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PubMed2002

The evolution of engrailed genes after duplication and speciation events.

Members of the engrailed class encode transcription factors involved in major steps of metazoan development. Few developmental regulatory genes have been studied in such a wide range of animals. Furthermore duplications of an ancestral engrailed gene independently generated multiple engrailed paralogues in several organisms. This offers the opportunity to reconstruct the evolution of the engrailed family and to study the processes involved in the functional diversification following speciation or duplication events. The ancestral function of engrailedis very likely involved in neurogenesis. Recent studies in Drosophila and mice have shown its crucial role in neuronal connectivity and neuromuscular targeting. engrailed was probably recruited very early for a role in segmentation through intercalary evolution. Several new functions were acquired later on in specific phyla. Some duplication events have been followed by the loss of one paralogue, whereas others have led to the functional diversification of the paralogues. The Duplication-Degenerescence-Complementation model recently proposed by Force et al. seems to be the main process involved in functional diversification after duplication events. This does not exclude acquisition of new functions for one or both paralogues after duplication. The acquisition of such new functions principally involves the evolution of cis-regulatory sequences, but evolution of the coding sequence has also been revealed. However, in all engrailed duplications studied, even in ancient chromosomal duplications, the paralogues have kept redundant functions. In fact, selection seems to maintain a certain redundancy between engrailed paralogues.

Animals↗
PubMed2006

EphB3 receptor and ligand expression in the adult rat brain.

Eph receptors and ligands are two families of proteins that control axonal guidance during development. Their expression was originally thought to be developmentally regulated but recent work has shown that several EphA receptors are expressed postnatally. The EphB3 receptors are expressed during embryonic development in multiple regions of the central nervous system but their potential expression and functional role in the adult brain is unknown. We used in situ hybridization, immunohistochemistry, and receptor affinity probe in situ staining to investigate EphB3 receptors mRNA, protein, and ligand (ephrin-B) expression, respectively, in the adult rat brain. Our results indicate that EphB3 receptor mRNA and protein are constitutively expressed in discrete regions of the adult rat brain including the cerebellum, raphe pallidus, hippocampus, entorhinal cortex, and both motor and sensory cortices. The spatial profile of EphB3 receptors was co-localized to regions of the brain that had a high level of EphB3 receptor binding ligands. Its expression pattern suggests that EphB3 may play a role in the maintenance of mature neuronal connections or re-arrangement of synaptic connections during late stages of development.

Animals↗
PubMed1979

Two different and compatible intraneuronal labels for ultrastructural study of synaptically related cells.

To examine the structural interactions between synaptically connected neurons in Aplysia, we have developed a method for simultaneously labeling two identified cell with different and compatible intraneuronal marking agents (horseradish peroxidase and [3H]N-acetyl-D-galactosamine) visible in both the light and electron microscopes. Combining these two agents within a single cell yields a third label.

Acetylgalactosamine↗
PubMed1986

Autoradiographic localization of mu- and delta-opiate receptors in the forebrain of the rat.

The autoradiographic distributions of mu opiate receptors, labeled in vitro by [125I]D-Ala2-MePhe4-Met(o)5-ol-enkephalin (FK), and delta-opiate receptors, labeled by [3H]D-Ala2-D-Leu5-enkephalin (DADLE) in the presence of oxymorphone to block high affinity binding to the mu site, were examined and compared in the forebrain of the rat. The mu- and delta-receptors were differentially distributed in most structures. mu Binding sites were found in nearly all gray matter structures and showed heterogeneous patterns of density that were correlated with cytoarchitecture and neuronal connections. Laminar density profiles were seen in laminated structures such as olfactory bulb, cerebral cortex and hippocampus. Highest mu binding densities were in striatal patches and the habenular streak. delta Sites had distinct laminar patterns in the main olfactory bulb and cortex which differed from the mu patterns. The external plexiform layer of the main olfactory bulb had the greatest density of delta binding sites; cortex and striatum were also densely labeled. The septum, globus pallidus, preoptic area and hypothalamus were lightly labeled by both ligands. The magnocellular hypothalamic nuclei had negligible mu and delta labeling. The thalamus had dense mu but sparse delta sites. mu And delta binding sites were both present in the amygdala but had different distributions. Two fiber tracts--optic tract and fasciculus retroflexus--had FK labeling. In contrast, a portion of the corpus callosum was labeled by DADLE and not by FK. The results suggest an association of mu-opiate receptors with sensory, especially olfactory, and limbic projections in the forebrain, and delta-opiate receptors with intrinsic and commissural forebrain pathways.

