Effects of microinjection of L-glutamate into locus coeruleus complex area on respiration.

The experiments were performed on 55 rabbits vagotomied, anesthetized with urethane and immobilized with flaxedil. Injection of L-glutamate (L-glu) into the locus coeruleus complex (Lc-Sc) area led to a marked increase in respiratory frequency (RF) and phrenic nerve discharge rate (phr.d) (16 +/- 3.5% and 6.5 +/- 2.5%; P < 0.01 and P < 0.05, respectively), a decrease in inspiratory and expiratory duration, and no obvious change in blood pressure (Bp) was observed. While prazosin (0.5 micrograms/microliters), yohimbin (4 micrograms/microliters) and propranolol (2 micrograms/microliters) were preinjected into the nuclei tractus solitraii (NTS) respectively, the above-mentioned effects of L-glu on respiration was blocked. These results indicate that the excitation of neurons in the Lc-Sc can induce an increase in RF and phr. d and the excitative effect of L-glu on RF was mediated by alpha 1, alpha 2 and beta-receptors in the NTS, while the effect on phr.d was mediated differently.