Enhanced methamphetamine self-administration in a neurodevelopmental rat model of schizophrenia

Glutamine and GABA alterations in cingulate cortex may underlie alcohol drinking in a rat model of co-occurring alcohol use disorder and schizophrenia: an 1H-MRS study

Alcohol use disorder commonly occurs in patients with schizophrenia and significantly worsens the clinical course of the disorder. The neurobiological underpinnings of alcohol drinking are not well understood. Magnetic resonance spectroscopy (MRS) has been used to assess the neurochemical substrates that may be associated with alcohol drinking in patients; however, the causal impact of these findings remains elusive, highlighting the need for studies in animal models. This study performed MRS in the neonatal ventral hippocampal lesioned (NVHL) rat model, a model of co-occurring schizophrenia and substance use disorders. NVHL lesions (or sham surgeries) were performed on post-natal day 7 and animals were given brief exposure to alcohol during adolescence (10% v/v in a 2-bottle choice design). Animals were re-exposed to alcohol during adulthood (20% v/v) until a stable drinking baseline was established, and then forced into abstinence to control for the effects of differential alcohol drinking. Animals were scanned for MRS after one month of abstinence. NVHL rats consumed significantly more alcohol than sham rats and in the cingulate cortex showed significantly higher levels of GABA and glutamine. Significantly lower GABA levels were observed in the nucleus accumbens. No differences between the NVHL and sham animals were observed in the hippocampus. Correlation analysis revealed that GABA and glutamine concentrations in the cingulate cortex significantly correlated with the rats' alcohol drinking prior to 30 days of forced abstinence. These findings suggest that a potential dysfunction in the glutamate/GABA-glutamine cycle may contribute to alcohol drinking in a rat model of schizophrenia, and this dysfunction could be targeted in future treatment-focused studies.

Advantages and Limitations of Animal Schizophrenia Models

Mental illness modeling is still a major challenge for scientists. Animal models of schizophrenia are essential to gain a better understanding of the disease etiopathology and mechanism of action of currently used antipsychotic drugs and help in the search for new and more effective therapies. We can distinguish among pharmacological, genetic, and neurodevelopmental models offering various neuroanatomical disorders and a different spectrum of symptoms of schizophrenia. Modeling schizophrenia is based on inducing damage or changes in the activity of relevant regions in the rodent brain (mainly the prefrontal cortex and hippocampus). Such artificially induced dysfunctions approximately correspond to the lesions found in patients with schizophrenia. However, notably, animal models of mental illness have numerous limitations and never fully reflect the disease state observed in humans.

Dropout Rates in Psychosocial Interventions for People With Both Severe Mental Illness and Substance Misuse: A Systematic Review and Meta-Analysis

INTRODUCTION

Over the years, many psychosocial interventions for individual having both a psychotic spectrum disorder and a substance use disorder diagnoses have been developed and studied. However, there is a high dropout rate among this clinical population.

OBJECTIVES

This meta-analysis aims to replicate a previous meta-analysis on the effects of psychosocial treatment for dual disorders, while including and determining the dropout rates in those type of interventions.

METHOD

Based on a Cochrane systematic review conducted in 2019, we conducted a meta-analysis including 40 randomized clinical trials on psychosocial treatment among persons suffering from schizophrenia spectrum disorder and substance use disorder.

RESULTS

A dropout rate of 27,2% was obtained. Stimulants use significantly affected dropout rates. Age, gender, diagnosis, alcohol and cannabis abuse, and duration of treatment did not affect dropout rates.

CONCLUSION

The 27,2% rate of dropout from psychosocial treatment highlights the need to engage participants having a dual diagnosis from the start by focusing on therapeutic alliance and motivation for treatment.

Partial and full deletion of nicotinic acetylcholine receptor α4 and β2 subunits reduces sensitivity to acute nicotine administration and development of tolerance following chronic nicotine administration

The diversity of nicotinic cholinergic receptor (nAChR) subunits underlies the complex responses to nicotine. Mice differing in the expression of α4 and β2 subunits, which are most widely expressed in brain, were evaluated for the responses to acute nicotine administration on Y-maze crossings and rears, open-field locomotion and body temperature following chronic treatment with nicotine (0, 0.25, 1.0 and 4.0 mg/kg/h). Deletion or partial deletion of the α4, β2 or both nAChR subunits reduced the sensitivity of mice to acute nicotine administration. This reduced sensitivity was gene dose-dependent. Modification of α4 subunit expression elicited a greater reduction in sensitivity than the modification of β2 subunit expression. No measurable tolerance was observed for mice of any genotype following chronic treatment with 0.25 mg/kg/h nicotine. Modest tolerance was noted following treatment with 1.0 mg/kg/h. Greater tolerance was observed following treatment with 4.0 mg/kg/h. The extent of tolerance differed among the mice depending on genotype: wild-type (α4 and β2) developed measurable tolerance for all four tests. Heterozygotes (α4, β2 and α4/β2) developed tolerance for only Y-maze crossings and body temperature. Null mutants (α4 and β2) did not become tolerant. However, following chronic treatment with 4.0 mg/kg/h nicotine, wild type, α4 and α4 mice displayed increased Y-maze crossings following acute administration of 0.5 mg/kg nicotine that may reflect the activity of α6β2*-nAChR. These results confirm the importance of the α4 and β2 nAChR subunits in mediating acute and chronic effects of nicotine on locomotion and body temperature in the mouse.

