The effects of locus coeruleus and norepinephrine in methamphetamine toxicity

Effects of exercise interventions on negative emotions, cognitive performance and drug craving in methamphetamine addiction

Introduction

Methamphetamine is currently one of the most commonly used addictive substances with strong addiction and a high relapse rate. This systematic review aims to examine the effectiveness of physical activity in improving negative emotions, cognitive impairment, and drug craving in people with methamphetamine use disorder (MUD).

Methods

A total of 17 studies out of 133 found from Embase and PubMed were identified, reporting results from 1836 participants from MUD populations. Original research using clearly described physical activity as interventions and reporting quantifiable outcomes of negative mood, cognitive function and drug craving level in people with MUD were eligible for inclusion. We included prospective studies, randomized controlled trials, or intervention studies, focusing on the neurological effects of physical activity on MUD.

Results

Taken together, the available clinical evidence showed that physical activity-based interventions may be effective in managing MUD-related withdrawal symptoms.

Discussion

Physical exercise may improve drug rehabilitation efficiency by improving negative emotions, cognitive behaviors, and drug cravings.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42024530359.

The raphe nuclei are the early lesion site of gastric α-synuclein propagation to the substantia nigra

Parkinson's disease (PD) is a neurodegeneration disease with α-synuclein accumulated in the substantia nigra pars compacta (SNpc) and most of the dopaminergic neurons are lost in SNpc while patients are diagnosed with PD. Exploring the pathology at an early stage contributes to the development of the disease-modifying strategy. Although the "gut-brain" hypothesis is proposed to explain the underlying mechanism, where the earlier lesioned site in the brain of gastric α-synuclein and how α-synuclein further spreads are not fully understood. Here we report that caudal raphe nuclei (CRN) are the early lesion site of gastric α-synuclein propagating through the spinal cord, while locus coeruleus (LC) and substantia nigra pars compacta (SNpc) were further affected over a time frame of 7 months. Pathological α-synuclein propagation via CRN leads to neuron loss and disordered neuron activity, accompanied by abnormal motor and non-motor behavior. Potential neuron circuits are observed among CRN, LC, and SNpc, which contribute to the venerability of dopaminergic neurons in SNpc. These results show that CRN is the key region for the gastric α-synuclein spread to the midbrain. Our study provides valuable details for the "gut-brain" hypothesis and proposes a valuable PD model for future research on early PD intervention.

Substance abuse and neurotransmission

The number of people who suffer from a substance abuse disorder has continued to rise over the last decade; particularly, the number of drug-related overdose deaths has sharply increased during the COVID-19 pandemic. Converging lines of clinical observations, supported by imaging and neuropsychological performance testing, have demonstrated that substance abuse-induced dysregulation of neurotransmissions in the brain is critical for development and expression of the addictive properties of abused substances. Recent scientific advances have allowed for better understanding of the neurobiological processes that mediates drugs of abuse and addiction. This chapter presents the past classic concepts and the recent advances in our knowledge about how cocaine, amphetamines, opioids, alcohol, and nicotine alter multiple neurotransmitter systems, which contribute to the behaviors associated with each drug. Additionally, we discuss the interactive effects of HIV-1 or COVID-19 and substance abuse on neurotransmission and neurobiological pathways. Finally, we introduce therapeutic strategies for development of pharmacotherapies for substance abuse disorders.

