R Djavadian

Adult neurogenesis in the hedgehog (Erinaceus concolor) and mole (Talpa europaea).

We investigated adult neurogenesis in two species of mammals belonging to the superorder Laurasiatheria, the southern white-breasted hedgehog (order Erinaceomorpha, species Erinaceus concolor) from Armenia and the European mole (order Soricomorpha, species Talpa europaea) from Poland. Neurogenesis in the brain of these species was examined immunohistochemically, using the endogenous markers doublecortin (DCX) and Ki-67, which are highly conserved among species. We found that in both the hedgehog and mole, like in the majority of earlier investigated mammals, neurogenesis continues in the subventricular zone (SVZ) of the lateral ventricles and in the dentate gyrus (DG). In the DG of both species, DCX-expressing cells and Ki-67-labeled cells were present in the subgranular and granular layers. In the mole, a strong bundle of DCX-labeled processes, presumably axons of granule cells, was observed in the center of the hilus. Proliferating cells (expressing Ki-67) were identified in the SVZ of lateral ventricles of both species, but neuronal precursor cells (expressing DCX) were also observed in the olfactory bulb (OB). In both species, the vast majority of cells expressing DCX in the OB were granule cells with radially orientated dendrites, although some periglomerular cells surrounding the glomeruli were also labeled. In addition, this paper is the first to show DCX-labeled fibers in the anterior commissure of the hedgehog and mole. These fibers must be axons of new neurons making interhemispheric connections between the two OB or piriform (olfactory) cortices. DCX-expressing neurons were observed in the striatum and piriform cortex of both hedgehog and mole. We postulate that in both species a fraction of cells newly generated in the SVZ migrates along the rostral migratory stream to the piriform cortex. This pattern of migration resembles that of the ‘second-wave neurons’ generated during embryonal development of the neocortex rather than the pattern observed during development of the allocortex. In spite of the presence of glial cells alongside DCX-expressing cells, we never found colocalization of DCX protein with a glial marker (vimentin or glial fibrillary acidic protein).

Chapter 18 Areas PMLS and 21a of cat visual cortex are not only functionally but also hodologically distinct

In several cats, paired visuotopically matched injections of retrogradely transported fluorescent dyes, diamidino yellow (DY) and fast blue (FB), were made into two visuotopically organized, functionally distinct extrastriate cortical areas, the posteromedial lateral suprasylvian area (PMLS area) and area 21a respectively. After an appropriate survival time, the numbers of thalamic, claustral and cortical cells which were single-labelled with each dye as well as the numbers of cells in these structures labelled with both dyes (double-labelled cells) were assessed. The clear majorities of thalamic cells projecting to PMLS area (DY labelled cells) and to area 21a (FB labelled cells) were located in the ipsilateral lateral posterior-pulvinar complex with smaller proportions located in the laminae C and the medial intralaminar nucleus of the ipsilateral dorsal lateral geniculate nucleus and several nuclei of the rostral intralaminar thalamic group. Despite the fact that DY labelled (PMLS-projecting) and FB labelled (area 21 a-projecting) cells in all thalamic nuclei were well intermingled, only 1-5% of retrogradely labelled thalamic cells projected to both areas (cells double-labelled with both dyes). Small proportions of retrogradely labelled cells were located in the ipsilateral and to a lesser extent the contralateral dorsocaudal claustra. The proportions of claustral neurons retrogradely labelled with both dyes varied from 4 to 9%. Over half of the cortical neurons labelled retrogradely from area 21a or PMLS area were located in the supragranular layers of the ipsilateral area 17, with smaller proportions located in the supragranular layers of the ipsilateral areas 18 and 19 and even smaller proportions located in mainly but not exclusively, the infragranular layers of the ipsilateral areas 21b and 20a. Again despite strong spatial intermingling of neurons labelled with DY and these labelled with FB, the proportions of associational cortical neurons double-labelled with both dyes were small (2 to 5.5%). Finally, small proportions of neurons retrogradely labelled with DY or FB were located, mainly but not exclusively, in the supragranular layers of the contralateral areas 17, 18, 19 and 21a. Again, the proportions of the double-labelled neurons in the contralateral cortices were small (1-4.5%). Thus, the present study indicates that despite the fact that the diencephalic and telencephalic inputs to the visuotopically corresponding parts of area 21a and PMLS area originate from the same nuclei, areas and layers, the two areas receive their afferents from the largely separate populations of neurons.

The expression of interleukin-6 and its receptor in various brain regions and their roles in exploratory behavior and stress responses.

