Expression of neuropeptides and nitric oxide synthase in neurones innervating the inflamed rat urinary bladder

Micturition reflexes become hyperexcitable with the development of a cystitis. In the present study the question is addressed, whether alterations in the expression of neuropeptides and nitric oxide synthase (NOS) in the neuronal pathways to the bladder may be involved in the hyperexcitability. Primary sensory neurones in the dorsal root ganglia (DRG) L1, L2, L6 and S1 as well as postganglionic efferent neurones in the major pelvic ganglia (MPG) that innervate the rat urinary bladder were labeled with retrogradely transported Fast Blue (FB). Immunocytochemical techniques were used to determine alterations in the expression of calcitonin gene-related peptide (CGRP), substance P (SP), galanin (GAL) and NOS in these neurones following mustard oil-induced inflammation of the urinary bladder. Instillation of 2.5% mustard oil into the bladder led to a massive leukocyte infiltration of the vesical tissues, partial damage of the mucosal layer and a marked hyperreflexia of the detrusor muscle. 48 h after induction of the cystitis the proportion of FB-labeled bladder afferent neurones that expressed CGRP and SP were significantly increased in both the rostral lumbar DRGs (L1, L2) and the lumbosacral DRGs (L6, S1) (CGRP, +15-38%; SP, +47-158%) as compared to control animals. However, there was a differential effect of the inflammation on the expression of GAL and NOS in bladder afferents at the two segmental levels examined. Significant alterations in the number of FB-labeled afferents exhibiting GAL immunoreactivity were mainly restricted to the lumbosacral DRGs L6 (+169%) and S1 (+60%). On the contrary, the proportion of NOS-immunoreactive bladder afferents significantly increased only in the rostral lumbar DRGs L1 (+144%) and L2 (+193%), while the level of NOS-expression was unaffected at the lumbosacral levels. Inflammation furthermore induced a significant increase (+275%) in the number of FB-labeled neurones in the MPGs that exhibited NOS immunoreactivity. These results indicate that an upregulation of CGRP-, SP-, GAL- and NOS-synthesis in sensory and efferent neurones is involved in the response to an acute cystitis. Because of the differences in the segmental pattern and degree of upregulation of these substances in bladder afferents that project to the rostral lumbar and lumbosacral spinal cord a different regulation of the sympathetic and parasympathetic efferent outflow to the urinary bladder is suggested. The involvement of CGRP, SP, GAL and NOS in the modulation of both excitatory and inhibitory mechanisms that control the cystitis-induced detrusor hyperreflexia is discussed.