Effects of cocaine and amphetamine on acetylcholine release in the hippocampus and caudate nucleus

β2* nAChR sensitivity modulates acquisition of cocaine self-administration in male rats

Signaling through nicotinic acetylcholine receptors (nAChRs) plays a role in cocaine reward and reinforcement, suggesting that the cholinergic system could be manipulated with therapeutics to modulate aspects of cocaine use disorder (CUD). We examined the interaction between nAChRs and cocaine reinforcement by expressing a hypersensitive β2 nAChR subunit (β2Leu9'Ser) in the ventral tegmental area of male Sprague Dawley rats. Compared to control rats, β2Leu9'Ser rats acquired (fixed ratio) intravenous cocaine self-administration faster and with greater likelihood. By contrast, β2Leu9'Ser rats were approximately equivalent to controls in their intake of cocaine on a progressive ratio schedule of reinforcement, suggesting differential effects of cholinergic signaling depending on experimental parameters. Like progressive ratio cocaine SA, β2Leu9'Ser rats and controls did not differ significantly in food SA assays, including acquisition on a fixed ratio schedule or in progressive ratio sessions. These results highlight the specific role of high-affinity, heteropentameric β2* (β2-containing) nAChRs in acquisition of cocaine SA, suggesting that mesolimbic acetylcholine signaling is active during this process.

Acetylcholine signaling genes are required for cocaine-stimulated egg laying in Caenorhabditis elegans

The toxicity and addictive liability associated with cocaine abuse are well-known. However, its mode of action is not completely understood, and effective pharmacotherapeutic interventions remain elusive. The cholinergic effects of cocaine on acetylcholine receptors, synthetic enzymes, and degradative enzymes have been the focus of relatively little empirical investigation. Due to its genetic tractability and anatomical simplicity, the egg laying circuit of the hermaphroditic nematode, Caenorhabditis elegans, is a powerful model system to precisely examine the genetic and molecular targets of cocaine in vivo. Here, we report a novel cocaine-induced behavioral phenotype in C. elegans, cocaine-stimulated egg laying. In addition, we present the results of an in vivo candidate suppression screen of synthetic enzymes, receptors, degradative enzymes, and downstream components of the intracellular signaling cascades of the main neurotransmitter systems that control C. elegans egg laying. Our results show that cocaine-stimulated egg laying is dependent on acetylcholine synthesis and synaptic release, functional nicotinic acetylcholine receptors, and the C. elegans acetylcholinesterases.

rTMS-Induced Changes in Glutamatergic and Dopaminergic Systems: Relevance to Cocaine and Methamphetamine Use Disorders

Cocaine use disorder and methamphetamine use disorder are chronic, relapsing disorders with no US Food and Drug Administration-approved interventions. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation tool that has been increasingly investigated as a possible therapeutic intervention for substance use disorders. rTMS may have the ability to induce beneficial neuroplasticity in abnormal circuits and networks in individuals with addiction. The aim of this review is to highlight the rationale and potential for rTMS to treat cocaine and methamphetamine dependence: we synthesize the outcomes of studies in healthy humans and animal models to identify and understand the neurobiological mechanisms of rTMS that seem most involved in addiction, focusing on the dopaminergic and glutamatergic systems. rTMS-induced changes to neurotransmitter systems include alterations to striatal dopamine release and metabolite levels, as well as to glutamate transporter and receptor expression, which may be relevant for ameliorating the aberrant plasticity observed in individuals with substance use disorders. We also discuss the clinical studies that have used rTMS in humans with cocaine and methamphetamine use disorders. Many such studies suggest changes in network connectivity following acute rTMS, which may underpin reduced craving following chronic rTMS. We suggest several possible future directions for research relating to the therapeutic potential of rTMS in addiction that would help fill current gaps in the literature. Such research would apply rTMS to animal models of addiction, developing a translational pipeline that would guide evidence-based rTMS treatment of cocaine and methamphetamine use disorder.

Rivastigmine does not alter cocaine-induced subjective effects or self-administration

BACKGROUND

Acetylcholinergic (ACh) neurons interface with the mesolimbic dopamine pathway implicated in addiction, and acetylcholinesterase inhibitors (AChEis) have been shown to reduce the immediate effects of cocaine and amount used. Our study is the first to examine if the safe and low-interaction AChEi rivastigmine (riv) alters the subjective effects produced by cocaine administration.

METHODS

Cocaine-dependent subjects were randomized to daily placebo, riv 3 mg, or riv 6 mg, administered inpatient for 10 days. On day 1 (pre-dose) and day 9, subjects received both IV cocaine 40 mg or placebo in a randomized order with subsequent serial assessments of visual analog scale (VAS) subjective effects and pharmacokinetic measurements. On day 10 all participants received one baseline dose of cocaine 20 mg with assessment of subjective effects, and were then able to purchase additional doses at 15 min intervals with study earnings.

RESULTS

40 subjects were randomized to placebo (n = 16), riv 3 mg (n = 13), or riv 6 mg (n = 12). All subjects completed the study and there were no demographic differences between treatment groups. Pre- and post- treatment, there were no significant pharmacokinetic differences (blood levels of cocaine, BE, EME) following cocaine administration. In a two-way ANOVA, IV cocaine significantly increased positive VAS category ratings compared to placebo, but rivastigmine treatment at either dose had no significant effect on any VAS category ratings. Similarly, there was no significant rivastigmine effect on any category in the day 10 cocaine administration, and no effect on number of subsequent doses participants purchased.

CONCLUSION

Rivastigmine 3 or 6 mg had no significant effect on the subjective effects of cocaine after 9 days of treatment. This is an important finding as other drugs in the AChEi class (donepezil, Huperzine A) have produced significant results, but differ in their receptor specificity and PK parameters.

The Effects of Amphetamine and Methamphetamine on the Release of Norepinephrine, Dopamine and Acetylcholine From the Brainstem Reticular Formation

Amphetamine (AMPH) and methamphetamine (METH) are widely abused psychostimulants, which produce a variety of psychomotor, autonomic and neurotoxic effects. The behavioral and neurotoxic effects of both compounds (from now on defined as AMPHs) stem from a fair molecular and anatomical specificity for catecholamine-containing neurons, which are placed in the brainstem reticular formation (RF). In fact, the structural cross-affinity joined with the presence of shared molecular targets between AMPHs and catecholamine provides the basis for a quite selective recruitment of brainstem catecholamine neurons following AMPHs administration. A great amount of investigations, commentary manuscripts and books reported a pivotal role of mesencephalic dopamine (DA)-containing neurons in producing behavioral and neurotoxic effects of AMPHs. Instead, the present review article focuses on catecholamine reticular neurons of the low brainstem. In fact, these nuclei add on DA mesencephalic cells to mediate the effects of AMPHs. Among these, we also include two pontine cholinergic nuclei. Finally, we discuss the conundrum of a mixed neuronal population, which extends from the pons to the periaqueductal gray (PAG). In this way, a number of reticular nuclei beyond classic DA mesencephalic cells are considered to extend the scenario underlying the neurobiology of AMPHs abuse. The mechanistic approach followed here to describe the action of AMPHs within the RF is rooted on the fine anatomy of this region of the brainstem. This is exemplified by a few medullary catecholamine neurons, which play a pivotal role compared with the bulk of peripheral sympathetic neurons in sustaining most of the cardiovascular effects induced by AMPHs.

Cocaine, nicotine, and their conditioned contexts enhance consolidation of object memory in rats

To test the hypothesis that drugs of abuse and their conditioned stimuli (CSs) enhance memory consolidation, the effects of post-training exposure to cocaine and nicotine were compared to the effects of post-training exposure to contextual stimuli that were paired with the effects of these drugs. Using the object recognition (OR) task, it was first demonstrated that both 10 and 20 mg/kg cocaine, and 0.2 and 0.4 mg/kg nicotine, enhanced recognition memory when administered immediately after, but not 6 h after the sample phase. To establish the drug CSs, rats were confined for 2 h in a chamber (the CS+) after injections of 20 mg/kg cocaine, or 0.4 mg/kg nicotine, and in another chamber (the CS−) after injections of vehicle. This was repeated over 10 d (5 drug/CS+ and 5 vehicle/CS− pairings in total). At the end of this conditioning period, when tested in a drug-free state, rats displayed conditioned hyperactivity in the CS+ relative to the CS−. More important, immediate, but not delayed, post-sample exposure to the cocaine CS+, or nicotine CS+, enhanced OR memory. Therefore, this study reports for the first time that contextual stimuli paired with cocaine and nicotine, like the drugs themselves, have the ability to enhance memory consolidation.

