Neurosecretory cells in the optic lobes of the brain and activity rhythms in Lycosa tarentula (Araneae: Lycosidae)

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Neurosecretory cells in the optic lobesof the brain and activity rhythms in Lycosa tarentula (Araneae: Lycosidae)Jacqueline Kovoor a , Arturo Muñoz-cuevas a & Joaquin Ortega-Escobar ba Zoologie-Arthropodes , Museum National d'Histoire Naturelle , 61rue de Buffon, 75231, Paris, Franceb Departamento de Psicología Biológica , Universidad Autónomade Madrid , 28049, Madrid, EspañaPublished online: 03 Feb 2007.

To cite this article: Jacqueline Kovoor , Arturo Muñoz-cuevas & Joaquin Ortega-Escobar (2005)Neurosecretory cells in the optic lobes of the brain and activity rhythms in Lycosa tarentula (Araneae: Lycosidae), Biological Rhythm Research, 36:3, 237-253, DOI: 10.1080/09291010500051659

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Neurosecretory cells in the optic lobes of the brain andactivity rhythms in Lycosa tarentula (Araneae: Lycosidae)

JACQUELINE KOVOOR1, ARTURO MUNOZ-CUEVAS1,

& JOAQUIN ORTEGA-ESCOBAR2

1Museum National d’Histoire Naturelle, Zoologie-Arthropodes, 61 rue de Buffon, 75231 Paris, France,

and 2Departamento de Psicologıa Biologica, Universidad Autonoma de Madrid, 28049-Madrid, Espana

AbstractSeveral paired groups of neurosecretory cells (NS) were identified in the dorsal cortical neurons of theoptic lobes of the brain of Lycosa tarentula (Araneae). Two large bottle-shaped cells (NS A1, A2) and acluster of ca. 20 smaller cells (NS B) were found between the lamina and medulla of the anterior medianeyes (AM). The forward oriented bundles of NS B axons run alongside large fibres linked to the synapticzones of the indirect eyes. In front of the arcuate body, an islet of about 10 fusiform cells (NS C1) sendsshort axons close to the internal cortical border. Other large cells (NS C2, C3) are found from themedulla of the AM to the anterior border of the central body. Their long axons end deeply in the brainneuropil. NS B and C1 function synchronously. The secretory cycles of NS A1 and A2 seem to be inopposition. The activity of these three types of NS depends on the phase of the day. Anatomicalrelationships of NS A, B and C1 with visual afferent/efferent fibres via synaptic buttons indicate a role ofthese cells in the modulation of circadian rhythms of visual and locomotor activity. On the other hand,NS C2 and C3, the functioning of which is not synchronous, might be involved in the modulation orcontrol of the elementary movements of L. tarentula when active or at rest.

Keywords: neurosecretion, optic lobes of the brain, histology, biological rhythms, Araneae, spiders

Introduction

According to recent studies, spontaneous locomotor activity and cyclic structural modifica-

tions of retinal rhabdoms of the chelicerate Lycosa tarentula (Araneae: Lycosidae) show a

circadian rhythmicity (Kovoor et al. 1995, 1999). It is also known that neurotransmitters and

neuromodulators such as serotonin, octopamine, other catecholamines and melatonin are

detectable in the brain of arachnids, and especially spiders (Fowler & Goodnight 1974; Meyer

et al. 1984; Carricaburu & Munoz-Cuevas 1987, 1998; Munoz-Cuevas & Carricaburu 1990,

2000; Schmid & Duncker 1993; Schmid et al. 1990; Seyfarth et al. 1990, 1993). The sites of

the secretion of neuromodulators or neurotransmitters in the brain cells have nevertheless

been rarely localized. A group of neurosecretory cells located in the suboesophageal ganglion,

close to the circum-oesophageal connectives, was indeed interpreted as the circadian clock of

Correspondence: J. Ortega-Escobar, Departamento de Psicologıa Biologica, Universidad Autonoma de Madrid, 28049-Madrid,

