as well as in the migrating granule cells just below the

EGL, revealing an arrest of granule cell migration in this

zone. Mis-orientation and hypertrophy of the Bergmann

glial fibres further hampered the journey of the granule

cells to their final destination. Possibly reelin overexpres-

sion also caused misalignment of the Purkinje cells and

inhibited the neurite growth leading to a significant

decrease in the spine density, main dendritic length and

width of the dendritic arbour. Thus, it is proposed that the

DLT exerts its neurotoxic effects possibly via the intra-

cellular accumulation and low release of reelin leading to

an impaired granule cell and Purkinje cell migration,

inhibition of neurite outgrowth and reduced spine density.

Such impaired cerebellar development leads to motor

coordination deficits.

Keywords Cerebellum � Deltamethrin �Granule cell migration � Prenatal toxicity �Purkinje cells � Reelin

Introduction

The vulnerability of the developing nervous system to

environmental toxicants is related mainly to the period of

exposure and is accelerated, if the exposure occurs during

the development of that organ. Neural development com-

mences in the second week of gestation in rats and con-

tinues until postnatal day 21, thus drawing many

vulnerability windows for adverse exposure. Pyrethroids

are synthetic insecticides and are being increasingly used in

veterinary, agriculture and home pest control (Amweg

et al. 2005; Wolansky et al. 2009; Soderlund 2010). Human

exposure to pyrethroids is well documented to pregnant

women, infants and children (Berkowitz et al. 2003; Heu-

dorf et al. 2004; Shafer et al. 2005). Proposed mechanism

of action of pyrethroids is the prolonged opening of the

neuronal voltage sensitive sodium channels (Vijverberg

and van den Bercken 1990) leading to altered neuronal

excitability and firing rates (Narahashi 2000).

Deltamethrin (DLT), [IUPAC name: (S)-a-cyano-3-

phenoxyphenyl (1R)-cis-3-(2,2-dibromovinyl)-2,2-dime-

thyl-cyclopropanecarboxylate)] is a widely used a-cyano

group containing type-II synthetic pyrethroid insecticide

inducing a prototype type II neurological syndrome char-

acterized by choreoathetosis and salivation (‘CS’ syn-

drome; Verschoyle and Aldridge 1980; Soderlund et al.

K. Kumar � N. Patro � I. Patro (&)

School of Studies in Neuroscience, Jiwaji University,

Gwalior 474011, Madhya Pradesh, India

e-mail: [email protected]

I. Patro

School of Studies in Zoology, Jiwaji University,

Gwalior 474011, Madhya Pradesh, India

123

Cell Mol Neurobiol (2013) 33:731–746

DOI 10.1007/s10571-013-9942-7

2002; Ray and Fry 2006; Wolansky et al. 2009). Neuronal

development involves proliferation of neuronal stem cells

followed by differentiation and migration to their exact

location in the brain. Most of them form synapses with

neighbouring cells and become functional, while others

undergo apoptosis (Gohlke et al. 2008). The proliferation,

differentiation, migration and positioning of neuronal and

glial cells are essential steps during the development of the

CNS (D’Arca et al. 2010).

Developing cerebellum provides an ideal tissue system

to study the fundamental mechanism of these processes

because of its simple structure and clear cytoarchitecture

with only a few neuron types (Sergaki et al. 2010). The

principal neurons of the cerebellum are developed from

two regions. All glutamatergic neurons, i.e. granule cells

and some neurons of deep cerebellar nuclei originate from

the rhombic lip, while the Purkinje neurons and all cere-

bellar interneurons and GABAergic neurons of the deep

cerebellar nuclei develop from the ventricular zone

(Chizhikov et al. 2006; Hevner et al. 2006). During early

postnatal life, granule cell precursors proliferate exten-

sively in the external granule cell layer (EGL) and then

migrate radially via contact guided Bergmann glial cell

processes and form the internal granule cell layer (IGL).

While the Purkinje cells move radially from the germinal

zone of the fourth ventricle towards the cerebellar cortical

surface, and then gets arranged in a single layer and sub-

sequently develop extensively arbourized dendritic tree

(Altman and Bayer 1995). Thus, the cell migration and

correct positioning of specific cell populations are the most

critical aspect of the brain development. Reelin is one such

protein that plays an important role in the architectonic

development of the CNS.

Reelin, an extracellular matrix glycoprotein is exclu-

sively expressed by all glutamatergic granule cells in the

cerebellum at all postnatal ages in rodents (Ramos-Moreno

et al. 2006; Sinagra et al. 2008). During early embryonic

life, reelin regulates the migration and formation of proper

cytoarchitecture of laminated regions of the CNS, viz.

neocortex, hippocampus and cerebellum (D’Arcangelo

et al. 1995; Tissir and Goffinet 2003; Frotscher 2010). In

addition, the role of reelin in modulation of synaptic

plasticity (Weeber et al. 2002; Beffert et al. 2005) and

dendritic growth (Matsuki et al. 2008; Niu et al. 2008)

during postnatal and adult life is also well documented.

Sinagra et al. (2008) demonstrated in a cerebellar culture

that reelin is secreted and bound by a homogenous popu-

lation of glutamatergic granule cells and most of the

components of the reelin signalling pathway, i.e., reelin

and reelin receptors, very low-density lipoprotein receptors

(VLDLR) and Apolipoprotein E receptor-2 (ApoER2) are

also expressed by cerebellar granule cells, imposing auto-

crine and/or paracrine effects on these neurons. However,

the reelin receptors are exclusively expressed by Purkinje

cells in the developing cerebellum in vivo (Perez-Garcia

et al. 2004); while only the splice variant of ApoER2 was

found to be expressed on the cells of the internal granular

layer (Hibi et al. 2009). Thus, in the cerebellum, the reelin

signalling is important for the Bergmann glial guided

migration of Purkinje and granule cells, positioning and

maturation of Purkinje cells, axon guidance, dendritic

morphology and synaptic plasticity (Yoshiki and Kusakabe

1998; Hevner 2008). However, the precise role of reelin in

postnatal and adult cerebellum needs further investigation.

