Amphetamine causes dopamine depletion and cell death in the mouse olfactory bulb

Manganese and Vanadium Co-Exposure Induces Severe Neurotoxicity in the Olfactory System: Relevance to Metal-Induced Parkinsonism

Chronic environmental exposure to toxic heavy metals, which often occurs as a mixture through occupational and industrial sources, has been implicated in various neurological disorders, including Parkinsonism. Vanadium pentoxide (V2O5) typically presents along with manganese (Mn), especially in welding rods and high-capacity batteries, including electric vehicle batteries; however, the neurotoxic effects of vanadium (V) and Mn co-exposure are largely unknown. In this study, we investigated the neurotoxic impact of MnCl2, V2O5, and MnCl2-V2O5 co-exposure in an animal model. C57BL/6 mice were intranasally administered either de-ionized water (vehicle), MnCl2 (252 µg) alone, V2O5 (182 µg) alone, or a mixture of MnCl2 (252 µg) and V2O5 (182 µg) three times a week for up to one month. Following exposure, we performed behavioral, neurochemical, and histological studies. Our results revealed dramatic decreases in olfactory bulb (OB) weight and levels of tyrosine hydroxylase, dopamine, and 3,4-dihydroxyphenylacetic acid in the treatment groups compared to the control group, with the Mn/V co-treatment group producing the most significant changes. Interestingly, increased levels of α-synuclein expression were observed in the substantia nigra (SN) of treated animals. Additionally, treatment groups exhibited locomotor deficits and olfactory dysfunction, with the co-treatment group producing the most severe deficits. The treatment groups exhibited increased levels of the oxidative stress marker 4-hydroxynonenal in the striatum and SN, as well as the upregulation of the pro-apoptotic protein PKCδ and accumulation of glomerular astroglia in the OB. The co-exposure of animals to Mn/V resulted in higher levels of these metals compared to other treatment groups. Taken together, our results suggest that co-exposure to Mn/V can adversely affect the olfactory and nigral systems. These results highlight the possible role of environmental metal mixtures in the etiology of Parkinsonism.

Neuroecotoxicology: Effects of environmental heavy metal exposure on the brain of African giant rats and the contribution of vanadium to the neuropathology

Increased exploitation of minerals has led to pollution of confined environments as documented in Nigeria Niger Delta. Information on the effects on brain of such exposure is limited. Due to its exploratory activities, the African giant rat (Cricetomys gambianus) (AGR) provides a unique model for neuroecotoxicological research to determine levels of animal and human exposure to different pollutants. This study aims to unravel neuropathological features of AGR sampled from three agro-ecological zones of Nigeria. Fifteen AGR were sampled according to previously determined data on heavy metal exposure: high vanadium, high lead, and low metals. Eighteen AGR were collected from low metal zone and divided into two groups. Control group received vehicle while SMV exposed group received 3 mg/kg sodium metavanadate (SMV) intraperitoneally for 14days. Brain immunohistochemical analyses were conducted, and ultrastructural changes were studied in experimentally exposed group. Results showed significant loss of tyrosin hydroxylase, parvalbumin, orexin-A and melanin concentration hormone containing neuronal populations in brains obtained from high vanadium and high lead zones and in experimentally intoxicated SMV groups. Similarly, significant decrease numbers of dendritic arborations; extracellular matrix density, perineuronal nets; astrocytes and microglia activations are documented in same groups. Ultrastructural studies revealed mass denudation, cilia loss, disintegration of ependymal layer and intense destructions of myelin sheaths in SMV exposed group. These are the first "neuroecotoxicological" findings in distinct neuronal cells. The implications of these findings are highly relevant for human population living in these areas, not only in Nigeria but also in similarly polluted areas elsewhere in the world.

