Effect of chronic ethanol ingestion on Purkinje and Golgi cell firing in vivo and on motor coordination in mice

Chronic use of cannabis might impair sensory error processing in the cerebellum through endocannabinoid dysregulation

Chronic use of cannabis leads to both motor deficits and the downregulation of CB₁ receptors (CB₁R) in the cerebellum. In turn, cerebellar damage is often related to impairments in motor learning and control. Further, a recent motor learning task that measures cerebellar-dependent adaptation has been shown to distinguish well between healthy subjects and chronic cannabis users. Thus, the deteriorating effects of chronic cannabis use in motor performance point to cerebellar adaptation as a key process to explain such deficits. We review the literature relating chronic cannabis use, the endocannabinoid system in the cerebellum, and different forms of cerebellar-dependent motor learning, to suggest that CB₁R downregulation leads to a generalized underestimation and misprocessing of the sensory errors driving synaptic updates in the cerebellar cortex. Further, we test our hypothesis with a computational model performing a motor adaptation task and reproduce the behavioral effect of decreased implicit adaptation that appears to be a sign of chronic cannabis use. Finally, we discuss the potential of our hypothesis to explain similar phenomena related to motor impairments following chronic alcohol dependency.

Chronic ethanol exposure during adolescence impairs simple spike activity of cerebellar Purkinje cells in vivo in mice

Cerebellar Purkinje cells (PCs) play critical roles in motor coordination and motor learning through their simple spike (SS) activity. Previous studies have shown that chronic ethanol exposure (CEE) in adolescents impairs learning, attention, and behavior, at least in part by impairing the activity of cerebellar PCs. In this study, we investigated the effect of CEE on the SS activity in urethane-anesthetized adolescent mice by in vivo electrophysiological recordings and pharmacological methods. Our results showed that the cerebellar PCs in CEE adolescent mice expressed a significant decrease in the frequency and an increase in the coefficient of variation (CV) of SS than control group. Blockade of ɤ-aminobutyric acid A (GABA_A) receptor did not change the frequency and CV of SS firing in control group but produced a significant increase in the frequency and a decrease in the CV of SS firing in CEE mice. The CEE-induced decrease in SS firing rate and increase in CV were abolished by application of an N-methyl-D-aspartate (NMDA) receptor blocker, D-APV, but not by anα-amino-3-hydroxy-5-methyl -4-isoxazolepropionic acid (AMPA) receptor antagonist, NBQX. Notably, the spontaneous spike rate of molecular layer interneurons (MLIs) in CEE mice was significantly higher than control group, which was also abolished by application of D-APV. These results indicate that adolescent CEE enhances the spontaneous spike firing rate of MLIs through activation of NMDA receptor, resulting in a depression in the SS activity of cerebellar PCs in vivo in mice.

Persistence of cerebellar ataxia during chronic ethanol exposure is associated with epigenetic up-regulation of Fmr1 gene expression in rat cerebellum

BACKGROUND

Alcohol intoxication produces ataxia by affecting the cerebellum, which coordinates movements. Fragile X mental retardation (FMR) protein is a complex regulator of RNA and synaptic plasticity implicated in fragile X-associated tremor/ataxia syndrome, which features ataxia and increased Fmr1 mRNA expression resulting from epigenetic dysregulation of FMRP. We recently demonstrated that acute ethanol-induced ataxia is associated with increased cerebellar Fmr1 gene expression via histone modifications in rats, but it is unknown whether similar behavioral and molecular changes occur following chronic ethanol exposure. Here, we investigated the effects of chronic ethanol exposure on ataxia and epigenetically regulated changes in Fmr1 expression in the cerebellum.

METHODS

Male adult Sprague-Dawley rats were trained on the accelerating rotarod and then fed with chronic ethanol or a control Lieber-DeCarli diet while undergoing periodic behavioral testing for ataxia during ethanol exposure and withdrawal. Cerebellar tissues were analyzed for expression of the Fmr1 gene and its targets using a real-time quantitative polymerase chain reaction assay. The epigenetic regulation of Fmr1 was also investigated using a chromatin immunoprecipitation assay.