We have earlier reported that DLT exposure during

postnatal period significantly affect the cerebellar lamina-

tion (Patro et al. 1997), proliferation and migration of

postnatally generated granule cells due to the delayed

appearance, disorganization and hypertrophy of Bergmann

glial fibres and astrogliosis (Patro and Patro 2005) and

results in reduced Purkinje cell dendritic arbourization and

motor activity (Patro et al. 2009). The present study was

undertaken to study the effects of DLT when exposed

during prenatal life, the time when the neural tube forma-

tion and nervous system development is initiated, and to

investigate whether such changes are worsened or remain

the same. This study also focuses whether the migration

and subsequent lamination defects are associated with

reelin expression, being it is well established role in these

events and further, if reelin could be a potential target for

DLT neurotoxicity during early brain development.

Experimental Procedures

Test Material

Technical grade DLT purchased as pure compound (98 %

purity) from Sigma was used in the present study.

Test Species and Husbandry

All the animals used for the present study were raised in the

animal house of the School of Studies in Neuroscience

according to the lay down rules of the Jiwaji University

Ethical Committee on Animal handling. All the animals

were maintained in an animal room designed to maintain

temperature at 25 ± 2 �C, relative humidity at *50 % and

a 12-h light and 12-h dark photoperiod. All animals were

fed with standard rat pellet feed and water ad libitum

throughout the study.

Breeding and Treatment

Healthy albino Wistar rats were used for breeding with two

females and one male housed in standard plastic cages

732 Cell Mol Neurobiol (2013) 33:731–746

123

(52 9 28 9 22 cm3). The estrous cycle of the female rats

was checked each morning by collecting vaginal smear on

a glass slide using a Pasteur pipette containing phosphate

buffered saline (PBS) and examined under the microscope.

Mating was confirmed by the presence of spermatozoa in

the vaginal smear. The day on which the vaginal plug was

observed was considered as the gestational day 0 (GD 0).

DLT was dissolved in dimethyl sulfoxide (DMSO, Sigma)

to provide a rapid and complete absorption, and then

injected at a dosage of 0.75 mg/kg body wt/day, i.p, to the

pregnant females during GD 7–10 (n = 6) and 11–14

(n = 6). The day the pups were born was designated as

postnatal day 0 (PND0). The animals were observed for

any clinical sign of toxicity and change in body weight as a

reaction to treatment during the entire period of treatment

till parturition.

The pups born to mothers exposed during GD 7–10 were

considered as DLT-I group, while the pups born to mothers

exposed during GD 11–14 were considered as DLT-II

group. Similar quantity of DMSO was injected to control

females (n = 6) and the pups born to these females were

used as age matched controls (Cont). All the experimental

protocols were pre-approved by the Institutional Ethical

Committee.

The pups born to both treated and control females were

anesthetized on PND’s 0, 3, 7, 12, 15, 21, 30, 60 and 90

(n = 3). The animals were perfusion-fixed (transcardially)

with 2 % paraformaldehyde prepared in 0.01 M phosphate

buffer (pH 7.4) after flushing with phosphate buffer saline

(PBS). The brains were dissected out and the cerebella

were separated and transected at the tectal level and post-

fixed in the same fixative for 24 h at 4 �C. The tissues were

then washed with the phosphate buffer and cryoprotected

in sucrose gradients (10, 20 and 30 % in phosphate buffer).

The sagittal sections (15 lm) were cut through the vermis

region of the cerebellum with a Leica cryotome (CM1900)

and collected on serially numbered gelatin-coated slides.

These slides were stored at -20 �C until immunohisto-

chemical procedures were performed.

Immunohistochemistry

Cryocut sections through the vermis region from the various

groups were selected and processed for the immunocyto-

chemical labelling with anti-GFAP and anti-reelin anti-

bodies. The tissues were air dried and rinsed in PBS to

remove cryomount. The tissues were incubated with 1 %

triton X-100 in PBS for 30 min for membrane permeabili-

zation. This was followed by three washings in PBS and

incubation with 1 % H2O2 in PBS for 20 min to block the

endogenous peroxidases. After three washings with PBS, the

sections were incubated with 1 % normal goat serum in PBS

for 60 min at room temperature in a humid chamber for

non-specific protein blocking. The sections were subse-

quently incubated overnight at 4 �C with rabbit polyclonal

antibodies, i.e. anti-GFAP (glial fibrillary acidic protein;

Dako) and Reelin (Sigma) at a titre of 1:1000 diluted with

1 % BSA in PBS. Next day, the sections were brought to

room temperature and then rinsed with three changes of PBS

for 5 min each and further incubated with secondary anti-

body, i.e. biotinylated goat anti-rabbit (diluted with 1 %

BSA in PBS, 1:100, Sigma) for 90 min. The sections were

again rinsed in PBS three times for 5 min each and incubated

with streptavidin biotin–horseradish peroxidase complex

(diluted with 1 % BSA in PBS, 1:100, Amersham) for

90 min. The sections after washing with PBS were incu-

bated with 0.025 % 3,30-diaminobenzidine tetrahydrochlo-

ride (DAB, Sigma) and 0.03 % hydrogen peroxide (BDH,

England) in PBS as substrate chromogen system for 20 min.

The sections after thorough washing in distilled water were

counterstained with 0.1 % cresyl violet acetate (Sigma

certified stain, C-5042), prepared in acetate buffer (pH 3.5)

air dried, dehydrated quickly in n-butyl alcohol, cleared in

xylene and mounted in DPX.

Image Analyses and Quantification

High quality colour images were captured using Leica

DM6000 microscope equipped with Leica DFC 420 RC

digital camera and Leica Application Suite (LAS) software.

All images were acquired at the same exposure and digital

gain settings to remove occurrence of false-immunoposi-

tivity across sections. The area fraction of reelin expression

was measured with NIH ImageJ software (http://www.rsb.

info.nih.gov/ij).

Cerebellar Layer Thickness Measurements

A separate set of pups from all the three groups were per-

fused with 10 % buffered formalin and processed for par-

affin sectioning. The cerebella were removed by transecting

at the tectal level, post-fixed overnight and then washed to

clear the formalin from the tissues. Tissue blocks were

dehydrated in an ascending series of alcohols, viz. 30, 50, 70

and 90 % by immersing the tissue blocks for 45 min in each.

