Functional properties of neurons in trigeminal subnucleus caudalis of the cat. II: modulation of responses to noxious and non-noxious stimulation by periaqueductal gray, nucleus raphe magnus, cerebral cortex and afferent influences, and effect of nalaxone - Sessle,B.J.; Hu,J.W.; Dubner,R.; Lucier,G.E. (J Neurophysiol, 1981)