RESULTS

Ataxic behavior measured by the accelerating rotarod behavioral test developed during chronic ethanol treatment and persisted at both the 8-h and 24-h withdrawal time points compared to control diet-fed rats. In addition, chronic ethanol treatment resulted in up-regulated expression of Fmr1 mRNA and increased activating epigenetic marks H3K27 acetylation and H3K4 trimethylation at 2 sites within the Fmr1 promoter. Finally, measurement of the expression of relevant FMRP mRNA targets in the cerebellum showed that chronic ethanol up-regulated cAMP response element binding (CREB) Creb1, Psd95, Grm5, and Grin2b mRNA expression without altering Grin2a, Eaa1, or histone acetyltransferases CREB binding protein (Cbp) or p300 mRNA transcripts.

CONCLUSIONS

These results suggest that epigenetic regulation of Fmr1 and subsequent FMRP regulation of target mRNA transcripts constitute neuroadaptations in the cerebellum that may underlie the persistence of ataxic behavior during chronic ethanol exposure and withdrawal.

Chronic Ethanol Exposure Enhances Facial Stimulation-Evoked Mossy Fiber-Granule Cell Synaptic Transmission via GluN2A Receptors in the Mouse Cerebellar Cortex

Sensory information is transferred to the cerebellar cortex via the mossy fiber–granule cell (MF–GC) pathway, which participates in motor coordination and motor learning. We previously reported that chronic ethanol exposure from adolescence facilitated the sensory-evoked molecular layer interneuron–Purkinje cell synaptic transmission in adult mice in vivo. Herein, we investigated the effect of chronic ethanol exposure from adolescence on facial stimulation-evoked MF–GC synaptic transmission in the adult mouse cerebellar cortex using electrophysiological recording techniques and pharmacological methods. Chronic ethanol exposure from adolescence induced an enhancement of facial stimulation-evoked MF–GC synaptic transmission in the cerebellar cortex of adult mice. The application of an N-methyl-D-aspartate receptor (NMDAR) antagonist, D-APV (250 μM), induced stronger depression of facial stimulation-evoked MF–GC synaptic transmission in chronic ethanol-exposed mice compared with that in control mice. Chronic ethanol exposure-induced facilitation of facial stimulation evoked by MF–GC synaptic transmission was abolished by a selective GluN2A antagonist, PEAQX (10 μM), but was unaffected by the application of a selective GluN2B antagonist, TCN-237 (10 μM), or a type 1 metabotropic glutamate receptor blocker, JNJ16259685 (10 μM). These results indicate that chronic ethanol exposure from adolescence enhances facial stimulation-evoked MF–GC synaptic transmission via GluN2A, which suggests that chronic ethanol exposure from adolescence impairs the high-fidelity transmission capability of sensory information in the cerebellar cortex by enhancing the NMDAR-mediated components of MF–GC synaptic transmission in adult mice in vivo.

Chronic ethanol exposure facilitates facial-evoked MLI-PC synaptic transmission via nitric oxide signaling pathway in vivo in mice

Ethanol (EtOH) exposure causes alterations of motor coordination, balance, behavior, speech, and certain cognitive functions are considered to be caused partly by impairment of cerebellar circuits function and modulation of synaptic transmission. The cerebellar cortical molecular layer interneuron-Purkinje cell (MLI-PC) synapses are critical for various information integration and transmission, which are sensitive to acute and chronic EtOH exposure. The aim of this study is to investigate the effect of chronic ethanol exposure on the facial stimulation-evoked MLI-PC synaptic transmission in urethane-anesthetized mice, by electrophysiological recording and pharmacological methods. Under current-clamp recording conditions, air-puff stimulation of ipsilateral whisker pad evoked MLI-PC synaptic transmission, which expressed an inhibitory component (P1) followed by a pause of simple spike (SS) firing in cerebellar PCs. Chronic ethanol exposure did not change the latency of the facial stimulation-evoked responses in cerebellar PCs, but induced significant enhancement of the stimulation-evoked MLI-PC synaptic transmission, which expressed increases in amplitude of P1 and pause of SS firing. The amplitude of P1 and pause of SS in ethanol exposure group were significant higher than that in control group. Cerebellar surface application of nitric oxide synthesis (NOS) inhibitor, L-NNA (5 mM) significantly decreased the amplitude of P1 and the pause of SS firing in EtOH exposure group, but did no effect on control group. In contrast, cerebellar surface application of NO donor, SNAP (100 μM) significantly increased the amplitude of P1 and the pause of SS firing in control group, but not in EtOH exposure group. These results indicated that chronic EtOH exposure significantly facilitated the sensory-evoked MLI-PC synaptic transmission via NO signaling pathway in mouse cerebellar cortex.

