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NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION

Role of ventrolateral medulla in generating the 10-Hz rhythm in sympathetic nerve discharge

Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan

Submitted 6 February 2007 ; accepted in final form 26 March 2007

We recorded changes in right inferior cardiac and either left inferior cardiac or left vertebral sympathetic nerve discharge (SND) produced by unilateral microinjections of GABA-A and excitatory amino acid (EAA) receptor antagonists into the ventrolateral medulla (VLM) of urethane-anesthetized, baroreceptor-denervated cats. Unilateral microinjections of GABA-A receptor antagonists, SR-95531 or bicuculline, into single tracks in VLM anywhere between 1 and 5 mm rostral to the obex eliminated or markedly reduced 10-Hz power in SND on both sides of the body. Low-frequency components (<6 Hz) of SND were unaffected. Complete blockade of the 10-Hz rhythm occurred with a dose of SR-95531 as low as 6.25 pmol in a 50-nl volume. Unilateral microinjections of the nonselective EAA receptor antagonist, kynurenate (KYN; 7.5 nmol), into the caudal or rostral VLM significantly reduced, but did not eliminate, 10-Hz SND ipsilateral to the injection sites, while 10-Hz SND contralateral to the injection sites was not significantly changed. These observations suggest that 1) GABAergic transmission in VLM is critical for generation of the 10-Hz rhythm, 2) the caudal and rostral portions of VLM act together to generate the 10-Hz rhythm, and 3) 10-Hz rhythm generation depends, at least in part, on tonic or phasic excitatory drive to GABAergic interneurons in caudal VLM and presympathetic neurons in rostral VLM. The data also suggest that pathways interconnecting the two halves of the brain stem play an important role in promoting 10-Hz rhythm generation.

GABAergic transmission; sympathetic rhythms; bicuculline; SR-95531; kynurenate

This article has been cited by other articles:

				H. S. Orer, G. L. Gebber, and S. M. Barman Role of serotonergic input to the ventrolateral medulla in expression of the 10-Hz sympathetic nerve rhythm Am J Physiol Regulatory Integrative Comp Physiol, May 1, 2008; 294(5): R1435 - R1444. [Abstract] [Full Text] [PDF]