Cocaine and Cocaethylene: Microdialysis Comparison of Brain Drug Levels and Effects on Dopamine and Serotonin

Abstract: Cocaethylene is a pharmacologically active metabolite resulting from concurrent cocaine and ethanol consumption. The effects of cocaine and cocaethylene on extracellular levels of dopamine in the nucleus accumbens, and serotonin in the striatum were characterized in vivo in the anesthetized rat. Both intravenous (3 μmol/kg) and intraperitoneal (44 μmol/kg) routes of administration were used. In addition to monitoring neurotransmitter levels, microdialysate levels of cocaine and cocaethylene were determined at 4-min intervals after intravenous administration, and at 20-min intervals after intraperitoneal administration. Extracellular levels of dopamine in the nucleus accumbens were increased to ∼400% of preinjection value by both cocaine and cocaethylene when administered intravenously. Cocaine caused a significant increase of striatal serotonin to 200% preinjection value, whereas cocaethylene had no effect. Brain levels of cocaine and cocaethylene after intravenous administration did not differ. After intraperitoneal administration, extracellular levels of dopamine in the nucleus accumbens were increased to 400% of preinjection levels by cocaine, but were only increased to 200% of preinjection levels by cocaethylene, the difference being statistically significant. Serotonin levels were increased to 360% of preinjection levels by cocaine, but only to 175% of preinjection value by cocaethylene. Levels of cocaine attained in brain were significantly higher than those for cocaethylene, suggesting pharmacokinetic differences with the intraperitoneal route. These results confirm in vivo that cocaethylene is more selective in its actions than cocaine with respect to dopamine and serotonin uptake. In addition, route-dependent differences in attainment of brain drug levels have been observed that may impact on interpretations of the relative potency of the reinforcement value of these compounds.     

The effect of adrenalectomy upon the absorption,distribution and metabolism of ethanol in the rat

There was an increase in blood ethanol levels following the intraperitoneal or intravenous administration of ethanol to rats 8 days after adrenalectomy, compared to control animals. This was due to a 20% decrease in total body water and an increased rate of absorption following intraperitoneal administration. There was no change in the rate of ethanol metabolism.     

In Vivo Microdialysis as a Technique to Monitor Drug Transport: Correlation of Extracellular Cocaine Levels and Dopamine Overflow in the Rat Brain

A sensitive and rapid HPLC-UV method for in vivo determinations of cocaine levels in extracellular fluid of specific brain regions and plasma is described. Free drug levels resulting from intravenous administration of cocaine were sampled using in vivo microdialysis probes simultaneously located in the jugular vein, nucleus accumbens, and anteromedial caudate-putamen of halothane-anesthetized rats. In a separate group of animals, the influence of cocaine on extracellular dopamine concentrations in the anteromedial caudate-putamen was also assessed. The time dependences of changes in cocaine concentration in each of the above regions were congruent, and peak concentrations were reached 10 min after the drug was administered. The half-lives of cocaine in the blood, nucleus accumbens, and anteromedial caudate-putamen were estimated to be 31.5, 29.1, and 21.4 min, respectively. A repeated injection of cocaine, given 90 min later, produced a maximal cocaine level and pharmacokinetic profile that were indistinguishable from those of the initial infusion. Cocaine was concentrated to a greater extent in brain than in blood, a feature consistent with the action of a lipophilic drug. In addition, extracellular dopamine levels measured in the anteromedial caudate-putamen following cocaine infusions closely mirrored those of cocaine itself. The ability to measure the free concentration of drugs by microdialysis should be applicable to a wide range of in vivo pharmacological studies.     

