Cocaine and "pharmacological kindling" in the rat

Neurologic Complications of Psychomotor Stimulant Abuse

Psychomotor stimulants are drugs that act on the central nervous system (CNS) to increase alertness, elevate mood, and produce a sense of well-being. These drugs also decrease appetite and the need for sleep. Stimulants can enhance stamina and improve performance in tasks that have been impaired by fatigue or boredom. Approved therapeutic applications of stimulants include attention deficit hyperactivity disorder (ADHD), narcolepsy, and obesity. These agents also possess potent reinforcing properties that can result in excessive self-administration and abuse. Chronic use is associated with adverse effects including psychosis, seizures, and cerebrovascular accidents, though these complications usually occur in individuals with preexisting risk factors. This chapter reviews the adverse neurologic consequences of chronic psychomotor stimulant use and abuse, with a focus on two prototypical stimulants methamphetamine and cocaine.

Pattern shift visual evoked potentials in abstinent cocaine-dependent, alcohol-dependent, and cross-dependent patients

The present study evaluated pattern shift visual evoked potential (VEP) amplitudes and latencies in four groups of adult subjects, characterized by the presence/absence of a recent history of alcohol dependence factorially crossed with the presence/absence of a recent history of cocaine dependence. All of the subjects were healthy and uncomplicated by histories of serious head injury, seizures (including drug-related seizures), and major medical, neurological, or psychiatric disorders. The subjects comprising the three patient groups were evaluated after 1 - 5 months of verified abstinence. Analyses of VEPs evoked by checkerboard reversal indicated a main effect of previous cocaine dependence on P100 latency. No main effect of previous alcohol dependence and no alcohol by cocaine dependence interaction were detected. The increased P100 latencies detected in abstinent, cocaine-dependent subjects are most likely related to cerebrovascular and neurological effects of chronic cocaine use.

Electroencephalographic activity and mood in cocaine-dependent outpatients: effects of cocaine cue exposure

Electroencephalographic (EEG) and subjective reactions to cocaine cues were evaluated in 18 cocaine-dependent outpatients, after 14 or fewer days of abstinence, and 16 noncocaine-dependent controls. EEG activity and desire for cocaine were recorded while subjects viewed three 5-min films that featured either cocaine-associated, erotic, or neutral stimuli. Other measures of mood state and cocaine craving, derived from the Mood Adjective Checklist and the Cocaine Craving Questionnaire, respectively, were recorded immediately after each film. Analyses of absolute EEG power within six frequency bands (delta, theta, slow and fast alpha, slow and fast beta) revealed no EEG abnormalities in the cocaine-dependent group under any condition. In both subject groups, the cocaine-associated and erotic films produced a similar reduction in total EEG power. The cocaine-associated and erotic films also produced a similar increase in the self-rated desire for cocaine, but this change only occurred in the cocaine-dependent group.

Development and expression of sensitization to cocaine's reinforcing properties: role of NMDA receptors

Acquisition of cocaine self-administration (0.125, 0.25 or 0.5 mg/kg/infusion) was assessed in rats that had received prior exposure to either saline or amphetamine (2.0 mg/kg). Acquisition of self-administration was dose-dependent, with the highest dose leading to the shortest latency to reliably discriminate between depression of a lever that resulted in drug delivery and an inactive lever. Latency to acquisition of the lever discrimination for rats that had received prior exposure to amphetamine was shorter than for the saline-pretreated counterparts in each cocaine dosage group. This suggests that repeated exposure to this drug prior to self-administration testing sensitized the rats to the reinforcing effects of cocaine. Co-administration of MK-801 (0.25 mg/kg, IP), a non-competitive NMDA antagonist, blocked the ability of chronic exposure to amphetamine to sensitize rats to cocaine. In experienced self-administering rats, acute pretreatment with MK-801 resulted in a loss of discriminative responding. The number of inactive lever responses was consistently higher than the number of active lever responses across all cocaine dosage groups. These data suggest that the NMDA receptor, possibly through interactions with dopamine systems, is critical for both the development and expression of sensitization to cocaine's reinforcing effects produced by intermittent preexposures to amphetamine.

Two types of neuroplasticities in the kindling phenomenon: effects of chronic MK-801 and methamphetamine

Using the low-frequency kindling technique, we studied the effects of chronic MK-801 and chronic methamphetamine (MAP) administration on hippocampal kindling seizure development. In experiment 1, MK-801 (0.05, 0.1 mg/kg i.p.) was administered 2 h before each electrical stimulation until kindling developed into stage-3 seizure. In experiment 2, we started daily electrical stimulations two weeks after the last injection of chronic MAP administration (6 mg/kg/day, 14 days). The number of stimulating pulses required for the triggering of epileptic afterdischarge (pulse-number threshold, PNT) was used as an indicator of the seizure threshold. PNT, afterdischarge duration (ADD) and behavioral seizure stage (BSS) of each induced seizure in the initial stage of kindling; the kindling rates for stage 3 and stage 5 seizures; seizure parameters at the completion of kindling of the drug-treated groups were recorded and compared to the values of each saline-treated control group. Our result showed that MK-801 administration prior to each electrical stimulation selectively and significantly increased PNT in the initial stage of kindling without affecting other seizure parameters. Chronic pretreatment of MAP caused a selective and significant decrease of PNT of the first two stimulations in the kindling process. Taken together with the previous studies, these results suggest that long-term potentiation plays an important role in the development of the excitability of seizure focus but not of the induced seizure's propagation in the hippocampal kindling phenomenon. Clinically MK-801 seems to be a more efficacious drug in preventing the induction of seizures than in suppressing the acquired seizures.

