Mechanism-based targeting of NMDA receptor functions

NMDA receptors (NRs) are key signaling proteins in the central nervous system and represent important targets for drug development in several neurologic disorders. They are critically involved with fundamental brain processes, and thus indiscriminate pharmacological suppression of NR currents has seen only modest therapeutic success so far. Targeting harmful NR receptor activities while sparing the receptor’s vital functions requires a better understanding of the complexity of NR activation reaction; of the range of mechanisms that modulate discrete receptor activities; and of the consequences of this modulation on specific receptor functions. A quantitative account of the NR activation pathway was recently proposed and validated. It describes the gating reaction as a sequential, multi-step process rather than a binary, on-off switch. Alongside isoform-specific modulators, state-specific modulators may represent sophisticated interventions with high potential for narrow, functional specifi city. Here I review physiologic mechanisms that control NR responses; the salient features of the NR activation reaction; and discuss the model’s validity and its implications for drug development and characterization.Submitted 25 May 2005; accepted 29 June 2005     

Tissue-specific modulation of rat glucocorticoid receptor binding activity by melatonin

The effect of melatonin and 2-Iodomelatonin on nuclear and cytosolic glucocorticoid receptors in the brain, pituitary, thymus and liver has been examined. The results indicate that both melatonin and 2-Iodomelatonin administration is associated with marked changes in the density and the affinity of cytosolic and nuclear forms of glucocorticoid receptors. These observations are discussed in the context of a possible involvement of pineal melatonin in the mechanisms regulating the behaviour and metabolism of steroid receptors.     

Ligand- and cell-dependent determinants of internalization and cAMP modulation by delta opioid receptor (DOR) agonists

Signaling bias refers to G protein-coupled receptor ligand ability to preferentially activate one type of signal over another. Bias to evoke signaling as opposed to sequestration has been proposed as a predictor of opioid ligand potential for generating tolerance. Here we measured whether delta opioid receptor agonists preferentially inhibited cyclase activity over internalization in HEK cells. Efficacy (τ) and affinity (KA) values were estimated from functional data and bias was calculated from efficiency coefficients (log τ/KA). This approach better represented the data as compared to alternative methods that estimate bias exclusively from τ values. Log (τ/KA) coefficients indicated that SNC-80 and UFP-512 promoted cyclase inhibition more efficiently than DOR internalization as compared to DPDPE (bias factor for SNC-80: 50 and for UFP-512: 132). Molecular determinants of internalization were different in HEK293 cells and neurons with βarrs contributing to internalization in both cell types, while PKC and GRK2 activities were only involved in neurons. Rank orders of ligand ability to engage different internalization mechanisms in neurons were compared to rank order of E _max values for cyclase assays in HEK cells. Comparison revealed a significant reversal in rank order for cyclase E _max values and βarr-dependent internalization in neurons, indicating that these responses were ligand-specific. Despite this evidence, and because kinases involved in internalization were not the same across cellular backgrounds, it is not possible to assert if the magnitude and nature of bias revealed by rank orders of maximal responses is the same as the one measured in HEK cells.     

Biological Redox Systems and Oxidative Stress

This account revolves around fascination and excitement with science. Early curiosity and fortunate opportunities can lead to a satisfying career. The privilege of performing basic research in biochemistry and molecular biology at a university coupled with teaching motivated students and working with dedicated co-workers makes for sustained thrust in the advance of knowledge. Research fields centered around cellular redox systems, oxidants and antioxidants, and the concept of oxidative stress. A noteworthy aspect is the global network of scientists joining in these endeavors worldwide. Dedicated to my wife, Nancy (Ph.D., UC Berkeley) Received 9 May 2007; accepted 10 May 2007     

Redox enzyme models from polymerized aminoacyladenylates

Résumé Des modèles d'enzymes d'oxydoréduction ont été préparés par polymérisation des 20 aminoacyladénylates en présence de flavine mononucléotide, d'hème et de chlorophylle. L'addition du cofacteur flavinique au cours de la polymérisation modifie la composition en acides aminés du polymère obtenu. L'article offre une discussion sur les taux de réaction, les absorptions optiques et de dispersion rotatoire et les propriétés générales des modèles d'enzymes d'oxydoréduction.

