Comparative Biochemistry of the Pineal Gland

The pineal gland is biochemically very active. In mammals, ithas the unique capacity to synthesize the hormone melatonin(N-acetyl-5-methoxy-tryptamine). Although the synthesis of melatoninis confined mainly to the pineal gland of all vertebrates, theeyes and brains of amphibians and fish also can form melatonin.Melatonin is synthesized in the pineal as follows: tryptophan 5-hydroxy-tryptophan serotonin N-acetylserotonin melatonin.The final step is catalyzed by the enzyme, hydroxyindole-O-methyltransferase (HIOMT), which is highly localized in the pinealof all vertebrate species examined. The activity of HIOMT ischanged when animals are kept in constant darkness or light.In rats, highest HIOMT activity is present in constant darkness,while the reverse occurs in avian species. In mammals, informationabout lighting reaches the pineal via the retina inferior accessoryoptic tract preganglionic sympathetic fibers superior cervicalganglia postganglionic fibers pineal parenchymal cells. Lightingmessages reach the hen's pineal via a nonretinal pathway. Studieswith tissue culture indicate that noradrenaline liberated fromsympathetic nerves stimulates synthesis of melatonin. Thereare circadian rhythms in pineal serotonin content which areendogenous and abolished by removal of superior cervical gangliaor by decentralization. There is also a 24-hour rhythm in pinealnoradrenaline. This rhythm is exogenous and is abolished byblinding or cutting the inferior accessory optic tract.     

Correlations of Melatonin Content in Pineal Gland, Blood, and Brain of Some Birds and Mammals

Diurnal, rhythmic variation of melatonin content in the pinealgland, blood serum, and brain have been found in chickens, withgreater amounts present in all tissues during nighttime thanduring daytime. Similar daily rhythms appear to occur in thepineal gland and serum of rats and in the serum and urine ofhumans. It is proposed that these correlated fluctuations inmelatonin levels are causally related, elevated pineal contentresulting in increased melatonin content of the blood and increasedaccumulation by the brain. The brain of chickens, especiallythe hypothalamus, appears to accumulate melatonin and is probablya primary site of action of melatonin.     

Substrates of Energy Metabolism of the Pituitary and Pineal Glands

The capability of the neurohypophysis, the adenohypophysis, and the pineal gland to oxidize nonesterified fatty acids and glucose as energy sources was studied in vivo. Fed and 48-h-starved rats had catheters placed in their femoral vessels. After they became conscious, an intravenous injection of one of the following was given: [1-14C]acetate, [1-14C]octanoate, [1-14C]-palmitate, or [2-14C]glucose. After 5 min the rats were sacrificed. These metabolites produce [14C]acetyl-CoA within the mitochondria when they are oxidized as metabolic fuels. On passage through the Krebs cycle a considerable portion of the 14C is trapped in large amino acid pools closely associated with the Krebs cycle; the appearance of 14C in these amino acids was taken as evidence of oxidation. As expected, brain structures behind the blood-brain barrier (cerebral cortex and caudate) showed considerable labeling of Krebs cycle-associated amino acids in both nutritional states when [2-14C]glucose was the substrate. Surprisingly, however, no label was detected in amino acids of the neurohypophysis or the pineal gland in starved rats and very little in fed rats. On the other hand, 14C from acetate and palmitate was extensively incorporated into amino acids of the pineal gland and the neurohypophysis, while little 14C labeling was found in the cerebral cortex and the caudate. Octanoate, which passes the blood-brain barrier readily, labeled amino acids of all tissues. The experiments demonstrated conclusively that the neural structures studied, which have no blood-brain barrier, do not rely heavily upon glucose as a fuel for oxidative energy metabolism, in contrast to the rest of the brain. The results also showed that nonesterified fatty acids may supply at least some of their energy requirements.     

Gastrointestinal Bacteria of Certain Antarctic Birds and Mammals

An investigation was carried out of the aerobic gram-negative intestinal flora of 158 penguins, 30 skuas, and 66 seals from the Antarctic and sub-Antarctic zones and Phillip Island. Among penguins and seals, 17% and 11%, respectively, were devoid of aerobic enteric organisms, but microscopic examination showed the presence of other bacteria. The coliforms outnumbered the paracolons and nonlactosefermenting bacteria; irregular coliform types and Escherichia coli were predominant. The present study indicated the effect of diet on the composition of the intestinal flora of the birds and mammals examined.     