Chronic Ethanol Consumption Impairs the Tactile-Evoked Long-Term Depression at Cerebellar Molecular Layer Interneuron-Purkinje Cell Synapses in vivo in Mice

The cerebellum is sensitive to ethanol (EtOH) consumption. Chronic EtOH consumption impairs motor learning by modulating the cerebellar circuitry synaptic transmission and long-term plasticity. Under in vitro conditions, acute EtOH inhibits both parallel fiber (PF) and climbing fiber (CF) long-term depression (LTD). However, thus far it has not been investigated how chronic EtOH consumption affects sensory stimulation-evoked LTD at the molecular layer interneurons (MLIs) to the Purkinje cell (PC) synapses (MLI-PC LTD) in the cerebellar cortex of living animals. In this study, we investigated the effect of chronic EtOH consumption on facial stimulation-evoked MLI-PC LTD, using an electrophysiological technique as well as pharmacological methods, in urethane-anesthetized mice. Our results showed that facial stimulation induced MLI–PC LTD in the control mice, but it could not be induced in mice with chronic EtOH consumption (0.8 g/kg; 28 days). Blocking the cannabinoid type 1 (CB1) receptor activity with AM-251, prevented MLI-PC LTD in the control mice, but revealed a nitric oxide (NO)-dependent long-term potentiation (LTP) of MLI–PC synaptic transmission (MLI-PC LTP) in the EtOH consumption mice. Notably, with the application of a NO donor, S-nitroso-N-Acetyl-D, L-penicillamine (SNAP) alone prevented the induction of MLI–PC LTD, but a mixture of SNAP and AM-251 revealed an MLI-PC LTP in control mice. In contrast, inhibiting NO synthase (NOS) revealed the facial stimulation-induced MLI-PC LTD in EtOH consumption mice. These results indicate that long-term EtOH consumption can impair the sensory stimulation-induced MLI–PC LTD via the activation of a NO signaling pathway in the cerebellar cortex in vivo in mice. Our results suggest that the chronic EtOH exposure causes a deficit in the cerebellar motor learning function and may be involved in the impaired MLI–PC GABAergic synaptic plasticity.

Gaze-evoked nystagmus induced by alcohol intoxication

KEY POINTS

The cerebellum is the core structure controlling gaze stability. Chronic cerebellar diseases and acute alcohol intoxication affect cerebellar function, inducing, among others, gaze instability as gaze-evoked nystagmus. Gaze-evoked nystagmus is characterized by increased centripetal eye-drift. It is used as an important diagnostic sign for patients with cerebellar degeneration and to assess the 'driving while intoxicated' condition. We quantified the effect of alcohol on gaze-holding using an approach allowing, for the first time, the comparison of deficits induced by alcohol intoxication and cerebellar degeneration. Our results showed that alcohol intoxication induces a two-fold increase of centripetal eye-drift. We establish analysis techniques for using controlled alcohol intake as a model to support the study of cerebellar deficits. The observed similarity between the effect of alcohol and the clinical signs observed in cerebellar patients suggests a possible pathomechanism for gaze-holding deficits.

ABSTRACT

Gaze-evoked nystagmus (GEN) is an ocular-motor finding commonly observed in cerebellar disease, characterized by increased centripetal eye-drift with centrifugal correcting saccades at eccentric gaze. With cerebellar degeneration being a rare and clinically heterogeneous disease, data from patients are limited. We hypothesized that a transient inhibition of cerebellar function by defined amounts of alcohol may provide a suitable model to study gaze-holding deficits in cerebellar disease. We recorded gaze-holding at varying horizontal eye positions in 15 healthy participants before and 30 min after alcohol intake required to reach 0.6‰ blood alcohol content (BAC). Changes in ocular-motor behaviour were quantified measuring eye-drift velocity as a continuous function of gaze eccentricity over a large range (±40 deg) of horizontal gaze angles and characterized using a two-parameter tangent model. The effect of alcohol on gaze stability was assessed analysing: (1) overall effects on the gaze-holding system, (2) specific effects on each eye and (3) differences between gaze angles in the temporal and nasal hemifields. For all subjects, alcohol consumption induced gaze instability, causing a two-fold increase [2.21 (0.55), median (median absolute deviation); P = 0.002] of eye-drift velocity at all eccentricities. Results were confirmed analysing each eye and hemifield independently. The alcohol-induced transient global deficit in gaze-holding matched the pattern previously described in patients with late-onset cerebellar degeneration. Controlled intake of alcohol seems a suitable disease model to study cerebellar GEN. With alcohol resulting in global cerebellar hypofunction, we hypothesize that patients matching the gaze-holding behaviour observed here suffered from diffuse deficits in the gaze-holding system as well.

Alcohol use across the lifespan: An analysis of adolescent and aged rodents and humans

Adolescence and old age are unique periods of the lifespan characterized by differential sensitivity to the effects of alcohol. Adolescents and the elderly appear to be more vulnerable to many of alcohol's physiological and behavioral effects compared to adults. The current review explores the differential effects of acute alcohol, predominantly in terms of motor function and cognition, in adolescent and aged humans and rodents. Adolescents are less sensitive to the sedative-hypnotic, anxiolytic, and motor-impairing effects of acute alcohol, but research results are less consistent as it relates to alcohol's effects on cognition. Specifically, previous research has shown adolescents to be more, less, and similarly sensitive to alcohol-induced cognitive deficits compared to adults. These equivocal findings suggest that learning acquisition may be differentially affected by ethanol compared to memory, or that ethanol-induced cognitive deficits are task-dependent. Older rodents appear to be particularly vulnerable to the motor- and cognitive-impairing effects of acute alcohol relative to younger adults. Given that alcohol consumption and abuse is prevalent throughout the lifespan, it is important to recognize age-related differences in response to acute and long-term alcohol. Unfortunately, diagnostic measures and treatment options for alcohol dependence are rarely dedicated to adolescent and aging populations. As discussed, although much scientific advancement has been made regarding the differential effects of alcohol between adolescents and adults, research with the aged is underrepresented. Future researchers should be aware that adolescents and the aged are uniquely affected by alcohol and should continue to investigate alcohol's effects at different stages of maturation.

Eyeblink Classical Conditioning in Alcoholism and Fetal Alcohol Spectrum Disorders

Alcoholism is a debilitating disorder that can take a significant toll on health and professional and personal relationships. Excessive alcohol consumption can have a serious impact on both drinkers and developing fetuses, leading to long-term learning impairments. Decades of research in laboratory animals and humans have demonstrated the value of eyeblink classical conditioning (EBC) as a well-characterized model system to study the neural mechanisms underlying associative learning. Behavioral EBC studies in adults with alcohol use disorders and in children with fetal alcohol spectrum disorders report a clear learning deficit in these two patient populations, suggesting alcohol-related damage to the cerebellum and associated structures. Insight into the neural mechanisms underlying these learning impairments has largely stemmed from laboratory animal studies. In this mini-review, we present and discuss exemplary animal findings and data from patient and neuroimaging studies. An improved understanding of the neural mechanisms underlying learning deficits in EBC related to alcoholism and prenatal alcohol exposure has the potential to advance the diagnoses, treatment, and prevention of these and other pediatric and adult disorders.

