Ethanol Withdrawal Hyperexcitability Research Articles

Neural Adaptation Leads to Cognitive Ethanol Dependence

Physiological alcohol dependence is a key adaptation to chronic ethanol consumption that underlies withdrawal symptoms, is thought to directly contribute to alcohol addiction behaviors, and is associated with cognitive problems such as deficits in learning and memory. Based on the idea that an ethanol-adapted (dependent) animal will perform better in a learning assay than an animal experiencing ethanol withdrawal will, we have used a learning paradigm to detect physiological ethanol dependence in Drosophila. Moderate ethanol consumption initially degrades the capacity of larvae to learn, but they eventually adapt and are able to learn as well as ethanol-naive animals. However, withholding ethanol from ethanol-adapted larvae impairs learning. Ethanol reinstatement restores the capacity to learn, thus demonstrating cognitive dependence on ethanol. The larval nervous system also shows ethanol-withdrawal hyperexcitability. Larvae reach ethanol concentrations equivalent to 0.05 to 0.08 blood-alcohol concentration-levels that would be mildly intoxicating in humans. These ethanol-induced changes in learning are not the product of sensory deficits or state-dependent learning. This is the first demonstration of cognitive ethanol dependence in an invertebrate genetic model system.

Tolerance to ethanol sedation and withdrawal hyper-excitability is mediated via neuropeptide Y Y1 and Y5 receptors

Aims Neuropeptide Y (NPY) is widely distributed throughout the brain and has been implicated in some of the actions of ethanol. The aim of the present study was to characterize the subtypes of NPY receptors in ethanol induced sedation, tolerance and withdrawal hyper-excitability. Main methods The loss of righting reflex paradigm was used to record the sleep duration in mice. Key findings The acute administration of ethanol (3–4 g per kg, i.p., 20% v/v) resulted in marked sedation. While prolonged ethanol consumption led to the development of tolerance, the mice showed hyper-excitability following ethanol withdrawal. Prior acute intracerebroventricular (i.c.v.) injection of NPY (5–20 ng per mouse) or NPY Y1 and Y5 receptors agonist [Leu 31, Pro 34]-NPY (0.02–0.2 ng per mouse) potentiated ethanol induced sedation. On the other hand, administration of selective NPY Y1 receptor antagonist BIBP3226 (5 ng per mouse, i.c.v.) inhibited ethanol induced sedation. Chronic concomitant treatment of NPY (20 ng per mouse, i.c.v.) or [Leu 31, Pro 34]-NPY (0.2 ng per mouse, i.c.v.) to ethanol-fed groups prevented the development of tolerance and attenuated withdrawal hyper-excitability. Moreover, acute treatment of NPY (5 ng per mouse, i.c.v.) or [Leu 31, Pro 34]-NPY (0.02 ng per mouse, i.c.v.) reversed the peak ethanol withdrawal hyper-excitability. Significance The results underscore a role for NPY Y1 and Y5 receptors in the ethanol induced sedation, tolerance and withdrawal hyper-excitability. We suggest that modulation of NPY Y1 and Y5 receptors may be a strategy to address the ethanol withdrawal conditions.

The role of GABAA receptors in the acute and chronic effects of ethanol: a decade of progress

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

Alcohol‐Induced Tolerance and Physical Dependence in Mice With Ethanol Insensitive α1 GABAA Receptors

