Specific modulation of social memory in rats by cholinomimetic and nootropic drugs, by benzodiazepine inverse agonists, but not by psychostimulants

Selective breeding of rats for high (HAB) and low (LAB) anxiety-related behaviour: A unique model for comorbid depression and social dysfunctions

Animal models of selective breeding for extremes in emotionality are a strong experimental approach to model psychopathologies. They became indispensable in order to increase our understanding of neurobiological, genetic, epigenetic, hormonal, and environmental mechanisms contributing to anxiety disorders and their association with depressive symptoms or social deficits. In the present review, we extensively discuss Wistar rats selectively bred for high (HAB) and low (LAB) anxiety-related behaviour on the elevated plus-maze. After 30 years of breeding, we can confirm the prominent differences between HAB and LAB rats in trait anxiety, which are accompanied by consistent differences in depressive-like, social and cognitive behaviours. We can further confirm a single nucleotide polymorphism in the vasopressin promotor of HAB rats causative for neuropeptide overexpression, and show that low (or high) anxiety and fear levels are unlikely due to visual dysfunctions. Thus, HAB and LAB rats continue to exist as a reliable tool to study the multiple facets underlying the pathology of high trait anxiety and its comorbidity with depression-like behaviour and social dysfunctions.

Structural and functional alterations in the retrosplenial cortex following neuropathic pain

Human and animal imaging studies demonstrated that chronic pain profoundly alters the structure and the functionality of several brain regions. In this article, we conducted a longitudinal and multimodal study to assess how chronic pain affects the brain. Using the spared nerve injury model which promotes both long-lasting mechanical and thermal allodynia/hyperalgesia but also pain-associated comorbidities, we showed that neuropathic pain deeply modified the intrinsic organization of the brain functional network 1 and 2 months after injury. We found that both functional metrics and connectivity of the part A of the retrosplenial granular cortex (RSgA) were significantly correlated with the development of neuropathic pain behaviours. In addition, we found that the functional RSgA connectivity to the subiculum and the prelimbic system are significantly increased in spared nerve injury animals and correlated with peripheral pain thresholds. These brain regions were previously linked to the development of comorbidities associated with neuropathic pain. Using a voxel-based morphometry approach, we showed that neuropathic pain induced a significant increase of the gray matter concentration within the RSgA, associated with a significant activation of both astrocytes and microglial cells. Together, functional and morphological imaging metrics of the RSgA could be used as a predictive biomarker of neuropathic pain.

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.

Developmental exposure to manganese induces lasting motor and cognitive impairment in rats

Exposure to high manganese (Mn) levels may damage the basal ganglia, leading to a syndrome analogous to Parkinson's disease, with motor and cognitive impairments. The molecular mechanisms underlying Mn neurotoxicity, particularly during development, still deserve further investigation. Herein, we addressed whether early-life Mn exposure affects motor coordination and cognitive function in adulthood and potential underlying mechanisms. Male Wistar rats were exposed intraperitoneally to saline (control) or MnCl2 (5, 10 or 20 mg/kg/day) from post-natal day (PND) 8-12. Behavioral tests were performed on PND 60-65 and biochemical analysis in the striatum and hippocampus were performed on PND14 or PND70. Rats exposed to Mn (10 and 20 mg/kg) performed significantly worse on the rotarod test than controls indicating motor coordination and balance impairments. The object and social recognition tasks were used to evaluate short-term memory. Rats exposed to the highest Mn dose failed to recognize a familiar object when replaced by a novel object as well as to recognize a familiar juvenile rat after a short period of time. However, Mn did not alter olfactory discrimination ability. In addition, Mn-treated rats displayed decreased levels of non-protein thiols (e.g. glutathione) and increased levels of glial fibrillary acidic protein (GFAP) in the striatum. Moreover, Mn significantly increased hippocampal glutathione peroxidase (GPx) activity. These findings demonstrate that acute low-level exposure to Mn during a critical neurodevelopmental period causes cognitive and motor dysfunctions that last into adulthood, that are accompanied by alterations in antioxidant defense system in both the hippocampus and striatum.

Monoarthritis-induced emotional and cognitive impairments in rats are sensitive to low systemic doses or intra-amygdala injections of morphine

Chronic pain is a multidimensional experience that not only includes changes in nociception but also impairments in emotional and cognitive functions, not often taken into account in preclinical research. The present study investigated emotional and cognitive impairments in an animal model of persistent inflammatory pain as well as the involvement of the basolateral complex (BLC) of the amygdala in these components. Monoarthritis was induced by intra-articular injection of complete Freund׳s adjuvant. Mechanical hypersensitivity, anxiety and depressive-like behaviours as well as cognitive capacities were assessed using several tests, such as von Frey, social interaction, open field, saccharin preference, spatial and social recognition memory tests. The effects of morphine administered systemically or into the BLC of the amygdala were also studied. Monoarthritic rats exhibited mechanical hypersensitivity, anxiety and depressive-like behaviours as well as cognitive impairments. Whereas low systemic doses and intra-BLC infusion of morphine failed to reduce mechanical hypersensitivity, they reversed monoarthritis-induced anxiety-like behaviours and cognitive impairments. Our findings further support a crucial role of amygdala in the effect of morphine on emotional/cognitive components of pain and not on mechanical hypersensitivity. Finally, our study highlights the interest of a multi-behavioural approach in the assessment of pain and the analgesic effect of drugs.

Towards improved animal models for evaluating social cognition and its disruption in schizophrenia: the CNTRICS initiative

Social cognition refers to processes used to monitor and interpret social signals from others, to decipher their state of mind, emotional status and intentions, and select appropriate social behaviour. Social cognition is sophisticated in humans, being embedded with verbal language and enacted in a complex cultural environment. Its disruption characterises the entire course of schizophrenia and is correlated with poor functional outcome. Further, deficits in social cognition are related to impairment in other cognitive domains, positive symptoms (paranoia and delusions) and negative symptoms (social withdrawal and reduced motivation). In light of the significance and inadequate management of social cognition deficits, there is a need for translatable experimental procedures for their study, and identification of effective pharmacotherapy. No single paradigm captures the multi-dimensional nature of social cognition, and procedures for assessing ability to infer mental states are not well-developed for experimental therapeutic settings. Accordingly, a recent CNTRICS meeting prioritised procedures for measuring a specific construct: "acquisition and recognition of affective (emotional) states", coupled to individual recognition. Two complementary paradigms for refinement were identified: social recognition/preference in rodents, and visual tracking of social scenes in non-human primates (NHPs). Social recognition is disrupted in genetic, developmental or pharmacological disease models for schizophrenia, and performance in both procedures is improved by the neuropeptide oxytocin. The present article surveys a broad range of procedures for studying social cognition in rodents and NHPs, discusses advantages and drawbacks, and focuses on development of social recognition/preference and gaze-following paradigms for improved study of social cognition deficits in schizophrenia and their potential treatment.

