Dopaminergic and glutamatergic mechanisms mediate the induction of FOS-like protein by cocaethylene

A Comprehensive View of the Neurotoxicity Mechanisms of Cocaine and Ethanol

Substance use disorder is an emerging problem concerning to human health, causing severe side effects, including neurotoxicity. The use of illegal drugs and the misuse of prescription or over-the-counter drugs are growing in this century, being one of the major public health problems. Ethanol and cocaine are one of the most frequently used drugs and, according to the National Institute on Drug Abuse, their concurrent consumption is one of the major causes for emergency hospital room visits. These molecules act in the brain through different mechanisms, altering the nervous system function. Researchers have focused the attention not just in the mechanism of action of these drugs, but also in the mechanism by which they damage the nervous tissue (neurotoxicity). Therefore, the goal of the present review is to provide a global perspective about the mechanisms of the neurotoxicity of cocaine and ethanol.

Tracing the Neuroanatomical Profiles of Reward Pathways with Markers of Neuronal Activation

Functional neuroanatomical tools have played an important role in proposing which structures underlie brain stimulation reward circuitry. This review focuses on studies employing metabolic markers of neuronal and glial activation, including 2-deoxyglucose, cytochrome oxidase, and glycogen phosphorylase, and a marker of cellular activation, the immediate early gene c-fos. The principles underlying each method, their application to the study of brain stimulation reward, and their strengths and limitations are described. The usefulness of this strategy in identifying candidate structures, and the degree of overlap in the patterns of activation arising from different markers is addressed in detail. How these data have contributed to an understanding of the organization of reward circuitry and directed our thinking towards an alternative framework of neuronal arrangement is discussed in the final section.

Rat strain differences to fluoxetine in striatal Fos-like proteins

Humans afflicted with mood disorders respond differently to antidepressant drug therapy. Different responses to psychoactive drugs are also observed in rats, and specific strains exhibit substantial differences in gene expression following synaptic activity. We examined the effects of fluoxetine on the induction of Fos-like proteins in Long-Evans and Sprague-Dawley rat brains. Fluoxetine elicited a strong induction of Fos in the striatum of Long-Evans but not Sprague-Dawley rats following acute drug exposure. This effect was specific to fluoxetine as two highly selective serotonin reuptake inhibitors, HD-31 and HD-50, as well as treatment with fenfluramine failed to replicate the observed differences in Fos. These differences in Fos expression between rat strains may represent variability in post-receptor pathways that ultimately mediate the therapeutic actions of fluoxetine.

Drugs of abuse and brain gene expression

Addictive drugs like cocaine, ethanol, and morphine activate signal transduction pathways that regulate brain gene expression. Such regulation is modulated by the presence of certain transcription factor proteins present in a given neuron. This article summarizes the effects of several addictive drugs on transcriptional processes contributing to the development of a drug-dependent state. The characterization of drug-induced changes in gene expression shows promise for improving our understanding of drug-addiction phenomena and cellular modes of cocaine, ethanol, and morphine action.

Functional heterogeneity in dopamine release and in the expression of Fos-like proteins within the rat striatal complex

The dorsolateral striatum, and the core and shell of the nucleus accumbens are three major anatomical regions of the striatal complex. The shell is considered as a part of the extended amygdala, and is involved in the control of motivation and reward. The core and the striatum are considered central to sensory motor integration. In this study we compared the responses of these three regions to mild stress and drugs of abuse by measuring extracellular dopamine (DA) concentrations and Fos-like immunoreactivity (Fos-LI). The results are summarrized as follows. (i) In unchallenged conditions, extracellular DA concentrations were highest in the dorsolateral striatum and lowest in the core, whereas Fos-LI was highest in the shell and lowest in the dorsolateral striatum. (ii) After challenges that increase DA by depolarizing DAergic neurons (injection stress or 2 mg/kg morphine), the shell presented the largest increase in DA levels and Fos-LI. (iii) After the administration of a DA-uptake blocker (15 mg/kg cocaine), the percentage increase in DA was still largest in the shell. However, the absolute increase in DA and Fos-LI in the shell and the dorsolateral striatum were similar. (iv) After a full D1 agonist (SKF82958), Fos-LI was highest in the shell and lowest in the dorsolateral striatum. In conclusion, the nucleus accumbens shell seems to be the area of the striatal complex most functionally reactive to stress and drugs of abuse. However, the dorsolateral striatum and the core appear functionally distinct, as for most of the parameters studied these two regions differed.

