Cortical-striatal integration of cocaine history and prefrontal dysfunction in animal modeling of dual diagnosis

Alteration of the PKA-CREB cascade in the mPFC accompanying prepulse inhibition deficits: evidence from adolescent social isolation and chronic SKF38393 injection during early adolescence

Prepulse inhibition (PPI) refers to the inhibition of the startle reflex that occurs when the startling stimulus is preceded by a weak prestimulus. Altered adolescent mPFC circuitry induced by early-life adversity might be a key source of PPI deficits. The current study focused on variations in the cyclic AMP (cAMP)/protein kinase A (PKA)-cAMP-response element-binding protein (CREB) pathway in the medial prefrontal cortex (mPFC). We found a negative relationship between PPI and the PKA-CREB cascade during adolescence by employing both developmental and pharmacologic manipulations. Experiment 1, with the early adolescent social isolation model [postnatal days (PNDs), 21-34), displayed a disrupted PPI at PND 35 and significantly altered PKA, phosphorylated CREB (p-CREB) and the ratio of p-CREB to CREB. In particular, the level of p-CREB was negatively related to PPI performance. In Experiment 2, SKF38393, a well-characterized activator of adenylate cyclase and cAMP/PKA, was chronically injected during early adolescence (PNDs 28-34). We sought to mimic potential biochemical changes, particularly PKA activation, which is possibly altered by adolescent social isolation, and to determine if PPI was disrupted, similar to the disruption associated with adolescent social isolation. On PND 35, PPI deficits were detected, as well as increased PKA, marginally increased CREB and no change occurred in p-CREB or the ratio of p-CREB to CREB. In particular, PKA activity was negatively related to PPI performance. Although these results are limited in suggesting a causal link between PPI deficits and PKA-CREB signaling, they may help to elucidate the role played by PKA-CREB in the mPFC in regulating PPI.

Comorbidity between depressive symptoms and substance use in-patients hospitalized for non-psychiatric diseases

INTRODUCTION

Epidemiological studies have shown a high prevalence and concurrence between depression and substance use. This is known as "dual diagnosis" and is associated with a worse prognosis for patients.

OBJECTIVE

To establish the comorbidity between depressive symptoms and substance abuse in patients admitted with acute or chronic diseases to a public hospital.

METHODS

A descriptive, cross-sectional study of prevalence which included 296 patients aged 18-65, to whom the PHQ-9 and ASSIST 3.0 scales were applied to determine the prevalence of depressive symptoms and substance abuse. Other clinical and sociodemographic variables were also taken into account.

RESULTS

50.7% were women with a median age of 41 and an interquartile range of 27 years. Moderate-to-severe depressive symptoms were found in 27.4% of the patients. Alcohol was the substance with the highest consumption in the previous 3 months with 53.7%, followed by cigarettes (47.6%), marijuana (26.7%) and cocaine (14.5%). A significant association was found between severe depressive symptoms PHQ-9 ≥ 20 and problematic use of alcohol, marijuana and cocaine (ASSIST score >26); alcohol (RP 27.30, 95% CI [2.37-314.16], P = 0.01); marijuana (RP 15.00, 95% CI [3.46-64.96], P = 0.001) and cocaine (RP 10.65, 95% CI [2.23-51.10], P = 0.01).

DISCUSSION

A high prevalence of depressive symptoms and substance use was found in patients hospitalised for non-psychiatric medical conditions, which worsens the prognosis of the underlying medical condition.

CONCLUSIONS

To provide better hospital care for patients, we need to give visibility to the problem of dual pathology. This could be achieved by conducting more related research in these clinical scenarios.

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.

Comorbidity between depressive symptoms and substance use in-patients hospitalized for non-psychiatric diseases

INTRODUCTION

Epidemiological studies have shown a high prevalence and concurrence between depression and substance use. This is known as "dual diagnosis" and is associated with a worse prognosis for patients.

OBJECTIVE

To establish the comorbidity between depressive symptoms and substance abuse in patients admitted with acute or chronic diseases to a public hospital.

