Pontine reticular unit responses to pelvic nerve and colonic mechanical stimulation in the dog

The role of pontine reticular units (PRU) responding to afferent impulses from the distal colon and anal mucosa was studied in dogs. The 465 PRU were classified into 4 groups on the basis of the pattern of discharge in response to afferent stimulation (AS) of rectal branches (RB) of the pelvic nerve: Group I (G-I) responded with a short burst (latency, 36 ± 16 msec); G-II responded with an early short burst (latency, 41 ± 21 msec), followed by a late long-lasting train of spikes (latency, 187 ± 110 msec); and G-III responded with a long-lasting train of spikes (latency, 189 ± 130 msec). G-IV had spontaneous discharges which were temporally inhibited by AS. G-II and G-III PRU showed remarkable facilitation similar to that of the long latency reflex discharges of RB. G-I PRU showed habituation. Most of G-II and G-III PRU discharged simultaneously with the reflex discharges of RB; these cause the contractions of defecation in the distal colon. In each group, 6.4-14.8% of PRU were reticulospinal units with descending axons running beyond the 1st lumbar segment of the spinal cord. It was concluded that the pontine defecation reflex center plays an essential role in defecating activity.