Calmodulin is abundant in the central nervous system, including the retina. However, the localization of calmodulin in the retina has not been described in detail. We therefore decided to investigate calmodulin localization in retinae from six vertebrate species, by using immunohistochemical labeling with four different rabbit polyclonal antibodies against calmodulin. The localization of calbindin-D28k, another calcium-binding protein already well described in retina, was compared. We found that calmodulin distribution is more highly conserved among species, contrasting with calbindin variability. The most striking result emerging is that calmodulin could not be detected in photoreceptors although other layers are intensely calmodulin-immunoreactive, casting doubt about a direct role of calmodulin in phototransduction. Horizontal cells are weakly calmodulin-immunoreactive, bipolar cells are calmodulin-immunoreactive except in turtle retina, numerous amacrine and ganglion cells are labeled in all species, and the fiber layer is always labeled. These data demonstrate that, while the calmodulin distribution in retina is similar among vertebrate species, selective differences in localization can be detected not only among the same cell types in different species but also among different cell types in the same species. The results showing differences in calmodulin immunoreactivity among cell types also provide further evidence that calmodulin expression in eukaryotes is not constitutive, in the sense that not every cell expresses similar levels of calmodulin.

S100B is the principal calcium-binding protein of astrocytes and known to be secreted to extracellular space. Although secreted S100B has been reported to promote neurite extension and cell survival via its receptor [receptor for advanced glycation end products (RAGE)], effects of extracellular S100B on neural activity have been mostly unexplored. Here, we demonstrate that secreted S100B enhances kainate-induced gamma oscillations. Local infusion of S100B in S100B(؊/؊) mice enhanced hippocampal kainate-induced gamma oscillations in vivo. In a complementary set of experiments, local application of anti-S100B antibody in wild-type mice attenuated the gamma oscillations. Both results indicate that the presence of extracellular S100B enhances the kainate-induced gamma oscillations. In acutely isolated hippocampal slices, kainate application increased S100B secretion in a neural-activity-dependent manner. Further pharmacological experiments revealed that S100B secretion was critically dependent on presynaptic release of neurotransmitter and activation of metabotropic glutamate receptor 3. Moreover, the kainate-induced gamma oscillations were attenuated by the genetic deletion or antibody blockade of RAGE in vivo. These results suggest RAGE activation by S100B enhances the gamma oscillations. Together, we propose a novel pathway of neuron-glia communications-astrocytic release of S100B modulates neural network activity through RAGE activation.

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Developmental changes in the distribution of parvalbumin-specific immunoreactivity in the brain, in particular in the cerebral cortex and hippocampus, were followed immunohistochemically in two different species, the rat and the Mongolian gerbil (Meriones unguiculatus) using an antibody raised against for rat parvalbumin. The gerbil is known to develop its auditory and visual capacity later than rat. In both the rat and gerbil, parvalbumin-specific immunoreactivity appeared after birth in both the cerebral cortex and hippocampus. The timing of the development of expression of parvalbumin varied among different parts of the cerebral cortex. The parietal cortex showed evidence of the earliest expression of parvalbumin whilst the occipital and temporal cortices expressed parvalbumin at a later stage of a development. This feature was common to both the rat and gerbil but occurred at a relatively later stage in the gerbil. The profile of the distribution of parvalbumin in the brain of the developing and adult gerbil was similar to that of the rat, but there were some differences. The frequency of bead-like structures on the dendrites of the parvalbumin-positive cells in the CA1 region of the hippocampus was markedly lower in the gerbil; instead, straight non-beaded fibers which ran vertically into the pyramidal layer were stained. Parvalbumin-positive fibers were also found in the cerebral cortex of the gerbil.

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The distribution of proteins in the cerebral cortex of a seizure-sensitive (SS) strain of gerbil and its seizure-resistant (SR) counterpart was profiled using two-dimensional gel electrophoresis. A series of proteins of similar molecular weight (around 83 kDa) showed small but consistent differences in their isoelectric point (pI) with indistinguishable profiles of distribution between the two strains. Amino acid sequences of peptides produced by limited proteolysis of each protein in the spots from the strains were identical or highly homologous to those of mitofilin, a mitochondrial inner membrane protein (IMMT) in humans. Analysis of cDNA sequences revealed the proteins of these spots to be gerbil mitofilin-like proteins (gIMMT), with a few base substitutions between SS and SR strains, in particular within a region near a putative transmembrane domain that is highly conserved in humans and gerbils. The amino acid at the site was acidic, Glu in humans and Asp in the strain SR of gerbil and a neutral, Asn in strain SS. In addition to these base substitutions, production of multiple species of mRNA for gIMMT by alternative splicing was observed.

S100B is a calcium-binding protein predominantly expressed in astrocytes. Previous studies using gene-manipulated animals have suggested that the protein has a role in synaptic plasticity and learning. In order to assess the physiological roles of the protein in active neural circuitry, we recorded spontaneous neural activities from various layers of the neocortex and hippocampus in urethane-anesthetized S100B knockout (KO) and wildtype (WT) control mice. Typical local field oscillation patterns including the slow (0.5-2 Hz) oscillations in the neocortex, theta (3-8 Hz) and sharp wave-associated ripple (120-180 Hz) oscillations in the hippocampus were observed in both genotypes. Comparisons of the frequency, power and peak amplitude have shown that these oscillatory patterns were virtually indistinguishable between WT and KO. When seizure was induced by intraperitoneal injection of kainic acid, a difference between WT and KO appeared in the CA1 radiatum local field potential pattern, where seizure events were characterized by prominent appearance of hyper-synchronous gamma band (30-80 Hz) activity. Although both genotypes developed seizures within 40 min, the gamma amplitude was significantly smaller during the development of seizures in KO mice. Our results suggest that deficiency of S100B does not have a profound impact on spontaneous neural activity in normal conditions. However, when neural activity was sufficiently raised, activation of S100B-related pathways may take effect, resulting in modulation of neural activities.