Central mediation of hormonal influences on instrumental avoidance conditioning.

Two behaviorally active hormones of the pituitary-adrenal system are adrenocorticotropic hormones (ACTH) and corticosterone, and their behavioral effects are facilitation and inhibition of performance of previously learned avoidance responses, respectively. Their uptake, distribution and effects on central nervous system are reviewed. Hypothalamic neurotransmitter control of corticotropin releasing hormone (CRH) is described together with hypothalamic and extra-hypothalamic (hippocampal) regulation of pituitary-adrenal activity. Extra-hypothalamic mediation of the behavioral effects of ACTH is evaluated. Recent isotopic mappings of the efferents of the hippocampal formation have identified pathways from hippocampal subiculum to hypothalamus and posterior lateral and anterior thalamic nuclei. The evidence reviewed suggests a complex circuit involving hippocampal subiculum, thalamus and hypothalamus may be involved both in regulating pituitary-adrenal responses to stress and in mediating the effects of ACTH on avoidance behavior.