Norepinephrine Protects against Methamphetamine Toxicity through β2-Adrenergic Receptors Promoting LC3 Compartmentalization

Norepinephrine (NE) neurons and extracellular NE exert some protective effects against a variety of insults, including methamphetamine (Meth)-induced cell damage. The intimate mechanism of protection remains difficult to be analyzed in vivo. In fact, this may occur directly on target neurons or as the indirect consequence of NE-induced alterations in the activity of trans-synaptic loops. Therefore, to elude neuronal networks, which may contribute to these effects in vivo, the present study investigates whether NE still protects when directly applied to Meth-treated PC12 cells. Meth was selected based on its detrimental effects along various specific brain areas. The study shows that NE directly protects in vitro against Meth-induced cell damage. The present study indicates that such an effect fully depends on the activation of plasma membrane β2-adrenergic receptors (ARs). Evidence indicates that β2-ARs activation restores autophagy, which is impaired by Meth administration. This occurs via restoration of the autophagy flux and, as assessed by ultrastructural morphometry, by preventing the dissipation of microtubule-associated protein 1 light chain 3 (LC3) from autophagy vacuoles to the cytosol, which is produced instead during Meth toxicity. These findings may have an impact in a variety of degenerative conditions characterized by NE deficiency along with autophagy impairment.

From Brain Organoids to Networking Assembloids: Implications for Neuroendocrinology and Stress Medicine

Brain organoids are three-dimensional cultures that contain multiple types of cells and cytoarchitectures, and resemble fetal human brain structurally and functionally. These organoids are being used increasingly to model brain development and disorders, however, they only partially recapitulate such processes, because of several limitations, including inability to mimic the distinct cortical layers, lack of functional neuronal circuitry as well as non-neural cells and gyrification, and increased cellular stress. Efforts to create improved brain organoid culture systems have led to region-specific organoids, vascularized organoids, glia-containing organoids, assembloids, sliced organoids and polarized organoids. Assembloids are fused region-specific organoids, which attempt to recapitulate inter-regional and inter-cellular interactions as well as neural circuitry development by combining multiple brain regions and/or cell lineages. As a result, assembloids can be used to model subtle functional aberrations that reflect complex neurodevelopmental, neuropsychiatric and neurodegenerative disorders. Mammalian organisms possess a highly complex neuroendocrine system, the stress system, whose main task is the preservation of systemic homeostasis, when the latter is threatened by adverse forces, the stressors. The main central parts of the stress system are the paraventricular nucleus of the hypothalamus and the locus caeruleus/norepinephrine-autonomic nervous system nuclei in the brainstem; these centers innervate each other and interact reciprocally as well as with various other CNS structures. Chronic dysregulation of the stress system has been implicated in major pathologies, the so-called chronic non-communicable diseases, including neuropsychiatric, neurodegenerative, cardiometabolic and autoimmune disorders, which lead to significant population morbidity and mortality. We speculate that brain organoids and/or assembloids could be used to model the development, regulation and dysregulation of the stress system and to better understand stress-related disorders. Novel brain organoid technologies, combined with high-throughput single-cell omics and gene editing, could, thus, have major implications for precision medicine.

The Role of Chinese Herbal Therapy in Methamphetamine Abuse and its Induced Psychiatric Symptoms

Repeated intake of methamphetamine (METH) leads to drug addiction, the inability to control intake, and strong drug cravings. It is also likely to cause psychiatric impairments, such as cognitive impairment, depression, and anxiety. Because the specific neurobiological mechanisms involved are complex and have not been fully and systematically elucidated, there is no established pharmacotherapy for METH abuse. Studies have found that a variety of Chinese herbal medicines have significant therapeutic effects on neuropsychiatric symptoms and have the advantage of multitarget comprehensive treatment. We conducted a systematic review, from neurobiological mechanisms to candidate Chinese herbal medicines, hoping to provide new perspectives and ideas for the prevention and treatment of METH abuse.

The role of the locus coeruleus in the generation of pathological anxiety

This review aims to synthesise a large pre-clinical and clinical literature related to a hypothesised role of the locus coeruleus norepinephrine system in responses to acute and chronic threat, as well as the emergence of pathological anxiety. The locus coeruleus has widespread norepinephrine projections throughout the central nervous system, which act to globally modulate arousal states and adaptive behavior, crucially positioned to play a significant role in modulating both ascending visceral and descending cortical neurocognitive information. In response to threat or a stressor, the locus coeruleus–norepinephrine system globally modulates arousal, alerting and orienting functions and can have a powerful effect on the regulation of multiple memory systems. Chronic stress leads to amplification of locus coeruleus reactivity to subsequent stressors, which is coupled with the emergence of pathological anxiety-like behaviors in rodents. While direct in vivo evidence for locus coeruleus dysfunction in humans with pathological anxiety remains limited, recent advances in high-resolution 7-T magnetic resonance imaging and computational modeling approaches are starting to provide new insights into locus coeruleus characteristics.

