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

Effects of ethanol on striatal dopamine overflow and clearance: an in vivo electrochemical study

Previous studies have shown that the neurotransmitter dopamine (DA) is implicated in the reinforcing effects of ethanol and other abused drugs. Ethanol also alters DA overflow and uptake in vivo. Further studies of the role of DA in the behavioral and neurochemical effects of ethanol may help explain the pharmacological mechanisms by which these effects are produced. In these studies we used in vivo electrochemical recordings to investigate the effects of ethanol (EtOH) on the dynamics of evoked DA overflow and DA uptake in rat dorsal striatum. Local applications of EtOH from a multibarrel micropipette did not produce detectable changes in extracellular levels of endogenous DA in the dorsal striatum. EtOH application did attenuate potassium (K+)-evoked overflow of DA in a time-dependent fashion. In contrast, tyramine-induced DA overflow, a calcium-independent process thought to be carrier mediated, was not altered by local EtOH application in the dorsal striatum. Striatal uptake of locally applied exogenous DA was decreased by nomifensine, an effect that was attenuated by locally applied EtOH. Taken together, these data suggest that one of the effects of EtOH on DA-containing nerve endings in the rat striatum involves functional changes in the high-affinity DA transporter associated with these nerve endings.

Effects of ethanol and nomifensine on NE clearance in the cerebellum of young and aged Fischer 344 rats

Rapid chronoamperometric recordings coupled with local application of drugs by pressure ejection were used to investigate the effects of nomifensine and ethanol (EtOH) on exogenous norepinephrine (NE) clearance in the cerebellum of young (5-month-old) and aged (24-26-month-old) male Fischer 344 rats. In the young rats, local nomifensine application prolonged exogenous NE clearance, indicating transporter mediated uptake inhibition. NE clearance was modestly but significantly prolonged in the aged rats as compared to the young rats, suggesting less efficient uptake. Consistent with this, there was little effect of nomifensine on NE clearance in the aged rats. In contrast to the effect of nomifensine, EtOH inhibited NE clearance in both young and aged rats. These data further support the hypothesis that one effect of EtOH in cerebellar NE systems is inhibition of NE uptake into NE-containing nerve terminals, and they also demonstrate that the effect of nomifensine on exogenous NE clearance in vivo in the cerebellum is altered by the aging process, while the effect of EtOH is not.

Effect of neonatal thyroid hormone alterations in CNS ethanol sensitivity in adult LS and SS mice

LS and SS mice develop their differential sensitivity to the motor-incoordinating and hypothermic effects of ethanol at 10-16 days after birth, when thyroid hormones (T4) show a transient peak. This rise in the thyroid hormones is an important element in the normal development of monoaminergic systems and thyroid hormones reach a significantly higher level in the less ethanol-sensitive SS mice than in the more ethanol-sensitive LS mice. Previous investigation have suggested the differential ethanol response of brain monoaminergic neuronal systems in adult LS and SS mice may be related to this development difference in thyroid status. To test the hypothesis that neonatal thyroid status can influence adult CNS ethanol sensitivity. LS and SS mice were treated neonatally with the thyrotropin-releasing hormone (TRH) and propylthiouracil (PTU) to enhance or diminish, respectively, thyroid status at this critical developmental period. The subsequent effect on adult CNS ethanol sensitivity was then determined. Contrary to expectations, both PTU and TRH administration attenuated the transient rise in plasma T4 levels at postnatal days 10-16 in LS mice and in both instances this was associated with decreased CNS ethanol sensitivity (sleep time and hypothermia) in adults. In SS mice, PTU treatment attenuated the postnatal rise in T4 levels as expected, whereas TRH treatment had no significant effect. However, neither neonatal treatment altered CNS ethanol sensitivity in adult SS mice. The decrease in ethanol-induced sleep times and hypothermia of neonatally treated LS mice was associated with an attenuation of ethanol-induced decreases in in vivo tyrosine and tryptophan hydroxylase activity that was not seen in the SS mice. These findings are consistent with the notion that the response of monoaminergic neuronal systems to ethanol is an important determinant of behavioral intoxication. However, the observation that neonatal administration of both TRH and PTU blunted the postnatal rise in thyroid levels in LS mice, yet both treatments resulted in a decrease in adult ethanol sensitivity in LS mice, indicates that the relationship between postnatal thyroid development and CNS ethanol sensitivity is more complex than originally hypothesized.

