Extracellular dopamine in the rat prefrontal cortex during reward-, punishment- and novelty-associated behaviour. Effects of diazepam

Attenuation of Spatial Memory in 5xFAD Mice by Halting Cholinesterases, Oxidative Stress and Neuroinflammation Using a Cyclopentanone Derivative

Alzheimer's disease (AD) is an irreversible and chronic neurological disorder that gradually destroys memory and thinking skills. The research study was designed to investigate the underlying molecular signaling involved in the neuroprotective effects of cyclopentanone derivative i.e., 2-(hydroxyl-(3-nitrophenyl)methyl)cyclopentanone (3NCP) as a therapeutic agent for AD. In this study, In vivo studies were carried out on a well-known 5xFAD mice model using different behavioural test models such as open field, rotarod, Morris water maze (MWM), and Y-maze tests. Furthermore, in vitro cholinesterase inhibition activity assays were carried out. The frontal cortex (FC) and hippocampus (HC) homogenates were tested for the levels/activities of cholinesterases, glutathione (GSH), glutathione S-transferase (GST), and catalase. Furthermore, the hippocampal expression of inflammatory cytokines was observed via RT-PCR and western blot. The results of in vivo studies show an enhancement in the learning behavior. The 3NCP treatment reduced latency time in MWM and Y-maze tests, also increase spontaneous alternation indicate significant effect of 3NCP on memory. Furthermore, open field and rotarod studies revealed that 3NCP does not cause motor coordination deficit. The results of the in vitro studies revealed that the IC50 values of the 3NCP against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) were 16.17 and 20.51 µg/mL, respectively. This decline in AChE and BChE was further supported by ex vivo studies. Further, the 3NCP mitigates the GSH level, GST, and catalase activities in HC and FC. The mRNA and protein expression of inflammatory cytokines (IL-1β, IL-6, TNF-α) markedly declined in RT-PCR and western blotting. The results of the current study conclusively demonstrate that 3NCP reduces oxidative stress and mitigates neuroinflammation in 5xFAD mice, implying that 3NCP may be a potential therapeutic candidate for AD treatment in the future.

Early postnatal neuroactive steroid manipulation differentially affects recognition memory and passive avoidance performance in male rats

Early postnatal neuroactive steroids (NAS) play a significant role in the neurodevelopment. Their alteration can modify adult behavior, such as anxiety or learning. For this reason, we set out to observe if neonatal NAS levels alteration affects two types of learning implying low or high levels of emotional content, such as recognition memory and aversive learning respectively. Thus, we tested allopregnanolone or finasteride administered from postnatal days 5-9. In adulthood, recognition memory was assessed using the object recognition test, as well as aversive learning throughout the passive avoidance test (PA). Because of the important emotional component of PA, which can be influencing learning, we evaluated anxiety-like behavior by means of the open field test (OF). The results indicated that those animals administered with finasteride showed higher recognition levels of a familiar object. On the other hand, they showed an impairment in a stressful learning, such as PA. However, no effects of finasteride were observed on anxiety-like behavior in OF, despite it has been reported that neonatal finasteride treatment can promote an anxiety-like profile in the elevated plus-maze test in adulthood. Regarding neonatal allopregnanolone, animals showed higher levels in OF exploration only when they were already familiar with the apparatus. Furthermore, neonatal allopregnanolone did not affect recognition memory or aversive learning. In conclusion, the neonatal NAS manipulation by means of finasteride differently affected two types of learning implying distinct stress levels. Altogether, the results show the importance of the emotional content to explain the effects of neonatal NAS manipulation on learning.

