Selective neurokinin NK1 and NK2 receptor agonists infused in the substantia nigra of the rat increase vacuous chewing.

Bilateral intranigral infusion of selective neurokinin NK1 and NK2 receptor agonists were made in freely moving rats followed by measurements of vacuous chewing frequencies for 30 min post-infusion. The NK1 receptor agonist, [Pro9] substance P, induced an immediate dose-related elevation of non-object directed vacuous chewing movements. There was a linear dose-response relation in the 0.5-5 nmol dose range. In experiments with the NK2 receptor agonist, [Lys5,MeLeu9,Nle10]neurokinin A-(4-10), the highest dose, 4.8 nmol, caused a less intensive but longer lasting increase of the vacuous chewing movement frequency. These findings may imply a role for neurokinins in the regulation of oral movements.