Correlation of behavioral and neurochemical effects of acute administration of cocaine in rats

The role of serotonin in drug use and addiction

The use of psychoactive drugs is a wide spread behaviour in human societies. The systematic use of a drug requires the establishment of different drug use-associated behaviours which need to be learned and controlled. However, controlled drug use may develop into compulsive drug use and addiction, a major psychiatric disorder with severe consequences for the individual and society. Here we review the role of the serotonergic (5-HT) system in the establishment of drug use-associated behaviours on the one hand and the transition and maintenance of addiction on the other hand for the drugs: cocaine, amphetamine, methamphetamine, MDMA (ecstasy), morphine/heroin, cannabis, alcohol, and nicotine. Results show a crucial, but distinct involvement of the 5-HT system in both processes with considerable overlap between psychostimulant and opioidergic drugs and alcohol. A new functional model suggests specific adaptations in the 5-HT system, which coincide with the establishment of controlled drug use-associated behaviours. These serotonergic adaptations render the nervous system susceptible to the transition to compulsive drug use behaviours and often overlap with genetic risk factors for addiction. Altogether we suggest a new trajectory by which serotonergic neuroadaptations induced by first drug exposure pave the way for the establishment of addiction.

Levodopa pharmacotherapy for cocaine dependence: choosing the optimal behavioral therapy platform

BACKGROUND

The dopamine precursor levodopa has shown some, albeit relatively weak, promise in treating cocaine dependence. This study sought to identify the most appropriate behavioral therapy platform for levodopa pharmacotherapy by evaluating its effect when administered in combination with behavioral platforms of varying intensities.

METHOD

A total of 161 treatment-seeking cocaine dependent subjects received sustained release levodopa/carbidopa (400/100mg bid, Sinemet) or placebo delivered in combination with Clinical Management (ClinMan); ClinMan+cognitive behavioral therapy (CBT); or ClinMan+CBT+voucher-based reinforcement therapy (VBRT) in a 12-week randomized, placebo-controlled, double-blind (for medication condition) trial. Medication compliance was monitored with riboflavin (100mg/capsule) and the Medication Event Monitoring System. Protocol compliance was addressed in weekly, 10-min nurse-delivered ClinMan sessions. Weekly, 1-h CBT sessions focused on coping skills training. VBRT (with escalating reinforcer value) provided cash-valued vouchers contingent on cocaine-negative urine toxicology results. Urine benzoylecgonine assays collected thrice-weekly were analyzed by intention-to-treat criteria using generalized linear mixed models.

RESULTS

Levodopa main effects were found on all outcome measures of cocaine use. Contrasts testing the levodopa-placebo difference within each behavioral platform found reliable effects, favoring levodopa, only in the VBRT platform. Levodopa treatment with vouchers produced higher proportions of cocaine-negative urines and longer periods of consecutive abstinence compared to other treatment combinations.

CONCLUSION

This is the first study to find a significant treatment effect for levodopa and, in doing so, to demonstrate that the magnitude of this effect is dependent upon conditions of the behavioral therapy platform. The data support use of levodopa with abstinence-based reinforcement therapy as one efficacious combination in cocaine dependence disorder treatment.

Clorgyline-induced modification of behavioral sensitization to quinpirole: effects on local cerebral glucose utilization

Sensitization refers to augmented behavioral responses produced by repeated, intermittent injections of dopaminergic psychostimulants. The locomotor manifestations observed after a sensitizing course of quinpirole, a D(2)/D(3) dopamine agonist, can be modified by the MAO(A) inhibitor clorgyline, by a mechanism apparently unrelated to its actions on MAO(A). Alterations in regional neuronal activity produced by quinpirole in quinpirole-sensitized rats with or without clorgyline pretreatment were assessed based on LCGU using the [(14)C]-2-deoxyglucose (2-DG) method. Adult, male Long-Evans rats (180-200 g, n=9-10/group) were subjected to an injection of either clorgyline (1.0 mg/kg, s.c.) or saline 90 min prior to an injection of quinpirole (0.5 mg/kg, s.c.) or saline, 1 set of injections administered every 3rd day for 10 sets. The 2-DG procedure was initiated 60 min after an 11th set of injections in freely moving rats. LCGU was determined by quantitative autoradiography. LCGU was decreased in a number of limbic (nucleus accumbens and ventral pallidum) and cortical (medial/ventral orbital and infralimbic) regions and in the raphe magnus nucleus in quinpirole-sensitized rats (P<0.05 vs. saline-saline). Quinpirole-sensitized rats pretreated with clorgyline had similar alterations in LCGU, but LCGU was higher in the locus coeruleus compared to quinpirole alone (P<0.05), was not decreased in the raphe magnus nucleus, and was decreased in the piriform cortex and septum. This implicates altered activity of the noradrenergic, serotonergic, olfactory, and limbic systems in the modified behavioral response to quinpirole with clorgyline pretreatment.

Serotonin and psychostimulant addiction: Focus on 5-HT1A-receptors

Serotonin(1A)-receptors (5-HT(1A)-Rs) are important components of the 5-HT system in the brain. As somatodendritic autoreceptors they control the activity of 5-HT neurons, and, as postsynaptic receptors, the activity in terminal areas. Cocaine (COC), amphetamine (AMPH), methamphetamine (METH) and 3,4-methylenedioxymethamphetamine ("Ecstasy", MDMA) are psychostimulant drugs that can lead to addiction-related behavior in humans and in animals. At the neurochemical level, these psychostimulant drugs interact with monoamine transporters and increase extracellular 5-HT, dopamine and noradrenalin activity in the brain. The increase in 5-HT, which, in addition to dopamine, is a core mechanism of action for drug addiction, hyperactivates 5-HT(1A)-Rs. Here, we first review the role of the various 5-HT(1A)-R populations in spontaneous behavior to provide a background to elucidate the contribution of the 5-HT(1A)-Rs to the organization of psychostimulant-induced addiction behavior. The progress achieved in this field shows the fundamental contribution of brain 5-HT(1A)-Rs to virtually all behaviors associated with psychostimulant addiction. Importantly, the contribution of pre- and postsynaptic 5-HT(1A)-Rs can be dissociated and frequently act in opposite directions. We conclude that 5-HT(1A)-autoreceptors mainly facilitate psychostimulant addiction-related behaviors by a limitation of the 5-HT response in terminal areas. Postsynaptic 5-HT(1A)-Rs, in contrast, predominantly inhibit the expression of various addiction-related behaviors directly. In addition, they may also influence the local 5-HT response by feedback mechanisms. The reviewed findings do not only show a crucial role of 5-HT(1A)-Rs in the control of brain 5-HT activity and spontaneous behavior, but also their complex role in the regulation of the psychostimulant-induced 5-HT response and subsequent addiction-related behaviors.

