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NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION

Medullary lateral tegmental field mediates the cardiovascular but not respiratory component of the Bezold-Jarisch reflex in the cat

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

Submitted 7 June 2005 ; accepted in final form 11 August 2005

We determined the effects of bilateral microinjection of muscimol and excitatory amino acid receptor antagonists into the medullary lateral tegmental field (LTF) on changes in sympathetic nerve discharge (SND), mean arterial pressure (MAP), and phrenic nerve activity (PNA; artificially ventilated cats) or intratracheal pressure (spontaneously breathing cats) elicited by right atrial administration of phenylbiguanide (PBG; i.e., the Bezold-Jarisch reflex) in dial-urethane anesthetized cats. The PBG-induced depressor response (–66 ± 8 mmHg; mean ± SE) was converted to a pressor response after muscimol microinjection in two of three spontaneously breathing cats and was markedly reduced in the other cat; however, the duration of apnea (20 ± 3 vs. 17 ± 7 s) was essentially unchanged. In seven paralyzed, artificially ventilated cats, muscimol microinjection significantly (P < 0.05) attenuated the PBG-induced fall in MAP (–39 ± 7 vs. –4 ± 4 mmHg) and the magnitude (–98 ± 1 vs. –35 ± 13%) and duration (15 ± 2 vs. 3 ± 2 s) of the sympathoinhibitory response. In contrast, the PBG-induced inhibition of PNA was unaffected (3 cats). Similar results were obtained by microinjection of an N-methyl-D-aspartate (NMDA) receptor antagonist, D(-)-2-amino-5-phosphonopentanoic acid, into the LTF. In contrast, neither the cardiovascular nor respiratory responses to PBG were altered by blockade of non-NMDA receptors with 1,2,3,4-tetrahydro-6-nitro-2,3-dioxobenzo[f]quinoxaline-7-sulfonamide. We conclude that the LTF subserves a critical role in mediating the sympathetic and cardiovascular components of the Bezold-Jarisch reflex. Moreover, these data show separation of the pathways mediating the respiratory and cardiovascular responses of this reflex at a level central to bulbospinal outflows to phrenic motoneurons and preganglionic sympathetic neurons.

cardiopulmonary chemosensitive afferent; medullary lateral tegmental field; phrenic nerve activity; sympathetic nerve discharge; vagal afferent

This article has been cited by other articles:

				L. M. Salo, R. L. Woods, C. R. Anderson, and R. M. McAllen Nonuniformity in the von Bezold-Jarisch reflex Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2007; 293(2): R714 - R720. [Abstract] [Full Text] [PDF]

				H. S. Orer, G. L. Gebber, and S. M. Barman Medullary lateral tegmental field neurons influence the timing and pattern of phrenic nerve activity in cats J Appl Physiol, August 1, 2006; 101(2): 521 - 530. [Abstract] [Full Text] [PDF]