Neurochemical Mechanisms Underlying Alcohol Addiction: Model Experiments on Rats

We measured the activities of the main alcohol-metabolizing enzymes (alcohol dehydrogenase, AlDH, and aldehyde dehydrogenase, AdhDH) in the blood serum, comparing these indices with the contents of ethanol and its main metabolite, acetaldehyde (AcAdh), in the blood, and also measured the contents of catecholamines (adrenaline, noradrenaline, and dopamine) in the blood and in different brain structures (hypothalamus, midbrain, and neocortex) of rats in the states of acute alcohol intoxication and chronic alcohol addiction. It was shown that, because of dissimilar changes in the activities of AlDH and AdhDH under conditions of alcohol intoxication, the dynamic balance between endogenous ethanol and AcAdh existing in the norm is disturbed, which results in an increase in the level of AcAdh. Such a phenomenon probably is one of the crucial factors underlying the development of alcohol addiction.     

Effects of an Analog of Vasopressin on the Content of Biogenic Amines in the Brain Structures and Blood of Rats in Alcohol Intoxication

On rats with genetically determined inclination to ethanol consumption under conditions of free choice between ethanol solution and water as liquids for drinking, we studied the effects of an analog of vasopressin (anVP, the tetrapeptide corresponding to the ring part of the molecule of this hormone) on the contents of noradrenaline (NA) and serotonin (5-HT) in the hypothalamus, midbrain, and neocortex and also on the contents of adrenaline (A), NA, and 5-HT in the blood. Injections of 1.0 g/kg anVP did not significantly change the above indices. Injections of this agent in a higher dose (5.0 g/kg) resulted in an increase in the content of NA in the hypothalamus by 80%, on average, and in a decrease in the A level in the blood by 40%. At the same time, the level of 5-HT in all the brain structures under study dropped rather sharply. After injection of 5.0 g/kg anVP against the background of acute alcohol intoxication (infusion of 4.0 g/kg ethanol into the stomach), the level of biogenic amines, which to a considerable extent changed under conditions of such intoxication, demonstrated clear trends toward normalization in all the studied brain structures.     

Isoforms of Aldehyde Dehydrogenase in the Brain Structures of Rats with Different Inclinations to Ethanol Consumption

We measured the levels of activity of aldehyde dehydrogenase (AdhDH, EC 1.2.1.3) manifested at different concentrations of acetaldehyde (AcAdh) in cytosol fractions from the tissues of the hypothalamus, midbrain, and neocortex of rats preferring an ethanol solution or pure water as liquids for drinking (ethanol- and water-preferring, EP and WP groups, respectively). Two AdhDH isoforms, with a high and a low affinity for AcAdh, were identified in the above brain structures. An AdhDH-1 isoform characterized by a higher affinity for AcAdh and a low value of the apparent Michaelis constant (K _m) was found in all studied brain structures of the EP rats. An analogous AdhDH-1 isoform found in cytosol fractions from the hypothalamus and midbrain of the WP rats showed a lower affinity for AcAdh and provided a lower maximum rate of reaction (V _max). In the neocortex cytosol fractions of the rats of this group, AdhDH-1 could not be identified. In EP rats, the level of AcAdh metabolism mediated by AdhDH was noticeably higher in cytosol fractions from the hypothalamus and midbrain, as compared with that in the respective fraction from the neocortex.     

Effects of Glycine on the Catecholamine Levels and Activities of Alcohol-Metabolizing Enzymes in Rats with Alcohol Intoxication and Addiction

