Comparative view of pineal gland morphology of nocturnal and diurnal birds of tropical origin

Although having a similar developmental pattern, the pineal gland of tropical birds varies in shape, size, and morphology, probably more than any other part of the avian brain. Following the old classification, we noted a solid follicular (transitional) type of the pineal gland in the nocturnal bird Athene brama, and a tubulo-follicular and elongated tubular types of pineal gland in diurnal birds Perdicula asiatica and Euroloncha punchulata, respectively. Detailed light (LM) and electron microscopic (EM) studies of the pineal gland from these tropical birds revealed the presence of a well-developed, functionally active gland in nocturnal birds (contrary to reports available until now). Unlike diurnal birds, the nocturnal bird A. brama has no deep pineal in the posterior region (near the habenular commissure). It could be that the deep encephalic receptors have no/fewer functions in nocturnal birds. At present, we were unable to define the significance of deep pineal in these tropical avian species. A notable difference in the proximodistal orientation of intrapineal follicles and parenchymatous cells was noted among these birds due to different habitats. Ultrastructurally, the pinealocytes exhibited great similarities in terms of secretory organelles, except for the presence of some peculiar membranous structure in E. punchulata. The pinealocytes have rudimentary photoreceptive features (e.g., outer segment) along with cytoplasmic organelles for secretory activity, suggesting both photosensory and photosecretory types of function. The present study also suggests more heterogenicity in pineal gland morphology (cellular architecture) among diurnal birds than the nocturnal one.     

Sensory and endocrine characteristics of the avian pineal organ

The avian pineal organ represents a transitional type between a photosensory organ of lower vertebrates and the endocrine gland of mammals and shows remarkable changes in its innervation and structure during ontogeny. In the avian pineal organ the progressive reduction of the pinealofugal component and the spectacular increase in pinealopetal sympathetic innervation occur in parallel. In domestic fowl the number of intrapineal AChE-positive (afferent) neurons decreases rapidly during ontogenetic development, whereas the sympathetic innervation becomes more prominent. Furthermore, the end vesicle of the pineal organ is an anatomical entity fully separated from the brain in the adult domestic fowl, as observed in some mammalian pineals. The avian pineal organ contains several types of photoreceptors with different photopigments and the synthesis of melatonin, the pineal hormone, is controlled by light. Immunoreactivity for photopigments is reduced during the posthatching development of chicken, whereas neuron-specific enolase (NSE)-immunoreactive pinealocytes increase remarkably in number in the end-vesicle of the domestic fowl with age, followed by a gradual expansion toward the proximal portion. NSE is the most acidic isoenzyme of the glycolytic enzyme enolase and is useful as a cytoplasmic marker of neurons and neuroendocrine tissue. The above-mentioned findings reflect the sequence of changes leading from pineal sense organs to pineal gland. The demonstration of melatonin receptors in a variety of avian peripheral tissues suggest a possible direct action of melatonin on the physiological functions of different organ systems in response to internal and external stimuli.     

Development and spatial organization of the air conduits in the lung of the domestic fowl, Gallus gallus variant domesticus

We employed macroscopic and ultrastructural techniques as well as intratracheal casting methods to investigate the pattern of development, categories, and arrangement of the air conduits in the chicken lung. The secondary bronchi included four medioventral (MVSB), 7-10 laterodorsal (LDSB), 1-3 lateroventral (LVSB), several sacobronchi, and 20-60 posterior secondary bronchi (POSB). The latter category has not been described before and is best discerned from the internal aspect of the mesobronchus. The secondary bronchi emerged directly from the mesobronchus, except for the sacobronchi, which sprouted from the air sacs. Parabronchi from the first MVSB coursed craniodorsally and inosculated their cognates from the first two LDSB. The parabronchi from the rest of the LDSB curved dorsomedially to join those from the rest of the MVSB at the dorsal border. Sprouting, migration, and anastomoses of the paleopulmonic parabronchi resulted in two groups of these air conduits; a cranial group oriented rostrocaudally and a dorsal group oriented dorsoventrally. The neopulmonic parabronchial network formed through profuse branching and anastomoses and occupied the ventrocaudal quarter of the lung. There were no differences in the number of secondary bronchi between the left and right lungs. Notably, a combination of several visualization techniques is requisite to adequately identify and enumerate all the categories of secondary bronchi present. The 3D arrangement of the air conduits ensures a sophisticated system, suitable for efficient gas exchange. Microsc. Res. Tech., 2008. (c) 2008 Wiley-Liss, Inc.     

