Simultaneous wireless and high-resolution detection of nucleus accumbens shell ethanol concentrations and free motion of rats upon voluntary ethanol intake.

Highly sensitive detection of ethanol concentrations in discrete brain regions of rats voluntarily accessing ethanol, with high temporal resolution, would represent a source of greatly desirable data in studies devoted to understanding the kinetics of the neurobiological basis of ethanol's ability to impact behavior. In the present study, we present a series of experiments aiming to validate and apply an original high-tech implantable device, consisting of the coupling, for the first time, of an amperometric biosensor for brain ethanol detection, with a sensor for detecting the microvibrations of the animal. This device allows the real-time comparison between the ethanol intake, its cerebral concentrations, and their effect on the motion when the animal is in the condition of voluntary drinking. To this end, we assessed in vitro the efficiency of three different biosensor designs loading diverse alcohol oxidase enzymes (AOx) obtained from three different AOx-donor strains: Hansenula polymorpha, Candida boidinii, and Pichia pastoris. In vitro data disclosed that the devices loading H. polymorpha and C. boidinii were similarly efficient (respectively, linear region slope [LRS]: 1.98 ± 0.07 and 1.38 ± 0.04 nA/mM) but significantly less than the P. pastoris-loaded one (LRS: 7.57 ± 0.12 nA/mM). The in vivo results indicate that this last biosensor design detected the rise of ethanol in the nucleus accumbens shell (AcbSh) after 15 minutes of voluntary 10% ethanol solution intake. At the same time, the microvibration sensor detected a significant increase in the rat's motion signal. Notably, both the biosensor and microvibration sensor described similar and parallel time-dependent U-shaped curves, thus providing a highly sensitive and time-locked high-resolution detection of the neurochemical and behavioral kinetics upon voluntary ethanol intake. The results overall indicate that such a dual telemetry unit represents a powerful device which, implanted in different brain areas, may boost further investigations on the neurobiological mechanisms that underlie ethanol-induced motor activity and reward.

Modulation of Delta(9)-THC-induced increase of cortical and hippocampal acetylcholine release by micro opioid and D(1) dopamine receptors.

The administration of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and synthetic cannabinoids stimulates acetylcholine (ACh) release in the rat prefrontal cortex (PFCx) and hippocampus as estimated by brain microdialysis. The present study was aimed at assessing whether the ability of Delta(9)-THC to stimulate ACh release is dependent upon opioid and dopamine (DA) receptors. Administration of the micro opioid receptor antagonists naloxone and naltrexone prevented the Delta(9)-THC-induced release of ACh in the PFCx and hippocampus. Similarly, bilateral infusion in the ventral tegmental area (VTA), 24h before Delta(9)-THC, of the pseudo-irreversible micro(1) antagonist naloxonazine completely prevented the increase of ACh release by Delta(9)-THC. Pre-treatment with the D(1) receptor antagonist SCH 39,166 reduced Delta(9)-THC-induced ACh release both in the PFCx and in the hippocampus. Since Delta(9)-THC has been shown to increase DA release in the nucleus accumbens (NAc) shell via a micro(1)-opioid receptor mediated mechanism located in the VTA (Tanda, G., Pontieri, F.E., Di Chiara, G., 1997. Cannabinoid and heroin activation of mesolimbic dopamine transmission by a common micro(1) opioid receptor mechanism. Science 276, 2048-2050.), we hypothesize that Delta(9)-THC-induced stimulation of ACh release in the PFCx and hippocampus is related to stimulation of endogenous opioids release in the VTA with secondary activation of DA neurons projecting to the NAc shell.

Drugs of abuse: biochemical surrogates of specific aspects of natural reward?