The Nucleus Accumbens: Mechanisms of Addiction across Drug Classes Reflect the Importance of Glutamate Homeostasis

The nucleus accumbens is a major input structure of the basal ganglia and integrates information from cortical and limbic structures to mediate goal-directed behaviors. Chronic exposure to several classes of drugs of abuse disrupts plasticity in this region, allowing drug-associated cues to engender a pathologic motivation for drug seeking. A number of alterations in glutamatergic transmission occur within the nucleus accumbens after withdrawal from chronic drug exposure. These drug-induced neuroadaptations serve as the molecular basis for relapse vulnerability. In this review, we focus on the role that glutamate signal transduction in the nucleus accumbens plays in addiction-related behaviors. First, we explore the nucleus accumbens, including the cell types and neuronal populations present as well as afferent and efferent connections. Next we discuss rodent models of addiction and assess the viability of these models for testing candidate pharmacotherapies for the prevention of relapse. Then we provide a review of the literature describing how synaptic plasticity in the accumbens is altered after exposure to drugs of abuse and withdrawal and also how pharmacological manipulation of glutamate systems in the accumbens can inhibit drug seeking in the laboratory setting. Finally, we examine results from clinical trials in which pharmacotherapies designed to manipulate glutamate systems have been effective in treating relapse in human patients. Further elucidation of how drugs of abuse alter glutamatergic plasticity within the accumbens will be necessary for the development of new therapeutics for the treatment of addiction across all classes of addictive substances.

Cholinesterase inhibitors, donepezil and rivastigmine, attenuate spatial memory and cognitive flexibility impairment induced by acute ethanol in the Barnes maze task in rats

Central cholinergic dysfunction contributes to acute spatial memory deficits produced by ethanol administration. Donepezil and rivastigmine elevate acetylcholine levels in the synaptic cleft through the inhibition of cholinesterases—enzymes involved in acetylcholine degradation. The aim of our study was to reveal whether donepezil (acetylcholinesterase inhibitor) and rivastigmine (also butyrylcholinesterase inhibitor) attenuate spatial memory impairment as induced by acute ethanol administration in the Barnes maze task (primary latency and number of errors in finding the escape box) in rats. Additionally, we compared the influence of these drugs on ethanol-disturbed memory. In the first experiment, the dose of ethanol (1.75 g/kg, i.p.) was selected that impaired spatial memory, but did not induce motor impairment. Next, we studied the influence of donepezil (1 and 3 mg/kg, i.p.), as well as rivastigmine (0.5 and 1 mg/kg, i.p.), given either before the probe trial or the reversal learning on ethanol-induced memory impairment. Our study demonstrated that these drugs, when given before the probe trial, were equally effective in attenuating ethanol-induced impairment in both test situations, whereas rivastigmine, at both doses (0.5 and 1 mg/kg, i.p.), and donepezil only at a higher dose (3 mg/kg, i.p.) given prior the reversal learning, attenuated the ethanol-induced impairment in cognitive flexibility. Thus, rivastigmine appears to exert more beneficial effect than donepezil in reversing ethanol-induced cognitive impairments—probably due to its wider spectrum of activity. In conclusion, the ethanol-induced spatial memory impairment may be attenuated by pharmacological manipulation of central cholinergic neurotransmission.

Citicoline in addictive disorders: a review of the literature

BACKGROUND

Citicoline is a dietary supplement that has been used as a neuroprotective agent for neurological disorders such as stroke and dementia. Citicoline influences acetylcholine, dopamine, and glutamate neurotransmitter systems; serves as an intermediate in phospholipid metabolism; and enhances the integrity of neuronal membranes. Interest has grown in citicoline as a treatment for addiction since it may have beneficial effects on craving, withdrawal symptoms, and cognitive functioning, as well as the ability to attenuate the neurotoxic effects of drugs of abuse.

OBJECTIVES

To review the literature on citicoline's use in addictive disorders.

METHODS

Using PubMed we conducted a narrative review of the clinical literature on citicoline related to addictive disorders from the years 1900-2013 using the following keywords: citicoline, CDP-choline, addiction, cocaine, alcohol, substance abuse, and substance dependence. Out of approximately 900 first hits, nine clinical studies have been included in this review.

RESULTS

Most addiction research investigated citicoline for cocaine use. The findings suggest that it is safe and well tolerated. Furthermore, citicoline appears to decrease craving and is associated with a reduction in cocaine use, at least at high doses in patients with both bipolar disorder and cocaine dependence. Limited data suggest citicoline may also hold promise for alcohol and cannabis dependence and in reducing food consumption.

CONCLUSIONS

Currently, there is limited research on the efficacy of citicoline for addictive disorders, but the available literature suggests promising results. Future research should employ larger sample sizes, increased dosing, and more complex study designs.

Amphetamine stimulates movement through thalamocortical glutamate release

The ventrolateral thalamus (VL) is a primary relay point between the basal ganglia and the primary motor cortex (M1). Using dual probe microdialysis and locomotor behavior monitoring, we investigated the contribution of VL input into M1 during amphetamine (AMPH)-stimulated monoamine release and hyperlocomotion in rats. Tetrodotoxin (10 μM) perfusion into the VL significantly lowered hyperactivity induced by AMPH (1 mg/kg i.p.). This behavioral response corresponded to reduced cortical glutamate and monoamine release. To determine which glutamate receptors the thalamocortical projections acted upon, we perfused either the α-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid (AMPA)/kainate receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione (NBQX) (10 μM) or the N-methyl-D-aspartic acid (NMDA) receptor antagonist (MK-801) intracortically followed by systemic AMPH. The results show that AMPA/kainate, and to a lesser extent NMDA receptors, mediated the observed effects. As glutamate-monoamine interactions could possibly occur through local or circuit-based mechanisms, we isolated and perfused M1 tissue ex vivo to determine the extent of local glutamate-dopamine interactions. Taken together, these results demonstrate that AMPH generates hyperlocomotive states via thalamocortical signaling and that cortical AMPA receptors are an important mediator of these effects. This study utilizes dual probe microdialysis sampling and comprehensive LC-MS analysis to determine the effects of amphetamine (1 mg/kg i.p.) on thalamocortical neurotransmission. Using pharmacological tools such as local thalamic tetrodotoxin (TTX) perfusion and glutamate antagonist at the cortical level, we demonstrate that thalamocortical glutamate (acting primarily through cortical AMPA receptors) is an essential component in amphetamine-induced hyperlocomotion.

Episodic memories and their relevance for psychoactive drug use and addiction

The majority of adult people in western societies regularly consume psychoactive drugs. While this consumption is integrated in everyday life activities and controlled in most consumers, it may escalate and result in drug addiction. Non-addicted drug use requires the systematic establishment of highly organized behaviors, such as drug-seeking and -taking. While a significant role for classical and instrumental learning processes is well established in drug use and abuse, declarative drug memories have largely been neglected in research. Episodic memories are an important part of the declarative memories. Here a role of episodic drug memories in the establishment of non-addicted drug use and its transition to addiction is suggested. In relation to psychoactive drug consumption, episodic drug memories are formed when a person prepares for consumption, when the drug is consumed and, most important, when acute effects, withdrawal, craving, and relapse are experienced. Episodic drug memories are one-trial memories with emotional components that can be much stronger than "normal" episodic memories. Their establishment coincides with drug-induced neuronal activation and plasticity. These memories may be highly extinction resistant and influence psychoactive drug consumption, in particular during initial establishment and at the transition to "drug instrumentalization." In that, understanding how addictive drugs interact with episodic memory circuits in the brain may provide crucial information for how drug use and addiction are established.

