Effects of (+/-)3,4-methylenedioxymethamphetamine, (+/-)3,4-methylenedioxyamphetamine and methamphetamine on temperature and activity in rhesus macaques.

Severe and malignant hyperthermia is a frequently reported factor in emergency department (ED) visits and fatalities in which use of amphetamine drugs, such as (+/-)3,4-methylenedioxymethamphetamine (MDMA), (+/-)3,4-methylenedioxyamphetamine (MDA) and (+)methamphetamine (METH), is confirmed. Individuals who use "ecstasy" are also often exposed, intentionally or otherwise, to several of these structurally-related compounds alone or in combination. In animal studies the degree of (subcritical) hyperthermia is often related to the severity of amphetamine-induced neurotoxicity, suggesting health risks to the human user even when emergency medical services are not invoked. A clear distinction of thermoregulatory risks posed by different amphetamines is therefore critical to understand factors that may produce medical emergency related to hyperthermia. The objective of this study was therefore to determine the relative thermoregulatory disruption produced by recreational doses of MDMA, MDA and METH in nonhuman primates. Body temperature and spontaneous home cage activity were monitored continuously in six male rhesus monkeys via radiotelemetric devices. The subjects were challenged intramuscularly with 0.56-2.4 mg/kg MDMA, 0.56-2.4 mg/kg MDA and 0.1-1.0 mg/kg METH. All three amphetamines significantly elevated temperature; however the time course of effects differed. The acute effect of METH lasted hours longer than MDA or MDMA and a disruption of nighttime circadian cooling was observed as long as 18 h after 1.0 mg/kg METH and 1.78-2.4 mg/kg MDA, but not after MDMA. Activity levels were only reliably increased by 0.32 mg/kg METH. It is concluded that while all three substituted amphetamines produce hyperthermia in rhesus monkeys, the effects do not depend on elevated locomotor activity and exhibit differences between compounds. The results highlight physiological risks posed both by recreational use of the amphetamines and by current trials for clinical MDMA use.

Neurophysiological profiles of replicate line 2 high-alcohol-drinking (HAD-2) and low-alcohol-drinking (LAD-2) rats.

RATIONALE: A select number of electrophysiological findings have been demonstrated to differentiate rat lines selectively bred for high and low ethanol preference. OBJECTIVE: In the present study, EEGs and event-related potentials (ERPs) of high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) rats from replicate line 2 (HAD-2 and LAD-2) were assessed to determine if their neurophysiological profiles are similar to selected lines previously evaluated. METHODS: Rats obtained from Indiana University were implanted with cortical and amygdalar recording electrodes. Baseline EEG and ERPs were assessed in ethanol-naïve HAD-2 and LAD-2 rats. Animals subsequently were trained to self-administer ethanol by using a sucrose-substitution procedure. RESULTS: Compared with LAD-2 rats, HAD-2 rats displayed greater parietal cortical power in the 6 to 32 Hz frequency range of the EEG. Greater parietal cortical peak frequency in the 2 to 4 Hz range and decreased frontal, parietal, and amygdalar peak frequencies in the 16 to 32 Hz frequency range were also seen. Compared with LAD-2 rats, HAD-2 rats had decreased P2 latency of ERPs recorded in the parietal cortex. HAD-2 rats also had greater frontal, parietal, and amygdalar P2 amplitudes, greater frontal and parietal cortical P1 amplitudes, and greater parietal cortical P3 amplitudes compared with LAD-2 rats. As anticipated, HAD-2 rats consumed significantly greater levels of sucrose, sucrose-ethanol, and ethanol over the course of the sucrose-substitution procedure compared with LAD-2 rats. CONCLUSIONS: These data suggest that increased cortical power is associated with high ethanol preference in a number of selectively bred rat lines. However, unique electrophysiological characteristics may index alcohol preference in each line.

Neuropeptide Y administration into the third ventricle does not increase sucrose or ethanol self-administration but does affect the cortical EEG and increases food intake.

RATIONALE: Several studies have provided indirect evidence that neuropeptide Y (NPY) may play a role in the regulation of ethanol consumption. However, the direct effects of central NPY administration on ethanol drinking are unclear. OBJECTIVE: This study examined the effects of NPY on ethanol, sucrose, and food consumption as well as its concomitant effects on the cortical EEG. METHODS: Wistar rats were implanted with cortical recording electrodes and a cannula in the third ventricle after using a sucrose substitution procedure to establish ethanol self-administration. NPY (0-15 microg/3.0 microl) was infused into the third ventricle prior to drinking sessions, when 10% ethanol (10E), 2% sucrose (2S), 0.5% sucrose (0.5S), or food were available. Behavior and cortical EEG were monitored during the sessions. RESULTS: NPY had no effect on the intake of 10E, 2S, or 0.5S, but NPY (15 microg/3.0 microl) significantly increased food intake. Under baseline drinking conditions, EEG power in the 6-8 Hz range was significantly greater when 2S was consumed compared to 10E. NPY decreased power in the 8-16 Hz range, decreased peak frequency in the 6-8 Hz range, and increased peak frequency in the 32-50 Hz range when 10E or 2S was available. CONCLUSIONS: These data suggest that NPY administration into the third ventricle preferentially regulates feeding compared to ethanol or sucrose drinking. In addition, since NPY significantly altered the cortical EEG in the absence of effects on ethanol and sucrose consumption, these data may indicate that NPY's cortical EEG effects are more related to its sedative or anxiolytic properties, rather than any effect on consumption.