Maternal immune activation is associated with a lower number of dopamine receptor 3-expressing granulocytes with no alterations in cocaine reward, resistance to extinction or cue-induced reinstatement

There is evidence for increased rates of drug use among schizophrenic patients. However, the causality in this relationship remains unclear. In the present work, we use a maternal immune activation model to test whether animals at high risk of developing a schizophrenia-like condition are more prone to acquire cocaine self-administration, show enhanced sensitivity to the reinforcing actions of cocaine or if they are resistant to extinction or vulnerable to relapse. Also, given that D3 and CB2 receptor expression in immune cells is altered in patients with schizophrenia, we examined the populations of immune cells expressing these receptors. Pregnant rats were daily injected with lipopolysaccharide (LPS) (2 mg/kg s.c.) or saline during pregnancy, and we tested prepulse inhibition -PPI- in the offspring. After this, one group of rats was submitted to cocaine self-administration (0.5 mg/kg) under fixed and progressive ratio schedules, dose-response testing, extinction and cue-induced drug-seeking. Another group was sacrificed to study the immune blood cells by flow cytometry. While rats born to LPS-treated mothers showed impaired PPI, there were no differences in cocaine self-administration acquisition, responsiveness to dose shifts, extinction or cue-induced reinstatement. Finally, there were fewer D3R⁺ granulocytes in the LPS-offspring and an exciting trend for CB2R⁺ lymphocytes to be more abundant in LPS-exposed rats. Our results indicate that the higher prevalence of cocaine abuse among people with schizophrenia is not due to a pre-existing pathology and suggest that D3R⁺ granulocytes and possibly CB2R⁺ lymphocytes could be potential biomarkers of schizophrenia.

Integrated Effects of Neonatal Ventral Hippocampal Lesions and Impoverished Social-Environmental Rearing on Endophenotypes of Mental Illness and Addiction Vulnerability

A wide range of mental illnesses show high rates of addiction comorbidities regardless of their genetic, neurodevelopmental, and/or adverse-environmental etiologies. Understanding how the spectrum of mental illnesses produce addiction vulnerability will be key to discovering more effective preventions and integrated treatments for adults with addiction and dual diagnosis comorbidities. A population of 131 rats containing a spectrum of etiological mental illness models and degrees of severity was experimentally generated by crossing neonatal ventral hippocampal lesions (NVHL; n = 68) or controls (SHAM-operated; n = 63) with adolescent rearing in environmentally/socially enriched (ENR; n = 66) or impoverished (IMP; n = 65) conditions. This population was divided into 2 experiments: first, examining NVHL and IMP effects on novelty and mild stress-induced locomotion across 3 adolescent ages; second, looking at initial cocaine reactivity and long-term cocaine behavioral sensitization in adulthood. NVHL and IMP-environmental conditions independently produced remarkably similar and robustly significant abnormalities of hyperreactivity to novelty, mild stress, and long-term cocaine sensitization. The combined NVHL-IMP groups showed the most severe phenotypes across the board, so that the mental illness and addiction vulnerability phenotypes increased together in severity in a consistent stepwise progression from the healthiest rats to those with the greatest loading of etiological models. These findings add weight to our understanding of mental illness and addiction vulnerability as brain disorders that are biologically and developmentally unified in ways that transcend etiological causes, and yet co-intensify with increased loading of etiological conditions. Combining neurodevelopmental and adverse-environmental models of mental illness may provide an approach to identifying and therapeutically targeting cortical-striatal-limbic network mechanisms that generate addiction and dual diagnosis diseases.

Polysubstance addiction vulnerability in mental illness: Concurrent alcohol and nicotine self-administration in the neurodevelopmental hippocampal lesion rat model of schizophrenia

Multiple addictions frequently occur in patients with mental illness. However, basic research on the brain-based linkages between these comorbidities is extremely limited. Toward characterizing the first animal modeling of polysubstance use and addiction vulnerability in schizophrenia, adolescent rats with neonatal ventral hippocampal lesions (NVHLs) and controls had 19 weekdays of 1 hour/day free access to alcohol/sucrose solutions (fading from 10% sucrose to 10% alcohol/2% sucrose on day 10) during postnatal days (PD 35-60). Starting in adulthood (PD 63), rats acquired lever pressing for concurrent oral alcohol (10% with 2% sucrose) and iv nicotine (0.015 mg/kg/injection) across 15 sessions. Subsequently, 10 operant extinction sessions and 3 reinstatement sessions examined drug seeking upon withholding of nicotine, then both nicotine and alcohol, then reintroduction. Adolescent alcohol consumption did not differ between NVHLs and controls. However, in adulthood, NVHLs showed increased lever pressing at alcohol and nicotine levers that progressed more strongly at the nicotine lever, even as most pressing by both groups was at the alcohol lever. In extinction, both groups showed expected declines in effort as drugs were withheld, but NVHLs persisted with greater pressing at both alcohol and nicotine levers. In reinstatement, alcohol reaccess increased pressing, with NVHLs showing greater nicotine lever activity overall. Developmental temporal-limbic abnormalities that produce mental illness can thus generate adult polydrug addiction vulnerability as a mechanism independent from putative cross-sensitization effects between addictive drugs. Further preclinical modeling of third-order (and higher) addiction-mental illness comorbidities may advance our understanding and treatment of these complex, yet common brain illnesses.

Depleting adult dentate gyrus neurogenesis increases cocaine-seeking behavior

The hippocampus is the main locus for adult dentate gyrus (DG) neurogenesis. A number of studies have shown that aberrant DG neurogenesis correlates with many neuropsychiatric disorders, including drug addiction. Although clear causal relationships have been established between DG neurogenesis and memory dysfunction or mood-related disorders, evidence of the causal role of DG neurogenesis in drug-seeking behaviors has not been established. Here we assessed the role of new DG neurons in cocaine self-administration using an inducible transgenic approach that selectively depletes adult DG neurogenesis. Our results show that transgenic mice with decreased adult DG neurogenesis exhibit increased motivation to self-administer cocaine and a higher seeking response to cocaine-related cues. These results identify adult hippocampal neurogenesis as a key factor in vulnerability to cocaine addiction.

The link between schizophrenia and substance use disorder: A unifying hypothesis

Substance use disorders occur commonly in patients with schizophrenia and dramatically worsen their overall clinical course. While the exact mechanisms contributing to substance use in schizophrenia are not known, a number of theories have been put forward to explain the basis of the co-occurrence of these disorders. We propose here a unifying hypothesis that combines recent evidence from epidemiological and genetic association studies with brain imaging and pre-clinical studies to provide an updated formulation regarding the basis of substance use in patients with schizophrenia. We suggest that the genetic determinants of risk for schizophrenia (especially within neural systems that contribute to the risk for both psychosis and addiction) make patients vulnerable to substance use. Since this vulnerability may arise prior to the appearance of psychotic symptoms, an increased use of substances in adolescence may both enhance the risk for developing a later substance use disorder, and also serve as an additional risk factor for the appearance of psychotic symptoms. Future studies that assess brain circuitry in a prospective longitudinal manner during adolescence prior to the appearance of psychotic symptoms could shed further light on the mechanistic underpinnings of these co-occurring disorders while identifying potential points of intervention for these difficult-to-treat co-occurring disorders.

Behavioral predictors of alcohol drinking in a neurodevelopmental rat model of schizophrenia and co-occurring alcohol use disorder

Alcohol use disorder commonly occurs in patients with schizophrenia and contributes greatly to its morbidity. Unfortunately, the neural and behavioral underpinnings of alcohol drinking in these patients are not well understood. In order to begin to understand the cognitive and reward-related changes that may contribute to alcohol drinking, this study was designed to address: 1) latent inhibition; 2) conditioning; and 3) extinction of autoshaping in a neurodevelopmental rat model with relevance to co-occurring schizophrenia and alcohol use disorders, the neonatal ventral hippocampal lesioned (NVHL) rat. NVHL lesions (or sham surgeries) were performed on post-natal day 7 (PND7) and animals were given brief exposure to alcohol during adolescent (PND 28-42). Latent inhibition of autoshaping, conditioning and extinction were assessed between PND 72-90. On PND90 animals were given alcohol again and allowed to establish stable drinking. Latent inhibition of autoshaping was found to be prolonged in the NVHL rats; the NVHL rats pre-exposed to the lever stimulus were slower to acquire autoshaping than sham pre-exposed rats. NVHL rats that were not pre-exposed to the lever stimulus did not differ during conditioning, but were slower to extinguish conditioned responding compared to sham controls. Finally, the NVHL rats from both groups drank significantly more alcohol than sham rats, and the extent of latent inhibition predicted future alcohol intake in the pre-exposed animals. These findings suggest that the latent inhibition of autoshaping procedure can be used to model cognitive- and reward-related dysfunctions in schizophrenia, and these dysfunctions may contribute to the development of co-occurring alcohol use.

Suppression of Methamphetamine Self-Administration by Ketamine Pre-treatment Is Absent in the Methylazoxymethanol (MAM) Rat Model of Schizophrenia

Ketamine may prove to be a potential candidate in treating the widespread drug addiction/substance abuse epidemic among patients with schizophrenia. Clinical studies have shown ketamine to reduce cocaine and heroin cravings. However, the use of ketamine remains controversial as it may exacerbate the symptoms of schizophrenia. Therefore, the aim of this study is to characterize the effects of ketamine on drug addiction in schizophrenia using the methylazoxymethanol (MAM) acetate rat model on operant IV methamphetamine (METH) self-administration. MAM was administered intraperitoneally (22 mg/kg) on gestational day 17. Locomotor activity test and later IV self-administration (IVSA) were then performed in the male offspring followed by a period of forced abstinence and relapse of METH taking. After reaching stable intakes in the relapse phase, ketamine (5 mg/kg) was administered intraperitoneally 30 min prior to the self-administration session. As documented previously, the MAM rats showed a lack of habituation in the locomotor activity test but developed stable maintenance of METH self-administration with no difference in operant behaviour to control animals. Results show that ketamine treatment significantly reduced the METH intake in the control animals but not in MAM animals. Ketamine effect on METH self-administration may be explained by increased glutamatergic signalling in the prefrontal cortex caused by the N-methyl-D-aspartate antagonism and disinhibition of GABA interneurons which was shown to be impaired in the MAM rats. This mechanism may at least partly explain the clinically proven anti-craving potential of ketamine and allow development of more specific anti-craving medications with fewer risks.

Reactivity to addictive drugs in the methylazoxymethanol (MAM) model of schizophrenia in male and female rats

OBJECTIVES

Patients with schizophrenia often suffer comorbid substance abuse regardless of gender. However, the vast majority of studies are only conducted in male subjects. Therefore, the aim of these experiments is to assess addictive behaviors of both sexes in a neurodevelopmental model of schizophrenia induced by prenatal methylazoxymethanol (MAM) acetate exposure.

METHODS

MAM (22 mg/kg) was administered intraperitoneally on gestational day 17. Two studies were performed in the offspring: (1) an alcohol-drinking procedure to assess daily intake of 20% alcohol and relapse-like behavior after a period of forced abstinence; (2) Methamphetamine (METH) intravenous self administration (IVSA) followed by forced abstinence and reinstatement phases.