METHODS

A descriptive, cross-sectional study of prevalence which included 296 patients aged 18 to 65, to whom the PHQ-9 and ASSIST 3.0 scales were applied to determine the prevalence of depressive symptoms and substance abuse. Other clinical and sociodemographic variables were also taken into account.

RESULTS

50.7% were women with a median age of 41 and an interquartile range of 27 years. Moderate-to-severe depressive symptoms were found in 27.4% of the patients. Alcohol was the substance with the highest consumption in the previous 3 months with 53.7%, followed by cigarettes (47.6%), marijuana (26.7%) and cocaine (14.5%). A significant association was found between severe depressive symptoms PHQ-9 ≥20 and problematic use of alcohol, marijuana and cocaine (ASSIST score>26); alcohol (RP 27.30, 95% CI [2.37-314.16], P=0.01); marijuana (RP 15.00, 95% CI [3.46-64.96], P=0.001) and cocaine (RP 10.65, 95% CI [2.23-51.10], P=0.01).

DISCUSSION

A high prevalence of depressive symptoms and substance use was found in patients hospitalized for non-psychiatric medical conditions, which worsens the prognosis of the underlying medical condition.

CONCLUSIONS

To provide better hospital care for patients, we need to give visibility to the problem of dual pathology. This could be achieved by conducting more related research in these clinical scenarios.

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.

The Penrose Effect and its acceleration by the war on drugs: a crisis of untranslated neuroscience and untreated addiction and mental illness

In 1939, British psychiatrist Lionel Penrose described an inverse relationship between mental health treatment infrastructure and criminal incarcerations. This relationship, later termed the 'Penrose Effect', has proven remarkably predictive of modern trends which have manifested as reciprocal components, referred to as 'deinstitutionalization' and 'mass incarceration'. In this review, we consider how a third dynamic-the criminalization of addiction via the 'War on Drugs', although unanticipated by Penrose, has likely amplified the Penrose Effect over the last 30 years, with devastating social, economic, and healthcare consequences. We discuss how synergy been the Penrose Effect and the War on Drugs has been mediated by, and reflects, a fundamental neurobiological connection between the brain diseases of mental illness and addiction. This neuroscience of dual diagnosis, also not anticipated by Penrose, is still not being adequately translated into improving clinical training, practice, or research, to treat patients across the mental illness-addictions comorbidity spectrum. This failure in translation, and the ongoing fragmentation and collapse of behavioral healthcare, has worsened the epidemic of untreated mental illness and addictions, while driving unsustainable government investment into mass incarceration and high-cost medical care that profits too exclusively on injuries and multi-organ diseases resulting from untreated addictions. Reversing the fragmentation and decline of behavioral healthcare with decisive action to co-integrate mental health and addiction training, care, and research-may be key to ending criminalization of mental illness and addiction, and refocusing the healthcare system on keeping the population healthy at the lowest possible cost.

Global white matter microstructural abnormalities associated with addiction liability score in drug naïve youth

Abnormalities in brain white matter (WM) structure have been reported in youths having a family history of substance use disorders (SUDs). It was hypothesized that these abnormalities constitute features of the liability for SUDs transmitted across generations. The association between severity of intergenerational risk for SUD, measured by the Transmissible Liability Index (TLI), and white matter microstructure was examined. Diffusion tensor imaging (DTI) measured WM microstructure in forty-four drug-naïve 10-14 year-olds (N = 19 with parental SUD). Metrics of WM microstructure (i.e., fractional anisotropy, radial diffusivity, mean diffusivity and axial diffusivity) were quantified across the whole brain and in four tracts of interest: anterior corona radiata, superior and inferior longitudinal fasciculi and superior fronto-occipital fasciculi. The TLI was completed by the youths, their parents and, when available, their teachers. The relationship between WM structure and TLI score across the entire group was evaluated using linear multiple regression and between group comparisons were also examined. Fractional anisotropy and radial diffusivity in multiple tracts across the brain were significantly associated with TLI scores. Confirming and extending prior research, the findings indicate that global atypicality in WM tracts was linearly related to liability for eventual SUD development in drug naïve youths.

