Depression of extra-cellular GABA and increase of NMDA-induced nitric oxide following acute intra-nuclear administration of alcohol in the cerebellar nuclei of the rat

Involvement of NMDA Receptors, Nitric Oxide, and GABA in Rostral Ventrolateral Medulla in Acute Ethanol-Induced Cardiovascular Responses in Rats

BACKGROUND

Consumption of ethanol (EtOH) (alcohol) has many effects on physiological functions, particularly those in the central nervous system (CNS) and cardiovascular system. Acute excessive intake of EtOH (alcohol intoxication) may cause hypotension and tachycardia. In this study, we examined the mechanistic involvement of glutamatergic N-methyl-d-aspartate (NMDA) receptors, nitric oxide (NO), and γ-aminobutyric acid (GABA) pathways in the CNS in acute EtOH-induced cardiovascular effects.

METHODS

EtOH was administered by intraperitoneal (IP) injection in Sprague-Dawley rats. The blood pressure (BP) and heart rate (HR) were measured in conscious and in urethane-anesthetized rats. Inhibitors were applied by intracerebroventricular (ICV) injection or by microinjection into rostral ventrolateral medulla (RVLM). Microdialysis was used to determine the level of glutamate, NO, and GABA in the RVLM.

RESULTS

IP injection of EtOH (3.2 g/kg) caused a significant decrease in BP in conscious and anesthetized rats and a late increase in HR in conscious rats. The cardiovascular effects of EtOH were significantly attenuated by ICV or by RVLM post treatment with ketamine (an NMDA receptor antagonist), N5-(nitroamidino)-L-2,5-diaminopentanoic acid (L-NNA; a NO synthase inhibitor), or bicuculline (a GABA receptor antagonist). EtOH caused an increase in the level of glutamate, NO, and GABA in the RVLM during the hypotensive responses. RVLM posttreatment with ketamine blocked the increase in NO and GABA levels; post treatment with L-NNA blocked the increase in GABA level.

CONCLUSIONS

Our results indicate that EtOH augmentation of glutamatergic NMDA receptors/NO/GABA pathways in the RVLM may participate in the hypotensive effects induced by acute administration of EtOH.

Metabotropic and ionotropic glutamate receptors as potential targets for the treatment of alcohol use disorder

Emerging evidence indicates that dysfunctional glutamate neurotransmission is critical in the initiation and development of alcohol and drug dependence. Alcohol consumption induced downregulation of glutamate transporter 1 (GLT-1) as reported in previous studies from our laboratory. Glutamate is the major excitatory neurotransmitter in the brain, which acts via interactions with several glutamate receptors. Alcohol consumption interferes with the glutamatergic signal transmission by altering the functions of these receptors. Among the glutamate receptors involved in alcohol-drinking behavior are the metabotropic receptors such as mGluR1/5, mGluR2/3, and mGluR7, as well as the ionotropic receptors, NMDA and AMPA. Preclinical studies using agonists and antagonists implicate these glutamatergic receptors in the development of alcohol use disorder (AUD). Therefore, the purpose of this review is to discuss the neurocircuitry involving glutamate transmission in animals exposed to alcohol and further outline the role of metabotropic and ionotropic receptors in the regulation of alcohol-drinking behavior. This review provides ample information about the potential therapeutic role of glutamatergic receptors for the treatment of AUD.

Ethanol-enhanced GABA release: a focus on G protein-coupled receptors

While research on the actions of ethanol at the GABAergic synapse has focused on postsynaptic mechanisms, recent data have demonstrated that ethanol also facilitates GABA release from presynaptic terminals in many, but not all, brain regions. The ability of ethanol to increase GABA release can be regulated by different G protein-coupled receptors (GPCRs), such as the cannabinoid-1 receptor, corticotropin-releasing factor 1 receptor, GABA(B) receptor, and the 5-hydroxytryptamine 2C receptor. The intracellular messengers linked to these GPCRs, including the calcium that is released from internal stores, also play a role in ethanol-enhanced GABA release. Hypotheses are proposed to explain how ethanol interacts with the GPCR pathways to increase GABA release and how this interaction contributes to the brain region specificity of ethanol-enhanced GABA release. Defining the mechanism of ethanol-facilitated GABA release will further our understanding of the GABAergic profile of ethanol and increase our knowledge of how GABAergic neurotransmission may contribute to the intoxicating effects of alcohol and to alcohol dependence.

