Effects of MK 801 and diazepam on the EEG of P and NP rats

Mechanisms underlying sleep-wake disturbances in alcoholism: focus on the cholinergic pedunculopontine tegmentum

Sleep-wake (S-W) disturbances are frequently associated with alcohol use disorders (AUD), occurring during periods of active drinking, withdrawal, and abstinence. These S-W disturbances can persist after months or even years of abstinence, suggesting that chronic alcohol consumption may have enduring negative effects on both homeostatic and circadian sleep processes. It is now generally accepted that S-W disturbances in alcohol-dependent individuals are a significant cause of relapse in drinking. Although significant progress has been made in identifying the socio-economic burden and health risks of alcohol addiction, the underlying neurobiological mechanisms that lead to S-W disorders in AUD are poorly understood. Marked progress has been made in understanding the basic neurobiological mechanisms of how different sleep stages are normally regulated. This review article in seeking to explain the neurobiological mechanisms underlying S-W disturbances associated with AUD, describes an evidence-based, easily testable, novel hypothesis that chronic alcohol consumption induces neuroadaptive changes in the cholinergic cell compartment of the pedunculopontine tegmentum (CCC-PPT). These changes include increases in N-methyl-d-aspartate (NMDA) and kainate receptor sensitivity and a decrease in gamma-aminobutyric acid (GABAB)-receptor sensitivity in the CCC-PPT. Together these changes are the primary pathophysiological mechanisms that underlie S-W disturbances in AUD. This review is targeted for both basic neuroscientists in alcohol addiction research and clinicians who are in search of new and more effective therapeutic interventions to treat and/or eliminate sleep disorders associated with AUD.

mTOR activation is required for the anti-alcohol effect of ketamine, but not memantine, in alcohol-preferring rats

Glutamate NMDA receptors mediate many molecular and behavioral effects of alcohol, and they play a key role in the development of excessive drinking. Uncompetitive NMDA receptor antagonists may, therefore, have therapeutic potential for alcoholism. The first aim was to compare the effects of the NMDA antagonists memantine and ketamine on ethanol and saccharin drinking in alcohol-preferring rats. The second aim was to determine whether the effects of the two NMDA receptor antagonists were mediated by the mammalian target of rapamycin (mTOR). TSRI Sardinian alcohol-preferring rats were allowed to self-administer either 10% w/v ethanol or 0.08% w/v saccharin, and water. Operant responding and motor activity were assessed following administration of either memantine (0-10mg/kg) or ketamine (0-20mg/kg). Finally, ethanol self-administration was assessed in rats administered with either memantine or ketamine but pretreated with the mTOR inhibitor rapamycin (2.5mg/kg). The uncompetitive NMDA receptor antagonists memantine and ketamine dose-dependently reduced ethanol drinking in alcohol-preferring rats; while memantine had a preferential effect on alcohol over saccharin, ketamine reduced responding for both solutions. Neither antagonist induced malaise, as shown by the lack of effect on water intake and motor activity. The mTOR inhibitor rapamycin blocked the effects of ketamine, but not those of memantine. Memantine and ketamine both reduce alcohol drinking in alcohol-preferring rats, but only memantine is selective for alcohol. The effects of ketamine, but not memantine, are mediated by mTOR. The results support the therapeutic potential of uncompetitive NMDA receptor antagonists, especially memantine, in alcohol addiction.

