We have demonstrated that astroglial activation is involved in the central sensitization induced in trigeminal subnucleus caudalis (Vc) nociceptive neurons by mustard oil (MO) application to the tooth pulp (Chiang et al. SfN Abst 518.10, 2004). The aim of this study was to test if microglia are also involved in central sensitization in Vc by the use of an inhibitor (SB203580) of p38 MAPK which is known to play a key role in the activation of spinal microglia. In urethane/a-chloralose-anesthetized adult male rats, extracellular recordings of single neuronal activity were made from nociceptive-specific (NS) neurons in Vc. The mechanoreceptive field (RF), mechanical activation threshold and responses to graded pinch or pressure of each neuron were assessed at baseline. Then 2 assessments were made at 5 and 15 min after a bolus application of SB203580 (i.t., 2.7 nmole in 10 µl saline) or continuous superfusion (i.t., 0.6 ml/hr) of saline (as control) onto Vc, and MO was next applied to the first maxillary mola...