Potentiation by low doses of selected neuroleptics of food-induced conditioned place preference in rats

Effects of dopamine modulation on chronic stress-induced deficits in reward learning

Anhedonia is characteristically preceded by chronic stress, likely involving downstream effects of glucocorticoid alterations on dopamine (DA) function. To elucidate the neural underpinnings of this interaction, we examined whether acute pharmacological modulation of DA alters reward learning after chronic mild stress (CMS). Forty-eight male Wistar rats were exposed to a 21-day CMS regime (n = 48 no stress controls) before completing the probabilistic reward task (PRT), a well-validated cross-species test of reward learning. We first examined whether stress-induced reward dysfunction could be restored by systemic injections of low-dose amisulpride (AMI), which increases DA transmission via D2-like autoreceptor blockade. Then, we investigated region-specific effects through bilateral infusions of quinpirole (QUIN), a D2-like receptor agonist, into either the nucleus accumbens core (NAcc) or medial prefrontal cortex (mPFC). Blunted reward learning in CMS animals was reversed by acute AMI administration, but this treatment did not alter reward learning in the no stress group. Elevated adrenal gland weight, a proxy for stress reactivity, predicted lower reward learning in the untreated CMS group. This effect was extinguished following AMI treatment. These findings might be attributed to significantly higher D2 receptor density in the NAcc of high stress reactive animals. To this end, NAcc QUIN infusions potentiated reward learning relative to mPFC QUIN infusions in CMS rats, but there was no effect in no stress control rats. Collectively, these findings suggest that DA modulation reverses stress-induced reward dysfunction, even among the most stress-reactive animals. The effect might depend on D2-like receptor activation in the mesolimbic system.

Biphasic reward effects are characteristic of both lorcaserin and drugs of abuse: implications for treatment of substance use disorders

Lorcaserin is a modestly selective agonist for 2C serotonin receptors (5-HT2CR). Despite early promising data, it recently failed to facilitate cocaine abstinence in patients and has been compared with dopamine antagonist medications (antipsychotics). Here, we review the effects of both classes on drug reinforcement. In addition to not being effective treatments for cocaine use disorder, both dopamine antagonists and lorcaserin can have biphasic effects on dopamine and reward behavior. Lower doses can cause enhanced drug taking with higher doses causing reductions. This biphasic pattern is shared with certain stimulants, opioids, and sedative-hypnotics, as well as compounds without abuse potential that include agonists for muscarinic and melatonin receptors. Additional factors associated with decreased drug taking include intermittent dosing for dopamine antagonists and use of progressive-ratio schedules for lorcaserin. Clinically relevant doses of lorcaserin were much lower than those that inhibited cocaine-reinforced behavior and can also augment this same behavior in different species. Diminished drug-reinforced behavior only occurred in animals after higher doses that are not suitable for use in patients. In conclusion, drugs of abuse and related compounds often act as biphasic modifiers of reward behavior, especially when evaluated over a broad range of doses. This property may reflect the underlying physiology of the reward system, allowing homeostatic influences on behavior.

The Association between Reward Sensitivity and Activity Engagement: the Influence of Delay Discounting and Anhedonia

Aim

Reward sensitivity affects individuals’ motivation to engage in goal-directed behavior. Other concepts, critical for reward appraisal, that potentially influence activity participation encompass delay discounting and anhedonia. The aim of this study was to test the hypothesis that anhedonia and delay discounting influence the relationship between reward sensitivity and activity engagement.

Methods

In total, 37 inpatient patients with an alcohol use disorder (AUD) and 37 matched healthy controls completed the behavioral activation system scale (BAS scale), the Pleasant Activities List (PAL), the Snaith–Hamilton Pleasure Scale (SHAPS) and the Delay Discounting Task (DDT).

Results

Patients differed from controls on SHAPS, DDT-k, PAL substance-related activities (SRA), but not BAS and PAL non-substance-related activities (non-SRA). Correlational analyses revealed a strong correlation between BAS and PAL non-SRA in both patients (r = 0.53) and controls (r = 0.47), but also with PAL-SRA in patients (r = 0.40), although not controls (r = 0.09). BAS was negatively correlated with SHAPS in both groups and with DDT in controls. SHAPS was negatively linked to PAL non-SRA in both groups. The BAS-PAL non-SRA relationship was influenced by discount rates in controls.

Conclusion

A strong link exists between reward sensitivity and engagement in non-SRA in both groups. Delay discounting affects the reward sensitivity and non-SRA association in healthy controls, while anhedonia did not impact the association between reward sensitivity and engagement in (non-)SRA in both conditions.

Parametric investigation of social place preference in adolescent mice

Social interaction promotes survival by helping animals to form stable and supportive groups. Additionally, maladaptive social behavior is a hallmark of disorders such as autism and schizophrenia. In many different animal species, including humans, social interaction can be inherently rewarding. Lately there has been growing interest in studying the neurobiological underpinnings of social interaction and learned social behavior in rodent behavioral models. One common procedure is conditioned place preference (CPP) to measure the rewarding effects of social interaction and social reward learning. Social CPP was originally used in rats but has been adapted recently for use in mice, enabling use of the vast array of genetic tools available in mice. Here we studied the role of age, sex, bedding, and prior social isolation on the expression of social CPP in male and female mice. We found that without social deprivation male mice display moderate and temporary social CPP during early adolescence but not adulthood. Early life social isolation increased social CPP in female but not male mice. In contrast, cocaine CPP was robust and long-lasting in male and female mice. Our results demonstrate that social CPP in mice is variable, occurring under only specific conditions, and that social isolation promotes social reward in female but not male mice. We discuss potential methodological and interpretive issues of the mouse social CPP model. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Pharmacological interventions in dysthymia

The results of early therapeutic trials (1960s and 70s) in mild chronic depression (neurotic patients) are difficult to extrapolate to dysthymia. Most studies conducted in the early 1980s showed reference drugs (TCAs and MAOIs) to be poorly effective in chronic mild depression usually defined with RDC. The most recent trials using DSM-III-R criteria for dysthymic recruitment showed TCAs, new MAOIs (RIMA) and SSRI to be effective. AU these compounds have a rather similar pharmacological mechanism of action. It is therefore of both practical and theoretical interest that amisulpride, a benzamide derivative blocking D2 and D3 pre-synaptic receptors, has been found effective in the treatment of dysthymia in different placebo and reference controlled trials. This result is in line with the pharmacological data on animal ‘anhedonic models’.

Dopamine D1/D2 receptors do not mediate the expression of conditioned place preference induced by the aftereffect of wheel running

BACKGROUND

Rats lever-press for access to running wheels suggesting that wheel running by itself is reinforcing. Furthermore, pairings of an episode of wheel running and subsequent confinement in a specific environment can establish a conditioned place preference (CPP). This finding implies that the reinforcing effects of wheel running outlast the actual occurrence of physical activity, a phenomenon referred to as aftereffect of wheel running. Aftereffect-induced CPP involves Pavlovian conditioning, i.e. repeated pairings of the aftereffect of wheel running with a specific environment creates a learned association between aftereffect and environment and, in turn, a preference for that environment. Given the involvement of dopamine systems in mediating effects of Pavlovian stimuli on appetitive behavior, a role of dopamine in mediating aftereffect-induced CPP seems plausible. Here we assessed whether the mixed D1/D2 receptor antagonist flupenthixol (0.25 mg/kg, i.p.) can block the expression of an aftereffect-induced CPP.

