Title

Attenuation Of Heart Rate Control And Neural Degeneration In Nucleus Ambiguus Following Chronic Intermittent Hypoxia In Young Adult Fischer 344 Rats

Keywords

baroreflex; cardiac ganglia; heart; intermittent hypoxia; nucleus ambiguus; parasympathetic

Abstract

Chronic intermittent hypoxia (CIH) attenuates baroreflex control of heart rate (HR). In this study, we assessed whether CIH exposure reduced nucleus ambiguus (NA) control of HR and induced neural degeneration in the NA. Fischer 344 (age: 3-4 months) rats were exposed to either room air (RA: normoxia) or intermittent hypoxia for 35-50 days. At the end of these exposures, animals were anesthetized with pentobarbital. HR responses to arterial blood pressure (AP) changes induced by phenylephrine (PE) and sodium nitroprusside (SNP) were measured. In another set of rats, HR and AP responses to l-glutamate (l-Glu) microinjections (10 mM, 20 nl) into the left NA and electrical stimulation of the left cervical vagus nerve at 1-30 Hz (0.5 mA, 1 ms) for 20 s were measured. Brainstem slices at the level of -800, -400, 0, +400, +800 μm relative to the obex were processed in additional rats using Nissl staining. The NA was identified by retrogradely labeling vagal motoneurons using the tracer tetramethylrhodamine dextran (TMR-D) which was injected into the ipsilateral nodose ganglion. We found that CIH significantly 1) reduced the baroreflex control of HR (slope RA: -1.2±0.2 bpm/mmHg; CIH -0.5±0.1 bpm/mmHg; P<0.05); 2) attenuated the HR responses to l-Glu injections into the NA [HR: -280±15 (RA) vs. -235±16 (CIH) beats/min; P<0.05]; 3) augmented the HR responses to electrical stimulation of the vagus (P<0.05); 4) induced a significant cellular loss in the NA region (P<0.05). Thus, CIH induces a cell loss in the NA region which may contribute to attenuation of baroreflex sensitivity and NA control of HR following CIH. © 2008 IBRO.

Publication Date

5-15-2008

Publication Title

Neuroscience

Volume

153

Issue

3

Number of Pages

709-720

Document Type

Article

Personal Identifier

scopus

DOI Link

https://doi.org/10.1016/j.neuroscience.2008.01.066

Socpus ID

43049170354 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/43049170354

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