Spain. Tel. + 34-91-4975188. Fax: + 34-91-4975215. E-mail: [email protected]

Biological Rhythm Research

July 2005; 36(3): 237 – 253

ISSN 0929-1016 print/ISSN 1744-4179 online # 2005 Taylor & Francis Group Ltd

DOI: 10.1080/09291010500051659

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visual sensitivity in a scorpion, Androctonus australis (Buthidae) (Fleissner & Schliwa 1977;

Fleissner & Heinrichs 1982; Fleissner & Fleissner 1985). Obviously similar cells were

described in Limulus polyphemus (Xiphosures) by Fahrenbach (1981) and Barlow et al.

(1989).

The anatomy and secretory cycle of several groups of neurosecretory cells found in the

optic lobes of L. tarentula are described below. The involvement of these cells in the

modulation or control of visual as well as spontaneous locomotor activity rhythms is suggested

and discussed.

Material and methods

L. tarentula was reared by J. O.-E. in Madrid to provide a sufficient number of adult females in

good condition.

Illumination rhythm

Selected specimens had been submitted to illumination cycles of 12 hours (L 8.00 h –D

20.00 h) at 1900 lx. The spontaneous locomotor activity rhythm of these animals were

registered during 15 days before they were treated for histological study. All treated animals

showed a ‘‘normal’’ locomotor activity rhythm, i.e. they were active at least for three hours

from the beginning of the dark phase, at about 20.00 h, as has been shown previously (Ortega-

Escobar, 2002).

Histology

Twelve adult females were studied. Sets of three of these animal prosomas were fixed in

Bouin’s aqueous fluid at the following times: 06.00 h, 12.00 h, 18.00 h and 24.00 h,

dehydrated, and embedded in paraffin. Serial sections, 7 mm thick, in the three orthogonal

planes, were treated by general histological stainings and histochemical reactions suited for

studying the visual system and the secretory cycle of neurosecretory cells in the optic lobes of

the brain. Structural conditions of photoreceptor rhabdoms were verified in all 12 animals.

Neurosecretory cells were characterized using aldehyde fuchsin and alcian blue on potassium

permanganate preoxidized sections, Mann-Dominici’s and Solcia et al.’s (1968) stainings,

and the p-dimethylaminobenzaldehyde reaction (Glenner & Lillie 1957). Technical

procedures are detailed in Gabe’s (1968) and Lillie and Fullmer’s (1976) handbooks.

Sections of male specimens previously studied were also treated. Furthermore, four females

which had been submitted to a 24 hour illumination were fixed at 06.00 h (two individuals) or

10.00 h (two individuals) and then treated similarly to the other 12 females.

Results

Anatomy

Three groups of neurosecretory cells have been identified at different levels of the optic lobes

(Figure 1). The most anterior group is localized at about 300 mm from the sagittal plane of the

prosoma and borders the fibre tract linking the first and second synaptic zones of the anterior

median retinae (AM S1 and AM S2). It comprises two symmetrical clusters, about 150 mm in

diameter, of some 20 odd particular cells in two categories (A and B) surrounded by globuli

(Figure 2).

238 J. Kovoor et al.

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On each side, two bottle-shaped A cells are 110 mm long; their nucleus (30 x 20 mm)

is found in their basal part which is 50 mm broad at the most. One of these two cells

Figure 1. Parasagittal section of an optic lobe of the brain till the arcuate body (AB) showing several sites of

neurosecretory cell groups. Masson-Goldner trichrome, green filter. AM S2: second synaptic zone of an anterior

median retina. Scale bar: 100 mm.

Figure 2. The most anterior group of neurosecretory cells (NS A1, A2, B) in a transversal section of the prosoma. Part

of an optic lobe, lateral region is on the right-hand side. Periodic acid-Schiff-Groat’s hematoxylin-methyl blue, green

filter. Scale bar: 50 mm.

