Cavernous Nerve Stimulation and Recording of Intracavernous Pressure in a Rat

This study describes a simplified surgical procedure and technique for performing cavernous nerve stimulation with the isolation of the nerve-electrode complex using silicone glue and intracavernous pressure measurement.

Transcript

The overall goals of this method are to describe a simplified surgical technique of penile crus cannulation for intracavernous pressure recording and the dissection and isolation of the cavernous nerve for electrostimulation. This experimental protocol can be used to study the pathophysiology of erectile dysfunction and test new therapies. The main advantage of this technique is that it's reproducible, fast, and reliable.

It has addressed and eliminated major pitfalls described in this tutorial. Though this method can provide insight into erectile dysfunction, the nerve electrode complex isolation with biocompatible silicone glue is applicable to electrostimulation of any peripheral nerve, allowing for physiological testing of other organs. To begin this procedure, after anesthetizing the animal, shave the lower half of its abdomen and perineum.

Scrub the animal with 70%alcohol and povidone iodine three times alternatively. After that, place the rat on a heated surgical pad in a supine position. Apply ointment on the eyes and keep the rat anesthetized via a nose cone with 2.5%isoflurane.

Then, perform the entire surgical procedure under an operating microscope on a drape. Subsequently, make a one centimeter skin incision five milliliters lateral to the midline starting at the level of the base of penis and extending downward. Use a Q-tip to carefully separate the fascia lateral to the scrotum.

After dissecting the fascia, use a pair of retractors to pull back the skin edges and the testicle and locate the ischial tuberosity using palpation with a cotton-tipped swab. Dissect through the adipose tissue medially until the ischiocavernosus muscle is visible. Use a pair of forceps to separate the muscle longitudinally and expose the tunica albuginea.

The tunica albuginea will appear as a bright white structure. After calibration of the system's settings, insert tubing through the skin of the perineum, making sure that it runs parallel to the penile crus. Then, leave the line in place and keep the incision moist with saline.

In this procedure, make a two centimeter lower midline abdominal incision through the skin. Create a matching incision through the fascia along the linea alba to expose the bladder and the prostate. Use the retractors to achieve good exposure.

Then, use cotton-tipped swabs to separate the prostate from the adipose tissue. Adjust the retractors and complete the dissection until obtaining clear visualization of the MPG and CN running on the dorsal lateral aspect of the prostate. After locating the MPG and CN, carefully incise the fascia overlying the nerve two to five millimeters distal to the MPG.

Next, spread the tissue on each side of the nerve and underneath it to free a four millimeter long portion and then slide a suture under the nerve. Elevate the nerve slightly with the help of the suture to facilitate placement of the hooks of the bipolar electrode around the nerve. Let an assistant mix the two component silicone glue with the tip of an insulin needle for five seconds.

Dry the nerve and apply the glue to the area around the hooks and the nerve. Keep the nerve elevated by pulling slightly on the electrode for approximately one minute to allow the glue to dry. Afterwards, remove the retractors, except for the retractors on the right side to avoid any pulling or twisting of the electrode.

Subsequently, wet the exposed organs with saline and lay gauze soaked in saline over the incision. In this procedure, restore visualization of the tunica albuginea using retractors. Make sure not to attach the retractors to the ischiocavernosus muscle, as it will distort the crus.

Next, attach the needle to PE50 tubing and flush the tubing with heparinized saline before introducing it into the tunica albuginea. Keep the tunica albuginea stretched and hold the overlying muscle distal to the point of insertion with your dominant hand. Then, hold the needle in your non-dominant hand and introduce it into the cavernous body.

Flush the line to confirm correct placement in the cavernous bodies without a leak. Insertion of the needle into the cavernous body for pressure recording constitutes a critical step. When deploying the needle into the crus, it's important that the crus is stretched and the needle is deployed parallel to its course.

Flush the tubing and press on the crus to test the line. Ensure that there are no leaks. After that, fasten the tubing to the table with tape to prevent accidental pulling on the line.

Then, remove the retractors. Set the parameters on a stimulator and apply stimulation for 50 seconds with a minimum of a one minute rest between stimulations. This figure shows a diminished first response with a stimulation of 50 millimeters mercury, which is followed by the second and third stimulation of 66 millimeters mercury.

Then, the subsequent measurements were recorded at the normal level at 73 millimeters mercury. And shown here is the stability of the results using this protocol with 10 back-to-back stimulations between 75 and 78 millimeters mercury. This figure shows the effective anesthesia doses on intracavernous pressure.

Decreased and more fluctuating response on increasing isoflurane compared to the stable response on 2%in the first two and the last three stimulations were observed. The blue trace on top shows the constant main arterial pressure. This figure shows the effect of anesthesia type on intracavernous pressure.

The initial stimulations performed under isoflurane anesthesia showed a pressure increase of 80 millimeters mercury. Once fentanyl midazolam was administered, there was an increase in response to 110 millimeters mercury. This figure demonstrates the effect of oxygen administration through the nose cone.

Discontinuing oxygen administration through the nose cone resulted in a significant reduction in cavernous pressure increase with cavernous nerve stimulation. No effect on the main arterial pressure was noted. Once mastered and if performed properly, this procedure can be completed in 30 minutes.

While performing the stimulations, it is important to remember that both type and level of anesthesia and oxygenation have a major impact on the intracavernous pressure. Following this procedure, different agents can be tested to answer questions related to pathophysiology of erectile dysfunction and introduction of new treatments. After watching this video, you should have a thorough understanding of how to perform cannula nerve stimulation including the isolation of the nerve electrocomplex with sealing glue and recording of the intracavernous pressure following minimally invasive dissection and cannulation of the cavernous parts.

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Journal (Medicine)

Cavernous Nerve Stimulation and Recording of Intracavernous Pressure in a Rat

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