Effect of cocaine and lidocaine on the expression of kindled seizures in the rat

Up-regulation of GABA(B) receptor mRNA and protein in the hippocampus of cocaine- and lidocaine-kindled rats

To evaluate the effect of GABA(B) receptor in drug-kindled seizures, the gene expression of GABA(B) receptor in cocaine- and lidocaine-kindled rats was examined in this study. Rats were injected (i.p.) daily with cocaine (55 mg/kg) or lidocaine (65 mg/kg) until they experienced a motor seizure (kindling). After kindling, rats received a 1-day, 10-day, or 30-day drug washout period. The rats in the 1-day washout group were killed after the washout. Those in the 10-day and 30-day groups were challenged either with drug or saline, and killed 24 h later. Control rats were injected and challenged with saline. GABA(B)R1a, 1b and R2 mRNAs in discrete regions of brain were detected by in situ hybridization; GABA(B)R1a protein level was measured by Western blotting. Ninety percent of the cocaine-treated rats and 100% of the lidocaine-treated rats were kindled by day 12. Those rats responded to the challenge cocaine or lidocaine with a motor seizure after the 10-day and 30-day washout. GABA(B) receptor mRNA and protein levels in the hippocampus were significantly increased after the 1-day and 10-day washout, but not the 30-day washout. In addition, the levels in drug-treated and drug-challenged rats were significantly greater than those in drug-treated and saline-challenged rats after the 10-day washout. Those data suggest that changes of GABA(B) receptor gene expression could be a factor underlying the development of drug-kindled seizure, but not a necessary component for the maintenance of this phenomenon.

Decreased cocaine- and lidocaine-induced seizure response by dextromethorphan and DNQX in rat

The present study investigated the effect of dextromethorphan and 6,7-dinitroquinoxaline-2,3-dione (DNQX) pre-treatment on the development of cocaine- and lidocaine-induced seizures. The dopaminergic action of cocaine was also studied. The NMDA antagonist dextromethorphan and the non-NMDA (AMPA/kainate) antagonist DNQX both significantly decreased the intensity of the seizure response to intravenous convulsant doses of cocaine and lidocaine individually (20 mg/kg) and in combination (5 mg/kg each). The incidence of seizures in rats receiving cocaine or lidocaine individually was significantly reduced by pre-treatment with dextromethorphan but not DNQX. Haloperidol did not have an effect on the incidence or intensity of seizures induced by cocaine or lidocaine, alone or in combination. The results suggest that local anesthetic-induced convulsive seizures are mediated by excitatory glutamate transmission through both NMDA and non-NMDA receptor systems.

Cocaine and lidocaine in combination are synergistic convulsants

The abuse of cocaine has dramatically increased in the recent decade. Cocaine obtained on the illegal market is rarely found in pure form. Most often it is adulterated with various substances, especially other local anesthetics. Lidocaine is one of the most common local anesthetics employed for adulteration of illicit cocaine. Toxicity due to the simultaneous ingestion of cocaine and lidocaine has been reported. Acute toxicity to cocaine and other local anesthetics is manifested in central nervous system aberrations, such as seizures and convulsions. This study investigated the convulsant potency of cocaine and lidocaine alone and in combination. Rats were administered intravenous injections of 5 mg/kg or 20 mg/kg of cocaine or lidocaine alone and in combination in equal proportion. Seizure activity and intensity were evaluated. The plasma concentration and brain content of each agent was also determined at the time of toxicity. The administration of 5 mg/kg of each drug alone did not yield seizure activity. However, the concomitant administration of 5 mg/kg of both cocaine and lidocaine produced a seizure response nearly equal to that produced after administration of 20 mg/kg of cocaine alone. Diazepam pre-treatment successfully antagonized the seizures induced by cocaine and lidocaine and raised the seizure threshold dose for the combination treatment by approximately four fold. The results suggest that cocaine and lidocaine interact synergistically to increase seizure activity and that the nature of this response occurs in part through a depression of inhibitory neuronal transmission.

