The effects of acute cocaine administration on auditory event-related potentials in rats

Cognitive enhancers for facilitating drug cue extinction: insights from animal models

Given the success of cue exposure (extinction) therapy combined with a cognitive enhancer for reducing anxiety, it is anticipated that this approach will prove more efficacious than exposure therapy alone in preventing relapse in individuals with substance use disorders. Several factors may undermine the efficacy of exposure therapy for substance use disorders, but we suspect that neurocognitive impairments associated with chronic drug use are an important contributing factor. Numerous insights on these issues are gained from research using animal models of addiction. In this review, the relationship between brain sites whose learning, memory and executive functions are impaired by chronic drug use and brain sites that are important for effective drug cue extinction learning is explored first. This is followed by an overview of animal research showing improved treatment outcome for drug addiction (e.g. alcohol, amphetamine, cocaine, heroin) when explicit extinction training is conducted in combination with acute dosing of a cognitive-enhancing drug. The mechanism by which cognitive enhancers are thought to exert their benefits is by facilitating consolidation of drug cue extinction memory after activation of glutamatergic receptors. Based on the encouraging work in animals, factors that may be important for the treatment of drug addiction are considered.

Association of the G1947A COMT (Val(108/158)Met) gene polymorphism with prefrontal P300 during information processing

BACKGROUND

A common functional polymorphism, G1947A, of the catechol-O-methyltransferase (COMT) enzyme has gained interest in schizophrenia research because of its critical involvement in cortical dopamine catabolism and frontal lobe function. An assumed mechanism of dopamine is the reduction of noise in prefrontal neural networks during information processing. Therefore, the hypothesis was tested whether a variation of the COMT genotype is associated with prefrontal noise, which is in part reflected by the frontal P300 amplitude. It was predicted that homozygous Met allele carriers have a lower frontal P300 amplitude.

METHODS

The P300 component (auditory oddball) was recorded in 49 schizophrenic patients and 170 healthy control subjects. Three single nucleotide polymorphisms (SNPs) of the COMT gene (G1947A, C1883G, and G1243A) were investigated.

RESULTS

We observed a significant effect of G1947A COMT genotype on frontal P300 amplitude, with evidence for a genotype x diagnosis interaction. Lower frontal P300 amplitudes occurred in homozygous carriers of the Met allele, particularly in schizophrenic patients.

CONCLUSIONS

The association of the frontal P300 amplitude with the G1947A COMT genotype further emphasizes the functional role of this SNP. As the finding was mainly observed in schizophrenic patients, this may indicate that additional factors are required to interact with COMT genotype to affect prefrontal function. The smaller frontal P300 amplitude in Met carriers suggests that the amount of noise in prefrontal neural networks during information processing might be in part under genetic control, which is mediated by dopamine.

Long latency event-related potentials in mice: effects of stimulus characteristics and strain

The P3, or P300 component of the event-related potentials (ERPs) is a positive going waveform that can be averaged from the EEG approximately 250-500 ms following the presentation of task or context 'relevant' stimuli. This potential has been demonstrated to be a sensitive measure of both normal and abnormal cognitive functioning. P300 models have been developed in monkeys, cats and rats. The aim of the present study was to develop an auditory ERP paradigm suitable for use in mice that resembled those used in humans and other animal models. The results of the studies showed that late positive potentials in the 200-400 ms range could be generated in cortical sites in response to auditory stimuli. Additionally, like passive ERPs recorded in humans, mouse ERPs were sensitive to changes in stimulus characteristics. An earlier negative component designated the N1 was found to be sensitive to tone frequency and loudness but not to stimulus probability, whereas the mouse P300 component was sensitive to probability but not to tone frequency or loudness. C57BL/6 mice, a strain known to have a strong alcohol preference, were found to have significantly lower P300 amplitudes when compared to the DBA/2 strain. These findings also parallel human studies, and studies of selected lines of rats, demonstrating that decrements in P300 amplitude can be associated with a genetic vulnerability to alcoholism/alcohol preference. These studies further suggest that ERPs are an electrophysiological assay suitable for the exploration of the effects of genetic manipulations on neurosensory processing in mice.

