PALDA

Modulation of inhibitory neurotransmission by the vanilloid receptor type 1 (TRPV1) in organotypically cultured mouse substantia gelatinosa neurons.[Pubmed:20451324]

Pain. 2010 Jul;150(1):128-40.

The vanilloid receptor type 1 (TRPV1) plays a pivotal role in modulating thermal, chemical, and inflammatory pain. TRPV1s are expressed in some dorsal horn (DH) neurons, but their contribution, if any, to central pain processing still remains unclear. We studied the effects of 2microM capsaicin-induced TRPV1 activation in organotypically cultured substantia gelatinosa neurons from post-natal (8-12) mice. Capsaicin affected sIPSC frequency (272+/-60% of control, n=14, P<0.02), but not amplitude (131+/-12% of control, n=14, P>0.05) in patch clamp recordings, also in the presence of 50microM AP-5 (frequency: 265+/-69% of control; n=8, P<0.05; amplitude: 156+/-28% of control; n=8, P>0.05). The frequency increase was reduced by TTX (181+/-21% of control; n=12, P<0.05). Pre-administration of I-RTX (1microM), a TRPV1 antagonist, prevented the capsaicin effect (frequency: 149+/-28% of control, P>0.05, n=12; amplitude: 97+/-4% of control, P>0.05, n=12). NADA (1microM), an endovanilloid/endocannabinoid agonist of TRPV1, induced a significant increase of sISPC frequency (191+/-40% of control; n=8, P<0.05) without affecting the amplitude (102+/-6% of control; n=8, P>0.05), and the co-application of two naturally occurring N-acyldopamines, PALDA (5microM) and STEARDA (5microM) that facilitate the effect of TRPV1 agonists, also induced a significant increase of sIPSC frequency (278+/-67% of control, n=6, P<0.05). The presence of TRPV1 protein and mRNA in DH neurons was confirmed by histological (immunocytochemistry, in situ PCR) and biochemical (Western blotting, PCR) procedures. These data show that TRPV1 modulates inhibitory neurotransmission in cultured substantia gelatinosa neurons, and suggest that endogenous agonists can activate the spinal receptors in vivo.

Actions of two naturally occurring saturated N-acyldopamines on transient receptor potential vanilloid 1 (TRPV1) channels.[Pubmed:15289293]

Br J Pharmacol. 2004 Sep;143(2):251-6.

Four long-chain, linear fatty acid dopamides (N-acyldopamines) have been identified in nervous bovine and rat tissues. Two unsaturated members of this family of lipids, N-arachidonoyl-dopamine (NADA) and N-oleoyl-dopamine, were shown to potently activate the transient receptor potential channel type V1 (TRPV1), also known as the vanilloid receptor type 1 for capsaicin. However, the other two congeners, N-palmitoyl- and N-stearoyl-dopamine (PALDA and STEARDA), are inactive on TRPV1. We have investigated here the possibility that the two compounds act by enhancing the effect of NADA on TRPV1 ('entourage' effect). When pre-incubated for 5 min with cells, both compounds dose-dependently enhanced NADA's TRPV1-mediated effect on intracellular Ca(2+) in human embryonic kidney cells overexpressing the human TRPV1. In the presence of either PALDA or STEARDA (0.1-10 microm), the EC(50) of NADA was lowered from approximately 90 to approximately 30 nm. The effect on intracellular Ca(2+) by another endovanilloid, N-arachidonoyl-ethanolamine (anandamide, 50 nm), was also enhanced dose-dependently by both PALDA and STEARDA. PALDA and STEARDA also acted in synergy with low pH (6.0-6.7) to enhance intracellular Ca(2+) via TRPV1. When co-injected with NADA (0.5 micrograms) in rat hind paws, STEARDA (5 micrograms) potentiated NADA's TRPV1-mediated nociceptive effect by significantly shortening the withdrawal latencies from a radiant heat source. STEARDA (1 and 10 micrograms) also enhanced the nocifensive behavior induced by carrageenan in a typical test of inflammatory pain. These data indicate that, despite their inactivity per se on TRPV1, PALDA and STEARDA may play a role as 'entourage' compounds on chemicophysical agents that interact with these receptors, with possible implications in inflammatory and neuropathic pain.

N-oleoyldopamine, a novel endogenous capsaicin-like lipid that produces hyperalgesia.[Pubmed:12569099]

J Biol Chem. 2003 Apr 18;278(16):13633-9.

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.