The hypothalamus: cross-roads of endocrine and behavioural regulation in grooming and aggression

Anatomical and functional studies show that the hypothalamus is at the junc tion of mechanisms involved in the exploratory appraisal phase of behaviour and mechanisms involved in the execution of specific consummatory acts. Ho wever, the hypothalamus is also a crucial link in endocrine regulation. In natural settings it has been shown that behavioural challenges produce larg e and fast increases in circulating hormones such as testosterone, prolacti n, corticotropin and corticosterone. The behavioural function and neural me chanisms of such fast neuroendocrine changes are not well understood. We su ggest that behaviourally specific hypothalamic mechanisms, at the cross-roa ds of behavioural and endocrine regulation, play a role in such neuroendocr ine changes. Mild stimulation of the hypothalamic aggressive area, produces stress levels of circulating prolactin, corticotropin, and corticosterone. Surprisingly luteinizing hormone does not change. This increase in stress hormones is due to the stimulation itself, and not caused by the stress of fighting. Similar increases in corticosterone are observed during electrica l stimulation of the hypothalamic self-grooming area. The corticosterone re sponse during self-grooming-evoking stimulation is negatively correlated wi th the amount of self-grooming observed, suggesting that circulating cortic osterone exerts a negative feedback control on grooming. Earlier literature , and preliminary data form our laboratory, show that circulating corticost erone exerts a fast positive feedback control over brain mechanisms involve d in aggressive behaviour. Such findings suggest that the hormonal response s caused by the activity of behaviourally specific areas of the hypothalamu s may be part of a regulation mechanism involved in facilitating or inhibit ing the very behavioural responses that can be evoked from those areas. We suggest that studying such mechanisms may provide a new approach to behavio ural dysfunctions associated with endocrine disorders and stress. (C) 1998 Elsevier Science Ltd. All rights reserved.