Event-related oscillations in the parietal cortex of adult alcohol-preferring (P) and alcohol-nonpreferring rats (NP)

The selectively bred alcohol-preferring (P) and -nonpreferring (NP) lines were developed from Wistar rats to model high and low voluntary alcohol consumption and have been demonstrated to exhibit many of the characteristics of human alcohol dependence. Electrophysiologic studies have shown P rats exhibit more electroencephalographic fast frequency activity and reduced P3 amplitude in the parietal cortex than NP rats, findings that are more common in alcohol-dependent individuals. Event-related oscillations (EROs) have been suggested to be good endophenotypes associated with ethanol dependence in clinical studies. Recently EROs have also been demonstrated to occur in rodents in response to stimuli that are similar to that used in human clinical studies. The objective of the present study was to characterize EROs in adult P and NP rats. A time-frequency representation method was used to determine delta, theta, and alpha/beta ERO energy and the degree of phase variation in the parietal cortex of adult P and NP rats. The present results suggest that the decrease in P3 amplitudes previously shown in P rats were not associated with changes in ERO energy but were significantly associated with decreases in evoked delta and alpha/beta phase locking. These studies demonstrate ERO measures may also be good endophenotypes in animal models of alcoholism.

Adolescent ethanol exposure: does it produce long-lasting electrophysiological effects?

This review discusses evidence for long-lasting neurophysiological changes that may occur following exposure to ethanol during adolescent development in animal models. Adolescence is the time that most individuals first experience ethanol exposure, and binge drinking is not uncommon during adolescence. If alcohol exposure is neurotoxic to the developing brain during adolescence, not unlike it is during fetal development, then understanding how ethanol affects the developing adolescent brain becomes a major public health issue. Adolescence is a critical time period when cognitive, emotional, and social maturation occurs and it is likely that ethanol exposure may affect these complex processes. To study the effects of ethanol on adolescent brain, animal models where the dose and time of exposure can be carefully controlled that closely mimic the human condition are needed. The studies reviewed provide evidence that demonstrates that relatively brief exposure to high levels of ethanol, via ethanol vapors, during a period corresponding to parts of adolescence in the rat is sufficient to cause long-lasting changes in functional brain activity. Disturbances in waking electroencephalogram and a reduction in the P3 component of the event-related potential (ERP) have been demonstrated in adult rats that were exposed to ethanol vapor during adolescence. Adolescent ethanol exposure was also found to produce long-lasting reductions in the mean duration of slow-wave sleep (SWS) episodes and the total amount of time spent in SWS, a finding consistent with a premature aging of sleep. Further studies are necessary to confirm these findings, in a range of strains, and to link those findings to the neuroanatomical and neurochemical mechanisms potentially underlying the lasting effects of adolescent ethanol exposure.

Effects of adolescent ethanol exposure on sleep in adult rats

Although adolescent ethanol (EtOH) exposure has been associated with long-lasting changes in brain function, little is known as to whether EtOH exposure during adolescence alters sleep and cortical arousal. This study examined protracted alterations in sleep in adult rats exposed to EtOH during adolescence. Adolescent male Wistar rats were exposed to EtOH vapor for 12 h/day for 5 weeks. Cortical electroencephalograms were obtained during 4-h recording sessions after 5 weeks of withdrawal from EtOH. Adolescent EtOH exposure significantly reduced the mean duration of slow-wave sleep (SWS) episodes and the total amount of time spent in SWS in EtOH-exposed rats, compared to controls. Spectral analysis revealed that adolescent EtOH exposure significantly increased cortical peak frequencies during SWS in the 2-4, 4-6, and 6-8 Hz bands. Taken together, our findings suggest that chronic EtOH exposure in adolescent rats reduces measures of SWS, an effect also seen as part of normal aging. Although the cellular and molecular mechanisms mediating the consequences of EtOH exposure on the aging process are not known, the similarities between adolescent EtOH exposure and aging merits further investigation.

Electrophysiological effects of dizocilpine (MK-801) in adult rats exposed to ethanol during adolescence

BACKGROUND

Despite evidence showing persistent changes in N-methyl-D-aspartate (NMDA)-receptor function following ethanol (EtOH) exposure, the contribution of NMDA systems to the long-term neurophysiological consequences of adolescent EtOH exposure is unclear. The aims of this study were the following: (1) to determine whether adolescent EtOH exposure produces neurophysiological changes after a prolonged withdrawal period in adult rats and (2) to assess protracted alterations in neurophysiological responses to the NMDA antagonist MK-801 in adult rats exposed to EtOH during adolescence.

