Dopaminergic neuromodulation of prefrontal cortex activity requires the NMDA receptor coagonist d-serine.

Prefrontal control of cognitive functions critically depends upon glutamatergic transmission and N-methyl D-aspartate (NMDA) receptors, the activity of which is regulated by dopamine. Yet whether the NMDA receptor coagonist d-serine is implicated in the dopamine-glutamate dialogue in the prefrontal cortex (PFC) and other brain areas remains unexplored. Here, using electrophysiological recordings, we show that d-serine is required for the fine-tuning of glutamatergic neurotransmission, neuronal excitability, and synaptic plasticity in the PFC through the actions of dopamine at D1 and D3 receptors. Using in vivo microdialysis, we show that D1 and D3 receptors exert a respective facilitatory and inhibitory influence on extracellular levels and activity of d-serine in the PFC, with actions expressed primarily via the cAMP/protein kinase A (PKA) signaling cascade. Further, using functional magnetic resonance imaging (fMRI) and behavioral assessment, we show that d-serine is required for the potentiation of cognition by D3R blockade as revealed in a test of novel object recognition memory. Collectively, these results unveil a key role for d-serine in the dopaminergic neuromodulation of glutamatergic transmission and PFC activity, findings with clear relevance to the pathogenesis and treatment of diverse brain disorders involving alterations in dopamine-glutamate cross-talk.

A pilot of the feasibility and usefulness of an aged obese model for use in stroke research.

Background: Animal models of stroke have been criticised as having poor predictive validity, lacking risk factors prevalent in an aging population. This pilot study examined the development of comorbidities in a combined aged and high-fat diet model, and then examined the feasibility of modelling stroke in such rats. Methods: Twelve-month old male Wistar-Han rats (n=15) were fed a 60% fat diet for 8 months during which monthly serial blood samples were taken to assess the development of metabolic syndrome and pro-inflammatory markers. Following this, to pilot the suitability of these rats for undergoing surgical models of stroke, they underwent 30min of middle cerebral artery occlusion (MCAO) alongside younger controls fed a standard diet (n=10). Survival, weight and functional outcome were monitored, and blood vessels and tissues collected for analysis. Results: A high fat diet in aged rats led to substantial obesity. These rats did not develop type 2 diabetes or hypertension. There was thickening of the thoracic arterial wall and vacuole formation in the liver; but of the cytokines examined changes were not seen. MCAO surgery and behavioural assessment was possible in this model (with some caveats discussed in manuscript). Conclusions: This study shows MCAO is possible in aged, obese rats. However, this model is not ideal for recapitulating the complex comorbidities commonly seen in stroke patients.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function.

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Gestational poly(I:C) attenuates, not exacerbates, the behavioral, cytokine and mTOR changes caused by isolation rearing in a rat 'dual-hit' model for neurodevelopmental disorders.

Many psychiatric illnesses have a multifactorial etiology involving genetic and environmental risk factors that trigger persistent neurodevelopmental impairments. Several risk factors have been individually replicated in rodents, to understand disease mechanisms and evaluate novel treatments, particularly for poorly-managed negative and cognitive symptoms. However, the complex interplay between various factors remains unclear. Rodent dual-hit neurodevelopmental models offer vital opportunities to examine this and explore new strategies for early therapeutic intervention. This study combined gestational administration of polyinosinic:polycytidylic acid (poly(I:C); PIC, to mimic viral infection during pregnancy) with post-weaning isolation of resulting offspring (to mirror adolescent social adversity). After in vitro and in vivo studies required for laboratory-specific PIC characterization and optimization, we administered 10 mg/kg i.p. PIC potassium salt to time-mated Lister hooded dams on gestational day 15. This induced transient hypothermia, sickness behavior and weight loss in the dams, and led to locomotor hyperactivity, elevated striatal cytokine levels, and increased frontal cortical JNK phosphorylation in the offspring at adulthood. Remarkably, instead of exacerbating the well-characterized isolation syndrome, gestational PIC exposure actually protected against a spectrum of isolation-induced behavioral and brain regional changes. Thus isolation reared rats exhibited locomotor hyperactivity, impaired associative memory and reversal learning, elevated hippocampal and frontal cortical cytokine levels, and increased mammalian target of rapamycin (mTOR) activation in the frontal cortex - which were not evident in isolates previously exposed to gestational PIC. Brains from adolescent littermates suggest little contribution of cytokines, mTOR or JNK to early development of the isolation syndrome, or resilience conferred by PIC. But notably hippocampal oxytocin, which can protect against stress, was higher in adolescent PIC-exposed isolates so might contribute to a more favorable outcome. These findings have implications for identifying individuals at risk for disorders like schizophrenia who may benefit from early therapeutic intervention, and justify preclinical assessment of whether adolescent oxytocin manipulations can modulate disease onset or progression.

