Quantifying erectile dysfunction two- and four- weeks after cavernous nerve injury: Rat model
Anna G. Quinlan, BA1, Sabrina Toft Hansen, MD2, Lars Lund, MD2, Peter Zvara, MD, PhD2.
1University of Vermont Larner College of Medicine, Burlington, VT, USA, 2University of Southern Denmark and Odense University Hospital, Odense, Denmark.
BACKGROUND: Stimulation of the cavernous nerve (CN) and recording of intracavernous pressure in a rat has been used since 1989 to investigate the etiology and examine possible treatments of erectile dysfunction. The microsurgical techniques used vary between laboratories, making comparison of data difficult. We have recently described a modification to the existing method that simplifies the procedure and improves its reproducibility. The goal of this study was to validate the modified experimental setup and address the time course of erectile dysfunction following bilateral CN injury.
METHODS: Bilateral CN injuries were made by exposing the nerves and inducing a crush injury by clamping them for two minutes with the microneedle holder. Two and four weeks following the injury, a vertical 1.5 cm skin incision was made next to the base of the penis. Palpation of ischial tuberosity was used to locate the distal portion of the penile crus with minimal dissection. A needle connected to a PE50 pressure line was inserted into the crus. After CN exposure, the electrode was placed under the nerve, the nerve was elevated, and dried. Biocompatible silicone glue was applied to isolate the electrode and nerve from the surrounding tissue. CN was stimulated using 1.5 mA, 16 Hz, 6 V, and 5 ms pulse width stimulation parameters, for 50 seconds. Three reproducible responses were analyzed for maximum and mean intracavernous pressure as well as the area under the curve. The comparison was made between three study groups: sham operated animals (n=5) which have their nerves exposed but not injured, animals two weeks (n=6), and animals four weeks after bilateral CN crush injury (n=6).
RESULTS: CN stimulations resulted in intracavernous pressure increase. Three reproducible responses were achieved in each animal. The average maximum and mean intracavernous pressure was 82 ± 4 and 71 ± 5 respectively in the sham group, 53 ± 4 and 41 ± 4 in the group two weeks following the nerve injury and 57 ± 3 and 39 ± 2 in the group four weeks following the bilateral CN injury (Figure 1). The area under the curve was 39.4 ± 2.32, 22.7 ± 1.5 and 21.9 ± 1.2 in sham and the two nerve injury groups respectively (Figure 2).
CONCLUSIONS: The isolation of the nerve with the silicone glue resulted in reproducible intracavernous pressure increase with the CN stimulation. The bilateral CN crush injury resulted in diminished erectile response with statistically significant decrease in all measured parameters. The obtained data show that this simplified model is reproducible. 
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