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

Desipramine potentiation of the acute depressant effects of ethanol: modulation by alpha2-adrenoreceptors and stress

Ethanol exerts effects on the brain noradrenergic system, and these are thought to contribute to the sedative/hypnotic (depressant) effects of ethanol. Recent studies suggest that the norepinephrine transporter (NET) plays an important role in modulating ethanol's depressant effects. The aim of the present study was to further characterize this role. Transporter blockers with varying affinity for NET versus the serotonin transporter (desipramine>fluoxetine>citalopram) were tested for their ability to alter ethanol's depressant effects, and for comparison, hypothermic effects. Effects of desipramine on another depressant, pentobarbital, were examined. Desipramine potentiation of ethanol's depressant effects was assessed following depletion of brain norepinephrine via N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4) treatment, or depletion of brain 5-HT via para-chlorophenylalanine methyl ester hydrochloride (PCPA) treatment. The effects of co-administration of either the selective alpha2-adrenoreceptor agonist (dexmedetomidine) or the selective alpha2-adrenoreceptor antagonist (atipamezole) on desipramine's effect on ethanol's depressant effects were examined. Given the close link between stress, ethanol and norepinephrine, desipramine potentiation of ethanol's depressant effects was tested following repeated forced swim stress. Results showed that desipramine, but not SERT-selective doses of citalopram or fluoxetine, strongly potentiated the depressant (not hypothermic) effects of ethanol. These effects were mimicked by dexmedetomidine and blocked by atipamezole, but not by depletion of either norepinephrine or 5-HT. Desipramine potentiation of ethanol's depressant effects was abolished following repeated stress. Present findings further support a major role for NET and the alpha2-adrenoreceptor in modulating the depressant effects of ethanol, with possible implications for understanding the role of noradrenergic dysfunction in stress-related alcoholism.

Studies on the sensitivity to alcohol and alcohol dependence

The role of genetic and environmental factors in the development of alcohol dependence is beginning to be investigated in Brazil. This paper reviews recent studies on genetic aspects of alcohol use and alcohol dependence, with emphasis on those carried out in Brazilian populations. Most findings replicated studies in developed countries, while some indicate new possible venues for investigation in the future. They underscore the need for a cross-cultural and interethnic approach to biomedical aspects of alcohol use and dependence.

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.

Serotonin modulates ethanol-induced depression in cerebellar Purkinje neurons

In the present study, we found that local application of serotonin (5-HT) potentiated ethanol-induced depressions of the spontaneous activity of Purkinje neurons in urethane-anesthetized rats. 5-HT also potentiated depressions induced by gamma-aminobutyric acid; however, this modulatory response was quantitatively smaller than 5-HT-induced potentiation of ethanol depression. Previous reports suggested that the release of 5-HT can be regulated by presynaptic 5-HT autoreceptors. We found that local application of methiothepin, which may induce 5-HT overflow through the inhibition of presynaptic autoreceptors, facilitated ethanol-mediated responses. This methiothepin effect was greatly diminished in neonatally 5,7-dihydroxytryptamine-lesioned animals, suggesting a presynaptic mechanism was involved. We also found that the 5-HT1A antagonist UH301 did not attenuate 5-HT-facilitated ethanol reactions. On the other hand, local application of 5-HT1B agonist CGS12066B potentiated ethanol-induced depression. Taken together, our data suggest that 5-HT can modulate ethanol-mediated electrophysiological depression, possibly mediated through 5-HT1B receptors in the cerebellum.

Effect of p-chlorophenylalanine and alpha-methyltyrosine on the antinociceptive effect of antidepressant drugs

The role of para-chlorophenylalanine and alpha-methyl-DL-p-tyrosine in the antinociceptive effects of the intracerebroventricular administration of the antidepressant drugs clomipramine, zimelidine, imipramine and maprotiline was studied using the acetic acid writhing test in mice. The results demonstrated an antinociceptive effect for all these antidepressants. Pretreatment with para-chlorophenylalanine significantly reduced the antinociception induced by the ED50's of imipramine and maprotiline, and did not modify the effects of zimelidine and clomipramine, pretreatment with alpha-methyl-tyrosine did not modify the antinociception induced by these drugs except maprotiline. Pretreatment with para-chlorophenylalanine plus alpha-methyltyrosine significantly reduced the antinociceptive effect of all the antidepressants tested. The main finding of the present study is that the association of para-chlorophenylalanine plus alpha-methyltyrosine reduced the antinociceptive action of all the antidepressants. This means that critical levels of both 5-HT and NA are responsible for mediating the antinociceptive effects of antidepressants on the writhing test in mice.

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)

Failure of ethanol to induce changes in gonadotropin gene expression in selectively bred ethanol-sensitive rats

The recent availability of genetically altered rat lines differing in sensitivity to ethanol (EtOH) has allowed deeper investigation into the mechanisms of EtOH-induced cellular toxicity in several systems. Since the male central reproductive axis has been demonstrated to be exquisitely sensitive to EtOH, studies were undertaken to determine if the gonadotropin suppression reported earlier could be duplicated in one of these selected rat lines. Castrated high alcohol sensitivity (HAS), low alcohol sensitivity (LAS) and control alcohol sensitivity (CAS) rats were given EtOH or saline acutely. Castrated non-selectively bred Sprague Dawley rats were treated similarly and used as an additional control. At sacrifice, serum and pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels were obtained and the mRNA levels for both gonadotropins assessed. In the selectivity bred animal there was essentially no change in serum or pituitary LH or FSH levels between EtOH and saline treated animals. The mRNA levels for both LH and FSH similarly were unaffected by EtOH, in striking contrast to the non-selectively bred Sprague Dawley rats where serum LH, FSH and beta-LH mRNA levels are markedly suppressed after EtOH exposure. The selectively bred lines of rats genetically manipulated for high or low EtOH sensitivity, as well as their non-selected controls, appeared to have a hypothalamic-pituitary reproductive unit that is resistant to EtOH. This is in contrast to Sprague-Dawley rats, where suppression of this axis previously has been consistently demonstrated.

