Regulation of orofacial movement: dopamine receptor mechanisms and mutant models.

Orofacial movements involve complex processes that include generators for down-stream patterns, with up-stream regulatory mechanisms. While the neurotransmitter dopamine plays a fundamental role, the role of individual dopamine receptor subtypes and their associated transduction mechanisms is unclear. Here we review systematic, comparative studies of orofacial function in mutant mice with "knockout" of D1, D2, D3, D4 or D5 receptors, or of their critical transduction component DARPP-32 at four levels: general orofacial behaviors within the mouse repertoire, as assessed naturalistically; individual components of orofacial movement, as assessed under non-naturalistic conditions; each of the above, as assessed also under challenge with a D1-like vs a D2-like agonist. Studies in these "knockouts" provide novel insights into the motoric "building blocks" that regulate orofacial function.