E. Colombari et Wt. Talman, DENERVATION SUPERSENSITIVITY TO GLUTAMATE IN THE NUCLEUS-TRACTUS-SOLITARII AFTER REMOVAL OF THE NODOSE GANGLION, Brain research, 677(1), 1995, pp. 110-116
If L-glutamate (L-Glu) is the transmitter released from cardiovascular
vagal afferent nerve fibers in the nucleus tractus solitarii (NTS), t
hen interruption of those afferents should lead to denervation superse
nsitivity to L-Glu in the NTS. Therefore, we sought to determine if do
se-related changes in arterial pressure (AP) and heart rate (HR) elici
ted by L-Glu microinjected into the NTS evolve after removal of the le
ft 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%) a
nd 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 micro
injeted alternately into the right and left dorsomedial NTS. In contro
l 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 thre
shold dose with injections on the lesioned side 10 days after ganglion
ectomy 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 th
e right (P < 0.05). In control, 5, and 15 day rats there were no signi
ficant 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.