Plasma cocaine levels, metabolites, and locomotor activity after subcutaneous cocaine injection are stable across the postpartum period in rats

Plasma levels of cocaine (COC) and two of its principle metabolites, benzoylecgonine (BE) and ecgonine methyl ester (EME) were determined by liquid chromatography-tandem mass spectrometry (LC/MS/MS) in samples collected up to 3 h after a subcutaneous injection of cocaine (10 mg/kg) on six different days between days 4 and 24 postpartum, a period of dramatic change in the endocrine state of the female rat. Locomotor activity was measured in the same animals during this period using automated animal activity monitors. Additional measures in males provide a link to existing literature. We found that plasma levels of cocaine and its metabolites, as well as their respective time courses, are remarkably uniform across the postpartum period in female rats, as are the effects of cocaine on locomotor activity. Data from males show accord with prior published values. COC and BE, but not EME levels, were higher in males, and the time courses of COC and BE levels after injection varied somewhat between postpartum females and males; however, neither baseline nor cocaine-induced locomotor activity differed between postpartum females and males. We conclude that in the postpartum rat, there are no significant differences in the peripheral processing or general accessibility of cocaine to the brain to activate motor systems across the postpartum period. These data are critical to our understanding of differences in the reward salience of cocaine across the postpartum period and in other adult rat models [Mattson BJ, Williams S, Rosenblatt JS, Morrell JI. Comparison of two positive reinforcing stimuli: pups and cocaine throughout the postpartum period. Behav Neurosci 2001;115:683-94, Mattson BJ, Williams SE, Rosenblatt JS, Morrell JI. Preferences for cocaine- or pup-associated chambers differentiate otherwise behaviorally identical postpartum maternal rats. Psychopharmacology (Berl) 2003;167:1-8].

Nucleus accumbens serotonin1A receptors control cocaine-induced hyperactivity but not local serotonin increase: an in vivo microdialysis study

The nucleus accumbens (Nac) is an important structure for cocaine-induced hyperactivity and receives a dense serotonergic (5-HT) innervation. Previous studies showed that a systemic activation of 5-HT(1A) receptors potentiates cocaine-induced hyperlocomotion, but attenuates the cocaine-induced 5-HT increase in the Nac. In order to address the role of Nac 5-HT(1A) receptors in the control of cocaine-induced and spontaneous behavioural activity and local 5-HT release, we used in vivo microdialysis in freely moving rats. The 5-HT(1A)-receptor agonist, 8-OH-DPAT (0, 1 and 10 microM), was applied locally into the Nac by reverse dialysis followed by a cocaine (10 mg/kg) or saline i.p. injection. The Nac 5-HT(1A)-receptor activation potentiated cocaine-induced hyperlocomotion, but attenuated rearing behaviour dose-dependently. Parallel to that, the cocaine-induced increase in Nac 5-HT dialysate level was unaffected, as were the decreases in 5-HIAA and DOPAC dialysate levels after cocaine. In saline treated rats, the local application of 8-OH-DPAT into the Nac affected neither spontaneous behavioural activity nor 5-HT, 5-HIAA or DOPAC dialysate levels in the Nac. These data suggest that Nac 5-HT(1A) receptors exert a bi-directional control of cocaine-induced hyperactivity, while not affecting spontaneous behaviour. Furthermore, accumbal 5-HT(1A) receptors do not appear to be directly involved in the acute effects of cocaine on 5-HT, 5-HIAA or DOPAC levels in the Nac.

Acute and chronic effects of cocaine on isolation-induced aggression in mice

The purpose of the present study was to investigate the effects of acute and chronic cocaine administration on aggressive behaviour in mice. The animals were made more aggressive by individual housing for a period of 6 weeks. Group-housed anosmic conspecifics which were not aggressive were used as intruder controls. In acute studies, cocaine induced no significant change in aggressive behaviour at low doses (0.5-5 mg/kg) but significantly decreased aggressive behaviour after doses of 10 and 20 mg/kg. Cocaine increased the isolation-induced aggressive behaviour in mice when they were injected twice daily for a week with low doses of 0.5 or 1 mg/kg. In particular, the latency to first attack was significantly decreased by the drug and the frequency of attack towards the non-aggressive intruder was dramatically increased. Higher cocaine doses (10 or 20 mg/kg) under the described treatment regimen decreased these agonistic repertories. Tolerance did not develop to the anti-aggressive effects of high doses of cocaine on continued treatment.

Influence of the cannabinoid agonist HU 210 on cocaine- and CQP 201-403-induced behavioural effects in rat

Acute injection of the cannabinoid agonist HU 210 (6.25-100 microg/kg, i.p.) dose-dependently inhibited rat locomotor activity and rearing, while subchronic treatment with the drug (once daily for 7 days) at the same doses only diminished locomotion. Acute but not subchronic administration of HU 210 (12.5-50 microg/kg, i.p.) potently counteracted acute and subchronic cocaine (15 mg/kg, i.p.)-induced hyperlocomotion and enhanced rearing. The acute cannabinoid (6.25-100 microg/kg, i.p.) also inhibited locomotor activity, stereotyped behaviour and shaking elicited by the D1/D2 agonist CQP 201-403 (500 microg/kg, i.p.). On the contrary, subchronic treatments with HU 210 enhanced CQP 201-403-induced locomotor activity and potently stimulated escape attempts. Discussion centers on the influence of cannabinoids on experimental models of psychosis.

