Gestational treatment with methylazoxymethanol (MAM) that disrupts hippocampal-dependent memory does not alter behavioural response to cocaine

Cognitive performance of the MAM-E17 schizophrenia model rats in different age-periods

Cognitive disturbances are among the most important features of schizophrenia, and have a significant role in the outcome of the disease. However, the treatment of cognitive symptoms is poorly effective. In order to develop new therapeutic opportunities, the MAM-E17 rat model of schizophrenia can be an appropriate implement. In the present study we investigated several cognitive capabilities of MAM-treated rats using radial arm maze (RAM) task, which corresponds to the recent research directives. Because of the diachronic appearance of schizophrenia symptoms and the early appearance of cognitive deficiencies, we carried out our experiments in three different age-periods of rats, i.e. in prepuberty, late puberty and adulthood. The performance of MAM-E17 rats was similar to control rats in the acquisition phase of RAM task, except for puberty. However, after rearrangement of reward positions (in the reverse paradigm) the number of errors of MAM-treated rats was higher in each age-period. In the reverse paradigm MAM-treated groups visited more frequently those non-rewarding arms, which were previously rewarding. Our results suggest that working memory of MAM-E17 rats is impaired. This deficit depends on the difficulty of the task and on the age-period. MAM-E17 rats seem to be more sensitive in puberty in comparison to controls. Diminished behavioral flexibility was shown as well. These behavioral results observed in MAM-E17 rats were similar to those of cognitive deficiencies in schizophrenia patients. Therefore, MAM-E17 model can be a useful implement for further research aiming to improve cognition in schizophrenia.

Evaluation of ultrasonic vocalizations in a neurodevelopmental model of schizophrenia during the early life stages of rats

In an animal neurodevelopmental model of schizophrenia, we investigated ultrasonic communication and social behavior in male and female rats. Pregnant dams were treated with methylazoxymethanol acetate (MAM; 22 mg/kg) at 17 days of gestation. First, we examined the ultrasonic vocalizations (USVs) emitted by 8-day-old pups isolated from their mothers and placed in a familiar or an unfamiliar environment. Second, we assessed tickling-induced USVs, social play (SP) behavior and accompanying USVs in 30-day-old juveniles. Independent of the prenatal treatment, sex differences were noted at both ages. In the pups isolated from their mothers, compared to the females, the males produced flatter calls with a lower frequency. Compared to the females, the tickling-induced male USVs were characterized by a higher frequency, and the male SP-induced USVs showed a broader bandwidth and more modulated structure. Additionally, the numbers of both SP-induced USVs and SP episodes in the males were higher than those in the females. In contrast, the MAM exposure reduced the ultrasonic communication and social behavior independent of age almost equally in the male and female rats. The MAM-exposed isolated pups and juveniles experiencing tickling and social interaction displayed lower USV bandwidths, suggesting that the complexity of their ultrasonic communication was reduced. In addition, the MAM-exposed juveniles demonstrated a lower number of 50-kHz "happy calls" and decreased SP duration, which is suggestive of social withdrawal or negative-like symptoms. These data demonstrate that young MAM-exposed rats display an atypical repertoire of USVs and reduced play behavior suggestive of communication deficits associated with schizophrenia.

MAM-E17 rat model impairments on a novel continuous performance task: effects of potential cognitive enhancing drugs

RATIONALE

Impairments in attention and inhibitory control are endophenotypic markers of neuropsychiatric disorders such as schizophrenia and represent key targets for therapeutic management. Robust preclinical models and assays sensitive to clinically relevant treatments are crucial for improving cognitive enhancement strategies.

OBJECTIVES

We assessed a rodent model with neural and behavioral features relevant to schizophrenia (gestational day 17 methylazoxymethanol acetate treatment (MAM-E17)) on a novel test of attention and executive function, and examined the impact of putative nootropic drugs.

METHODS

MAM-E17 and sham control rats were trained on a novel touchscreen-based rodent continuous performance test (rCPT) designed to closely mimic the human CPT paradigm. Performance following acute, systemic treatment with an array of pharmacological compounds was investigated.

RESULTS

Two cohorts of MAM-E17 rats were impaired on rCPT performance including deficits in sensitivity (d') and increased false alarm rates (FARs). Sulpiride (0-30 mg/kg) dose-dependently reduced elevated FAR in MAM-E17 rats whereas low-dose modafinil (8 mg/kg) only improved d' in sham controls. ABT-594 (5.9-19.4 μg/kg) and modafinil (64 mg/kg) showed expected stimulant-like effects, while LSN2463359 (5 mg/kg), RO493858 (10 mg/kg), atomoxetine (0.3-1 mg/kg), and sulpiride (30 mg/kg) showed expected suppressant effects on performance across all animals. Donepezil (0.1-1 mg/kg) showed near-significant enhancements in d', and EVP-6124 (0.3-3 mg/kg) exerted no effects in the rCPT paradigm.

CONCLUSION

The MAM-E17 model exhibits robust and replicable impairments in rCPT performance that resemble attention and inhibitory control deficits seen in schizophrenia. Pharmacological profiles were highly consistent with known drug effects on cognition in preclinical and clinical studies. The rCPT is a sensitive and reliable tool with high translational potential for understanding the etiology and treatment of disorders affecting attention and executive dysfunction.

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.

