The effects of lobeline and naltrexone on methamphetamine-induced place preference and striatal dopamine and serotonin levels in adolescent rats with a history of maternal separation

Natural products as the therapeutic strategies for addiction

World Drug Report 2023 concluded that 296 million people abused drugs, 39.5 million became addiction and 494,000 died as a direct or indirect result of addiction. Addiction has become a growing problem that affects individuals, their families, societies, countries and even the world. However, treatment for addiction is only limited to some developed countries because of the high cost, difficult implementation, and time consuming. Therefore, there is an urgent need to develop a low-cost, effective drug for the development of addiction treatment in more countries, which is essential for the stability and sustainable development of the world. In this review, it provided an overview of the abuse of common addictive drugs, related disorders, and current therapeutic regimen worldwide, and summarized the mechanisms of drug addiction as reward circuits, neuroadaptation and plasticity, cognitive decision-making, genetics, and environment. According to their chemical structure, 43 natural products and 5 herbal combinations with potential to treat addiction were classified, and their sources, pharmacological effects and clinical trials were introduced. It was also found that mitragine, ibogine, L-tetrahydropalmatine and crocin had greater potential for anti-addiction.

Nicotine-mediated therapy for Parkinson's disease in transgenic Caenorhabditis elegans model

Parkinson's disease resultant in the degeneration of Dopaminergic neurons and accumulation of α-synuclein in the substantia nigra pars compacta. The synthetic therapeutics for Parkinson's disease have moderate symptomatic benefits but cannot prevent or delay disease progression. In this study, nicotine was employed by using transgenic Caenorhabditis elegans Parkinson's disease models to minimize the Parkinson's disease symptoms. The results showed that the nicotine at 100, 150, and 200 μM doses reduced degeneration of Dopaminergic neurons caused by 6-hydroxydopamine (14, 33, and 40%), lowered the aggregative toxicity of α-synuclein by 53, 56, and 78%, respectively. The reduction in food-sensing behavioral disabilities of BZ555 was observed to be 18, 49, and 86%, respectively, with nicotine concentrations of 100 μM, 150 μM, and 200 μM. Additionally, nicotine was found to enhance Daf-16 nuclear translocation by 14, 31, and 49%, and dose-dependently increased SOD-3 expression by 10, 19, and 23%. In summary, the nicotine might a promising therapy option for Parkinson's disease.

Sex differences in addiction-relevant behavioral outcomes in rodents following early life stress

In humans, exposure to early life stress (ELS) is an established risk factor for the development of substance use disorders (SUDs) during later life. Similarly, rodents exposed to ELS involving disrupted mother-infant interactions, such as maternal separation (MS) or adverse caregiving due to scarcity-adversity induced by limited bedding and nesting (LBN) conditions, also exhibit long-term alterations in alcohol and drug consumption. In both humans and rodents, there is a range of addiction-related behaviors that are associated with drug use and even predictive of subsequent SUDs. In rodents, these include increased anxiety-like behavior, impulsivity, and novelty-seeking, altered alcohol and drug intake patterns, as well as disrupted reward-related processes involving consummatory and social behaviors. Importantly, the expression of these behaviors often varies throughout the lifespan. Moreover, preclinical studies suggest that sex differences play a role in how exposure to ELS impacts reward and addiction-related phenotypes as well as underlying brain reward circuitry. Here, addiction-relevant behavioral outcomes and mesolimbic dopamine (DA) dysfunction resulting from ELS in the form of MS and LBN are discussed with a focus on age- and sex-dependent effects. Overall, these findings suggest that ELS may increase susceptibility for later life drug use and SUDs by interfering with the normal maturation of reward-related brain and behavioral function.

