Excitatory amino acid recognition sites coupled with inositol phospholipid metabolism: developmental changes and interaction with alpha 1-adrenoceptors.

Abstract

Glutamate, aspartate, ibotenate, and quisqualate activate inositol phospholipid hydrolysis in hippocampal slices prepared from brains of 6-to 8-day-old rats.The stimulation by glutamate and aspartate progressively declines during postnatal development and is negligible after the 24th day of life. In contrast, the stimulation of inositol phospholipid hydrolysis by norepinephrine is low in hippocampal slices from newborn animals and increases during development, reaching mature values after the 35th day of life. In adult hippocampal slices, the stimulation of inositol phospholipid hydrolysis elicited by norepinephrine is inhibited by glutamate in a concentration-dependent fashion. This inhibition can also be brought about by aspartate, 2-amino-4-phosphonobutanoate, and L-phosphoserine, a product ofendogenous phosphatidylserine hydrolysis. ([3H]Ins-1-P) in brain slices treated with Li'. Li' has been found to block the conversion of [3H]Ins-1-P into inositol by inhibiting the enzyme inositol-1-phosphatase (9, 10).Sprague-Dawley rats of various ages (6,8,12,15,19,24, and 35 days) were decapitated. The brains were rapidly removed from the skulls and dissected on ice. Hippocampus, corpus striatum, cerebral cortex, and hypothalamus were sliced (350 x 350 ,m) with a McIlwain tissue chopper, and the slices immediately were suspended in Krebs-Hensleit buffer (118 mM NaCl/4.7 mM KCl/1.3 mM CaCl2/1.2 mM K2HPO4/1.2 mM MgSO4/25 mM NaHCO3/11.7 mM glucose, equilibrated with 95%02/5% CO2 to raise the pH to 7.4) and incubated at 37°C for 30-45 min with three intermediate changes of the buffer. Forty microliters of gravitypacked slices were then transferred to 3-ml vials containing 0.3 ,M myo-[2-3H]inositol (New England Nuclear, specific activity 16.5 Ci/mmol; 1 Ci = 37 GBq) in a final volume of 275 ,ul. After 60 min of incubation, LiCl (7 mM) was added, followed, 20 min later, by transmitter receptor agonists. Antagonists were sometimes added 5 min prior to the agonists. After 60 min, the slices were washed three times with buffer and the reaction (cleavage of inositol phosphates from membrane phospholipids) was stopped by addition of 0.9 ml of chloroform/methanol (1:2). Identical results were obtained when slices were washed free of [3H]inositol before the addition of transmitter receptor agonists. The content of [3H]Ins-1-P was determined according to Berridge et al. (10). Proteins were measured as described by Lowry et al. (11). al-Adrenergic Receptor Binding Assay. The characteristics of a1-adrenergic recognition sites were studied in crude synaptic membranes prepared from rat hippocampus, using [3H]prazosin as a selective ligand, as described (12). RESULTS Age-Dependent Stimulation of PtdIns 1931The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Endogenous activation of metabotropic glutamate receptors supports the proliferation and survival of neural progenitor cells

“…Here, we focus on metabotropic glutamate (mGlu) receptors, which are implicated in the regulation of developmental plasticity. [6][7][8][9][10][11][12][13][14][15][16] mGlu receptors form a family of eight subtypes, of which mGlu1 and mGlu5 are coupled to polyphosphoinositide (PI) hydrolysis, whereas all other subtypes are negatively coupled to adenylyl cyclase in heterologous expression systems. 17,18 Although mGlu receptors regulate synaptic transmission, some of the subtypes (particularly, the mGlu5 receptor) are expressed at developmental stages that precede synaptic formation and are also found in nonneuronal tissues.…”

Expression of metabotropic glutamate receptors in the rat and human testis

“…Agonist-stimulated inositol phospholipid hydrolysis was examined by measuring the accumulation of [ 3 H]inositol monophosphate ([ 3 H]InsP) as described previously (Nicoletti et al 1986). In brief, 350 350 µm slices cut from the rat testis were added to 250 µl Krebs-Henseleit buffer (equilibrated with 95% O 2 / 5% CO 2 to pH 7·4) and then incubated for 1 h at 37 C with 1 µCi/tube myo--[ 3 H]inositol (specific activity 16·5 Ci/mmol; NEN Life Science Products Inc., Boston, MA, USA) to label membrane inositol phospholipids.…”

Developmental Switch in Synaptic Mechanisms of Hippocampal Metabotropic Glutamate Receptor-Dependent Long-Term Depression

“…Specifically, we examined the developmental changes of LTD, which rely on group 1 metabotropic glutamate receptors (mGluRs) and dendritic protein synthesis (mGluR-LTD) (Huber et al, 2000). This work was motivated by findings that group 1 mGluR function (measured as phosphoinositide turnover) and synaptic polyribosome number peak during the period of synapse formation and maturation [approximately postnatal day 7 (P7) to P15 in the hippocampus], suggesting that mGluR-LTD plays a significant role in the plasticity of developing synapses Falk, 1985, 1991;Nicoletti et al, 1986;Dudek et al, 1989;Palmer et al, 1990;Casabona et al, 1997).…”