Abstract: Objective To explore the role of collateral branch of cavernous nerves (CN) in penile erection in rats and its importance in establishing CN injury rat models. Methods Thirty-six 3~5 months old male SD rats were used. Six rats were used to identify and observe the branches of major pelvic ganglion (MPG) under the operating microscope, the other 30 rats were divided into 3 groups randomly, including (I) sham-operated group, (II) bilateral main branch of CN ablated group and (III) bilateral main and collateral branches of CN ablated group. The erectile ability of rats were evaluated with apomorphine test respectively 7 days and 30 days after surgery. Then 4% flluoro-gold solution were injected into bilateral corpus cavernosum of penis in all rats under anesthesia, and the rats were sacrificed and their bilateral MPGs were obtained for tracing the flluoro-gold under the fluorescent microscope 5 days later. Results The main branch of CN and some fine fibers arised from the MPGs were identified on the surface of dorsolateral lobes of the prostate. 7 days after surgery, the times of rat penile erection in group was 2.0±0.7, but no penile erection was found in both group II and III. 30 days after surgery, the group II rats still showed no erection, the erectile response was appeared in group II rats after administration of apomorphine, but the erection times of group II (0.9±0.7) was still less than that of group I (2.8±0.6)(P<0.05). 5 days after injection of fluoro-gold solution, much more brighter positive stained neural cells were observed in MPGs of group II than those of group III (P<0.01). Conclusions Some tiny nerve fibers, the collateral branches of CN derived from MPG, may play a part role in penile erection of rats, and the influence of these collateral branches should be taken into consideration when creating a erectile dysfunction rat model induced by CN injury.

Key words: Cavernous nerve(CN), Rat, Animal model, Collateral branch