Ethanol-induced changes in tyrosine hydroxylase activity in brains of mice selectively bred for differences in sensitivity to ethanol

A possible neuroprotective property of ethanol and/or NeuroAiD on the modulation of cognitive function

Cognitive impairments and poor performance on tasks needing behavioral flexibility are observable in chronic alcohol exposure. NeuroAid decreases cognitive deficits and improves functional outcomes by restoring neuronal circuits. The aim of the current study was to assess the hypothesis that ethanol exposure would induce neurobehavioral defects which may be reversed by the neuroprotective property of NeuroAid. Adult male Wistar rats were treated with saline, ethanol (0.2 g/kg), NeuroAid (0.8 g/kg) and ethanol (0.2 g/kg) + NeuroAid (0.8 g/kg). Then, behavioral tests were performed using the Y-maze apparatus, hot-plate and tail-flick apparatuses, locomotion apparatus as well as the loss of righting reflex (LORR) and hanging protocols (performance in a wire hanging test). Our results indicated that intraperitoneal (i.p.) administration of ethanol alone and administration of ethanol along with NeuroAid for one week reversed ethanol-induced spatial memory deficits in rats (P < 0.01). Interestingly, treatment with ethanol (0.2 g/kg) for one week induced nociception (P < 0.01). Moreover, one week administration of ethanol (0.2 g/kg) along with NeuroAid (0.8 g/kg) increased latency to LORR (P < 0.001) while four weeks administration of ethanol (0.2 g/kg) along with NeuroAid (0.8 g/kg) decreased sleep time (P < 0.01). In addition, a single administration of all drugs did not alter locomotor activity (P > 0.05) and hanging (P > 0.05). Improvement of behavioral tasks after one-week i.p. administration of ethanol and/or NeuroAid in comparison with a single administration of ethanol and/or NeuroAid may be due to the neuroprotective property of ethanol and/or NeuroAiD.

Acute alcohol exposure increases tyrosine hydroxylase protein expression and dopamine synthesis in zebrafish

Zebrafish have become a popular animal model for investigating the effects of alcohol on the brain and behaviour. Acute exposure to alcohol has been shown to alter dopaminergic signalling in zebrafish, but the underlying mechanisms have not been well defined. In the current study, we characterize the effects of alcohol on the zebrafish dopaminergic system by focusing on tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Using western blot analysis, we demonstrate that a 60min exposure to 1% alcohol increases tyrosine hydroxylase protein expression in the zebrafish brain. Enzymatic activity assays confirmed that alcohol also increases tyrosine hydroxylase enzymatic activity, whereas HPLC analysis demonstrated increased levels of whole-brain dopamine and its metabolite DOPAC. In addition to activation of the dopaminergic system, behavioural analysis revealed accompanying increase of distance traveled following 1% alcohol exposure. These findings suggest that acute alcohol exposure elevates dopamine synthesis via increased tyrosine hydroxylase protein expression. Our results support the hypothesis that alcohol alters dopaminergic signalling in the zebrafish brain in a similar manner as compared to mammals.

Differences in the bimodal effects of morphine in the vas deferens of two strains of rats

1. The effect of morphine on the smooth muscle of the isolated vas deferens of Sprague-Dawley and Wistar rats was studied. 2. Morphine produces pre- and post-synaptic effects on the contractile activity of the vasa deferentia. 3. The pre-synaptic action is an increase in the basal tension of the vas deferens. 4. The post-synaptic effect is a bimodal change in the height of the muscular twitch induced by neurogenic transmural stimulation. 5. Sprague-Dawley rats are more sensitive than Wistar rats to the actions of morphine. 6. The morphine induced responses were antagonized by naloxone better in Wistar than Sprague-Dawley rats. 7. The findings obtained suggest a genetic differences in the synthesis of opioid subtype receptors.

Selected mouse lines, alcohol and behavior

The technique of selective breeding has been employed to develop a number of mouse lines differing in genetic sensitivity to specific effects of ethanol. Genetic animal models for sensitivity to the hypnotic, thermoregulatory, excitatory, and dependence-producing effects of alcohol have been developed. These genetic animal models have been utilized in numerous studies to assess the bases for those genetic differences, and to determine the specific neurochemical and neurophysiological bases for ethanol's actions. Work with these lines has challenged some long-held beliefs about ethanol's mechanisms of action. For example, lines genetically sensitive to one effect of ethanol are not necessarily sensitive to others, which demonstrates that no single set of genes modulates all ethanol effects. LS mice, selected for sensitivity to ethanol anesthesia, are not similarly sensitive to all anesthetic drugs, which demonstrates that all such drugs cannot have a common mechanism of action. On the other hand, WSP mice, genetically susceptible to the development of severe ethanol withdrawal, show a similar predisposition to diazepam and phenobarbital withdrawal, which suggests that there may be a common set of genes underlying drug dependencies. Studies with these models have also revealed important new directions for future mechanism-oriented research. Several studies implicate brain gamma-aminobutyric acid and dopamine systems as potentially important mediators of susceptibility to alcohol intoxication. The stability of the genetic animal models across laboratories and generations will continue to increase their power as analytic tools.