Plasma cocaine levels and locomotor activity after systemic injection in virgin and in lactating maternal female rats

We have determined the temporal pattern of plasma cocaine levels and increased activity that result from acute systemic injections of cocaine to female rats in two different endocrine and behavioral states, in nonmaternal virgins and in lactating maternal dams. Plasma levels of cocaine as well as ambulatory and rearing activity were determined every 30 min for a total of 300 min after subcutaneous injections of either 10, 20, or 40 mg/kg of cocaine. Virgin females had no prior drug history, whereas lactating, maternal dams had received two cocaine injections before activity testing. Within 30 min after an injection, cocaine in the plasma and activity were substantially elevated, and generally remained so for 270-300 min. Overall, plasma cocaine levels and activity were well correlated and followed a predictable dose-response pattern. The onset, peak, duration, and decline of activity corresponded generally to the onset, peak, duration, and decline of plasma cocaine. For virgins, mean ambulatory activity increased 2.5-4.0-fold over baseline, whereas in lactating females activity increased 5-11-fold over baseline. Stereotypy did not occur. Although the general responsivity of these females to cocaine was very similar to that reported for males, there are differences in the timing of peak activity and the return of activity to baseline when the virgins and the lactating dams are compared to each other and to reports by others on male rats. These data support the hypothesis that endocrine or behavioral state may influence the responsiveness of animals to cocaine.

Effects of diet on sensitization to cocaine-induced stereotypy in female rats

The progressive increase in cocaine-induced stereotyped behavior that accompanies repeated cocaine injections (sensitization) was examined in rats consuming different diets. Adult female Sprague-Dawley rats were fed one of three diets: low protein (6% casein), adequate protein (25% casein), or a standard chow diet. Following 1 week of adaptation to the diets, the rats were injected every 3-4 days with either cocaine (30 mg/kg, IP) or saline, and the total amount of stereotypy was measured over a 90-min interval following each of four injections. Cocaine-induced stereotypy peaked at 40-50 min following each injection, after which it declined for all diet groups. With repeated injections, the total amount of stereotypy increased in all diet groups. By the fourth injection, the low protein diet group (6% casein) exhibited a slower onset and a possibly prolonged duration of cocaine-induced stereotypy when compared with the two adequate protein diet groups (25% casein and chow). Interestingly, the rats in the two purified diet groups (6% casein and 25% casein) exhibited significantly more stereotypy across injections than those in the chow diet group. Weight differences did not explain the differences in stereotypy present among the diet groups. This study concludes that diet significantly alters the pattern of cocaine-induced stereotypy in female rats, especially after repeated exposure.

Involvement of dopamine D2 receptors in the effect of cocaine on sexual behaviour and stretching-yawning of male rats

The effect of cocaine (7.5, 15 and 30 mg/kg) administered in acute or subchronic mode, on the mating behaviour of sexually active male rats varied in a dose- and mode-dependent manner. Regardless of mode of treatment, 30 mg/kg markedly impaired the rats copulatory ability and impairment continued for a week after suspension of subchronic treatment. An acute dose of 15 mg/kg reduced intromission frequency, while in subchronic mode it also reduced ejaculation latency. Mount frequency was increased by 7.5 and 15 mg/kg, but only on first injection. In the case of sexually-naive male rats, acute administration of cocaine (3-30 mg/kg) stimulated penile erections at 7.5 mg/kg and motor hyperactivity at all doses. (-) Eticlopride (0.025 and 0.05 mg/kg), a DA D2 antagonist, counteracted cocaine-induced motor hyperactivity but not penile erection, which it enhanced. (-) Eticlopride at the same doses also antagonized cocaine potentiation of lisuride (0.2 mg/kg)-induced behavioural effects. When male rats treated with subchronic cocaine (15 mg/kg) were injected with the DA D2 agonist SND 919 (0.1 mg/kg), they displayed a more marked stretching-yawning behaviour than control animals receiving SND 919 at the same dose. The involvement of DA D2 receptors in cocaine-induced effects is suggested.

Influence of eticlopride on cocaine- and DA D2 agonist-induced behavioral effects in rats

The influence of the DA D2 antagonist (-) eticlopride on cocaine- and DA D2 agonist-induced behavioral effects was investigated by means of two series of experiments, in rats. In the first 10-day series, coadministration of (-) eticlopride (10 and 50 micrograms/kg, SC) always potently inhibited cocaine (15 mg/kg, IP)-induced hypermotility but did not modify the penile erection (PE)-enhancement produced by the drug at the first injection; it actually counteracted the inhibitory effect of subchronic cocaine on PE. In the second series, (-) eticlopride, at the same doses, antagonized PE elicited by various DA D2 agonists at nonstereotyping doses; when, along with PE, stereotyped behavior was induced, only the latter was inhibited by (-) eticlopride, which even increased PE.

Cocaine washed out syndrome in a patient with acute myocardial infarction

We present the case of a 34-year-old woman with cocaine-associated chest pain and hypersomnulence, who, because of her inability to report chest pain, and her comfortable appearance, was admitted to telemetry for a diagnosis of low-probability rule-out myocardial infarction. Her chest pain was incompletely relieved, and she subsequently was transferred to the intensive care unit and ruled in for myocardial infarction. We discuss the clinical syndrome of cocaine-related depressed level of consciousness, and its relationship to evaluation of cocaine-related chest pain.

