Somatostatin regulates excitatory amino acid receptor-mediated fast excitatory postsynaptic potential components in vagal motoneurons.

Somatostatin is considered to be a brain neurotransmitter/neuromodulator; however, there is little concrete information on how this peptide contributes to generation of synaptic potentials in the mammalian central nervous tissue. Recently, a well-defined somatostatin-containing pathway has been traced from the subnucleus centralis of the solitarial complex to the compact formation of the nucleus ambiguus. Moreover, we have demonstrated both in vivo and in vitro that somatostatin enhances glutamate but inhibits acetylcholine excitation of ambigual motoneurons, suggesting involvement of this peptide in central oesophagomotor transmission. The availability of a brainstem slice containing this pathway has allowed us to characterize an excitatory amino acid receptor-mediated excitatory postsynaptic potential in compact formation neurons. This excitatory postsynaptic potential is unusual because its rising phase involves activation of N-methyl-D-aspartate receptors. Here we report that somatostatin participates in ambigual excitatory postsynaptic potential generation by permitting expression of the N-methyl-D-aspartate receptor-mediated component, thereby regulating fast information transfer in this pathway.