Polysynaptic connections between Barrington's nucleus and sacral preganglionic neurons

The pontine micturition center, or Barrington's nucleus, is an essential component in the micturition reflex. The purpose of the present study is to examine the connections between Barrington's nucleus and sacral preganglionic neurons with an electrophysiological method using an intracellular recording technique. When the bladder pressure was near 0mmH2O, electrical stimulation of Barrington's nucleus either evoked no postsynaptic potential or evoked very small excitatory postsynaptic potentials (EPSPs) with ambiguous onset, in sacral preganglionic neurons. However, when the bladder showed micturition contraction, electrical stimulation of the nucleus evoked clear EPSPs in sacral preganglionic neurons. Latencies of EPSPs ranged from 21.9 to 47.5ms. The onset of the EPSPs was not fixed in any of the preganglionic neurons, indicating that they were evoked polysynaptically. The results thus demonstrated that the descending pathway from Barrington's nucleus to the sacral preganglionic neurons is polysynaptic. The results also showed that the descending pathway is strongly facilitated during the voiding phase, whereas this facilitatory effect is very weak when the bladder pressure is low. The study supports the idea that continuous firings of Barrington's nucleus are needed to activate the sacral preganglionic neurons that innervate the bladder muscle.