Neurosecretory cells in the brain of Lycosa tarentula 239

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(NS A1) lies along the dorso-lateral border of the optic lobe, its proximal region is

inserted between the fibre tract succeeding to AM S1 and the cluster of NS B cells

and globuli (Figure 5). The basal part of NS A2 is more internally applied on the

ventral face of the fibre tract; its neck is elongated amongst the globuli, toward the

neuropil (Figure 2).

The bunch of NS B cells is made up of closely packed fusiform somata, which send their

long straight axons as a tight bundle oriented forwards. These fibres run alongside efferent or

afferent fibres linked to the indirect eye synaptic zones, in the axial region of the optic lobes

(Figures 3 and 4). Synaptic buttons are clearly observed between the NS B processes and the

visual interneurons (Figure 4).

Cortical cell layers comprising other neurosecretory cells lie between the second

synaptic zone of the anterior median retinae (AM S2) and the arcuate body (AB). Just

next to the anterior lobe of the arcuate body, an oval cluster of about 10 cells (NS

C1) is enclosed in the internal half of cortical cells (Figure 6). These NS C1 are

fusiform, 72 – 75 mm long, with a nucleus 9 mm in diameter in females and 55 mm long

with a nucleus 12 – 13 mm in diameter in males. Their very thin processes meet

afferent/efferent fibres linked to AM S2, in the neuropil bordering the cortical cells

(Figure 7).

Large-sized neurosecretory cells (NS C2, NS C3) are more or less aligned or sparse

alongside various other types of neurons of the optic lobe dorsal cortex which precedes the

arcuate body. The round distal part of NS C3 contains the nucleus (diameter:14 mm) and lies

Figure 3. Cluster of NS B cells and axons. Horizontal section. Ferric ferricyanide-fast nuclear red, orange filter. Scale

bar: 25 mm.


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on the cortical basal lamina. Its shape is that of an ampulla, the very long neck (15 mm wide)

of which is inserted between other cortical cells. NS C2 and NS C3 differ by their total lengths

only, which are 80 or 100 – 120 mm, respectively. Long processes of these cells reach the

midbrain neuropil.

Figure 4. Axons of NS B cells contact wide interneurons through synaptic buttons. Transverse section, plumbic

hematoxylin, green filter. Scale bar: 25 mm.

Figure 5. NS A1 cell covering the basal part of NS B cells. Transverse section, one-step trichrome, orange filter. Scale

bar: 25 mm.


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Secretory cycle of neurosecretory cells

Cytological features of NS A1 and NS A2, especially seen when sections are stained by

aldehyde fuchsin or alcian blue after potassium permanganate oxidization, suggest a non-

synchronous functioning, or even opposite secretory cycles of these two cells. In NS A1,

Figure 6. NS C1 cells (arrow) close to the arcuate body (AB). Periodic acid-Schiff-Groat’s hematoxyline-methyl blue,

green filter. C2, C3 :NS C2, NS C3. Scale bar: 50 mm.

Figure 7. The cluster of NS C1 and its connexion (arrow) to fibres linked to the AM retina second synaptic zone.

Parasagittal section. Periodic acid-Schiff-Groat’s hematoxylin, green filter. Scale bar: 25 mm.


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synthesis of the secretory products takes place during the diurnal and partly nocturnal phases

(Figure 8); at 24.00 h, secretion accumulates in the apical cytoplasm of the cell body (Figure

10); at 06.00 h it is released (Figure 11). Signs of synthesis appear only at 18.00 h in NS A2

cytoplasm (Figure 8). While secretory products do not figure in the cell at any time, the

cytoplasm appears most often as a loose network (Figure 10).

All NS B cells function synchronously. Synthesis of neurosecretory products occurs mostly

during the illuminated phase; at 18.00 h, secretion is present in the apical half of the cells,

above the nucleus. At 24.00 h, NS B cells are still full of secretion (Figures 9 and 10); at

06.00, aldehyde fuchsin staining, rather weak, indicates that a neurosecretory product has

been released at least partly (Figure 11).

Cytological variations throughout the day are seen in NS C1 similar to those of NS B.