We studied in rats the effects of peroral glycine introduction on the contents of catecholamines (CA) – noradrenaline (NA) and dopamine (DA) – in different brain structures (hypothalamus, midbrain, and neocortex), as well as the levels of adrenaline (A), NA, and DA in the blood and the activity of alcohol-metabolizing (AlM) enzymes – alcohol dehydrogenase (AlDH) and aldehyde dehydrogenase (AdhDH) – in the blood serum. The experimental group included animals with a disposition to alcohol consumption under conditions of free choice for drinking between an alcohol solution and water. The measurements were performed in animals in the state of acute alcohol intoxication (i.p. injection of 4 g/kg ethanol) or chronic alcohol addiction (formed due to a 3-month-long free access to ethanol solution). Introduction of 150 mg/kg glycine increased the NA and DA contents (the latter, to a lesser extent) in all examined brain structures; the NA level in the blood increased, while that of DA decreased. Under conditions of acute alcohol intoxication and chronic alcohol addiction, the ratio of the activities of AlM enzymes, AdhDH/AlDH, was significantly shifted toward values indicative of accumulation of acetaldehyde (AcAdh) in the tissues. This was accompanied by noticeable modifications of the CA contents in the brain structures and blood of the rats; in particular, the [DA]/[NA] ratio in the brain significantly increased. Introduction of glycine under conditions of acute alcohol intoxication provided normalization of the AdhDH/AlDH activity ratio. Obvious trends toward normalization of the CA levels in the brain structures were also observed in both acute and chronic experiments. In the latter case, the glycine treatment course resulted in a drop in the daily alcohol consumption by the animals. We conclude that glycine, which binds AcAdh and modifies the metabolism of CA transmitters, exerts a significant corrective influence on the pathogenetic mechanisms of alcohol addiction. Our experimental findings demonstrate that there are contact points between the acetaldehyde and catecholamine hypotheses of pathogenesis of alcoholism.     

乙醛在小鼠酒依赖性行为中的作用研究

乙醛为酒精代谢的中间产物,但其在酒依赖中的作用不清楚.通过条件化位置偏好(CPP)和条件化味觉偏好(CTP)试验,分析乙醛对小鼠乙醇依赖性行为的影响,研究乙醛在酒依赖中的作用.研究发现,经0.8%乙醇预处理7d后,小鼠训练8次则表现出对乙醇的条件化位置偏好(n=6,P<0.01),而经乙醛训练的小鼠则对乙醛无明显条件化偏好行为(n=6,P>0.05).当用0.8%乙醇、0.4%乙醛混合训练乙醇依赖性小鼠时,其位置偏好行为减弱(n=6,P<0.01).10%乙醇预处理的小鼠味觉偏好乙醇(n=6,P<0.01),而当乙醇中加入1%乙醛时,其味觉偏好现象减弱(n=6,P<0.01).1%乙醛训练7d后的小鼠不表现对乙醇的味觉偏好,但选择摄入乙醛及乙醇、乙醛混合溶液的量有所增加.结果表明乙醛在小鼠酒依赖行为中可能存在一定促进作用.     

Effects of Chronic Ethanol Administration on Serotonin Metabolism in the Various Regions of the Rat Brain

Changes in serotonin (5-HT) and 5-hydroxy indole acetic acid (5-HIAA), its major metabolite, in cerebral cortex, corpus striatum and hippocampus were investigated at 10^th and 21^st days of chronic ethanol ingestion in Wistar rats. Ethanol (7.2% v/v) was given to rats in a modified liquid diet. Biochemical analysis was performed in two groups of ethanol-treated and control rats (n = 6 for each group). Rats in each group were decapitated at the 10^th and 21^st days of ethanol consumption. Brains were removed and cerebral cortex, corpus striatum and hippocampus were dissected. 5-HT and 5-HIAA levels were measured in respective brain regions by using high performance liquid chromatography. In cerebral cortex and corpus striatum, 5-HT levels were significantly lower than control at the 10^th day of ethanol consumption. At the 21^st day, the levels tended to remain low, but not significantly different statistically. In hippocampus, 5-HIAA levels were significantly higher than control at 10^th day of ethanol consumption. Increased 5-HIAA level returned to control values at the 21^st day of ethanol consumption. Our results suggest that, 5-HT clearly seems to play a critical role in the brain at the 10^th day of chronic ethanol consumption.     