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)

Genetically determined differences in the antagonistic effect of pressure on ethanol-induced loss of righting reflex in mice

Hyperbaric exposure antagonizes ethanol's behavioral effects in a wide variety of species. Recent studies indicating that there are genetically determined differences in the effects of body temperature manipulation on ethanol sensitivity suggested that genotype might also influence the effects of hyperbaric exposure on ethanol intoxication. To investigate this possibility, ethanol injected long sleep (LS)/Ibg (2.7 g/kg), short sleep (SS)/Ibg (4.8 g/kg), 129/J (2.9 g/kg), and C57BL/6J (3.6 g/kg) mice were exposed to one atmosphere absolute (ATA) air or to one or 12 ATA helium-oxygen (heliox) at ambient temperatures selected to offset ethanol and helium-induced hypothermia. Hyperbaric exposure significantly reduced loss of righting reflex (LORR) duration in LS, 129, and C57 mice, but not in SS mice. A second experiment found that hyperbaric exposure significantly reduced LORR duration and increased the blood ethanol concentration (BEC) at return of righting reflex (RORR) in LS mice, but did not significantly affect either measure in SS mice. These results indicate that exposure to 12 ATA heliox antagonizes ethanol-induced LORR in LS, 129 and C57 mice, but not in SS mice. Taken with previous results, the present findings suggest that the antagonism in LS, 129, and C57 mice reflects a pressure-induced decrease in brain sensitivity to ethanol and that the lack of antagonism in SS mice cannot be explained by pressure-induced or genotypic differences in ethanol pharmacokinetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective breeding of rats differing in sensitivity to the effects of acute ethanol administration

Selective breeding of rats for sensitivity to the anesthetic effects of ethanol is being carried out with rats derived from the genetically heterogeneous N/Nih stock. Thirteen generations of within family selection have been achieved with replicate high (HAS), low (LAS) and control alcohol sensitive (CAS) lines. Significant separation between lines on sleep time and blood ethanol concentration (BEC) at awakening following ethanol administration has been achieved. In general, the results obtained so far replicate the findings with short (SS) and long (LS) sleep mice. One exception is that the high alcohol sensitivity rats (HAS) also appear more sensitive to pentobarbital relative to LAS rats. This finding is opposite to that which occurs with SS and LS mice where the low ethanol sensitive SS mice appear more sensitive to pentobarbital than the LS mice.

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)

The relationship between brain temperature during intoxication and ethanol sensitivity in LS and SS mice

The present study characterized the relationship between brain temperature, rectal temperature, and ethanol sensitivity in the selectivity bred long-sleep (LS) and short-sleep (SS) mice. Radiotelemetric brain probe implanted and nonimplanted LS/lbg and SS/lbg male mice were injected with 2.5 and 4.9 g/kg ethanol, respectively, before exposure to ambient temperatures of 15 degrees C, 22 degrees C, or 34 degrees C. Ambient temperature significantly affected rectal temperature, brain temperature, and ethanol sensitivity, measured by impairment of righting reflex. Brain and rectal temperatures at return of righting reflex (RORR) were highly correlated. In SS mice brain and rectal temperatures at RORR were significantly positively correlated with loss of righting reflex (LORR) duration and significantly negatively correlated with blood ethanol concentration (BEC) at RORR. In LS mice rectal temperature at RORR was significantly negatively correlated with LORR duration, while both brain and rectal temperature at RORR were significantly positively correlated with BEC at RORR. The strength of the correlations and r2 values generated from linear regression analysis indicates that body temperature during intoxication can explain up to 52% of the variability in ethanol sensitivity in SS mice, but only 19% of the variability in ethanol sensitivity in LS mice. The correlational analyses are consistent with previous results based on comparisons between rectal temperature and ethanol sensitivity and extend to direct brain temperature measurement the evidence that decreasing temperature during intoxication decreases ethanol sensitivity in SS mice and increases ethanol sensitivity in LS mice.(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.

NMDA agonists and antagonists alter the hypnotic response to ethanol in LS and SS mice

Involvement of glutamate neurotransmission in the differential response of long-sleep (LS) and short-sleep (SS) mice to acute ethanol was examined by measuring the effect of centrally administered glutamate receptor agonists and antagonists on blood ethanol concentration (BEC) at loss of righting response following intragastric administration of ethanol. NMDA coinjected with glycine, and quinolinic acid (QA), decreased sensitivity to ethanol in both lines of mice. SS mice were more sensitive to QA than were LS. The NMDA antagonists 2-amino-5-phosphonovaleric acid (APV), MK-801 and an inhibitor of glutamate synthesis, methionine sulfoximine, increased sensitivity to ethanol in both lines of mice. MK-801 effects were line dependent with SS being more sensitive. In addition, coinjection of APV, Mg++ or Zn++ with QA blocked the decrease in sensitivity seen with QA alone. These results demonstrate that NMDA agonists and antagonists alter the acute hypnotic response to ethanol in both LS and SS mice, and support the hypothesis that ethanol exerts its effects in part by altering glutamatergic neurotransmission.

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.