Cocaethylene: effects on brain systems and behavior

Cocaethylene is a psychoactive metabolite formed during the combined consumption of cocaine and ethanol. In this brief review, we discuss several well-characterized effects of this metabolite with an emphasis on the neurobiological and behavioral correlates of polydrug addiction. Included herein are the descriptions of some of the changes in trans-synaptic transmission and their relationship to pathological behaviors associated with a chronic, drug-dependent state that may be altered by the spatial or temporal dynamics of cocaethylene.

Behavior and drug measurements in Long-Evans and Sprague-Dawley rats after ethanol-cocaine exposure

Long-Evans and Sprague-Dawley rats show differential behavioral responses to cocaethylene, a metabolite derived from the simultaneous ingestion of ethanol and cocaine. Such differences may also be manifested when these outbred strains are exposed to ethanol and cocaine. To test this hypothesis, both strains were fed an ethanol-diet (8.7% v/v) in conjunction with cocaine (15 mg/kg) injections for 15 days. The following parameters were evaluated: (a) ethanol consumption, (b) cocaine-induced behavioral activity, (c) blood ethanol levels, (d) blood, liver, or brain cocaine and cocaethylene levels, and (e) liver catalase and esterase activity. We found that Long-Evans rats drank significantly more of the ethanol diet relative to the Sprague-Dawley line during the first few days of the test session. This rat phenotype also differed significantly from the Sprague-Dawley line in terms of behavioral activity after cocaine administration. Blood ethanol levels did not differ between strains. Similarly, we failed to detect strain-dependent differences in blood, liver, or brain cocaine levels as measured by gas chromatography/mass spectrometry. Cocaethylene levels, however, were higher in blood and brain of Long-Evans relative to Sprague-Dawley cohorts. Although the ethanol-cocaine regimen produced a marked suppression of catalase and esterase activity compared with control-fed rats, this suppression was roughly equivalent in both rat phenotypes. These data are discussed in the context of genotypic background and vulnerability to polysubstance abuse.

Effects of cocaethylene on dopamine and serotonin synthesis in Long-Evans and Sprague-Dawley brains

We examined the behavioral and neurochemical effects of cocaethylene treatment in Long-Evans (LE) and Sprague-Dawley (SD) rats. Cocaethylene-induced behaviors were significantly less in LE rats. Cocaethylene caused an inhibition of dopamine synthesis in the caudate nucleus and nucleus accumbens that was equivalent in both rat lines. Serotonin synthesis was also suppressed by cocaethylene treatment, however this phenomenon was less pronounced when compared with the effects on dopamine synthesis.

Activating properties of cocaine and cocaethylene in a behavioral preparation of Drosophila melanogaster

The use of Drosophila as a model to study the behavioral consequences of stimulant drugs was analyzed in an active preparation of decapitated Drosophila. Application of cocaine and cocaethylene to discrete nerve cord cells regulating motor programs of behavior produced striking patterns of behavioral activity in a concentration-related manner. In general, intense circling behavior and significant wing buzzing activity were distinguishable behavioral markers in flies treated with mM concentrations of cocaine or cocaethylene. The significant changes in motor behavior induced by stimulant drugs in decapitated flies were not reproduced by the application of apomorphine, a direct dopamine (DA) agonist, or octopamine, a naturally occurring transmitter in arthropods. Because both cocaine and cocaethylene interfere with DA reuptake in mammals, we characterized the role of DA receptors mediating increased stereotypy and motor behavior in flies. Coadministration of SCH-23390, a specific D1 receptor antagonist, significantly attenuated the behavior-activating properties of cocaine and cocaethylene in this active experimental preparation. Therefore, the receptor protein mediating the behavioral responses to stimulant drugs in Drosophila is pharmacologically similar to the mammalian D1 subtype. In rats, cocaine- and cocaethylene-induced behavioral activity is complex, with increasing evidence that the D1 receptor interacts significantly with N-methyl-D-aspartate (NMDA) receptor pathways to produce an altered behavioral phenotype. To further characterize additional receptor subtypes targeted by the actions of cocaine and cocaethylene, we pretreated flies with MK-801 and dextromethorphan. Both of these drugs are potent, selective noncompetitive NMDA receptor antagonists. Interestingly, MK-801 and dextromethorphan profoundly reduced the behavior-activating properties of cocaine and cocaethylene in Drosophila. Therefore, as in rats, the NMDA (and D1) receptor pathways in this arthropod represent obligatory targets for the behavioral effects of stimulant drugs.