Neurosecretion accumulates during the light phase; cells are full at 18.00 h (Figures 6 and 7)

and the product reaches their apical end at 24.00 h, just before release (Figures 12 and 13).

Neurosecretion release seems to be the signal of the diurnal restoration of the rhabdoms of the

median anterior retinae which can be observed several hours later. Synthetic activity of NS C1

occurs continuously the whole day; nevertheless, it seems to be at a minimum at 06.00 h,

since the diameter of rhabdoms in the anterior median retinae is also the smallest.

Largest neurosecretory cells in the optic lobes, NS C2 and NS C3, the processes of which

deeply plunge in the brain neuropil, show diverse cytological features whatever the phase of

the day. At the four experimental times, some NS C2 or NS C3 are full of secretion while

others show numerous ergastoplasmic lamellae and a large nucleolus or seem to have released

their secretory product (Figure 14).

In the particular case of the animals submitted to 24 hours of continuous illumination, and

fixed at 06.00 h or 10.00 h, NS A1 and NS A2 had not released their secretory products. On

the contrary, the cytoplasm of NS A1 shows characteristics of a synthetic activity: numerous

ergastoplasmic lamellae and a large nucleolus in the nucleus. NS A2 also showed a large

nucleolus while the cytoplasm contained dense masses surrounded by lamellae (Figure 15).

On the other hand, NS C2 and NS C3 were filled with secretion (Figures 16 and 17). These

animals had been completely motionless during their lengthened illumination phase.

Figure 8. NS A1, A2 and B cells at 18.00 h. Cytological aspect of secretion elaboration in all cells (in black). Mann-

Dominici, orange filter. Scale bar: 50 mm.


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Discussion

Among the neurosecretory cells which have been described above in the optic lobes of L.

tarentula, only NS C2 and NS C3 may be assimilated to the aboral neurosecretory cells

decribed by Kuhne (1959: ‘‘aborale protecerebrale Zellgruppe’’) in Pardosa lugubris

(Lycosidae), Tegenaria derhami and Araneus cornutus, and later by Meier (1967) in thomisids

and dysderids. The presence of these cells is thus considered to be a common feature of all

spiders. Other groups of neurosecretory cells, NS A, B and C1, were not mentioned by these

two authors in their inventory of the whole central nervous system of spiders. The localization,

Figure 10. NS A1, A2 and B cells at 24.00 h. Note the opposite aspects of NS A cells. Phosphotungstic hematoxylin,

green filter. Scale bar: 50 mm.

Figure 9. NS B cells at 24.00 h.. Secretion is accumulated in the supranuclear region of the cells (arrow heads).

Mann-Dominici, orange filter. Scale bar: 20 mm.


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and anatomical functional characteristics of the NS cells described here, with reports

concerning other arthropods, suggest that neurosecretion in the optic lobes is involved in the

control of circadian rhythms of locomotor and visual activity in Lycosa tarentula.

Insects

In numerous insects, especially in cockroaches and crickets and also in Drosophila, it has been

demonstrated that secretions of neurosecretory cells found in the optic lobes of the brain are

Figure 12. NS C1 cells at 23.00 h. Oxidization-aldehyde fuchsin-one-step trichrome, green filter. Scale bar: 50 mm.

Figure 11. NS A1 and B at 06.00 h. Secretion (in black) is present in the neck of NS A (arrow), and near the apex of

NS B cells (arrow heads). Oxidization-aldehyde fuchsin-one-step trichrome, green filter. Scale bar: 25 mm.


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involved in the regulation of locomotor and/or visual activity (see review article by Helfrich-

Forster et al. 1998).

Chelicerates

The circadian rhythmicity of retinal sensitivity has been studied in the chelicerate Limulus

polyphemus (Barlow et al. 1977; Chamberlain & Barlow 1979). Lateral eyes are more sensitive

during the night than during the day. In these eyes, the activity of the efferent innervation is

Figure 13. Detail of Figure 12. Trails (black) of secretion leave the cells which contact fibres linked to the second

synaptic zone of an anterior median retina. Scale bar: 25 mm.

