Emergent Synchronous Bursting of Oxytocin Neuronal Network
(A) A typical burst in a model cell plotted as instantaneous firing rate (each point is the reciprocal of the interval since the previous spike). This profile is essentially indistinguishable to burst profiles observed in vivo. (B) Consensus interspike interval distribution (see ) of 23 oxytocin cells recorded from the supraoptic nucleus in vivo (circles) compared with that generated by the model (squares). In both cases, histograms were constructed from spike activity between the bursts. The individual distributions were normalized to the height of the mode and averaged; bars are S.E.M. (C) Mean profiles of milk-ejection bursts from a real oxytocin cell (circles) and from a model cell (squares). Each profile is constructed from 17 bursts, and shows the mean+S.E. instantaneous firing rate plotted for each interspike interval within the bursts. (D) Mean instantaneous firing rates vs. time of occurrence on a semi-log plot from a real oxytocin cell (circles, red dashed line) and from a model cell (squares, blue line). The semi-log plot displays more clearly the effect on instantaneous frequency just before a burst, and it shows that, in both real cells and model cells, most bursts begin with a slight decrease in instantaneous firing rate. In the model this is because most cells are usually follower cells - a burst has begun elsewhere, and the first indication of this is a decrease in synaptic input as a result of the inhibitory effects of cannabinoids. The bursts begin only when the excitatory effect of oxytocin exceeds this.