CNS monoamine levels and the effect of DSP4 on ethanol sensitivity in LS and SS mice

Brain area monoamine levels were determined in selectively-bred ethanol sensitive (LS) and insensitive (SS) mice. Norepinephrine, dopamine and serotonin were measured using high performance liquid chromatography coupled with electrochemical detection. Brain regions studied included cerebellum, brain stem, striatum, frontal cortex, hippocampus and hypothalamus. LS and SS mice exhibited similar regional monamine levels with the exception of differences in brain stem and cerebellar norepinephrine levels. The role of norepinephrine in regulating ethanol sensitivity of these mice was investigated using the neurotoxin, DSP4 (selectively lesions central noradrenergic pathways). Treatment with DSP4 did not alter ethanol sensitivity in the LS or SS mice, measured by duration of righting response loss and blood ethanol concentration at its recovery. Differences in brain stem and cerebellar norepinephrine levels between the LS and SS mice were considerably smaller than the large decreases in levels produced in both lines by DSP4. It is concluded that although synaptically-released monoamines may influence ethanol responses, norepinephrine probably does not directly mediate differences in behavioral sensitivity to ethanol between these mouse lines.

Effects of 6-hydroxydopamine on brain catecholamines and on acute actions of ethanol in LS/Ibg and SS/Ibg mice

LS/Ibg (LS) and SS/Ibg (SS) mice differ in ethanol-induced duration of loss of righting response or sleep time, hypothermia, hyperglycemia, and blood ethanol concentrations at regaining righting response. These differences in response to ethanol are a result of differences in central nervous system sensitivity and are mediated by polygenic systems. Studies have indicated that catecholaminergic systems may be involved in the differential effects of ethanol in LS and SS lines of mice (Masserano JM, Weiner N: Investigations into the neurochemical mechanisms mediating differences in ethanol sensitivity in two lines of mice. J Pharmacol Exp Ther 221:404-408, 1982). In this study the neurotoxin, 6-hydroxydopamine (6-OHDA), intracerebroventricular, was used to test this hypothesis. Administration of 6-OHDA markedly altered thermoregulation in LS mice but produced little effect in SS mice, and ethanol-induced hyperglycemia was attenuated in both LS and SS mice by 6-OHDA. Ethanol-induced sleep time was increased in SS mice pretreated with 100 micrograms of 6-OHDA, intracerebroventricular, whereas this response in LS mice was unaffected by 6-OHDA administration. Changes in sleep time were not related to changes in blood ethanol concentrations, indicating that 6-OHDA alters ethanol-induced sleep time by mechanisms other than brain sensitivity. Levels of norepinephrine and dopamine were determined in three brain regions, and the altered capacities for thermoregulation and glucoregulation were associated with changes in hypothalamic catecholamine levels.

Biochemical genetic variants in mice selectively bred for sensitivity or resistance to ethanol-induced sedation

The distribution of biochemical genetic variants was examined among eight inbred strains of mice, which served as contributors to a heterogeneous stock of mice (HS), and in short-sleep (SS) and long-sleep (LS) mice, selectively bred from the HS stock for differential ethanol sensitivity. Fifteen loci for enzymes of alcohol and aldehyde metabolism, as well as 12 other biochemical loci, were investigated. Thirteen of these loci exhibited allelic variation between strains, of which six were separately fixed in the SS and LS mice. Comparisons of genetic similarity coefficients, based upon the distributions of allelic variants for the loci examined, with behavioural sensitivities (sleep-time) to an acute dose of ethanol for the inbred and selected strains of mice, indicated no correlations between these data. This suggests that this collective group of loci are not useful indicators of the genes selectively bred in the SS and LS strains, which are responsible for the differential sensitivities to acute doses of ethanol.