Figure 14. NS C3 cells at 18.00 h. Different cytological aspects of these cells. Oxidization-aldehyde fuchsin-one-step

trichrome, green filter. Scale bar: 50 mm.


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controlled by a group of neurons of the cheliceral ganglion (Calman & Battelle 1991). But it

has not yet been ascertained that these neurons solely constitute the circadian clock (Calman

& Battelle, 1991).

The sensitivity of the median eyes of the scorpion Androctonus australis shows a

circadian rhythm. Circadian impulses are transmitted to the optic nerve via

neurosecretory fibres the cell bodies of which are situated in the tritocerebrum

(Heinrichs & Fleissner 1987). As in Limulus, these neurons may be the circadian clock

or a part of it only.

Figure 15. NS A1, A2 and B cells at 06.00 h., after a 24 hours illumination. Plumbic hematoxylin, green filter. Scale

bar: 25 mm.

Figure 16. NS C3 cells at 06.00 h., after a 24 hours illumination. Oxidization-aldehyde fuchsin-trichrome, green

filter. Scale bar: 50 mm.


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In spiders Argiope amoena and A. bruennichii, Yamashita and Tateda (1981) found that

there is an efferent input to the retina, generated by an endogenous circadian clock, that

enhances the sensitivity of the retina. More recently, Yamashita (2002) has studied the

circadian oscillation of sensitivity in the anterior median eye of several species (the garden

spider Araneus ventricosus, the jumping spider Menemerus confusus, and the orb-weaving

spiders Argiope amoena and A. bruennichii). While Araneus and Argiope show a circadian

oscillation of sensitivity, Menemerus do not show any.

In several spiders, fibres have been found in the retina that show neurosecretory

morphological characteristics. For example, Uehara et al. (1993) found efferent fibres in

the retina of the liphistiid spider Neptathela kimurai; these fibres contained both small clear

vesicles and large electron dense granules, and branched repeatedly with varicosities

providing sinaptoid contacts with the receptor cells. In a wolf spider, Lycosa erythrognata or

L. thorelli, Melamed and Trujillo-Cenoz (1966) noted the presence of ‘‘clear fibres’’ that

contained numerous dark granules and clusters of small vesicles. They observed specialized

areas of contact between these fibres and the photoreceptor cells.

In the spider Lycosa tarentula, the situation is more complex than in other chelicerates

previously studied. The former is a burrowing species, both day and night active; visually

guided behaviour and locomotor activity are synchronized by the visual system (Ortega-

Escobar, 2002). On the other hand, each pair of eyes of L. tarentula exhibits its own functional

characteristics: the rhythm of rhabdom renewal is proper to each retina type (Kovoor et al.

1995, 1999). Optic masses corresponding to the anterior median retinae are isolated from

those of the three other pairs of indirect retinae (anterior lateral AL, posterior lateral PL and

posterior median PM) in a dorsal superficial region of the optic lobes and linked to the arcuate

body.

In the animals studied, the rhabdom diameter in the anterior median retinae were at a

minimum at about 06.00 h and a maximum at 18.00 h. Variations of the diameter, as well as

the surface, of rhabdoms were rather small as compared to those in the indirect retinae;

nevertheless, we assume that the secretory product of NS C1, clustered in the vicinity of the

arcuate body, is involved in the modulation of the circadian modifications of AM rhabdoms.

The secretion of these cells would pass along the fibres linked to the synaptic zones of AM. Its

Figure 17. Detail of Figure 16. Scale bar: 25 mm.


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release would be the signal for initiating the restoration of the rhabdoms which can be

observed several hours later. Connexions of NS C1 axons have been detected with fibres of

the AM tract only. Anterior median eyes are not at all involved in the control of entrainment

of locomotor rhythm (Ortega-Escobar, 2002). It can thus be concluded that NS C1 are

unlikely to be modulators or oscillators of this rhythm.

