Oxytocin and cholecystokinin induce grooming behavior in the ventral tegmentum of the rat.

Oxytocin (OXY) and cholecystokinin (CCK) coexist in neurons of the supraoptic nucleus and the paraventricular nucleus of the hypothalamus of the rat (Cell Tissue Res., 221 (1981) 227-231). Behavioral analysis of one possible terminal field of the OXY-CCK coexistence, the caudal region of the mesencephalic ventral tegmentum, was undertaken to investigate the functional significance of this coexistence. Both OXY and CCK were found to induce grooming behaviors when microinjected into the ventral tegmental area (VTA) of awake rats. Combinations of one low and one higher dose of OXY and CCK yielded grooming scores which were not significantly different from grooming scores induced by each peptide alone. In this case of putative coexistence of two peptides without a 'classical' neurotransmitter, each peptide appears to have a behavioral function, and the interaction between the two peptides may be competitive.