In this paper it is argued that drugs of abuse act on specific neurotransmitter pathways and by this mechanism elicit neurochemical changes that mimic some aspects of the overall pattern of the neurochemical effects of natural rewarding stimuli. Thus, drugs of abuse are biochemically homologous to specific aspects of natural rewarding stimuli. The behavioral similarity between drugs of abuse and natural stimuli, including that of being rewarding, results from their common property of activating neurochemically specific pathways. Natural stimuli accomplish this result indirectly through their sensory properties and incentive learning while drugs stimulate by a direct central action the critical reward pathways. Many drugs of abuse mimic the incentive properties of natural stimuli and their ability to stimulate mesolimbic dopamine pathways (Fig. 1). Both natural rewards and drugs of abuse, including amphetamine, cocaine and other psychostimulants, preferentially stimulate dopamine transmission in the mesolimbic nucleus accumbens compared with the dorsal caudate, an area related to the extrapyramidal motor system. Although many drugs of abuse mimic the incentive aspect of natural reward, this is probably not an absolute prerequisite for conferring to a drug some abuse liability. It might be predicted that certain drugs might be abused as a result of their action at sites located beyond dopamine or by mimicking other aspects of naturally rewarding stimuli such as the 'functional' (or trophotropic). This might be the case with opiates (which also mimic the 'incentive' aspect) and of benzodiazepines, as a result of activation of the central opioid reward system and of the central gamma-aminobutyric acid (GABA)-benzodiazepine system respectively. The hypothesis appears to have heuristic value as it predicts that biochemical mechanisms important for the rewarding properties of drugs of abuse are expected to play a role also in natural reward. One test of this hypothesis is offered by the observation that the 5-hydroxytryptamine (5-HT) system, through 5-HT3 receptors, and the central opioid system, through delta-opioid receptors, can contribute to the mechanism of the dopamine-activating properties of certain drugs of abuse. On this basis it would be predicted that drugs acting on 5-HT3 and on delta-opioid receptors would interfere with or mimic certain aspects of natural rewarding stimuli.

Pharmacology of sensory stimulation-evoked increases in frontal cortical acetylcholine release.

Recent research has demonstrated that a variety of sensory stimuli can increase acetylcholine release in the frontal cortex of rats. The aim of the present experiments was to investigate the pharmacological regulation of sensory stimulation-induced increases in the activity of basal forebrain cholinergic neurons. To this end, the effects of agonists and antagonists at a variety of neurotransmitter receptors on basal and tactile stimulation-evoked increases in frontal cortical acetylcholine release were studied using in vivo brain microdialysis. Tactile stimulation, produced by gently stroking the rat's neck with a nylon brush for 20 min, significantly increased frontal cortical acetylcholine release by more than 100% above baseline. The noradrenergic alpha2 agonist clonidine (0.1 or 0.2 mg/kg) and alpha1 antagonist prazosin (1 mg/kg) failed to affect basal cortical acetylcholine release; however, both compounds significantly reduced the increases evoked by sensory stimulation. In contrast, the alpha2 antagonist yohimbine (3 mg/kg) increased basal cortical acetylcholine release, thereby preventing meaningful investigation of its effects on tactile stimulation-evoked increases. The benzodiazepine agonist diazepam (5 mg/kg) reduced, and the GABA(A) receptor antagonist picrotoxin (2 mg/kg) increased basal cortical acetylcholine release; in addition, diazepam attenuated the increases in cortical acetylcholine release evoked by tactile stimulation. While dopaminergic D1 (SCH 23390, 0.15 mg/kg) and D2 (raclopride, 1 mg/kg) receptor antagonists did not by themselves significantly influence the increases evoked by tactile stimulation, their co-administration produced a significant reduction. The opioid receptor antagonist naltrexone (1.5 mg/kg) failed to affect either basal or tactile stimulation-evoked increases in acetylcholine overflow. Finally, the non-competitive N-methyl-D-aspartate receptor antagonist, dizocilpine maleate (MK-801; 0.025 and 0.05 mg/kg) increased basal cortical acetylcholine release. These results confirm that cortically projecting cholinergic neurons are activated by sensory stimuli, and indicate that the increases in cortical acetylcholine release produced by tactile stimulation are inhibited by stimulation of alpha2 or blockade of alpha1 noradrenergic receptors, and by enhanced GABAergic transmission. In addition, simultaneous blockade of dopamine D1 and D2 receptors appears necessary to achieve a significant reduction of sensory stimulation-evoked acetylcholine release in the frontal cortex. The results are consistent with the hypothesis that cortical acetylcholine release is a component of the neurochemistry of arousal and/or attention and indicate that this is modulated by GABAergic, noradrenergic and dopaminergic systems. In contrast, endogenous opioid actions do not appear to be involved.

