A "Drug-Dependent" Immune System Can Compromise Protection against Infection: The Relationships between Psychostimulants and HIV.

Psychostimulant use is a major comorbidity in people living with HIV, which was initially explained by them adopting risky behaviors that facilitate HIV transmission. However, the effects of drug use on the immune system might also influence this phenomenon. Psychostimulants act on peripheral immune cells even before they reach the central nervous system (CNS) and their effects on immunity are likely to influence HIV infection. Beyond their canonical activities, classic neurotransmitters and neuromodulators are expressed by peripheral immune cells (e.g., dopamine and enkephalins), which display immunomodulatory properties and could be influenced by psychostimulants. Immune receptors, like Toll-like receptors (TLRs) on microglia, are modulated by cocaine and amphetamine exposure. Since peripheral immunocytes also express TLRs, they may be similarly affected by psychostimulants. In this review, we will summarize how psychostimulants are currently thought to influence peripheral immunity, mainly focusing on catecholamines, enkephalins and TLR4, and shed light on how these drugs might affect HIV infection. We will try to shift from the classic CNS perspective and adopt a more holistic view, addressing the potential impact of psychostimulants on the peripheral immune system and how their systemic effects could influence HIV infection.

Transplantation with Lewis bone marrow induces the reinstatement of cocaine-seeking behavior in male F344 resistant rats.

One of the main challenges to understand drug addiction is defining the biological mechanisms that underlie individual differences in recidivism. Studies of these mechanisms have mainly focused on the brain, yet we demonstrate here a significant influence of the peripheral immune system on this phenomenon. Lewis (LEW) and Fischer 344 (F344) rats have different immunological profiles and they display a distinct vulnerability to the reinforcing effects of cocaine, with F344 more resistant to reinstate cocaine-seeking behavior. Bone marrow from male LEW and F344 rats was transferred to male F344 rats (F344/LEW-BM and F344/F344-BM, respectively), and these rats were trained to self-administer cocaine over 21 days. Following extinction, these animals received a sub-threshold primer dose of cocaine to evaluate reinstatement. F344/LEW-BM but not F344/F344-BM rats reinstated cocaine-seeking behavior, in conjunction with changes in their peripheral immune cell populations to a profile that corresponded to that of the LEW donors. After cocaine exposure, higher CD4+ T-cells and lower CD4+CD25+ T-cells levels were observed in F344/LEW-BM rats referred to control, and the splenic expression of Il-17a, Tgf-ß, Tlr-2, Tlr-4 and Il-1ß was altered in both groups. We propose that peripheral T-cells respond to cocaine, with CD4+ T-cells in particular undergoing Th17 polarization and generating long-term memory, these cells releasing mediators that trigger central mechanisms to induce reinstatement after a second encounter. This immune response may explain the high rates of recidivism observed despite long periods of detoxification, shedding light on the mechanisms underlying the vulnerability and resilience of specific individuals, and opening new perspectives for personalized medicine in the treatment of relapse.

Extended-access methamphetamine self-administration elicits neuroinflammatory response along with blood-brain barrier breakdown.

Methamphetamine (METH) is a highly addictive psychostimulant drug that can lead to neurological and psychiatric abnormalities. Several studies have explored the central impact of METH use, but the mechanism(s) underlying blood-brain barrier (BBB) dysfunction and associated neuroinflammatory processes after chronic METH consumption are still unclear. Important findings in the field are mainly based on in vitro approaches and animal studies using an acute METH paradigm, and not much is known about the neurovascular alterations under a chronic drug use. Thus, the present study aimed to fill this crucial gap by exploring the effect of METH-self administration on BBB function and neuroinflammatory responses. Herein, we observed an increase of BBB permeability characterized by Evans blue and albumin extravasation in the rat hippocampus and striatum triggered by extended-access METH self-administration followed by forced abstinence. Also, there was a clear structural alteration of blood vessels showed by the down-regulation of collagen IV staining, which is an important protein of the endothelial basement membrane, together with a decrease of intercellular junction protein levels, namely claudin-5, occludin and vascular endothelial-cadherin. Additionally, we observed an up-regulation of vascular cell and intercellular adhesion molecule, concomitant with the presence of T cell antigen CD4 and tissue macrophage marker CD169 in the brain parenchyma. Rats trained to self-administer METH also presented a neuroinflammatory profile characterized by microglial activation, astrogliosis and increased pro-inflammatory mediators, namely tumor necrosis factor-alpha, interleukine-1 beta, and matrix metalloproteinase-9. Overall, our data provide new insights into METH abuse consequences, with a special focus on neurovascular dysfunction and neuroinflammatory response, which may help to find novel approaches to prevent or diminish brain dysfunction triggered by this overwhelming illicit drug.

