Behavioral responses of the chronically instrumented sheep fetus to chemosensory stimuli presented in utero.

Fetal sheep were surgically prepared on Days 113-114 of gestation with an array of chronic instruments for recording electromyographic data (EMG) in oral--facial, axial, and limb muscles and heart rate (FHR). Fetuses also were fitted with an intraoral catheter for infusion of chemosensory fluids (isotonic saline, quinine, colostrum, sucrose) onto the surface of the tongue. Individual subjects received chemosensory infusions on Days 134-137. Fetuses showed consistent oral responses to quinine and milk, but did not respond to isotonic saline or sucrose. Different patterns of motor responses suggest that fetuses discriminated among different concentrations of quinine. The expression of tachycardia to quinine and bradycardia to milk also suggested differential responding to chemosensory fluids that differ in hedonic qualities. Detailed characterization of fetal responses to these stimuli in utero confirm the functionality of the gustatory system in the sheep fetus near term.