Chronic lithium attenuates dopamine D1-receptor mediated increases in acetylcholine release in rat frontal cortex.

The effects of chronic lithium treatment on methylphenidate-, D1 dopamine receptor agonist (A-77636)-, and tactile stimulation-induced increases in frontal cortical acetylcholine release were studied in the rat using in vivo brain microdialysis. Cortical acetylcholine release in control rats was maximally stimulated by methylphenidate (1.25 and 2.5 mg/kg) to 173% and 212% above baseline, respectively. The effect of methylphenidate (2.5 mg/kg) was blocked by pretreatment with the dopamine D1 receptor antagonist SCH 23390 (0.3 mg/kg). Chronic treatment with lithium chloride (3-4 weeks) produced plasma lithium concentrations of 0.45 +/- 0.02 meq/l. Chronic lithium significantly reduced increases in cortical acetylcholine release produced by methylphenidate. Stimulation of dopamine D1 receptors with the full D1 receptor agonist A-77636 (0.73 mg/kg) increased cortical acetylcholine release. Chronic lithium significantly reduced this effect of A-77636. In contrast, lithium failed to influence the increases of cortical acetylcholine release produced by tactile stimulation. These results suggest that while lithium does not influence normal, arousal-related increase in cortical acetylcholine release, this ion selectively attenuates dopamine mediated increases and/or abnormally large increases, which in the present circumstances were pharmacologically induced. The relevance of these findings to the antimanic actions of lithium is discussed.

SCH 23390 blocks drug-conditioned place-preference and place-aversion: anhedonia (lack of reward) or apathy (lack of motivation) after dopamine-receptor blockade?

The influence of the D1 antagonist SCH 23390 on the motivational properties of rewarding (morphine, nicotine and diazepam) and aversive (naloxone, phencyclidine and picrotoxin) drugs was studied in the rat in a two-compartment place-conditioning paradigm, which included a pre-conditioning test for spontaneous place-preference. The specific D1 dopamine-receptor antagonist SCH 23390 (0.05 mg/kg SC), paired with both compartments or, separately, with the preferred or with the non-preferred compartment, failed to affect the spontaneous unconditioned preference of the animal. Pairing of morphine (1.0 mg/kg SC), nicotine (0.6 mg/kg SC) or diazepam (1.0 mg/kg IP) with the less preferred compartment induced significant preference for that compartment. Pairing of SCH 23390 (0.05 mg/kg SC) with both compartments completely blocked the place-preference induced by morphine, nicotine and diazepam. Naloxone (0.8 mg/kg SC), phencyclidine (2.5 mg/kg SC) or picrotoxin (2.0 mg/kg IP) paired with the preferred compartment elicited place-aversion. Pairing of SCH 23390 (0.05 mg/kg SC) with both compartments abolished also the place-aversion induced by naloxone, phencyclidine and picrotoxin. The results indicate that blockade of dopamine transmission blocks the motivational properties of rewarding as well as aversive stimuli. It is suggested that neuroleptics rather than simply blocking the rewarding impact of positive reinforcers (anhedonia, lack of pleasure) exert a more general influence on conditioned behaviour by blocking the affective impact of negative as well as positive reinforcers (apathy, lack of motivation).

5HT3 receptor antagonists block morphine- and nicotine- but not amphetamine-induced reward.

