Temporally distinct impairments in cognitive function following a sensitizing regimen of methamphetamine

Indiana University-Purdue University Indianapolis (IUPUI)Methamphetamine (MA) is a widely abused psychostimulant that has been shown to evoke an array of neurobiological abnormalities and cognitive deficits in humans and in rodent models (Marshall & O'Dell, 2012). Alterations in cognitive function after repeated drug use may lead to impaired decision-making, a lack of behavioral control, and ultimately the inability to abstain from drug use. Human studies have shown that alterations in neurobiology resulting from prolonged MA use may lead to a number of cognitive deficits, including impairments in executive function, learning, memory, and impulsivity. These impairments, specifically those that engage the prefrontal cortex (PFC) or hippocampus (HC), may persist or recover based on the duration of abstinence. In rodents, repeated intermittent injections of MA yield protracted changes in neurobiology and behavior, which have been shown to effectively model a number of the biological and cognitive abnormalities observed in addiction. In order to assess the temporal evolution of impaired cognitive function throughout abstinence, sensitization was first induced in rats (7 x 5.0 mg/kg MA over 14 days). MA-treated rats initially exhibited a robust increase in locomotion that transitioned to stereotypy as the induction phase progressed. Then, the effects of MA sensitization on social interaction (SI), temporal order recognition (TOR) and novel object recognition (NOR) was assessed at one-day and 30-days post induction. No differences were observed in SI in either group or after a single injection of MA. However, an acute injection of 5.0 mg/kg of MA 30-minutes prior to testing dramatically reduced SI time. Impairments in TOR and NOR were observed in MA-treated rats after one day of abstinence, and impairments in TOR, but not NOR, were observed on day 30 of abstinence. No differences in TOR and NOR after a single injection of MA or saline were observed. These data establish that after 30 days of abstinence from a sensitizing regimen of MA, the ability to recall the temporal sequence that two stimuli were encountered was impaired and that was not attributable to impaired novelty detection. These data also suggest that at least some of the neurocognitive abnormalities caused by chronic MA administration may normalize after prolonged abstinence, since the ability to detect novelty recovered after 30 days of abstinence. These data provide compelling support that, since MA-sensitization caused temporal deficits in memory, PFC and HC function may be differentially impaired throughout the time course of abstinence

Effects of methamphetamine on sexual behavior

Methamphetamine (Meth) is a highly addictive psychostimulant associated with enhanced sexual desire, arousal, and sexual pleasure. Moreover, Meth abuse is frequently linked with the practice of sexual risk behavior and increased prevalence of Human Immunodeficiency Virus (HIV). Currently, the neurobiological basis for this drug-sex nexus is unknown. Moreover, there is a lack of studies investigating the effects of Meth on sexual behavior and more importantly, compulsive sex-seeking behavior, under controlled experimental settings in animal models. First, using immuhistochemistry for mating- and Meth-induced neural activation it was demonstrated that Meth administration in male rats activates neurons in brain regions of the limbic system that are involved in the regulation of sexual behavior. Specifically, Meth and mating co-activated neurons in the nucleus accumbens (NAc) core and shell, basolateral amygdala (BLA), anterior cingulate (ACA) and orbitofrontal (OFC) cortices. Second, the effects of acute or chronic administration of Meth on different aspects of sexual behavior were tested including motivation and performance, compulsive behavior, and reward. Results showed that high doses of Meth inhibited sexual motivation and performance. Next, to investigate Meth effects on compulsive sexual behavior a paradigm was established in which visceral illness induced by lithium chloride (LiCl) was paired with sexual reward. A low Meth dose (1mg/kg; s.c.) that does not impair sexual function had long-term effects on compulsive sexual behavior. Specifically, two weeks following the last Meth administration, Meth-pretreated males displayed sex-seeking behavior despite having learned the adverse consequences of mating. This effect was dependent on Meth administration being concurrent with sexual experience. Finally, using a conditioned place preference (CPP) paradigm, it was shown that concurrent Meth and sex experience was required for enhanced CPP for mating with Meth and for Meth alone. In contrast, reward for mating alone was decreased. Together, these findings illustrate that Meth can activate the same neurons as sexual behavior and in turn may alter this natural reward behavior. Moreover, these data indicate that the association between drug use and mating may be required for expression of compulsive sex behavior reported by Meth users and is correlated with increased reward seeking for concurrent Meth exposure and mating

