Sympathetic overactivity and altered respiratory control are commonly observed after chronic intermittent hypoxia (CIH) exposure. However, the central mechanisms underlying such neurovegetative dysfunctions remain unclear. Herein we hypothesized that CIH (6% O2 every 9 min, 8 h/day, 10 days) in juvenile rats alters glutamatergic transmission in the commissural nucleus tractus solitarius (cNTS), a pivotal site for integration of peripheral chemoreceptor inputs. Using an in situ working heart-brainstem preparation, L-glutamate microinjections (1, 3 and 10 mM) into the cNTS of control rats (n=8) evoked increases in thoracic sympathetic (tSN) and central vagus (cVN) activities combined with inhibition of phrenic nerve (PN) activity. Besides, the ionotropic glutamatergic receptor antagonism with kynurenic acid (KYN, 250 mM) in the cNTS of control group (n=7) increased PN burst duration and frequency. In the CIH group (n=10), the magnitude of L-glutamate-induced cVN excitation was smaller and the PN inhibitory response was blunted (P<0.05). In addition, KYN microinjections into the cNTS of CIH rats (n=9) did not alter PN burst duration and produced smaller increases in its frequency in comparison to controls. Moreover, KYN microinjections into the cNTS attenuated the sympathoexcitatory response to peripheral chemoreflex activation in control but not in CIH rats (P<0.05). These functional CIH-induced alterations were accompanied by a significant 10% increase of NMDAR1 and GluR2/3 receptor subunit density in the cNTS (n=3-8, P<0.05), evaluated by western-blot. These data indicate that glutamatergic transmission is altered in the cNTS of CIH rats and may contribute to the sympathetic and respiratory changes observed in this experimental model.
- glutamatergic transmission
- Copyright © 2011, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology