Biomedical subjects

Susan M Huang

Publications and source records attributed to Susan M Huang.

8 recordsLinked to original sources

PubMed2005

Enhancement of spontaneous and heat-evoked activity in spinal nociceptive neurons by the endovanilloid/endocannabinoid N-arachidonoyldopamine (NADA).

N-arachidonoyldopamine (NADA) is an endogenous molecule found in the nervous system that is capable of acting as a vanilloid agonist via the TRPV1 receptor and as a cannabinoid agonist via the CB1 receptor. Using anesthetized rats, we investigated the neural correlates of behavioral thermal hyperalgesia produced by NADA. Extracellular single cell electrophysiology was conducted to assess the effects of peripheral administration of NADA (i.pl.) on nociceptive neurons in the dorsal horn of the spinal cord. Injection of NADA in the hindpaw caused increased spontaneous discharge of spinal nociceptive neurons compared with injection of vehicle. The neurons also displayed magnified responses to application of thermal stimuli ranging from 34 to 52 degrees C. NADA-induced neural hypersensitivity was dose dependent (EC50 = 1.55 microg) and TRPV1 dependent, as the effect was abolished by co-administration of the TRPV1 antagonist 5'-iodoresiniferatoxin (I-RTX). In contrast, co-administration of the CB1 antagonist SR 141716A did not attenuate this effect. These results suggest that the enhanced responses of spinal nociceptive neurons likely underlie the behavioral thermal hyperalgesia and implicate a possible pain-sensitizing role of endogenous NADA mediated by TRPV1 in the periphery.

Action Potentials↗

PubMed2004

Targeted lipidomics: fatty acid amides and pain modulation.

Mass spectrometric approaches to the identification and quantification of lipid signalling molecules are reviewed. Fatty acid amides are an important new class of lipid signalling molecules which include oleamide, the endocannabinoid anandamide, the endovanilloid/endocannabinoid N-arachidonoyldopamine (NADA) and the endovanilloid N-oleoyldopamine (OLDA) among many others. This diverse group of endogenous compounds comprises combinations of acyl backbones coupled by an amide bond to any of a variety of different small polar molecules such as ethanolamine, various amino acids, and catecholamines. Many fatty acid amides appear to play a role in pain and inflammation. Targeted lipidomics of fatty acid amides aims to identify new members of this diverse class of compounds, of which only a few representative molecules have been characterized to date. This effort has been made feasible by advances in chromatography and mass spectrometry, which permits: (1) identification of compounds present in complex mixtures, (2) astronomical increases in sensitivity due to miniaturization of HPLC components, and (3) novel scanning modes that permit the identification of compounds exhibiting similar structural components. Insofar as lipid signalling molecules such as prostanoids, leukotrienes and endocannabinoids operate via G-protein coupled receptors (GPCR), it appears likely that many of the numerous lipids awaiting identification may serve as ligands for any of the greater than 150 orphan GPCRs.

Amides↗

PubMed2004

Cannabinoid signaling in rat cerebellar granule cells: G-protein activation, inhibition of glutamate release and endogenous cannabinoids.

Previous studies have indicated that cannabinoids inhibit presynaptic neurotransmitter release in brain through CB1 receptors. To examine this issue in a primary neuronal culture system, rat cerebellar granule cells (CGCs) were prepared. [35S]GTPgammaS binding assays in saponin-permeabilized CGCs showed that G-protein activation by the CB1 agonist, WIN55212-2, and adenosine A1 agonist, phenylisopropyladenosine, was maximal during the second week in culture. Delta9-tetrahydrocannabinol stimulated [35S]GTPgammaS binding to a lesser degree than WIN55212-2, and the antagonists SR141716A and AM281 acted as inverse agonists in intact CGCs, but not in CGC membrane preparations. Ten micromolar WIN55212-2 and Delta9-tetrahydrocannabinol decreased depolarization-evoked efflux of [3H]-D-aspartate from CGCs by 32% and 13%, respectively. SR141716A and AM281 increased [3H]-D-aspartate release by 28%. The fatty acid amide hydrolase (FAAH) inhibitor phenylmethylsulfonyl fluoride (PMSF) and the anandamide uptake inhibitor AM404 inhibited transmitter release, implying that the antagonist effects were mediated by blockade of endocannabinoid activity. Levels of endocannabinoids (both anandamide and 2-arachidonyl glycerol [2-AG]) in extracts of the cells and cell incubation buffer were increased by PMSF pre-treatment. Depolarization with KCl significantly decreased the amount of anandamide and 2-AG in PMSF-treated CGCs. These results suggest that endogenous cannabinoids inhibit neurotransmitter release in CGCs, which may also release endocannabioids upon neural stimulation.

Animals↗

PubMed2003

N-oleoyldopamine, a novel endogenous capsaicin-like lipid that produces hyperalgesia.

