Key result
Tachycardia induced by dorsomedial hypothalamus stimulation was markedly suppressed by injection of muscimol into the raphe pallidus, but unaffected by saline.
Tachycardia evoked by disinhibition of the dorsomedial hypothalamus is mediated through activation of neurons in the medullary raphe pallidus, revealing a novel neural pathway for stress-induced cardiac stimulation.
Should not yet alter clinical management of stress tachycardia; hypothesis-generating for central autonomic pathways in animal models.
Activation of neurons in the region of the dorsomedial hypothalamus (DMH) appears to generate the sympathetically mediated tachycardia seen in experimental stress in rats. The purpose of this study was to assess the role of neurons in the area of the medullary raphe pallidus (RP) in the tachycardia caused by stimulation of the DMH. The cardiovascular response to microinjection of the GABA(A) receptor antagonist bicuculline methiodide (BMI) 10 pmol (100 nl)(-1) into the DMH was assessed before, and after, injection of the GABA(A) receptor agonist muscimol 80 pmol (100 nl)(-1) or saline vehicle 100 nl into the RP in urethane-anaesthetized rats. Tachycardia evoked by microinjection of BMI into the DMH was mimicked by microinjection of BMI 30 pmol (75 nl)(-1) into the RP. This DMH-induced tachycardia was markedly suppressed after injection of muscimol into the RP, but the response was unaffected by injection of saline into the same region. Thus, DMH-induced tachycardia is mediated through activation of neurons in the area of the RP, suggesting that these neurons may play a previously unrecognized role in stress-induced cardiac stimulation.
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Samuels et al. (2002) studied Tachycardia. Muscimol injection into the raphe pallidus vs. Saline vehicle was evaluated on Tachycardia evoked by microinjection of bicuculline methiodide into the dorsomedial hypothalamus. Tachycardia induced by dorsomedial hypothalamus stimulation was markedly suppressed by injection of muscimol into the raphe pallidus, but unaffected by saline.
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