Therapeutic efficacy of environmental enrichment for substance use disorders

Addiction to drug and alcohol is regarded as a major health problem worldwide for which available treatments show limited effectiveness. The biggest challenge remains to enhance the capacities of interventions to reduce craving, prevent relapse and promote long-term recovery. New strategies to meet these challenges are being explored. Findings from preclinical work suggest that environmental enrichment (EE) holds therapeutic potential for the treatment of substance use disorders, as demonstrated in a number of animal models of drug abuse. The EE intervention introduced after drug exposure leads to attenuation of compulsive drug taking, attenuation of the rewarding (and reinforcing) effects of drugs, reductions in control of behavior by drug cues, and, very importantly, relapse prevention. Clinical work also suggests that multidimensional EE interventions (involving physical activity, social interaction, vocational training, recreational and community involvement) might produce similar therapeutic effects, if implemented continuously and rigorously. In this review we survey preclinical and clinical studies assessing the efficacy of EE as a behavioral intervention for substance use disorders and address related challenges. We also review work providing empirical evidence for EE-induced neuroplasticity within the mesocorticolimbic system that is believed to contribute to the seemingly therapeutic effects of EE on drug and alcohol-related behaviors.

Long-Term Citalopram Treatment Alters the Stress Responses of the Cortical Dopamine and Noradrenaline Systems: the Role of Cortical 5-HT1A Receptors

BACKGROUND

Cortical dopamine and noradrenaline are involved in the stress response. Citalopram, a selective serotonin reuptake inhibitor, has direct and indirect effects on the serotonergic system. Furthermore, long-term treatment with citalopram affects the dopamine and noradrenaline systems, which could contribute to the therapeutic action of antidepressants.

METHODS

The effects of long-term treatment with citalopram on the responses of the dopamine and noradrenaline systems in the rat prefrontal cortex to acute handling stress were evaluated using in vivo microdialysis.

RESULTS

Acute handling stress increased dopamine and noradrenaline levels in the prefrontal cortex. The dopamine and noradrenaline responses were suppressed by local infusion of a 5-HT1A receptor agonist, 7-(Dipropylamino)-5,6,7,8-tetrahydronaphthalen-1-ol;hydrobromide, into the prefrontal cortex. The dopamine response was abolished by long-term treatment with citalopram, and the abolished dopamine response was reversed by local infusion of a 5-HT1A receptor antagonist, (Z)-but-2-enedioic acid;N-[2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl]-N-pyridin-2-ylcyclohexanecarboxamide into the prefrontal cortex. On the other hand, long-term treatment with citalopram reduced the basal noradrenaline levels (approximately 40% of the controls), but not the basal dopamine levels. The noradrenaline response was maintained despite the low basal noradrenaline levels. Signaling from the 5-HT1A receptors and α2-adrenoceptors was not involved in the decrease in the basal noradrenaline levels but partially affected the noradrenaline response.

CONCLUSIONS

Chronic citalopram treatment differentially suppresses the dopamine and noradrenaline systems in the prefrontal cortex, and the dopamine stress response was preferentially controlled by upregulating 5-HT1A receptor signaling. Our findings provide insight into how antidepressants modulate the dopamine and noradrenaline systems to overcome acute stress.

The dopaminergic response to acute stress in health and psychopathology: A systematic review

Previous work in animals has shown that dopamine (DA) in cortex and striatum plays an essential role in stress processing. For the first time, we systematically reviewed the in vivo evidence for DAergic stress processing in health and psychopathology in humans. All studies included (n studies=25, n observations=324) utilized DA D2/3 positron emission tomography and measured DAergic activity during an acute stress challenge. The evidence in healthy volunteers (HV) suggests that physiological, but not psychological, stress consistently increases striatal DA release. Instead, increased medial prefrontal cortex (mPFC) DAergic activity in HV was observed during psychological stress. Across brain regions, stress-related DAergic activity was correlated with the physiological and psychological intensity of the stressor. The magnitude of stress-induced DA release was dependent on rearing conditions, personality traits and genetic variations in several SNPs. In psychopathology, preliminary evidence was found for stress-related dorsal striatal DAergic hyperactivity in psychosis spectrum and a blunted response in chronic cannabis use and pain-related disorders, but results were inconsistent. Physiological stress-induced DAergic activity in striatum in HV may reflect somatosensory properties of the stressor and readiness for active fight-or-flight behavior. DAergic activity in HV in the ventral striatum and mPFC may be more related to expectations about the stressor and threat evaluation, respectively. Future studies with increased sample size in HV and psychopathology assessing the functional relevance of stress-induced DAergic activity, the association between cortical and subcortical DAergic activity and the direct comparison of different stressors are necessary to conclusively elucidate the role of the DA system in the stress response.

