Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains x, 78 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 71-78).

abstract: The failure to withhold inappropriate behavior is a central component of most impulse control disorders, including Attention Deficit Hyperactivity Disorder (ADHD). The present study examined the effects of housing environment and methylphenidate (a drug often prescribed for ADHD) on the performance of rats in two response inhibition tasks: differential reinforcement of low rate (DRL) and fixed minimum interval (FMI). Both tasks required rats to wait a fixed amount of time (6 s) before emitting a reinforced response. The capacity to withhold the target response (volitional inhibition) and timing precision were estimated on the basis of performance in each of the tasks. Paradoxically, rats housed in a mildly enriched environment that included a conspecific displayed less volitional inhibition in both tasks compared to rats housed in an isolated environment. Enriched housing, however, increased timing precision. Acute administration of methylphenidate partially reversed the effects of enriched housing. Implications of these results in the assessment and treatment of ADHD-related impulsivity are discussed. / Dissertation/Thesis / M.A. Psychology 2011

Lever pressing was maintained by a concurrent token production schedule in rats. Token deliveries (i.e., ½" steel ball bearings) were assigned probabilistically to the right or left lever (on 1:3 or 1:9 ratio for Experiment 1 and 1:6 ratio for Experiment 2). The location of the rich lever remained constant within session, but varied across daily sessions according to a pseudorandom binary sequence. Once assigned to a lever, token delivery was arranged by a random interval 15 s schedule. Transition to token exchange was determined by varying exchange-production schedules that varied after each condition (FR 1 for Experiment 1; and RR 2, FR 2, RR 3, and FR 4 for Experiment 2). During token exchange, depositing a token in the receptacle was reinforced with access to sweetened condensed milk. The generalized matching law provided an adequate description of the session wide ratio of left to right lever presses, detecting considerable undermatching across all conditions. Sensitivity to the token ratios were best described by the current session's reinforcement ratio in comparison to the prior two session's reinforcement ratios. One of four subjects showed increased response rates across successive token deliveries in the exchange-production schedule while the remaining subjects showed the opposite effects of decreased response rates as tokens were earned. Similarly, sensitivity to token-production ratios increased across successive token deliveries for one of four subjects. Differences between subjects can be explained by the duration of elicited sign tracking of tokens, measured by duration of postreinforcement pausing and direct observation of rats during sessions.

The distributional range of the Tete veld rat, Aethomys ineptus, extends from the Limpopo Province in the north through to the south of KwaZulu Natal. The Tete veld rat is a seasonal breeder, with the breeding period confmed to the wet summer months of the year in the Gauteng Province of South Africa. The seasonality of reproduction in the Tete veld rat is confirmed by reproductive tract morphometrics, ovarian histology, plasma progesterone, and oestradiol-17β in females, and testicular histology and plasma testosterone concentrations in males. The presence of some spermatogenic activity and spermatozoa in the epididymides, as well as some follicular activity and raised circulating progesterone, and oestradiol-17β concentrations in some females during winter intimates that the Tete veld rat is possibly an opportunistic breeder. Reproduction during winter is presumably restricted by food availability and adverse winter conditions. The Namaqua rock mouse, Aethomys Namaquensis, on the other hand is widely distributed in the southern African subregion. Reproductive tract morphometrics, ovarian histology, plasma progesterone and oestradiol-17β in females, and testicular histology, seminiferous tubule diameters and plasma testosterone concentrations in males confirm that the Namaqua rock mouse is a strictly seasonal breeder. The breeding period starts in October and extends to the end of February. The absence of Graafian follicles, corpora lutea, corpora albicans, corpus hemorrhagicum, lower plasma progesterone and oestradiol concentrations in females, and small seminiferous tubule diameters, and lower testosterone concentrations during winter months suggest that reproduction is completely inhibited during this period of the year. Photoperiodic responsiveness was determined in both the Tete veld rat and the Namaqua rock mouse by exposing the animals to long day (LD) and short day (SD) lengths. Testicular mass expressed against body mass, testicular volume, and seminiferous tubule diameters were significantly larger and plasma testosterone concentrations were significantly higher in males subjected to a long day photoperiod than in males exposed to a short day. These fmdings suggest that both species are photoperiodically responsive and that photoperiod could potentially play a role in reproduction in both the Tete veld rat and the Namaqua rock mouse. In conclusion, the results in this study suggest that the Tete veld rat is a seasonal breeder with the breeding period confined to the rainy summer months in South Africa. The breeding season starts in October and extends to April. Reproduction in the Tete veld rat appears to involve photoperiod. The Namaqua rock mouse is a strictly seasonal breeder with a breeding period occurring between October and the end of February. Breeding during the winter months is completely inhibited. The Namaqua rock mouse may also utilize photoperiod to initiate reproductive events. / Dissertation (MSc)--University of Pretoria, 2006. / Zoology and Entomology / Unrestricted

