Correlation between electrophysiology and morphology of three groups of neuron in the dorsal commissural nucleus of lumbosacral spinal cord of maturerats studied in vitro

The dorsal commissural nucleus (DCN) in the lumbosacral spinal cord receive s afferent inputs from the pelvic organs via pudendal and pelvic nerves. El ectrophysiological and morphological properties of neurons in the DCN of L6 -S1 were examined using whole-cell recordings with biocytin-filled electrod es in transverse slices of mature rat spinal cord. Neurons were categorized into three groups according to their discharge in response to suprathresho ld depolarizing pulses; neurons with tonic (19/42) and phasic (13/42) firin g patterns, and neurons (10/42) that fired in bursts arising from a Ca2+-de pendent hump. The predominantly fusiform somata of neurons labeled during r ecording (n = 31) had on average 3.1 primary dendrites, 7.5 terminating den dritic branches, 3.1 axon collaterals, and 14.2 axon terminations per neuro n. The groups were morphologically distinct on the basis of their dendritic branching patterns. Phasic neurons (n = 10) had the most elaborate dendrit ic branching and the largest numbers of axon collaterals. All tonic neurons (n = 11) had axons/collaterals projecting to the intermediolateral area bu t none to the funiculi, suggesting that they function as interneurons in lo cal autonomic reflexes. Many axons/collaterals of all phasic neurons lay wi thin the DON, suggesting that they integrate segmental and descending input s. Seven of 10 neurons with Ca2(+)-dependent humps had axons/collaterals ex tending into one of the funiculi, suggesting that they project intersegment ally or to the brain. Ca2+ hump neurons also had more axons/collaterals wit hin the DCN and fewer in the intermediolateral area than tonic neurons. Thi s correlation between firing pattern and morphology is an important step to ward defining the cellular pathways regulating pelvic function. (C) 2001 Wi ley-Liss, Inc.