Modifications in chromatin morphology and organization during sheep oogenesis

This research has been designed to study the major events of nuclear remodeling that characterize sheep oocytes during the early stage of folliculogenesis (transition from preantral to antral stage). In particular, the modifications in large-scale chromatin configuration, the global DNA methylation, and the process of telomere elongation have been investigated as crucial events of oocyte nuclear maturity. In addition, the spatio-temporal distribution of the major enzymes involved in DNA methylation, the DNA methyltransferase 1 (Dnmt1), and in telomere elongation, telomerase catalytic subunit (TERT), have been described. To these aims, the nuclei of isolated oocytes were investigated using immunocytochemistry and Q-FISH analyses. In absence of preliminary information, these nuclear determinants were compared with those of fully competent germ cells obtained from medium and preovulatory antral follicles. The nuclei of sheep oocytes acquired a condensed chromatin configuration, stable high levels of global DNA methylation, and a definitive telomere length already in the majority of late growing stage oocytes (110 microm) derived from early antral follicles. In addition, while the process of methylation resulted strictly related to oocyte diameter, the telomeric program appeared to be highly chromatin configuration-dependent. The translocation of Dnmt1 and TERT from the nucleus to the cytoplasm in the oocytes derived from early antral follicles seems to confirm the definitive chromatin asset of these germ cells. In conclusion, changes in large-scale chromatin structure, epigenesis, and telomere size in the sheep are established prior to oocyte acquires the ability to resume meiosis.     

The role of microtubules in cellular organization and endocytosis in the plant pathogen Ustilago maydis

Microtubules are an important part of the eukaryotic cytoskeleton, which participates in numerous essential cellular processes. In fungi interphase microtubules mediate cell polarity and participate in polar growth. However, our understanding of their detailed role in fungal growth is just at the beginning. In growing cells of the plant pathogenic fungus Ustilago maydis microtubules are organized by polar microtubule organizing centres that focus the microtubule minus ends at the small bud. Two opposing motor complexes utilize this microtubule polarity. Cytoplasmic dynein and a kinesin of the Unc104/Kif1A family of kinesins mediate rapid bi‐directional transport of early endosomes. A balance of their activity is required for cell cycle‐dependent accumulation of early endosomes at the growth site, the rear cell pole and the region of cell cleavage. Mutant phenotypes suggest that these endosomes participate in polar growth, bud site selection and cell separation. Therefore, our data suggest that endocytotic membrane recycling participates in local exocytosis, and that the microtubule cytoskeleton has a crucial role in this process.     

Sexual dimorphism in the neuronal circuits of the quail preoptic and limbic regions.

A sexually dimorphic nucleus is located in the preoptic area of Japanese quail and plays a key role in the activation of male copulatory behavior. The medial preoptic nucleus (POM) is significantly larger in adult male than in adult female quail. Its volume is steroid-sensitive in adulthood and consequently decreases after castration but is restored to normal levels by a treatment with exogenous testosterone. This volumetric difference appears to result only from a sex difference in the adult hormonal milieu and is not affected by embryonic treatments that permanently modify sexual behavior (no organizational effects). In contrast, some cytoarchitectonic features of the POM such as the size of neurons in the dorso-lateral part of nucleus appear to be irreversibly affected by embryonic steroids. The POM is characterized by the presence of a wide variety of neurotransmitters, neuropeptides, and receptors and can be specifically identified by the presence of a dense cluster of aromatase-immunoreactive cells, by a high density of neurotensin-immunoreactive cells and fibers and by a dense vasotocinergic innervation. Some of these neurochemical markers of the dimorphic nucleus are themselves modulated by steroids. Many of these neurochemical changes appear to play a causal role in the control of male sexual behavior. The quail POM thus represents an excellent model for the analysis of steroid-induced brain plasticity in a behaviorally relevant context.     

Comparative ultrastructure and cytochemistry of the avian pineal organ

The breeding of birds is expected to solve problems of nourishment for the growing human population. The function of the pineal organ synchronizing sexual activity and environmental light periods is important for successful reproduction. Comparative morphology of the avian pineal completes data furnished by experiments on some frequently used laboratory animals about the functional organization of the organ. According to comparative histological data, the pineal of vertebrates is originally a double organ (the "third" and the "fourth eye"). One of them often lies extracranially, perceiving direct solar radiation, and the other, located intracranially, is supposed to measure diffuse brightness of the environment. Birds have only a single pineal, presumably originating from the intracranial pineal of lower vertebrates. Developing from the epithalamus, the avian pineal organ histologically seems not to be a simple gland ("pineal gland") but a complex part of the brain composed of various pinealocytes and neurons that are embedded in an ependymal/glial network. In contrast to organs of "directional view" that develop large photoreceptor outer segments (retina, parietal pineal eye of reptiles) in order to decode two-dimensional images of the environment, the "densitometer"-like pineal organ seems to increase their photoreceptor membrane content by multiplying the number of photoreceptor perikarya and developing follicle-like foldings of its wall during evolution ("folded retina"). Photoreceptor membranes of avian pinealocytes can be stained by antibodies against various photoreceptor-specific compounds, among others, opsins, including pineal opsins. Photoreceptors immunoreacting with antibodies to chicken pinopsin were also found in the reptilian pineal organ. Similar to cones and rods representing the first neurons of the retina in the lateral eye, pinealocytes of birds possess an axonal effector process which terminates on the vascular surface of the organ as a neurohormonal ending, or forms ribbon-containing synapses on pineal neurons. Serotonin is detectable immunocytochemically on the granular vesicles accumulated in neurohormonal terminals. Pinealocytic perikarya and axon terminals also bind immunocytochemically recognizable excitatory amino acids. Peripheral autonomic fibers entering the pineal organ through its meningeal cover terminate near blood vessels. Being vasomotor fibers, they presumably regulate the blood supply of the pineal tissue according to the different levels of light-dependent pineal cell activity.     

