Effects of delta 9-tetrahydrocannabinol on the levels of cyclic adenosine 3',5'-monophosphate in mouse brain

Dopamine: biphasic dose responses

The present article indicates that dopamine and/or its agonists induce biphasic dose-response relationships for numerous endpoints. These include locomotion, pain sensitivity, blood pressure, prolactin secretion, oxytocin release, heart rate, memory, and neuronal adenylate cyclase activity. Biphasic responses were reported predominantly with male Sprague-Dawley rats, but also with mice, dogs, monkeys, and humans. Regardless of the model or endpoint the maximum changes from the control were always modest being within the 10 to 80% range. The range of stimulatory responses was quite variable, extending from slightly greater than a factor of 10 for the endpoints such as memory, pain-vocalization, and diastolic blood pressure to the 10(6) range for prolactin release and the 10(8) range for oxytocin release. Mechanistic studies suggested that the stimulatory and inhibitory effects of dopamine are mediated by different receptors or receptor subtypes having opposite actions and different ligand affinities.

Delta9-tetrahydrocannabinol increases sequence-specific AP-1 DNA-binding activity and Fos-related antigens in the rat brain

Delta-9-tetrahydrocannabinol (delta9-THC), the psychoactive principle of marijuana, has been shown to upregulate the mRNA levels of immediate-early genes in the rat brain. Using electrophoretic mobility-shift assay and one-dimensional Western blot, we here report that delta9-THC increases Activator protein-1 (AP-1) DNA-binding and Fos-related antigen activity in discrete areas of the rat brain. One hour after the intraperitoneal administration of delta9-THC at a dose of 10 or 15 mg/kg, AP-1 DNA-binding activity in the nucleus accumbens increased by 33 and 49%, respectively, while Western blot showed an increase in both c-Fos, FosB, Fra-1 (Fos-related antigen) and Fra-2. In the cingulate cortex and caudate-putamen, delta9-THC significantly increased AP-1 DNA-binding activity only at the highest dose used (57 and 71%, respectively). While in the caudate-putamen the increase in AP-1 DNA binding was mainly due to an elevation of the c-Fos and FosB proteins, the same phenomenon depended on the FosB, Fra-1 and Fra-2 peptides in the cingulate cortex. The effect of delta9-THC on the AP-1 DNA binding and the Fos-related antigens in the nucleus accumbens was blocked by the specific cannabinoid antagonist SR141716 A (3 mg/kg i.p.). delta9-THC failed to modify Specificity protein 1 (Sp1) DNA-binding activity. The results indicate that delta9-THC activates gene coding for AP-1 DNA-binding proteins by acting on cannabinoid receptors, and induces a different transcriptional program on the early-immediate gene of the Fos family, in different areas in the rat brain, suggesting that this mechanism might be involved in the central actions of cannabinoids.

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

THC is the major psychoactive constituent of marijuana and is known to produce psychopharmacological effects in humans. These studies were designed to determine whether acute or chronic exposure to marijuana smoke or THC produces in vitro or in vivo neurochemical alterations in rat or monkey brain. For the in vitro study, THC was added (1-100 nM) to membranes prepared from different regions of the rat brain and muscarinic cholinergic (MCh) receptor binding was measured. For the acute in vivo study, rats were injected IP with vehicle, 1, 3, 10, or 30 mg THC/kg and sacrificed 2 h later. For the chronic study, rats were gavaged with vehicle or 10 or 20 mg THC/kg daily, 5 days/week for 90 days and sacrificed either 24 h or 2 months later. Rhesus monkeys were exposed to the smoke of a single 2.6% THC cigarette once a day, 2 or 7 days a week for 1 year. Approximately 7 months after the last exposure, animals were sacrificed by overdose with pentobarbital for neurochemical analyses. In vitro exposure to THC produced a dose-dependent inhibition of MCh receptor binding in several brain areas. This inhibition of MCh receptor binding, however, was also observed with two other nonpsychoactive derivatives of marijuana, cannabidiol and cannabinol. In the rat in vivo study, we found no significant changes in MCh or other neurotransmitter receptor binding in hippocampus, frontal cortex or caudate nucleus after acute or chronic exposure to THC. In the monkey brain, we found no alterations in the concentration of neurotransmitters in caudate nucleus, frontal cortex, hypothalamus or brain stem.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of delta 9-tetrahydrocannabinol and other cannabinoids on cAMP accumulation in synaptosomes

