Central GABAergic mechanisms are involved in apnea induced by SLN stimulation in piglets

Stimulation of the superior laryngeal nerve (SLN) results in apnea in anima ls of different species, the mechanism of which is not known. We studied th e effect of the GABA, receptor blocker bicuculline, given intravenously and intracisternally, on apnea induced by SLN stimulation. Eighteen 5- to 10-d ay-old piglets were studied: bicuculline was administered intravenously to nine animals and intracisternally to nine animals. The animals were anesthe tized and then decerebrated, vagotomized, ventilated, and paralyzed. The ph renic nerve responses to four levels of electrical SLN stimulation were mea sured before and after bicuculline. SLN stimulation caused a significant de crease in phrenic nerve amplitude, phrenic nerve frequency, minute phrenic activity, and inspiratory time (P < 0.01) that was proportional to the leve l of electrical stimulation. Increased levels of stimulation were more like ly to induce apnea during stimulation that often persisted beyond cessation of the stimulus. Bicuculline, administered intravenously or intracisternal ly, decreased the SLN stimulation-induced decrease in phrenic nerve amplitu de, minute phrenic activity, and phrenic nerve frequency (P < 0.05). Bicucu lline also reduced SLN-induced apnea and duration of poststimulation apnea (P < 0.05). We conclude that centrally mediated GABAergic pathways are invo lved in laryngeal stimulation-induced apnea.