RESULTS

MAM exposure during the prenatal period did not change alcohol drinking regardless of sex. However, MAM females showed higher alcohol consumption in comparison to MAM males. The METH IVSA study revealed only a modest increase of drug consumption in MAM males, while there was no difference between the female groups. Reinstatement data showed no effect of the MAM model in either sex, but suggested increased responding in female rats.

CONCLUSIONS

This study suggests that female sex and schizophrenia-like phenotype may work synergistically to enhance alcohol consumption. However, future research is needed to establish paradigms in which these findings would be readily assessed to test anti-addiction treatments.

Research Domain Criteria versus DSM V: How does this debate affect attempts to model corticostriatal dysfunction in animals?

For decades, the nosology of mental illness has been based largely upon the descriptions in the Diagnostic and Statistical Manual of the American Psychiatric Association (DSM). A recent challenge to the DSM approach to psychiatric nosology from the National Institute on Mental Health (USA) defines Research Domain Criteria (RDoC) as an alternative. For RDoC, psychiatric illnesses are not defined as discrete categories, but instead as specific behavioral dysfunctions irrespective of DSM diagnostic categories. This approach was driven by two primary weaknesses noted in the DSM: (1) the same symptoms occur in very different disease states; and (2) DSM criteria lack grounding in the underlying biological causes of mental illness. RDoC intends to ground psychiatric nosology in those underlying mechanisms. This review addresses the suitability of RDoC vs. DSM from the view of modeling mental illness in animals. A consideration of all types of psychiatric dysfunction is beyond the scope of this review, which will focus on models of conditions associated with frontostriatal dysfunction.

The Neonatal Ventral Hippocampal Lesion (NVHL) Rodent Model of Schizophrenia

Animal models are crucial to the study of the neurobiological bases of psychiatric disorders, but schizophrenia is a particularly challenging disorder to model given the complexity and heavily verbal nature of its symptoms. This unit describes a developmental surgical rodent model of schizophrenia, the neonatal ventral hippocampal lesion (NVHL) model. This widely used model produces reliable behavioral abnormalities that are comparable to those observed in patients, as well as anatomical and neurophysiological disruptions in forebrain areas that are also implicated in schizophrenia. A brief background of the development and validity of the NVHL model is discussed here, along with detailed procedures for producing the model in rats. Critical issues particular to neonatal surgery are discussed, and representative histological and behavioral results are presented. © 2016 by John Wiley & Sons, Inc.

Functional evidence for a direct excitatory projection from the lateral habenula to the ventral tegmental area in the rat

The lateral habenula, a phylogenetically conserved epithalamic structure, is activated by aversive stimuli and reward omission. Excitatory efferents from the lateral habenula predominately inhibit midbrain dopamine neuronal firing through a disynaptic, feedforward inhibitory mechanism involving the rostromedial tegmental nucleus. However, the lateral habenula also directly targets dopamine neurons within the ventral tegmental area, suggesting that opposing actions may result from increased lateral habenula activity. In the present study, we tested the effect of habenular efferent stimulation on dopamine and nondopamine neurons in the ventral tegmental area of Sprague-Dawley rats using a parasagittal brain slice preparation. Single pulse stimulation of the fasciculus retroflexus excited 48% of dopamine neurons and 51% of nondopamine neurons in the ventral tegmental area of rat pups. These proportions were not altered by excision of the rostromedial tegmental nucleus and were evident in both cortical- and striatal-projecting dopamine neurons. Glutamate receptor antagonists blocked this excitation, and fasciculus retroflexus stimulation elicited evoked excitatory postsynaptic potentials with a nearly constant onset latency, indicative of a monosynaptic, glutamatergic connection. Comparison of responses in rat pups and young adults showed no significant difference in the proportion of neurons excited by fasciculus retroflexus stimulation. Our data indicate that the well-known, indirect inhibitory effect of lateral habenula activation on midbrain dopamine neurons is complemented by a significant, direct excitatory effect. This pathway may contribute to the role of midbrain dopamine neurons in processing aversive stimuli and salience.

Animal Models of Maladaptive Traits: Disorders in Sensorimotor Gating and Attentional Quantifiable Responses as Possible Endophenotypes

Traditional diagnostic scales are based on a number of symptoms to evaluate and classify mental diseases. In many cases, this process becomes subjective, since the patient must calibrate the magnitude of his/her symptoms and therefore the severity of his/her disorder. A completely different approach is based on the study of the more vulnerable traits of cognitive disorders. In this regard, animal models of mental illness could be a useful tool to characterize indicators of possible cognitive dysfunctions in humans. Specifically, several cognitive disorders such as schizophrenia involve a dysfunction in the mesocorticolimbic dopaminergic system during development. These variations in dopamine levels or dopamine receptor sensibility correlate with many behavioral disturbances. These behaviors may be included in a specific phenotype and may be analyzed under controlled conditions in the laboratory. The present study provides an introductory overview of different quantitative traits that could be used as a possible risk indicator for different mental disorders, helping to define a specific endophenotype. Specifically, we examine different experimental procedures to measure impaired response in attention linked to sensorimotor gating as a possible personality trait involved in maladaptive behaviors.

