Excitatory amino acid neurotransmission in the primary gustatory nucleus of the goldfish Carassius auratus.

The vagal lobe in goldfish is a laminated structure in the midmedulla responsible for processing vagal gustatory input from the oropharynx. The anatomical arrangement of the vagal lobe is conducive to an in vitro slice preparation for investigating the physiology and pharmacology of primary gustatory fibers. Postsynaptic population responses (N2 and N3) were evoked from sensory layers of the vagal lobe following stimulation of the incoming vagal fibers. Application of 100 microM kynurenic acid, a broad spectrum glutamate receptor antagonist, abolished or significantly decreased the evoked responses. These results indicate that excitatory amino acids are the neurotransmitter at the first relay in the taste pathway in the central nervous system.