Figure 6.

Postsynaptic depolarizing effects of carbachol on PH neurons. A, An example of the experimental protocol. A hyperpolarizing current pulse (0.3 nA, 300 msec; at a frequency of 0.2 Hz) was presented 300 msec in advance of a subthreshold stimulus applied to the PPRF to evoke an EPSP in the postsynaptic PH neuron. B, The addition of TTX (1 μm) to the bath removed EPSPs because of action potential blocking. The asterisk indicates that the cell was not responsive to intracellular current injection. In this situation, superfusion with carbachol (25 μm) evoked a noticeable depolarization of the membrane potential, with no evident change in the input resistance of the recorded neuron. The maximum depolarizing level evoked by carbachol is indicated (Vm). The depolarizing effect of carbachol disappeared after the cell was washed with the bathing solution. Washing also allowed the reappearance of EPSPs evoked by PPRF stimulation. The arrows indicate the points at which recordings were expanded in time to show EPSPs evoked by PPRF stimulation and membrane potential during the presentation of hyperpolarizing pulses. The dotted line indicates the membrane resting potential. Vm, Maximum membrane potential evoked by carbachol superfusion.