The effect of two potent and specific antagonists of 5HT3 receptors, ICS 205-930 and MDL 72222, on the reinforcing properties of amphetamine, morphine and nicotine was studied in rats. Drug-induced reinforcement was assessed by measuring drug-conditioned place preference. ICS 205-930 and MDL 72222 dose-dependently reduced the place preference induced by morphine (1.0 mg/kg SC). At doses of 0.030 mg/kg SC the two antagonists completely blocked morphine-induced place preference while doses of 0.015 mg/kg SC significantly reduced it. ICS 205-930 and MDL 72222 at doses of 0.030 mg/kg SC also prevented the place preference induced by nicotine (0.6 mg/kg SC). In contrast, ICS 205-930 and MDL 72222 up to doses of 0.030 mg/kg SC failed to modify the place preference elicited by amphetamine (1.0 mg/kg SC). The results indicate that 5HT3 receptors are specifically involved in the reinforcing properties of morphine and nicotine.

Blockade of acquisition of drug-conditioned place aversion by 5HT3 antagonists.

The effect of two 5HT3 antagonists, ICS 205-930 and MDL 72222, on drug-induced place aversion was studied in a two-compartment apparatus with a procedure including a pre-test for spontaneous preference. Naloxone (0.8 mg/kg SC), phencyclidine (2.5 mg/kg SC) and picrotoxin (2.0 mg/kg IP) paired with the preferred compartment elicited a significant place aversion. ICS 205-930 and MDL 72222 failed to modify spontaneous place preference when paired with both compartments. ICS 205-930 (30 micrograms/kg SC) paired with the preferred and, in other experiments, with the non-preferred compartment, also failed to modify spontaneous preference. ICS 205-930 (7.5, 15 and 30 micrograms/kg SC), paired with both compartments, dose-dependently reduced the place aversion induced by naloxone (0.8 mg/kg SC), phencyclidine (2.5 mg/kg SC) and picrotoxin (2.0 mg/kg IP). MDL 72222 (30 micrograms/kg SC) paired with both compartments had a similar effect. The result indicate that 5HT, via 5HT3 receptors, plays a role in the aversive properties of drug stimuli.

Behavioural sensitization after repeated exposure to Delta 9-tetrahydrocannabinol and cross-sensitization with morphine.

RATIONALE: Repeated exposure to several drugs of abuse has been reported to induce behavioural sensitization. So far no evidence has been provided that such a phenomenon also applies to cannabinoids. OBJECTIVES: In this study we investigated if repeated exposure to Delta(9)-tetrahydrocannabinol (Delta(9)-THC) induces behavioural sensitization. In addition we tested the possibility of cross-sensitization between Delta(9)-THC and morphine. METHODS: Male Sprague-Dawley rats were administered for 3 days, twice daily, with increasing doses of Delta(9)-tetrahydrocannabinol (2, 4 and 8 mg/kg i.p.) or increasing doses of morphine (10, 20 and 40 mg/kg s.c.) or vehicle. After a washout of 14 days the animals were challenged with Delta(9)-THC (75 and 150 microg/kg i.v.), with a synthetic cannabinoid agonist WIN55212-2 (75 and 150 microg/kg i.v.) or with morphine (0.5 mg/kg i.v.), through a catheter inserted into the left femoral vein 24 h before, and the behaviour recorded. RESULTS: Rats previously administered with Delta(9)-THC showed a greater behavioural activation compared to controls in response to challenge with Delta(9)-THC (150 microg/kg i.v.) and to challenge with morphine (0.5 mg/kg i.v.). Similar to that observed after repeated opiates, this behavioural sensitization was characterized by stereotyped activity. Animals administered with a schedule of morphine that induces behavioural sensitization to morphine also showed a behavioural sensitization to challenge with cannabinoids (Delta(9)-HC and WIN55212-2, 75 and 150 microg/kg i.v.). The effect of the challenge with Delta(9)-THC was prevented by the administration of the CB1 antagonist SR141716A (1 mg/kg i.p.), 40 min beforehand. CONCLUSIONS: The results of the present study demonstrate that repeated exposure to Delta(9)-THC induces behavioural sensitization not only to cannabinoids but also to opiates. This cross-sensitization was symmetrical since rats behaviourally sensitized to morphine were also sensitized to cannabinoids. These observations further support the evidence of an interaction between the opioid and the cannabinoid system and might provide a neurobiological basis for a relationship between cannabis use and opiate abuse.