Paranoia as a deficit in non-social belief updating

Paranoia is the belief that harm is intended by others. It may arise from selective pressures to infer and avoid social threats, particularly in ambiguous or changing circumstances. We propose that uncertainty may be sufficient to elicit learning differences in paranoid individuals, without social threat. We used reversal learning behavior and computational modeling to estimate belief updating across individuals with and without mental illness, online participants, and rats chronically exposed to methamphetamine, an elicitor of paranoia in humans. Paranoia is associated with a stronger prior on volatility, accompanied by elevated sensitivity to perceived changes in the task environment. Methamphetamine exposure in rats recapitulates this impaired uncertainty-driven belief updating and rigid anticipation of a volatile environment. Our work provides evidence of fundamental, domain-general learning differences in paranoid individuals. This paradigm enables further assessment of the interplay between uncertainty and belief-updating across individuals and species.

Everyone has had fleeting concerns that others might be against them at some point in their lives. Sometimes these concerns can escalate into paranoia and become debilitating. Paranoia is a common symptom in serious mental illnesses like schizophrenia. It can cause extreme distress and is linked with an increased risk of violence towards oneself or others. Understanding what happens in the brains of people experiencing paranoia might lead to better ways to treat or manage it.

Some experts argue that paranoia is caused by errors in the way people assess social situations. An alternative idea is that paranoia stems from the way the brain forms and updates beliefs about the world. Now, Reed et al. show that both people with paranoia and rats exposed to a paranoia-inducing substance expect the world will change frequently, change their minds often, and have a harder time learning in response to changing circumstances.

In the experiments, human volunteers with and without psychiatric disorders played a game where the best choices change. Then, the participants completed a survey to assess their level of paranoia. People with higher levels of paranoia predicted more changes would occur and made less predictable choices. In a second set of experiments, rats were put in a cage with three holes where they sometimes received sugar rewards. Some of the rats received methamphetamine, a drug that causes paranoia in humans. Rats given the drug also expected the location of the sugar reward would change often. The drugged animals had harder time learning and adapting to changing circumstances.

The experiments suggest that brain processes found in both rats, which are less social than humans, and humans contribute to paranoia. This suggests paranoia may make it harder to update beliefs. This may help scientists understand what causes paranoia and develop therapies or drugs that can reduce paranoia. This information may also help scientists understand why during societal crises like wars or natural disasters humans are prone to believing conspiracies. This is particularly important now as the world grapples with climate change and a global pandemic. Reed et al. note paranoia may impede the coordination of collaborative solutions to these challenging situations.

Effects of Exercise on Depression, Anxiety, Cognitive Control, Craving, Physical Fitness and Quality of Life in Methamphetamine-Dependent Patients

Methamphetamine (MA) abuse results in a variety of harmful changes in mood states and cognitive function, together with declined physical health and quality of life. Recent studies highlighted the therapeutic potential of physical exercise on MA addiction. Physical exercise improves emotional state and general health conditions, enhances cognitive function, reduces relapse rate, and facilitates abstinence, thereby improves the overall quality of life of the drug users. This review summarizes the present situation of physical exercise on MA-dependent patients with both animal and clinical population results.