The potential role of dopamine D₃ receptor neurotransmission in cognition

Currently available treatments have limited pro-cognitive effects for neuropsychiatric disorders, such as schizophrenia, Parkinson's disease and Alzheimer's disease. The primary objective of this work is to review the literature on the role of dopamine D₃ receptors in cognition, and propose dopamine D₃ receptor antagonists as possible cognitive enhancers for neuropsychiatric disorders. A literature search was performed to identify animal and human studies on D₃ receptors and cognition using PubMed, MEDLINE and EMBASE. The search terms included "dopamine D₃ receptor" and "cognition". The literature search identified 164 articles. The results revealed: (1) D₃ receptors are associated with cognitive functioning in both healthy individuals and those with neuropsychiatric disorders; (2) D₃ receptor blockade appears to enhance while D₃ receptor agonism seems to impair cognitive function, including memory, attention, learning, processing speed, social recognition and executive function independent of age; and (3) D₃ receptor antagonists may exert their pro-cognitive effect by enhancing the release of acetylcholine in the prefrontal cortex, disinhibiting the activity of dopamine neurons projecting to the nucleus accumbens or prefrontal cortex, or activating CREB signaling in the hippocampus. These findings suggest that D₃ receptor blockade may enhance cognitive performance in healthy individuals and treat cognitive dysfunction in individuals with a neuropsychiatric disorder. Clinical trials are needed to confirm these effects.

Testing social acoustic memory in rats: effects of stimulus configuration and long-term memory on the induction of social approach behavior by appetitive 50-kHz ultrasonic vocalizations

Rats emit distinct types of ultrasonic vocalizations (USVs), which serve as situation-dependent affective signals. In appetitive situations, such as rough-and-tumble-play, high-frequency 50-kHz USVs occur, whereas low-frequency 22-kHz USVs can be observed in aversive situations, such as social defeat. USVs serve distinct communicative functions and induce call-specific behavioral responses in the receiver. While aversive 22-kHz USVs serve as alarm calls and induce behavioral inhibition, appetitive 50-kHz USVs have a pro-social communicative function and elicit social approach behavior, supporting the notion that they serve as social contact calls to (re)establish or maintain contact among conspecifics. The aim of the present study was to use the rat's ability to communicate in the ultrasonic range via high-frequency 50-kHz USVs in order to develop a test for social acoustic memory in rats with relevance for human verbal memory. Verbal learning and memory is among the seven cognitive domains identified as commonly deficient in human schizophrenia patients, but particularly difficult to model. We therefore tested whether the induction of social approach behavior by playback of appetitive 50-kHz USVs is dependent on (1) acoustic stimulus configuration and (2) social long-term memory, and whether (3) social long-term memory effects can be blocked by the administration of scopolamine, a muscarinic acetylcholine antagonist producing amnesia. Results show that social approach behavior in response to playback of natural 50-kHz USVs depends on acoustic stimulus configuration and occurs only when sound energy is concentrated to a critical frequency band in the ultrasonic range. Social approach behavior was detected during the first exposure to playback of 50-kHz USVs, whereas no such response was observed during the second exposure 1week later, indicating a stable memory trace. In contrast, when memory formation was blocked by i.p. administration of scopolamine (0.5mg/kg or 1.5mg/kg) immediately after the first exposure, rats displayed social approach behavior during the second exposure as well. Induction of social approach behavior in response to repeated playback of natural 50-kHz USVs may therefore provide a new and rather unique approach for testing social acoustic memory in rats with relevance to human verbal memory.

Social recognition task in the rat

Among the numerous tasks designed for assessing distinct memory processes, the social recognition task in the rat offers the opportunity to evaluate a form of short-term working memory in the domain of social cognition, and its modification by pharmacological agents or physiopathological states, such as aging. Social cognition in humans is obviously of great importance and its deficits, e.g., during aging and Alzheimer's dementia, often have dramatic consequences for the patient and their environment. Two protocols are described in this unit that permit evaluation of positive and negative drug effects on social recognition memory in adult male rats and beneficial drug effects on age-related social recognition amnesia in aged male rats.

Social recognition assay in the rat

Neuropsychiatric disorders encompass a broad patient population in a variety of disease states across all age groups and are often accompanied by deficits in short-term/working memory. However, most preclinical models that allow for an assessment of cognitive enhancement do not provide robust behavioral readouts with a level of throughput sufficient to support modern drug discovery efforts. The rat social recognition assay presented in this unit is one exception that has been increasingly employed to test new chemical entities for enhancing cognitive activity. The test is simple in design and takes advantage of the spontaneous behavior of rats to investigate conspecifics. The protocol in this unit is designed to evaluate the effects of a test substance on the short-term/working memory of adult male rats employing 30-min or 2-hr pretreatment times.

Testing declarative memory in laboratory rats and mice using the nonconditioned social discrimination procedure

Testing declarative memory in laboratory rodents can provide insights into the fundamental mechanisms underlying this type of learning and memory processing, and these insights are likely to be applicable to humans. Here we provide a detailed description of the social discrimination procedure used to investigate recognition memory in rats and mice, as established during the last 20 years in our laboratory. The test is based on the use of olfactory signals for social communication in rodents; this involves a direct encounter between conspecifics, during which the investigatory behavior of the experimental subject serves as an index for learning and memory performance. The procedure is inexpensive, fast and very reliable, but it requires well-trained human observers. We include recent modifications to the procedure that allow memory extinction to be investigated by retroactive and proactive interference, and that enable the dissociated analysis of the central nervous processing of the volatile fraction of an individual's olfactory signature. Depending on the memory retention interval under study (short-term memory, intermediate-term memory, long-term memory or long-lasting memory), the protocol takes ~10 min or up to several days to complete.

Involvement of the cholinergic system in conditioning and perceptual memory

The cholinergic systems play a pivotal role in learning and memory, and have been the centre of attention when it comes to diseases containing cognitive deficits. It is therefore not surprising, that the cholinergic transmitter system has experienced detailed examination of its role in numerous behavioural situations not least with the perspective that cognition may be rescued with appropriate cholinergic 'boosters'. Here we reviewed the literature on (i) cholinergic lesions, (ii) pharmacological intervention of muscarinic or nicotinic system, or (iii) genetic deletion of selective receptor subtypes with respect to sensory discrimination and conditioning procedures. We consider visual, auditory, olfactory and somatosensory processing first before discussing more complex tasks such as startle responses, latent inhibition, negative patterning, eye blink and fear conditioning, and passive avoidance paradigms. An overarching reoccurring theme is that lesions of the cholinergic projection neurones of the basal forebrain impact negatively on acquisition learning in these paradigms and blockade of muscarinic (and to a lesser extent nicotinic) receptors in the target structures produce similar behavioural deficits. While these pertain mainly to impairments in acquisition learning, some rare cases extend to memory consolidation. Such single case observations warranted replication and more in-depth studies. Intriguingly, receptor blockade or receptor gene knockout repeatedly produced contradictory results (for example in fear conditioning) and combined studies, in which genetically altered mice are pharmacological manipulated, are so far missing. However, they are desperately needed to clarify underlying reasons for these contradictions. Consistently, stimulation of either muscarinic (mainly M(1)) or nicotinic (predominantly α7) receptors was beneficial for learning and memory formation across all paradigms supporting the notion that research into the development and mechanisms of novel and better cholinomimetics may prove useful in the treatment of neurodegenerative or psychiatric disorders with cognitive endophenotypes.

Neural correlates of olfactory learning: Critical role of centrifugal neuromodulation

The mammalian olfactory system is well established for its remarkable capability of undergoing experience-dependent plasticity. Although this process involves changes at multiple stages throughout the central olfactory pathway, even the early stages of processing, such as the olfactory bulb and piriform cortex, can display a high degree of plasticity. As in other sensory systems, this plasticity can be controlled by centrifugal inputs from brain regions known to be involved in attention and learning processes. Specifically, both the bulb and cortex receive heavy inputs from cholinergic, noradrenergic, and serotonergic modulatory systems. These neuromodulators are shown to have profound effects on both odor processing and odor memory by acting on both inhibitory local interneurons and output neurons in both regions.

Mutant mouse models: genotype-phenotype relationships to negative symptoms in schizophrenia

Negative symptoms encompass diminution in emotional expression and motivation, some of which relate to human attributes that may not be accessible readily in animals. Additionally, their refractoriness to treatment precludes therapeutic validation of putative models. This review considers critically the application of mutant mouse models to the study of the pathobiology of negative symptoms. It focuses on 4 main approaches: genes related to the pathobiology of schizophrenia, genes associated with risk for schizophrenia, neurodevelopmental-synaptic genes, and variant approaches from other areas of neurobiology. Despite rapid advances over the past several years, it is clear that we continue to face substantive challenges in applying mutant models to better understand the pathobiology of negative symptoms: the majority of evidence relates to impairments in social behavior, with only limited data relating to anhedonia and negligible data concerning avolition and other features; even for the most widely examined feature, social behavior, studies have used diverse assessments thereof; modelling must proceed in cognizance of increasing evidence that genes and pathobiologies implicated in schizophrenia overlap with other psychotic disorders, particularly bipolar disorder. Despite the caveats and challenges, several mutant lines evidence a phenotype for at least one index of social behavior. Though this may suggest superficially some shared relationship to negative symptoms, it is not yet possible to specify either the scope or the pathobiology of that relationship for any given gene. The breadth and depth of ongoing studies in mutants hold the prospect of addressing these shortcomings.

Scopolamine-induced deficits in social memory in mice: reversal by donepezil

Deficits in social behaviour is a characteristic of numerous mental disorders including autism, schizophrenia, depression and Alzheimer's disease. For the assessment of pharmacological and genetic experimental disease models, conventional social interaction tasks bear the uncertainty that any drug-induced abnormality of the investigator may feed back to the drug-free companion modifying its reactions. A considerable technical improvement was recently reported by Moy et al. [Moy SS, Nadler JJ, Perez A, Barbaro RP, Johns JM, Magnuson T, et al. Sociability and preference for social novelty in five inbred strains: an approach to assess autistic-like behaviours in mice. Genes Brain Behav 2004;3:287-302] in which the drug free partner is confined to a small cage and social contacts of the investigator are recorded uncontaminated of any social reactions of the stranger. Using this novel behavioural paradigm, we here show in C57Bl/6 female mice that sociability (social interaction with a stranger mouse) is not impaired after administration of the anxiolytic diazepam (0.1-1 mg/kg) or the muscarinic antagonist scopolamine hydrobromide (0.1-1 mg/kg). However, social memory tested after a short time interval was impaired by both drugs in a dose-dependent manner (diazepam: > or = 0.5mg/kg; scopolamine: > or = 0.3mg/kg). The scopolamine-induced short-term memory deficit was reversed to normal by the choline esterase inhibitor donepezil (1 mg/kg). Given this dependence of social recognition on the cholinergic system, combined with the clinical observation of reduced social contacts in dementia patients, sociability may offer a novel endpoint biomarker with translational value in experimental models of cognitive dysfunction.

Using the MATRICS to guide development of a preclinical cognitive test battery for research in schizophrenia

Cognitive deficits in schizophrenia are among the core symptoms of the disease, correlate with functional outcome, and are not well treated with current antipsychotic therapies. In order to bring together academic, industrial, and governmental bodies to address this great 'unmet therapeutic need', the NIMH sponsored the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative. Through careful factor analysis and consensus of expert opinion, MATRICS identified seven domains of cognition that are deficient in schizophrenia (attention/vigilance, working memory, reasoning and problem solving, processing speed, visual learning and memory, verbal learning and memory, and social cognition) and recommended a specific neuropsychological test battery to probe these domains. In order to move the field forward and outline an approach for translational research, there is a need for a "preclinical MATRICS" to develop a rodent test battery that is appropriate for drug development. In this review, we outline such an approach and review current rodent tasks that target these seven domains of cognition. The rodent tasks are discussed in terms of their validity for probing each cognitive domain as well as a brief overview of the pharmacology and manipulations relevant to schizophrenia for each task.

Blockade of dopamine D(3) receptors in frontal cortex, but not in sub-cortical structures, enhances social recognition in rats: similar actions of D(1) receptor agonists, but not of D(2) antagonists

Though D(3) receptor antagonists can enhance cognitive function, their sites of action remain unexplored. This issue was addressed employing a model of social recognition in rats, and the actions of D(3) antagonists were compared to D(1) agonists that likewise possess pro-cognitive properties. Infusion of the highly selective D(3) antagonists, S33084 and SB277,011 (0.04-2.5 microg/side), into the frontal cortex (FCX) dose-dependently reversed the deficit in recognition induced by a delay. By contrast, the preferential D(2) antagonist, L741,626 (0.63-5.0) had no effect. The action of S33084 was regionally specific inasmuch as its injection into the nucleus accumbens or striatum was ineffective. A similar increase of recognition was obtained upon injection of the D(1) agonist, SKF81297 (0.04-0.63), into the FCX though it was also active (0.63) in the nucleus accumbens. These data suggest that D(3) receptors modulating social recognition are localized in FCX, and underpin their pertinence as targets for antipsychotic agents.

The melanin-concentrating hormone1 receptor antagonists, SNAP-7941 and GW3430, enhance social recognition and dialysate levels of acetylcholine in the frontal cortex of rats

Melanin-concentrating hormone (MCH)1 receptors are widely expressed in limbic structures and cortex. Their inactivation is associated with anxiolytic and antidepressive properties but little information is available concerning cognition. This issue was addressed using the selective antagonists, SNAP-7941 and GW3430, in a social recognition paradigm in rats. The muscarinic blocker, scopolamine (1.25 mg/kg s.c.), reduced social recognition, an action dose-dependently blocked by SNAP-7941 and GW3430 (0.63-10.0 and 20.0-80.0 mg/kg i.p., respectively) which did not themselves display amnesic properties. Further, in a protocol where a spontaneous deficit was induced by a prolonged inter-session delay, SNAP-7941 and GW3430 dose-dependently enhanced social recognition. In dialysis studies, SNAP-7941 (0.63-40.0 mg/kg i.p.) and GW3430 (10.0-40.0 mg/kg i.p.) elevated extracellular levels of acetylcholine (ACh) in the frontal cortex (FCX) of freely moving rats. The SNAP-7941 effect was specific, as it did not increase levels of ACh in ventral and dorsal hippocampus: moreover, it did not modify levels of noradrenaline, dopamine, serotonin and glutamate in FCX. Active doses of SNAP-7941 and GW3430 corresponded to doses (2.5-40.0 and 10.0-80.0 mg/kg i.p., respectively) exerting anxiolytic properties in Vogel conflict and ultrasonic vocalization tests, and antidepressant actions in forced swim, isolation-induced aggression and marble-burying procedures. In contrast to SNAP-7941 and GW3430, the benzodiazepine, diazepam, decreased social recognition and dialysate levels of ACh, while the tricyclic, imipramine, reduced social recognition and failed to enhance cholinergic transmission. In conclusion, at anxiolytic and antidepressant doses, SNAP-7941 and GW3430 improve social recognition and elevate extracellular ACh levels in FCX. This profile differentiates MCH1 receptor antagonists from conventional anxiolytic and antidepressant agents.

Mouse social recognition and preference

Social recognition in mice is represented by a simple pattern of behavior that can be accurately and reliably quantified by trained observers. The paradigm presented in this unit takes advantage of an ethologically relevant phenomenon marked by a vigorous and species-typical sequence of investigatory behaviors that occurs when conspecifics meet. Recognition is noted by decreased investigation of a previously encountered animal.

Pro-cognitive effects of 5-HT6 receptor antagonists in the social recognition procedure in rats: implication of the frontal cortex

RATIONALE

5-HT6 receptor antagonists improve cognitive processes in rodents. However, their site(s) of action remains unexplored and their influence upon social memory has been little investigated.

OBJECTIVES

We examined the influence of 5-HT6 receptor ligands upon social memory in rats by use of systemic or local administration into the frontal cortex (FCX), striatum, or nucleus basalis magnocellularis (NBM).

MATERIALS AND METHODS

The social recognition test is based upon the ability of an adult rat to recognize a younger conspecific during the second of two 5-min sessions. In a procedure without an inter-session interval, the actions of drugs alone and the ability to reverse "amnesia" induced by the muscarinic antagonist, scopolamine (1.25 mg/kg, s.c.), were examined. The potential promnesic effect of drugs was also investigated in another procedure where a spontaneous deficit of recognition was induced by a 120-min inter-session interval.

RESULTS

The 5-HT6 receptor agonist, WAY-181187 (10.0 mg/kg, i.p.), significantly impaired social recognition. This effect was abolished by the 5-HT6 receptor antagonists, SB-271046 (20.0 mg/kg, i.p.) and SB-258585 (10.0 mg/kg, i.p.). These agents also abolished scopolamine-induced amnesia (10.0 and 2.5 mg/kg, i.p., respectively) and reversed the delay-induced deficit (10.0-20.0 and 2.5-10.0 mg/kg, i.p., respectively). WAY-181187 into the FCX significantly impaired social recognition (0.16-0.63 microg/side). Conversely, SB-271046 into the FCX (2.5-5.0 microg/side), but neither into the striatum nor the NBM, significantly reversed spontaneous deficit.

CONCLUSION

These results indicate that 5-HT6 receptors modulate social recognition by actions in the FCX and underpin their pertinence as targets for the treatment of psychiatric disorders in which cognitive function is compromised.

Blockade of the metabotropic glutamate 2/3 receptors enhances social memory via the AMPA receptor in rats

The present study examined the role of mGlu(2/3) receptors in short-term social memory using the social recognition paradigm in rats in which an adult rat is exposed to the same juvenile rat in two successive interactions. Intraperitoneal administration of the mGlu(2/3) receptor antagonist MGS0039 (0.3-3 mg/kg) or the ampakine CX546 (0.3-3 mg/kg) significantly and dose-dependently reduced the adult rat's social investigation of the same juvenile rat during the second encounter which occurred 120 min after the first encounter, indicating that both MGS0039 and CX546 enhanced social recognition. Pretreatment with the AMPA receptor antagonist NBQX (0.1-1 mg/kg, s.c.) significantly attenuated the effects of MGS0039 (3 mg/kg, i.p.) in the social recognition test. These results suggest that the mGlu(2/3) receptor blockade increases social recognition memory, presumably through stimulation of the AMPA receptor.

Selective blockade of dopamine D(3) versus D(2) receptors enhances frontocortical cholinergic transmission and social memory in rats: a parallel neurochemical and behavioural analysis

Though dopaminergic mechanisms modulate cholinergic transmission and cognitive function, the significance of specific receptor subtypes remains uncertain. Here, we examined the roles of dopamine D(3) versus D(2) receptors. By analogy with tacrine (0.16-2.5 mg/kg, s.c.), the selective D(3) receptor antagonists, S33084 (0.01-0.63) and SB277,011 (0.63-40.0), elicited dose-dependent, pronounced and sustained elevations in dialysis levels of acetylcholine (ACh) in the frontal cortex, but not the hippocampus, of freely-moving rats. The actions of these antagonists were stereospecifically mimicked by (+)S14297 (1.25), whereas its inactive distomer, (-)S17777, was ineffective. The preferential D(2) receptor antagonist, L741,626 (10.0), failed to modify levels of ACh. S33084 (0.01-0.63) and SB277,011 (0.16-2.5) also mimicked tacrine (0.04-0.63) by dose-dependently attenuating the deleterious influence of scopolamine (1.25) upon social memory (recognition by an adult rat of a juvenile conspecific). Further, (+)S14297 (1.25) versus (-)S17777 stereospecifically blocked the action of scopolamine. Using an intersession interval of 120 min (spontaneous loss of recognition), S33084 (0.04-0.63), SB277,011 (0.16-10.0) and (+)S14297 (0.63-10.0) likewise mimicked tacrine (0.16-2.5) in enhancing social memory. In contrast, L741,626 (0.16-10.0) displayed amnesic properties. In conclusion, selective blockade of D(3) receptors facilitates frontocortical cholinergic transmission and improves social memory in rats. These data support the pertinence of D(3) receptors as a target for treatment of disorders in which cognitive function is compromised.

F15063, a compound with D2/D3 antagonist, 5-HT 1A agonist and D4 partial agonist properties. III. Activity in models of cognition and negative symptoms

BACKGROUND AND PURPOSE

The D(2)/D(3) receptor antagonist, D(4) receptor partial agonist, and high efficacy 5-HT(1A) receptor agonist F15063 was shown to be highly efficacious and potent in rodent models of activity against positive symptoms of schizophrenia. However F15063 induced neither catalepsy nor the 'serotonin syndrome'. Here, we evaluated its profile in rat models predictive of efficacy against negative symptoms/cognitive deficits of schizophrenia.

EXPERIMENTAL APPROACH

F15063, given i.p., was assessed in models of behavioural deficits induced by interference with the NMDA/glutamatergic (phencyclidine: PCP) or cholinergic (scopolamine) systems.

KEY RESULTS

Through 5-HT(1A) activation, F15063 partially alleviated (MED: 0.04 mg kg(-1)) PCP-induced social interaction deficit between two adult rats, without effect by itself, underlining its potential to combat negative symptoms. At doses above 0.16 mg kg(-1), F15063 reduced interaction by itself. F15063 (0.16 mg kg(-1)) selectively re-established PCP-impaired 'cognitive flexibility' in a reversal learning task, suggesting potential against adaptability deficits. F15063 (0.04-0.63 mg kg(-1)) also reversed scopolamine-induced amnesia in a juvenile-adult rat social recognition test, indicative of a pro-cholinergic influence. Activity in this latter test is consistent with its D(4) partial agonism, as it was blocked by the D(4) antagonist L745,870. Finally, F15063 up to 40 mg kg(-1) did not disrupt basal prepulse inhibition of startle reflex in rats, a marker of sensorimotor gating.

CONCLUSIONS AND IMPLICATIONS

The balance of D(2)/D(3), D(4) and 5-HT(1A) receptor interactions of F15063 yields a promising profile of activity in models of cognitive deficits and negative symptoms of schizophrenia.

Pilocarpine improves olfactory discrimination and social recognition memory deficits in 24 month-old rats

Muscarinic receptor agonists have been suggested as potential drugs to counteract age-related cognitive decline since critical changes in cholinergic system occur with aging. Recently, we demonstrated that single administration of the non-selective muscarinic receptor agonist pilocarpine prevents age-related spatial learning impairments in rats. In addition, increasing evidence suggests that areas in the central nervous system processing olfactory information are affected at the early stages of age-related diseases, such as Alzheimer's disease, and that specific olfactory testing may represent an important tool in the diagnosis of these diseases. In the present study, olfactory discrimination and short-term social memory of 3 and 24 month-old rats were assessed with the olfactory discrimination and social recognition memory tasks, respectively. The actions of the repeated treatment with pilocarpine (30 mg/kg, i.p.; once per day for 21 days) in relation to age-related effects on olfactory and cognitive functions were also studied. The 24 month-old rats exhibited significantly impaired performance in both models, demonstrating deficits in their odour discrimination and in their ability to recognize a juvenile rat after a short period of time. The treatment with pilocarpine improved in a specific manner these age-related deficits in 24 month-old rats without altering their motor performance. The present results extend the notion of the participation of muscarinic receptors in control of olfactory functions and reinforce the potential of muscarinic receptor agonists for the treatment of age-related cognitive decline.

A neural cell adhesion molecule–derived fibroblast growth factor receptor agonist, the FGL-peptide, promotes early postnatal sensorimotor development and enhances social memory retention

The neural cell adhesion molecule (NCAM) belongs to the immunoglobulin (Ig) superfamily and is composed extracellularly of five Ig-like and two fibronectin type III (F3) modules. It plays a pivotal role in neuronal development and synaptic plasticity. NCAM signals via a direct interaction with the fibroblast growth factor receptor (FGFR). A 15-amino-acid long peptide, the FG loop (FGL) peptide, that is derived from the second F3 module of NCAM has been found to activate FGFR1. We here report that the FGL peptide, when administered intranasally to newborn rats, accelerated early postnatal development of coordination skills. In adult animals s.c. administration of FGL resulted in a prolonged retention of social memory. We found that FGL rapidly penetrated into the blood and cerebrospinal fluid after both intranasal and s.c. administration and remained detectable in the fluids for up to 5 hours.

Antagonistic interaction between adenosine A2A and dopamine D2 receptors modulates the social recognition memory in reserpine-treated rats

Increasing evidence suggests that antagonistic interactions between specific subtypes of adenosine and dopamine receptors in the basal ganglia are involved in the control of motor activity. However, there are few studies investigating this interaction in other brain regions and its role in additional functions. In the present study, we evaluated whether reserpine-treated rats (1.0 mg/kg, i.p.) exhibit altered social recognition memory abilities. The effects of acute administration of the dopamine receptor agonists 7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3 benzazepine (SKF 38393, dopamine D(1) receptor agonist) and quinpirole (dopamine D(2) receptor agonist), together with the adenosine receptor antagonists caffeine (non-selective), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, adenosine A(1) receptor antagonist) and 4-(2-[7-amino-2-{2-furyl}{1,2,4}triazolo-{2,3-a}{1,3,5}triazin-5-yl-amino]ethyl)phenol (ZM241385, adenosine A(2A) receptor antagonist), were also investigated. Twenty-four hours after treatment, reserpine-treated rats exhibited a significant disruption in the ability to recognize a juvenile rat after a short period of time. These animals did not show any motor deficit. The social recognition disruption induced by reserpine was reversed by acute treatment with quinpirole (0.05-0.1 mg/kg, i.p.), caffeine (10.0-30.0 mg/kg, i.p.) or ZM241385 (0.5-1.0 mg/kg, i.p.), but not with SKF 38393 (0.5-3.0 mg/kg, i.p.) or DPCPX (0.5-3.0 mg/kg, i.p.). Moreover, a synergistic response was observed following the co-administration of 'non-effective' doses of ZM241385 (0.1 mg/kg, i.p.) and quinpirole (0.01 mg/kg, i.p.). These results reinforce and extend the notion of antagonistic interactions between adenosine and dopamine receptors, and demonstrate, for the first time, that the blockade of adenosine A(2A) receptors and the activation of dopamine D(2) receptors can reverse the social recognition deficits induced by reserpine in rats.

SSR181507, a dopamine D(2) receptor antagonist and 5-HT(1A) receptor agonist, alleviates disturbances of novelty discrimination in a social context in rats, a putative model of selective attention deficit

RATIONALE

Selective attention deficit, characterised by the inability to differentiate relevant from irrelevant information, is considered to underlie many cognitive deficits of schizophrenia, and appears to be only marginally responsive to treatment with current antipsychotics.

OBJECTIVES

We compared the activity of the putative atypical antipsychotic SSR181507 (a dopamine D(2) receptor antagonist and 5HT(1A) receptor agonist) with reference compounds, on disturbances of novelty discrimination in a social context in rats, a behavioural paradigm that putatively models selective attention deficit.

METHODS

A first (familiar) juvenile rat was presented to an adult rat for a period (P1) of 30 min. A second (novel) juvenile was then introduced at the end of P1 for a period (P2) of 5 min. The ability of the adult rat to discriminate between the two juveniles, presented at the same time, was evaluated by measuring the ratio of the time spent in interaction with the novel vs the familiar juvenile during P2.

RESULTS

Adult rats spent more time exploring the novel than the familiar juvenile. This novelty discrimination capacity was disrupted by: (1) parametric modification of the procedure (reduction of time spent in contact with the familiar juvenile during P1); (2) acute injection of psychotomimetics that are known to induce schizophrenia-like symptoms in humans, such as phencyclidine (PCP; 3 mg/kg, i.p.) and d-amphetamine (1 mg/kg, i.p.) and (3) neonatal treatment with PCP (three injections of 10 mg/kg, s.c.), a model based on the neurodevelopmental hypothesis of schizophrenia. The potential atypical antipsychotic SSR181507 (0.03-3 mg/kg, i.p.) and the atypical antipsychotics clozapine (0.1-1 mg/kg, i.p.) and amisulpride (1-3 mg/kg, i.p.) attenuated deficits in novelty discrimination produced by parametric manipulation and by acute or neonatal treatment with PCP. The typical antipsychotic haloperidol (up to 0.3 mg/kg, i.p.) attenuated only deficits in novelty discrimination produced by parametric modification.

CONCLUSION

Collectively, these results suggest that SSR181507 can alleviate disturbances of novelty discrimination in a social context in rats, and that this paradigm may represent a suitable animal model of selective attention deficits observed in schizophrenia.

Blockade of adenosine A2A receptors reverses short-term social memory impairments in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) exhibit impairment across several cognitive domains such as attention, short-term memory and spatial reference memory. These cognitive deficits have been variously attributed to disrupted dopaminergic, cholinergic and adenosinergic neurotransmitter function. However, social memory in SHR has not been investigated. In the present study, we therefore evaluated whether SHR exhibit altered short-term social memory abilities compared to normotensive Wistar rats (WIS) through two experimental paradigms (social recognition and habituation-dishabituation tests). We also compared the performance of SHR and WIS rats in the object recognition test. SHR exhibited significantly impaired performance in both models of social memory, but not in the object recognition test, demonstrating a selective deficit in the ability to recognize a juvenile rat after a short period of time. The administration of acute doses of the non-selective adenosine receptor antagonist caffeine (3.0 or 10.0 mg/kg, i.p.) and the adenosine A2A receptor antagonist 4-(2-[7-amino-2-[2-furyl][1,2,4]triazolo-[2,3-a][1,3,5]triazin-5-yl-amino]ethyl) phenol (ZM241385, 0.5 or 1.0 mg/kg, i.p.) but not the adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 1.0 or 3.0 mg/kg, i.p.) reversed this social memory impairment in SHR, but these treatments did not alter the hypertension state. These results demonstrate an impairment of short-term social memory in SHR and the involvement of the adenosine A2A receptors in this alteration.

Modulation of short-term social memory in rats by adenosine A1 and A(2A) receptors

The recognition of an unfamiliar juvenile rat by an adult rat has been shown to imply short-term memory processes. The present study was designed to examine the role of adenosine receptors in the short-term social memory of rats using the social recognition paradigm. Adenosine (5.0-10.0 mg/kg), the selective adenosine A1 receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA, 0.025-0.05 mg/kg) and the selective adenosine A(2A) receptor agonist N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)ethyl]adenosine (DPMA, 1.0-5.0 mg/kg), given by i.p. route 30 min before the test, disrupted the juvenile recognition ability of adult rats. This negative effect of adenosine (5.0 mg/kg, i.p.) on social memory was prevented by pretreatment with the non-selective adenosine receptor antagonist caffeine (10.0 mg/kg, i.p.), the adenosine A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 1.0 mg/kg, i.p.) and the adenosine A(2A) antagonist 4-(2-[7-amino-2-{2-furyl}{1,2,4}triazolo-{2,3-a}{1,3,5}triazin-5-yl-amino]ethyl)phenol (ZM241385, 1.0 mg/kg, i.p.). Furthermore, acute administration of caffeine (10.0-30.0 mg/kg, i.p.), DPCPX (1.0-3.0 mg/kg, i.p.) or ZM241385 (0.5-1.0 mg/kg, i.p.) improved the short-term social memory in a specific manner. These results indicate that adenosine modulates the short-term social memory in rats by acting on both A1 and A(2A) receptors, with adenosine receptor agonists and antagonists, respectively, disrupting and enhancing the social memory.

Facilitation of short-term social memory by ethanol in rats is mediated by dopaminergic receptors

Ethanol is a drug that has apparently opposite effects on memory processes depending on when it is given relative to the task, as well as the nature of the task under study. Recently, we demonstrated that acute low doses of ethanol (0.5 and 1.0 g/kg, i.p.) improve the short-term social memory in rats in a specific and time-dependent manner, and that this action is, at least in part, related to opioid, but not to muscarinic receptors. In the present study, we evaluated whether this positive effect of ethanol on the short-term memory of rats is related to a reducing impact of interference during the task through two different procedures: the introduction of an unfamiliar juvenile rat or the placing of the adult rat in the open field during the inter-exposure interval. The actions of reserpine (0.4 and 0.8 mg/kg, s.c.), haloperidol (0.05 and 0.2 mg/kg, i.p.), the D2 receptor antagonist sulpiride (20.0 and 50.0 mg/kg, i.p.) and the D1 receptor antagonist SCH 23390 (0.01 and 0.03 mg/kg, s.c.) and their interaction with ethanol (1.0 g/kg, i.p.) in relation to short-term memory were also studied. The administration of ethanol (1.0 g/kg, i.p.), immediately after the end of the first presentation, did not reduce the effect on social memory of the introduction of an unfamiliar juvenile or placing the adult rat in the open field during the inter-exposure interval. The facilitatory effect of ethanol on social memory was inhibited by the pretreatment with reserpine and it was antagonized by the administration of haloperidol or sulpiride, but not by SCH 23390. These results indicate that the facilitation of short-term social memory by ethanol is not related to a reduction in the deleterious impact of interference and that this action of ethanol is mediated, at least in part, by D2 receptors, but not by D1 dopaminergic receptors.

The serotonin1A receptor partial agonist S15535 [4-(benzodioxan-5-yl)1-(indan-2-yl)piperazine] enhances cholinergic transmission and cognitive function in rodents: a combined neurochemical and behavioral analysis

These studies examined the influence of the selective 5-hydroxytryptamine (serotonin) (5-HT)(1A) receptor partial agonist S15535 [4-(benzodioxan-5-yl)1-(indan-2-yl)piperazine] upon cholinergic transmission and cognitive function in rodents. In the absence of acetylcholinesterase inhibitors, S15535 dose-dependently (0.04-5.0 mg/kg s.c.) elevated dialysis levels of acetylcholine in the frontal cortex and dorsal hippocampus of freely moving rats. In the cortex, the selective 5-HT(1A) receptor antagonist WAY100,635 [(N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclo-hexanecarboxamide) fumarate] dose-dependently (0.0025-0.63) blocked this action of S15535. By contrast, in dorsal hippocampus, WAY100,635 mimicked the induction of acetylcholine release by S15535. In a social recognition paradigm, S15535 dose-dependently (0.16-10.0) improved retention, an action blocked by WAY100,635 (0.16), which was ineffective alone. Furthermore, S15535 dose-dependently (0.04-2.5) and WAY100,635 reversibly abolished amnesic properties of the muscarinic antagonist scopolamine (0.63) in this procedure. Cognitive deficits provoked by scopolamine in autoshaping and Morris water-maze procedures were likewise blocked by S15535 at doses of 0.63 to 10.0 and 0.16 to 2.5, respectively. In a two-platform spatial discrimination task, in which S15535 similarly abrogates cognitive deficits elicited by scopolamine, injection of S15535 (1.0 and 10.0 microg) into dorsal hippocampus blocked amnesic effects of the 5-HT(1A) agonist 8-hydroxy-2-dipropylaminotetralin (0.5 microg). Finally, S15535 (0.16-0.63) improved performance in a spatial, delayed nonmatching to sample model in mice, and in an operant delayed nonmatching to sample model in old rats, S15535 (1.25-5.0 mg/kg p.o.) increased response accuracy and reduced latency to respond. In conclusion, S15535 reinforces frontocortical and hippocampal release of acetylcholine and displays a broad-based pattern of procognitive properties. Its actions involve both blockade of postsynaptic 5-HT(1A) receptors and engagement of 5-HT(1A) autoreceptors.

Non-specific effect of fear conditioning and specific effect of social defeat on social recognition memory performance in female rats

The so called "emotion learning" literature describes the ability of distressing and aversive unconditioned stimuli to classically condition a learned avoidance response. In order to investigate the impact of experience with noxious stimuli in one conditioning context on learning and memory performance in a separate, non-aversively motivated task, juvenile recognition ability was examined in adult female rats exposed previously to one of two environmental stressors. In particular, experimental adult rats were either socially defeated by exposure to an aggressive conspecific rat or fear conditioned using single or multiple pairings with footshock prior to performance of the social recognition task. Experiment 1 established that repeated exposure to a single juvenile resulted in social memory formation reflected in decreased social investigation from the first to the second exposure. Experiment 2 documented that both single and multiple pairings of an environment with footshock produced robust freezing behavior (90-95% suppression of activity). In addition, fear conditioning produced a non-specific 5-60% increase in social investigation time in both single and multiple-pairing fear conditioned groups which confounded the ability of the social recognition measure to assess effects of fear conditioning on learning and memory performance per se. In contrast, Experiment 3 documented that when social recognition memory performance was impaired to 85% of control levels by imposition of a 2 h delay, exposure to a social defeat stressor reinstated optimal social recognition memory performance. These findings suggest that the after effects of fear conditioning include non-specific alteration of social investigation whereas exposure to conspecific aggression enhances subsequent social recognition memory.

Prefrontocortical dopamine loss in rats delays long-term extinction of contextual conditioned fear, and reduces social interaction without affecting short-term social interaction memory

Prefrontal dopamine loss delays extinction of cued fear conditioning responses, but its role in contextual fear conditioning has not been explored. Medial prefrontal lesions also enhance social interaction in rats, but the role of prefrontal dopamine loss on social interaction memory is not known. Besides, a role for subcortical accumbal dopamine on mnesic changes after prefrontal dopamine manipulation has been proposed but not explored. The objective was to study the involvement of dopaminergic neurotransmission in the medial prefrontal cortex (mPFC) and nucleus accumbens in two mnesic tasks: contextual fear conditioning and social interaction memory. For contextual fear conditioning, short- and long-term freezing responses after an electric shock were studied, as well as extinction retention. Regarding social interaction memory, the recognition of a juvenile, a very sensitive short-term memory test, was used. Dopamine loss was carried out by injection of 6-hydroxydopamine, and postmortem catecholamine levels were analyzed by high-performance liquid chromatography. Prefrontocortical dopamine loss (>76%) led to a reactive enhancement of accumbal dopamine content (p<0.01), supporting the hypothesis that a hyperdopaminergic tone emerges in the nucleus accumbens after prefrontocortical dopamine loss. In lesioned rats, long-term extinction of contextual fear conditioning was significantly delayed and extinction retention was impaired without changes in acquisition and short-term contextual fear conditioning and, on the other hand, acquisition and short-term social interaction memory were not affected, although time spent on social interaction was significantly reduced. Added dopamine loss in the nucleus accumbens (>76%) did not alter these behavioral changes. In summary, the results of the present study indicate that the dopaminergic network in the mPFC (but not in the nucleus accumbens) coordinates the normal long-term extinction of contextual fear conditioning responses without affecting their acquisition, and it is involved in time spent on social interaction, but not acquisition and short-term social interaction memory.

Involvement of central muscarinic receptors in social and nonsocial learning in sheep

Within 12 h following parturition, ewes develop visual and auditory recognition of their lamb. To investigate whether central cholinergic muscarinic transmission plays a specific role in this social learning, we studied the effects of a muscarinic antagonist on neonate recognition via visual/auditory cues and acquisition of a nonsocial visual discrimination. Injections of scopolamine (100 microg/kg; a muscarinic antagonist crossing the blood-brain barrier) after birth did not affect maternal behavior but impaired visual/auditory recognition of the offspring. Recognition impairment did not occur in mothers treated with methylscopolamine (100 microg/kg; a peripheral muscarinic antagonist), indicating that central muscarinic transmission is specifically involved in this social learning. Similar doses of scopolamine strongly delayed learning of a nonsocial, visual discrimination task in comparison to either control or methylscopolamine-treated ewes. Performance on this task was not affected when scopolamine treatment was applied after learning, demonstrating that central muscarinic receptors are necessary for acquisition but not for retrieval. These results suggest that the central muscarinic transmission participates in the establishment of visual/auditory recognition of conspecifics. Moreover, activation of central muscarinic receptors is critical for learning regardless of the social properties of the stimulus.

Neuronal overexpression of "readthrough" acetylcholinesterase is associated with antisense-suppressible behavioral impairments

Molecular origin(s) of the diverse behavioral responses to anticholinesterases were explored in behaviorally impaired transgenic (Tg) FVB/N mice expressing synaptic human acetylcholinesterase (hAChE-S). Untreated hAChE-S Tg, unlike naïve FVB/N mice, presented variably intense neuronal overexpression of the alternatively spliced, stress-induced mouse "readthrough" mAChE-R mRNA. Both strains displayed similar diurnal patterns of locomotor activity that were impaired 3 days after a day-to-night switch. However, hAChE-S Tg, but not FVB/N mice responded to the circadian switch with irregular, diverse bursts of increased locomotor activity. In social recognition tests, controls displayed short-term recognition, reflected by decreased exploration of a familiar, compared to a novel juvenile conspecific as well as inverse correlation between social recognition and cortical and hippocampal AChE specific activities. In contrast, transgenics presented poor recognition, retrievable by tetrahydroaminoacridine (tacrine, 1.5 mg kg(-1)). Tacrine's effect was short-lived (24 h) suppression of the abnormal social recognition pattern in transgenics. Efficacy of antisense treatment was directly correlated with AChE-R levels and the severity of the impaired phenotype, being most apparent in transgenics presenting highly abnormal pre-treatment behavior. These findings demonstrate that neuronal AChE-R overproduction is involved in various behavioral impairments and anticholinesterase responses, and point to the antisense strategy as a potential approach for re-establishing cholinergic balance.

Ethanol improves short-term social memory in rats. Involvement of opioid and muscarinic receptors

Some human and animal studies have demonstrated enhancement of memory processes when ethanol was administered immediately after training and subjects were later tested in the drug-free state. The aim of this study was to evaluate the effect of acute ethanol administration (0.5, 1.0 and 2.0 g/kg) by intraperitoneal (i.p.) and oral route on short-term memory, using the social recognition test in rats. The actions of scopolamine (0.06 and 0.5 mg/kg, i.p.) and naloxone (1.0 mg/kg, i.p.) and their interaction with ethanol in relation to short-term memory were also studied. The doses of ethanol used did not show any sedative effect, which was assessed by measuring locomotor activity. The results indicate that acute low doses of ethanol (0.5 and 1.0 g/kg, i.p.) improve the short-term olfactory memory in rats in a specific and time-dependent manner, and that this action is, at least in part, related to opioid, but not to muscarinic receptors. In addition, these findings confirm that the social recognition test in rats is a useful and reliable model to investigate short-term memory affected by ethanol.

Selective lesions of basal forebrain cholinergic neurons produce anterograde and retrograde deficits in a social transmission of food preference task in rats

We examined the performance of Long-Evans rats with 192 IgG-saporin lesions of the medial septum/vertical limb of the diagonal band (MS/VDB) or nucleus basalis magnocellularis/substantia innominata (NBM/SI), which removed cholinergic projections mainly to hippocampus or neocortex, respectively. We studied the effects of these lesions on anterograde and retrograde memory for a natural form of hippocampal-dependent associative memory, the social transmission of food preference. In a study of anterograde memory, MS/VDB lesions did not affect the immediate, 24-h or 3-week retention of the task. In contrast, NBM/SI lesions severely impaired immediate and 24-h retention. In a study of retrograde memory in which rats acquired the food preference 5 days or 1 day before surgery and they were tested 10-11 days after surgery, MS/VDB-lesioned rats showed striking memory deficits for the preference acquired at a long delay (5 days) before surgery, although all lesioned rats exhibited poorer retention on both retest sessions than on their pretest performance. Subsequent testing of new anterograde learning in these rats revealed no disrupting effects of lesions on a standard two-choice test. When rats were administered a three-choice test, in which the target food was presented along with two more options, NBM/SI-lesioned rats were somewhat impaired on a 24-h retention test. These results provide evidence that NBM/SI and MS/VDB cholinergic neurons are differentially involved in a social memory task that uses olfactory cues, suggesting a role for these neurons in acquisition and consolidation/retrieval of nonspatial declarative memory.

SL65.0155, a novel 5-hydroxytryptamine(4) receptor partial agonist with potent cognition-enhancing properties

SL65.0155 [5-(8-amino-7-chloro-2,3-dihydro-1,4-benzodioxin-5-yl)-3-[1-(2-phenyl ethyl)-4-piperidinyl]-1,3,4-oxadiazol-2(3H)-one monohydrochloride] is a novel benzodioxanoxadiazolone compound with high affinity for human 5-hydroxytryptamine (5-HT)(4) receptors (K(i) of 0.6 nM) and good selectivity (greater than 100-fold for all other receptors tested). In cells expressing the 5-HT(4(b)) and 5-HT(4(e)) splice variants, SL65.0155 acted as a partial agonist, stimulating cAMP production with a maximal effect of 40 to 50% of serotonin. However, in the rat esophagus preparation, SL65.0155 acted as a 5-HT(4) antagonist with a pK(b) of 8.81. In addition, SL65.0155 potently improved performance in several tests of learning and memory. In the object recognition task, it improved retention at 24 h when administered i.p. or p.o. (0.001-0.1 mg/kg). This effect was antagonized by the 5-HT(4) antagonist SDZ 205,557, itself without effect, demonstrating that the promnesic effects of SL65.0155 are mediated by 5-HT(4) agonism. SL65.0155 also reversed the cognitive deficits of aged rats in the linear maze task and the scopolamine-induced deficit of mice in the water maze task. Furthermore, the combined administration of an inactive dose of SL65.0155 with the cholinesterase inhibitor rivastigmine resulted in a significant promnesic effect, suggesting a synergistic interaction. SL65.0155 was devoid of unwanted cardiovascular, gastrointestinal, or central nervous system effects with doses up to more than 100-fold higher than those active in the cognitive tests. These results characterize SL65.0155 as a novel promnesic agent acting via 5-HT(4) receptors, with an excellent preclinical profile. Its broad range of activity in cognitive tests and synergism with cholinesterase inhibitors suggest that SL65.0155 represents a promising new agent for the treatment of dementia.

