Binge-eating disorder: Clinical and therapeutic advances.

Binge-eating disorder (BED) is the most prevalent eating disorder with estimates of 2-5% of the general adult population. Nonetheless, its pathophysiology is poorly understood. Furthermore, there exist few therapeutic options for its effective treatment. Here we review the current state of binge-eating neurobiology and pharmacology, drawing from clinical therapeutic, neuroimaging, cognitive, human genetic and animal model studies. These studies, which are still in their infancy, indicate that while there are many gaps in our knowledge, several key neural substrates appear to underpin binge-eating and may be conserved between human and animals. This observation suggests that behavioral intermediate phenotypes or endophenotypes relevant to BED may be modeled in animals, facilitating the identification and testing of novel pharmacological targets. The development of novel, safe and effective pharmacological therapies for the treatment of BED will enhance the ability of clinicians to provide optimal care for people with BED.

Investigation of impulsivity in binge-eating rats in a delay-discounting task and its prevention by the d-amphetamine prodrug, lisdexamfetamine.

Freely-fed, female, rats were trained in a two-lever, delay-discounting task: one lever delivered a single chocolate-flavoured pellet immediately and the other a three-pellet reward after increasing delay (0, 4, 8, 16, 32 s). Rats were divided into two groups (i.e. binge-eating rats given irregular, limited access to chocolate in addition to normal chow and controls maintained on normal chow). Both groups exhibited increased preference for the immediate reward as the delay interval was lengthened. The discounting rate was significantly greater in binge-eating rats than non-binge-eating controls, especially as the behaviour became more established indicating that increased impulsivity and intolerance of delayed reward are part of the psychopathology of binge-eating. Lisdexamfetamine (0.8 mg/kg, orally ( d-amphetamine base)) reversed the reduced preference of binge-eating rats for larger rewards at delay intervals of 4 s, 8 s and 32 s and across all sessions. Lisdexamfetamine-treated binge-eating rats consumed the same number of pellets as vehicle-treated, binge-eating rats and non-binge-eating controls eliminating the possibility lisdexamfetamine's actions on appetite or satiety mediated its effects on operant responding for food pellets in delay-discounting. In summary, binge-eating rats showed increased impulsive choice compared with non-binge-eating controls that was reversed by lisdexamfetamine, complementing results showing lisdexamfetamine reduced impulsiveness scores in patients with binge-eating disorder.

Dopamine and µ-opioid receptor dysregulation in the brains of binge-eating female rats - possible relevance in the psychopathology and treatment of binge-eating disorder.

Adult, female rats given irregular, limited access to chocolate develop binge-eating behaviour with normal bodyweight and compulsive/perseverative and impulsive behaviours similar to those in binge-eating disorder. We investigated whether (a) dysregulated central nervous system dopaminergic and opioidergic systems are part of the psychopathology of binge-eating and (b) these neurotransmitter systems may mediate the actions of drugs ameliorating binge-eating disorder psychopathology. Binge-eating produced a 39% reduction of striatal D1 receptors with 22% and 23% reductions in medial and lateral caudate putamen and a 22% increase of striatal µ-opioid receptors. There was no change in D1 receptor density in nucleus accumbens, medial prefrontal cortex or dorsolateral frontal cortex, striatal D2 receptors and dopamine reuptake transporter sites, or µ-opioid receptors in frontal cortex. There were no changes in ligand affinities. The concentrations of monoamines, metabolites and estimates of dopamine (dopamine/dihydroxyphenylacetic acid ratio) and serotonin/5-hydroxyindolacetic acid ratio turnover rates were unchanged in striatum and frontal cortex. However, turnover of dopamine and serotonin in the hypothalamus was increased ~20% and ~15%, respectively. Striatal transmission via D1 receptors is decreased in binge-eating rats while µ-opioid receptor signalling may be increased. These changes are consistent with the attenuation of binge-eating by lisdexamfetamine, which increases catecholaminergic neurotransmission, and nalmefene, a µ-opioid antagonist.

