Medullary A1 noradrenergic neurones may mediate oxytocin release after noxious stimuli.

Noxious stimuli facilitate oxytocin release from the pituitary. Oxytocin cells receive excitatory synaptic inputs from the noradrenergic neurones located in the medulla oblongata. Oxytocin release after noxious stimuli is blocked by noradrenaline depletion in the brain. Here, we examined effects of noxious stimuli upon noradrenaline release within the supraoptic nucleus. Electric footshocks or mustard oil application to the foot pad facilitated noradrenaline release in the nucleus. Noradrenaline release after noxious stimuli was impaired by microinjections with a GABA(A) receptor agonist, muscimol, or an alpha 2 adrenoceptor agonist, clonidine, into the A1 noradrenergic cell regions. From these and reported data, we conclude that the medullary A1 noradrenergic neurones contribute, at least in part, to oxytocin release from the pituitary after noxious stimuli.