Memory consolidation — Mechanisms and opportunities for enhancement

Memory consolidation is the process by which relevant information is selected and transferred from a short-term, fragile state, into a stable, longer term domain from which it can be recalled. Effective memory underpins our ability to carry out everyday activities. When memory consolidation fails, such as in Alzheimer’s disease, the consequences can be devastating. Understanding the neurobiology of memory will help develop treatments for patients with memory loss. Here we describe the myriad processes involved in memory consolidation, including cholinergic and dopaminergic neurotransmission predominantly in hippocampal networks. We discuss established therapies as well as potential novel strategies for boosting cognition. Future approaches to enhancement of memory consolidation include not only pharmacological and neurosurgical treatments, but also lifestyle interventions — for example, modifications to sleep, exercise and diet.

Elimination of the vesicular acetylcholine transporter in the striatum reveals regulation of behaviour by cholinergic-glutamatergic co-transmission

A novel mouse model that eliminates cholinergic neurotransmission in the striatum while leaving glutamate release intact reveals differential effects on cocaine-induced behavior and dopaminergic responses.

Cholinergic neurons in the striatum are thought to play major regulatory functions in motor behaviour and reward. These neurons express two vesicular transporters that can load either acetylcholine or glutamate into synaptic vesicles. Consequently cholinergic neurons can release both neurotransmitters, making it difficult to discern their individual contributions for the regulation of striatal functions. Here we have dissected the specific roles of acetylcholine release for striatal-dependent behaviour in mice by selective elimination of the vesicular acetylcholine transporter (VAChT) from striatal cholinergic neurons. Analysis of several behavioural parameters indicates that elimination of VAChT had only marginal consequences in striatum-related tasks and did not affect spontaneous locomotion, cocaine-induced hyperactivity, or its reward properties. However, dopaminergic sensitivity of medium spiny neurons (MSN) and the behavioural outputs in response to direct dopaminergic agonists were enhanced, likely due to increased expression/function of dopamine receptors in the striatum. These observations indicate that previous functions attributed to striatal cholinergic neurons in spontaneous locomotor activity and in the rewarding responses to cocaine are mediated by glutamate and not by acetylcholine release. Our experiments demonstrate how one population of neurons can use two distinct neurotransmitters to differentially regulate a given circuitry. The data also raise the possibility of using VAChT as a target to boost dopaminergic function and decrease high striatal cholinergic activity, common neurochemical alterations in individuals affected with Parkinson's disease.

The neurotransmitters dopamine and acetylcholine play opposite roles in the striatum (a brain region involved in motor control and reward-related behaviour), and their balance is thought to be critical for striatal function. Acetylcholine in the striatum has been linked to a number of functions, including control of locomotor activity and response to drugs of abuse. However, striatal cholinergic interneurons can also release glutamate (in addition to acetylcholine) and it is presently unclear how these two neurotransmitters regulate striatal-dependent behaviour. Previous work has attempted to resolve this issue by ablating cholinergic neurons in the striatum, but this causes loss of both cholinergic and glutamatergic neurotransmission. In this study, we created a novel genetic mouse model which allowed us to selectively interfere with secretion of acetylcholine in the striatum, while leaving total striatal glutamate release intact. In these mice, we observed minimally altered behavioural responses to cocaine, suggesting that striatal glutamate, rather than acetylcholine, is critical for cocaine-induced behavioural manifestations. Furthermore, elimination of striatal acetylcholine release affects how striatal output neurons respond to dopamine, by up-regulating dopaminergic receptors and changing behavioural responses to dopaminergic agonists. Our experiments highlight a previously unappreciated physiological role of cholinergic-glutamatergic co-transmission and demonstrate how a population of neurons can use two distinct neurotransmitters to differentially regulate behaviour.

CaMKIIα, a modulator of M4 muscarinic acetylcholine receptors

G protein-coupled receptors (GPCRs) are subject to the regulation by protein kinases. By controlling the phosphorylation-dephosphorylation balance, protein kinases actively modify GPCR expression and function. In a recent study, we have identified a novel phosphorylation-dependent regulation of Gαi/o-coupled muscarinic acetylcholine receptors. A synapse-enriched protein kinase, Ca(2+)/calmodulin-dependent protein kinase II (CaMKIIα), binds directly and selectively to second intracellular loops of muscarinic M4 receptors (M4Rs). This Ca(2+)-sensitive binding enables CaMKIIα to phosphorylate M4Rs at a selective threonine residue. In rat striatal neurons which abundantly express M4Rs, rapid cytoplasmic Ca(2+) rises enhance the association of CaMKIIα with M4Rs and increase threonine phosphorylation of the receptor. This CaMKIIα-mediated phosphorylation results in a potentiation of M4R activity, which is critical for controlling cellular and behavioral responsivity to dopamine stimulation. In sum, our data identify a novel kinase-GPCR interaction. Through a Ca(2+)/activity-sensitive manner, CaMKIIα contributes to maintaining acetylcholine-dopamine homeostasis in the basal ganglia.

Centrality of striatal cholinergic transmission in Basal Ganglia function

Work over the past two decades revealed a previously unexpected role for striatal cholinergic interneurons in the context of basal ganglia function. The recognition that these interneurons are essential in synaptic plasticity and motor learning represents a significant step ahead in deciphering how the striatum processes cortical inputs, and why pathological circumstances cause motor dysfunction. Loss of the reciprocal modulation between dopaminergic inputs and the intrinsic cholinergic innervation within the striatum appears to be the trigger for pathophysiological changes occurring in basal ganglia disorders. Accordingly, there is now compelling evidence showing profound changes in cholinergic markers in these disorders, in particular Parkinson's disease and dystonia. Based on converging experimental and clinical evidence, we provide an overview of the role of striatal cholinergic transmission in physiological and pathological conditions, in the context of the pathogenesis of movement disorders.

Altered neural cholinergic receptor systems in cocaine-addicted subjects

Changes in the brain's cholinergic receptor systems underlie several neuropsychiatric disorders, including Alzheimer's disease, schizophrenia, and depression. An emerging preclinical literature also reveals that acetylcoholine may have an important function in addictive processes, including reward, learning, and memory. This study was designed to assess alterations in cholinergic receptor systems in limbic regions of abstinent cocaine-addicted subjects compared with healthy controls. On three separate days, 23 1- to 6-week abstinent, cocaine- (and mostly nicotine-) addicted subjects and 22 sex-, age-, and race-matched control subjects were administered the muscarinic and nicotinic cholinergic agonist physostigmine, the muscarinic antagonist scopolamine, and saline. Regional cerebral blood flow (rCBF) after each infusion was determined using single photon emission-computed tomography. Both cholinergic probes induced rCBF changes (p<0.005) in relatively distinct, cholinergic-rich, limbic brain regions. After physostigmine, cocaine-addicted subjects showed altered rCBF, relative to controls, in limbic regions, including the left hippocampus, left amygdala, and right insula. Group differences in the right dorsolateral prefrontal cortex, posterior cingulate, and middle temporal gyrus were also evident. Scopolamine also revealed group differences in the left hippocampus and right insula as well as the posterior cingulate and middle temporal gyrus. Cocaine addicted and controls differ in their subcortical, limbic, and cortical response to cholinergic probes in areas relevant to craving, learning, and memory. Cholinergic systems may offer a pharmacologic target for cocaine addiction treatment.

CaMKIIalpha interacts with M4 muscarinic receptors to control receptor and psychomotor function

Muscarinic acetylcholine receptors (mAChRs) are widely expressed in the mammalian brain and are essential for neuronal functions. These receptors are believed to be actively regulated by intracellular signals, although the underlying mechanisms are largely unknown. In this study, we show that Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) binds directly and selectively to one of five mAChR subtypes, M4 receptors (M4Rs), at their C-terminal regions of second intracellular loops. This binding relies on Ca(2+) activation of the kinase and leads to the phosphorylation of M4Rs at a specific threonine site (Thr145). Complementary in vivo studies in rat striatal neurons enriched with M4Rs confirm that rising Ca(2+) recruits CaMKIIalpha to M4Rs to potentiate receptor signalling, which controls behavioural sensitivity to dopamine stimulation in an activity-dependent manner. Our data identify a new model of protein-protein interactions. In a Ca(2+)-sensitive manner, CaMKIIalpha regulates M4R efficacy and controls the acetylcholine-dopamine balance in the basal ganglia and also the dynamics of movement.