Toward early estimation and treatment of addiction vulnerability: radial arm maze and N-acetyl cysteine before cocaine sensitization or nicotine self-administration in neonatal ventral hippocampal lesion rats

RATIONAL

Prefrontal cortical (PFC)-hippocampal-striatal circuits, interconnected via glutamatergic signaling, are dysfunctional in mental illnesses that involve addiction vulnerability.

OBJECTIVES

In healthy and neurodevelopmentally altered rats, we examined how Radial Arm Maze (RAM) performance estimates addiction vulnerability, and how starting a glutamatergic modulating agent, N-acetyl cysteine (NAC) in adolescence alters adult mental illness and/or addiction phenotypes.

METHODS

Rats with neonatal ventral hippocampal lesions (NVHL) vs. SHAM-operated controls were randomized to NAC vs. saline in adolescence followed by cognitive testing (RAM) in early adulthood and then cocaine behavioral sensitization (experiment 1; n = 80) or nicotine self-administration (experiment 2; n = 12).

RESULTS

In experiment 1, NVHL rats showed over-consumption of food (Froot-Loops (FL)) baiting the RAM with poor working memory (low-arm entries to repeat (ETR)), producing an elevated FL to ETR ratio ("FLETR"; p < 0.001). FLETR was the best linear estimator (compared to FL or ETR) of magnitude of long-term cocaine sensitization (R ² = 0.14, p < 0.001). NAC treatment did not alter FL, ETR, FLETR, or cocaine sensitization. In experiment 2, FLETR also significantly and uniquely correlated with subsequent drug seeking during nicotine-induced reinstatement after extinction of nicotine self-administration (R ² = 0.47, p < 0.01). NAC did not alter RAM performance, but significantly reversed NVHL-induced increases in nicotine seeking during extinction and reinstatement.

CONCLUSIONS

These findings demonstrate the utility of animal models of mental illness with addiction vulnerability for developing novel diagnostic measures of PFC-hippocampal-striatal circuit dysfunction that may reflect addiction risk. Such tests may direct pharmacological treatments prior to adulthood and addictive drug exposure, to prevent or treat adult addictions.

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.

Animal Models of Deficient Sensorimotor Gating in Schizophrenia: Are They Still Relevant?

Animal models of impaired sensorimotor gating, as assessed by prepulse inhibition (PPI) of startle, have demonstrated clear validity at face, predictive, and construct levels for schizophrenia therapeutics, neurophysiological endophenotypes, and potential causative insults for this group of disorders. However, with the growing recognition of the heterogeneity of the schizophrenias, and the less sanguine view of the clinical value of antipsychotic (AP) medications, our field must look beyond "validity," to assess the actual utility of these models. At a substantial cost in terms of research support and intellectual capital, what has come from these models, that we can say has actually helped schizophrenia patients? Such introspection is timely, as we are reassessing not only our view of the genetic and pathophysiological diversity of these disorders, but also the predominant strategies for SZ therapeutics; indeed, our field is gaining awareness that we must move away from a "find what's broke and fix it" approach, toward identifying spared neural and cognitive function in SZ patients, and matching these residual neural assets with learning-based therapies. Perhaps, construct-valid models that identify evidence of "spared function" in neural substrates might reveal opportunities for future therapeutics and allow us to study these substrates at a mechanistic level to maximize opportunities for neuroplasticity. Such an effort will require a retooling of our models, and more importantly, a re-evaluation of their utility. For animal models to remain relevant in the search for schizophrenia therapeutics, they will need to focus less on what is valid and focus more on what is useful.

