The present thesis examined the potential interaction between postingestive cues and the dopamine antagonist pimozide on the inhibition of sucrose sham intake. Coadministration of CCK and pimozide IP produced additive inhibitory effects on sham feeding of 4% or 17.1% sucrose. Manipulations of blood glucose levels by infusion of 10% dextrose or injection of 0.1U insulin SC did not interact with pimozide to alter the latter drug's inhibition of 34.2% sucrose sham feeding. Separate experiments verified that these manipulations significantly altered blood glucose levels compared to a control 0.9% saline infusion IV. Infusions of d-glucose into the lateral ventricle significantly enhanced the inhibitory effects of pimozide on 34.2% sucrose sham intake compared to infusions of!glucose or 2-deoxy-glucose. Infusions of d-glucose into the third ventricle, however, significantly attenuated the inhibitory effects of pimozide on 34.2% sucrose sham feeding compared to the control l-glucose infusions. These results collectively suggest that some postingestive cues, such as elevations in third ventricle glucose levels, are indeed capable of inhibiting the suppressive effects of pimozide on sucrose sham feeding. / Thesis / Master of Science (MSc)

Diet selection and self-medication are fundamental to the survival of all species. The abilities to choose healthy foods in response to past consequences are basic elements of evolution. This study explores self-medication regarding tannins both as a medication and as a dietary challenge. In the first study, sheep with natural parasite infections were offered a low quality supplement containing a dose of tannins considered to be therapeutic (medicine), while the control infected lambs received the same supplement without tannins (placebo). This study included a group of parasite-free lambs. The parasitized lambs ate more of the tannin containing supplement than non-parasitized lambs for the first 12 d of the study, when parasite burdens were high, but differences became smaller and disappeared towards the end of the study when parasite burdens decreased. This result indicated lambs ability to detect the presence of internal parasites and to learn to ingest tannin when followed by relief from parasite burdens.In the second study, lambs grazed on pastures with forages containing saponins (alfalfa),iiialkaloids (endophyte-infected tall fescue) and tannins (birdsfoot trefoil). I observed the foraging behavior of groups of lambs after intra-ruminal infusions of tannins (treatment). Lambs that first received intraruminal infusions of tannins and then were offered 2-way choices between varieties of forages with high and low concentrations of either saponins, alkaloids, or tannins increased their preference for the high-saponin variety of alfalfa and the high-alkaloid variety of tall fescue relative to lambs not infused with tannins (controls). Lambs infused with tannins and offered choices among the 3 forages with high concentrations of secondary compounds also manifested higher preference for the high-alkaloid variety of tall fescue than control lambs. In contrast, lambs infused with tannin reduced their preference for the high-tannin variety of birdsfoot trefoil.This research has implications for many situations where forages with secondary compounds are available but underutilized. Landscapes where such forages are available could be used effectively with little or no harm to livestock if medicinal forages or supplements are made available and offered as alternatives so animals can learn about their benefits of chemical complementarities among different plant species.