Raphe magnus/pallidus neurons regulate tail but not mesenteric arterial blood flow in rats
Section snippets
Experimental procedures
Successful experiments were performed on eight male Sprague–Dawley rats (350–450 g) obtained from the Flinders University Breeding Colony. All experimental procedures were approved by the Flinders University of South Australia Animal Ethics Committee. All efforts were made to minimize animal suffering with each anesthetized animal being used for both electrical and chemical stimulation experiments to minimize the number of animals used. Animals were anesthetized by inhalation of 1–2% halothane
Responses to lip pinch and trigeminal tract stimulation
In response to a pinch of the lip, arterial pressure increased from 122±3 to 146±4 mm Hg, heart rate increased from 398±14 to 411±13 beats/min, and tail flow increased from 37±4 to 42±4 cm/s (all changes significant, P<0.01, n=8). These changes occurred rapidly, during the 3-s pinch period, lasted only a few seconds, and quickly returned to control levels at the end of the pinch. Mesenteric flow did not alter significantly (19±2 to 18±2 cm/s, P>0.05, n=8). Vascular conductance (mean flow
Discussion
To the best of our knowledge, our present experiments in rats are the first studies directly measuring tail blood flow in response to excitation or inhibition of lower brainstem neuronal function in this species. Low-amplitude electrical stimulation in a very restricted portion of the rostral midline medulla, in the region of raphe magus/raphe pallidus, promptly reduced tail blood flow to near-zero values for the duration of the stimulation, with no change in mesenteric blood flow and no
Conclusion
Our data provide evidence that raphe magnus/pallidus/parapyramidal neurons have relatively selective regulatory control over the tail cutaneous vascular bed in rats, as is also the case in rabbits. There is a robust direct raphe-spinal pathway, so that effects on the tail bed may well be mediated by a direct raphe-spinal connection to sympathetic pre-ganglionic neurons, rather than by an additional brainstem or spinal relay. It could be that one subpopulation of raphe-spinal neurons mediates
Acknowledgements
Our research was supported by the National Health and Medical Research Council and by the National Heart Foundation of Australia. We thank Joseph Garcia, Kate Barber and Nigel Pedersen for technical assistance.
References (25)
- et al.
Raphe pallidus and parapyramidal neurons regulate ear pinna vascular conductance in the rabbit
Neurosci. Lett.
(1999) - et al.
The influence of the ventrolateral medulla on thermoregulatory circulations in the rat
J. Auton. Nerv. Syst.
(1994) Raphe pallidus and raphe obscurus projections to the intermediolateral cell column in the rat
Brain Res.
(1981)- et al.
Synchronous changes in ear and tail blood flow following salient and noxious stimuli in rabbits
Brain Res.
(1999) - et al.
Raphe region mediates changes in cutaneous vascular tone elicited by stimulation of amygdala and hypothalamus in rabbits
Brain Res.
(2001) - et al.
Adrenal epinephrine secretion is not regulated by sympathoinhibitory neurons in the caudal ventrolateral medulla
Brain Res.
(1999) - et al.
The lumbar preganglionic sympathetic supply to rat tail and hindpaw
J. Auton. Nerv. Syst.
(1998) - et al.
Differential control of sympathetic drive to the rat tail artery and kidney by medullary premotor cell groups
Brain Res.
(1999) - et al.
Magnitude of skin vasomotor reflex represents the intensity of nociception under general anesthesia
J. Auton. Nerv. Syst.
(1998) - et al.
CNS cell groups projecting to sympathetic outflow of tail artery: neural circuits involved in heat loss in the rat
Brain Res.
(1998)
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