Alterations in spatial memory and anxiety in the MAM E17 rat model of hippocampal pathology in schizophrenia

Adult rats exposed to methylazoxymethanol acetate (MAM) at embryonic day 17 (E17) display robust pathological alterations in the hippocampus. However, discrepancies exist in the literature regarding the behavioural effects of this pre-natal manipulation. Therefore, a systematic assessment of MAM E17-induced behavioural alterations was conducted using a battery of dorsal and ventral hippocampus-dependent tests. Compared to saline controls, MAM E17-treated rats displayed deficits in spatial reference memory in both the aversive hidden platform watermaze task and an appetitive Y-maze task. Deficits in the spatial reference memory watermaze task were replicated across three different cohorts and two laboratories. In contrast, there was little, or no, effect on the non-spatial, visible platform watermaze task or an appetitive, non-spatial, visual discrimination task, respectively. MAM rats were also impaired in the spatial novelty preference task which assesses short-term memory, and displayed reduced anxiety levels in the elevated plus maze task. Thus, MAM E17 administration resulted in abnormal spatial information processing and reduced anxiety in a number of hippocampus-dependent behavioural tests, paralleling the effects of dorsal and ventral hippocampal lesions, respectively. These findings corroborate recent pathological and physiological studies, further highlighting the usefulness of MAM E17 as a model of hippocampal dysfunction in at least some aspects of schizophrenia.

The role of α5 GABAA receptor agonists in the treatment of cognitive deficits in schizophrenia

Currently available pharmacotherapies for the treatment of schizophrenia are ineffective in restoring the disrupted cognitive function associated with this disorder. As such, there is a continued search for more viable novel drug targets. Engaging in cognitive behaviors is associated with distinct coordinated oscillatory activity across brain regions, in particular the hippocampus and prefrontal cortex. In schizophrenia patients, pathological alterations in the functionality of GABAergic interneurons in the PFC and HPC responsible for generating network oscillations are thought to contribute to impaired cognition. Destabilized GABAergic interneuron activity in the HPC is further associated with aberrant increases in HPC output and enhanced dopamine neuron activity. Consequently, drugs directed at restoring HPC function could impact both oscillatory activity along with dopamine tone. There is compelling evidence from animal models of schizophrenia that allosteric modulation of the α5 subunit of the GABAA receptor is a viable means of resolving aberrant dopamine system activity through indirect alteration of HPC output. Consequently, these compounds are promising for their potential in also ameliorating cognitive deficits attributed to dysfunction in HPC network activity.

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.

Gestational methylazoxymethanol exposure leads to NMDAR dysfunction in hippocampus during early development and lasting deficits in learning

The N-methyl-D-aspartate (NMDA) receptor has long been associated with learning and memory processes as well as diseased states, particularly in schizophrenia (SZ). Additionally, SZ is increasingly recognized as a neurodevelopmental disorder with cognitive impairments often preceding the onset of psychosis. However, the cause of these cognitive deficits and what initiates the pathological process is unknown. Growing evidence has implicated the glutamate system and, in particular, N-methyl-D-aspartate receptor (NMDAR) dysfunction in the pathophysiology of SZ. Yet, the vast majority of SZ-related research has focused on NMDAR function in adults leaving the role of NMDARs during development uncharacterized. We used the prenatal methylazoxymethanol acetate (MAM, E17) exposure model to determine the alterations of NMDAR protein levels and function, as well as associated cognitive deficits during development. We found that MAM-exposed animals have significantly altered NMDAR protein levels and function in the juvenile and adolescent hippocampus. Furthermore, these changes are associated with learning and memory deficits in the Morris Water Maze. Thus, in the prenatal MAM-exposure SZ model, NMDAR expression and function is altered during the critical period of hippocampal development. These changes may be involved in disease initiation and cognitive impairment in the early stage of SZ.

Daily treadmill exercise attenuates cocaine cue-induced reinstatement and cocaine induced locomotor response but increases cocaine-primed reinstatement

Exercise affects neuroplasticity and neurotransmission including dopamine (DA), which modulates drug-taking behavior. Previous research in rodents has shown that exercise may attenuate the rewarding effects of drugs of abuse. The present study examined the effects of high and low exercise on cocaine responses in male Wistar rats that had been trained to self-administer and were compared to a group of sedentary rats. High exercise rats (HE) ran daily on a treadmill for 2h and low exercise (LE) ran daily for 1h. After 6 weeks of this exercise regimen, rats were tested over 2 days for reinstatement (day 1: cue-induced reinstatement; day 2: cocaine-primed reinstatement). During cue-induced reinstatement, the sedentary rats showed the expected increase in active lever responses when compared to maintenance, whereas these increased responses were inhibited in the exercised rats (HE and LE). During cocaine-primed reinstatement, however, there was a significant increase in active lever presses when compared to maintenance only in the HE group. This data suggests that chronic exercise during abstinence attenuates the cue-induced reinstatement seen in the sedentary rats by 26% (LE) and 21% (HE). In contrast, only the high exercise rats exhibited sensitized cocaine-seeking behavior (active lever presses) following cocaine-primed reinstatement. Finally, while sedentary rats increased locomotor activity during cocaine-primed reinstatement over that seen with cocaine during maintenance, this was not observed in the exercised rats, suggesting that exercise may interfere with the sensitized locomotor response during cocaine reinstatement.