The role of excitatory amino acids in behavioral sensitization to psychomotor stimulants

Behavioral sensitization refers to the progressive augmentation of behavioral responses to psychomotor stimulants that develops during their repeated administration and persists even after long periods of withdrawal. It provides an animal model for the intensification of drug craving believed to underlie addiction in humans. Mechanistic similarities between sensitization and other forms of neuronal plasticity were first suggested on the basis of the ability of N-methyl-D-aspartate (NMDA) receptor antagonists to prevent the development of sensitization [Karler, R., Calder, L. D., Chaudhry, I. A. and Turkanis, S. A. (1989) Blockade of "reverse tolerance" to cocaine and amphetamine by MK-801. Life Sci., 45, 599-606]. This article will review the large number of subsequent studies addressing: (1) the roles of NMDA, alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and metabotropic glutamate receptors in the development and expression of behavioral sensitization, (2) excitatory amino acids (EAAs) and the role of conditioning in sensitization, (3) controversies regarding EAA involvement in behavioral sensitization based on studies with MK-801, (4) the effects of acute and repeated stimulant administration on EAA neurochemistry and EAA receptor expression, and (5) the neuroanatomy of EAA involvement in sensitization. To summarize, NMDA, AMPA metabotropic glutamate receptors all participate in the development of sensitization, while maintenance of the sensitized state involves alterations in neurochemical measures of EAA transmission as well as in the expression and sensitivity of AMPA and NMDA receptors. While behavioral sensitization likely involves complex neuronal circuits, with EAAs participating at several points within this circuitry, EAA projections originating in prefrontal cortex may play a particularly important role in the development of sensitization, perhaps via their regulatory effects on midbrain dopamine neurons. The review concludes by critically evaluating various hypotheses to account for EAA involvement in the development of behavioral sensitization, and considering the question of whether EAA receptors are involved in mediating the rewarding effects of psychomotor stimulants and sensitization of such rewarding effects.

Cocaethylene stimulates the secretion of ACTH and corticosterone and the transcriptional activation of hypothalamic NGFI-B

Cocaethylene is an active cocaine metabolite formed by hepatic carboxylesterases in the presence of alcohol. The effects of cocaethylene on the hypothalamic-pituitary-adrenal (HPA) axis were investigated in vivo using adrenocorticotropic hormone (ACTH) and corticosterone secretion as indices of peripheral stimulation. To ascertain the central effects of cocaethylene on discrete neurons of the paraventricular nucleus (PVN) of the hypothalamus, a specific cRNA probe was used to follow changes in the transcriptional activation of nerve growth factor I-B (NGFI-B), a member of the family of immediate-early genes. Intravenous (i.v.) injection of cocaethylene (16 mumol/kg) to rats produced a marked but transient increase in plasma levels of ACTH and corticosterone within 10 min of drug exposure. Secretion of these hormones was accompanied by elevated levels of NGFI-B mRNA detected 30 min after i.v. or intraperitoneal (i.p., 60 mumol/kg) cocaethylene administration. The transcriptional stimulation of this immediate-early gene within parvocellular secretory neurons was relatively brief in duration, returning to basal levels by 180 min after drug exposure. As expected both routes of cocaethylene administration produced an increase in locomotor activity compared to saline-vehicle rats, with no differences between i.v. or i.p. routes with respect to duration of behavioral activation. Taken together, these findings indicate that cocaethylene has neuroendocrine properties on its own, targeting a critical region of the brain that regulates stressful events in the body. This, combined with other neurochemical properties, points to the possibility of cocaethylene augmenting the effects of a drug-dependent state.