Role of the Pineal in the Circadian System of Birds

Pinealectomy of sparrows abolishes the free running rhythm oflocomotor activity in constant darkness. Without their pineals,sparrows still entrain to light-dark cycles and show other signsthat they retain part, but not all, of the circadian system.Interruption of either the neural input to the pineal or itsneural output, or both, does not abolish the free running rhythm.Rhythmicity can be restored to a pinealectomized bird by implantingthe pineal of a donor into the anterior chamber of its eye.A model of the circadian system controlling locomotor behavioris proposed to account for these facts. We suggest that theavian pineal contains a self-sustained oscillator, and as aconsequence, produces a rhythmic hormonal output. Circadianfluctuations of this hormone entrain a damped oscillator locatedelsewhere, which in turn drives the locomotor activity. Eachoscillator has separate access to environmental light cycles.The behavior of a pinealectomized bird is determined exclusivelyby its damped oscillator. It does not free run because it lacksthe self-sustained oscillator which, however, can be restoredby transplantation. The transplanted pineal continues its self-sustainedcircadian hormonal output which entrains the damped oscillatorand restores the system to its normal state.     

Heterogeneity of Glia in the Retina and Optic Nerve of Birds and Mammals

We have recently described a novel type of glial cell that is scattered across the inner layers of the avian retina [1]. These cells are stimulated by insulin-like growth factor 1 (IGF1) to proliferate, migrate distally into the retina, and up-regulate the nestin-related intermediate filament transitin. These changes in glial activity correspond with increased susceptibility of neurons to excitotoxic damage. This novel cell-type has been termed the Non-astrocytic Inner Retinal Glia-like (NIRG) cells. The purpose of the study was to investigate whether the retinas of non-avian species contain cells that resemble NIRG cells. We assayed for NIRG cells by probing for the expression of Sox2, Sox9, Nkx2.2, vimentin and nestin. NIRG cells were distinguished from astrocytes by a lack of expression for Glial Fibrilliary Acidic Protein (GFAP). We examined the retinas of adult mice, guinea pigs, dogs and monkeys (Macaca fasicularis). In the mouse retina and optic nerve head, we identified numerous astrocytes that expressed GFAP, S100β, Sox2 and Sox9; however, we found no evidence for NIRG-like cells that were positive for Nkx2.2, nestin, and negative for GFAP. In the guinea pig retina, we did not find astrocytes or NIRG cells in the retina, whereas we identified astrocytes in the optic nerve. In the eyes of dogs and monkeys, we found astrocytes and NIRG-like cells scattered across inner layers of the retina and within the optic nerve. We conclude that NIRG-like cells are present in the retinas of canines and non-human primates, whereas the retinas of mice and guinea pigs do not contain NIRG cells.     

Competition Among Insects, Birds and Mammals for Conifer Steeds

Species of at least 5 orders of insects, 6 families of birds,and 2 orders of mammals, in various combinations, can exploitthe cones and seeds of most species of conifers. Lodgepole pineis the exception to this pattern of broad taxonomic diversityof seed predators in that only pine squirrels and coreid bugsattack its serotinous cones. The contrast between lodgepolepine and other conifers demonstrates that large intrinsic variationin the abundance of a resource fosters the evolution of a broadrange of taxonomic groups to exploit the resource. The diversegroups'are limited by different predators and alternate resourceswhen conifer seeds independently decrease in abundance.     

Identifying Environmental Determinants of Diurnal Distribution in Marine Birds and Mammals

Marine birds and mammals move between various habitats during the day as they engage in behaviors related to resting, sleeping, preening, feeding, and breeding. The per capita rates of movement between these habitats, and hence the habitat occupancy dynamics, often are functions of environmental variables such as tide height, solar elevation, wind speed, and temperature. If the system recovers rapidly after disturbance, differential equation models of occupancy dynamics can be reduced to algebraic equations on two time scales. Identification of environmental factors that influence movement between habitats requires time series census data collected in both the absence and presence of disturbance.     