Regionally selective requirement for D1/D5 dopaminergic neurotransmission in the medial prefrontal cortex in object-in-place associative recognition memory

Object-in-place (OiP) memory is critical for remembering the location in which an object was last encountered and depends conjointly on the medial prefrontal cortex, perirhinal cortex, and hippocampus. Here we examined the role of dopamine D₁/D₅ receptor neurotransmission within these brain regions for OiP memory. Bilateral infusion of D₁/D₅ receptor antagonists SCH23390 or SKF83566 into the medial prefrontal cortex, prior to memory acquisition, impaired OiP performance following a 5 min or 1 h delay. Retrieval was unaffected. Intraperirhinal or intrahippocampal infusions of SCH23390 had no effect. These results reveal a selective role for D₁/D₅ receptors in the mPFC during OiP memory encoding.

Potent attenuation of context fear by extinction training contiguous with acquisition

Studies on the behavioral mechanisms underlying contextual fear conditioning (CFC) have demonstrated the importance of preshock context exposure in the formation of aversive context memories. However, there has been comparatively little investigation of the effects of context exposure immediately after the shock. Some models predict that nonreinforced context exposure at the end of the acquisition session will strongly influence the strength of conditioning and/or recruit distinct neural mechanisms relative to extinction after acquisition. Here we investigate the effects of manipulating postshock context exposure on CFC in mice. Prolonging the period of context exposure immediately following the shock caused a significant and durable reduction in conditioned fear. This immediate postshock context exposure was more effective at attenuating conditioned fear than was an equivalent amount of context exposure a day or more after acquisition. The results suggest that nonreinforced exposure to the context influences conditioned fear through distinct mechanisms depending on whether it occurs during acquisition or after it. The superiority of immediate postshock context exposure was specific to single-shock CFC; in two-shock CFC, immediate and delayed postshock context exposure had similar effects. Consistent with previous reports, we hypothesize that the effectiveness of extinction is modulated by emotional state, and procedures engendering higher postshock freezing (such as two-shock CFC) are associated with weaker immediate extinction.

Involvement of the cannabinoid CB1 receptor in modulation of dopamine output in the prefrontal cortex associated with food restriction in rats

Increase in dopamine output on corticolimbic structures, such as medial prefrontal cortex (mPFC) and nucleus accumbens, has been related to reward effects associated with palatable food or food presentation after a fasting period. The endocannabinoid system regulates feeding behavior through a modulatory action on different neurotransmitter systems, including the dopaminergic system. To elucidate the involvement of type 1 cannabinoid receptors in the regulation of dopamine output in the mPFC associated with feeding in hungry rats, we restricted the food availability to a 2-h period daily for 3 weeks. In food-restricted rats the extracellular dopamine concentration in the mPFC increased starting 80 min before food presentation and returned to baseline after food removal. These changes were attenuated in animals treated with the CB1 receptor antagonist SR141716. To better understand how food restriction can change the response of mesocortical dopaminergic neurons, we studied several components of the neuronal circuit that regulates dopamine output in the mPFC. Patch-clamp experiments revealed that the inhibitory effect of the CB1 receptor agonist WIN 55,212-2 on GABAergic sIPSC frequency was diminished in mPFC neurons of FR compared to fed ad libitum rats. The basal sIPSC frequency resulted reduced in mPFC neurons of food-restricted rats, suggestive of an altered regulation of presynaptic GABA release; these changes were accompanied by an enhanced excitability of mPFC and ventral tegmental area neurons. Finally, type 1 cannabinoid receptor expression in the mPFC was reduced in food-restricted rats. Together, our data support an involvement of the endocannabinoid system in regulation of dopamine release in the mPFC through changes in GABA inhibitory synapses and suggest that the emphasized feeding-associated increase in dopamine output in the mPFC of food-restricted rats might be correlated with an altered expression and function of type 1 cannabinoid receptor in this brain region.

