Chronic marijuana smoke exposure in the rhesus monkey. IV: Neurochemical effects and comparison to acute and chronic exposure to delta-9-tetrahydrocannabinol (THC) in rats

Δ 9-Tetrahydrocannabinol Toxicity and Validation of Cannabidiol on Brain Dopamine Levels: An Assessment on Cannabis Duplicity

Δ9-tetrahydrocannabinol (THC) of cannabis is the main psychoactive component which is a global significant concern to human health. Evaluation on THC reported its drastic effect on the brain dopaminergic (DAergic) system stimulating mesolimbic DA containing neurons thereby increasing the level of striatal DA. Cannabidiol (CBD), with its anxiolytic and anti-psychotic property, is potent to ameliorate the THC-induced DAergic variations. Legal authorization of cannabis use and its analogs in most countries led to a drastic dispute in the elicitation of cannabis products. With a recent increase in cannabis-induced disorder rates, the present review highlighted the detrimental effects of THC and the effects of CBD on THC induced alterations in DA synthesis and release. Alongside the reported data, uses of cannabis as a therapeutic medium in a number of health complications are also being briefly reviewed. These evaluated reports led to an anticipation of additional research contradictory to the findings of THC and CBD activity in the brain DAergic system and their medical implementations as therapeutics.

Clinical and Preclinical Evidence for Functional Interactions of Cannabidiol and Δ9-Tetrahydrocannabinol

The plant Cannabis sativa, commonly called cannabis or marijuana, has been used for its psychotropic and mind-altering side effects for millennia. There has been growing attention in recent years on its potential therapeutic efficacy as municipalities and legislative bodies in the United States, Canada, and other countries grapple with enacting policy to facilitate the use of cannabis or its constituents for medical purposes. There are >550 chemical compounds and >100 phytocannabinoids isolated from cannabis, including Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD). THC is thought to produce the main psychoactive effects of cannabis, while CBD does not appear to have similar effects. Studies conflict as to whether CBD attenuates or exacerbates the behavioral and cognitive effects of THC. This includes effects of CBD on THC-induced anxiety, psychosis, and cognitive deficits. In this article, we review the available evidence on the pharmacology and behavioral interactions of THC and CBD from preclinical and human studies, particularly with reference to anxiety and psychosis-like symptoms. Both THC and CBD, as well as other cannabinoid molecules, are currently being evaluated for medicinal purposes, separately and in combination. Future cannabis-related policy decisions should include consideration of scientific findings, including the individual and interactive effects of CBD and THC.

The effects of Δ9-tetrahydrocannabinol on the dopamine system

The effects of Δ9-tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, are a pressing concern for global mental health. Patterns of cannabis use are changing drastically owing to legalization, the availability of synthetic analogues (commonly termed spice), cannavaping and an emphasis on the purported therapeutic effects of cannabis. Many of the reinforcing effects of THC are mediated by the dopamine system. Owing to the complexity of the cannabinoid-dopamine interactions that take place, there is conflicting evidence from human and animal studies concerning the effects of THC on the dopamine system. Acute THC administration causes increased dopamine release and neuron activity, whereas long-term use is associated with blunting of the dopamine system. Future research must examine the long-term and developmental dopaminergic effects of THC.

Darwinian depression

BACKGROUND

The standard evolutionary explanation for depression is that being in an emotionally depressed state is adaptive.

METHOD

The article first undertakes a critical review of the extant literature. It then provides an alternative evolutionary explanation for event-based depression and elation. It argues that being in a depressed state is not adaptive (indeed, quite the opposite), but that the threat of depression for bad outcomes and the promise of pleasure for good outcomes are adaptive because they motivate the individual toward undertaking effort that increases fitness. The article then explains reasons for failure in the motivation system and the mood disorders that arise as a consequence.

RESULTS

The article explains why motivation depends on both elation and depression and why individual happiness is not permanently improved by winning the lottery (or permanently reduced by becoming wheelchair bound). It explains the comorbidity of bipolar disorder and panic disorder, why mood stabilizers tend to reduce motivation, and when anti-depressants are unlikely to cure "laziness."

LIMITATIONS

The evolutionary explanation for depression does not directly provide clinical criteria for determining when major depressive disorder is present nor has it yet provided new treatment strategies for mood disorders.

CONCLUSIONS

The theory presented here provides a coherent explanation for depression and elation and leads research in a different direction from previous evolutionary explanations.

Effects of the cannabinoid ligand SR 141716A alone or in combination with delta9-tetrahydrocannabinol or scopolamine on learning in squirrel monkeys

To investigate the effects of the cannabinoids on learning and on scopolamine-induced disruptions in learning, delta9-tetrahydrocannabinol (delta9-THC), SR 141716A (an antagonist at CB1 receptors) and scopolamine were administered to squirrel monkeys responding in a repeated-acquisition task. In this task, monkeys acquired a different three-response sequence each session and responding was maintained by food presentation under a second-order fixed-ratio 5 schedule. When either delta9-THC (0.1-0.56 mg/kg, i.m.) or SR 141716A (1-10 mg/kg, i.m.) was administered alone, 60 and 75 min before the session, respectively, both cannabinoid ligands dose-dependently decreased the overall rate of responding and increased the overall percentage of errors. However, at a dose that had little or no effect alone (i.e. 1 mg/kg), SR 141716A antagonized the disruptive effects of delta9-THC (0.18-1.8 mg/kg) on acquisition, shifting the dose-effect curves for rate of responding and percentage of errors at least 1/2 log unit to the right. Finally, when either delta9-THC (0.001-1 mg/kg) or SR 141716A (0.32-10 mg/kg) was administered with scopolamine (0.01 or 0.032 mg/kg, 15 min before the session), greater rate-decreasing and error-increasing effects were obtained than with scopolamine alone. These results suggest that while low doses of SR 141716A can antagonize the effects of delta9-THC in squirrel monkeys, high doses can also disrupt acquisition when administered alone and potentiate the disruptive effects of scopolamine on acquisition.

Desensitization of Fos protein induction in rat striatum and nucleus accumbens following repeated administration of delta9-tetrahydrocannabinol

The purpose of the present study was to clarify the effect of repeated administration of delta9-tetrahydrocannabinol (THC) on Fos protein induction in the rat brain. Pretreatment of rats for 3 days with THC (10 mg/kg, i.p.) attenuated the effect of THC (10 mg/kg) to induce the expression of Fos protein in rat striatum and nucleus accumbens. This desensitization of Fos protein induction might explain the rapid development of behavioral tolerance to repeated administration of THC.

Chronic exposure to delta 9-tetrahydrocannabinol fails to irreversibly alter brain cannabinoid receptors

The effects of chronic delta 9-tetrahydrocannabinol (delta 9-THC) and marijuana administration on the properties of brain cannabinoid receptor populations of the rat and monkey, respectively, were examined in this study. It was determined that the properties of the cannabinoid receptors in the striatum, cerebral cortex, cerebellum, hippocampus, and brainstem/spinal cord of the rat do not appear to be irreversibly altered by chronic exposure to delta 9-THC. Similarly, the cannabinoid receptors in the caudate, prefrontal cortex, and cerebellum of the monkey do not appear to be irreversibly altered by chronic exposure to marijuana smoke.