Effectuation of adaptive stability and postural alignment strategies are decreased by alcohol intoxication

Human stability control is a complex process comprising contributions from several partly independent mechanisms such as coordination, feedback and feed-forward control, and adaptation. Acute alcohol intoxication impairs these functions and is recognized as a major contributor to fall traumas. The study aimed to investigate how alcohol intoxication at .06% and .10% blood alcohol concentration (BAC) affected the movement spans and control of posture alignment. The angular positions of the head, shoulder, hip and knees relative to the ankles were measured with a 3D motion analysis system in 25 healthy adults during standing with eyes open or closed and with or without vibratory balance perturbations. Alcohol intoxication significantly increased the movement spans of the head, shoulders, hip and knees in anteroposterior and lateral directions during quiet stance (p < or = .047 and p < or = .003) and balance perturbations (p<.001, both directions). Alcohol intoxication also decreased the ability to reduce the movement spans through adaptation in both anteroposterior (p < or = .011) and lateral (p < or = .004) directions. When sober and submitted to balance perturbations, the subjects aligned the head, shoulders, hip and knees more forward relative to the ankle joint (p < .001), hence adopting a more resilient posture increasing the safety margin for backward falls. Alcohol intoxication significantly delayed this forward realignment (p < or = .022). Alcohol intoxication did not cause any significant posture realignment in the lateral direction. Thus, initiation of adaptive posture realignments to alcohol or other disruptions might be context dependent and associated with reaching a certain level of stability threats.

Third trimester-equivalent ethanol exposure does not alter complex spikes and climbing fiber long-term depression in cerebellar Purkinje neurons from juvenile rats

BACKGROUND

Studies indicate that exposure to ethanol (EtOH) during fetal development damages cerebellar Purkinje cells (PCs). PC proximal dendrites receive glutamatergic input from climbing fibers (CFs) originating at the inferior olive. CF input produces a characteristic response in PCs known as the complex spike (CS). During the first 2 weeks of life in rodents (equivalent to the human third trimester of pregnancy), CF-PC synapses undergo profound refinement. Here, we characterized the impact of EtOH exposure during this period on CF-evoked responses in PCs.

METHODS

Using vapor chambers, neonatal rat pups and their mothers were exposed to air or EtOH for 4 h/d between postnatal day 2 (P2) and P12 (pup serum EtOH concentration, 0.16 g/dl). The function of CF-PC synapses was characterized using patch-clamp electrophysiological techniques in acute slices from the cerebellar vermis. Experiments were performed soon after EtOH withdrawal, when perisomatic CFs are still being eliminated (P15 to P17), and after weaning when CF dendritic translocation is almost complete (P21 to P34).

RESULTS

Neither the baseline characteristics of the CS (Na(+) spike amplitude, area, coastline index, and afterhyperpolarization [AHP] amplitude) nor the type-1 metabotropic glutamate receptor (mGluR1)-mediated component of both the CS and AHP were significantly affected by EtOH exposure at P15 to P17 or P21 to P34. The mGluR1-dependent long-term depression (LTD) of CF-evoked excitatory postsynaptic currents was not significantly affected by EtOH exposure at P21 to P34.

CONCLUSIONS

EtOH exposure during the third trimester equivalent neither affected basal characteristics of the CS nor CF-LTD at rat cerebellar PCs from juvenile rats.

Use of the expanded panel of BXD mice narrow QTL regions in ethanol-induced locomotor activation and motor incoordination

BACKGROUND

Alcohol-related responses are under strong genetic regulation. A wealth of alcohol-related data from recombinant inbred (RI) mouse strains enables genetic correlation and mapping of these traits. Previous studies using RI strains have identified numerous chromosomal locations that underlie differential alcohol sensitivity, although the regions identified are typically large. One means to improve power and precision for genetic analysis is to use a larger genetic reference population. The expanded panel of BXD RI mice was used to identify quantitative trait loci (QTLs) associated with sensitivity to locomotor stimulatory and motor incoordinating effects of alcohol. The goals of this study were to determine whether previously reported QTLs were replicated and refined and to determine whether novel QTLs would be identified.