The Effect of Endurance Training on Regional Serotonin Metabolism in the Brain During Early Stage of Detraining Period in the Female Rat

1. The effect was examined of a single bout of nonexhaustive endurance exercise on tryptophan (Try), serotonin (5-HT), 5-hydroxyindolacetic acid (5-HIAA), and tryptophan hydroxylase (TpH) levels in different parts of rat brain (brain cortex, cerebellum, hypothalamus, midbrain striatum, medulla) on the last day of endurance training and 48 h later (detraining period).2. Female rats were subjected to a 6-week endurance training programme. The effectiveness of the training was evaluated by measuring anaerobic threshold (AT). High performance liquid chromatography (HPLC) was used to determine regional Try, 5-HT, and 5-HIAA contents in the brain, and thin layer chromatography followed by gas-liquid chromatography was used to determine blood levels of free fatty acids. Regional TpH levels were measured by Western blot analysis.3. In the two rat groups subjected to endurance training, in all brain regions studied but cerebellum, 5-HT content was significantly lower after the last bout of nonexhaustive endurance exercise than in resting control rats that were not subjected to the training. Similarly, the cortical and striatal, but not cerebellar, 5-HT/Try ratios were significantly lower in the trained rats at the end of the last training session and at the end of a single bout of nonexhaustive exercise administered after a 48-h detraining period than in the controls. TpH protein level was decreased by 15–25% after the last bout of exercise either during the training process or after the and 1 h bout of endurance exercise performed 48 h after cessation of endurance training in brain cortex and striatum but not cerebellar.4. These results indicate that the reduction in 5-HT level was the adaptive response to endurance training. The lowered 5-HT/Try ratio and lowered TpH protein level attained after the training process suggests and that this change may be, at least partially, attributed to downregulation of TpH activity.     

The Role of Platelet Serotonin and Depression in the Acute Coronary Syndrome Population

Platelet serotonin has been associated with depression and coronary artery disease. Understanding the association between platelet serotonin and depressive symptoms during acute coronary syndrome (ACS) may explain some of the ACS events seen in depressed individuals. The objectives were to evaluate whether levels of platelet serotonin during an ACS event differ between individuals who screen positive or negative for depressive symptoms and to determine if a linear relationship exists. In this cross-sectional study, data were collected on 51 patients with ACS. Multiple linear regression models were examined. Platelet serotonin levels were not significantly different between the depressed and non-depressed groups (β = -4.093 and p = .293); a linear relationship was not found (β = -.254 and p = .250). In conclusion, a relationship between platelet serotonin and depressive symptoms was not found. It remains unclear if an association exists between platelet serotonin levels and depressive symptoms during hospitalization for ACS.     

Serotonin promotes feminization of the sexually dimorphic nucleus of the preoptic area,but not the calbindin cell group

Testosterone and its metabolites masculinize the brain during a critical perinatal window, including the relative volume of sexually dimorphic brain areas such as the sexually dimorphic nucleus of the preoptic area (SDN), which is larger in males than females. Serotonin (5HT) may mediate this hormone action, since 5HT given during the second week of life decreases (i.e., feminizes) SDN volume in males and testosterone‐treated females. Although previous work indicates that the 5HT_2A/2C receptor is sufficient to induce feminization, it is unclear whether other serotonin receptors are required and which subpopulation(s) of SDN cells are specifically organized by 5HT. Therefore, we injected male and female Sprague‐Dawley rat pups with saline, a nonselective 5HTR agonist, a 5HT_2A/2C agonist, or a 5HT_2A/2C antagonist over several timecourses in early life, and measured the Nissl‐SDN as well as a calbindin+ subdivision of the SDN, the CALB‐SDN. When examined on postnatal day 18 or early adulthood, the size of the Nissl‐SDN was feminized in males treated with any of the serotonergic drugs, eliminating the typical sex difference. In contrast, the sex difference in CALB‐SDN size was maintained regardless of serotoninergic drug treatment. This pattern suggests that although gonadal hormones shape the whole SDN, individual cellular phenotypes respond to different intermediary signals to become sexually dimorphic. Specifically, 5HT mediates sexual differentiation of non‐calbindin population(s) within the SDN. The results also caution against using measurement of the CALB‐SDN in isolation, as the absence of an effect on the CALB‐SDN does not preclude an effect on the overall nucleus. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 76: 1241–1253, 2016     

