Giovanna Carta

Cannabinoids decrease acetylcholine release in the medial-prefrontal cortex and hippocampus, reversal by SR 141716A

The effect of delta9-tetrahydrocannabinol, the psychoactive principle of marijuana, and [R-(+)-(2,3-dihydro-5-methyl-3-[[4-morpholinylmethyl]pyrol[1,2,3-d e-]-1,4-benzoxazin-6y)(1-naphthalenyl)methanone monomethanesulfonate] (WIN 55,212-2), a synthetic cannabinoid receptor agonist, on the acetylcholine output in the medial-prefrontal cortex and hippocampus was studied by microdialysis in freely moving rats. The administration of delta9-tetrahydrocannabinol (1 and 5 mg/kg i.p.) and WIN 55,212-2 (5 and 10 mg/kg i.p.) produced a long lasting inhibition of acetylcholine release in both areas. The inhibitory effect of delta9-tetrahydrocannabinol and WIN 55,212-2 was suppressed in both areas by the specific cannabinoid CB1 receptor antagonist, [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1H-pyrazole-3carboxamide]HCl (SR 141716A), at the dose of 0.1 mg/kg i.p., per se ineffective to modify basal acetylcholine release. Most interestingly, SR 141716A alone at higher doses increased acetylcholine release both in the medial-prefrontal cortex (3 mg/kg i.p.) and hippocampus (1 and 3 mg/kg i.p.), suggesting that acetylcholine output is tonically inhibited by endogenous cannabinoids. Since the inhibitory effect of delta9-tetrahydrocannabinol is produced by doses within those relevant to human use of marijuana, our results suggest that the negative effects of the latter on cognitive processes may be explained by its ability to reduce acetylcholine release in the medial-prefrontal cortex and hippocampus. Conversely, cannabinoid receptor antagonists may offer potential treatments for cognitive deficits.

Inhibition of hippocampal acetylcholine release by cannabinoids: reversal by SR 141716A

Two synthetic cannabinoids, WIN 55,212-2 {R-(+)-(2,3-dihydro-5-methyl-3-[{4-morpholinylmethyl]pyrol [1,2,3-de]-1,4-benzoxazin-6-yl)(1-naphthalenyl)methanone monomethanesulfonate} (5.0 and 10 mg/kg i.p.) and CP 55,940 {[1a,2-(R)-5-(1.1-dimethylheptyl)-2-[5-hydroxy-2-(3-hydroxypropyl) cyclohexyl]-phenol} {[1a,2-(R)-5-(1,1-dimethylheptyl)-2-[5-hydroxy-2-(3-hydroxypropyl) cyclohexyl]-phenol} (0.5 and 1.0 mg/kg i.p.), inhibited acetylcholine release in the rat hippocampus. The inhibition was prevented by the cannabinoid receptor antagonist, SR 141716A {N-(piperidin-1-yl)-5-(4- chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide} HCl, at the dose of 0.1 mg/kg i.p. Higher doses of SR 141716A (1.0 and 3.0 mg/kg i.p.) themselves increased hippocampal acetylcholine release, suggesting that acetylcholine output is tonically inhibited by endogenous cannabinoids. The results also suggest that the negative effects of marijuana on learning and memory may depend on cannabinoid receptor-mediated inhibition of acetylcholine release.

Inhibition of hippocampal acetylcholine release after acute and repeated Δ9-tetrahydrocannabinol in rats

The effects of acute and repeated administration of Delta9-tetrahydrocannabinol (Delta9-THC), the psychoactive principle of marijuana, on acetylcholine release in the hippocampus was studied in freely moving rats by microdialysis. The acute intraperitoneal (i.p.) administration of Delta9-THC at the doses of 2.5 and 5 mg/kg reduced acetylcholine release by about 25% and 45%, respectively. A dose of 7.5 mg/kg produced no further reduction. Delta9-THC effects were antagonized by the cannabinoid CB1 antagonist SR141716A at the i.p. dose of 1 mg/kg, per se ineffective in modifying acetylcholine concentrations. After a repeated exposure (twice daily for up to seven days) to Delta9-THC (7.5 mg/kg, i.p.) or vehicle (0.3 ml/kg, i.p.), the inhibitory effect of Delta9-THC (2.5 and 5 mg/kg, i.p) on acetylcholine release was not reduced. The results confirm previous observations that cannabinoids inhibit acetylcholine release through cannabinoid CB1 receptors, and indicate that no tolerance to this effects develops after a repeated Delta9-THC administration.

