Distribution of SNAP-25 in transient neuronal circuitries of the developing human forebrain

Central nervous system development of cats (Felis catus L. 1758)

The morphological similarities of vertebrates' embryonic development are used as a criterion for choosing animal models that can be used in biomedical research. This study describes the embryonic and fetal development of the domestic cat's central nervous system from 15 days after conception until birth. In total, fifty-seven samples of embryos and fetuses were carefully dissected and analyzed microscopically. The closure of the neural tube was observed between 14-15th days of gestation. The differentiation of the primordial cerebral vesicles was observed from the 17th day of gestation. On the 19th day of gestation, the formation of the choroid plexus began, and on the 20th day of gestation, the brain and brainstem were well-identified macroscopically. On the 24th day of gestation, four layers of cells from the cerebral cortex were described, and on the 60th day, six layers of cells were present. The cerebellar cortex had the three classic cortical layers at this stage. The morphological aspects of embryonic and fetal development in cats were very similar to the stages of development of the human nervous system. As such, this study provided relevant information that highlights the domestic cat as an animal model option for preclinical research on infectious and non-infectious neurological diseases in humans.

Baicalin regulates the dopamine system to control the core symptoms of ADHD

We aimed to test the therapeutic effects of baicalin on attention deficit hyperactivity disorder (ADHD) in an animal model and to explain the potential mechanism. We investigated the therapeutic effects and mechanisms of baicalin in a spontaneously hypertensive rat (SHR) model of ADHD depending on the dopamine (DA) deficit theory. In this study, fifty SHRs were randomly divided into five groups: methylphenidate (MPH), baicalin (50 mg/kg, 100 mg/kg, or 150 mg/kg), and saline-treated. Ten Wistar Kyoto (WKY) rats were used as controls. All rats were orally administered the treatment for four weeks. Motor activity, spatial learning and memory ability were assessed with the open-field and Morris water-maze tests. The mRNA and protein levels of tyrosine hydroxylase (TH), vesicular monoamine transporter 2 (VMAT2), synaptosomal-associated protein of molecular mass 25kD (SNAP25) and synataxin 1a in synaptosomes were detected with real-time polymerase chain reaction (PCR) and Western blot. In addition, DA levels were measured in the prefrontal cortex and striatum. The results indicated that both MPH and baicalin at doses of 150 mg/kg and 100 mg/kg significantly decreased the hyperactivity and improved the spatial learning memory deficit in the SHRs and increased the synaptosomal mRNA and protein levels of TH, SNAP25, VMAT2 and synataxin 1a compared with saline treatment. MPH significantly increased DA levels in both the prefrontal cortex (PFC) and striatum, while baicalin significantly increased DA levels only in the striatum. The results of the present study showed that baicalin treatment was effective for controlling the core symptoms of ADHD. Baicalin increased DA levels only in the striatum, which suggested that baicalin may target the striatum. The increased DA levels may partially be attributed to the increased mRNA and protein expression of TH, SNAP25, VMAT2, and syntaxin 1a. Therefore, these results suggested that the pharmacological effects of baicalin were associated with the synthesis, vesicular localization, and release of DA and might be effective in treating ADHD. However, further studies are required to better understand the molecular mechanisms underlying these findings.

Validation of In utero Tractography of Human Fetal Commissural and Internal Capsule Fibers with Histological Structure Tensor Analysis

Diffusion tensor imaging (DTI) and tractography offer the unique possibility to visualize the developing white matter macroanatomy of the human fetal brain in vivo and in utero and are currently under investigation for their potential use in the diagnosis of developmental pathologies of the human central nervous system. However, in order to establish in utero DTI as a clinical imaging tool, an independent comparison between macroscopic imaging and microscopic histology data in the same subject is needed. The present study aimed to cross-validate normal as well as abnormal in utero tractography results of commissural and internal capsule fibers in human fetal brains using postmortem histological structure tensor (ST) analysis. In utero tractography findings from two structurally unremarkable and five abnormal fetal brains were compared to the results of postmortem ST analysis applied to digitalized whole hemisphere sections of the same subjects. An approach to perform ST-based deterministic tractography in histological sections was implemented to overcome limitations in correlating in utero tractography to postmortem histology data. ST analysis and histology-based tractography of fetal brain sections enabled the direct assessment of the anisotropic organization and main fiber orientation of fetal telencephalic layers on a micro- and macroscopic scale, and validated in utero tractography results of corpus callosum and internal capsule fiber tracts. Cross-validation of abnormal in utero tractography results could be achieved in four subjects with agenesis of the corpus callosum (ACC) and in two cases with malformations of internal capsule fibers. In addition, potential limitations of current DTI-based in utero tractography could be demonstrated in several brain regions. Combining the three-dimensional nature of DTI-based in utero tractography with the microscopic resolution provided by histological ST analysis may ultimately facilitate a more complete morphologic characterization of axon guidance disorders at prenatal stages of human brain development.