Effect of acute or daily cocaine administration on cellular immune response and virus infection in mice

The effects of in vivo cocaine administrations on cellular cytotoxicity were studied. Cocaine induced a dose-related immunosuppression of natural killer cell activity, with maximal depression at 1-5 mg/kg. In addition, the degree of inhibition following a single intraperitoneal (i.p.) or intravenous cocaine dose (acute treatment, 1 mg/kg) was similar to that after repeated administration (subchronic treatment: 1 mg/kg/day i.p. for 7 consecutive days or subcutaneous administration by Alzet 2001 osmotic minipumps). T cells from cocaine-treated mice failed to generate cytotoxic T lymphocytes (CTL) in mixed lymphocyte cultures and acute or subchronic cocaine treatment also inhibited CTL generation in vivo. On the other hand, acute administration induced a very rapid (24-hour) inhibition of natural cytotoxicity, with a return to normal within 72 h after treatment. By contrast, repeated doses led to more protracted immunologic consequences and a delayed recovery (144 h). The effect of cocaine on susceptibility to influenza virus (PR8) infection was also investigated. Both acute and subchronic treatment significantly decreased resistance to PR8 infection. The results clearly indicate that cocaine has a potent suppressive effect on cellular immunity and that abuse can adversely affect the outcome of infectious diseases.     

Long-term continuous intraperitoneal insulin treatment in brittle diabetes.

Attempts to achieve a fair metabolic equilibrium in a young woman with brittle diabetes by continuous subcutaneous, intramuscular, and continuous intravenous administration of insulin were unsuccessful. Continuous intraperitoneal administration of insulin through a permanently inserted polyethylene catheter connected to an open-loop peristaltic pump led to an appreciable improvement in mean blood glucose concentration, mean amplitude of glycaemic excursions, and M value and to normalisation of intermediate metabolic products. The peritoneal catheter was well tolerated for over 120 days without appreciable adverse effects. This case suggests that long-term intraperitoneal administration of insulin is a feasible therapeutic approach in the management of brittle diabetes.     

EFFECT OF DRUGS ON RAT BRAIN, CEREBROSPINAL FLUID AND BLOOD GABA CONTENT

Acute administration of GABA transaminase inhibitors to rats results in a dose-dependent increase in both brain and blood GABA content and administration of isonicotinic acid hydrazide (INH), at a dose which decreases the amount of brain GABA, also lowers blood levels of this amino acid. Chronic treatment (10 days) with INH (20mg/kg), y-acetylenic-GABA (10 mg/kg) or aminooxyacetic acid (AOAA) (10 mg/kg) results in a significant elevation in both rat brain and blood GABA concentrations. At the doses studied, only AOAA caused a significant elevation in CSF GABA content. Co-administration of pyridoxal phosphate (2 mg/kg) blocks the chronic INH-induced rise in blood GABA but does not affect the increase in brain content of this amino acid. Chronic administration of di-n-propylacetate (20 mg/kg) did not significantly alter brain, blood or CSF GABA levels. The results suggest that, under the proper conditions, changes in blood GABA levels after administration of inhibitors of GABA synthesis or degradation may be an indirect indicator of changes in the brain content of this amino acid. Blood GABA determinations may be useful for studying the biochemical effectiveness of GABA transaminase inhibitors in man.     

Effects of low dose cocaine on REM sleep in the freely moving rat

Cocaine administration can be disruptive to sleep. In compulsive cocaine users, sleep disruption may be a factor contributing to relapse. The effects of cocaine on sleep, particularly those produced by low doses, have not been extensively studied. Low dose cocaine may stimulate brain reward systems that are linked to the liability of abusing of this drug. This study was designed to assess the effects of the acute administration of low to moderate cocaine doses on sleep in the rat. Polygraphic recordings were obtained from freely moving, chronically instrumented rats over a 6-h period after the administration of either cocaine (as a 2.5-10 mg/kg intraperitoneal dose) or saline. Following cocaine administration, time spent by the rats in wakefulness increased and slow wave sleep decreased in a dose-dependent manner, compared to controls. These changes lasted between 1 to 3 h following the cocaine administration. Rapid eye movement (REM) sleep was decreased during a 2- to 3-h period following the injection of 5 and 10 mg/kg doses of cocaine. In contrast, REM sleep increased during the periods 2-4 h after the administration of 2.5 and 5 mg/kg doses of cocaine. These results indicate that sleep can be significantly altered by low doses of cocaine when administered subacutely.     