Effects of Methotrexate on Biopterin Levels and Synthesis in Rat Cultured Pineal Glands

Abstract: Culture of rat pineal glands in methotrexate (0.5, 5, or 10 μM) for 6 or 24 h did not alter pineal tetrahydrobiopterin (85–90% of total biopterin in cultured glands), except for a decrease of 30% after 24 h culture in 10 μM methotrexate. However, pineal dihydrobiopterin and/or biopterin (10–15% of total biopterin) was increased by methotrexate up to 2.5-fold. Biopterin detected in the culture medium following pineal culture was also increased to a similar extent after methotrexate treatment and appeared to represent leakage of pineal dihydrobiopterin and/or biopterin. Culture of glands in 5 μM methotrexate did not alter the conversion of [U-¹⁴C]-guanosine to [¹⁴C]biopterin, suggesting that pineal tetrahydrobiopterin synthesis was not altered by methotrexate. Complete inhibition of dihydrofolate reductase activity measured in pineal homogenates was obtained following culture of glands in all concentrations of methotrexate studied. Therefore, dihydrofolate reductase and dihydrobiopterin do not appear to be involved in a major biosynthetic pathway for pineal tetrahydrobiopterin from GTP, although they may have a minor role in tetrahydrobiopterin synthesis.     

Neopterin Retards Loss of Serotonin N-Acetyltransferase Activity from Cultured Chick Pineal Glands

Abstract: d -Neopterin at 10 μ M delayed start of the decline of serotonin N -acetyltransferase (NAT) activity from the peak level in the cycle exhibited by chick pineal glands cultured under standard conditions in the dark. A less marked retardation of decline of NAT activity was found with glands cultured under diurnal illumination or those exposed prematurely to light. There were no significant effects of neopterin on the increases of NAT activity or peak levels of activity developed. The pteridine also retarded loss of NAT activity from the peak level developed in the dark when the time of explanting into culture was later in the (solar) day, but not when it was earlier. Neopterin had no effect on the cycle in cyclic GMP content of cultured chick pineal glands.     

Independent Evolution of Transcriptional Inactivation on Sex Chromosomes in Birds and Mammals

X chromosome inactivation in eutherian mammals has been thought to be tightly controlled, as expected from a mechanism that compensates for the different dosage of X-borne genes in XX females and XY males. However, many X genes escape inactivation in humans, inactivation of the X in marsupials is partial, and the unrelated sex chromosomes of monotreme mammals have incomplete and gene-specific inactivation of X-linked genes. The bird ZW sex chromosome system represents a third independently evolved amniote sex chromosome system with dosage compensation, albeit partial and gene-specific, via an unknown mechanism (i.e. upregulation of the single Z in females, down regulation of one or both Zs in males, or a combination). We used RNA-fluorescent in situ hybridization (RNA-FISH) to demonstrate, on individual fibroblast cells, inactivation of 11 genes on the chicken Z and 28 genes on the X chromosomes of platypus. Each gene displayed a reproducible frequency of 1Z/1X-active and 2Z/2X-active cells in the homogametic sex. Our results indicate that the probability of inactivation is controlled on a gene-by-gene basis (or small domains) on the chicken Z and platypus X chromosomes. This regulatory mechanism must have been exapted independently to the non-homologous sex chromosomes in birds and mammals in response to an over-expressed Z or X in the homogametic sex, highlighting the universal importance that (at least partial) silencing plays in the evolution on amniote dosage compensation and, therefore, the differentiation of sex chromosomes.     

Maternal Testosterone and Offspring Sex-Ratio in Birds and Mammals: A Meta-Analysis

Sex allocation theory predicts that parents should bias offspring sex to maximize their fitness in a given context. Quantifying the fitness benefits of offspring sex-ratio biases would be facilitated by a better knowledge of their underlying mechanism(s) and associated costs. The hypothesis that steroid hormones are involved in sex determination has gained in popularity recently. Being influenced by external stimuli and involved in a range of physiological processes, they could be a ubiquitous mediator of environmental conditions influencing sex-ratio with low fitness costs. Previous studies indicated that higher maternal testosterone levels led to the overproduction of sons around conception in both birds and mammals. We conducted a systematic review (including meta-analysis) of these studies and, as predicted, we found a weak positive and significant overall effect of maternal testosterone on the proportion of sons. Neither taxa, nor the type of study (experimental/observational), or the timing of timing testosterone manipulation/measure were significant predictors of offspring sex-ratio, which may be explained by low statistical power in addition to low variability between effect sizes. Our meta-analysis provides evidence for a general positive influence of maternal testosterone around conception on the proportion of sons across birds and mammals, although less confidently so for the latter. It begs for more large-scale experimental studies, especially on mammals, and ideally in the wild. It may also have some important consequences for the poultry industry.     