Abnormal context-reward associations in an immune-mediated neurodevelopmental mouse model with relevance to schizophrenia

Impairments in central reward processing constitute an important aspect of the negative symptoms of schizophrenia. Despite its clinical relevance, the etiology of deficient reward processing in schizophrenia remains largely unknown. Here, we used an epidemiologically informed mouse model of schizophrenia to explore the effects of prenatal immune activation on reward-related functions. The model is based on maternal administration of the viral mimic PolyI:C and has been developed in relation to the epidemiological evidence demonstrating enhanced risk of schizophrenia and related disorders following prenatal maternal infection. We show that prenatal immune activation induces selective deficits in the expression (but not acquisition) of conditioned place preference for a natural reward (sucrose) without changing hedonic or neophobic responses to the reward. On the other hand, prenatal immune activation led to enhanced place preference for the psychostimulant drug cocaine, while it attenuated the locomotor reaction to the drug. The prenatal exposure did not alter negative reinforcement learning as assessed using a contextual fear conditioning paradigm. Our findings suggest that the nature of reward-related abnormalities following prenatal immune challenge depends on the specificity of the reward (natural reward vs drug of abuse) as well as on the valence domain (positive vs negative reinforcement learning). Moreover, our data indicate that reward abnormalities emerging in prenatally immune-challenged offspring may, at least in part, stem from an inability to retrieve previously established context-reward associations and to integrate such information for appropriate goal-directed behavior.

Light alcohol intake during adolescence induces alcohol addiction in a neurodevelopmental model of schizophrenia

Schizophrenia is a mental disorder characterized by a series of positive, negative or cognitive symptoms but with also the particularity of exhibiting a high rate of co-morbid use of drugs of abuse. While more than 80% of schizophrenics are smokers, the second most consumed drug is alcohol, with dramatic consequences on frequency and intensity of psychotic episodes and on life expectancy. Here we investigated the impact of light alcohol intake during adolescence on the subsequent occurrence of alcohol addiction-like behavior in neonatal ventral hippocampal lesion (NVHL) rats, a neurodevelopmental model of schizophrenia. Our findings demonstrated an increased liability to addictive behaviors in adult NVHL rats after voluntary alcohol intake during adolescence. NVHL rats displayed several signs of alcohol use disorder such as a loss of control over alcohol intake and high motivation to consume alcohol, associated with a higher resistance to extinction. In addition, once NVHL rats relapsed, they maintained higher drinking levels than controls. We finally showed that the anti-addictive drug naltrexone is efficient in reducing excessive alcohol intake in NVHL rats. Our results are in accordance with epidemiological studies underlying the particular vulnerability to alcohol addiction after adolescent exposure to alcohol and highlight the fact that schizophrenic subjects may be particularly at risk even after light alcohol consumption. Based on these results, it seems particularly relevant to prevent early onset of alcohol use in at-risk subjects and thus to reduce the incidence of co-morbid alcohol abuse in psychotic patients.

Hippocampal neurogenesis protects against cocaine-primed relapse

Accumulating evidence demonstrates a functional role for the hippocampus in mediating relapse to cocaine-seeking behavior and extinction-induced inhibition of cocaine seeking, and dentate gyrus neurogenesis in the hippocampus may have a role. Here, we tested the hypothesis that disruption of normal hippocampal activity during extinction alters relapse to cocaine-seeking behavior as a function of dentate gyrus neurogenesis. Adult rats were trained to self-administer cocaine on a fixed-ratio schedule, followed by extinction and cocaine-primed reinstatement testing. Some rats received low-frequency stimulation (LFS; 2 Hz for 25 minutes) after each extinction session in the dorsal or ventral hippocampal formation. All rats received an injection of the mitotic marker 5-bromo-2'-deoxyuridine (BrdU) to label developing dentate gyrus neurons during self-administration, as well as before or after extinction and LFS. We found that LFS during extinction did not alter extinction behavior but enhanced cocaine-primed reinstatement. Cocaine self-administration reduced levels of 24-day-old BrdU cells and dentate gyrus neurogenesis, which was normalized by extinction. LFS during extinction prevented extinction-induced normalization of dentate gyrus neurogenesis and potentiated cocaine-induced reinstatement of drug seeking. LFS inhibition of extinction-induced neurogenesis was not due to enhanced cell death, revealed by quantification of activated caspase3-labeled cells. These data suggest that LFS during extinction disrupts hippocampal networking by disrupting neurogenesis and also strengthens relapse-like behaviors. Thus, newly born dentate gyrus neurons during withdrawal and extinction learning facilitate hippocampal networking that mediates extinction-induced inhibition of cocaine seeking and may play a key role in preventing relapse.

Negative symptoms of schizophrenia: clinical characteristics, pathophysiological substrates, experimental models and prospects for improved treatment

Schizophrenia is a complex and multifactorial disorder generally diagnosed in young adults at the time of the first psychotic episode of delusions and hallucinations. These positive symptoms can be controlled in most patients by currently-available antipsychotics. Conversely, they are poorly effective against concomitant neurocognitive dysfunction, deficits in social cognition and negative symptoms (NS), which strongly contribute to poor functional outcome. The precise notion of NS has evolved over the past century, with recent studies - underpinned by novel rating methods - suggesting two major sub-domains: "decreased emotional expression", incorporating blunted affect and poverty of speech, and "avolition", which embraces amotivation, asociality and "anhedonia" (inability to anticipate pleasure). Recent studies implicate a dysfunction of frontocortico-temporal networks in the aetiology of NS, together with a disruption of cortico-striatal circuits, though other structures are also involved, like the insular and parietal cortices, amygdala and thalamus. At the cellular level, a disruption of GABAergic-glutamatergic balance, dopaminergic signalling and, possibly, oxytocinergic and cannibinoidergic transmission may be involved. Several agents are currently under clinical investigation for the potentially improved control of NS, including oxytocin itself, N-Methyl-d-Aspartate receptor modulators and minocycline. Further, magnetic-electrical "stimulation" strategies to recruit cortical circuits and "cognitive-behavioural-psychosocial" therapies likewise hold promise. To acquire novel insights into the causes and treatment of NS, experimental study is crucial, and opportunities are emerging for improved genetic, pharmacological and developmental modelling, together with more refined readouts related to deficits in reward, sociality and "expression". The present article comprises an integrative overview of the above issues as a platform for this Special Issue of European Neuropsychopharmacology in which five clinical and five preclinical articles treat individual themes in greater detail. This Volume provides, then, a framework for progress in the understanding - and ultimately control - of the debilitating NS of schizophrenia.

