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Am J Physiol Regul Integr Comp Physiol 278: R1643-R1650, 2000;
0363-6119/00 $5.00
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Vol. 278, Issue 6, R1643-R1650, June 2000

A projection from the ventral tegmental area to the periaqueductal gray involved in cardiovascular regulation

Gilbert J. Kirouac and Quentin J. Pittman

Division of Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland, A1B 3V6; Neuroscience Research Group, University of Calgary, Alberta, T2N 4N1, Canada

Experiments were done in alpha -chloralose-anesthetized rats to determine a pathway mediating the cardiovascular depressor responses elicited from stimulation of the ventral tegmental area (VTA). The magnitude of the depressor responses elicited by glutamate stimulation (0.1 M/30 nl) of the VTA was examined after neuronal block produced by microinjections of lidocaine into ascending fiber bundles leaving the VTA to innervate the forebrain and thalamus. Bilateral microinjections of 1 µl of 4% lidocaine in the medial forebrain bundle (n = 6) and in the periventricular fibers of the midbrain (n = 5) did not attenuate the depressor response from stimulation of the VTA. Experiments were done using the anterograde tracer biotinylated dextran amine to identify descending projections from the VTA to cardiovascular centers in the brain stem. Examination of the nucleus of the solitary tract, ventrolateral medulla, and A5 catecholaminergic cell group revealed few or no fibers or terminals. Occasional fibers and some terminals were observed in the nucleus of raphe magnus, parabrachial nucleus, and locus ceruleus. A very dense bilateral projection was found to the ventrolateral periaqueductal gray (PAGvl) and dorsal raphe nucleus adjacent to the PAGvl. Bilateral injections of 4% lidocaine (n = 4) or 10 mM cobalt chloride (n = 5) into the PAGvl region attenuated the depressor responses elicited by stimulation of the VTA by ~50%. These experiments indicate that the depressor responses elicited from activation of the VTA are mediated in part by a pathway to a cardiovascular depressor area located in the PAGvl.

medial forebrain bundle; biotinylated dextran; lidocaine; blood pressure; pathway


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Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
S. Cavun and W. R. Millington
Evidence that hemorrhagic hypotension is mediated by the ventrolateral periaqueductal gray region
Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2001; 281(3): R747 - R752.
[Abstract] [Full Text] [PDF]




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