Amygdala↗
PubMed1987

Different postnatal ontogeny of two [3H]neurotensin binding sites in rat brain.

Two distinct neurotensin binding sites have been identified in rat brain: the NT1-acceptor site (levocabastine-sensitive) and the NT2-receptor site. In rat forebrain, NT2-receptors were present at birth, revealed a maximal level (13.8 fmol/mg tissue) on day 10 of postnatal life but a much lower plateau (3.0 fmol/mg tissue) in adult rats. NT1-acceptors were not detected before day 10 and became maximal at day 30. It is suggested that the loss of NT2-receptor sites during the postnatal development may be the expression of the regression of a transient redundancy of neuronal connections.

Animals↗
PubMed1987

DL-2-[3,4-3H]amino-4-phosphonobutyrate binding sites in the rat hippocampus: distribution and possible physiological role.

Binding sites for the novel, glutamate-like radioligand DL-2-[3,4-3H]amino-4-phosphonobutyrate (DL-[3H]APB) on rat hippocampal synaptic membranes were identified and characterised. The existence of a single, saturable population of binding sites was demonstrated. These appeared to be indistinguishable, in terms of their pharmacological profile and ionic dependence, from those described previously in the striatum and whole brain. The distribution of these sites was also examined using a number of discrete neuronal lesions. A majority of sites (approx. 55%) were located on dentate gyrus granule cells. Smaller populations appeared to be situated on perforant path terminals and on pyramidal cells. However, L-APB was found to be ineffective as an inhibitor of basal and potassium evoked D-[3H]aspartate release from hippocampal slices. A presynaptic location can therefore presumably be ruled out. The likely postsynaptic location of DL-[3H]APB-binding sites in the hippocampus suggests that this site may be involved in synaptic neurotransmission. This possibility is discussed with regard to electrophysiological data concerning the synaptic pharmacology of neuronal connections within the hippocampus.

Amino Acids↗
PubMed1988

Role of the ventromedial hypothalamus in the regulation of adenohypophyseal immunoreactive dynorphin in the rat.

In this study, we have examined the role of the dorsomedial (DMH), ventromedial (VMH) and arcuate (ARH) nuclei of the hypothalamus in the control of hypothalamic and pituitary immunoreactive (ir) dynorphin (Dyn) A and ir-Dyn B in the rat, by evaluating the effect of discrete, bilateral radiofrequency lesions in these structures. Lesions limited to the VMH reduced the content of ir-Dyn in the anterior pituitary but not in the neurointermediate lobe or in the hypothalamus. Gel chromatographic analysis of anterior pituitary extracts confirmed that ir-Dyn is mainly associated with high molecular weight forms containing Dyn A and Dyn B in their sequence. Anterior pituitary extracts of VMH-lesioned rats displayed a clearly lower proportion of these forms. Destruction of the DMH affected only the hypothalamic content of ir-Dyn; ablation of the ARH did not cause any significant change. Our results suggest that ablation of the VMH may disrupt critical neuronal connections to the median eminence originating in this nucleus or crossing it and participating in control of the adenohypophyseal pool of ir-Dyn.

Animals↗
PubMed1990

Sulfonylurea binding sites associated with ATP-regulated K+ channels in the central nervous system: autoradiographic analysis of their distribution and ontogenesis, and of their localization in mutant mice cerebellum.