Neurochemical characteristics associated with ethanol preference in selected alcohol-preferring and -nonpreferring rats: a quantitative microdialysis study.

BACKGROUND: Rodent lines selected for alcohol preference and nonpreference have been used extensively to determine the neurobiological basis of alcohol-seeking behavior. Evidence suggests that innate differences in the mesolimbic dopamine and serotonin systems may contribute to disparate alcohol-seeking behaviors between these selected lines. Therefore, the purpose of this study was to identify neurochemical characteristics which may predict ethanol preference in selected alcohol-preferring and -nonpreferring rats [high-alcohol-preferring (HAD), low-alcohol-preferring (LAD), Alko alcohol (AA), Alko nonalcohol (ANA), Wistar]. METHODS: Basal release of dopamine (DA) and serotonin (5-HT) in the nucleus accumbens of ethanol-naive rats was analyzed for its relationship with subsequent measures of ethanol preference. Initially, basal extracellular DA and 5-HT levels were measured by "no-net-flux" quantitative microdialysis. Subsequently, the dopaminergic response to systemic ethanol administration (1.5 g/kg; intraperitoneal) was determined. After completion of the neurochemical tests, the rats received unlimited two-bottle, free-choice access to 10% (w/v) ethanol and water in the home cage for 28 days. RESULTS: Analysis of the data across individual animals revealed that extracellular dopamine levels ([DA]e; r = + 0.64;p < 0.006) and the percent of baseline increase in DA (%incrDA; r = + 0.77;p < 0.001) due to ethanol were significant predictors of ethanol preference. Comparison of the data between genetic lines yielded a significant relationship between preference and %incrDA (r = + 0.87; p < 0.05). Analysis of the data across animals within each line and their respective control line determined that in the AA/ANA line pair (r = + 0.67; p < 0.03) and Wistar line (r = + 0.66; p < 0.03) %incrDA was a significant predictor of preference. In the HAD/LAD line pair, %incrDA (r = + 0.56; p < 0.005) and [DA]e (r = + 0.86; p < 0.004) were significant predictors of ethanol preference. CONCLUSIONS: Overall, these findings suggest that elevated extracellular levels of dopamine within the nucleus accumbens and a greater responsivity to enhancements in DA release by ethanol may be factors which contribute to high-alcohol preference. Furthermore, the data suggest that alcohol may be more reinforcing in animals that exhibit an enhanced dopaminergic response to the first ethanol exposure, and that this effect may subsequently be associated with high-alcohol-seeking behavior.

Approaches to understanding the neurobiological regulation of ethanol self-administration: a young investigators forum.

The article represents the proceedings of a symposium at the 2000 RSA Meeting in Denver, Colorado. The co-chairs were Cristine L. Czachowski and Craig J. Slawecki. The presentations were (1) Behavioral assessment of ethanol seeking and self-administration, by Cristine L. Czachowski; (2) Electrophysiological measures of ethanol preference and reinforcing efficacy, by Craig J. Slawecki; (3) Genetic differences in locomotor sensitization and reward phenotypes associated with bidirectional selection for alcohol preference in mice, by Nicholas J. Grahame; (4) Transgenic and knockout mouse models: Powerful tools for investigating the neurobiology of alcoholism, by Todd E. Thiele; and (5) Neurochemical characteristics that may predict ethanol preference in selected P and NP rats: A quantitative microdialysis study, by Simon N. Katner.

Ethanol-associated olfactory stimuli reinstate ethanol-seeking behavior after extinction and modify extracellular dopamine levels in the nucleus accumbens.

