Figure 4.

Stimulation of OX₁ alone activates a noisy cation current in LDT and DR neurons and enhance voltage-dependent Ca²⁺ transients mediated by L-type Ca²⁺ channels in LDT, DR, and LC neurons. (A₁) Holding current (at −60 mV; Ibase; bottom trace) and membrane current noise (Irms; top trace) were measured every 30 s starting before bath application of 300 nM orexin-A (horizontal bar) from LDT neurons in OX^−/−₂ slices. Orexin produced an inward shift in holding current that was accompanied by an increase in current noise. (A₂). The I-V curve of the orexin-evoked inward current (I_Orx) was obtained by subtracting the membrane current produced by a voltage ramp between −100 and −35 mV prior to orexin-A application from that obtained during the peak of the orexin-A-evoked inward current. These currents were similar to those obtained from LDT neurons in C57BL6 slices. (B₁) Orexin-A (300 nM) has a similar, but larger effect on the holding current (Ibase, bottom) and membrane current noise (Irms, top) in DR neurons recorded in OX^−/−₂ slices. (B₂) The I-V relation for the orexin-evoked inward current (I_Orx) in a DR neuron from an OX^−/−₂ slice was similar that that observed in DR neurons from C57BL6 slices. (C,D,E). The L-channel antagonist, nifedipine (10 μM) attenuated the Ca²⁺-transients evoked by voltage-steps from −60 to −30 mV in LDT (C), DR (D), and LC (E) neurons from OX^−/−₂ slices and completely blocked the enhancement of these transients by orexin-A (300 nM). Top traces show somatic Ca²⁺-dependent fluorescence (dF/F); Middle traces show whole-cell current; Bottom traces show membrane voltage. Calibration bar labels in (E), also apply to (C) and (D).