Cocaine-induced behavioral sensitization is not associated with loss of GABA-immunoreactive neurons in the amygdala

We investigated whether cocaine-induced behavioral sensitization (15 mg/kg, twice daily for 7 days) is associated with changes in gamma-aminobutyric acid (GABA) neurons in the lateral-basolateral amygdala of male Sprague-Dawley rats. The number of GABA-immunoreactive neurons in the amygdala did not differ between cocaine- and saline-treated rats. Although some aspects of this behavioral phenomenon parallel the kindling model of epilepsy, limbic alterations in GABA neurons do not appear to be associated with behavioral sensitization to cocaine.

Amphetamine sensitization and amygdala kindling: pharmacological evaluation of catecholaminergic and cholinergic mechanisms

Chronic pharmacological experiments were conducted to evaluate the relationship between sensitization induced by repeated administration of amphetamine (AMPH) and electrical stimulation of the amygdala. While AMPH withdrawal did not influence the kindling process, AMPH administered during the kindling procedure increased the rate at which seizures evolved, and under these conditions withdrawal from chronic AMPH further facilitated the propensity to kindle. Haloperidol (HAL) treatment failed to block the stimulant-induced increase in kindling acquisition indicating that changes in dopamine (DA) are not necessary for the AMPH/kindling synergism to develop. Scopolamine dose-dependently retarded kindling evolution irrespective of prior AMPH pretreatment also ruling out a cholinergic mechanism in the kindling sensitization. Subsequent experiments assessed the interactive effects of AMPH and desipramine (DMI) on the kindling process. Animals chronically exposed to AMPH and switched to DMI treatment during the kindling procedure kindled faster than control subjects. In addition, withdrawal from DMI preexposure advanced the AMPH-induced increase in kindling rate. These results were discussed in terms of the role of norepinephrine-mediated inhibition of the kindling process, and were related to drug-elicited alterations in beta-adrenergic receptor functioning. Taken together, these findings implicate the amygdala as an important structure in the development of non-DA forms of AMPH sensitization.

Genetic factors influence changes in sensitivity to the convulsant properties of cocaine following chronic treatment

Repeated administration of doses of cocaine below the threshold for seizure induction results in the development of an increased susceptibility to cocaine-induced seizures (cocaine-kindling). Genetic differences in susceptibility to cocaine-kindled seizures were evaluated in 4 inbred mouse strains and compared with susceptibility to seizures induced by acute administration of cocaine. The acute administration of cocaine produced convulsant activity in mice from all 4 genotypes, however, there were significant differences in the dose of cocaine required to induce seizures. C57 mice were highly susceptible and SJL mice highly resistant to convulsions induced by acute administration of cocaine, while BALB and DBA mice showed an intermediate degree of seizure susceptibility. The repeated administration of subconvulsant doses of cocaine resulted in rapid sensitization to cocaine-induced seizures. The 4 strains differed in the rate at which sensitization to cocaine-induced seizures developed, with the SJL strain being most sensitive and the C57 strain the least sensitive to the cocaine-kindling process. The susceptibility of the 4 strains to cocaine kindling was virtually opposite to their susceptibility to seizures induced by the acute administration of cocaine, suggesting that different mechanisms may be involved in the control of acute and kindled seizures did not persist upon further exposure to cocaine. Following a period of increased sensitivity to cocaine-induced seizures, tolerance to the convulsant properties of cocaine developed among C57, BALB and DBA mice. Only among the SJL mice did the development of a kindled state persist upon repeated exposure to cocaine. These differences emphasize the potential importance of inheritance in determining the effects of cocaine and suggest novel approaches to understanding the the mechanisms underlying the effects of cocaine.

Anticonvulsant modification of cocaine-induced toxicity in the rat

A number of anticonvulsant drugs were studied for their efficacy in preventing seizures and death from intoxication with cocaine. Rats were first pretreated with the test drug then subjected to large doses of intraperitoneally administered cocaine. In this model, control animals developed seizures in approximately 6 min, followed by death in approximately 10 min. Statistically significant protection against seizures and death was afforded by pretreatment with diazepam, phenobarbitol and the blocker of the uptake of gamma-aminobutyric acid (GABA), SKF 100330A. Only partial protection was afforded by the N-methyl-d-aspartate (NMDA) antagonist MK 801, the benzodiazepine antagonist, flumazenil and the novel aminobenzamide, LY 201116. Valproic acid and phenytoin demonstrated limited efficacy against cocaine-induced seizures, without consistently reducing death. Carbamazepine and ethosuximide did not significantly reduce seizures or death. In this model of acute cocaine toxicity, the anticonvulsants diazepam, phenobarbital and the blocker of the uptake of GABA, SKF 100330A were the most effective in protecting rats from cocaine-induced seizures and death. These data offer insight into future approaches for the treatment of patients with the acute toxic effects of cocaine.