Cocaine. Selective regional effects on central monoamines

Cocaine HCl (0, 10, or 50 mg/kg) was injected into adult male ICR mice ip. Thirty minutes later, the brains were removed, and nine regions were isolated: olfactory bulbs, olfactory tubercles, prefrontal cortex, septum, striatum, amygdala, hypothalamus, hippocampus, and thalamus. Using high-performance liquid chromatography, concentrations of norepinephrine, dopamine, serotonin, and their major metabolites and the metabolite/neurotransmitter ratios were determined as an indicator of utilization. Serotonergic systems responded most dramatically. 5HIAA/5-HT decreases were seen in all the brain regions, except the septum, hippocampus, and olfactory bulbs. In most instances, the alterations were dose-dependent. The most profound changes were seen in the amygdala, prefrontal cortex, hypothalamus, and thalamus. For noradrenergic systems, significant responses were seen only in the amygdala, prefrontal cortex, and hypothalamus, but then only at the lower dose. The dopaminergic responses were more complex and not always dose-dependent. The DOPAC/DA ratio was decreased only in the amygdala and striatum at the lower dose, and the olfactory tubercles at the higher dose. It was increased in the septum. The HVA/DA ratios were decreased in the amygdala, prefrontal cortex, and hypothalamus, but only at the lower dose (like MHPG/NE). The 3MT/DA ratio was decreased in the thalamus at the lower dose and in the olfactory tubercles at the higher dose, whereas it was increased in the prefrontal cortex at the lower dose. The HVA and DOPAC routes of degradation were both utilized only by the amygdala. Thus, cocaine produced its most comprehensive effects in this nucleus, as well as the greatest absolute percentage changes for all three of the monoamine systems studied.

Alterations in the dopaminergic receptor system after chronic administration of cocaine

Several studies suggest that one of the most important factors contributing to cocaine dependence is an alteration in the actions of the neurotransmitter dopamine in the central nervous system. In order to understand some of the neuroreceptor consequences of cocaine administration, groups of rats were injected with cocaine (2 daily doses of 15 mg/kg) for 1 to 21 days. Binding of [3H]cocaine, [3H]SCH23390, [3H]raclopride, and [3H]BTCP in striatal and cortical tissue from the treated animals was compared to controls. [3H]Cocaine binding was increased by the drug in the striatum and cortex at days 14 and 21, respectively. The binding of [3H]SCH23390 to D1 dopamine receptors was significantly increased at day 3 of cocaine exposure. In striatal membranes, [3H]BTCP binding to dopamine uptake sites was significantly increased after day 7, whereas binding in cortical membranes was increased from day 1. [3H]Raclopride binding to D2 dopamine receptors remained unchanged throughout the study in both cortical and striatal tissues. These results indicate that repeated exposure to cocaine produces an upregulation (possible supersensitivity) in cortical D1, cocaine, and DA-uptake sites which occurs in a time-dependent manner. These increases are coupled with an upregulation in striatal D1, cocaine, and DA-uptake sites, without simultaneous changes in D2 receptors. Thus, cocaine's effects are not uniformly distributed across all brain regions, but rather are focused within areas of the dopamine system.

Cocaine abuse in North America: a milestone in history

The euphoric effects of coca leaves have been known to mankind for thousands of years. Yet the first epidemic of cocaine use in America occurred during the late 19th century. Initially, there were no laws restricting the consumption or sale of cocaine. In fact, cocaine was freely available in drug stores, saloons, from mail-order vendors, and even in grocery stores. It is reported that one drug manufacturer, in 1885, was selling cocaine in 15 different forms, including cigarettes, cheroots, inhalants, cordials, crystals, and solutions. Many famous imported wines, such as "Vin Mariani," contained a mixture of wine and coca. For consumers on budgets, the wonder drug was available as Coca-Cola and dozens of other soda pops and pick-me-up drinks. One of them even had a simple and direct name, Dope. Soon enough, the ill effects of cocaine became apparent, and by the 1920s cocaine was the most feared of all illicit drugs. Most states began enacting laws against cocaine use. President William Taft proclaimed cocaine as Public Enemy No. 1, and in 1914 the Congress passed the Harrison act, which tightly regulated the distribution and sale of cocaine. By the late 1950s, cocaine use in the United States was simply considered a problem in the past. Unfortunately, the people who were aware of the nation's first cocaine epidemic gradually passed away, and America once again was ready for its fling with cocaine in the 1960s. Today, it is estimated that upwards of 50 million Americans, that is one in four, have used cocaine. In addition, another fifty thousand people use this substance for the first time each day. More than 6 million Americans use cocaine on a regular basis. Little wonder, then, that America as well as the other countries have declared a "War on Drugs." In this review, pharmacology of cocaine, major complications arising from its use, and efforts to curb its abuse are discussed.

Cocaine and regional brain monoamines in mice

Cocaine HCl (0, 10, or 50 mg/kg) was injected into adult male ICR mice IP. Thirty minutes later, brains were removed and nine regions were isolated: olfactory bulbs (OB), olfactory tubercles (OT), prefrontal cortex (PC), septum (SP), striatum (ST), amygdala (AMY), hypothalamus (HT), hippocampus (HC), and thalamus (TH). Using high-performance liquid chromatography, concentrations of norepinephrine (NE), dopamine (DA), serotonin (5-HT), and their major metabolites were determined. At 10 mg/kg cocaine, NE levels were increased in the AMY and its metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), was decreased in the PC, AMY, and HT. DA levels were also increased in the AMY, while its intracellular metabolite, dihydroxyphenylacetic acid (DOPAC), was decreased in the ST and its extracellular metabolite, homovanillic acid (HVA), was decreased in the PC. 3-Methoxytyramine (3-MT) levels were not altered in any tissue. 5-HT levels were increased in the AMY, HT, and TH, while its metabolite 5-hydroxyindoleacetic acid (5-HIAA) was decreased in the OB and ST. MHPG/NE ratios were decreased in the PC, AMY, and HT as were those for HVA/DA. DOPAC/DA ratios were decreased in the ST and AMY and increased in the SP while those for 3-MT/DA were decreased in the TH and increased in the PC. 5-HIAA/5-HT ratios were decreased in the AMY, HC and TH. At 50 mg/kg cocaine, there was an increase in DA in the TH. There was a decrease in DOPAC, HVA, and 3-MT, as well as the DOPAC/DA ratio in the ST. In the OT, there was a decrease in DOPAC, the DOPAC/DA ratio, 3-MT, and the 3-MT/DA ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Cocaine euphoria, dysphoria, and tolerance assessed using drug-induced changes in brain-stimulation reward