N-Arachidonoyldopamine (NADA) was recently identified as an endogenous ligand for the vanilloid type 1 receptor (VR1). Further analysis of the bovine striatal extract from which NADA was isolated indicated the existence of substances corresponding in molecular mass to N-oleoyldopamine (OLDA), N-palmitoyldopamine (PALDA), and N-stearoyldopamine (STEARDA). Quadrupole time-of-flight mass spectrometric analysis of bovine striatal extracts revealed the existence of OLDA, PALDA, and STEARDA as endogenous compounds in the mammalian brain. PALDA and STEARDA failed to affect calcium influx in VR1-transfected human embryonic kidney (HEK) 293 cells or paw withdrawal latencies from a radiant heat source, and there was no evidence of spontaneous pain behavior. By contrast, OLDA induced calcium influx (EC(50) = 36 nm), reduced the latency of paw withdrawal from a radiant heat source in a dose-dependent manner (EC(50) = 0.72 microg), and produced nocifensive behavior. These effects were blocked by co-administration of the VR1 antagonist iodo-resiniferatoxin (10 nm for HEK cells and 1 microg/50 micro;l for pain behavior). These findings demonstrate the existence of an endogenous compound in the brain that is similar to capsaicin and NADA in its chemical structure and activity on VR1. Unlike NADA, OLDA was only a weak ligand for rat CB1 receptors; but like NADA, it was recognized by the anandamide membrane transporter while being a poor substrate for fatty-acid amide hydrolase. Analysis of the activity of six additional synthetic and potentially endogenous N-acyldopamine indicated the requirement of a long unsaturated fatty acid chain for an optimal functional interaction with VR1 receptors.

Animals↗

PubMed2002

Endocannabinoids and related fatty acid derivatives in pain modulation.

The brain produces at least five compounds that possess sub-micromolar affinity for cannabinoid receptors: anandamide, 2-arachidonoylglycerol, noladin ether, virodhamine, and N-arachidonoyldopamine (NADA). One function of these and/or related compounds is to suppress pain sensitivity. Much evidence supports a role of endocannabinoids in pain modulation in general, and some evidence points to the role of particular endocannabinoids. Related endogenous fatty acid derivatives such as oleamide, palmitoylethanolamide, 2-lineoylglycerol, 2-palmitoylglycerol, and a family of arachidonoyl amino acids may interact with endocannabinoids in the modulation of pain sensitivity.

Animals↗

PubMed2002

Regulation of anandamide tissue levels by N-arachidonylglycine.

N-arachidonylglycine (NAGly), the carboxylic analog of the endocannabinoid anandamide, occurs in rat and bovine brain as well as in peripheral sites and shows activity against tonic, formalin-induced pain. It was also observed, using cell membrane preparations, that it inhibits the hydrolytic activity of fatty acid amide hydrolase (FAAH) on anandamide (N-arachidonylethanolamide). These data suggested that it may serve as an endogenous regulator of tissue anandamide concentrations. In this report, we show findings derived from mass spectrometric analyses, indicating that blood levels of anandamide in rats given 10 mg/kg p.o. of NAGly were increased significantly by more than 9-fold when compared with vehicle-treated controls. In vitro evidence in RAW 264.7 cells using a deuterium-labeled NAGly demonstrated that it was not a precursor or source of arachidonic acid for the observed 50% rise in anandamide levels, suggesting that the increase was due to some effect other than increased biosynthesis of anandamide. Moreover, the findings presented here suggest that NAGly can serve as a model for the design of agents to provide pharmacological control of tissue anandamide concentrations.

Animals↗

PubMed2002

An endogenous capsaicin-like substance with high potency at recombinant and native vanilloid VR1 receptors.

The vanilloid receptor VR1 is a nonselective cation channel that is most abundant in peripheral sensory fibers but also is found in several brain nuclei. VR1 is gated by protons, heat, and the pungent ingredient of "hot" chili peppers, capsaicin. To date, no endogenous compound with potency at this receptor comparable to that of capsaicin has been identified. Here we examined the hypothesis, based on previous structure-activity relationship studies and the availability of biosynthetic precursors, that N-arachidonoyl-dopamine (NADA) is an endogenous "capsaicin-like" substance in mammalian nervous tissues. We found that NADA occurs in nervous tissues, with the highest concentrations being found in the striatum, hippocampus, and cerebellum and the lowest concentrations in the dorsal root ganglion. We also gained evidence for the existence of two possible routes for NADA biosynthesis and mechanisms for its inactivation in rat brain. NADA activates both human and rat VR1 overexpressed in human embryonic kidney (HEK)293 cells, with potency (EC(50) approximately 50 nM) and efficacy similar to those of capsaicin. Furthermore, NADA potently activates native vanilloid receptors in neurons from rat dorsal root ganglion and hippocampus, thereby inducing the release of substance P and calcitonin gene-related peptide (CGRP) from dorsal spinal cord slices and enhancing hippocampal paired-pulse depression, respectively. Intradermal NADA also induces VR1-mediated thermal hyperalgesia (EC(50) = 1.5 +/- 0.3 microg). Our data demonstrate the existence of a brain substance similar to capsaicin not only with respect to its chemical structure but also to its potency at VR1 receptors.

Animals↗

PubMed2002

Cannabinoid analgesia.

During the last decade, rigorous scientific methods have been applied to determine the effects of cannabinoids on nociceptive neurotransmission. Cannabinoids have been observed to markedly decrease signalling in specific neural pathways that transmit messages about pain. These effects were found to be due to the suppression of spinal and thalamic nociceptive neurons, and independent of any actions on either the motor system or sensory neurons that transmit messages related to non-nociceptive stimulation. Spinal, supraspinal, and peripheral sites of cannabinoid analgesia have been identified. The discovery of endocannabinoids raised the question of their natural role in pain. Multiple lines of evidence indicate that endocannabinoids serve naturally to suppress pain. While it is now clear that cannabinoids suppress nociceptive neurotransmission, more work is needed to establish the clinical utility of these compounds. The few human studies conducted to date produced mixed results, with more promising findings coming from studies of clinical pain as compared with experimental pain. The therapeutic potential of cannabinoids remains an important topic for future investigations.

Analgesics↗