Immune-driven alterations in mucin sulphation is an important mediator of Trichuris muris helminth expulsion.

Mucins are heavily glycosylated proteins that give mucus its gel-like properties. Moreover, the glycans decorating the mucin protein core can alter the protective properties of the mucus barrier. To investigate whether these alterations could be parasite-induced we utilized the Trichuris muris (T. muris) infection model, using different infection doses and strains of mice that are resistant (high dose infection in BALB/c and C57BL6 mice) or susceptible (high dose infection in AKR and low dose infection in BALB/c mice) to chronic infection by T. muris. During chronicity, within the immediate vicinity of the T. muris helminth the goblet cell thecae contained mainly sialylated mucins. In contrast, the goblet cells within the epithelial crypts in the resistant models contained mainly sulphated mucins. Maintained mucin sulphation was promoted by TH2-immune responses, in particular IL-13, and contributed to the protective properties of the mucus layer, making it less vulnerable to degradation by T. muris excretory secretory products. Mucin sulphation was markedly reduced in the caecal goblet cells in the sulphate anion transporter-1 (Sat-1) deficient mice. We found that Sat-1 deficient mice were susceptible to chronic infection despite a strong TH2-immune response. Lower sulphation levels lead to decreased efficiency of establishment of T. muris infection, independent of egg hatching. This study highlights the complex process by which immune-regulated alterations in mucin glycosylation occur following T. muris infection, which contributes to clearance of parasitic infection.

Lisdexamfetamine reduces the compulsive and perseverative behaviour of binge-eating rats in a novel food reward/punished responding conflict model.

Compulsive and perseverative behaviour in binge-eating, female, Wistar rats was investigated in a novel food reward/punished responding conflict model. Rats were trained to perform the conditioned avoidance response task. When proficient, the paradigm was altered to a food-associated conflict test by placing a chocolate-filled jar (empty jar for controls) in one compartment of the shuttle box. Entry into the compartment with the jar triggered the conditioning stimulus after a variable interval, and foot-shock 10 seconds later if the rat did not leave. Residence in the 'safe' compartment with no jar did not initiate trials or foot-shocks. By frequently entering the chocolate-paired compartment, binge-eating rats completed their 10 trials more quickly than non-binge controls. Binge-eating rats spent a greater percentage of the session in the chocolate-paired compartment, received foot-shocks more frequently, and tolerated foot-shocks for longer periods; all consistent with compulsive and perseverative behaviour. The d-amphetamine prodrug, lisdexamfetamine, has recently received US approval for the treatment of moderate to severe binge-eating disorder in adults. Lisdexamfetamine (0.8 mg/kg po [d-amphetamine base]) decreased chocolate consumption by binge-eating rats by 55% and markedly reduced compulsive and perseverative responding in the model. These findings complement clinical results showing lisdexamfetamine reduced compulsiveness scores in subjects with binge-eating disorder.

The neurobiological basis of binge-eating disorder.

Relatively little is known about the neuropathophysiology of binge-eating disorder (BED). Here, the evidence from neuroimaging, neurocognitive, genetics, and animal studies are reviewed to synthesize our current understanding of the pathophysiology of BED. Binge-eating disorder may be conceptualized as an impulsive/compulsive disorder, with altered reward sensitivity and food-related attentional biases. Neuroimaging studies suggest there are corticostriatal circuitry alterations in BED similar to those observed in substance abuse, including altered function of prefrontal, insular, and orbitofrontal cortices and the striatum. Human genetics and animal studies suggest that there are changes in neurotransmitter networks, including dopaminergic and opioidergic systems, associated with binge-eating behaviors. Overall, the current evidence suggests that BED may be related to maladaptation of the corticostriatal circuitry regulating motivation and impulse control similar to that found in other impulsive/compulsive disorders. Further studies are needed to understand the genetics of BED and how neurotransmitter activity and neurocircuitry function are altered in BED and how pharmacotherapies may influence these systems to reduce BED symptoms.