A comparison has been made of the formate-C¹⁴ incorporation into the nucleic acid purines and thymine of regenerating rat liver and Novikoff hepatoma in vivo. The effects of these tissues on one another, and on the host tissues has been studied. The utilization of formate by the nucleic acids of Novikoff hepatoma and regenerating rat liver was not significantly altered in animals containing both of these rapidly dividing tissues. The results indicated that the demand for formate by one of the rapidly growing tissues did not lower the uptake of formate by the nucleic acids of the other tissue. Furthermore it was indicated that nucleic acid synthesis in regenerating liver did not alter the synthesis of nucleic acids in other tissues. Regenerating liver and Novikoff hepatoma had no effect on the nucleic acid metabolism of the host tissues of animals bearing one or both of these tissues. These results are not completely in agreement with those reported in the literature. In a preliminary experiment a radioactive suspension of Novikoff hepatoma was transplanted into rats. Twenty percent of the injected radioactivity was recovered in the urine during the first 24 hours of tumor growth. The specific activities of the nucleic acid bases of the tumor, obtained after 24 hours of growth, were negligible. These findings indicated that the nucleic acids of the donor tumor suspension were not utilized in the synthesis of the nucleic acids of the growing tumor. / Medicine, Faculty of / Biochemistry and Molecular Biology, Department of / Graduate

Young Wistar female rats weaned at 25 days were placed on a control diet, or a diet extremely deficient in phosphorus but adequate in all other respects. After five weeks on the diet they were injected with 10 microcuries of high specific activity radiocalcium. The animals were killed at varying periods after injection and samples of bone, teeth and soft tissues were taken for chemical, radio-isotope, and histological analysis. The phosphorus deficient animals showed a marked demineralization of the skeleton, lower radiocalcium uptake by bone and higher radiocalcium uptake by the teeth. The accretion and resorption rate of bone in the phosphorus deficient animals was markedly reduced. The resorption rate, however, was higher than the accretion rate and accounted for the reduced mineralization of the bone. The femur of the rachitic animal had an exchangeable calcium portion of 13% as compared to 4-8% in the control animal. The teeth of the phosphorus deficient animal showed a reduced accretion and attrition rate, and a statistically evident difference in the chemical calcium and phosphorus content. The accretion rate was higher than the attrition rate, so that the teeth remained well mineralized. The depression of the accretion rate was not as marked as that observed in the bone, therefore, the marked demineralization of the rachitic animals' bones was not evident in the teeth. The serum plasma levels for calcium and phosphorus were 9.43 mg.% and 2.86 mg.% in the rachitic animal and 9.91 mg.% and 7.24 mg.% in the control animal. The disappearance of plasma radiocalcium was not as rapid in the rachitic animals. Starvation of phosphorus deficient animals resulted in a lower plasma calcium and raised plasma phosphorus level similar to that observed in parathyroidectomized animals. The soft tissue calcium concentration in the rachitic animals as compared to the control animals was higher for all soft tissues examined with exception of the kidney and blood plasma where there was no significant difference. The amount of calcium in the various muscle compartments was calculated. The rachitic animal had a higher intra-cellular calcium concentration and the same extra-cellular concentration when compared with the control animal. There was no difference in the phosphorus concentration of the control and rachitic animals' soft tissues. Histological studies of the femur of the rachitic and control animal showed that the rachitic femur had a wider epiphyseal cartilage which was not uniform in width. The bone trabeculae showed wide irregular seams of uncalcified osteoid matrix. Histological and calcium analysis of the kidneys of the phosphorus deficient animals showed no evidence of calcium deposits or nephrocalcinosis. Histological studies of the parathyroid glands of rachitic animals showed a decrease, in the volume of the glands, in the size of the nuclear surface, and in the amount of cytoplasm present, when compared to the glands of the control animals. This study of calcium kinetics in the phosphorus deficient animal coupled with the histological findings shows the possibility that phosphorus deficiency in rats produces a hypoparathyroid condition as a homeostatic mechanism to conserve phosphorus for the soft tissues. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