Development of neurochemical and behavioral sensitivity to ethanol in long-sleep and short-sleep mice

The postnatal development of certain neurochemical correlates of CNS ethanol sensitivity was examined in the long-sleep (LS) and short-sleep (SS) mice. The differences in sensitivity to the motor-incoordinating and hypothermic effects of ethanol emerged during the second and third weeks of life. Prior studies have shown the sleep time differences between LS and SS mice became significant at 8-10 days of age whereas the present results established that the differences in ethanol-induced hypothermia became prominent at 12-16 days of age. Previous results from our laboratory suggested that the greater CNS ethanol behavioral sensitivity (sleep time and hypothermia) of LS mice is related to the greater ethanol-induced depression of brain monoamine synthesis in the LS line. The timing of the developmental changes in neurochemical ethanol sensitivity in LS and SS mice was found to parallel that found in the development of behavioral ethanol sensitivity as follows. Ethanol-induced decreases in in vivo tyrosine hydroxylase activity in the cerebellum, hypothalamus, and brain stem did not differ between LS and SS mice at postnatal day 8, but became substantially greater in LS mice between postnatal days 8 and 12, coincident with the appearance of the greater sleep times of LS mice. Likewise, ethanol-induced decreases in in vivo tryptophan hydroxylase activity in the dorsal raphe and hypothalamus, which were similar in LS and SS mice at postnatal days 8 and 12, became significantly greater in LS mice by postnatal day 16, the age at which their increased sensitivity to ethanol-induced hypothermia appeared.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol inhibits the uptake of exogenous norepinephrine from the extracellular space of the rat cerebellum

Rapid chronoamperometric recordings using nafion-coated carbon fiber electrodes coupled with pressure-ejection of drugs were used to investigate the effects of ethanol on norepinephrine (NE)-containing nerve terminals in the urethane-anesthetized Fischer 344 rat. Local application of ethanol from a double-barrel micropipette did not produce detectable changes in extracellular levels of NE in the rat cerebellar cortex. However, when ethanol was applied prior to local application of NE, it was seen to inhibit the uptake of NE from the extracellular space. These results were compared to the effects seen from the local application of a known high-affinity uptake inhibitor, nomifensine. Nomifensine was found to inhibit the extracellular uptake of NE in rat cerebeller cortex similar to ethanol. Our results support the hypothesis that one effect of ethanol on the noradrenergic system of the rat cerebellum is an alteration in the uptake of NE into NE-containing nerve endings. In addition, the present data concerning ethanol-induced inhibition of NE clearance or uptake support our previous electrophysiological studies in which we found that ethanol can potentiate the modulatory effects of beta-agonists on GABA responses of cerebellar Purkinje neurons.

Selective breeding for initial sensitivity to ethanol

Selective breeding for initial sensitivity to ethanol has been carried out by a number of investigators in order to investigate the mechanisms by which ethanol brings about a myriad of effects on the mammalian central nervous system. In addition the availability of these selectively bred animals provides clues to the causes of the genetic predisposition of humans to alcoholism. Eventually it is envisioned that the synteny between the mouse and human genomes will allow identification of specific genes responsible for acute effects of ethanol in both species as well as clues as to how alcoholism in humans can be better identified, prevented, and treated.