Effects of acamprosate and some polyamine site ligands of NMDA receptor on short-term memory in rats

The aim of this study was to evaluate the effect of multiple acamprosate (500.0 mg/kg, p.o.) administration on short-term memory, using the social recognition test in rats. Ifenprodil (1.0 mg/kg, i.p.), arcaine (5.0 mg/kg, i.p.) and spermidine (20.0 mg/kg, i.p.) were chosen as polyamine ligands and their action or interaction with acamprosate was also studied. The doses used did not show any sedative activity, which was assessed by measuring locomotor activity and the hypnotic effect of ethanol. The findings suggest that acute acamprosate treatment did not impair short-term memory. Multiple acamprosate and a single spermidine or arcaine administration led to better performance in the memory test, whereas no significant difference was observed in ifenprodil-treated rats. Co-administration of a single arcaine or spermidine dose with multiple acamprosate produced worse results. This means that the effect of repeated acamprosate administration can be changed by the co-administration of other polyamine ligands, so that care should be taken in interpreting.

The neuroendocrine basis of social recognition

All social relationships are dependent on an organism's ability to remember conspecifics. Social memory may be a unique form of memory, critical for reproduction, territorial defense, and the establishment of dominance hierarchies in a natural context. In the laboratory, social memory can be assessed reliably by measuring the reduction in investigation of a familiar partner relative to novel conspecifics. The neurohypophyseal neuropeptides oxytocin and vasopressin have been shown to influence a number of forms of social behavior, including affiliation, aggression, and reproduction. This article reviews vasopressin and oxytocin effects on social cognition, particularly the acquisition and retention of social recognition in rats and mice. Studies in rats have demonstrated that vasopressin in specific neural pathways, such as the lateral septum, is necessary for social recognition. As vasopressin facilitates recall when given after an initial encounter, the peptide appears important for the consolidation not the acquisition of a social memory. Although oxytocin has complex effects on social memory in rats, mice with a null mutation of the oxytocin gene are completely socially amnestic without other cognitive deficits evident. As oxytocin given centrally before but not after the initial encounter restores social recognition in these mutant mice, the neuropeptide appears critical for the acquisition rather than the consolidation phase of memory. Oxytocin's effects on social memory are mediated via a discrete cell population in the medial amygdala. These findings support the hypothesis that vasopressin and oxytocin are essential for social memory, although they appear to influence different cognitive processes and may modulate different neural systems. (c) Elsevier Science.

Oxytocin in the medial amygdala is essential for social recognition in the mouse

Oxytocin (OT) knock-out mice fail to recognize familiar conspecifics after repeated social exposures, despite normal olfactory and spatial learning abilities. OT treatment fully restores social recognition. Here we demonstrate that OT acts in the medial amygdala during the initial exposure to facilitate social recognition. OT given before, but not after, the initial encounter restores social recognition in OT knock-out mice. Using c-Fos immunoreactivity (Fos-IR) as a marker of neuronal activation in this initial encounter, we found similar neuronal activation in the wild-type (WT) and OT knock-out mouse in olfactory bulbs, piriform cortex, cortical amygdala, and the lateral septum. Wild-type, but not OT knock-out mice exhibited an induction of Fos-IR in the medial amygdala. Projections sites of the medial amygdala also failed to show a Fos-IR induction in the OT knock-out mice. OT knock-out, but not WT, mice showed dramatic increases in Fos-IR in the somatosensory cortex and the hippocampus, suggesting alternative processing of social cues in these animals. With site-specific injections of OT and an OT antagonist, we demonstrate that OT receptor activation in the medial amygdala is both necessary and sufficient for social recognition in the mouse.

Nisoxetine infusion into the olfactory bulb enhances the capacity for male rats to identify conspecifics

In the present report, the norepinephrine uptake inhibitor nisoxetine as well as a cocktail of nisoxetine and the alpha-adrenergic receptor antagonist phentolamine were infused unilaterally into the olfactory bulb during microdialysis to assess their effects upon the capacity of male rats to identify conspecifics. A social discrimination test was conducted while simultaneously measuring olfactory bulb norepinephrine output in the dialysate before, during, and after behavioral testing. Nisoxetine significantly increased norepinephrine levels in the olfactory bulb compared with the Ringer's solution control group. Following such increases in olfactory bulb norepinephrine, identification responses were enhanced compared with that observed in the Ringer's control. In the presence of phentolamine, nisoxetine elevated olfactory bulb norepinephrine to levels similar to that obtained in the nisoxetine alone group, however, investigatory responses directed to the conspecifics indicated an absence of identification capacity similar to that observed in the Ringer's control group. These results reveal a direct link between norepinephrine transmission in the olfactory bulb and enhanced identification via its activation of postsynaptic alpha-adrenergic receptors. These results also show that inhibition of norepinephrine uptake may represent an important mechanism involved with the enhancement of social identification and suggest a possible novel effect for the antidepressant nisoxetine.

Ultrasonic vocalizations as an index of social memory in female mice

Ultrasonic vocalization (UV) as a measure of social memory was investigated in female mice. UVs emitted by a resident female in the presence of a same-sex partner were measured during a 3-min, pretest social interaction. In a second 3-min test session, mice were reexposed to the familiar partner or presented with a novel partner. In the first case, there was a decline in UVs emitted by resident mice when the intervals between the 2 sessions were 15, 30, or 60 min. After 24 hr, this effect disappeared. In contrast, with a novel female partner, the number of UVs remained unchanged. Scopolamine (0.05 mg/kg ip) disrupted this memory process: Drug-treated females did not show the expected decrease in UVs when reexposed to the familiar female after 30 min. This study provides behavioral and pharmacological evidence that ultrasonic calls can be used as a measure of social memory in female mice.

Cholinergic basal forebrain is critical for social transmission of food preferences

Studies using selective lesions of basal forebrain cholinergic neurons suggest that these neurons play a role in attentional processing, but not learning and memory. However, the tests of learning and memory used thus far have been restricted largely to spatial tasks. In the present study, we examined whether the cholinergic basal forebrain plays a role in a form of nonspatial associative memory, the social transmission of food preferences. Sham-operated control rats were compared to rats with 192 IgG-saporin lesions of the medial septum/diagonal band cholinergic projections to hippocampus or nucleus basalis magnocellularis/substantia innominata cholinergic projections to neocortex. Both lesions impaired 24-h retention of a learned social food preference relative to controls, despite performance on an immediate retention trial that was indistinguishable from controls. Moreover, 24-h retention of the socially learned food preference correlated strongly with cholinergic enzymatic activity in the neocortex, but not in the hippocampus. Immunohistochemical data confirmed significant and selective lesion-induced cholinergic depletions in the intended brain regions. These data provide evidence that the cholinergic basal forebrain, particularly the cholinergic projection to neocortex, is involved in the formation and/or retrieval of social memories related to food preference, and suggest a role for cortical acetylcholine in consolidation of associative memory processes.