METHODS

Adolescent male Wistar rats were exposed to EtOH vapor for 12 h/d for 5 weeks. The effects of MK-801 (0.0 to 0.1 mg/kg, intraperitoneally) on the electroencephalogram (EEG) and auditory event-related potentials (ERPs) were assessed after 8 weeks of abstinence from EtOH.

RESULTS

Experiments in aim 1 revealed that adolescent EtOH exposure reduced EEG variability in the frontal cortex in the 4 to 6 Hz band but had no effect on cortical and hippocampal EEG power and ERPs. Experiments in aim 2 showed that MK-801 significantly reduced EEG power in the parietal cortex (4 to 6 Hz, 6 to 8 Hz, 8 to 16 Hz, 16 to 32 Hz) and hippocampus (16 to 32 Hz) and EEG variability in the parietal cortex (6 to 8 Hz, 16 to 32 Hz) following adolescent EtOH exposure. MK-801 produced a significant decrease in hippocampal EEG variability (4 to 6 Hz, 8 to 16 Hz, 16 to 32 Hz) in control, but not in EtOH-exposed rats. MK-801 reduced frontal P1 ERP amplitude and latency in response to the rare tone in EtOH-exposed rats compared to controls. In contrast, MK-801 significantly reduced P3 ERP amplitude and latency in control, but not in EtOH-exposed rats.

CONCLUSIONS

The effects of MK-801 on hippocampal EEG variability and P3 ERP amplitude and latency are significantly attenuated after a prolonged withdrawal period following adolescent EtOH exposure. However, the inhibitory effects of MK-801 on cortical and hippocampal EEG power were enhanced in rats exposed to EtOH during adolescence. Taken together, these data suggest protracted changes in NMDA systems following adolescent EtOH exposure.

Learning large-scale spatial relationships in a maze and effects of MK-801 on retrieval in the rhesus monkey

Monkeys have strong abilities to remember the visual properties of potential food sources for survival in the nature. The present study demonstrated the first observations of rhesus monkeys learning to solve complex spatial mazes in which routes were guided by visual cues. Three monkeys were trained in a maze (6 m x 6 m) included of four different mazes. We recorded the cue and cup errors, latencies, and pathway for each trial. The data showed that monkeys learned the target place after three days in the first maze and spent a shorter time in learning the following mazes. The maze was an efficient method to measure the ability and proceeding of spatial memory in monkeys. Moreover, working memory can also be tested by using the maze. MK-801 at 0.02 mg/kg but not at 0.005 mg/kg impaired monkeys' retrieval of spatial memory after they learned all four mazes. The present maze may provide an efficient method to help bridging the gap in cognition between nonhuman primates and humans, and in particular to gain insight into human cognitive function and dysfunction.

EEG effect of basal forebrain neuropeptide Y administration in urethane anaesthetized rats

Neuropeptide Y (NPY) is present both in local neurons as well as in fibers in the basal forebrain (BF), an area that plays an important role in the regulation of cortical activation. In previous studies, NPY axons were found to innervate corticopetal cholinergic cells in this area. In addition, identified NPY positive neurons have been shown to be silent during cortical activation, but active during slow EEG waves. However, no in vivo studies have shown the effect of local NPY release in the BF on the EEG. In the present experiments, the EEG was examined following NPY injection (0.5 microl, 300-500 pmol) into the BF of urethane-anaesthetized rats. Fronto-parietal EEG was recorded on both sides and relative EEG power was calculated in the delta (0-3 Hz), theta (3-9 Hz), alpha (9-16 Hz) and beta (16-48 Hz) frequency bands. We found a significant increase in relative delta power and a decrease in the power of all higher frequency bands (theta, alpha, beta) after NPY injection. These results suggest that NPY can inhibit cortical activation via the BF.

