Cocaine: tolerance to its convulsant and cardiorespiratory stimulating effects in the monkey

Amelioration of the cardiovascular effects of cocaine in rhesus monkeys by a long-acting mutant form of cocaine esterase

A long-acting mutant form of a naturally occurring bacterial cocaine esterase (T172R/G173Q CocE; double mutant CocE (DM CocE)) has previously been shown to antagonize the reinforcing, convulsant, and lethal effects of cocaine in rodents. However, the effectiveness and therapeutic characteristics of DM CocE in nonhuman primates, in a more clinically relevant context, are unknown. The current studies were aimed at (1) characterizing the cardiovascular effects of cocaine in freely moving rhesus monkeys, (2) evaluating the capacity of DM CocE to ameliorate these cocaine-induced cardiovascular effects when administered 10 min after cocaine, and (3) assessing the immunological responses of monkeys to DM CocE following repeated administration. Intravenous administration of cocaine produced dose-dependent increases in mean arterial pressure (MAP) and heart rate (HR) that persisted throughout the 2-h observation period following a dose of 3.2 mg/kg cocaine. Cocaine failed to produce reliable changes in electrocardiograph (ECG) parameters, body temperature, and locomotor activity. DM CocE produced a rapid and dose-dependent amelioration of the cardiovascular effects, with saline-like MAP measures restored within 5-10 min, and saline-like HR measures restored within 20-40 min of DM CocE administration. Although administration of DM CocE produced increases in anti-CocE antibodies, they did not appear to have a neutralizing effect on the capacity of DM CocE to reverse the cardiovascular effects of cocaine. In conclusion, these findings in monkeys provide strong evidence to suggest that highly efficient cocaine esterases, such as DM CocE, can provide a potential therapeutic option for treatment of acute cocaine intoxication in humans.

Cocaine-induced breakdown of the blood-brain barrier and neurotoxicity

Role of cocaine in influencing blood-brain barrier (BBB) function is still unknown. Available evidences suggest that cocaine administration results in acute hyperthermia and alterations in brain serotonin metabolism. Since hyperthermia is capable to induce the breakdown of the BBB either directly or through altered serotonin metabolism, a possibility exists that cocaine may induce neurotoxicity by causing BBB disruption. This hypothesis is discussed in this review largely based on our own laboratory investigations. Our observations in rats demonstrate that cocaine depending on the dose and routes of administration induces profound hyperthermia, increased plasma and brain serotonin levels leading to BBB breakdown and brain edema formation. Furthermore, cocaine was able to enhance cellular stress as seen by upregulation of heat shock protein (HSP 72 kD) expression and resulted in marked neuronal and glial cell damages at the time of the BBB dysfunction. Taken together, these observations are the first to suggest that cocaine-induced BBB disruption is instrumental in precipitating brain pathology. The possible mechanisms of cocaine-induced BBB breakdown and neurotoxicity are discussed.

Effect of binge cocaine treatment on hindlimb vascular function

Chronic cocaine abuse is known to cause endothelial dysfunction and atherosclerosis. The present study investigated the effect of binge cocaine treatment, a model for chronic cocaine abuse, on the blood flow responses to the adrenergic agonists norepinephrine, phenylephrine and isoproterenol, the endothelium-dependent vasodilator acetylcholine, and the endothelium independent vasodilator sodium nitroprusside (SNP) in the hindlimb vascular bed of male Sprague Dawley rats. Rats received either single binge or double binge treatment. Each binge treatment consisted of three doses of cocaine (30 mg kg(-1) i.p.) for 3 days. For double binge treatment, there was a 4 day recovery period between the binges. At the end of the treatment the rats were anesthetized and agonists were administered into the right hindlimb circulation through a catheter in the left iliac artery and blood flow responses were measured with a flow probe around the right iliac artery. Rats receiving double cocaine binges showed a significant decrease in the magnitude and duration of the blood flow response to norepinephrine and a decrease in the duration of the blood flow response to phenylephrine, isoproterenol and acetylcholine when compared with saline controls. The blood flow response to SNP was not changed. Total plasma nitrate-nitrite levels were significantly reduced and big endothelin levels were significantly increased in rats receiving double cocaine binges. This study demonstrates that binge cocaine treatment can alter endothelial function, while not changing smooth muscle function, and impairs the adrenergic pathway.