Neuropeptide S stimulates dopaminergic neurotransmission in the medial prefrontal cortex

Neuropeptide S (NPS) is known to produce anxiolytic-like effects and facilitate extinction of conditioned fear. Catecholaminergic neurotransmission in the medial prefrontal cortex (mPFC) has been suggested to be crucially involved in these brain functions. In the current study, we investigated the effect of NPS on the release of dopamine and serotonin in the mPFC by in vivo microdialysis in rats. Central administration of NPS dose-dependently enhanced extracellular levels of dopamine and its major metabolite 3,4-dihydroxyphenylacetic acid, with maximal effects lasting up to 120 min. In contrast, no effect on serotonergic neurotransmission was detected. Dopamine release in the mPFC has been previously linked to modulation of anxiety states and fear extinction. The present results may thus provide a physiological and anatomical basis for the reported effects of NPS on these behaviors.

Binge-like eating in mice

OBJECTIVE

Given the lack of reliable murine model of binge-like eating, we tried to induce this pathological behavior in mice.

METHOD

We used an experimental protocol mimicking the etiological factors involved in the development of binge eating in humans, that is, food restriction, refeeding (R-R) in presence of high palatable food, and stress (S).

RESULTS

Mice subjected to at least three cycles of R-R plus S (forced swimming stress), showed a binge-like behavior evident as early as 4 h, persisting 24 h after stress application and not associated to depressive-like behavior. However, after the third R-R/S cycle, food intakes of mice returned to normal levels.

DISCUSSION

(i) at least three cycles of R-R plus S are required to promote abnormal eating in mice, (ii) this is not associated to depressive-like behaviors, and (iii) the enhanced pathological behavior showed a transient nature not persisting after the third R-R/S cycle.

Prefrontal dopamine efflux during exposure to drug-associated contextual cues in rats with prior repeated methamphetamine

Conditioned stimulus-reward response and prefrontal dopamine efflux under context previously paired with methamphetamine administration were assessed in rats with or without prior sensitizing regimen. Sensitizing pretreatment was administered with methamphetamine (1mg/kg, every other day for six sessions) for behavioral sensitization. The animals received methamphetamine (1mg/kg) or saline injection (each for six sessions) to pair with distinct contexts on alternate days to induce conditioned place preference. Then, dopamine outflows in the medial prefrontal cortex were analyzed on the next day via microdialysis study as animals exposed to the methamphetamine or saline-paired context, respectively. Prefrontal DA efflux increased in those rats without sensitizing pretreatment, while they occupied the methamphetamine-paired chamber. The rats with prior sensitizing regimen demonstrated more robust conditioned place preference than those without pretreatment, however, their dopamine efflux was attenuated, while remaining in methamphetamine-paired context. It is suggested that the attenuated responsiveness of mesocortical dopamine transmission in prior sensitized rats may, at least in part, be responsible for their augmented conditioned place preference, which resulted from activation of related brain areas that together strengthen the associative learning to drug-related stimuli. This paradigm may reflect a dysregulated prefrontal function in the methamphetamine abusers.