Early-life adversity increases anxiety-like behavior and modifies synaptic protein expression in a region-specific manner

Early-life adversity (ELA) can induce persistent neurological changes and increase the risk for developing affective or substance use disorders. Disruptions to the reward circuitry of the brain and pathways serving motivation and emotion have been implicated in the link between ELA and altered adult behavior. The molecular mechanisms that mediate the long-term effects of ELA, however, are not fully understood. We examined whether ELA in the form of neonatal maternal separation (MatSep) modifies behavior and synaptic protein expression in adults. We hypothesized that MatSep would affect dopaminergic and glutamatergic signaling and enhance sensitivity to methamphetamine (Meth) reward or increase anxiety. Male Wistar rats were subjected to MatSep for 180 min/d on postnatal days (PND) 2-14 and allowed to grow to adulthood (PND 60) with no further manipulation. The hippocampus (Hipp), medial prefrontal cortex (mPFC), nucleus accumbens (NAc), and caudate putamen (CPu) were isolated from one subgroup of animals and subjected to Western blot and protein quantitation for tyrosine hydroxylase (TH), α-synuclein (ALPHA), NMDA receptor (NMDAR), dopamine receptor-1 (D1) and -2 (D2), dopamine transporter (DAT), and postsynaptic density 95 (PSD95). Separate group of animals were tested for anxiety-like behavior and conditioned place preference (CPP) to Meth at 0.0, 0.1, and 1.0 mg/kg doses. MatSep rats displayed an increase in basal levels of anxiety-like behavior compared to control animals. MatSep rats also demonstrated CPP to Meth, but their responses did not differ significantly from controls at any drug dose. Increased NMDAR, D2, and ALPHA expression was observed in the NAc and CPu following MatSep; D2 and ALPHA levels were also elevated in the mPFC, along with DAT. MatSep rats had reduced D1 expression in the mPFC and Hipp, with the Hipp also showing a reduction in D2. Only the CPu showed elevated TH and decreased DAT expression levels. No significant changes were found in PSD95 expression in MatSep rats. In conclusion, ELA is associated with long-lasting and region-specific changes in synaptic protein expression that diminish dopamine neurotransmission and increase anxiety-like behavior in adults. These findings illustrate potential mechanisms through which ELA may increase vulnerability to stress-related illness.

Peri-adolescent exposure to (meth)amphetamine in animal models

Experimentation with psychoactive drugs is often initiated in the peri-adolescent period, but knowledge of differences in the outcomes of peri-adolescent- vs adult-initiated exposure is incomplete. We consider the existing animal research in this area for (meth)amphetamines. Established for a number of phenotypes, is lower sensitivity of peri-adolescents than adults to acute effects of (meth)amphetamines, including neurotoxic effects of binge-level exposure. More variable are data for long-term consequences of peri-adolescent exposure on motivational and cognitive traits. Moreover, investigations often exclude an adult-initiated exposure group critical for answering questions about outcomes unique to peri-adolescent initiation. Despite this, it is clear from the animal research that (meth)amphetamine exposure during the peri-adolescent period, whether self- or other-administered, impacts brain motivational circuitry and cognitive function, and alters adult sensitivity to other drugs and natural rewards. Such consequences occurring in humans have the potential to predispose toward unfortunate and potentially disastrous family, social and livelihood outcomes.

The Synaptic Vesicle Glycoprotein 2: Structure, Function, and Disease Relevance

The synaptic vesicle glycoprotein 2 (SV2) family is comprised of three paralogues: SV2A, SV2B, and SV2C. In vertebrates, SV2s are 12-transmembrane proteins present on every secretory vesicle, including synaptic vesicles, and are critical to neurotransmission. Structural and functional studies suggest that SV2 proteins may play several roles to promote proper vesicular function. Among these roles are their potential to stabilize the transmitter content of vesicles, to maintain and orient the releasable pool of vesicles, and to regulate vesicular calcium sensitivity to ensure efficient, coordinated release of the transmitter. The SV2 family is highly relevant to human health in a number of ways. First, SV2A plays a role in neuronal excitability and as such is the specific target for the antiepileptic drug levetiracetam. SV2 proteins also act as the target by which potent neurotoxins, particularly botulinum, gain access to neurons and exert their toxicity. Both SV2B and SV2C are increasingly implicated in diseases such as Alzheimer's disease and Parkinson's disease. Interestingly, despite decades of intensive research, their exact function remains elusive. Thus, SV2 proteins are intriguing in their potentially diverse roles within the presynaptic terminal, and several recent developments have enhanced our understanding and appreciation of the protein family. Here, we review the structure and function of SV2 proteins as well as their relevance to disease and therapeutic development.