Influence of thyrotropin-releasing hormone and catecholaminergic interactions on CNS ethanol sensitivity

The role of catecholamine neuronal systems in mediating the analeptic and thermogenic effects of thyrotropin-releasing hormone (TRH) was examined in long-sleep (LS) and short-sleep (SS) mice. TRH [0.1 to 40 micrograms, intracerebroventricularly (icv)] was associated with a reduction in the sleep times of LS mice, but no dose of TRH had any effect on sleep times of SS mice. However, TRH (20 micrograms, icv) produced a 1.0 degree to 1.5 degrees C attenuation of the ethanol-induced hypothermia in both LS and SS mice. TRH did not change the rate of ethanol elimination in either line of mice, suggesting that the reduction in LS sleep times and attenuation of LS and SS hypothermia were due to decreased CNS ethanol sensitivity rather than an increase in the rate of ethanol metabolism. TRH (20 micrograms, icv) given alone produced an activation of central and peripheral catecholamine systems in LS, but not SS mice, as reflected by an increase in the in vivo tyrosine hydroxylase (TH) activity in the brain and adrenal gland. TRH, given with ethanol, prevented or attenuated ethanol-induced decreases in the brain and adrenal gland in vivo TH activity in LS mice but not SS mice. Thus, there was an association between the ability of TRH to produce an activation of catecholamine neuronal systems (increased rate of catecholamine biosynthesis) and the analeptic action of TRH to reduce the CNS depressant effects of ethanol (decreased sleep times).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effects of electroconvulsive shock and haloperidol on in vivo tyrosine hydroxylation and tetrahydrobiopterin in the brain of rats with 6-hydroxydopamine lesions

We have evaluated the effects of electroconvulsive shock (ECS) and haloperidol treatment on the in vivo tyrosine hydroxylation rate and the tetrahydrobiopterin levels in the nigrostriatal system of 6-OHDA-lesioned rats. The rate of DOPA accumulation was significantly decreased by 96% in the ipsilateral striatum and by 50% in substantia nigra of the 6-OHDA-lesioned rats compared to the control activity of contralateral non-lesioned striatum and substantia nigra. The loss of total biopterin was found to be 75% and 50% in the ipsilateral striatum and substantia nigra, respectively. Following administration of haloperidol, the rate of DOPA accumulation increased significantly in the striatum and substantia nigra on the lesioned side compared to that in the vehicle treatment group. Application of ECS also significantly increased the rate of DOPA accumulation in the ipsilateral striatum and substantia nigra compared to that obtained in the non-shocked rats. The biopterin levels in the nigrostriatal system of 6-OHDA-lesioned were elevated significantly in the striatum after haloperidol treatment; in contrast the biopterin levels were unchanged in response to ECS. Our results show that both haloperidol and ECS significantly enhanced the rate of in vivo tyrosine hydroxylation in the striatum and substantia nigra of rats with greater than 90% lesions. These results suggest that the nigrostriatal system, although up-regulated following 6-OHDA lesions, still maintains the potential for further up-regulation of dopaminergic function in response to haloperidol and ECS treatment.

Regional catecholamine levels in brains of normal and ethanol-tolerant long-sleep and short-sleep mice

The objective of this study was to further investigate neurochemicals which might modulate congenital differences in sensitivity to the acute and chronic effects of ethanol. Catecholamine levels were measured in the cortex, hippocampus, midbrain and cerebellum of long-sleep (LS) and short-sleep (SS) mice. These measurements revealed that norepinephrine (NE) levels were equivalent in all these brain regions of both strains except for a significantly greater concentration in the midbrain of LS mice. The hippocampus, cortex and cerebellum of SS mice contained more epinephrine (E) than for LS mice. Likewise, the hippocampus and cerebellum of SS mice had higher levels of dopamine (DA), while in the midbrain this amine was more abundant in LS mice. Following 7-10 days of ethanol ingestion, both LS and SS mice exhibited a significant reduction in the duration of ethanol-induced loss of righting reflex. This tolerant state was associated with a depletion of NE in the hippocampus and cortex of both strains. NE was also significantly reduced in the midbrain of LS and the cerebellum of SS mice. On the other hand, E levels were unaltered except for a reduction in the hippocampus of tolerant SS mice. DA levels declined in all brain regions of tolerant mice except for the cerebellum of LS mice and the midbrain of SS mice where a significant increase and no change in DA concentration was detected, respectively. Interestingly, the brain levels of 3-methoxy-4-hydroxyphenylglycol were uniformly increased during the tolerant state for both strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of norepinephrine on phosphatidylinositol 4,5-bisphosphate stimulated hydrolysis in brains of mice genetically selected for differences in ethanol sensitivity