Dual-acting agents for improving cognition and real-world function in Alzheimer's disease: Focus on 5-HT6 and D3 receptors as hubs.

To date, there are no interventions that impede the inexorable progression of Alzheimer's disease (AD), and currently-available drugs cholinesterase (AChE) inhibitors and the N-Methyl-d-Aspartate receptor antagonist, memantine, offer only modest symptomatic benefit. Moreover, a range of mechanistically-diverse agents (glutamatergic, histaminergic, monoaminergic, cholinergic) have disappointed in clinical trials, alone and/or in association with AChE inhibitors. This includes serotonin (5-HT) receptor-6 antagonists, despite compelling preclinical observations in rodents and primates suggesting a positive influence on cognition. The emphasis has so far been on high selectivity. However, for a multi-factorial disorder like idiopathic AD, 5-HT6 antagonists possessing additional pharmacological actions might be more effective, by analogy to "multi-target" antipsychotics. Based on this notion, drug discovery programmes have coupled 5-HT6 blockade to 5-HT4 agonism and inhibition of AchE. Further, combined 5-HT6/dopamine D3 receptor (D3) antagonists are of especial interest since D3 blockade mirrors 5-HT6 antagonism in exerting broad-based pro-cognitive properties in animals. Moreover, 5-HT6 and dopamine D3 antagonists promote neurocognition and social cognition via both distinctive and convergent actions expressed mainly in frontal cortex, including suppression of mTOR over-activation and reinforcement of cholinergic and glutamatergic transmission. In addition, 5-HT6 blockade affords potential anti-anxiety, anti-depressive and anti-epileptic properties, and antagonising 5-HT6 receptors may be associated with neuroprotective ("disease-modifying") properties. Finally D3 antagonism may counter psychotic episodes and D3 receptors themselves offer a promising hub for multi-target agents. The present article reviews the status of "R and D" into multi-target 5-HT6 and D3 ligands for improved treatment of AD and other neurodegenerative disorders of aging. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

Comparative Pro-cognitive and Neurochemical Profiles of Glycine Modulatory Site Agonists and Glycine Reuptake Inhibitors in the Rat: Potential Relevance to Cognitive Dysfunction and Its Management.

Frontocortical NMDA receptors are pivotal in regulating cognition and mood, are hypofunctional in schizophrenia, and may contribute to autistic spectrum disorders. Despite extensive interest in agents potentiating activity at the co-agonist glycine modulatory site, few comparative functional studies exist. This study systematically compared the actions of the glycine reuptake inhibitors, sarcosine (40-200 mg/kg) and ORG24598 (0.63-5 mg/kg), the agonists, glycine (40-800 mg/kg), and D-serine (10-160 mg/kg) and the partial agonists, S18841 (2.5 mg/kg s.c.) and D-cycloserine (2.5-40 mg/kg) that all dose-dependently prevented scopolamine disruption of social recognition in adult rats. Over similar dose ranges, they also prevented a delay-induced impairment of novel object recognition (NOR). Glycine reuptake inhibitors specifically elevated glycine but not D-serine levels in rat prefrontal cortical (PFC) microdialysates, while glycine and D-serine markedly increased levels of glycine and D-serine, respectively. D-Cycloserine slightly elevated D-serine levels. Conversely, S18841 exerted no influence on glycine, D-serine, other amino acids, monamines, or acetylcholine. Reversal of NOR deficits by systemic S18841 was prevented by the NMDA receptor antagonist, CPP (20 mg/kg), and the glycine modulatory site antagonist, L701,324 (10 mg/kg). S18841 blocked deficits in NOR following microinjection into the PFC (2.5-10 µg/side) but not the striatum. Finally, in rats socially isolated from weaning (a neurodevelopmental model of schizophrenia), S18841 (2.5 and 10 mg/kg s.c.) reversed impairment of NOR and contextual fear-motivated learning without altering isolation-induced hyperactivity. In conclusion, despite contrasting neurochemical profiles, partial glycine site agonists and glycine reuptake inhibitors exhibit comparable pro-cognitive effects in rats of potential relevance to treatment of schizophrenia and other brain disorders where cognitive performance is impaired.

