Signalling pathways involved in the sensitisation of mouse nociceptive neurones by nerve growth factor.
Nerve growth factor (NGF) causes a rapid sensitisation of nociceptive sensory neurones to painful thermal stimuli owing to an action on the heat and capsaicin receptor TRPV1 (formerly known as VR1). We have developed a new technique to study this rapid sensitisation of TRPV1 by monitoring the effects of NGF on the increase in intracellular calcium concentration ([Ca2+]i) following exposure to capsaicin. Brief applications of capsaicin caused a rise in [Ca2+]i, and NGF was found to enhance this rise in 37 % of capsaicin-responsive neurones within 2 min. Pathways responsible for transducing the sensitisation of TRPV1 by TrkA, the NGF receptor, were characterised by observing the effects of inhibitors of key members of NGF-activated second messenger signalling cascades. Specific inhibitors of the ras/MEK (mitogen-activated protein and extracellular signal-regulated kinases) pathway and of phospholipase C did not abolish the NGF-induced sensitisation, but wortmannin, a specific inhibitor of phosphatidylinositol-3-kinase (PI3K), totally abolished the effect of NGF. Pharmacological blockade of protein kinase C (PKC) or calcium-calmodulin-dependent protein kinase II (CaMK II) activation also prevented NGF-induced sensitisation, while blockade of protein kinase A (PKA) was without effect. These data indicate that the crucial early pathway activated by NGF involves PI3K, while PKC and CaMK II are also involved, probably at subsequent stages of the NGF-activated signalling pathway.
Bonnington
Jennifer K
JK
Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK. pam42@cam.ac.uk
McNaughton
Peter A
PA
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000502:physiology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002211:Capsaicin / Q000494:pharmacology; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D006358:Hot Temperature; D007090:Image Interpretation, Computer-Assisted; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D020932:Nerve Growth Factor / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020917:Receptor, trkA / Q000187:drug effects / Q000502:physiology; D017483:Receptors, Vasopressin / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors; D018631:ras Proteins / Q000378:metabolism
D004791:Enzyme Inhibitors; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017483:Receptors, Vasopressin; D020932:Nerve Growth Factor; D020917:Receptor, trkA; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010738:Type C Phospholipases; D018631:ras Proteins; D002211:Capsaicin; D002118:Calcium