Ian Walling

Treatment of Allodynia by Occipital Nerve Stimulation in Chronic Migraine Rodent.

BACKGROUND Occipital nerve stimulation (ONS) is a therapy that benefits one-third of medically refractory chronic migraine (CM) patients. How ONS affects sensory thresholds and whether modulation of thresholds could predict which patients respond to the therapy remains unclear. OBJECTIVE To examine the effects of ONS on mechanical and thermal thresholds in a rodent CM model to better elucidate its mechanism of action. METHODS Male Sprague-Dawley rats were implanted bilaterally with electrodes to produce ONS. The CM cohort was infused with inflammatory media epidurally based on a validated model, whereas shams were not. Thresholds were evaluated with von Frey filaments and hot plate and thermode tests. RESULTS No baseline differences in sensory thresholds were found between the sham (n = 16) and CM (n = 16) groups. After headache induction, CM animals demonstrated mechanical allodynia in the occiput, periorbital region, forepaws, and hind paws (P < .05). In CM animals, ONS increased mechanical thresholds in all regions (P < .001), whereas in shams, it did not. ONS did not affect thermal thresholds in either group. CONCLUSION We show that ONS improves mechanical thresholds in a rodent CM model, but not in shams. Our finding that mechanical but not thermal thresholds are altered with ONS suggests a more significant modulation of A-α/β fibers than of C fibers. Assessing the ability of ONS to reduce mechanical thresholds during a trial period could potentially be used to predict which patients respond.

353 High-Intensity Ultrasound for the Treatment of Vincristine-Induced Neuropathic Pain.

INTRODUCTION Vincristine is a commonly used chemotherapeutic agent but is associated with debilitating peripheral neuropathy that is often refractory to traditional medication. We explore 1 neuromodulatory option, high-intensity focused ultrasound (HIFU), which may work by altering neuronal activity. Thus, we focus on the efficacy of HIFU in treating vincristine-induced neuropathy (VIN) in the animal model. METHODS VIN rodents were created using a previously used animal model, and neuropathy was confirmed by mechanical and thermal testing using Von Frey Filaments (VFF), Randal-Selitto (RS), hot plate (HP), and tail-flick tests (TF). The VFF and RS tests are measures of innocuous and noxious mechanical thresholds, respectively, and the HP and TF are measures of paw and tail withdrawal times to thermal stimuli. These tests were performed before neuropathy induction, after a 2-week induction period, at 24 hours after HIFU and at 48 hours after HIFU. HIFU was applied to the L5 dorsal root ganglion of the left hind paw at 3 W for 2 minutes. RESULTS Although we only have 1 animal in our HIFU group thus far, our preliminary data suggest that HIFU increases mechanical and thermal thresholds compared with HIFU sham animals (n = 5). Specifically, innocuous and noxious mechanical thresholds were increased as measured with the VFF and RS tests, and thermal thresholds were also increased as measured by the HP test at 48 hours after HIFU application. Our HIFU animal did not exhibit increased TF thresholds. CONCLUSION Our preliminary data suggest that high-intensity ultrasound may be an effective way to increase mechanical and thermal thresholds in VIN.INTRODUCTION:Vincristine is a commonly used chemotherapeutic agent but is associated with debilitating peripheral neuropathy that is often refractory to traditional medication. We explore 1 neuromodulatory option, high-intensity focused ultrasound (HIFU), which may work by altering neuronal activity

Gap junction blockers attenuate beta oscillations and improve forelimb function in hemiparkinsonian rats