The tissues were finally dehydrated by immersing in two

changes of absolute alcohol for 30 min each. The tissues

were then cleared with two changes of toluene 45 min each,

infiltrated with Paraplast (Sigma, m. p. 56–58 �C) for 4 h in

a pre-heated incubator to 58 �C. Paraffin blocks were pre-

pared and serial sections were cut at a thickness of 6 lm

using Leica RM 2135 microtome. The sections were stained

with 0.1 % cresyl violet acetate (Sigma certified stain,

C-5042), prepared in acetate buffer (pH 3.5). Cresyl violet

stained sections (through vermis region) were used for

morphometric studies, i.e. the thickness measurement of

Cell Mol Neurobiol (2013) 33:731–746 733

123

http://www.rsb.info.nih.gov/ij

http://www.rsb.info.nih.gov/ij

various cerebellar layers using an ocular micrometer scale

fitted in the eye piece of a microscope. In total, 20 readings

were taken for each layer measurement, 2 from each folium

as per the sites shown in Fig. 1a, b.

Rapid Golgi Impregnation

Rapid Golgi impregnation method (modified from Stensaas

1967 by Patro et al. 2009) was used to study the dendritic

arbourization and dendritic spine counts in normal and DLT

treated developing rat cerebella. The cerebella from both the

treated and control pups (3 pups each parameter) were dis-

sected out after ether anaesthesia and directly immersed in

Golgi fixative (potassium dichromate—5 g, chloral

hydrate—5 g, glutaraldehyde—8 ml, formaldehyde—6 ml

and dimethyl sulphoxide—10 drops; total volume was made

to 100 ml with distilled water) in dark amber bottles for

4 days. The tissues blocks were rinsed briefly with 0.75 %

aqueous solution of silver nitrate (Qualigens) to remove any

precipitates and then transferred to the fresh solution of

AgNO3 and left for 5 days in dark. Following this the tissues

were properly washed in 70 % alcohol to remove any pre-

cipitates and 100 lm thick sections were cut using a Leica

automatic vibratome (VT1000S). The sections were picked

one by one and collected in 70 % alcohol, dehydrated in

absolute alcohol, cleared in xylene and mounted in DPX. All

the sections through the vermis regions were scanned and

visualized with Leica DM6000 microscope fitted with a

digital camera.

Motor Coordination

Motor coordination was assessed using a motor driven

treadmill, Rotamex-5 from Columbus instruments. The test

was consistently performed between 9.00 am to 4.00 pm in

rat pups from the age of 21 days onwards when true

walking develops. The Rotarod consists of a semi-enclosed

chamber which contains a series of 32 infrared beams

(diameter 3 cm and width 5 cm) and a rotating rod

suspended at a height of 35 cm above the floor. The ani-

mals were acclimatized for three consecutive days before

the day of final recording at start speed of 2 rpm and a

maximum speed of 8 rpm for a total duration of 100 s. The

final recording was performed at a start speed of 2 rpm and

maximum speed of 40 rpm for a total duration of 420 s,

24 h after the last acclimatization for all animal groups.

The latency to fall was recorded automatically by the

photocells as the total length of time spent by the animal on

the rotating rod with the help of software (Rotamex 5).

Minimum of four final recordings were taken for the same

animal group and the results were averaged to obtain a

single mean value for each animal.

Statistical Analysis

All the data was expressed as mean ± standard error of

means (SEM) and were analysed by one-way analysis of

variance (ANOVA) followed by Tukey’s post hoc test for

multiple comparisons using SigmaStat version 3.5 for

Windows. Values of p B 0.05 were considered significant.

Results

No signs of toxicity were observed during the period of

treatment. There was no mortality of the treated pregnant

females or the pups born to them. No significant difference

in body weight of the DLT-treated and vehicle treated

mothers was found. However, the body weight of both the

treated group pups (DLT-I and DLT-II) remained signifi-

cantly low as compared with their age matched controls

(Table 1; Fig. 2).

Cerebellar Layer Thickness

Cerebellar cortical lamination in rodents is a completely

postnatal event and simultaneously the expansion of the

cerebellar cortex also takes place. Such processes require

I

II

III

IV

VIaV

VIb-c

VII

VIII

IX

X

a

ML

EGL

PCL

IGL

bFig. 1 Schematic

representation of sagittal section

from the vermis region of rat

cerebellum. a Rectangularboxes shown with red colour(folia VII) indicate the sites

selected from each of the X

folia. b Four different layers:

EGL external granular layer, MLmolecular layer, PCL Purkinje

cell layer, IGL internal granular

layer as delineated by arrows.

The magnification scale is

50 lm (Color figure online)


123

the migration of the prenatally born neurons to form spe-

cific layers, i.e. Purkinje cell layer and molecular layer and

also the genesis and migration of neurons forming internal

granular layer. Thus, the appearance and organization of

cortical lamination have been investigated following

maternal exposure of DLT in cresyl violet stained cere-

bellar sections through vermis region at various postnatal

ages, i.e. 0, 3, 7, 12, 15, 21, 30, 60 and 90 days (Fig. 3b, c,

e, f, h, i, k, l).

Extensive proliferation and migration of the progenitors

in the EGL during early postnatal period leads to the for-

mation of IGL. Histo-morphometric analysis depicted that

there was a gradual increase in the EGL thickness from 0 to

7 days control cerebella after which there was a gradual

decline, leading to a complete depletion of EGL in 21-day-

old pups (Fig. 3a, d, g, j). However, in both the DLT

treated groups studied, i.e. DLT-I and DLT-II, there was a

reduced and delayed growth of the EGL reaching to a peak

at P12, and then declined gradually (Table 2; Fig. 4a).

Thus, on day 7, there was a significant reduction in the

EGL thickness in both DLT-I and II groups (F2,39 = 3.8;

p B 0.05). However, a significantly thicker EGL was

recorded following DLT treatment in the DLT-I group on

days 12 and 15 (F2,39 = 4.3, 3.9, respectively; p B 0.05)

and in DLT-II group on day 12 (F2,39 = 4.2; p B 0.05). A

comparatively thicker EGL was recorded on day 21 fol-

lowing DLT exposure than 21 day controls, but was

insignificant.

Mean molecular layer (ML) thickness was observed to

be significantly reduced following DLT exposure in both

DLT-I and II groups at P12 (F2,39 = 3.5, 3.6, respectively;

p B 0.05) and DLT-I at P15 (F2,39 = 3.8; p B 0.05).

However, till P60, the ML thickness remained low in

treated group cerebella and was regained to normal values

by P90 only (Table 2; Fig. 4b).