RESULTS

In line with earlier studies, our results demonstrate that rats displayed a conditioned preference for environments paired with the aftereffect of wheel running and further show that the magnitude of CPP was not related to the wheel running rate. Furthermore, we found that flupenthixol (0.25 mg/kg, i.p.) reduced locomotor activity but did not attenuate the expression of an aftereffect-induced CPP.

CONCLUSION

The expression of a CPP produced by the aftereffect of wheel running seems not to depend on dopamine D1/D2 receptor activation.

Litter size reduction alters insulin signaling in the ventral tegmental area and influences dopamine-related behaviors in adult rats

Postnatal overfeeding is a well-known model of early-life induced obesity and glucose intolerance in rats. However, little is known about its impact on insulin signaling in specific brain regions such as the mesocorticolimbic system, and its putative effects on dopamine-related hedonic food intake in adulthood. For this study, rat litters were standardized to 4 (small litter - SL) or 8 pups (control - NL) at postnatal day 1. Weaning was at day 21, and all tests were conducted after day 60 of life in male rats. In Experiment 1, we demonstrated that the SL animals were heavier than the NL at all time points and had decreased AKT/pAKT ratio in the Ventral Tegmental Area (VTA), without differences in the skeletal muscle insulin signaling in response to insulin injection. In Experiment 2, the standard rat chow intake was addressed using an automated system (BioDAQ, Research Diets(®)), and showed no differences between the groups. On the other hand, the SL animals ingested more sweet food in response to the 1 min tail-pinch challenge and did not develop conditioned place preference to sweet food. In Experiment 3 we showed that the SL rats had increased VTA TH content but had no difference in this protein in response to a sweet food challenge, as the NL had. The SL rats also showed decreased levels of dopamine D2 receptors in the nucleus accumbens. Here we showed that early postnatal overfeeding was linked to an altered functioning of the mesolimbic dopamine pathway, which was associated with altered insulin signaling in the VTA, suggesting increased sensitivity, and expression of important proteins of the dopaminergic system.

Why fat is so preferable: from oral fat detection to inducing reward in the brain

Potential mechanisms underlying the high palatability of fat can be assessed by reviewing animal studies on fat detection and brain patterns during reward behavior. Fatty acids are likely recognized by receptors on taste buds, with the signals transmitted to the brain through taste nerves. Ingested oil is broken down and absorbed in the gastrointestinal tract, which also sends signals to the brain through unknown mechanisms. Information from both sensory receptors and peripheral tissue is integrated by the brain, resulting in a strong appetite for fatty foods via a reward system. Understanding mechanisms of fat recognition will prove valuable in the development of strategies to manage the high palatability of foods.

The role of dopaminergic transmission through D1-like and D2-like receptors in amphetamine-induced rat ultrasonic vocalizations

RATIONALE

Systemic amphetamine (AMPH) administration increases the rate of 50-kHz ultrasonic vocalizations (USVs) in adult rats and preferentially enhances the 'trill' subtype; these effects of AMPH critically depend on noradrenergic transmission, but the possible contributions of dopamine are unclear.

OBJECTIVE

To assess the role of dopamine in 50-kHz USVs emitted drug-free and following systemic AMPH administration.

METHODS

Adult male Long-Evans rats pre-selected for high AMPH-induced calling rates were tested with AMPH (1 mg/kg, intraperitoneal (IP)) and saline following pretreatment with the following dopamine receptor antagonists: SCH 23390 (0.005-0.02 mg/kg, subcutaneous (SC)), SCH 39166 (0.03-0.3 mg/kg, SC), haloperidol (0.1, 0.2 mg/kg, IP), sulpiride (20-80 mg/kg, SC), raclopride (0.1-0.5 mg/kg, SC), clozapine (4 mg/kg, SC), risperidone (0.5 mg/kg, SC), and pimozide (1 mg/kg, IP). The dopamine and noradrenaline reuptake inhibitors (GBR 12909 and nisoxetine, respectively) were also tested, alone and in combination.

RESULTS

SCH 23390, SCH 39166, haloperidol, and raclopride dose-dependently inhibited vocalizations under AMPH and suppressed the proportion of trill calls. Sulpiride, however, had no discernable effect on call rate or profile, even at a high dose that reduced locomotor activity. Single doses of clozapine, risperidone, and pimozide all markedly decreased calling under saline and AMPH. Finally, GBR 12909 and nisoxetine failed to promote 50-kHz USVs detectably or alter the subtype profile, when tested alone or in combination.

CONCLUSIONS

The rate of 50-kHz USVs and the call subtype profile following systemic AMPH administration depends on dopaminergic neurotransmission through D1-like and D2-like receptors. However, inhibiting dopamine and/or noradrenaline reuptake appears insufficient to induce calling.

Noradrenergic versus dopaminergic modulation of impulsivity, attention and monitoring behaviour in rats performing the stop-signal task: possible relevance to ADHD

RATIONALE

Deficient response inhibition is a prominent feature of many pathological conditions characterised by impulsive and compulsive behaviour. Clinically effective doses of catecholamine reuptake inhibitors are able to improve such inhibitory deficits as measured by the stop-signal task (SST) in humans and other animals. However, the precise therapeutic mode of action of these compounds in terms of their relative effects on dopamine (DA) and noradrenaline (NA) systems in prefrontal cortical and striatal regions mediating attention and cognitive control remains unclear.

OBJECTIVES

We sought to fractionate the effects of global catecholaminergic manipulations on SST performance by using receptor-specific compounds for NA or DA. The results are described in terms of the effects of modulating specific receptor subtypes on various behavioural measures such as response inhibition, perseveration, sustained attention, error monitoring and motivation.

RESULTS

Blockade of α2-adrenoceptors improved sustained attention and response inhibition, whereas α1 and β1/2 adrenergic receptor antagonists disrupted go performance and sustained attention, respectively. No relevant effects were obtained after targeting DA D1, D2 or D4 receptors, while both a D3 receptor agonist and antagonist improved post-error slowing and compulsive nose-poke behaviour, though generally impairing other task measures.

CONCLUSIONS

Our results suggest that the use of specific pharmacological agents targeting α2 and β noradrenergic receptors may improve existing treatments for attentional deficits and impulsivity, whereas DA D3 receptors may modulate error monitoring and perseverative behaviour.

Ghrelin and food reward: the story of potential underlying substrates

The incidence of obesity is increasing at an alarming rate and this worldwide epidemic represents a significant decrease in life span and quality of life of a large part of the affected population. Therefore an understanding of mechanisms underlying food overconsumption and obesity development is urgent and essential to find potential treatments. Research investigating mechanisms underlying obesity and the control of food intake has recently experienced a major shift in focus, from the brain's hypothalamus to additional important neural circuits controlling emotion, cognition and motivated behavior. Among them, the mesolimbic system, and the changes in reward and motivated behavior for food, emerge as new promising treatment targets. Furthermore, there is also growing appreciation of the impact of peripheral hormones that signal nutrition status to the mesolimbic areas, and especially the only known circulating orexigenic hormone, ghrelin. This review article provides a synthesis of recent evidence concerning the impact of manipulation of ghrelin and its receptor on models of food reward/food motivation behavior and the mesolimbic circuitry. Particular attention is given to the potential neurocircuitry and neurotransmitter systems downstream of ghrelin's effects on food reward.