On the other hand it can be suggested, from the observation of numerous synaptic

button-like between NS B axons and interneurons joining the synaptic zones of the

indirect retinae (cf. Figure 5), that NS B could act as a modulator or even oscillator of the

rhythmic changes of the rhabdoms in AL, PL, and PM retinae, and also of locomotor

rhythm. It was demonstrated by Ortega-Escobar (2002) that when anterior lateral eyes

only are left uncovered, spontaneous locomotor rhythm of L. tarentula tallies with an

advance or delay of the illumination cycle. The release of the NS B secretory product

between 24.00 h and 06.00 h would have the effect of stimulating rhabdom restoration in

AL retinae, for example, which takes place some hours later, while locomotor activity

would be abolished.

A correlation between a particular phase of the secretory cycle of NS A, C2, and C3, with

the initiation of spontaneous locomotor activity, which occurs at about 20.00 h in L. tarentula,

is difficult to establish. Nevertheless, data obtained from several females submitted to

24 hours of continuous illumination, and fixed in the morning, has led us to suggest the

following. In the two NS A of these animals, the cytoplasm appeared to be ‘‘blocked’’ in

synthetic phase of the secretory cycle, while the release of their products should have occurred

before fixation. In the same animals, all NS C2 and C3 were full of secretion. These animals

had been totally motionless all through the 24 hours. It is thus quite possible that the secretory

products of NS A and NS C2 and C3 are involved in the regulation of certain aspects of the

spontaneous locomotor activity in L. tarentula. NS A might represent a part of the circadian

clock for locomotor activity; NS C2 and C3 which send their processes deeply into the central

neuropil of the brain might establish connexions with neuromotor fibres or interneurons

linked to the suboesophageal ganglion, especially to locomotor appendage ganglions.

Gronenberg (1990), analysing the functional organization of sensory interneurons in the

nervous system of Cupiennius salei (Araneae, Ctenidae), described ‘‘ascending’’ interneurons

from the longitudinal tracts of the suboesophageal ganglion to the brain, and other

‘‘descending’’ interneurons from the posterior part of the corpora pedunculata (dorsal

anterior to the arcuate body) to median longitudinal tracts of the suboesophageal ganglion.

Although no precise study has been made on these type of interneurons and their

arborisations, anatomical data already collected (Kovoor et al. in press) in the optic lobes

suggest that interneuron organization of L. tarentula is close to that of C. salei. That

strengthens our hypothesis.

Most probably the various groups of neurosecretory cells in the optic lobes of L. tarentula

have distinct functions: their secretory products control or modulate only a part of the visual

activity (NS C1), or operate at the same time on visual and spontaneous locomotor activities

(NS B), or even modulate only locomotor activity (NS A, NS C2 and C3).

Neurotransmitters, neuromodulators

The identification of neurotransmitters or neuromodulators produced by neurosecretory cells

described above can be only speculative, based on biochemical and physiological studies

made on arthropods, among which are some chelicerates. The main candidates which may be

proposed are serotonin (5-hydroxytryptamine), octopamine, dopamine, adrenaline and

noradrenaline, and also melatonin.


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Serotonin

According to Muszynska-Pytel and Cymborowsky (1978a, 1978b), a correlation does exist

between serotonin concentration in the central body, rich in neurosecretory elements, a

secretion of neurosecretory cells of the pars intercerebralis, and the locomotor activity of

crickets (Acheta domestica) during the day. Control of the locomotor rhythm of crickets

depends on the opposite activities of two neuromodulators. The pars intercerebralis product

has not been identified.

In chelicerates, serotonin was rarely detected. The cyclic production of secrotonin related

to locomotor activity was demonstrated in Leiobunum longipes (Opiliones) by Fowler and

Goodnight (1966, 1974). Injections of serotonin in the dorsal vessel of other opilions

(Discocyrtus dilatatus, Gonyleptidae) cause a modulation of the amplitude of electroretino-

grams which is greater in the day-time than at night (Munoz-Cuevas & Carricaburu, 1990).