The role of acetylcholine in cocaine addiction

Central nervous system cholinergic neurons arise from several discrete sources, project to multiple brain regions, and exert specific effects on reward, learning, and memory. These processes are critical for the development and persistence of addictive disorders. Although other neurotransmitters, including dopamine, glutamate, and serotonin, have been the primary focus of drug research to date, a growing preclinical literature reveals a critical role of acetylcholine (ACh) in the experience and progression of drug use. This review will present and integrate the findings regarding the role of ACh in drug dependence, with a primary focus on cocaine and the muscarinic ACh system. Mesostriatal ACh appears to mediate reinforcement through its effect on reward, satiation, and aversion, and chronic cocaine administration produces neuroadaptive changes in the striatum. ACh is further involved in the acquisition of conditional associations that underlie cocaine self-administration and context-dependent sensitization, the acquisition of associations in conditioned learning, and drug procurement through its effects on arousal and attention. Long-term cocaine use may induce neuronal alterations in the brain that affect the ACh system and impair executive function, possibly contributing to the disruptions in decision making that characterize this population. These primarily preclinical studies suggest that ACh exerts a myriad of effects on the addictive process and that persistent changes to the ACh system following chronic drug use may exacerbate the risk of relapse during recovery. Ultimately, ACh modulation may be a potential target for pharmacological treatment interventions in cocaine-addicted subjects. However, the complicated neurocircuitry of the cholinergic system, the multiple ACh receptor subtypes, the confluence of excitatory and inhibitory ACh inputs, and the unique properties of the striatal cholinergic interneurons suggest that a precise target of cholinergic manipulation will be required to impact substance use in the clinical population.

Actions of 3,4-methylenedioxymethamphetamine (MDMA) on cerebral dopaminergic, serotonergic and cholinergic neurons

3,4-Methylenedioxymethamphetamine (MDMA) is an amphetamine derivative and a popular drug of abuse that exhibits mild hallucinogenic and rewarding properties and engenders feelings of connectedness and openness. The unique psychopharmacological profile of this drug of abuse most likely is derived from the property of MDMA to promote the release of dopamine and serotonin (5-HT) in multiple brain regions. The present review highlights primarily data from studies employing in vivo microdialysis that detail the actions of MDMA on the release of these neurotransmitters. Data from in vivo microdialysis experiments indicate that MDMA, like most amphetamine derivatives, increases the release of dopamine in the striatum, n. accumbens and prefrontal cortex. However, the release of dopamine evoked by MDMA in each of these brain regions appears to be modulated by concomitantly released 5-HT and the subsequent activation of 5-HT2A/C or 5-HT2B/C receptors. In addition to its stimulatory effect on the release of monoamines, MDMA also enhances the release of acetylcholine in the striatum, hippocampus and prefrontal cortex, and this cholinergic response appears to be secondary to the activation of histaminergic, dopaminergic and/or serotonergic receptors. Beyond the acute stimulatory effect of MDMA on neurotransmitter release, MDMA also increases the extracellular concentration of energy substrates, e.g., glucose and lactate in the brain. In contrast to the acute stimulatory actions of MDMA on the release of monoamines and acetylcholine, the repeated administration of high doses of MDMA is thought to result in a selective neurotoxicity to 5-HT axon terminals in the rat. Additional studies are reviewed that focus on the alterations in neurotransmitter responses to pharmacological and physiological stimuli that accompany MDMA-induced 5-HT neurotoxicity.

Impact of 6-hydroxydopamine lesions and cocaine exposure on mu-opioid receptor expression and regulation of cholinergic transmission in the limbic-prefrontal territory of the rat dorsal striatum

Information processing within the striatum is regulated by local circuits involving dopamine, cholinergic interneurons and neuropeptides released by recurrent collaterals of striatal output neurons. In the limbic-prefrontal territory of the dorsal striatum, enkephalin inhibits the NMDA-evoked release of acetylcholine directly through micro-opioid receptors (MORs) located on cholinergic interneurons and indirectly through MORs of output neurons of striosomes. In this territory, we investigated the consequence of changes in dopamine transmission, bilateral 6-hydroxydopamine-induced degeneration of striatal dopaminergic innervation or cocaine (acute and chronic) exposure on (i) MOR expression in both cholinergic interneurons and output neurons of striosomes, and (ii) the direct and indirect enkephalin-MOR regulations of the NMDA-evoked release of acetylcholine. Expression of MORs in cholinergic interneurons was preserved after 6-hydroxydopamine and down-regulated after cocaine treatments. Accordingly, the direct enkephalin-MOR control of acetylcholine release was preserved after 6-hydroxydopamine treatment and lost after cocaine exposure. Expression of MORs in output neurons of striosomes was down-regulated in the 6-hydroxydopamine situation and either preserved or up-regulated after acute or chronic cocaine exposure, respectively. Accordingly, the indirect enkephalin-MOR control of acetylcholine release disappeared in the 6-hydroxydopamine situation but surprisingly, despite preservation of MORs in striosomes, disappeared after cocaine treatment. Showing that MORs of striosomes are still functional in this situation, the MOR agonist [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin inhibited the NMDA-evoked release of acetylcholine after cocaine exposure. Therefore, alteration in the regulation of cholinergic transmission by the enkephalin-MOR system might play a major role in the motivational and cognitive disorders associated with dopamine dysfunctions in fronto-cortico-basal ganglia circuits.

Differential effects of nicotinic antagonists perfused into the nucleus accumbens or the ventral tegmental area on cocaine-induced dopamine release in the nucleus accumbens of mice

RATIONALE

The mesolimbic dopamine (DA) system is considered a principal site for nicotine-cocaine interactions.

OBJECTIVES AND METHODS

The aim of this paper is to study the effects of local perfusions (through the microdialysis cannula) of nicotinic acetylcholine receptor (nAChR) antagonists in the ventral tegmental area (VTA, where mesolimbic DA cell bodies are located) or nucleus accumbens (nAc, where mesolimbic DA nerve terminals project) on cocaine-elicited increase in DA levels in the nAc of mice using intracerebral microdialysis.

RESULTS

Intra-nAc perfusion of mecamylamine (a nonselective central nicotinic antagonist) or coperfusion of methyllycaconitine (MLA, 10 nM) and dihydro-beta-erythroidine (DHbetaE, 10-100 muM) decreased cocaine-elicited increase in DA perfusate levels. In contrast, intra-nAc perfusion of MLA alone (a relatively selective antagonist of alpha7 subunit-containing nAChRs) increased, while DHbetaE (a relatively selective antagonist of heteromeric nAChR subtypes) did not alter, cocaine-elicited increase in DA perfusate levels. Intra-VTA perfusion of MLA (100 nM) or DHbetaE (100 micro M) significantly increased the cocaine-elicited increase of DA levels in the nAc or VTA, whereas DHbetaE and MLA coperfusion or mecamylamine perfusion had no significant effect.

CONCLUSIONS

These results show that intra-nAc and intra-VTA perfusion of nAChR antagonists differentially affect cocaine-elicited increase in DA levels in a region and subtype-specific manner. This suggests that multiple cholinergic/nicotinic pathways influence the effects of cocaine on mesolimbic DA neurons in complex, and sometimes opposing, patterns.

Inhibition of both alpha7* and beta2* nicotinic acetylcholine receptors is necessary to prevent development of sensitization to cocaine-elicited increases in extracellular dopamine levels in the ventral striatum

RATIONALE

Several studies have suggested that nicotine treatment can modulate the behavioral and neurochemical responses to other psychostimulants, such as cocaine.

OBJECTIVES

The current study examined the hypothesis that nicotinic acetylcholine receptor (nAChR) blockade influences the ability of cocaine to elicit increases in extracellular dopamine levels.

