Behavioral and hypothalamic‐pituitary‐adrenal responses to anterodorsal thalami nuclei lesions and variable chronic stress in maternally separated rats

Hyperosmolarity-induced vasopressin expression and intrinsic excitability of supraoptic neurons of adult offspring are changed by early maternal separation

Adverse early life experiences can produce long-lasting changes in neurocircuits. The aim of this study was to investigate the programming effects of early maternal separation on the adult offspring vasopressin system. We hypothesized that subjecting adult rats to 4.5 h of daily maternal separation between postnatal days 1 - 21 will have altered hyperosmolarity-induced Avp expression and the response of supraoptic (SON) neurons to electrical and osmotic stimulation. We measured Avp mRNA and hn-RNA in the SON and in the paraventricular nucleus (PVN) by quantitative PCR, and assessed the intrinsic excitability of magnocellular SON neurons as well as their osmotic responses by the patch-clamp technique. In maternally-separated rats we found that basal and osmolarity-induced Avp mRNA gene expression was upregulated in the SON, whereas osmolarity-induced Avp hn-RNA gene expression was abolished. Similarly, in the PVN of maternally-separated rats the osmolarity-induced Avp mRNA gene expression was blunted. The supraoptic neurons of separated rats also had greater excitability than those of non-separated rats. Our results indicate that early maternal separation has long-term consequences on basal and hyperosmolarity-induced Avp hypothalamic expression as well as on the intrinsic excitability of magnocellular supraoptic neurons.

Early maternal separation and chronic variable stress in adulthood changes the neural activity and the expression of glucocorticoid receptor in limbic structures

There is increasing evidence that early adverse experience contributes to the development of stress susceptibility, and increases the onset of stress-related psychiatric disorders in stressful environments in adulthood. This study addressed whether or not prolonged maternal separation, a well-established model of early stress, affects adult limbic areas related to the regulation of the hypothalamic-pituitary-adrenal axis in exposure to chronic variable stress in adulthood. Rats were subjected to daily maternal separation for 4.5h during postnatal days 1-21. As adults, the animals were exposed to a variable chronic stress paradigm of 24 days. Persistent changes were assessed in glucocorticoid receptor density and Fos activity in the anterodorsal thalamic nuclei, mammillary nuclei and retrosplenial cortex. Immunohistochemical analysis revealed that adult maternally separated animals had increased levels of c-Fos immunoreactivity in the anterodorsal thalamic nuclei as well as in the mammillary nuclei compared to normal non-maternally separated animals. Chronic variable stress in maternally separated and non-maternally separated animals diminished glucocorticoid receptor density in the anterodorsal thalamic nuclei but not in the rest of the nuclei analyzed. These results indicate that c-Fos immunoreactivity as well as glucocorticoid receptor expression in the anterodorsal thalamic nuclei and mammillary nuclei exhibit long-term alterations in adult rats following repeated maternal separation and subsequent stress exposure. Recognition of these adaptations helps to define the brain regions and neural circuitry associated with persistent alterations induced by early life environment and the development of stress-associated disorders.

Amitriptyline treatment under chronic stress conditions: effect on circulating catecholamines and anxiety in early maternally separated rats

The aim of this work was to determine the effect of amitriptyline (AMI) on peripheral outcomes such as plasma epinephrine (E) and norepinephrine (NE) concentration and anxiety-like behavior displayed in the plus maze test in adult male Wistar rats under variable chronic stress and daily oral administration of AMI (5 mg/kg). Animals were previously isolated from the mother for 4.5 hr every day for the first 3 weeks of life. Administration of the antidepressant AMI reduced anxiety-like behavior in animals submitted only to chronic stress but not in early maternally separated (MS) subjects or in animals subjected to the two types of stresses.