Nicotine is more addictive, not more cognitively therapeutic in a neurodevelopmental model of schizophrenia produced by neonatal ventral hippocampal lesions

Nicotine dependence is the leading cause of death in the United States. However, research on high rates of nicotine use in mental illness has primarily explained this co-morbidity as reflecting nicotine's therapeutic benefits, especially for cognitive symptoms, equating smoking with ‘self-medication’. We used a leading neurodevelopmental model of mental illness in rats to prospectively test the alternative possibility that nicotine dependence pervades mental illness because nicotine is simply more addictive in mentally ill brains that involve developmental hippocampal dysfunction. Neonatal ventral hippocampal lesions (NVHL) have previously been demonstrated to produce post-adolescent-onset, pharmacological, neurobiological and cognitive-deficit features of schizophrenia. Here, we show that NVHLs increase adult nicotine self-administration, potentiating acquisition-intake, total nicotine consumed and drug seeking. Behavioral sensitization to nicotine in adolescence prior to self-administration is not accentuated by NVHLs in contrast to increased nicotine self-administration and behavioral sensitization documented in adult NVHL rats, suggesting periadolescent neurodevelopmental onset of nicotine addiction vulnerability in the NVHL model. Delivering a nicotine regimen approximating the exposure used in the sensitization and self-administration experiments (i.e. as a treatment) to adult rats did not specifically reverse NVHL-induced cortical-hippocampal-dependent cognitive deficits and actually worsened cognitive efficiency after nicotine treatment stopped, generating deficits that resemble those due to NVHLs. These findings represent the first prospective evidence demonstrating a causal link between disease processes in schizophrenia and nicotine addiction. Developmental cortical-temporal limbic dysfunction in mental illness may thus amplify nicotine's reinforcing effects and addiction risk and severity, even while producing cognitive deficits that are not specifically or substantially reversible with nicotine.

Histological correlates of N40 auditory evoked potentials in adult rats after neonatal ventral hippocampal lesion: animal model of schizophrenia

The neonatal ventral hippocampal lesion (NVHL) is an established neurodevelopmental rat model of schizophrenia. Rats with NVHL exhibit several behavioral, molecular and physiological abnormalities that are similar to those found in schizophrenics. Schizophrenia is a severe psychiatric illness characterized by profound disturbances of mental functions including neurophysiological deficits in brain information processing. These deficits can be assessed by auditory evoked potentials (AEPs), where schizophrenics exhibit abnormalities in amplitude, duration and latency of such AEPs. The aim of the present study was to compare the density of cells in the temporal cerebral cortex and the N40-AEP of adult NVHL rats versus adult sham rats. We found that rats with NVHL exhibit significant lower amplitude of the N40-AEP and a significant lower number of cells in bilateral regions of the temporal cerebral cortex compared to sham rats. Because the AEP recordings were obtained from anesthetized rats, we suggest that NVHL leads to inappropriate innervation in thalamic-cortical pathways in the adult rat, leading to altered function of cortical networks involved in processing of primary auditory information.

Transcranial magnetic stimulation: potential treatment for co-occurring alcohol, traumatic brain injury and posttraumatic stress disorders

Alcohol use disorder (AUD), mild traumatic brain injury (mTBI), and posttraumatic stress disorder (PTSD) commonly co-occur (AUD + mTBI + PTSD). These conditions have overlapping symptoms which are, in part, reflective of overlapping neuropathology. These conditions become problematic because their co-occurrence can exacerbate symptoms. Therefore, treatments must be developed that are inclusive to all three conditions. Repetitive transcranial magnetic stimulation (rTMS) is non-invasive and may be an ideal treatment for co-occurring AUD + mTBI + PTSD. There is accumulating evidence on rTMS as a treatment for people with AUD, mTBI, and PTSD each alone. However, there are no published studies to date on rTMS as a treatment for co-occurring AUD + mTBI + PTSD. This review article advances the knowledge base for rTMS as a treatment for AUD + mTBI + PTSD. This review provides background information about these co-occurring conditions as well as rTMS. The existing literature on rTMS as a treatment for people with AUD, TBI, and PTSD each alone is reviewed. Finally, neurobiological findings in support of a theoretical model are discussed to inform TMS as a treatment for co-occurring AUD + mTBI + PTSD. The peer-reviewed literature was identified by targeted literature searches using PubMed and supplemented by cross-referencing the bibliographies of relevant review articles. The existing evidence on rTMS as a treatment for these conditions in isolation, coupled with the overlapping neuropathology and symptomology of these conditions, suggests that rTMS may be well suited for the treatment of these conditions together.