Evaluating negative-symptom-like behavioural changes in developmental models of schizophrenia

Many lines of evidence suggest that schizophrenia has a major developmental component and that environmental factors that disrupt key stages of development, such as maternal stress during pregnancy as a result of infection or malnutrition, can increase the risk of developing schizophrenia in later life. This review examines how non-clinical neurodevelopmental models pertinent to schizophrenia have been evaluated for their ability to reproduce behavioural deficits related to the negative symptoms of schizophrenia. The more frequently used are the prenatal application of the mitotoxic agent methylazoxymethanol, prenatal immune challenge and the neonatal ventral hippocampus lesion model. In general they have been extensively evaluated in models considered relevant to positive symptoms of schizophrenia. In contrast, very few studies have examined tests related to negative symptoms and, when they have, it has almost exclusively been a social interaction model. Other aspects related to negative symptoms such as anhedonia, affective flattening and avolition have almost never been studied. Further studies examining other components of negative symptomatology are needed to more clearly associate these deficits with a schizophrenia-like profile as social withdrawal is a hallmark of many disorders. Although there are no truly effective treatments for negative symptoms, better characterisation with a broader range of drugs used in schizophrenia will be necessary to better evaluate the utility of these models. In summary, developmental models of schizophrenia have been extensively studied as models of positive symptoms but, given the unmet need in the clinic, the same effort now needs to be made with regard to negative symptoms.

Cortical-striatal gene expression in neonatal hippocampal lesion (NVHL)-amplified cocaine sensitization

Cortical-striatal circuit dysfunction in mental illness may enhance addiction vulnerability. Neonatal ventral hippocampal lesions (NVHL) model this dual diagnosis causality by producing a schizophrenia syndrome with enhanced responsiveness to addictive drugs. Rat genome-wide microarrays containing >24 000 probesets were used to examine separate and co-occurring effects of NVHLs and cocaine sensitization (15 mg/kg/day × 5 days) on gene expression within medial prefrontal cortex (MPFC), nucleus accumbens (NAC), and caudate-putamen (CAPU). Two weeks after NVHLs robustly amplified cocaine behavioral sensitization, brains were harvested for genes of interest defined as those altered at P < 0.001 by NVHL or cocaine effects or interactions. Among 135 genes so impacted, NVHLs altered twofold more than cocaine, with half of all changes in the NAC. Although no genes were changed in the same direction by both NVHL and cocaine history, the anatomy and directionality of significant changes suggested synergy on the neural circuit level generative of compounded behavioral phenotypes: NVHL predominantly downregulated expression in MPFC and NAC while NVHL and cocaine history mostly upregulated CAPU expression. From 75 named genes altered by NVHL or cocaine, 27 had expression levels that correlated significantly with degree of behavioral sensitization, including 11 downregulated by NVHL in MPFC/NAC, and 10 upregulated by NVHL or cocaine in CAPU. These findings suggest that structural and functional impoverishment of prefrontal-cortical-accumbens circuits in mental illness is associated with abnormal striatal plasticity compounding with that in addictive disease. Polygenetic interactions impacting neuronal signaling and morphology within these networks likely contribute to addiction vulnerability in mental illness.

Adult hippocampal neurogenesis in the pathogenesis of addiction and dual diagnosis disorders

BACKGROUND

As knowledge deepens about how new neurons are born, differentiate, and wire into the adult mammalian brain, growing evidence depicts hippocampal neurogenesis as a special form of neuroplasticity that may be impaired across psychiatric disorders. This review provides an integrated-evidence based framework describing a neurogenic basis for addictions and addiction vulnerability in mental illness.

METHODS

Basic studies conducted over the last decade examining the effects of addictive drugs on adult neurogenesis and the impact of neurogenic activity on addictive behavior were compiled and integrated with relevant neurocomputational and human studies.

RESULTS

While suppression of hippocampal neurogenic proliferation appears to be a universal property of addictive drugs, the pathophysiology of addictions involves neuroadaptative processes within frontal-cortical-striatal motivation circuits that the neurogenic hippocampus regulates via direct projections. States of suppressed neurogenic activity may simultaneously underlie psychiatric and cognitive symptoms, but also confer or signify hippocampal dysfunction that heightens addiction vulnerability in mental illness as a basis for dual diagnosis disorders.

CONCLUSIONS

Research on pharmacological, behavioral and experiential strategies that enhance adaptive regulation of hippocampal neurogenesis holds potential in advancing preventative and integrative treatment strategies for addictions and dual diagnosis disorders.

Using rodents to model schizophrenia and substance use comorbidity

Schizophrenia and substance use disorders (SUD) often occur together, yet it is unclear why this is the case or how best to manage dual diagnosis. Rodent models are well suited to study how genes and environment interact to impact neurodevelopment, brain function and behaviors relevant to dual diagnosis. Indeed a variety of rodent models for schizophrenia display behavioral and physiological features relevant to SUD including: neurodevelopmental models, models of a rare variant (Disc1), to models of common variants (neurexin, dysbindin and neuregulin), and models of various gene-drug interactions. Thus it may be worthwhile to probe models of schizophrenia for insights relevant to SUD and dual diagnosis. However, future studies on dual diagnosis should involve characterization beyond measuring locomotor responses to self-administration tasks, include drug classes other than psychostimulants, and dissect the neuroadaptations that underlie risk for dual diagnosis.