Although many people consume alcohol (ethanol), it remains unknown why some become addicted. Elucidating the molecular mechanisms of tolerance and physical dependence (withdrawal) may provide insight into alcohol addiction. While the exact molecular mechanisms of ethanol action are unclear, gamma-aminobutyric acid type A receptors (GABA(A)-Rs) have been extensively implicated in ethanol action. The alpha1 GABA(A)-R subunit is associated with tolerance and physical dependence, but its exact role remains unknown. In this report, we tested the hypothesis that alpha1-GABA(A)-Rs mediate in part these effects of ethanol. Ethanol-induced behavioral responses related to tolerance and physical dependence were investigated in knockin (KI) mice that have ethanol-insensitive alpha1 GABA(A)-Rs and wildtype (WT) controls. Acute functional tolerance (AFT) was assessed using the stationary dowel and loss of righting reflex (LORR) assays. Chronic tolerance was assessed on the LORR, fixed speed rotarod, hypothermia, and radiant tail-flick assays following 10 consecutive days of ethanol exposure. Withdrawal-related hyperexcitability was assessed by handling-induced convulsions following 3 cycles of ethanol vapor exposure/withdrawal. Immunoblots were used to assess alpha1 protein levels. Compared with controls, KI mice displayed decreased AFT and chronic tolerance to ethanol-induced motor ataxia, and also displayed heightened ethanol-withdrawal hyperexcitability. No differences between WT and KI mice were seen in other ethanol-induced behavioral measures. Following chronic exposure to ethanol, control mice displayed reductions in alpha1 protein levels, but KIs did not. We conclude that alpha1-GABA(A)-Rs play a role in tolerance to ethanol-induced motor ataxia and withdrawal-related hyperexcitability. However, other aspects of behavioral tolerance and physical dependence do not rely on alpha1-containing GABA(A)-Rs.

Aberrant Synaptic Activation ofN-Methyl-d-aspartate Receptors Underlies Ethanol Withdrawal Hyperexcitability

Chronic ethanol exposure may induce neuroadaptive responses in N-methyl-d-aspartate (NMDA) receptors, which are thought to underlie a variety of alcohol-related brain disorders. Here, we demonstrate that hyperexcitability triggered by withdrawal from chronic ethanol exposure is associated with increases in both synaptic NMDA receptor expression and activation. Withdrawal from chronic ethanol exposure (75 mM ethanol, 5-9 days) elicited robust and prolonged epileptiform activity in CA1 pyramidal neurons from hippocampal explants, which was absolutely dependent upon NMDA receptor activation but independent of chronic inhibition of protein kinase A (PKA). Analysis of Sr(2+)-supported asynchronous NMDA receptor-mediated miniature excitatory postsynaptic currents (mEPSCs) was employed to assess changes in NMDA neurotransmission. After chronic exposure, ethanol withdrawal was associated with an increase in mEPSC amplitude 3.38-fold over that after withdrawal from acute ethanol exposure. Analysis of paired evoked alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid EPSCs and spontaneous mEPSCs indicated that withdrawal after chronic exposure was also associated with a selective increase in action potential evoked but not spontaneous transmitter release probability. Immunoblot analysis revealed significant increases in total NR1, NR2A, and NR2B subunit expression after chronic exposure and unaffected by PKA-inhibition manner. Confocal imaging studies indicate that increased NR1 subunit expression was associated with increased density of NR1 expression on dendrites in parallel with a selective increase in the size of NR1 puncta on dendritic spines. Therefore, neuroadaptation to chronic ethanol exposure in NMDA synaptic transmission is responsible for aberrant network excitability after withdrawal and results from changes in both postsynaptic function as well as presynaptic release.

Ethanol withdrawal seizure susceptibility is associated with upregulation of L- and P-type Ca 2+ channel currents in rat inferior colliculus neurons

Calcium currents in the inferior colliculus (IC) are thought to play an important role in ethanol withdrawal hyperexcitability. Here, we report on the modulation of Ca 2+ channel currents in acutely dissociated IC neurons of rats, exhibiting higher incidence of audiogenic seizures when subjected to ethanol withdrawal. Whole cell Ca 2+ channel currents were activated by depolarizing pulses from a holding potential of –90 mV, in 10 mV increments, using barium (Ba 2+) as the charge carrier. The high threshold voltage-activated (HVA) Ca 2+ channel current density increased significantly in IC neurons following ethanol withdrawal. The gating parameters of HVA Ca 2+ channel currents were only slightly altered, while the fraction of current that did not fully inactivate at positive potentials increased significantly following ethanol withdrawal. Pharmacological dissection of HVA Ca 2+ channel currents suggested that the enhanced current, associated with increased incidence of audiogenic seizures following ethanol withdrawal, was carried by L- and P-type Ca 2+ channels. The upregulation of L- and P-type currents may be responsible for IC neuronal hyperexcitability associated with increased susceptibility to ethanol withdrawal seizures.