Comorbid substance use disorder in schizophrenia: a selective overview of neurobiological and cognitive underpinnings

Although individuals with schizophrenia show a lifetime prevalence of 50% for suffering from a comorbid substance use disorder, substance abuse usually represents an exclusion criterion for studies on schizophrenia. This implies that surprisingly little is known about a large group of patients who are particularly difficult to treat. The aim of the present work is to provide a brief and non-exhaustive overview of the current knowledgebase about neurobiological and cognitive underpinnings for dual diagnosis schizophrenia patients. Studies published within the last 20 years were considered using computerized search engines. The focus was on nicotine, caffeine, alcohol, cannabis and cocaine being among the most common substances of abuse. All drugs of abuse target dopaminergic, glutamatergic and GABAergic transmission which are also involved in the pathophysiology of schizophrenia. Current literature suggests that neurocognitive function might beless disrupted in substance-abusing compared to non-abusing schizophrenia patients, but in particular the neuroimaging database on this topic is sparse. Detrimental effects on brain structure and function were shown for patients for whom alcohol is the main substance of abuse. It is as yet unclear whether this finding might be an artifact of age differences of patient subgroups with different substance abuse patterns. More research is warranted on the specific neurocognitive underpinnings of schizophrenia patients abusing distinct psychoactive substances. Treatment programs might either benefit from preserved cognitive function as a resource or specifically target cognitive impairment in different subgroups of addicted schizophrenia patients.

Molecular and cellular mechanisms of dopamine-mediated behavioral plasticity in the striatum

The striatum is the input structure of the basal ganglia system. By integrating glutamatergic signals from cortical and subcortical regions and dopaminergic signals from mesolimbic nuclei the striatum functions as an important neural substrate for procedural and motor learning as well as for reward-guided behaviors. In addition, striatal activity is significantly altered in pathological conditions in which either a loss of dopamine innervation (Parkinson's disease) or aberrant dopamine-mediated signaling (drug addiction and L-DOPA induced dyskinesia) occurs. Here we discuss cellular mechanisms of striatal synaptic plasticity and aspects of cell signaling underlying striatum-dependent behavior, with a major focus on the neuromodulatory action of the endocannabinoid system and on the role of the Ras-ERK cascade.

Cocaine self-administration differentially modulates the expression of endogenous cannabinoid system-related proteins in the hippocampus of Lewis vs. Fischer 344 rats

The endocannabinoids anandamide and 2-arachidonyl glycerol (2-AG) are modulators of glutamate and γ-aminobutyric acid (GABA), two transmitters involved in cocaine addiction. However, little is known on the effects of cocaine on the enzymes that produce and degrade endocannabinoids. The present work addresses the effects of cocaine self-administration on the immunohistochemical expression of endocannabinoid signalling (ECS)-related proteins in the hippocampus. The study has been performed on two different strains of rats, Lewis (Lew) and Fischer 344 (F344), which are characterized for displaying a differential sensitivity to cocaine, thus making them suitable in the study of vulnerability to drug addiction. Both strains showed differences in the expression of ECS-related proteins in the hippocampus, i.e. Lew rats exhibited lower CB1 expression but higher CB2 expression than F344 rats. After setting similar cocaine self-administration, both strains showed clear differences in the expression of ECS-related proteins, which were differentially restricted to either the 2-AG or anandamide signalling pathways in a self-administration training/drug-dependent manner. The decreases observed in CB1 expression and N-acyl phosphatidylethanolamine phospholipase D:fatty acid amino hydrolase ratio after saline self-administration were enhanced only in cocaine self-administered Lew rats. CB2 expression increase and diacylglycerol lipase α:monoacylglycerol lipase ratio decrease detected after saline self-administration were blocked only in cocaine self-administered F344 rats. These findings indicate that cocaine may regulate hippocampal GABA/glutamate synapses by directly modulating endocannabinoid production/degradation enzymes and that these actions are strain-dependent. This differential response suggests that the endogenous cannabinoid system might contribute to genotype/strain differences on the sensitivity to self-administration training and cocaine addiction.