Anhedonia and substance dependence: clinical correlates and treatment options

Anhedonia is a condition in which the capacity of experiencing pleasure is totally or partially lost, and it refers to both a state symptom in various psychiatric disorders and a personality trait. It has a putative neural substrate, originating in the dopaminergic mesolimbic and mesocortical reward circuit. Anhedonia frequently occurs in mood disorders, as a negative symptom in schizophrenia, and in substance use disorders. In particular, we focus our attention on the relationships occurring between anhedonia and substance use disorders, as highlighted by many studies. Several authors suggested that anhedonia is an important factor involved in relapse as well as in the transition from recreational use to excessive drug intake. In particular, anhedonia has been found to be a frequent feature in alcoholics and addicted patients during acute and chronic withdrawal as well as in cocaine, stimulant, and cannabis abusers. Furthermore, in subjects with a substance dependence disorder, there is a significant correlation between anhedonia, craving, intensity of withdrawal symptoms, and psychosocial and personality characteristics. Therefore treating anhedonia in detoxified alcohol-dependent subjects could be critical in terms of relapse prevention strategies, given its strong relationship with craving.

Intragastric infusion of glucose enhances the rewarding effect of sorbitol fatty acid ester ingestion as measured by conditioned place preference in mice

We investigated substances that induce a rewarding effect during the postingestive process using the conditioned place preference (CPP) test. Although mice showed high affinity for a low-energy fat substitute--sorbitol fatty acid esters and low-concentration linoleic acid solution--they did not exhibit a place preference toward a voluntary intake of fat substitute in the CPP test. However, during a conditioning session of CPP that involved intragastric administration of corn oil immediately before the intake of the fat substitute, the test mice displayed a place preference. Similarly, intragastric administration of glucose, galactose, and dextrin also induced CPP; however, fructose, mannose, and a nonmetabolized carbohydrate did not. These results suggest that administration of corn oil and glucose has the same postingestive effect with regard to inducing CPP and that the structural specificity of carbohydrates influences the postingestive effect.

Alcohol protracted withdrawal syndrome: the role of anhedonia

AIMS

The aim of the present study is to characterize the relevance of withdrawal symptoms during the first 12 months of abstinence and their relation to anhedonia and craving.

METHODS

102 detoxified subjects meeting clinical criteria for Alcohol Dependence in Remission were recruited at various time since the detoxification and subdivided into four groups according to the length of abstinence (group 1: 15-30 days; group 2: 30-90 days; group 3: 90-180 days; group 4: 180-360). Withdrawal symptomatology was assessed through the Clinical Institute Withdrawal Assessment for Alcohol (CIWA-Ar). The Visual Analogue Scale (VAS) for craving, the Snaith-Hamilton Pleasure Scale (SHAPS) and the Subscale for Anhedonia in the Scale for the Assessment of Negative Symptoms (SANSanh) where the other instruments employed.

RESULTS

Both anhedonia and withdrawal symptoms were identified in all the groups considered. SHAPS score and VAS for craving showed a significant difference between group 1 and groups 2, 3, and 4. As to CIWA-Ar items, apart from "orientation/clouding of sensorium" that was higher in groups 3 and 4 with respect to both groups 1 and 2, withdrawal symptoms were not significantly different between the periods considered. SHAPS and SANSanh were positively correlated to CIWA-Ar total score, "nausea and vomiting," and "headache/fullness in head."

DISCUSSION

The results of this study suggest the relevance of protracted withdrawal well beyond the limited period following the abrupt cessation of alcohol intake. The clinical dimension of anhedonia cannot be separated from the other behavioral symptoms of withdrawal and should be considered as part of the same process.

Conditioned place preferences (CPPs) to high-caloric "snack foods" in rat strains genetically prone vs. resistant to diet-induced obesity: resistance to naltrexone blockade

A previous study in our laboratory using Sprague-Dawley (SD) male rats showed that conditioned place preferences (CPPs) can be learned to two different high-caloric "snack foods"--one high in sugar (Froot Loops cereal: FL) vs. one high in fat (Cheetos: C), and that both preferences were mediated by endogenous opioids. Using the same CPP apparatus and procedures, two genetic sub-strains of SD rats, one selectively bred for diet-induced obesity (DIO) vs. another bred for diet resistance to obesity (DR), were used in this investigation. The experiment determined if (a) CPPs can be created in both strains using the same high-caloric "snack foods" and, (b) if CPPs existed, were they opioid dependent. Four non-deprived groups of eight male rats, half being of each strain, were given 20 min sessions to eat either FL or C in one side of a three-chamber CPP apparatus vs. chow on the opposite side over alternating days of a 20 day period. Each predetermined side had distinctly different environmental cues. Following conditioning, rats were tested during 10 min sessions to see if CPPs existed to the "snack food" trained sides. During conditioning and testing, bodyweights, intakes of foods, and activity were measured. Both FL and C generated strong CPPs that were equivalent in both strains. In contrast to our previous study in the parent strain, doses of 0, 0.50, 1.0, 2.5, and 5.0 mg/kg of the opioid antagonist, naltrexone, had no effect on blocking these CPPs. These results show that (a) DIO and DR rats can learn CPPs (i.e., "exhibit food cravings") as well as their parent strain after periodic access to high-caloric palatable foods, but imply that (b) some physiological system other than the endogenous opioid system mediates such learning.

GPR expression in the rat taste bud relating to fatty acid sensing

We investigated the expression of G protein-coupled receptor GPR40 and GPR120 in the rat tongue. Using reverse transcription polymerase chain reaction, we detected a significant expression of GPR120 mRNA in the epithelium of the circumvallate papillae but not in the nonsensory epithelium, while the expression of GPR40 mRNA was undetectable in the sensory papillae. Western blotting analysis of colon and circumvallate papillae for GPR120 showed a protein band with a molecular weight that corresponds to that of GPR120, indicating that this antibody could recognize a native form of GPR120. Immunohistochemistry using anti-GPR120 antibody revealed GPR120 immunoreactivity in the enteroendocrine cells of the colon. Furthermore, some cells in each taste bud were stained positively with more intense labeling in the apical part of the cells. These results suggested that GPR120 is expressed in the taste cells of the circumvallate papillae to sense dietary fat, like the receptor expressed in the enteroendocrine cells.