Selectivity of the protective effects of dihydropyridine calcium channel antagonists against the ethanol withdrawal syndrome

Four dihydropyridine calcium channel antagonists were compared for their ability to protect against the hyperexcitability produced in mice by withdrawal from chronic ethanol treatment and to protect against seizures due to bicuculline or pentylenetetrazol. Comparison was also made of their effects on locomotor activity, body temperature and motor co-ordination, and with the corresponding effects of the benzodiazepine, diazepam. Nitrendipine, nimodipine, nicardipine (at 50 and 10 mg/kg) and isradipine (at 10 and 4 mg/kg) decreased the withdrawal hyperexcitability, but showed no anticonvulsant action against either bicuculline or pentylenetetrazol. Diazepam (1.5 and 4 mg/kg) both protected against the withdrawal signs and decreased seizure incidence after bicuculline and pentylenetetrazol, although the latter effects were of shorter duration than those on the withdrawal signs. The four dihydropyridines decreased spontaneous locomotor activity, an effect which lasted up to 6 h. Only isradipine and diazepam had any ataxic actions at the doses tested. All the dihydropyridines had hypothermic actions, considerably shorter in duration than effects on withdrawal hyperexcitability, with little evidence of dose dependence, except for nicardipine, which had a larger, dose-related, hypothermic action. Of the four compounds, isradipine was more potent in terms of dose, but not any more selective for effectiveness against the withdrawal signs, than the other three dihydropyridines, and nicardipine was slightly less effective in protecting against the withdrawal signs. The results indicate that the anticonvulsant effects of the dihydropyridines were selective for ethanol withdrawal hyperexcitability, whereas diazepam showed no such selectivity.

Ethanol withdrawal hyperexcitability in vivo and in isolated mouse hippocampal slices.

Withdrawal hyperexcitability was seen in isolated mouse hippocampal slices, prepared after chronic treatment with ethanol, by inhalation for 2 weeks. The pattern of hyperexcitability differed from those seen previously when a different method of ethanol administration and a different strain of mice were used. Thresholds for field potentials were decreased, but the transient increase in paired pulse potentiation, reported earlier, was not evident. Chronic administration of the calcium channel antagonist, isradipine (PN-200-110) during ethanol treatment significantly decreased the withdrawal syndrome, both in vivo and in vitro. Brain concentrations of isradipine during the test period were found to be sufficient to produce acute effects on the withdrawal hyperexcitability. No changes were seen in the field potentials when slices were prepared after treatment with isradipine alone. A small, but significant, increase in excitability was seen in vivo after the treatment with isradipine alone. Previous studies showed that isradipine did not protect against the hyperexcitability due to gamma-aminobutyric acid (GABA)A antagonism, so the results suggest that neuronal calcium channels may be involved in ethanol withdrawal hyperexcitability, but decreases in GABAA inhibition may not be important.

Effects of Ethanol on Ion Channels

Ion channels play critical roles in nervous system function, from initiating rapid synaptic activity to propagation of action potentials. Studies have indicated that many of the effects of ethanol on the nervous system are likely caused by the actions of ethanol on ion channels. Ion channels are multimeric structures that gate ions through subtle changes in tertiary structure. Ethanol readily enters molecular sites within multimeric ion channels, modifying intermolecular forces and bonds that are important for the open-close-inactivation kinetic properties of channels. The diversity of channel composition caused by the multimeric structure results in subtypes of channels that have a spectrum of sensitivity to ethanol that translates into brain regional differences in ethanol sensitivity, in part caused by differences in ion channel subunit composition. Ethanol has been shown to affect both receptor-activated ion channels and voltage-gated ion channels. The acute intoxicating and incoordinating effects of ethanol are probably related to inhibition of subtypes of NMDA-glutamate receptor ion channels and potentiation of certain subtypes of GABAA receptor ion channels. Effects on these channels, as well as glycine, nicotinic cholinergic, serotonergic, and other ion channels, likely contribute to the euphoric, sedative, and other acute actions of ethanol. Changes in ion channel subunit composition, density, and properties probably also contribute to ethanol tolerance, dependence, withdrawal hyperexcitability, and neurotoxicity. A substantial number of studies have implicated glutamate NMDA receptor, GABAA, and L-type voltage-gated calcium channels in the adaptive changes in the brain during chronic ethanol exposure. The diversity of ion channels subunits, their prominent role in brain function, and ethanol action are likely to make them important contributors to alcoholism and alcohol abuse.

