Inhibitory response of locus coeruleus neurons to caloric stimulation in rats

研究了氨基乙酯麻醉大鼠前庭热刺激对蓝斑（LC）神经元活动的影响。通过聚乙烯管用热水（44‰）或冷水（30‰）冲洗中耳腔。大多数神经元在热刺激下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长，持续时间长（约3 min）。对耳廓的热刺激、对中耳37℃的水冲洗、对迷路切除后中耳的热刺激均不能抑制LC神经元放电。热刺激对LC神经元的抑制作用可被二胡兰的离子吸附作用减弱。这些结果表明，热刺激对LC神经元放电的主要作用是抑制，并且热刺激诱导的LC神经元的抑制是由GABA_A受体介导的。然后，我们检查了吻侧侧髓质（VML）或舌下前置核（PrII）病变对热刺激引起的LC神经元抑制的影响。VML病变减弱了热刺激诱导的LC神经元抑制，而PrII病变则没有。这一发现表明，前庭抑制LC神经元是由VML介导的。提示去甲肾上腺素能LC神经元活性的抑制与前庭-自主神经反射有关。

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.