Exaggerated cue-induced reinstatement of cocaine seeking but not incubation of cocaine craving in a developmental rat model of schizophrenia

RATIONALE

Patients with schizophrenia exhibit high comorbidity for substance abuse, but the biological underpinnings of this dual-diagnosis condition are still unclear. Previous studies have shown that rats with a neonatal ventral hippocampal lesion (NVHL), a widely used developmental animal model of schizophrenia, exhibit increased cocaine and methamphetamine self-administration and cocaine-induced reinstatement.

OBJECTIVE

Here, we assessed whether a NVHL would also potentiate cue-induced reinstatement of cocaine seeking and the time-dependent increases in cue-induced cocaine seeking after withdrawal (incubation of cocaine craving) in adult rats.

METHODS

Rats were trained to self-administer cocaine (3 or 6 h/day with 0.75 mg kg(-1) infusion(-1) paired with a tone-light cue) for 10 days, followed by extinction training (3 h/day) and cue-induced reinstatement of cocaine seeking. Other rats were tested for incubation of cocaine craving, assessed in extinction tests 1 and 30 days after the last self-administration session.

RESULTS

Although there was no significant difference in cocaine intake between NVHL and sham controls, NVHL rats took significantly longer to reach an a priori set extinction criterion and exhibited enhanced cue-induced reinstatement. However, while cue-induced cocaine seeking was higher after 30 days than after 1 day of withdrawal (incubation of cocaine craving), the NVHL had no effect on this incubation.

CONCLUSION

These data confirm previous reports on enhanced resistance to extinction after NVHL and demonstrate that NVHL rats exhibit enhanced cue-induced reinstatement of cocaine seeking after extinction, a measure of drug relapse.

Cortical disinhibition in the neonatal ventral hippocampal lesion model of schizophrenia: new vistas on possible therapeutic approaches

The neonatal ventral hippocampal lesion (NVHL) model of schizophrenia has been extensively used in many laboratories over the past couple of decades. With more than 120 publications from over 15 research groups, this developmental model yields a number of schizophrenia-relevant behavioral, neurochemical and electrophysiological deficits. An important aspect of this model is the delayed emergence of alterations, typically during adolescence despite the manipulation that causes them having been performed during the first postnatal week. Such delayed timing reflects the periadolescent onset of schizophrenia symptoms and may be related to the protracted maturation of cortical circuits, affected in both the disease and the NVHL model. Here, I will review the work we have done regarding the maturation of prefrontal cortical-accumbens circuits during adolescence, and how this maturation is affected in rats with a NVHL. One of the principal elements affected in NVHL rats is the dopamine modulation of prefrontal cortical interneurons, and this finding is convergent with data from many other developmental, genetic and pharmacological models. An altered maturation of interneuron function would yield a disinhibited cortex, and this opens the way to novel therapeutic approaches for treatment and even prevention of schizophrenia.

Adolescent onset of cortical disinhibition in schizophrenia: insights from animal models

Schizophrenia and related mental disorders are common and devastating conditions for which we have a limited understanding of their origin and mechanisms. Although this apparent lack of progress despite vast research efforts could be due to difficulties in reproducing the disease in animals, animal work is now providing important insight onto possible pathophysiological changes in the brain. Postmortem studies of human brains have provided data indicating altered local inhibitory circuits in the cerebral cortex in schizophrenia and different developmental, pharmacological, and genetic animal models converge in revealing deficits in cortical interneuron function that can be associated with neurophysiological and behavioral alterations resembling aspects of the disease. Schizophrenia pathophysiology has a complex developmental trajectory because overt symptoms become evident during late adolescence despite earlier events contributing to the disease. The late incidence of schizophrenia can be explained by the protracted maturation of brain circuits implicated in the disease, particularly during adolescence. Excitatory and inhibitory processes in cortical circuits are tightly modulated by dopamine (DA), and many aspects of DA function in cortical regions acquire their adult profile during adolescence. This maturation fails to occur or is abnormal in several different rodent models of schizophrenia, yielding a number of functional and behavioral deficits relevant to the disease. Thus, periadolescent changes in cortical inhibitory circuits are a critical developmental stage likely implicated in the transition to schizophrenia. These observations provide the foundation for novel research-based therapeutic approaches and perhaps will even lead to ways to prevent the progression of the disease in predisposed subjects.

Alcohol seeking and consumption in the NVHL neurodevelopmental rat model of schizophrenia

Alcohol abuse in schizophrenia exceeds rates in the general population and worsens illness outcomes. Neonatal ventral hippocampal lesion (NVHL) rats model multiple schizophrenia dimensions including addiction vulnerability. This study compared NVHL vs. SHAM-controls in operant alcohol seeking and consumption. NVHLs enhanced consumption of combined ethanol/sucrose solution but neither ethanol or sucrose only solutions, consistent with increased vulnerability specific to carbohydrate-laden alcohol beverages typically consumed in early stages of human alcoholism.