Amphetamine exposure alters behaviors, and neuronal and neurochemical activation in the brain of female prairie voles

Previous studies have shown that 3-day d-amphetamine (AMPH) treatment effectively induced conditioned place preferences (CPP) and impaired pair bonding behaviors in prairie voles (Microtus ochrogaster). Using this established animal model and treatment regimen, we examined the effects of the demonstrated threshold rewarding dose of AMPH on various behaviors and their potential underlying neurochemical systems in the brain of female prairie voles. Our data show that 3-day AMPH injections (0.2 mg/kg/day) impaired social recognition and decreased depressive-like behavior in females without affecting their locomotion and anxiety-like behaviors. AMPH treatment also decreased neuronal activation indicated by the labeling of the early growth response protein 1 (Egr-1) as well as the number of neurons double-labeled for Egr-1 and corticotrophin-releasing hormone (CRH) in the dentate gyrus (DG) of the hippocampus and paraventricular nucleus of the hypothalamus (PVN) in the brain. Further, AMPH treatment decreased the number of neurons double-labeled for Egr-1 and tyrosine hydroxylase (TH) but did not affect oxytocinergic neurons in the PVN or cell proliferation and neurogenesis markers in the DG. These data not only demonstrate potential roles of the brain CRH and dopamine systems in mediating disrupted social recognition and depressive-like behaviors by AMPH in female prairie voles, but also further confirm the utility of the prairie vole model for studying interactions between psychostimulants and social behaviors.

Prolonged Amphetamine Exposures Increase the Endogenous Human Dopamine Receptors 2 at the Cellular Membrane in Cells Lacking the Dopamine Transporter

The dopamine 2 receptors (D2R) are G-protein coupled receptors expressed both in pre- and post-synaptic terminals that play an important role in mediating the physiological and behavioral effects of amphetamine (Amph). Previous studies have indicated that the effects of Amph at the D2R mainly rely on the ability of Amph to robustly increase extracellular dopamine through the dopamine transporter (DAT). This implies that the effects of Amph on D2R require the neurotransmitter dopamine. However, because of its lipophilic nature, Amph can cross the cellular membrane and thus potentially affect D2R expression independently of dopamine and DAT, e.g., in post-synaptic terminals. Here we used an in vitro system to study whether Amph affects total expression, cellular distribution, and function of the human D2R (hD2R), endogenously expressed in HEK293 cells. By performing Western blot experiments, we found that prolonged treatments with 1 or 50 μM Amph cause a significant decrease of the endogenous hD2R in cells transfected with human DAT (hDAT). On the other hand, in cells lacking expression of DAT, quantification of the hD2R-mediated changes in cAMP, biotinylation assays, Western blots and imaging experiments demonstrated an increase of hD2R at the cellular membrane after 15-h treatments with Amph. Moreover, imaging data suggested that barbadin, a specific inhibitor of the βarrestin-βadaptin interaction, blocked the Amph-induced increase of hD2R. Taken together our data suggest that prolonged exposures to Amph decrease or increase the endogenous hD2R at the cellular membrane in HEK293 cells expressing or lacking hDAT, respectively. Considering that this drug is often consumed for prolonged periods, during which tolerance develops, our data suggest that even in absence of DAT or dopamine, Amph can still alter D2R distribution and function.

Classic and evolving animal models in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease with motor and non-motor symptoms. PD is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and deficiency of dopamine in the striatal region. The primary objective in PD research is to understand the pathogenesis, targets, and development of therapeutic interventions to control the progress of the disease. The anatomical and physiological resemblances between humans and animals gathered the researcher's attention towards the use of animals in PD research. Due to varying age of onset, symptoms, and progression rate, PD becomes heterogeneous which demands the variety of animal models to study diverse features of the disease. Parkinson is a multifactorial disorder, selection of models become important as not a single model shows all the biochemical features of the disease. Currently, conventional pharmacological, neurotoxin-induced, genetically modified and cellular models are available for PD research, but none of them recapitulate all the biochemical characteristics of the disease. In this review, we included the updated knowledge on the main features of currently available in vivo and in vitro models as well as their strengths and weaknesses.