Effects of atypical antipsychotic drugs on intralipid intake and cocaine-induced hyperactivity in rats

Clozapine and olanzapine have been shown to acutely stimulate consumption of a fat emulsion (Intralipid) by male Lister hooded rats. We initially investigated the extent of any sex difference in Intralipid hyperphagia associated with olanzapine treatment. We then examined the degree of Intralipid hyperphagia produced by a range of atypical antipsychotic drugs having different associations with human weight gain, and also determined their effects on cocaine-stimulated locomotor activity as a measure of functional dopamine antagonism in vivo. Olanzapine (0.1-1 mg/kg) stimulated Intralipid intake to an equal extent in male and female rats. Quetiapine (10 mg/kg) also stimulated Intralipid intake whereas ziprasidone (0.3-10 mg/kg) or risperidone (0.03-0.3 mg/kg) did not have this effect. All of the compounds, except quetiapine, reduced cocaine-stimulated locomotor activity but the relationship to the degree of Intralipid hyperphagia was variable. Since there was a positive relationship between Intralipid hyperphagia and the reported extent of human body weight gain, we conclude that Intralipid hyperphagia may have predictive value for this drug-associated side effect and is not related to the dopamine antagonist properties of these agents.

Effect of opioid antagonism on conditioned place preferences to snack foods

Previous research has shown that food-deprived rats acquire conditioned place preferences (CPPs) to sweet liquids that are largely attenuated by the opioid antagonist naltrexone (NAL). This study determined if ad libitum Chow-fed rats can learn CPPs when given relatively brief exposures to different solid snack foods (SFs) -- one high in sugar (Froot Loops cereal: FL) vs. one high in fat (Cheetos: C). Two groups of 16 male rats were trained during 20-min sessions to eat either FL or C in one side of a three-chambered CPP apparatus vs. Chow in the opposite side on alternating days for 20 days. Rats ate considerably more SFs of both types than Chow during the conditioning sessions (SFs: about 23 kcal versus Chow: about 7 kcal). Ten-minute tests for CPPs in the absence of SFs showed that the time spent on SF-conditioned sides increased significantly compared to pre-conditioning tests. Analyses of variance for re-tested CCPs after 0.1, 1.0, 2.5, and 5.0mg/kg NAL showed dose-dependent suppressions of CPPs to both SFs. These data show that consuming sweet or fatty SFs can become reliably associated with environmental cues in the non-deprived state. The endogenous opioid system, which mediates hedonic aspects of palatable food intake, appears to mediate these learned associations.

Cannabinoid CB1 receptors are involved in motivational effects of nicotine in rats

RATIONALE

The endocannabinoid system plays a role in mediating the appetitive value of a variety of reinforcing compounds, either natural rewards or drugs of abuse, but little is known about its involvement in the incentive properties of nicotine.

OBJECTIVES

The objective of the study is to evaluate whether activation of CB1 cannabinoid receptors is necessary for the establishment and the short- and long-term expression of nicotine-induced conditioned place preference (CPP). This was studied in rats subjected to an unbiased, one-compartment place conditioning procedure, using the selective CB1 receptor antagonist, rimonabant, as a pharmacological tool.

METHODS

Wistar rats, given previous experience with nicotine in their home cage, were subjected to eight alternating nicotine (0.006-0.6 mg/kg s.c.) and saline pairings with distinct floor textures in an open field and given a test session, with no nicotine injection, in the open field whose floor was covered by two quadrants of the saline-paired texture and two quadrants of the nicotine-paired texture. Rimonabant (0.3-3 mg/kg i.p.) was administered 30 min before each nicotine (0.06 mg/kg) pairing to assess its effect on the establishment of nicotine-CPP. To study the effects of CB1 receptor blockade on short- and long-term expression of nicotine-CPP, rimonabant was administered as a single injection 30 min before the test session, conducted either 24 h, 3 weeks or 12 weeks after the last conditioning session.

RESULTS

Rats developed reliable and robust CPP to the 0.06- and 0.125-mg/kg doses of nicotine. Once established, CPP persisted for at least 12 weeks without additional exposure to nicotine and the test apparatus. Pre-pairing injections of rimonabant (3 mg/kg, but not lower doses) prevented the acquisition of nicotine-CPP, and a single pretest administration of rimonabant (3 mg/kg) abolished the expression of nicotine-CPP when the test session took place 24 h after the last conditioning session. However, rimonabant (3 mg/kg) did not antagonize the expression of nicotine-CPP when the test session was conducted 3 or 12 weeks after the acquisition phase.

CONCLUSIONS

The endocannabinoids are a necessary component in both the perception by rats of the motivational value of nicotine and the short-term capacity of nicotine-paired conditioned stimuli to elicit approach behaviour. In contrast, the acute blockade of CB1 receptors no longer impairs the long-term control of behaviour by nicotine-associated environmental cues. These data provide support to the notion that the blockade of CB1 receptors can oppose tobacco dependence, withdrawal and even relapse, though the time window of efficacy and/or the schedule of administration remain to be established.

Anhedonia and substance-related symptoms in detoxified substance-dependent subjects: a correlation study

Anhedonia is a condition in which the capacity of experiencing pleasure is totally or partially lost, frequently occurring in mood disorders, as a negative symptom in schizophrenia, and in substance use disorders. In order to test a set of instruments for anhedonia in a population of detoxified opiate, alcohol and multiple substance-dependent subjects, 70 individuals were recruited from three different clinical settings. The following scales were applied: Snaith-Hamilton Pleasure Scale (SHAPS), Bech-Rafaelsen Melancholia Scale (BRMS), Scale for the Assessment of Negative Symptoms (SANS), specific withdrawal scales, and visual analogue scales (VAS) for hedonic capability and substance craving. The scales measuring anhedonia either directly (SHAPS, VAS for hedonic capability) or in some key items (SANS, BRMS) were significantly correlated with each other. The period of time since detoxification was inversely correlated with anhedonia and withdrawal symptomatology. Craving was positively correlated with anhedonia. Out of the total sample, only 18.5% could be defined as psychometrically anhedonic. The same correlations were found in this subsample. The composite instrument employed for assessing anhedonia and hedonic capability was found to be sensitive enough to detect such a dimension in the population considered, with the single scales significantly interrelated. In conclusion, we found interrelations between hedonic capability, craving and protracted withdrawal, particularly in opiate-dependent subjects. The strongest association occurred between hedonic capability and craving.

Antipsychotic and antidepressive effects of second generation antipsychotics: two different pharmacological mechanisms?

Second generation antipsychotics display antidepressive effects in schizophrenic patients that are more pronounced than those of traditional neuroleptics and that go beyond antidepressive effects secondary to the reduction of positive symptoms. The antidepressive potential of second generation antipsychotics is presumably related to their pharmacological mechanisms, which differ from those of traditional neuroleptics. Among others, 5-HT(2A) antagonism is of special relevance for most of the new antipsychotics in this respect. But also special interactions with the dopaminergic system, as is the case with amisulpride and aripiprazole, or noradrenalin- and/or serotonin-reuptake-inhibition, as with ziprasidone and zotepine, should be considered. It can be summarised that the antipsychotic and antidepressive effects of second generation antipsychotics are mostly based on different pharmacological mechanisms. This might be especially true for direct antidepressive effects, i. e. antidepressive effects that are not mediated by the reduction of positive symptoms.