Epigenetic Effects Induced by Methamphetamine and Methamphetamine-Dependent Oxidative Stress

Methamphetamine is a widely abused drug, which possesses neurotoxic activity and powerful addictive effects. Understanding methamphetamine toxicity is key beyond the field of drug abuse since it allows getting an insight into the molecular mechanisms which operate in a variety of neuropsychiatric disorders. In fact, key alterations produced by methamphetamine involve dopamine neurotransmission in a way, which is reminiscent of spontaneous neurodegeneration and psychiatric schizophrenia. Thus, understanding the molecular mechanisms operated by methamphetamine represents a wide window to understand both the addicted brain and a variety of neuropsychiatric disorders. This overlapping, which is already present when looking at the molecular and cellular events promoted immediately after methamphetamine intake, becomes impressive when plastic changes induced in the brain of methamphetamine-addicted patients are considered. Thus, the present manuscript is an attempt to encompass all the molecular events starting at the presynaptic dopamine terminals to reach the nucleus of postsynaptic neurons to explain how specific neurotransmitters and signaling cascades produce persistent genetic modifications, which shift neuronal phenotype and induce behavioral alterations. A special emphasis is posed on disclosing those early and delayed molecular events, which translate an altered neurotransmitter function into epigenetic events, which are derived from the translation of postsynaptic noncanonical signaling into altered gene regulation. All epigenetic effects are considered in light of their persistent changes induced in the postsynaptic neurons including sensitization and desensitization, priming, and shift of neuronal phenotype.

Striatal Reinnervation Process after Acute Methamphetamine-Induced Dopaminergic Degeneration in Mice

Methamphetamine (METH), an amphetamine derivate, may increase the risk of developing Parkinson's disease (PD). Human and animal studies have shown that METH produces persistent dopaminergic neurotoxicity in the nigrostriatal pathway, despite initial partial recovery. To determine the processes leading to early compensation, we studied the detailed morphology and distribution of tyrosine hydroxylase immunoreactive fibers (TH-ir) classified by their thickness (types I-IV) before and after METH. Applying three established neurotoxic regimens of METH: single high dose (1 × 30 mg/kg), multiple lower doses (3 × 5 mg/kg) or (3 × 10 mg/kg), we show that METH primarily damages type I fibers (the thinner ones), and to a much lesser extend types II-IV fibers including sterile axons. The striatal TH terminal partial recovery process, consisting of a progressive regrowth increases in types II, III, and IV fibers, demonstrated by co-localization of GAP-43, a sprouting marker, was observed 3 days post-METH treatment. In addition, we demonstrate the presence of growth-cone-like TH-ir structures, indicative of new terminal generation as well as improvement in motor functions after 3 days. A temporal relationship was observed between decreases in TH-expression and increases in silver staining, a marker of degeneration. Striatal regeneration was associated with an increase in astroglia and decrease in microglia expression, suggesting a possible role for the neuroimmune system in regenerative processes. Identification of regenerative compensatory mechanisms in response to neurotoxic agents could point to novel mechanisms in countering the neurotoxicity and/or enhancing the regenerative processes.

Repeated methamphetamine and modafinil induce differential cognitive effects and specific histone acetylation and DNA methylation profiles in the mouse medial prefrontal cortex

