Synaptic relationships between proopiomelanocortin- and ghrelin-containing neurons in the rat arcuate nucleus

Both proopiomelanocortin (POMC) and ghrelin peptides are implicated in the feeding regulation. The synaptic relationships between POMC- and ghrelin-containing neurons in the hypothalamic arcuate nucleus were studied using double-immunostaining methods at the light and electron microscope levels. Many POMC-like immunoreactive axon terminals were found to be apposed to ghrelin-like immunoreactive neurons and also to make synapses with ghrelin-like immunoreactive neuronal perikarya and dendritic processes. Most of the synapses were symmetrical in shape. A small number of synapses made by ghrelin-like immunoreactive axon terminals on POMC-like immunoreactive neurons were also identified. Both the POMC- and ghrelin-like immunoreactive neurons were found to contain large dense granular vesicles. These data suggest that the POMC-producing neurons are modulated via synaptic communication with ghrelin-containing neurons. Moreover, ghrelin-containing neurons may also have a feedback effect on POMC-containing neurons through direct synaptic contacts.