The effects of cocaine on gonadal steroid hormones and LH in male and female rhesus monkeys

Cocaine stimulates significant increases in estradiol, testosterone (T), and luteinizing hormone (LH) in rhesus monkeys, but the temporal interactions between the gonadal steroid hormones and LH have not been determined. The effects of i.v. cocaine (0.8 mg/kg) or saline placebo administration on estradiol, T, and LH were compared in follicular phase female and male rhesus monkeys. Samples for hormone analysis were collected at 2-min intervals for 20 min, then at 10-min intervals for 50 min. Peak plasma cocaine levels were detected at 4 min and pharmacokinetic analyses showed no significant gender differences. Baseline hormone levels were equivalent before saline and cocaine administration, and saline did not alter LH or estradiol levels. In females, when baseline estradiol levels were low (< 100 pg/ml), LH increased significantly within 8 min after cocaine administration (P < 0.05), but when baseline estradiol levels were high (> 100 pg/ml), LH levels did not change significantly after cocaine administration. Estradiol and T increased significantly after LH, within 16 min after cocaine administration (P < 0.01-0.001). In males, significant LH increases were detected at 16 min after cocaine administration (P < 0.05-0.001), but estradiol and T did not change significantly. Thus, cocaine may stimulate significant increases in estradiol and T in females but not in males. These rapid hormonal changes may contribute to cocaine's abuse-related effects, as well as to disruptions of the menstrual cycle during chronic cocaine administration.

Ovarian steroid hormone modulation of the acute effects of cocaine on luteinizing hormone and prolactin levels in ovariectomized rhesus monkeys

Cocaine stimulates significant increases in luteinizing hormone (LH) and decreases prolactin levels in gonadally intact rhesus monkeys, but cocaine did not alter plasma levels of these anterior pituitary hormones in ovariectomized females. These findings suggested that ovarian steroid hormones may contribute to the endocrine effects of acute cocaine administration. To test this hypothesis, the acute effects of cocaine and placebo-cocaine on plasma LH and prolactin levels were examined in five ovariectomized rhesus females during three chronic hormone replacement conditions: 1) estradiol (E2beta) treatment (0.0015-0.006 mg/kg/day i.m.), 2) progesterone treatment (0.32 mg/kg/day i.m.), and 3) combinations of progesterone (0.32 mg/kg/day i.m.) and E2beta (0.002 and 0.004 mg/kg/day i.m.). Cocaine (0.8 mg/kg i.v.) did not alter prolactin or LH in ovariectomized monkeys without ovarian steroid replacement. During chronic estradiol treatment, cocaine produced an estradiol dose-dependent decrease in prolactin. Cocaine also decreased prolactin during treatment with progesterone alone and progesterone + E2beta (0.004 mg/kg/day i.m.). Cocaine stimulated a significant increase in LH during treatment with progesterone alone, but not during treatment with progesterone + E2beta, or three of four estradiol treatment doses. Cocaine pharmacokinetics did not differ as a function of hormone replacement conditions. Together, these data suggest that both E2beta and progesterone modulate cocaine's effects on prolactin, whereas E2beta alone and in combination with progesterone, do not facilitate LH release in response to cocaine in ovariectomized rhesus females.

Cardiovascular disorders associated with cocaine use: myths and truths

Cocaine produces a pattern of cardiovascular responses that are associated with apparent myocardial ischemia, arrhythmias, and other life-threatening complications in some individuals. Despite recent efforts to better understand the causes of cocaine-induced cardiovascular dysfunction, there remain a number of unanswered questions regarding the specific mechanisms by which cocaine elicits hemodynamic responses. This review will describe the actions of cocaine on the cardiovascular system and the evidence for the mechanisms by which cocaine elicits hemodynamic and pathologic responses in humans and animals. The emphasis will be on experimental data that provide the basis for our understanding of the mechanisms of cardiovascular toxicity associated with cocaine. More importantly, this review will identify several controversies regarding the causes of cocaine-induced cardiovascular toxicity that as yet are still debated. The evidence supporting these findings will be described. Finally, this review will outline the obvious deficits in our current concepts regarding the cardiovascular actions of cocaine in hope of encouraging additional studies on this grave problem in our society.