Age-related differences in appetitive trace conditioning and novel object recognition procedures.

Appetitive trace conditioning (TC) was examined over 6 months in younger-adult (2-8 months) and middle-aged (12-18 months) male Wistar RccHan rats, to test for early age-related impairment in working memory. Novel object recognition (NOR) was included as a comparison task, to provide a positive control in the event that the expected impairment in TC was not demonstrated. The results showed that TC improved at both ages at the 2 s but not at the 10 s trace interval. There was, however, evidence for reduced improvement from one day to the next in the middle-aged cohort tested with the 2 s trace conditioned stimulus. Moreover, within the 10 s trace, responding progressively distributed later in the trace interval, in the younger-adult but not the middle-aged cohort. Middle-aged rats showed NOR discriminative impairment at a 24 h but not at a 10 min retention interval. Object exploration was overall reduced in middle-aged rats and further reduced longitudinally. At the end of the study, assessing neurochemistry by HPLC-ED showed reduced 5-HIAA/5-HT in the dorsal striatum of the middle-aged rats and some correlations between striatal 5-HIAA/5-HT and activity parameters. Overall the results suggest that, taken in isolation, age-related impairments may be overcome by experience. This recovery in performance was seen despite the drop in activity levels in older animals, which might be expected to contribute to cognitive decline.

Oxytocin attenuates phencyclidine hyperactivity and increases social interaction and nucleus accumben dopamine release in rats.

The pituitary neuropeptide oxytocin promotes social behavior, and is a potential adjunct therapy for social deficits in schizophrenia and autism. Oxytocin may mediate pro-social effects by modulating monoamine release in limbic and cortical areas, which was investigated herein using in vivo microdialysis, after establishing a dose that did not produce accompanying sedative or thermoregulatory effects that could concomitantly influence behavior. The effects of oxytocin (0.03-0.3 mg/kg subcutaneous) on locomotor activity, core body temperature, and social behavior (social interaction and ultrasonic vocalizations) were examined in adult male Lister-hooded rats, using selective antagonists to determine the role of oxytocin and vasopressin V1a receptors. Dopamine and serotonin efflux in the prefrontal cortex and nucleus accumbens of conscious rats were assessed using microdialysis. 0.3 mg/kg oxytocin modestly reduced activity and caused hypothermia but only the latter was attenuated by the V1a receptor antagonist, SR49059 (1 mg/kg intraperitoneal). Oxytocin at 0.1 mg/kg, which did not alter activity and had little effect on temperature, significantly attenuated phencyclidine-induced hyperactivity and increased social interaction between unfamiliar rats without altering the number or pattern of ultrasonic vocalizations. In the same rats, oxytocin (0.1 mg/kg) selectively elevated dopamine overflow in the nucleus accumbens, but not prefrontal cortex, without influencing serotonin efflux. Systemic oxytocin administration attenuated phencyclidine-induced hyperactivity and increased pro-social behavior without decreasing core body temperature and selectively enhanced nucleus accumbens dopamine release, consistent with activation of mesocorticolimbic circuits regulating associative/reward behavior being involved. This highlights the therapeutic potential of oxytocin to treat social behavioral deficits seen in psychiatric disorders such as schizophrenia.