The localization of a putative ATP-regulated K+ channel in normal rat and neurological mutant mice was studied by light microscopic quantitative autoradiography using a tritiated glibenclamide, an antidiabetic sulfonylurea. Glibenclamide binding sites presented a heterogeneous distribution in the rat central nervous system. Their density was particularly important in substantia nigra reticulata, septohippocampal nucleus, globus pallidus, neocortex, molecular layer of cerebellum, CA3 field and dentate gyrus of hippocampus. Conversely hypothalamic areas, medulla oblongata and spinal cord contained only low amounts of glibenclamide receptors. The ontogenesis of sulfonylurea binding sites was a postnatal phenomenon and seemed to correlate with the maturation of neuronal connectivity. In the cerebellum of neurological mutant mice, the autoradiographic patterns were different to that of wild-type cerebellum. In particular, in the molecular layer of weaver cerebellum, a decrease of 82% of binding site density suggested a presynaptic position of glibenclamide receptors in parallel fibers.

ATP-Binding Cassette Transporters↗
PubMed1990

Effects of unilateral intrahippocampal injection of MK-801 upon local cerebral glucose utilisation in conscious rats.

The effects of unilateral intrahippocampal injections of the non-competitive NMDA receptor antagonist, MK-801, on local cerebral glucose utilisation have been examined in conscious rats using [14C]2-deoxyglucose autoradiography. The intrahippocampal injection of MK-801 (10 nmol) induced significant marked increases in glucose use in the ipsilateral hippocampus molecular layer and dentate gyrus (by 31 and 44%, respectively). Function-related glucose use in brain regions with known neuronal connections with the site of drug administration (e.g. entorhinal cortex, septal nucleus, mamillary body) was minimally altered after intrahippocampal MK-801 administration. Blockade of hippocampal NMDA receptors does not appear to modify activity, as reflected in local glucose utilisation, in hippocampal afferent and efferent circuits in conscious rats.

Animals↗
PubMed1993

Enhanced expression of nitric oxide synthase by rat retina following pterygopalatine parasympathetic denervation.

Removal of the pterygopalatine ganglion enhanced the expression of nitric oxide synthase (NOS) in the ipsilateral rat retina and optic nerve by immunohistochemical and biochemical criteria. The denervation procedure did not alter the apparent histochemical reactivity of retinal cells normally immunoreactive for NOS but did induce expression in retinal ganglion cells and their axons in the retinal nerve fiber layer and optic nerve. After denervation, the induced NOS immunohistochemical reactivity was consistently visualized by day 7, reached a maximum intensity during days 14 to 28, and thereafter gradually attenuated to become barely detectable by microscopy at 10 weeks. Biochemical assays performed two weeks after pterygopalatine denervation confirmed the immunohistochemical observations, especially with regard to the optic nerve. The induced enzyme activity in both retina and optic nerve showed calcium dependency. These results point towards interactions of the ocular parasympathetic innervation and the retina, between which no known neuronal connections exist.

Amino Acid Oxidoreductases↗
PubMedDate not supplied

Is there a neural basis for borderline splitting?

It is proposed here that borderline splitting and borderline pathology may have a neural basis. For the infant who splits its emotional and cognitive constitution of its mother during separation-individuation, the "good mother"--"bad mother" engram may be lateralized in the brain in a different way than for an infant who does not use this defense. The infant may be developmentally vulnerable to the effects of splitting during separation-individuation (18 to 36 months) because interhemispheric communication necessary for mental unity is not possible at this time, since neurons connecting left and right hemispheres are not totally myelinated and because the infant has not yet fully acquired language, a prerequisite for an integrated psychological reality. Two separate, unintegrated--and alternating--mental systems may come into being. Later, as myelination is completed, the infant's split emotional and cognitive constitutions of mother and of self may create a neural "template" for splitting all further experience and behavior through the two separate, alternating mental systems. The possibility that emotional trauma occurring later than separation-individuation, and involving other issues, may be the occasion for splitting is considered, as well as the possibility that a congenital abnormality in brain structure or function may be a primary factor in borderline pathology. Ways to test the hypothesis that borderline splitting has a neural basis are suggested.

