Inhomogeneous hippocampal activation along the rostrocaudal axis in mice after exploration of novel environment

Levels of the c-Fos protein expression in neurons were used as an index of neural activation in the hippocampus of C57BL/6 mice after their exploration of novel environments. C-Fos expression was measured at 8 levels along the rostrocaudal axis of the hippocampus. In Experiment 1, C57BL/6 mice were trained in a modified 8-arm radial maze to find the entry to a home cage through a target arm (1 day, 6 trials). Animals of control group were trained to enter the home cage through an isolated arm. In mice trained in 8-arm maze, functional rostrocaudal inhomogeneity of hippocampus was found. C-Fos expression was increased, mainly, in the caudal parts of CA1, CA3 and dentate gyrus as compared to the control group. In Experiment 2, C57BL/6 mice were tested (1 day, 6 trials) in a novel open-field arena. In this case, c-Fos activity was increased in CA1 (to a greater extent in the caudal than in rostral parts) and CA3 and dentate gyrus (equally in rostrocaudal direction). Significant positive correlations between the exploration activity and density of c-Fos positive cells were found in both experiments. The findings suggest that exploration in novel environment differentially affects the hippocampal subfields along the hippocampal rostrocaudal axis.     

Developmental gene expression profiling along the tonotopic axis of the mouse cochlea

The mammalian cochlear duct is tonotopically organized such that the basal cochlea is tuned to high frequency sounds and the apical cochlea to low frequency sounds. In an effort to understand how this tonotopic organization is established, we searched for genes that are differentially expressed along the tonotopic axis during neonatal development. Cochlear tissues dissected from P0 and P8 mice were divided into three equal pieces, representing the base, middle and apex, and gene expression profiles were determined using the microarray technique. The gene expression profiles were grouped according to changes in expression levels along the tonotopic axis as well as changes during neonatal development. The classified groups were further analyzed by functional annotation clustering analysis to determine whether genes associated with specific biological function or processes are particularly enriched in each group. These analyses identified several candidate genes that may be involved in cochlear development and acquisition of tonotopy. We examined the expression domains for a few candidate genes in the developing mouse cochlea. Tnc (tenacin C) and Nov (nephroblastoma overexpressed gene) are expressed in the basilar membrane, with increased expression toward the apex, which may contribute to graded changes in the structure of the basilar membrane along the tonotopic axis. In addition, Fst (Follistatin), an antagonist of TGF-β/BMP signaling, is expressed in the lesser epithelial ridge and at gradually higher levels towards the apex. The graded expression pattern of Fst is established at the time of cochlear specification and maintained throughout embryonic and postnatal development, suggesting its possible role in the organization of tonotopy. Our data will provide a good resource for investigating the developmental mechanisms of the mammalian cochlea including the acquisition of tonotopy.     

Hox gene expression reveals regionalization along the anteroposterior axis of the zebrafish notochord

 The vertebrate Hox genes have been shown to confer regional identity along the anteroposterior axis of the developing embryo, especially within the central nervous system (CNS) and the paraxial mesoderm. The notochord has been shown to play vital roles in patterning adjacent tissues along both the dorsoventral and mediolateral axes. However, the notochord’s role in imparting anteroposterior information to adjacent structures is less well understood, especially as the notochord shows no morphological distinctions along the anteroposterior axis and is not generally described as a segmental or compartmentalized structure. Here we report that four zebrafish hox genes: hoxb1, hoxb5, hoxc6 and hoxc8 are regionally expressed along the anteroposterior extent of the developing notochord. Notochord expression for each gene is transient, but maintains a definite, gene-specific anterior limit throughout its duration. The hox gene expression in the zebrafish notochord is spatially colinear with those genes lying most 3’ in the hox clusters having the most anterior limits. The expression patterns of these hox cluster genes in the zebrafish are the most direct molecular evidence for a system of anteroposterior regionalization of the notochord in any vertebrate studied to date. Received: 30 March 1998 / Accepted: 16 June 1998     

Novel gene expression patterns along the proximo-distal axis of the mouse embryo before gastrulation

Background  

To date, the earliest stage at which the orientation of the anterior-posterior axis in the mouse embryo is distinguishable by asymmetric gene expression is shortly after E5.5. At E5.5, prospective anterior markers are expressed at the distal tip of the embryo, whereas prospective posterior markers are expressed more proximally, close to the boundary with the extraembryonic region.     