Bufuralol metabolism by guinea pig adrenal and hepatic microsomes

Previous investigations demonstrated that CYP2D16 was expressed at high levels in guinea pig adrenal microsomes. The studies presented here were done to determine whether adrenal metabolism of bufuralol (BUF), a model CYP2D substrate, was similar to that in the liver. Guinea pig adrenal microsomes converted BUF to 1'-hydroxybufuralol (1'-OH-BUF) as the major metabolite and smaller amounts of a compound identified as 6-hydroxybufuralol (6-OH-BUF). In contrast, 6-OH-BUF was the major product formed by hepatic microsomal preparations. The apparent Km values were similar for 1'-OH-BUF and 6-OH-BUF production in each tissue. Quinidine, a selective CYP2D inhibitor, decreased the production of both BUF metabolites equally in liver and adrenal microsomes. Cortisol also caused equivalent decreases in the rates of 1'-OH-BUF and 6-OH-BUF formation by adrenal microsomes, but had no effect on hepatic BUF metabolism. Although both BUF metabolites may be produced by CYP2D16, unknown factors appear to effect some differences in the catalytic characteristics of BUF metabolism in adrenal and liver. The large amount of 6-OH-BUF produced distinguishes BUF metabolism in guinea pigs from that in other species previously studied.

Acute and chronic alcohol-cocaine interactions in rats

The widespread combined use of alcohol and cocaine across the United States underscores the importance of understanding how the actions of those two agents interact upon important physiological regulatory processes. In an experiment exploring acute ethanol-cocaine interactions, 16 rats were given 2.0 g/kg (IP) doses of ethanol at time zero. Two hours later, half of the rats were given cocaine (20 mg/kg, IP), while the other half were given injections of saline. The group given cocaine displayed a prolongation of the hypothermia condition induced by ethanol injection. In a chronic experiment, three groups of rats (n = 6-8) were exposed for an 11-day period to daily IP injections of 10 mg/kg cocaine, 20 mg/kg of cocaine, or saline. On day 12 these groups did not differ in their response to loss of the righting reflex induced by a 3.0 g/kg dose of ethanol. However, recovery from ethanol hypothermia was more rapid in the rats exposed to chronic cocaine. In summary, these initial studies provide evidence for exacerbation of the acute hypothermic effects of ethanol when a cocaine challenge is given 2 h after ethanol. In contrast, ethanol hypothermia was observed to be reduced when tested on day 12 after an 11-day chronic regimen of cocaine. Other dosage regimens and response measures need to be tested to understand the full scope of acute and chronic cocaine-ethanol interactions and the possible health consequences.

Cocaine's effects on neuroendocrine systems: clinical and preclinical studies

This review examines the effects of cocaine on the neuroendocrine system and summarizes findings from clinical studies of cocaine abusers and preclinical studies in rodents and rhesus monkeys. The effects of acute and chronic cocaine administration on anterior pituitary, gonadal, and adrenal hormones are described, and the functional consequences of chronic cocaine exposure are discussed. Many of cocaine's acute effects on the endocrine system are consistent with its actions as a monoamine reuptake inhibitor. Acute cocaine administration stimulates release of gonadotropins, ACTH, and cortisol or corticosterone and suppresses prolactin levels. It has been difficult to detect changes in basal levels of most hormones or alterations in hormone responsiveness to a challenge dose of cocaine or other agents after chronic cocaine treatment. Interpretation of clinical data is often complicated by polydrug abuse involving opiates and alcohol as well as cocaine. However, preclinical studies of the effects of chronic cocaine exposure on integrated neuroendocrine function have revealed disruptions of the estrous cycle in rats and the menstrual cycle in rhesus monkeys. Furthermore, the menstrual cycle disorders observed in rhesus monkeys parallel those reported in women who abuse cocaine. Much remains to be learned about cocaine's interactions with the endocrine system and the consequences of cocaine abuse for reproductive function.

Mechanism of the systemic, left ventricular, and coronary vascular tolerance to a binge of cocaine in conscious dogs

BACKGROUND

Prior experimental studies have emphasized the cardiovascular effects of acute, single doses of cocaine. However, cardiovascular complications are most often reported in chronic users, who have been exposed to repetitive doses of cocaine. It remains unclear whether there is tolerance or sensitization to the systemic, left ventricular, and coronary hemodynamic effects of a binge of cocaine.

