Raphe magnus/pallidus neurons regulate tail but not mesenteric arterial blood flow in rats

doi:10.1016/S0306-4522(01)00251-2

Neuroscience

Volume 105, Issue 4, 22 August 2001, Pages 923-929

https://doi.org/10.1016/S0306-4522(01)00251-2 Get rights and content

Abstract

In urethane-anesthetized rats with body temperature maintained at 39–40°C, electrical stimulation of raphe magnus/pallidus/parapyramidal region within 0.5 mm of the ventral medullary surface reduced arterial blood flow to the tail cutaneous bed (measured with a chronically implanted Doppler ultrasonic flowmeter) from 28±5 to 6±1 cm/s (P<0.01), without changing mesenteric arterial blood flow, and with only small, variable changes in arterial pressure. Injection of bicuculline (50 pmol in 50 nl) at the same site reduced tail flow from 19±2 to 3±1 cm/s (P<0.01), again without significantly changing mesenteric flow, but with a moderate increase in arterial pressure. When the rat was cooled to reduce basal tail blood flow, injection of muscimol (1 nmol in 100 nl) or GABA (100 nmol in 100 nl) into the raphe site restored tail blood flow to 93±4% of the pre-cooling level.

These recordings are the first reported direct measurements of rat tail blood flow changes elicited by alteration of neuronal function in the brainstem. The rostral medullary raphe controls the tail cutaneous vascular bed in a relatively selective manner. Our findings add to evidence that raphe magnus/pallidus/parapyramidal neurons are involved in regulating cutaneous blood flow in response to changes in body temperature in the rat.

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.

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Raphe magnus/pallidus neurons regulate tail but not mesenteric arterial blood flow in rats

Abstract

Section snippets

Experimental procedures

Responses to lip pinch and trigeminal tract stimulation

Discussion

Conclusion

Acknowledgements

Neurosci. Lett.

J. Auton. Nerv. Syst.

Brain Res.

Brain Res.

Brain Res.

Brain Res.

J. Auton. Nerv. Syst.

Brain Res.

J. Auton. Nerv. Syst.

Brain Res.

Neurosci. Lett.

Neuroscience