Differential involvement of dopamine D1 and D2 receptors and inhibition by dopamine of hypothalamic VMN neurons in early postnatally overfed juvenile rats.

Dopamine is among the neurotransmitters involved in central regulation of food intake, and body weight control. To study possible changes in neuronal responses to dopamine, single unit activity of the ventromedial hypothalamic nucleus (VMN) was recorded in brain slices of normal and obese rats. The latter had developed overweight throughout juvenile life (p < 0.05) by early postnatal over-nourishment due to a reduction of litter size from 3rd to 21st day of life (small litters, SL). With effective concentrations of about 100-500 nM/I dopamine inhibited significantly more VMN neurons in obese than normal rats (Chi-square p < 0.05). While D2 receptors in the VMN are reported to mediate inhibition of food intake, the responses to dopamine were blocked by D2 receptor antagonists in significantly fewer neurons of SL than normal rats (p < 0.05). Furthemore, including results of action of D1 receptor agonists we found that significantly more neurons in SL than NL rats seem to express D1 receptors. Thus, increased suppression by dopamine of firing of VMN neurons that signal satiety with a rise in the discharge rate, and changed expression or activity of dopamine receptors might contribute to increased feeding behavior in juvenile rats hyperphagic and overweight due to early postnatal overfeeding.