Disorders in memory and learning in offspring of alcoholized female rats,and a possibility for correction of these changes

We studied the effect of alcohol intoxication of albino female rats on the process of learning and memory of their adult (two-month-old) offspring and also a possibility for correction of the observed changes using dolivin. During pregnancy and lactation, female rat of the experimental group obtained 15% solution of ethanol instead of water. To estimate the successfulness of spatial learning of their offspring, we used a multiway elevated labyrinth; the level of consolidation of memory traces was estimated using a passive avoidance test in a chamber with dark and illuminated sections. In the tested offspring rats, prenatal exposure to ethanol induced dramatic drops in the indices of both the above tests. The use of dolivin simultaneously with ethanol exposure allowed us to demonstrate the clear protective properties of this complex preparation containing such antioxidants as hypoxen and vitamin E: disorders in behavior of the offspring of alcoholized females were smoothed significantly. Neirofiziologiya/Neurophysiology, Vol. 40, No. 2, pp. 130–136, March–April, 2008.     

An increase of collagen biosynthesis in livers of rats submitted to chronic intoxication with ethanol

Summary It was found that chronic intoxication of rats with ethanol results in a dictinct, progressive increase of 5³H-proline incorporation into collagen synthesized by liver. At the same time biosynthesis of other proline-containing proteins in rat liver slightly decreases. These effects precede the morphological symptoms of liver damage induced by ethanol.     

Inhibition of striatal‐enriched tyrosine phosphatase 61 in the dorsomedial striatum is sufficient to increased ethanol consumption

The STriatal‐Enriched protein tyrosine Phosphatase 61 (STEP₆₁) inhibits the activity of the tyrosine kinase Fyn and dephosphorylates the GluN2B subunit of the NMDA receptor, whereas the protein kinase A phosphorylation of STEP₆₁ inhibits the activity of the phosphatase (Pharmacol. Rev., 64, 2012 , p. 65). Previously, we found that ethanol activates Fyn in the dorsomedial striatum (DMS) leading to GluN2B phosphorylation, which, in turn, underlies the development of ethanol intake (J. Neurosci., 30, 2010 , p. 10187). Here, we tested the hypothesis that inhibition of STEP₆₁ by ethanol is upstream of Fyn/GluN2B. We show that exposure of mice to ethanol increased STEP₆₁ phosphorylation in the DMS, which was maintained after withdrawal and was not observed in other striatal regions. Specific knockdown of STEP₆₁ in the DMS of mice enhanced ethanol‐mediated Fyn activation and GluN2B phosphorylation, and increased ethanol intake without altering the level of water, saccharine, quinine consumption or spontaneous locomotor activity. Together, our data suggest that blockade of STEP₆₁ activity in response to ethanol is sufficient for the activation of the Fyn/GluN2B pathway in the DMS. Being upstream of Fyn and GluN2B, inactive STEP₆₁ in the DMS primes the induction of ethanol intake.

     

Decrease of Serotonin Transporters in Blood Platelets after Epileptic Seizures

Serotonin transporter (SERT) was studied by [³H]-paroxetine binding in blood platelets from controls and epileptic patients with generalized convulsive seizures. The average K_D and B_Max were not different in the two cases. However, a significant decrease was found in the serotonin transporter density in the platelet membranes from patients having undergone an epileptic seizure less than 4 days before. This circumstance may indicate a homeostatic reaction to the epileptic attack.     

VNTR Polymorphisms of the Serotonin Transporter and Dopamine Transporter Genes in Male Opiate Addicts

VNTR polymorphisms of the serotonin transporter (hSERT) and dopamine transporter (DAT1) gene were studied in male opiate addicts. Samples of ethnic Russians and ethnic Tatars did not differ in genotype and allele frequencies. Homozygosity at hSERT (especially 10/10) was associated with early opiate addiction, while genotype 12/10 proved to be protective. In the case of DAT1, genotype 9/9 was associated with early opiate addiction. The combination of hSERT genotype 10/10 with DAT1 genotype 10/10 was shown to be a risk factor of opiate abuse under 16 years of age.     