METHODS AND RESULTS

We studied 11 conscious, chronically instrumented dogs to determine the systemic pressor, inotropic, chronotropic, and coronary vascular resistance responses to cocaine (1 mg/kg IV) administered every 25 minutes for five doses. There was progressive tolerance to the systemic pressor (mean arterial pressure: first dose, +42 +/- 4% from 97 +/- 2 mm Hg; fifth dose, +8 +/- 3% from 116 +/- 7 mm Hg; P < .01) and heart rate (first dose, +45 +/- 8% from 93 +/- 5 bpm; fifth dose, +8 +/- 2% from 109 +/- 9 bpm; P < .01) responses and abolition of the positive inotropic (left ventricular dP/dt: first dose, +19 +/- 4% from 2824 +/- 75 mm Hg/s; fifth dose, -3 +/- 5% from 2531 +/- 436 mm Hg/s; P < .01) and coronary vasoconstrictor (coronary vascular resistance: first dose, +38 +/- 9% from 1.9 mm Hg.mL-1.min-1; fifth dose, -7 +/- 2% from 2.6 +/- 0.2 mm Hg. mL-1.min-1; P < .01) responses to a binge of cocaine despite progressive increases in peak plasma cocaine concentrations. In contrast, both the plasma norepinephrine and epinephrine responses were attenuated with repetitive exposure to cocaine, whereas myocardial alpha and beta-adrenergic responsiveness was maintained.

CONCLUSIONS

Repetitive cocaine administration is associated with the development of early and progressive tolerance to systemic, left ventricular, and coronary vascular effects of cocaine. The mechanism of the tolerance involves neither impaired myocardial nor coronary vascular responsiveness to adrenergic stimulation but, rather, attenuated catecholamine responses to repetitive cocaine administration.

Tolerance to and residual effects of cocaine in squirrel monkeys depend on reinforcement-schedule parameter

Lever pressing by 4 squirrel monkeys was maintained under a three-component multiple fixed-ratio schedule of food presentation; components differed with respect to ratio size. For each monkey, acute administration of cocaine (0.03 to 1.3 mg/kg, i.m.) produced dose-dependent decreases in overall response rate in each component. During repeated daily administration of 1.0 mg/kg of cocaine, tolerance developed to the rate-decreasing effects under each of the ratio contingencies, but developed to a greater extent and was evident in earlier parts of sessions for performance under the smaller ratios. Response rates of 2 monkeys increased above nondrug control levels despite the putative reinforcer not being consumed during the session. When saline or a smaller dose of cocaine was substituted for 1.0 mg/kg, response rates often were suppressed below nondrug control-level responding. This suppressive effect was observed in each monkey and was more likely to be observed and/or to be of greater magnitude in large-ratio components for 3 of the 4 monkeys. When saline was administered chronically at the end of the chronic-drug phase, response rates remained suppressed in the large-ratio component for 2 of the monkeys. There was, therefore, a schedule-dependent dissociation between behavioral tolerance and the residual effects: Tolerance was greater when small ratios were arranged, whereas the residual effects were more pronounced when larger ratios were arranged.

Subjective response during continuous infusion of cocaine

The relationship between the subjective effects induced by IV cocaine injection(s) and cocaine plasma concentrations is complex and difficult to interpret. We designed a study in which bolus loading doses of cocaine followed by 4-hr placebo infusions were compared with the same bolus loading doses of cocaine followed by 4-hr infusions of cocaine calculated to maintain the peak plasma concentrations produced by the bolus. Seven cocaine-using volunteers were successfully studied using a randomized double-blind design, in which self- and observer-rating scales were used to measure drug effects. After the cocaine bolus loading doses, scores for most subjective measures remained elevated when the bolus was followed by a cocaine infusion. In contrast, the subjective responses returned to baseline when the bolus was followed by a placebo infusion. However, self-estimates of the intensity of the cocaine "rush" were not altered by the presence of active cocaine infusions and returned rapidly to baseline.

Intravenous cocaine: psychiatric effects, biological mechanisms

Volunteer addicts were administered iv loading doses of cocaine, followed by 4-hr cocaine infusions that maintained steady-state conditions. The loading doses were followed by the "rush" and "high" subjective effects that users typically experience; cocaine infusions maintained the experience of drug "high", but not "rush". In a subsequent experiment, haloperidol pretreatment did not alter cocaine "rush" but partially attenuated cocaine "high." During cocaine infusions, we also noted suspicious and paranoid behavior, which were blindly rated by nurses. During one of the infusion conditions, the degree of suspiciousness observed was related to the amount of cocaine previously administered. Although cardiovascular responses to cocaine were marked, we found no alterations in plasma catecholamines following cocaine administrations. Baseline homovanillic acid (HVA) levels, however, were related to the degree of suspiciousness observed following cocaine dosing. The potential contributions of dopaminergic systems and physiological sensitization to the development of the psychiatric toxicity of cocaine are discussed.

