A GABAergic mechanism in the inhibition of cardiac vagal reflexes

A depressor response and bradycardia were produced by aortic nerve stimulation in urethane-chloralose-anaesthetized, paralyzed and artificially ventilated rabbits. Stimulation of the superficial peroneal nerve (SP) or rostral ventrolateral medulla (rVLM) inhibited the aortic nerve stimulation-evoked bradycardia, which was also inhibited by direct microinjection of GABA into the dorsal vagus nucleus (DVN). Application of bicuculline methiodide into the same medullary area antagonized the effect of GABA and partially or completely abolished the SP or rVLM stimulation-produced inhibition. However, strychnine hydrochloride had no effect on the SP or rVLM stimulation-produced inhibition. These observations indicate that GABAergic system present at the DVN is possibly involved in the inhibition of evoked bradycardia during somatic afferent and rVLM stimulation.