Requirement of Hippocampal Neurogenesis for the Behavioral Effects of Antidepressants

Santarelli, Luca ; Saxe, Michael ; Gross, Cornelius ; Surget, Alexandre ; Battaglia, Fortunato ; Dulawa, Stephanie ; Weisstaub, Noelia ;

Lee, James ; Duman, Ronald ; Arancio, Ottavio ; Belzung, Catherine ; Hen, Rene

Science. 2003, 301 : 805-809

Speaker : Chih-Ya Cheng

•Most AD 5HT &(or) NA => monoaminergic hypothesis

•ADs produce a rapid increase in extracellular levels of 5-HT and NA , the onset of an appreciable clinical effect usually takes at least 3 to 4 weeks (Wong et al., 2001)

Depression and anxiety disorders : pathophysiology ?

Duman et al., 1997

•Post-mortem & brain imaging : atrophy or loss of neurons in the PFC and hippocampus (depressed and anxious p’t) (Gurvits et al., 1996 ; Shan et al., 1998 ; Sheline et al., 1996), may be reversed by ADs (Czeh et al., 2001). •Stress -cell death, dendritic shrinkage, and decreased levels of neurotrophins within the hippocampus (McEwen et al., 1999 ; Duman et al., 1997 ; Sapolsky et al., 1998), reduction in hippocampal granule cell neurogenesis (Gould et al., 1998).

adult hippocampal neurogenesis is decreased by stress increased by chronic antidepressants

(Gould et al., 1998 ; Malberg et al., 2000)

=> suggests that this process may be involved in both the

pathogenesis and treatment of mood disorders.

novelty-suppressed feeding test (NSF)

•Few behavioral paradigms have been able to reliably demonstrate changes in mouse behavior after chronic, but not acute, treatment with ADs (Cryan et al., 2002). •all three antidepressants (but not haloperidol) produced significant decreases in latency to feed in mice treated for 28 days.•The slow appearance of these changes resembles the delay in the onset of AD efficacy in humans.

Mean % of vehicle control latency SEMN=13-15 / per group

129/SvEv : 3~5 M5min

5min

50cm 20cm

24hrs 飢餓測量 5mins老鼠放周圍放回籠子測 5min

•Various antidepressant treatments including fluoxetine, increase neurogenesis in the DG (Malberg et al., 2000)

•Fluoxetine 60 % increase (DG) for 11 or 28 days, but it had no effect after 5 days.

Chronic fluoxetine treatment increases BrdU uptake and neurogenesis in the DG

28 days

N=7-10

i.p.

Confocal micrograph of cell double-labeled for BrdU and NeuN or GFAP

NeuN : neuron-specific nuclear proteinGFAP : glial fibrillary acidic protein

As previously reported, these proportions were not influenced by AD treatment (Malberg et al., 2000)

neuronal marker(NeuN)70 ± 2%

astroglial marker

15 ± 3%

•5-HT1A receptor : mood and anxiety-related behaviors (Sargent, 2000 ; Gross, 2002)

•KO mice displayed a higher latency than their littermate controls to begin feeding - anxiety-like behaviors (Gross, 2002 )

•KO mice were insensitive to the effects of chronic fluoxetine but were still responsive to both imipramine and desipramine.

N=10-15

Requirement of 5-HT1A receptor for fluoxetine’s effects on anxiety-related behaviors and hippocampal neurogenesis

1A,1B,1D,1E,1F,2C….

•8-OH-DPAT (5HT1A-selective agonist)

•8-OH-DPAT significantly decreased latency to feed in WT mice but was ineffective in KO mice, indicating that its effects were mediated by 5-HT1A receptors.

N=11-20

To determine whether activation of 5-HT1A receptors is sufficient to alter NSF behavior

N=11-20N=10-15

•Fluoxetine caused a doubling of BrdU-labeled cells in WT mice but had no effect in KO mice. (Further paralleling the behavioral data)

•To test whether activation of this receptor is sufficient to enhance cell proliferation, we treated WT and KO mice chronically with 8-OH-DPAT or vehicle before BrdU injection.

N=6-7

C

D

N=7-9

- 5HT1A receptor

fluoxetine

neurogenic effects

behavioral effects

?

x-irradiation

Effects of hippocampal irradiation

Long-term reductions in cell proliferation within the DG have previously been reported after low-dose x-irradiation of the heads of rats (Tada et al., 2000).

Irradiation resulted in ~85% reduction in BrdU-positive cells in the SGZ. This effect persisted at the time of behavioral testing and lasted for at least 8 weeks after delivery of the final x-ray dose.

15-Gy dose

S-shamX-ray

sham sham

V F V F

V F V F

- 5HT1A receptor

fluoxetine

neurogenic effects

behavioral effects

?

x-irradiation

Requirement of 5-HT1A receptors for fluoxetine’s effects on anxiety-related behaviors and hippocampus neurogenesis

AD treatment caused a significant reduction in latency to feed in sham mice, but this effect was absent in irradiated mice.

N=25-35

To determine whether the effect of irradiation on antidepressant response specifically involved the brain region containing the hippocampus

1.rostral to the hippocampus : SVZ2.caudal to the hippocampus : nonneurogenic cerebellar region (CRB)

There was a significant main effect of drug treatment on latency across all groups and no effect of x-ray, indicating that neither SVZ nor CRB irradiation attenuates the response to ADs.

N=13-15

CUS (chronic unpredictable stress)

1.A second behavioral test2.results in a deterioration of (1)coat and (2)grooming response 3.reversed by chronic, but not acute, AD treatment (Griebel et al., 2002)

5 weeks

(repeated sawdust changing, removal of sawdust, damp sawdust, substitution of sawdust with 37’C water)

(mice were positioned in the empty cage of another male)

(4 light/dark successions of 30min every 24 hrs)

1.Alterations of the bedding

2.cage tilting (45’)

3.predator sounds (15min)

4.cage shift

5.light to dark or dark to light shifts

BALB

Cryan et al., 2002

•Fluoxetine significantly improved the state of the fur in sham mice, and this effect was absent in irradiated mice.•grooming latency was decreased by fluoxetine in sham mice but not in irradiated mice.

N=6-8

N=6-8

BALB

- 5HT1A receptor

fluoxetine

neurogenic effects

behavioral effects

?

x-irradiation

Supplement-2

X-ray does not affect hippocampus morphology

cell number and total volumeFour weeks later

•Nissl-stained sections

•Stereological analysis 1.Cell number2.Total volumn of the DG

500um

The brain area targeted by irradiation : (1)hippocampus(2)hypothalamus (neuroendocrine)

=> serum corticosterone before and after open-field stress(3)amygdala(fear and anxiety responses)

=> a cued fear conditioning paradigmTo assess the possibility that the behavioral effects observed after irradiation result from damage to these structures

Supplement-3 X-ray does not affect neuroendocrine response to stress , or cued fear conditioning

- 5HT1A receptor

neurogenic effects

behavioral effects

x-irradiation

Our results suggest that strategies aimed at stimulating hippocampal neurogenesis could provide novel avenues for the treatment of anxiety and depressive disorders.

Requirement of Hippocampal Neurogenesis for the Behavioral Effects of Antidepressants

fluoxetine

the lack of effect of irradiation on basal behavioral responses in the NSF and CUS suggests that our focal x-ray procedure does not elicit a nonspecific behavioral impairment.

The specificity of the effects of hippocampal irradiation is also supported by the fact that the irradiation of other brain regions does not alter the behavioral response to ADs in the NSF test.

functional properties of neurons

response to antidepressants

baseline conditions