MATERIALS AND METHODS

Pharmacological studies using nicotinic antagonists as well as genetic inactivation of beta2* nAChRs were used to determine the effect of nAChR blockade on dopamine levels in ventral striatum elicited by acute or repeated administrations of cocaine in mice.

RESULTS

Administration of mecamylamine (a general nicotinic antagonist that is not highly selective for individual nAChR subtypes) or co-administration of methyllycaconitine (a more selective antagonist of alpha7* nAChRs) with dihydro-beta-erythroidine (a more selective antagonist of beta2* nAChRs and other heteromeric nAChR subtypes) prevented sensitization of cocaine-elicited increases in extracellular DA levels in the ventral striatum in wild-type mice. In contrast, neither of the more specific antagonists alone was effective in preventing sensitization. Finally, methyllycaconitine administration prevents sensitization in beta2-/- mice but not in beta2+/+ or wild-type mice.

CONCLUSIONS

These data indicate that inhibition of both alpha7* and beta2* nAChRs is necessary to prevent development of sensitization of cocaine-elicited increases in extracellular dopamine levels in the ventral striatum of mice.

3,4-Methylenedioxymethamphetamine enhances the release of acetylcholine in the prefrontal cortex and dorsal hippocampus of the rat

RATIONALE

The neurochemical effects produced by acute administration of 3,4-methylenedioxymethamphetamine (MDMA) on the monoaminergic systems in the brain are well documented; however, there has been little consideration of the potential effects of MDMA on other neurotransmitter systems.

OBJECTIVE

The present study was designed to investigate the acute effect of MDMA on cholinergic neurons by measuring acetylcholine (ACh) release in the medial prefrontal cortex (PFC) and dorsal hippocampus, terminal regions of cholinergic projection neurons originating in the basal forebrain.

METHODS

In vivo microdialysis and high-performance liquid chromatography with electrochemical detection (HPLC-ED) were used to assess the effects of MDMA on the extracellular concentration of ACh in the PFC and dorsal hippocampus of the rat.

RESULTS

The systemic administration of MDMA (3-20 mg/kg, i.p.) resulted in an increased extracellular concentration of ACh in the PFC and dorsal hippocampus. Reverse dialysis of MDMA (100 microM) into the PFC and hippocampus also increased ACh release in these brain regions. Treatment with parachlorophenylalanine and alpha-methyl-para-tyrosine, inhibitors of serotonin (5-HT) and dopamine (DA) synthesis, respectively, significantly attenuated the release of ACh stimulated by MDMA in the PFC, but not in the dorsal hippocampus.

CONCLUSIONS

MDMA exerts a stimulatory effect on the release of ACh in the PFC and dorsal hippocampus in vivo, possibly by mechanisms localized within these brain regions. In addition, these results suggest that the MDMA-induced release of ACh in the PFC involves both serotonergic and dopaminergic mechanisms.

3,4-Methylenedioxymethamphetamine (MDMA) enhances the release of acetylcholine by 5-HT4 and D1 receptor mechanisms in the rat prefrontal cortex

3,4-Methylenedioxymethamphetamine (MDMA), an amphetamine analog, has been shown recently to increase the release of acetylcholine (ACh) in the prefrontal cortex (PFC). The present study further characterizes the stimulatory effect of MDMA on cortical ACh release and examines the role of serotonin (5-HT) and dopamine (DA) receptors in this response. The extracellular concentration of ACh was increased dose-dependently and similarly by the (+) and (-) enantiomers of MDMA (5 and 20 mg/kg, i.p.). The systemic administration of the 5-HT(4) antagonist SDZ 205,557 (1 mg/kg, i.p.), but not the 5-HT(2A/2B/2C) antagonist LY-53,857 (3 mg/kg, i.p.), significantly decreased cortical ACh release induced by MDMA. The MDMA-induced increase in the extracellular concentration of ACh also was significantly blunted in rats treated with the D(1) receptor antagonist SCH 23390 (0.5 mg/kg, i.p.). The extent to which the coadministration of SDZ 205,557 and SCH 23390 suppressed the MDMA-induced release of ACh in the PFC was no greater than that produced by either antagonist alone. These results suggest that the 5-HT(4) and D(1) receptor subtypes contribute to the mechanism by which MDMA increases ACh release in the PFC.

The Importance of Brainstem Cholinergic Neurons in the Pressor Response to Cocaine

After intracisternal injection, 140 nmol (48 microg) of cocaine (but not lidocaine or procaine) evoked an increase in mean arterial pressure (MAP) of 41 mm Hg. The increase in MAP began within 1 min after injection and lasted 10 to 15 min. The pressor response to intracisternal injection of cocaine was not mediated through central alpha-adrenergic receptors, but intracisternal pretreatment with D1 or D2 dopamine receptor antagonists shortened the duration of the response. Pretreatment with intracisternal injection of hemicholinium-3 to deplete medullary acetylcholine produced a dose-dependent inhibition of the pressor and tachycardic responses to intracisternal injection of cocaine. Central pretreatment with hemicholinium-3 also inhibited the pressor response to intravenous injection of 0.5 mg/kg cocaine. Atropine pretreatment was only partly effective in blocking the pressor and tachycardic responses to intracisternal injection of cocaine. However, a single intracisternal injection of the nicotinic ganglionic receptor blocker hexamethonium inhibited the pressor response to cocaine administered intracisternally 24 h later, and on each of the following 4 days. The blocking effect of hexamethonium was not mimicked by the alpha7 selective antagonist methyllycaconitine or by the alpha4beta2 subtype-preferring antagonist dihydro-beta-erythroidine. The data suggest that the pressor response to cocaine is mediated by medullary acetylcholine release on to nicotinic receptors of the ganglionic type, enhancing the output of bulbospinal sympathetic premotor neurons. Our results provide new evidence for the prolonged inactivation of relevant central nicotinic receptors by nicotinic receptor antagonists, and suggest that such compounds might be used safely for cocaine overdose, as well as for antiabuse issues without the concern for autonomic side effects.

Die neuropsychologischen Effekte von Kokain

Zusammenfassung: Kokainkonsumenten sind in der Regel entweder Gelegenheitskonsumenten mit geringem und relativ gut kontrollierbarem Kokainkonsum oder Kokainabhängige, die exzessiv große Mengen Kokain einnehmen (Binge-Taking). Neuropsychologische Untersuchungen bei Gelegenheitskonsumenten mit kleinen bis mittleren Kokaindosen, die geeignet sind, “Euphorie” und “Hochgefühle” auszulösen, ergaben bisher keine Hinweise auf neuropsychologische Funktionsbeeinträchtigungen in der akuten Phase. Vielmehr wurden in der akuten Kokainphase verbesserte Aufmerksamkeitsleistungen und schnellere Reaktionszeiten gemessen, die bis zum Beginn der postakuten Phase anhielten. Explizite Untersuchungen zur postakuten Phase oder Studien über die Effekte von Kokain in einem hohen Dosisbereich liegen derzeit nicht vor. Kokainabhängige weisen in einem Abstinenzzeitraum von bis zu mindestens 3 Monaten neuropsychologische, neurologische und unter Umständen auch psychiatrische Defizite auf. Deutliche Defizite abstinenter Kokainabhängiger wurden bei der Aufmerksamkeitsleistung, der Konzentration, der inhibitorischen Kontrolle und im Gedächtnis gefunden, wobei die verschiedenen Gedächtnistypen unterschiedlich betroffen sind. Kommt es bei Kokainabhängigen zu einer erneuten Kokaineinnahme, d.h. zu einer Binge-Phase, so ist unmittelbar danach in der so genannten Crash-Phase noch zusätzlich mit zum Teil schweren emotional-motivationalen Beeinträchtigungen zu rechnen.

