Serotonin (5-HT) Activation of Immortalized Hypothalamic Neuronal Cells Through the 5-HT1B Serotonin Receptor

Serotonin [or 5-hydroxytryptamine or (5-HT)] has been implicated as a key modulator in energy homeostasis and a primary focus in the treatment of obesity. There is growing evidence that 5-HT, acting through the 5-HT 1B receptor (5-HT1BR) in the paraventricular nucleus of the hypothalamus (PVN), is important to this regulation. However, there is some contention as to whether 5-HT1BR action occurs directly on PVN neurons or indirectly via inhibitory inputs into the PVN. To address these questions, we used a novel clonal, hypothalamic neuronal cell model, adult mouse hypothalamic-2/30 (mHypoA-2/30), expressing a PVN-specific marker, single-minded homolog 1, as well as a complement of PVN neuropeptides, including TRH, vasopressin, ghrelin, nucleobindin-2, and galanin. Adult mouse hypothalamic-2/30 neurons were also found to express the 5-HT1BR and 5-HT 6 receptor, but not 2C, all previously linked to feeding regulation. Direct serotonergic stimulation (100 nM to 10 mu M) of these neurons resulted in dose-dependent cFos activation. 5-HT (10 mu M) suppressed forskolin-induced cAMP levels and induced a rise in intracellular Ca2+ through ER Ca2+ release, effects that were mimicked by the 5-HT1BR agonists, CGS12066B and CP93129, and that were attenuated in the presence of the 5-HT1BR-specific inhibitors, GR55562 and isamoltane hemifumarate. Modest transcriptional changes in ghrelin and nucleobindin-2 were also observed in response to 100 nM and 10 mu M 5-HT, respectively. These findings support the model wherein 5-HT action through the 1B receptor subtype occurs directly on PVN neurons, leading to potential modification of neuronal transcriptional and secretory machinery. (Endocrinology 153: 4862-4873, 2012)