Genetically engineered "Supermice" (Mus musculus, transgenic strain Tg[MT-1,rGH],Bri2) possess multiple copies of rat growth hormone genes yielding growth rates 220% that of normal mice. To discover how Supermice alter their acquisition and allocation of resources under elevated costs of growth, a resource allocation study was conducted on forty 50-day-old normal and transgenic male mice. Individual dry mass budgets were used to compare rates of growth, consumption, faecal deposition, digestive assimilation, and respiration over 11-day intervals. The mean body mass of transgenic mice was 153% that of normal animals during this period. Surprisingly, on a mass-specific basis, Supermice consumed 6% less food despite their higher investment in growth (normal: 0.50 ± 0.01 mg food/mg dry body mass per day; Supermice: 0.47 ± 0.01 mg food/mg dry body mass per day). Assimilation efficiency was also slightly lower in Supermice (64.1%) than in normal animals (66.7%). Enhanced growth was achieved entirely through improved conversion efficiencies. Gross and net production efficiencies of Supermice were 227 and 244% those of controls, respectively. Such increased efficiencies appeared to be the result of diverting resources from processes such as behaviour, longevity assurance, and other respiratory demands. Evidence for such trade-offs supports the "principle of allocation," a key assumption for theories of life-history evolution.

Lifetime reproduction of female transgenic rat growth hormone (TRrGH) mice and their normal siblings was evaluated on a high-protein (38%) diet, a standard diet (23% protein), and the standard diet supplemented with sucrose cubes. Compared with those on the standard diet, normal mice fed the high-protein diet showed significant increases in litter size, number of litters, and lifetime fecundity. Number of litters and lifetime fecundity were also enhanced in normal mice fed sucrose. TRrGH mice showed no significant improvements in reproduction on the high-protein diet, but they were significantly smaller. Sucrose dramatically improved reproduction of TRrGH mice, with no reduction in mature mass. The percentage of fertile TRrGH mice increased from 45% on standard chow to 71% with sucrose. The number and size of litters of TRrGH mice also significantly increased with sucrose, mean lifetime fecundity doubling from 9 pups on standard food to 18 pups on sucrose. However, TRrGH mice did not attain the reproductive success of normal mice on any diet. These results suggest that TRrGH mice are energetically stressed by enforced channelling of energy into growth. An immense literature addresses infertility due to energy limitation and stress generally. We synthesize these aspects with growth hormone transgenesis to derive an integrated view of neuroendocrine energy regulation relevant to restoring fertility of transgenic GH animals.

Sleep is required for the consolidation of memory for complex tasks, and elements of the growth-hormone (GH) axis may regulate sleep. The GH axis also up-regulates protein synthesis, which is required for memory consolidation. Transgenic rat GH mice (TRGHM) express plasma GH at levels 100-300 times normal and sleep 3.4 h longer (30%) than their normal siblings. Consequently, we hypothesized that they might show superior ability to learn a complex task (8-choice radial maze); 47% of the TRGHM learned the task before any normal mice. All 17 TRGHM learned the task, but 33% of the 18 normal mice learned little. TRGHM learned the task significantly faster than normal mice (p < 0.05) and made half as many errors in doing so, even when the normal nonlearners were excluded from the analysis. Whereas normal mice expressed a linear learning curve, TRGHM showed exponentially declining error rates. The contribution of the GH axis to cognition is conspicuously sparse in literature syntheses of knowledge concerning neuroendocrine mechanisms of learning and memory. This paper synthesizes the crucial role of major components of the GH axis in brain functioning into a holistic framework, integrating learning, sleep, free radicals, aging, and neurodegenerative diseases. TRGHM show both enhanced learning in youth and accelerated aging. Thus, they may provide a powerful new probe for use in gaining an understanding of aspects of central nervous system functioning, which is highly relevant to human health.

Lifetime consumption rates of male transgenic growth hormone (GH) mice and normal controls were measured on either a 38% protein diet (HP), the standard rodent diet (STD) (23.5% protein), or the standard diet supplemented with a free choice of sucrose (CARB). On STD, daily intake of normal mice increased little at sizes greater than 20 g, but larger transgenic mice ate progressively more. Both kinds of mice showed declining daily mass-specific consumption with increasing age. Transgenic mice consistently ate 13.3% less food than normal mice on a mass-specific basis across all ages. On the self-selective CARB diet, normal mice exhibited increasing age-specific daily consumption, whereas transgenic mice exhibited a trend towards age-related decline in mass-specific feeding that proved significant on the basis of body mass. Transgenic mice ingested more sucrose than standard chow and this did not vary with age. In contrast, normal mice ate less sucrose than chow and chose a declining proportion of sucrose with age. Transgenic and normal mice showed a unitary relationship of daily intake of HP in relation to body mass, resulting in constant mass-specific feeding across all ages. Transgenic GH animals, including livestock, show numerous defects that we have attributed to relative energetic stress associated with excessive allocation to lean growth. This is exacerbated by failure to offset increased demands of growth by increasing mass-specific feeding. Results presented here document altered feeding regulation in transgenic GH mice and suggest underlying mechanisms.Résumé : Les taux de consommation durant toute la vie ont été mesurés chez des mâles de souris à hormone de croissance (GH) transgénique soumises à un régime alimentaire contenant 38% de protéines (HP), à un régime standard de rongeur (STD) contenant 23,5% de protéines ou à un régime standard additionné de sucroses au choix (CARB). Au régime STD, la consommation chez les souris normales augmente peu aux tailles supérieures à 20 g, mais les souris transgéniques plus grosses augmentent progressivement leur consommation de nourriture. Les souris des deux types diminuent leur consommation quotidienne de nourriture en fonction de leur masse à mesure qu'elles vieillissent. Les souris transgéniques mangent 13,3% moins de nourriture par unité de masse à tout âge. Au régime CARB, les souris normales augmentent leur consommation quotidienne en fonction de leur âge, alors qu'en vieillissant, les souris transgéniques ont tendance à diminuer significativement leur consommation quotidienne de nourriture par unité de masse. Les souris transgéniques consomment plus de sucroses que de moulée standard, une tendance qui ne varie pas avec l'âge. En revanche, les souris normales consomment moins de sucroses que de moulée et, en vieillissant, intègrent une proportion progressivement moins grande de sucrose dans leur régime. Chez les souris des deux types, il y a une relation unitaire entre la consommation quotidienne de protéines et la masse corporelle, ce qui résulte en une ali...

Case-based teaching and learning strategies can offer instructors effective pedagogical tools to scaffold student learning through activities designed to fulfill teaching objectives and desired student learning outcomes. In science disciplines, programs strive to impart knowledge in addition to providing students environments through which they can learn through collaboration. Case-based studies can effectively expose students to the process of science and encourage them to work through facts, analyze data, formulate solutions, draw conclusions, and predict consequences. Despite the versatility of case studies as teaching and learning tools, many factors influence their implementation in a given teaching environment. Inasmuch, the manner in which they are used is typically dependent upon specific teaching and learning objectives and the historical context of the course (e.g., student enrolment, year of instruction, lecture vs. lab vs. tutorial settings). In this article, we discuss two novel approaches for case-based teaching and learning in Biology as a means to convey lecture content, encourage students to apply fundamental concepts taught in lectures, while exposing them to the process of science in a dynamic environment.