Increased NADPH-diaphorase reactivity in bladder afferent pathways following urethral obstruction in guinea pigs

The distribution of reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) reactivity and its alterations after urethral obstruction were examined histochemically in bladder afferent pathways in male guinea pigs. The bladder afferent neurons in L6-S2 dorsal root ganglia (DRG) and their central projections in the corresponding spinal cord segments were identified by retrograde axonal transport following injection of Fast Blue (FB) into the bladder walls. In control animals, a large number of DRG neurons in L6-S2 segments were moderately or weakly stained for NADPH-d, with a small number of them being intensely stained. Following urethral obstruction, NADPH-d reactivity was noticeably increased in the same cells beginning at 24 hours, and was markedly enhanced at 48 hours. Results of cell count showed that the number of intensely stained NADPH-d cells was significantly increased in L6-S2 DRG of the urethral obstructed animals when compared with that of the controls (P < 0.01). In the corresponding spinal cord segments, NADPH-d reactivity in the fibre bundle extending from the Lissauer's tract to the sacral parasympathetic nucleus (SPN) became more pronounced. In sections double labelled for NADPH-d and FB, increased NADPH-d reactivity was detected in the FB-labelled bladder afferent neurons in DRG and their projections in the spinal cord. Present results indicate that neuronal NADPH-d in the bladder afferent pathways is plastic and could be upregulated following urethral obstruction. It is suggested that such alteration may be involved in the processing of nociceptive inputs as a result of overdistension of the bladder after urethral obstruction.