不同能量水平日粮对中卫山羊瘤胃内环境指标的影响

瘤胃液pH值是反映反刍动物瘤胃内环境是否适宜和稳定的最主要的指标之一,瘤胃液 pH值的高低在很大程度上受饲料中碳水化合物的种类、采食量以及降解速率的影响,不同种类和不同结构的碳水化合物在瘤胃中的发酵速率和发酵结果是不同的 .通常非结构性碳水化合物(如淀粉、蔗糖和果胶等)的发酵速率较快,而结构性碳水化合物的发酵速率较慢.除提供能量外,挥发性脂肪酸(Volatile fatty acids, VFA)中的丙酸还是反刍动物体内葡萄糖合成的主要前体物,而乙酸和丁酸则是反刍动物体内脂肪合成的主要前体物.本试验采集试验瘘管羊的瘤胃液,分析不同能量水平日粮对中卫山羊瘤胃液pH,NH3-N和VFA的影响,为制定中卫山羊饲养标准提供依据.     

Skin-pigment regulation of vitamin-D biosynthesis in man

The known correlation between the color of human skin and latitude (Fig. 2) is explainable in terms of two opposing positive adaptations to solar ultraviolet radiation, weak in northern latitudes in winter yet powerful the year around near the equator. In northern latitudes there is selection for white skins that allow maximum photoactivation of 7-dehydrocholesterol into vitamin D at low intensities of ultraviolet radiation. In southern latitudes, on the other hand, there is selection for black skins able to prevent up to 95 percent of the incident ultraviolet from reaching the deeper layers of the skin where vitamin D is synthesized. Selection against the twin dangers of rickets on the one hand and toxic doses of vitamin D on the other would thus explain the world-wide correlation observed between skin pigmentation and nearness to the equator.     

Behavioral maintenance of high concentrations of blood ethanol and physical dependence in the rat

Rats maintained on an intermittent food schedule with an available ethanol solution drink to excess (13.1 grams of ethanol per kilogram of body weight, daily). Removal of ethanol produces symptoms of physical dependence including death from tonic-clonic seizures. Overindulgence in oral self-administration of an aqueous ethanol solution, resulting in unequivocal physical dependence, approximates a model of human alcoholism.     

Corticosterone regulation of tryptophan hydroxylase in midbrain of the rat

The tryptophan hydroxylase activity in the rat midbrain decreases after adrenalectomy and is restored by treatment with corticosterone. Cycloheximide, adminiistered intracisternally, prevents the restoration of the enzyme activity by corticosterone. Cycloheximide administration to adrenalectomized rats resutlts in a further decrease in the enzyme activity. an indication that the enzyme has a rapid turnover even in the absence of corticosterone.     

Behavioral measurement of neural poststimulation excitability cycle: pain cells in the brain of the rat

A new technique in which elicited behavior of the freely moving rat is used to measure the poststimulation excitability cycle of the central neurons mediating that behavior has been adapted from accepted methods of neurophysiology. A continuous train of pairs of brief pulses was delivered to pain systems in the midbrain. Rate of lever pressing to achieve 3-second rests from this stimulation was measured as a function of the interval separating the pulses within pairs. Evidence for latent addition, absolute refractory period, temporal summation, and adaptation was demonstrated. Obtained relationships suggested that three sets of fibers may carry the aversive signal and that synaptic integration of pain in the brain may be related to Stevens' power law functions.     

Hepatic microsomal enzymes in man and rat: induction and inhibition by ethanol

The feeding of ethanol increased significantly the activities of hepatic pentobarbital and benzpyrene hydroxylases in rats, and, in human volunteers, doubled pentobarbital hydroxylase activity. In vitro ethanol inhibited aniline, pentobarbital, and benzpyrene hydroxylases. These data may explain, at least in part, the increased tolerance of alcoholics to sedatives when sober, and the enhanced sensitivity to sedatives when inebriated.     

Hormonal regulation of gonadotropin receptors and steroidogenesis in cultured fetal rat tests

Gonadotropic activation of the adult rat testis in vitro and in vivo is followed by down-regulation of luteinizing hormone receptors and decreased androgen responses to subsequent hormonal stimulation. In contrast, treatment of cultured fetal testes with gonadotropins and dibutyryl adenosine 3',5'-monophosphate enhanced steroidogenic responsiveness and did not cause the luteinizing hormone-receptor loss and desensitization that is characteristic of the adult gonad. The analysis of gonadotropin receptors and action in cultured fetal testis cells facilitates developmental studies of gonadal function, and has revealed significant differences in the responses of fetal and adult Leydig cells to gonadotropic regulation.     

Dietary regulation of galactose-metabolizing enzymes: adaptive changes in rat jejunum

The effects of dietary galactose, sucrose, fructose, glucose, casein, and fasting upon the activity of four galactose-metabolizing enzymes (galactokinase, galactose-1-phosphate uridyltransferase, uridine diphosphate galactose 4-epimerase, and galactose dehydrogenase) were studied in the jejunum of rats. Galactose produced the greatest increase in enzyme activity, fructose and sucrose produced effects intermediate between galactose and glucose, and casein produced a greater activity increase than fasting, but less than the sugars.     

Behavioral phylogenies and the direction of evolution

A model for using mate preference data to deduce the direction of evolution between populations related by founder events or population bottlenecks is examined. Data from a wide range of organisms satisfying the necessary constraints of population structure are compatible with the model developed by K. Y. Kaneshiro from studies of Hawaiian Drosophila.     

Recurrent herpes in the rabbit and man

Herpesvirus was present in secretory glands and frequently in tears of rabbits with recurrent herpetic keratitis even in the absence of corneal lesions. In normal people, herpesvirus could be cultured from saliva and tears. Chronic virus multiplication in structures such as the lacrimal and salivary glands, rather than latency, may cause recurrent herpetic disease.     

Radiation and the sex ratio in man

An analysis of new data concerning the sex of children born to the survivors of the atomic bombings of Hiroshima and Nagasaki, together with a reanalysis of the data previously presented by Neel and Schull (9), reveals significant changes in the sex ratio of these children, changes in the direction to be expected if exposure had resulted in the induction of sex-linked lethal mutations (16).     

Otolithic membranes of the saccule and utricle in man

The otolithic membranes of the human saccule and utricle can be prepared as whole mounts or surface specimens for microscopic examination. They are not simple, homogeneous, gelatinous structures as heretofore described. Instead, each shows a definite and characteristic fibrillar design, which appears to be correlated with the known cytoarchitectural pattern of the underlying neuroepithelium.