Compartmentalization of cerebral cortical germinal zones in a lissencephalic primate and gyrencephalic rodent

Previous studies of macaque and human cortices identified cytoarchitectonically distinct germinal zones; the ventricular zone inner subventricular zone (ISVZ), and outer subventricular zone (OSVZ). To date, the OSVZ has only been described in gyrencephalic brains, separated from the ISVZ by an inner fiber layer and considered a milestone that triggered increased neocortical neurogenesis. However, this observation has only been assessed in a handful of species without the identification of the different progenitor populations. We examined the Amazonian rodent agouti (Dasyprocta agouti) and the marmoset monkey (Callithrix jacchus) to further understand relationships among progenitor compartmentalization, proportions of various cortical progenitors, and degree of cortical folding. We identified a similar cytoarchitectonic distinction between the OSVZ and ISVZ at midgestation in both species. In the marmoset, we quantified the ventricular and abventricular divisions and observed similar proportions as previously described for the human and ferret brains. The proportions of radial glia, intermediate progenitors, and outer radial glial cell (oRG) populations were similar in midgestation lissencephalic marmoset as in gyrencephalic human or ferret. Our findings suggest that cytoarchitectonic subdivisions of SVZ are an evolutionary trend and not a primate specific feature, and a large population of oRG can be seen regardless of cortical folding.

Development of axonal pathways in the human fetal fronto-limbic brain: histochemical characterization and diffusion tensor imaging

The development of cortical axonal pathways in the human brain begins during the transition between the embryonic and fetal period, happens in a series of sequential events, and leads to the establishment of major long trajectories by the neonatal period. We have correlated histochemical markers (acetylcholinesterase (AChE) histochemistry, antibody against synaptic protein SNAP-25 (SNAP-25-immunoreactivity) and neurofilament 200) with the diffusion tensor imaging (DTI) database in order to make a reconstruction of the origin, growth pattern and termination of the pathways in the period between 8 and 34 postconceptual weeks (PCW). Histological sections revealed that the initial outgrowth and formation of joined trajectories of subcortico-frontal pathways (external capsule, cerebral stalk-internal capsule) and limbic bundles (fornix, stria terminalis, amygdaloid radiation) occur by 10 PCW. As early as 11 PCW, major afferent fibers invade the corticostriatal junction. At 13-14 PCW, axonal pathways from the thalamus and basal forebrain approach the deep moiety of the cortical plate, causing the first lamination. The period between 15 and 18 PCW is dominated by elaboration of the periventricular crossroads, sagittal strata and spread of fibers in the subplate and marginal zone. Tracing of fibers in the subplate with DTI is unsuccessful due to the isotropy of this zone. Penetration of the cortical plate occurs after 24-26 PCW. In conclusion, frontal axonal pathways form the periventricular crossroads, sagittal strata and 'waiting' compartments during the path-finding and penetration of the cortical plate. Histochemistry is advantageous in the demonstration of a growth pattern, whereas DTI is unique for demonstrating axonal trajectories. The complexity of fibers is the biological substrate of selective vulnerability of the fetal white matter.

Normal gut microbiota modulates brain development and behavior

Microbial colonization of mammals is an evolution-driven process that modulate host physiology, many of which are associated with immunity and nutrient intake. Here, we report that colonization by gut microbiota impacts mammalian brain development and subsequent adult behavior. Using measures of motor activity and anxiety-like behavior, we demonstrate that germ free (GF) mice display increased motor activity and reduced anxiety, compared with specific pathogen free (SPF) mice with a normal gut microbiota. This behavioral phenotype is associated with altered expression of genes known to be involved in second messenger pathways and synaptic long-term potentiation in brain regions implicated in motor control and anxiety-like behavior. GF mice exposed to gut microbiota early in life display similar characteristics as SPF mice, including reduced expression of PSD-95 and synaptophysin in the striatum. Hence, our results suggest that the microbial colonization process initiates signaling mechanisms that affect neuronal circuits involved in motor control and anxiety behavior.

