In Vivo Telemetry to Record Long-Term Cardiovascular Parameters, Temperature, and Activity in Spinal Cord Injury Rat Models

The scope of my research is to optimize telemetric implant surgery for long-term recording of physiological parameters in spinal contused rats. The most recent development in our field includes characterizing acute, chronic, progressive, cardiovascular, temperature activity changes after spinal cord injury. To begin, using a syringe, fill the pressure catheter tip of a telemetric implant with biocompatible gel.

After sterilizing the implants by sequentially immersing them for 24 hours each in detergent, cold sterilant and 0.9%sodium chloride, keep them submerged in 0.9%sodium chloride. Cover a heating pad with surgical underpads followed by sterile drape towels to maintain a sterile field. Set the heating pad to 37 to 38 degrees Celsius.

To an anesthetized rat, subcutaneously administer buprenorphine, meloxicam and five milliliters of 0.9%normal saline, then apply lubricating gel to its eyes. Shave the abdominal area from one centimeter above the urethral orifice to the mid-abdomen using an electric shaver. Disinfect the exposed skin.

Then place a press-and-seal barrier and cut an opening to expose the surgical site. After confirming the depth of anesthesia via toe pinch, make a 4.5-to-five-centimeter midline skin incision from above the urethral orifice and perform an abdominal incision. Secure the visceral organs with saline-soaked, 16-ply gauze sponges and metal retractors.

Using two fine forceps, gently separate fat bodies to expose the descending aorta and vena cava. Hold the fat bodies with one forceps and use the other to dissect. Perform blunt dissection approximately 0.5 centimeters below the renal artery to separate the descending aorta from the vena cava.

Further separate the aorta from underlying fat to create space for angled forceps insertion. Insert angled forceps under the descending aorta through the dissected space. Tear the connective tissue between the aorta and vena cava using forceps.

Then pass a sterile 4-0 silk thread underneath the descending aorta and secure both ends with a hemostat. Temporarily mono-occlude the descending aorta proximal to the catheter insertion point. Remove the implant from the sodium chloride and inspect the pressure catheter tip for air bubbles or gaps.

After turning on the implant using a magnet and radio, add gel if needed before insertion. Have another experimenter hold the hemostat at about a 45-degree angle and make adjustments to minimize or eliminate blood backflow. Pierce the upper wall of the descending aorta using a twisted 21-gauge needle and insert the pressure catheter tip 1.5 to two centimeters into the descending aorta.

Use a vein pick to guide the catheter if needed, and loosen the occlusion thread to advance the catheter. Clean the surrounding blood and apply tissue adhesive to secure the implant. Allow 30 to 45 seconds for the adhesive to dry, then check for blood leakage.

Cut and remove occlusion thread using fine scissors and forceps. Confirm the implant status via radio telemetry. Then remove the retractor and gauze, and anchor the implant to the body while intraperitoneally using non-absorbable sutures.

Next, close the abdominal wall using absorbable sutures in an interrupted pattern, and close the skin using an intradermal continuous technique. Clean the incision with hydrogen peroxide, followed by povidone iodine. Apply triple antibiotic cream to the incision site and follow the post-surgical care.

Perform spinal cord injury two weeks later using IH Impactor device. Then transfer the injured rats onto telemetric plates in a cage for data acquisition. To begin data recording, launch the Ponemah software.

Click Create under the Experiment tab and label the experiment. Under the Hardware tab, click on Edit APR Configuration. Then choose the APR and click on Add to move to the available region.

Now, Press Edit PhysioTel HD MX2 Configuration in the Hardware tab to select the MX2, then click on Add and confirm that it appears in the left panel. Add implants assigned to different animals from the implant inventory on the right side to the middle and left panels. Click on each implant and connect it to a different receiver plate, then save and exit once all connections are made.

Now, navigate to the Setup tab, then press Experimental Setup and click on Enable Page. Choose the black background, then select the subject before adding the pressure in the label and changing the unit to millimeters of mercury. Set the low and high values, and choose a color for displaying blood pressure traces.

Go to the Setup tab again and choose Subject Setup. Click on the animal number, select the gender and species, and click on Pressure to enable parameters. If heart rate needs to be displayed, click on Heart Rate.

Click Apply Channel Settings to Similar Channels if connecting more than one implant, then click OK.Next, click on Start All Continuous at the top of the screen to visualize blood pressure recording traces. For data exporting, go to the Experiment tab. Click on Open, and select the data from the intended folder.

Navigate to the Action tab. Click on Start Review, and select the subject number, desired signal types and time range. Set the logging rate to determine how the data are segmented in seconds, minutes, or hours.

Once selections are complete, go to the Experiment tab and choose Save Marked Sections, followed by Save Derived Data. Finally, go to the Actions tab and click on Close Review Session to end the data export. Eight weeks after spinal cord injury, colorectal distension induced a minimum increase of 20 millimeters of mercury in systolic blood pressure during one-minute stimulation compared with baseline, demonstrating development of autonomic dysreflexia.

Systolic blood pressure, diastolic blood pressure and mean arterial pressure were elevated one to two days post-spinal cord injury compared with pre-injury recordings. Heart rate showed increased fluctuations following spinal cord injury compared with pre-injury recordings. Core body temperature regulation was disrupted during the first two days after spinal cord injury, and animal activity was reduced substantially following spinal cord injury compared with pre-injury activity.

The advantage of our protocol is minimizing the procedural challenges, improving survival, and enabling continuous recording in freely moving, awake animals. Our findings will advance research by providing an in-depth understanding of autonomic changes during the acute and chronic phases of spinal cord injury. Our results pave the way for new questions by addressing key gaps and providing a foundation for deeper insight into autonomic dysfunction after spinal cord injury.