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 (EC50 Ϸ 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 (EC50 ‫؍‬ 1.5 ؎ 0.3 g). 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. V anilloid receptors of type 1 (VR1) are nonselective cation channels, expressed in peripheral sensory C and A␦ fibers and gated by nociceptive stimuli such as low pH, heat, and some plant toxins, of which capsaicin, the pungent principle of chili peppers, is the best known example (1-4). Evidence obtained by several laboratories and using different techniques (5-10) showed that VR1 is present also in the central nervous system, where it is unlikely to be the target of noxious heat and low pH, thus suggesting the existence of brain endogenous agonists for this receptor (11). Indeed, lipid mediators previously known to serve other functions in the brain, i.e., the endocannabinoid anandamide and some lipoxygenase derivatives, activate VR1, albeit with a potency considerably lower than that of capsaicin (12)(13)(14). The antinociceptive effects of VR1 blockers in two models of inflammatory hyperalgesia (15, 16) suggest that ''endovanilloids'' might be produced also by peripheral tissues and act in concert with locally enhanced temperature and acidity during inflammation.If an endovanilloid did exist, what would be the structural prerequisites that would allow for an optimal interaction with vanilloid receptors? Structure-activity relationship studies for vanilloid receptors have indicated that both the vanillyl-amine moiety and a long, unsaturated acyl chain are necessary to...

SUMMARY1. Intracellular recording techniques were used to characterize monosynaptic inhibitory postsynaptic potentials (IPSPs) and currents (IPSCs) in rat hippocampal slices and to study the mechanism of paired-pulse depression of these synaptic responses. This was achieved by stimulation in stratum radiatum close (< 0 5 mm) to an intracellularly recorded CAI neurone after pharmacological blockade of all excitatory synaptic transmission.2. Under these conditions, low-frequency stimulation (0 033 Hz) evoked a pure biphasic IPSP, which had a short and constant latency to onset. This IPSP was blocked by tetrodotoxin (1 tM) suggesting that it resulted from the electrical stimulation of the axons and/or cell bodies of a monosynaptic inhibitory pathway.3. Picrotoxin (100 /tM) abolished the early component of the biphasic IPSP/C. It left an intact, pure late IPSP/C (IPSP/CB) which had a latency to onset of 29 + 2 ms, latency to peak of 139 +4 ms, a duration of 723+ 135 (range 390-1730) ms and a reversal potential of -93 + 2 mV. The duration was highly dependent on the stimulus intensity whereas the latency to onset was largely independent of the stimulus intensity. The IPSP/CB was reduced or abolished by 1 mM-phaclofen.4. Phaclofen (1 mM) and 2-hydroxy-saclofen (0-1-1-0 mm) reversibly depressed (60-100%) the late component of the biphasic IPSP/C and, where maximally effective, left a pure, early IPSP/C (IPSP/CA). The IPSP/CA had a latency to onset of 3 ms or less, a latency to peak of 17 + 1 ms, a duration of 225 + 3 ms and a reversal potential of -75 + 2 mV.5. Two shocks of identical strength were applied in close succession to characterize, and to study the mechanisms underlying, frequency-dependent depression of inhibitory synaptic responses. Paired-pulse depression was seen for both phases of the biphasic IPSP/C and of the pure IPSP/CB, recorded in the presence of picrotoxin. Paired-pulse depression was not accompanied by changes in the reversal potential of either component, indicating that it was caused by a reduction in the two synaptic conductances. Paired-pulse depression was greater when high stimulus intensities were employed.6. Paired stimuli were applied at separation intervals of between 5 ms and 10 s to determine the temporal profile of frequency-dependent depression. Paired-pulse depression of both IPSCA and IPSCB was most pronounced at an interstimulus MS 7998PHY 424 17 C. H. DAVIES AND OTHERS interval of 100-125 ms and ceased to occur at intervals greater than 5-10 s. Linear summation of IPSCs was seen with intervals of 10 ms or less.7. At rest, (-)-baclofen (5 #M) produced a small hyperpolarization (or outward current) associated with a slight increase in membrane conductance and abolished both components of the inhibitory synaptic response. Effects were stereoselective and reversible. A tenfold lower concentration of (-)-baclofen selectively depressed the synaptic response, causing depressions of 41 + 3 and 54 + 4% for the early and late components, respectively. This effect was reversed by 1 mM-p...

The N-methyl-D-aspartate (NMDA)-subtype of glutamate receptors has been well described as a result of the early appearance of NMDA antagonists, but no potent antagonist for the "non-NMDA" glutamate receptors has been available. Quinoxalinediones have now been found to be potent and competitive antagonists at non-NMDA glutamate receptors. These compounds will be useful in the determination of the structure-activity relations of quisqualate and kainate receptors and the role of such receptors in synaptic transmission in the mammalian brain.

Axonal injury is considered the major cause of disability in patients with multiple sclerosis (MS), but the underlying effector mechanisms are poorly understood. Starting with a proteomics-based approach, we identified neurofascin-specific autoantibodies in patients with MS. These autoantibodies recognize the native form of the extracellular domains of both neurofascin 186 (NF186), a neuronal protein concentrated in myelinated fibers at nodes of Ranvier, and NF155, the oligodendrocyte-specific isoform of neurofascin. Our in vitro studies with hippocampal slice cultures indicate that neurofascin antibodies inhibit axonal conduction in a complement-dependent manner. To evaluate whether circulating antineurofascin antibodies mediate a pathogenic effect in vivo, we cotransferred these antibodies with myelin oligodendrocyte glycoprotein–specific encephalitogenic T cells to mimic the inflammatory pathology of MS and breach the blood–brain barrier. In this animal model, antibodies to neurofascin selectively targeted nodes of Ranvier, resulting in deposition of complement, axonal injury, and disease exacerbation. Collectively, these results identify a novel mechanism of immune-mediated axonal injury that can contribute to axonal pathology in MS.

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