GianLuigi Gessa

Cannabinoids activate mesolimbic dopamine neurons by an action on cannabinoid CB1 receptors

The present study was designed to determine if cannabinoids share with other drugs of abuse the ability to stimulate mesolimbic dopaminergic neurons and if this effect is mediated by cannabinoid receptors. To this end, the effects of the prototypical cannabinoid, delta9 tetrahydrocannabinol ¿(-)-trans-(6aR,10aR)-6a,7,8,10a-tetrahydro-6,6,9-trimethyl- 3-pentyl-6H-dibenzo[b,d]pyran-1-ol¿, and the two highly potent synthetic cannabinoids, ¿(R)-(+)-[2,3-dihydro-5-methyl-3-[(4-morpholinyl)-methyl]pyrrolo[1,2,3-d e]-1,4-benzoxazin-6-yl, +(1-naphtalenyl)methanone¿ WIN 55,212-2 and ¿(-)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl )-cicloexan-1-ol¿ CP 55,940, on the spontaneous discharge rate of meso-accumbens dopamine (A10 dopamine) neurons were studied in rats. The intravenous administration of delta9-tetrahydrocannabinol, WIN 55,212-2 and CP 55,940 (0.0625-1.0 mg/kg) produced a dose-dependent increase in the spontaneous firing of A10 dopamine neurons both in non-anesthetized and anesthetized rats, with a maximal percent increase of 120, 187 and 155 in non-anesthetized and 33, 102 and 52, respectively, in anesthetized rats. The stimulant response to cannabinoids was suppressed by the specific cannabinoid receptor antagonist ¿N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-me thyl-1H-pyrazole-3-carboxamide¿ SR 141716A, indicating a cannabinoid receptor-mediated effect. These findings support the contention that cannabinoids regulate mesolimbic dopamine transmission and may help to explain the addictive properties of marijuana.

Dose-dependent absorption and elimination of gamma-hydroxybutyric acid in healthy volunteers

SummaryGamma-hydroxybutyric acid (GHB) is effective in treatment of the alcohol and opiate withdrawal syndromes. Its absorption and disposition kinetics have been studied in 8 healthy male volunteers following oral administration of single doses of 12.5, 25 and 50 mg kg−1.The AUC increased disproportionately with the dose and so the apparent oral clearance decreased significantly as the dose was increased, whereas the terminal half-life and mean residence time increased. The peak plasma concentrations normalised to the lowest dose fell significantly with increasing doses, whilst the corresponding peak times increased.These findings suggest that both the oral absorption and the elimination of GHB are capacity-limited processes. GHB did not bind to significant extent to plasma proteins over the therapeutic concentration range.The pharmacokinetic parameters in healthy volunteers were not significantly different from those previously observed in alcohol-dependent patients with compensated alcoholic liver disease.

Low doses of γ-hydroxybutyric acid stimulate the firing rate of dopaminergic neurons in unanesthetized rats

In unanesthetized rats the intravenous (i.v.) administration of gamma-hydroxybutyric acid (GHB) at the doses of 50-400 mg/kg produced a dose-related stimulation (10-56%) of the firing rate of dopaminergic (DA) neurons in the pars compacta of the substantia nigra. Doses of 1000 and 1500 mg/kg inhibited the firing rate almost completely. In unanesthetized rats the intraperitoneal injection of GHB at the dose of 750 mg/kg produced a brief initial stimulation (23%) followed by a modest reduction in the firing rate (29%). On the other hand, in chloral hydrate-anesthetized rats the i.v. administration of GHB at cumulative doses of up to 200 mg/kg failed to modify the firing rate of DA neurons, while a cumulative dose of 400 mg/kg suppressed neuronal firing. The results indicate that sub-anesthetic doses of GHB stimulate the firing rate of DA neurons in unanesthetized rats.