Proconvulsant and anticonvulsant effects in mice of acute and chronic treatment with cocaine

The proconvulsant and anticonvulsant effects of acute and chronic exposure to cocaine were investigated in adult, male, CF-1 mice. The proconvulsant effects of cocaine in mice only manifested themselves after daily exposure to motor-stimulant doses. Although daily treatment decreased electroshock convulsion threshold, no motor convulsions were observed. Animals in the proconvulsant state, however, kindled to electrically-induced convulsions more rapidly than did controls. Furthermore, daily treatment with cocaine and electroshock also enhanced the development of electrical kindling. These results illustrate that the excitatory properties of cocaine in the CNS can enhance phenomena which cause a persistent increase in excitability of the CNS. In contrast to the proconvulsant activity after chronic exposure, cocaine, administered acutely, in motor-stimulant doses, was anticonvulsant in a variety of tests using electroshock and chemically-induced convulsions. The drug elevated electroshock thresholds for both minimal and maximal convulsions and these responses were not blocked by haloperidol. In tests for minimal chemically-induced convulsions, cocaine elevated the threshold to N-methyl-DL-aspartate, but not to bicuculline; against maximal convulsions, the drug was anticonvulsant against both N-methyl-DL-aspartate and bicuculline. Cocaine did not affect convulsion thresholds for strychnine, arecoline or aminophylline; these data suggest that the anticonvulsant action of cocaine is relatively selective for the gamma-aminobutyric acid (GABA) and glutamate systems.

Effect of cocaine and lidocaine on the development of kindled seizures

The effect of a subconvulsive dose of cocaine or lidocaine on the development of kindling was studied in male Long-Evans rats. Animals were divided into three groups and kindled by daily electrical stimulation of the pyriform cortex. Fifteen minutes before each stimulation each animal received an intraperitoneal injection of either saline, 20 mg/kg cocaine hydrochloride, or 20 mg/kg lidocaine hydrochloride. Following kindling the drug treatment was discontinued and the transfer of kindling to a nondrug state was assessed by test stimulations given 2, 6, and 48 days after the last day of kindling. Both cocaine and lidocaine dramatically accelerated the development of kindling. Furthermore, the duration of clonus at kindling criterion was significantly longer in lidocaine-treated animals than in animals treated with saline, and the onset of clonus in cocaine-treated animals occurred significantly sooner after stimulation. However, this performance did not transfer fully to the nondrug state, with some animals failing to exhibit clonus. Among those animals exhibiting clonus at nondrug tests, afterdischarge duration was significantly higher in cocaine-treated than in saline-treated animals, but clonus duration was no longer elevated in lidocaine-treated animals, and the latency to clonus rose dramatically in animals previously treated with either cocaine or lidocaine. These results indicate that a subconvulsive dose of cocaine or lidocaine can facilitate the development of kindling when the drug is active at the time of electrical stimulation, apparently by means of the local anesthetic action shared by the two drugs. The kindling produced in this fashion is not entirely equivalent to kindling produced by electrical stimulation alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Formamidine pesticides enhance susceptibility to kindled seizures in amygdala and hippocampus of the rat

Electrical kindling of the amygdala and hippocampus was used to evaluate the effects of two formamidines, chlordimeform (CDF) and amitraz (AMZ), upon seizures susceptibility in the rat. Male Long-Evans rats were implanted with electrodes in the amygdala or dorsal dentate gyrus, and injected IP daily with 40 mg/kg CDF, 50 mg/kg AMZ, or equal volumes of their respective vehicles. Afterdischarge (AD) thresholds were determined after the first injection. Animals were then stimulated twice daily, 2 and 4 hours postinjeciton, at a standard 200 microA stimulus intensity until three stage 5 generalized seizures ensued. Both CDF and AMZ significantly facilitated amygdaloid kindling rate, and CDF also facilitated hippocampal kindling rate. The effects of AMZ on hippocampal kindling were not assessed. AD durations were prolonged in the formamidine-treated groups, but there was no effect on AD thresholds. The alpha-2 adrenergic agonist and/or local anesthetic-like properties of these compounds may be responsible for these seizure enhancing effects.

Evidence for a relationship between amphetamine sensitization and electrical kindling of the amygdala

Several schedules of long-term amphetamine administration were evaluated on the development of kindling from the amygdala. Consistent with earlier work involving the effects of chronic exposure to stimulant drugs, withdrawal from chronic amphetamine treatment had little or no effect on kindling. Facilitation of kindling was observed, however, under several schedules of drug treatment. The synergism between amphetamine and kindling was evident during drug schedules in which animals were maintained on drug treatment during the kindling procedure. Under these conditions, the facilitating effects of repeated amphetamine treatment varied as a function of prior experience with the drug. Our findings indicate a relationship between processes involved in amphetamine sensitization and kindling. These data have implications in relation to behavioral observations involving the development of postamphetamine depression during drug withdrawal, and amphetamine sensitization after drug challenge.

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.