In vivo effects of antibodies from patients with anti-NMDA receptor encephalitis: further evidence of synaptic glutamatergic dysfunction

Background

A severe encephalitis that associates with auto-antibodies to the NR1 subunit of the NMDA receptor (NMDA-R) was recently reported. Patients' antibodies cause a decrease of the density of NMDA-R and synaptic mediated currents, but the in vivo effects on the extracellular glutamate and glutamatergic transmission are unknown.

Methods

We investigated the acute metabolic effects of patients' CSF and purified IgG injected in vivo. Injections were performed in CA1 area of Ammon's horn and in premotor cortex in rats.

Results

Patient's CSF increased the concentrations of glutamate in the extracellular space. The increase was dose-dependent and was dramatic with purified IgG. Patients' CSF impaired both the NMDA- and the AMPA-mediated synaptic regulation of glutamate, and did not affect the glial transport of glutamate. Blockade of GABA-A receptors was associated with a marked elevation of extra-cellular levels of glutamate following a pretreatment with patients' CSF.

Conclusion

These results support a direct role of NMDA-R antibodies upon altering glutamatergic transmission. Furthermore, we provide additional evidence in vivo that NMDA-R antibodies deregulate the glutamatergic pathways and that the encephalitis associated with these antibodies is an auto-immune synaptic disorder.

Oxidative stress in anxiety and comorbid disorders

Anxiety disorders, depression, and alcohol use disorder are common neuropsychiatric diseases that often occur together. Oxidative stress has been suggested to contribute to their etiology. Oxidative stress is a consequence of either increased generation of reactive oxygen species or impaired enzymatic or non-enzymatic defense against it. When excessive it leads to damage of all major classes of macromolecules, and therefore affects several fundamentally important cellular functions. Consequences that are especially detrimental to the proper functioning of the brain include mitochondrial dysfunction, altered neuronal signaling, and inhibition of neurogenesis. Each of these can further contribute to increased oxidative stress, leading to additional burden to the brain. In this review, we will provide an overview of recent work on oxidative stress markers in human patients with anxiety, depressive, or alcohol use disorders, and in relevant animal models. In addition, putative oxidative stress-related mechanisms important for neuropsychiatric diseases are discussed. Despite the considerable interest this field has obtained, the detailed mechanisms that link oxidative stress to the pathogenesis of neuropsychiatric diseases remain largely unknown. Since this pathway may be amenable to pharmacological intervention, further studies are warranted.

Past, present and future therapeutics for cerebellar ataxias

Cerebellar ataxias are a group of disabling neurological disorders. Patients exhibit a cerebellar syndrome and can also present with extra-cerebellar deficits, namely pigmentary retinopathy, extrapyramidal movement disorders, pyramidal signs, cortical symptoms (seizures, cognitive impairment/behavioural symptoms), and peripheral neuropathy. Recently, deficits in cognitive operations have been unraveled. Cerebellar ataxias are heterogeneous both at the phenotypic and genotypic point of view. Therapeutical trials performed during these last 4 decades have failed in most cases, in particular because drugs were not targeting a deleterious pathway, but were given to counteract putative defects in neurotransmission. The identification of the causative mutations of many hereditary ataxias, the development of relevant animal models and the recent identifications of the molecular mechanisms underlying ataxias are impacting on the development of new drugs. We provide an overview of the pharmacological treatments currently used in the clinical practice and we discuss the drugs under development.

Ethanol-mediated operant learning in the infant rat leads to increased ethanol intake during adolescence

Recent studies indicate that the infant rat has high affinity for ethanol ingestion and marked sensitivity to the drug's reinforcing effects [Spear, N.E., Molina, J.C. Fetal or infantile exposure to ethanol promotes ethanol ingestion in adolescence and adulthood: a theoretical review. Alcohol Clin Exp Res 2005; 29: 909-29.]. A novel operant technique was developed to analyze reinforcing effects of ethanol delivery during the third postnatal week. The impact of this ethanol-reinforcement experience upon subsequent ethanol consumption during adolescence (postnatal weeks 5-6) was also examined. In Experiment 1, pups (postnatal days 14-17) were given an explicit contingency between nose-poking behavior and intraoral delivery of either water or 3.75% v/v ethanol (paired groups). Yoked controls (pups receiving either reinforcer independently of their behavior) were also included. Paired subjects reinforced with ethanol exhibited rapid and robust operant conditioning leading to blood ethanol concentrations in the 25-48 mg% range. In Experiment 2, a higher ethanol concentration (7.5% v/v) provided significant reinforcement. During adolescence, animals originally reinforced with 3.75% v/v ethanol exhibited greater ingestion of ethanol than control animals without prior ethanol reinforcement. These results indicate that, without extensive initiation to ethanol, infant rats rapidly learn to gain access to ethanol and that this experience has a significant impact upon later ethanol intake patterns.

