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Cardiovascular responses elicited by chemical stimulation of the C1 area of the rostral ventrolateral medulla in conscious, unrestrained rats
area
Bachelard, ikpt. of Physiology and Pharmacol~,
N.. Gardener,
S.M. and Bennett,
of the
rostra!
T.
Medical School, Queens Medical Centre, Nottingham, NG7 2UH, U.K.
StimuIation of the Cl area of the rostral ventrolateral medulla increases blood pressure (BP) and heart rate (HR) in anaesthetised rats (Ross et al., 1984). The purpose of the present study was to examine the cardiovascular responses produced by chemical stimulation of the Cl area in conscious, unrestrained rats. Under anaesthesia, male Wistar rats were placed in a stereotaxic frame and a guide cannula was unilaterally implanted (caudal-rostral, - P1.8, lateral, + 1.6, vertical, -8.5 mm relative to bregma) above the left Cl region 8 days before the experiment. Twenty four h before the experiment, catheters were inserted in the distal abdominal aorta and jugular vein for cardiovascular measurements and drug injections, respectively. At the beginning of the experiment the Cl area received a control injection of CSF (0.3 ~1). Changes in BP and HR were recorded for 90 min, and then an injection of L-glutamate (0.3 pl; 0.24-2.4 nmol) was given. Changes in BP and HR were recorded for a further 90 min. In some animals, 15 mm before the Cl injection of L-glutamate, pentolinium was given i.v. (bolus 5 mg kg-’ and infusion 5 mg kg-’ h” ). Differences between cardiovascular effects produced by Cl stimulation in the absence and presence of pentolinium were examined using Student’s unpaired t-test. Stimulation of the Cl area produced a dose-dependent increase in BP which was generally associated with a bradycardia; both effects were completely abolished by pentolinium. Some of the results are summarised in Table 1. Table 1 Cardiowscular changes elicited by microinjection of L-glutamate (2.4 nmol) in the Cl area. Values are mean fS.E.M.; versus control.
Systolic blood pressure (mm Hg) Diastolic blood pressure (mm Hg) Heart Rate (beats min- ’ )
Control (n = 10) _- “.._-_____ +64k 6 +47+ 3 -5SflO
_.“_,
* P < 0.05
+ Pentolinium (n = 5) -3f6+ 0*4* -8+8*
The results indicate that chemical stimulation of the Cl area in conscious animals produces effects on BP qualitatively similar to those observed in anaesthetized rats, although the former are more sensitive (Bachelard and Marsden. 1989). The results with pentolinium confirm that stimulation of the Cl area of the rostra1 ventrolateral medulla can provide direct and/or indirect excitatory drive to the preganglionic sympathetic neurones of the spinal cord. erences Ross. C-A-. D.A. Ruggiero. D.H. Park. T&f. Job. A.F. Sverl, J. Femandez-Pardal. J.M. Saavedra and D.J. Reis, 1984, J. Neurosci. 4, 474. Bachelard. H. and C.A.. Marsden. 1989, Br. J. Pharmacol. 98.697P.
Bachelard, ikpt. of Physiology and Pharmacol~,
N.. Gardener,
S.M. and Bennett,
of the
rostra!
T.
Medical School, Queens Medical Centre, Nottingham, NG7 2UH, U.K.
StimuIation of the Cl area of the rostral ventrolateral medulla increases blood pressure (BP) and heart rate (HR) in anaesthetised rats (Ross et al., 1984). The purpose of the present study was to examine the cardiovascular responses produced by chemical stimulation of the Cl area in conscious, unrestrained rats. Under anaesthesia, male Wistar rats were placed in a stereotaxic frame and a guide cannula was unilaterally implanted (caudal-rostral, - P1.8, lateral, + 1.6, vertical, -8.5 mm relative to bregma) above the left Cl region 8 days before the experiment. Twenty four h before the experiment, catheters were inserted in the distal abdominal aorta and jugular vein for cardiovascular measurements and drug injections, respectively. At the beginning of the experiment the Cl area received a control injection of CSF (0.3 ~1). Changes in BP and HR were recorded for 90 min, and then an injection of L-glutamate (0.3 pl; 0.24-2.4 nmol) was given. Changes in BP and HR were recorded for a further 90 min. In some animals, 15 mm before the Cl injection of L-glutamate, pentolinium was given i.v. (bolus 5 mg kg-’ and infusion 5 mg kg-’ h” ). Differences between cardiovascular effects produced by Cl stimulation in the absence and presence of pentolinium were examined using Student’s unpaired t-test. Stimulation of the Cl area produced a dose-dependent increase in BP which was generally associated with a bradycardia; both effects were completely abolished by pentolinium. Some of the results are summarised in Table 1. Table 1 Cardiowscular changes elicited by microinjection of L-glutamate (2.4 nmol) in the Cl area. Values are mean fS.E.M.; versus control.
Systolic blood pressure (mm Hg) Diastolic blood pressure (mm Hg) Heart Rate (beats min- ’ )
Control (n = 10) _- “.._-_____ +64k 6 +47+ 3 -5SflO
_.“_,
* P < 0.05
+ Pentolinium (n = 5) -3f6+ 0*4* -8+8*
The results indicate that chemical stimulation of the Cl area in conscious animals produces effects on BP qualitatively similar to those observed in anaesthetized rats, although the former are more sensitive (Bachelard and Marsden. 1989). The results with pentolinium confirm that stimulation of the Cl area of the rostra1 ventrolateral medulla can provide direct and/or indirect excitatory drive to the preganglionic sympathetic neurones of the spinal cord. erences Ross. C-A-. D.A. Ruggiero. D.H. Park. T&f. Job. A.F. Sverl, J. Femandez-Pardal. J.M. Saavedra and D.J. Reis, 1984, J. Neurosci. 4, 474. Bachelard. H. and C.A.. Marsden. 1989, Br. J. Pharmacol. 98.697P.