Evidence for alterations of synaptic inputs to sacral spinal reflex circuits after spinal cord transection in the cat.

Quantitative electron microscopy was used to study potential alterations in the synaptic inputs to HRP-labeled preganglionic neurons (PGNs) in the sacral parasympathetic nucleus (SPN) and to motoneurons (MNs) in Onuf's nucleus (ON) after short (4 days)- or longterm (10-11 weeks) spinal transection as compared to normal controls. Transection resulted in an apparent reorganization and replacement of synaptic input to ON MNs whereas chronic denervation of PGNs in the SPN was observed. These synaptic alterations may play a role in the changes in the eliminative reflexes (e.g., bladder-sphincter dyssynergia, induction of cutaneously elicited elimination) that are observed after spinal cord lesions.