Fos protein immunoreactivity in the developing olfactory bulbs of normal and naris-occluded rats

Immediate early genes such as c-fos may be a route through which extracellular events affect genomic expression. Expression of immediate early genes is important in the transcriptional regulation necessary for the normal development of the nervous system. Developmental patterns of Fos protein (the product of c-fos immediate early gene expression) were studied in the main olfactory bulb of the rat using immunocytochemistry. Embryonic Day 21 (E21, the last prenatal day), as well as Postnatal Day 0 (P0), P1, P5, P10, P15, P20 and P30 subjects were examined. Although staining was absent in the E21 bulb, there was a rapid onset of Fos synthesis within hours after birth. Distribution of Fos-immunoreactive (Fos-ir) nuclei corresponded to the sequence of bulb maturation: numerous mitral/tufted and granule cells were labeled on P0, followed by the appearance of Fos-ir in the nuclei of periglomerular cells and an increase in the number of stained granule cells with development. Surgical closure of an external naris on P1 resulted in a 70% reduction in the number of Fos-ir granule cell nuclei as early as 2 h after the manipulation. During the next 30 days, levels of Fos staining further diminished in experimental bulbs when compared to their contralateral controls. Nevertheless, electrical stimulation of the contralateral bulb in P20 pups resulted in a robust increase of Fos labeling in most main and accessory olfactory bulb mitral cells and in many granule and periglomerular neurons, suggesting that the experimental bulbs remain competent to express Fos protein.

The effects of amphetamine preexposure on electrical kindling of the hippocampus and related transfer phenomena

Earlier research has established that repeated amphetamine administration can interact synergistically with the processes responsible for the genesis of kindled seizures after intermittent electrical stimulation of the amygdala. In this study, the effects of amphetamine preexposure on primary hippocampal kindling, secondary kindling of the contralateral amygdala, and rekindling of the original hippocampal focus were evaluated. It was shown that amphetamine treatment did not modify kindling rates when electrodes were situated in the dorsal hippocampus. However, transfer kindling of the contralateral amygdala evolved after fewer afterdischarges, and rekindling of the dorsal hippocampus progressed significantly faster in amphetamine-pretreated animals. The effects of amphetamine on ventral hippocampal kindling were also determined, and it was found that although epileptogenesis developed more rapidly relative to the dorsal region of this structure, kindling rates were not affected by amphetamine preexposure. These results were related to the possibility that the amygdala might have a unique function in the relationship between kindling- and stimulant-induced sensitization effects.

Hyperthermia sensitizes rats to cocaine's proconvulsive effects and unmasks EEG evidence of kindling after chronic cocaine

In phase I, 64 male and female Sprague-Dawley rat siblings from 8 litters were divided equally among 4 treatment groups; saline plus normothermia (S37), saline plus hyperthermia (S45), cocaine (30 mg/kg) plus normothermia (C37), and cocaine plus hyperthermia (C45) and treated daily from 45-60 days of age. Cocaine plus hyperthermia produced protracted, intense and often fatal convulsions, whereas animals from either treatment alone did not convulse. Subsequently, 12 males, representing all phase I treatment groups equally, were implanted with telemetric transmitters to monitor the EEG and core body temperature in phase II. Survivors of this second phase were exposed to one trial each of saline plus hyperthermia, cocaine plus normothermia, and cocaine plus hyperthermia, in that order. The data obtained suggests that 1) the telemetered EEG and temperature can be used to detect changes reflecting sensitization/kindling in the absence of behavioral expression (convulsions), 2) analysis of EEG power spectral bands and body temperature curves showed that a history of daily cocaine exposure seems to have contributed more than daily hyperthermia to subsequently observed seizure patterns and thermic responses, and, finally, 3) cocaine plus hyperthermia resulted in a shorter latency to convulse and a lower maximal EEG seizure voltage, while increasing the variety, severity and duration of its behavioral expression (convulsion).

Differential sensitivity of long-sleep and short-sleep mice to high doses of cocaine

The cocaine sensitivity of male and female long-sleep (LS) and short-sleep (SS) mice, which have been selectively bred for differential ethanol-induced "sleep-time," was examined in a battery of behavioral and physiological tests. Differences between these two mouse lines were subtle and were seen primarily at high doses. At high doses, SS mice were more sensitive than LS mice, particularly to cocaine-induced hypothermia; however, significant hypothermia was not seen except at doses which were very near to the seizure threshold. During a 60-min test of locomotor activity, LS mice showed greater stimulation of Y-maze activity by 20 mg/kg cocaine than SS mice. Consistent with the finding of subtle differences in sensitivity to low doses of cocaine. LS and SS mice did not differ in sensitivity to cocaine inhibition of synaptosomal uptake of [3H]-dopamine, [3H]-norepinephrine or [3H]-5-hydroxytryptamine. However, consistent with the finding of differential sensitivity to high doses of cocaine, SS mice were more sensitive to the seizure-producing effects of the cocaine and lidocaine, a local anesthetic. It is hypothesized that the differential sensitivity of these mouse lines to high doses of cocaine is due to differential sensitivity to cocaine's actions on systems that regulate local anesthetic effects. Selective breeding for differential duration of alcohol-induced "sleep-time" may have resulted in differential ion channel structure or function in these mice.

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.