METHODS

Following an i.p. dose of 2.25 g/kg of ethanol (EtOH) or saline control, locomotor activation was assessed using an activity chamber and motor incoordination was assessed using the accelerating rotarod. Male and female BXD mice from over 55 strains were tested. Two treatment paradigms were utilized to evaluate the effects of EtOH versus saline treatment-order.

RESULTS

Activity chamber measures showed significant differences in strain, sex, and treatment-order whereas rotarod measures showed significant differences in strain and treatment-order. Significant QTLs for various measures of EtOH-induced locomotor activation were identified on chromosomes 2 and 5 that narrowed QTL regions previously identified from 19 to < 2 Mb. Further, a novel significant QTL for EtOH-induced motor incoordination on chromosome 7 was identified.

CONCLUSIONS

Using the expanded RI BXD panel, along with a high precision marker map, several novel QTLs were found and several previously identified QTL regions were confirmed and narrowed. The isogenic nature of the population facilitated detection of treatment-order and sex-specific differences. Smaller QTL regions reduced the number of positional candidates thereby increasing the efficiency with which polymorphisms underlying the QTL will be identified.

Ethanol affects NMDA receptor signaling at climbing fiber-Purkinje cell synapses in mice and impairs cerebellar LTD

Ethanol profoundly influences cerebellar circuit function and motor control. It has recently been demonstrated that functional N-methyl-(D)-aspartate (NMDA) receptors are postsynaptically expressed at climbing fiber (CF) to Purkinje cell synapses in the adult cerebellum. Using whole cell patch-clamp recordings from mouse cerebellar slices, we examined whether ethanol can affect NMDA receptor signaling in mature Purkinje cells. NMDA receptor-mediated currents were isolated by bath application of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzol[f]quinoxaline (NBQX). The remaining (D)-2-amino-5-phosphonovaleric acid ((D)-APV)-sensitive current was reduced by ethanol at concentrations as low as 10 mM. At a concentration of 50 mM ethanol, the blockade of (D)-APV-sensitive CF-excitatory postsynaptic currents was significantly stronger. Ethanol also altered the waveform of CF-evoked complex spikes by reducing the afterdepolarization. This effect was not seen when NMDA receptors were blocked by (D)-APV before ethanol wash-in. In contrast to CF synaptic transmission, parallel fiber (PF) synaptic inputs were not affected by ethanol. Finally, ethanol (10 mM) impaired long-term depression (LTD) at PF to Purkinje cell synapses as induced under control conditions by paired PF and CF activity. However, LTD induced by pairing PF stimulation with depolarizing voltage steps (substituting for CF activation) was not blocked by ethanol. These observations suggest that the sensitivity of cerebellar circuit function and plasticity to low concentrations of ethanol may be caused by an ethanol-mediated impairment of NMDA receptor signaling at CF synapses onto cerebellar Purkinje cells.

Blood alcohol concentration at 0.06 and 0.10% causes a complex multifaceted deterioration of body movement control

Alcohol-related falls are recognized as a major contributor to the occurrence of traumatic brain injury. The control of upright standing balance is complex and composes of contributions from several partly independent mechanisms such as appropriate information from multiple sensory systems and correct feedback and feed forward movement control. Analysis of multisegmented body movement offers a rarely used option for detecting the fine motor problems associated with alcohol intoxication. The study aims were to investigate whether (1) alcohol intoxication at 0.06 and 0.10% blood alcohol concentration (BAC) affected the body movements under unperturbed and perturbed standing; and (2) alcohol affected the ability for sensorimotor adaptation. Body movements were recorded in 25 participants (13 women and 12 men, mean age 25.1 years) at five locations (ankle, knee, hip, shoulder, and head) during quiet standing and during balance perturbations from pseudorandom pulses of calf muscle vibration over 200s with eyes closed or open. Tests were performed at 0.00, 0.06, and 0.10% BAC. The study revealed several significant findings: (1) an alcohol dose-specific effect; (2) a direction-specific stability decrease from alcohol intoxication; (3) a movement pattern change related to the level of alcohol intoxication during unperturbed standing and perturbed standing; (4) a sensorimotor adaptation deterioration with increased alcohol intoxication; and (5) that vision provided a weaker contribution to postural control during alcohol intoxication. Hence, alcohol intoxication at 0.06 and 0.10% BAC causes a complex multifaceted deterioration of human postural control.