The impact of early life stress on the central oxytocin system and susceptibility for drug addiction: Applicability of oxytocin as a pharmacotherapy

Early life trauma is strongly associated with an increased vulnerability to abuse illicit drugs and the impairment of neural development. This includes alterations to the development of the oxytocin system, which plays a pivotal role in the regulation of social behaviours and emotion. Dysregulation of this important system also contributes to increased susceptibility to develop drug addiction. In this review, we provide an overview of the animal models of early life stress that are widely used, and discuss the impact that early life stress has on drug-taking behaviour in adolescence and adulthood in both sexes. We link this to the changes that early life stress has on the endogenous oxytocin system, and how exogenously administered oxytocin may help to re-establish functioning of the system, and in turn, reduce drug-taking behaviour.

Role of Plant Derived Alkaloids and Their Mechanism in Neurodegenerative Disorders

Neurodegenerative diseases are conventionally demarcated as disorders with selective loss of neurons. Conventional as well as newer molecules have been tested but they offer just symptomatic advantages along with abundant side effects. The discovery of more compelling molecules that can halt the pathology of these diseases will be considered as a miracle of present time. Several synthetic compounds are available but they may cause several other health issues. Therefore, natural molecules from the plants and other sources are being discovered to replace available medicines. In conventional medicational therapies, several plants have been reported to bestow remedial effects. Phytochemicals from medicinal plants can provide a better and safer alternative to synthetic molecules. Many phytochemicals have been identified that cure the human body from a number of diseases. The present article reviews the potential efficacy of plant-derived alkaloids, which possess potential therapeutic effects against several NDDs including Alzheimer's disease (AD), Huntington disease (HD), Parkinson's disease (PD), Epilepsy, Schizophrenia, and stroke. Alkaloids include isoquinoline, indole, pyrroloindole, oxindole, piperidine, pyridine, aporphine, vinca, β-carboline, methylxanthene, lycopodium, and erythrine byproducts. Alkaloids constitute positive roles in ameliorating pathophysiology of these illnesses by functioning as muscarinic and adenosine receptors agonists, anti-oxidant, anti-amyloid and MAO inhibitors, acetylcholinestrase and butyrylcholinesterase inhibitor, inhibitor of α-synuclein aggregation, dopaminergic and nicotine agonist, and NMDA antagonist.

Chronic variable stress and intravenous methamphetamine self-administration - Role of individual differences in behavioral and physiological reactivity to novelty

Stress is a contributing factor to the development and maintenance of addiction in humans. However, few studies have shown that stress potentiates the rewarding and/or reinforcing effects of methamphetamine in rodent models of addiction. The present study assessed the effects of exposure to 14 days of chronic variable stress (CVS), or no stress as a control (CON), on the rewarding and reinforcing effects of methamphetamine in adult rats using the conditioned place preference (Experiment 1) and intravenous self-administration (Experiment 2) paradigms. In Experiment 2, we also assessed individual differences in open field locomotor activity, anxiety-like behavior in the elevated plus maze (EPM), and physiological responses to a novel environment as possible predictors of methamphetamine intake patterns. Exposure to CVS for 14 days did not affect overall measures of methamphetamine conditioned reward or reinforcement. However, analyses of individual differences and direct vs. indirect effects revealed that rats exhibiting high physiological reactivity and locomotor activity in the EPM and open field tests self-administered more methamphetamine and reached higher breakpoints for drug reinforcement than rats exhibiting low reactivity. In addition, CVS exposure significantly increased the proportion of rats that exhibited high reactivity, and high reactivity was significantly correlated with increased levels of methamphetamine intake. These findings suggest that individual differences in physiological and locomotor reactivity to novel environments, as well as their interactions with stress history, predict patterns of drug intake in rodent models of methamphetamine addiction. Such predictors may eventually inform future strategies for implementing individualized treatment strategies for amphetamine use disorders.

