Increased spinal expression of c-Fos following stimulation of the lower urinary tract in chronic spinal cord-injured rats

c-Fos expression was studied in the lumbar and sacral spinal cord regions i nvolved in processing afferent input from the lower urinary tract and a com parison was made between spinal cord-injured (SCI) animals and control anim als with intact neuraxes. Afferent pathways from the lower urinary tract we re activated either by insertion of a catheter through the urethra into the urinary bladder or by catheterisation plus induction of reflex micturition contractions by intravesical saline infusion. Placement of a catheter alon e elicited Fos expression in a similar number of neurones in SCI and contro l rats mainly in the medial dorsal horn (MDH) and dorsal commissure (DCM) i n the segments L1-2 and L5-S1 with a maximum in L5. Additional saline infus ion induced low-frequency, high-amplitude, rhythmic bladder contractions of long duration in the rats with intact spinal cords, whereas in SCI rats, b ladder distension elicited reflex contractions at a higher frequency, small er amplitude and shorter duration. However, the basal and mean bladder pres sure, as well as the total contraction time relative to the whole recording time, was not significantly different. Distension-induced bladder contract ions markedly increased Fos expression primarily in the spinal segments L5- S1 in the control rats, where the majority of bladder and urethral afferent fibres terminates. Fos-positive cells were located in the MDH, lateral dor sal horn (LDH), DCM and the lateral aspect of laminae V-VII. Compared to co ntrols, Fos expression after spinal cord injury (SCI) occurred in a signifi cantly greater number of neurones throughout the segments L3-S1 following i nduction of bladder reflexes. The greatest proportional increase in the num ber of Fos-positive cells occurred in L3-5 which normally receive only litt le afferent input from the urinary bladder. Cell numbers predominantly incr eased in the LDH and lateral lamina V-VII. The data are consistent with the concept of a neuroplastic reorganisation of spinal pathways after SCI. Unm asking of silent synapses or formation of new connections by afferent axona l sprouting caudal to the lesion, as evident from the increased numbers of cells expressing Fos after bladder distension, could be factors underlying the emergence of reflexogenic micturition in chronic SCI rats.