We examined the involvement of interleukin-6 (IL-6) and its receptor IL-6Rα on behavior and stress responses in mice. In the open field, both wild-type (WT) and IL-6 deficient mice displayed similar levels of locomotor activity; however, IL-6 deficient mice spent more time in the central part of the arena compared to control WT mice. After behavioral testing, mice were subjected to stress and then sacrificed. The levels of IL-6 and its receptor in their brains were determined. Immunohistochemical labeling of brain sections for IL-6 showed a high level of expression in the subventricular zone of the lateral ventricles and in the border zone of the third and fourth ventricles. Interestingly, 95% of the IL-6-expressing cells had an astrocytic phenotype, and the remaining 5% were microglial cells. A low level of IL-6 expression was observed in the olfactory bulb, hypothalamus, hippocampus, cerebral cortex, cerebellum, midbrain and several brainstem structures. The vast majority of IL-6-expressing cells in these structures had a neuronal phenotype. Stress increased the number of IL-6-immunoreactive astrocytes and microglial cells. The levels of the IL-6Rα receptor were increased in the hypothalamus of stressed mice. Therefore, in this study, we describe for the first time the distribution of IL-6 in various types of brain cells and in previously unreported regions, such as the subventricular zone of the lateral ventricle. Moreover, we provide data on regional distribution and expression within specific cell phenotypes. This highly differential expression of IL-6 indicates its specific roles in the regulation of neuronal and astrocytic functions, in addition to the roles of IL-6 and its receptor IL-6Rα in stress responses.

Distribution and function of TrkB receptors in the developing brain of the opossum Monodelphis domestica

The expression, development pattern, spatiotemporal distribution, and function of TrkB receptors were investigated during the postnatal brain development of the opossum. Full‐length TrkB receptor expression was detectable in the newborn opossum, whereas three different short forms that are expressed in the adult brain were almost undetectable in the newborn opossum brain. The highest level of full‐length TrkB receptor expression was observed at P35, which corresponds to the time of eye opening. We found that in different brain structures, TrkB receptors were localized in various compartments of cells. The hypothalamus was distinguished by the presence of TrkB receptors not only in cell bodies but also in the neuropil. Double immunofluroscent staining for TrkB and a marker for the identification of the cell phenotype in several brain regions such as the olfactory bulb, hippocampus, thalamus, and cerebellum showed that unlike in eutherians, in the opossum, TrkB receptors were predominantly expressed in neurons. A lack of TrkB receptors in glial cells, particularly astrocytes and oligodendrocytes, provides evidence that TrkB receptors can play a functionally different role in marsupials than in eutherians. The effects of TrkB signaling on the development of cortical progenitor cells were examined in vitro using shRNAs. Blockade of the endogenous TrkB receptor expression induced a decrease in the number of progenitor cells proliferation, whereas the number of apoptotic progenitor cells increased. These changes were statistically significant but relatively small. In contrast, TrkB signaling was strongly involved in regulation of the cortical progenitor cell differentiation process.

Neonatal depletion of serotonin increases the numbers of callosally projecting neurons in cat visual areas 17 and 18

We investigated the influence of neonatal depletion of serotonin on the developmental reduction of callosal connections in cat visual cortex. Neonatal kittens were injected with 5,7-dihydroxytryptamine. At the age of 3 months, Fast Blue was injected into visual areas of one hemisphere in these and control cats and retrogradely labeled perikarya were mapped in the opposite hemisphere. In both groups callosally projecting neurons were found in a 3-5 mm wide belt centered on the transient zone of areas 17 and 18. However, numbers of labeled neurons were twice higher in the serotonin-depleted cats. We postulate that normally serotonin intensifies the process of axon pruning by augmenting developmental plasticity, therefore its depletion reduced the plasticity and more axons targeting callosal zones were stabilized, even though ectopic projections were still eliminated.

Postnatal treatment with NAN-190 but not with 5-HT1A receptor agonists retards growth of the rat brain.

We investigated the influence of prolonged administration of the 5‐HT1A receptor agonists (8‐OH‐DPAT or buspirone) or its antagonist, NAN‐190 to rat pups on development of their cortical barrel field. Pups were injected daily with the drugs starting from the day of birth till either the 5th postnatal day or the 22–25th postnatal day and were perfused one day later. Square areas of their whisker barrel fields were measured on tangential sections of the cortex stained for cytochrome oxidase. Injections of 8‐OH‐DPAT or buspirone till the 5th postnatal day did not change any of the investigated parameters, while injections of NAN‐190 resulted in 15% reduction of the pups’ body and brain weight and proportional reduction of the square area of their barrel fields. Groups treated till the 22–25th postnatal day showed similar results. Some of these pups were injected with [C14]2‐deoxyglucose to investigate the strength of responses of their cortical barrels to stimulation of corresponding vibrissae. The cortical area labeled with 2‐deoxyglucose after stimulation of vibrissae of the row C was narrower in the NAN‐190 injected rats. This functional deficit was more pronounced than the anatomical one, which resembled the effects of neonatal serotonin depletion (Neuroreport, 1997). Therefore, the results of injecting NAN‐190 to the rat pups point to a deficit of trophic developmental influences of serotonin, adding new arguments for the hypothesis of a trophic role of 5‐HT1A receptors in the brain development.

