Regulation of the milk ejection reflex in the XXXX .

@entity35 @entity4774 @entity398
Extracellular recordings were made from neurones in or near the supraoptic nucleus in suckled lactating @entity35 under @entity4774 anaesthesia to investigate the mechanism by which the firing of @entity398 cells is synchronized during reflex milk ejection. Cells synaptically driven but not antidromically activated by neural stalk stimulation, which thus probably receive an afferent input from supraoptic neurones, were classified as 'regular' or 'bursters' on the basis of their spontaneous electrical activity. The majority (twelve out of eighteen) of synaptically excited cells (o.d.+) were bursters and the majority of inhibited (o.d.-) cells (eleven out of nineteen) were regular, but only one o.d.+ burster showed any change of activity (inhibition) before milk ejection. Putative @entity398 cells in suckled lactating @entity35 showed a firing pattern between milk-ejection bursts which could not be distinguished from that of putative @entity398 cells in male animals. The mode interspike interval between milk ejections was 47.1 +/- 3.1 ms (mean +/- S.E. of mean) compared with 47.3 +/- 3.3 ms in male @entity35 , and fewer than 1.4% of interspike intervals were less than 20 ms in duration. By contrast, within milk-ejection bursts 40% of interspike intervals were in the range 8-20 ms. Short trains (10 or 20) of pulses applied to the neural stalk at regular (5 min) intervals, in an attempt to simulate the initial part of the milk ejection burst, failed to trigger bursts. In only 2 of 150 tests was the interval between train and milk-ejection burst less than 10 s, and after the pulse train all but one cell showed reduced activity for 1-3 s. The trains of pulses were however not without effect: they significantly (P less than 0.01) enhanced the chance of a milk-ejection burst occurring within the next 2.5 min. Our observation that pulse trains do not trigger bursts suggests that local positive feed-back mechanisms are not responsible for orchestrating the activation of @entity398 cells during the milk-ejection reflex. Moreover, because spontaneous tiring pattern is the same in lactating and non-lactating @entity35 , we found no evidence that the anatomical changes in the synaptic organization within the supraoptic nuclei in lactation have any influence on the firing of @entity398 cells. It is likely, however, since pulse trains alter the timing of milk ejections, that @entity398 released locally in the region of the supraoptic nucleus can influence reflex milk ejection.(ABSTRACT TRUNCATED AT 400 WORDS)