Plasticity in the electrophysiological properties of oxytocin neurons.

In mammals, the neurohypophysial hormone oxytocin (OT) is released into the bloodstream during labor and lactation to promote uterine contraction and milk ejection, respectively. Electrophysiological studies have established that OT neurons fire in brief, synchronized bursts during this release. During pregnancy and lactation, the intrinsic membrane and synaptic properties of OT, and to a lesser extent vasopressin (VP) neurons, are altered as a part of the adaptation to these specialized states. During lactation OT neurons specifically exhibit an enhanced rebound depolarization which could assist in instigating bursts and an increased gating of firing frequency which is correlated with an enhanced Ca(2+)-dependent after hyperpolarization. Spike broadening occurs in both VP and OT neurons, but in OT neurons this and other changes are present during late pregnancy, suggesting involvement of steroidal hormones in programming neuronal adaptations. Excitatory and inhibitory synaptic activity also are altered by reproductive state. There is a doubling of glutamatergic activity specific to OT neurons which is consistent with an increase in terminal numbers, but this is accompanied by an increase in paired-pulse facilitation, suggesting an increase in the probability of glutamate release during lactation as well. Together with profound changes in both pre- and postsynaptic GABAergic synaptic activity, these data suggest that neurosecretory, and particularly OT neuronal, properties are state-dependent. These modifications may adjust the responsiveness of these neurons to afferent stimulation during periods of increased hormone demand and thereby enhance stimulus-secretion coupling.     

视觉仿生学研究现状及展望

主要针对人眼仿生学,介绍了视觉仿生学研究的现状及部分代表性成果,并加以阐述其特性。最后总结了视觉仿生学研究的发展趋势。     

Distribution of neurotrophin and TrK receptor-like immunoreactivity in the adrenal gland of birds

The occurrence and localization of neurotrophins and their specific TrK receptor-like proteins in the adrenal gland of chicken, duck and ostrich were examined by immunohistochemical methods. In all species studied NGF-, TrK A- and TrK C-like immunoreactivity was observed in neurons and fibers of adrenal ganglia. Thin TrK A- and TrK C-like immunoreactive fibers were also observed among chromaffin cells. NT-3-like immunoreactivity was detected in chromaffin cells as revealed by the double immunolabelings NT-3/chromogranin A and NT-3/DbetaH. The interrenal tissue never showed IR to any neurotrophins and TrK tested, and none of the adrenal structures displayed immunoreactivity to BDNF and TrK B. Double immunolabelings NGF/TrK A, NGF/TrK C and TrK A/TrK C showed colocalization in some neurons and fibers in adrenal ganglia. In adrenal glands of the species studied, the distribution of neurotrophins and TrK receptors could suggest an involvement of NT-3 on neuronal populations innervating adrenal ganglia by means of its high affinity receptor TrK C and low affinity receptor TrK A. In addition, NGF could be utilized by neuronal populations of adrenal ganglia through its preferential receptor TrK A by an autocrine or paracrine modality of action.     

The photoreceptive cells of the pineal gland in adult zebrafish (Danio rerio)

The zebrafish pineal gland plays a fundamental role in the regulation of the circadian rhythm through the melatonin secretion. The pinealocytes, also called photoreceptive cells, are considered the morphofunctional unit of pineal gland. In literature, the anatomical features, the cellular characteristics, and the pinealocytes morphology of zebrafish pineal gland have not been previously described in detail. Therefore, this study was undertaken to analyze the structure and ultrastructure, as well as the immunohistochemical profile of the zebrafish pineal gland with particular reference to the pinealocytes. Here, we demonstrated, using RT-PCR, immunohistochemistry and transmission electron microscopy, the expression of the mRNA for rhodopsin in the pineal gland of zebrafish, as well as its cellular localization exclusively in the pinealocytes of adult zebrafish. Moreover, the ultrastructural observations demonstrated that the pinealocytes were constituted by an outer segment with numerous lamellar membranes, an inner segment with many mitochondria, and a basal pole with the synapses. Our results taken together demonstrated a central role of zebrafish pinealocytes in the control of pineal gland functions.     

