Uridine activates fast transmembrane Ca2+ ion fluxes in rat brain homogenates

Excitatory receptors responsive to extracellular pyrimidine nucleotides have been identi®ed [1±6]. Although there is evidence for uridine acting as a CNS depressant [7,8], suggestions for an excitatory role in the CNS have so far not been supported by any direct evidence at the molecular level [9]. Hepatic uridine [10] enters the extracellular space of the brain, and subsequently brain cells, from the blood, where it can be phosphorylated and incorporated into RNA or be catabolized to uracil [11,12]. Since the extracellular concentration of uridine has been found to be increased by high K+ in the rat thalamus [13], it was of interest to study uridineresponsive cation ¯uxes through brain membranes. Here we describe a ¯uorescent tracer method to study uridine-activated Ca2+ and K+ ion translocation in suspensions of resealed plasmalemma fragments and nerve endings on the time scale achievable by stopped-¯ow spectroscopy. Uptake, release and binding of radiolabeled uridine in suspensions of synaptosomes and synaptosomal membranes, respectively, were also measured. Cerebral ±cortical suspensions were controlled by HPLC analyses of endogenous purines and pyrimidines

Quinazolone-Alkyl-Carboxylic Acid Derivatives Inhibit Transmembrane Ca 2ϩ Ion Flux to (ϩ)-(S)-␣-Amino-3-hydroxy- 5-methylisoxazole-4-propionic Acid

ABSTRACT Comparison of the kinetics of the inward Ca 2ϩ ion flux to (S)-␣-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid [(S)-AMPA] in cerebrocortical homogenates and that of the previously reported transmembrane Na ϩ ion influx mediated by an AMPA receptor in hippocampal homogenates established that the agonist-induced opening of the AMPA receptor channels occurs in two kinetically distinguishable phases. Here we report that the 2-methyl-4-oxo-3H-quinazoline-3-acetic acid (Q1) inhibits the major slow-phase response specifically, whereas the acetyl piperidine derivative (Q5) is a more potent inhibitor of the fast-phase response. Both the quinazolone-3-propionic acid (Q2) and the quinazolone-3-acetic acid methyl ester (Q3) enhanced the slow-phase response to (S)-AMPA. The information provided by docking different Q1, Q2, and Q5 models at the ligand-binding core of iGluRs were used to define agonistic and antagonistic modes of interactions. Based on the effects of quinazolone-3-alkyl-carboxylic acid derivatives on specific [ 3 H]Glu binding and kinetically distinguishable Ca 2ϩ ion permeability responses to (S)-AMPA and molecular modeling, the fast-and the slow-phase (S)-AMPA-elicited Ca 2ϩ ion fluxes were corresponded to different subunit compositions and degrees of S1S2 bridging interaction relative to substitution of kainate thereupon. Substitutions of agonists and antagonists into the iGluR2 S1S2 ligand binding core induced different modes of domain-domain bridging. The seminal information on the structure of an ionotropic glutamate receptor (iGluR) in complex with the neurotoxic agonist, kainate 3 H]Glu binding in rat brain cortical homogenates containing resealed plasmalemmal vesicles and nerve endings were performed to clarify the subunit compositions of receptors in the interpretation of the data as well as to justify the use of the iGluR2-S1-S2 crystal structure to model the ligand docking that modulates Ca 2ϩ ion flux. We attempt, on the basis of these results, 1) to integrate kinetics, pharmacological profile, and three-dimensional structure of the receptor-ligand complex to understand the molecular features of the Glu-gated ion channel-ligand interactions, and 2) to identify prerequisites for AMPA receptor agonist and antagonist specifics, by relating results from measurements of an AMPA receptor function with the relative position of the agonist-binding-site domains

Multifractal analysis of information processing in hippocampal neural ensembles during working memory under Δ9-tetrahydrocannabinol administration

BACKGROUND: Multifractal analysis quantifies the time-scale-invariant properties in data by describing the structure of variability over time. By applying this analysis to hippocampal interspike interval sequences recorded during performance of a working memory task, a measure of long-range temporal correlations and multifractal dynamics can reveal single neuron correlates of information processing. NEW METHOD: Wavelet leaders-based multifractal analysis (WLMA) was applied to hippocampal interspike intervals recorded during a working memory task. WLMA can be used to identify neurons likely to exhibit information processing relevant to operation of brain–computer interfaces and nonlinear neuronal models. RESULTS: Neurons involved in memory processing (“Functional Cell Types” or FCTs) showed a greater degree of multifractal firing properties than neurons without task-relevant firing characteristics. In addition, previously unidentified FCTs were revealed because multifractal analysis suggested further functional classification. The cannabinoid-type 1 receptor partial agonist, tetrahydrocannabinol (THC), selectively reduced multifractal dynamics in FCT neurons compared to non-FCT neurons. COMPARISON WITH EXISTING METHODS: WLMA is an objective tool for quantifying the memory-correlated complexity represented by FCTs that reveals additional information compared to classification of FCTs using traditional z-scores to identify neuronal correlates of behavioral events. CONCLUSION: z-Score-based FCT classification provides limited information about the dynamical range of neuronal activity characterized by WLMA. Increased complexity, as measured with multifractal analysis, may be a marker of functional involvement in memory processing. The level of multifractal attributes can be used to differentially emphasize neural signals to improve computational models and algorithms underlying brain–computer interfaces