The present study examined the effect of prenatal stress in rats from days 13-20 of gestation on anxiogenic behaviour in the elevated plus maze (EPM) together with changes in the gene expression of corticotrophin-releasing hormone (CRH), its receptors, CRHR1 and CRHR2, as well as CRH binding protein (CRH-BP) in the paraventricular nucleus (PVN) and amygdala of their male and female offspring. Both prenatally-stressed (PS) males and females showed heightened anxiety in the EPM. Prenatal stress did not alter the gene expression of CRH or its receptors in the male PVN, although it decreased CRH-BP mRNA, which could augment the activity of free CRH. In the PVN of PS females, there was an increase in the expression of CRH, coupled with a decrease in that of CRHR2 and CRH-BP. These changes are compatible with the greater activation of the hypothalamic pituitary adrenal axis to stress in females. Anxiogenic behaviour of PS rats was associated with a reduction of CRHR2 mRNA and of CRH-BP mRNA in the amygdala of males and an increase in CRH mRNA and decrease in CRHR2 mRNA in females. Two hours after acute stress of exposure to the elevated plus maze in which heightened anxiety was manifested, increases were seen only in the amygdala of females in CRH and CRHR1 signalling, whereas CRHR2 mRNA was reduced in both sexes. The data show that both prenatal stress and acute stress in adulthood have a differential sex-dependent effect on the expression of CRH its receptors and binding protein in the PVN and amygdala of rats.
It is still not clear whether the selective serotonin reuptake inhibitors frequently prescribed to depressed pregnant women improve the behavioural outcome in their children. The current study investigated whether administration of citalopram to pregnant rats could prevent anxiety and depressive-like behaviour induced by gestational stress in their offspring, and restore the expression of serotonin 1A autoreceptors in GABAergic interneurons in the medial prefrontal cortex and dorsal raphe nuclei in males, and of corticotropin-releasing factor type 2 receptors in GABAergic interneurons in the dorsal raphe nuclei in females. Activation of these receptors modulates serotonergic transmission to target areas and is reduced in a sex-dependent manner by prenatal stress. Citalopram (10 mg/kg/day), administered orally from day 7 of gestation until 21 days postpartum, prevented the increase in anxiety in stressed mothers but did not reduce anxiety and depressive-like behaviour in their offspring and even induced depressive-like behaviour in the offspring of control mothers. Citalopram failed to restore the reduction in the expression of serotonin 1A autoreceptors in the prefrontal cortex of males and in corticotropin-releasing factor type 2 receptors in the dorsal raphe nuclei of females induced by prenatal stress. Prenatal citalopram did not prevent the behavioural changes or reduction in serotonergic transmission to target areas induced by prenatal stress. It had adverse behavioural effects in the offspring of control rats, which, together with the lack of any change in prenatally-stressed rats, may be due to inhibition of the foetal serotonin transporter thereby preventing normal development of the serotonin system.
Male and female rats show differences in the expression of 5HT1AR and CRFR2 protein that are selectively reduced by prenatal stress. Reversal by citalopram of the changes in the expression of these receptors induced by prenatal stress support their role in the aetiology of anxiety.
Stress during pregnancy in humans is known to be a risk factor for neuropsychiatric disorders in the offspring. Prenatal stress in rats caused depressive-like behavior that was restored to that of controls by maternal treatment with ladostigil (8.5 mg/kg per day), a brain-selective monoamine oxidase (MAO) inhibitor that prevented increased anxiety-like behavior in stressed mothers. Ladostigil inhibited maternal striatal MAO-A and -B by 45-50% at the time the pups were weaned. Using resting state-functional connectivity magnetic resonance imaging on rat male offspring of control mothers, and mothers stressed during gestation with and without ladostigil treatment, we identified neuronal connections that differed between these groups. The percentage of significant connections within a predefined predominantly limbic network in control rats was 23.3 within the right and 22.0 within the left hemisphere. Prenatal stress disturbed hemispheric symmetry, resulting in 30.2 and 21.6%, significant connections in the right and left hemispheres, respectively, but this was fully restored in the maternal ladostigil group to 24.6% in both hemispheres. All connections that were modified in prenatally stressed rats and restored by maternal drug treatment were associated with the dopaminergic system. Specifically, we observed that restoration of the connections of the right nucleus accumbens shell with frontal areas, the cingulate, septum and motor and sensory cortices, and those of the right globus pallidus with the infra-limbic and the dentate gyrus, were most important for prevention of depressive-like behavior.
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