The Effect of Early Life Stress on Methamphetamine Damage in the Striatum

Methamphetamine (METH) abuse impacts the global economy through costs associated with drug enforcement, emergency room visits, and treatment. Hyperthermia is a leading cause of METH induced emergency room visits and may lead to neural damage. Previous research has demonstrated early life stress, such as childhood abuse, increases the likelihood of developing a substance abuse disorder. However, the effects of early life stress on neuronal damage induced by chronic METH administration are unknown. We aimed to elucidate the effects of early life stress on METH induced dopamine damage in the striatum. Animals were separated three hours per day during the first two weeks of development or 15 minutes for control. In adulthood, rats received either a subcutaneous 0.9% saline or 5.0 mg/kg METH injection every two hours for a total of four injections. Rectal temperatures were taken before the first injection and one hour after each subsequent injection. Seven days after testing, rats were euthanized and striatum was collected for quantification of tyrosine hydroxylase (TH) and dopamine transporter (DAT) content by Western blot. METH significantly elevated core body temperature in males and decreased striatal DAT and TH content and this effect was potentiated by early life stress. Females did not exhibit an effect of METH except in the elevated heat condition in the preliminary study, which significantly decreased DAT levels. We further ran a preliminary study looking at early life stress, METH dosing in adulthood during ambient (22-23°C) or elevated (27-30°C) temperature .Preliminary results indicated a replication of experiment one with no effect of elevated temperatures. These studies indicate maternal separation increases METH induced damage in males, and females are less susceptible to METH induced damage

Inflammasome Activation by Methamphetamine Potentiates Lipopolysaccharide Stimulation of IL-1β Production in Microglia

Methamphetamine (Meth) is a psychostimulant drug that is widely abused all around the world. The administration of Meth causes a strong instant euphoria effect, and long-term of abuse is correlative of drug-dependence and neurotoxicity. The neuroimaging studies demonstrated that the long-term abuse of Meth is associated with the reduction of the dopamine transporter (DAT) and vesicular monoamine transporter (VMAT2) in the striatum. Neuroinflammation is well-accepted as an important mechanism underlying the Meth-induced neurotoxicity. The over-activated microglia were found both in Meth human abusers and animal models. NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) inflammasome is the most predominant Nod-like receptor (NLR) expressed in microglia and is involved in the pathogenesis of many neurodegenerative diseases. In recent years, multiple lines of evidence suggest that the activation of NLRP3 inflammasome is associated with drug abuse induced innate immune system activation both in central nervous system (CNS) and peripheral nervous system (PNS). We investigated the role of NLRP3 inflammasome in Meth-induced microglial activation. Meth induced the production of mitochondrial ROS and disruption of lysosomal membrane integrity, which served as the second activation signal of NLRP3 inflammasome. The activation of NLRP3 inflammasome led to the cleavage of pro-IL-1β and subsequent release of biologically active IL-1β. By blocking the inflammasome activation, we successfully attenuated the neuronal apoptosis induced by supernatants of Meth-treated microglia. It is well-known that Meth abuse exacerbates HIV-1-associated neurocognitive disorders (HAND). However, the mechanism of how Meth potentiates HAND is not fully understood. Ample evidence indicates that both Meth and HIV-1 cause microglial activation and resultant secretion of proinflammatory molecules leading to neuronal injury and ultimately the development of HAND. Inflammasome is the key signaling platform involved in HIV-1-associated microglia activation and the production of proinflammatory molecules. We studied the synergistic effects of HIV-1 glycoprotein protein 120 (gp120) and Meth in microglial NLRP3 inflammasome activation. Gp120 upregulated the pro-IL-1β and thus, primed the microglia as the first signal. The subsequent stimulation of Meth as the second signal further activates the inflammasome that promotes the processing and release of IL-1β. The overactivated ROS system is potentially relative to gp120- and Meth-induced inflammasome activation

Cell-Specific Spinophilin Function Underlying Striatal Motor Adaptations Associated with Amphetamine-Induced Behavioral Sensitization