Effects of lisdexamfetamine and s-citalopram, alone and in combination, on effort-related choice behavior in the rat.

RATIONALE: Effort-related motivational symptoms, such as anergia, psychomotor retardation, and fatigue, are an important aspect of depression and other disorders. Motivational symptoms are resistant to some treatments, including serotonin transport (SERT) inhibitors. OBJECTIVES: Tests of effort-based choice using operant behavior tasks (e.g., concurrent lever pressing/ chow feeding tasks) can be used as animal models of motivational symptoms. Tests of effort-related choice allow animals to choose between high-effort actions that lead to more highly valued rewards vs. low-effort alternatives that lead to less valued rewards (i.e., less preferred or lower magnitude). Rats treated with the vesicular monoamine transport inhibitor tetrabenazine, or the cytokine interleukin-1ß (IL-1ß), which are associated with depressive symptoms in humans, can alter effort-related choice, reducing selection of the high effort alternative (lever pressing) while increasing intake of freely available chow. METHODS: The present studies focused upon the ability of lisdexamfetamine (LDX) to increase exertion of effort in rats responding on effort-based choice tasks under several different conditions. RESULTS: LDX attenuated the shift from fixed ratio 5 lever pressing to chow intake induced by tetrabenazine and IL-1ß. In contrast, the SERT inhibitor s-citalopram failed to reverse the effects of tetrabenazine. When given in combination with tetrabenazine+s-citalopram, LDX significantly increased lever pressing output compared to tetrabenaine+citalopram alone. LDX also increased work output in rats responding on a progressive ratio/chow feeding choice task. CONCLUSIONS: LDX can increase work output in rats responding on effort-based choice tasks, which may have implications for understanding the neurochemistry of motivational symptoms in humans.

The effects in rats of lisdexamfetamine in combination with olanzapine on mesocorticolimbic dopamine efflux, striatal dopamine D2 receptor occupancy and stimulus generalization to a D-amphetamine cue.

The etiology of schizophrenia is poorly understood and two principle hypotheses have dominated the field. Firstly, that subcortical dopamine function is enhanced while cortical dopamine function is reduced and secondly, that cortical glutamate systems are dysfunctional. It is also widely accepted that currently used antipsychotics have essentially no impact on cognitive deficits and persistent negative symptoms in schizophrenia. Reduced dopamine transmission via dopamine D1 receptors in the prefrontal cortex has been hypothesized to be involved in the aetiology of these symptom domains and enhancing cortical dopamine transmission within an optimal window has been suggested to be potentially beneficial. In these pre-clinical studies we have determined that combined administration of the d-amphetamine pro-drug, lisdexamfetamine and the atypical antipsychotic olanzapine increased dopamine efflux in the rat prefrontal cortex and nucleus accumbens to an extent greater than either drug given separately without affecting olanzapine's ability to block striatal dopamine D2 receptors which is important for its antipsychotic activity. Furthermore, in an established rodent model used to compare the subjective effects of novel compounds the ability of lisdexamfetamine to generalize to a d-amphetamine cue was dose-dependently attenuated when co-administered with olanzapine suggesting that lisdexamfetamine may produce less marked subjective effects when administered adjunctively with olanzapine.

Effects of lisdexamfetamine in a rat model of binge-eating.

