Fig. 1.

Neurons of the medial septum/diagonal band region are excited by the Hcrt peptides in a reversible, reproducible, concentration-dependent manner. a, Response of an MSDB neuron to repeated applications of Hcrt2. Note the lack of desensitization. This cell was also excited by muscarine (data not shown). b, Bar chart summarizes the reproducibility of the Hcrt2 response. c, The response of an ACh-excited MSDB neuron to a 20 min application of 0.3 μm Hcrt2. Only a minimal reduction in the response was observed. Note that a second 2 min application of Hcrt2 produced a similar response. d, Bar chart summarizes the magnitude of the Hcrt2 excitation in MSDB neurons. e, The concentration dependence of the Hcrt response in an MSDB neuron. The response of this neuron to 3 and 10 nm Hcrt2 is not shown. f, Concentration–response curve summarizes the effect of Hcrt2 on three neurons. An EC₅₀ value of 207 nm was obtained.g, h, Chart record shows the response of muscarine-excited MSDB neuron to equimolar concentrations of Hcrt1 and Hcrt2 peptides. Note that both peptides induced responses of a similar magnitude. BL, Baseline.