Maintaining abstinence from alcohol with γ-hydroxybutyric acid

-hydroxybutyric acid (GHB), a metabolite of GABA with neurotransmitter and neuromodulatory functions, has been introduced into clinical practice for the management of alcoholism. As well as being effective in preventing the withdrawal syndrome in both laboratory animals and in man, GHB is capable of inducing short-term and medium-term abstinence from alcohol in about 60–70% of patients treated. About 30% of patients are non-responders. In our experience these patients usually report a lack, or merely a temporary reduction of craving not sufficient to control the desire for alcohol. Because the drug is usually divided into three daily doses despite its short half-life, we investigated the usefulness of dividing GHB into six doses for non-responders. Patients with current alcoholism according to DSM III R criteria were admitted to the study. They were treated with GHB at a dose of 50 mg/kg orally three times/day for 8 weeks (phase 1) and without the use of drugs that can potentially influence the craving for alcohol. Patients who were abstinent throughout phase 1 were requested to take the same dose of GHB at the same intervals for a further 8 weeks (phase 2), while patients who continued to drink alcohol during phase 1 were requested to take the same dose of the drug divided into six daily doses for a further 8 weeks (phase 2). In both phase 1 and phase 2, drug administration was entrusted to a family member. Patients were checked as outpatients every 2 weeks in both phases; at each visit, psychological support counselling was provided and abstinence was evaluated on the basis of the patient’s selfevaluation and on that of a family member, and on the basis of laboratory tests (blood alcohol concentration, gamma-

Cannabinoid receptor antagonists counteract sensorimotor gating deficits in the phencyclidine model of psychosis.

Clinical and laboratory findings suggest that cannabinoids and their receptors are implicated in schizophrenia. The role of cannabinoids in schizophrenia remains however poorly understood, as data are often contradictory. The primary aim of this study was to investigate whether the cannabinoid CB1 receptor antagonists rimonabant and AM251 are able to reverse deficits of sensorimotor gating induced by phencyclidine and to mimic the ‘atypical’ antipsychotic profile of clozapine. The prepulse inhibition (PPI) of the startle reflex was used to measure deficits of sensorimotor gating. PPI-disruptive effects of phencyclidine and their antagonism by rimonabant, AM251, and clozapine were studied in rats. The effects of rimonabant were carefully examined taking into account dose ranges, vehicle, and route of administration. We also examined the ability of rimonabant to reduce the PPI-disruptive effects of dizocilpine and apomorphine. Rimonabant as well as AM251 significantly counteracted the phencyclidine-disruptive model of PPI, comparable to the restoring effect of clozapine; no augmentation effect was observed with rimonabant and clozapine as cotreatment. Rimonabant also significantly attenuated the PPI disruptive effects of dizocilpine and apomorphine. Taken together, our results indicate that CB1 receptor antagonists do produce ‘atypical’ antipsychotic profile mimicking that of clozapine in the phencyclidine disruption of sensorimotor gating. Our findings further suggest that CB1 receptor antagonism may be involved in restoring disturbed interactions between the activity of the endocannabinoid system and glutamate neurotransmitter system implied in schizophrenia.

Benzodiazepine-induced voraciousness in cats and inhibition of amphetamine-anorexia

Abstract The effect of different benzodiazepines on food intake was studied in cats which had been trained to eat their daily food within 3 hours, under conditions in which emotional factors were not present. When benzodiazepines were administered (at a dose ranging from 0.1 to 3 mg/Kg) before feeding, they increased both the total amount of food eaten and also the rate at which food was injested. When they were administered at the end of the feeding period, these compounds made the animals resume eating voraciously. The order of decreasing potency of the benzodiazepines tested was: oxazepam, N-methyl-lorazepam, diazepam, chlordiazepoxide, pinazepam, medazepam. Oxazepam (3 mg/Kg) stimulated maximally the food intake, even when administered up to 12 hours before feeding. Finally, oxazepam antagonized the anorexigenic effect of d-amphetamine, but did not influence amphetamine-induced hyperactivity and stereotyped behavior.

Marked decrease of A10 dopamine neuronal firing during ethanol withdrawal syndrome in rats

The electrophysiological activity of mesoaccumbens dopaminergic neurons was monitored during the ethanol-withdrawal syndrome in ethanol-dependent and in control rats. Spontaneous firing was reduced by about half in ethanol-dependent rats as compared to controls. Likewise, the number of spikes/burst was also reduced in ethanol-dependent rats. These results are consistent with the reduction in dopamine release observed during ethanol-withdrawal syndrome and may provide the basis for the aversive effects of the ethanol-withdrawal syndrome.

Depolarization inactivation of dopamine neurons: an artifact?

