Blockade of cholinergic communication in 19-110 pairs resulted in enhanced electrical synaptic communication. A, Neurotransmitter release from neuron 110 onto neuron 19 is cholinergic. For cell pairs possessing strictly chemical synaptic connections, PSPs that occurred in neuron 19 in response to APs evoked in neuron 110 were eliminated during bath application of 10 μm curare (d-TC). After curare wash, PSPs returned to their original levels [n = 8; traces represent pre, during (flat) and post application]. Vertical bar equals 10 mV, horizontal bar equals 95 msec. B, Neurotransmitter release from neuron 110 onto neuron 19 results in an inhibitory PSP. Electrodes filled with 1.5 m KAc were used to perform recordings from 19-110 pairs. Under these recording conditions, hyperpolarizing PSPs were detected in neuron 19 in response to APs evoked in neuron 110. Vertical bar equals 5 mV, horizontal bar equals 95 msec. C, 19-110 pairs were paired into contact and cultured for 24 hr in CM containing 10 μm d-TC, 10 μm Hex, or 10 μm vehicle (Co). A significant enhancement of electrical coupling was seen both in the presence of curare (*p < 0.0005) and hexamethonium bromide (†p < 0.005) compared with controls. (ECCs: Co = 0.30 ± 0.06, n = 9; d-TC = 0.73 ± 0.06, n = 6; Hex = 0.59 ± 0.05, n = 8). Histogram represents mean ± SEM.