N-Acetylaspartylglutamate: possible role as the neurotransmitter of the lateral olfactory tract.

N-Acetylaspartylglutamate, an endogenous brain peptide that binds with high affinity to a subpopulation of glutamate-binding sites in rat brain, is excitatory on rat piriform cortex pyramidal cells studied in a perfused brain slice. Both the monosynaptic excitation of the pyramidal cells elicited by stimulation of the lateral olfactory tract and the response to N-acetylaspartylglutamate were blocked by DL-2-amino-4-phosphonobutyrate but not by other excitatory amino acid antagonists. Responses to glutamate and aspartate, previously considered to be candidates as the lateral olfactory tract transmitter, were unaffected by 2-amino-4-phosphonobutyrate. Three days after unilateral bulbectomy there was a significant decrease in concentrations of N-acetylaspartylglutamate as well as aspartate, N-acetylaspartate, and gamma-aminobutyrate in the pyriform cortex of the side from which the olfactory bulb had been removed. These results are consistent with the possibility that N-acetylaspartylglutamate is the endogenous transmitter of the lateral olfactory tract.