The pre-clinical behavioural pharmacology of 3,4-methylenedioxymethamphetamine (MDMA)

3,4-Methylenedioxymethamphetamine (MDMA) is a relatively novel drug of abuse and as such little is currently known of its behavioural pharmacology. This review aims to examine whether MDMA represents a novel class of abused drug. MDMA is known as a selective serotonergic neurotoxin in a variety of animal species but acutely it is a potent releaser and/or reuptake inhibitor of presynaptic serotonin, dopamine, noradrenaline, and acetylcholine. Interaction of these effects contributes to its behavioural pharmacology, in particular its effects on body temperature. Drug discrimination studies indicate that MDMA and related drugs produce unique interoceptive effects which have led to their classification as entactogens. This is supported by results from other behavioural paradigms although there is evidence for dose dependency of MDMA-specific effects. MDMA also produces conditioned place preference but is not a potent reinforcer in self-administration studies. These unique behavioural effects probably underlie its current popularity. MDMA is found in the street drug ecstasy but it may not be appropriate to equate the two as other drugs are routinely found in ecstasy tablets

Cocaine increases serotonergic activity in the hippocampus and nucleus accumbens in vivo: 5-HT1a-receptor antagonism blocks behavioral but potentiates serotonergic activation

The hippocampus is an important mediator of learning and reinforcement, but its role in cocaine effects has received little attention. Neuronal activity in the hippocampus and the nucleus accumbens (Nac) depend on serotonergic (5-HT) transmission. Here we describe for the first time a cocaine-induced increase in 5-HT concentration in the hippocampus and the Nac parallel to behavioral activation. In addition, pretreatment with the 5-HT(1A)-receptor antagonist WAY 100635 blocked the behavioral activation after cocaine while potentiating the 5-HT increase in the hippocampus and the Nac. In vivo microdialysis was used in behaving rats to measure extracellular concentration of 5-HT in the hippocampus and the Nac. Four groups of animals received one of the following drug combinations: WAY 100635 (0.4 mg/kg) and cocaine (10 mg/kg), saline and cocaine (10 mg/kg), WAY 100635 (0.4 mg/kg) and saline, or saline and saline. The injections were administered i.p. and spaced 30 min apart. It was found that 1.) cocaine, at a dose that activates behavior, increases 5-HT levels in the hippocampus and in the Nac, and 2.) 5-HT(1A)-receptor antagonism can cause a dissociation of the hippocampal and Nac 5-HT activity from behavioral activation after cocaine. These results are discussed within the framework of the hippocampal-accumbens projection and its contribution to behavioral activity. They suggest that the hippocampus may have a role in mediating the behavioral and neurochemical effects of cocaine.

Cocaine-responsive gene expression changes in rat hippocampus

Chronic cocaine use is known to elicit changes in the pattern of gene expression within the brain. The hippocampus plays a critical role in learning and memory and may also play a role in mediating behaviors associated with cocaine abuse. To profile the gene expression response of the hippocampus to chronic cocaine treatment, cDNA hybridization arrays were used to illuminate cocaine-regulated genes in rats treated non-contingently with a binge model of cocaine (45 mg/kg/day, i.p.) for 14 days. Validation of mRNA changes illuminated by hybridization array analysis was accomplished by measuring immunoreactive protein (via specific immunoblots). The induction of protein kinase Calpha, potassium channel 1.1, and metabotropic glutamate receptor 5 seen by hybridization arrays was confirmed at the level of protein. Immunoblot screening of previously described cocaine-responsive genes demonstrated increased levels of protein tyrosine kinase 2, beta-catenin, and protein kinase Cepsilon. While some of these changes exist in previously described cocaine-responsive models, others are novel to any model of cocaine use. The inductions of potassium channel 1.1, protein tyrosine kinase 2 and metabotropic glutamate receptor 5 are novel findings to hippocampal cocaine-responsive gene expression. These proteins have been shown to subserve learning and memory and/or long-term potentiation functions within the hippocampus. Additionally, these genes are known to interact with one another, forming a more complex pattern of gene expression changes. The findings suggest altered expression of genes with a number of different functions in the rat hippocampus after a 'binge' style of non-contingent cocaine administration. These changes in gene expression may play roles in neuronal plasticity and the behavioral phenomena associated with cocaine abuse.

Caudate-putamen and nucleus accumbens extracellular acetylcholine responses to methamphetamine binges

Exposure of experimental animals to an escalating dose, multiple binge pattern of methamphetamine administration results in the progressive emergence of a unique behavioral profile, which includes a significant decrease in the duration of the stereotypy phase as well as a profound increase and qualitative change in the locomotor activation. This behavioral profile is associated with a selective decrease in the caudate-putamen but not nucleus accumbens extracellular dopamine response. Since the acetylcholine interneurons in these regions are partly under the control of the mesostriatal and mesoaccumbens dopamine inputs, changes in the activation of these interneurons should parallel the regionally differential dopamine responses during multiple binge treatment. Therefore, we characterized the caudate-putamen and nucleus accumbens extracellular acetylcholine responses to escalating-dose, multiple binge methamphetamine administration. An acute methamphetamine binge decreased acetylcholine levels in caudate-putamen, but had no effect on levels in nucleus accumbens. Furthermore, corresponding to the selective decrease in the dopamine response, the caudate-putamen but not nucleus accumbens extracellular acetylcholine response exhibited tolerance with repeated binge exposures; i.e. the decrease in acetylcholine associated with the acute methamphetamine binge was attenuated with multiple binge exposure. These results are consistent with our hypothesis and suggest that the regionally differential acetylcholine responses reflect one functional consequence of the escalating-dose, multiple binge stimulant treatment.

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.

Application of in vivo microdialysis to the study of cholinergic systems

The application of in vivo microdialysis to the study of acetylcholine (ACh) release has contributed greatly to our understanding of cholinergic brain systems. This article reviews standard experimental procedures for dialysis probe selection and implantation, perfusion parameters, neurochemical detection, and data analysis as they relate to microdialysis assessments of cholinergic function. Particular attention is focused on the unique methodological considerations that arise when in vivo microdialysis is dedicated expressly to the recovery and measurement of ACh as opposed to other neurotransmitters. Limitations of the microdialysis technique are discussed, as well as methodological adaptations that may prove useful in overcoming these limitations. This is followed by an overview of recent studies in which the application of in vivo microdialysis has been used to characterize the basic pharmacology and physiology of cholinergic neurons. Finally, the usefulness of the microdialysis approach for testing hypotheses regarding the cholinergic systems' involvement in cognitive processes is examined. It can be concluded that, in addition to being a versatile and practical method for studying the neurochemistry of cholinergic brain systems, in vivo microdialysis represents a valuable tool in our efforts to better comprehend ACh's underlying role in a variety of behavioral processes.

Age-related modifications of effects of ketamine and propofol on rat hippocampal acetylcholine release studied by in vivo brain microdialysis

BACKGROUND

We sometimes encounter impairment of learning and memory after general anesthesia in elderly patients. The aim of this study was to examine age-related modifications of the effects of ketamine and propofol on rat hippocampal acetylcholine (ACh) release because hippocampal cholinergic neurons are supposed to be involved in learning and memory.

METHODS

The experiments were performed on male Wistar young rats (2 months old) and old rats (18 months old), using in vivo brain microdialysis technique under freely moving condition. After initial sampling of three collections, test drugs were administered. The ACh release was determined by the HPLC-ECD method.

RESULTS

In old rats, the hippocampal basal ACh release was significantly lower than in young rats. Ketamine (25 and 50 mg kg(-1) i.p.) increased and propofol (25 and 50 mg kg(-1) i.p.) decreased the hippocampal ACh release in both young and old rats. Furthermore, ketamine 50 mg kg(-1) i.p. (anesthetic dose) produced facilitatory effects on the hippocampal ACh release in young rats (193% of the basal release), while in old rats the same dose of ketamine i.p. produced more pronounced facilitatory effects on the hippocampal ACh release (317% of the basal release). On the other hand, propofol 50 mg kg(-1) i.p. (anesthetic dose) produced inhibitory effects on the hippocampal ACh release in young rats (56% of control) and in old rats (77% of control). Although the maximal inhibitory peak effects of propofol 50 mg kg(-1) i.p. did not differ significantly between young rats and old rats, decrease of the hippocampal ACh release in old rats persisted longer than in young rats.