Effects of chronic Δ9-tetrahydrocannabinol treatment on hippocampal extracellular acetylcholine concentration and alternation performance in the T-maze

Delta(9)-Tetrahydrocannabinol (Delta(9)-THC), the psychoactive ingredient of cannabis sativa, reduces both extracellular hippocampal acetylcholine concentration and correct alternation tasks in the T-maze. The principal aim of this study was to determine whether a chronic Delta(9)-THC treatment would induce tolerance both to the reduction of extracellular hippocampal acetylcholine concentration and memory deficit produced by the drug. Our results show that a chronic Delta(9)-THC treatment (5mg/kg, i.p., twice daily for two weeks) did not produce tolerance to the inhibitory effects induced by the drug. Moreover, no strict temporal correlation between the two Delta(9)-THC effects was observed: the inhibition in extracellular acetylcholine concentration appeared only 80 min after treatment, while the reduction of correct alternation tasks in the T-maze began after 20 min. The cognitive and cholinergic effects induced by a chronic Delta(9)-THC treatment were completely blocked by the CB(1) cannabinoid receptor antagonist SR 141716A, indicating an involvement of CB(1) cannabinoid receptors in the persistent negative effects induced by the drug. These findings confirm the proposition that CB(1) cannabinoid receptors mediate the negative effects induced by Delta(9)-THC both on hippocampal extracellular acetylcholine concentration and correct alternation tasks in the T-maze, and they indicate that these effects may be differentiated. However, the major outcome of this work is the demonstration that no tolerance to the two inhibitory effects develops after a chronic Delta(9)-THC treatment.

Permissive Role of Dopamine D2 Receptors in the Hypothermia Induced by Δ9-Tetrahydrocannabinol in Rats

Abstract Cannabinoids produce analgesia, hypomotility, catalepsy, cognitive deficits and positive reinforcement. Moreover, Δ 9 -tetrahydrocannabinol ( 9 -THC) and synthetic cannabinoids stimulate dopaminergic neurons and increase dopamine release in different brain areas. In order to clarify the role of endogenously released dopamine in the hypothermic response to cannabinoids, the effect of D 1 and D 2 dopamine receptor agonists and antagonists on Δ 9 -THC–induced hypothermia was studied in rats. Δ 9 -THC (2.5 and 5 mg/kg intraperitoneally [IP]) decreased body temperature in a dose-related manner. This effect was antagonized not only as expected by the CB 1 cannabinoid receptor antagonist SR 141716A (0.5 mg/kg, IP) but also, unexpectedly, by the dopaminergic D 2 receptor antagonists S(-)-sulpiride (5 and 10 mg/kg, IP) and S(-)-raclopride (1 and 3 mg/kg, IP). Conversely, the hypothermic effect of Δ 9 -tetrahydrocannabinol was potentiated by the D 2 dopamine receptor agonists (-)-quinpirole (0.025 and 0.500 mg/kg, SC) and (+)-bromocriptine (0.5 and 1 mg/kg, IP). In contrast, the Δ 9 -THC–induced hypothermic effect was not modified by either by the D 1 dopamine agonist SKF 38393 (10 mg/kg SC) or by the D 1 dopamine antagonist SCH 23390 (0.5 mg/kg SC). These results suggest that the D 2 dopamine receptors have a permissive role in the hypothermic action of cannabinoids.

Reduction of dopamine release and synthesis by repeated amphetamine treatment : Role in behavioral sensitization

Changes in extracellular dopamine concentration in the ventral striatum during repeated amphetamine administration and over the first 7 days of withdrawal were studied by transversal microdialysis in freely moving rats. 2 days after fiber implantation rats were treated with either amphetamine (1.5 mg/kg i.p.) or saline every 12 h for 14 days. In amphetamine-treated rats, the baseline extracellular dopamine concentration, preceding the morning treatment, increased from 0.43 +/- 0.01 on day 1 up to 0.59 +/- 0.02 pmol/40 microliters sample on day 3 of treatment. Thereafter, dopamine fell rapidly on day 5(0.16 +/- 0.01 pmol/40 microliters) and remained at approximately the level reached on day 7(0.11 +/- 0.01 pmol/40 microliters) throughout the treatment and also over the 7 days of withdrawal. In contrast, in control rats, the extracellular dopamine concentration (0.40 +/- 0.01 pmol/40 microliters, on day 1) decreased progressively during the first days of treatment to reach a fairly stable value on day 4 (0.25 +/- 0.01 pmol/40 microliters sample). Thereafter, dopamine remained stable at this level throughout the remaining period of experimentation. Challenge with amphetamine (1.5 mg/kg i.p.) of animals treated with amphetamine for 10 days or withdrawn for 7 days produced a potentiated motor response compared to that in control rats but much less marked dopamine releasing effects. Dopamine synthesis in the ventral striatum, measured as L-dihydroxyphenylalanine formation after blockade of dihydroxyphenylalanine decarboxylase, was found to be reduced by approximately 60% after 2 weeks of amphetamine treatment and in animals withdrawn for 1 day or 7 days. These results indicate that repeated amphetamine treatment causes persistent inhibition of dopamine synthesis and release in the ventral striatum. Such inhibition may be a compensatory response to the repeated stimulation of postsynaptic dopamine receptors by the endogenously released dopamine and also the cause of postsynaptic sensitization to dopamine action.