Bidirectional plasticity in the primate inferior olive induced by chronic ethanol intoxication and sustained abstinence

The brain adapts to chronic ethanol intoxication by altering synaptic and ion-channel function to increase excitability, a homeostatic counterbalance to inhibition by alcohol. Delirium tremens occurs when those adaptations are unmasked during withdrawal, but little is known about whether the primate brain returns to normal with repeated bouts of ethanol abuse and abstinence. Here, we show a form of bidirectional plasticity of pacemaking currents induced by chronic heavy drinking within the inferior olive of cynomolgus monkeys. Intracellular recordings of inferior olive neurons demonstrated that ethanol inhibited the tail current triggered by release from hyperpolarization (I(tail)). Both the slow deactivation of hyperpolarization-activated cyclic nucleotide-gated channels conducting the hyperpolarization-activated inward current and the activation of Ca(v)3.1 channels conducting the T-type calcium current (I(T)) contributed to I(tail), but ethanol inhibited only the I(T) component of I(tail). Recordings of inferior olive neurons obtained from chronically intoxicated monkeys revealed a significant up-regulation in I(tail) that was induced by 1 y of daily ethanol self-administration. The up-regulation was caused by a specific increase in I(T) which (i) greatly increased neurons' susceptibility for rebound excitation following hyperpolarization and (ii) may have accounted for intention tremors observed during ethanol withdrawal. In another set of monkeys, sustained abstinence produced the opposite effects: (i) a reduction in rebound excitability and (ii) a down-regulation of I(tail) caused by the down-regulation of both the hyperpolarization-activated inward current and I(T). Bidirectional plasticity of two hyperpolarization-sensitive currents following chronic ethanol abuse and abstinence may underlie persistent brain dysfunction in primates and be a target for therapy.

Ethanol acutely modulates mGluR1-dependent long-term depression in cerebellum

BACKGROUND

Acute and chronic ethanol exposure produces profound impairments in motor functioning. Individuals with lower sensitivity to the acute motor impairing effects of ethanol have an increased risk of developing alcohol dependence and abuse, and infants with subtle delays in motor coordination development may have an increased risk for subsequently developing alcoholism. Thus, understanding the mechanism by which ethanol disrupts motor functioning is very important.

METHODS

Parasagittal slices of the cerebellar vermis (250 microM thick) were prepared from P17 to 20 Sprague-Dawley rats. Whole-cell recordings of Purkinje cells were obtained with an Axopatch 200B amplifier. Parallel fiber-Purkinje cell synaptic currents were sampled at 1 kHz and digitized at 10 kHz, and synaptic long-term depression (LTD) was observed in either external or internal application of ethanol for comparison.

RESULTS

We determined whether ethanol acutely affects parallel fiber LTD using whole-cell patch-clamp recordings from Purkinje cells. Application of ethanol both externally (50 mM) and internally (17 and 10 mM) significantly suppressed mGluR-mediate slow currents. Short-term external ethanol exposure (50 but not 17 mM) during tetanus blocked mGluR-dependent parallel fiber LTD. Furthermore, internal 17 and 10 mM ethanol completely inhibited this LTD.

CONCLUSIONS

The results of the current study demonstrate that ethanol acutely suppresses parallel fiber LTD and may influence the mGluR-mediated slow current intracellularly. This study, plus previous evidence by Carta and colleagues (2006) and Belmeguenai and colleagues (2008), suggests significant actions of ethanol on mGluR-mediated currents and its dependent plasticity in brain.

