Ethanol dependence in the rat: role of non-specific and limbic regions in the withdrawal reaction

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.

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.

Comparison of the Onset of Hypoactivity and Anxiety-Like Behavior During Alcohol Withdrawal in Adolescent and Adult Rats

BACKGROUND

Early life alcohol use is associated with increased alcoholism risk. It has been suggested that alterations in the sensitivity of adolescents to the acute effects of ethanol may contribute to this risk by promoting excessive intake. However, an enhanced propensity for developing ethanol dependence or withdrawal-related behavior could also contribute to increased risk. The objective of these studies was to compare the appearance of ethanol withdrawal-related behaviors in adolescent and adult rats.

METHODS

Male Sprague-Dawley rats were exposed to ethanol vapor (12 hr/day) for 12 or 14 days during adolescence or adulthood. In the first study, locomotor activity was assessed after 2, 4, 7, 10, and 14 days of ethanol exposure. In the second study, open field behavior was assessed after 5 or 12 days of ethanol exposure. In follow-up studies, changes in sucrose preference during ethanol withdrawal and motor activity during food restriction were assessed in adolescent rats. Withdrawal assessments were made 7 to 9 hr after daily exposure ended.

RESULTS

Hypoactivity emerged rapidly in adolescent rats during ethanol withdrawal in activity tests, but comparable reductions were not found in adult rats. However, hypoactivity developed in both adolescents and adults in the novel open field. Enhanced anxiety-like behavior in the open field was not observed in either age group during withdrawal. Finally, sucrose preference was unchanged during ethanol withdrawal, and food restriction increased motor activity in adolescent rats.

CONCLUSIONS

These data confirm that symptoms of withdrawal may be differentially expressed in adolescent and adult rats. However, discrepancies in hypoactivity between studies suggest that assessment in a novel versus familiar environment may influence the expression of withdrawal-related behaviors.

Consequences of Multiple Withdrawals From Alcohol

This article represents the proceedings of a symposium at the 2003 annual meeting of the Research Society on Alcoholism in Fort Lauderdale, FL, organized by Theodora Duka and chaired by Dai Stephens. The purpose of the symposium was to examine the effects of multiple experiences of withdrawal from alcohol in animals made dependent on alcohol and in humans who are alcohol dependent. Parallels were drawn to the effects of repeated short-lived high-content alcohol exposures in animals and in humans who are social drinkers but indulge in binge drinking. The presentations were (1) Multiple detoxifications and risk of relapse in abstinent alcoholics, by John Gentry and Robert Malcolm; (2) Emotional and cognitive impairments after long-term use of alcohol: relationship to multiple detoxifications and binge drinking, by Theodora Duka; (3) The effect of repeated withdrawal from ethanol on conditioning to appetitive stimuli, by Tamzin Ripley, Gilyanna Borlikova, and Dai Stephens; (4) Alcohol withdrawal kindling: electrographic measures in a murine model of behavioral seizure sensitization, by Lynn Veatch and Howard Becker; and (5) Binge drinking induced changes in CNS, by Fulton Crews.

Integrative Neurobiology of the Alcohol Withdrawal Syndrome???From Anxiety to Seizures

This article represents the proceedings of a symposium presented at the 2003 Research Society on Alcoholism meeting in Ft. Lauderdale, Florida, organized and chaired by Carl L. Faingold. The presentations were (1) Overview, by Carl L. Faingold; (2) Stress, Multiple Alcohol Withdrawals, and Anxiety, by Darin Knapp; (3) Relationship Between Genetic Differences in Alcohol Drinking and Alcohol Withdrawal, by Julia Chester; (4) Neuronal Mechanisms in the Network for Alcohol Withdrawal Seizures: Modulation by Excitatory Amino Acid Receptors, by Carl L. Faingold; and (5) Treatment of Acute Alcohol Withdrawal and Long-Lasting Alterations in Hippocampal Neuronal Networks, by Larry P. Gonzalez. The presentations emphasized the importance of using intact behaving animals to advance the understanding of the human alcohol withdrawal syndrome. This involves applying and amplifying the neurophysiological and neurotransmitter findings observed in vitro to the network-based neurobiological mechanisms that are involved in several important aspects of the specific behaviors observed clinically. The symposium provided evidence that the organizational aspects of neuronal networks in the intact nervous system add another nexus for the action of alcohol and drugs to treat alcohol withdrawal that may not be readily studied in isolated neural elements used in in vitro approaches.