Functional diversity along the transverse axis of hippocampal area CA1

Decades of neuroscience research have shed light on the hippocampus as a key structure for the formation of episodic memory. The hippocampus is divided into distinct subfields – CA1, CA2 and CA3. While accumulating evidence points to cellular and synaptic heterogeneity within each subfield, this heterogeneity has not received much attention in computational and behavioural studies and subfields have until recently been considered functionally uniform. However, a couple of recent studies have demonstrated prominent functional differences along the proximodistal axis of the CA1 subfield. Here, we review anatomical and physiological differences that might give rise to heterogeneity along the proximodistal axis of CA1 as well as the functional implications of such heterogeneity. We suggest that such heterogeneity in CA1 operates dynamically in the sense that the CA1 network alternates, on a subsecond scale, between a state where the network is primarily responsive to functionally segregated direct inputs from entorhinal cortex and a state where cells predominantly are controlled by more integrated inputs from CA3.     

Distribution of acetylcholinesterase along the dorso-ventral axis of the hippocampal formation in the rabbit

Abstract— The cholesterol ester hydrolase of rat brain, localized almost exclusively in the myelin sheath, has been solubilized from the acidic high-molecular-weight protein fraction of purified myelin. Solubilization required both high ionic strength and an amphoteric detergent, Miranol H2M. Solubilized preparations with apparent purification factors of 300–500 fold over the starting homogenate still contained approx 25% lipid but were retarded on the Sephadex G-200 column. The enzyme was reversibly precipitated when the concentration of either Miranol H2M or KCI was lowered below certain critical levels. The soluble enzyme was characterized for the pH optimum, linearity against incubation time and enzyme protein, and apparent K_m. Activity was dependent on the presence of exogenously added lipid. Phosphatidylserine at optimum concentrations stimulated the hydrolytic activity 25-Fold. Effects of other lipids, bile salts, cations, heating and potential inhibitors were examined. β-Naphthyl oleate was a competitive inhibitor but both β-naphthyl acetate and cholesteryl butyrate were non-competitive inhibitors. These results suggested a heterogenous nature of the rat myelin cholesterol ester hydrolase, possibly with different specificities with respect to the chain length of the acyl group of substrates.     

Regulation of c-Fos expression in the rat olfactory bulbs during olfactory learning

The distribution of c-Fos-immunopositive neurons was examined in the mitral/tufted and granular cell layers in the medium part of the main olfactory bulbs of 18-day-old rats after they had been trained for propionic acid vapour-guided search for dam in the Y-maze. On the next day these pups exhibited a strong preference for the propionic acid odor as compared to the control pups trained for this task without the odor cue and odor-familiarized pups exposed to propionic acid as a novel neutral stimulus. Exposure to propionic acid produced a moderate activation of c-Fos expression, mainly in the granular layer of the dorsomedial part of the bulb. Training in the Y-maze devoid of odor cues resulted in diffuse increase in the number of c-Fos-positive neurons both in the mitral and granular cell layers in all parts of the olfactory bulb. Maze training with the odor cue produced activation of c-Fos expression (which significantly exceeded the non-odor Y-maze group) in the dorsomedial olfactory bulb. These data suggest that associative olfactory conditioning results in activation of c-Fos expression that combines the effect of diffuse motivational excitation and specific olfactory input to the neurons which process odor cues.     