The purpose of the present investigation was to study the effect of prolonged protein-calorie malnutrition on intestinal disaccharidase activities and on disaccharide absorption, as carbohydrate intolerance is a major problem in children suffering from protein-calorie malnutrition. Four groups of rats (90 to 120 grams) were fed the following diets for 8 to 9 weeks: control (18% lactalbumin, 66% carbohydrate); low protein low carbohydrate (0.5% lactalbumin, 66% carbohydrate); low protein high carbohydrate (0.5% lactalbumin, 83.5% carbohydrate); and low protein restricted (1% lactalbumin, restricted to 4 grams per day). After 8.5 weeks, part of the group on the 0.5% lactalbumin low carbohydrate diet was fed the control diet (18% lactalbumin, 66% carbohydrate) for 8 weeks. At the end of the feeding period, the following assays were performed: 1) in vivo absorption of radioactive (¹⁴C) lactose, sucrose, and maltose; 2) activities of intestinal lactase, sucrase, and maltase; 3) plasma albumin concentrations; and 4) mucosal protein concentrations. In the three protein deficient groups (0.5% lactalbumin low carbohydrate, 0.5% lactalbumin high carbohydrate, and 1% lactalbumin), the activity of both the jejunal and ileal disaccharidases and the absorption of lactose, sucrose and maltose were significantly higher when compared with the controls. The jejunal sucrase and maltase activities were significantly higher in the 0.5% lactalbumin high carbohydrate group than in the 0.5% lactalbumin low carbohydrate group, but the absorption of lactose, sucrose and maltose were alike. When the 1% lactalbumin (restricted to 4 grams per day) and the 0.5% lactalbumin low carbohydrate groups were compared, there were no statistically significant differences in the specific activities of the intestinal disaccharidases or the absorption of the disaccharides. The absorption of lactose, sucrose, or maltose were similar in the controls and the protein repleted group. The disaccharidase activities were also similar in these two groups except for a significant depression of jejunal maltase and ileal sucrase and maltase activities in the protein repleted group. Therefore, these results indicate that protein deprivation in rats for 8.5 weeks causes an increase in specific activities of the intestinal disaccharidases in both the jejunum and ileum, and that these changes caused by protein depletion may be reversed by feeding a diet high in protein. Also, an increase in the carbohydrate content of the protein deficient diet results in an induction of jejunal sucrase and maltase activities. The high specific activity of the intestinal disaccharidases following protein-calorie malnutrition may be in part due to a preferential loss of structural proteins rather than to an increase in enzymatic protein in the intestinal mucosa. The increase in the disaccharidase activities in the protein deficient rats is accompanied by an increase in disaccharide absorption which could be due to the higher levels of disaccharidases or to an increase in the transport of the constituent monosaccharides. The demonstration of statistically significant differences in sucrase and maltase activities between the 0.5% lactalbumin high carbohydrate and the 0.5% lactalbumin low carbohydrate groups without a concomitant increase in sucrose and maltose absorption, supports the view that the higher absorption of sucrose and maltose in the protein deficient rats is a result of increased monosaccharide transport. The results of this study are not consistent with the suggestion that protein-calorie malnutrition is responsible for disaccharide intolerance in children. / Land and Food Systems, Faculty of / Graduate