Dissociation of μ-opioid receptor and CRF-R1 antagonist effects on escalated ethanol consumption and mPFC serotonin in C57BL/6J mice

Both the opioid antagonist naltrexone and corticotropin-releasing factor type-1 receptor (CRF-R1) antagonists have been investigated for the treatment of alcoholism. The current study examines the combination of naltrexone and CP154526 to reduce intermittent access ethanol drinking [intermittent access to alcohol (IAA)] in C57BL/6J male mice, and if these compounds reduce drinking via serotonergic mechanisms in the dorsal raphe nucleus (DRN). Systemic injections and chronic intracerebroventricular infusions of naltrexone, CP154526 or CP376395 transiently decreased IAA drinking. Immunohistochemistry revealed CRF-R1 or μ-opioid receptor immunoreactivity was co-localized in tryptophan hydroxylase (TPH)-immunoreactive neurons as well as non-TPH neurons in the DRN. Mice with a history of IAA or continuous access to alcohol were microinjected with artificial cerebral spinal fluid, naltrexone, CP154526 or the combination into the DRN or the median raphe nucleus (MRN). Either intra-DRN naltrexone or CP154526 reduced IAA in the initial 2 hours of fluid access, but the combination did not additively suppress IAA, suggesting a common mechanism via which these two compounds affect intermittent drinking. These alcohol-reducing effects were localized to the DRN of IAA drinkers, as intra-MRN injections only significantly suppressed water drinking, and continuous access drinkers were not affected by CRF-R1 antagonism. Extracellular serotonin was measured in the medial prefrontal cortex (mPFC) using in vivo microdialysis after intra-DRN microinjections in another group of mice. Intra-DRN CP154526 increased serotonin impulse flow to the mPFC while naltrexone did not. This suggests the mPFC may not be an essential location to intermittent drinking, as evidenced by different effects on serotonin signaling to the forebrain yet similar behavioral findings.

Neurodevelopmental Animal Models Reveal the Convergent Role of Neurotransmitter Systems, Inflammation, and Oxidative Stress as Biomarkers of Schizophrenia: Implications for Novel Drug Development

Schizophrenia is a life altering disease with a complex etiology and pathophysiology, and although antipsychotics are valuable in treating the disorder, certain symptoms and/or sufferers remain resistant to treatment. Our poor understanding of the underlying neuropathological mechanisms of schizophrenia hinders the discovery and development of improved pharmacological treatment, so that filling these gaps is of utmost importance for an improved outcome. A vast amount of clinical data has strongly implicated the role of inflammation and oxidative insults in the pathophysiology of schizophrenia. Preclinical studies using animal models are fundamental in our understanding of disease development and pathology as well as the discovery and development of novel treatment options. In particular, social isolation rearing (SIR) and pre- or postnatal inflammation (PPNI) have shown great promise in mimicking the biobehavioral manifestations of schizophrenia. Furthermore, the "dual-hit" hypothesis of schizophrenia states that a first adverse event such as genetic predisposition or a prenatal insult renders an individual susceptible to develop the disease, while a second insult (e.g., postnatal inflammation, environmental adversity, or drug abuse) may be necessary to precipitate the full-blown syndrome. Animal models that emphasize the "dual-hit" hypothesis therefore provide valuable insight into understanding disease progression. In this Review, we will discuss SIR, PPNI, as well as possible "dual-hit" animal models within the context of the redox-immune-inflammatory hypothesis of schizophrenia, correlating such changes with the recognized monoamine and behavioral alterations of schizophrenia. Finally, based on these models, we will review new therapeutic options, especially those targeting immune-inflammatory and redox pathways.