Electrophysiological Effects of Allopregnanolone in Rats With a History of Ethanol Exposure

BACKGROUND

Sensitivity to the anticonvulsant effects of allopregnanolone (ALLO) is enhanced during the early phase of ethanol (EtOH) withdrawal. However, it is unclear whether this enhanced sensitivity generalizes to ALLO's neurobehavioral effects during protracted abstinence. The purpose of this study was to examine the neurophysiological effects of ALLO in rats with a history of chronic EtOH exposure after a protracted period of abstinence.

METHODS

Male Wistar rats were exposed to EtOH vapor for 14 hr/day for 5 weeks. Blood EtOH levels were maintained between 200 and 250 mg/dl. The effects of ALLO (0.0-10 mg/kg, intraperitoneally) on motor activity, the electroencephalogram (EEG), and auditory event-related potentials then were assessed after 6 to 8 weeks of abstinence from EtOH.

RESULTS

ALLO's effects on the EEG were consistent with previous studies and were unaffected by EtOH exposure. ALLO increased high-frequency EEG power and shifted peak EEG frequencies in a benzodiazepine- and barbiturate-like manner in both the cortex and the hippocampus. The effects of ALLO on event-related potentials were attenuated in rats with a history of EtOH exposure. Low doses of ALLO (1 and 5 mg/kg) reduced cortical P1 amplitude in response to the standard tone but only in the control group. ALLO also increased N1 amplitude in the hippocampus of the control group while having no significant effect in EtOH-exposed rats. Low doses of ALLO (1 and 5 mg/kg) were found to increase motor activity.

CONCLUSIONS

These data indicate that a history of EtOH exposure attenuates some of the neurophysiological effects of ALLO in a manner consistent with cross-tolerance. Taken together, these data suggest that increased sensitivity to ALLO's neurobehavioral effects is limited to the early phases of EtOH withdrawal and may not extend to more protracted periods of abstinence.

N-methyl-D-aspartate glutamate receptors and alcoholism: reward, dependence, treatment, and vulnerability

This review takes a translational neuroscience perspective on the role of glutamate systems in human ethanol abuse and dependence. Ethanol is a simple molecule with profound effects on many chemical systems in the brain. Glutamate is the primary excitatory neurotransmitter in the brain. Glutamatergic systems are targets for the actions of ethanol via its antagonism of the N-methyl-D-aspartate (NMDA) subtype of the glutamate receptor and other mechanisms. The modulation of glutamatergic function by ethanol contributes to both euphoric and dysphoric consequences of ethanol intoxication. Adaptations within glutamatergic systems appear to contribute to ethanol tolerance and dependence and to both acute and protracted features of ethanol withdrawal. Perhaps because of the important glutamatergic mediation of the behavioral effects of ethanol, glutamatergic systems appear to contribute to the vulnerability to alcoholism, and novel glutamatergic agents may play a role in the treatment of ethanol abuse and dependence.

EEG and ERP profiles in the high alcohol preferring (HAP) and low alcohol preferring (LAP) mice: relationship to ethanol preference