Ethanol withdrawal hyperexcitability in vitro is selectively decreased by a competitive NMDA receptor antagonist

Hippocampal slices were prepared immediately after withdrawal from chronic ethanol in vivo. The decreases in thresholds for production of single and multiple population spikes seen after the ethanol treatment were not evident when CGP39551 was included in the perfusion medium at 20 μM. The decrease in paired pulse potentiation seen during ethanol withdrawal, however, was not prevented by CGP39551. For comparison, the effects of CGP39551, at the same concentration, were examined on the changes in field potentials seen in control slices when the magnesium concentration in the bathing medium was lowered to 250 μM. The decreases in thresholds for multiple population spikes produced by the lowered magnesium were prevented, but not other changes including decreases in single spike thresholds. In addition, this 20 μM concentration of CGP39551 did not prevent epileptiform activity, measured by decreases in thresholds for production of single and multiple population spikes caused by addition of the GABA A antagonist, bicuculline, to control hippocampal slices.

Calcium-dependent hyperexcitability of hippocampal CA1 pyramidal cells in an in vitro slice after ethanol withdrawal of the rat

The physiological profiles contributing to hyperexcitability of hippocampal CA1 neurons following ethanol withdrawal (EW) were examined in an in vitro slice preparation obtained from EW rats. Sixty-two percent of CA1 neurons in slices from EW rats exhibited intrinsic burst property which was rarely observed in those from control animals. The mean duration of plateau component of calcium (Ca) spikes was significantly increased after EW. The burst response evoked by either synaptic or direct stimulation in hippocampal CA1 neurons from EW rats was markedly depressed by high Mg solution but not by flunarizine. Furthermore, 6-cyano-7-nitroquinoxaline-2,3-dione, a non-NMDA receptor antagonist, markedly depressed the synaptically evoked burst response, while [(±)-2-carboxypiperazine-4-yl-]-propyl-1-phosphonic acid, a selective N- methyl- d - aspartate (NMDA) receptor antagonist, slightly delayed the onset of the response. The results indicate that an increase in the number of bursting hippocampal CA1 neurons associated with an augmentation of the plateau component of Ca spike contributes to the genesis of hyperexcitability in EW rats. Furthermore, non-NMDA receptor-mediated EPSP is mainly responsible for a synaptic induction of the burst response. These results are consistent with the involvement of high-threshold Ca channels in EW hyperexcitability.

Potentiation of [formula omitted] receptor-dependent afterdischarges in rat dentate gyrus following in vitro ethanol withdrawal

The contribution of NMDA receptors to neuronal hyperexcitability following in vitro ethanol withdrawal was examined using afterdischarges (ADs) in rat dentate gyrus as a model system. ADs were evoked by high frequency stimuli and blocked by N- methyl- d-aspartate (NMDA) receptor antagonists. Ethanol (75 mM) inhibited ADs, and following in vitro ethanol withdrawal, the duration of afterdischarges was significantly enhanced (37 ± 2%, n = 21). Therefore, in vitro ethanol exposure with subsequent withdrawal is associated with an enhancement of NMDA receptor-dependent afterdischarges. These results are consistent with the involvement of NMDA receptors in ethanol withdrawal hyperexcitability.

Changes in voltage‐operated calcium channels modify ethanol withdrawal hyperexcitability in mouse hippocampal slices