Behavioral tolerance to cocaine in squirrel monkeys: acute and chronic effects on complex operant behavior

Four food-deprived squirrel monkeys were trained to emit complex sequences of responses. The sequences involved pressing lighted response keys in orders dictated by colors that illuminated the keys, and ranged in length from two to five responses. Appropriate completion of these behavioral chains could be followed by food presentation. Acute administration of a range of doses (0.1-1.7 mg/kg) of cocaine hydrochloride produced dose-related decreases in the rate of completing chains and in accuracy of performance during chains. There was little evidence that the drug's effects on overall accuracy were related to the length of the chain. Three of the monkeys were exposed to daily administration of a large dose of cocaine, first after daily sessions and then prior to sessions. Daily postsession administration did not alter the dose-effect curves, but daily presession injection did, indicating the development of behavioral or "contingent" tolerance. In all cases, tolerance was accompanied by an increase in reinforcement frequency relative to the frequency observed following acute administration. Omission of the daily dose during presession drug administration resulted in performance near original control levels indicating essentially no withdrawal effect. The findings illustrate the importance of behavioral factors in the development of tolerance to cocaine in a primate.

Effects of chronic treatment of methamphetamine and imipramine on amygdaloid seizure's generation

We assessed the effects of chronic treatment of methamphetamine (1-2 mg/kg/day, i.p., 17 days) and imipramine (2-8 mg/kg/day, p.o., 17 days) on amygdala-generating seizures using the kindling method induced by low-frequency electrical stimulations. The number of stimulating pulses required for the triggering of epileptic afterdischarge (pulse-number threshold: PNT) is the indicator of seizure generating threshold. A PNT elevation followed by its reduction occurred, compared to the pretreatment level, during a 2 mg/kg/day chronic methamphetamine treatment. A reduction in the PNT and triggered afterdischarge durations occurred during a chronic imipramine treatment. These results indicate that both methamphetamine and imipramine reduced the seizure generating threshold by repeated applications. It is suggested that this finding might be related to the psychoactive potency and associated neurochemical changes which are known to be caused by these drugs.

Cocaine tolerance: acute versus chronic effects as dependent upon fixed-ratio size

The effects of cocaine on operant behavior were studied by examining fixed-ratio value as a factor in the development of tolerance. Pigeons pecked a response key under a three-component multiple schedule, with each bird being exposed to fixed-ratio values that were categorized as small, medium, or large. Administered acutely, cocaine (1.0 to 10.0 mg/kg) produced dose-related decreases in overall rate of responding. Responding maintained by the largest ratio was decreased by lower doses than those required to reduce rates of responding maintained by the other two ratio schedules. Following repeated daily administration of 5.6 mg/kg of cocaine, dose-effect functions (obtained from sessions during the chronic regimen by making substitutions for the daily dose) indicated tolerance under the smaller ratios, but no tolerance or less tolerance under the largest ratio. Thus, whether tolerance developed, and the degree to which it developed, depended on the ratio value. The results are partially consistent with the notion that tolerance to drug effects on schedule-controlled behavior will develop if drug administration initially reduces reinforcement frequency, but they indicate that reinforcement loss alone is not a sufficient condition for the generation of tolerance under such conditions. The findings suggest that amount of responding required for reinforcement, or "effort," may contribute to the development of tolerance to effects of cocaine.

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.

