Neural mechanisms underlying the milk ejection burst and reflex

One of the more interesting and complex phenomena involving neurohypophysial hormones is the milk ejection reflex and the events surrounding it. Accordingly, many investigations over the years have taken up the challenge of elucidating its myriad aspects. Much has been learned from in vivo preparations about the sequence of events that so regularly occurs: important priming by maternal behaviours, the intermittent rhythms, gating of bursting, synchrony of the oxytocin (OXT) neuronal bursts emitted intermittently in response to the continuous suckling of the young and the factors that influence the amplitude of the bursts/milk ejections (e.g. number of suckling pups). In vivo electrophysiological studies are constrained by the infeasibility of routinely recording transmembrane events and, therefore, cannot offer detailed membrane and/or synaptic analyses. Recent studies have developed an in vitro model of OXT neuronal bursting that has allowed more mechanistic analyses of these bursts as well as factors involved in their generation and structure. Here we review many of the cellular and molecular mechanisms that have been shown to underlie the milk ejection bursts, as revealed by in vitro analyses.