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PubMed2002

Molecular mechanisms governing Pcdh-gamma gene expression: evidence for a multiple promoter and cis-alternative splicing model.

The genomic architecture of protocadherin (Pcdh) gene clusters is remarkably similar to that of the immunoglobulin and T cell receptor gene clusters, and can potentially provide significant molecular diversity. Pcdh genes are abundantly expressed in the central nervous system. These molecules are primary candidates for establishing specific neuronal connectivity. Despite the extensive analyses of the genomic structure of both human and mouse Pcdh gene clusters, the definitive molecular mechanisms that control Pcdh gene expression are still unknown. Four theories have been proposed, including (1) DNA recombination followed by cis-splicing, (2) single promoter and cis-alternative splicing, (3) multiple promoters and cis-alternative splicing, and (4) multiple promoters and trans-splicing. Using a combination of molecular and genetic analyses, we evaluated the four models at the Pcdh-gamma locus. Our analysis provides evidence that the transcription of individual Pcdh-gamma genes is under the control of a distinct but related promoter upstream of each Pcdh-gamma variable exon, and posttranscriptional processing of each Pcdh-gamma transcript is predominantly mediated through cis-alternative splicing.

Alleles↗
PubMed2001

A layered neural continuum architecture in attention and seizure disorders.

Neural continuum theory concerns regions containing large numbers of neurons. Connections within a region are not specified and those between regions are probabilistic. Constituent cells can be treated as purely "excitatory" or "inhibitory." In a layered geometry, with a time delay between layers, delay is the variable controlling the linear behavior of the system, in particular, growth of small disturbances. Two layers of cells of opposite types structurally resemble and functionally model the attention centers of the brain (the reticular formation). Attention shifts among competing regions through changes in local inhibitory time waves and their spatial propagation. Increase in delay above a critical value, leads to large amplitude, spatially uniform activity; non-linear extension of the two-layer model predicts potentials in qualitative agreement with those observed during seizures. The preferentially amplified spatial-frequency of normal waves remains relatively constant with delay. Since it is proportional to the locally varying mean lateral axonal extent, spatial-frequency is a signature by which the most compelling region can be recognized by higher brain centers.

Attention↗
PubMed2001

An approach to the complexity of the brain.

The establishment of ordered neuronal connections is supposed to take place under the control of specific cell adhesion molecules (CAM) which guide neuroblasts and axons to their appropriate destination. The extreme complexity of the nervous system does not provide a favorable medium for the development of deterministic connections. Simon's [112] theorems offer a mean to approach the high level of complexity of the nervous system. The basic tenet is that complex systems are hierarchically organized and decomposable. Such systems can arise by selective trial and error mechanisms. Subsystems in complex systems only interact in an aggregate manner, and no significant information is lost if the detail of aggregate interactions is ignored. A number of nervous activities, which qualify for these requirements, are shown. The following sources of selection are considered: internal and external feedbacks, previous experience, plasticity in simple structures, and the characteristic geometry of dendrites. The role played by CAMs and other membrane-associated molecules is discussed in the sense that they are either inductor molecules that turn on different homeobox genes, or downstream products of genes, or both. These molecules control cellular and tissular differentiation in the developing brain creating sources of selection required for the trial and error process in the organization of the nervous tissue.

Animals↗
PubMed1995

Involvement of serotonin in developmental plasticity of kitten visual cortex.