Drug addiction as a disorder of associative learning. Role of nucleus accumbens shell/extended amygdala dopamine.

Conventional reinforcers phasically stimulate dopamine transmission in the nucleus accumbens shell. This property undergoes one-trial habituation consistent with a role of nucleus accumbens shell dopamine in associative learning. Experimental studies with place- and taste-conditioning paradigms confirm this role. Addictive drugs share with conventional reinforcers the property of stimulating dopamine transmission in the nucleus accumbens shell. This response, however, undergoes one-trial habituation in the case of conventional reinforcers but not of drugs. Resistance to habituation allows drugs to repetitively activate dopamine transmission in the shell upon repeated self-administration. This process abnormally facilitates associative learning, leading to the attribution of excessive motivational value to discrete stimuli or contexts predictive of drug availability. Addiction is therefore the expression of the excessive control over behavior acquired by drug-related stimuli as a result of abnormal strenghtening of stimulus-drug contingencies by nondecremental drug-induced stimulation of dopamine transmission in the nucleus accumbens shell.

A within-subjects microdialysis/behavioural study of the role of striatal acetylcholine in D1-dependent turning.

In rats lesioned with 6-hydroxydopamine (6-OHDA) the effect of the noncompetitive N-methyl D-aspartate (NMDA) receptor antagonist, MK-801, the dopamine (DA) D2 receptor agonist quinpirole and the A2A adenosine antagonist SCH 58261 was studied on acetylcholine (ACh) release in the lesioned striatum and contralateral turning behaviour stimulated by the administration of the DA D1 receptor agonist CY 208-243. Administration of CY 208-243 (75, 100 and 200 microg/kg) to 6-OHDA-lesioned rats dose-dependently stimulated ACh release and induced contralateral turning. MK-801 (50 and 100 microg/kg) reduced basal ACh release (max 22%) and did not elicit any turning. MK-801 (50 and 100 microg/kg) potentiated the contralateral turning, but failed to modify the stimulation of ACh release elicited by 100 and 200 microg/kg of CY 208-243. MK-801 (100 microg/kg) prevented the increase in striatal ACh release evoked by the lower dose of CY 208-243 (75 microg/kg) but contralateral turning was not observed. The D2 receptor agonist quinpirole (30 and 60 microg/kg) elicited low-intensity contralateral turning and decreased basal ACh release. Quinpirole potentiated the D1-mediated contralateral turning behaviour elicited by CY 208-243 (100 microg/kg), but failed to affect the increase in ACh release elicited by the D1 agonist. The adenosine A2A receptor antagonist SCH 58261 (1 microg/kg i.v.) failed per se to elicit contralateral turning behaviour. SCH 58261 potentiated the contraversive turning induced by CY 208-243 but failed to affect the increase of ACh release. The results of the present study indicate that blockade of NMDA receptors by MK-801. stimulation of DA D2 receptors by quinpirole and blockade of adenosine A2A receptors by SCH 58261 potentiate the D1-mediated contralateral turning behaviour in DA denervated rats without affecting the action of the D1 agonist on ACh release. These observations do not support the hypothesis that the potentiation of D1-dependent contralateral turning by MK-801, quinpirole or SCH 58261 is mediated by changes in D1-stimulated release of ACh in the striatum.

Dopamine D(1) receptor-mediated control of striatal acetylcholine release by endogenous dopamine.