Post-weaning social isolation of rats leads to long-term disruption of the gut microbiota-immune-brain axis.

Early-life stress is an established risk for the development of psychiatric disorders. Post-weaning isolation rearing of rats produces lasting developmental changes in behavior and brain function that may have translational pathophysiological relevance to alterations seen in schizophrenia, but the underlying mechanisms are unclear. Accumulating evidence supports the premise that gut microbiota influence brain development and function by affecting inflammatory mediators, the hypothalamic-pituitaryadrenal axis and neurotransmission, but there is little knowledge of whether the microbiota-gut-brain axis might contribute to the development of schizophrenia-related behaviors. To this end the effects of social isolation (SI; a well-validated animal model for schizophrenia)-induced changes in rat behavior were correlated with alterations in gut microbiota, hippocampal neurogenesis and brain cytokine levels. Twenty-four male Lister hooded rats were housed in social groups (group-housed, GH, 3 littermates per cage) or alone (SI) from weaning (post-natal day 24) for four weeks before recording open field exploration, locomotor activity/novel object discrimination (NOD), elevated plus maze, conditioned freezing response (CFR) and restraint stress at one week intervals. Post-mortem caecal microbiota composition, cortical and hippocampal cytokines and neurogenesis were correlated to indices of behavioral changes. SI rats were hyperactive in the open field and locomotor activity chambers traveling further than GH controls in the less aversive peripheral zone. While SI rats showed few alterations in plus maze or NOD they froze for significantly less time than GH following conditioning in the CFR paradigm, consistent with impaired associative learning and memory. SI rats had significantly fewer BrdU/NeuN positive cells in the dentate gyrus than GH controls. SI rats had altered microbiota composition with increases in Actinobacteria and decreases in the class Clostridia compared to GH controls. Differences were also noted at genus level. Positive correlations were seen between microbiota, hippocampal IL-6 and IL-10, conditioned freezing and open field exploration. Adverse early-life stress resulting from continuous SI increased several indices of 'anxiety-like' behavior and impaired associative learning and memory accompanied by changes to gut microbiota, reduced hippocampal IL-6, IL-10 and neurogenesis. This study suggests that early-life stress may produce long-lasting changes in gut microbiota contributing to development of abnormal neuronal and endocrine function and behavior which could play a pivotal role in the aetiology of psychiatric illness.

Infections Up to 76 Days After Stroke Increase Disability and Death.

Early infection after stroke is associated with a poor outcome. We aimed to determine whether delayed infections (up to 76 days post-stroke) are associated with poor outcome at 90 days. Data came from the international Efficacy of Nitric Oxide Stroke (ENOS, ISRCTN99414122) trial. Post hoc data on infections were obtained from serious adverse events reports between 1 and 76 days following stroke in this large cohort of patients. Regression models accounting for baseline covariates were used to analyse fatalities and functional outcomes (modified Rankin Scale (mRS), Barthel Index, Euro-Qol-5D) at 90 days, in patients with infection compared to those without infection. Of 4011 patients, 242 (6.0%) developed one or more serious infections. Infections were associated with an increased risk of death (p < 0.001) and an increased likelihood of dependency (measured by mRS) compared to those of all other patients (p < 0.001). This remained when only surviving patients were analysed, indicating that the worsening of functional outcome is not due to mortality (p < 0.001). In addition, the timing of the infection after stroke did not alter its detrimental association with fatality (p = 0.14) or functional outcome (p = 0.47). In conclusion, severe post-stroke infections, whether occurring early or late after stroke, are associated with an increased risk of death and poorer functional outcome, independent of differences in baseline characteristics or treatment. Not only are strategies needed for reducing the risk of infection immediately after stroke, but also during the first 3 months following a stroke. This study is registered: ISRCTN registry, number ISRCTN99414122, ClinicalTrials.gov Identifier, NCT00989716.

Hippocampal Neural Disinhibition Causes Attentional and Memory Deficits.