During a critical period of postnatal development, neuronal connections in the kitten visual cortex are susceptible to experience-dependent modifications. These modifications are facilitated by the neuromodulators noradrenaline and acetylcholine. To address the question of whether serotonin (5-hydroxytryptamine; 5-HT), the other major neuromodulator in the cerebral cortex, also plays a role in developmental plasticity, we investigated whether interference with serotoninergic transmission in the kitten visual cortex affects ocular dominance (OD) plasticity. The serotonin neurotoxin 5,7-dihydroxytryptamine or the serotonin receptor blockers ketanserin and methysergide were infused into the visual cortex of kittens undergoing monocular deprivation. We found that both methods of disrupting serotoninergic transmission reduced OD plasticity. However, to be effective, the receptor blockers ketanserin and methysergide had to be applied in combination, suggesting that coactivation of serotonin receptor subtypes of both the 5-HT1 and 5-HT2 families have a permissive function in OD plasticity. Since activation of 5-HT2 receptors stimulates phosphoinositide hydrolysis, our data suggest that second messengers from the phospholipid pathway may play an important role in developmental plasticity of visual cortex.

5,7-Dihydroxytryptamine↗
PubMed1991

Hypothalamic blood flow autoregulation remains unaltered following surgical and pharmacological blockade of central vasopressin.

Experiments were carried out in urethane anaesthetized, ventilated rats to determine if brain arginine-vasopressin (AVP) plays a physiological role in cerebral blood flow autoregulation. Autoregulation was tested by determining local hypothalamic blood flow in the mediobasal hypothalamic area (HBF; H2-gas clearance technique) during consecutive stepwise lowering of systemic mean arterial pressure to 80, 60 and 40 mm Hg, by hemorrhage. Endogenous AVP was blocked by transecting the rostral, lateral and dorsal neuronal connections of the hypothalamus (including the median eminence) from all major brain areas, by bilateral transection of the vasopressin-containing fibres in the hypothalamo-hypophyseal tract to the median eminence at the level of the lateral retrochiasmatic area (RCAL), and finally by intracerebroventricular (i.c.v.) administration of an AVP antagonist, d(CH2)5Tyr(Me)AVP (AAVP). Significant increases of daily water intake indicated impaired vasopressin release following both types of surgical transection. Resting HBF was significantly elevated both after surgical isolation of the hypothalamus and after 10 ng AAVP administration compared to controls. Blood flow autoregulation in the hypothalamic region was seriously impaired following surgical isolation of the hypothalamus. However, HBF autoregulation remained just as effective as that of the control rats following either selective bilateral transection of the vasopressin pathways or following AAVP treatment. The present data indicate that AVP may play a role in the control of resting hypothalamic blood flow, but does not support a role of AVP in HBF autoregulatory mechanisms.

Animals↗
PubMed1986

Utilization of a polyethylene enclosure for nerve tracing studies in the rat ovary.

A commonly used technique for mapping neuronal connections in the peripheral nervous system involves the injection of a tracer substance into a peripheral organ. The tracer is taken up by nerve terminals at the injection site and transported retrogradely to motor or sensory perikarya where it can be visualized. One of the pitfalls of this technique is that tracer may leak from the injection site, enter nerve terminals adjacent to the injection area and thus cause erroneous interpretations. Similarly, some tracers may enter blood vessels and be taken up by nerve cell bodies indiscriminately. In order to circumvent these potential problems in studies on the innervation of the rat ovary, a polyethylene enclosure for the organ was fabricated from a BEEM capsule. The retrograde tracer, True blue, was then applied topically on the ovarian surface inside the enclosure. In chronic experiments, specifically labeled ovarian nerve cell bodies were identified in dorsal root and preaortic ganglia. Utilization of this simple and effective enclosure eliminates the false-positive and non-specific labeling of perikarya due to diffusion and blood-borne transport of the tracer from the injection area.

Animals↗
PubMed1986

Synaptic relationships between neurons containing vasopressin, gastrin-releasing peptide, vasoactive intestinal polypeptide, and glutamate decarboxylase immunoreactivity in the suprachiasmatic nucleus: dual ultrastructural immunocytochemistry with gold-substituted silver peroxidase.

