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

Abstract

In maternally separated rats, variable chronic stress decreased the emotional reactivity and provoked a state of hypoactivity of the hypothalamic-pituitary-adrenal system at 3 months old but increased its activity after the open field test. The anterodorsal thalami nuclei control of the endocrine response under stress conditions was not manifested however its seems activate grooming behavior.The development of behavioral and endocrine response to stress is influenced by early postnatal environment. On the other hand, the anterodorsal thalami nuclei exert an inhibitory influence on the hypothalamic-pituitary-adrenal system under basal and stressful conditions. The aim of this work is to determine the magnitude of behavioral and hypothalamic-pituitary-adrenal responses to variable chronic stress in adult female rats with anterodorsal thalami nuclei lesions, previously isolated for 4.5h daily during the first 3 weeks of life. The groups were: non-maternally separated sham and lesioned, maternally separated sham and lesioned with variable chronic stress with and without open field test.At 3 months old, under variable chronic stress, maternal separation provoked an increase in ambulation in sham and lesioned animals (P<0.01) but this parameter was not modified by lesion in either non-maternally separated or maternally separated groups. Neither the lesion nor the maternal separation changed the defecation and rearing parameter. Grooming behavior was lower in maternally separated lesioned rats (P<0.05). Under variable chronic stress maternal separation decreased adrenocorticotrophin hormone in comparison with non-maternally separated (P<0.001) and the lesion did not alter this response. Regarding corticosterone concentrations, maternal separation did not affect this hormone under variable chronic stress conditions and after the open field test there was an increase of this in both non-maternally separated and maternally separated sham and lesioned (P<0.001).