A widely accepted theory postulates that, in rats, chronic treatment with neuroleptics causes the depolarization inactivation of the majority of midbrain dopamine (DA) neurons. The present study was aimed to verify whether general anesthesia and/or other factors might contribute to the depolarization inactivation of A9 and A10 DA neurons. To investigate on the possible role played by DA receptor subtypes, three representatives DA antagonists were used: haloperidol (a mixed D1/D2), (-)-sulpiride (a selective D2) and SCH 23390 (a selective D1). In agreement with previous studies, where neuronal sampling was carried out in animals under chloral hydrate anesthesia, chronic treatment with haloperidol (0.5 mg/kg daily for 21–28 d) produced a profound reduction (about 80%) in the number of spontaneously active A9 DA neurons. However, when neuronal sampling was performed in unanesthetized rats, the single administration of haloperidol, (-)-sulpiride, or SCH 23390 (0.5, 25, and 0.3 mg/kg respectively 2–3 hr beforehand) increased the number of spontaneously active A9 and A10 DA neurons and their firing rate, whereas the chronic administration of these drugs (daily for 21– 28 d) failed to reduce the number of spontaneously active A9 and A10 DA neurons. The inhibitory effect of apomorphine on the firing rate of A9 and A10 DA neurons was prevented 3–4 hr after the acute or last injection of chronic haloperidol or (-)-sulpiride. However, the inhibitory effect was potentiated 24 hr after the last administration of the chronic regimen with these neuroleptics, but it was not influenced by either acute or chronic treatment with SCH 23390.(ABSTRACT TRUNCATED AT 250 WORDS)

γ-Hydroxybutyrate inhibits excitatory postsynaptic potentials in rat hippocampal slices

Abstract γ-Hydroxybutyrate (GHB) has been shown to mimic different central actions of ethanol, to suppress alcohol withdrawal syndrome, and to reduce alcohol consumption both in rats and in humans. The aim of the present study was to determine if GHB shared with alcohol the ability to inhibit glutamate action at both NMDA and AMPA/kainate receptors. The NMDA or the AMPA/kainate receptors-mediated postsynaptic potentials were evoked in CA1 pyramidal neurons by stimulation of Schaffer-collateral commissural fibers in the presence of CGP 35348, bicuculline to block the GABA B and GABA A receptors, and 10 μM 6,7-dinitroquinoxaline-2,3-dione (DNQX) or 30 μM dl -2-amino-5-phosphonovalerate (d-APV) to block AMPA/kainate or NMDA receptors, respectively. GHB (600 μM) produced a depression of both NMDA and AMPA/kainate receptors-mediated excitatory postsynaptic potentials with recovery on washout. The GHB receptors antagonist, NCS-382, at the concentration of 500 μM had no effect per se on these responses but prevented the depressant effect of GHB (600 μM) on the NMDA and AMPA/kainate-mediated responses. In the paired-pulse experiments, GHB (600 μM) depressed the amplitude of the first and the second evoked AMPA/kainate excitatory postsynaptic potentials, and significantly increased the paired-pulse facilitation (PPF). These results suggest that GHB inhibits excitatory synaptic transmission at Schaffer-collateral commissural–pyramidal neurons synapses by decreasing the probability of release of glutamate.

Brain dialysis provides evidence for D2-dopamine receptors modulating noradrenaline release in the rat frontal cortex

The frontal cortex of the rat receives dopaminergic and noradrenergic nerve terminals from the ventral tegmental area and the locus coeruleus, respectively, ct2-Adrenoceptors and D-2 dopamine (DA) receptors are present in this area, but their location and role are not clear. Peripheral noradrenergic nerve terminals have both a2-adrenoceptors and D-2 presynaptic receptors and the stimulation of either results in the inhibition of noradrenaline (NA) release (see Langer, 1980). The presence in the central noradrenergic nerve terminals of presynaptic a2-adrenoceptors modulating NA release has been shown in vitro (Galzin et al., 1982) and, more recently, in vivo by brain dialysis applied to the rat frontal cortex (LHeureux et al., 1986). However, little is known of the presence of presynaptic D-2 receptors on noradrenergic nerve terminals in this area. We have used the technique of intracerebral dialysis in conscious freely moving rats in order to investigate if D-2 receptors other than ct2-adrenoceptors might control the release of NA from nerve terminals in the frontal cortex. Brain microdialysis was performed in male Sprague-Dawley CD 350-400 g (Charles River, Italy) freely moving rats essentially as described by Imperato and Di Chiara (1984), using bicarbonate Krebs-Ringer buffer pH 7.4 as perfus-