In order to examine the morphological substrates for neuronal connections between cells of the hypothalamic suprachiasmatic nucleus (SCN) that contain immunoreactivity for different neurotransmitters, a double ultrastructural immunocytochemical analysis was used. For double immunostaining, the first neuroactive substance antigen was labeled with gold-substituted silver-intensified peroxidase (GSSP), which results in a granular gold deposit of high electron and light opacity. The second antigen was labeled with peroxidase and a diaminobenzidine chromagen. The GSSP reaction product greatly increased the visibility of immunoreactive structures, with both light and electron microscopy. Intensification with the GSSP method worked at all depths of thick tissue sections as determined with analysis of immunostained sections cut perpendicular to their flat surface, and with analysis of thick 80-micron sections of brain tissue into which horseradish peroxidase (HRP) has been microinjected. On a nitrocellulose dot-blot comparison of different substrates for HRP, the GSSP intensification compared favorably with tetramethylbenzidine, but unlike tetramethylbenzidine, the GSSP was stable in a wide range of buffers. In addition to diaminobenzidine, the GSSP reaction was used to intensify and stabilize both the Hanker-Yates reagent and tetramethylbenzidine on the nitrocellulose model system. Through the use of the GSSP reaction, five new synaptic relationships in the suprachiasmatic nucleus were revealed. By increasing the sensitivity of the peroxidase method by silver-gold intensification, immunoreaction product could be found in dendrites at a greater distance from the perikaryon than in nonintensified material. Because of this greater sensitivity, the neuroactive substance contained in the cell of origin of a dendrite could sometimes be identified. Boutons immunoreactive for vasopressin-associated neurophysin were found to make synaptic contact with postsynaptic dendrites that also contained vasopressin-neurophysin immunoreactivity. Similarly, boutons containing gastrin-releasing peptide immunoreactivity made synaptic contact with cells also exhibiting gastrin-releasing peptide immunoreactivity. Neurons stained with GSSP reaction product could be easily discriminated from those containing only HRP-precipitated diaminobenzidine, allowing the simultaneous use of these two markers in the same 30-micron tissue section and subsequently in ultrathin sections for electron microscopy.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2002

Syndecan-3-deficient mice exhibit enhanced LTP and impaired hippocampus-dependent memory.

Syndecan-3 (N-syndecan) is a transmembrane heparan sulfate proteoglycan expressed predominantly in the nervous system in a developmentally regulated manner. Syndecan-3 has been suggested to play a role in the development and plasticity of neuronal connections by linking extracellular signals to the regulation of the cytoskeleton. To study its physiological functions, we produced mice deficient in syndecan-3 by gene targeting. The mutant animals are healthy, are fertile, and have no apparent defects in the structure of the brain. We focused on characterizing the functions of the hippocampus, a brain area where expression of syndecan-3 is prominent in adults. Mice lacking syndecan-3 exhibited an enhanced level of long-term potentiation (LTP) in area CA1, while basal synaptic transmission and short-term plasticity were similar to those in wild-type animals. Further, the mutant mice were not responsive to the syndecan-3 ligand heparin-binding growth-associated molecule, which inhibits LTP in area CA1 in wild-type animals. Behavioral testing of the syndecan-3-deficient mice revealed impaired performance in tasks assessing hippocampal functioning. We suggest that syndecan-3 acts as an important modulator of synaptic plasticity that influences hippocampus-dependent memory.

Animals↗
PubMed1996

In vivo observations of timecourse and distribution of morphological dynamics in Xenopus retinotectal axon arbors.