Measurements of hippocampal excitability were made from area CA1 of isolated mouse hippocampal slices, prepared after chronic ethanol treatment in vivo, and the effects of the stereoisomers of the dihydropyridine Bay K 8644, that act at calcium channels, were investigated. The decrease in the threshold stimulation required to produce a single population spike, the leftward shift in the population spike input-output curves, and the increase in population spike amplitude, that were seen during ethanol withdrawal, were all increased by the (-) isomer of Bay K 8644. This isomer has been shown to increase opening of calcium channels. These effects of ethanol withdrawal were decreased by the (+) isomer of Bay K 8644, that is a calcium channel blocker. In contrast, the increase in paired-pulse potentiation of the population spike, seen during the initial phase of ethanol withdrawal, was significantly decreased by both isomers of Bay K 8644. After the chronic ethanol treatment, single orthodromic stimuli produced epileptiform field potentials, consisting of two independent phases, a short latency series of multiple population spikes, superimposed upon the initial observed EPSP, and a longer latency train of spikes, occurring on a second EPSP, temporally distinct from the first. The (-) isomer of Bay K 8644 increased both these phases of epileptiform activity during ethanol withdrawal in a dose-dependent manner, while (+)-Bay K 8644 reduced the initial phase of multiple spiking and abolished the later phase. In slices from control animals, the higher concentration of (-)-Bay K 8644 (2 microM), but not the lower concentration (500 nM) decreased the stimulation required to produce multiple population spikes. Neither produced the long latency epileptiform activity. The (+) isomer of Bay K 8644 had no effect on control recordings. Lesioning the Schaffer collateral-commissural fibre pathway, or removing area CA3, in slices from ethanol-treated animals, abolished the later phase of epileptiform activity without affecting the initial multiple spiking. Intracellular recordings from area CA1 showed both the short latency and the longer latency epileptiform activities in slices from ethanol-treated mice and in control hippocampal slices after application of the (-) isomer of Bay K 8644, but these patterns of activity were not seen in control slices in the absence of Bay K 8644. Spontaneous activity during ethanol withdrawal was seen in intracellular recordings, but such activity was not seen in the field potential recordings.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in intrinsic inhibition in isolated hippocampal slices during ethanol withdrawal; lack of correlation with withdrawal hyperexcitability.

1. Intracellular recordings were made from pyramidal cells in area CA1 in mouse isolated hippocampal slices, after chronic ethanol treatment in vivo. 2. Fast i.p.s.ps were isolated by injection of the impaled neurones with QX314 (to block fast sodium currents and the slow i.p.s.p.) and stimulating the interneurones in the presence of the glutamatergic blockers, CNQX and APV. 3. The isolated fast-inhibitory postsynaptic potential (f.-i.p.s.p.) was measured at intervals during the 7 h withdrawal period. The reversal potential and sensitivity to bicuculline suggested that the isolated f.-i.p.s.p. was mediated by activation of the GABAA receptor-chloride ionophore complex. 4. Measurement of stimulus-response relationships for the f.-i.p.s.ps revealed an initial increase in the maximum size of the i.p.s.p., evoked from a membrane potential of -50 mV, seen at 2 h into ethanol withdrawal. This was attributed to a negative shift in the reversal potential, Ei.p.s.p., with no observed change in conductance, Gi.p.s.p. 5. No differences in f.-i.p.s.ps evoked during ethanol withdrawal or in control slices were seen at 4 h or 6 h. At these times, epileptiform activity was seen in previous field potential recordings. 6. Paired pulse depression of the f.-i.p.s.p. was significantly increased at 2 h into withdrawal, when a 150 ms pulse interval was used. No differences were seen at later times in the ethanol withdrawal period. 7. The results suggest that ethanol withdrawal hyperexcitability in isolated hippocampal slices is not caused by primary decreases in inhibition mediated by the GABAA receptor-chloride ionophore complex.4. Measurement of stimulus-response relationships for the f.-i.p.s.ps revealed an initial increase in the maximum size of the i.p.s.p., evoked from a membrane potential of - 50 mV, seen at 2 h into ethanol withdrawal. This was attributed to a negative shift in the reversal potential, Ejp.sp with no observed change in conductance, Gj ps p.5. No differences in f.-i.p.s.ps evoked during ethanol withdrawal or in control slices were seen at 4 h or 6 h. At these times, epileptiform activity was seen in previous field potential recordings.6. Paired pulse depression of the f.-i.p.s.p. was significantly increased at 2 h into withdrawal, when a 150 ms pulse interval was used. No differences were seen at later times in the ethanol withdrawal period.7. The results suggest that ethanol withdrawal hyperexcitability in isolated hippocampal slices is not caused by primary decreases in inhibition mediated by the GABAA receptor-chloride ionophore complex.The increase in the f.-i.p.s.p. during the initial stages of the withdrawal might prevent the overt expression of epileptiform activity at this time.

