Fig. 4.

Calcium responses to hypocretin. A, Based on fura-2 calcium recordings, neurons from the lateral hypothalamus (LH), the site of the hypocretin immunoreactive cell bodies, showed strong responses to hypocretin (HCRT) (1 μm) and clear recovery after two bath applications of the peptide. Horizontal lines above Ca²⁺ trace indicate time of drug application. Except for Figure 3C, all other experiments used hypocretin-2. B, Medial hypothalamus cells also showed strong Ca²⁺ elevations in response to hypocretin but no response to the C-terminal 1–17 (1–17) peptide of preprohypocretin (1 μm). C, Hypocretin-1 (HCRT: 1), using the 33 amino acid structure with the double disulfide bonds found for orexin A, and hypocretin-2 (HCRT: 2) were compared. Each evoked a Ca²⁺ rise in this typical medial hypothalamic neuron. D, Hypothalamic neuron that showed an increasing peak response to increasing concentrations of the peptide, with no response to 1 nm hypocretin, a response to 10 nm hypocretin, and a bigger response to 100 nmhypocretin.