Binge-eating disorder is a common psychiatric disorder affecting ~2% of adults. Binge-eating was initiated in freely-fed, lean, adult, female rats by giving unpredictable, intermittent access to ground, milk chocolate over four weeks. The rats avidly consumed chocolate during 2 hr binge sessions, with compensatory reductions of normal chow intake in these sessions and the days thereafter. Bodyweights of binge-eating rats were normal. The model's predictive validity was explored using nalmefene (0.1-1.0mg/kg), R-baclofen (1.0-10mg/kg) and SB-334867 (3.0-30 mg/kg) (orexin-1 antagonist), which all selectively decreased chocolate bingeing without reducing chow intake. Sibutramine (0.3-5.0mg/kg) non-selectively reduced chocolate and chow consumption. Olanzapine (0.3-3.0mg/kg) was without effect and rolipram (1.0-10mg/kg) abolished all ingestive behaviour. The pro-drug, lisdexamfetamine (LDX; 0.1-1.5mg/kg), dose-dependently reduced chocolate bingeing by ⩽ 71% without significantly decreasing normal chow intake. Its metabolite, D-amphetamine (0.1-1.0mg/kg), dose-dependently and preferentially decreased chocolate bingeing ⩽ 56%. Using selective antagonists to characterize LDX's actions revealed the reduction of chocolate bingeing was partially blocked by prazosin (α1-adrenoceptor; 0.3 and 1.0mg/kg) and possibly by SCH-23390 (D1; 0.1mg/kg). RX821002 (α2-adrenoceptor; 0.1 and 0.3mg/kg) and raclopride (D2; 0.3 and 0.5mg/kg) were without effect. The results indicate that LDX, via its metabolite, d-amphetamine, reduces chocolate bingeing, partly by indirect activation of α1-adrenoceptors and perhaps D1 receptors.

Effects of lisdexamfetamine alone and in combination with s-citalopram on acetylcholine and histamine efflux in the rat pre-frontal cortex and ventral hippocampus.

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by poor attention, impulse control and hyperactivity. A significant proportion of ADHD patients are also co-morbid for other psychiatric problems including mood disorders and these patients may be managed with a combination of psychostimulants and anti-depressants. While it is generally accepted that enhanced catecholamine signalling via the action of psychostimulants is likely responsible for the cognitive improvement in ADHD, other neurotransmitters including acetylcholine and histamine may be involved. In the present study, we have examined the effect of lisdexamfetamine dimesylate (LDX), an amphetamine pro-drug that is approved for the treatment of ADHD on acetylcholine and histamine efflux in pre-frontal cortex and hippocampus alone and in combination with the anti-depressant s-citalopram. LDX increased cortical acetylcholine efflux, an effect that was not significantly altered by co-administration of s-citalopram. Cortical and hippocampal histamine were markedly increased by LDX, an effect that was attenuated in the hippocampus but not in pre-frontal cortex when co-administered with s-citalopram. Taken together, these results suggest that efflux of acetylcholine and histamine may be involved in the therapeutic effects of LDX and are differentially influenced by the co-administration of s-citalopram. Attention deficit hyperactivity disorder (ADHD) is characterized by poor attention, impulse control and hyperactivity. Some ADHD patients are also co-morbid for mood disorders and may be managed with psychostimulants (e.g. lisdexamfetamine, LDX) and anti-depressants (e.g. s-citalopram). LDX increased the efflux of acetylcholine and histamine, neurotransmitters involved in cognitive function, which were differentially influenced when co-administered with s-citalopram. Acetylcholine and histamine may be involved in the therapeutic effects of LDX and are differentially affected by the co-administration of s-citalopram.

Preclinical pharmacology of amphetamine: implications for the treatment of neuropsychiatric disorders.

The primary mechanism by which amphetamine exerts its neurobehavioral effects is through an enhancement of synaptic monoamine levels, which is mediated by interactions with monoamine transporters, storage, and metabolism. However, preclinical data are now emerging that support more widespread neurobiologic effects for amphetamine. This review describes preclinical evidence suggesting that direct interactions of amphetamine with monoamine systems, which results in increased synaptic monoamine availability, has downstream effects on nonmonoaminergic systems, including glutamate, endogenous opioid, endocannabinoid, and acetylcholine systems. Furthermore, evidence suggests that amphetamine can modulate synaptic plasticity through modulation of glutamatergic systems, intracellular signaling cascades, and neurotrophic factor activity. Functional activity of these systems is implicated in the regulation of neurobehavioral processes that include cognition, mood, motivated behavior/hedonic processes/addiction, and arousal. As such, the ability of amphetamine to influence the function of systems that mediate these processes suggests amphetamine-based agents may have utility in the treatment of psychiatric disorders in which these systems and processes are dysfunctional. Amphetamine-based agents are currently approved by the US Food and Drug Administration only for the treatment of attention-deficit/hyperactivity disorder and narcolepsy. Preclinical and clinical research for amphetamine-based pharmacotherapy for other psychiatric disease states is examined. This should encourage further research on the preclinical pharmacology of amphetamine and its implications for the treatment of neuropsychiatric disorders.