Selective long-term potentiation in the pyriform cortex

Electrical stimulation of the olfactory bulb (OB) produces an evoked potential in the pyriform cortex (PC) characterized by an initial surface-negative wave (period 1) representing activation of PC pyramidal cells via the lateral olfactory tract, followed by a surface-positive wave (period 2) which is temporally associated with recurrent and feed-forward inhibition. The experiment reported here examined the changes that occur in the PC evoked potential following a pattern of stimulation that has been found to produce short- and long-term potentiation (LTP) in other areas of the forebrain. Male Long-Evans rats with electrodes in the OB and PC were divided into two groups. LTP animals received high-frequency stimulation of the OB (30 trains of 10 pulses each at a frequency of 100 Hz). Control animals received the same number of pulses at a lower frequency (1 Hz). This procedure was repeated 6 times at 2-day intervals. Neither high- nor low-frequency stimulation altered period 1 of the PC evoked potential, indicating that synaptic input arriving via the lateral olfactory tract was unaffected. However, LTP animals exhibited a marked increase in the amplitude and duration of period 2 which appeared to reflect two separate processes: a short-term change that peaked within 30 min of the trains; and a long-term change that accumulated across the 6 treatments. LTP of period 2 persisted in latent form for at least 32 days after the last treatment. Control animals exhibited only small changes that were attributed to the paired-pulse stimulation used for testing rather than the 1 Hz Control trains. These results suggest that repeated high-frequency stimulation of the OB causes a persistent alteration in the way information is processed within the PC. The form of LTP demonstrated here is markedly different from that found in the hippocampal formation, where potentiation of the monosynaptic excitatory postsynaptic potential is a prominent effect. The functional significance of this change cannot be determined with certainty from the present experiment, but available evidence suggests that it represents an enhancement of inhibitory processes within the PC.

Cocaine stimulates adrenocorticotropin (ACTH) secretion through a corticotropin-releasing factor (CRF)-mediated mechanism

Cocaine was injected intravenously to non-anesthetized, freely moving adult male rats and caused dose-dependent elevations in plasma adrenocorticotropin (ACTH) levels. The observation that this stimulatory effect was completely abolished by pretreatment with a corticotropin-releasing factor (CRF) antiserum, coupled with the lack of effect of cocaine on ACTH secretion by cultured pituitary cells, suggests that cocaine acts within the brain to release endogenous CRF.

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 olfactory bulb kindling on evoked potentials in the pyriform cortex

The potential evoked in the pyriform cortex by single-pulse stimulation of the olfactory bulb was examined before and after single and repeated elicitation of an epileptiform afterdischarge produced by stimulation of the olfactory bulb. A single afterdischarge (AD) produced a rapid (i.e. within 5 min) increase in the amplitude of an early surface-negative wave and duration of a later surface-positive wave. These effects persisted at least 48-72 h. Repeated elicitation of ADs resulted in kindling. A large increase in the amplitude of a later surface-negative wave (approximately 25 ms latency) occurred during kindling. This wave remained significantly elevated for at least 72 h after the last AD. Long-term potentiation of the early surface-negative wave was produced by kindling or two focal ADs. A short-term effect which was consistently observed following a focal or generalized AD was a prolongation of a late surface-positive wave. These effects are discussed in relation to long-term potentiation, postseizure inhibition, and kindling development.

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.

Frequency-related, bidirectional limbic responses to cocaine: comparisons with amphetamine and lidocaine

Dual effects of cocaine on the electrical excitability of limbic structures were investigated by determining current thresholds for afterdischarges (AD) evoked by low and high frequency electrical stimulation. Cocaine, lidocaine and D-amphetamine treatments were compared in order to assess the extent to which cocaine's local anesthetic and monoaminergic actions contribute to its effects on limbic afterdischarges. Afterdischarge threshold, duration and propagation for both 3 and 50 Hz stimulation of the amygdala, hippocampus and septal area were tested following saline, cocaine (5 mg/kg), lidocaine (5 mg/kg) and D-amphetamine (2.5-5 mg/kg). Results provide clear evidence that cocaine has a bidirectional effect on hippocampal and amygdalar AD thresholds--significantly increasing sensitivity to low frequency stimulation while significantly decreasing sensitivity to high frequency stimulation at identical brain sites. A frequency-dependent threshold effect also occurred at the septal area. In addition, cocaine reduced limbic AD duration and propagation; these effects proved unrelated to the direction of AD threshold changes. Cocaine effects on afterdischarges differed significantly from those of amphetamine and lidocaine. Comparisons with amphetamine and lidocaine suggest that cocaine's local anesthetic action, but not its monoaminergic properties, may contribute to reductions in limbic afterdischarge duration and propagation. However, it is unlikely that either monoaminergic or local anesthetic actions are responsible for cocaine's pronounced dual effect on the electrical excitability of major limbic structures. This bidirectional drug effect has interesting neurobiological implications and, in addition, offers a potentially valuable tool for new research on frequency-related functions of the limbic system.