The role of dopamine D(1) and D(2) receptors in the control of acetylcholine release in the dorsal striatum by endogenous dopamine was investigated by monitoring with microdialysis the effect of the separate or combined administration of the dopamine D(1) receptor antagonist, SCH 39166 ¿(-)-trans-6,7,7a,8,9, 13b-exahydro-3-chloro-2-hydroxy-N-methyl-5H-benzo-[d]-nap hto-[2, 1b]-azepine hydrochloride¿ (50 microg/kg subcutaneous (s.c.)), of the dopamine D(2)/D(3) receptor agonist, quinpirole (trans-(-)-4aR, 4a,5,6,7,8,8a,9-octahydro-5-propyl-1H-pyrazolo-(3,4-g)-quinoline hydrochloride) (5 and 10 microg/kg s.c.), and of the D(3) receptor selective agonist, PD 128,907 [S(+)-(4aR,10bR)-3,4,4a, 10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano-[4,3-b]-1,4-oxazin -9-ol hydrochloride] (50 microg/kg s.c.), on in vivo dopamine and acetylcholine release. Microdialysis was performed with a Ringer containing low concentrations (0.01 microM) of the acetylcholinesterase inhibitor, neostigmine. Quinpirole (10 microg/kg s.c.) decreased striatal dopamine and acetylcholine release. Administration of PD 128,907 (50 microg/kg) decreased dopamine but failed to affect acetylcholine release. SCH 39166 (50 microg/kg s.c.) stimulated dopamine release and reduced acetylcholine release. Pretreatment with quinpirole reduced (5 microg/kg s.c.) or completely prevented (10 microg/kg s.c.) the stimulation of dopamine release elicited by SCH 39166 (50 microg/kg s.c.); on the other hand, pretreatment with quinpirole (5 and 10 microg/kg) potentiated the reduction of striatal acetylcholine release induced by SCH 39166 (50 microg/kg s.c.). Similarly, pretreatment with PD 128,907 (50 microg/kg) which prevented the increase of dopamine release induced by SCH 39166 (50 microg/kg), potentiated the reduction of striatal acetylcholine transmission elicited by SCH 39166. Thus, pretreatment with low doses of quinpirole or PD 128,907 influences in opposite manner the effect of SCH 39166 on striatal dopamine and acetylcholine release, counteracting the increase of dopamine release and potentiating the decrease in acetylcholine release. These results provide further evidence for the existence of a tonic stimulatory input of endogenous dopamine on striatal acetylcholine transmission mediated by dopamine D(1) receptors.

Local application of SCH 39166 reversibly and dose-dependently decreases acetylcholine release in the rat striatum.

The effect of local application by reverse dialysis of the dopamine D(1) receptor antagonist (-)-trans-6,7,7a,8,9, 13b-exahydro-3-chloro-2-hydroxy-N-methyl-5H-benzo-[d]-nap hto-[2, 1b]-azepine hydrochloride (SCH 39166) on acetylcholine release was studied in awake, freely moving rats implanted with concentric microdialysis probes in the dorsal striatum. In these experiments, the reversible acetylcholine esterase inhibitor, neostigmine, was added to the perfusion solution at two different concentrations, 0.01 and 0.1 microM. SCH 39166 (1, 5 and 10 microM), in the presence of 0.01 microM neostigmine, reversibly decreased striatal acetylcholine release (1 microM SCH 39166 by 8+/-4%; 5 microM SCH 39166 by 24+/-5%; 10 microM SCH 39166 by 27+/-7%, from basal). Similarly, SCH 39166, applied in the presence of a higher neostigmine concentration (0.1 microM), decreased striatal acetylcholine release by 14+/-4% at 1 microM, by 28+/-8% at 5 microM and by 30+/-5% at 10 microM, in a dose-dependent and time-dependent manner. These results are consistent with the existence of a facilitatory tone of dopamine on striatal acetylcholine transmission mediated by dopamine D(1) receptors located on striatal cholinergic interneurons.

Blockade of delta-opioid receptors in the nucleus accumbens prevents ethanol-induced stimulation of dopamine release.

Naltrindole, a specific delta-opioid antagonist, infused by reverse dialysis in the nucleus accumbens of freely moving rats completely prevented the increase in extracellular dopamine concentrations elicited in the nucleus accumbens by ethanol (1.0 g/kg i.p.) as well as by the delta-opioid receptor agonist [D-Ala2]deltorphin II (50 microM), also perfused by reverse dialysis, but not by cocaine (15 mg/kg s.c.). The results provide in vivo evidence for a critical role of delta-opioid receptors in the dopamine-releasing properties of ethanol in vivo.