Indiana University-Purdue University Indianapolis (IUPUI)Striatal-mediated pathological disease-states such as Obsessive-Compulsive Disorder (OCD), Parkinson’s Disease (PD), and psychostimulant drug addiction/abuse are coupled with distinct motor movement abnormalities. In addition, these disorders are associated with perturbed synaptic transmission. Proper synaptic transmission is critical for maintaining neuronal communication. Furthermore, in many striatal-dependent disease-states, the principle striatal neurons, medium spiny neurons (MSNs), exhibit differential perturbations in downstream signaling. Signal transduction pathways that are localized to the glutamatergic post-synaptic density (PSD) of GABAergic MSNs regulate protein phosphorylation in a tightly controlled manner. Alterations in the control of this phosphorylation in striatal MSNs are observed in myriad striatal pathological diseasestates and can give rise to perturbations in synaptic transmission. While serine/threonine kinases obtain substrate specificity, in part, by phosphorylating specific consensus sites, serine/threonine phosphatases such as protein phosphatase 1 (PP1) are much more promiscuous. To obtain substrate selectivity, PP1 associates with targeting proteins. The major targeting protein for PP1 in the PSD of striatal dendritic spines is spinophilin. Spinophilin not only binds PP1, but also concurrently interacts with myriad synaptic proteins. Interestingly, dopamine depletion, an animal model of PD, modulates spinophilin protein-protein interactions in the striatum. However, spinophilin function on basal striatal-mediated motor behaviors such as the rotarod or under hyperdopaminergic states such as those observed following psychostimulant-induced behavioral sensitization are less well characterized. To elucidate spinophilin function more specifically, we have generated multiple transgenic animals that allow for cell type-specific loss of spinophilin as well as cell-specific interrogation of spinophilin protein interactions. Here, I report the functional role of spinophilin in regulating striatal mediated motor behaviors and functional changes associated with amphetamine-induced locomotor sensitization. In addition, we define changes in spinophilin protein-protein interactions that may mediate these behavioral changes. Furthermore, global loss of spinophilin abrogates amphetamine-induced sensitization and plays a critical role in striatal motor learning and performance. The data suggest that the striatal spinophilin protein interactome is upregulated in MSNs following psychostimulant administration. In addition, loss of spinophilin changes protein expression in myriad psychostimulant-mediated striatal adaptations. Taken together the data suggests that spinophilin’s protein-protein interactions in the striatum are obligate for appropriate striatal mediated motor function

EFFECTS OF THE NOVEL ATYPICAL ANTIPSYCHOTIC, ARIPIPRAZOLE, ON RATS PERFORMING SIGNALED AND UNSIGNALED TEMPORAL DISCRIMINATION TASKS.

