Fig. 10.

Direct 5-HT excitation in SNr GABA neurons. (A) Immunostaining for 5-HT transporter protein reveals a very dense 5-HT axonal network that intermingles with PV-positive GABA neurons in SNr. (B) Endogenous 5-HT induces a tonic depolarization in SNr GABA neurons that is enhanced by blocking 5-HT re-uptake with 2 µM fluoxetine. Action potentials were blocked by 1 µM TTX. Ionotropic glutamate receptors and GABA_A receptors were blocked. (C) bath applied 5-HT induced a linear, voltage-independent inward current below action potential threshold. The whole cell conductance was increased during 5-HT application, indicating an opening of ion channels (e.g. TRPC3 channels), not a closing of background K channels. Note the remarkable similarity between this 5-HT current and the TRP current shown in Fig. 3C,D.A and B are unpublished data of FMZ. C is adapted from Stanford and Lacey, 1996a, with permission.