Age-dependent effects of repeated methamphetamine exposure on locomotor activity and attentional function in rats

Many adolescents use amphetamines which are the second most common abused illegal drugs. Methamphetamine (Meth), as a potent amphetamine affects attentional functions. However, the most significant factor for susceptibility to Meth is the age of exposure, most studies have examined the effects of Meth after early adolescence stage. The present experiment was aimed to investigate some possible short- and long-term effects of Meth at two distinct points of adolescence stage (early versus late) on 1) locomotor activity in adolescent rats and 2) attentional functions in their adulthood. Rats received Meth (5 mg/kg, i.p., for consecutive 10 days) during early adolescence (postnatal days (PND) 30-39) or late adolescence (PND 50-59). Locomotor activity was assessed after the first and tenth injections. Then, in adulthood, rats were trained and tested on the Five-choice serial reaction time task (5-CSRTT) to display possible attentional impairments. The first Meth administration in early exposed adolescent (EEA) group produced the highest level of activity, compared with the first exposure in late exposed adolescent (LEA) group and tenth administrations in both groups. In adulthood, LEA group significantly delayed learning the 5-CSRTT and exhibited attentional impairments, as demonstrated by significant reduced response accuracy and increased omission errors under pharmacological challenge, compared with control group. The susceptibility to Meth depends on the age of exposure and Meth administration during late adolescence stage may cause prolonged attentional deficits in adulthood.

Effect of a binge-like dosing regimen of methamphetamine on dopamine levels and tyrosine hydroxylase expressing neurons in the rat brain

Methamphetamine, an amphetamine derivative, is a powerful psychomotor stimulant and commonly used drug of abuse. This study examined the effect of binge-like methamphetamine (MA) dosing (4 × 4 mg/kg, s.c., 2 h apart) on regional dopamine and dopaminergic metabolite levels in rat brain at a range of early time points after final dose (2-48 h). Body temperature was elevated when measured 2 h after the last dose. MA increased dopamine levels in the frontal cortex 2 and 24 h after the last dose. The dopamine level was also increased in the amygdala at 24 h. No change was observed in the striatum at any time point, but levels of the dopamine metabolite DOPAC were markedly reduced at 24 and 48 h. Tyrosine hydroxylase expression is induced downstream of dopamine activity, and it is the rate limiting enzyme in dopamine synthesis. The effect of MA binge-like dosing on the volume of tyrosine hydroxylase containing cell bodies and the area fraction of tyrosine hydroxylase containing fibres was also assessed. MA increased the area fraction of tyrosine hydroxylase fibres in the frontal cortex and reduced the volume of tyrosine hydroxylase containing cell bodies 2 h after last dose in the ventral tegmental area and the substantia nigra. An increase in cell body volume in the substantia nigra was observed 48 h after treatment. These findings collectively highlight the importance of the dopaminergic system in methamphetamine induced effects, identify the frontal cortex, amygdala and striatum as key regions that undergo early changes in response to binge-like methamphetamine dosing and provide evidence of time-dependent effects on the cell bodies and fibres of tyrosine hydroxylase expressing neurons.

The Intersection of Central Dopamine System and Stroke: Potential Avenues Aiming at Enhancement of Motor Recovery

Dopamine, a major neurotransmitter, plays a role in a wide range of brain sensorimotor functions. Parkinson's disease and schizophrenia are two major human neuropsychiatric disorders typically associated with dysfunctional dopamine activity levels, which can be alleviated through the druggability of the dopaminergic systems. Meanwhile, several studies suggest that optimal brain dopamine activity levels are also significantly impacted in other serious neurological conditions, notably stroke, but this has yet to be fully appreciated at both basic and clinical research levels. This is of utmost importance as there is a need for better treatments to improve recovery from stroke. Here, we discuss the state of knowledge regarding the modulation of dopaminergic systems following stroke, and the use of dopamine boosting therapies in animal stroke models to improve stroke recovery. Indeed, studies in animals and humans show stroke leads to changes in dopamine functioning. Moreover, evidence from animal stroke models suggests stimulation of dopamine receptors may be a promising therapeutic approach for enhancing motor recovery from stroke. With respect to the latter, we discuss the evidence for several possible receptor-linked mechanisms by which improved motor recovery may be mediated. One avenue of particular promise is the subtype-selective stimulation of dopamine receptors in conjunction with physical therapy. However, results from clinical trials so far have been more mixed due to a number of potential reasons including, targeting of the wrong patient populations and use of drugs which modulate a wide array of receptors. Notwithstanding these issues, it is hoped that future research endeavors will assist in the development of more refined dopaminergic therapeutic approaches to enhance stroke recovery.

