DENERVATION SUPERSENSITIVITY TO GLUTAMATE IN THE NUCLEUS-TRACTUS-SOLITARII AFTER REMOVAL OF THE NODOSE GANGLION

If L-glutamate (L-Glu) is the transmitter released from cardiovascular vagal afferent nerve fibers in the nucleus tractus solitarii (NTS), then interruption of those afferents should lead to denervation supersensitivity to L-Glu in the NTS. Therefore, we sought to determine if dose-related changes in arterial pressure (AP) and heart rate (HR) elicited by L-Glu microinjected into the NTS evolve after removal of the left nodose ganglion in rats. Twelve rats served as unoperated controls; and eight were studied 5 days, eleven 10 days, and nine 15 days after ganglionectomy. Each rat was anesthetized with halothane (1.5-2.0%) and cannulated for recording AP and HR. After exposure of the brainstem, vehicle or L-Glu (3, 30, 75, 150, 300 and 1500 pmol/50 nl) was microinjeted alternately into the right and left dorsomedial NTS. In control animals, and in animals 5 days and 15 days after ganglionectomy, the lowest dose of L-Glu that produced a significant fall of mean AP (-10 +/- 2, -5 +/- 2, -6 +/- 1 mmHg, respectively) was 30 pmoles. The threshold dose with injections on the lesioned side 10 days after ganglionectomy was 3 pmol (-8 +/- 2 mmHg). In rats studied at 10 days, but not in control, 5 or 15 day rats, the dose-responses for injections made on the left were shifted significantly to the left of those made on the right (P < 0.05). In control, 5, and 15 day rats there were no significant differences between dose-related responses elicited from right and left NTS. Responses of HR did not differ between groups of animals or sides of injection. These results suggest that supersensitivity to L-Glu evolves after nodose ganglionectomy and further support a role for L-Glu as a transmitter of cardiovascular afferents in the NTS.