Effects of neuroactive compounds, noxious and cardiovascular stimuli on the release of amino acids in the rat locus coeruleus.

The release of excitatory amino acids (glutamate, aspartate), inhibitory amino acids (GABA, taurine) and arginine was determined in the locus coeruleus (LC) of anaesthetized rats. The neuronal origin of stimulated amino acid release was verified by superfusion with neuroactive compounds. Electrical stimulation of the sciatic nerve, as well as mechanical footshock, enhanced LC release rates of glutamate and aspartate without influencing those of taurine and arginine. GABA release rate was increased slightly after some delay. Excitatory amino acid release was not influenced by changes in blood pressure. The results provide direct neurochemical evidence that noxious stimuli activate LC neurons via the glutamate and aspartate input into this nucleus.