Amphetamine, but not methylphenidate, increases ethanol intake in adolescent male, but not in female, rats

INTRODUCTION

There has been an increasing interest in analyzing the interactions between stimulants and ethanol during childhood and adolescence. Stimulants are used to treat attention-deficit hyperactivity disorder (ADHD) in these developmental stages, during which ethanol initiation and escalation often occur.

METHODS

This study assessed the effects of repeated d-amphetamine (AMPH) or methylphenidate (MPH) treatment during adolescence [male and female Wistar rats, between postnatal day (PD) 28 to PD34, approximately] on the initiation of ethanol intake during a later section of adolescence (PD35 to PD40).

RESULTS

Amphetamine and MPH exerted reliable acute motor stimulant effects, but there was no indication of sensitized motor or anxiety responses. MPH did not affect dopamine (DA) levels, whereas AMPH significantly reduced insular levels of DA in both sexes and norepinephrine levels in females only. Repeated treatment with AMPH, but not with MPH, enhanced ethanol intake during late adolescence in male, but not in female, rats.

CONCLUSION

A short treatment with AMPH during adolescence significantly altered DA levels in the insula, both in male and females, and significantly enhanced ethanol intake in males. The present results suggest that, in adolescent males, a very brief history of AMPH exposure can facilitate the initiation of ethanol intake.

Acute administration of fenproporex increased acetylcholinesterase activity in brain of young rats

Fenproporex is the second most commonly amphetamine-based anorectic consumed worldwide; this drug is rapidly converted into amphetamine, in vivo, and acts by increasing dopamine levels in the synaptic cleft. Considering that fenproporex effects on the central nervous system are still poorly known and that acetylcholinesterase is a regulatory enzyme which is involved in cholinergic synapses and may indirectly modulate the release of dopamine, the present study investigated the effects of acute administration of fenproporex on acetylcholinesterase activity in brain of young rats. Young male Wistar rats received a single injection of fenproporex (6.25, 12.5 or 25mg/kg i.p.) or vehicle (2% Tween 80). Two hours after the injection, the rats were killed by decapitation and the brain was removed for evaluation of acetylcholinesterase activity. Results showed that fenproporex administration increased acetylcholinesterase activity in the hippocampus and posterior cortex, whereas in the prefrontal cortex, striatum and cerebellum the enzyme activity was not altered. In conclusion, in the present study we demonstrated that acute administration of fenproporex exerts an effect in the cholinergic system causing an increase in the activity of acetylcholinesterase in a dose-dependent manner in the hippocampus and posterior cortex. Thus, we suggest that the imbalance in cholinergic homeostasis could be considered as an important pathophysiological mechanism underlying the brain damage observed in patients who use amphetamines such as fenproporex.

Vanadium exposure induces olfactory dysfunction in an animal model of metal neurotoxicity

Epidemiological evidence indicates chronic environmental exposure to transition metals may play a role in chronic neurodegenerative conditions such as Parkinson's disease (PD). Chronic inhalation exposure to welding fumes containing metal mixtures may be associated with development of PD. A significant amount of vanadium is present in welding fumes, as vanadium pentoxide (V2O5), and incorporation of vanadium in the production of high strength steel has become more common. Despite the increased vanadium use in recent years, the neurotoxicological effects of this metal are not well characterized. Recently, we demonstrated that V2O5 induces dopaminergic neurotoxicity via protein kinase C delta (PKCδ)-dependent oxidative signaling mechanisms in dopaminergic neuronal cells. Since anosmia (inability to perceive odors) and non-motor deficits are considered to be early symptoms of neurological diseases, in the present study, we examined the effect of V2O5 on the olfactory bulb in animal models. To mimic the inhalation exposure, we intranasally administered C57 black mice a low-dose of 182μg of V2O5 three times a week for one month, and behavioral, neurochemical and biochemical studies were performed. Our results revealed a significant decrease in olfactory bulb weights, tyrosine hydroxylase (TH) levels, levels of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) and increases in astroglia of the glomerular layer of the olfactory bulb in the treatment groups relative to vehicle controls. Neurochemical changes were accompanied by impaired olfaction and locomotion. These findings suggest that nasal exposure to V2O5 adversely affects olfactory bulbs, resulting in neurobehavioral and neurochemical impairments. These results expand our understanding of vanadium neurotoxicity in environmentally-linked neurological conditions.

