Consequences of Spinal Cord Injury during the Neonatal Period on Micturition Reflexes in the Rat

Abstract

This study examined the changes in micturition reflexes following spinal cord transection in neonatal rats to determine: (1) whether injury to the immature nervous system allows greater recovery of function than injury in adult animals and (2) whether the management of the lower urinary tract during the initial period following spinal injury influences the subsequent recovery of function. In one experiment, bladder-to-bladder reflexes in decerebrate neonatal rats (Day 15-Day 26) were tested 5-11 days after T8-T10 spinalization. While there was no difference in the amplitude and duration of reflex bladder contractions or bladder capacity between these pups and their nonspinalized controls, the spinalized pups exhibited incomplete voiding and an uncoordinated urethral sphincter (bladder/ sphincter dyssynergia). It is concluded that the dyssynergia is inherent to the spinal micturition reflexes and is not due to an initial period of bladder areflexia and overdistension since in both the control and spinalized neonates micturition is initiated by a somatobladder reflex triggered when the mother licks the perineum. A second experiment tested whether neonatal spinal cord injury led to improved bladder function in adulthood. Postnatal Day 1 rat pups were spinalized at T8-T10 and returned to their mothers for the remainder of the neonatal period, and their bladder reflexes were tested 4-6 months later under urethane anesthesia. These rats showed the same lower urinary tract dysfunctions (bladder/sphincter dyssynergia, high residual volumes, decreased percentage voided volumes, and large-amplitude, long-duration bladder contractions) as adult rats that were spinalized as adults. It is concluded that spinal cord injury in neonates and adult animals leads to a similar disruption of voiding reflexes.