Monoaminergic and local anesthetic components of cocaine's effects on kindled seizure expression

Male Long-Evans rats were kindled via daily electrical stimulation of the left prepyriform cortex. The animals were then used in two experiments which examined the pharmacological basis of cocaine's effects on three mutually exclusive components of the kindled seizure, which were the following: (a) latency to clonus, (b) clonus duration, and (c) duration of AD outlasting clonus. The first experiment compared the effects produced by cocaine HCl (20 mg/kg, IP), lidocaine HCl (20 mg/kg, IP), and amphetamine sulfate (2.5 mg/kg, IP). The results indicated that both cocaine and lidocaine reduced the duration of kindled AD, latency to clonus, and duration of AD persisting beyond clonus, thus suggesting that these cocaine effects are mediated by local anesthetic mechanisms. Only cocaine reduced clonus duration, which suggests that this cocaine effect is not produced by a local anesthetic action. The second experiment examined the effects of cocaine following the administration of three dose levels of the monoamine antagonists haloperidol, prazosin, yohimbine, propranolol, or metergoline (selected for their ability to block dopamine, alpha-1-norepinephrine, alpha-2-norepinephrine, beta-norepinephrine, and serotonin receptors, respectively). The results of this experiment found no support for a monoaminergic contribution to cocaine's effect on clonus latency or AD after clonus. However, results for prazosin, which reduced clonus duration and exhibited an additive effect with cocaine on this variable, suggest that cocaine's norepinephrine action (especially on the alpha-norepinephrine systems) may modulate clonus duration.

Cocaine and "pharmacological kindling" in the rat

The concept of "pharmacological kindling" has been used to explain the behavioral sensitization to cocaine produced by repeated administration of subconvulsive doses. This idea was tested by the repeated administration of cocaine to rats followed by electrical kindling of the olfactory bulb (a site at which cocaine has prominent electrophysiologic effects). No significant effect of cocaine on kindling was found. The relationship of this finding to studies using other drugs is discussed.

Effect of cocaine on afterdischarge threshold in previously kindled rats

Previous experiments have yielded conflicting reports on the effect of cocaine on the after discharge (AD) threshold for electrical stimulation. The present study was designed to determine if differences in the type of stimulation used could account for these discrepancies. Male Long-Evans rats which had been previously kindled by stimulation of the olfactory bulb were used to determine the AD threshold of the olfactory bulb following the intraperitoneal injection of saline or 20 mg/kg cocaine hydrochloride. AD's were elicited by trains of square-wave pulses which varied in frequency and train duration. Cocaine significantly increase the amount of current required to produce AD's using stimulus trains with frequencies of 30-100 pulses/sec, while evidence of a decrease in AD threshold by cocaine was found at a frequency of 20 pulses/sec. The results suggest that cocaine has opposite effects on AD threshold at high and low frequencies of stimulation.

Origin of cocaine- and lidocaine-induced spindle activity within the olfactory forebrain of the rat

Cocaine and other local anesthetics produce a characteristic form of electrical activity in the olfactory forebrain consisting of bursts of sinusoidal potentials (spindles) in the range of 20-50 c/sec. The purpose of the present experiment was to determine if this drug-induced spindle activity is generated by the same neuronal elements in the olfactory bulb (OB) and prepyriform cortex (PPC) which generate naturally occurring olfactory spindles. Rats with chronically implanted electrodes in the OB and PPC were injected with doses of cocaine or lidocaine hydrochloride sufficient to produce spindles (5 mg/kg i.v. or 40 mg/kg i.p.). Drug-induced and naturally occurring spindles exhibited similar anterior-posterior amplitude profiles, with the highest amplitude in the OB and the lowest in the posterior PPC. Multipolar recordings from the PPC indicated that the amplitude of naturally occurring and drug-induced spindles was highest at sites near the superficial pyramidal cell layer of the PPC and lower at sites 1-2 mm more dorsal. Furthermore, both naturally occurring and drug-induced spindles exhibited a polarity reversal near the superficial pyramidal cell layer of the PPC and the mitral cell layer of the OB. Finally, neither form of spindle occurred when nasal air flow (olfactory stimulation) was prevented. These observations suggest that cocaine- and lidocaine-induced spindles are generated in the OB and PPC by the same neuronal elements which also produce naturally occurring olfactory spindles.

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.