Effect of cavernous nerve freezing on protein and gene expression of nitric oxide synthase in the rat penis and pelvic ganglia.

Abstract

Cryoablation of the prostate has been reported to induce impotence as a result of cavernous nerve injury. This study is designed to investigate the early and late effects of cavernosal nerve cryoablation on erectile function and nitric oxide synthase (NOS) containing nerves in the rat penis and pelvic ganglia. Forty male rats were divided into two groups (n = 20 each). The first group underwent unilateral cavernous nerve freezing (experimental group). Before their euthanization at 1 and 3 months (10 rats each), erectile function was assessed by electrostimulation of the cavernous nerves. The second group served as a control and was euthanized at the same time points. Nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase staining was used to identify NOS in the penile nerve fibers of the mid-shaft segment and neurons of the pelvic ganglia. Western blot, RT-PCR and immunostaining techniques were used to identify protein and gene expression of eNOS, iNOS, and nNOS. One month after unilateral cavernosal nerve freezing, there was a significant decrease in NOS-containing nerve fibers in the dorsal and intracavernosal nerves and ipsilateral pelvic ganglia as compared with the intact side. At three months, the number of NOS containing nerve fibers in the above-mentioned nerves and ganglia showed a significant increase on the frozen side but not the intact side. Electrostimulation of the frozen nerve after three months revealed a significantly higher maximal intracavernosal pressure and a shorter latency period than the one-month group. At three months, immunoblot showed up-regulation of eNOS and nNOS protein expression in the penile tissue. RT-PCR showed up-regulation of nNOS gene expression in the pelvic ganglia of the frozen side. Immunostaining confirmed the results of western blot and showed significant increase of the nNOS positive staining in the frozen side of the penile tissue after three months. There was no difference in iNOS after three months between both sides. Our repeated eNOS immunostaining was not successful. The results show that intracavernous pressure response to neurostimulation markedly decreased at one month and then partially recovered three months after cavernosal nerve freezing. A similar pattern of changes of the NOS-containing nerve fibers in dorsal nerves, intracavernosal nerves, and pelvic ganglia were observed. This alteration in erectile function and NOS-containing nerves was associated with differential gene and protein expression of the three subtypes of NOS.