Chronic D-amphetamine administered from childhood to adulthood dose-dependently increases the survival of new neurons in the hippocampus of male C57BL/6J mice

Adderall is widely prescribed for attention deficit hyperactivity disorder (ADHD) though long term neurological effects of the main ingredient d-amphetamine are not well understood. The purpose of this study was to examine effects of clinically prescribed doses of d-amphetamine and one abuse dose administered from childhood to adulthood on adult hippocampal neurogenesis and activation of the granule layer of the dentate gyrus. Beginning in early adolescence (age 28 days) to adulthood (age 71), male C57BL/6J mice were administered twice daily i.p. injections of vehicle, 0.25, 0.5 or 2mg/kg d-amphetamine. Locomotor activity was measured in home cages by video tracking. At age 53-56, mice received bromodeoxyuridine (BrdU) injections to label dividing cells. Immunohistochemical detection of BrdU, neuronal nuclear protein (NeuN), doublecortin (DCX) and Ki67 was used to measure neurogenesis and cell proliferation at age 71. ΔFosB was measured as an indicator of repeated neuronal activation. An additional cohort of mice was treated similarly except euthanized at age 58 to measure activation of granule neurons from d-amphetamine (by detection of c-Fos) and cell proliferation (Ki67) at a time when the fate of BrdU cells would have been determined in the first cohort. d-Amphetamine dose-dependently increased survival and differentiation of BrdU cells into neurons and increased number of DCX cells without affecting the number of Ki67 cells. Low doses of d-amphetamine decreased c-Fos and ΔFosB in the granule layer. Only the high dose induced substantial locomotor stimulation and sensitization. Results suggest both therapeutic and abuse doses of d-amphetamine increase the number of new neurons in the hippocampus when administered from adolescence to adulthood by increasing survival and differentiation of cells into neurons not by increasing progenitor cell proliferation. Mechanisms for amphetamine-induced neurogenesis are unknown but appear activity independent. Results suggest part of the beneficial effects of therapeutic doses of d-amphetamine for ADHD could be via increased hippocampal neurogenesis.

Cocaine and MDMA Induce Cellular and Molecular Changes in Adult Neurogenic Systems: Functional Implications

The capacity of the brain to generate new adult neurons is a recent discovery that challenges the old theory of an immutable adult brain. A new and fascinating field of research now focuses on this regenerative process. The two brain systems that constantly produce new adult neurons, known as the adult neurogenic systems, are the dentate gyrus (DG) of the hippocampus and the lateral ventricules/olfactory bulb system. Both systems are involved in memory and learning processes. Different drugs of abuse, such as cocaine and MDMA, have been shown to produce cellular and molecular changes that affect adult neurogenesis. This review summarizes the effects that these drugs have on the adult neurogenic systems. The functional relevance of adult neurogenesis is obscured by the functions of the systems that integrate adult neurons. Therefore, we explore the effects that cocaine and MDMA produce not only on adult neurogenesis, but also on the DG and olfactory bulbs. Finally, we discuss the possible role of new adult neurons in cocaine- and MDMA-induced impairments. We conclude that, although harmful drug effects are produced at multiple physiological and anatomical levels, the specific consequences of reduced hippocampus neurogenesis are unclear and require further exploration.

