• Energy Research
• Neuroscience Letters close
• Neuroscience close

Our previous work indicated a role for fyn-kinase in mediating several ethanol- and GABA(A) agonist-mediated behaviors. In the present work we investigate behavioral sensitivity to ethanol and several GABA(A) compounds in mice that over-express fyn-kinase in forebrain to further characterize the role of this non-receptor tyrosine kinase in the mediation of ethanol sensitivity. Transgenic mice over-expressing fyn-kinase were tested for sensitivity to ethanol-induced loss of righting reflex and ethanol preference drinking using a two-bottle choice drinking paradigm. Loss of righting reflex induced by 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP; GABA(A) agonist) and etomidate (GABA(A) positive allosteric modulator) were also assessed. Fyn over-expressing mice exhibited shorter durations of ethanol-induced loss of righting reflex in the absence of differences in the rate of blood ethanol clearance, and exhibited reduced ethanol preference drinking. The genotypes did not differ in initial sensitivity to ethanol-induced loss of righting reflex suggesting development of greater acute tolerance to this ethanol action. Fyn over-expressing and wild-type mice also did not differ in sensitivity to loss of righting reflex induced by THIP and etomidate. The present results suggest regional specificity for fyn-kinase in the modulation of ethanol and GABAergic behavioral sensitivity. Fyn-kinase over-expression in forebrain structures modulates ethanol's hypnotic actions, as well as ethanol preference and consumption. Moreover, fyn over-expression in forebrain does not alter hypnotic sensitivity to THIP or etomidate, supporting data from fyn null mutant mice suggesting that cerebellar structures mediate the hypnotic actions of these GABAergic compounds.

The effect of chronic ethanol treatment (CET) for 21-26 weeks on the neurotrophic activity contained in the rat hippocampus (HPC) was determined with a bioassay in cultures of dissociated dorsal root ganglion cells (DRG) obtained from E7-8 chick embryos. Extracts of the HPC from CET or pair-fed control rats were used as experimental media, and neuronal survival and neurite-outgrowth of DRG cultures were determined. Both neuronal survival (-25%) and neurite-outgrowth (-50%) were reduced in the presence of HPC extracts from CET rats relative to controls. These data suggest that CET reduces the neurotrophic content of the HPC which may result in damage to septohippocampal neurons.

We have previously demonstrated that ibotenate (IBO) injected into the pedunculopontine tegmental nucleus (PPTg) damages all neurones there while quinolinate (QUIN) makes relatively selective lesions of cholinergic neurones. We now compare the effects of two anaesthetics, sodium pentobarbitone and Avertin (tribromoethanol/tert-amylalcohol dissolved in ethanol, saline and phosphate buffer) on three doses of IBO and QUIN in the PPTg. Diaphorase-positive cell loss after QUIN was attenuated under barbiturate, the relative selectivity of QUIN for diaphorase-positive neurones was lost and lesion volumes were uniformly small compared with lesions made under Avertin anaesthesia. IBO toxicity was unaffected by anaesthesia. These data are discussed with reference to the actions of excitotoxins at glutamate receptor subtypes and interactions of barbiturates with the GABAA receptor.

Cortical cultures of rat brain neurons were exposed to ethanol (100 mM) for 4 days in order to examine whether the pharmacological characteristics of N-methyl-D-aspartate (NMDA) receptors expressed by these neurons were altered by this treatment. In fura-2 loaded control neurons, NMDA (plus 10 microM glycine) stimulated a dose-dependent increase in intracellular calcium concentrations with an estimated EC50 value of 6.8 microM. NMDA-stimulated increases in intracellular calcium reached a plateau at approximately 30 microM with no further increases observed at 100 microM. The EC50 value for NMDA in ethanol-exposed neurons was reduced to 1.8 microM with no alteration in the maximal response. Similarly, the EC50 value for glycine (tested with 100 microM NMDA) was reduced from 2.3 microM in control cultures to 0.67 microM in ethanol-treated cultures. Ifenprodil inhibited NMDA-stimulated increases in intracellular calcium in control cultures only at concentrations of 3 microM and above, with 100 microM producing approximately a 58% inhibition. In ethanol-treated cultures, 0.3 microM ifenprodil inhibited the NMDA response by approximately 60% with 100 microM ifenprodil producing a 72% inhibition. Over the concentration range of ifenprodil tested, half-maximal inhibition occurred at 1.4 microM and 0.18 microM, respectively, for control and ethanol-treated neurons. Although chronic ethanol treatment appeared to alter the sensitivity of neurons to NMDA agonists and antagonists, the inhibitory effects of 50 mM ethanol on NMDA-stimulated increases in intracellular calcium were not different between control (28% inhibition) and ethanol-treated neurons (27% inhibition). Finally, the changes in NMDA receptor sensitivity observed in ethanol-treated neurons were accompanied by an enhanced sensitivity to the neurotoxic effects of NMDA as measured by propidium iodide staining. These results suggest that chronic exposure of neurons to ethanol may result in an altered expression of agonist-sensitive/ifenprodil selective NMDA receptor subunits.