Neurophysiological measures, such as decreased P300 amplitude and altered EEG alpha activity, have been associated with increased alcoholism risk. The purpose of the present study was to extend the assessment of the neurophysiological indices associated with alcohol consumption to a recently developed mouse model of high ethanol consumption, the first replicate line of high alcohol preferring (HAP-1) and low alcohol preferring (LAP-1) mice. Male HAP-1, LAP-1, and HS mice from the Institute for Behavioral Genetics at the University of Colorado Health Science Center (i.e., HS/Ibg mice) were implanted with cortical electrodes. EEG activity, and event related potentials (ERPs) were then examined. Following electrophysiological assessment, ethanol preference was assessed to examine the relationship between neurophysiological indices and ethanol consumption. EEG analyses revealed that HAPs and HS/Ibgs had greater peak frequency in the 2-4-Hz band and lower peak frequency in the 6-8- and 1-50-Hz bands of the cortical EEG compared to LAPs. Compared to HAPs, LAPs and HS/Ibgs had decreased peak EEG frequency in the 8-16-Hz band. Decreased parietal cortical power from 8 to 50 Hz was associated with high initial ethanol preference in HAP mice. In regards to ERPs, P1 amplitude was greater in HAPs compared to both LAPs and HS/Ibgs and the P3 latency in LAPs was decreased compared to both HAPs and HS/Ibgs. As expected, HAPs consumed more ethanol and had higher ethanol preference than LAPs and HS/Ibgs. There were no significant differences in ethanol intake or preference between HS/Ibgs and LAPs. These data indicate that selective breeding of the HAP and LAP lines has resulted in the divergence of EEG and ERP phenotypes. The differences observed suggest that increased cortical P1 amplitude and altered cortical EEG activity in the 8-50-Hz frequency range may be neurophysiological 'risk factors' associated with high ethanol consumption in mice. Decreased P3 latency in LAPs compared to HAPs and HS/Ibgs mice may be a 'protective factor'.

Neonatal nicotine exposure alters hippocampal EEG and event-related potentials (ERPs) in rats

A consensus is forming that nicotine can damage the developing rat central nervous system. However, few studies have assessed the electrophysiological effects of neonatal nicotine exposure in rodents in brain regions known to be sensitive to the teratogenic properties of nicotine. In a previous study it was reported that 1.0 and 4.0 mg/kg/day nicotine exposure from postnatal days 4-9, a developmental period corresponding to human third-trimester exposure, significantly altered hippocampal event-related potentials (ERPs) but did not effect cortical ERPs, cortical EEG, or hippocampal EEG. Because alterations in behavior and cortical/hippocampal neurochemistry and morphology have been reported following nicotine exposure, the present study used a higher dose of nicotine during the postnatal period (6.0 mg/kg/day) determine if functional changes in the EEG of these regions might contribute to behavioral changes that have been observed. Male Sprague-Dawley rats were exposed to 6. 0 mg/kg/day nicotine via gastric infusion using an artificial rearing, "pup-in-the-cup," technique for 6 consecutive days (postnatal days 4-9). At adulthood, EEG and auditory ERPs were recorded from the cortex and hippocampus. There were no significant differences in EEG or ERPs recorded from the cortex between nicotine-treated and control subjects. Examination of the hippocampal EEG revealed significantly decreased power in the 1-2-Hz frequency band of nicotine-treated rats. In addition, there was a significantly attenuated P300 ERP response to a noise tone in the nicotine-treated rats compared to controls. These data indicate that neonatal nicotine exposure alters functional activity in the hippocampus of adult rats. These effects are likely to be the result of synaptic disorganization in the hippocampus, and indicate that neonatal nicotine exposure exerts teratogenic effects on the developing central nervous system, particularly the hippocampus, which persist into adulthood.

The contribution of electrophysiology to knowledge of the acute and chronic effects of ethanol

This review describes the effects of ethanol on the components of neuronal transmission and the relationship of such effects to the behavioural actions of ethanol. The concentrations of ethanol with acute actions on voltage-sensitive ion channels are first described, then the actions of ethanol on ligand-gated ion channels, including those controlled by cholinergic receptors, 5-hydroxytryptamine receptors, the various excitatory amino acid receptors, and gamma-aminobutyric acid receptors. Acute effects of ethanol are then described on brain areas thought to be involved in arousal and attention, the reinforcing effects of ethanol, the production of euphoria, the actions of ethanol on motor control, and the amnesic effects of ethanol; the acute effects of ethanol demonstrated by EEG studies are also discussed. Chronic effects of alcohol on neuronal transmission are described in the context of the various components of the ethanol withdrawal syndrome, withdrawal hyperexcitability, dysphoria and anhedonia, withdrawal anxiety, craving, and relapse drinking. Electrophysiological studies on the genetic influences on the effects of ethanol are discussed, particularly the acute actions of ethanol and electrophysiological differences reported in individuals predisposed to alcoholism. The conclusion notes the concentration of studies on the classical transmitters, with relative neglect of the effects of ethanol on peptides and on neuronal interactions between brain areas and integrated patterns of neuronal activity.