During normal cerebellar development, Purkinje cell

monolayer arrangement is achieved by P7 and after that

there is an expansion of the layer because of the growth of

the Purkinje cell till 21 days. The Purkinje cell layer (PCL)

remained significantly thicker following DLT exposure and

in both the treated pups, i.e. DLT-I and DLT-II, there was a

significant increase in PCL thickness on P12 (F2,39 = 10.3,

4.4, respectively; p B 0.01, 0.05) and P15 (F2,39 = 9.6,

4.1, respectively; p B 0.01, 0.05). However, the PCL

remained thicker throughout the entire period of study till

P90, although, statistically insignificant at p = 0.05

(Table 2; Fig. 4c).

The mean thickness of the IGL was also found to be

reduced in the DLT-treated groups as compared with their

respective controls. The difference was found to be sig-

nificant on days 12 and 15 (F2,39 = 4.5, 4.2, respectively;

p B 0.01, 0.05) in DLT-I group and on day 12

(F2,39 = 4.8; p B 0.05) in DLT-II group. However, the

IGL thickness remained low throughout the period of

study, and did not reach to the normal control values until

maturity, i.e. P90 (Table 2; Fig. 4d).

Reelin Immunohistochemistry

Reelin is a large extracellular glycoprotein of 420–

450 kDa. In developing cerebellum, it is secreted by

Table 1 The body weight of the developing rat pups (g) following maternal exposure to deltamethrin during gestation

Groups 0 day 3 days 7 days 12 days 15 days 21 days 30 days 90 days

Body weight during postnatal life

Controla 9.7 ± 0.5 13.0 ± 0.4 19.3 ± 0.7 27.5 ± 0.4 32.7 ± 0.7 41.2 ± 1.1 48.9 ± 1.7 202 ± 1.2

DLT-Ib 7.5 ± 0.5 8.2 ± 0.5* 12.7 ± 0.5* 17.2 ± 0.9* 21.2 ± 0.6* 24.4 ± 0.8* 33.5 ± 1.1* 166 ± 3**

DLT-IIc 7.1 ± 0.4 9.9 ± 0.6* 14.7 ± 0.6* 19.5 ± 1.1* 23.3 ± 0.8* 25.4 ± 1.0* 34.8 ± 1.0* 173 ± 2.9**

Values are expressed as mean ± SEM (n = 6)

* p \ 0.05 for DLT-I and DLT-II versus control; ** p \ 0.01 for DLT-I and DLT-II versus control (one-way ANOVA followed by post hoc

Tukey’s test for multiple comparison among groups)a Vehicle treated (equal volume of DMSO only) groupb DLT dissolved in DMSO at a dose of 0.75 mg/kg body weight at GD 7–10c DLT dissolved in DMSO at a dose of 0.75 mg/kg body weight at GD 11–14

0

50

100

150

200

250

0d 3d 7d 12d 15d 21d 30d 90d

Bo

dy

wei

gh

t (g

)

Postnatal age (days)

Cont

DLT-I

DLT-II

* * * * ** ** * *

****

**

Fig. 2 Graph represents the body weight presented as the mean ±

SEM of the 6 pups/parameter/time point in control (Cont), DLT-I and

DLT-II groups. *DLT-I and DLT-II versus cont; p \ 0.05, **DLT-I

and DLT-II versus cont; p \ 0.01


123

glutamatergic granule cells and plays a key role in

instructing neurons to achieve normal differentiation when

they reach their final destination at the end of the radial

migration. Reelin immunohistochemistry revealed its spe-

cific expression by the cells of EGL and the granule cells of

the IGL (Fig. 5a, d, g, j, n, q). Quantification of the reelin

expression in the control cerebella depicted an intense

expression on 3rd postnatal day, a subsequent down regu-

lation till 12th day, and then a steep decline with a

significant down regulation of expression by postnatal day

21 (Table 3; Fig. 6). Following DLT exposure, a signifi-

cantly enhanced expression of reelin was recorded in both

the cells of the EGL and IGL. In the DLT-I group, the

reelin expression was significantly high at all the age-

points studied, i.e. 0, 3, 7, 12 and 15 (Fig. 5b, e, h, k, l, o, r),

while in DLT-II group as well the reelin was over

expressed till postnatal day 21 (Fig. 5c, f, i, m, p, s), but

the significant difference was found only on 0, 7 and

Cont DLT-IIDLT-I

12d

EGL

ML

PCL

IGL

WM

a b c

15d

d e f

21d

g h i

90d

j k l

Fig. 3 Photomicrographs showing cresyl violet stained sagittal

sections from the cerebellar vermal region of control (a, d, g, j),DLT-I (b, e, h, k) and DLT-II (c, f, i, l) group pups at various age

points. Arrows (black) represents the granule cells in the EGL,

arrowheads (red) shows arrested granule cell migration and thick fatarrows (red) represents distorted Purkinje cell monolayer arrange-

ment and clustering. WM white matter. The scale bar is 50 lm (Color

figure online)


123

15 days postnatally (Table 3; Fig. 6). On postnatal day 15

in DLT-I group cerebella, an ectopic expression of reelin

was observed in the EGL as well as in the migrating

granule cells just below the EGL, revealing an arrest of

granule cell migration in this zone (Fig. 5h, k, l). However,

by day 21, when most of the granule cell migration is over,

reelin expression still remain statistically different in both

DLT-I and DLT-II group cerebella as compared with their

age-matched controls, but values were significant only in

DLT-II group (Table 3; Fig. 6).

GFAP Immunohistochemistry

Bergmann glia, the unipolar cerebellar astrocytes are

involved in the migration of granule cells in the developing

cerebellum during early postnatal life. Similar to astro-

cytes, the GFAP antibody also acts as a specific marker for

Bergmann glia as well. Anti-GFAP immunolabeling and

co-staining with cresyl violet enabled us to study the

migration of granule cells from the EGL, the site of

their origin to the IGL where they are finally going to

reside in the adult cerebellum. During normal cerebellar

development, the granule cell proliferation and migration

occurs during PND0-21. The Bergmann glial fibres appears

immediately after birth and run straight between the ven-

tricular and the pial surface with their cell bodies lying at

the base of the Purkinje cells and the processes anchored at

the pial surface, leading to the normal migration of the

granule cells. The migration was observed to be at peak

from postnatal days of 7–15. However, the migration still

continued till PND21, when the EGL was completely

seized (Fig. 3h, i). In the DLT treated cerebella, the GFAP

immunolabelled Bergmann glial fibres were disorganised

and hypertrophied (Fig. 7b, c, e, f, h, i, k, l) as compared

with their thin and straight morphology in the controls

(Fig. 7a, d, g, j). At the same time, these fibres were more

strongly labelled with GFAP. Such disorganised morphol-

ogy and mal-orientation of Bergmann glial fibres were

more prominent in DLT-I group (Fig. 7b, e, h, k) as com-

pared with the DLT-II group preparations (Fig. 7c, f, i, l).

