Glutamate is the fast excitatory neurotransmitter of small cardioactive peptide - containing Aplysia radula mechanoafferent neuron B21

B21 is a radula mechanoafferent neuron in the mollusc Aplysia which likely plays a crucial role in integrating environmental cues into the feeding mot or program. To facilitate understanding B21's interactions with its postsyn aptic followers, we sought to identify its neurotransmitter. We find that B 21 makes a chemical synapse onto the follower neuron B8. Although B21-induc ed excitatory postsynaptic potentials (EPSPs) in B8 paradoxically diminish in amplitude with B8 hyperpolarization, we show that an inwardly rectifying current is responsible. We conclude that these B21-induced EPSPs are likel y glutamatergic as they are blocked by the glutamate antagonist DNQX. Furth ermore, B8 exhibits a depolarizing response to exogenous glutamate, which i s antagonized by DNQX. Finally, exogenous glutamate occludes B21-evoked EPS Ps in B8. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.