Preclinical pharmacokinetics, pharmacology and toxicology of lisdexamfetamine: a novel d-amphetamine pro-drug.

Lisdexamfetamine dimesylate (LDX) is a novel pro-drug of d-amphetamine that is currently used for the treatment of attention-deficit/hyperactivity disorder in children aged ≥ 6 years and adults. LDX is enzymatically cleaved to form d-amphetamine following contact with red blood cells, which reduces the rate of appearance and magnitude of d-amphetamine concentration in the blood and hence the brain when compared with immediate-release d-amphetamine at equimolar doses. Thus, the increase of striatal dopamine efflux and subsequent increase of locomotor activity following d-amphetamine is less prominent and slower to attain maximal effect following an equimolar dose of LDX. Furthermore, unlike d-amphetamine, the pharmacodynamic effects of LDX are independent of the route of administration underlining the requirement to be hydrolyzed by contact with red blood cells. It is conceivable that these pharmacokinetic and pharmacodynamic differences may impact the psychostimulant properties of LDX in the clinic. This article reviews the preclinical pharmacokinetics, pharmacology, and toxicology of LDX. This article is part of the Special Issue entitled 'CNS Stimulants'.

Mechanism based neurotoxicity of mGlu5 positive allosteric modulators--development challenges for a promising novel antipsychotic target.

Previous work has suggested that activation of mGlu5 receptor augments NMDA receptor function and thereby may constitute a rational approach addressing glutamate hypofunction in schizophrenia and a target for novel antipsychotic drug development. Here, we report the in vitro activity, in vivo efficacy and safety profile of 5PAM523 (4-Fluorophenyl){(2R,5S)-5-[5-(5-fluoropyridin-2-yl)-1,2,4-oxadiazol-3-yl]-2-methylpiperidin-1-yl}methanone), a structurally novel positive allosteric modulator selective of mGlu5. In cells expressing human mGlu5 receptor, 5PAM523 potentiated threshold responses to glutamate in fluorometric calcium assays, but does not have any intrinsic agonist activity. 5PAM523 acts as an allosteric modulator as suggested by the binding studies showing that 5PAM523 did not displace the binding of the orthosteric ligand quisqualic acid, but did partially compete with the negative allosteric modulator, MPyEP. In vivo, 5PAM523 reversed amphetamine-induced locomotor activity in rats. Therefore, both the in vitro and in vivo data demonstrate that 5PAM523 acts as a selective mGlu5 PAM and exhibits anti-psychotic like activity. To study the potential for adverse effects and particularly neurotoxicity, brain histopathological exams were performed in rats treated for 4 days with 5PAM523 or vehicle. The brain exam revealed moderate to severe neuronal necrosis in the rats treated with the doses of 30 and 50 mg/kg, particularly in the auditory cortex and hippocampus. To investigate whether this neurotoxicity is mechanism specific to 5PAM523, similar safety studies were carried out with three other structurally distinct selective mGlu5 PAMs. Results revealed a comparable pattern of neuronal cell death. Finally, 5PAM523 was tested in mGlu5 knock-out (KO) and wild type (WT) mice. mGlu5 WT mice treated with 5PAM523 for 4 days at 100 mg/kg presented significant neuronal death in the auditory cortex and hippocampus. Conversely, mGlu5 KO mice did not show any neuronal loss by histopathology, suggesting that enhancement of mGlu5 function is responsible for the toxicity of 5PAM523. This study reveals for the first time that augmentation of mGlu5 function with selective allosteric modulators results in neurotoxicity.