Methamphetamine (METH) and modafinil are psychostimulants with different long-term cognitive profiles: METH is addictive and leads to cognitive decline, whereas modafinil has little abuse liability and is a cognitive enhancer. Increasing evidence implicates epigenetic mechanisms of gene regulation behind the lasting changes that drugs of abuse and other psychotropic compounds induce in the brain, like the control of gene expression by histones 3 and 4 tails acetylation (H3ac and H4ac) and DNA cytosine methylation (5-mC). Mice were treated with a seven-day repeated METH, modafinil or vehicle protocol and evaluated in the novel object recognition (NOR) test or sacrificed 4days after last injection for molecular assays. We evaluated total H3ac, H4ac and 5-mC levels in the medial prefrontal cortex (mPFC), H3ac and H4ac promotor enrichment (ChIP) and mRNA expression (RT-PCR) of neurotransmitter systems involved in arousal, wakefulness and cognitive control, like dopaminergic (Drd1 and Drd2), α-adrenergic (Adra1a and Adra1b), orexinergic (Hcrtr1 and Hcrtr2), histaminergic (Hrh1 and Hrh3) and glutamatergic (AMPA Gria1 and NMDA Grin1) receptors. Repeated METH and modafinil treatment elicited different cognitive outcomes in the NOR test, where modafinil-treated mice performed as controls and METH-treated mice showed impaired recognition memory. METH-treated mice also showed i) decreased levels of total H3ac and H4ac, and increased levels of 5-mC, ii) decreased H3ac enrichment at promoters of Drd2, Hcrtr1/2, Hrh1 and Grin1, and increased H4ac enrichment at Drd1, Hrh1 and Grin1, iii) increased mRNA of Drd1a, Grin1 and Gria1. Modafinil-treated mice shared none of these effects and showed increased H3ac enrichment and mRNA expression at Adra1b. Modafinil and METH showed similar effects linked to decreased H3ac in Hrh3, increased H4ac in Hcrtr1, and decreased mRNA expression of Hcrtr2. The specific METH-induced epigenetic and transcriptional changes described here may be related to the long-term cognitive decline effects of the drug and its detrimental effects on mPFC function. The lack of similar epigenetic effects of chronic modafinil administration supports this notion.

A Focus on the Beneficial Effects of Alpha Synuclein and a Re-Appraisal of Synucleinopathies

Alpha synuclein (α-syn) belongs to a class of proteins which are commonly considered to play a detrimental role in neuronal survival. This assumption is based on the occurrence of a severe neuronal degeneration in patients carrying a multiplication of the α-syn gene (SNCA) and in a variety of experimental models, where overexpression of α-syn leads to cell death and neurological impairment. In these conditions, a higher amount of normally structured α-syn produces a damage, which is even worse compared with that produced by α-syn owning an abnormal structure (as occurring following point gene mutations). In line with this, knocking out the expression of α-syn is reported to protect from specific neurotoxins such as 1-methyl, 4-phenyl 1,2,3,6-tetrahydropyridine (MPTP). In the present review we briefly discuss these well-known detrimental effects but we focus on findings showing that, in specific conditions α-syn is beneficial for cell survival. This occurs during methamphetamine intoxication which is counteracted by endogenous α-syn. Similarly, the dysfunction of the chaperone cysteine-string protein- alpha leads to cell pathology which is counteracted by over-expressing α-syn. In line with this, an increased expression of α-syn protects against oxidative damage produced by dopamine. Remarkably, when the lack of α-syn is combined with a depletion of β- and γ- synucleins, alterations in brain structure and function occur. This review tries to balance the evidence showing a beneficial effect with the bulk of data reporting a detrimental effect of endogenous α-syn. The specific role of α-syn as a chaperone protein is discussed to explain such a dual effect.

Conditional Depletion of Hippocampal Brain-Derived Neurotrophic Factor Exacerbates Neuropathology in a Mouse Model of Alzheimer's Disease

Damage occurring to noradrenergic neurons in the locus coeruleus (LC) contributes to the evolution of neuroinflammation and neurodegeneration in a variety of conditions and diseases. One cause of LC damage may be loss of neurotrophic support from LC target regions. We tested this hypothesis by conditional unilateral knockout of brain-derived neurotrophic factor (BDNF) in adult mice. To evaluate the consequences of BDNF loss in the context of neurodegeneration, the mice harbored familial mutations for human amyloid precursor protein and presenilin-1. In these mice, BDNF depletion reduced tyrosine hydroxylase staining, a marker of noradrenergic neurons, in the rostral LC. BDNF depletion also reduced noradrenergic innervation in the hippocampus, the frontal cortex, and molecular layer of the cerebellum, assessed by staining for dopamine beta hydroxylase. BDNF depletion led to an increase in cortical amyloid plaque numbers and size but was without effect on plaque numbers in the striatum, a site with minimal innervation from the LC. Interestingly, cortical Iba1 staining for microglia was reduced by BDNF depletion and was correlated with reduced dopamine beta hydroxylase staining. These data demonstrate that reduction of BDNF levels in an LC target region can cause retrograde damage to LC neurons, leading to exacerbation of neuropathology in distinct LC target areas. Methods to reduce BDNF loss or supplement BDNF levels may be of value to reduce neurodegenerative processes normally limited by LC noradrenergic activities.

