Proceedings of The Physiological Society
University of Manchester (2010) Proc Physiol Soc 19, PC236
Activation of the MAP-Kinase signalling pathway and Fos expression by Neurokinin-1 and NMDA receptors in rat trigeminal nucleus caudalis in-vitro: mechanisms of trigeminal pain
T. Aggarwal1, C. E. Allen2, M. A. Worsley2, A. Billinton3, F. M. Boissonade2, A. E. King1
1. Institute for Membrane & Systems Biology, University of Leeds, Leeds, United Kingdom. 2. Oral & Maxillofacial Surgery, University of Sheffield, Sheffield, United Kingdom. 3. Neurosciences CEDD, GlaxoSmithKline, Harlow, United Kingdom.
Prolonged neuronal activity is a contributory factor in central sensitisation within nociceptive pathways triggered by inflammation or neuropathic injury. Activity-dependent sensitization is believed to be consequent to activation of intracellular signal transduction cascades that can trigger transcriptional modifications. In spinal dorsal horn, glutamate and substance P activate the mitogen-activated protein (MAP)-kinase signalling cascade and increase expression of the transcription factor Fos, both events being linked to spinal sensitization and chronic pain (Woolf & Costigan, 1999, Proc.Natl.Acad.Sci.USA, 96:7723-77230). The extent to which such mechanisms contribute to chronic trigeminal pain has been less well studied. We have used a trigeminal slice preparation to evaluate expression of two MAP Kinases, namely phosphorylated p-38 (p-p38) and ERK (p-ERK) following activation of either N-methly-D-aspartate (NMDA) or neuokinin-1 (NK1) receptors. In addition, we have determined whether the same agonists can alter expression of Fos which is indirectly linked to the MAP-kinase cascade. Brainstems were removed from rats (Wistar, 28 days) under anaesthesia (pentobarbital, 50 mg/kg i.p.) and after transcardiac perfusion with chilled sucrose-containing artificial cerebro-spinal fluid (ACSF). All procedures were carried out in accordance with current UK legislation. Tissue from trigeminal caudalis region was incubated initially for 2 hr in ACSF (37 °C) followed by 1 hr incubation in ACSF alone or in drug-containing solution (NMDA, 20 μM or [Sar9, Met(O2)11]-SP, 20 μM). After drug exposure, brainstem tissue was incubated for a further period of 1 hr in ACSF. Tetrodotoxin (TTX, 10 μM) was present throughout the protocol to eliminate indirect interneuronal activation. Sections were post-fixed and processed immunocytochemically for visualization of one of Fos, pERK or p-p38 within trigeminal caudalis. Data revealed an increased expression of Fos in response to NMDA (n = 7, P < 0.05) or [Sar9, Met(O2)11]-SP (n = 8, P < 0.05) whereas p-ERK expression levels were not significantly enhanced (NMDA, n = 5, P > 0.05; [Sar9, Met(O2)11]-SP, n = 5, P > 0.05). Both agonists elicited enhanced expression levels for p-p38 (NMDA, n = 3; [Sar9, Met(O2)11]-SP, n = 3) within trigeminal caudalis. These data indicate differential activation of p-p38, p-ERK and Fos by substance P (NK1R) and glutamate (NMDA) receptors within trigeminal caudalis. Further studies will be required to determine the role, of the MAP-kinase signalling cascade in sensitisation within trigeminal caudalis following peripheral insult.
Where applicable, experiments conform with Society ethical requirements