Enkephalin is essential for the molecular and behavioral expression of cocaine sensitization.

Behavioral sensitization to cocaine is associated to neuroadaptations that contribute to addiction. Enkephalin is highly expressed in mesocorticolimbic areas associated with cocaine-induced sensitization; however, their influence on cocaine-dependent behavioral and neuronal plasticity has not been explained. In this study, we employed a knockout (KO) model to investigate the contribution of enkephalin in cocaine-induced behavioral sensitization. Wild-type (WT) and proenkephalin KO mice were treated with cocaine once daily for 9 days to induce sensitization. Additionally, to clarify the observations in KO mice, the same procedure was applied in C57BL/6 mice, except that naloxone was administered before each cocaine injection. All animals received a cocaine challenge on days 15 and 21 of the treatment to evaluate the expression of locomotor sensitization. On day 21, microdialysis measures of accumbal extracellular dopamine, Western blotting for GluR1 AMPA receptor (AMPAR), phosphorylated ERK2 (pERK2), CREB (pCREB), TrKB (pTrkB) were performed in brain areas relevant for sensitization from KO and WT and/or naloxone- and vehicle pre-treated animals. We found that KO mice do not develop sensitization to the stimulating properties of cocaine on locomotor activity and on dopamine release in the nucleus accumbens (NAc). Furthermore, pivotal neuroadaptations such as the increase in pTrkB receptor, pERK/CREB and AMPAR related to sensitized responses were absent in the NAc from KO mice. Consistently, full abrogation of cocaine-induced behavioral and neuronal plasticity after naloxone pre-treatment was observed. We show for first time that the proenkephalin system is essential in regulating long-lasting pivotal neuroadaptations in the NAc underlying behavioral sensitization to cocaine.

Strain differences in the expression of endocannabinoid genes and in cannabinoid receptor binding in the brain of Lewis and Fischer 344 rats.

The Lewis (LEW) and Fischer 344 (F344) rat strains have been proposed as a model to study certain genetic influences on drug use. These strains differ in terms of the self-administration of several drugs, and in their expression of various components of the dopaminergic, glutamatergic, GABAergic and endogenous opioid neurotransmitter systems. As the endocannabinoid system is linked to these systems, we investigated whether these two strains exhibit differences in cannabinoid receptor binding and in the expression of cannabinoid-related genes. Quantitative autoradiography of [(3)H]-CP 55,940 binding levels and real-time PCR assays were used. F344 rats displayed higher levels of cannabinoid receptor binding in the lateral globus pallidus and weaker CNR1 gene expression in the prefrontal cortex (PFc) than LEW rats. Moreover, the N-acyl phosphatidylethanolamine-specific phospholipase D/fatty acid amide hydrolase ratio was greater in the PFc and NAcc of F344 rats. Our results suggest that the endocannabinoid system may be a mediator of the individual differences that exist in the susceptibility to the rewarding effects of drugs of abuse.

Sex-specific disturbances of the glutamate/GABA balance in the hippocampus of adult rats subjected to adolescent cannabinoid exposure.