The potent and selective dopamine D1 receptor agonist A-77636 increases cortical and hippocampal acetylcholine release in the rat.

The effects of systemic administration of the full dopamine D1 receptor agonist A-77636 on acetylcholine release in rat frontal cortex and hippocampus were studied using in vivo microdialysis. Administration of A-77636 (4 mumol/kg s.c.) greatly (> 230%) increased both cortical and hippocampal acetylcholine release for more than 3 h; at a lower dose (1 mumol/kg s.c.) A-77636 significantly stimulated cortical but not hippocampal acetylcholine release. The effect of the higher dose of A-77636 on cortical acetylcholine release was blocked by the dopamine D1 receptor antagonist SCH 23390 (300 micrograms/kg s.c.). These results confirm that stimulation of dopamine D1 receptors facilitates cortical and hippocampal acetylcholine release in vivo, and indicate that these two structures are differentially sensitive to this effect. They also raise the possibility that dopamine D1 receptor agonists may be useful in the treatment of cortical and hippocampal acetylcholine deficit-related syndromes.

Differential inhibitory effects of a 5-HT3 antagonist on drug-induced stimulation of dopamine release.

The effects of a potent and specific antagonist of 5-HT3 receptors, ICS 205-930, on the dopamine (DA)-releasing properties of morphine (1.0 mg/kg s.c.), nicotine (0.6 mg/kg s.c.), ethanol (1.0 g/kg i.p.) and amphetamine (0.25 and 1.0 mg/kg s.c.) were studied in rats. DA release was estimated by trans-cerebral dialysis in the nucleus accumbens of freely moving rats. ICS 205-930 (15-30 micrograms/kg s.c.) failed to modify the basal output of DA and its metabolites, however, ICS 205-930 dose dependently reduced the stimulation of DA release by morphine, nicotine and ethanol. Thus, at doses of 30 micrograms/kg s.c., ICS 205-930 completely prevented the morphine-, nicotine- and ethanol-induced stimulation of DA release in the nucleus accumbens; doses of 15 micrograms/kg s.c. partially prevented the morphine-, nicotine- and ethanol-induced stimulation of DA release while doses of 7.5 micrograms/kg s.c. were ineffective. In contrast, ICS 205-930 (up to 30 micrograms/kg s.c.) failed to affect the amphetamine-induced stimulation of DA release in the nucleus accumbens. The inhibitory effects of ICS 205-930 (15 and 30 micrograms/kg s.c.) on the drug-induced stimulation of DA release could also be extended to the neuroleptic haloperidol (0.1 mg/kg s.c.). The results indicate that blockade of 5-HT3 receptors selectively prevents the stimulation of DA release induced by drugs known to stimulate the firing activity of DA neurons.

Cannabinoid CB(1) receptor agonists increase rat cortical and hippocampal acetylcholine release in vivo.

Intravenous administration of the cannabinoid CB(1) receptor agonists (R-(+)-[2, 3-Dihydro-5-methyl-3[morpholinyl)methyl]-pyrrolo[1,2,3-de]-1, 4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate), WIN 55,212-2 (10, 37.5, 75 and 150 microg/kg), and ((6aR)-trans-3-(1, 1-Dimethylheptyl)-6a,7,10,10a-tetrahydro-1-hydroxy-6, 6-dimethyl-6H-dibenzo[b,d]pyran-9-methanol), HU 210 (1 and 4 microg/kg) dose-dependently increased acetylcholine release in dialysates from the prefrontal cortex and the hippocampus of freely moving rats. Administration of the cannabinoid receptor antagonist [N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3 carboxamide]HCl, SR 141716A, at a dose that per se did not affect basal acetylcholine release (2. 5 microg/kg), prevented the increase of acetylcholine release by WIN 55,212-2 (150 microg/kg i.v.) or by HU 210 (4 microg/kg i.v.) in both areas. These data demonstrate that, at low i.v. doses, the synthetic cannabinoid CB(1) receptor agonists, WIN 55,212-2 and HU 210 stimulate cortical and hippocampal acetylcholine release.