Even there was a clear cut indication of delayed migration as

evident from peak migration on 12th and 15th postnatal days

(Fig. 7d–i) and a persistence of EGL till PND21 (Figs. 3h, i,

and 7j, k, l). A comparatively more number of astrocytes with

Table 2 Thickness of various cerebellar cortical layers during postnatal development following maternal exposure to deltamethrin during

gestation

Groups 0 day 3 days 7 days 12 days 15 days 21 days 30 days

EGL thickness (lm)

Conta 17 ± 2.5 30 ± 0.9 38 ± 1.2 27 ± 1.4 15 ± 1.0 1.8 ± 0.8 1.4 ± 0.7

DLT-Ib 13 ± 2.4 25 ± 1.3 31 ± 1.9* 36 ± 1.9* 24 ± 1.5* 2.3 ± 0.4 1.5 ± 0.4

DLT-IIc 15 ± 1.5 27 ± 1.1 30 ± 1.8* 35 ± 1.3* 21 ± 1.7 2.5 ± 0.5 1.5 ± 0.4

Groups 12 days 15 days 21 days 30 days 60 days 90 days

ML thickness (lm)

Conta 86 ± 3.2 152 ± 7.3 170 ± 3 187 ± 8.1 198 ± 7.2 181 ± 14

DLT-Ib 41 ± 2.9* 105 ± 6.2* 146 ± 7.7 180 ± 14.8 174 ± 9.4 182 ± 18.5

DLT-IIc 53 ± 3.1* 122 ± 7.3 150 ± 3 173 ± 12.6 184 ± 13.4 181 ± 15.9

PCL thickness (lm)

Conta 20 ± 0.6 21 ± 1.2 23 ± 0.7 23 ± 1.3 22 ± 0.5 21 ± 0.7

DLT-Ib 26 ± 0.7** 27 ± 0.8** 27 ± 0.4 25 ± 0.5 25 ± 0.6 23 ± 0.5

DLT-IIc 24 ± 1.1* 25 ± 0.7* 24 ± 1.1 24 ± 1.2 24 ± 0.4 23 ± 0.6

IGL thickness (lm)

Conta 97 ± 11.5 122 ± 11.5 132 ± 9.2 135 ± 10.6 140 ± 13 150 ± 21.3

DLT-Ib 67 ± 11.7* 83 ± 9.1* 120 ± 10.4 125 ± 9.2 130 ± 11.5 145 ± 17.3

DLT-IIc 70 ± 12.2* 102 ± 8.2 117 ± 11.3 130 ± 11.4 135 ± 15 146 ± 19.5

Values are expressed as mean ± SEM (30 readings from 3 pups/parameter/time point)

EGL external granular layer, ML molecular layer, PCL Purkinje cell layer, IGL internal granular layer




123

activated morphology were also observed in the granule cell

layer of both the treated groups as compared with their age

matched controls (Fig. 7b, c, e, f, h, i, k, l). Upregulation of

GFAP both in the Bergmann glial fibres and the astrocytes

were indicating the sign of astrogliosis following DLT-

exposure.

Phenotypic Maturation and Dendritogenesis of Purkinje

Neurons

Purkinje cell morphogenesis and dendritogenesis in the

developing cerebella of rats following maternal exposure

of DLT was studied by using rapid Golgi technique. Pre-

natally formed Purkinje neurons undergo a series of mor-

phogenetic changes during early postnatal life to become

mature. Such changes include their dispersion and align-

ment in a monolayer, appearance of a transient apical

growth cone and subsequent appearance of apical dendrites

invading the developing molecular layer. The primary

dendrite arbourizes and forms secondary and tertiary

branches with subsequent formation of spines that prolif-

erate in great numbers. Such changes were clearly seen in

the developing cerebella of control rat pups during post-

natal life, PND7 to PND21 days. The Purkinje cells were

aligned in a monolayer by the end of the 1st week and

started extending their primary dendrites in the ML. By

postnatal day 12, a well developed dendritic arbour with

primary, secondary and tertiary branches with spines were

observed (Fig. 8a). This dendritic arbour was further

elaborated to take up a rectangular area within the

molecular layer (Fig. 8d, g, j).

However, the Purkinje cells in the cerebella of rat pups

born to mothers exposed to DLT during two different

gestational periods possessed marked somal and dendritic

abnormalities. In both the DLT-treated groups, an incon-

sistent and non-uniform pattern of abnormal Purkinje cell

arrangement was observed in either or both ML and IGL.

At sites, the cells were present in clusters with their cell

soma closely adhering each other. Such clustering was

more often in 12- and 15-day-old treated preparations

(Fig. 8b) and were not at all seen once the rat pups became

mature, i.e. by PND30. Purkinje cells possessing more than

one somal process (extrasomal processes) with secondary

and tertiary dendrite like processes was a common occur-

rence (Fig. 8b, c, f). In addition, the Purkinje cell somas

with their dendrites lying parallel to the pial surface or

drooping towards the IGL (Fig. 8b, c, e, f, h) was also a

frequent feature following DLT exposure in contrast to the

straight Purkinje cell arbour, perpendicular to the pial

surface in age matched controls (Fig. 8a, d, g, j).