Adolescence is a period of active synaptic remodelling and plasticity and as such, a developmental phase of particular vulnerability to the effects of environmental insults. The endogenous cannabinoid system regulates central nervous system development and cannabinoid exposure during adolescence has been linked to several alterations to hippocampal-dependent processes such as cognition and emotion, which rely on intact glutamatergic and GABAergic systems. Here we show that K(+)-induced γ-amino butyric acid (GABA) release increases in the CA1 hippocampal field of Wistar rats of both sexes that were treated chronically with the cannabinoid agonist CP 55,940 (CP55940) during adolescence. GABA(B) receptors levels also increased in cannabinoid-exposed rats. In addition, CP55940-treated females exhibit reduced GABA transporter gene expression (GAT-1), increased GABA(A) receptor expression, as well as decreased K(+)-induced glutamate release and NMDA receptor levels. CP55940 administration did not affect the glial (EAAT2) or neuronal (EAAT3) glutamate transporter gene expression in either males or females, and nor were any changes in the mGlu5 receptor protein levels observed. Taken together, these results show that while the exacerbated GABA release induced by early cannabinoid exposure may be compensated by an increment in GABA(B) receptors, which normally function as inhibitory autoreceptors, adolescent cannabinoid exposure in the females disturbs the normal balance between glutamate and GABA transmission. These observations may provide important insight into the neuronal basis of the well-documented alterations in cognitive and emotional processes induced by adolescent cannabinoid exposure.

Decrease of lymphoproliferative response by amphetamine is mediated by dopamine from the nucleus accumbens: influence on splenic met-enkephalin levels.

Despite the mesocorticolimbic dopaminergic pathway being one of the main substrates underlying stimulating and reinforcing effects induced by psychostimulant drugs, there is little information regarding its role in their effects at the immune level. We have previously demonstrated that acute exposure to amphetamine (5 mg/kg, i.p.) induced an inhibitory effect on the splenic T-cell proliferative response, along with an increase in the methionine(met)-enkephalin content at limbic and immune levels, 4 days after drug administration. In this study, we investigated if a possible dopamine mechanism underlies these amphetamine-induced effects by administering D1 and D2 dopaminergic antagonists or a dopaminergic terminal neurotoxin before the drug. Pre-treatment with either SCH-23390 (0.1 mg/kg, i.p.) or raclopride (0.1 mg/kg, i.p.), a D1 or D2 dopaminergic receptor antagonist, respectively, abrogated the effects of amphetamine on the lymphoproliferative response and on met-enkephalin levels of the spleen. The amphetamine-induced increase in limbic met-enkephalin content was suppressed by SCH-23390 but not by raclopride pre-treatment. Finally, an intra-accumbens 6-hydroxy-dopamine injection administered 2 weeks previously prevented amphetamine-induced effects on the lymphoproliferative response and on met-enkephalin levels in the prefrontal cortex and spleen. These findings strongly suggest that D1 and D2 dopaminergic receptors are involved in amphetamine-induced effects at immune level as regards the lymphoproliferative response and the changes in spleen met-enkephalin content, whereas limbic met-enkephalin levels were modulated only by the D1 dopaminergic receptors. In addition, this study showed that a mesolimbic component modulated amphetamine-induced effects on the immune response, as previously shown at a behavioral level.

The AT1 angiotensin II receptor blockade attenuates the development of amphetamine-induced behavioral sensitization in a two-injection protocol.

It has been shown that a single exposure to amphetamine is sufficient to induce long-term behavioral, neurochemical, and neuroendocrine sensitization in rats. Dopaminergic neurotransmission in the nucleus accumbens and the caudate-putamen plays a critical role in the addictive properties of drugs of abuse. Angiotensin (Ang) II receptors are found on the soma and terminals of mesolimbic dopaminergic neurons and it has been shown that Ang II acting through its AT1 receptors facilitates dopamine release. The hypothesis was tested that Ang II AT1 receptors are involved in the neuroadaptative changes induced by a single exposure to amphetamine and that such changes are related to the development of behavioral and neurochemical sensitization. For this purpose, the study examined the expression of amphetamine-enhanced (0.5 mg kg⁻¹ i.p.) locomotor activity in animals pretreated with candesartan, an AT1 blocker, (3 mg kg⁻¹ p.o. x 5 days), 3 weeks after an amphetamine injection (5 mg kg⁻¹ i.p.). Dopaminergic hyperreactivity was tested by measuring the 3H-DA release in vitro from caudate-putamen and nucleus accumbens slices, induced by K+ stimulus. It was confirmed the behavioral sensitization in the two-injection protocol and candesartan pretreatment attenuate this response. It was also found that AT1 blockade pretreatment did not affect the locomotor response to dopamine agonists. In respect to the neurochemical sensitization tested using ex vivo 3H-DA release experiments it was found that AT1 receptor pretreatment blunted the enhanced response induced by K+ stimulus. The results support the idea that the development of neuroadaptive changes induced by amphetamine involves brain AT1 Ang II receptor activation.