The Neuroanatomy of the Reticular Nucleus Locus Coeruleus in Alzheimer's Disease

Alzheimer’s Disease (AD) features the accumulation of β-amyloid and Tau aggregates, which deposit as extracellular plaques and intracellular neurofibrillary tangles (NFTs), respectively. Neuronal Tau aggregates may appear early in life, in the absence of clinical symptoms. This occurs in the brainstem reticular formation and mostly within Locus Coeruleus (LC), which is consistently affected during AD. LC is the main source of forebrain norepinephrine (NE) and it modulates a variety of functions including sleep-waking cycle, alertness, synaptic plasticity, and memory. The iso-dendritic nature of LC neurons allows their axons to spread NE throughout the whole forebrain. Likewise, a prion-like hypothesis suggests that Tau aggregates may travel along LC axons to reach out cortical neurons. Despite this timing is compatible with cross-sectional studies, there is no actual evidence for a causal relationship between these events. In the present mini-review, we dedicate special emphasis to those various mechanisms that may link degeneration of LC neurons to the onset of AD pathology. This includes the hypothesis that a damage to LC neurons contributes to the onset of dementia due to a loss of neuroprotective effects or, even the chance that, LC degenerates independently from cortical pathology. At the same time, since LC neurons are lost in a variety of neuropsychiatric disorders we considered which molecular mechanism may render these brainstem neurons so vulnerable.

Chronic Methamphetamine Effects on Brain Structure and Function in Rats

Methamphetamine (MA) addiction is a growing epidemic worldwide. Chronic MA use has been shown to lead to neurotoxicity in rodents and humans. Magnetic resonance imaging (MRI) studies in MA users have shown enlarged striatal volumes and positron emission tomography (PET) studies have shown decreased brain glucose metabolism (BGluM) in the striatum of detoxified MA users. The present study examines structural changes of the brain, observes microglial activation, and assesses changes in brain function, in response to chronic MA treatment. Rats were randomly split into three distinct treatment groups and treated daily for four months, via i.p. injection, with saline (controls), or low dose (LD) MA (4 mg/kg), or high dose (HD) MA (8 mg/kg). Sixteen weeks into the treatment period, rats were injected with a glucose analog, [¹⁸F] fluorodeoxyglucose (FDG), and their brains were scanned with micro-PET to assess regional BGluM. At the end of MA treatment, magnetic resonance imaging at 21T was performed on perfused rats to determine regional brain volume and in vitro [³H]PK 11195 autoradiography was performed on fresh-frozen brain tissue to measure microglia activation. When compared with controls, chronic HD MA-treated rats had enlarged striatal volumes and increases in [³H]PK 11195 binding in striatum, the nucleus accumbens, frontal cortical areas, the rhinal cortices, and the cerebellar nuclei. FDG microPET imaging showed that LD MA-treated rats had higher BGluM in insular and somatosensory cortices, face sensory nucleus of the thalamus, and brainstem reticular formation, while HD MA-treated rats had higher BGluM in primary and higher order somatosensory and the retrosplenial cortices, compared with controls. HD and LD MA-treated rats had lower BGluM in the tail of the striatum, rhinal cortex, and subiculum and HD MA also had lower BGluM in hippocampus than controls. These results corroborate clinical findings and help further examine the mechanisms behind MA-induced neurotoxicity.