Effect of cocaine and pentylenetetrazol on cortical kindling

The effect of drug-induced convulsions on subsequent cortical kindling was studied in male Long-Evans rats. Animals experienced three intravenous infusions of physiological saline at 3 day intervals, or three convulsions induced by the infusion of cocaine or pentylenetetrazol (PTZ). Beginning eight days after the last infusion, all animals were kindled by stimulation of the anterior neocortex (area 6). PTZ-induced convulsions facilitated the development of both the behavioral convulsion and the electrographic seizure during cortical kindling, while cocaine-induced convulsions facilitated only the development of the electrographic seizure. Comparison of these results with previous research indicates that convulsions induced by these two drugs have long-lasting effects on brain function which differ both in their anatomical distribution and in the nature of the effects produced. These drugs also differed in their acute effects at subconvulsant doses on the expression of cortically kindled seizures. Cocaine (and lidocaine, another local anesthetic) substantially elevated afterdischarge (AD) threshold and inhibited the focal component of the cortically kindled seizure. PTZ had no significant effect on either of these variables but significantly increased AD duration. In addition to these drug effects, a substantial inhibitory effect on seizure expression was observed, both during kindling and afterwards, when ADs were elicited daily but not when they were separated by 3 days or more. This finding suggests that the large number of ADs typically required for cortical kindling may be due in part to daily stimulation.

Cocaine: an overview of current issues

A period of ascendancy of cocaine use has had implications in matters of science, public health, and national and international politics and has been the subject of numerous reviews. The present paper provides a critical overview concerning use and prevalence, and addresses a range of current issues of interest. Patterns of use, dose, tolerance, sensitization, routes of administration, and hazards of use are considered based on laboratory, epidemiological, and clinical data. Aspects of treatment are discussed. The need for developing a model of drug abuse recognizing pharmacological-neurochemical-behavioral-environmental interactions is noted. Suggestions are made concerning future directions of policy and research. The need to develop scientific goals and public policy vis-à-vis cocaine, and other stimulants, based on a historical perspective as well as current concerns is emphasized.

Effects of acute and daily cocaine administration on performance under a delayed-matching-to-sample procedure

Food deprived pigeons were trained under a procedure in which trials began with the transillumination of one of three keys by red or green light. Pecking this key extinguished the light behind it and, after a variable delay (0.05, 0.5, 1.0, 2.0, or 4.0 sec), was followed by illumination of the two other keys, one by red light and one by green. Pecks on the key that was the same color as the previously illuminated key could produce access to food. High levels of accuracy were obtained at all delays. The acute and chronic effects of cocaine on performance generated by this procedure (delayed-matching-to-sample) were studied. Acutely, cocaine (0.56-10.0 mg/kg) produced dose-related decreases in accuracy and in rate of completing trials. Accuracy at the longest delay was more sensitive to cocaine's effects. Daily administration of a comparatively large dose (5.6 mg/kg) resulted in tolerance to the rate-reducing and accuracy-reducing effects of large doses.

Intranasal cocaine: dose relationships of psychological effects and plasma levels

We compared the psychological effects of three doses of intranasal cocaine hydrochloride (.2, .75, and 1.5 mg/kg) with cocaine plasma concentrations in four volunteers. Intranasal lidocaine hydrochloride (.2 mg/kg) was used as a topically active placebo. Peak "high" ratings were related to both dose and peak plasma concentrations. At a given plasma concentration, "high" ratings were greater when plasma levels were increasing than when they were decreasing. This indicates that acute tolerance by tachphylaxis occurred after single doses. The cocaine "high" was a pleasant feeling but was without distinctive sensations. The dramatic effects of intranasal cocaine on the street may be related to larger or repeated doses as well as the setting.

Facilitation of kindling by convulsions induced by cocaine or lidocaine but not pentylenetetrazol

The effect of drug-induced convulsions on kindling was studied in male Long-Evans rats. In Experiment 1 rats experienced a single convulsion induced by the intravenous infusion of cocaine, lidocaine, or pentylenetetrazol (PTZ), or received a control infusion of saline. Beginning eight days later all animals were kindled by daily stimulation of the olfactory bulb. Animals which had been convulsed by cocaine or lidocaine kindled significantly faster than either saline controls or PTZ-convulsed animals, which did not differ significantly. Experiment 2 was conducted to determine if an effect of PTZ on kindling could be obtained with repeated convulsions. Rats experienced three convulsions induced by cocaine or PTZ at 72 hr intervals, or control infusions of saline. Kindling began on the eighth day after the last infusion. Cocaine-convulsed animals again kindled significantly faster than saline or PTZ-convulsed animals, which did not differ significantly. The cocaine animals also had significantly longer afterdischarges than the saline group at the end of kindling and when stimulated again 21 days after kindling was completed. These results suggest that the facilitating effect of cocaine-induced convulsions is not a general property of all convulsants but is a more specific effect which is apparently shared by other local anesthetics.