Sensitization to amphetamine occurs simultaneously at immune level and in met-enkephalin of the nucleus accumbens and spleen: an involved NMDA glutamatergic mechanism.

Administration of psychostimulants can elicit a sensitized response to the stimulating and reinforcing properties of the drugs, although there is scarce information regarding their effects at immune level. We previously demonstrated that an acute exposure to amphetamine (5 mg/kg, i.p.) induced an inhibitory effect on the splenic T-cell proliferative response, along with an increase in met-enkephalin at limbic and immune levels, 4 days following drug administration. In this study, we evaluated the amphetamine-induced effects at weeks one and three after the same single dose treatment (5 mg/kg, i.p.) on the lymphoproliferative response and on the met-enkephalin in the nucleus accumbens (NAc), prefrontal cortex (PfC), spleen and thymus. It was demonstrated that these effects disappeared completely after three weeks, although re-exposure to an amphetamine challenge induced the expression of sensitization to the effects of amphetamine on the lymphoproliferative response and on the met-enkephalin from NAc, spleen and thymus, but not in the PfC. Pre-treatment with MK-801 (0.1 mg/kg, i.p.), an N-methyl-d-aspartate (NMDA) glutamatergic receptor antagonist, blocked the effects of a single amphetamine exposure on the lymphoproliferative response and on met-enkephalin in the NAc and spleen. Furthermore, the NMDA receptor antagonist administered prior to amphetamine challenge also blocked the expression of sensitization in both parameters evaluated. These findings show a long-lasting amphetamine-induced sensitization phenomenon at the immune level in a parallel way to that occurring in the limbic and immune enkephalineric system. A glutamate mechanism is implied in the long-term amphetamine-induced effects at immune level and in the met-enkephalin from NAc and spleen.

A dopamine mechanism is implied in the acquisition and expression of amphetamine and stress-induced effects observed in the lymphocyte subpopulations.

Drugs of abuse and stress are associated with changes in circulating cell populations and reductions in cell-mediated immune responses. The main goal of this study was to determine the influence of repeated and acute d-amphetamine treatments on the foot-shock stress-induced effects on the peripheral lymphocyte subpopulations, and the involvement of a dopamine mechanism in the development and expression of this phenomenon. Wistar rats received an acute (5 mg/kg/day i.p.) or a repeated (2 mg/kg/day i.p. during 9 days) amphetamine treatment, and were exposed to a foot-shock stress (1 mA, 3 s) 4 days after the last amphetamine injection. Another group was administered with haloperidol (1 mg/kg/day i.p.) 15 min previous to each daily amphetamine injection or previous to the foot-shock stress session. Then, blood cells stained with monoclonal antibodies against CD3-FITC, CD8-PE and CD4-Cy-Chrome, and against CD161a-FITC, CD3-PE, and CD45RA-Cy-Crhome, were analyzed by multiparameter flow cytometry. The exposure to a foot-shock stress induced a decrease in the absolute number of peripheral lymphocytes, as well as in CD4+ and CD8+ T-cells and B-cells in acute and repeatedly amphetamine-treated rats, whereas the NK-cell population remained unchanged. Haloperidol administration previous to each drug administration or the foot-shock stress session reversed these effects. This study provides strong evidence that dopamine can play a more general role in the influence of amphetamine on the stress-induced effects on the lymphocyte subsets.