The NK₁ Receptor Antagonist SR140333 Inhibits Capsaicin-Induced ERK Phosphorylation in Sensory Neurons

Abstract

Primary sensory neurons respond to a vigorous excitation via the capsaicin receptor/TRPV1 cation channel by a phosphorylation of the Jak/STAT pathway as measured by phospho-STAT3, and of the Ras/Raf-MAPK pathway as measured by phospho-MAPK/ERK1/2. In the present investigation a possible involvement of NK₁ receptors in the capsaicin-induced activation of these signal transduction pathways was investigated by protein extraction and Western immunoblotting. Phospho-MAPK/ERK1/2 and phospho-STAT3 were determined in the dorsal root ganglia (DRG) and in the sciatic nerve of rats at 3 and 6 h following a systemic capsaicin treatment without or with the pretreatment of the selective NK₁ receptor antagonist SR140333 (1 mg/kg s.c.; 3 h before capsaicin). Capsaicin evoked a threefold increase in phospho-ERK in the sciatic nerve and a two- to threefold increase in the DRG at 3 h and 6 h after the treatment. SR140333 markedly attenuated the capsaicin-induced increase in phosphorylated ERK. In the sciatic nerve the difference was significant at each individual time point (3 and 6 h, p < 0.001). In the DRG the difference was significant when the data at 3 h and 6 h were combined (p < 0.05), but not when individual time points were considered. Capsaicin evoked a four- to fivefold increase in phospho-STAT3 in the sciatic nerve and a twofold increase in the DRG at 3 and 6 h after the treatment. SR140333 less markedly attenuated the capsaicin-induced increase in phosphorylated STAT3: whereas in the sciatic nerve the difference was significant when the data at 3 h and 6 h were combined (p < 0.05), no such treatment effect of SR140333 was observed in the DRG. The expression of TRPV1 mRNA, a specific marker of capsaicin-sensitive small sensory neurons, was investigated by RT-PCR 4 days after the capsaicin treatment. Treatment of rats with SR140333 had no influence on the long-term downregulation of TRPV1 mRNA by capsaicin. Based on the present results and previous findings it can be postulated that the capsaicin-induced ERK phosphorylation in sensory neurons is not a direct effect by capsaicin, but that rather substance P release from the stimulated sensory neurons with an NK₁-mediated nerve growth factor (NGF) production is involved.

Capsaicin, Nociception and Pain

“…It seems also possible that—at least under certain conditions—neurokinin 1 (NK1) and neurokinin 2 receptor-mediated mechanisms are involved in the induction of phosphorylated extracellular signal-regulated kinase (pERK) after stimulation of primary sensory neurons (PSNs) with capsaicin, an effect not solely directly linked to the binding of the vanilloid to TRPV1 channels [27]. However, as PSNs release substance P in response to capsaicin challenge, such a possibility still needs to be confirmed in full.…”

Capsaicin‐ and Mustard Oil‐Induced Extracellular Signal‐Regulated Protein Kinase Phosphorylation in Sensory Neurons in vivo: Effects of Neurokinins 1 and 2 Receptor Antagonists and of a Nitric Oxide Synthase Inhibitor

“…The time course of p‐ERK1/2 induction was different in these two treatment modes: perineural capsaicin induced a rapid and vigorous excitation of sensory neurons with a maximum of ERK1/2 phosphorylation in the sensory axons already after 30 min., whereas following the subcutaneous application the peak of ERK1/2 phosphorylation was reached 4 hr after treatment. As we have already shown in a previous investigation, that p‐ERK1/2 following systemic capsaicin is attenuated by the substance P (NK 1 receptor) antagonist SR140333 pointing towards an involvement of substance P and NK 1 receptors at some level of the excitation of sensory neurons [16]. It was proposed that NK 1 –NGF production from mast cells or macrophages/monocytes with subsequent activation of sensory neurons via the NGF receptor (TrkA) is involved in the induction of intracellular ERK1/2 phosphorylation that evolved over a time period of several hours [14,33,34].…”

“…The level of p‐ERK1/2 was not different in animals that received only capsaicin vehicle injections subcutaneously in the neck region (n = 3; data not shown). Because it has been shown before that phosphorylation of ERK1/2 peaks between 3 hr and 6 hr after the systemic capsaicin treatment, only the time‐point 4 hr was considered in the present study [16]. Systemic capsaicin injection subcutaneously in the neck region evoked a 3‐fold increase in p‐ERK1/2 in the sciatic nerve and in the dorsal root ganglia at this time‐point (fig.…”

“…A rather weak basal level of p‐ERK1/2 was present in the sciatic nerve and in dorsal root ganglia of control animals as has been shown before by our group (fig. 1) [16]. The level of p‐ERK1/2 was not different in animals that received only capsaicin vehicle injections subcutaneously in the neck region (n = 3; data not shown).…”

“…Local perineural capsaicin treatment of the rat sciatic nerve is an experimental model suited to investigate the direct activation of sensory neuron axons via TRPV1. The perineural treatment site, which is protected from the surrounding tissue by a paraffin film, could allow further insights into the chain of events already investigated in the systemic capsaicin treatment [16]. The perineural capsaicin treatment takes place in a quasi‐isolated in vivo tissue chamber and should activate ERK1/2 via TRPV1 without any secondary mediators [17,18].…”