State dependent response of the locus caeruleus neurons to bladder distention

The precise mechanism by which normal persons wake upon urinary sensation is unclear. The locus caeruleus in the pons is suggested to be involved in the activating systems for arousal. We evaluated the effects of bladder distention on the neural activity in the l. caeruleus under different states of anesthesia.

Experiments were performed on 20 male Sprague-Dawley rats. The spontaneous discharge rate of single neurons in and around the l. caeruleus was recorded with the rat under urethane anesthesia administered intraperitoneally, while the electroencephalogram was monitored simultaneously. The changes of the discharge rate of the neurons were observed during saline infusion into the bladder or during tail pinch stimulation. After recording the location of the neurons was confirmed histologically.

Of 42 l. coeruleus neurons whose response was examined during deep anesthesia 31 showed an excitatory response to bladder distention, followed by a change in electroencephalogram pattern to a faster and smaller rate, while the remaining 11 showed no response. Of 28 l. coeruleus neurons examined during light anesthesia only 1 neuron was excited and the remaining 27 showed no response. Virtually all of the l. coeruleus neurons unresponsive to bladder distention were responsive to tail pinch stimulation. Of the nonnoradrenergic neurons ventromedial to the l. coeruleus 4 of 7 during deep anesthesia and 5 of 8 during light anesthesia showed an excitatory response to distention.

The excitatory response of the l. coeruleus neurons to bladder distention was strongly affected by the state of anesthesia. The response was observed only during deep anesthesia and was accompanied by lightening of the anesthesia. L. coeruleus may be involved in arousal which is mediated by bladder distention.