In contrast to other atypical antipsychotics, aripiprazole (ARZ) acts as a partial agonist, rather than an antagonist, at dopamine D2 receptors (Burris et al, 2002; Jordan et al, 2002). This unique pharmacology is thought to be essential to its multi-faceted use in the treatment of other disorders, particularly in its use as an adjunctive treatment for Major Depressive Disorder (Biler & Blondeau, 2011). Currently, little treatment is available to attenuate cognitive dysfunction in schizophrenic individuals (Schatzberg et al, 2010). However, clinical and neurocognitive studies have reported ARZ to improve cognition in schizophrenic subjects (Leuchet et al, 2003; Schatzberg et al, 2010), as well as attenuate working memory impairments and attentional deficits in animal models of psychosis (Carli et al, 2010; Nordquest et al, 2008; Nagi et a, 2008). Further evaluation of ARZ is needed to assess its ability to ameliorate higher-order cognitive processes in a laboratory behavioral pharmacological context. Differential-reinforcement-of-low-rates (DRL) is an operant timing schedule that requires animals to produce inter-response-times (IRTs) greater than a criterion temporal interval to obtain a reward. Because animals must temporally regulate their responses and internally estimate the criterion duration, successful performance on the DRL task is dependent on both temporal processing and controlled timing behaviors. Since individuals with schizophrenia exhibit temporal processing deficits (Carroll et al, 2008; Elveag et al, 2008; Tysk et al, 1990), the DRL schedule can be utilized to evaluate the effects of ARZ to attenuate timing behaviors in a laboratory animal model of psychosis. In the studies presented here, water-deprived male Sprague-Dawley rats were trained to perform a DRL-72 second schedule that was either signaled (DRLS-72; n = 8) or unsignaled (DRLU-72; n = 8). Upon making a correct response (IRT ≥ 72s), rats were given a small amount (0.06mL) of distilled water as reinforcement. Subjects were trained to perform the task in operant chambers with force-plate technology (Fowler et al, 2001), which allowed for high-precision measurements of locomotor activity (e.g., spatial patterning, distance traveled) and response characteristics (e.g., response durations, peak force of responses). Before drug treatment, DRLS-72 rats were significantly more successful at operant performance (e.g., higher reinforcement rates, longer IRTs) than DRLU-72 rats. In addition, DRLS-72 rats were less restricted in their spatial patterning and engaged in more locomotion, suggesting rats under the signaled contingency were less likely to engage in timing behaviors than DRLU-72 rats. These results reflect a difference of task difficulty between the two DRL schedules: The ability to perceive and respond to an external stimulus (DRLS-72 condition) was less demanding and difficult than internally estimating the temporal criterion (DRLU-72 condition). The acute administration of ARZ (1.0, 3.0, and 6.0mg/kg) at the beginning of the session induced right-ward shifts in IRT frequency distributions and lengthened median IRT values, though this effect was greater in the DRLU-72 group. This latter finding is likely due to the increased reliance of DRLU-72 rats on timing behaviors and temporal processing--behaviors and processes that are sensitive to the pharmacological modulation of brain dopamine systems (Hinton & Meck, 1997; Meck, 1983). Similar to other antipsychotics on DRL-mediated behavior (Wiley et al, 2000; O'Donnell & Seiden, 1983), ARZ generally altered operant behavior by dose-dependently reducing non-burst and burst response rates and reinforcement rates in both DRL groups. However, the 1mg/kg dose improved DRLU-72 operant performance by significantly increasing reinforcement rates and decreasing response rates--an effect that is similar to antidepressants (O'Donnell & Seiden, 1983). In a separate experiment, 16 naive rats were again trained to perform the DRLS-72 (n = 8) and DRLU-72 (n = 7) task. After completing seven 4-hr sessions of DRLS-72 or DRLU-72 (28 hours of training), rats were administered 5.0mg/kg amphetamine (AMPH) over several sessions to model a state of psychosis (Young et al, 2010). To evaluate the effects of ARZ to attenuate schizophrenic-like cognitive and behavioral deficits, rats were first administered AMPH immediately preceding the operant session, followed 30 minutes later by acute injections of 1.0, 3.0, or 6.0mg/kg ARZ. AMPH treatment produced a consistent pattern of behavior in rats: Subjects engaged in focused stereotypy during the first portion (approximately 1.5-hr) of the session followed by hyperlocomotion and operant-directed behavior in the latter portion (approximately 2.5-hr). AMPH induced timing deficits in DRLU-72 rats by shifting IRT distributions to the left and reducing median IRT values. In addition, AMPH treatment significantly impaired DRLU-72 performance by increasing non-burst responses rates, reducing reinforcement rates, and disrupting space usage relative to non-AMPH behavioral sessions. However, AMPH treatment did not induce timing deficits in DRLS-72 rats. AMPH did not significantly alter DRLS-72 IRT distributions, median IRTs, space usage, and reinforcement rates when compared to non-AMPH treatment sessions. This result implies that AMPH treatment induced schizophrenic-like timing deficits in DRLU-72 rats, but not DRLS-72 rats. It is likely that AMPH induced greater impairments in the DRLU-72 condition because the unsignaled DRL contingency was substantially more cognitively demanding than the DRLS-72 condition. In AMPH-treated rats, ARZ administration dose-dependently reduced hyperlocomotion and hastened recovery time from focused stereotypy. ARZ partially reversed the effects of AMPH in both DRL groups by significantly reducing non-burst responses, increasing median IRT values, and shifting IRT distributions to the right. However, ARZ could not completely attenuate AMPH-induced impairments in operant performance and collateral activity for DRLU-72 rats, suggesting that ARZ was limited in its capacity to attenuate schizophrenic-like cognitive and behavioral deficits that were induced by AMPH