Systemic cocaine challenge after chronic cocaine treatment reveals sensitization of extracellular dopamine levels in nucleus accumbens but direct cocaine perfusion into nucleus accumbens does not: implications for the neural locus of cocaine sensitization

Rats were treated chronically with 20 mg/kg/day cocaine (by intraperitoneal injection) for 16 days, followed by 7 days of cocaine wash-out. On the next day, rats were challenged with an acute dose of cocaine administered by one of two routes (systemic or intracranial), and extracellular dopamine (DA) in the nucleus accumbens (Acb) was measured by in vivo microdialysis. Rats acutely challenged systemically with 20 mg/kg cocaine showed enhanced Acb extracellular DA levels (compared to control rats that had not previously received chronic cocaine). However, rats acutely challenged with intracranial cocaine by perfusion of 10⁻⁵ M cocaine directly into the Acb did not. It is suggested that both the development and triggering of cocaine sensitization, as manifested by enhanced Acb DA content to subsequent acute cocaine challenge, may involve more than just neural mechanisms occurring locally within the Acb.     

Chronic cocaine administration decreases norepinephrine-induced phosphoinositide hydrolysis in rat aorta.

The effect of chronic cocaine administration on norepinephrine stimulated hydrolysis of inositol 1,4,5-trisphosphate from the membrane phosphatidylinositol phosphate pool in isolated rat aorta was investigated. Rats received saline (controls), or 10 or 20 mg/kg cocaine once a day for 15 days. This treatment resulted in a dose-dependent reduction in norepinephrine (0.36 microM) stimulated phosphoinositide hydrolysis. The effect of acute cocaine was determined by adding 30 microM cocaine to the in vitro incubation solution. When aortas were exposed to cocaine and norepinephrine simultaneously, in vitro, inositol phosphate formation doubled. By itself, cocaine did not affect phosphoinositide hydrolysis. Contraction of aortic helical strips by norepinephrine decreased in tissues from rats chronically treated with 20 mg/kg cocaine. In vitro cocaine shifted the norepinephrine concentration/response curve to the left and increased the maximum response. Neither acute nor chronic cocaine treatment affected prazosin's apparent dissociation constant, suggesting that cocaine did not affect receptor affinity. These data suggest that chronic, but not acute cocaine administration may interfere with pharmacomechanical coupling in rat aorta.     

Tissue distribution of cocaine in the pregnant rat

Cocaine hydrochloride was administered by single intraperitoneal (IP) doses to pregnant rats at day 18 or 19 of gestation. Plasma and tissue cocaine and norcocaine concentrations were measured by high-pressure liquid chromatography. Pharmacokinetic analysis of concentration versus time data showed rapid distribution of cocaine and its metabolite to maternal and fetal tissues. The area under the cocaine concentration versus time curve (AUC) in fetus compared to maternal plasma was 3.33. The half-life of cocaine in the maternal plasma and fetus was 46 and 55 minutes, respectively, similar to values reported for cocaine elimination half-life in human plasma. The order of cocaine concentrations was placenta greater than fetal liver greater than maternal heart greater than whole fetus greater than fetal brain greater than maternal brain = maternal plasma. Norcocaine concentrations were usually less than 20% of cocaine concentrations in plasma and tissues. These results support extensive fetal exposure to cocaine following administration to pregnant rodents. Pharmacodynamic studies of cocaine in pregnancy should consider the effects of the drug on the developing fetus.     

Cocaine induced secretion of ACTH, beta-endorphin, and corticosterone

The effect of intraperitoneal administration of cocaine on the concentrations of hypothalamic corticotropin releasing factor like-immunoreactivity (CRF-LI), plasma ACTH, beta-endorphin, and corticosterone was investigated. Groups of rats were injected with 20 mg/kg cocaine HCI or 0.9% NaCl and then killed 0, 10, 20, 30 or 60 minutes later. Hypothalamic CRF-LI, plasma ACTH, beta-endorphin, and corticosterone concentrations were determined by radioimmunoassay. A significant increase in plasma ACTH, beta-endorphin, and corticosterone concentrations was observed after cocaine administration. In contrast, cocaine had no significant effect on hypothalamic CRF-LI concentrations. Intravenous administration of 0.5 and 2.0 mg/kg cocaine to rats in which the endogenous release of CRF was blocked by chlorpromazine, morphine, and pentobarbital elicited a significant increase in plasma corticosterone concentrations. These results demonstrate that cocaine induces the release of ACTH, beta-endorphin, and corticosterone and suggest that this response is mediated at the pituitary level.     