Behavioral sensitization is thought to play a significant role in drug addiction. L-type calcium channels have been implicated in sensitization to stimulant and opiate drugs but it is unclear if these channels also contribute to sensitization to ethanol. The effects of three L-type calcium channel blockers, nifedipine (1-7.5 mg/kg), diltiazem (12.5-50 mg/kg), and verapamil (12.5 and 25 mg/kg), on sensitization to ethanol (2 g/kg) were examined in DBA/2J mice. All three blockers reduced but did not prevent expression of sensitization. Only nifedipine blocked acquisition of sensitization. Nifedipine and verapamil decreased blood ethanol levels. The current findings suggest L-type calcium channels do not play a substantial role in sensitization to ethanol and that the neural mechanisms underlying sensitization to ethanol are distinct from those mediating sensitization to stimulants and opiates.

Exposure to alcohol in utero has been associated with hypothyroidism and a variety of developmental defects characteristic of thyroid dysfunction. The present work examined whether these abnormalities could be reversed in infant rats treated with thyroid hormones. Subjects were offspring of dams which were on the following diet regimen during gestation: (1) free access to liquid diet containing ethanol (alcohol pups); (2) an equal volume of isocaloric liquid diet (pair-fed pups); or (3) ad libitum control diet (control pups). Neonates from each group were foster-nursed by control dams, and received triiodothyronine (T3; 0.1 mg/kg/day; s.c.) or saline treatments on postnatal days 1 to 10. The alcohol neonates displayed reduced serum thyroxine which was restored to normal by postnatal day 14. In addition, these pups showed a delayed appearance of developmental landmarks, including righting reflex, dental eruption, auditory startle response and eye opening. The retarded incisor eruption and eye opening were reversed in alcohol pups by T3 treatments. The present data suggest that at least some of the developmental abnormalities associated with prenatal alcohol exposure are attributable to perinatal hypothyroidism and can be restored by early hormone replacement therapy.

The characteristics of long-term potentiation (LTP) in the hippocampus of rats prenatally exposed to ethanol and treated postnatally with nootropic compounds L-pyroglutamyl-D-alanine-amide (L-pGlu-D-AlaNH2, PGA) or piracetam were studied using in vitro slice preparations. LTP was induced in the CA1 region by the orthodromic stimulation of the stratum radiatum with one train of 100 pulses (100 Hz, 1 s). The probability of LTP development in the hippocampus of young rats was significantly reduced by prenatal exposure to alcohol. This plasticity deficit was completely reversed by daily injections of PGA, 1 mg/kg for 12 days (8-19 days of postnatal development) but not of piracetam, 100 mg/kg. PGA (0.5 microM) also prevented the inhibition of LTP development in hippocampal slices perfused with ethanol, 20 or 50 mM. The data indicate that PGA effectively restores synaptic plasticity after both prenatal and acute exposure to ethanol and suggest that impaired LTP may be a useful model for studying the mechanisms of action of nootropic compounds.

We previously found that ethanol inhibits muscarinic receptor-induced proliferation of rat cortical astrocytes and human astrocytoma cells and suggested this as a possible mechanism involved in its developmental neurotoxicity. We also observed that, though several signal transduction pathways are relevant for carbachol-induced cell proliferation, activation of PKC zeta and p70S6 kinase is selectively inhibited by low concentrations of ethanol. In the present study we used fetal human astrocytes to expand these findings to a direct target of ethanol in humans. Astrocyte cultures, deriving from legally aborted fetuses, were stained for GFAP and shown to be 90-95% pure. Carbachol induced increases in [(3)H]thymidine and BrdU incorporation in synchronized cells. Carbachol-induced DNA synthesis was strongly inhibited by ethanol. Carbachol also induced phosphorylation of (Thr410)PKC zeta, (Ser473)Akt, and (Thr389)p70S6 kinase, and ethanol (50 mM) inhibited phosphorylation of PKC zeta and p70S6 kinase, but not of Akt. These results expand previous findings in rat astrocytes and human astrocytoma cells and suggest that intracellular signal transduction pathways activated by muscarinic receptors may represent a relevant target for the developmental neurotoxicity of ethanol in humans.

Acetate is the primary product of ethanol catabolism and can accumulate in the blood at concentrations of up to 2 mM following ethanol consumption. It has been suggested that some of the pharmacological actions of ethanol are mediated via acetate, which can lead indirectly to the release of endogenous adenosine. In the present experiments this hypothesis was tested by examining the effects of exogenous sodium acetate on the physiology of hippocampal slices from rat brain. Acetate had no significant effect on intracellular responses recorded from CA1 pyramidal neurons or on extracellular field potentials evoked from the either the CA1 region or the dentate gyrus. There was also no significant difference in responses to the adenosine receptor antagonist theophylline in CA1 pyramidal neurons recorded using intracellular filling solutions containing potassium acetate, KCl, or potassium methylsulfate. These results suggest that the presence of acetate, either in the extracellular medium or within an intracellular electrode, does not induce a significant increase in adenosine receptor activation in the hippocampus.