Prenatal ethanol exposure reduces phosphoinositide hydrolysis stimulated by quisqualate in rat cerebellar granule cell cultures

Acute and chronic effects of ethanol on learning-related synaptic plasticity

Alcoholism is associated with acute and long-term cognitive dysfunction including memory impairment, resulting in substantial disability and cost to society. Thus, understanding how ethanol impairs cognition is essential for developing treatment strategies to dampen its adverse impact. Memory processing is thought to involve persistent, use-dependent changes in synaptic transmission, and ethanol alters the activity of multiple signaling molecules involved in synaptic processing, including modulation of the glutamate and gamma-aminobutyric acid (GABA) transmitter systems that mediate most fast excitatory and inhibitory transmission in the brain. Effects on glutamate and GABA receptors contribute to ethanol-induced changes in long-term potentiation (LTP) and long-term depression (LTD), forms of synaptic plasticity thought to underlie memory acquisition. In this paper, we review the effects of ethanol on learning-related forms of synaptic plasticity with emphasis on changes observed in the hippocampus, a brain region that is critical for encoding contextual and episodic memories. We also include studies in other brain regions as they pertain to altered cognitive and mental function. Comparison of effects in the hippocampus to other brain regions is instructive for understanding the complexities of ethanol's acute and long-term pharmacological consequences.

Chronic Ethanol-Induced Subtype- and Subregion-Specific Decrease in the mRNA Expression of Metabotropic Glutamate Receptors in Rat Hippocampus

BACKGROUND

Chronic ethanol consumption is known to induce adaptive changes in the hippocampal glutamatergic transmission and alter NMDA receptor binding and subunit expression. Metabotropic glutamate (mGlu) receptors have been shown to function as modulators of neuronal excitability and can fine tune glutamatergic transmission. This study was aimed to determine whether chronic ethanol treatment could change the messenger RNA (mRNA) expression of mGlu receptors in the hippocampus.

METHODS

Male Sprague Dawley rats were fed a Lieber-DeCarli liquid diet with 5% (w/v) ethanol or isocaloric amount of maltose for 2 months. Quantitative in situ hybridization was carried out using coronal brain sections through the hippocampus.

RESULTS

The results revealed decreases in mRNA expression of several mGlu receptors in different subregions of the hippocampus. In the dentate gyrus, mGlu3 and mGlu5 receptor mRNA levels were significantly lower in the ethanol-treated rats than in the control rats. In the CA3 region, the mRNA expression of mGlu1, mGlu5, and mGlu7 receptors showed substantial decreases after ethanol exposure. The mGlu7 receptor mRNA levels were also declined in the CA1 region and the polymorph layer of the dentate gyrus. No changes were found in mRNA expression of mGlu2, mGlu4, and mGlu8 receptors.

CONCLUSIONS

Considering the involvement of hippocampal mGlu receptors in learning and memory processes as well as in neurotoxicity and seizure production, the reduced expression of these receptors might contribute to ethanol withdrawal-induced seizures and also may play a role in cognitive deficits and brain damage caused by long-term ethanol consumption.

Prenatal ethanol exposure enhances glutamate release stimulated by quisqualate in rat cerebellar granule cell cultures

Effects of prenatal ethanol exposure on extracellular glutamate accumulation stimulated by glutamate receptor agonists were studied in rat cerebellar granule cell cultures. The prenatal exposure to ethanol was achieved via maternal consumption of a Sustacal liquid diet containing either 5% ethanol or isocaloric sucrose (pair-fed) substituted for ethanol from gestation d 11 until the day of parturition. Neither the basal level of extracellular glutamate nor the increased accumulation of glutamate stimulated by KCl (40 mM) or by ionotropic glutamate receptor agonists, N-methyl-D-aspartate (NMDA) or kainate (KA) (100 microM each), in cells prepared from the ethanol-fed group was significantly different from that in cells prepared from the pair-fed group. Glutamate accumulation stimulated by quisqualate (QA, 100 microM) or by trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (t-ACPD, 250 microM) in the ethanol-fed group was higher than that in the pair-fed group by 116 and 36%, respectively. In the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 100 microM), an ionotropic QA receptor antagonist, the QA-induced accumulation of glutamate in the ethanol-fed group was still higher than that in the pair-fed group. In the presence of MK-801 (5 microM), an antagonist of the NMDA receptor, the enhanced accumulation of glutamate stimulated by either QA or t-ACPD was still observable in the ethanol-fed group as compared to the pair-fed group. Addition of (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG, 500 microM), a selective antagonist of the metabotropic glutamate receptor, abolished the enhanced accumulation of glutamate stimulated by either QA or t-ACPD in the ethanol-fed group. Although immunoblotting of mGluR1 and mGluR2/3 did not show apparent differences between the pair-fed and the ethanol-fed groups, the overall results suggest that the effect of prenatal ethanol exposure was selectively through a pathway mediated by the metabotropic glutamate receptor.

Intrauterine hypoxia-ischemia reduces phosphoinositide hydrolysis stimulated by metabotropic glutamate receptor agonists in cultured rat cerebellar granule cells

Effects of intrauterine hypoxia-ischemia (HI) on receptor-stimulated phosphoinositide (PPI) hydrolysis were studied in rat cerebellar granule cell cultures prepared from an in utero HI model. On gestation day 17, HI conditions were achieved by complete clamping of the uterine vasculature for 30 min followed by removal of the clamps to permit reperfusion. Sham operation (SH, surgery without vasculature ligation) was performed as the control. Intrauterine HI did not affect the basal level of PPI hydrolysis (in the absence of stimulants) in cells prepared from either the SH or the HI group. PPI hydrolysis stimulated by quisqualate (QA) or trans-(1S,3R)-1-amino-1,3-cyclo-pentanedicarboxylic acid (trans-ACPD) was significantly reduced in cells prepared from the HI group, whereas intrauterine HI did not affect the PPI hydrolysis induced by ionotropic glutamate receptor agonists or by norepinephrine or serotonin. At a dose range of 100-300 microM, QA-stimulated PPI hydrolysis in cells prepared from the SH group increased by 3-to 4.5-fold, while this increase was only 2- to 2.5-fold in cells prepared from the HI group. Presence of L-NG-monomethyl-arginine (L-NMMA), a nitric oxide (NO) synthase inhibitor, did not increase QA-stimulated PPI hydrolysis in cells prepared from either the SH or the HI group, indicating that stimulation of NO formation is unlikely involved in the suppressive effects of intrauterine HI on QA-induced PPI hydrolysis. The QA-stimulated PPI hydrolysis in cells prepared from the HI group, but not from the SH group, was further inhibited by L-(+)-2-amino-3-phosphono-propionic acid (L-AP3). The overall results suggest that intrauterine HI has long-lasting suppressive effects on metabotropic glutamate receptor agonist-stimulated PPI hydrolysis and these effects might be associated with alterations in expression of metabotropic glutamate receptor subtypes.