Next, I would like to have Brian Kazuba. Is he here? Yes, great. Okay, so next we'll be speaking about the effects of subthalamic DBS with gabapentin and morphine on mechanical and thermal thresholds in six hydroxydopamine lesioned rats. So, hello. So, to clarify, I'm a second-year medical student in Dr. Julie Politsis's lab, and I'll talk about my project. So, these are our disclosures with Dr. Politsis. So, Parkinson's disease, what do we usually think of? Most often, we think about the motor symptoms, so tremors, bradykinesia, the rigidity, but we often tend to overlook the non-motor symptoms, and that includes pain, depression, sleep disorders. In fact, pain is the most common non-motor symptom in Parkinson's disease, affecting up to 85%. So, studies have shown that Parkinson's disease patients have a reduced mechanical and thermal threshold. Essentially, what that means is that they are more sensitive to contact touch or changes in temperature. And so, pharmacotherapy has focused on trying to raise those thresholds in conjunction of treating their pain. So, there's medication treatments, physical therapy, massage, botulin toxin injections, but those often tend to be refractory in patients, especially many medications pose side effects that includes hallucinations that can be a challenge in patients in a population that has a high fall risk. So, another question becomes neuromodulation. So, subthalamic deep brain stimulation is currently approved for treating and managing the patient's motor symptoms, but not their non-motor symptoms. So, studies have started to look at where this deep brain stimulation might be affecting their non-motor symptoms, and it has shown that up to 80% have significant pain relief with STN-DBS. However, because deep brain stimulation is not being modulated specifically for pain, but for their motor symptoms, as studies started to look at this, they found that not all patients see the same effect of their improvement with their pain. And also, in another study in 2015, it found that in an eight-year follow-up, up to 74% of patients develop new pain symptoms over time. And so, the question became whether can deep brain stimulation be optimized or modulated, you know, to also affect that treatment with pain. And so, this study we looked at to determine whether two different frequencies, so high-frequency stimulation at 150 hertz or low-frequency stimulation at 50 hertz, given with two different medications that have known effects on the descending inhibition pain pathway, which is also evidence to be involved with subthalamic deep brain stimulation, whether there is increased sensory thresholds in PD rats using the 6-hydroxydopamine model for chronic pain in Parkinson's disease. And so, what we did was a 6-hydroxydopamine unilateral right forebrain bundle lesion using a stereotactic device on the rats, and we also did the subthalamic deep brain stimulation electrode implant. And two weeks later, we did a limb asymmetry test, and that test is essentially performed to confirm the PD behavior, the phenotype. And afterwards, we did five days of testing without any drug, looking at the comparisons between no stimulation, low-frequency, or high-frequency. And then, finally, the last four days, we did it with a drug. And in conclusion, we did a perfusion and tyrosine hydroxylase staining to confirm the PD pathophysiology, dopaminergic cell loss, and correct electrode placements in these rats. So, these are our behavioral testing. Our primary outcome measure was the von Frey test, which we use filaments of various strengths, similar to what's used in the clinic. Then, we also perform a supplementary Randall-Soleto test and a hot plate test to measure the thermal thresholds. So, what we found here in our eight rats for the gabapentin, as a representative, we showed these are our confirmatory lesions with the STN electrode to find that they were in the correct place using our Cressel violet stain. And right here, to confirm the PD pathophysiology, we did our limb asymmetry test, where we showed that there was a greater than 90% average right paw touches for PD phenotype and for pathophysiology, we showed that there was a greater than 70% average dopaminergic cell loss in both the striatum, represented with one of our slides, in C, and the substantia nigra pars compacta, represented right here in D. And so, with our results for our primary outcome measure test, which is the von Frey test for mechanical thresholds, what we showed was that an analysis of variance found that the particular day testing was performed did not make a difference. And so, we performed a 2A ANOVA, and right here, you can see without drug, this is baseline levels at off stimulation. When you apply low-frequency or high-frequency stimulation, there was a significant increase in those thresholds from baseline levels. However, when you applied, we applied 15 milligrams per kilogram intraperitoneal injection of gabapentin, there was a significant reduction back to those baseline levels from when applied with low-frequency stimulation at 50 hertz. Each of these dots represents our individual rats. So, right here, this is our hot plate test for thermal thresholds with gabapentin, and you can see that there was a significant increase with high-frequency stimulation. And then, this dot right here is one of the rats. You can show that there is some variability amongst each individual rat, similar to what you see in the clinic. There is variability among each individual patient, similar in chronic pain with Parkinson's. And then, with our morphine study, applying morphine at 1 milligram per kilogram, which was our lowest dose, already raised our baseline up to our cutoff value thresholds. And so, we were not able to measure the differences between high or low-frequency stimulation, so we're currently looking at lower dosages there. And then, this all comes back to our study that we published last year, where we looked at duloxetine. Duloxetine is a serotonin norepinephrine reuptake inhibitor, which is often given for patients to manage pain in the clinic. And what we showed was that high-frequency stimulation alone raised thresholds significantly from baseline. High-frequency stimulation with duloxetine combined also raised significant from baseline. However, it was an almost twofold increase compared to either high-frequency stimulation alone or duloxetine, the medication alone. And so, it suggests that there could be some additive or synergistic interaction between medication and deep brain stimulation. And currently, Dr. Pulitsis is looking at this further in the clinic with her patients. And Miriam Xiao, she will be talking very shortly about what she's looking for there in the basic science model with duloxetine and deep brain stimulation. And so, our final conclusions is that duloxetine combined with high-frequency stimulation shows a significant increase in Bonn-Frey thresholds compared to either intervention alone. And then gabapentin combined with low-frequency stimulation showed an attenuation back to baseline levels. And then finally, with morphine, we're currently looking at lower thresholds to make that comparison between off-stimulation versus lower high-frequency stimulation. And then finally, here are our acknowledgments with everyone to help with the project. Thank you.

subthalamic deep brain stimulation

pain

Parkinson's disease

non-motor symptoms

DBS effects