The mGluR7 allosteric agonist AMN082 produces antidepressant-like effects by modulating glutamatergic signaling.

Currently prescribed antidepressants affect the reuptake and/or metabolism of biogenic amines. Unfortunately for patients, these treatments require several weeks to produce significant symptom remission. However, recently it has been found that ketamine, a dissociative anesthetic agent that noncompetitively antagonizes NMDA (N-Methyl-d-aspartic acid) receptors, has rapid antidepressant effects at sub-anesthetic doses in clinically depressed patients. These findings indicate that modulation of the glutamatergic system could be an efficient way to achieve antidepressant activity. For this reason, other mechanisms influencing glutamatergic functioning have gained interest. For example, the metabotropic glutamate receptor 7 (mGluR7) allosteric agonist AMN082 (N,N'-dibenzyhydryl-ethane-1,2-diamine dihydrochloride) has been shown to be effective in the forced swim and tail-suspension test, behavioral assays sensitive to antidepressants. Here we extend the characterization of AMN082 by demonstrating its effects on differential reinforcement of low rates of responding (DRL)-30, another assay sensitive to antidepressants. Furthermore, we show the engagement of glutamatergic signaling by demonstrating the ability of the selective AMPA (2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid) receptor antagonist NBQX (2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[f]quinoxaline-2,3-dione) to reverse the effects of AMN082 in the tail suspension test. In contrast, NBQX failed to reverse the effects of imipramine in the same behavioral test. Finally, we report that behaviorally efficacious doses of AMN082 modulate phosphorylation of AMPA and NMDA receptor subunits in the hippocampus. These results suggest that the antidepressant-like effects of AMN082 are, at least in part, due to modulation of AMPA and NMDA receptor activity. Therefore, our findings confirm the hypothesis that mGluR7 could represent a novel target for treating depression.

The Therapeutic Potential of D-Amino Acid Oxidase (DAAO) Inhibitors.

D-amino acid oxidase (DAAO) is a flavoenzyme that degrades D-amino acids through the process of oxidative deamination. DAAO regulation of D-amino acid levels has been associated with several physiological processes ranging from hormone secretion to synaptic transmission and cognition. Recent genetic studies have identified a mutation on chromosome 13 in schizophrenia patients that encodes two gene products (G30 and G72) that are associated with DAAO. Furthermore, DAAO expression and enzyme activity has been reported to be increased in post mortem brain tissue samples from patients with schizophrenia compared to healthy controls. D-serine, a D-amino acid that is regulated by DAAO, is a potent, endogenous co-agonist of the N-methyl-D-aspartic acid (NMDA) receptor. Because NMDA receptor dysfunction is thought to be involved in the positive (psychotic), negative and cognitive symptoms in schizophrenia, there has been much interest in developing potent and selective DAAO inhibitors for the treatment of this disease. Several research reports have been published that describe the synthesis and biological effects of novel, selective, small molecule inhibitors of DAAO. Many of these compounds have been shown, when given systemically, to increase D-serine concentrations in the blood and brain. However, the efficacy of these compounds in behavioral assays that measure antipsychotic potential and pro-cognitive effects in laboratory animals has been inconsistent. This article highlights and reviews research advances for DAAO inhibitors published in peer reviewed journals.

MK-801 produces a deficit in sucrose preference that is reversed by clozapine, D-serine, and the metabotropic glutamate 5 receptor positive allosteric modulator CDPPB: relevance to negative symptoms associated with schizophrenia?