The role of the cerebellum in the pathophysiology and treatment of neuropsychiatric disorders: a review

The cerebellum has traditionally been looked upon as a brain area primarily involved in motor behaviour. The last decade has however heralded the cerebellum as a brain region of renewed interest for neuropsychiatric disorders. This renewed interest is fuelled by new insights obtained from neuroanatomical research, modern functional neuroimaging and transcranial magnetic stimulation studies. In this review, evidence in support of cerebellar involvement in neuropsychiatric disorders will be presented. In addition, transcranial magnetic stimulation will be introduced as a novel way to study cerebellar contributions to the pathophysiology of psychiatric disorders. In conclusion, a new functional concept of the cerebellum as more than simply a brain area regulating motor control appears mandatory and the involvement of the cerebellum should be considered when studying the neurological basis of neuropsychiatric disorders.

A possible mechanism for the beneficial effect of ethanol in essential tremor

BACKGROUND

Essential tremor is one of the most common movement disorders in elderly people. The hypothesis of a disregulation of N-methyl-D-aspartate (NMDA) pathways has been suggested. It was shown experimentally that infusion of NMDA in cerebellar nuclei down-regulates glutamate release.

METHODS

We assessed the effects of intranuclear administration of harmaline on the NMDA-mediated regulation of glutamate in rats using reverse dialysis. We hypothesized that ethanol, which improves essential tremor in the clinic, antagonizes the effect of harmaline upon glutamatergic transmission. We tested the interaction of ethanol and harmaline upon glycerol (a marker of membrane turn-over), lactate, and pyruvate concentrations.

RESULTS

Harmaline increased the concentrations of glutamate and impaired the NMDA-mediated regulation of glutamate. Ethanol decreased the concentrations of glutamate during NMDA stimulation in case of pre-administration with harmaline. Concentrations of glycerol rose with harmaline. Glycerol levels markedly decreased during NMDA infusion when inhibitors of nitric oxide synthase, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate antagonists or NMDA antagonists were administered. Harmaline increased lactate/pyruvate ratios during NMDA infusion but these ratios returned to normal values in presence of ethanol.

DISCUSSION

We provide a possible mechanism for the beneficial effect of ethanol on essential tremor. The concept of glutamatergic disregulation underlying essential tremor is highlighted. Consequences for our understanding of essential tremor are discussed.

Differential effects of ethanol and midazolam upon the devaluation of an aversive memory in infant rats

In infant rats, low doses of ethanol (EtOH) have been found to attenuate the aversive representation of an unconditioned stimulus (US) as assessed through a revaluation paradigm. This may be explained by early anxiolytic properties of EtOH. The present set of experiments was aimed at analyzing possible mechanisms of these putative antianxiety effects of EtOH. In the first experiment, EtOH's effects upon the expression of citric acid-induced distress calls were compared with varying doses of midazolam (MDZ), a fast-acting gamma-aminobutyric acid type A (GABA(A)) agonist. Similar calming effects of 0.5 g/kg EtOH and 0.09 mg/kg MDZ were observed. Both drugs were then assessed in their capability to alter the expression of a conditioned aversion by devaluing the US. Aversive conditioning was conducted on postnatal day 14 (PD14) by pairing a lemon odor (conditioned stimulus, CS) with intraoral stimulation of citric acid (US). Control animals experienced both stimuli in an explicitly unrelated fashion. On PD15, pups were briefly exposed to the citric acid solution under the effects of 0.5 g/kg EtOH, 0.09 mg/kg MDZ, or the respective vehicle for each drug. Pups were then tested in a two-way odor preference test (lemon vs. cineole). Both vehicle- and MDZ-treated animals spent significantly less time near the lemon CS, thus expressing a citric acid-mediated odor aversion. This conditioned response was completely inhibited in pups that received 0.5 g/kg EtOH. Locomotor patterns at test were not affected by either EtOH or MDZ administration. A higher dose of MDZ (0.18 mg/kg, intraperitoneal) was also ineffective in attenuating the aversive memory. In summary, EtOH's devaluating capabilities are not shared by MDZ, indicating that these effects of EtOH may not be GABA mediated. Appetitive motivational properties of EtOH or non-GABA(A)-mediated antianxiety effects [i.e., N-methyl-D-aspartic acid (NMDA) related] could underlie this devaluation effect of EtOH.