CONCLUSION

Ketamine produced more pronounced facilitatory effects on the hippocampal ACh release in old rats, as compared with young rats. On the other hand, propofol has inhibitory effects on the hippocampal ACh release in young and old rats. The aging process may suppress the ability to recover from the inhibitory anesthetic state induced by propofol.

Transgenic rescue of SNAP-25 restores dopamine-modulated synaptic transmission in the coloboma mutant

Many of the molecular components constituting the exocytotic machinery responsible for neurotransmitter release have been identified, yet the precise role played by these proteins in synaptic transmission, and their impact on neural function, has not been resolved. The mouse mutation coloboma is a contiguous gene defect that leads to electrophysiological and behavioral deficits and includes the gene-encoding SNAP-25, an integral component of the synaptic vesicle-docking/fusion core complex. The involvement of SNAP-25 in the hyperactive behavior of coloboma mice, which can be ameliorated by the indirect dopaminergic agonist, amphetamine, has been demonstrated by genetic rescue using a SNAP-25 transgene. Coloboma mice also exhibit increased recurrent inhibition, reduced theta rhythm by tail-pinch and reduced long-term potentiation in the hippocampal dentate gyrus that, as the hyperkinesis seen in these mutants suggests, may reflect impaired monoaminergic modulation. We sought to identify neurophysiological correlates of the rescued hyperactivity within hippocampal synaptic circuitry of SNAP-25 transgenic coloboma mutant mice. In contrast to the differences between coloboma and wild-type mice, there was no significant difference in the duration or amplitude of theta rhythmic activity (4-6 Hz) induced by tail-pinch (10 s), afferent-evoked field potentials, or paired-pulse responses recorded in the dentate gyrus of SNAP-25 transgenic coloboma and wild-type mice. Amphetamine (3.0 mg/kg, i.p.) produced disinhibition of dentate paired-pulse responses in both SNAP-25 transgenic and wild-type mice but increased inhibition in non-transgenic coloboma mice. These findings support the hypothesis that alteration of monoaminergic neurotransmission, which can be reversed by the indirect agonist, amphetamine, is particularly sensitive to alterations in the expression of SNAP-25.

Selective alpha 7 nicotinic receptor stimulation normalizes chronic cocaine-induced loss of hippocampal sensory inhibition in C3H mice

BACKGROUND

A physiological alteration associated with schizophrenic and manic psychoses is diminished inhibition of the electrophysiological response to repeated auditory stimuli. This deficit also occurs in cocaine addicts. Studies in animals show that such inhibition is decreased by noradrenergic receptor stimulation and that the inhibition is enhanced by nicotinic cholinergic receptor stimulation.

METHODS

C3H mice were treated for 7 days with cocaine. They were then prepared for electrophysiological recording. After the effects of cocaine treatment were observed, they were treated with nicotine agonists.

RESULTS

Chronic cocaine administration markedly diminished inhibition of the hippocampal-evoked response to repeated auditory stimuli. The loss of inhibition was reversed by acute treatment with either nicotine or the selective alpha 7 nicotinic agonist 3-(2,4)-dimethoxybenzylidine anabaseine (DMXB; GTS21). The effects of nicotine showed tachyphylaxis, whereas those of DMXB did not.

CONCLUSIONS

This reversal of cocaine's effect by nicotinic agonists is consistent with previous pharmacological studies of the inhibition of auditory response. Additionally, the ability of nicotinic agonists to reverse a physiological defect associated with psychosis may have therapeutic implications for the neuropsychiatric sequelae of cocaine addiction in humans.

Long-term changes in connexin32 gap junction protein and mRNA expression following cocaine self-administration in rats

Considerable evidence indicates a critical role for dopamine in the reinforcing effects of cocaine. Because dopamine has been shown to be a critical modulator of gap junction communication in both eye and brain, we sought to examine whether extended intravenous cocaine self-administration would affect the expression of gap junction channel-forming proteins (connexins). Using ELISA, Western analysis, immunohistochemistry, semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR), and non-radioactive in situ hybridization, we demonstrate that withdrawal from chronic cocaine self-administration causes lasting changes in connexin32 (Cx32) expression in the nucleus accumbens and hippocampus at 2, 7 and 21 days after the last cocaine injection. A sustained decrease in Cx32 protein and mRNA levels is noted in areas that have been implicated in cocaine craving (i.e. nucleus accumbens and subfields of the hippocampal formation). A progressive increase in gap junction protein and mRNA expression is noted in areas that become hyperexcitable after chronic cocaine exposure (i.e. CA1 hippocampal neurons). We speculate that gap junction communication may be critically involved in reinforcement processes and neuroadaptive changes produced by drugs of abuse.

Strain-dependent involvement of D1 and D2 dopamine receptors in muscarinic cholinergic influences on memory storage

These experiments examined the interaction of muscarinic and dopaminergic systems in influencing memory for one-trial inhibitory avoidance training in mice of the C57BL/6 and DBA/2 strains. In both strains, immediate post-training systemic administration of the muscarinic cholinergic agonist oxotremorine enhanced retention and the cholinergic antagonist atropine impaired retention. No effects were seen with injections 2 h post-training. Furthermore, the drugs did not affect retention performance of animals that received no footshock on the training trial. These results confirm previous findings indicating that muscarinic cholinergic drugs affect memory by influencing memory consolidation. In C57 mice, pretreatment with selective D1 or D2 dopamine (DA) receptor agonists (SKF 38393 or LY 171555, respectively) in otherwise non-effective doses (5 and 0.25 mg/kg, respectively) potentiated the effects of oxotremorine (0.04 mg/kg). Furthermore, in C57 mice pretreatment with selective D1 or D2 receptor antagonists (SCH 23390 or (-)-sulpiride) in otherwise non-effective doses (0.025 and 6 mg/kg, respectively) blocked the memory enhancing effects of oxotremorine. The memory impairing effects of atropine (3 mg/kg) were blocked by the D1 and D2 selective agonists and potentiated by the selective D1 or D2 antagonists. In contrast, in DBA mice, the D1 and D2 selective agonists antagonised the memory enhancing effects of oxotremorine (0.02 mg/kg) and potentiated the effects of atropine (2 mg/kg). Furthermore, the D1 and D2 antagonists potentiated the effects of oxotremorine and antagonised those of atropine. These findings indicate that although muscarinic cholinergic influences on memory storage are comparable in mice of these two strains, the cholinergic-dopaminergic interactions are opposite in the two strains. These results have implications for hypotheses of cholinergic and dopaminergic regulation of memory storage.

The effect of methamphetamine on the release of acetylcholine in the rat striatum

We examined the effect of methamphetamine on the release of acetylcholine in the striatum of freely moving rats, using an in vivo microdialysis method. The basal level of acetylcholine was 3.67+/-0.47 pmol/30 microl per 15 min in the presence of neostigmine (10 microM). Tetrodotoxin (1 microM), a selective blocker of voltage-dependent Na+ channels, markedly inhibited the release of acetylcholine in the striatal perfusates. Apomorphine (1.0 mg/kg, i.p.), a dopamine receptor agonist, also significantly attenuated acetylcholine release. Methamphetamine (0.1 and 0.5 mg/kg, i.p.) did not immediately affect acetylcholine release in the striatum, but a dose of 1.0 mg/kg (i.p.) induced an increase of acetylcholine release in the striatum at 15-60 min. Striatal infusion of methamphetamine (5 and 10 microM) did not influence acetylcholine release. The increase following intraperitoneal administration of methamphetamine was slightly diminished by haloperidol (0.5 mg/kg). After microinjection of the neurotoxin, 6-hydroxydopamine (6 microg/3 microl), in the substantia nigra 7 days before, the increase of acetylcholine induced by the administration of methamphetamine (1.0 mg/kg) was slightly attenuated, whereas the administration of reserpine (2 mg/kg, i.p.) 24 h before, combined with alpha-methyl-p-tyrosine (300 mg/kg, i.p.) 2.5 h before, completely blocked the increase in release of acetylcholine. These findings suggest that methamphetamine exerts an excitatory influence on striatal acetylcholine release in freely moving rats, and that this excitatory effect involves the dopaminergic system and the catecholaminergic system.