The effects of delta 9-THC and other cannabinoids on cAMP levels in synaptosomes from mouse brains were investigated in order to determine whether cannabinoids produced their behavioral effects through alterations in adenylate cyclase. delta 9-THC (0.01-10 microM) did not significantly alter basal cAMP levels, whereas delta 9-THC and other cannabinoids were able to alter forskolin-stimulated cAMP levels in synaptosomes. In general, three kinds of responses were observed. Some cannabinoids displayed a modest, concentration-dependent decrease in cAMP levels, producing significant inhibition between 1-10 microM. Other cannabinoids, including delta 9-THC and delta 8-THC, appeared to produce a biphasic effect in that inhibition of cAMP was observed only at a single concentration. Finally, some analogs were unable to significantly alter forskolin-stimulated cAMP. There was not a clear relationship between the ability of the cannabinoids to alter cAMP levels in synaptosomes and the behavioral effects observed in mice. However, it was demonstrated that the analogs which are the most potent in producing cannabimimetic effects in mice were the analogs which inhibited cAMP in a concentration-dependent manner. While cannabinoids were able to alter cAMP levels in synaptosomes, the ability to alter cAMP levels does not appear to be absolutely necessary for the production of cannabinoid effects in mice.

Cannabinoid receptors and modulation of cyclic AMP accumulation in the rat brain

The mechanism by which cannabinoid compounds produce their effects in the rat brain was evaluated in this investigation. Cannabinoid receptors, quantitated by [3H]CP-55,940 binding, were found in greatest abundance in the rat cortex, cerebellum, hippocampus, and striatum, with smaller but significant binding also found in the hypothalamus, brainstem, and spinal cord. Using rat brain slice preparations, we evaluated the effect of desacetyllevonantradol on basal and forskolin-stimulated cyclic AMP accumulation in the regions exhibiting the greatest cannabinoid receptor density. Desacetyllevonantradol (10 microM) reduced cyclic AMP levels in the hippocampus, frontal cortex, and striatum. In the cerebellum, however, the response to desacetyllevonantradol was biphasic with cyclic AMP accumulation being decreased at lower and increased at higher concentrations. Desacetyllevonantradol reduced cyclic AMP accumulation in isoproterenol-stimulated slices in the cortex and cerebellum, but not in the hippocampus. Cells that responded to vasoactive intestinal peptide with an increase in cyclic AMP accumulation in the hippocampus and cortex also responded to desacetyllevonantradol. The modulation of cyclic AMP accumulation by desacetyllevonantradol could be attenuated following stereotaxic implantation of pertussis toxin, supporting the involvement of a G protein in the cannabinoid response in the brain. However, other actions of cannabinoid compounds may also affect the cyclic AMP levels in brain slice preparations.

Effects of acute cannabis use on urinary neurotransmitter metabolites and cyclic nucleotides in man

The noradrenaline, dopamine and serotonin metabolites methoxyhydroxyphenylglycol (MHPG), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA), as well as the cyclic nucleotides c-AMP and c-GMP were estimated in urine samples of five normal volunteers. Ten control samples and two samples after cannabis use were analyzed for each volunteer. Cannabis use caused significant decreases in MHPG and c-AMP, and increases in HVA, while 5-HIAA and c-GMP excretion remained unchanged. The results indicate that cannabis use interferes with catecholaminergic mechanisms in man, decreasing the noradrenaline and increasing dopamine turnover, probably through action on presynaptic receptors.