Periadolescent alcohol exposure has lasting effects on adult neurophysiological function in rats

Most individuals have their first experience with ethanol (EtOH) consumption as adolescents. Episodes of high EtOH drinking, lasting from hours to days (i.e. binges), are not uncommon. Thus, adolescent EtOH drinking has become a significant health concern due to the possible protracted effects of high doses of EtOH on behavior and the developing brain. This study assessed the effects of brief high levels of EtOH during periadolescence on subsequent behavior and electrophysiology in adult rats. Male Sprague-Dawley rats were exposed to EtOH vapor for 5 days (i.e. postnatal days 35-40) or 10 days (i.e. postnatal days 30-40) for 12 h/day. Locomotor activity, EEG activity, and event-related potentials (ERPs) were then assessed at 1 and 6-7 weeks post EtOH exposure. Significant differences in locomotor activity were not observed at 1 week or 6-7 weeks post-ethanol exposure. However, EtOH exposure did have long-term electrophysiological effects. EtOH exposure increased the frequency of the EEG in the 1-2 Hz range in the parietal cortex and the 16-32 Hz range in the hippocampus. EtOH exposure also increased hippocampal N2 amplitude, decreased hippocampal P3 amplitude, and decreased cortical and hippocampal P2 amplitudes. While these findings are generally similar to those reported following long-term ethanol exposure during adulthood, alcohol exposure during adolescence appears to produce more robust hippocampal effects following shorter periods of exposure. In addition, these data indicate that, in the absence of overt behavioral differences, there are long-lasting changes in the functional brain activity of adult rats briefly exposed to high levels of EtOH during the periadolescent period.

Repeated ethanol withdrawal produces site-dependent increases in EEG spiking

Recent studies have suggested an important kindling-like exacerbation of ethanol withdrawal symptoms after repeated cycles of ethanol intoxication and withdrawal. Few studies, however, have evaluated the effect of multiple episodes of intoxication and withdrawal on spontaneous EEG activity after cessation of ethanol intake. In this study, electrographic activity in cortical and subcortical structures male Sprague-Dawley rats was examined after multiple cycles of ethanol intoxication and withdrawal. After surgical implantation of electrodes, animals received repeated cycles of chronic ethanol exposure in vapor inhalation chambers for 10 or 20 days, with 4-day withdrawal periods between each. Upon removal from the inhalation chamber, spontaneous EEG activity was recorded intermittently for 72 hr. These data were then examined for the presence of spikes and sharp waves. Results indicate that the levels of spike and sharp wave activity observed vary with both length of ethanol exposure and with the number of withdrawal cycles, and that these effects varied with neuronal site. Changes in spike and sharp wave activity were first observed within hippocampal areas, with other subcortical and cortical sites showing increased activity after additional ethanol exposure or additional cycles of intoxication and withdrawal. Hippocampal areas CA1 and CA3 differed significantly from one another in their response to chronic ethanol exposure, with area CA1 most affected by changes in amount of ethanol exposure and are CA3 most affected by number of withdrawal cycles. These results indicate an increased severity of the ethanol withdrawal syndrome after repeated ethanol withdrawal episodes and suggest differential, site-specific changes in neuronal excitability.

Ethanol dependence and withdrawal selectively alter localized cerebral glucose utilization

The 2-deoxyglucose technique was used to determine local cerebral glucose utilization (LCGU) in over 50 brain regions of rats physically dependent upon ethanol and compared to those of acutely intoxicated and those undergoing an overt ethanol-withdrawal syndrome. Dependent-intoxicated rats (average blood ethanol concentration 64 mM) had decreased LCGU in 13/54 regions, including those associated with the limbic system, cerebellum, and motor system. The ethanol withdrawal syndrome was associated with 17/50 gray regions showing an increase, including regions involved with motor function, auditory system, and mammillary bodies-anterior thalamus-cingulate cortex pathway. The most pronounced differences between these groups occurred in regions associated with motor function, cerebellar function, anterior thalamus, and median raphe. Comparisons between dependent-intoxicated and acutely intoxicated rats (average blood ethanol concentration 66 mM) revealed that acute intoxication was associated with a relatively greater reduction in LCGU in regions involved with sensory-related functions, mammillary bodies, and median raphe. With the development of dependence, adaptation occurred in these regions except for inferior colliculus and median raphe. Dependence was also associated with a relative decrease in LCGU in white matter, limbic system, and extrapyramidal motor system.

Alcoholism and panic disorder: is the comorbidity more than coincidence?

