Anandamide Excites Central Terminals of Dorsal Root Ganglion Neurons via Vanilloid Receptor-1 Activation

Abstract

Recently, the cannabinoid (CB) receptor agonist anandamide (AEA) has been shown to excite perivascular terminals of primary sensory neurons via activation of the vanilloid receptor-1 (VR-1). To determine whether AEA stimulates central terminals of these neurons, via VR-1 activation, we studied the release of calcitonin gene-related peptide (CGRP)-and substance P (SP)-like immunoreactivities (LI) from slices of rat dorsal spinal cord. Mobilization of Ca 2ϩ in rat dorsal root ganglion (DRG) neurons in culture was also studied. AEA (0.1-10 M) increased the outflow of CGRP-LI and SP-LI from slices of the rat dorsal spinal cord in a Ca 2ϩ -dependent manner and increased [Ca 2ϩ ] i in capsaicin-sensitive cultured DRG neurons. Both effects of AEA were abolished by capsaicin pretreatment and by the VR-1 antagonist capsazepine but not affected by the CB receptor antagonists AM281 or AM630. Both neuropeptide release and Ca 2ϩ mobilization induced by electrical field stimulation (EFS) were inhibited by a low concentration of AEA (10 nM). Inhibition by AEA of EFS-induced responses was reversed by AM281 and AM630, but was not affected by capsazepine. Results indicate that stimulation of VR-1 with high concentrations of AEA excites central terminals of capsaicin-sensitive DRG neurons, thus causing neuropeptide release in the dorsal spinal cord. This novel activity opposes the CB receptor-mediated inhibitory action of low concentrations AEA. However, only if large amounts of endogenous AEA could be produced at the level of the dorsal spinal cord, they may not inhibit, but rather activate, nociceptive sensory neurons.

Mechanisms of Prolonged Presynaptic Ca2+Signaling and Glutamate Release Induced by TRPV1 Activation in Rat Sensory Neurons

“…Putative TRPV1 agonists in the CNS include protons, anandamide, NADA, and lipoxygenase products, and the effects of these endogenous compounds depend on the phosphorylation state of the receptor (Tognetto et al, 2001;Huang et al, 2002;Bhave and Gereau, 2004;Premkumar et al, 2004;De Petrocellis and Di Marzo, 2005). We found that, like capsaicin, NADA induced a prolonged presynaptic [Ca 2ϩ ] i elevation and synaptic activity at sensory synapses (Fig.…”

“…9F ). TRPV1 activation also induces the release of substance P and CGRP in the dorsal spinal cord (Tognetto et al, 2001;Huang et al, 2002), and both these peptides may contribute to central sensitization (Khasabov et al, 2002;Sun et al, 2004). According to our model, mitochondria would sustain the accumulation of these peptides in the spinal cord.…”

“…Indeed, TRPV1 colocalizes with the presynaptic protein synaptophysin, and TRPV1-positive axonal boutons containing synaptic vesicles have been observed by electron microscopy (Guo et al, 1999;Hwang et al, 2004). Moreover, stimulation of the central terminals of primary afferents with endovanilloids or capsaicin triggers the release of calcitonin gene-related peptide (CGRP) and substance P and induces glutamatergic synaptic transmission (Yang et al, 1998;Tognetto et al, 2001;Huang et al, 2002;Nakatsuka et al, 2002;Labrakakis and MacDermott, 2003). Although Ca 2ϩ dynamics at the sites of transmitter release are crucial for TRPV1-mediated responses, the mechanisms that shape presynaptic Ca 2ϩ signals in primary sensory neurons remain unknown.…”

Modulation of Peripheral Sensory Neurons by the Immune System: Implications for Pain Therapy

“…Other studies in cultured DRG neurons reported biphasic effects of anandamide. Thus, the release of CGRP or Ca 2ϩ influx was decreased in a CB receptordependent manner by low concentrations of anandamide but was enhanced in a TRPV1-sensitive fashion by higher anandamide amounts (Tognetto et al, 2001;Ahluwalia et al, 2003). Anandamide also evoked excitation of C and A␦ nociceptors innervating healthy and arthritic rat joints in in vivo electrophysiological recordings (Gauldie et al, 2001).…”

Stimulation of FcγRI on Primary Sensory Neurons Increases Insulin-Like Growth Factor-I Production, Thereby Reducing Reperfusion-Induced Renal Injury in Mice

“…Dorsal root ganglion (DRG) neurons from the lumber, cervical, and thoracic region were dissected from WT mice as described previously (23). In brief, DRG neurons were placed in ice-cold sterile calcium-and magnesium-free Dulbecco's PBS (Life Technologies, Grand Island, NY).…”