Changes in neuronal structure can contribute to the plasticity of neuronal connections in the developing and mature nervous system. However, the expectation that they would occur slowly precluded many from considering structural changes as a mechanism underlying synaptic plasticity that occurs over a period of minutes to hours. We took time-lapse confocal images of retinotectal axon arbors to determine the timecourse, magnitude, and distribution of changes in axon arbor structure within living Xenopus tadpoles. Images of axons were collected at intervals of 3 min, 30 min, and 2 h over total observation periods up to 8 h. Branch additions and retractions in arbors imaged at 3 or 30 min intervals were confined to shorter branches. Sites of additions and retractions were distributed throughout the arbor. The average lifetime of branches was about 10 min. Branches of up to 10 microns could be added to the arbor within a single 3 min observation interval. Observations of arbors at 3 min intervals showed rapid changes in the structure of branchtips, including transitions from lamellar growth cones to more streamlined tips, growth cone collaps, and re-extension. Simple branchtips were motile and appeared capable of exploratory behavior when viewed in time-lapse movies. In arbors imaged at 2-h intervals over a total of 8 h, morphological changes included longer branches, tens of microns in length. An average of 50% of the total branch length in the arbor was remodeled within 8 h. The data indicate that the elaboration of the arbor occurs by the random addition of branches throughout the arbor, followed by the selective stabilization of a small fraction of the new branches and the retraction of the majority of branches. Stabilized branches can then elongate and support the addition of more branches. These data show that structural changes in presynaptic axons can occur very rapidly even in complex arbors and can therefore play a role in forms of neuronal plasticity that operate on a timescale of minutes.

Animals↗
PubMed1998

Calcium imaging and multielectrode recordings of global patterns of activity in the developing nervous system.

Complex but coordinated interactions involving ensembles of neuronal cells result in the accurate processing of information in the adult central nervous system. However, recent studies monitoring the global patterns of activity of neuronal populations have demonstrated that immature neurons also interact to produce coordinated patterns of activity during the early stages of development. In particular, these patterns of coordinated activity occur during the period when neuronal connections are established, thus leading us to believe that such activity patterns might underlie the precision to which many neural pathways are wired up. Multielectrode recording and calcium imaging are two of the techniques that have been instrumental in revealing the spatial and temporal properties of the coordinated activity of developing neural networks in vitro. While multielectrode arrays measure the action potential activity of the cells, calcium imaging permits changes in intracellular calcium levels to be monitored over time. Both techniques have been used successfully to monitor the activity of cellular networks in culture, but they have also been applied in assessing the patterns of activity in intact or semi-intact pieces of neural tissues, such as the developing retina, neocortex and spinal cord. More recently, it has also been possible to correlate the structure and function of the cellular components of the networks by combining intracellular dye filling with the multineuronal recordings. In this review, brief descriptions and the applications of the two techniques will be presented, and the advantages and limitations of multielectrode array will be compared with that of calcium imaging using recordings of the developing mammalian retina as the primary example.

Action Potentials↗
PubMed1996

Distribution of nitric oxide synthase-immunoreactive neurons in fetal rat brains at embryonic day 15 and day 19.

Although nitric oxide (NO) is hypothesized to play a role in the modelling of neuronal connections in the developing brain, no precise histological information has been reported on nitric oxide synthase immunoreactive (NOS-IR) structures in the embryonic brain. Thus, we examined the distribution of NOS-IR structures in the rat brain at embryonic day 15 (E15) and day 19 (E19), as a stage of early embryonic neurogenesis and active synaptogenesis, respectively. In the brain at E15, a few NOS-IR cell bodies were observed in the diencephalon near the 3rd ventricle and in the pons. By E19, the number of NOS-IR cells was greatly increased. Many NOS-IR cells were distributed throughout the forebrain and the medulla oblongata. NOS-IR cells of the neostriatum were located in its ventrolateral two-thirds. NOS-IR cells in the hypothalamus were distributed densely in the medial part while sparsely in the latero-ventral part, suggesting medio-lateroventral directions of NOS development. In the lower brainstem, on the other hand, NOS-IR cells were distributed in a similar pattern to that reported in adult rat, indicating earlier development of synaptic refinement in this area. The number of NOS-IR cells in the cerebral cortex and the cerebellum was very few.

Animals↗
PubMed2001

Nicotine-induced alterations in the expression of nicotinic receptors in primary cultures from human prenatal brain.