BACKGROUND: Alcohol craving or automatic behavioral responses provoked by alcohol-related cues are thought to contribute to relapse risk in abstinent individuals. However, there is to date only limited direct experimental evidence that supports this hypothesis. The present study employed an operant response-reinstatement model to examine the effects of ethanol-associated environmental stimuli on alcohol-seeking behavior and extracellular dopamine (DA) levels in the nucleus accumbens (NAcc). METHODS: Male Wistar rats were prepared with intracerebral guide cannulae for microdialysis and trained to operantly self-administer ethanol in the presence of discrete olfactory discriminative stimuli (Sdelta's) signaling the availability of ethanol (10% w/v) versus a nonrewarding stimulus (a 50 microM quinine HCl solution). After the discrimination learning phase, responding for ethanol (and quinine) was extinguished by withholding the drinking solutions as well as the corresponding Sdelta's. After reaching and maintaining an extinction criterion of < or = 5 responses/session, the rats were exposed noncontingently to the ethanol and nonreward Sdelta's but without the availability of ethanol or quinine. RESULTS: The ethanol Sdelta's, but not nonreward Sdelta's, elicited significant recovery of responding. Exposure to the operant chamber during a 20 min "waiting period" before presentation of the Ss's was associated with a small but significant increase in dialysate DA levels. Subsequent exposure to the ethanol Sdelta and onset of the reinstatement session was accompanied by a small but significant decrease in DA efflux. Exposure to the nonreward Sdelta did not alter DA levels. CONCLUSIONS: The behavioral data confirm that ethanol-predictive discriminative stimuli reliably elicit ethanol-seeking behavior after extinction. The increase in DA efflux during the waiting period confirms earlier findings and suggests that anticipation of access to ethanol activates mesolimbic DA neurons. The decrease in DA efflux after onset of the reinstatement session in animals that were presented with the ethanol Sdelta's may reflect neurochemical events associated with the mismatch between the predicted (i.e., ethanol availability) and actual (i.e., absence of ethanol) stimulus events. This possibility is supported by the lack of changes in DA efflux in rats that were presented with the nonreward Sdelta's, a test condition that did not involve such a mismatch. Overall, the findings provide further evidence for a role of conditioning processes in the control of alcohol-seeking behavior and, by extension, support the hypothesis that conditioned responses to drug-related stimuli may be an important factor in chronic alcohol abuse and relapse.

Reinstatement of alcohol-seeking behavior by drug-associated discriminative stimuli after prolonged extinction in the rat.

Clinical observations suggest that stimuli associated with the availability or consumption of ethanol can evoke subjective feelings of craving and trigger episodes of relapse in abstinent alcoholics. To study the motivational significance of alcohol-related environmental cues experimentally, the effects of discriminative stimuli previously predictive of alcohol availability on the reinstatement of ethanol-seeking behavior were examined. Wistar rats were trained to lever-press for 10% (w/v) ethanol or water in the presence of distinct auditory cues. The rats were then subjected to an extinction phase where lever presses had no scheduled consequences. After extinction, the animals were exposed to the respective auditory cues without the availability of ethanol or water. Neither the ethanol (SA+) nor water-associated (SA-) auditory cue increased responding over extinction levels. In contrast, subsequent presentation of an olfactory cue associated with ethanol (SO+), but not a water-associated (SO-) cue significantly reinstated lever pressing behavior in the absence of the primary reinforcer. Moreover, responding elicited by the concurrent presentation of the SO+ and SA+ was selectively attenuated by the opiate antagonist naltrexone (0.25 mg/kg; s.c.). The results suggest that ethanol-associated cues can reinstate extinguished ethanol-seeking behavior in rats, but that the efficacy of these stimuli may be modality-specific. In addition, the present procedures may be useful for studying neurobiological mechanisms of alcohol-seeking behavior and relapse.

Alcohol intake of P rats is regulated by muscarinic receptors in the pedunculopontine nucleus and VTA.

Experiments were conducted to determine whether muscarinic receptors within the pedunculopontine nucleus (PPN) and ventral tegmental area (VTA) are involved in regulating ethanol drinking behavior in the alcohol-preferring P line of rats. Female P rats were given limited access (2 h/day) to 10% (v/v) ethanol and 0.0125% (g/100 ml) saccharin solutions. Food was available ad libitum. Cholinergic agents were microinjected unilaterally into the PPN or VTA immediately prior to ethanol access. Intra-PPN carbachol (1-4 microg/0.5 microl), which can inhibit cholinergic neuronal activity within the PPN, decreased ethanol (70% decrease at the highest dose; p < 0.05) and saccharin (90% decrease at the highest dose; p < 0.05) intake in a dose-dependent manner within the first 30 min. Intra-PPN scopolamine (5-15 microg/0.5 microl), which can stimulate cholinergic neuronal activity within the PPN, decreased ethanol intake in a dose-dependent manner within the first 30 min (65% decrease at the highest dose; p < 0.05) without reducing saccharin intake. Intra-VTA methylscopolamine (1-10 microg/0.5 microl), a muscarinic antagonist, significantly (p < 0.05) reduced ethanol (60% decrease at the highest dose) and saccharin (50% decrease at the highest dose) intakes during the 2-h access period. Intra-VTA carbachol, a cholinergic agonist (1 and 2 microg/0.5 microl) decreased ethanol consumption in a dose-dependent manner within the first 60 min (50% decrease at the highest dose) without reducing saccharin intake. Overall, these results support an involvement of the cholinergic PPN-VTA system in regulating alcohol drinking and general consummatory behaviors of the P line of rats.

