The refined biomimetic NeuroDigm GEL™ model of neuropathic pain in a mature rat

The Therapeutic Effectiveness of Full Spectrum Hemp Oil Using a Chronic Neuropathic Pain Model

BACKGROUND

Few models exist that can control for placebo and expectancy effects commonly observed in clinical trials measuring 'Cannabis' pharmacodynamics. We used the Foramen Rotundum Inflammatory Constriction Trigeminal Infraorbital Nerve injury (FRICT-ION) model to measure the effect of "full-spectrum" whole plant extracted hemp oil on chronic neuropathic pain sensitivity in mice.

METHODS

Male BALBc mice were submitted to the FRICT-ION chronic neuropathic pain model with oral insertion through an incision in the buccal/cheek crease of 3 mm of chromic gut suture (4-0). The suture, wedged along the V2 trigeminal nerve branch, creates a continuous irritation that develops into secondary mechanical hypersensitivity on the snout. Von Frey filament stimuli on the mouse whisker pad was used to assess the mechanical pain threshold from 0-6 h following dosing among animals (n = 6) exposed to 5 μL of whole plant extracted hemp oil combined with a peanut butter vehicle (0.138 mg/kg), the vehicle alone (n = 3) 7 weeks post-surgery, or a naïve control condition (n = 3).

RESULTS

Mechanical allodynia was alleviated within 1 h (d = 2.50, p < 0.001) with a peak reversal effect at 4 h (d = 7.21, p < 0.001) and remained significant throughout the 6 h observation window. There was no threshold change on contralateral whisker pad after hemp oil administration, demonstrating the localization of anesthetic response to affected areas.

CONCLUSION

Future research should focus on how whole plant extracted hemp oil affects multi-sensory and cognitive-attentional systems that process pain.

Minimally Invasive Oral Surgery Induction of the FRICT-ION Chronic Neuropathic Pain Model

An easily induced preclinical trigeminal neuropathic nerve injury model is described here for the study of chronic pain, the model acronym FRICT-ION (Foramen Rotundum Inflammatory Constriction Trigeminal InfraOrbital Nerve). In patients, neuropathic pain is thought to be related to vascular alignment or multiple sclerosis along this small trigeminal nerve branch (V2) innervating the maxillary teeth and middle third of the face. With no detectable outward physical signs, the FRICT-ION model is ideal for blinded studies. The acronym FRICT-ION applied relates to the persistence of the trigeminal neuropathic pain model likely due to sliding irritation with normal chewing in the mice. A step-by-step method to induce the mild chronic rodent neuropathic pain model is described here. The surgery is performed orally through a tiny surgical slit inside the cheek crease to align a chromic gut suture irritant along the nerve as it passes into the skull. The model allows testing of non-evoked subjective measures and evoked quantitative mechanical hypersensitivity (allodynia) testing with von Frey filaments through at least 10-14 weeks (100 days). Anxiety and depression behaviors develop within 3-6 weeks relevant to the affective component of chronic pain. While many pain drugs have failed based on testing performed in the acute animal models available, the more stable and easily replicated trigeminal inflammatory compression model is the better suited for understanding both mechanistic and affective components of nerve injury-induced chronic neuropathic pain states as well as the more ideal for preclinical trials of novel non-opioid pain relief therapies.

Variable criteria sequential stopping rule: Validity and power with repeated measures ANOVA, multiple correlation, MANOVA and relation to Chi-square distribution

The variable criteria sequential stopping rule (vcSSR) is an efficient way to add sample size to planned ANOVA tests while holding the observed rate of Type I errors, α_o, constant. The only difference from regular null hypothesis testing is that criteria for stopping the experiment are obtained from a table based on the desired power, rate of Type I errors, and beginning sample size. The vcSSR was developed using between-subjects ANOVAs, but it should work with p values from any type of F test. In the present study, the α_o remained constant at the nominal level when using the previously published table of criteria with repeated measures designs with various numbers of treatments per subject, Type I error rates, values of ρ, and four different sample size models. New power curves allow researchers to select the optimal sample size model for a repeated measures experiment. The criteria held α_o constant either when used with a multiple correlation that varied the sample size model and the number of predictor variables, or when used with MANOVA with multiple groups and two levels of a within-subject variable at various levels of ρ. Although not recommended for use with χ² tests such as the Friedman rank ANOVA test, the vcSSR produces predictable results based on the relation between F and χ². Together, the data confirm the view that the vcSSR can be used to control Type I errors during sequential sampling with any t- or F-statistic rather than being restricted to certain ANOVA designs.

The refined biomimetic NeuroDigm GEL™ model of neuropathic pain in a mature rat

Background: Many humans suffering with chronic neuropathic pain have no objective evidence of an etiological lesion or disease. Frequently their persistent pain occurs after the healing of a soft tissue injury. Based on clinical observations over time, our hypothesis was that after an injury in mammals the process of tissue repair could cause chronic neural pain. Our objectives were to create the delayed onset of neuropathic pain in rats with minimal nerve trauma using a physiologic hydrogel, and characterize the rats' responses to known analgesics and a targeted biologic. Methods: In mature male Sprague Dawley rats (age 9.5 months) a percutaneous implant of tissue-derived hydrogel was placed in the musculofascial tunnel of the distal tibial nerve. Subcutaneous morphine (3 mg/kg), celecoxib (10 mg/kg), gabapentin (25 mg/kg) and duloxetine (10 mg/kg) were each screened in the model three times each over 5 months after pain behaviors developed. Sham and control groups were used in all screenings. A pilot study followed in which recombinant human erythropoietin (200 units) was injected by the GEL™ neural procedure site. Results: The GEL group gradually developed mechanical hypersensitivity lasting months. Morphine, initially effective, had less analgesia over time. Celecoxib produced no analgesia, while gabapentin and duloxetine at low doses demonstrated profound analgesia at all times tested. The injected erythropoietin markedly decreased bilateral pain behavior that had been present for over 4 months, p ≤ 0.001. Histology of the GEL group tibial nerve revealed a site of focal neural remodeling, with neural regeneration, as found in nerve biopsies of patients with neuropathic pain. Conclusion: The refined NeuroDigm GEL™ model induces a neural response resulting in robust neuropathic pain behavior. The analgesic responses in this model reflect known responses of humans with neuropathic pain. The targeted recombinant human erythropoietin at the ectopic neural lesion appears to alleviate the persistent pain behavior in the GEL™ model rodents.