A very prominent impact of DLT exposure was

observed in the Purkinje cells dendritic arbourization. In

0

9

18

27

36

45

0d 3d 7d 12d 15d 21d 30d

EG

L T

hic

knes

s (µ

m)


Cont

DLT-I

DLT-II

*

**

**

a

0

50

100

150

200

250

12d 15d 21d 30d 60d 90d

ML

Th

ickn

ess

(µm

)


Cont

DLT-I

DLT-II**

*

b

0

5

10

15

20

25

30

12d 15d 21d 30d 60d 90d

PC

L T

hic

knes

s (µ

m)


Cont

DLT-I

DLT-II

** **

**

c

0

30

60

90

120

150

180

12d 15d 21d 30d 60d 90dIG

L T

hic

knes

s (µ

m)


Cont

DLT-I

DLT-II

**

*

d

Fig. 4 Graph represents the thickness (lm) of various cerebellar

cortical layers. Data is presented as the mean ± SEM of the 30

readings from 3 pups/parameter/time point in control, DLT-I and

DLT-II groups. *DLT-I and DLT-II versus cont, p \ 0.05; **DLT-I

and DLT-II versus cont, p \ 0.01


123

15d

j k l m

N O P

21d

q r s

h

3d

a b c

d e f

g i

EGL ML

PCL

IGL

n o p

Cont DLT-IIDLT-I

Fig. 5 Photomicrographs showing reelin immunolabelling in the

cerebellum (vermis) of control, DLT-I and DLT-II group pups

(n = 3). Arrows indicates the reelin positive cells in the EGL (black

arrows) and granule cells in ML and IGL (red arrows). The scale baris 50 lm (Color figure online)


123

both the treated groups, there was a clear cut reduction in

the total rectangular area occupied by the dendritic arbour

in the molecular layer as compared with their age-matched

controls. This was clearly evident from the morphometric

studies for the measurement of length and width of the

dendritic arbour. A significant (p \ 0.01; 0.05) reduction in

both the length and width was found at all time points

studied in both the treated groups as compared with their

age-matched control (Table 4; Fig. 9b, c). In controls, the

Purkinje cells presented normal morphology and extensive

dendritic arbourization with primary, secondary and ter-

tiary branches with spiny branchlets extending into the

molecular layer up to the pial surface (Fig. 8a, d, g, j).

However, in both the treated groups the primary and sec-

ondary dendrites were quite prevalent, but tertiary branches

and spiny branches were remarkably reduced or absent.

Many Purkinje cells in all the parameters of treated

groups had long main dendrites without branching, in many

cases acquiring ‘S’ form rather than straight perpendicular

to the pial surface (Fig. 8h). Even the primary and

secondary dendrites were thick and stumpy and at times not

extending up to the pial surface (Fig. 8b, c, k) rather

swaying away from the pial surface (Fig. 8b, c, h). Such

changes were consistently seen throughout the period of

study, i.e. from PND12 to PND90 (Fig. 8b, c, e, f, h, i, k, l)

when the animals attain reproductive maturity.

Dendritic spine density was another feature that was

significantly affected in pups born to DLT exposed moth-

ers. In controls there was a gradual and linear increase in

the spine density with increasing age, i.e. in PND12 to

PND90 from 16.7 ± 0.5 to 22.3 ± 0.55. However, in both

the treated groups the increase in the number of spines was

much less and the spine density was significantly reduced

at all postnatal days studied. The data has been shown in

Table 4 and Fig. 9a.

Motor Coordination

Impact of maternal DLT exposure on the acquisition of

motor coordination was assessed as the total length of time

spent by the animals on the rotating rod of the rotarod. In

the accelerating rotarod test from 2 rpm to 40 rpm for

420 s, the latency to fall was lying between 27 ± 2.3 and

37.3 ± 2.5 s in PND21 to PND90 control rat pups,

respectively. However, the animals from both the treated

groups fell faster from the rotating rotarod leading to sig-

nificantly lower latency to fall at all the time points

(p \ 0.01; 0.05) and is expressed in Table 5 and Fig. 10.

Discussion

Developing cerebellum in neonates is a useful system to

study the basic mechanisms that regulates proliferation,

migration and differentiation of neuronal precursors

required for the histogenesis and the formation of proper

cytoarchitecture. The cerebellar development is complete

Table 3 Area fraction of reelin immunoreactivity in the cerebellar cortex during early postnatal life following maternal exposure to deltamethrin

during gestation

Group 0 day 3 days 7 days 12 days 15 days 21 days

Area fraction (%)

Conta 27 ± 11.02 29 ± 0.5 27 ± 1.04 25 ± 2.5 14 ± 0.65 3.9 ± 0.6

DLT-Ib 33 ± 0.5* 39 ± 0.7**, ## 31.8 ± 0.3* 36 ± 2.6**, # 27 ± 2.5** 5.9 ± 0.67

DLT-IIc 31 ± 0.34* 32 ± 0.6 37 ± 0.5**, # 29 ± 2.5 28 ± 2.9** 7.7 ± 0.5*

Values are expressed as mean ± SEM (30 readings from 3 pups/parameter/time point)

* p \ 0.05 for DLT-I and DLT-II versus control; ** p \ 0.01 for DLT-I and DLT-II versus control; # p \ 0.05 for DLT-I versus DLT-II;## p \ 0.05 for DLT-I versus DLT-II (one-way ANOVA followed by post hoc Tukey’s test for multiple comparison among groups)a Vehicle treated (equal volume of DMSO only) groupb DLT dissolved in DMSO at a dose of 0.75 mg/kg body weight at GD 7–10c DLT dissolved in DMSO at a dose of 0.75 mg/kg body weight at GD 11–14

0

5

10

15

20

25

30

35

40

45

0d 3d 7d 12d 15d 21d

Are

a fr

acti

on

(%

)


ContDLT-IDLT-II

**

** ** **

****

## #

*

#

*

Fig. 6 Area fraction of reelin immunoreactivity presented as the

mean ± SEM control, DLT-I and DLT-II groups. Control, DLT-I and

DLT-II groups (n = 3) at various postnatal ages. *DLT-I and DLT-II

versus cont, p \ 0.05, **DLT-I and DLT-II versus cont, P \ 0.01,#DLT-I versus DLT-II, p \ 0.05, ##DLT-I versus DLT-II, p \ 0.01


123

by the third postnatal week in rodents. Granule cells, the

major excitatory neuron population of cerebellum are

generated postnatally in the EGL and migrate through

contact-guided migration along the Bergmann glial pro-

cesses (Rakic 1977; Hatten et al. 1997; Patro and Patro

2005). The Purkinje neurons generated prenatally from the

germinal zone of the fourth ventricle migrate towards the

cerebellar surface and settle into a monolayer. Reelin, a

large secreted protein is crucial for such migration and

laminar arrangement of neurons in the neocortex, hippo-

campus, cerebellum and spinal cord (D’Arcangelo et al.

