Raphe region mediates changes in cutaneous vascular tone elicited by stimulation of amygdala and hypothalamus in rabbits.
Raphe pallidus/parapyramidal neurons control cutaneous vasoconstriction induced by noxious stimuli. To determine whether they mediate forebrain-induced cutaneous vasoconstriction, we assessed changes in ear pinna blood flow elicited by electrical stimulation of amygdala and hypothalamus before and after injection of muscimol into the raphe/parapyramidal region. We compared ear flow with simultaneously recorded mesenteric flow. Experiments were performed in rabbits anesthetized with urethane (1.25-1.5 g/kg), paralysed and mechanically ventilated. Amygdala stimulation reduced skin conductance from 0.32+/-0.06 to 0.10+/-0.02 cm/s per mmHg (P<0.05, n=9), without effect on mesenteric conductance. Hypothalamic stimulation caused vasoconstriction in both cutaneous and mesenteric beds (conductances fell from 0.27+/-0.05 to 0.05+/-0.02 cm/s per mmHg and from 0.27+/-0.06 to 0.14+/-0.04 cm/s per mmHg (P<0.05, n=9), respectively). Muscimol microinjection (5 nmol in 100 nl) to raphe/parapyramidal region eliminated amygdala- and hypothalamus-induced skin vasoconstriction (pre-stimulus conductance 0.42+/-0.13 and 0.41+/-0.11 cm/s per mmHg, post-stimulus 0.41+/-0.12 and 0.39+/-0.10 cm/s per mmHg, respectively), but not hypothalamically-induced mesenteric vasoconstriction (pre-stimulus 0.29+/-0.06, post-stimulus 0.16+/-0.03 cm/s per mmHg, P<0.05, n=8). The latter was strongly attenuated by bilateral injection of muscimol to the rostral ventrolateral medulla. Data suggest that descending hypothalamo-spinal and amygdala-spinal pathways constricting the cutaneous vascular bed relay in the raphe/parapyramidal area. A relay in the rostral ventrolateral medulla contributes substantially to mesenteric vasoconstriction elicited from the hypothalamus.
Nalivaiko
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Department of Physiology, Center for Neuroscience, Flinders University, SA 5042, Bedford Park, Australia. eugene.nalivaiko@flinders.edu.au
Blessing
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D000679:Amygdala / Q000166:cytology / Q000502:physiology*; D000818:Animals; D004558:Electric Stimulation; D018755:GABA Agonists / Q000494:pharmacology; D007031:Hypothalamus / Q000166:cytology / Q000502:physiology*; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D009118:Muscimol / Q000494:pharmacology; D009434:Neural Pathways / Q000166:cytology / Q000502:physiology*; D010146:Pain / Q000503:physiopathology; D011817:Rabbits; D011903:Raphe Nuclei / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology*; D012867:Skin / Q000098:blood supply; D013152:Splanchnic Circulation / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology*
D018755:GABA Agonists; D009118:Muscimol