Denervation supersensitivity to glutamate in the nucleus tractus solitarii after removal of the nodose ganglion

Ifl-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 tol-Glu in the NTS. Therefore, we sought to determine if dose-related changes in arterial pressure (AP) and heart rate (HR) elicited byl-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 orl-Glu (3, 30, 75, 150, 300 and 1500 pmol/50 nl) was microinjected alternately into the right and left dorsomedial NTS. In control animals, and in animals 5 days and 15 days after ganglionectomy, the lowest dose ofl-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 tol-Glu evolves after nodose ganglionectomy and further support a role forl-Glu as a transmitter of cardiovascular afferents in the NTS.