The nicotinic receptor proteins and gene transcripts for the different nicotinic receptor subunits exist in human prenatal brain already at 4-5 weeks of gestation. The early presence of nicotinic receptors suggests an important role for these receptors in modulating dendritic outgrowth, establishment of neuronal connections and synaptogenesis during development. When measurements of nicotinic receptors using [(3)H]epibatidine (labelling both the alpha3 and alpha4 subtype) and [(3)H]cytisine (labelling the alpha4 subtype) were performed in intact cells from the cortex, subcortical forebrain and mesencephalon (7.5-11 weeks of gestation), the highest specific binding for both ligands was detected in cells from mesencephalon, followed by subcortical forebrain and cortex. The effects of nicotine exposure were studied in primary cultures of prenatal brain (7.5-11 weeks of gestation). Treatment with nicotine (1-100 microM) for 3 days significantly increased the specific binding of [(3)H]epibatidine and [(3)H]cytisine in cortical cells but not in cells from subcortical forebrain and mesencephalon brain regions, indicating region-specific differences in the sensitivity to nicotine exposure. Relative quantification of mRNA showed that the expression of the nicotinic receptor subunits alpha3 and alpha7, but not alpha4, was increased in cortical cells after nicotine treatment. These findings support the assumption of a potential risk of disturbance in the functional role of nicotinic receptors during brain development as a consequence of maternal smoking during pregnancy.

Alkaloids↗
PubMed1995

In vitro development of vertebrate central synapses.

This article deals with basic determinants of synaptic efficacy during development of glutamatergic and GABAergic synaptic transmission: location and number of release sites, release probability and single cell-activated (unitary) conductances. We hypothesize that both types of neuronal connections differ in major aspects of synaptogenesis. Disregarding the fact that various test models and cell types could render diverging results, it can be observed that glutamatergic terminals display a preference for dendrites, whereas GABAergic terminals select soma locations at initial stages of development. Glutamatergic synapses are characterised by receptor accumulation in the region of terminal apposition, whereas in GABAergic synapses receptor concentration is weak, if present at all. The expression of glutamate receptors (GluRs), but not GABAA receptors is under control of interneurons. Developmental changes in glutamatergic synaptic transmission have not yet been assessed by quantal analysis. For GABAergic synapses, first results are now available from a culture preparation of the rat superior colliculus. In general terms, functional maturation seemed to lag behind the formation of structurally differentiated release sites. Compound binomial analysis revealed that during in vitro development a considerable fraction of GABAergic terminals remained in a low efficacy release state (p < 0.2). A developmental increase in synaptic strength was reached by the appearance of singular highly effective release sites. Presynaptic maturation could be manipulated by long-term drug treatment. Addition of GluR antagonists significantly increased amplitudes and decreased the coefficients of variations of evoked inhibitory postsynaptic currents. Thus, the strength of inhibitory synaptic transmission could be influenced by the status of heteronymous synaptic input.

Animals↗
PubMed1995

Decreased expression of the embryonic form of the neural cell adhesion molecule in schizophrenic brains.

The regulated expression of neural cell adhesion molecule (NCAM) isoforms in the brain is critical for many neurodevelopmental processes including neurulation, axonal outgrowth, and the establishment of neuronal connectivity. We have investigated the expression of the major adult isoforms of NCAM (NCAM-180, NCAM-140, and NCAM-120) and its embryonic highly polysialylated isoform (PSA-NCAM) in the hippocampal region of postmortem brains from 10 schizophrenic and 11 control individuals. Immunohistochemical analysis with a monoclonal antibody recognizing the PSA-NCAM revealed immunoreactivity primarily in the dentate gyrus and in a subset of cells in the hilus region. We have observed a 20-95% reduction in the number of hilar PSA-NCAM-immunoreactive cells in the great majority of schizophrenic brains. The change in PSA-NCAM immunoreactivity is not obvious in other hippocampal subfields. Western blots of tissues from the hippocampal region (as well as from the frontal cortex) probed with a polyclonal antibody recognizing all NCAM isoforms did not reveal significant changes in the overall expression of NCAM, suggesting that the decrease in PSA-NCAM-immunoreactive cells may be related to post-translational processing of the molecule. The expression of this embryonic form of NCAM has been proposed to be related to synaptic rearrangement and plasticity. Therefore, the decrease in PSA-NCAM immunoreactivity in schizophrenic hippocampi may suggest an altered plasticity of this structure in a large proportion of schizophrenic brains. These findings may bear significance to the "neurodevelopmental hypothesis" of schizophrenia.