Effects of a dopamine D3 receptor ligand, BP 897, on acquisition and expression of food-, morphine-, and cocaine-induced conditioned place preference, and food-seeking behavior in rats

The present study addressed the role of dopaminergic D(3) receptors (D(3)R) in motivational processes in rats. The effects of the selective D(3)R partial agonist, BP 897 (0.25-1 mg/kg, i.p.), on the establishment and the expression of conditioned place preference (CPP) supported by food, morphine (4 mg/kg, s.c.), or cocaine (2 mg/kg, s.c.) were investigated using an unbiased, one-compartment, place-conditioning procedure. When administered alone, BP 897 (0.05-2 mg/kg, i.p.) did not support CPP; on the contrary, conditioned place avoidance (CPA) was observed at 1 mg/kg, suggesting that this dose of BP 897 could be perceived as aversive. When given before each cocaine injection during the conditioning phase, BP 897 (1 mg/kg) prevented the establishment of CPP, and a single administration of BP 897 (0.5 and 1 mg/kg) before the test session impaired the expression of cocaine CPP. In contrast, neither the establishment nor the expression of food- and morphine-CPP were significantly altered by BP 897 (up to 1 mg/kg), whereas the full but less selective D(3)/D(2)R agonists, 7-OH-DPAT (0.5-2 mug/kg, s.c.) and quinelorane (1 mug/kg, s.c.), prevented the acquisition of food CPP. In a within-session extinction schedule of lever pressing for food, BP 897 (0.06-2 mg/kg) was ineffective in potentiating response reinstatement induced by the noncontingent delivery of two food pellets, in contrast with quinelorane and 7-OH-DPAT where previous studies showed to be efficient in this respect (Duarte et al, 2003). These results indicate that BP 897 has no positive appetitive value on its own, and that a moderate degree of stimulation of D(3)R is not sufficient to modulate food-primed food-seeking behavior or alter incentive motivation for food, morphine, and/or their associated cues. However, D(3)R are likely involved in the perception of the rewarding value of cocaine and cocaine-paired cues. This suggests that the appetitive effects of cocaine are subserved by mechanisms different, at least in part, from those of morphine and food, and that D(3)R play a role only in the former.

Amisulpride: limbic specificity and the mechanism of antipsychotic atypicality

Amisulpride clearly has the clinical profile of an atypical antipsychotic, characterised in particular by its lower propensity to induce extrapyramidal side effects as well as its greater efficacy in treating negative symptoms compared with classical neuroleptics. In addition to the clinical advantages over classical neuroleptics, it has also been demonstrated that the clinical profile of amisulpride is comparable to that of other modern atypical neuroleptics. Animal data also allow the conclusion to be drawn that amisulpride has an atypical profile. For example, amisulpride does not provoke catalepsy which is characteristic of postsynaptic D2 blockade in the rat. The induction of catalepsy in animal models is usually seen as an indicator of the propensity to induce extrapyramidal side effects in patients. In relation to the widely accepted hypothesis that the inclusion of 5-HT2A antagonism in addition to D2 antagonism is of great relevance for the atypicality of an antipsychotic, and given the fact that amisulpride lacks 5-HT2A antagonism, the pharmacological explanation of the clinically well-proven atypicality of amisulpride is of great interest. Based on basic research and in vivo imaging studies, two mechanisms in particular seem to explain the atypicality of amisulpride: preferential action on limbic D2/D3 receptors and preferential blockade of presynaptic D2/D3 receptors. In addition, the fast dissociation hypothesis can contribute to the explanation of the atypical clinical profile of amisulpride. The relevance of the D3 blockade in the context of atypicality is not yet completely clear.

Nucleus accumbens shell and core dopamine: differential role in behavior and addiction

Drug addiction can be conceptualized as a disturbance of behavior motivated by drug-conditioned incentives. This abnormality has been explained by Incentive-Sensitization and Allostatic-Counteradaptive theories as the result of non-associative mechanisms acting at the stage of the expression of incentive motivation and responding for drug reinforcement. Each one of these theories, however, does not account per se for two basic properties of the motivational disturbance of drug addiction: (1). focussing on drug- at the expenses of non-drug-incentives; (2). virtual irreversibility. To account for the above aspects we have proposed an associative learning hypothesis. According to this hypothesis the basic disturbance of drug addiction takes place at the stage of acquisition of motivation and in particular of Pavlovian incentive learning. Drugs share with non-drug rewards the property of stimulating dopamine (DA) transmission in the nucleus accumbens shell but this effect does not undergo habituation upon repeated drug exposure, as instead is the case of non-drug rewards. Repetitive, non-decremental stimulation of DA transmission by drugs in the nucleus accumbens septi (NAc) shell abnormally strengthens stimulus-drug associations. Thus, stimuli contingent upon drug reward acquire powerful incentive properties after a relatively limited number of predictive associations with the drug and become particularly resistant to extinction. Non-contingent occurrence of drug-conditioned incentive cues or contexts strongly facilitates and eventually reinstates drug self-administration. Repeated drug exposure also induces a process of sensitization of drug-induced stimulation of DA transmission in the NAc core. The precise significance of this adaptive change for the mechanism of drug addiction is unclear given the complexity and uncertainties surrounding the role of NAc core DA in responding but might be more directly related to instrumental performance.

Effects of amisulpride on consummatory negative contrast

Two groups of rats, 'shifted' (32-4% sucrose) and 'unshifted' (4-4% sucrose), were given access to sucrose solutions for 5 min/day for 10 days. On day 11, shifted animals had access to a devalued incentive (4% sucrose) and subgroups of each group received doses of amisulpride (10 or 60 mg/kg, i.p.) or its vehicle before a 10-min access period to sucrose solutions. Lick frequency was measured both pre- and post-shift. A high dose of amisulpride reduced successive negative contrast (SNC) after a brief period of exposure to the devalued stimulus, whereas a low dose had no effect. The acute effects of high doses of amisulpride seem to act on contrast effects in a similar way to anxiolytic compounds such as the benzodiazepine, chlordiazepoxide.

Amisulpride: a review of its use in the management of schizophrenia

Amisulpride, a substituted benzamide derivative, is a second-generation (atypical) antipsychotic. At low doses, it enhances dopaminergic neurotransmission by preferentially blocking presynaptic dopamine D2/D3 autoreceptors. At higher doses, amisupride antagonises postsynaptic dopamine D2 and D3 receptors, preferentially in the limbic system rather than the striatum, thereby reducing dopaminergic transmission. In patients with acute exacerbations of schizophrenia, the recommended dosage of amisulpride is 400 to 800 mg/day, although dosages < or =1200 mg/day may be administered. In comparative trials, amisulpride administered within this range (400 to 1200 mg/day) was as effective as haloperidol 5 to 40 mg/day, flupenthixol 25 mg/day and risperidone 8 mg/day in patients with acute exacerbations of schizophrenia with predominantly positive symptoms. Amisulpride was more effective than haloperidol but equally effective as risperidone in controlling negative symptoms. Amisulpride 400 to 800 mg/day was more effective than haloperidol, risperidone and flupenthixol in controlling affective symptoms in these patients. In randomised, double-blind trials involving patients with predominantly negative symptoms of schizophrenia, amisulpride 50 to 300 mg/day was more effective than placebo. Amisulpride is effective as maintenance therapy in patients with chronic schizophrenia. Long-term treatment with amisulpride was associated with improvements in quality of life and social functioning. Amisulpride is generally well tolerated. In well-controlled trials, the neurological tolerability profile (including ratings on extrapyramidal symptom scales) of amisulpride 400 to 1200 mg/day was superior to that of the conventional antipsychotics (haloperidol or flupenthixol), but was similar to that of the atypical antipsychotic risperidone. At low dosages of amisulpride (< or =300 mg/day), the incidence of adverse events (including extrapyramidal symptoms) reported with amisulpride was similar to that with placebo.