Environmental enrichment decreases responding for visual novelty

Previous research has demonstrated that rats reared in an enriched condition (EC) with novel objects and social partners self-administer less amphetamine compared to rats raised in an isolated condition (IC). However, it is unclear if the enrichment-induced decrease in stimulant self-administration generalizes to non-drug rewards such as those provided by novel environmental stimuli. In the current study, EC, IC, and social condition (SC) rats were raised from 21 to 51 days of age before being tested in a two-lever operant conditioning chamber in which responding on one lever (active lever) resulted in illumination of a cue light. In Experiment 1, rats were initially assessed for baseline responding (no contingency) and then the contingent light was introduced. EC rats responded less than IC rats for the contingent light stimulus; however, EC rats also displayed a lower rate of baseline responding. In Experiment 2, rats were trained initially to lever press for a sucrose reward to decrease differences in baseline responding. While sucrose pretraining decreased baseline response differences between groups, EC rats still responded less for the contingent light stimulus than IC or SC rats. These results suggest that environmental enrichment decreases the incentive value of visual novelty.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Benzodiazepine effect of 125I-iomazenil–benzodiazepine receptor binding and serum corticosterone level in a rat model

To test the change in free or unoccupied benzodiazepine receptor (BZR) density in response to diazepam, we investigated (125)I-iomazenil ((125)I-IMZ) binding and serum corticosterone levels in a rat model. Wistar male rats, which received psychological stress using a communication box for 5 days, were divided into two groups according to the amount of administered diazepam: no diazepam [D (0)] group and 10 mg/kg per day [D (10)] group of 12 rats each. The standardized uptake value (SUV) of (125)I-IMZ of the D (10) group were significantly lower (P < .05) than those of the D (0) group in the frontal, parietal and temporal cortices, globus pallidus, hippocampus, amygdala and hypothalamus. The serum corticosterone level ratio in the D (10) group was significantly lower than that in the D (0) group (P < .05). From the change in serum corticosterone levels, diazepam attenuated the psychological stress produced by the physical stress to animals in adjacent compartments. From the reduced binding of (125)I-IMZ, it is clear that diazepam competed with endogenous ligand for the free BZR sites, and the frontal, parietal and temporal cortices, globus pallidus, hippocampus, amygdala and hypothalamus are important areas in which (125)I-IMZ binding is strongly affected by administration of diazepam.

Sensitivity to reward: implications for overeating and overweight

Sensitivity to reward (STR)-a personality trait firmly rooted in the neurobiology of the mesolimbic dopamine system-has been strongly implicated in the risk for addiction. This construct describes the ability to derive pleasure or reward from natural reinforcers like food, and from pharmacologic rewards like addictive drugs. Recently experts in the field of addiction research have acknowledged that psychomotor stimulant drugs are no longer at the heart of all addictions, and that brain circuits can also be deranged with natural rewards like food. The present study tested a model in which STR was expected to relate positively to overeating, which in turn would be associated with higher body weight in woman aged 25-45 years. As predicted, STR was correlated positively with measures of emotional overeating. Also, overweight woman were significantly more sensitive to reward than those of normal weight. Interestingly, however, the obese woman (Body Mass Index>30) were more anhedonic than the overweight woman (Body Mass Index>25<30). These findings are discussed in the context of neuroadaptations to overactivity of brain reward circuits. Results also indicate that STR may serve as a risk factor for overeating and overweight, especially in cultures such as ours where palatable, calorically-dense food is plentiful.

Blockade by the cannabinoid CB1 receptor antagonist, rimonabant (SR141716), of the potentiation by quinelorane of food-primed reinstatement of food-seeking behavior