Small Rises in Plasma Choline Reverse the Negative Arteriovenous Difference of Brain Choline

The concentrations of free choline in blood plasma from a peripheral artery and from the transverse sinus, in the CSF, and in total brain homogenate, have been measured in untreated rats and in rats after acute intraperitoneal administration of choline chloride. In untreated rats, the arteriovenous difference of brain choline was related to the arterial choline level. At low arterial blood levels (less than 10 microM) as observed under fasting conditions, the arteriovenous difference was negative (about -2 microM), indicating a net release of choline from the brain of about 1.6 nmol/g/min. In rats with spontaneously high arterial blood levels (greater than 15 microM), the arteriovenous difference was positive, implying a marked net uptake of choline by the brain (3.1 nmol/g/min). The CSF choline concentration, which reflects changes in the extracellular choline concentration, also increased with increasing plasma levels and closely paralleled the gradually rising net uptake. Acute administration of 6, 20, or 60 mg of choline chloride/kg caused, in a dose-dependent manner, a sharp rise of the arterial blood levels and the CSF choline, and reversed the arteriovenous difference of choline to markedly positive values. The total free choline in the brain rose only initially and to a quantitatively negligible extent. Thus, the amount of choline taken up by the brain within 30 min was stored almost completely in a metabolized form and was sufficient to sustain the release of choline from the brain as long as the plasma level remained low. We conclude that the extracellular choline concentration of the brain closely parallels fluctuations in the plasma level of choline.(ABSTRACT TRUNCATED AT 250 WORDS)     

In vivo effects of peroxovanadium compounds in BB rats

Peroxovanadium compounds, each containing an oxo ligand, one or two peroxo anions, and an ancillary ligand in the inner coordination sphere of vanadium, were synthesized, crystallized and characterized by⁵¹V NMR as>95% pure. They markedly decreased plasma glucose in insulin-deprived diabetic BB rats, with a nadir occurring between 60 and 100 min after intravenous, intraperitoneal or subcutaneous administration. Plasma glucose was reduced after oral administration in insulin-treated and in insulin-deprived BB rats. When compared to sodium orthovanadate, peroxovanadium compounds exhibited a markedly greater potency on a molar basis, and in relation to their toxicity. Thein vivo potency can be predicted by the degree of phosphotyrosine phosphatase inhibition observedin vitro. These are the first agents other than insulin that can acutely and markedly reduce plasma glucose in hypoinsulinemic diabetic BB rats.Abbreviations V Vanadium - pV peroxovanadium - IRK insulin receptor kinase - PTP phosphotyrosine phosphatase - BW body weight - IV intravenous - IP intraperitoneal - SC subcutaneous     

Dye permeability and alkaline phosphatase activity of testicular capillaries in the postnatal rat

Summary Staining of testicular and epididymal tissues after intravenous, intraperitoneal or subcutaneous administration of a number of dyes was investigated in rats at different stages of postnatal development. After light green injections heavy staining of both testis and epididymis was visible to the naked eye in neonatal animals up to the age of 10 days, while in rats over 15 days old no appreciable staining of the testis could be seen, although the caput epididymis was strongly coloured. From 3–8 hours after subcutaneous acriflavine administration, the nuclei in the blood vessel walls of the testis, as well as the nuclei in the rete testis, tubuli efferentes and caput epididymis, fluoresced in all age groups. The nuclei of the interstitial and tubular cells were stained intensely until the age of 5 days. Thereafter the intensity gradually diminished until the age of 20 days, when no nuclear fluorescence was visible in the seminiferous tubules and even the interstitial nuclei fluoresced weakly or not at all.The histochemical alkaline phosphatase activity of the testicular capillaries was studied by Gomori's method, using fresh and postfixed cryostat sections from postnatal rat testes. The testicular capillaries exhibited appreciable activity at the age of 10 days.On the basis of the present and previous observations on the permeability of the testicular capillaries, the existence of a blood-testis barrier in the puberal and adult rat testis is suggested.Development of the blood-testis barrier and the alkaline phosphatase activity of the testicular capillaries are suggested to reflect general vascular maturation at the beginning of puberty in the rat.Supported by grants from Yrjö Jahnsson's Foundation and P. O. Klingendahl Foundation.     