CONCLUSION

In comparative trials, amisulpride 400 to 1200 mg/day showed efficacy in reducing overall symptomatology and positive symptoms similar to that of conventional antipsychotics and newer atypical antipsychotics in patients with acute exacerbations of schizophrenia. Moreover, its effective alleviation of negative and affective symptoms, its lower association with extrapyramidal symptoms and loss of cognitive function than conventional antipsychotics and its long-term efficacy justifies consideration of the use of higher dosages of amisulpride in this group of patients. Consequently, the dosage of amisulpride that is recommended in patients with acute exacerbations of schizophrenia is 400 to 800 mg/day, although dosages < or =1200 mg/day may be administered. Lower dosages of amisulpride (50 to 300 mg/day) should be considered for the management of patients with negative symptoms of schizophrenia. Amisulpride is a first-line treatment option in the management of schizophrenia in the acute phase and for the maintenance of treatment response.

A single blind comparison of amisulpride, fluoxetine and clomipramine in the treatment of restricting anorectics

1. The study evaluated the efficacy of amisulpride, fluoxetine and clomipramine at the beginning of the re-feeding phase of the treatment of restricting anorexia nervosa according to DSM-IV criteria. 2. 13 patients, mean weight 37.61 kg +/- 9.80 SD, were treated with clomipramine at a mean dosage of 57.69 mg +/- 25.79 SD; 10 patients, mean weight 40.90 kg +/- 6.98 SD, were treated with fluoxetine at a mean dosage of 28.00 mg +/- 10.32 SD; 12 patients, mean weight 38.41 kg +/- 8.33 SD, were treated with amisulpride at a mean dosage of 50.00 mg +/- 0.00 SD. 3. Clinical evaluation was carried out under single-blind condition at basal time and after three months by a structured clinical interview, the Eating Disorder Interview based on Long Interval Follow-up Evaluation (LIFE II BEI). 4. Patients treated with amisulpride showed a more significant increase (p=0.016) of mean weight. Concerning weight phobia, body image disturbance and amenorrhoea, no significant difference resulted.

In vivo extrastriatal and striatal D2 dopamine receptor blockade by amisulpride in schizophrenia

Amisulpride, a substituted benzamide with high affinity for dopamine D2 and D3 receptors only, has been reported to have therapeutic effects on both negative and positive schizophrenic symptoms, although at distinct dose ranges (50-300 mg/day vs. 400-1,200 mg/day). The purpose of this study was to investigate the binding of amisulpride to extrastriatal (i.e., thalamus and temporal cortex) and striatal D2 dopamine receptors with respect to plasma amisulpride determinations. Ten patients with schizophrenia treated with amisulpride over a wide range of doses (25-1,200 mg/day) were studied. Positron emission tomography images were acquired by using 76Br-FLB-457, a highly specific antagonist of the D2 and D3 dopamine receptors. Binding indexes (BI) in the regions studied were estimated with reference to values from six healthy subjects. A curvilinear relationship was demonstrated between plasma concentration of amisulpride and the BI in extrastriatal regions. The BI also varied as a function of plasma concentration in striatum. Furthermore, the data provide evidence for different binding profiles: low plasma concentrations (28-92 ng/mL) induced marked extrastriatal binding and low striatal binding, whereas higher plasma concentrations (>153 ng/mL) induced marked binding both in extrastriatal and striatal regions. Dose-dependent differential binding profiles of amisulpride to D2 receptors in extrastriatal and striatal regions were demonstrated, and two therapeutic ranges of plasma concentrations for negative and positive schizophrenic symptoms, respectively, are suggested.

Effects of oil intake in the conditioned place preference test in mice

We investigated the effects of corn oil intake in the conditioned place preference (CPP) test in mice. Voluntary intake of corn oil in the light box in the CPP test showed place preference, but its peroral administration 60 min before conditioning did not show either place preference or aversion. Acquisition of the place preference by corn oil intake was blocked by i.p. injection of SCH 23390 (0.03 mg/kg) and haloperidol (0.1 mg/kg), but not by that of (+/-)-sulpiride (100 mg/kg), (-)-sulpiride (100 mg/kg), and L-741, 626 (1 mg/kg) 15 min before conditioning. These results suggest that stimulation of corn oil in the oral cavity, but not its postingestive effects, have positive reinforcing effects and the stimulation of corn oil is at least partly mediated via dopaminergic systems through the D(1) receptors. Moreover, the present results suggest that the CPP test is useful for the study of preferable stimulation and rewarding effects of food intake.

Pharmacological and molecular targets in the search for novel antipsychotics

The recent enthusiasm among clinicians for the so-called 'atypical antipsychotics' has both improved treatment for schizophrenic patients and provided a welcome stimulus for basic research on antipsychotic mechanisms. Even the newer drugs have shortcomings, and research is underway aimed at identifying novel agents with greater efficacy and safety. Much of this effort is directed towards compounds which, in addition to blocking dopamine receptors, also act on other neurotransmitter receptors such as 5-HT2, 5-HT1A and alpha2-adrenergic receptors. However, there is also a large amount of scientific activity seeking to discover and develop selective dopamine receptor subtype antagonists (including compounds which specifically block D3 or D4 receptors) or drugs that specifically target the dopamine autoreceptor. Finally, a number of drug development programmes are searching for non-dopaminergic antipsychotics. Drugs that do not have affinity for dopamine receptors but act through neurotensin, sigma or cannabinoid CB1 receptors or glutamatergic mechanisms are currently being evaluated. If any of these agents prove to have clinical efficacy this may lead to a third generation of antipsychotics. It is likely, however, that the mechanisms of action of such drugs will nevertheless imply the intimate involvement of dopaminergic pathways.

Pharmacology of sucrose-reinforced place-preference conditioning: effects of naltrexone

Two experiments investigated the role of the opioid system in sucrose-reinforced conditioned place preferences (CPPs) in rats. Experiment 1 examined the effects of a general opioid antagonist, naltrexone, on the expression of a CPP acquired in the absence of the drug. Subjects were trained to associate one compartment of a two-compartment chamber with sucrose and the other compartment with water. Rats displayed a preference for the sucrose-associated compartment in a choice test without sugar or water available following vehicle saline treatment. Naltrexone doses of 2.5 and 5.0 mg/kg reduced this preference for the sucrose-associated compartment. Experiment 2 examined the effects of naltrexone on the acquisition as well as the expression of CPPS. Different groups of rats received daily injections of either saline, 0.1, 1.0, or 5.0 mg/kg of naltrexone prior to each training session, and then these groups were given a choice test for the CPP after saline or naltrexone injections. Although naltrexone treatment attenuated the expression of CPPs in each group relative to saline treatment, there were no group differences during these tests in the magnitude of the preferences. Moreover, all groups displayed equal acquisition of CPPs despite the fact that naltrexone dose dependently decreased sucrose intake during the training phase. Together, the results indicate that the opioid system modulates the expression but not the acquisition of sucrose-reinforced CPPs.