It has been shown previously that the selective cannabinoid CB1 receptor antagonist, rimonabant (SR141716), reduced the intake of palatable food as well as the self-administration of several drugs of abuse, suggesting that endocannabinoid systems play a role in brain reward function. The present study investigated whether a cannabinoid step was involved in food-seeking behavior induced by explicit stimuli, using an operant reinstatement procedure in rats. Experimental sessions consisted of a 15-min food rewarded period, followed by a 45-min extinction period. Rimonabant did not affect the response reinstatement induced by noncontingent delivery of food pellets, but prevented (0.03-0.3 mg/kg) the potentiation by quinelorane, a dopamine D3 receptor-preferring agonist, of food-seeking behavior. A possible link between cannabinoid processes and D3- and/or D2-mediated dopaminergic transmission was further investigated by studying Fos protein expression in cortico-limbic structures in D3 (D3-/-) and D2 (D2-/-) knockout mice. Rimonabant (10 mg/kg) increased Fos immunoreactivity in the prefrontal cortex (pFCortex) and in the shell but not the core of the nucleus accumbens (NAcc). Fos induction by this dose of rimonabant was not seen in mice lacking CB1 receptors, providing clear evidence for the involvement of CB1 receptors. In the NAcc shell, the effect of rimonabant was suppressed in D3-/-, but remained unchanged in D2-/- mice. In contrast, Fos expression by rimonabant in the pFCortex was impervious to D2 or D3 receptor deletion. In conclusion, these data indicate first that rimonabant prevented the enhancement by quinelorane of the appetitive value of food pellets unexpectedly delivered during extinction and second that rimonabant effects might involve D3 receptor-mediated processes. Overall, these results are consistent with the notion that endocannabinoid functions control brain reward processes and in particular the capacity of explicit stimuli to precipitate food-seeking behavior.

Behavioral Responses Are Altered in Piglets with Decreased Frontal Cortex Docosahexaenoic Acid

Docosahexaenoic acid [22:6(n-3)] is required in large amounts for membrane lipid synthesis during brain growth. The functional importance of differences in dietary fatty acid intakes that alter brain 22:6(n-3), however, is not well understood. We used a dietary approach to manipulate 22:6(n-3) in piglet brain and assessed the effects on behavior and change in behavior on an elevated plus maze after administration of L-dihydroxyphenylalanine (L-Dopa) or sulperide, a dopamine D2 receptor blocker. Piglets were fed 1.2% energy 18:2(n-6) and 0.05% energy 18:3(n-3) (low PUFA), or 10.7% energy 18:2(n-6), 1.1% energy 18:3(n-3), 0.3% energy 20:4(n-6) and 0.3% energy 22:6(n-3) (high PUFA) from 1 d of age and behavior assessed at 18-22 d of age. At 30 d of age, frontal cortex dopamine, and phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidyethanolamine (PE) and phosphatidylinositol (PI) fatty acids were quantified. Piglets fed the low PUFA diet had fewer arm entries on the maze than piglets fed the high PUFA diet, P = 0.02. L-Dopa increased the open (P = 0.005) and closed (P = 0.04) arm entries by piglets fed the low PUFA diet. Behavior did not differ between piglets fed the low and high PUFA diets when given L-Dopa. Frontal cortex PC, PS and PE 22:6(n-3) was lower and 22:5(n-6) was higher in piglets fed the low compared with the high PUFA diet, P < 0.01. Our work establishes the neonatal piglet as a model with which to study the behavioral effects of diet-induced changes in brain 22:6(n-3), and provides functional evidence that brain 22:6(n-3) is important in central dopamine metabolism.

Facilitation of appetitive pavlovian conditioning by d-amphetamine in the shell, but not the core, of the nucleus accumbens

The effects of postsession d-amphetamine within subregions of the ventral and dorsal striatum on appetitive Pavlovian learning were assessed. Rats acquired a conditioned approach response on presentation of a stimulus predictive of 10% sucrose solution (unconditioned stimulus [US]), but not during equally frequent presentations of a stimulus uncorrelated with the US. In Experiment 1, postsession d-amphetamine infusions enhanced acquisition of conditioned responding, with no effect on control measures. In Experiment 2, rats received postsession d-amphetamine in the accumbens shell or core. Shell infusions facilitated conditioning; core infusions did not. In Experiment 3, dorsomedial striatal infusions of d-amphetamine also were ineffective. In sum, dopaminergic activation within the shell, but not the core, of the nucleus accumbens facilitates the acquisition of a Pavlovian association.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