Parkinsons disease (PD) is a neurodegenerative disease characterized by akinesia, bradykinesia, resting tremors and postural instability. Although various models have been developed to explain basal ganglia (BG) pathophysiology in PD, the recent reports that dominant beta (β) oscillations (12-30Hz) in BG nuclei of PD patients and parkinsonian animals coincide with motor dysfunction has led to an emerging idea that these oscillations may be a characteristic of PD. Due to the recent realization of these oscillations, the cellular and network mechanism(s) that underlie this process remain ill-defined. Here, we postulate that gap junctions (GJs) can contribute to β oscillations in the BG of hemiparkinsonian rats and inhibiting their activity will disrupt neuronal synchrony, diminish these oscillations and improve motor function. To test this, we injected the GJ blockers carbenoxolone (CBX) or octanol in the right globus pallidus externa (GPe) of anesthetized hemiparkinsonian rats and noted whether subsequent changes in β oscillatory activity occurred using in vivo electrophysiology. We found that systemic treatment of 200mg/kg CBX attenuated normalized GPe β oscillatory activity from 6.10±1.29 arbitrary units (A.U.) (pre-CBX) to 2.48±0.87 A.U. (post-CBX) with maximal attenuation occurring 90.0±20.5min after injection. The systemic treatment of octanol (350mg/kg) also decreased β oscillatory activity in a similar manner to CBX treatment with β oscillatory activity decreasing from 3.58±0.89 (pre-octanol) to 2.57±1.08 after octanol injection. Next, 1μl CBX (200mg/kg) was directly injected into the GPe of anesthetized hemiparkinsonian rats; 59.2±19.0min after injection, β oscillations in this BG nucleus decreased from 3.62±1.17 A.U. to 1.67±0.62 A.U. Interestingly, we were able to elicit β oscillations in the GPe of naive non-parkinsonian rats by increasing GJ activity with 1μl trimethylamine (TMA, 500nM). Finally, we systemically injected CBX (200mg/kg) into hemiparkinsonian rats which attenuated dominant β oscillations in the right GPe and also improved left forepaw akinesia in the step test. Conversely, direct injection of TMA into the right GPe of naive rats induced contralateral left forelimb akinesia. Overall, our results suggest that GJs contribute to β oscillations in the GPe of hemiparkinsonian rats.

Effects of subthalamic deep brain stimulation with duloxetine on mechanical and thermal thresholds in 6OHDA lesioned rats

Chronic pain is the most common non-motor symptom of Parkinsons disease (PD) and is often overlooked. Unilateral 6-hydroxydopamine (6-OHDA) medial forebrain bundle lesioned rats used as models for PD exhibit decreased sensory thresholds in the left hindpaw. Subthalamic deep brain stimulation (STN DBS) increases mechanical thresholds and offers improvements with chronic pain in PD patients. However, individual responses to STN high frequency stimulation (HFS) in parkinsonian rats vary with 58% showing over 100% improvement, 25% showing 30-55% improvement, and 17% showing no improvement. Here we augment STN DBS by supplementing with a serotonin-norepinephrine reuptake inhibitor commonly prescribed for pain, duloxetine. Duloxetine was administered intraperitoneally (30mg/kg) in 15 parkinsonian rats unilaterally implanted with STN stimulating electrodes in the lesioned right hemisphere. Sensory thresholds were tested using von Frey, Randall-Selitto and hot-plate tests with or without duloxetine, and stimulation to the STN at HFS (150Hz), low frequency (LFS, 50Hz), or off stimulation. With HFS or LFS alone (left paw; p=0.016; p=0.024, respectively), animals exhibited a higher mechanical thresholds stable in the three days of testing, but not with duloxetine alone (left paw; p=0.183). Interestingly, the combination of duloxetine and HFS produced significantly higher mechanical thresholds than duloxetine alone (left paw, p=0.002), HFS alone (left paw, p=0.028), or baseline levels (left paw; p<0.001). These findings show that duloxetine paired with STN HFS increases mechanical thresholds in 6-OHDA-lesioned animals more than either treatment alone. It is possible that duloxetine augments STN DBS with a central and peripheral additive effect, though a synergistic mechanism has not been excluded.

Subthalamic deep brain stimulation alters neuronal firing in canonical pain nuclei in a 6-hydroxydopamine lesioned rat model of Parkinson's disease.

