Tolerance to delta9-tetrahydrocannabinol in adapted and nonadapted rabbits

Phytocannabinoids as novel therapeutic agents in CNS disorders

The Cannabis sativa herb contains over 100 phytocannabinoid (pCB) compounds and has been used for thousands of years for both recreational and medicinal purposes. In the past two decades, characterisation of the body's endogenous cannabinoid (CB) (endocannabinoid, eCB) system (ECS) has highlighted activation of central CB(1) receptors by the major pCB, Δ(9)-tetrahydrocannabinol (Δ(9)-THC) as the primary mediator of the psychoactive, hyperphagic and some of the potentially therapeutic properties of ingested cannabis. Whilst Δ(9)-THC is the most prevalent and widely studied pCB, it is also the predominant psychotropic component of cannabis, a property that likely limits its widespread therapeutic use as an isolated agent. In this regard, research focus has recently widened to include other pCBs including cannabidiol (CBD), cannabigerol (CBG), Δ(9)tetrahydrocannabivarin (Δ(9)-THCV) and cannabidivarin (CBDV), some of which show potential as therapeutic agents in preclinical models of CNS disease. Moreover, it is becoming evident that these non-Δ(9)-THC pCBs act at a wide range of pharmacological targets, not solely limited to CB receptors. Disorders that could be targeted include epilepsy, neurodegenerative diseases, affective disorders and the central modulation of feeding behaviour. Here, we review pCB effects in preclinical models of CNS disease and, where available, clinical trial data that support therapeutic effects. Such developments may soon yield the first non-Δ(9)-THC pCB-based medicines.

Behavioral effects of THC as a function of environment and prior drug experience

Holtzman albino rats were divided into 4 groups, and on 5 consecutive days each group was exposed to one of 4 conditions. The drug-adapted group was given delta-9-tetrahydrocannabinol (THC) (0.0, 0.5, 2.5 or 5.0 mg/kg PO) in their home cages, while the environment-adapted group was given vehicle and placed for one hr in the chamber where they were later tested. The naive group was given vehicle in their home cages and the drug + environment adapted group was given THC and placed in the test chamber. One week later, all rats were given either 0.0, 0.5, 2.5, or 5.0 mg/kg THC and placed in the test chamber where standing, sitting, and behavioral activity were measured. The results showed that the behavioral effects of THC are a function of environmental familiarity in rats who are drug naive but not in rats given prior exposure to THC.

The ontogeny of delta-9-tetrahydrocannabinol responsiveness in the rabbit

An autosomal recessive condition (thc/thc) in our closed colony of New Zealand White rabbits (Uaz:NZW-thc) results in nonfatal, behavioral convulsions following intravenous (i.v.) injections of delta-9-tetrahydrocannabinol (THC) and other psychoactive cannabinoids of marijuana. The ontogeny of the convulsive response was evaluated in potential THC-seizure-susceptible (SS) rabbits from postnatal Days (PN) 15-548. Ages of nonsusceptibility (PN 15-23), partial susceptibility (PN 24-38), and complete susceptibility (PN 39-548) were found. Also, open-field activity was determined in PN 14-25 THC-SS and THC-seizure-resistant (SR) rabbits. Administration of THC during the seizure-insensitive period resulted in genotype-dependent alternations in photocell activity and sprawling.