INDUCTION OF C-FOS EXPRESSION IN SPINAL NEURONS BY NOCICEPTIVE AND NONNOCICEPTIVE STIMULATION OF LUT

Expression of c-fos gene in spinal neurons was detected with an immuno cytochemical technique to study the spinal processing of nociceptive a nd nonnociceptive input from the lower urinary tract (LUT) of the uret han-anesthetized rat. Two preparations were used to activate afferent pathways in the LUT: 1) the urinary bladder was exposed through an abd ominal incision, and saline or 1% acetic acid solution was infused dir ectly into the bladder lumen and expelled through the urethra; and 2) the bladder was catheterized through the urethra, and the urethral out let was ligated to allow distension and reflex contractions to occur u nder isovolumetric conditions. The first preparation mimicked the phys iological changes occurring during normal voiding, whereas the second preparation generated high (presumably nociceptive) pressures when the bladder contracted against a closed outlet. The results indicate that distension-induced voiding increased c-fos expression largely in the region of the sacral parasympathetic nucleus (52% of the total number of cells/L, section) and the dorsal commissure (25% of the total numbe r of cells), whereas nociceptive stimuli markedly increased the number of c-fos-positive cells in the dorsal commissure (3.5X increase above the number induced by distension, representing 50% of the total numbe r of cells/L, section). Bladder contractions against a closed outlet e licited a distribution of c-fos-positive cells similar to that induced by chemical irritation. Drugs that suppressed bladder reflexes did no t reduce c-fos induced by distension, indicating that voiding reflexes do not contribute to c-fos expression.