Currently prescribed antipsychotics attenuate the positive symptoms of schizophrenia but fail or only mildly improve negative symptoms. The present study aimed to establish an animal model of negative symptoms by examining the effects of the NMDA receptor antagonist MK-801 on sucrose preference. We sought to validate the model by examining the effects of clozapine and D-serine, for which there are positive clinical data regarding their effects on negative symptoms, and haloperidol which is clinically ineffective. We extended our analysis by examining CDPPB, an mGlu5 receptor positive allosteric modulator. Acute MK-801 produced effects indicative of a shift in the hedonic experience of sucrose not confounded by disruptions in motor abilities or taste as revealed by: 1) a decrease in sucrose intake at low concentrations (0.8% or 1.2%), but no effect on water, 2) an increase in consumption for higher (7%) sucrose concentrations, reflecting a shift to the right in the concentration-consumption curve, and 3) no effect on quinine intake. Sub-chronic clozapine and acute d-serine attenuated the MK-801-induced deficit in 1.2% sucrose consumption, whereas sub-chronic haloperidol (0.02 mg/kg) did not. Finally, acute treatment with CDPPB also attenuated this deficit. These data suggest that this model may be useful for identifying novel agents that improve negative symptoms, and that compounds which enhance NMDA receptor function, such as mGlu5 receptor PAMs, may have clinical utility in this regard.

The behavioral and neurochemical effects of a novel D-amino acid oxidase inhibitor compound 8 [4H-thieno [3,2-b]pyrrole-5-carboxylic acid] and D-serine.

Multiple studies indicate that N-methyl-D-aspartate (NMDA) receptor hypofunction underlies some of the deficits associated with schizophrenia. One approach for improving NMDA receptor function is to enhance occupancy of the glycine modulatory site on the NMDA receptor by increasing the availability of the endogenous coagonists D-serine. Here, we characterized a novel D-amino acid oxidase (DAAO) inhibitor, compound 8 [4H-thieno [3,2-b]pyrrole-5-carboxylic acid] and compared it with D-serine. Compound 8 is a moderately potent inhibitor of human (IC(50), 145 nM) and rat (IC(50), 114 nM) DAAO in vitro. In rats, compound 8 (200 mg/kg) decreased kidney DAAO activity by approximately 96% and brain DAAO activity by approximately 80%. This marked decrease in DAAO activity resulted in a significant (p < 0.001) elevation in both plasma (220% of control) and cerebrospinal fluid (CSF; 175% of control) D-serine concentration. However, compound 8 failed to significantly influence amphetamine-induced psychomotor activity, nucleus accumbens dopamine release, or an MK-801 (dizocilpine maleate)-induced deficit in novel object recognition in rats. In contrast, high doses of D-serine attenuated both amphetamine-induced psychomotor activity and dopamine release and also improved performance in novel object recognition. Behaviorally efficacious doses of D-serine (1280 mg/kg) increased CSF levels of D-serine 40-fold above that achieved by the maximal dose of compound 8. These findings demonstrate that pharmacological inhibition of DAAO significantly increases D-serine concentration in the periphery and central nervous system. However, acute inhibition of DAAO appears not to be sufficient to increase D-serine to concentrations required to produce antipsychotic and cognitive enhancing effects similar to those observed after administration of high doses of exogenous D-serine.

Chronic low dose corticosterone exposure decreased hippocampal cell proliferation, volume and induced anxiety and depression like behaviours in mice.

A dysregulated hypothalamic-pituitary-adrenal axis (HPA) has been implicated in major depressive disorder and most commonly used animal models of depression have been shown to elevate circulating levels of plasma corticosterone. We have compared the effects of chronic and acute corticosterone administration on hippocampal cell proliferation (as measured by BrdU immunohistochemistry), hippocampal volume and the appearance of anxiety (light dark box) and depression (forced swim test) like behaviours in CD1 mice. We have also examined the effects of chronic administration of fluoxetine and imipramine on these parameters. Chronic (14 days) but not acute treatment with corticosterone resulted in reduced hippocampal cell proliferation and granule cell layer volume, these changes were prevented by co-administration of imipramine and fluoxetine. In contrast, acute and 7 day but not 14 or 21 day treatment with corticosterone gave rise to a "depressed" phenotype in the forced swim test. Mice treated for 14 days with corticosterone also developed an anxious phenotype in the light dark box but only upon repeated testing. The results presented here demonstrate that moderately elevated corticosterone for a prolonged period is sufficient to induce cellular changes in the hippocampus that are prevented by chronic administration of antidepressants.