Studies on alcoholic patients have found a higher than expected prevalence of panic disorder, and suggest a positive correlation between the level of alcohol consumption and severity of anxiety. Conversely, there is an increased prevalence of alcoholism among patients with panic disorder and their blood relatives. A comparison of symptoms, physiological and neurochemical changes known to occur in both alcohol withdrawal and panic disorder reveals a degree of similarity between the 2 conditions. Based on the data, we propose that the chemical and cognitive changes occurring as the result of repeated alcohol withdrawals may kindle and condition coincidence of panic attacks in susceptible individuals. Implications of our postulates for treatment of alcohol withdrawal and panic disorder in alcoholics and for future studies are discussed.

Alcohol withdrawal-induced changes in brain biogenic amines in mice: influence of the genotype

Alterations in striatal and hippocampal dopamine (DA) and serotonin (5HT) activities were investigated in two inbred strains of mice (C57B1 and Balb/c) after 3 withdrawal periods following 5 months chronic ethanol administration. Two groups of animals with different levels of ethanol administration (15% and 30%, v/v) were examined. A striking strain dependency has been noted. Striatal dopaminergic mechanisms of the Balb/c strain are profoundly disturbed in both groups. In contrast no changes were noted for either transmitter activities in C57B1 mice at any withdrawal time studied. Strain dependency has also been noted for hippocampal serotonin neurotransmission, since only Balb/c mice showed a progressive decrease in 5HT levels. These impairments observed in striatum and hippocampus could be involved in motor incoordinations and convulsions often associated with the withdrawal syndrome. The differences in withdrawal effects we noted between the two strains may be linked to the specific chemical neuroanatomy of the strains. Such specificities could be implied in the well known variability of withdrawal induced behavior in man.

Spontaneous versus elicited seizures following ethanol withdrawal: differential time course

Ethanol withdrawal symptoms in clinical populations are observed to occur in unique clusters which differ in time of onset relative to the time of withdrawal and in their duration. Since periods of mild symptoms are sometimes observed between these clusters of more severe symptoms, the symptom clusters may reflect separate periods of hyperexcitability during which times different neuronal mechanisms are involved. To investigate this possibility in an animal model of ethanol withdrawal, rats were chronically exposed to ethanol in vapor inhalation chambers. Upon withdrawal from this exposure regimen, the time course of spontaneous seizure activity was observed for a period of 84 hr and compared to sensitivity to seizures elicited by audiogenic stimuli or by the convulsant drug picrotoxin. Spontaneous seizure events were observed to occur in clusters, and these clusters were differentially correlated with periods of increased sensitivity to induced seizure activity. These results further support the suggestion that seizure sensitivity during ethanol withdrawal may indicate the involvement of multiple, independent, neuronal mechanisms.

Cerebral 2-deoxyglucose uptake in rats during ethanol withdrawal and postwithdrawal

The overt ethanol withdrawal syndrome is associated with a generalized increase in cerebral uptake of 2-deoxyglucose. Relatively high elevations of 2-deoxyglucose were observed in many structures associated with motor function, the mamillary body-anterior thalamus-cingulate cortex pathway, many thalamic nuclei, and the raphe. Overtly withdrawing rats had higher levels of 2-deoxyglucose than postwithdrawing animals that had been abstinent for 1-5 weeks in 96% of the gray areas evaluated. Postwithdrawal was associated with increased amounts of 2-deoxyglucose in comparison to controls in 80% of the gray areas evaluated. Postwithdrawal and control rats did not differ in some areas involved with motor function and some limbic structures, such as the mamillary body-anterior thalamus-cingulate cortex pathway. It is concluded that the ethanol-withdrawal syndrome results in alterations in cerebral physiology, some of which persist for at least 5 weeks postwithdrawal.

Ethanol and polyneuropathy

Two groups of alcoholics (30 patients each)--identified by the MALT score--were examined. Clinical and laboratory investigations showed no connection between thiamine, riboflavin, or Vitamin B6 deficiency and development of the polyneuropathy. Neither the polyneuropathy nor the diminished sensory conduction velocity were related to malnutrition. The relation between the duration of alcoholism and symptoms of polyneuropathy was highly significant in one group. The neurotoxicity of ethanol was confirmed in an experiment with rats.

Changes in physostigmine-induced hippocampal seizures during ethanol withdrawal

Hippocampal cholinergic neurons are sensitive to acute ethanol administration, and specific alterations are seen in the functioning of these neurons following chronic ethanol. The present study examined the effects of chronic ethanol exposure and withdrawal on the sensitivity of the hippocampus to local injection of physostigmine, an inhibitor of acetylcholine metabolism. While intrahippocampal physostigmine elicited hippocampal seizure activity in 80% of the animals tested during withdrawal from chronic exposure to low levels of ethanol, seizure activity was elicited in only 30% of ethanol-naive subjects. These results suggest that chronic ethanol exposure may increase the sensitivity of hippocampal neurons to cholinergic stimulation, and that some of the symptoms of ethanol withdrawal may be related to this change.