The time course of cocaine-induced changes in self-stimulation thresholds were used to evaluate cocaine euphoria and dysphoria as a function of the chronicity of drug treatment, dosage level, and the spacing of injections. It was assumed that cocaine-induced decreases in thresholds were indicative of cocaine euphoria, while increases in thresholds reflected rebound dysphoric responses to cocaine administration. Three experiments were performed using self-stimulating rats implanted with ventral tegmental area electrodes. Cocaine's threshold-lowering effects were evident 15 min postinjection (IP) with thresholds returning to baseline by approximately 3.0 h after treatment. Little evidence for cocaine-induced increases in thresholds was observed during periods of chronic cocaine treatment. However, thresholds were slightly elevated upon withdrawal from chronic cocaine treatment in Experiments 2 and 3. No evidence of tolerance or sensitization to cocaine-induced shifts in thresholds was noted with single daily injections, while multiple daily injections produced tolerance to cocaine's threshold-lowering effects. It is concluded that cocaine's ability to enhance brain-stimulation reward is highly reliable and robust, while decreases in brain-stimulation reward associated with chronic cocaine treatment are less reliable and difficult to demonstrate. The possible influence of drug dosage on the induction of cocaine dysphoria and the ability of various self-stimulation procedures to measure dysphoric effects are discussed.

Chronic cocaine enhances serotonin autoregulation and serotonin uptake binding

Repeated cocaine intoxication can result in the development of behavioral sensitization in animals and psychosis in humans, phenomena that have been associated with alterations in dopamine (DA) function. Using electrophysiologic and autoradiographic techniques, modifications of central serotonin (5-hydroxytryptamine; 5-HT) systems were investigated in rats treated with a regimen of cocaine administration that produced behavioral sensitization. The inhibitory response of single 5-HT neurons in the dorsal raphe (DR) to (-)-cocaine, the 5-HT uptake inhibitor fluoxetine or the 5-HT1A agonist 8-hydroxy-2-[di-N-propylamino]tetralin (8-OHDPAT) was significantly enhanced in cocaine-treated rats. Furthermore, several brain areas that contain either cell bodies (DR) or terminals for 5-HT (medial and sulcal prefrontal cortex, frontal cortex) showed cocaine-induced elevations in [3H]imipramine-labeled 5-HT uptake sites, while [3H]-8-OHDPAT-labeled 5-HT1A receptors were decreased only in the central medial amygdala. These results suggest that modifications of autoregulatory mechanisms secondary to alterations of 5-HT uptake processes may contribute to the development of cocaine sensitization.

Recent Advances in Pharmacological Research on Alcohol

Alcohol dependence is a major public health problem. Studies have shown that a person dependent on alcohol often coabuses other substances, such as cocaine. Cocaine is a powerful stimulant whereas ethanol is generally considered to be a depressant, with some stimulating properties. The subjective effects of these two substances in a dependent individual may often appear to be more similar than they are different. Animals also self-administer both substances. Basically, although both substances have anesthetic properties and both act to functionally increase catecholaminergic function, especially that of dopamine, there are some differences in their actions. Both alcohol and cocaine have various effects on several neurotransmitters and systems, which ultimately interact to produce the feeling of well-being avidly sought by many individuals today. This drive often eventually produces a dependence which has associated social and medical consequences. It seems likely that the neurochemical changes that ensue following abuse of these substances underlie the phenomena of dependence, tolerance, and subsequent withdrawal. The apparent similarities and differences between these two substances will be reviewed in this chapter.

Response to novelty predicts the locomotor and nucleus accumbens dopamine response to cocaine

The relationship between a rat's locomotor response to a novel environment and its behavioral and dopaminergic responses to cocaine was examined. Subjects were divided into two groups based on their locomotor response to a novel environment. Subjects who had a novelty response above the median were classified as high responders (HR), while those with a novelty response below the median were classified as low responders (LR). Following administration of cocaine-HCl (0, 2.5, 5.0, 10.0, or 15.0 mg/kg), HR rats showed a greater locomotor response than LR rats. Moreover, there was a significant correlation between a subject's locomotor response to the novel environment and the locomotor response to either 10.0 (r = 0.65) or 15.0 (r = 0.92) mg/kg cocaine. In a separate experiment, the extracellular concentration of dopamine in the nucleus accumbens (NACC) was monitored using microdialysis procedures. Following cocaine administration (15.0 mg/kg) HR rats showed a larger NACC dopamine response and greater locomotor activity than LR rats. In addition, there was a threefold greater locomotor activity to dopamine ratio in HR rats than in LR rats. A correlation between a subject's locomotor response to a novel environment and the dopaminergic response to cocaine was also evident. These results suggest that differences in the locomotor response to cocaine can, to some degree, be predicted by a rat's locomotor response to a novel environment, and that variations in dopamine-dependent mechanisms of the NACC may underlie these individual differences.

Cocaine-induced locomotor activity in rats

Rats were injected SC or IP with a dose of cocaine at 20 mg/kg twice daily or saline (2 ml/kg) for 15 consecutive doses. Horizontal (including ambulatory and repetitive activity) and ambulatory locomotor activities were assessed following the first (acute) and the 15th (chronic) injections. Total locomotor activity (area under curve, AUC) following the acute and the chronic administration of cocaine were comparable, regardless of the route of drug administration. However, the temporal patterns of activity were significantly different; the peak of locomotor activity occurred earlier (chronic vs. acute, 20 vs. 40 min after IP; 130 vs. 180 min after SC) following chronic cocaine administration. Furthermore, the peak activity was significantly higher (3-fold after IP and 50% after SC) in chronically than in acutely treated rats, providing evidence for sensitization. In contrast, activity in the late session (240-280 min after SC) was significantly lower following the chronic SC cocaine administration, providing evidence for desensitization. The absolute slope values of the ascending phase and the descending phase were significantly larger following chronic administration of cocaine than that following the acute dosing. The possibility of changes in locomotor activity with alteration of pharmacokinetics on chronic cocaine treatment is discussed.