Antidepressant-like activity of amisulpride in two animal models of depression

Clinical reports suggest that amisulpride, in addition to its antipsychotic efficacy, may also have antidepressant properties. The present study was designed to evaluate potential antidepressant-like activity of amisulpride in two behavioural procedures: the forced swim test (FST) and the chronic mild stress (CMS) model. The duration of immobility time in FST was reduced by subchronic (three injections over a 24 h period) administration of imipramine (10 mg/kg) and amisulpride (1 and 3 mg/kg), although the effect of imipramine was more potent. The 5 mg/kg dose of amisulpride was marginally effective and higher doses of 10 and 30 mg/kg were inactive. In CMS, the stress-induced decrease in the consumption of 1% sucrose solution was gradually reversed by chronic treatment with imipramine (10 mg/kg) and amisulpride (5 and 10 mg/kg). Lower (1 or 3 mg/kg) or higher (30 mg/kg) doses of amisulpride were inactive. The magnitude of the effect of active doses of amisulpride in the CMS model was comparable to that of imipramine but its onset of action was faster; at the most active dose of 10 mg/kg, amisulpride significantly increased the sucrose intake in stressed animals within 2 weeks of treatment while imipramine required 4 weeks before first effects on the stress-induced deficit in sucrose consumption could be observed. These results provide further support for clinical observations that amisulpride may possess potent and rapid antidepressant activity.

Effects of 50mg amisulpride on EEG, psychomotor and cognitive functions in healthy sleep-deprived subjects

Amisulpride, a substituted benzamide, binds selectively to the dopamine D2- and D3-receptors. It has higher affinity for limbic compared to striatal dopamine receptors in vivo. At low doses, amisulpride facilitates dopamine transmission via a selective blockade of presynaptic D2- and D3-receptors. Amisulpride is an active antipsychotic compound effective at low doses for negative symptoms and at high doses for positive symptoms of schizophrenia. The CNS profile of multiple doses of a low dosage regimen of amisulpride (50 mg once daily for 4 days) was assessed in a randomised, double-blind, 3-way crossover, placebo-controlled study carried out in 12 young sleep-deprived (for 36 h) subjects, using EEG and various measures of psychomotor and cognitive functions. Caffeine slow release (600 mg) was used as a positive reference. Multiple doses of 50 mg amisulpride once daily were devoid of any detrimental effects on EEG and psychomotor performance and cognitive function after total sleep deprivation. In addition, 50mg amisulpride partially antagonized the deleterious effects of sleep deprivation on EEG and subjective sedation as shown by trends, and a significant increase in EEG relative beta power and a decrease in subjective sedation. These effects were more pronounced at the end of sleep deprivation, suggesting possible alerting effects of amisulpride at this dose level. Caffeine significantly antagonized the detrimental effects of sleep deprivation on vigilance (increase in EEG beta waves, speed of reaction, sustained attention and reduction in subjective sedation). In conclusion, the present results demonstrate that 50 mg amisulpride is devoid of detrimental effects on EEG, psychomotor and cognitive performance after sleep deprivation, a situation well-known to amplify such effects if they exist. Moreover, some data suggest possible alerting effects of this low dosage regimen of amisulpride.

Dysthymia: clinical picture, extent of overlap with chronic fatigue syndrome, neuropharmacological considerations, and new therapeutic vistas

Dysthymia, as defined in the American Psychiatric Association and International Classification of Mental Disorders, refers to a prevalent form of subthreshold depressive pathology with gloominess, anhedonia, low drive and energy, low self-esteem and pessimistic outlook. Although comorbidity with panic, social phobic, and alcohol use disorders has been described, the most significant association is with major depressive episodes. Family history is loaded with affective, including bipolar, disorders. The latter finding explains why dysthymia, especially when onset is in childhood, can lead to hypomanic switches, both spontaneously and upon pharmacologic challenge in as many as 30%. Indeed, antidepressants from different classes -tricyclic antidepressants (TCAs), monoamine oxidase inhibitors (MAOIs), reversible inhibitors of monoamine oxidase A (RIMAs), selective serotonin-reuptake inhibitors (SSRIs) and, more recently, amisulpride, and spanning noradrenergic, serotonergic as well as dopaminergic mechanisms of action - have been shown to be effective against dysthymia in an average of 65% of cases. This is a promising development because social and characterologic disturbances so pervasive in dysthymia often, though not always, recede with continued pharmacotherapy beyond acute treatment. Despite symptomatic overlap of dysthymia with chronic fatigue syndrome - especially with respect to the cluster of symptoms consisting of low drive, lethargy, lassitude and poor concentration - neither the psychopathologic status, nor the pharmacologic response profile of the latter syndrome is presently understood. Chronic fatigue today is where dysthymia was two decades ago. We submit that the basic science - clinical paradigm that has proven so successful in dysthymia could, before too long, crack down the conundrum of chronic fatigue as well. At a more practical level, we raise the possibility that a subgroup within the chronic fatigue group represents a variant of dysthymia.

Involvement of serotonin and dopamine in the mechanism of action of novel antidepressant drugs: a review

Several hypotheses regarding the physiopathology of major depression exist. Attention has been focused on cerebral monoaminergic systems, the dysfunction of which is thought to underlie various aspects of depressive symptomatology. There is extensive literature describing the involvement of serotonergic and dopaminergic systems in the mechanism of action of antidepressant drugs. However, a unitary analysis of the data in terms of interaction between different monoaminergic systems is still lacking. In this article, studies reporting the biochemical, behavioral, and clinical effects of tricyclic antidepressants (TCAs), monoamine oxidase inhibitors (MAOIs), selective serotonin reuptake inhibitors (SSRIs), selective blockers of presynaptic dopamine (DA) receptors, and antagonists of serotonin-2 (5-hydroxytryptamine-2 [5-HT2]) receptors were reviewed. Analysis of the current literature indicates that long-term treatment with antidepressants causes adaptive changes of the serotonergic and dopaminergic systems. In particular, long-term administration of TCAs enhances the responsiveness of postsynaptic serotonin receptors to iontophoretically applied serotonin and potentiates the behavioral responses to both direct and indirect dopaminergic agonists. Repeated administration of SSRIs and MAOIs increases serotonergic transmission by desensitizing the inhibitory 5-HT1A somatodendritic and terminal 5-HT1B/1D autoreceptors. Selective blockers of DA autoreceptors exert their antidepressant effect by enhancing DA release. A similar mechanism of action could be hypothesized for 5-HT2 receptor antagonists. There is general agreement that the clinical effect of antidepressant drugs, which becomes evident only after long-term treatment, is caused by their ability to induce adaptive changes of the monoaminergic systems. Increases in both serotonergic and dopaminergic function have been consistently found after long-term treatment with various classes of antidepressant drugs. Recent studies have focused on the functional interaction between the serotonergic and dopaminergic systems to explain the mechanism of the antidepressant action of SSRIs and 5-HT2 antagonists.

