Histological and neurotrophic changes triggered by varying models of bladder inflammation

Purpose: We determined whether bladder inflammation causes elevated expression of nerve growth factor by bladder parenchymal cells, leading to alterations in neurons innervating the bladder. To answer this question biochemical, histological and neuronal size data were obtained in rats following various experimental models of bladder inflammation. Materials and Methods: Chemical (2.5% formalin), immune (lipopolysaccharide 2 x 10(4) cfu/ml.) and mechanical (chromic catgut) inflammation was evaluated at various times and compared to control bladders. Hematoxylin and eosin, and Giemsa staining was done to characterize inflammation and quantify mast cells in the bladder. Nerve growth factor protein and messenger RNA were assayed in the bladder and major pelvic ganglion using 2-site enzyme-linked immunosorbent assay and reverse transcriptase-polymerase chain reaction, respectively. Retrograde axonal tracing was done to size bladder neurons in the major pelvic and dorsal root ganglia. Results: All forms of inflammation increased bladder weight and produced diffuse hyperplasia, intramural edema, acute and chronic inflammatory cells, infiltration and mastocytosis. Generally bladder inflammation resulted in a 50% increase in nerve growth factor and 52% to 58% enlargement of peripheral neurons. Conclusions: Inflammation results in altered nerve growth factor content of the bladder, and morphological changes in sensory and motor neurons innervating the bladder. Such neuroplasticity may be a possible explanation for the association of bladder inflammation with long-term symptoms and pain after inflammation subsides.