VMN dopaminergic graft and feeding pattern in obese Zucker rats

OBJECTIVE: To study the role of dopamine in the ventromedial hypothalamus ( VMN) in the regulation of meal size and meal number during obesity. METHODS: Embryonic mesencephalic cells rich in dopaminergic neurons from le an rats were grafted into the VMN of obese Zucker rats. Since food intake i s the product of meal size and number, these variables were measured using a rat 'eater meter'. Dopamine and serotonin concentrations in the VWN were assayed in grafted and control rats via in vivo microdialysis and HPLC two months after transplantation. RESULTS: Food intake increased in grafted rats due to an increase of both m eal size and meal number 2 weeks after implantation and to an increase of m eat size with insufficient compensatory decrease of meal number 2 months af ter transplantation. Grafted rats showed higher absolute dopamine and lower serotonin concentrations in the VMN. CONCLUSION: It would appear that an increase of dopamine and a decrease of serotonin in the VWN of grafted obese rats may correlate with increase in m eal number and meal size, respectively. Since obese Zucker rats usually dis play an enlarged meal size, we deduce from the data that chronically elevat ed VMN dopamine and low serotonin are involved in producing the large meal size observed during obesity.