Electroencephalographic and behavioral correlates in rats during repeated ethanol withdrawal syndromes

Rats chronically implanted with electrodes in the amygdala, thalamus, hippocampus, and cortex were addicted twice, separated by an interval of 2 weeks, with 18 days of ethanol liquid diet. The diet consumption and the blood ethanol levels (BELs) were carefully controlled twice a day during both addictive phases. After ethanol removal the behavioral and electroencephalographic (EEG) changes were continuously monitored for 24 h. During each withdrawal the behavioral and EEG changes appeared at the same time, the EEG changes being of shorter duration. Behavioral and EEG changes (primarily in hippocampus) were more severe and of earlier onset during the second withdrawal. In spite of an ethanol liquid diet intake comparable to that of the first addiction, during the ethanol readdiction the BELs were found to fluctuate. The results support the hypothesis of an ethanol withdrawal potentiation through a mechanism of kindling of different brain areas related to the observed BEL fluctuations.

Ethanol-withdrawal syndrome associated with both general and localized increases in glucose uptake in rat brain

Glucose uptake was studied in the brains of rats undergoing an overt ethanol-withdrawal syndrome by 2-deoxy-D-[14C]glucose autoradiography. In addition to a general increase in glucose uptake, localized alterations were observed in sensorimotor cortex, globus pallidus, thalamus and cerebellum. The results suggest that the ethanol-withdrawal syndrome is associated with a general increase in glucose metabolism as well as localized increases in functionally distinct regions of sensory and motor brain regions.

Acute and chronic opiate effects on single units and EEG of medial thalamus and hippocampus: a latency analysis

Medial thalamic (MT), and hippocampal (HPC) EEG, and single unit activity, and frontal cortical (CTX) EEG were recorded following IV infusions of 0.625 mg morphine/kg in drug-naive, and following 0.0125 mg naloxone/kg in morphine-dependent paralyzed rats. Particular effort was made to assess the latency of the responses in relation to the appearance of high-voltage bursts in the CTX EEG (which has been shown to correlate well with the behavioral state of the animal) and thereby to assess the possible primacy of the effects. In MT, the predominant effect of morphine on units of naive animals was a decrease in activity; that of naloxone in dependent animals, an increase in activity. Morphine decreased theta activity in the MT EEG, while naloxone precipitated theta activity. In the case of morphine, the majority of unit changes preceded CTX EEG changes; in the case of naloxone, most MT unit and EEG changes either coincided with or followed the changed CTX EEG. In contrast, HPC units were relatively unresponsive to morphine, but the HPC EEG often showed marked spiking following the infusion that generally preceded the appearance of spindles in the CTX. Naloxone caused increases and decreases in HPC unit activity, but these changes as well as those of the HPC EEG (also to theta) generally followed corresponding changes in the CTX EEG. The possibility that both areas might be primary sites of action of morphine, but not naloxone, was discussed.

Morphine withdrawal syndrome: differential participation of structures located within the amygdaloid complex and striatum of the rat

The participation of amygdaloid and striatal structures in the various signs of morphine withdrawal syndrome (MWS) has been investigated using two complementary approaches: intracerebral application of naloxone in various nuclei of dependent rats and effects of various lesions and transections on systemically induced MWS. In morphine dependent rats local application of naloxone (10 micrograms in 0.1 microliter solution) in the vicinity of either the central nucleus of the amygdala or the lateral anterior nucleus but not in adjacent amygdaloid or striatal nuclei elicited the jump sign. Diarrhea was more frequently elicited by application of naloxone in the striatum or centromedial amygdala than the basolateral parts of the complex. In contrast, there was no specific anatomical correlates to the remaining signs including wet shakes, paw tremor, teeth chattering and chewing. Bilateral electrolytic lesion of the central amygdala or combined transection of the stria terminalis and so-called ventral amygdalofugal pathway eliminated the jump without affecting the remaining signs. In contrast a large bilateral destruction of the entire striatrum did not significantly affect the various signs. Bilateral transection of the stria terminalis reduced only the occurrence of the wet shakes. Also, a transection of the medial forebrain bundle considerably reduced the 3 main signs, i.e. jump, wet shakes and diarrhea. These results suggest that, in analogy to the acute actions of morphine, MWS should not be considered as a unitary phenomenon but as an ensemble of signs which probably reflect the intense activation induced by naloxone in a number of brain sites consequent to the abrupt interruption of opioid actions in a dependent animal. The significance of these results is discussed with reference to previous anatomical, biochemical and behavioural studies performed on the amygdala.