The production site of the neuromodulator is unknown. However, several groups of

immunoreactive, serotonin-like cells were identified in the suboesophageal ganglion and

cheliceral neuromers, but not in the optic lobes, of a spider, Cupiennius salei (Ctenidae)

(Seyfarth et al., 1990). Besides, a histochemical demonstration of serotonin, by the p-

dimethylaminobenzaldehyde reaction, failed in the brain of L. tarentula.

Octopamine

It was well established in the chelicerate Limulus that the circadian rhythm of sensitivity of the

lateral retinae was mainly controlled by octopamine (Battelle 1980, 1990: Battelle & Evans

1984; Evans et al. 1983; Calman & Battelle 1991; Lee & Wise 1991) transiting via efferent

fibres of brain cells surrounded by ganglionic cells of the medullar group (Chamberlain &

Barlow 1980). Similarly in the scorpion Androctonus australis, octopamine released by two

symmetrical groups of cells and their efferents localized in the brain is also the main

neurotransmitter governing the retinal sensitivity (Fleissner & Fleissner 1985).

Octopamine was not found in the brain of spiders as a neurotransmitter controlling the

visual or locomotor systems. However, Seyfarth et al. (1993) have localized octopamine, by

immunocytochemistry, in a series of neurosecretory elements of the suboesophageal and

cheliceral ganglions of Cupiennius salei. The arborizations of these neurons may diffuse

octopamine towards the arcuate body which does not produce this neurotransmitter by itself.

The rhythm of secretion of octopamine has not been studied in C. salei.

Catecholamines

According to the studies of Meyer et al. (1984), adrenaline, noradrenaline and dopamine are

present in the central nervous system of spiders. The quantities of these neurotransmitters are

higher in vagrant spiders such as Lycosidae and Salticidae the behaviour of which is visually

guided, than in Theraphosidae, or sedentary web spiders such as Agelenidae and Araneidae.

Exogenous dopamine and noradrenaline, and also modafinil (R), result in variations of the

electroretinograms of L. tarentula depending on the type of retina recorded and the phase of

activity (Carricaburu & Munoz-Cuevas 1998; Munoz-Cuevas & Carricaburu 2000).

Melatonin

Melatonin has been found almost throughout the animal kingdom. Its role is important as a

neurotransmitter controlling circadian rhythms adjusted to alternative light and darkness


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(Vivien-Roels & Pevet 1986). Melatonin was demonstrated for the first time in the eyes and

brain of a spider (L. tarentula) in 1998 (unpublished results; dosages of melatonin by

radioimmunoassays were carried out in the Laboratory of Dr. B. Vivien-Roels, Laboratoire de

Neurobiologie des Rhytmes, Universite Louis Pasteur, Strasbourg (France) whom we warmly

thank for her cooperation). Nocturnal concentrations were higher than diurnal concentra-

tions. Injected in the dorsal vessel of the spider, melatonin causes an increase of nocturnal

responses (ERG) and has little effect on diurnal responses of indirect retinae the rhythmic

activity of which is more diurnal than nocturnal (unpublished results).The reverse is observed

when dopamine or noradrenaline are tested: catecholamines and melatonin are thus active in

opposing phases on the indirect eyes of L. tarentula. In the anterior lateral eyes of the orb-

weaving spiders, Argiope amoena and A. bruennichii, Yamashita and Arita (1995) could change

the ERG waveform by exogenous application of octopamine during the day. In contrast,

exogenous application during night-time had little or no effect.

Melatonin and catecholamines represent good candidates to be neuromodulators or

neurotransmitters of locomotor and/or visual activities of L. tarentula. We suggest that NS A

and NS B cells could rhythmically synthesize and diffuse them into the brain.

Immunocytochemical tests should be carried out, especially in the sites described above, to

answer the still open questions concerning circadian clocks and activity rhythm modulation in

spiders.

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Documents

Neurosecretory cells in the optic lobes of the brain and activity rhythms in Lycosa tarentula (Araneae: Lycosidae)