Characterization of TRPM8-expressing neurons in the adult mouse hypothalamus

Transient receptor potential melastatin 8 (TRPM8) is a menthol receptor that detects cold temperatures and influences behaviors and autonomic functions under cold stimuli. Despite the well-documented peripheral roles of TRPM8, the evaluation of its central functions is still of great interest. The present study clarifies the nature of a subpopulation of TRPM8-expressing neurons in the adult mice. Combined in situ hybridization and immunohistochemistry revealed that TRPM8-expressing neurons are exclusively positive for glutamate decarboxylase 67 mRNA signals in the lateral septal nucleus (LS) and preoptic area (POA) but produced no positive signal for vesicular glutamate transporter 2. Double labeling immunohistochemistry showed the colocalization of TRPM8 with vesicular GABA transporter at axonal terminals. Immunohistochemistry further revealed that TRPM8-expressing neurons frequently expressed calbindin and calretinin in the LS, but not in the POA. TRPM8-expressing neurons in the POA expressed a prostaglandin E2 receptor, EP3, and neurotensin, whereas expression in the LS was minimal. These results indicate that hypothalamic TRPM8-expressing neurons are inhibitory GABAergic, while the expression profile of calcium-binding proteins, neurotensin, and EP3 differs between the POA and LS.