Borderline Personality Disorder↗
PubMed1985

Organization of geniculate inputs to visual cortical cells in the cat.

Neuronal connectivity between a geniculate cell and a striate cortical cell was examined by cross-correlograms between their impulse activities. Delayed positive correlations were found in 82 pairs, and the onset delay of the positivity was short enough in 65 pairs to infer that the geniculate cell monosynaptically excited the cortical cell. These monosynaptic excitations were found in both simple and complex cells. By determining connectivity of a cortical cell with multiple geniculate cells, the convergence of X and Y geniculate cells and that of on-center and off-center geniculate cells was demonstrated in several striate cells.

Action Potentials↗
PubMed1995

Complementary gradients in expression and binding of ELF-1 and Mek4 in development of the topographic retinotectal projection map.

Topographic maps with a defined spatial ordering of neuronal connections are a key feature of brain organization. Such maps are believed to develop in response to complementary position-specific labels in presynaptic and postsynaptic fields. However, the complementary labeling molecules are not known. In the well-studied visual map of retinal axons projecting to the tectum, the labels are hypothesized to be in gradients, without needing large numbers of cell-specific molecules. We recently cloned ELF-1 as a ligand for Eph family receptors. Here, RNA hybridization shows matching expression gradients for ELF-1 in the tectum and its receptor Mek4 in the retina. Binding activity detected with alkaline phosphatase fusions of ELF-1 and Mek4 also reveals gradients and provides direct evidence for molecular complementarity of gradients in reciprocal fields. ELF-1 and Mek4 may therefore play roles in retinotectal development and have properties predicted of topographic mapping labels.

Amino Acid Sequence↗
PubMed1981

Central sites and mechanisms of action of nicotine.

Research conducted in this laboratory over the last ten years has been directed towards determining possible CNS sites and mechanisms by which nicotine is producing its psychopharmacological effects. To accomplish these goals, a drug discrimination paradigm was utilized in which rats were trained to detect nicotine using a two-lever operant procedure. In this situation nicotine acted as a discriminative stimulus (DS) to correct lever responding. In other words rats had to be able to differentiate nicotine's effects from saline in order to obtain a food reinforcement. The ability of nicotine to exert its DS effects appear to be dependent upon a stimulation of central nicotinic-cholinergic receptors which are stereospecific to (-)-nicotine. Interestingly, the nicotine DS could not be mimicked or potentiated by elevating brain acetylcholine levels centrally suggesting that the receptor action was non-cholinergic. Additional studies indicated that nicotine is acting at both reticular formation and hippocampus sites. The hippocampal site of nicotine action also appears to be dependent on a dopamine neuron connection as well.

Animals↗
PubMed1996

The concept of transcortical cell assemblies: a key to the understanding of cortical lateralization and interhemispheric interaction.

According to Hebb, elements of higher cognitive processes, such as concepts, words and mental images, are realized in the brain as cortical cell assemblies, i.e. large and strongly connected neuron populations that form functional units. Neurons belonging to such assemblies may be scattered over wide cortical areas, and some cell assemblies may even comprise neurons of both hemispheres (transcortical assemblies). If full activation (ignition) of an assembly leads to fast circulation of neuronal activity in the assembly, this process should be visible in high-frequency cortical responses. Some evidence will be reviewed that cell assembly ignition indeed leads to changes in high-frequency cortical responses which can be recorded in the EEG and MEG. Within the cell assembly-framework, the question of cortical laterality translates into the question of how neurons of transcortical assemblies are balanced between the hemispheres. This approach allows for different degrees of laterality. Recent evidence is summarized that the degree of laterality indeed differs between language units. For example, the cortical representation of certain words appears to be strongly lateralized to the left hemisphere while those of others are less lateralized. If neurons of both hemispheres are part of one assembly bihemispheric processing should lead to a processing advantage compared to processing in the dominant hemisphere alone. The latter appears to be the case for lexical processing, as revealed by recent behavioral studies. In conclusion, the cell assembly-framework suggests a more fine-grained description of the issue of cortical laterality; it is not appropriate to ask whether "modules" supporting higher cortical functions are located either in the left or right hemisphere. Rather, it appears fruitful to ask how the neurons of transcortical cell assemblies are balanced between the hemispheres.