Subconvulsive hippocampal neural disinhibition, that is reduced GABAergic inhibition, has been implicated in neuropsychiatric disorders characterized by attentional and memory deficits, including schizophrenia and age-related cognitive decline. Considering that neural disinhibition may disrupt both intra-hippocampal processing and processing in hippocampal projection sites, we hypothesized that hippocampal disinhibition disrupts hippocampus-dependent memory performance and, based on strong hippocampo-prefrontal connectivity, also prefrontal-dependent attention. In support of this hypothesis, we report that acute hippocampal disinhibition by microinfusion of the GABA-A receptor antagonist picrotoxin in rats impaired hippocampus-dependent everyday-type rapid place learning performance on the watermaze delayed-matching-to-place test and prefrontal-dependent attentional performance on the 5-choice-serial-reaction-time test, which does not normally require the hippocampus. For comparison, we also examined psychosis-related sensorimotor effects, using startle/prepulse inhibition (PPI) and locomotor testing. Hippocampal picrotoxin moderately increased locomotion and slightly reduced startle reactivity, without affecting PPI. In vivo electrophysiological recordings in the vicinity of the infusion site showed that picrotoxin mainly enhanced burst firing of hippocampal neurons. In conclusion, hippocampal neural disinhibition disrupts hippocampus-dependent memory performance and also manifests through deficits in not normally hippocampus-dependent attentional performance. These behavioral deficits may reflect a disrupted control of burst firing, which may disrupt hippocampal processing and cause aberrant drive to hippocampal projection sites.

The dopamine D3-preferring D2/D3 dopamine receptor partial agonist, cariprazine, reverses behavioural changes in a rat neurodevelopmental model for schizophrenia.

Current antipsychotic medication is largely ineffective against the negative and cognitive symptoms of schizophrenia. One promising therapeutic development is to design new molecules that balance actions on dopamine D2 and D3 receptors to maximise benefits and limit adverse effects. This study used two rodent paradigms to investigate the action of the dopamine D3-preferring D3/D2 receptor partial agonist cariprazine. In adult male rats, cariprazine (0.03-0.3 mg/kg i.p.), and the atypical antipsychotic aripiprazole (1-3 mg/kg i.p.) caused dose-dependent reversal of a delay-induced impairment in novel object recognition (NOR). Treating neonatal rat pups with phencyclidine (PCP) and subsequent social isolation produced a syndrome of behavioural alterations in adulthood including hyperactivity in a novel arena, deficits in NOR and fear motivated learning and memory, and a reduction and change in pattern of social interaction accompanied by increased ultrasonic vocalisations (USVs). Acute administration of cariprazine (0.1 and 0.3 mg/kg) and aripiprazole (3 mg/kg) to resultant adult rats reduced neonatal PCP-social isolation induced locomotor hyperactivity and reversed NOR deficits. Cariprazine (0.3 mg/kg) caused a limited reversal of the social interaction deficit but neither drug affected the change in USVs or the deficit in fear motivated learning and memory. Results suggest that in the behavioural tests investigated cariprazine is at least as effective as aripiprazole and in some paradigms it showed additional beneficial features further supporting the advantage of combined dopamine D3/D2 receptor targeting. These findings support recent clinical studies demonstrating the efficacy of cariprazine in treatment of negative symptoms and functional impairment in schizophrenia patients.

Contribution of serotonin and dopamine to changes in core body temperature and locomotor activity in rats following repeated administration of mephedrone.

