Species-specific susceptibility to cannabis-induced convulsions.

BACKGROUND AND PURPOSE: Numerous claims are made for cannabis' therapeutic utility upon human seizures, but concerns persist about risks. A potential confounder is the presence of both Δ9 -tetrahydrocannabinol (THC), variously reported to be pro- and anticonvulsant, and cannabidiol (CBD), widely confirmed as anticonvulsant. Therefore, we investigated effects of prolonged exposure to different THC/CBD cannabis extracts on seizure activity and associated measures of endocannabinoid (eCB) system signalling. EXPERIMENTAL APPROACH: Cannabis extract effects on in vivo neurological and behavioural responses, and on bioanalyte levels, were measured in rats and dogs. Extract effects on seizure activity were measured using electroencephalography telemetry in rats. eCB signalling was also investigated using radioligand binding in cannabis extract-treated rats and treatment-naïve rat, mouse, chicken, dog and human tissue. KEY RESULTS: Prolonged exposure to cannabis extracts caused spontaneous, generalized seizures, subserved by epileptiform discharges in rats, but not dogs, and produced higher THC, but lower 11-hydroxy-THC (11-OH-THC) and CBD, plasma concentrations in rats versus dogs. In the same rats, prolonged exposure to cannabis also impaired cannabinoid type 1 receptor (CB1 receptor)-mediated signalling. Profiling CB1 receptor expression, basal activity, extent of activation and sensitivity to THC suggested interspecies differences in eCB signalling, being more pronounced in a species that exhibited cannabis extract-induced seizures (rat) than one that did not (dog). CONCLUSIONS AND IMPLICATIONS: Sustained cannabis extract treatment caused differential seizure, behavioural and bioanalyte levels between rats and dogs. Supporting radioligand binding data suggest species differences in eCB signalling. Interspecies variations may have important implications for predicting cannabis-induced convulsions from animal models. LINKED ARTICLES: This article is part of a themed section on 8th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Endocannabinoid regulation of spinal nociceptive processing in a model of neuropathic pain.

Models of neuropathic pain are associated with elevated spinal levels of endocannabinoids (ECs) and altered expression of cannabinoid receptors on primary sensory afferents and post-synaptic cells in the spinal cord. We investigated the impact of these changes on the spinal processing of sensory inputs in a model of neuropathic pain. Extracellular single-unit recordings of spinal neurones were made in anaesthetized neuropathic and sham-operated rats. The effects of spinal administration of the cannabinoid CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251) and the cannabinoid receptor type 2 (CB(2)) receptor antagonist N-[(1S)-endo-1,3,3-trimethylbicycloheptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528) on mechanically-evoked responses of spinal neurones were determined. The effects of spinal administration of (5Z,8Z11Z,14Z)-N-(3-furanylmethyl)-5,8,11,14-eicosatetraenamide (UCM707), which binds to CB(2) receptors and alters transport of ECs, on evoked responses of spinal neurones and spinal levels of ECs were also determined. The cannabinoid CB(1) receptor antagonist AM251, but not the CB(2) receptor antagonist, significantly facilitated 10-g-evoked responses of spinal neurones in neuropathic, but not sham-operated, rats. Spinal administration of UCM707 did not alter spinal levels of ECs but did significantly inhibit mechanically-evoked responses of neurones in neuropathic, but not sham-operated, rats. Pharmacological studies indicated that the selective inhibitory effects of spinal UCM707 in neuropathic rats were mediated by activation of spinal CB(2) receptors, as well as a contribution from transient receptor potential vanilloid 1 (TRPV1) channels. This work demonstrates that changes in the EC receptor system in the spinal cord of neuropathic rats influence the processing of sensory inputs, in particular low-weight inputs that drive allodynia, and indicates novel effects of drugs acting via multiple elements of this receptor system.

Prostanoid receptor EP1 and Cox-2 in injured human nerves and a rat model of nerve injury: a time-course study.

BACKGROUND: Recent studies show that inflammatory processes may contribute to neuropathic pain. Cyclooxygenase-2 (Cox-2) is an inducible enzyme responsible for production of prostanoids, which may sensitise sensory neurones via the EP1 receptor. We have recently reported that while macrophages infiltrate injured nerves within days of injury, they express increased Cox-2-immunoreactivity (Cox-2-IR) from 2 to 3 weeks after injury. We have now investigated the time course of EP1 and Cox-2 changes in injured human nerves and dorsal root ganglia (DRG), and the chronic constriction nerve injury (CCI) model in the rat. METHODS: Tissue sections were immunostained with specific antibodies to EP1, Cox-2, CD68 (human macrophage marker) or OX42 (rat microglial marker), and neurofilaments (NF), prior to image analysis, from the following: human brachial plexus nerves (21 to 196 days post-injury), painful neuromas (9 days to 12 years post-injury), avulsion injured DRG, control nerves and DRG, and rat CCI model tissues. EP1 and NF-immunoreactive nerve fibres were quantified by image analysis. RESULTS: EP1:NF ratio was significantly increased in human brachial plexus nerve fibres, both proximal and distal to injury, in comparison with uninjured nerves. Sensory neurones in injured human DRG showed a significant acute increase of EP1-IR intensity. While there was a rapid increase in EP1-fibres and CD-68 positive macrophages, Cox-2 increase was apparent later, but was persistent in human painful neuromas for years. A similar time-course of changes was found in the rat CCI model with the above markers, both in the injured nerves and ipsilateral dorsal spinal cord. CONCLUSION: Different stages of infiltration and activation of macrophages may be observed in the peripheral and central nervous system following peripheral nerve injury. EP1 receptor level increase in sensory neurones, and macrophage infiltration, appears to precede increased Cox-2 expression by macrophages. However, other methods for detecting Cox-2 levels and activity are required. EP1 antagonists may show therapeutic effects in acute and chronic neuropathic pain, in addition to inflammatory pain.

Cyclooxygenase-2 (Cox-2) in injured human nerve and a rat model of nerve injury.

Inflammation associated with nerve injury produces a number of pathogenic chemical mediators of which prostanoids are a potent component. Cyclooxygenases (Cox-1 and Cox-2) are the enzymes responsible for prostanoid production. We have investigated Cox-2 immunoreactivity (Cox-2-IR) and glial activation in human injured (n = 16) and uninjured (n = 8) nerves and in the chronic constriction injury (CCI) model of nerve injury in the rat, using immunohistological and autoradiographic methods. Tissues were immunostained with antibodies to Cox-2, CD-68 (human macrophage marker), OX42 (rat microglial marker), or incubated with tritiated PK11195 (marker of glial activation), prior to image analysis. In human nerves, Cox-2-IR was detected in cells with morphology and distribution similar to macrophages/microglia - these were increased significantly in human nerve proximal to injury (p < 0.002), reaching a peak at 4-6 weeks after injury. In the rat CCI model, at 40 days after injury, microglia-like cells with Cox-2-IR were increased significantly in the injured nerve (p < 0.004) and ipsilateral dorsal spinal cord (p < 0.008). PK11195-binding results were similar for Cox-2-IR in chronic injured human nerve and rat tissues. These findings suggest that Cox-2-immunoreactive cells could play a role in processes associated with Wallerian degeneration, nerve regeneration, and the development of persistent pain. Selection of patients 4-6 weeks after nerve injury would be more likely to show any efficacy of Cox-2 inhibitors.