Inhibitory response of locus coeruleus neurons to caloric stimulation in rats

本实验观察了前庭冷热刺激对乌拉坦麻醉大鼠蓝斑(LC)神经元活动的影响。用热水(44ﾟC)或冷水(30ﾟC)通过聚乙烯管冲洗中耳腔。大多数神经元对热量刺激的反应表现出神经元放电的抑制。热刺激对LC神经元放电的抑制潜伏期较长，持续时间较长(约3min)。无论是耳廓的热刺激，还是37ﾟ℃的水灌洗中耳，或迷路切除后对中耳的热刺激，都不能抑制LC神经元的放电。荷包牡丹碱可减弱热刺激对LC神经元的抑制作用。这些结果表明，热刺激对LC神经元放电的主要作用是抑制，热刺激引起的LC神经元放电抑制是由GABA_A受体介导的。然后，我们研究了损毁延髓头侧室外侧核(VML)或舌下前置核(PRII)对热刺激引起的LC神经元抑制的影响。损毁VML可减弱热刺激诱导的LC神经元抑制，但损毁Prii不能。提示去甲肾上腺素能LC神经元的前庭抑制活动参与前庭自主神经反射。

We examined the effects of caloric vestibular stimulation on the neuronal activity of the locus coeruleus (LC) in urethane-anesthetized rats. The middle ear cavity was irrigated with hot (44ﾟC) or cold (30ﾟC) water through a polyethylene tube. Most neurons exhibited suppression of neuronal discharge in response to caloric stimulation. The suppression of LC neuronal discharge following caloric stimulation occured with a long latency and lasted a long period of time (about 3 min). Neither caloric stimulation of the auricle, nor irrigation of the middle ear with water at 37ﾟC,nor caloric stimulation of the middle ear after labyrinthectomy inhibited LC neuronal discharge. The caloric stimulation-induced LC neuronal inhibition was attenuated by the iontophoretic applocation of bicuculline. These findings indicate that the predominant effect of caloric stimulation on LC neuronal discharge is inhibitory, and that the caloric stimulation-induced LC ncuronal in inhibition is mediated by GABA_A receptors. We then examined the effects of lesions in the rostral vcntrolateral medulla (VML) or in the nucleus prepositus hypoglossi (PrII) on LC neuronal inhibition caused by caloric stimulation. VML lesions attenuated caloric stimulation-induced LC neuronal inhibition, but PrII lesions did not. This finding indicates that vestibular inhibition of LC neurons is mediated by VML.It is suggested that the suppressed activity of noradrenergic LC neurons is involved in the vestibulo-autonomic reflex.