Chlorpyrifos: Ecotoxicological Risk Assessment for Birds and Mammals in Corn Agroecosystems

A tiered risk assessment was conducted for the use of granular and liquid formulations of chlorpyrifos in corn agroecosystems in the U.S. The initial screening Tier I assessment suggested that under high-exposure scenarios the granular and some spray formulations present potential hazards to birds. Higher tiered probabilistic risk assessments were conducted separately for the granular and liquid formulations. The probabilistic assessment indicated that risk to birds from exposure to granular formulation is small and that this route of exposure would not be a significant source of mortality. Similarly, the assessment of potential exposure of birds to food items contaminated with chlorpyrifos showed that the risk from exposure via food was small, even if it was assumed that birds feed only on the treated fields. Although they have potentially greater sensitivity to chlorpyrifos, effects in nestling birds consuming food items from fields treated with granular chlorpyrifos were negligible. However, risks to young birds may be greater where the major source of food is from fields treated with liquid formulations of chlorpyrifos. A review of field studies showed that wildlife mortality incidents associated with use of either granular or liquid formulations of chlorpyrifos are not widely apparent in agroecosystems. Based on the multiple lines of evidence, we conclude that the presumption that chlorpyrifos use in corn agroecosystems will result in extensive mortality of terrestrial wildlife, particularly birds and mammals, is not supported by the scientific evidence.     

佛坪自然保护区食竹鸟兽种类的初步调查

1991~2004年采用检查死亡个体的胃或嗉囊内容物、新鲜粪便和在野外直接观察动物采食的3种方法,在陕西佛坪国家级自然保护区对食竹的鸟兽种类进行了初步调查。巴山木竹和秦岭箭竹是大熊猫采食的主要食物资源。除大熊猫外,采食这两种竹的鸟兽有38种,隶属6目14科,其中鸟类9种,兽类29种。大量采食、中等采食和少量采食竹类的物种分别为1种、5种和33种,所占比例分别为2.6%、12.8%和84.6%。39种鸟兽均采食竹笋,其中32种只采食竹笋。黑熊和野猪是食竹笋量比较大的大型兽类,羚牛、鬣羚和斑羚3种牛科动物全年都采食竹类,其中以羚牛对竹叶的采食量最大。这些食竹鸟兽一方面直接与大熊猫竞争食物资源,特别是竹笋,另外也会间接地影响大熊猫对竹类的利用。     

陕西屋梁山自然保护区鸟兽物种多样性初步研究

2005年对秦岭西段南坡的屋梁山自然保护区的鸟兽物种多样性进行了初步调查.在保护区内发现有166种鸟类和68种兽类.其中29种是中国特有种,37种是国家重点保护动物,21种鸟兽具有灭绝风险.在区系组成方面,南方动物区系占有优势,但鸟类的过渡性特征更明显.根据海拔和生境划分的三个垂直分布带,每个分布带鸟兽的多样性组成都不相同.基于对鸟兽物种多样性的评价,表明屋梁山保护区具有较高的保护价值.     

Social Mating System and Sex-Biased Dispersal in Mammals and Birds: A Phylogenetic Analysis

The hypothesis that patterns of sex-biased dispersal are related to social mating system in mammals and birds has gained widespread acceptance over the past 30 years. However, two major complications have obscured the relationship between these two behaviors: 1) dispersal frequency and dispersal distance, which measure different aspects of the dispersal process, have often been confounded, and 2) the relationship between mating system and sex-biased dispersal in these vertebrate groups has not been examined using modern phylogenetic comparative methods. Here, we present a phylogenetic analysis of the relationship between mating system and sex-biased dispersal in mammals and birds. Results indicate that the evolution of female-biased dispersal in mammals may be more likely on monogamous branches of the phylogeny, and that females may disperse farther than males in socially monogamous mammalian species. However, we found no support for a relationship between social mating system and sex-biased dispersal in birds when the effects of phylogeny are taken into consideration. We caution that although there are larger-scale behavioral differences in mating system and sex-biased dispersal between mammals and birds, mating system and sex-biased dispersal are far from perfectly associated within these taxa.