The psychoactive effects of mephedrone are commonly compared with those of 3,4-methylenedioxymethamphetamine, but because of a shorter duration of action, users often employ repeated administration to maintain its psychoactive effects. This study examined the effects of repeated mephedrone administration on locomotor activity, body temperature and striatal dopamine and 5-hydroxytryptamine (5-HT) levels and the role of dopaminergic and serotonergic neurons in these responses. Adult male Lister hooded rats received three injections of vehicle (1 ml/kg, i.p.) or mephedrone HCl (10 mg/kg) at 2 h intervals for radiotelemetry (temperature and activity) or microdialysis (dopamine and 5-HT) measurements. Intracerebroventricular pre-treatment (21 to 28 days earlier) with 5,7-dihydroxytryptamine (150 µg) or 6-hydroxydopamine (300 µg) was used to examine the impact of 5-HT or dopamine depletion on mephedrone-induced changes in temperature and activity. A final study examined the influence of i.p. pre-treatment (-30 min) with the 5-HT1A receptor antagonist WAY-100635 (0.5 mg/kg), 5-HT1B receptor antagonist GR 127935 (3 mg/kg) or the 5-HT7 receptor antagonist SB-258719 (10 mg/kg) on mephedrone-induced changes in locomotor activity and rectal temperature. Mephedrone caused rapid-onset hyperactivity, hypothermia (attenuated on repeat dosing) and increased striatal dopamine and 5-HT release following each injection. Mephedrone-induced hyperactivity was attenuated by 5-HT depletion and 5-HT1B receptor antagonism, whereas the hypothermia was completely abolished by 5-HT depletion and lessened by 5-HT1A receptor antagonism. These findings suggest that stimulation of central 5-HT release and/or inhibition of 5-HT reuptake play a pivotal role in both the hyperlocomotor and hypothermic effects of mephedrone, which are mediated in part via 5-HT1B and 5-HT1A receptors.

Dopamine D1 receptor stimulation modulates the formation and retrieval of novel object recognition memory: Role of the prelimbic cortex.

Previous studies have shown that dopamine D1 receptor antagonists impair novel object recognition memory but the effects of dopamine D1 receptor stimulation remain to be determined. This study investigated the effects of the selective dopamine D1 receptor agonist SKF81297 on acquisition and retrieval in the novel object recognition task in male Wistar rats. SKF81297 (0.4 and 0.8 mg/kg s.c.) given 15 min before the sampling phase impaired novel object recognition evaluated 10 min or 24 h later. The same treatments also reduced novel object recognition memory tested 24 h after the sampling phase and when given 15 min before the choice session. These data indicate that D1 receptor stimulation modulates both the encoding and retrieval of object recognition memory. Microinfusion of SKF81297 (0.025 or 0.05 µg/side) into the prelimbic sub-region of the medial prefrontal cortex (mPFC) in this case 10 min before the sampling phase also impaired novel object recognition memory, suggesting that the mPFC is one important site mediating the effects of D1 receptor stimulation on visual recognition memory.

Too little and too much: hypoactivation and disinhibition of medial prefrontal cortex cause attentional deficits.

Attentional deficits are core symptoms of schizophrenia, contributing strongly to disability. Prefrontal dysfunction has emerged as a candidate mechanism, with clinical evidence for prefrontal hypoactivation and disinhibition (reduced GABAergic inhibition), possibly reflecting different patient subpopulations. Here, we tested in rats whether imbalanced prefrontal neural activity impairs attention. To induce prefrontal hypoactivation or disinhibition, we microinfused the GABA-A receptor agonist muscimol (C4H6N2O2; 62.5, 125, 250 ng/side) or antagonist picrotoxin (C30H34O13; 75, 150, 300 ng/side), respectively, into the medial prefrontal cortex. Using the five-choice serial reaction time (5CSRT) test, we showed that both muscimol and picrotoxin impaired attention (reduced accuracy, increased omissions). Muscimol also impaired response control (increased premature responses). In addition, muscimol dose dependently reduced open-field locomotor activity, whereas 300 ng of picrotoxin caused locomotor hyperactivity; sensorimotor gating (startle prepulse inhibition) was unaffected. Therefore, infusion effects on the 5CSRT test can be dissociated from sensorimotor effects. Combining microinfusions with in vivo electrophysiology, we showed that muscimol inhibited prefrontal firing, whereas picrotoxin increased firing, mainly within bursts. Muscimol reduced and picrotoxin enhanced bursting and both drugs changed the temporal pattern of bursting. Picrotoxin also markedly enhanced prefrontal LFP power. Therefore, prefrontal hypoactivation and disinhibition both cause attentional deficits. Considering the electrophysiological findings, this suggests that attention requires appropriately tuned prefrontal activity. Apart from attentional deficits, prefrontal disinhibition caused additional neurobehavioral changes that may be relevant to schizophrenia pathophysiology, including enhanced prefrontal bursting and locomotor hyperactivity, which have been linked to psychosis-related dopamine hyperfunction.