Genes that control dorsoventral polarity affect gene expression along the anteroposterior axis of the Drosophila embryo

At least 13 genes control the establishment of dorsoventral polarity in the Drosophila embryo and more than 30 genes control the anteroposterior pattern of body segments. Each group of genes is thought to control pattern formation along one body axis, independently of the other group. We have used the expression of the fushi tarazu (ftz) segmentation gene as a positional marker to investigate the relationship between the dorsoventral and anteroposterior axes. The ftz gene is normally expressed in seven transverse stripes. Changes in the striped pattern in embryos mutant for other genes (or progeny of females homozygous for maternal-effect mutations) can reveal alterations of cell fate resulting from such mutations. We show that in the absence of any of ten maternal-effect dorsoventral polarity gene functions, the characteristic stripes of ftz protein are altered. Normally there is a difference between ftz stripe spacing on the dorsal and ventral sides of the embryo; in dorsalized mutant embryos the ftz stripes appear to be altered so that dorsal-type spacing occurs on all sides of the embryo. These results indicate that cells respond to dorsoventral positional information in establishing early patterns of gene expression along the anteroposterior axis and that there may be more significant interactions between the different axes of positional information than previously determined.     

Serotonin receptor expression along the dorsal-ventral axis of mouse hippocampus

Using in situ hybridization, we describe, for the first time, the profiles of expression of serotonin receptors (Htr/5-HTR) along the dorsal-ventral axis of mouse hippocampus. cRNA probes for most Htrs, excluding Htr6, were used. All hippocampal subregions and the entorhinal cortex cells providing input into the hippocampus were examined. The study shows that some, but not all, Htrs are expressed in the cells of the hippocampal circuitry. At both the subfield and the cell type levels, a somewhat overlapping pattern is observed. Four serotonin receptors, Htr1a, Htr2a, Htr2c and Htr7, display an expression pattern that changes along the dorsal-ventral axis of the hippocampus. Given the proposed functional differentiation of the hippocampus along its long axis, with the dorsal pole more involved in cognitive functions and the ventral pole more involved in mood and anxiety, our results suggest that serotonin receptors enriched in the ventral pole probably contribute to mood- and anxiety-related behaviours.     

Novel patterns of the gene expression regulation in the prestalk region along the antero-posterior axis during multicellular development of Dictyostelium

Simultaneous hybridization with differentially labeled fluorescent probes for in situ hybridization analysis revealed several novel expression patterns of prestalk genes during multicellular development of Dictyostelium. Seven prestalk genes and one prespore gene (pspA) were analyzed in this study. The patterns identified here indicate that prestalk cells are more heterogeneous than previously thought. Heterogeneity was observed in peripheral prestalk tissues such as the pstAO domain of a slug and the prestalk region surrounding a stalk tube of a culminant. Heterogeneity was also observed in the core pstAB cells of the slug and immature stalk cells within the stalk tube. The upper- and lower-cups of a late culminant were also composed of several subdomains.     

Systems genetic analysis of hippocampal neuroanatomy and spatial learning in mice

Variation in hippocampal neuroanatomy correlates well with spatial learning ability in mice. Here, we have studied both hippocampal neuroanatomy and behavior in 53 isogenic BXD recombinant strains derived from C57BL/6J and DBA/2J parents. A combination of experimental, neuroinformatic and systems genetics methods was used to test the genetic bases of variation and covariation among traits. Data were collected on seven hippocampal subregions in CA3 and CA4 after testing spatial memory in an eight‐arm radial maze task. Quantitative trait loci were identified for hippocampal structure, including the areas of the intra‐ and infrapyramidal mossy fibers (IIPMFs), stratum radiatum and stratum pyramidale, and for a spatial learning parameter, error rate. We identified multiple loci and gene variants linked to either structural differences or behavior. Gpc4 and Tenm2 are strong candidate genes that may modulate IIPMF areas. Analysis of gene expression networks and trait correlations highlight several processes influencing morphometrical variation and spatial learning.     

c-Fos expression in the midbrain periaqueductal gray after chemoreceptor and baroreceptor activation

