Excitatory effects of intraventricular injections of oxytocin on the milk ejection reflex in the rat.

The effects of oxytocin, administered into the 3rd cerebral ventricle, on the milk ejection reflex, were studied in urethane-anaesthetized lactating rats. Intramammary pressure, electrical activity of oxytocinergic neurones and EEG were recorded simultaneously. Intraventricular injection of oxytocin (6, 60 and 600 microU) significantly increased both milk ejection frequency and the number of spikes in the oxytocinergic neurones characteristic bursts. The amount of hormone released for each milk ejection was higher after intraventricular oxytocin injection than before. The strongly excitatory effect of intraventricular oxytocin injection on the milk ejection reflex was not reproduced with arginine-vasopressin.