Evolution of the primate visual system: Anterograde degeneration studies of the tecto-pulvinar system

A partial answer to the question of the precocious development of the temporal lobe in fossil lemurs is offered by the presentation of evidence that in the tree shrew, in prosimians, and probably in all primates the temporal lobe contains primary visual cortex. The visual pathway to the temporal lobe is achieved by relays through the superficial layers of the superior colliculus and pulvinar nucleus. This pathway parallels the geniculo-striate system. Still a third visual system can be identified with sensory-motor connections in the deeper layers of the superior colliculus.     

Biomarkers of effects: the immune system

© 2005 Wiley Periodicals, Inc. J Biochem Mol Toxicol 19:177–179, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20075     

Coherence in nervous system design: the visual system of Pantodon buchholzi

One of the more unusual visual systems of the Actinopterygii is that of Pantodon buchholzi (Osteoglossomorpha: Osteoglossidae). Its adaptations associate neuroanatomy at different levels of the visual system with ecological and behavioural correlates and demonstrate that the visual system of this fish has adapted for simultaneous vision in air and water. The visual field is divided into three distinct areas: for viewing into the water column, into air, and for viewing the aquatic reflection from the underside of the water surface. Cone diameters in different retinal areas correlate with the differing physical constraints in the respective visual field. Retinal differentiation between the aquatic and aerial views is paralleled at different levels of the central nervous system. A diencephalic nucleus receives both direct and indirect (tectal) afferent input from only the aerial visual system and a specific type of cell in the optic tectum is preferentially distributed in the tectum processing aerial inputs. Distinctions within a single sensory system suggest that some behaviours may be organized according to visual field. For Pantodon, feeding is initiated by stimuli seen by the ventral hemiretina so the anatomical specializations may well play an important role as elements in a feeding circuit.     

Working outside the system: an update on the unconventional behavior of the renin-angiotensin system components

The renin-angiotensin system (RAS) plays an important role in regulating arterial pressure, blood volume, thirst, cardiac function, and cellular growth. Both a circulating and multiple tissue-localized systems have been identified, and are generally portrayed as a series of reactions that occur sequentially with a single outcome: angiotensinogen is cleaved by renin to form angiotensin I, which in turn is processed by angiotensin-converting enzyme (ACE) to angiotensin II, which then activates either the AT1 or the AT2 plasma membrane receptor. Evidence has emerged, however, showing that some RAS components play important roles outside of this canonical scheme. This article provides an overview of some recently identified extra-system functions. In addition to forming angiotensin II, ACE is a multifunctional enzyme equally important in the metabolism of vasodilator and antifibrotic peptides. As the membrane-bound form, ACE functions as a "receptor" that initiates intracellular signaling leading to gene expression. Both angiotensin I and II may lead to actions that are independent of, or even oppose, those of the RAS via their metabolism by the novel ACE-homologue ACE2. The two angiotensin II receptor types have ligand-independent roles that influence cellular signaling and growth, some of which may result from the ability to form hetero-dimers with other 7-transmembrane receptors. Finally, intracellular angiotensin II has been demonstrated to have actions on cell-communication, gene expression, and cellular growth, through both receptor-dependent and independent means. A greater understanding of these extra-system functions of the RAS components may aid in the development of novel treatments for hypertension, myocardial ischemia, and heart failure.     

Development of the musculoskeletal system: meeting the neighbors

In March 2011, researchers met for the second Batsheva Seminar on Integrative Perspectives on the Development of the Musculoskeletal System. This meeting was a unique opportunity for researchers working on muscle, connective tissue, tendons, ligaments and bone to discuss the development of the musculoskeleton, recognizing that it is an integrated, functional system. The talks and discussions at this meeting highlighted that interactions between the different tissue components are crucial for musculoskeletal morphogenesis.     

Roots: The thymus: Maestro of the immune system

The thymus has been an enigmatic organ for centuries. Its true function was revealed only in 1961 when it was shown to be responsible for the proper development of the immune system. This finding has revolutionized the science of immunology and has led to a better understanding of the mechanisms involved in resistance to infections and of the pathogenesis of autoimmune and immunodeficiency diseases.     

Olfactory system gamma oscillations: the physiological dissection of a cognitive neural system

Oscillatory phenomena have been a focus of dynamical systems research since the time of the classical studies on the pendulum by Galileo. Fast cortical oscillations also have a long and storied history in neurophysiology, and olfactory oscillations have led the way with a depth of explanation not present in the literature of most other cortical systems. From the earliest studies of odor-evoked oscillations by Adrian, many reports have focused on mechanisms and functional associations of these oscillations, in particular for the so-called gamma oscillations. As a result, much information is now available regarding the biophysical mechanisms that underlie the oscillations in the mammalian olfactory system. Recent studies have expanded on these and addressed functionality directly in mammals and in the analogous insect system. Sub-bands within the rodent gamma oscillatory band associated with specific behavioral and cognitive states have also been identified. All this makes oscillatory neuronal networks a unique interdisciplinary platform from which to study neurocognitive and dynamical phenomena in intact, freely behaving animals. We present here a summary of what has been learned about the functional role and mechanisms of gamma oscillations in the olfactory system as a guide for similar studies in other cortical systems.

Autopoiesis: the status of its system logic

The concept of autopoiesis, amended as a system theory, is necessary and sufficient to provide an operational definition of life, a set of criteria by which the living are categorically distinguished from the non-living. Limitations are placed on the domains in which autopoiesis may be exhibited.     

A recurrent system incorporating characteristics of the visual system: a model for the function of backward neural connections in the visual system

A recurrent system is constructed in order to investigate the role of the backward neural connections found in the primate visual system. The system incorporates a layer to perform localized spatial frequency analysis of input images, a function which has been assumed to take place in the primary visual cortex. The function of the system is examined by simulation. The results show that the system can separate an object pattern from its background, irrespective of its precise position. The acceptable displacement range for input images is determined from the width of the window function used to calculate the local Fourier transform. A multilayer version of the above recurrent system is also constructed.