Involvement of CNS cholinergic systems in alcohol drinking of P rats.

Experiments were undertaken to determine if CNS muscarinic- and nicotinic-cholinergic receptors are involved in regulating alcohol drinking of rats from the selectively-bred alcohol-preferring P line. Intracerebroventricular (i.c.v.) drug infusions were administered into the lateral ventricle of female P rats 15 minutes before ethanol access. The muscarinic antagonists pirenzepine and scopolamine were tested on limited access (4 hours/day) to a 10% (v/v) ethanol solution. Food and water were available ad libitum. Nicotine and the nicotinic antagonist mecamylamine were tested on limited access (4 hours/day) to 10% (v/v) ethanol and 0.0125% saccharin solutions. Food was available ad libitum and water was available during the remaining 20 hours. The baseline ethanol intakes ranged between an average of 3.0 ± 0.3 g/kg/4 hours and 3.4 ± 0.3 g/kg/4 hours. Administration of 40-100 m g pirenzepine (M1-selective antagonist) had no effect on ethanol, food or water consumption. However, 20-80 m g scopolamine, a non-selective muscarinic antagonist, dosedependently decreased ethanol intake as much as 60% (p < 0.05) without altering food or water consumption. The nicotinic antagonist mecamylamine (20-120 m g) did not alter ethanol intake, but nicotine (40-80 m g) dose-dependently decreased ethanol drinking as much as 60% within the first 30 minutes (p < 0.05) without an effect on saccharin intake. The results suggest that: (a), muscarinic receptors, with the possible exception of the M1 subtype, are involved in regulating alcohol drinking and (b), activation of nicotinic receptors can reduce alcohol drinking of the P line of rats.

Ethanol anticipation enhances dopamine efflux in the nucleus accumbens of alcohol-preferring (P) but not Wistar rats.

It has been argued that the anticipation of ethanol consumption can activate reinforcement substrates involved in alcohol-seeking behavior. To test this hypothesis nucleus accumbens (NAc) dopamine (DA) efflux was monitored in alcohol-preferring (P) and Wistar rats. Rats from each line were divided into two groups: one trained to self-administer 0.05% saccharin and the other trained to self-administer 10% (w/v) ethanol. On the test day dopamine efflux was monitored in all animals during saccharin self-administration. In ethanol-expecting P rats, self-administration of saccharin produced a significant elevation in extracellular DA (150% of baseline within the first 15-20min). In contrast, a significant increase in extracellular DA was only observed during the final 30min of the test session in ethanol-expecting Wistar rats self-administering saccharin. The self-administration of saccharin in animals expecting the sweetener failed to elevate extracellular DA in both strains. Overall, these results suggest that the mere expectation of ethanol availability enhances the efflux of DA in the NAc of the P, but not the Wistar rat, which may play a role in the initiation or maintenance of ethanol seeking behavior in the P line.

Effects of cholinergic agents on locomotor activity of P and NP rats.

Experiments were undertaken to compare the selectively bred, alcohol-preferring (P) and alcohol-nonpreferring (NP) rat lines for differences in the locomotor activity (LMA) response to intracerebroventricular infusions of muscarinic- and nicotinic-cholinergic agents. Scopolamine, a nonselective muscarinic antagonist (40 to 120 micrograms/0.5 microliters), dose-dependently increased LMA in both P and NP rats (up to 90 to 100% above baseline; p < 0.05). On the other hand, pirenzepine, a selective M1 muscarinic antagonist (10 to 80 micrograms/0.5 microliters), decreased LMA in P and NP rats (as much as 35 to 40% below control values; p < 0.05). Mecamylamine, a nicotinic antagonist (20 to 80 micrograms/0.5 microliters), also decreased LMA in P and NP rats (as much as 30 to 40% below baseline; p < 0.05). The agonist nicotine (20 to 80 micrograms/0.5 microliters) dose-dependently decreased LMA in both P and NP rats (to a maximum of approximately 60 to 65% below control values; p < 0.05). Based on standardized z-scores, NP rats were more sensitive (p < 0.05) to the locomotor depressant effects of nicotine than P rats, whereas no differences were observed for standardized z-scores between the P and NP lines on the effects of scopolamine, pirenzepine, or mecamylamine on LMA. The results suggest that subtypes of muscarinic and nicotinic receptors are involved in regulating LMA in a complex manner, with the M1 subtype possibly mediating behavioral activation, and that P and NP rats may possess innate differences in CNS nicotinic receptors regulating LMA.