Effect of presynaptic membrane potential on electrical vs . chemical synaptic 4 transmission

40 41 The growing realization that electrical coupling is present in the mammalian brain has 42 sparked renewed interest in determining its functional significance and contrasting it with 43 chemical transmission. One question of interest is whether the two types of transmission 44 can be selectively regulated, e.g., if a cell makes both types of connections can electrical 45 transmission occur in the absence of chemical transmission? We explore this issue in an 46 experimentally advantageous preparation. B21, the neuron we study is an Aplysia 47 sensory neuron involved in feeding that makes electrical and chemical connections with 48 other identified cells. Previously we demonstrated that chemical synaptic transmission is 49 membrane potential dependent. It occurs when B21 is centrally depolarized prior to and 50 during peripheral activation, but does not occur if B21 is peripherally activated at its 51 resting membrane potential. In this report we study effects of membrane potential on 52 electrical transmission. We demonstrate that maximal potentiation occurs in different 53 voltage ranges for the two types of transmission, with potentiation of electrical 54 transmission occurring at more hyperpolarized potentials (i.e., requiring less central 55 depolarization). Further we describe a physiologically relevant type of stimulus that 56 induces both spiking and an envelope of depolarization in the somatic region of B21. 57 This depolarization does not induce functional chemical synaptic transmission, but is 58 comparable to the depolarization needed to maximally potentiate electrical transmission. 59 In this study we therefore characterize a situation where electrical and chemical 60 transmission can be selectively controlled by membrane potential. 61 62