Measuring reward with the conditioned place preference paradigm: a comprehensive review of drug effects, recent progress and new issues

This review gives an overview of recent findings and developments in research on brain mechanisms of reward and reinforcement from studies using the place preference conditioning paradigm, with emphasis on those studies that have been published within the last decade. Methodological issues of the paradigm (such as design of the conditioning apparatus, biased vs unbiased conditioning, state dependency effects) are discussed. Results from studies using systemic and local (intracranial) drug administration, natural reinforcers, and non-drug treatments and from studies examining the effects of lesions are presented. Papers reporting on conditioned place aversion (CPA) experiments are also included. A special emphasis is put on the issue of tolerance and sensitization to the rewarding properties of drugs. Transmitter systems that have been investigated with respect to their involvement in brain reward mechanisms include dopamine, opioids, acetylcholine, GABA, serotonin, glutamate, substance P, and cholecystokinin, the motivational significance of which has been examined either directly, by using respective agonist or antagonist drugs, or indirectly, by studying the effects of these drugs on the reward induced by other drugs. For a number of these transmitters, detailed studies have been conducted to delineate the receptor subtype(s) responsible for the mediation of the observed drug effects, particularly in the case of dopamine, the opioids, serotonin and glutamate. Brain sites that have been implicated in the mediation of drug-induced place conditioning include the 'traditional' brain reward sites, ventral tegmental area and nucleus accumbens, but the medial prefrontal cortex, ventral pallidum, amygdala and the pedunculopontine tegmental nucleus have also been shown to play important roles in the mediation of place conditioning induced by drugs or natural reinforcers. Thus, although the paradigm has also been criticized because of some inherent methodological problems, it is clear that during the past decade place preference conditioning has become a valuable and firmly established and very widely used tool in behavioural pharmacology and addiction research.

Continued trends in the conditioned place preference literature from 1992 to 1996, inclusive, with a cross-indexed bibliography

In light of the overwhelming response to the previous publication in Neuroscience and Biobehavioral Reviews (1993, 17, 21-41) regarding trends in place conditioning (either preference or aversion), the present work constitutes a five-year follow-up to review the empirical research in this behavioral paradigm from 1992 to 1996, inclusively. The behavioral technique has grown as indicated by the number of publications over the last five years which equals those authored over the 35 years covered by our last survey. The previous work used descriptive statistics to explore topical issues, whereas the present work discusses trends since that time and hopes to provide an exhaustive bibliography of the CPP literature, including articles, published abstracts, book chapters and reviews, as well as providing a cross-index of identified key words/drugs tested.

Anhedonia and relapse in alcoholism

The aim of this study was to determine the role of anhedonia among other psychopathological dimensions in the relapse of alcoholics 6 months after withdrawal. Psychometric assessments included: the Social and Physical Anhedonia Scales, the Sensation Seeking Scale, the Pleasure-Displeasure Scale (including Fawcett-Clark's Pleasure Scale), the Depressive Mood Scale, the Thymasthenic Syndrome Rating Scale and the Comprehensive Psychopathological Rating Scale. Forty-four alcoholics participated in the study. The baseline values recorded during the second week of treatment showed that the more anhedonic the alcoholics were, the less they sought sensations. Type 2 alcoholics (Cloninger's classification) scored higher on the Thrill and Adventure Seeking Subscale. Relapsed alcoholics had higher baseline values on the Thrill and Adventure Seeking Subscale. This was in agreement with the step-wise discriminant analysis which showed that this subscale was the main variable that differentiated abstinent alcoholics from those who relapsed. Our results indicate that anhedonia does not predict relapse.

Amisulpride, and atypical antipsychotic, in the treatment of acute episodes of schizophrenia: a dose-ranging study vs. haloperidol. The Amisulpride Study Group

This 4-week, double-blind, randomized study was undertaken to determine the dose-response relationship of amisulpride in 319 patients with acute exacerbation of schizophrenia. Fixed doses of amisulpride (400, 800 and 1200 mg/day) and haloperidol (16 mg/day) were compared to amisulpride, 100 mg/day, as a potentially subtherapeutic dose. Efficacy data (BPRS total score and PANSS positive subscale) in the amisulpride groups generated a bell-shaped dose-response curve, with 400 mg/day and 800 mg/day being the most effective treatments for positive symptoms. Parkinsonism did not increase significantly between baseline and endpoint with amisulpride 400, 800 and 1200 mg/day compared to the amisulpride 100 mg/day group, whereas the difference was significant for haloperidol (P<0.05). It is concluded that amisulpride 400 mg and 800 mg/day is highly effective in treating the positive symptoms of schizophrenia, with less extrapyramidal side-effects than haloperidol 16 mg/day.

Effects of amisulpride, an atypical antipsychotic which blocks preferentially presynaptic dopamine autoreceptors, on integrated functional cerebral activity in the rat

Amisulpride, a benzamide derivative with an atypical neuroleptic profile relieves the negative symptoms of schizophrenia when administered at low doses (50-150 mg). In an attempt to define the anatomical substrates involved in this action we have studied the effects of amisulpride on regional cerebral glucose utilisation (RCGU) in the awake lightly restrained rat, by quantitative autoradiography using [14C]2-deoxyglucose ([14C]2-DG). Amisulpride was administered 1 h before [14C]2DG i.v. injection, at a dose of 5 mg/kg which resulted in a striatal D2 receptor occupancy of 10% similar to that induced by doses of this compound used for the treatment of negative symptoms of schizophrenia. Amisulpride induced significant RCGU increases in cortical areas, in visual relays, in auditory structures and in several limbic structures. The pattern of changes in RCGU seen with amisulpride clearly differs from that of haloperidol, given at a dose resulting in a similar occupancy of striatal D2 receptors (0.01 mg/kg), which was mostly ineffective. The amisulpride-induced activation of RCGU in specific brain areas involved in the control of cognitive functions and motivational and emotional behavior, may at least in part, explain the efficacy of this compound in the treatment of negative symptoms of schizophrenia.

Bidirectional effects of dopamine D2 receptor antagonists on responding for a conditioned reinforcer

In general, the administration of dopamine (DA) antagonists has been shown to result in the attenuation of reward processes. Recently, however, it has been suggested that low doses of DA antagonists can enhance the incentive value of a primary reinforcer. The present study examined the effect of DA receptor antagonists on responding for a conditioned stimulus (CS) and compared their effects to that produced by d-amphetamine. For 12 days, food-deprived rats were trained to associate a CS with a food reward. In the test phase, the CS was presented following a response on one of two levers (CR), whereas responding on the other lever (NCR) had no consequence. Low doses of d-amphetamine (0.5 mg/kg), sulpiride (4 mg/kg), pimozide (0.025 mg/kg), and raclopride (0.05 mg/kg) selectively enhanced responding on CR. A low dose of haloperidol (0.01 mg/kg) led to a nonspecific increase in lever responding. Treatment with larger doses of these compounds as well as with the D1 antagonist SCH23390 attenuated responding on CR. Both CR and NCR responding were reduced following administration of higher doses of d-amphetamine. Results indicate that responding for a conditioned reinforcer is potentiated following administration of low doses of D2 receptor antagonists, suggesting that D2 receptor blockade can facilitate incentive motivation.