Emergent Synchronous Bursting of Oxytocin Neuronal Network
(A) Raster plots showing the spikes generated by all the cells of the model in two bursts. (B) We considered a network with the same number of cells and bundles (and the same mean connectivity, ) but where the number of dendrites varied in each bundle. For each cell, the leader/follower character was measured by its mean ‘advantage’. The mean ‘advantage’ (start time relative to other cells, averaged over 120 bursts), plotted for each cell against the number of dendro-dendritic connections, shows that bursts are more likely to start in regions of the network where dendritic bundling is more pronounced. (C) The index of dispersion of the firing rate before bursts (in spikes/0.5 s, averaged over 5-s intervals; each point is an average over all cells and 136 bursts). The increase shows that firing is increasingly irregular just before a burst. The index of dispersion is the ratio of the SD of the firing rate to the mean firing rate over the same period. In the absence of retrograde attenuation by endocannabinoids (i.e. when α is set to 0), there is no increase in the index of dispersion, so the increased variability reflects the increasing antagonism between the excitatory effects of oxytocin and the inhibitory effects of endocannabinoids. (D) The cross-correlation of firing rates before bursts (in spikes/0.5 s; cross-correlations measured over 5 s-intervals, with zero time lag; average over 136 bursts; bars are S.E.M.). The blue squares are means of the cross-correlations between all pairs of cells in the network; the red circles are the mean ‘intra-bundle’ cross-correlations (the mean cross-correlation of all the pairs of cells projecting to the same bundle).