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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
-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
This article has been cited by other articles:
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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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