Cocaine's effects on the discrimination of simple and complex auditory stimuli by baboons

The effects of cocaine on tone frequency discriminations by baboons were examined and compared with previous data for more complex acoustic stimuli (speech sounds) to see if cocaine's perceptual effects on these discriminations depends upon the type of stimulus employed (i.e., tones vs. speech sounds). Baboons pressed a lever to produce one repeating "standard" tone and released the lever only when one of four other "comparison" tones occasionally occurred in place of the standard tone. Cocaine's effects were assessed once or twice weekly by giving an intramuscular injection of cocaine hydrochloride (0.01-0.56 mg/kg) immediately prior to performing the task and by examining correct detections and reaction times for each tone following drug administration. Cocaine impaired tone discriminability, with greater impairments occurring for those tones that were more similar in frequency to the standard tone. Cocaine's perceptual effects occurred within 20-70 min following drug administration. Cocaine also impaired or facilitated the speed of responding to auditory stimuli, depending upon the drug dose and subject. The results demonstrate that cocaine can impair auditory discriminations involving simple tones, as well as speech sounds, and further supports the suggestion that cocaine's effects are focused on CNS mechanisms related to the use of pitch cues.

Enhancement of attention processing by Kantroll in healthy humans: a pilot study

This is the first report in humans of the effects of daily ingestion of a specific amino acid mixture, Kantroll, on cognitive event-related potentials (ERPs) associated with performance. Cognitive ERPs were generated by two computerized visual attention tasks, the Spatial Orientation Task (SOT) and Contingent Continuous Performance Task (CCPT), in normal young adult volunteers, where each subject acted as his own control for testing before and after 28-30 days of amino acid ingestion. A statistically significant amplitude enhancement of the P300 component of the ERPs was seen after Kantroll for both tasks, as well as improvement with respect to cognitive processing speeds. The enhancement of neurophysiologic function observed in this study on normal controls is consistent with the facilitation of recovery of individuals with RDS (i.e., substance use disorder, ADHD, carbohydrate bingeing) following the ingestion of the amino acid supplement, Kantroll, and warrants additional placebo-controlled, double-blind, studies to confirm and extend these results.

Cocaine's effects on speech sound identification and reaction times in baboons

The effects of cocaine on speech sound discriminations was examined to determine whether cocaine's previously demonstrated effect in reducing speech sound discriminability was dependent upon either the type of stimuli employed (simple tones versus complex speech) or the procedure (stimulus detection versus stimulus discrimination). Because of demonstrated similarities in the way that baboons and humans discriminate speech, and in the way the CNS is thought to encode and process speech sounds in these two species, baboons were trained to perform a choice procedure to identify the occurrence of different synthetic vowel sounds (see text). Animals held down a lever and released the lever only when one of four target vowels sounded, and not when a fifth, standard vowel sounded. Acute IM administration of cocaine (0.0032-1.0 mg/kg) produced dose-dependent decreases in vowel discriminability that were mostly due to elevations in false alarms (i.e., releases to the standard vowel) following cocaine. Cocaine also shortened reaction times to the stimuli in two of three baboons, but to a much lesser extent than observed previously. These results suggest that cocaine may interfere with the ability of the CNS to process the acoustic cues in speech sounds, and that the effects of cocaine on reaction times may depend upon the complexity of the reaction time procedure employed.

Cocaine accumulates in dopamine-rich regions of primate brain after i.v. administration: comparison with mazindol distribution