Mechanical suppression of essential tremor

This paper describes a new treatment for essential tremor. A wearable orthosis, which can be adapted to each configuration of each joint of the upper limb, is able to apply effective dynamic force between consecutive segments of the upper limb and change its biomechanical characteristics. The orthosis is controlled by a computer with a dedicated software application that distinguishes between real time tremor and voluntary movement. The wearable orthosis is able to detect position, rate and acceleration of rotation of the joint by means of a chip gyroscope. This technology was evaluated in six patients suffering from essential tremor. The technique is non invasive and represents an alternative to medication and deep brain stimulation.

Evaluation of a wearable orthosis and an associated algorithm for tremor suppression

We describe a wearable orthosis and an associated algorithm for the simultaneous assessment and treatment of essential tremor, one of the most common movement disorders in humans involving an overactivity of the olivo-cerebellar pathways. A motor providing effective viscosity is fixed on a wearable orthosis in the upper limbs. The motor is controlled by a personal computer with software processing in real time the position and rate of rotation of the joint detected by a chip gyroscope. The orthosis can be used in a monitoring mode and in an active mode. The range of tremor suppression of the signals above the orthosis operational limit ranges from about 3% (percentile 5) to about 79% (percentile 95) in relation to energy in the monitoring mode. Considering both postural and kinetic, the mean tremor energy decreased from 55.49 +/- 22.93 rad2 s(-3) in the monitoring mode to 15.66 +/- 7.29 rad2 s(-3) in the active mode. Medians of power reduction were below 60% for the wrist and the elbow. In addition to supplying new information on the interactions between kinematics, dynamics and tremor genesis, this non-invasive technique is an alternative to current therapies. This new approach will provide new insights into the understanding of motor control.

PATHOMECHANISMS IN CHANNELOPATHIES OF SKELETAL MUSCLE AND BRAIN

Ion channelopathies are a diverse array of human disorders caused by mutations in ion channel genes. This review focuses on the pathogenic mechanisms of channelopathies affecting skeletal muscle and brain arising from mutations of voltage-gated ion channels and fast ligand-gated ion channels expressed at the surface membrane. Derangements in channel function alter the electrical excitability of the cell and thereby increase susceptibility to transient symptomatic attacks including myasthenia, periodic paralysis, myotonic stiffness, seizures, headache, dyskinesia, or episodic ataxia. Although these disorders are rare, they stand out as exemplary cases for which disease pathogenesis can be traced from a point mutation to altered protein function, to altered cellular activity, and to clinical phenotype. The study of these disorders has provided insights on channel structure-function relations, the physiological roles of ion channels, and rational approaches toward therapeutic intervention for many disorders of cellular excitability.

Molecular basis of inherited calcium channelopathies: role of mutations in pore-forming subunits

The pore-forming alpha subunits of voltage-gated calcium channels contain the essential biophysical machinery that underlies calcium influx in response to cell depolarization. In combination with requisite auxiliary subunits, these pore subunits form calcium channel complexes that are pivotal to the physiology and pharmacology of diverse cells ranging from sperm to neurons. Not surprisingly, mutations in the pore subunits generate diverse pathologies, termed channelopathies, that range from failures in excitation-contraction coupling to night blindness. Over the last decade, major insights into the mechanisms of pathogenesis have been derived from animals showing spontaneous or induced mutations. In parallel, there has been considerable growth in our understanding of the workings of voltage-gated ion channels from a structure-function, regulation and cell biology perspective. Here we document our current understanding of the mutations underlying channelopathies involving the voltage-gated calcium channel alpha subunits in humans and other species.