Adult↗
PubMed1994

Postnatal development of glial fibrillary acidic protein, vimentin and S100 protein in monkey visual cortex: evidence for a transient reduction of GFAP immunoreactivity.

In the cerebral cortex of some species, the gradual appearance of glial fibrillary acidic protein (GFAP) is often interpreted as reflecting the parallel maturation of neuronal connectivity. We studied the postnatal maturation of astrocytes in the primary visual cortex of Callithrix jacchus using antibodies against GFAP, vimentin and S100 protein as immunohistochemical markers. In the cortical grey matter of this species, the overall GFAP-immunoreactivity (IR) as measured by image analysis is high at birth (130% of the adult value), decreases until about 3 months (80%) and increases again towards adult values (100%). Vimentin-IR was high at birth, and declined towards 3 months and later. In contrast, S100-IR augmented postnatally in neuropil, and showed a laminar shift of maximum IR from layer IV to supragranular layers during ontogenesis. The decrease of GFAP-IR is predominantly due to changes in density of GFAP-positive (+) astrocytes within cortical tissue (newborn: 18,600 GFAP+astrocytes/mm3; 1 month: 11,600/mm3; 3 months: 5,700/mm3; adult: 10,200/mm3), while the overall number of astrocytes remained relatively constant as shown by the number of S100-positive astrocytic cell bodies. At times of low GFAP-IR a reduced area density of intermediate filaments was found in astrocytes by electron microscopy. The period of reduced GFAP-expression coincides with the time of prominent synapse remodeling in the visual cortex of marmosets. These data suggest that GFAP-expression may depend on functional conditions rather than time-dependent maturation.

Aging↗
PubMed1997

Mitral/tufted cell activity is attenuated and becomes uncoupled from respiration following naris closure.

Patterned neural activity helps to establish neuronal connectivity, produce coding of sensory information, and shape synaptic strengths. Here we demonstrate that normal olfactory bulb development might rely on spatial and temporal patterns of afferent neural activity. Neonatal naris occlusion profoundly impacts the development of the ipsilateral olfactory bulb, including reduced bulb volume, decreased protein synthesis, and increased cell death. Relatively few morphologic changes occur if closure is performed postweaning. We examined the immediate electrophysiological consequences of occlusion across this developmentally sensitive period by recording spontaneous and odor-driven mitral/tufted cell responses while the naris was open, closed, and then reopened. In 1-week-old animals, occlusion severely attenuated spontaneous activity, and presentation of the broad-spectrum odorant amyl acetate failed to evoke responses. In 2- and 4-week old rats, spontaneous activity was also reduced by naris closure. However, some cells remained responsive to concentrated odors, even in animals with transected anterior commissures, suggesting passage of odors across the septal window or retronasal pathways. In all age groups, cellular activity became uncoupled from the respiratory cycle. Approximately 47% (18 of 38) of the mitral/tufted cells exhibited activity that was correlated with respiration in the open-naris state, while only 5% (2 of 38) were coupled during naris closure. These data (a) indicate that naris closure reduces both spontaneous and odor-evoked responses, and (b) provide an electrophysiological correlate to a sensitive period in bulb development. The loss of respiration-related synchrony and the reduced activity of mitral/tufted cells may synergistically contribute to the diverse consequences of naris closure on bulb development.