Experiments were carried out to investigate the extent to which habituation of the flexor reflex depended on mechanisms operating at spinal interneurones. An attempt was made to cause selective degeneration of interneurones in the spinal cord of the rat by subjecting the cord to a period of ischaemia. Ischaemia was produced by temporary occlusion of the thoracic aorta. The flexor withdrawal reflex was tested 3, 7 or 14 days after occlusion. When compared with data from control animals it was found that ischaemia had resulted in both a qualitative change and a quantitative diminution in the amount of habituation which occurred during the presentation of 400 uniform stimuli. It was concluded that this impairment of the habituation process was a consequence of degeneration of interneurones which normally cause progressive inhibition of the excitatory flexor reflex pathway. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

Hyperplasia was induced by physical and chemical means. The resulting goitres were examined by electron microscopy, and the basement membranes were analyzed by stereological methods. The basement membrane in experimental colloid goitre was found to be significantly thinner than its control. A consideration of the course of the various goitres and of the chemical nature of basement membranes leads to the conclusion that the thinning of the basement membrane was the result of stretching. / Science, Faculty of / Zoology, Department of / Graduate

The histochemical localisation of ATPase enzymatic activity at the level of the electron microscope was carried out on adult and newborn kidney tissue pre-fixed in 5% glutaraldehyde buffered with 0.1 M sodium cacodylate. Both the lead method at pH 7.2 and the calcium method at pH 9.4 were used. The effects of the modifiers PHMB and L-cysteine were also studied. In the adult rat kidney, the observations of other investigators on kidney ATPase activity were substantiated. Reaction precipitate was localised at the brush border of the proximal tubules, the membranes of the basal and lateral interdigitations of the proximal and distal tubules, and the plasma membranes of the podocytic foot processes. PHMB exerted an inhibitory effect on distal tubular activity at both pH 7.2 and pH 9.4, while cysteine was inhibitory only at pH 9.4. Glomerular ATPase activity was inhibited by PHMB and L-cysteine at pH 9.4. In the newborn rat kidney, ATPase enzymatic activity was observed in the tubular elements as well as in the glomeruli. In the undifferentiated tubules, reaction product was abundant on the lateral membranes between individual cells. The luminal and basal plasma membranes, which were simple in contour, showed little or no accumulation of precipitate. However, as the microvilli became long and slender in the early stages of the differentiation of the brush border, there was a concomitant increase in the intensity of the ATPase enzymatic reaction. Similarly, reaction product became associated with the developing basal interdigitations. In the immature glomerulus, reaction precipitate was most often observed where two sets of membranes were in apposition. With differentiation, enzymatic activity was localised primarily on the podocytic foot processes. The localisation of ATPase activity at pH 9.4 was found to be influenced by the time of pre-fixation in glutaraldehyde while ATPase activity at pH 7.2 was not affected. At pH 7.2, neither tubular nor glomerular ATPase enzymatic activity responded to PHMB or L-cysteine. For both adult and newborn kidneys, the correlation between structure and function was briefly considered. The adult kidney is an important and efficient homeostatic organ. In urine formation various substances are transported across the cell membranes of the glomeruli and tubules. Ultrastructurally, the glomeruli and tubules show modifications characteristic of cells engaged in active transport processes. There is a large increase in plasma membrane surface area, as exemplified by the intricate inter-digitations of the podocytic foot processes, the elaborate basal and lateral infoldings, and the brush border of the proximal tubules. Much ATPase activity was found associated-with these plasma membranes. The newborn kidney is not as efficient as the adult kidney in maintaining body homeostasis. It is not only functionally but also morphologically immature. Most of the tubules and glomeruli are undifferentiated and do not show specialisations of the plasma membranes as seen in the adult kidney. There is also a relatively smaller amount of ATPase present in the newborn kidney. For both adult and newborn kidneys, it was postulated that at least two types of ATPases with different pH optima are present on the plasma membranes of the tubules and glomeruli. / Medicine, Faculty of / Graduate