Molecular Markers in the Study of Non-model Vertebrates: Their Significant Contributions to the Current Knowledge of Tetrapod Glial Cells and Fish Olfactory Neurons

Principles of odor coding in vertebrates and artificial chemosensory systems

The biological olfactory system is the sensory system responsible for the detection of the chemical composition of the environment. Several attempts to mimic biological olfactory systems have led to various artificial olfactory systems using different technical approaches. Here we provide a parallel description of biological olfactory systems and their technical counterparts. We start with a presentation of the input to the systems, the stimuli, and treat the interface between the external world and the environment where receptor neurons or artificial chemosensors reside. We then delineate the functions of receptor neurons and chemosensors as well as their overall I-O relationships. Up to this point, our account of the systems goes along similar lines. The next processing steps differ considerably: while in biology the processing step following the receptor neurons is the "integration" and "processing" of receptor neuron outputs in the olfactory bulb, this step has various realizations in electronic noses. For a long period of time, the signal processing stages beyond the olfactory bulb, i.e., the higher olfactory centers were little studied. Only recently there has been a marked growth of studies tackling the information processing in these centers. In electronic noses, a third stage of processing has virtually never been considered. In this review, we provide an up-to-date overview of the current knowledge of both fields and, for the first time, attempt to tie them together. We hope it will be a breeding ground for better information, communication, and data exchange between very related but so far little connected fields.

Radial Glial Cells: New Views on Old Questions

Radial glial cells (RGC) are at the center of brain development in vertebrates, acting as progenitors for neurons and macroglia (oligodendrocytes and astrocytes) and as guides for migration of neurons from the ventricular surface to their final positions in the brain. These cells originate from neuroepithelial cells (NEC) from which they inherit their epithelial features and polarized morphology, with processes extending from the ventricular to the pial surface of the embryonic cerebrum. We have learnt a great deal since the first descriptions of these cells at the end of the nineteenth century. However, there are still questions regarding how and when NEC transform into RGC or about the function of intermediate filaments such as glial fibrillary acidic protein (GFAP) in RGCs and their dynamics during neurogenesis. For example, it is not clear why RGCs in primates, including humans, express GFAP at the onset of cortical neurogenesis while in rodents it is expressed when it is essentially complete. Based on an ultrastructural analysis of GFAP expression and cell morphology of dividing progenitors in the developing neocortex of the macaque monkey, we show that RGCs become the main progenitor in the developing cerebrum by the start of neurogenesis, as all dividing cells show glial features such as GFAP expression and lack of tight junctions. Also, our data suggest that RGCs retract their apical process during mitosis. We discuss our findings in the context of the role and molecular characteristics of RGCs in the vertebrate brain, their differences with NECs and their dynamic behavior during the process of neurogenesis.