Inhibition of 5-HT2 receptor-mediated head-twitch response by cocaine via indirect stimulation of adrenergic alpha 2 and serotonergic 5-HT1A receptors

Cocaine inhibits the 5-HT2-mediated (+/-)-DOI-induced head-twitch response (HTR) in mice in a dose-dependent manner. In order to investigate the possible inhibitory mechanism(s) of cocaine on 5-HT2 receptor function, we studied the effects of the selective adrenergic alpha 2 receptor antagonist yohimbine and the beta-adrenergic/5-HT1 receptor antagonist alprenolol, and the 5-HT3 antagonist ICS 205-930 on the inhibitory action of cocaine on the (+/-)-DOI-induced HTR. Neither yohimbine (0.1 and 0.5 mg/kg) nor alprenolol (10 mg/kg) pretreatment had any significant effect on the (+/-)-DOI-induced HTR. However, both antagonists prevented the inhibitory effects of cocaine on the (+/-)-DOI-induced HTR. The 5-HT3 antagonist ICS 205-930 neither produced HTR nor decreased the (+/-)-DOI-induced HTR frequency. The present results suggest that cocaine inhibits 5-HT2 receptor function by increasing the synaptic concentration of norepinephrine and serotonin via inhibition of their uptake and thus indirectly stimulating the respective inhibitory adrenergic alpha 2 and serotonergic 5-HT1A receptors. Furthermore, cocaine's 5-HT3 antagonist properties appear not to play a role in the inhibition of head-twitch behavior.

Neurologic complications of cocaine abuse

The neurologic complications of cocaine toxicity are responsible for a major portion of the morbidity and mortality associated with cocaine. Most of the complications appear to be related to the hyperadrenergic state induced by cocaine and may be treated symptomatically. Diazepam is the most effective drug for cocaine-induced seizures.

Effects of carbamazepine on self-administration of intravenously delivered cocaine in rats

Carbamazepine (Tegretol) is widely used therapeutically as an anticonvulsant. Based on an hypothesis that links electrical kindling in the limbic system (leading to seizures) to reverse tolerance or sensitivity to cocaine's effects, carbamazepine is being tested as a treatment for human cocaine users. The purpose of this experiment was to examine the effects of carbamazepine on intravenous cocaine self-administration in rats. Rats self-administered intravenously delivered cocaine (0.2 mg/kg) under a fixed-ratio 4 schedule. When cocaine injections reached stable levels, carbamazepine was mixed with the rats' food for 8 days. Three doses of carbamazepine were tested (80, 120, and 160 mg/kg) in different groups of 5 rats each. The rats were later separated into groups with a high (greater than 750 infusions) and a low (500-750 infusions) cocaine baseline. Two control groups of 5 rats each received carbamazepine treatments (120 or 160 mg/kg) and self-administered an orally delivered solution of glucose and saccharin (G + S). At the highest carbamazepine dose in the high cocaine baseline group, carbamazepine reduced cocaine infusions by at least 50 percent and food intake by approximately 25 percent during the 8 days of treatment. Cocaine infusions returned to baseline within 24 hr after the regular diet was restored. Carbamazepine had a minimal effect in groups of rats with lower cocaine baselines. Responding reinforced by the G + S solution was reduced by both the 120 and 160 mg/kg carbamazepine doses. Water intake was not systematically affected by the addition of carbamazepine to the food; however, activity measures were significantly lower in some groups at the higher carbamazepine doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of acute and subacute cocaine administration on the CNS dopaminergic system in Wistar-Kyoto and spontaneously hypertensive rats: I. Levels of dopamine and metabolites

Effects of acute and subacute cocaine administration on dopamine (DA) and its metabolites in striata and nucleus accumbens of nine week-old Wistar-Kyoto and spontaneously hypertensive rats were studied. Levels of DA,3,4-dihydroxphenylacetic acid (DOPAC) and homovanillic acid (HVA) were determined by HPLC-EC. There were no differences in DA levels in striata and nucleus accumbens between control WKY and SHR. Levels of DA in two brain regions were unaffected in groups treated acutely with cocaine. Both strains showed a significant increase in striatal HVA 2 hr after cocaine injection. Seven day treatment declined DA levels in striatum of WKY and in nucleus accumbens of SHR. However, only WKY treated subacutely with cocaine showed significantly increased HVA either with or without changes in DOPAC in nucleus accumbens and striatum, respectively. Increased DOPAC/DA and HVA/DA ratios appeared only in striatum of WKY and in nucleus accumbens of SHR following subacute treatment. These results suggest that subacute cocaine administration affects DA levels in striata and nucleus accumbens differently between WKY and SHR.

The influence of cocaine self-administration on in vivo dopamine and acetylcholine neurotransmission in rat caudate-putamen

Presynaptic dopamine and acetylcholine transmission in the anteroventral (limbic) caudate-putamen were studied by microdialysis in freely moving rats during cocaine self-administration sessions. Acute cocaine exposure elevated dopamine (DA) overflow in drug-naive animals. However, during repeated cocaine administration, the drug-induced elevation of DA was attenuated in animals previously exposed (during the prior 9 days) to cocaine. The diminished dopamine response in repeatedly treated animals while self-administering cocaine was speculated to be due to increased activity of DA transport carrier and/or supersensitive receptors modulating DA release. During repeated cocaine administration, extracellular acetylcholine levels in animals previously exposed to cocaine were found to be significantly decreased compared with controls. The findings of the study may suggest a functional development of supersensitive DA receptors postsynaptic to the DA terminal (located on cholinergic neurons) as a consequence of previous cocaine exposure. Such supersensitivity would allow for a reduced DA signal to be amplified at the postsynaptic level during repeated cocaine self-administration.