CORBA和XML在虚拟制造组织集成中的应用

CORBA和XML是虚拟制造组织集成中的两种技术。CORBA的优势是在方法的重用上,而XML是在数据的独立性上。两者的结合应用为虚拟制造组织的集成提供一个更加强有力的途径,为此本文提出了CORBA和XML结合应用的三层客户机/服务器模式。     

Coalignment of the muscle cell and nucleus,cell geometry and Vv in the tunica media of monkey cerebral arteries,by electron microscopy

We undertook to ascertain how well aligned is the rod-shaped nucleus within the spindle-shaped cell of vascular muscle in order that we might use the darkly staining nucleus in histological sections to indicate precisely the directional alignment of the cell. We fixed cerebral arteries from five monkeys under physiological pressure and embedded portions of the tissue so that mid-plane longitudinal sections of the arteries were obtained; the circumferentially arranged muscle cells were cut in cross-section. From the electron micrographs we obtained the cross-sectional profile of the cell and its nucleus, determining that the centre of the nucleus was on average 9·5 ± 5·8% (SD) away from the centre of the cell (expressed as a ratio of the cellular diameter). We calculated the alignment between the cell and nucleus to be from 0 to 3°, and obtained a volume fraction of 59% for muscle tissue in the tunica media of these arteries.     

曲柄滑块机构在Cosmosmotion中的运动分析

曲柄滑块是机械中的一个常用机构，Cosmosmotion是Solid Works的CAE插件，可精确建立各种复杂的实际仿真模型，笔者介绍如何利用它分析曲柄滑块机构。     

Spatial and functional relationships between air conduits and blood capillaries in the pulmonary gas exchange tissue of adult and developing chickens

The documented data regarding the three-dimensional structure of the air capillaries (ACs), the ultimate sites of gas exchange in the avian lung is contradictory. Further, the mode of gas exchange, described as cross-current has not been clearly elucidated. We studied the temporal and spatial arrangement of the terminal air conduits of the chicken lung and their relationship with the blood capillaries (BCs) in embryos as well as the definitive architecture in adults. Several visualization techniques that included corrosion casting, light microscopy as well as scanning and transmission electron microscopy were used. Two to six infundibulae extend from each atrium and give rise to numerous ACs that spread centrifugally. Majority of the ACs are tubular structures that give off branches, which anastomose with their neighboring cognates. Some ACs have globular shapes and a few are blind-ending tapering tubes. During inauguration, the luminal aspects of the ACs are characterized by numerous microvillus-like microplicae, which are formed during the complex processes of cell attenuation and canalization of the ACs. The parabronchial exchange BCs, initially inaugurated as disorganized meshworks, are reoriented via pillar formation to lie predominantly orthogonal to the long axes of the ACs. The remodeling of the retiform meshworks by intussusceptive angiogenesis essentially accomplishes a cross-current system at the gas exchange interface in the adults, where BCs form ring-like patterns around the ACs, thus establishing a cross-current system. Our findings clarify the mode of gas exchange in the parabronchial mantle and illuminate the basis for the functional efficiency of the avian lung.     

New anti-actin drugs in the study of the organization and function of the actin cytoskeleton.

The high degree of structural and molecular complexity of the actin-based cytoskeleton, combined with its ability to reorganize rapidly and locally in response to stimuli, and its force-generating properties, have made it difficult to assess how the different actin structures are assembled in cells, and how they regulate cell behavior. An obvious approach to study the relationships between actin organization, dynamics, and functions is the specific perturbation of actin structures using pharmacological means. Until recently there were only a few agents available that interfered with cellular activities by binding to actin and most of our knowledge concerning the involvement of actin in basic cellular processes was based on the extensive use of the cytochalasins. In recent years we have identified an increasing number of actin-targeted marine natural products, including the latrunculins, jasplakinolides (jaspamides), swinholide A, misakinolide A, halichondramides, and pectenotoxin II, which are discussed in this article. All these marine-sponge-derived compounds are unusual macrolides and can be classified into several major families, each with its own distinct chemical structures. We describe the current state of knowledge concerning the actin-binding properties of these compounds and show that each class of drugs alters the distribution patterns of actin in a unique way, and that even within a chemical class, structurally similar compounds can have different biochemical properties and cellular effects. We also discuss the effects of these new drugs on fenestrae formation in liver endothelial cells as an example of their usefulness as powerful tools to selectively unmask actin-mediated dynamic processes.     

Structural organization of the thylakoid membrane: Freeze-fracture and immunocytochemical analysis

This article summarizes our ultrastructural studies on the organization of the thylakoid membrane of green algae and higher plants. We have used freeze-fracture and immunogold labeling to investigate the lateral distribution of the components in the membrane, their interactions, and the folding of their polypeptide chains in the membrane.