Figure 10.

5-HT_1BRs and GABA_BRs are located on the same presynaptic terminals. CA1 pyramidal neurons were recorded with electrodes containing BoNT/C, Alexa, and Fluo-5F. Two hundred action potentials (1 Hz, 35 min post whole cell) eliminated primed vesicles before recording. a, Action potential-evoked Ca²⁺ transients recorded by line scanning over CA1 pyramidal neuron presynaptic varicosities in the subiculum. (top trace, Control; CP93129, bottom; 1 μm). To make clear the sequential reduction of Ca²⁺ transient amplitude the image data from over the varicosity is shown as ΔF/F in pseudocolor after background subtraction from the images. b, Graph shows the integrated signals of three averaged responses in Control (black), CP93129 (1 μm; red), and in CP93129 (1 μm) plus baclofen (100 μm; purple). c, Action potentials that evoked Ca²⁺ transients in a and b. d, Schematic of presynaptic GPCR targets. At primed vesicles 5-HT_1BRs and their associated G-proteins interact with SNARE C terminals. GABA_BRs interact with Ca²⁺ channels. e, BoNT/C treatment prevents priming, freeing 5-HT_1BRs to modulate Ca²⁺ channels similarly to GABA_BRs.