Evolution of dose-related cardiovascular responses to L-glutamate microinjected into the nucleus tractus solitarii after removal of the nodose ganglion in rat.

1. In this study, we sought to determine if sensitivity to dose-related changes in arterial pressure (AP) and heart rate (HR) elicited by microinjection of L-glutamate (L-GLU) into the nucleus tractus solitarii (NTS) evolves after deafferentation in adult male Sprague-Dawley rats. 2. Twelve rats served as unoperated controls; and eight were studied 5 days, eleven 10 days and nine 15 days after ganglionectomy. Each rat was anaesthetized (halothane 1.5-2.0%) and cannulated for recording AP and HR. Vehicle or L-GLU (3, 30, 75, 150, 300 and 1500 pmole/50 nL) was microinjected into the right and left NTS. Injection sites were confirmed histologically. 3. 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 AP was 30 pmole. The threshold dose with injections on the lesioned side 10 days after ganglionectomy was 3 pmole. In rats studied at 10 days, but not in control, 5 or 15 day rats, dose-related responses for injections made on the left were shifted significantly to the left of those made on the right (P < 0.05). 4. 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. 5. These results suggest that supersensitivity to L-GLU evolves after nodose ganglionectomy and support a role for L-GLU as a transmitter of cardiovascular afferents in the NTS.