INTRODUCTION Chronic pain is one of the most common non-motor symptoms of Parkinsons disease (PD) affecting up to 85% of patients. Previous studies have established that reduced mechanical and thermal thresholds occur in both idiopathic PD patients and animal models of PD, suggesting that changes may occur in sensory processing circuits. Improvements in sensory thresholds are achieved using subthalamic nucleus (STN) deep brain stimulation (DBS), however the mechanism by which this occurs remains unresolved. MATERIALS AND METHODS We examined unilateral medial forebrain bundle 6-hydroxydopamine (6OHDA) rat model of PD to determine whether STN DBS alters neuronal firing rates in brain areas involved in ascending and descending pain processing. Specifically, single unit in vivo recordings were conducted in the anterior cingulate cortex (ACC), the periaqueductal grey (PAG), and the ventral posteriolateral nucleus of the thalamus (VPL), before, during and after stimulation was applied to the STN at 50 or 150Hz. RESULTS Sham and 6OHDA lesioned animals have similar neuronal firing activity in the VPL, ACC and PAG before stimulation was applied (p>0.05). In 6OHDA lesioned rats, both low frequency stimulation (LFS) (p<0.01) and high frequency stimulation (HFS) (p<0.05) attenuated firing frequency in the ACC. In shams, only LFS decreased firing frequency. A subset of neurons in the PAG was significantly attenuated in both sham and 6OHDA lesioned animals during HFS and LFS (p<0.05), while another subset of PAG neuronal activity significantly increased in 6OHDA lesioned rats during HFS (p<0.05). Finally, low or high frequency STN DBS did not alter neuronal firing frequencies in the VPL. CONCLUSIONS Our results suggest that STN DBS alters neuronal firing in descending pain circuits. We hypothesize that STN DBS attenuates excitatory projections from the ACC to the PAG in 6OHDA lesioned rats. Following this, neurons in the PAG respond by either increasing (during HFS only) or decreasing (during both LFS and HFS), which may modulate descending facilitation or inhibition at the level of the spinal cord. Future work should address specific neuronal changes in the ACC and PAG that occur in a freely moving parkinsonian animal during a pain stimulus treated with STN DBS.

Deep Brain Stimulation of the Ventral Pallidum Attenuates Epileptiform Activity and Seizing Behavior in Pilocarpine-Treated Rats.

BACKGROUND Brain stimulation is effective for people with intractable epilepsy. However, modulating neural targets that provide greater efficacy to more individuals is still needed. OBJECTIVE/HYPOTHESIS We investigate whether bilateral deep brain stimulation of the ventral pallidum (VP-DBS) has potent seizure control in pilocarpine-treated rats. METHODS VP-DBS (50 Hz) was applied prior to generalized forebrain seizures or after generalized brainstem seizures manifested. Behavioral seizures were assessed using a modified Racine scale. In vitro and in vivo electrophysiological techniques were employed to identify how VP-DBS affects proximal and distal neuronal activity. The open field test was used to see if acute and chronic VP-DBS affected gross motor function or arousal state. Parametric and non-parametric statistics with post-hoc analysis were performed. RESULTS VP-DBS prior to pilocarpine prevented behavioral forebrain and brainstem seizures in most animals (n = 15). VP-DBS after brainstem seizures emerged prevented or reduced the appearance of subsequent behavioral brainstem seizures (n = 11). VP-DBS attenuated epileptiform activity in the hippocampus (n = 5), but not in the primary somatosensory cortex (S1) (n = 4) in vivo. Electrical stimulation in the VP increased VP GABAergic neuronal firing activity from 3.1 ± 1.4 Hz to 7.6 ± 1.7 Hz (n = 8) in vitro and reduced substantia nigra reticulata and superior colliculus neuronal spiking activity from 25.4 ± 3.3 Hz to 18.2 ± 1.4 Hz (n = 6) and 18.2 ± 1.4 Hz to 11.0 ± 1.1 Hz (n = 18), respectively, in vivo. CONCLUSION VP-DBS can be a novel and potent therapeutic approach for individuals with intractable epilepsy.