The effect of amygdala kindling on spontaneous and cocaine-induced motor activity and lidocaine seizures

Interactions of amygdala kindling and drug effects were explored in two experiments. Pretreatment with cocaine (40 mg/kg, IP) for 10 days did not significantly affect the rate of amygdala kindling compared to saline or non-kindled controls. In contrast, daily amygdala kindling with 200 microA for 0.5 s for 20 days substantially altered subsequent behavioral responses in a long-lasting fashion. Animals showed decreased spontaneous vertical rearing activity, as well as decreased cocaine-induced vertical activity. In contrast, they were more reactive to the direct dopamine receptor agonist apomorphine. Eighteen days following completion of amygdala kindling, kindled animals were more sensitive to lidocaine-induced convulsions; 88% of kindled animals, but only 24% of the implanted sham-stimulated controls, had seizures. These data suggest that amygdala kindling may produce long-lasting changes in selected spontaneous and drug-induced behaviors, as well as convulsive thresholds. Possible physiological and neurological changes underlying this altered responsivity are discussed.

Differential effects of cocaine on limbic excitability

Effects of cocaine on the initiation and maintenance of electrically induced limbic afterdischarges (AD) were studied in cats. Current thresholds for evoking AD in the hippocampus, amygdala and septal region were determined following alternating saline and cocaine administrations. Three subconvulsant doses (1--10 mg/kg, IM) were tested at 96 hour intervals. The cocaine administrations significantly decreased the current required to initiate AD in both the hippocampus and amygdala. This effect was dose-related; it was found when limbic discharges were localized and also after fully developed motor convulsions were evoked. By contrast, septal AD thresholds were unchanged. In addition, dose-related reductions in AD duration were induced at all limbic sites tested. Restrictions in propagation to distant sites occurred during early stages of seizure development. Progressive changes did not develop following either repeated tests of single-dose effects or during a six week period of daily cocaine administration. These results suggest that cocaine has preferential excitatory effects on closely related limbic structures, increasing the sensitivity of the hippocampus and amygdala to direct electrical stimulation. A concurrent, independent inhibitory action is implied by the reduced duration of limbic afterdischarges. The absence of progressive electrophysiological responses suggests that there is no potentiation of limbic excitatory effects following the repeated administration of doses which do not induce focal epileptiform activity.

Altered response to apomorphine and haloperidol after nine days of cocaine injections

Sprague Dawley rats, pretreated with nine daily injections of 20 mg/Kg cocaine or saline, were evaluated for aspects of their behavioral response to apomorphine, haloperidol, or cocaine, twenty-four hours after their last pretreatment injection. Data obtained from saline and cocaine pretreated animals indicated that: cocaine pretreated rats were more sensitive to haloperidol-induced catalepsy, less responsive to some of the stereotypic effects of apomorphine and similar in their responses to the anticataleptic properties of cocaine.

Four deaths due to intravenous injection of cocaine

Cocaine is a potent psychotropic drug that alters mood and behavior by stimulating the central nervous system. Deaths from abuse of cocaine are relatively rare. Most such deaths appear to be related to the intravenous injection of the drug. Acute fatal cocaine intoxication is characterized by headache, cold sweats, rapid pulse, tremors and nausea, followed by convulsions, unconsciousness and death. The prime mode of death appears to be respiratory paralysis, secondary to the effects of cocaine on the medullary portion of the brain. This paper presents four deaths due to acute cocaine intoxication following intravenous injection. Blood concentrations of cocaine were 0.11, 0.37, 0.36 and 0.75 mg/dl.

Cocaine and pseudococaine: comparative effects on electrical after-discharge in the limbic system of cats

The effects of cocaine and its dextroisomer pseudococaine on electrical after-discharge (AD) evoked by electrical stimulation of the hippocampus or amygdala were studied in cats with electrodes implanted in the brain. Intravenous injection of cocaine (2.0 to 4.0 mg/kg doses) produced a suppressive effect on the AD while producing low-voltage fast waves (LVFWs) in the electrical activities of the brain (EEG) associated with behavioral excitation. In contrast, pseudococaine at the same dose as cocaine failed to show a significant suppressive effect on the AD except at high doses (5.0 mg/kg). Pseudococaine produced high-voltage slow waves (HVSWs) in the EEG associated with behavioral depression. A linear dose-response relationship was observed for the suppressive effect of cocaine on the AD. The results suggested that the limbic system may be involved as a primary site of action of cocaine in the central nervous system (CNS).