The effects of norepinephrine on phosphoinositide turnover were evaluated in five brain regions of the long sleep (LS) and short sleep (SS) mice. These mice were selectively bred for differences in central nervous system sensitivity to ethanol with the LS exhibiting much greater sensitivity to a hypnotic dose of ethanol than the SS, as determined by the ability of the mice to regain their righting reflex. Norepinephrine (10(-3) M, 10(-4) M, and 10(-5) M) significantly increased phosphoinositide turnover in the hippocampus, hypothalamus, locus ceruleus, cerebellum, and cortex within each line of mice. Basal and norepinephrine-stimulated phosphoinositide turnover were significantly higher in the SS mice as compared with the LS mice in the cerebellum and cortex but not the other brain regions. Incorporation of 3H-inositol into 3H-phosphatidylinositols was not different between SS and LS mice in the cerebellum and cortex. The greater norepinephrine-stimulated phosphoinositide turnover in the cerebellum and cortex of the SS versus the LS mice may contribute to the CNS sensitivity to ethanol in these two lines of mice. However, ethanol (500 mM) had no effect on basal or norepinephrine-stimulated phosphoinositide turnover in any of the five brain areas examined in the LS and SS mice.

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.

Further studies on the neurochemical mechanisms mediating differences in ethanol sensitivity in LS and SS mice

Long-sleep (LS) and short-sleep (SS) lines of mice were selectively bred for differences in CNS sensitivity to ethanol with LS mice exhibiting much greater sensitivity to hypnotic doses of ethanol (4.0-4.5 g/kg) than SS mice. The influence of peripheral and central catecholamine neuronal systems on ethanol sensitivity (sleep time) in LS and SS mice was examined following administration of reserpine, alpha-methyl-p-tyrosine and 6-hydroxydopamine. Ten days after a single dose of reserpine, tyrosine hydroxylase activity was increased in the brain and adrenal gland of LS mice but only in the brain of SS mice relative to untreated mice. Brain catecholamine levels in the reserpine-treated mice were 25-50% lower in both LS and SS mice compared to levels in untreated mice. These changes were associated with a 41% reduction in LS sleep time, but a 90% increase in SS sleep time. SS mice were also more susceptible to the lethal effects of reserpine. The increased mortality of SS mice may relate to a greater degree of reserpine-induced hypothermia and a slower rate of recovery of brain catecholamine levels. Neonatal LS and SS mice treated with 6-hydroxydopamine exhibited increased levels of catecholamines in the locus ceruleus, decreased levels in the cerebellum and unchanged levels in the hypothalamus at 60 days of age. These changes were associated with a modest decrease (10%) in LS sleep time and a marked increase (200%) in SS sleep time. alpha-Methyl-p-tyrosine decreased brain catecholamine levels of both lines by 30-50% while LS sleep times were unchanged and SS sleep times were increased by 45%.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

A comparison of ethanol absorption and narcosis in long- and short-sleep mice following intraperitoneal or intragastric ethanol administration

Blood ethanol concentrations (BEC) were determined in Long-Sleep (LS) and Short-Sleep (SS) mice during a 30 min period following ethanol (ETOH) administration. Absorption of ETOH was rapid and followed a similar time course in the two lines after intraperitoneal (IP) administration of 3.8 or 4.5 g/kg. Following intragastric (IG) administration, slower absorption and lower peak BECs were noted in both lines, but in LS mice this effect was more pronounced. The two routes of administration were not effective in altering duration of loss of the righting reflex (LRR), or waking BECs following 4.5 g/kg ETOH. LS mice had the expected longer LRR durations and lower BECs at waking than did SS mice. Differences in absorption rate and peak BEC are concluded to be unrelated to ETOH neurosensitivity in these mice.