The effects of cocaine on multivariate locomotor behavior and defecation

The present study utilized a multifactorial open-field analysis (Digiscan activity) to assess behavioral changes induced by various doses of cocaine known to stimulate locomotion. The measures that were implemented included ambulation, rearing, stereotypic behavior, rotational movements and changes in defecation levels. Thirty-two male Sprague-Dawley rats were habituated to Digiscan-16 Animal Activity Monitors (Omnitech Electronics, Columbus, OH) before being injected with 0.0, 10, 20 or 30 mg/kg cocaine. Rats were kept on a reversed light/dark schedule and tested in the middle of the dark cycle. It was found that cocaine consistently increased activity measures; most prominently affecting the rotational and ambulatory indices. Interestingly, this 'activity print' appeared to be dose-dependent and specific to cocaine. Open-field defecation levels were compared to home-cage levels as an additional behavioral correlate. Defecation decreased under all doses of cocaine as compared to control levels (saline injection). This result is attributed to cocaine's weakly sympathomimetic effect.

Immunomodulation by cocaine--a neuroendocrine mediated response

Cocaine acts directly on lymphoid cells and indirectly modulates the immune response by affecting the level of neuroendocrine hormones. In vitro, very high concentrations of cocaine inhibit different immune responses, while plasma levels following cocaine use have no effect. The results of the few published in vivo studies are contradictory, showing stimulatory, suppressive or no effect on lymphoid cells. The indirect effects of cocaine on the immune system could be mediated by ACTH, beta-endorphin and corticosterone. Anorectic effect associated with nutritional deficiencies of drug users could additionally affect the immune response by cocaine.

Bromocriptine and amantadine in cocaine detoxification

The effects of bromocriptine and amantadine in treating cocaine withdrawal were compared. Withdrawal symptoms are thought to be due to central dopamine depletion. Both bromocriptine and amantadine are dopamine agonists previously reported to diminish withdrawal symptoms. Thirty subjects were withdrawn for 30 days with amantadine, bromocriptine, or placebo. Bromocriptine and amantadine were more effective than placebo for 15 days. Amantadine's effectiveness then declined so that it was no more effective than placebo by experiment's end. Bromocriptine was significantly more effective than both throughout the latter phase of the study. Amantadine's decline in effectiveness is hypothesized to be due to stimulation of dopamine release.

Response by the neurotensin systems of the basal ganglia to cocaine treatment

Multiple administrations of high doses of cocaine had profound effects on the neurotensin (NT) systems of the basal ganglia. Approximately 200-300% increases in striatal content of neurotensin-like immunoreactivity (NTLI) were observed 1-8 h following five doses of 30 mg/kg per dose of cocaine. The effect subsided by 48 h after treatment. Significant changes in striatal NTLI levels were not observed after a single dose of this stimulant. The nigral NT systems appeared to be even more sensitive to cocaine administration. Compared to striatal changes, increases in nigral NTLI content were greater (as much as 455% of control), required lower cocaine doses (20 mg/kg per dose), lasted longer (still elevated to 200% of control after 48 h) and were significant following a single cocaine exposure. The response of the striatal NT systems to cocaine appeared to be mediated principally by dopamine D-1 receptors, while both D-1 and D-2 receptors contributed to the response by the nigral NT projections. Specific dopamine, but not serotonin, uptake blockers caused increases in striatal and nigral NTLI concentrations similar to that seen with cocaine treatments, suggesting that interference with the dopamine uptake carrier complex by cocaine was responsible for its actions on extrapyramidal NT systems.

Prenatal cocaine exposure fails to modify neurobehavioral responses and the striatal dopaminergic system in newborn rats

1. The effects of cocaine on locomotor activity and striatal dopaminergic receptors and dopamine turnover were studied in rat pups exposed to cocaine (30 mg/kg/day) throughout the entire gestational period. 2. Prenatal exposure to cocaine did not alter the motor coordination or spontaneous locomotor activity in the offspring. 3. No change in the characteristics of dopaminergic receptors and the rate of dopamine turnover was detected in the striatum.

Cocaine: an in vivo microdialysis evaluation of its acute action on dopamine transmission in rat striatum

The effects of cocaine on dopamine (DA) neurotransmission were evaluated by in vivo microdialysis in the striatum of halothane-anesthetized rats. Intravenous cocaine produced a dose-dependent, transient increase of the extracellular concentration of DA, with a peak response within 10 min and a return to control level by 30 min. The sharp DA response pattern was abolished in a calcium-free environment, indicating that DA release enhanced by cocaine originates from a vesicular storage pool. Continuous administration of cocaine (via the perfusion medium) directly into the nigrostriatal terminal region also produced a dose-dependent increase in DA release. Low concentrations (10(-5) M and 10(-6) M) of cocaine maintained DA at a constant stable level, consistent with the effects observed after potent DA uptake inhibitory agents (e.g., nomifensine and Lu19005). However, continuous exposure to high concentrations (greater than or equal to 10(-4) M) induced a transient elevation of DA within 20 min, following which DA decreased to a stable but high level; this decrease might reflect tolerance to the effect of cocaine. Administration of cocaine (10(-3) M) into the substantia nigra did not change striatal DA release. The local striatal action of cocaine was less potent than amphetamine in elevating DA overflow and in its effect on DA metabolism. These findings suggest that the fast transient enhancement of DA by intravenous cocaine is most likely a consequence of the transient presence of cocaine in the terminal region, correlating with the well-known rapid pharmacokinetic and behavioral aspects of the drug.

Effects of cocaine on release and uptake of dopamine in vivo: differentiation by mathematical modeling

Although considerable effort has been invested trying to distinguish between the effects of cocaine on dopamine (DA) uptake and release in both in vitro and in vivo experiments, disagreement over the specific actions of cocaine remains. The results obtained by combining experimental extracellular DA data with a mathematical model of the dopaminergic neuron allow examination of the cocaine uptake inhibition/release question. The extracellular DA concentration profile observed following a 30 mg/kg IP cocaine injection can be modeled if both pre- and postsynaptic uptake are competitively inhibited by cocaine with or without an enhanced DA release effect. However, if cocaine elicits enhanced DA release, modeling predicts a 40% increase over basal levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and a 30% increase in homovanillic acid (HVA) at 60 minutes following a 30 mg/kg IP cocaine injection. Reported DOPAC and HVA data for similar cocaine doses indicate little change in either DOPAC or HVA. These data agree best with modeled metabolite predictions for little or no cocaine-enhanced DA release.