The Vogel conflict test: procedural aspects, gamma-aminobutyric acid, glutamate and monoamines

A multitude of mechanisms are involved in the control of emotion and in the response to stress. These incorporate mediators/targets as diverse as gamma-aminobutyric acid (GABA), excitatory amino acids, monoamines, hormones, neurotrophins and various neuropeptides. Behavioural models are indispensable for characterization of the neuronal substrates underlying their implication in the etiology of anxiety, and of their potential therapeutic pertinence to its management. Of considerable significance in this regard are conflict paradigms in which the influence of drugs upon conditioned (trained) behaviours is examined. For example, the Vogel conflict test, which was introduced some 30 years ago, measures the ability of drugs to release the drinking behaviour of water-deprived rats exposed to a mild aversive stimulus ("punishment"). This model, of which numerous procedural variants are discussed herein, has been widely used in the evaluation of potential anxiolytic agents. In particular, it has been exploited in the characterization of drugs interacting with GABAergic, glutamatergic and monoaminergic networks, the actions of which in the Vogel conflict test are summarized in this article. More recently, the effects of drugs acting at neuropeptide receptors have been examined with this model. It is concluded that the Vogel conflict test is of considerable utility for rapid exploration of the actions of anxiolytic (and anxiogenic) drugs. Indeed, in view of its clinical relevance, broader exploitation of the Vogel conflict test in the identification of novel classes of anxiolytic agents, and in the determination of their mechanisms of action, would prove instructive.

The open field as a paradigm to measure the effects of drugs on anxiety-like behaviors: a review

The open field is a very popular animal model of anxiety-like behavior. An overview of the literature on the action elicited by effective or putative anxiolytics in animal subjected to this procedure indicates that classical treatments such as benzodiazepine receptor full agonists or 5-HT(1A) receptor full or partial agonists elicit an anxiolytic-like effect in this procedure in most cases (approximately 2/3). However, compounds (triazolobenzodiazepines such as adinazolam and alprazolam, selective serotonin reuptake inhibitors) that have a different spectrum of therapeutic efficacy in anxiety disorders such as panic attacks, generalized anxiety disorder or obsessive-compulsive disorder were poorly effective as anxiolytics in the open field test, suggesting that this paradigm may not model features of anxiety disorders. The procedure is also relevant for the study of compounds endowed with anxiogenic effects, as such effects were detected after treatments with benzodiazepine receptor inverse agonists or with corticotropin releasing factor (CRF) receptor agonists.

Distinct pattern of c-fos mRNA expression after systemic and intra-accumbens amphetamine and MK-801

Pharmacological manipulation of both dopamine and glutamate systems affects motor responses in laboratory animals. The two systems, however, seem to act in opposite ways, since direct or indirect activation of dopamine receptors induces similar stimulatory effects to those seen following blockade of N-methyl-D-aspartate receptors. In the present study we compared the pattern of c-fos activation induced by systemic and intra-accumbens administration of the non-competitive N-methyl-D-aspartate antagonist MK-801 and the indirect dopamine agonist amphetamine. Systemic MK-801 induced c-fos mRNA expression in the motor cortex and preferentially in the motor thalamus, i.e. ventrolateral nucleus. Systemic amphetamine, on the other hand, enhanced c-fos mRNA expression in the shell of the accumbens and in limbic thalamic nuclei such as the anteroventral and anterodorsal nuclei. The main effect observed after intra-accumbens administrations of either drug was enhanced c-fos expression in the thalamus, somewhat similar to what seen following systemic administration. In fact also in this case there was a preferential activation of the limbic thalamus by amphetamine and the motor thalamus by MK-801. The present results confirm that different neural substrates underlie behavioral effects induced by systemic administrations of N-methyl-D-aspartate receptor antagonists and dopamine agonists. Further they suggest that intra-accumbens manipulation of the two neural systems could affect different efferent pathways from this structure activating different thalamic targets.