γ-Hydroxybutyric acid and baclofen decrease extracellular acetylcholine levels in the hippocampus via GABAB receptors

Abstract The effect of γ-hydroxybutyric acid (GHB) and baclofen, a GABAB receptor agonist, on extracellular hippocampal acetylcholine levels was studied in freely moving rats by microdialysis. GHB (200 and 500 mg/kg, i.p.) reduced in a dose-dependent manner, extracellular hippocampal acetylcholine concentrations and this effect was prevented by the GABAB receptor antagonist (2S)(+)-5,5-Dimethyl-2-morpholineacetic acid (SCH 50911), at the dose of 20 mg/kg (i.p.), while the putative GHB receptor antagonist 6,7,8,9-Tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid (NCS 382) was ineffective. Similar to GHB, the GABAB agonist baclofen (10 and 20 mg/kg, i.p.) produced a dose-related reduction in extracellular acetylcholine concentrations which was prevented by SCH 50911. These findings indicate that GHB-induced reduction of hippocampal acetylcholine release is mediated by GABAB receptors and support a possible involvement of hippocampal GABAB receptors in the control of cognitive processes and in the claimed amnesic effect of GHB intoxication.

Melatonin reduces anxiety induced by lipopolysaccharide in the rat

In male Sprague-Dawley rats intraperitoneal (i.p.) injection of Escherichia coli lipopolysaccharide (0.25, 0.50 and 1 mg/kg) increased anxiety levels. This effect was reversed by a prior, concomitant, and subsequent i.p. treatment with melatonin (4 and 6 mg/kg). As the effects of melatonin upon the actions induced by lipopolysaccharide were reversed by the melatonin receptor antagonist luzindole (30 and 60 mg/kg, i.p.), we argued that they are, but not only, melatonin receptor mediated. These findings, in accordance with our previous works, suggest that melatonin could be useful in the treatment of sickness behaviour associated with systemic infection diseases or as adjuvant in the anti-anxiety therapy.

Rapid increase in basal acetylcholine release in the hippocampus of freely moving rats induced by withdrawal from long-term ethanol intoxication

The effect of ethanol withdrawal on hippocampal acetylcholine (ACh) release was investigated by brain microdialysis in rats rendered ethanol dependent by repeated forced administration of a 20% ethanol solution for 7 days. The behavioral signs of ethanol withdrawal were accompanied by an increase in hippocampal ACh output that was significantly 6 h after the last ethanol administration, reached a maximum (fourfold) at 12 h, and persisted for >72 h. Administration of diazepam (5 mg/kg, i.p.) or gamma-hydroxybutyrate (1 g/kg, intragastric) 12 h after the last ethanol administration completely antagonized, within 30 min, the increase in ACh output induced by ethanol withdrawal. Thus, the rapid and marked increase in ACh output might contribute to the changes in cognitive function associated with ethanol withdrawal, and the septohippocampal cholinergic system may play a major role in the response to withdrawal of addictive drugs.

Dopamine D2 receptor antagonists prevent Δ9-tetrahydrocannabinol-induced antinociception in rats

Δ9-Tetrahydrocannabinol (1 and 5 mg/kg, i.p.) produced, dose-dependently, antinociceptive effects using hot plate and tail flick tests in rats. These effects were suppressed not only by the cannabinoid CB1 receptor antagonist SR 141716A (0.5 mg/kg; i.p.) but also by the dopamine D2 receptor antagonists S(−)-sulpiride (5 and 10 mg/kg; i.p.) and S(−)-raclopride (1.5 and 3 mg/kg; i.p.). Conversely, Δ9-tetrahydrocannabinol antinociceptive effects were potentiated by the dopamine D2 receptor agonists (−)-quinpirole (0.025 mg/kg, s.c.) and (+)-bromocriptine (0.5 and 1 mg/kg; i.p.). Our results indicate that the antinociceptive effects of Δ9-tetrahydrocannabinol are mediated by the concomitant activation of cannabinoid CB1 and dopamine D2 receptors and that dopamine D2 receptor agonists may be useful in improving the analgesic effects of cannabinoids.