Occipital Nerve Stimulation Attenuates Neuronal Firing Response to Mechanical Stimuli in the Ventral Posteromedial Thalamus of a Rodent Model of Chronic Migraine.

BACKGROUND Chronic migraine (CM) is a highly debilitating disease, and many patients remain refractory to medicinal therapy. Given the convergent nature of neuronal networks in the ventral posteromedial nucleus (VPM) and the evidence of sensitization of pain circuitry in this disease, we hypothesize CM rats will have increased VPM neuronal firing, which can be attenuated using occipital nerve stimulation (ONS). OBJECTIVE To determine whether VPM firing frequency differs between CM and sham rats, and whether ONS significantly alters firing rates during the application of mechanical stimuli. METHODS Fourteen male Sprague-Dawley rats were infused with inflammatory media once daily through an epidural cannula for 2 wk to induce a CM state. Sham animals (n = 6) underwent cannula surgery but received no inflammatory media. ONS electrodes were implanted bilaterally and single-unit recordings were performed in the VPM of anesthetized rats during mechanical stimulation of the face and forepaw in the presence and absence of ONS. RESULTS CM rats had significantly higher neuronal firing rates (P < .001) and bursting activity (P < .01) in response to mechanical stimuli when compared to shams. ONS significantly reduced neuronal firing in the VPM of CM rats during the application of 0.8 g (P = .04), 4.0 g (P = .04), and 15.0 g (P = .02) Von Frey filaments. ONS reduced bursting activity in CM rats during the 4.0 and 15 g filaments (P < .05). No significant changes in bursting activity or firing frequency were noted in sham animals during ONS. CONCLUSION We demonstrate that neuronal spike frequencies and bursting activity in the VPM are increased in an animal model of CM compared to shams. Our results suggest that the mechanism of ONS may involve attenuation of neurons in the VPM of CM rats during the application of mechanical stimuli.

120 Effects of Subthalamic Deep Brain Stimulation With Duloxetine on Mechanical and Thermal Thresholds in 6-Hydroxydopamine-Lesioned Rats.

INTRODUCTION Chronic pain is the most reported nonmotor symptom of Parkinson Disease (PD) patients. Both clinical and preclinical trials have shown mechanical and thermal thresholds to be reduced with PD. The mechanisms of pain in PD are not fully understood, and patients seek relief through a range of therapies, including subthalamic deep brain stimulation (STN DBS) and pharmaceuticals such as gabapentin, NSAIDs, or duloxetine. We hypothesize that combining STN DBS with administration of duloxetine in a unilateral 6-hydroxydopamine (6OHDA) lesion model will improve thresholds. METHODS Male Sprague-Dawley rats underwent craniotomy for simultaneous right 6OHDA medial forebrain bundle lesion and right STN electrode implantation. Parkinsonian phenotype was determined using 80% limb use asymmetry via a limb asymmetry test (LAT). Mechanical and thermal threshold testing was performed using vonFrey filaments (VF) and Randall-Selitto (RS) and hot plate (HPT), respectively. Animals underwent 9 days of testing, alternating VF and RS with HPT. Testing was performed each day with animals receiving no stimulation, 150 Hz stimulation, and 50 Hz stimulation in a randomized order. After behavioral testing, rats were perfused with paraformaldehyde and the brains were extracted for electrode placement verification and immunohistochemical evaluation of unilateral dopamine depletion. RESULTS Significant improvement in time on the hot plate occurred between baseline and on-duloxetine testing (P = .0257). STN DBS alone showed significant improvement in VF thresholds at 150 Hz stimulation on all testing days (pDay1 = 0.0265, pDay2 = 0.0002, pDay3 = 0.0220). STN DBS with duloxetine presented significant improvement in mechanical thresholds vs both duloxetine (P = .0069) and STN DBS (P = .0189) by themselves; VF thresholds nearly doubled from STN DBS alone. CONCLUSION Duloxetine and 150 Hz STN DBS combined produced larger increases in VF threshold tests than either intervention alone. Duloxetine and STN DBS have a potentially additive effect in modulating mechanical sensitivity in 6OHDA-lesioned rats.METHODS: This prospective study was performed on patients undergoing percutaneous CT-guided cordotomy for unilateral intractable cancer pain. Preand postoperative quantitative sensory testing as well as visual analog scale (VAS) pain assessments were performed. Postoperative DTI images of the high cervical spinal cord were obtained on postoperative day 1. Fractional anisotropy (FA) and mean diffusivity (MD) were measured from regions of interest drawn within the spinal cord at the level of the lesion. DTI metrics were correlated with the number of lesions as well as early postoperative pain outcomes.

