Recent anatomical investigations have revealed that the striatum is an intrinsically heterogeneous structure that forms multiple parallel circuits with different cortical areas. The present series of experiments investigated the possibility that such anatomical diversity may promote functional differences between subregions of the rat dorsal striatum. Using different versions of the water maze and radial arm maze tasks, evidence is presented showing that the medial and lateral subregions of the caudate-putamen make distinct contributions to behaviors guided by either ambient spatial or discrete cues. The findings support a multiple subsystems view of dorsal striatal function. Specifically, the lateral (sensorimotor-innervated) caudate-putamen may mediate the process of habit formation based on simple stimulus-response associations, whereas the medial (limbic-innervated) caudate-putamen may contribute to the cognitive/spatial control of behavior in competitive response situations. Further evidence is presented suggesting that the medial caudate-putamen is functionally related to the hippocampal system. Together, these structures may form a functional limbic circuit that mediates the serial processing of cognitive/spatial information.

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The effect of melatonin, a hormone that triggers biological rhythms, was examined in relation to food intake and macronutrient selection. Wistar rats (n = 48) of both sexes were divided into 3 groups and offered a simultaneous choice of 2 diets: a carbohydrate-rich diet and a protein-rich diet, with a different type of carbohydrate and protein in each of the groups. Increased short- (4h post-injection) and long-term (12h post-injection) nocturnal total food intake was found following intraperitoneal administration of melatonin (10 000 and 15 000 pg/ml blood) at dark onset. Melatonin increased short-term carbohydrate-rich diet intake similarly across sensory contrasting diets (dextrin/cornstarch, cornstarch, and sucrose/cornstarch) and genders. However, melatonin caused an inconsistent increase in protein-rich diet intake across the various diets (casein, soy isolate, and egg protein) and genders. In conclusion, melatonin favors carbohydrate intake at the beginning of the activity period, and may act as a time indicator that provides a night signal.

Graduation date: 1938

The experiments reported in this thesis attempted to examine the influence of thirst on the extinction of taste aversions in rats. Differences in the amount of stimulus exposure and deprivation state between groups were controlled for. The first experiment presented two novel flavours twelve times to rats when either thirsty or sated. A preference for the flavour presented when thirsty was established. The next three experiments examined whether this preference would accelerate the extinction of a taste aversion, by first pairing a novel flavour with lithium and then presenting the conditioned flavour when rats were either sated or thirsty. No evidence of accelerated extinction was found. The final two experiments examined whether the associatively-activated representation of sucrose could function to extinguish a taste-aversion to that sucrose without presenting sucrose itself. No evidence of representation-mediated extinction was found despite evidence that the context was associated with sucrose. The results indicate that the extinction of conditioned taste aversions is not influenced by counter-conditioning due to thirst relief, and extinction of such aversions appears to be due to similar processes as other forms of conditioning.

Thesis (M.S.)--University of Akron, Dept. of Biology, 2007. / "December, 2007." Title from electronic thesis title page (viewed 02/27/2008) Advisor, Bruce Cushing; Co-Advisor, Ronald Salisbury; Faculty reader, Monte Turner; Department Chair, Bruce Cushing; Dean of the College, Ronald F. Levant; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.