Neonatal phencyclidine administration and post-weaning social isolation as a dual-hit model of 'schizophrenia-like' behaviour in the rat.

RATIONALE: Schizophrenia is a debilitating disorder comprising positive, negative and cognitive deficits with a poorly defined neurobiological aetiology; therefore, animal models with greater translational reliability are essential to develop improved therapies. OBJECTIVES: This study combines two developmental challenges in rats, neonatal phencyclidine (PCP) injection and subsequent rearing in social isolation from weaning, to attempt to produce more robust behavioural deficits with greater translational relevance to schizophrenia than either challenge alone. METHODS: Forty-two male Lister-hooded rat pups received the N-methyl-D-aspartate (NMDA) receptor antagonist, phencyclidine (PCP, 10 mg/kg, s.c.), or vehicle on post-natal day (PND) 7, 9 and 11 and were weaned on PND 23 into group housing (saline-treated n = 11 or PCP-treated n = 10) or isolation (saline n = 10 or PCP n = 11). Six weeks post-weaning, novelty- and PCP-induced (3.2 mg/kg) locomotor activity, novel object discrimination, prepulse inhibition of acoustic startle and contextual memory in a conditioned emotion response (CER) were recorded. RESULTS: Isolation rearing alone significantly elevated baseline locomotor activity and induced visual recognition memory impairment in novel object discrimination. Neonatal PCP treatment did not induce locomotor sensitisation to a subsequent acute PCP injection, but it impaired prepulse inhibition when combined with isolation rearing. CER freezing behaviour was significantly reduced by isolation rearing but an even greater effect occurred when combined with neonatal PCP treatment. CONCLUSIONS: Neonatal PCP and isolation rearing both produce behavioural deficits in adult rats, but combined treatment caused a wider range of more severe cognitive impairments, providing a more comprehensive preclinical model to determine the neurobiological aetiology of schizophrenia than either treatment alone.

The antimalarial drug quinine interferes with serotonin biosynthesis and action.

The major antimalarial drug quinine perturbs uptake of the essential amino acid tryptophan, and patients with low plasma tryptophan are predisposed to adverse quinine reactions; symptoms of which are similar to indications of tryptophan depletion. As tryptophan is a precursor of the neurotransmitter serotonin (5-HT), here we test the hypothesis that quinine disrupts serotonin function. Quinine inhibited serotonin-induced proliferation of yeast as well as human (SHSY5Y) cells. One possible cause of this effect is through inhibition of 5-HT receptor activation by quinine, as we observed here. Furthermore, cells exhibited marked decreases in serotonin production during incubation with quinine. By assaying activity and kinetics of the rate-limiting enzyme for serotonin biosynthesis, tryptophan hydroxylase (TPH2), we showed that quinine competitively inhibits TPH2 in the presence of the substrate tryptophan. The study shows that quinine disrupts both serotonin biosynthesis and function, giving important new insight to the action of quinine on mammalian cells.

Lentiviral delivery of a vesicular glutamate transporter 1 (VGLUT1)-targeting short hairpin RNA vector into the mouse hippocampus impairs cognition.

