Electrophysiological properties of subpopulations of melanin-concentrating hormone neurons

Melanin-concentrating hormone (MCH) neurons are essential regulators of diverse physiological states including energy homeostasis, sleep-wake cycle, and memory. MCH neurons also occupy different brain regions: the lateral hypothalamic area (LHA), medial hypothalamus (MH) and zona incerta (ZI). Furthermore, a proportion of MCH neurons co-express cocaine and amphetamine regulated transcript (CART). Therefore, we hypothesized that MCH neurons in distinct anatomical areas or with differential CART expression represent functional subgroups to enable them to perform diverse functions. Whole cell patch clamp recording was performed on acute mouse brain slices in three MCH neuron-rich areas: MH, LHA and ZI. Following recording, a subset of cells was immunohistochemically identified as MCH+/CART+ or MCH+/CART- neurons. MCH neurons in the LHA and MH were more excitable than ZI neurons, firing more action potentials (AP) when stimulated, although no difference was found in the resting membrane potential (RMP) and AP waveform parameters. Additionally, MCH+/CART- neurons had more depolarized RMP and fired more APs than MCH+/CART+ neurons, suggesting that MCH+/CART- neurons are more excitable. Notably, MCH+/CART- neurons displayed an H-current, which was absent in MCH+/CART+ neurons. To our knowledge, this is the first study to describe the presence of H-current in a subpopulation of MCH neurons. These differences in intrinsic membrane properties could contribute to how MCH neuron subpopulations function within the network.