We investigated the location, physi-(EPSP) and the VD2/3 bath-applied dopamine (100ology, and modulation of an identified synapse from mM) response displayed a similar decrease in input the central nervous system (CNS) of the mollusk Lymresistance and a similar predicted reversal potential naea stagnalis. Specifically, the excitatory synapse (031 vs. 026 mV), indicating that the synapse and from interneuron right pedal dorsal one (RPeD1) to exogenous dopamine activate the same conductance. neurons visceral dorsal two and three (VD2/3) was Finally, bath-applied serotonin (10 mM) rapidly and examined. The gross and fine morphology of these reversibly depressed the RPeD1 r VD2/3 synapse but neurons was determined by staining with Lucifer yeldid not affect the VD2/3 bath-applied dopamine (100low or sulforhodamine. In preparations where RPeD1 mM) response, suggesting a presynaptic locus of acwas stained with Lucifer yellow and VD2/3 with sulfotion for serotonin. The effect of serotonin was not rhodamine, the axon collaterals occupied similar reassociated with any changes to the pre-or postsynapgions, suggesting that these neurons make physical tic membrane potential and input resistance, or the contact in the CNS. Digital confocal microscopy of presynaptic action potential half-width. The RPeD1 r these preparations revealed that presynaptic varicosi-VD2/3 synapse provides an opportunity to examine ties made apparent contact (synapses) with smooth the anatomy and physiology of transmission, and is postsynaptic axon collaterals. The number of putative amenable to the study of neuromodulation. แญง 1997 synapses per preparation was about five to 10. Re-