Possible role of prostaglandins in the effects of the cannabinoids on adenylate cyclase activity

In vitro, the cannabinoids delta 9-tetrahydrocannabinol (delta 9-THC), 11-OH-delta 9-THC, cannabidiol and cannabinol all increased adenylate cyclase activity in mouse cerebral cortical homogenates. Levonantradol, a synthetic cannabinoid analog, also increased adenylate cyclase activity while its optical isomer dextronantradol did not. The increases in enzyme activity produced by the active compounds were biphasic with significant increases at 10 microM and/or 30 microM concentrations with return to control levels at 100 microM. The increases did not occur in the absence of added GTP nor did delta 9-THC have any effect on fluoride-stimulation of adenylate cyclase activity. The prostaglandin synthetase inhibitors acetyl salicylic acid and indomethacin and the phospholipase A2 inhibitor quinacrine all abolished the increase in adenylate cyclase activity produced by delta 9-THC, suggesting the involvement of prostaglandins in this cannabinoid action.

Biphasic nature of the effects of delta9-tetrahydrocannabinol on body temperature and brain amines of the rat

The effects of i.v. injected delta9-tetrahydrocannabinol (delta9-THC) on behaviour, body temperature and levels of brain monoamines, measured spectrophotofluorimetrically, of the rat were determined. Doses of delta9-THC in the range of 0.05--5.0 mg/kg produced biphasic changes in behaviour, body temperature and levels of 5-hydroxyindoleacetic acid (5-HIAA). The whole brain levels of dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) were not altered by delta9-THC. The subjective behavioural biphasic responses did not appear to be dose related, whereas the biphasic changes in body temperature and brain levels of 5-HIAA were dose-related. Low doses of delta9-THC (0.05 and 0.1 mg/kg) caused hyperthermia, while doses of 1.0, 2.0 and 5.0 mg/kg induced hypothermia. On the other hand, 0.05 mg/kg delta9-THC significantly reduced, whereas doses of 1.0, 2.0 and 5.0 mg/kg significantly increased the 5-HIAA levels in a dose-related manner. It is concluded that an inverse relationship exists between delta9-THC-induced changes in body temperature and alterations in brain 5-HIAA levels.

Effect of some cannabinoids on naloxone-precipitated abstinence in morphine-dependent mice

Mice were rendered morphine-dependent by the subcutaneous implantation of a pellet containing 75 mg of morphine base; 72 h after the implantation, the animals were injected intraperitoneally either with vehicle or with various doses of delta9-tetrahydrocannabinol, delta8-tetrahydrocannabinol, cannabidiol, cannabinol, or 11-hydroxy-delta8-tetrahydrocannabinol. Thirty minutes after injection of the cannabinoids, the antagonist, naloxone HC1, was administered to induce the stereotyped withdrawal jumping syndrome. The dose of naloxone needed to induce withdrawal jumping in 50% of the animals (ED50) was determined for each dose of the cannabinoids. All of the cannabinoids inhibited the naloxone-precipitated morphine abstinence as evidenced by an increase in the naloxone ED50. Two additional signs of morphine abstinence, defecation and rearing behavior, were also suppressed by the cannabinoids. The relative effectiveness of the cannabinoids in inhibiting morphine abstinence appeared to be in the following order: delta9-tetrahydrocannabinol greater than delta8-tetrahydrocannabinol greater than 11-hydroxy-delta8-tetrahydrocannabinol greater than cannabidiol greater than cannabinol. These data suggest that cannabinoids may be useful in facilitating narcotic detoxification.

Inhibition of naloxone-induced withdrawal in morphine dependent mice by 1-trans-delta9-tetrahydrocannabinol

The effects of various doses of 1-trans-delta9-tetrahydrocannabinol (delta9-THC) on naloxone-induced withdrawal were studied in mice rendered dependent on morphine by the pellet implantation procedure. When administered i.p., 30 min prior to naloxone, delta9-THC, inhibited the naloxone-induced withdrawal jumping response. Two other signs of morphine withdrawal (defecation and rearing behavior) were also suppressed by deltapTHC. It is suggested that delta9-THC or some of its derivatives may have potential use in narcotic detoxification.