Bromocriptine-desipramine protocol in treatment of cocaine addiction

Thirty-six male cocaine abusers, in withdrawal, were studied for 99 days in a double-blind design. Treatment with bromocriptine was significantly more effective than placebo in alleviating withdrawal symptoms. Adding desipramine to the bromocriptine regimen was significantly more effective than either placebo or bromocriptine alone. The authors hypothesize that these results support a model of dopamine depletion and receptor supersensitivity in cocaine withdrawal.

Bromocriptine therapy in cocaine withdrawal

Twenty-four cocaine addicts who experienced withdrawal symptoms were studied for six weeks in a double-blind design. Half of the group received daily treatment with bromocriptine and the other half with placebo. Significant relief with bromocriptine was seen almost immediately and continued throughout the detoxification period. The authors speculate that the results are consistent with the "dopamine-depletion model" of cocaine withdrawal.

Space-based abstinence: alleviation of withdrawal symptoms in combinative cocaine-phencyclidine abuse

Twenty male combinative cocaine free-base/phencyclidine (space-base) abusers were studied for forty-five days, in a double-blind design. Treatment with desipramine was significantly more effective than placebo in alleviating abstinence symptoms. This study tends to support the catecholamine-depletion hypothesis of cocaine and phencyclidine withdrawal.

Structural requirements for cocaine congeners to interact with dopamine and serotonin uptake sites in mouse brain and to induce stereotyped behavior

We report here saturation analysis of [3H]cocaine binding in various mouse brain regions, and the necessary structure-activity relationships for cocaine congeners to inhibit Na+-dependent [3H]cocaine binding and [3H]dopamine uptake in the mouse striatum, and to inhibit [3H]cocaine binding that cannot be stimulated by Na+ and [3H]serotonin uptake in the mouse cerebral cortex. Generally similar structure-activity relationships were noted for all these processes. The ester linkage between the tropane and phenyl rings was not required for activity, in contrast to the configuration of the groups on C2, and to a lesser extent C3, in the tropane ring. Stereospecificity was evident from the differences between cocaine and (+)-pseudococaine, and between WIN 35,065-2 and WIN 35,065-3. There were remarkable differences between the above structure-activity relationships and those for local anesthetic activity of cocaine congeners, indicating that sodium channels were not labeled to a measurable extent with [3H]cocaine under the present conditions. Preliminary data indicated a significant correlation between the potencies of cocaine congeners in inhibiting the Na+-dependent binding of [3H]cocaine and their potencies in inducing stereotyped sniffing upon intraventricular administration.

Locomotor effects of cocaine, cocaine congeners, and local anesthetics in mice

Spontaneous locomotor activity of mice was stimulated by IP administration of cocaine and its closely related phenyltropane analogs. In contrast, locomotion was inhibited by IP administration of cocaine congeners such as norcocaine, (+)-pseudococaine, and tropacocaine, and of isomers of phenyltropane analogs. Also inhibitory were the local anesthetics procaine, tetracaine, benzocaine, lidocaine, and prilocaine. The locomotor inhibition induced by IP norcocaine or tetracaine could be reversed by subsequent treatment with cocaine. Both cocaine and norcocaine were centrally stimulatory when injected intracerebroventricularly. The rank order of potencies of cocaine congeners and local anesthetics in depressing locomotion was similar to that of their potencies in interacting with sodium channels. From these results we infer that the locomotor depression induced by systemic administration of cocaine congeners results from a local anesthetic action involving inhibition of the ion conductance of sodium channels.

New concepts in cocaine addiction: the dopamine depletion hypothesis

Euphoric properties of cocaine lead to the development of chronic abuse, and appear to involve the acute activation of central DA neuronal systems. This is based upon known effects of cocaine on DA neurons, and the role played by DA in reward states and self-stimulation behavior. With chronic cocaine use, neurotransmitter and neuroendocrine alterations occur. DA depletion is hypothesized to result from overstimulation of these neurons and excessive synaptic metabolism of the neurotransmitter. DA depletion may underlie dysphoric aspects of cocaine abstinence, and cocaine urges. Neurochemical disruptions caused by cocaine are consistent with the concept of "physical" rather than "psychological" addiction. Possible pharmacological interventions in cocaine addiction are outlined and the psychological approach to these patients is discussed.

Classical conditioning, decay and extinction of cocaine-induced hyperactivity and stereotypy

Following 10 daily pairings of multiple conditioned stimuli with injection of cocaine (15 mg/kg), the presentation of the stimuli alone elicited behaviors in rats similar to those induced by cocaine. The behaviors included increased duration or frequency of rearing, sniffing, head bobbing, and horizontal locomotor activity (crossing). The level of the conditioned response for several of these behaviors approximated that induced by the drug itself. The conditioned drug effect showed decay over 15 days but little extinction during 4 daily trials. Brain concentrations of the dopamine metabolites, homovanillic acid and dihydroxyphenylacetic acid, were similar in the conditioned and pseudoconditioned control groups in both the caudate and mesolimbic areas. The behavioral results demonstrate that, in a classical conditioning paradigm, previously neutral stimuli can elicit behaviors similar to those induced by cocaine and that certain conditioned responses show time related decline. This agrees with the reported conditioning of amphetamine's behavioral effects but differs in terms of the action on brain dopamine turnover.

Sensitization to the behavioral effects of cocaine: modification by Pavlovian conditioning

Sensitization to the behavioral effects of cocaine was more pronounced following drug administration in the presence of cues previously associated with cocaine administration than in their absence. Furthermore, sensitization was attenuated by repeated presentations of the usual predrug cues followed only by saline, i.e. sensitization was extinguishable. These findings indicate that Pavlovian conditioning contributes to sensitization, and have implications for treatment of stimulant abuse.