Salsolinol Facilitates Glutamatergic Transmission to Dopamine Neurons in the Posterior Ventral Tegmental Area of Rats

Although in vivo evidence indicates that salsolinol, the condensation product of acetaldehyde and dopamine, has properties that may contribute to alcohol abuse, the underlying mechanisms have not been fully elucidated. We have reported previously that salsolinol stimulates dopamine neurons in the posterior ventral tegmental area (p-VTA) partly by reducing inhibitory GABAergic transmission, and that ethanol increases glutamatergic transmission to VTA-dopamine neurons via the activation of dopamine D1 receptors (D1Rs). In this study, we tested the hypothesis that salsolinol stimulates dopamine neurons involving activation of D1Rs. By using whole-cell recordings on p-VTA-dopamine neurons in acute brain slices of rats, we found that salsolinol-induced increase in spike frequency of dopamine neurons was substantially attenuated by DL-2-amino-5-phosphono-valeric acid and 6, 7-dinitroquinoxaline-2, 3-dione, the antagonists of glutamatergic N-Methyl-D-aspartic acid and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors. Moreover, salsolinol increased the amplitude of evoked excitatory postsynaptic currents (EPSCs) and the frequency but not the amplitude of spontaneous EPSCs. Additionally, SKF83566, a D1R antagonist attenuated the salsolinol-induced facilitation of EPSCs and of spontaneous firing of dopamine neurons. Our data reveal that salsolinol enhances glutamatergic transmission onto dopamine neurons via activation of D1Rs at the glutamatergic afferents in dopamine neurons, which contributes to salsolinol's stimulating effect on p-VTA dopamine neurons. This appears to be a novel mechanism which contributes toward rewarding properties of salsolinol

Lesion of the Cerebellar Noradrenergic Innervation Enhances the Harmaline-Induced Tremor in Rats

Abnormal synchronous activation of the glutamatergic olivo-cerebellar pathway has been suggested to be crucial for the harmaline-induced tremor. The cerebellum receives two catecholaminergic pathways: the dopaminergic pathway arising from the ventral tegmental area/substantia nigra pars compacta, and the noradrenergic one from the locus coeruleus. The aim of the present study was to examine a contribution of the cerebellar catecholaminergic innervations to the harmaline-induced tremor in rats. Rats were injected bilaterally into the cerebellar vermis with 6-hydroxydopamine (6-OHDA; 8 μg/0.5 μl) either alone or this treatment was preceded (30 min earlier) by desipramine (15 mg/kg ip). Harmaline was administered to animals in doses of 7.5 or 15 mg/kg ip. Tremor of forelimbs was measured as a number of episodes during a 90-min observation. Rats were killed by decapitation 30 or 120 min after harmaline treatment. The levels of dopamine, noradrenaline, serotonin, and their metabolites were measured by HPLC in the cerebellum, substantia nigra, caudate–putamen, and frontal cortex. 6-OHDA injected alone enhanced the harmaline-induced tremor. Furthermore, it decreased the noradrenaline level by ca. 40–80% in the cerebellum and increased the levels of serotonin and 5-HIAA in the caudate–putamen and frontal cortex in untreated and/or harmaline-treated animals. When 6-OHDA treatment was preceded by desipramine, it decreased dopaminergic transmission in some regions of the cerebellum while inducing its compensatory activation in others. The latter lesion did not markedly influence the tremor induced by harmaline. The present study indicates that noradrenergic innervation of the cerebellum interacts with cerebral serotonergic systems and plays an inhibitory role in the harmaline-induced tremor

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Tryprophan metbolism in alcoholism. Tryptophan but not excitatory amino acid availablity to the brain is increased before the appearance of the alcohol-withdrawal syndrome in men

Tryptophan (Trp) metabolism and disposition and excitatory and other amino acid concentrations were determined in alcohol-dependent subjects in relation to the alcohol-withdrawal syndrome (AWS). Parameters were examined in 12 alcohol-dependent male subjects, undergoing elective upper digestive tract tumour resection, and 12 age-, gender-, and medication-matched controls on three occasions: pre-operatively, post-operatively, and immediately before (i.e. within 24 h of) the appearance of the AWS. No significant differences were observed between controls and alcoholic subjects on the first or second ot these occasions. On the third occasion, within 24 h of the appearance of the AWS, alcoholics showed a dramatic elevation (117%) in free serum Trp concentration and a consequent increase (111%) in the ratio of [free Trp]/[competing ammo acids], which is an accurate predictor of Trp entry into the brain. Increases were also observed on this third occasion in concentrations of total Trp (49%), cortisol (123%), and norharman (137%). Concentrations of glutamate, glycine, aspartate, serine, and taurine did not differ significantly within or between the control and alcohol-dependent groups of subjects on any of the three occasions. The possible significance of the Trp and related metabolic changes in relation to the behavioural features of the AWS is discussed

Five exon 1 variants of mu opioid receptor and vulnerability to alcohol dependence

The human {my} opioid receptor (hMOR) gene is a prime candidate gene responsible for addictive disorders. The present association study tested the hypothesis that hMOR exon 1 variants elicit susceptibility to alcohol dependence. We have analyzed five nucleotide changes in exon 1 of the hMOR gene. Three of them are in the 5′ untranslated region of exon 1 at positions -172G/T, -111C/T and -38C/A, the remaining two variants cause amino acid substitutions: + 17C/T (Ala6Val) and + 118A/G (Asn40Asp). Our population-based association study included 327 German alcohol-dependent subjects and 340 ethnically matched controls. The lack of an allelic association suggests that the analyzed hMOR exon 1 variants do not contribute a common and substantial effect to the genetically determined vulnerability of alcohol dependence

Human mu-opioid receptor variation and alcohol dependence

Mu-Opioid receptor-mediated neurotransmission is involved in the reward, tolerance, and withdrawal effects of alcohol. The present association study tested the hypothesis that the common Asn40Asp substitution polymorphism in the N-terminal domain of the human mu-opioid receptor (OPRM) confers vulnerability to subtypes of alcohol dependence. The genotypes of the Asn40Asp substitution polymorphism were assessed in 327 German alcohol-dependent subjects (according to ICD-10) and in 340 control subjects of German descent, using an assay based on allele-specific polymerase chain reaction. To select alcoholics with a presumed high genetic load, three subgroups were delineated, marked by (1) a family history of parental alcoholism (n = 114); (2) the inability to abstain from alcohol before the age of 26 years (n = 73); and (3) a history of alcohol withdrawal seizure or delirium (n = 107). The frequency of the Asp40 allele did not differ significantly between the controls [f(Asp40) = 0.078] and either the entire group of alcoholics [f(Asp40) = 0.107; p = 0.066], or the alcoholics with parental alcoholism [f(Asp40) = 0.114; p = 0.094], or the early-onset alcoholics [f(Asp40) = 0.096; p = 0.471,[ or the alcoholics with severe withdrawal symptoms [f(Asp40) = 0.098; p = 0.350]. Our results do not provide evidence that the common Asn40Asp substitution polymorphism of the OPRM gene contributes a major effect to the pathogenesis of alcohol dependence