Glutamate is the principle excitatory neurotransmitter in the mammalian brain, and dysregulation of glutamatergic neurotransmission is implicated in the pathophysiology of several psychiatric and neurological diseases. This study utilized novel lentiviral short hairpin RNA (shRNA) vectors to target expression of the vesicular glutamate transporter 1 (VGLUT1) following injection into the dorsal hippocampus of adult mice, as partial reductions in VGLUT1 expression should attenuate glutamatergic signaling and similar reductions have been reported in schizophrenia. The VGLUT1-targeting vector attenuated tonic glutamate release in the dorsal hippocampus without affecting GABA, and selectively impaired novel object discrimination (NOD) and retention (but not acquisition) in the Morris water maze, without influencing contextual fear-motivated learning or causing any adverse locomotor or central immune effects. This pattern of cognitive impairment is consistent with the accumulating evidence for functional differentiation along the dorsoventral axis of the hippocampus, and supports the involvement of dorsal hippocampal glutamatergic neurotransmission in both spatial and nonspatial memory. Future use of this nonpharmacological VGLUT1 knockdown mouse model could improve our understanding of glutamatergic neurobiology and aid assessment of novel therapies for cognitive deficits such as those seen in schizophrenia.

In vivo neurometabolic profiling to characterize the effects of social isolation and ketamine-induced NMDA antagonism: a rodent study at 7.0 T.

Continued efforts are undertaken to develop animal models of schizophrenia with translational value in the quest for much needed novel drugs. Existing models mimic specific neurobiological aspects of schizophrenia, but not its full complexity. Here, we used proton magnetic resonance spectroscopy ((1)H-MRS) to assess the metabolic profile in the prefrontal cortex (PFC) of two established models, rearing in social isolation and acute N-methyl-D-aspartate receptor (NMDA-R) antagonism and their combination. Rats reared in social isolation or group housed underwent (1)H-MRS at baseline and dynamically after ketamine challenge (25mg/kg, intraperitoneal) under isoflurane anesthesia. A 7 T animal scanner was used to perform spectra acquisition from the anterior cingulate/medial PFC. LCModel was used for metabolite quantification and effects of rearing and ketamine injection were analyzed. Social isolation did not lead to significant differences in the metabolic profile of the PFC at baseline. Ketamine induced a significant increase in glutamine in both groups with significance specifically reached by the group-housed animals alone. Only rats reared in social isolation showed a significant 11% γ-aminobutyric acid (GABA) decrease. This study provides preliminary evidence that social interactions in early life predict the glutamatergic and GABAergic response to acute NMDA-R blockade. The similarity between the prefrontal GABA reduction in patients with schizophrenia and in rats reared as social isolates after challenge with ketamine suggests good potential translational value of this combined animal model for drug development.

The atypical antipsychotic risperidone reverses the recognition memory deficits induced by post-weaning social isolation in rats.

RATIONALE: Rearing rats in isolation from weaning is an established preclinical neurodevelopmental model which induces behavioural deficits with apparent translational relevance to some core symptoms of schizophrenia. OBJECTIVE: This study evaluated the ability of the atypical antipsychotic risperidone to reverse behavioural deficits induced by post-weaning social isolation of rat pups and to further characterise the predictive validity of this model. METHOD: Forty-five male Lister hooded rats were housed in groups of 3-4 (n = 16) or singly (n = 29) for 4 weeks immediately after weaning on postnatal day (PND) 22-24. On PND 51, novel cage-induced locomotor activity (LMA) was assessed to subdivide rats into groups balanced for behavioural response. On PNDs 58, 59, 65 and 72, rats received either vehicle (1 ml/kg; i.p.) or risperidone (0.2 or 0.5 mg/kg; i.p.) 30 min prior to testing in LMA, novel object discrimination (NOD), prepulse inhibition (PPI) of acoustic startle and conditioned emotional response (CER) learning paradigms, respectively. RESULTS: Isolation rearing had no effect on PPI, but produced LMA hyperactivity and impaired NOD and CER compared to group-housed controls. Risperidone caused a dose-dependent reduction in LMA, irrespective of rearing condition, but selectively reversed the NOD deficit in isolation-reared rats. Risperidone did not reverse the isolation rearing-induced CER deficit. CONCLUSIONS: Similar to its clinical profile, risperidone only partially reverses the schizophrenic symptomology; since it reversed some, but not all, of the learning and memory deficits induced by post-weaning isolation, the isolation rearing model may be useful to predict antipsychotic activity of novel therapeutic agents.