The pattern of Fos-like immunoreactivity (FLI) in the periaqueductal gray (PAG) associated with activation of arterial chemoreceptors versus baroreceptor afferents was examined in urethane-anesthetized rats. Chemoreflex responses elicited by repeat intravenous injections of potassium cyanide (KCN; 90 microg/kg) significantly increased FLI in all columns of the PAG relative to saline-injected animals. Pressor responses elicited by intravenous phenylephrine (PE) produced a similar pattern of increased FLI throughout the PAG except in the dorsomedial and lateral columns of the caudal PAG, where FLI was minimal. Chemoreflex responses were unaltered by blockade of excitatory amino acid receptors in the dorsomedial PAG, and < 10% of the neurons of the caudal PAG that expressed FLI after KCN stimulation were retrogradely labeled from the A5 region of the caudal ventrolateral pons. These results indicate that integration of chemoreceptor inputs occurs primarily in the dorsal and lateral columns of the caudal PAG, but these neurons have little direct descending influence over lower brain stem regions integral to the central arterial chemoreflex arc.     

Defining global gene expression changes of the hypothalamic-pituitary-gonadal axis in female sGnRH-antisense transgenic common carp (Cyprinus carpio)

Background

The hypothalamic-pituitary-gonadal (HPG) axis is critical in the development and regulation of reproduction in fish. The inhibition of neuropeptide gonadotropin-releasing hormone (GnRH) expression may diminish or severely hamper gonadal development due to it being the key regulator of the axis, and then provide a model for the comprehensive study of the expression patterns of genes with respect to the fish reproductive system.

Methodology/Principal Findings

In a previous study we injected 342 fertilized eggs from the common carp (Cyprinus carpio) with a gene construct that expressed antisense sGnRH. Four years later, we found a total of 38 transgenic fish with abnormal or missing gonads. From this group we selected the 12 sterile females with abnormal ovaries in which we combined suppression subtractive hybridization (SSH) and cDNA microarray analysis to define changes in gene expression of the HPG axis in the present study. As a result, nine, 28, and 212 genes were separately identified as being differentially expressed in hypothalamus, pituitary, and ovary, of which 87 genes were novel. The number of down- and up-regulated genes was five and four (hypothalamus), 16 and 12 (pituitary), 119 and 93 (ovary), respectively. Functional analyses showed that these genes involved in several biological processes, such as biosynthesis, organogenesis, metabolism pathways, immune systems, transport links, and apoptosis. Within these categories, significant genes for neuropeptides, gonadotropins, metabolic, oogenesis and inflammatory factors were identified.

Conclusions/Significance

This study indicated the progressive scaling-up effect of hypothalamic sGnRH antisense on the pituitary and ovary receptors of female carp and provided comprehensive data with respect to global changes in gene expression throughout the HPG signaling pathway, contributing towards improving our understanding of the molecular mechanisms and regulative pathways in the reproductive system of teleost fish.     

Serotonin receptor expression along the dorsal–ventral axis of mouse hippocampus

Using in situ hybridization, we describe, for the first time, the profiles of expression of serotonin receptors (Htr/5-HTR) along the dorsal–ventral axis of mouse hippocampus. cRNA probes for most Htrs, excluding Htr6, were used. All hippocampal subregions and the entorhinal cortex cells providing input into the hippocampus were examined. The study shows that some, but not all, Htrs are expressed in the cells of the hippocampal circuitry. At both the subfield and the cell type levels, a somewhat overlapping pattern is observed. Four serotonin receptors, Htr1a, Htr2a, Htr2c and Htr7, display an expression pattern that changes along the dorsal–ventral axis of the hippocampus. Given the proposed functional differentiation of the hippocampus along its long axis, with the dorsal pole more involved in cognitive functions and the ventral pole more involved in mood and anxiety, our results suggest that serotonin receptors enriched in the ventral pole probably contribute to mood- and anxiety-related behaviours.