Focus: Addiction: Perceptions of Family Alcohol Use in a Young Adult Sample

Perceptions of family alcohol use have been linked to adolescent alcohol use behaviors, yet there have been no studies that have assessed this relationship in young adults. This study examined perceptions of family alcohol use and their association with participants’ self-reported alcohol use. Participants included 171 undergraduate students (mean age = 21.67, 71.9 percent female, 75.4 percent Caucasian). Participants completed measures assessing quantity and frequency of alcohol use, negative consequences of use, and sibling relationship quality. They also reported their perceptions of alcohol use for siblings and parents during a typical week. Perceptions of siblings’ quantity of weekly alcohol use were significantly associated with participants’ quantity of alcohol use (r = .21, p = .006) and frequency of alcohol use (r = .23, p = .002). Perceptions of parental alcohol use were not related to the participants’ alcohol use patterns.     

A periodic dosing model of fetal alcohol syndrome in the pig-tailed macaque (Macaca nemestrina)

A nonhuman primate on a periodic ethanol dosing schedule should provide a model of fetal alcohol syndrome (FAS) most relevant to the majority of pregnant women who are “social drinkers” and can exercise reasonable control over their ethanol intake. In this pilot study, four pregnant pig-tailed macaques (Macaca nemestrina) received ethanol once a week from 40 days' gestation. Doses were 2.5 gm/kg for three moderate-dose animals (MDAs) and 4.1 gm/kg for one high-dose animal (HDA). Peak blood ethanol levels reached a mean of 240–256 mg/dl for the MDAs and averaged 379 mg/dl for the HDA. Peak acetaldehyde did not vary with dose. One MDA aborted after the first dose. The other three pregnancies were compared with eight to ten control pregnancies, and the infants' development over the first six months was compared with that of the control offspring. Nutritional status of the pregnant females was normal. The fetal heart rate response to maternal restraint was absent in the HDA. Gestational duration and simian Apgar scores were normal. All three infants were abnormally large, and two were also abnormally heavy, with body weight appropriate to skeletal size. Skeletal maturation, judged by ossification and tooth eruption, was not accelerated. The high-dose infant (HDI) was scaphocephalic, with an underdeveloped cranial base and midface, and its brain was small and dysplastic; its reflex, motor, and cognitive development were retarded. One moderate-dose infant (MDI) had some brain abnormalities; it was hyperkinetic and showed developmental retardation on several behavioral measures. The other MDI was normal. We conclude that the periodic model offers an effective means of investigating FAS in M. nemestrina. Furthermore, when nutrition is maintained, intermittent intake of ethanol by the pregnant primate does not necessarily reatard fetal growth.     

Migration and differentiation of gonadotropin-releasing hormone-producing neurons in the brain of mouse fetus exposed to excess of serotonin

The work has been carried out on mice of the Tg8 line with knockout of gene of monoamineoxidase A with an increase of serotonin and noradrenaline content in the brain, and on mice of the C3H line with unchanged genome and normal concentration of monoamines. An immunocytochemical study has been performed of development of neurons producing gonadotropin-releasing hormone (GnRH) under conditions of excess of serotonin and noradrenaline in the mice in embryogenesis. The GnRH-neurons were revealed at the 18th day of embryonic development in telencephalon along trajectory of their migration from olfactory bulbs to the retrochiasmatic area. In telencephalon of mouse embryos of the Tg8 line, a redistribution of the GnRH-neurons along their migration trajectory was observed as compared with embryos of the C3H line mice. The percent of the GnRH-neurons in the Tg8 mouse embryos in caudal parts of the migration trajectory was lower than in rostral parts, the opposite distribution of the neurons being observed in the C3H line mouse embryos; at the excess of serotonin and noradrenaline in the Tg8 line mouse embryos, the total amount of GnRH-neurons in the brain was lower than in the C3H mice. In males of the Tg8 line mice under conditions of excess of serotonin and noradrenaline the optical density of neurons, which correlated with the GnRH concentration in the cell, was higher than in control mice. Thus, in the Tg8 mice under conditions of the serotonin and noradrenaline excess, migration of the GnRH-neurons to their final anlage in hypothalamus is accelerated as well as the total number of the GnRH-neurons decreases, which indicates a decrease of proliferation of cells-precursors and the earlier differentiation of neurons.     