Hippocampal Bcl-2 expression is selectively increased following chronic but not acute treatment with antidepressants, 5-HT(1A) or 5-HT(2C/2B) receptor antagonists.

Expression of the anti-apoptotic protein Bcl-2 has been shown to increase in the hippocampus and cortex following chronic administration of mood stabilizers such as lithium and valproate, but the effects of long-term antidepressant administration have not been demonstrated. CD1 mice were dosed either acutely or chronically with either antidepressants or 5-HT receptor subtype selective antagonists. Cortex, hippocampus and hypothalamus from these mice were analysed by Western blot for changes in expression of Bcl-2 and Bax protein. Fourteen day but not acute treatment with citalopram (20 mg/kg), imipramine (10 mg/kg) and amitriptyline (10 mg/kg) in mice significantly elevated hippocampal Bcl-2 protein expression as compared to vehicle treated animals (59, 48 and 42% respectively). Similarly, fourteen day but not acute treatment with the 5-HT(1A) and 5-HT(2C/2B) receptor antagonists WAY100635 (0.3 mg/kg) and SB221284 (1 mg/kg) also markedly and significantly increased hippocampal Bcl-2 expression (95 and 52% respectively). Bcl-2 expression was unaffected in cortex by any treatment. There was a smaller increase of hippocampal Bax protein levels following treatment with imipramine after 1 or 14 days, and following citalopram and amitriptyline after 14 but not 1 day. These data present the first substantive evidence that clinically used antidepressants increase the expression of hippocampal Bcl-2 as did chronic blockade of 5-HT(1A) and 5-HT(2C/2B) receptors, which may be involved in the mechanism of action of antidepressants. The induction of hippocampal Bcl-2 expression by long-term antidepressant treatment may contribute to the clinical efficacy of such compounds via its well described neurotrophic and/or anti-apoptotic effects on neuronal function.

Effects of acute and chronic treatment with fluoxetine on stress-induced hyperthermia in telemetered rats and mice.

Preclinical and clinical evidence suggests that anxiolytic effects are observed after chronic administration of the selective serotonin reuptake inhibitor fluoxetine. In contrast, acute treatment may increase signs of anxiety. The present study examined the effects of acute and chronic administration of fluoxetine on a physiological measure of anxiety, stress-induced hyperthermia, in rats and mice using radiotelemetry to record core temperature and locomotor activity and ethologically relevant stressors to evoke the hyperthermic response. In both species, the benzodiazepine agonist chlordiazepoxide reduced stress-induced hyperthermia at doses (5 mg/kg i.p. rat, 10 mg/kg p.o. mouse) that had no significant effect on locomotor activity. Similarly, in both species, chronic (21 days) treatment with fluoxetine attenuated the hyperthermic response without significantly affecting locomotor activity. However, acute fluoxetine elicited species-specific effects. Thus in mice, stress-induced hyperthermia and activity were unaffected by fluoxetine (20 mg/kg p.o.) consistent with a lack of anxiolytic or anxiogenic activity. In contrast, in rats, fluoxetine (10 mg/kg i.p.) caused a significant baseline hypothermia in the absence of stress, confounding further interpretation. In conclusion, stress-induced hyperthermia in mice was unaffected by acute treatment and significantly reduced by chronic treatment with fluoxetine. However, in rats chronic administration of fluoxetine significantly reduced stress-induced hyperthermia while the effects of acute treatment were confounded by a decrease in body temperature in the absence of stress. Together, these observations support the view that chronic administration of fluoxetine is anxiolytic; however, the stress-induced hyperthermia assay does not reveal anxiogenic effects of acute administration of fluoxetine in rats or mice.