Extracellular Concentrations of Cocaine and Dopamine Are Enhanced During Chronic Cocaine Administration

Chronic cocaine administration produces significant increases in cocaine-induced locomotor activity and stereotypy. In vivo microdialysis procedures were used to monitor extracellular dopamine (DA) and cocaine concentrations in the nucleus accumbens (N ACC) and cocaine concentrations in plasma of animals that received chronic or acute cocaine treatments. Following a cocaine challenge injection, concentrations of both cocaine and DA increased to significantly higher levels over time in animals that had received daily cocaine injections for 10 or 30 days than in control animals that received daily injections of saline. Concentrations of cocaine and DA in the N ACC reached maximum levels in the first 30 min following a challenge injection of cocaine. The maximum cocaine concentrations of 10- and 30-day chronic animals were, respectively, 186% and 156%, whereas the maximum DA concentrations were 264% and 216% above the maximum values observed in acute control animals. The results indicate that reverse tolerance effects observed following chronic cocaine administration may in part be accounted for by increased cocaine concentrations. Furthermore, chronic cocaine administration (over a 10- or 30-day period) increased the concentration of cocaine detected in plasma above control levels following a challenge injection. The increase in brain concentrations of cocaine in chronic animals is apparently due to increased concentrations of cocaine in plasma. A physiological change occurs in the periphery as a result of chronic cocaine administration that increases cocaine concentrations in plasma, increases extracellular cocaine levels in the brain, and increases the extracellular concentration of DA in the N ACC.     

Effect of prolonged intermittent thyrotropin-releasing hormone administration to fetal and neonatal rats.

Fetal and neonatal rats received daily subcutaneous injections of 10 microgram thyrotropin-releasing hormone (TRH) until 7 or 14 days postnatally. At 70 days the pups were challenged with 1 microgram TRH intravenously via an indwelling jugular cannula. Basal serum thyroxine, triiodothyronine, and thyroid-stimulating hormone (TSH) concentrations did not differ among the three groups. The mean TSH responses as determined by the mean peak TSH concentration and the total TSH response as determined by planimetry were not significantly different, and there was no significant difference in pituitary TSH content following the TRH challenge among the three groups. This study suggests that the integrity of the hypothalamo--pituitary axis in adult rats cannot be affected by the repeated administration of pharmacologic doses of TRH during the perinatal period.     

A warmer ambient temperature increases the passage of interleukin-1beta into the brains of old rats

We have demonstrated that after intraperitoneal lipopolysaccharide (LPS) injection, old rats mount fevers similar to those of young rats at an ambient temperature (Ta) of 31 degrees C, but not at 21 degrees C. The same is true for intraperitoneal or intravenous IL-1beta administration. The underlying mechanism responsible for blunted fever in old rats may be a deficiency in communication between the periphery and the brain. Possibly, peripheral cytokine actions are altered in old rats, such that the signal that reaches the brain is diminished. Here, we hypothesized that at standard laboratory temperatures, not enough IL-1beta is reaching the brain for fever to occur and that a warmer Ta would increase the influx of IL-1beta into the brain, enabling old rats to generate fever. Young (3-5 mo) and old (23-29 mo) Long-Evans rats were maintained for 3 days at either Ta 21 or 31 degrees C prior to intravenous injection with radiolabeled IL-1beta to measure passage across the blood-brain barrier. Young rats showed similar influx of IL-1beta into the brain at the two Tas, but old rats showed significant influx only at the warmer Ta. These data suggest that the lack of fever at a cool Ta may be due to a reduced influx of IL-1beta into the brain.     