Brief communication. Comparative pharmacology of norcocaine in M. mulatta and M. fascicularis

Norcocaine was administered intravenously (0.05, 0.5, 5.0 mg/kg) to three chaired unanesthetized male rhesus monkeys and to three chaired male cynomolgus monkeys. Respiration rate, heart rate and rectal temperature were monitored. In the rhesus monkeys tachycardia and hyperventilation resulted. However, similar qualitative and quantitative changes were not observed in the cynomolgus species. There was a statistically significant difference in the response to norcocaine across species. These results indicate that cynomolgus monkeys are either less sensitive or respond differently than rhesus monkeys to some of the pharmacological effects of norcocaine. Furthermore, these data confirm that norcocaine is an active derivative of cocaine in both rhesus and cynomolgus monkeys.

Alteration in pattern of EEG activities and convulsant effect of cocaine following chronic adminsitration in the rhesus monkey

The effects of chronic administration of high doses of cocaine were studied in monkeys (Ss) with electrodes implanted in the brain. The Ss were injected daily with cocaine at a minimal convulsant dose (MCD) during polygraphic recording of EEGs, eye movement, respiratory and heart rates. The initial cocaine MCDs ranged from 3.2 to 6.5 mg/kg i.v. in ten Ss and markedly increased on each successive day following repeated daily injection (75--100% increase within 5--12 days). The elevated daily cocaine MCD was maintained for 1.5--2 months, and thereafter it gradually decreased and stabilized at levels between 20 and 30% above baseline within 2 months. During this period, the duration of daily convulsions evoked by cocaine MCD markedly decreased and stabilized at a constant level (30--35 sec) along with the latency of convulsions. The pattern of daily convulsions evoked by cocaine MCD changed from multiple episodes of intermittent tonic-clonic convulsions, which occurred during the earlier stage (1--2 months) of chronic treatment, to a single episode of sustained tonic-clonic convulsion. The Ss became extremely placid and tame or were profoundly depressed in their overall behavior most of the time. Simultaneously, the Ss continuously showed persistent rhythmic slow waves (5--6 c/sec) predominantly in the neocortex and limbic system structures. The results strongly suggested that chronic cocaine administration at high doses caused relatively permanent alteration of EEGs and behavior in the Ss, and the limbic system structures played an important role in the effect.

Comparative effects of cocaine and pseudococaine on EEG activities, cardiorespiratory functions, and self-administration behavior in the rhesus monkey

The effects of cocaine and pseudococaine on the EEGs, heart and respiratory rates, and self-administration behavior were studied in rhesus monkeys. An intravenous injection of cocaine (2.5 and 4.0 mg/kg) in the monkey produced low-voltage fast waves (LVFWs) in the EEGs and behavioral hyperexcitation accompanied by marked increases in the heart and respiratory rates with mydriasis and excessive salivation. In contrast, pseudococaine produced high-voltage slow waves (HVSWs) in the EEGs and behavioral depression accompanied by the same symptoms of the autonomic functions as those produced by cocaine. Both isomers were self-administered by the monkeys. During cocaine self-administration sessions, the animals showed hyperexcitation in their overall behavior, while with pseudococaine they showed almost normal behavioral responses. These results suggest that cocaine produced excitatory effects and pseudococaine inhibitory effects on the EEGs and behavior. Both isomers stimulate the heart and respiratory rates, and were self-administered by the monkeys.

Comparison of the convulsant effects of cocaine and pseudococaine in the rhesus monkey

The convulsant effects of cocaine and its C2-epimer, pseudococaine on EEG, respiration, heart rate and behavior were studied in the rhesus monkeys with electrodes implanted in the brain. Intravenous injections of cocaine (3.0 to 8.0 mg/kg) and pseudococaine (3.0 to 7.0 mg/kg) in the animals produced a similar pattern of clonic convulsions accompanied by marked increases in the heart and respiratory rates with mydriasis and excessive salivation. However, both isomers showed different effects on the EEG and animal's behavior following convulsions; e.g., the cocaine-induced convulsions were followed by low-voltage fast waves in the EEGs associated with behavioral hyperexcitation, while pseudococaine-induced convulsions were followed by high-voltage slow waves associated with behavioral depression and drowsiness with intermittent sleep. Pseudococaine was more potent than cocaine in producing convulsions in the same monkeys. The durations of convulsions produced by these drugs were dose-dependent.