Figure 2. Thermosensing in the lateral hypothalamus/perifornical area is intrinsic and unique to orexin neurons.

Aa, orexin neurons display I_h (sag upon hyperpolarization), rebound depolarization following hyperpolarization, minimal spike adaptation and spontaneous activity. The grey trace shows spontaneous activity during no current injection. Ab, a rise in temperature induces a reversible outward current in orexin neurons. Ba, top, characteristics of a typical non-orexin neuron examined in the lateral hypothalamus/perifornical area. Scale is the same as in Aa. Inset shows the characteristic afterhyperpolarization seen in this cell type. Bottom, the current clamp protocol used in Aa and Ba. Bb, temperature change does not affect these non-orexin neurons. C, time–effect plot of warming on orexin (n= 5) and non-orexin neurons (n= 4). Warming started at time zero and lasted for 3–4 min. The response is specific to orexin neurons. **P < 0.01, ***P < 0.001, two-way ANOVA with Bonferroni test. D, a representative cell attached patch experiment showing no apparent temperature effect on the firing activity of non-orexin neurons.