Brain Mapping↗
PubMed1980

Uptake sites of horseradish peroxidase after injection into peritoneal structures: defining some pitfalls.

Following injection of horseradish peroxidase (HRP) either into the jejunal wall or the peritoneal cavity, neurons in the dorsal motor nucleus of the vagus nerve, celiac, nodose and spinal ganglia, and ventral and lateral horns of the spinal cord from the mid-thoracic to lumbar segments were labeled. When HRP was injected into the wall of the exteriorized gut, neurons of the spinal cord were not labeled. Furthermore, there was a significant decrease in the number of labeled neurons in the dorsal motor nucleus and ganglia examined. These results indicate that HRP injected into the intestinal wall could leak into the peritoneal cavity and be taken up and transported to neuronal cell bodies by nerve fibers not terminating in the injection area. The leakage of HRP to nearby abdominal structures and its subsequent uptake by nerve fibers is attributed to the lack of a diffusion barrier across the surfaces of the intestinal wall and the abdominal structures. It is suggested that in applying the HRP techniques for the study of neuronal connections in the peripheral nervous system, it is essential that carefully pla-ned control experiments be undertaken which can overcome the problem of mislabeling due to diffusion from the injection site.

Animals↗
PubMed1988

Simple microcomputer system for mapping tissue sections with the light microscope.

We describe a method for two-dimensional mapping of tissue sections that makes use of a drawing tube, microscope stage encoders and a microcomputer. The drawing tube views the graphics monitor and superimposes the image of the screen cursor and on-screen menus on the specimen image. Thus, the position of every landmark in each microscopic field can be mapped without stage movement while directly viewing the specimen through the microscope. A mouse is used for data entry and program control. Fields mapped in this way are then assembled into a complete map, which can include line drawings as well as up to 20 landmark types. The coordinate values of all landmarks mapped are stored and remain accessible for editing and analysis. High resolution plots are produced. Specialized functions include grain counting, area and perimeter calculations as well as a perimeter limiter that predefines the area to be mapped. The system uses general purpose hardware that is widely available. Many hitherto time-consuming tasks, such as detailed mapping of cell positions, regions of immunocytochemical staining, degenerating fibers, neuronal connections or any other anatomical feature, can be done in a fraction of the time and effort previously involved. These labor savings can be realized while maintaining the highest resolution and enabling statistical analysis since the data are already in digital form.

Animals↗
PubMed1993

Expression of olfactory receptor and transduction genes during rat development.

The molecular components of olfactory reception and regulation are expressed in a tissue-specific manner. The functional attributes mediated by some of these proteins have been previously shown to display a well-defined developmental emergence during the last week of rat gestation. To gain a better understanding of the relations between chemosensory function and neuronal development, we studied the ontogeny of 7 olfactory-specific genes by quantitative PCR. Relative levels of expression during rat development were determined for each gene, starting at embryonic day 15 (E15) and ending at postnatal day 35 (P35). In addition, the level of expression of the different genes was quantified in juvenile rats. The onset of expression for olfactory receptors and the olfactory cation channel at embryonic day 19 (E19) coincides with the functional maturation of the sensory neurons. Olfactory G-protein and adenylyl cyclase are expressed earlier (approximately E16) while olfactory biotransformation enzymes appear later (E20-E21), just before birth. The sequence of developmental expression of olfactory receptor genes has possible implications to the establishment of neuronal connectivity in this sensory pathway.

Animals↗