Regional effects of apomorphine on rat brain cholecystokinin-8 like immunoreactivity following electrolytic lesions of the ventral tegmental area.

After bilateral electrocoagulation of the ventral tegmental area (VTA) of rats, apomorphine (APO) was administered intraperitoneally to study the effect on the cholecystokinin-8 like immunoreactivity (CCK-8 IR) in the medial prefrontal cortex, the anterior and posterior part of the nucleus accumbens and the corpus striatum. In the medial prefrontal cortex and the posterior part of the nucleus accumbens, CCK-8 IR was markedly decreased by lesioning of the VTA. Then recovery of CCK-8 IR was noted in the APO treated rats following electrolytic lesioning of the VTA. This recovery corresponds to the response of CCK neurons not originating in the VTA or CCK interneurons to APO via DA receptors. In the anterior part of the nucleus accumbens and the corpus striatum, no significant decrease in CCK-8 IR was noted even following lesioning of the VTA. APO administration following the lesioning, however, resulted in a marked increase in CCK-8 IR in the anterior part of the nucleus accumbens and the corpus striatum. According to this result, in these sites, very few CCK neurons originating in the VTA exist and CCK neurons originating in sites other than the VTA or CCK interneurons react on APO via DA receptors.