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The support from a National Science Foundation Development Program grant to the University of Texas is gratefully acknowledged as is the assistance ofDirk Schenkkan and Mrs.Sandra Smith.     

Cortical modulation of pain

The sensation commonly referred to as pain has two components. The first is the sensory-discriminative component and provides information on location, modality and intensity of stimuli. The second is the affective-motivational component and refers to the emotional responses (fear, distress etc.) and the urge to respond evoked by the somatic sensation, and at the cortical level these two components appear to be located in different regions. The cortex probably influences pain by two different mechanisms. There is good evidence that the cortex can reduce pain by interrupting the transmission of noxious information from the spinal cord level by activating descending pain modulatory systems located in the brainstem. Less well established is the idea that modulation can also occur at the cortical level to change the affective-motivational aspects of nociception so that pain is perceived but looses its emotional and aversive component.Received 28 June 2004; received after revision 17 August 2004; accepted 21 August 2004     

Evidence for a modulation of the stress response by the pineal gland

Summary Wistar rats show a circadian variation in their response to stress. Pinealectomy exacerbates stress-induced gastric ulceration in rats. This effect is counteracted by melatonin administration.     

Evidence for a modulation of the stress response by the pineal gland

Wistar rats show a circadian variation in their response to stress. Pinealectomy exacerbates stress-induced gastric ulceration in rats. This effect is counteracted by melatonin administration.     

An efferent respiratory modulation demonstrated in the olfactory bulb of the rat

The multiunit activity from mitral cells in the Rat olfactory bulb is modulated according to the respiratory cycle. Respiration and neuronal activity still coincide in tracheotomized animals, provided the olfactory peduncle is left intact.     

Calcium channel modulation by beta-adrenergic neurotransmitters in the heart

Calcium ions play a crucial role in the regulation of the heart beat. During each action potential Ca2+ ions flow into the cell and are directly and indirectly involved in generation of pacemaker potentials and of contractile force. Adrenergic and cholinergic neurotransmitters modulate Ca2+ influx. The most detailed analysis has been made on the mechanism of the beta-adrenergic effect on calcium channels in cardiac cell membranes. This is briefly summarized in a personal account, while for more detailed information the reader is referred to more extensive recent reviews.     

ADAM proteases: ligand processing and modulation of the Notch pathway

ADAM metalloproteases play important roles in development and disease. One of the key functions of ADAMs is the proteolytic processing of Notch receptors and their ligands. ADAM-mediated cleavage of Notch represents the first step in regulated intramembrane proteolysis of the receptor, leading to activation of the Notch pathway. Recent reports indicate that the transmembrane Notch ligands also undergo ADAM-mediated processing in cultured cells and in vivo. The proteolytic processing of Notch ligands modulates the strength and duration of Notch signals, leads to generation of soluble intracellular domains of the ligands, and may support a bi-directional signaling between cells.     

On the solvent-extraction of acetylcholine receptor

Chloroform/methanol rechromatography on Sephadex LH-20 of fractions isolated from organic solvent extracts of E. electricus electric organs exhibited alterations in elution point compared to the original chromatography. Additionally, 3H decamethonium bromide did not coelute with any of the observed fractions. It is concluded that as presently described the organic solvent isolation procedure for the cholinergic receptor exhibits undesirable characteristics.     

On the solvent-extraction of acetylcholine receptor

Summary Chloroform/methanol rechromatography on Sephadex LH-20 of fractions isolated from organic solvent extracts ofE. electricus electric organs exhibited alterations in elution point compared to the original chromatography. Additionally,³H decamethonium bromide did not coelute with any of the observed fractions. It is concluded that as presently described the organic solvent isolation procedure for the cholinergic receptor exhibits undesirable characteristics.Acknowledgments. The authors thank Dan Burrough and Rick O'Brien for their competent technical assistance. Naval Medical Research Development and Command, Research Work Unit No. MRO41.06.01.0021. The opinions and assertions contained herein are the private ones of the writers and are not to be construed as official or reflecting the views of the Navy Department or the naval service at large.