Coupling of gene expression in medial prefrontal cortex and nucleus accumbens after neonatal ventral hippocampal lesions accompanies deficits in sensorimotor gating and auditory processing in rats

BACKGROUND

After neonatal ventral hippocampal lesions (NVHLs), adult rats exhibit evidence of neural processing deficits relevant to schizophrenia, including reduced prepulse inhibition (PPI) of acoustic startle and impaired sensory processing. In intact rats, the regulation of PPI by the ventral hippocampus (VH) is mediated via interactions with medial prefrontal cortex (mPFC) and nucleus accumbens (NAC). We assessed PPI, auditory-evoked responses and expression of 7 schizophrenia-related genes in mPFC and NAC, in adult rats after sham- or real NVHLs.

METHODS

Male inbred Buffalo (BUF) rat pups (d7; n=36) received either vehicle or ibotenic acid infusion into the VH. PPI and auditory-evoked dentate gyrus local field potentials (LFPs) were measured on d56 and d66, respectively. Brains were processed for RT-PCR measures of mPFC and NAC Comt, Erbb4, Grid2, Ncam1, Slc1a2, Nrg1 and Reln.

RESULTS

NVHL rats exhibited significant deficits in PPI (p=0.005) and LFPs (p<0.015) proportional to lesion size. Sham vs. NVHL rats did not differ in gene expression levels in mPFC or NAC. As we previously reported, multiple gene expression levels were highly correlated within- (mean r's≈0.5), but not across-brain regions (mean r's≈0). However, for three genes--Comt, Slc1a2 and Ncam1--after NVHLs, expression levels became significantly correlated, or "coupled," across the mPFC and NAC (p's<0.03, 0.002 and 0.05, respectively), and the degree of "coupling" increased with VH lesion size.

CONCLUSIONS

After NVHLs that disrupt PPI and auditory processing, specific gene expression levels suggest an abnormal functional coupling of the mPFC and NAC. This model of VH-mPFC-NAC network dysfunction after NVHLs may have implications for understanding the neural basis for PPI- and related sensory processing deficits in schizophrenia patients.

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.

Auditory steady state responses in a schizophrenia rat model probed by excitatory/inhibitory receptor manipulation

Alterations in neural synchrony and oscillations may contribute to the pathophysiology of schizophrenia and reflect aberrations in cortical glutamatergic and GABAergic neurotransmission. We tested the effects of a GABA agonist and an NMDA antagonist on auditory steady state responses (ASSRs) in awake rats with neonatal ventral hippocampal lesions (NVHLs) as a neurodevelopmental model of schizophrenia. NVHL vs. SHAM lesioned rats were injected with saline then either ketamine (NMDA antagonist) or muscimol (GABA(A) agonist). Time-frequency analyses examined alterations in phase locking (consistency) across trials and changes in total power (magnitude). ASSRs were compared at five stimulation frequencies (10, 20, 30, 40, and 50 Hz). In SHAM rats, phase locking and power generally increased with stimulation frequency. Both ketamine and muscimol also increased phase locking and power in SHAM rats, but mostly in the 20 to 40 Hz range. NVHL and ketamine altered the frequency dependence of phase locking, while only ketamine changed power frequency dependence. Muscimol affected power, but not phase locking, in the NVHL rats. NVHL and ketamine models of schizophrenia produce similar independent effects on ASSR, potentially representing similar forms of cortical network/glutamatergic dysfunction, albeit the effects of ketamine were more robust. Muscimol produced NVHL-dependent reductions in ASSR measures, suggesting that cortical networks in this model are intolerant to post-synaptic GABAergic stimulation. These findings suggest the utility of combining lesion, pharmacological, and ASSR approaches in understanding neural mechanisms underlying disturbed synchrony in schizophrenia.