Genetic inactivation of pleiotrophin triggers amphetamine-induced cell loss in the substantia nigra and enhances amphetamine neurotoxicity in the striatum

Pleiotrophin (PTN) is a neurotrophic factor with important effects in survival and differentiation of dopaminergic neurons that has been suggested to play important roles in drug of abuse-induced neurotoxicity. To test this hypothesis, we have studied the effects of amphetamine (10 mg/kg, four times, every 2 h) on the nigrostriatal pathway of PTN genetically deficient (PTN-/-) mice. We found that amphetamine causes a significantly enhanced loss of dopaminergic terminals in the striatum of PTN-/- mice compared to wild type (WT+/+) mice. In addition, we found a significant decrease ( approximately 20%) of tyrosine hydroxylase (TH)-positive neurons only in the substantia nigra of amphetamine-treated PTN-/- mice, whereas this area of WT+/+ animals remained unaffected after amphetamine treatment. This effect was accompanied by enhanced amphetamine-induced astrocytosis in the substantia nigra of PTN-/- mice. Interestingly, we found a significant decrease in the phosphorylation levels of p42 extracellular-signal regulated kinase (ERK2) in both saline- and amphetamine-treated PTN-/- mice, whereas phosphorylation of p44 ERK (ERK1) was almost abolished in the striatum of PTN-/- mice compared to WT+/+ mice, suggesting that basal deficiencies in the phosphorylation levels of ERK1/2 could underlie the higher vulnerability of PTN-/- mice to amphetamine-induced neurotoxic effects. The data suggest an important role of PTN in the protection of nigrostriatal pathways against amphetamine insult.

Dietary restriction mitigates cocaine-induced alterations of olfactory bulb cellular plasticity and gene expression, and behavior

Because the olfactory system plays a major role in food consumption, and because 'food addiction' and associated morbidities have reached epidemic proportions, we tested the hypothesis that dietary energy restriction can modify adverse effects of cocaine on behavior and olfactory cellular and molecular plasticity. Mice maintained on an alternate day fasting (ADF) diet exhibited increased baseline locomotion and increased cocaine-sensitized locomotion during cocaine conditioning, despite no change in cocaine conditioned place preference, compared with mice fed ad libitum. Levels of dopamine and its metabolites in the olfactory bulb (OB) were suppressed in mice on the ADF diet compared with mice on the control diet, independent of acute or chronic cocaine treatment. The expression of several enzymes involved in dopamine metabolism including tyrosine hydroxylase, monoamine oxidases A and B, and catechol-O-methyltransferase were significantly reduced in OBs of mice on the ADF diet. Both acute and chronic administration of cocaine suppressed the production of new OB cells, and this effect of cocaine was attenuated in mice on the ADF diet. Cocaine administration to mice on the control diet resulted in up-regulation of OB genes involved in mitochondrial energy metabolism, synaptic plasticity, cellular stress responses, and calcium- and cAMP-mediated signaling, whereas multiple olfactory receptor genes were down-regulated by cocaine treatment. ADF abolished many of the effects of cocaine on OB gene expression. Our findings reveal that dietary energy intake modifies the neural substrates underlying some of the behavioral and physiological responses to repeated cocaine treatment, and also suggest novel roles for the olfactory system in addiction. The data further suggest that modification of dietary energy intake could provide a novel potential approach to addiction treatments.

Amphetamine toxicities: classical and emerging mechanisms

The drugs of abuse, methamphetamine and MDMA, produce long-term decreases in markers of biogenic amine neurotransmission. These decreases have been traditionally linked to nerve terminals and are evident in a variety of species, including rodents, nonhuman primates, and humans. Recent studies indicate that the damage produced by these drugs may be more widespread than originally believed. Changes indicative of damage to cell bodies of biogenic and nonbiogenic amine-containing neurons in several brain areas and endothelial cells that make up the blood-brain barrier have been reported. The processes that mediate this damage involve not only oxidative stress but also include excitotoxic mechanisms, neuroinflammation, the ubiquitin proteasome system, as well as mitochondrial and neurotrophic factor dysfunction. These mechanisms also underlie the toxicity associated with chronic stress and human immunodeficiency virus (HIV) infection, both of which have been shown to augment the toxicity to methamphetamine. Overall, multiple mechanisms are involved and interact to promote neurotoxicity to methamphetamine and MDMA. Moreover, the high coincidence of substituted amphetamine abuse by humans with HIV and/or chronic stress exposure suggests a potential enhanced vulnerability of these individuals to the neurotoxic actions of the amphetamines.