Differential participation of hippocampal formation in cocaine-induced cortical electroencephalographic desynchronization and penile erection in the rat

We evaluated the role of the hippocampal formation in cocaine-induced cortical electroencephalographic (EEG) desynchronization and penile erection. Adult, male Sprague-Dawley rats anesthetized and maintained by chloral hydrate were used. Intravenous (1.5 or 3.0 mg/kg) administration of cocaine dose-dependently increased intracavernous pressure (ICP), our experimental index for penile erection. This was accompanied by desynchronization of EEG activity recorded from the somatosensory cortex (cEEG), as represented by a decrease in root mean square (RMS) and an increase in mean power frequency (MPF) values. There was a simultaneous increase in the RMS values, without significant changes in the MPF values of EEG signals recorded from the hippocampal formation (hEEG). In animals that received prior application of 10% xylocaine either intrathecally (i.t.) at the L6-S1 spinal levels or directly into the bilateral hippocampal formation, the RMS values of both cEEG and hEEG signals induced by cocaine (1.5 or 3.0 mg/kg, i.v.) were appreciably reduced, along with a further increase in ICP. Unilateral microinjection of cocaine (15 or 30 microg) into the hippocampal formation elicited discernible excitation of both cEEG and hEEG signals. Intriguingly, the ICP underwent a significant and dose-dependent reduction, which was discernibly antagonized by i.t. application of xylocaine. We conclude that cocaine may effect cortical EEG desynchronization but cause a reduction in ICP via an action on the hippocampal formation.

D1 and D2 dopamine receptor mediation of amphetamine-induced acetylcholine release in nucleus accumbens

To assess the interaction of dopamine and acetylcholine systems in the rat nucleus accumbens in response to direct D-amphetamine administration, in vivo microdialysis measures of acetylcholine were used during reverse dialysis of amphetamine alone and in combination with D1 and D2 receptor antagonists SCH 23390 and sulpiride, respectively. During a 15-min exposure to amphetamine (50 microM) in the nucleus accumbens, acetylcholine increased to 33% above pre-infusion levels, became maximal at 15 min post-infusion (+41%) and gradually returned to baseline levels by 60 min post-amphetamine. Conversely, amphetamine (1 mM) administration caused a biphasic change in acetylcholine release with a trend toward a decrease (-14%) during exposure followed by a significant increase (+36%) at 30 min post-amphetamine that returned to baseline levels by 60 min after infusion. The increases observed during amphetamine (50 microM) exposure and during recovery from amphetamine (1 mM) were both blocked by co-administration with the D1 antagonist, SCH 23390 (10 microM), but not with the D2 antagonist, sulpiride (10 microM). Co-infusion of sulpiride eliminated the trend toward reduced acetylcholine release observed during 1 mM amphetamine whereas co-administration of SCH 23390 potentiated this decrease. A possible tonic D1 facilitation of nucleus accumbens acetylcholine release was indicated by the consistent reductions in acetylcholine release observed during infusion of SCH 23390. These results suggest that amphetamine administration in the nucleus accumbens induces a bidirectional change in acetylcholine release that is dependent on dose and opposing effects of nucleus accumbens D1 and D2 activation. In general, relatively low doses of amphetamine administered into the nucleus accumbens caused an increase in acetylcholine release that was dependent on dopamine D1 receptors whereas higher doses of amphetamine resulted in a D2-mediated decrease.

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.

Effects of lesions of the nucleus basalis magnocellularis on the acquisition of cocaine self-administration in rats

The nucleus basalis magnocellularis (NBM) is one element in the limbic cortical-ventral striatal circuitry that has been implicated in reinforcement processes. The present study examined the involvement of the cholinergic neurons of the NBM in mediating aspects of cocaine reinforcement. Lesions of the NBM were made by injecting 0.01 M AMPA into the subpallidal basal forebrain. Following 4 days' recovery, rats were implanted chronically with catheters in the jugular vein. In three separate experiments, rats were trained to acquire cocaine self-administration under a FR1 schedule of reinforcement at doses of 0.25, 0.083 and 0.028 mg/injection. A dose-effect function was also determined at the end of the acquisition experiments using five different doses of cocaine (0.009, 0.028, 0.083, 0.25, 0.50 mg/injection) and saline which were presented once daily in a Latin square design. There were no significant differences between groups in the acquisition of cocaine self-administration at any of the three doses studied (0.028, 0.083 and 0.25 mg/injection), although at the lowest dose, lesioned animals responded at greater levels on both active and inactive levers. However, a shift to the left in the cocaine dose-response function was observed revealing that the lesioned group self-administered significantly higher amounts of low doses of cocaine than control rats. These data suggest that the integrity of the NBM is not a critical determinant of the reinforcing effects of cocaine during the acquisition of self-administration of the drug, but that NBM-dependent cholinergic mechanisms may nevertheless interact with the neural substrates mediating the reinforcing properties of cocaine. The data are relevant to recent hypotheses of functional interactions between the dopaminergic system and the cholinergic NBM.

Cocaine-induced increase in cortical acetylcholine release: interaction with the hypothalamo-pituitary-adrenal axis

An influence on drug-taking behaviours of the stress-related hypothalamo-pituitary-adrenal (HPA) axis and its final hormonal mediator, corticosterone, has previously been demonstrated. A role for cortically projecting cholinergic neurons in these behaviours can also be proposed. The experiments presented here examine the effect of the drug of abuse cocaine (15 mg/kg) on the release of acetylcholine (ACh) in the cortex of freely moving rats, using the technique of in vivo microdialysis. To assess a possible modulatory influence of the HPA axis via its final hormonal mediator corticosterone, the cocaine-induced effect on cortical ACh release in intact rats was compared to that in adrenalectomized (ADX) rats, which thus lacked their endogenous source of corticosterone, and in ADX rats in which the cocaine-induced corticosterone peak and/or the basal circadian concentrations of serum corticosterone were simulated by replacement treatments. The results reported here demonstrate that cortical ACh release is greatly increased by cocaine in intact rats; ADX prolongs the return to basal levels of cortical ACh, and the chronic replacement of circadian levels of corticosterone normalizes this effect. In contrast, during the plateau period of cocaine-induced increased cortical ACh release, where no effect of ADX is evident, rats with chronic replacement of corticosterone show an attenuated cocaine-induced cortical ACh release, and the acute replacement of the cocaine-induced corticosterone secretion further attenuates this response. These results demonstrate that cocaine stimulates cortically projecting cholinergic neurons, and that the HPA hormone corticosterone modulates this interaction in a complex manner which merits further investigation.

Beneficial effects of thiamine on recognition memory and P300 in abstinent cocaine-dependent patients

The present study evaluated the effects of thiamine vs. placebo on memory task performance and event-related electroencephalographic potentials in eight abstinent cocaine-dependent patients. Patients orally ingested 5 g of thiamine and 5 g of a lactose placebo on two separate days scheduled approximately 1 week apart. The order of administration was randomized. Double-blind procedures were followed. Approximately 3 h after ingesting the capsules, patients completed Sternberg's (1975) memory scanning task during which performance and event-related potentials (P300) were recorded simultaneously. Thiamine was found to significantly improve recognition accuracy and P300 amplitude, at the midline parietal (Pz) electrode. The improvement was most reliable under conditions of increased memory load. These preliminary findings justify a further examination of the relation between thiamine's hypothesized effects on central nervous system cholinergic function, and the direct and indirect effects of cocaine abuse.

Increased hippocampal acetylcholine release during a working memory task

In this study we examined whether the food-reinforced alternation performance was associated with increased acetylcholine output in the dorsal hippocampus. Rats were trained to acquire the task using a T-maze. The control group consisted of rats introduced into the T-maze to run only on the day of dialysis. Acetylcholine release increased significantly in control rats only in the first 10 min after they were put into the T-maze. In trained rats acetylcholine output increased in the waiting cage as well as during trials in the T-maze. The increase in acetylcholine output in rats that had learned the task was significantly greater than in control rats.