EVIDENCE THAT CHANGES IN HIPPOCAMPAL EXCITABILITY <italic>IN VITRO</italic> ARE CAUSED BY WITHDRAWAL FROM CHRONIC <italic>IN VIVO</italic> ETHANOL ADMINISTRATION

A complex pattern of changes in the field potentials recorded from mouse hippocampal slices, prepared after chronic ethanol treatment in vivo, has previously been demonstrated in this laboratory. In the present study, recordings from slices prepared immediately after 2 weeks of ethanol treatment, showed only an increase in paired pulse potentiation, compared with controls, whereas recordings made immediately after 16 weeks of ethanol administration showed decreases in the thresholds for single and multiple population spikes, increases in paired pulse potentiation and epileptiform activity. In hippocampal slices prepared after 24 hr withdrawal, following 16 weeks of ethanol treatment, there were no signs of hyperexcitability in the field potentials. Ratings of convulsive behaviour were increased in mice during a 12-hr period after withdrawal from 16 weeks of ethanol treatment. Corresponding behaviour ratings for the mice given ethanol for 2 weeks, or those withdrawn for 24 hr after 16 weeks ethanol treatment, were not significantly different from control values. It was concluded that epileptiform activity seen in hippocampal slices after prolonged ethanol administration may contribute to the ethanol withdrawal hyperexcitability seen in vivo.

A calcium channel antagonist stereoselectively decreases ethanol withdrawal hyperexcitability but not that due to bicuculline, in hippocampal slices

1. Extracellular recordings were made from CA1 area of isolated hippocampal slices of the mouse after chronic ethanol administration in vivo, with orthodromic stimulation of the Schaffer collateral/commissural fibres. 2. The (+)-isomer of the calcium channel antagonist PN 200-110 (isradipine) significantly decreased all the recorded signs of hyperexcitability in the slices during ethanol withdrawal. These included increased paired pulse potentiation and decreases in the thresholds for elicitation of single and multiple population spikes. 3. The (-)-isomer of PN 200-100 did not affect ethanol withdrawal hyperexcitability in the slices. 4. Neither isomer of PN 200-110 affected the field potentials in slices from control animals. 5. The gamma-aminobutyric acid (GABA) antagonist, bicuculline, lowered thresholds for eliciting population spikes in hippocampal slices from untreated animals. The active, (+)-isomer of PN 200-110 did not affect this action of bicuculline in hippocampal slices from untreated animals. 6. The stereoisomerism of the action of PN 200-110 on ethanol withdrawal hyperexcitability in the hippocampal slice was therefore the same as that seen in blockade of calcium channels. The results suggested that ethanol withdrawal hyperexcitability recorded in the isolated hippocampal slice involved increased activity of voltage-sensitive calcium channels.

Modification of dopamine receptor-mediated processes after chronic ethanol intoxication: a possible mechanism.

Animals undergoing withdrawal from chronic ethanol treatment displayed significantly impaired function of dopaminergic systems in the CNS. Autonomic and behavioral response to dopaminergic agonists were reduced, as was the stimulation by dopamine of dopamine-sensitive adenylate cyclase from the striatal region of brain. In addition, the ability of neuroleptics to stimulate tryosine hydroxylase activity in the subcortex was diminished. These findings suggested a decreased sensitivity of dopaminergic receptors during ethanol withdrawal, and in time course of appearance and disappearance, the decreased sensitivity appeared to parallel ethanol withdrawal hyper-excitability. Moreover, the responsiveness of dopamine-sensitive adenylate cyclase could be restored by in vitro exposure to physiologically attainable concentrations of ethanol, suggesting that this system had become dependent on the presence of ethanol for normal function. The mechanism of the decreased sensitivity, in particular for the adenylate cyclase, but perhaps also for other dopamine receptor-mediated processesx, may be inefficient coupling between receptor and enzyme, as a result of changes in neuronal membrane structure produced by chronic exposure to ethanol and withdrawal.