BK channels control cerebellar Purkinje and Golgi cell rhythmicity in vivo

Calcium signaling plays a central role in normal CNS functioning and dysfunction. As cerebellar Purkinje cells express the major regulatory elements of calcium control and represent the sole integrative output of the cerebellar cortex, changes in neural activity- and calcium-mediated membrane properties of these cells are expected to provide important insights into both intrinsic and network physiology of the cerebellum. We studied the electrophysiological behavior of Purkinje cells in genetically engineered alert mice that do not express BK calcium-activated potassium channels and in wild-type mice with pharmacological BK inactivation. We confirmed BK expression in Purkinje cells and also demonstrated it in Golgi cells. We demonstrated that either genetic or pharmacological BK inactivation leads to ataxia and to the emergence of a beta oscillatory field potential in the cerebellar cortex. This oscillation is correlated with enhanced rhythmicity and synchronicity of both Purkinje and Golgi cells. We hypothesize that the temporal coding modification of the spike firing of both Purkinje and Golgi cells leads to the pharmacologically or genetically induced ataxia.

Effects of maternal alcohol consumption during breastfeeding on motor and cerebellar Purkinje cells behavior in mice

Purkinje cells (PCs) are the sole output from the cerebellar cortex. Their electrophysiological behavior may serve as indicator of chronic ethanol effects on the cerebellum. Here, we studied the effects of ethanol consumption through breastfeeding on motor behavior, histology and PCs electrophysiology. Mice with different maternal drinking regimen (ethanol, E or sucrose, S) during prenatal (E/and S/) and postnatal period (/E and/S) were compared. Motor performance in the runway and rotarod tests was significantly worse in mice exposed to ethanol prenatally (E/E and E/S) than in mice exposed to sucrose (S/S), with a limited influence, if any, of mother regimen during lactation (E/S vs E/E). A loss of 20-25% of PCs was found for both E/S and E/E compared to S/S mice but PC numbers were similar in S/E and S/S. Mean PC spontaneous simple spike firing rate and rhythmicity were higher in E/S and E/E than in S/S but there was no difference between S/E and S/S. Complex spike frequency was similar in all groups. In contrast, complex spike duration and the related pause induced on the simple spike firing were shorter in E/E and in E/S, but no difference was found between S/E and S/S. We conclude that cerebellar dysfunction induced by maternal ethanol consumption in mice depends upon the drinking regimen during pregnancy and not during lactation.

Alcohol impairs long-term depression at the cerebellar parallel fiber-Purkinje cell synapse

Acute alcohol consumption causes deficits in motor coordination and gait, suggesting an involvement of cerebellar circuits, which play a role in the fine adjustment of movements and in motor learning. It has previously been shown that ethanol modulates inhibitory transmission in the cerebellum and affects synaptic transmission and plasticity at excitatory climbing fiber (CF) to Purkinje cell synapses. However, it has not been examined thus far how acute ethanol application affects long-term depression (LTD) and long-term potentiation (LTP) at excitatory parallel fiber (PF) to Purkinje cell synapses, which are assumed to mediate forms of cerebellar motor learning. To examine ethanol effects on PF synaptic transmission and plasticity, we performed whole cell patch-clamp recordings from Purkinje cells in rat cerebellar slices. We found that ethanol (50 mM) selectively blocked PF-LTD induction, whereas it did not change the amplitude of excitatory postsynaptic currents at PF synapses. In contrast, ethanol application reduced voltage-gated calcium currents and type 1 metabotropic glutamate receptor (mGluR1)-dependent responses in Purkinje cells, both of which are involved in PF-LTD induction. The selectivity of these effects is emphasized by the observation that ethanol did not impair PF-LTP and that PF-LTP could readily be induced in the presence of the group I mGluR antagonist AIDA or the mGluR1a antagonist LY367385. Taken together, these findings identify calcium currents and mGluR1-dependent signaling pathways as potential ethanol targets and suggest that an ethanol-induced blockade of PF-LTD could contribute to the motor coordination deficits resulting from alcohol consumption.