Gabab Regulation of Methamphetamine-Induced Associative Learning

Addiction is a chronic, relapsing disorder for which strikingly few effective therapies exist, and there are no FDA-approved pharmacotherapies for methamphetamine (Meth) addition. There is an immense need to identify the neurobiological underpinnings of psychostimulant addiction and develop efficacious drug therapies to compliment the current mainstay treatment of behavioral/cognitive therapy. Re-exposure to cues associated with psychostimulants (e.g., drug paraphernalia) increase neuronal activity and can elicit drug-craving and -seeking; an effect which is profound and long-lasting. A mechanism to disrupt those brain processes which are necessary to maintain the association may reduce the incidence of cue-elicited relapse. Conditioned place preference (CPP) is a behavioral paradigm in which subjects (humans and rodents) learn to associate the rewarding properties of Meth with particular contextual cues. After the association develops subjects will choose to spend more time in the drug-associated context over a non-drug paired context. This behavior is thought to reflect the increased salience attributed to drug-associated cues. Thus, CPP is a valuable research tool to evaluate the neuronal adaptations associated with drug-induced associative learning and provides a means to evaluate the utility of potential pharmacotherapies to reduce the salience of drug-associated cues. As the major inhibitory neurotransmitter in the brain, GABA neurotransmission influences a number of drug-induced behaviors (e.g., CPP) as well as mnemonic processes (e.g., learning and memory). Accordingly, the metabotropic GABAB receptor has recently emerged as a potential therapeutic target for drug addiction. Administration of the direct acting GABAB receptor agonist baclofen has revealed positive outcomes in clinical trials; however, the side effects associated with baclofen limit its clinical utility. Positive allosteric modulators (PAMs) of the GABAB receptor augment GABAB receptor signaling without the side effects of the agonist making it a better alternative to agonist therapy. The current project sought to determine the role of the GABAB receptor in the maintenance of Meth-induced CPP. To do so, the GABAB receptor agonist baclofen and GABAB receptor positive allosteric modulators fendiline, GS39783, and CGP7930 were administered after the learned association developed (Meth-induced CPP) in order to determine if augmenting GABAB receptor signaling would disrupt the maintenance of the behavior. These experiments will shed light on the role of GABAB receptors in the maintenance of Meth-induced associative learning and evaluate the utility of GABAB receptor activators to reduce the salience of psychostimulant-associated cues

Cognitive dysfunction and schizophrenia : Modelling attentional impairment with psychotomimetics. Investigating attentional impairment and structural brain abnormalities following phencyclidine administration: Enhancing translatability between preclinical and clinical tests of attention utilising the modified 5-choice task in rats - the 5-Choice Continuous Performance Test.

This thesis consisted of experiments designed to explore the construct of attention and investigate the disruptive effects of psychotomimetics, with a specific focus on NMDA antagonists. Phencyclidine (PCP) was administered through a variety of treatment regimens in order to to determine the ability of inducing cognitive-specific disruptions in attentional functioning. The hypothesis that sub-chronic exposure to PCP would result in persistent attentional impairment was tested, using the 5-choice serial reaction time task (5-CSRTT). The 5-CSRTT assesses not only visuospatial attention, but also components of impulsivity, compulsivity, speed of processing and motivation. It was determined that an additional task-related intervention that increased the attentional load was required to elucidate attentional impairment following sub-chronic PCP treatment. The ability of rats to perform the modified version of the 5-CSRTT, known as the 5-choice continuous performance test (5C-CPT), was investigated. The 5C-CPT was implemented to provide a task that may have greater analogy to the human CPT, than the original 5-CSRTT. The consequence of dopaminergic D1 system activation was investigated. It was revealed that D1 partial agonism improved attentional performance in a baseline-dependent manner. Following successful acquisition of the task, it was shown that repeated PCP treatment induced cognitive disruption that was cognitive-specific, and not confounded by generalised response disruption. Furthermore, a partial attenuation of the PCP-induced performance disruption was achieved following administration of the D1 partial agonist, SKF 38393. Moreover, sub-chronic PCP treatment was shown to impair 5C-CPT performance in the drug-free state. However, an additional challenge that further increased the attentional load was needed to elucidate a performance deficit. This highlighted that sustained attention/vigilance is sensitive to persistent impairment following sub-chronic PCP administration in a manner consistent with deficits observed in schizophrenia patients. This prompted the investigation that tested the hypothesis that sub-chronic PCP treatment could induce enduring structural deficits in regions associated with attentional performance. Magnetic resonance imaging (MRI) was conducted, in conjunction with 5-CSRTT and pre-pulse inhibition (PPI). It was revealed that sub-chronic PCP treatment resulted in morphological brain abnormalities in brain regions associated with 5-CSRTT performance. This was coupled with deficits in sustained attentional performance following an increase in attentional load, yet PPI was unaffected. Taken together, these findings suggested sub-chronic PCP treatment impairs attentional functionality, an effect that dissociates between effortful and passive attentional processes