1995; Ogawa et al. 1995; Tissir and Goffinet 2003; Sinagra

et al. 2008; Forster et al. 2010). The functions of reelin are

mediated through its receptors which trigger a complex

signalling cascade (Herz and Chen 2006).

In the present study, a significant overexpression of re-

elin was observed following prenatal exposure to DLT both

in the cells of EGL and IGL at all time points studied. In

addition, an ectopic expression of reelin was also observed

in the EGL as well as in the migrating granule cells just

below the EGL, indicating an arrest of granule cell

migration in this zone. Such reelin overexpression fol-

lowing DLT exposure suggests its intracellular accumula-

tion, either due to the failure of its release or blockade of its

Cont DLT-IIDLT-I

7d

12d

15d

21d

a b c

d e f

g h i

j k l

MLPCL

IGL

Fig. 7 Photomicrographs showing GFAP immunohistochemistry on

sagittal sections from the cerebellar vermal region of control, DLT-I

and DLT-II group (n = 3). Arrows (black) represents the cresyl violet

stained granule cells in EGL, arrowheads (red) represents GFAP

positive Bergmann glial fibres and arrows (red) represents GFAP

positive astrocytes in IGL. The scale bar is 50 lm (Color figure online)


123

secretion from the granule cells. Such intracellular accu-

mulation accounts for an increase in its density and strong

immunopositivity near the EGL. Reelin expressing cere-

bellar granule cells both synthesize and secrete reelin,

blockade of its secretion or release interferes with the reelin

signalling and is thus directly responsible for the abnormal

and mis-oriented migration of granule cells. If such chan-

ges are dependent or secondary, the neurotoxic effects

imposed by DLT through voltage sensitive sodium chan-

nels need to be studied. In the absence of reelin signalling,

the migrating granule cells aggregate below the EGL due to

the arrest of their migration. Such cellular traffic jam was

also reported in Dab 1 mutants (Olson et al. 2006) and

reeler mouse (Pinto-Lord et al. 1982). Olson et al. (2006)

believed that the cells superficial to migrating neurons

obstruct further migration and thus result in the formation

12d

Cont DLT-IIDLT-I

21d

30d

90d

ba c

d fe

g ih

j lk

Fig. 8 Photomicrographs showing rapid Golgi stained sagittal sections from the cerebellar vermal region of control, DLT-I and DLT-II group

(n = 3). Arrows indicates the Golgi stained Purkinje neurons with distorted morphology. The scale bar is 50 lm


123

of the ectopic zone. Similar results has also been recorded

with the transgenic mouse model where the reelin over-

expression in adult brain was found to alter the pattern of

neuronal migration of newly generated neurons in the SVZ

leading to the formation of an ectopic zone during adult

neurogenesis. A reduced number of granule cells in the

granule cell layer were also observed as a result of the

arrest of migration of the newly formed neurons (Pujadas

et al. 2010). In an experiment on cultured hippocampal

cells, blockage of reelin secretory pathway with brefeldin

A (BFA) perturbs the homeostasis of NMDA receptors

(NMDARs, Campo et al. 2009) as a result of the lack of

continuous secretion. Such defects are believed to play a

major role in the development of neuropsychiatric disor-

ders such as schizophrenia (Mohn et al. 1999; Guidotti

et al. 2000).

Our results further find support from a more recent study

of Duveau et al. (2011) where they reported in a model of

temporal lobe epilepsy induced by intra-hippocampal kai-

nic acid injection that the strong reelin immunopositivity of

the Cajal-Retzius cells was due to intracellular accumula-

tion resembling the morphology of these cells in reelin

Orleans (relnorl/orl) mice, which express the secretion-

deficient 310-kDa reelin fragment. Such intracellular

accumulation of reelin was explained due to the absence of

signal peptide for secretion located at the C-terminus (Rice

and Curran 2001).

Bergmann glial fibres act as specific guide for the cer-

ebellar granule cell migration were also found to be mis-

aligned, hypertrophied and strongly GFAP labelled,

indicating astrogliosis following DLT exposure during

prenatal life. Such defects in Bergmann glial processes

were also reported to affect granule cell migration conse-

quent upon DLT exposure during early postnatal life (Patro

and Patro 2005). Radial glial cells have also been reported

to be specifically vulnerable to a variety of prenatal insults,

viz. alcohol (Miller and Robertson 1993), methylmercury

(Choi et al. 1996), ionising radiation (Roper et al. 1997)

and methylazoxymethanol (MAM, Spalice et al. 2009).

Reelin secretion defects observed in this investigation

following DLT exposure could also be correlated with

Bergmann glia mis-orientation and hypertrophy as reelin

has been reported to promote extension and maintenance of

radial glial scaffold in the hippocampus of reeler mutant

mouse when exposed to reelin exogenously (Frotscher

et al. 2003). Lack of reelin has been found to result in

aberrant migration of cortical neuron and misalignment

radial glial fibres (Hunter-Schaedle 1997; Hartfuss et al.

2003). Any disruption in radial glial scaffold causes

migrational disorders leading to mental retardation, epi-

lepsy, schizophrenia, autism, etc. (Pang et al. 2008; Spalice

et al. 2009; Verrotti et al. 2009).

An ectopic Purkinje cell arrangement with marked so-

mal and dendritic abnormalities in the DLT treated cere-

bella of both the treated groups were also a prominent

observation of this study. Purkinje cell possessing extra-

somal processes, drooping dendritic tree, a significantly

reduced and stunted dendritic arbour and spine density as

seen through Golgi studies, was a common occurrence.

