Preproenkephalin mRNA expression in nucleus caudalis neurons is enhanced by trigeminal stimulation.

Electrical stimulation of trigeminal afferents increases expression of preproenkephalin mRNA in neurons of laminae I and II of the trigeminal nucleus caudalis in animals sacrificed 6 hours after the end of stimulation. More neurons express, and positive cells express at higher levels. These neurons thus express the mRNA corresponding to a major pain-modulating neurotransmitter gene with significant input-related plasticity.