Putative identification of proopiomelanocortin and neuropeptide-Y neurons of the arcuate nucleus by their response to leptin: in vivo electrophysiology study in male and female rats

The arcuate nucleus (ARN) of the hypothalamus is involved in multiple biological functions, such as feeding, sexual activity, and the regulation of the cardiovascular system. It was reported that leptin increased c-Fos expression in the proopiomelanocortin (POMC)- and decreased it in the neuropeptide-Y (NPY)-positive neurons of the ARN, suggesting that it stimulates the former, and inhibits the later. This study aimed at the direct electrophysiological examination of the effect of leptin on ARN neurons and to investigate potential sex-dimorphic changes. Wistar rats were anesthetized with urethane and the electrodes were inserted into the ARN. After a spontaneous active neuron was recorded for at least one minute, leptin was administered intravenously, and the firing activity of the same neuron was recorded for two additional minutes. It was found that approximately half of the ARN neurons had an excitatory, and another half an inhibitory response to the leptin administration. The excitability of the neurons with excitatory response to leptin was not different between the sexes. The average firing rate of the neurons with inhibitory response to leptin in females was, however, significantly lower comparing to the males. The obtained results demonstrate that the ARN neurons with stimulatory response to leptin are POMC and those with inhibitory response are NPY neurons. NPY Y1 receptor be might responsible, at least in part, for the sex differences in the excitability of the neurons putatively identified as NPY neurons.