Reelin being a major component mediating the migration

Table 4 Purkinje cell spine density, and width and length of the dendritic arbour (lm) in the cerebellum of developing rats following maternal

exposure to deltamethrin during gestation

Groups 12 days 15 days 21 days 30 days 60 days 90 days

Spine density/10 lm of dendrite

Conta 16.7 ± 0.5 18.7 ± 0.9 20.7 ± 0.4 20.5 ± 0.6 21.7 ± 0.6 22.3 ± 0.5

DLT-Ib 11.9 ± 1.2* 14.8 ± 0.6* 17.5 ± 1.2* 17.7 ± 1.1* 18.2 ± 0.5* 20.1 ± 0.6*

DLT-IIc 14.1 ± 0.5* 15 ± 0.6* 19 ± 0.9* 17 ± 1.3* 19.6 ± 0.9 20.2 ± 0.7*

Width of the dendritic arbour (lm)

Conta 85.5 ± 0.5 106 ± 1.5 135.2 ± 3.3 131.8 ± 3.5 134. ± 2.3 146.5 ± 2.3

DLT-Ib 52.7 ± 3.4** 70 ± 4.5** 99.2 ± 3.6** 97.7 ± 4.8* 98.3 ± 4.3** 97.5 ± 3.6**

DLT-IIc 61 ± 3.6** 79.5 ± 4.4** 104 ± 3.6** 102.7 ± 5.7* 91.2 ± 4.8** 97.5 ± 2.9**

Length of the dendritic arbour (lm)

Conta 101.5 ± 1.6 128 ± 2.2 163 ± 2.9 171.2 ± 2.8 173.1. ± 3.5 170 ± 2.6

DLT-Ib 70 ± 3.5** 91.5 ± 3.5** 116.2 ± 4.8** 141.4 ± 2.9** 151 ± 2.9* 141.9 ± 4.5**

DLT-IIc 75.7 ± 4** 102 ± 5.1** 125.7 ± 4.6** 131.8 ± 4.3** 147.6 ± 4.8* 130.6 ± 5.3**

Values are expressed as mean ± SEM (from 3 pups/parameter/time point)




123

and positioning of the Purkinje cell, defective reelin sig-

nalling is possibly responsible for their ectopic arrange-

ment and much affected dendritogenesis and spine density.

Reelin is known to exert its function by binding to and

activating its very low-density lipoprotein receptors

(VLDLR) and ApoER2 (Trommsdorff et al. 1999; Herz

and Chen 2006) on the surface of the Purkinje cells. The

abnormalities associated with the dendritic arbourization

and spine formation following DLT exposure could be a

secondary defect resulting from the misalignment and

ectopic arrangement of the Purkinje cells. Dendritic

arbours are also substantially stunted and disorganised in

reeler mice (Tabata and Nakajima 2002; Niu et al. 2004),

scrambler mutant mice (Rice and Curran 1999), Cend1

knock-out mice (Sergaki et al. 2010) and Dab-1 suppressed

cortical neurons (Olson et al. 2006), many of them directly

or indirectly influencing the reelin pathway.

Impaired cerebellar lamination and morphological

defects in Purkinje neurons are directly associated with the

functional impairment related to motor coordination. Our

findings with rotarod test suggests that the latency to fall of

the rotating rod was significantly less in the DLT treated

animals even at adulthood clearly, suggesting that the

structural abnormalities due to defective reelin expression

possibly directly affects the cerebellar functional output.

However, the role of reelin in developmental neurotoxicity

0

20

40

60

80

100

120

140

160

12d 15d 21d 30d 60d 90d

Wid

th o

f th

e d

end

riti

c ar

bo

r (µ

m)


Cont

DLT-I

DLT-II

****

********

**

** ** ***

*

b

0

40

80

120

160

200

12d 15d 21d 30d 60d 90dLen

gth

of

den

dri

tic

arb

or

(µm

)


Cont

DLT-I

DLT-II

*

*

**

** **

****

****

**

**

**

c

0

5

10

15

20

25

12d 15d 21d 30d 60d 90dSp

ine

den

sity

/10µ

m o

f d

end

rite


Cont

DLT-I

DLT-II

** * **

***

*

**

a

Fig. 9 Graph represents the measurement (mean ± SEM) of the

Spine density (a), width of the dendritic arbour (b) and length of the

dendritic arbour (c) of Purkinje neurons in control, DLT-I and DLT-II

group animals (n = 3). *DLT-I and DLT-II versus cont, p \ 0.05,

**DLT-I and DLT-II versus cont, p \ 0.01

Table 5 Motor coordination impairment in the developing rat pups

following maternal exposure to deltamethrin during gestation

Groups 21 days 30 days 60 days 90 days

Latency to fall (s) from the accelerating rotarod

Conta 27.2 ± 2.3 34.8 ± 1.9 37.0 ± 2.1 37.3 ± 2.5

DLT-Ib 12.1 ± 1.9** 23.0 ± 2.3** 16.1 ± 1.3** 21.0 ± 1.2**

DLT-IIc

16.4 ± 1.4* 24.9 ± 1.9 20.8 ± 1.6* 17.1 ± 1.3**

Values are expressed as mean ± SEM (n = 6)

* p \ 0.05 for DLT-I and DLT-II versus control; ** p \ 0.01 for DLT-Iand DLT-II versus control (one-way ANOVA followed by post hocTukey’s test for multiple comparison among groups)a Vehicle treated (equal volume of DMSO only) groupb DLT dissolved in DMSO at a dose of 0.75 mg/kg body weight at GD7–10c DLT dissolved in DMSO at a dose of 0.75 mg/kg body weight at GD11–14

0

9

18

27

36

45

21d 30d 60d 90d

Lat

ency

to

dro

p (

sec)


Cont

DLT-I

DLT-II

*

**

**** **

***

Fig. 10 Rotarod performance of the control, DLT-I and DLT-II

group animals (n = 6), presented as the mean ± SEM of the time

spent on the rotating rod. *DLT-I and DLT-II versus cont, p \ 0.05,

**DLT-I and DLT-II versus cont, p \ 0.01


123

of environmental agents has not been explored till date,

while its importance in neurodegeneration and b-amyloid

induced synaptic depression was reported in Alzheimer’s

disease (Beffert et al. 2006; Botella-Lopez et al. 2006;

Durakoglugil et al. 2009; Knuesel et al. 2009), suggesting

its role in the pathogenesis of neurological diseases. Thus,

it is proposed that DLT at a dose as low as 1/200th of the

LD50 which could be close to the environmental exposure

to the pregnant women due to their occupational or resi-

dential proximity to such insecticide treated farmlands

causes the defects in neuronal migration and subsequent

lamina formation through reelin by its overexpression and/

or blockade of its release and signalling.

Acknowledgments Financial support from the Indian Council of

Medical Research, New Delhi is thankfully acknowledged. Kamendra

Kumar is a Department of Biotechnology (DBT) Senior Research

Fellow. Facilities developed through the DBT-Human Resource

Development and Bioinformatics Infrastructural facility through

Department of Biotechnology Grants used in this study are thankfully

acknowledged.

Conflict of interest Authors have no conflict of interest.

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Impaired Structural and Functional Development of Cerebellum Following Gestational Exposure of Deltamethrin in Rats: Role of Reelin