Systemic ghrelin sensitizes cocaine-induced hyperlocomotion in rats

The feeding-relevant pathway by which food restriction (FR) augments cocaine action is unknown. Systemic administration of the 28-amino acid acylated peptide ghrelin (1-10 nmol) increases food intake in rats and circulating levels of rat ghrelin are up-regulated by FR. The present experiment examined the impact of repeated administration of ghrelin or vehicle on the subsequent capacity of cocaine to enhance locomotion in rats. Male Sprague-Dawley rats were pretreated daily for seven days with 0, 5 or 10 nmol rat ghrelin (i.p.) in the home cage. On the 8th day, rats were transported to a testing room, placed in a locomotion chamber for 15 min, and then injected (i.p.) with 0, 7.5, or 15 mg/kg cocaine hydrochloride. Locomotor activity was monitored over a 45 min post-cocaine period. Pretreatment with 5 or 10 nmol ghrelin alone did not significantly increase basal locomotion relative to that of the 0 nmol ghrelin group. Rats pretreated with 5 nmol or 10 nmol ghrelin showed an enhanced locomotor response after treatment with 15 mg/kg cocaine relative to rats treated with 0 nmol ghrelin. These results indicate that acute injection of ghrelin, at a feeding-relevant dose, can augment the acute effects of cocaine on locomotion in rats.     

Escalation of cocaine self-administration does not depend on altered cocaine-induced nucleus accumbens dopamine levels

Previous studies showed that prolonged access to cocaine or heroin self-administration (long access, or LgA) produces an escalation in drug intake not observed with limited access to the drug (short access, or ShA). The present experiment employed in vivo microdialysis to test the role of alterations in drug pharmacokinetics and/or efficacy in increasing dopamine (DA) levels in the nucleus accumbens (NAcc) during cocaine intake escalation. In experiment 1, both ShA and LgA rats were challenged with passive intravenous administration of cocaine (0.125-1 mg/injection). Regardless of the doses tested, there was no difference between groups in the ability of cocaine to increase NAcc DA levels and no group differences in the temporal profile of dialysate cocaine levels. In experiment 2, cocaine and DA concentrations were measured during cocaine self-administration. Self-administration produced sustained increases of DA in the NAcc with LgA rats maintaining greater steady levels of DA (750% of baseline) than ShA rats (400% of baseline). The difference in the LgA versus ShA rats was not due to differences in the efficacy of cocaine to elevate DA levels, or in the rate of cocaine metabolism, but was directly related to the amount of self-administered cocaine. These findings show that changes in cocaine efficacy or pharmacokinetics do not play a critical role in cocaine intake escalation.     

Lobeline augments and inhibits cocaine-induced hyperactivity in rats

Lobeline has high affinity for nicotinic receptors and alters presynaptic dopamine storage and release in brain. Moreover, lobeline decreases the reinforcing and locomotor-activating properties of methamphetamine, suggesting that lobeline may be a pharmacotherapy for psychostimulant abuse. This study determined if lobeline alters cocaine-induced hyperactivity and if lobeline alters the induction and/or expression of sensitization to cocaine. On Days 1-12, male rats were administered lobeline (0.3 or 1.0 mg/kg) or saline, placed in an automated activity monitor for 20 min, administered cocaine (10, 20 or 30 mg/kg) or saline and returned to the monitor for 60 min. On Day 13, the effect of lobeline on the induction and expression of sensitization to cocaine was determined. Lobeline did not alter the effect of cocaine after acute injection. However, 1.0 mg/kg lobeline attenuated cocaine (10 and 20 mg/kg)-induced hyperactivity after repeated administration and prevented the development of sensitization to these cocaine doses. Interestingly, 0.3 mg/kg lobeline augmented cocaine (10 mg/kg)-induced hyperactivity after repeated administration. Lobeline did not alter the effect of 30 mg/kg cocaine. The present results indicate a complex interaction of lobeline with cocaine and support other research indicating a role for nicotinic receptors in the development of sensitization to psychostimulants.