Mutant DISC1 affects methamphetamine-induced sensitization and conditioned place preference: a comorbidity model

Genetic factors involved in neuroplasticity have been implicated in major psychiatric illnesses such as schizophrenia, depression, and substance abuse. Given its extended interactome, variants in the Disrupted-In-Schizophrenia-1 (DISC1) gene could contribute to drug addiction and psychiatric diseases. Thus, we evaluated how dominant-negative mutant DISC1 influenced the neurobehavioral and molecular effects of methamphetamine (METH). Control and mutant DISC1 mice were studied before or after treatment with non-toxic escalating dose (ED) of METH. In naïve mice, we assessed METH-induced conditioned place preference (CPP), dopamine (DA) D2 receptor density and the basal and METH-induced activity of DISC1 partners, AKT and GSK-3β in the ventral striatum. In ED-treated mice, 4 weeks after METH treatment, we evaluated fear conditioning, depression-like responses in forced swim test, and the basal and METH-induced activity of AKT and GSK-3β in the ventral striatum. We found impairment in METH-induced CPP, decreased DA D2 receptor density and altered METH-induced phosphorylation of AKT and GSK-3β in naïve DISC1 female mice. The ED regimen was not neurotoxic as evidenced by unaltered brain regional monoamine tissue content. Mutant DISC1 significantly delayed METH ED-produced sensitization and affected drug-induced phosphorylation of AKT and GSK-3β in female mice. Our results suggest that perturbations in DISC1 functions in the ventral striatum may impact the molecular mechanisms of reward and sensitization, contributing to comorbidity between drug abuse and major mental diseases.

Selective deficits in spatial working memory in the neonatal ventral hippocampal lesion rat model of schizophrenia

The neonatal ventral hippocampal lesion (NVHL) manipulation is a neurodevelopmental animal model of schizophrenia that produces abnormalities in the prefrontal cortex and nucleus accumbens, both efferent targets of the hippocampus, and leads to spatial working memory impairments. To investigate the neuroanatomical basis of spatial working memory in NVHL animals, we assessed performance in two radial arm maze tasks known to be differentially sensitive to the two hippocampal efferent pathways, and measured levels of neuronal activation (Fos immunoreactivity [Fos-IR]) in the prefrontal cortex and nucleus accumbens following task performance. Neonatal rats (postnatal day 6-8) received excitotoxic lesions of the ventral hippocampus (n=25), or a sham procedure (infusions of artificial cerebrospinal fluid; n=22). Upon reaching adulthood, animals were trained in either a non-delayed random foraging task or a spatial delayed win-shift task. NVHL animals were impaired on the spatial delayed win-shift task, which depends on communication between hippocampus and prefrontal cortex, but were unimpaired on the non-delayed random foraging task, which requires connections between hippocampus and nucleus accumbens. Fos-IR in the nucleus accumbens was greater in NVHL animals than in shams following the random foraging task, despite similar levels of performance, while no group differences in Fos-IR in either the nucleus accumbens or prefrontal cortex were observed following win-shift performance. These results suggest that although the NVHL manipulation disrupts development of hippocampal efferents to both the prefrontal cortex and the nucleus accumbens, the disruption of hippocampal-prefrontal pathways has the dominant behavioral effect on spatial performance in NVHL rats.

MRI and X-ray scanning images of the brain of 3-, 6- and 9-month-old rats with bilateral neonatal ventral hippocampus lesions

Rats with bilateral neonatal ventral hippocampus lesions (NVHL) are commonly used for modeling developmental aspects of the pathophysiology of schizophrenia. Given that functional changes become significant only after puberty, NVHL as well as sham-operated rats were analyzed at the ages of 21, 42 and 63days (i.e. as pups, adolescents and adults), using MRI to examine the damage caused by surgery over time. Morphometric evaluations were considered and lesions were classified as small, medium and large. The volume of lesions increased regularly with age, to a greater extent than increases in overall brain size. This was relatively linear, corresponding to a gradually shrinking forebrain, and these observations held true for each class of lesions considered. Following the observation that the lesion procedure elicited calcifications in the brain, the same rats were subjected to 3D X-ray scanning the day after each MRI session, allowing precise measurements of skull size to be carried out. The NVHL rats had smaller skulls; however, the dimensions of the calcifications did not grow more than the skull size over time. The mechanisms underlying the progressive anatomical changes following surgery are discussed, and we propose this in vivo follow-up method to investigate therapeutic strategies aimed at countering or limiting the post-lesion consequences of a neonatal brain damage.

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.