Animals↗
PubMed1983

Cross-correlation analysis of geniculostriate neuronal relationships in cats.

The organization of geniculate inputs to a cat's visual cortical cell was studied by a cross-correlation technique. Simultaneous extracellular recordings were made in the lateral geniculate nucleus and in the striate cortex, and neuronal connectivity between a geniculate cell and a striate cell was examined by cross-correlograms of their impulse discharges under photic stimuli. Of 243 pairs of geniculate and striate cells with overlapping receptive fields, 82 showed positive correlations with short (0.9-2.7 ms) delay times. The delays in 65 of the 82 pairs were short enough to infer that the geniculate cell exerted monosynaptic excitatory action on the striate cell. Monosynaptic excitations were found in all types of striate cells. Those in cells with exclusively an on area or an off area (E-on/off cells) or in simple cells originated mostly from X geniculate cells; those in special-complex cells originated exclusively from Y geniculate cells; and those in standard-complex cells arose from both X and Y geniculate cells. The convergence number from geniculate cells to an E-on/off or simple striate cell was estimated as more than 10, since about 1/10 of the discharges from an E-on/off or simple cell in response to a moving stimulus was correlated with discharges from a geniculate cell. A larger convergence number (more than 30) was obtained for complex cells. Convergence from 2 to 5 geniculate cells was actually demonstrated in 17 of the 32 striate cells, each of which was tested in pair with 3-14 geniculate cells. The converging inputs thus observed included both X and Y geniculate cells in one E-on, one simple, and three standard-complex cells. They included both on-center and off-center geniculate cells in one simple, one special-complex, and five standard-complex cells. Under stimulation with a stationary light slit, the center fields but not the surround fields of geniculate cells were found to contribute to the receptive fields of the simple striate cells. However, the surround fields of geniculate cells contributed to the subliminal response areas flanking the central areas of E-on/off cells. The center fields of the geniculate cells also contributed to the central areas of the E-on/off cells. These observations suggest different models for simple cells and E-on/off cells as regards the organization of their geniculate inputs; simple cells may receive inputs from both on-center and off-center geniculate cells, but E-on/off cells receive inputs only from one or the other of them.

Animals↗
PubMed1999

R-cadherin expression in the developing and adult zebrafish visual system.

Cell adhesion molecules in the cadherin family have been implicated in histogenesis and maintenance of cellular structure and function in several organs. Zebrafish have emerged as an important new developmental model, but only three zebrafish cadherin molecules have been identified to date (N-cadherin, paraxial protocadherin, and VN-cadherin). We began a systematic study to identify other zebrafish cadherins by screening zebrafish cDNA libraries using an antibody raised to the cytoplasmic domain of mouse E-cadherin. Here, we report a partial cDNA with extensive sequence homology to R-cadherin. Spatial and temporal expression of this putative zebrafish R-cadherin was examined in embryos and adults by Northern analysis, RNase protection, and in situ hybridization. R-cadherin message increased during embryogenesis up to 80 hours postfertilization (hpf) and persisted in adults. In the embryonic brain, R-cadherin was first expressed in groups of cells in the diencephalon and pretectum. In adult zebrafish brain, R-cadherin continued to be expressed in several specific regions including primary visual targets. In the retina, R-cadherin was first detected at about 33 hours postfertilization in the retinal ganglion cell layer and the inner part of the inner nuclear layer. Expression levels were highest during periods of axon outgrowth and synaptogenesis. Retrograde labeling of the optic nerve with 1,1'-dioctadecyl-3,3,3',3', tetramethylindocarbocyanine perchlorate (DiI) followed by in situ hybridization confirmed that a subset of retinal ganglion cells in the embryo expressed R-cadherin message. In the adult, R-cadherin expression continued in a subpopulation of retinal ganglion cells. These results suggest that R-cadherin-mediated adhesion plays a role in development and maintenance of neuronal connections in zebrafish visual system.

Age Factors↗