Fig. 3.

Effect of muscarinic receptor antagonists on Cy3–192IgG-labeled and unlabeled MSDB neurons. A, Recording from a Cy3–192IgG-labeled cholinergic neuron shows that although atropine (3 μm) had no effect on the baseline firing rate, it did block the inhibitory effect of exogenously applied muscarine. B, In contrast, in a Cy3–192IgG-unlabeled neuron (presumably, GABAergic), a low nanomolar concentration of atropine reduced basal firing rates and also blocked the effect of exogenous muscarine but had little effect on norepinephrine (NE)-induced excitation; NE has been shown previously to excite septohippocampal GABA neurons (Alreja and Liu, 1996). C, The bar chart summarizes the effects of muscarinic drugs on Cy3–192IgG-labeled (i.e., cholinergic) and Cy3–192IgG-unlabeled neurons. Note that atropine had no effect on Cy3-labeled neurons; unlabeled neurons that are excited by muscarine show a decrease in basal firing rates in the presence of atropine.Con, Control. **p < 0.005.