Alpha-methyl-para-tyrosine effects in mice selectively bred for differences in sensitivity to ethanol

The responses of catecholamine systems in long sleep (LS) and short sleep (SS) mice to alpha-methyl-p-tyrosine (AMPT) have been examined. Marked differences were found between LS and SS mice in the dose necessary for maximal brain catecholamine depletion and in the time-course of the catecholamine depletion. Brain catecholamines in the LS mice were depleted by lower doses of AMPT and the levels remained depressed for longer periods of time in this line of mice. These differences may be explained only partially by an increased susceptibility of the LS mice to the hypothermia and toxic effects caused by AMPT administration, as they persist with non-toxic AMPT dosage regimens and under conditions where the degree of hypothermia is comparable in both lines of mice. In addition, there were no differences between the Ki values for the effect of AMPT on the tyrosine hydroxylase from striata of these mouse lines. The primary cause of the heightened response to AMPT in LS mice would appear to be pharmacokinetic in nature, as brain and plasma peak levels of AMPT in LS mice were greater and the levels remained higher for a longer time. The depletion of brain tyrosine by AMPT combined with the lower affinity of the LS striatal tyrosine hydroxylase for the substrate tyrosine may also contribute to the heightened response in LS mice.

Reinterpretation of the literature indicates differential sensitivities of long-sleep and short-sleep mice are not specific to alcohol

This paper reviews the findings and conclusions of the literature pertinent to the Long-Sleep and Short-Sleep selectively-bred lines of mice and challenges the widely-held notion that the selective breeding program was successful in separating alleles for specific sensitivities to just alcohol. Rather, it is argued that these lines of mice were selected for differing activity of a more general process. Recent evidence, as well as reevaluated previous evidence, indicates that Long-Sleep mice are more sensitive to the soporific effects of three major classes of CNS depressants (alcohols, barbiturates, and benzodiazepines), as well as many other anesthesia-inducing compounds (adenosine, chloral hydrate, trichloroethanol, paraldehyde, nitrous oxide, enflurane, and isoflurane). Further, much evidence also supports the conclusion that most of these hypnotic-depressants and anesthetics could exert their soporific influence by a potentiation of GABA activity. The other characteristic of interest in this regard is susceptibility to convulsions. Short-Sleep mice have significantly lower thresholds to both flurothyl-induced and bicuculline-induced convulsions, as well as being more likely to suffer from paroxysms during ethanol withdrawal.

Effect of ethanol on tyrosine hydroxylation in brain regions of long and short sleep mice

The effect of ethanol on the in vivo rate of tyrosine hydroxylation in 6 brain regions was examined in two lines of mice selectively bred for a differential sensitivity to ethanol. The mice are designated long-sleep (LS) and short-sleep (SS) and lose their righting reflex for a duration of 100 minutes (LS) and 13 minutes (SS) following an intraperitoneal dose of ethanol of 4.0 g/kg. DOPA accumulation after NSD-1015 administration was measured in the absence and presence of ethanol (4.0 g/kg, IP) in the periods 5-35 minutes and 85-115 minutes after saline or ethanol. There were no differences between the lines in either basal catecholamine levels or basal tyrosine hydroxylation rates (as measured by DOPA accumulation) in any brain region except the cerebellum, where the norepinephrine content in the SS mice is 33% greater and the tyrosine hydroxylation rate is 25% higher than that in the LS mice. In the presence of ethanol, there was a differential effect on the in vivo tyrosine hydroxylation rate. In the cerebellum of both LS and SS mice there was a decreased rate of tyrosine hydroxylation in the early period after ethanol, but the rate in the cerebellum of SS mice returned to the control value at 85-115 min. At that time, the rate in LS mice is still decreased. In the locus ceruleus, hypothalamus and frontal cortex, ethanol has no effect on the rate of tyrosine hydroxylation in either LS or SS mice during the early period, but ethanol decreases the rate during the later period in the LS mice only.(ABSTRACT TRUNCATED AT 250 WORDS)

Apomorphine effects on behavioral response to ethanol in mice selectively bred for differential sensitivity to ethanol

Two lines of mice selectively bred for differences in response to a hypnotic dose of ethanol were administered apomorphine alone or in combination with ethanol. When administered by itself, apomorphine produced similar dose-dependent depression of locomotor activity and increases in stereotypy in the two lines. Doses of apomorphine (0.5 microM/kg and 2 microM/kg) thought to bind only presynaptic dopamine receptors blocked the slight locomotor activation to 1.5 g/kg ethanol in the ethanol-sensitive Long-Sleep (LS) mice; in the ethanol-insensitive Short-Sleep (SS) mice which show marked activation to all subhypnotic doses of ethanol, these doses of apomorphine only attenuated the activation. A higher apomorphine dose (8 microM/kg) antagonized the locomotor depressant effects of 2.0 and 2.5 g/kg of ethanol in LS mice but did not alter the shape of the SS ethanol dose response curve for locomotor activity. Apomorphine (2 and 8 microM/kg) potentiated ethanol-induced loss of the righting reflex in LS mice in a dose dependent fashion, but did not alter this soporific effect of ethanol in SS mice. These findings extend the data base suggesting a role for dopamine both in the mechanism(s) differentiating the LS and SS mice and the stimulant and intoxicating properties of ethanol.