Intravenous administration of ecstasy (3,4-methylendioxymethamphetamine) enhances cortical and striatal acetylcholine release in vivo.

The effect of intravenous administration of 3,4-methylendioxymethamphetamine (MDMA), in a range of doses (0.32-3.2 mg/kg) that have been shown to maintain self-administration behaviour in rats, on in vivo acetylcholine release from rat prefrontal cortex and dorsal striatum was studied by means of microdialysis with vertical concentric probes. Intravenous administration of MDMA dose-dependently increased basal acetylcholine release from the prefrontal cortex to 57+/-21%, 98+/-20%, 102+/-7% and 141+/-14% above baseline, at doses of 0.32, 0.64, 1.0 and 3.2 mg/kg, respectively. MDMA also stimulated striatal acetylcholine release at the dose of 3.2 mg/kg i.v. (the maximal increase being 32+/-3% above baseline) while at the dose of 1 mg/kg i.v., MDMA failed to affect basal acetylcholine output. Administration of MDMA also dose-dependently stimulated behaviour. The results of the present study show that MDMA affects measures of central cholinergic neurotransmission in vivo and suggest that at least some of the psychomotor stimulant actions of MDMA might be positively coupled with an increase in prefrontal cortical and striatal acetylcholine release.

Delta9-tetrahydrocannabinol enhances cortical and hippocampal acetylcholine release in vivo: a microdialysis study.

The intravenous administration of synthetic cannabinoid agonists was recently shown to dose dependently increase acetylcholine release from the rat prefrontal cortex and hippocampus (Eur. J. Pharmacol. 401 (2000) 179]. We report here that the active ingredient of cannabis preparations, delta9-tetrahydrocannabinol, administered at 10, 37.5, 75 and 150 microg/kg, dose dependently stimulated acetylcholine release from rat prefrontal cortex and hippocampus estimated by means of in vivo brain microdialysis with vertical concentric probes. At these doses, delta9-tetrahydrocannabinol induced behavioural stimulation. The administration of the CB1 receptor antagonist, ([N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3carboxamide]HCl) SR 141716A (200 microg/kg i.p.) significantly reduced the effect of delta9-tetrahydrocannabinol (75 microg/kg i.v.) on acetylcholine release from rat prefrontal cortex and hippocampus.

D1 receptor blockade stereospecifically impairs the acquisition of drug-conditioned place preference and place aversion.

The motivational effects of dopamine (DA) D1 receptor blockade and its influence on the motivational effects of amphetamine (1.0mg/kg s.c.), morphine (1.0mg/kg s.c.) and lithium (40mg/kg s.c.) were studied in a place-conditioning paradigm. Drugs tested were two potent D1 receptor antagonists, SCH 23390 and SCH 39166, that differ in the poor affinity of the latter for 5-HT(2) receptors, and SCH 23388, the inactive enantiomer of SCH 23390. SCH 23390 and SCH 39166, at low doses (12.5 and 25µg/kg s.c.), paired for 30min with one compartment, elicited place aversion. Higher doses of the D1 antagonists or pairing for 60min with one compartment failed to elicit place aversion. SCH 39166 (50µg/kg s.c.) paired with both compartments completely prevented the place-aversion elicited by SCH 23390 (12.5µg/kg s.c.). SCH 23390 and SCH 39166 at low doses (12.5 and 25µg/kg s.c. respectively), paired with both compartments, abolished amphetamine-induced place preference. The D1 antagonists also impaired the acquisition of morphine-induced place preference and lithium-induced place aversion but only at higher doses (50 and 100µg/kg s.c.). These effects were stereospecific as the inactive enantiomer SCH 23388, up to a dose of 500µg/kg s.c. failed to impair the acquisition of amphetamine and morphine-induced place preference. It is concluded that DA plays a dual role in motivation: one role is that of assigning motivational valence to stimuli in relation to changes in DA transmission; another role of DA relates to the learning process involved in the acquisition of positive as well as negative incentive properties by otherwise neutral stimuli (incentive learning).