Neurontensin studies in alcohol naive, preferring and non-preferring rats

Neurotensin is a tridecapeptide, present in the central nervous system and the gastrointestinal tract in man and animals. Previous studies in mice selectively bred for differences in hypnotic sensitivity to ethanol have provided data to suggest that neurotensinergic systems may mediate differences in ethanol's actions in these animals. The present study sought to determine if brain neurotensin levels differed between two lines of rats which have been selectively bred for alcohol preferring or non-preferring behaviors. In addition, electroencephalographic and event-related potential responses to intracerebroventricular saline and neurotensin (10 or 30 microg) were evaluated between the rat lines. Similar to human subjects at high genetic risk for alcoholism, preferring rats were found to have more electroencephalographic fast frequency activity and lowered amplitude of the P3 component of the event-related potential in cortical sites under the saline condition. Overall, electrophysiological response to neurotensin, in the two rats lines, was substantially similar to what has been reported previously in outbred Wistar rats, and consisted of dose-related decreases in overall electroencephalographic spectral power concomitant with increases in amplitude and decreases in the latency of the N1 component of the event-related potential. However, differences in neurotensin responses between the preferring and non-preferring rat lines were also found. The differences in electroencephalographic high-frequency activity and in P3 amplitude seen between the rat lines under control conditions were eliminated by administration of neurotensin. In addition, preferring rats appeared to be more sensitive to neurotensin-induced increases in N1 amplitude. Brain neurotensin concentrations were also found to differ between the lines. Significantly lower concentrations of neurotensin were found in the frontal cortex of preferring rats when compared to non-preferring rats or outbred Wistars. Taken together, these studies suggest that differences in the regulation of neurotensin neurons may contribute to the expression of behavioral preference for ethanol consumption in selective rat lines. Additionally, drugs targeting the neurotensinergic system may plausibly be of utility in the treatment of alcoholism.

Neurophysiological effects of intracerebroventricular administration of urocortin

The recently isolated Corticotropin Releasing Factor (CRF) related peptide, urocortin, has been reported to elicit a different behavioral profile than that of CRF. CRF is a potent anxiogenic agent and stimulant of motor activity whereas under similar conditions urocortin is a potent anorectic and mild locomotor stimulant. The neurophysiological effects of this newly synthesized peptide have not yet been examined. The present study evaluated the effects of intracerebroventricular administration of 3 doses of urocortin on the electroencephalogram (EEG) and on Event-Related Potentials (ERPs) in rats. Twenty male Wistar rats were implanted with electrodes in the amygdala and dorsal hippocampus, a cannula into the lateral ventricle, and skull surface electrodes over the frontal and parietal cortices. Following recovery from surgery, urocortin (0.01-1.0 microg) was infused into the lateral ventricle 5 min prior to the recording of EEG (10 min) and ERPs (10 min). Urocortin at any of the doses, did not produce any electrographic or behavioral signs of seizure activity. The predominant effect of urocortin infusion on EEG spectral activity was an increase in mean power in the 4-16 Hz range in the frontal cortex and a decrease in EEG stability in the frontal cortex and amygdala. Urocortin administration also decreased the latency of the P3 component of the ERP in the amygdala and hippocampus. These neurophysiological effects, that only partially overlap with those of CRF, are consistent with the behavioral profile described following urocortin administration in rats. Overall, these data further support the assertion that urocortin functions as a mild CNS stimulant enhancing arousal, as measured by EEG, and modulating the speed of stimulus evaluation as measured by ERPs.