Transient receptor potential vanilloid 1 (TRPV1)-containing afferent neurons convey nociceptive indicators

Transient receptor potential vanilloid 1 (TRPV1)-containing afferent neurons convey nociceptive indicators and play an essential role in pain sensation. adult mouse small- to medium-sized afferent neurons and treatment with NGF (100 ng/ml) for 30 minutes significantly increased the number of neurons that responded to capsaicin (as indicated by increased intracellular Ca2+ concentration). Pretreatment with the CB1 agonist ACEA (10 nM) inhibited the NGF-induced response and this effect of ACEA was reversed by a selective CB1 antagonist. Further pretreatment with ACEA inhibited NGF-induced phosphorylation of AKT. Blocking PI3 kinase activity also attenuated the NGF-induced increase in HG-10-102-01 the number of neurons that responded to capsaicin. Our results indicate that this analgesic effect of CB1 activation may in part be due to inhibition of NGF-induced sensitization of TRPV1 and also that the effect of CB1 activation is at least partly mediated by attenuation of NGF-induced increased PI3 signaling. test. p values < 0.05 were considered significant. RESULTS Presence of CB1 TRPV1 and trkA in adult mouse afferent neurons Specific antibodies revealed positive immunostaining for trkA TRPV1 and CB1 in Mouse monoclonal to GSK3 alpha small- to medium-sized afferent neurons (Physique 1). Cells were considered labeled with the specific antibody when the fluorescent intensity was distinctively higher than controls. Replacing specific antibodies with normal rabbit or goat IgG resulted in complete lack of specific staining (Physique 1 lower right panel). Under the experimental conditions used 49.2 ± 3.9 % 53.9 ± 4.3 % and 62.1 ± 3.8 % neurons were positive for trkA TRPV1 and CB1 respectively (n = 6). Triple co-localization staining revealed that 30.6 ± 3.6 % neurons expressed all three proteins (n = 6). Physique 1 A: Representative photoimages showing localization of trkA TRPV1 and CB1 in adult mouse DRG neurons (arrow heads). Neurons were considered labeled with the specific antibody when the fluorescent intensity HG-10-102-01 was distinctively higher than background. Using … Effects of NGF on capsaicin-induced increase in [Ca2+]i Exposure of neurons to capsaicin was generally characterized by a rapid increase in [Ca2+]i and the amplitude and duration of capsaicin-induced responses varied considerably among neurons (Physique 2A). Exposure to capsaicin (300 nM) induced a rapid increase in [Ca2+]i in about one-third of the neurons (30.2 ± 1.2 % n = 8 Figure 2B). Exposure to NGF (100 ng/ml) for 30 minutes did not affect basal [Ca2+]i in neurons (not shown). Treatment with NGF HG-10-102-01 significantly increased the number of neurons that responded to capsaicin (41.4 ± 1.8 % n = 8 p < 0.01 vs capsaicin-treated group; Physique 2B). Physique 2 A: HG-10-102-01 Representative tracings illustrating that capsaicin (300 nM) induced a rapid increase in intracellular Ca2+ concentrations in about one third of the neurons and the amplitude and duration of capsaicin-induced responses varied considerably among neurons. ... Effects of the selective CB1 agonist ACEA on NGF-induced responses Exposure to ACEA (10 nM) did not affect basal [Ca2+]i or the number of neurons that responded to capsaicin (Physique 2B). Treatment with ACEA abolished the NGF-induced increase in the number of neurons that responded to capsaicin (30.1 ± 1.3 % n = 8 p < 0.01 vs NGF-treated group) and this effect of ACEA was reversed by pretreatment with HG-10-102-01 the selective CB1 antagonist AM251 (100 nM 41.3 ± 2.6 % n = 8 p < 0.01 vs ACEA+NGF-treated group; Physique 2B). Treatment with AM251 (100 nM) alone did not affect the NGF-induced increase in the number of neurons that responded to capsaicin (42.1 ± 4.3 % vs NGF-treated group n = 8 p > 0.05). Effects of the selective CB1 agonist ACEA on signaling pathways involved in NGF-induced responses Immunoblotting exhibited that exposure to capsaicin alone for 2 minutes did not alter abundance of phosphorylated AKT (Physique 3A 0.93 ± 0.07 vs basal level 1 ± 0.02 n = 5 p > 0.05) or ERK1/2 (Figrue 3B 1.12 ± 0.22 vs basal level 1 ± 0.21 n = 5 p > 0.05). Treatment with NGF and capsaicin increased phosphorylation of AKT (Physique 3A 3.1 ± 0.56 n= 5 p < 0.05 HG-10-102-01 vs basal level) and ERK1/2.