Serotonin catabolism in the central and enteric nervous systems of rats upon induction of serotonin syndrome

Serotonin, a well-known neurotransmitter in mammals, has been linked to a number of neurological and gastrointestinal disorders. One of these disorders, serotonin syndrome, is a potentially deadly condition caused by increased levels of serotonin in the extracellular space. Information on the neurochemical effects of serotonin syndrome on serotonin catabolism is lacking, particularly in relation to the enteric system of the gastrointestinal tract. Here the catabolism of serotonin is monitored in rats with pharmacologically induced serotonin syndrome, with the catabolites characterized using a specialized capillary electrophoresis system with laser-induced native fluorescence detection. Animals induced with serotonin syndrome demonstrate striking increases in the levels of serotonin and its metabolites. In the brain, levels of serotonin increased 2- to 3-fold in animals induced with serotonin syndrome. A major serotonin metabolite, 5-hydroxyindole acetic acid, increased 10- to 100-fold in experimental animals. Similar results were observed in the gastrointestinal tissues; in the small intestines, serotonin levels increased 4- to 5-fold. Concentrations of 5-hydroxyindole acetic acid increased 32- to 100-fold in the intestinal tissues of experimental animals. Serotonin sulfate showed surprisingly large increases, marking what may be the first time the compound has been reported in rat intestinal tissues.     

Content of Serotonin in the Blood at High Physic Loadings as a Possible Factor Influencing Central Effects of This Monoamine

We measured the contents of serotonin and histamine in the blood plasma of 62 high-ranking athletes specialized on cyclic sporting disciplines and of 20 generally healthy subjects involved only in amateur sports (a control group). The concentration of serotonin in the blood of the examined sportsmen was, on average, 133% of the respective index in the control group (109 ± 11 ng/ml vs 82 ± 13 ng/ml; P < 0.05). The level of serotonin in the blood plasma demonstrated certain correlations with the dynamics of competition score against the background of similar training loadings, with the heart rate of the tested subjects in the resting state, and with the phase of the training cycle. After a test physical loading (veloergometer test), the level of serotonin dropped somewhat, and such a drop was smaller the better the adaptation to long-term loadings. We discuss the possibility that serotonin present in the circulation can exert a certain influence on the central effects of this monoamine (reactions realized by the systems of serotonergic neurons, and neuroendocrine activity of the epiphysis) despite the fact that the blood-brain barrier represents a significant resistivity hindering the diffusion exchange between the pools of this monoamine in the cerebral tissues and blood.     

Function and Mechanism of Myelin Regulation in Alcohol Abuse and Alcoholism

Excessive alcohol use has adverse effects on the central nervous system (CNS) and can lead to alcohol use disorders (AUDs). Recent studies have suggested that myelin reductions may directly contribute to CNS dysfunctions associated with AUDs. Myelin consists of compact lipid membranes wrapped around axons to provide electrical insulation and trophic support. Regulation of myelin is considered as a new form of neural plasticity due to its profound impacts on the computation of neural networks. In this review, the authors first discuss experimental evidence showing how alcohol exposure causes demyelination in different brain regions, often accompanied by deficits in cognition and emotion. Next, they discuss postulated molecular and cellular mechanisms underlying alcohol's impact on myelin. It is clear that more extensive investigations are needed in this important but underexplored research field in order to gain a better understanding of the myelin‐behavior relationship and to develop new treatment strategies for AUDs.