CacyBP/SIP, a Hsp90 binding chaperone, in cellular stress response

CacyBP/SIP interacts with Hsp90 and is able to protect proteins from denaturation and/or aggregation induced by elevated temperature. In this work we studied the influence of different stress factors on CacyBP/SIP level in HEp-2 cells. We have found that H2O2 and radicicol treatment resulted in a significant increase (up to 40%) in the CacyBP/SIP level. We have also found that HEp-2 cells overexpressing CacyBP/SIP were more resistant to stress-induced death. Further studies have revealed that the Hsf1 transcription factor binds to the CacyBP/SIP gene promoter and up-regulates CacyBP/SIP expression under stress conditions. To check whether the CacyBP/SIP protein might play a role in stress responses in vivo, we analyzed its level in selected brain structures of control and stressed mice. We have found that the level of the CacyBP/SIP protein was higher in the thalamus/hypothalamus, hippocampus and brainstem of stressed mice. Thus, the presented results clearly indicate that CacyBP/SIP is involved in cellular stress response.

Roles of the exon junction complex components in the central nervous system: a mini review

Abstract The exon junction complex (EJC) consists of four core proteins: Magoh, RNA-binding motif 8A (Rbm8a, also known as Y14), eukaryotic initiation factor 4A3 (eIF4A3, also known as DDX48), and metastatic lymph node 51 (MLN51, also known as Casc3 or Barentsz), which are involved in the regulation of many processes occurring between gene transcription and protein translation. Its main role is to assemble into spliceosomes at the exon-exon junction of mRNA during splicing. It is, therefore, a range of functions concerning post-splicing events such as mRNA translocation, translation, and nonsense-mediated mRNA decay (NMD). Apart from this, proteins of the EJC control the splicing of specific pre-mRNAs, for example, splicing of the mapk transcript. Recent studies support essential functions of EJC proteins in oocytes and, after fertilization, in all stages of zygote development, as well as the growth of the embryo, including the development of the nervous system. During the development of the central nervous system (CNS), the EJC controls mitosis, regulating both symmetric and asymmetric cell divisions. Reduced levels of EJC components cause microcephaly. In the adult brain, Y14 and eIF4A3 appear to be involved in synaptic plasticity and in learning and memory. In this review, we focus on the involvement of EJC components in brain development and its functioning under normal conditions.

Inhibition of TrkB- and TrkC-Signaling Pathways Affects Neurogenesis in the Opossum Developing Neocortex

We have previously reported that the blockage of TrkB and TrkC signaling in primary culture of opossum neocortical cells affects neurogenesis that involves a range of processes including cell proliferation, differentiation, and survival. Here, we studied whether TrkB and TrkC activity specifically affects various types of progenitor cell populations during neocortex formation in the Monodelphis opossum in vivo. We found that the inhibition of TrkB and TrkC activities affects the same proliferative cellular phenotype, but TrkC causes more pronounced changes in the rate of cell divisions. Additionally, inhibition of TrkB and TrkC does not affect apoptosis in vivo, which was found in cell culture experiments. The lack of TrkB and TrkC receptor activity caused the arrest of newly generated neurons; therefore, they could not penetrate the subplate zone. We suggest that at this time point in development, migration consists of 2 steps. During the initial step, neurons migrate and reach the base of the subplate, whereas during the next step the migration of neurons to their final position is regulated by TrkB or TrkC signaling.

193 Changes in the activity of vibrissal column induced by neonetal depletion of serotonin in rat

Dopaminergic projections from the midbrain play an important role for the development of the basal ganglia. The present study is concerned with the question whether dopamine (DA) affects morphological development of striatal GABAergic neurons and which signal recognitton and transduction mechanisms are involved in the control of differentiation. Striatal cells from embryonic day 17 rat fetuses were grown for 7 days and treated with DA or selective Dl-or D2-like receptor agonists (SKF 38393 or quinpirole, respectively) for 1 h. At various times after termination of treatment, cells were immunostained for growth associated protein 43 (E-50) or Fos-like proteins. Morphological parameters including growth cones, neurite length, numbers of bifurcations, and soma size per neuron were assessed. DA as well as SKF 38393, but not quinpirole, increased the numbers of growth cones, total process length and arborization. This effect took several hours to evolve, remained stable for at least 24 hours, and could be blocked by the Dl-like receptor antagonist SCH 23390 or by cycloheximide. Activation of D l-like but not DZ-like receptors also increased the number of Fos-positive neurons. This effect was restrictet to B-50 negative neurons. Our data demonstrate for the first time a positive regulatory effect of DA on striatal morphogenesis and establish the existence of a signaling pathway encompassing D&like receptors but not necessarily induction of c-fos. Supported by the Deursche Forschungsgenleinschafr.