Attenuation of the midbrain-evoked defence reaction by selective
stimulation of medullary raphe neurones in rats.
Schenberg, Luiz C., and Thelma A. Lovick.
Department of Physiology, The Medical School, University of
Birmingham, Birmingham B15 2TT UK
APStracts 2:0166R, 1995.
In rats anaesthetised with alphaxalone/alphadolone, electrical
stimulation in the dorsal periaqueductal grey matter (PAG) evoked a
cardiovascular defence reaction with increases in blood pressure,
heart rate, femoral conductance and respiratory activity but a
decrease in renal conductance. These responses were attenuated
significantly following microinjection of 200 nl 0.1 M d,l
-homocysteic acid (DLH) into nucleus raphe magnus (NRM, n = 12) or
nucleus raphe obscurus (NRO, n = 22). The maximum reduction in the
pressor response was similar following stimulation in NRM (-36.3%)
and NRO (-37.3%). The reduction of the tachycardia, however, was
greater following stimulation in NRM (-78.1%) compared to NRO (
-34.6%). The maximum reduction in the PAG-evoked vasodilatation of the
hind limb averaged -55.7% and -55.3% following stimulation of NRM and
NRO, respectively, whilst the renal vasoconstriction was reduced by
-66.4% and -79.0%. The PAG-evoked increase in respiratory amplitude
was attenuated only following stimulation of NRO. It is concluded
that neurones in NRM and NRO may be involved in modulating the level
of excitability of neurones in the midbrain defence area and/or in
its efferent pathway.
Received 14 June 1994; accepted in final form 22 June 1995.
APS Manuscript Number R328-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.