Methamphetamine compromises gap junctional communication in astrocytes and neurons

Methamphetamine (meth) is a central nervous system (CNS) stimulant that results in psychological and physical dependency. The long-term effects of meth within the CNS include neuronal plasticity changes, blood-brain barrier compromise, inflammation, electrical dysfunction, neuronal/glial toxicity, and an increased risk to infectious diseases including HIV. Most of the reported meth effects in the CNS are related to dysregulation of chemical synapses by altering the release and uptake of neurotransmitters, especially dopamine, norepinephrine, and epinephrine. However, little is known about the effects of meth on connexin (Cx) containing channels, such as gap junctions (GJ) and hemichannels (HC). We examined the effects of meth on Cx expression, function, and its role in NeuroAIDS. We found that meth altered Cx expression and localization, decreased GJ communication between neurons and astrocytes, and induced the opening of Cx43/Cx36 HC. Furthermore, we found that these changes in GJ and HC induced by meth treatment were mediated by activation of dopamine receptors, suggesting that dysregulation of dopamine signaling induced by meth is essential for GJ and HC compromise. Meth-induced changes in GJ and HC contributed to amplified CNS toxicity by dysregulating glutamate metabolism and increasing the susceptibility of neurons and astrocytes to bystander apoptosis induced by HIV. Together, our results indicate that connexin containing channels, GJ and HC, are essential in the pathogenesis of meth and increase the sensitivity of the CNS to HIV CNS disease. Methamphetamine (meth) is an extremely addictive central nervous system stimulant. Meth reduced gap junctional (GJ) communication by inducing internalization of connexin-43 (Cx43) in astrocytes and reducing expression of Cx36 in neurons by a mechanism involving activation of dopamine receptors (see cartoon). Meth-induced changes in Cx containing channels increased extracellular levels of glutamate and resulted in higher sensitivity of neurons and astrocytes to apoptosis in response to HIV infection.

Specificity and impact of adrenergic projections to the midbrain dopamine system

Dopamine (DA) is a neuromodulator that regulates different brain circuits involved in cognitive functions, motor coordination, and emotions. Dysregulation of DA is associated with many neurological and psychiatric disorders such as Parkinson's disease and substance abuse. Several lines of research have shown that the midbrain DA system is regulated by the central adrenergic system. This review focuses on adrenergic interactions with midbrain DA neurons. It discusses the current neuroanatomy including source of adrenergic innervation, type of synapses, and adrenoceptors expression. It also discusses adrenergic regulation of DA cell activity and neurotransmitter release. Finally, it reviews several neurological and psychiatric disorders where changes in adrenergic system are associated with dysregulation of the midbrain DA system. This article is part of a Special Issue entitled SI: Noradrenergic System.

Diminished serum repetin levels in patients with schizophrenia and bipolar disorder

Repetin (RPTN) protein is a member of S100 family and is known to be expressed in the normal epidermis. Here we show that RPTN is ubiquitously expressed in both mouse and human brain, with relatively high levels in choroid plexus, hippocampus and prefrontal cortex. To investigate the expression of RPTN in neuropsychiatric disorders, we determined serum levels of RPTN in patients with schizophrenia (n = 88) or bipolar disorder (n = 34) and in chronic psychostimulant users (n = 91). We also studied its expression in a mouse model of chronic unpredictable mild stress (CUMS). The results showed that serum RPTN levels were significantly diminished in patients with schizophrenia and bipolar disorder or in psychostimulant users, compared with healthy subjects (n = 115) or age-matched controls (n = 92) (p < 0.0001). In CUMS mice, RPTN expression in hippocampus and prefrontal cortex was reduced with progression of the CUMS procedure; the serum RPTN level remained unchanged. Since CUMS is a model for depression and methamphetamine (METH) abuse induced psychosis recapitulates many of the psychotic symptoms of schizophrenia, the results from this study may imply that RPTN plays a potential role in emotional and cognitive processing; its decrease in serum may indicate its involvement in the pathogenesis of schizophrenia and bipolar disorder.