The ganglionic eminence--a putative intermediate target of amygdaloid connections

The superior part of the ganglionic eminence has been shown to act as an intermediate target for outgrowing axons of projections between the thalamus and the cerebral cortex. This study aims at investigating whether amygdaloid projections transiently contact the inferior portion of the human ganglionic eminence which directly borders upon the amygdala. Between 16 and 20 weeks of gestation a high number of small fiber bundles which were immunolabelled with anti-MAP1b and anti-SNAP-25 could be traced from the amygdala towards the mantle zone of the ganglionic eminence. These fiber bundles left a fiber system which coursed from the amygdala towards the entorhinal cortex. Within the mantle zone of the ganglionic eminence immunoreactive puncta indicative of fiber termination were observed. After 22 weeks of gestation the number of fibers entering the ganglionic eminence gradually decreased. These results provide the first evidence that the marginal zone of the inferior ganglionic eminence is likely to constitute an intermediate target for growing axons which belong the amygdaloid projection to the entorhinal cortex.

Ganglionic eminence of the human fetal brain--new vistas

This review deals with recent findings concerning the complex functions of the ganglionic eminence (GE), which represents a conspicuous domain of the telencephalic proliferative zone and persists nearly throughout fetal life. The GE not only contains precursor neurons of the basal ganglia, it also contributes significantly to the population of interneurons in the cerebral cortex and to a population of thalamic neurons. The latter migrate through a distinct transient structure, the gangliothalamic body (GTB). The GE also represents an intermediate target for growing thalamic axons (on their way to the cerebral cortex) and cortical axons (on their way to the thalamus). In developmental neuropathology the GE plays an important role in prematurely born infants. The pathogenesis of GE bleedings is discussed with regard to the abundant expression of interleukin-6 (IL-6) receptors on GE cells. The consequences of such bleedings are discussed in view of cellular responses, such as the induction of leukemia inhibitory factor (LIF) expression in GE cells after hemorrhage.

Expression of calbindin and calretinin in the human ganglionic eminence

The conspicuous ganglionic eminence representing a part of the telencephalic proliferative zone contains neuroblasts of the striatum. Recently it has been found to contribute significantly to the class of interneurons in the cerebral cortex. Subpopulations of cortical interneurons contain calretinin and calbindin. The expression of calretinin and calbindin in the ganglionic eminence and adjacent areas has been investigated immunocytochemically during fetal development using the brains of 10 infants ranging in age from 16 and 26 weeks gestation. Between 16 and 20 weeks gestation, numerous calretinin-immunreactive nerve cells are found in the ganglionic eminence, particularly in the mantle and the intermediate zones. The number of calretinin-immunoreactive cells decreases gradually from 21 weeks gestation onwards. Larger calbindin-immunoreactive cells are seen in the ganglionic eminence, and their number increases from 20 weeks gestation in the mantle zone. These results may indicate that calretinin-immunoreactive precursor cells, found in the ganglionic eminence, tangentially migrate toward the cortex. Moreover, the mantle zone displaying a specific calretinin and calbindin immunolabeling may represent an intermediate target for outgrowing axons. The findings are discussed with regard to central nervous system complications in preterm infants involving the ganglionic eminence.

Expression of leukemia inhibitory factor in the ganglionic eminence of the human fetal brain after bleedings

Bleedings in the ganglionic eminence (GE) being a prominent domain of the telencephalic proliferative zone is a frequent complication of preterm infants. Such bleedings may induce cellular responses in the vicinity of the lesion. Using immunohistochemistry, this study demonstrates for the first time that leukemia inhibitory factor (LIF) belonging to the family of neuropoetic cytokines is expressed in GE cells up to 200 microm from the lesion (six brains, gestational age 22-26 weeks); whereas control brains do not exhibit any LIF-immunoreactive cells in the GE. The expression of LIF in cases with bleedings may interfere with normal developmental processes taking place within the ganglionic eminence.

Expression of MAP1a and MAP1b in the ganglionic eminence and the internal capsule of the human fetal brain

The expression of microtubule-associated proteins 1a and 1b (MAP1a and 1b) were investigated in two transient structures, the ganglionic eminence (GE) being a prominent part of the telencephalic proliferative zone and the perireticular nucleus (PR) within the internal capsule (IC). Anti-MAP1a immunolabels PR neurons from 18 weeks of gestation (wg) onwards, whereas anti-MAP1b immunolabels long IC fibers between 18 and 22 wg. MAP1b is further present in thalamic fibers that seem to terminate at the medial margin of the GE, in a moderate number of cells of the GE and its medial extension, the gangliothalamic body (GTB). From 26 to 33 wg MAP1b is expressed in short fiber bundles of the IC, a few MAP1b-positive cells are seen in the GE. MAP1a has so far been described to appear in differentiated neurons and to be related to late developmental events. However, the transient PR being involved in axonal guidance as an intermediate target shows a precocious MAP1a-expression. The MAP1b-finding that thalamocortical fibers accumulate at the GE-margin indicates that this region represents an intermediate target for these fibers. The short MAP1b fiber bundles found in the IC are in accordance with cell culture experiments showing that MAP1b is concentrated in distal parts of outgrowing axons.