Pharmacological and neurochemical evidence suggest that brain dopamine systems, and the dopamine transporter in particular, contribute significantly to the behavioral effects and reinforcing properties of cocaine. The first objective of this study was to determine whether the brain distribution of cocaine supports these conclusions. A high resolution neuroanatomical map of cocaine disposition in brain after i.v. administration was developed. [3H]Cocaine ([3H](-)-cocaine) was administered to squirrel monkeys (Saimiri sciureus) at a trace dose (0.001 mg/kg) and at doses at or above the threshold for producing behavioral effects (0.1 mg/kg, 0.3 mg/kg). After 15 min, ex vivo autoradiography revealed the highest accumulation of [3H]cocaine in dopamine-rich brain regions, including the caudate nucleus, putamen, and nucleus accumbens/olfactory tubercle. The norepinephrine-rich locus coeruleus, the hippocampus, and amygdala also accumulated large quantities of [3H]cocaine. Moderately high levels were found in the stria terminalis, medial septum, substantia nigra, and other regions. Lowest levels were found in the cerebellum. A high and positive correlation was established for the brain distribution of [3H]cocaine administered at trace or at behaviorally relevant doses (r: 0.94; P < 0.001). To determine whether radioactivity represented [3H]cocaine or its metabolic products, tissue extracts from brain regions with high levels of cocaine were subjected to thin layer chromatography using two solvent systems. In caudate-putamen, nucleus accumbens, cortex, and hippocampus, radioactivity comigrated with standard [3H]cocaine. In substantia nigra, less than 70% of the radioactivity comigrated with [3H]cocaine, suggesting that cocaine metabolites are generated more rapidly in the substantia nigra than in other brain regions. The second objective was to determine the brain distribution of mazindol, a potent norepinephrine and dopamine transport inhibitor with low abuse liability in humans. The disposition of intravenously administered [3H]mazindol in brain (0.001 mg/kg, 0.007 mg/kg) was surveyed by ex vivo autoradiography. In sharp contrast to [3H]cocaine distribution, the highest accumulation of [3H]mazindol was localized in the norepinephrine-rich pineal gland, discrete regions of the hypothalamus (paraventricular nucleus, supraoptic nucleus), and the locus coeruleus. Moderately high levels were detected in the caudate-putamen, nucleus accumbens, and other regions. The following conclusions were drawn: (1) Although dopamine-rich brain regions are principal targets of cocaine after i.v. administration to the nonhuman primate, other prominent targets of cocaine (locus coeruleus, hippocampus, and amygdala) may contribute to the acute and chronic effects of cocaine.(ABSTRACT TRUNCATED AT 400 WORDS)

Long-latency event-related potentials in rats: effects of task and stimulus parameters

Animal models of event-related potentials have recently been developed in rats in order to gain further understanding of the psychobiological variables which underlie these waveforms. In the present study, unanesthetized male Wistar rats, chronically implanted with electrodes, were utilized in order to: (i) compare event-related potentials recorded following the presentation of passively presented auditory stimuli from different neocortical, hippocampal and perihippocampal sites; (ii) test the effects of changes in stimulus probability and loudness on event-related potentials recorded from those sites; and (iii) record event-related potentials from rats who were actively performing in a tone discrimination task. The results of these studies showed that in all electrode sites (frontal cortex, parietal cortex, entorhinal cortex, hippocampus) a series of large amplitude potentials in the 10-200 ms latency range could be recorded in response to passively presented stimuli. Late positive potentials in the 300-400 ms range were only identified in recordings from the posterior cortex, entorhinal area, and dorsal hippocampus. Some of these late positive components were also found to be sensitive to changes in stimulus probability. A similar series of waves were detected in a paradigm where rats were required to actively discriminate between two tones; however, the morphologies of the waveforms were found to be more distinct. These studies suggest that rats may be good subjects for the exploration of the neural origins of event-related potentials. These studies demonstrate that rats performing in an auditory discrimination task can generate electrophysiological potentials which are time locked to the onset of a "cognitively relevant" stimulus (event-related potentials). These potentials can be recorded in limbic (hippocampus and amygdala) and cortical (parietal cortex) brain sites. The event-related potentials recorded in rats respond to changes in stimulus parameters in a similar fashion to those previously described in monkeys and human subjects. The identification of a rat model of event-related potentials provides an opportunity to further explore the neural origins of event-related potentials, to estimate the role of genetics in determining individual variation in waveforms, as well as to provide electrophysiological assays of the effects of various drugs on neurosensory and cognitive processing.