Endogenous opiates and behavior: 2012

This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Lobeline shows protective effects against MPTP-induced dopaminergic neuron death and attenuates behavior deficits in animals

We previously demonstrated that lobeline effectively inhibited dopamine transporter (DAT)-mediated dopamine (DA) transportation. Therefore, the present study aimed to investigate whether lobeline shows protective effects against neurotoxin-induced cell death in vivo. Mice were administered 30 mg/kg 1-methyl-4-phenyl-1,2,3,6-tetra-hydropyridine (MPTP) and treated with 80 mg/kg L-dopa, 10 mg/kg GBR12935 or 1 or 3 mg/kg lobeline, respectively, via injection. Rotarod and swim tests as well as tyrosine hydroxylase (TH) immunohistochemistry were carried out to evaluate the effects of these drugs. Compared with L-DA and GBR12935, lobeline (3 mg/kg administered via intraperitoneal injection) on behavior and dopaminergic neurons. Compared with L-DA and GBR12935, lobeline (3 mg/kg injected subcutaneously) significantly reduced MPTP induced locomotive deficits detected in behavioral tests. In addition, TH immunostaining showed that lobeline (3 mg/kg) markedly decreased the neurotoxin-induced immunoreactivity loss in the substantia nigra and striatum. Lobeline may be useful in the protection of dopaminergic neurons and may alleviate the symptoms of Parkinson's disease.

The Effects of Maternal Separation on Adult Methamphetamine Self-Administration, Extinction, Reinstatement, and MeCP2 Immunoreactivity in the Nucleus Accumbens

The maternal separation (MS) paradigm is an animal model of early life stress. Animals subjected to MS during the first 2 weeks of life display altered behavioral and neuroendocrinological stress responses as adults. MS also produces altered responsiveness to and self-administration (SA) of various drugs of abuse including cocaine, ethanol, and amphetamine. However, no studies have yet examined the effects of MS on methamphetamine (METH) SA. This study was performed to examine the effects of MS on the acquisition of METH SA, extinction, and reinstatement of METH-seeking behavior in adulthood. Given the known influence of early life stress and drug exposure on epigenetic processes, we also investigated group differences in levels of the epigenetic marker methyl CpG binding protein 2 (MeCP2) in the nucleus accumbens (NAc) core. Long-Evans pups and dams were separated on postnatal days (PND) 2-14 for either 180 (MS180) or 15 min (MS15). Male offspring were allowed to acquire METH SA (0.05 mg/kg/infusion) in 15 2-h daily sessions starting at PND67, followed by extinction training and cue-induced reinstatement of METH-seeking behavior. Rats were then assessed for MeCP2 levels in the NAc core by immunohistochemistry. The MS180 group self-administered significantly more METH and acquired SA earlier than the MS15 group. No group differences in extinction or cue-induced reinstatement were observed. MS15 rats had significantly elevated MeCP2-immunoreactive cells in the NAc core as compared to MS180 rats. Together, these data suggest that MS has lasting influences on METH SA as well as epigenetic processes in the brain reward circuitry.

Emotional valence and context of social influences on drug abuse-related behavior in animal models of social stress and prosocial interaction

RATIONALE

Social factors are important determinants of drug dependence and relapse.

OBJECTIVES

We reviewed pre-clinical literature examining the role of social experiences from early life through the development of drug dependence and relapse, emphasizing two aspects of these experiences: (1) whether the social interaction is appetitive or aversive and (2) whether the social interaction occurs within or outside of the drug-taking context.

METHODS

The models reviewed include neonatal care, isolation, social defeat, chronic subordination, and prosocial interactions. We review results from these models in regard to effects on self-administration and conditioned place preference established with alcohol, psychostimulants, and opiates.

RESULTS

We suggest that in general, when the interactions occur outside of the drug-taking context, prosocial interactions are protective against drug abuse-related behaviors, whereas social stressors facilitate these behaviors. By contrast, positive or negative social interactions occurring within the drug-taking context may interact with other risk factors to enhance or inhibit these behaviors.

CONCLUSIONS

Despite differences in the nature and complexity of human social behavior compared to other species, the evolving animal literature provides useful models for understanding social influences on drug abuse-related behavior that will allow for research on the behavioral and biological mechanisms involved. The models have contributed to understanding social influences on initiation and maintenance of drug use, but more research is needed to understand social influences on drug relapse.