Methamphetamine reduces LTP and increases baseline synaptic transmission in the CA1 region of mouse hippocampus

Methamphetamine (METH) is an addictive psychostimulant whose societal impact is on the rise. Emerging evidence suggests that psychostimulants alter synaptic plasticity in the brain--which may partly account for their adverse effects. While it is known that METH increases the extracellular concentration of monoamines dopamine, serotonin, and norepinephrine, it is not clear how METH alters glutamatergic transmission. Within this context, the aim of the present study was to investigate the effects of acute and systemic METH on basal synaptic transmission and long-term potentiation (LTP; an activity-induced increase in synaptic efficacy) in CA1 sub-field in the hippocampus. Both the acute ex vivo application of METH to hippocampal slices and systemic administration of METH decreased LTP. Interestingly, the acute ex vivo application of METH at a concentration of 30 or 60 microM increased baseline synaptic transmission as well as decreased LTP. Pretreatment with eticlopride (D2-like receptor antagonist) did not alter the effects of METH on synaptic transmission or LTP. In contrast, pretreatment with D1/D5 dopamine receptor antagonist SCH23390 or 5-HT1A receptor antagonist NAN-190 abrogated the effect of METH on synaptic transmission. Furthermore, METH did not increase baseline synaptic transmission in D1 dopamine receptor haploinsufficient mice. Our findings suggest that METH affects excitatory synaptic transmission via activation of dopamine and serotonin receptor systems in the hippocampus. This modulation may contribute to synaptic maladaption induced by METH addiction and/or METH-mediated cognitive dysfunction.

Ventral and dorsal striatal dopamine efflux and behavior in rats with simple vs. co-morbid histories of cocaine sensitization and neonatal ventral hippocampal lesions

RATIONAL

Exposing animal models of mental illness to addictive drugs provides an approach to understanding the neural etiology of dual diagnosis disorders. Previous studies have shown that neonatal ventral hippocampal lesions (NVHL) in rats produce features of both schizophrenia and addiction vulnerability.

OBJECTIVE

This study investigated ventral and dorsal striatal dopamine (DA) efflux in NVHL rats combined with behavioral sensitization to cocaine.

METHODS

Adult NVHL vs. SHAM-operated rats underwent a 5-day injection series of cocaine (15 mg/kg/day) vs. saline. One week later, rats were cannulated in nucleus accumbens SHELL, CORE, or caudate-putamen. Another week later, in vivo microdialysis sampled DA during locomotor testing in which a single cocaine injection (15 mg/kg) was delivered.

RESULTS

NVHLs and cocaine history significantly increased behavioral activation approximately 2-fold over SHAM-saline history rats. DA efflux curves corresponded time dependently with the cocaine injection and locomotor curves and varied significantly by striatal region: Baseline DA levels increased 5-fold while cocaine-stimulated DA efflux decreased by half across a ventral to dorsal striatal gradient. However, NVHLs, prior cocaine history, and individual differences in behavior were not underpinned by differential DA efflux overall or within any striatal region.

CONCLUSION

Differences in ventral/dorsal striatal DA efflux are not present in and are not required for producing differential levels of acute cocaine-induced behavioral activation in NVHLs with and without a behaviorally sensitizing cocaine history. These findings suggest other neurotransmitter systems, and alterations in striatal network function post-synaptic to DA transmission are more important to understanding the interactive effects of addictive drugs and mental illness.

A Nicotine Challenge to the Self-Medication Hypothesis in a Neurodevelopmental Animal Model of Schizophrenia

Nicotine addiction is the leading cause of premature illness and death in the general population. Up to half of all cigarettes are consumed by a minority of the population: persons with schizophrenia and other forms of mental illness. Ironically, despite nicotine dependence being considered a serious and deadly form of addiction in the general population, research on smoking in mental illness is predominantly guided by the idea that smoking has beneficial medication-like treatment effects. This article considers pitfalls of adherence to the self-medication hypothesis as an exclusively held dogma. New evidence from animal modeling work suggests the need to broaden hypothesis-driven research on smoking in mental illness. Adolescent smoking could predispose to mental illness and/or increased nicotine dependence in schizophrenia may represent an involuntary, general addiction vulnerability that has little to do with the 'helpful' psychoactive effects of nicotine or other drugs.

The neonatal ventral hippocampal lesion as a heuristic neurodevelopmental model of schizophrenia

Traditionally, animal models of schizophrenia were predominantly pharmacological constructs focused on phenomena linked to dopamine and glutamate neurotransmitter systems, and were created by direct perturbations of these systems. A number of developmental models were subsequently generated that allowed testing of hypotheses about the origin of the disease, mimicked a wider array of clinical and neurobiological features of schizophrenia, and opened new avenues for developing novel treatment strategies. The most thoroughly characterized (approximately 100 primary research articles) is the neonatal ventral hippocampal lesion (NVHL) model, which is the subject of this review. We highlight its advantages and limitations, and how it may offer clues about the extent to which positive, negative, cognitive, and other aspects of schizophrenia, including addiction vulnerability, represent inter-related pathophysiological mechanisms.

Desperately driven and no brakes: developmental stress exposure and subsequent risk for substance abuse

Adverse life events are associated with a wide range of psychopathology, including an increased risk for substance abuse. In this review, we focus on the inter-relationship between exposure to adversity and brain development, and relate this to enhanced windows of vulnerability. This review encompasses clinical and preclinical data, drawing evidence from epidemiological studies, morphometric and functional imaging studies, and molecular biology and genetics. The interaction of exposure during a sensitive period and maturational events produces a cascade that leads to the initiation of substance use at younger ages, and increases the likelihood of addiction by adolescence or early adulthood. A stress-incubation/corticolimbic dysfunction model is proposed based on the interplay of stress exposure, development stage, and neuromaturational events that may explain the seeking of specific classes of drugs later in life. Three main factors contribute to this age-based progression of increased drug use: (1) a sensitized stress response system; (2) sensitive periods of vulnerability; and (3) maturational processes during adolescence. Together, these factors may explain why exposure to early adversity increases risk to abuse substances during adolescence.