Intrahypothalamic Serotonergic Neurons

Serotonin's role as a neuronal transmitter was established already forty years ago, and the anatomy and many of the functions of the major serotonergic systems have been carefully mapped. The intimate association of serotonergic mechanisms with central control of food intake has also been extensively studied. While the present concepts of serotonergic functions rely on the ascending, raphe nuclei-originating serotonergic pathways, there is an accumulating evidence to support that hypothalamic neurons may also exhibit many features normally attributed to serotonergic neurons only. Neurons in the hypothalamic arcuate and periventricular nuclei express tryptophan hydroxylase, the serotonin synthesizing enzyme, while they do not transport or synthesize serotonin. On the other hand, dorsomedial nucleus contains a select population of neurons that do actively accumulate serotonin, while they do not express tryptophan hydroxylase. These and some other serotonin-associated features of the hypothalamic neuronal groups are discussed. Finally the present data is projected against the prevailing concept of hypothalamic regulation of food intake.