External focused ultrasound treatment for neuropathic pain induced by common peroneal nerve injury

Neuropathic pain caused by nerve injury or compressive lesions is a debilitating condition lacking effective, long-term treatments. Our objective was to assess the effects of external focused ultrasound on sensory thresholds utilizing a common peroneal injury rat model. CPNI was induced by ligating the CPN of the left hind paw. Neuropathic phenotype was confirmed using the Von Frey Fibers (VFF) with a 50% mechanical detection threshold below 4.0. The Place Escape Avoidance Paradigm (PEAP) was employed as a behavioral correlate. External FUS treatment was applied to the left L4,5 DRG at 8 W for 3-min. There were two treatment groups; one received a single FUS treatment, while the other received two. Control groups consisted of one sham CPNI group that received FUS treatment and a CPNI group that received sham FUS treatment. Behavioral tests were conducted pre-CPNI surgery, 1-week post-surgery, and for 1-week post-FUS treatment(s). CPNI surgery resulted in lower VFF mechanical thresholds in the left hind paw compared to baseline (p < 0.0001) and increased proportion of time spent on bright side compared to baseline values on PEAP (p = 0.0473), indicating neuropathic state. FUS treatment increased VFF thresholds after 24-hours (p < 0.0001), 48-h (p = 0.0079), and 72-h (p = 0.0164). VFF returned to baseline values from day 4-7. Following a second FUS treatment on day 8, increased mechanical thresholds were similarly observed after 24-h (p = 0.0021), 48-h (p < 0.0001), and 72-h (p = 0.0256). Control group analysis showed (1) CPNI rats experienced no change in mechanical thresholds following sham FUS treatment and (2) Sham CPNI rats receiving FUS did not experience significantly different mechanical thresholds compared to baseline and post-CPNI values. Post-FUS histological analysis demonstrated healthy ganglion cells without chromatolysis. Our results demonstrate changes in VFF and PEAP in rats who underwent CPNI. Single and multiple doses of external FUS increase mechanical thresholds without inducing histological damage. Based on our results, we have demonstrated the potential of FUS to serve as a non-pharmacological and non-ablative neuromodulatory approach for the treatment of allodynia and neuropathic pain.

The use of focused ultrasound for the treatment of cutaneous allodynia associated with chronic migraine

Chronic migraines (CM) are the third most common disease and are refractory to medical treatment in 15% of patients. Currently, temporary relief is achieved with steroid blocks or pulsed radiofrequency ablation, which have short-term benefits. Our project aims to develop a non-invasive treatment for medically refractory chronic migraine, which does not require a permanent implant. This project investigates the safety and effectiveness of pulsed focused ultrasound (FUS) in a validated rodent headache model of cutaneous allodynia associated with chronic migraine (CM) as compared to sumatriptan and ablative lesioning. We demonstrate a significant reduction in mechanical thresholds as measured through Von Frey filaments in CM in the forepaw and periorbital region (p < 0.001). Sumatriptan and pulsed FUS both significantly improve thresholds at day 3 after treatment in the periorbital region. Ablative lesioning has no effect. This study provides initial evidence that FUS may provide an important therapeutic option for patients suffering from CM.