Ganglion Cell Soma Research Articles

Modulation of mitochondria in the axon and soma of retinal ganglion cells in a rat glaucoma model

Mitochondrial abnormality has been implicated in various models of retinal ganglion cell (RGC) degeneration. We investigated modulation of mitochondrial membrane permeability and apoptosis-inducing factor (AIF) translocation in a rat experimental glaucoma model. A decrease in MitoTracker-labeled mitochondria around the lamina area of the optic nerve was observed in the glaucomatous eye. Immunoblot analysis for axonal motor proteins showed that a significant decrease in kinesin 1 and myosin Va levels in the glaucomatous optic nerve. A significant decrease in mitochondrial thioredoxin 2 (Trx2) level was observed in the optic nerve after intraocular pressure (IOP) elevation. Translocation of AIF from the mitochondria to the axoplasm and nucleus was observed in the axon and cell body, respectively. Trx2 over-expression in the mitochondrial membrane of RGC-5 cells inhibited AIF translocation, resulting in cytoprotective effect against neurotoxicity induced by TNF-α/buthionine sulfoximine treatment. In vivo transfection was performed with EGFP-Trx2 plasmid and electroporation. Over-expression of Trx2 in the retina and optic nerve indicated the protective effect against high IOP induced axonal degeneration. Thus, the decreased mitochondrial membrane potential and subsequent AIF translocation were involved in the glaucomatous neurodegeneration. Furthermore, modulation of mitochondria through the inhibition of AIF translocation may become a new treatment strategy for neurodegenerative disease, such as glaucoma.

Differential actions of urocortins on neurons of the myenteric division of the enteric nervous system in guinea pig distal colon

Urocortins (Ucns) 1, 2 and 3 are corticotropin-releasing factor (CRF)-related neuropeptides and may be involved in neural regulation of colonic motor functions. Nevertheless, details of the neural mechanism of action for Ucns have been unclear. We have, here, tested the hypothesis that Ucns act in the enteric nervous system (ENS) to influence colonic motor behaviour. We used intracellular recording with 'sharp' microelectrodes, followed by intraneuronal injection of biocytin, and immunohistochemical localization of CRF(1) and CRF(2) receptors in guinea pig colonic tissue. Application of Ucn1 depolarized membrane potentials and elevated excitability in 58% of AH-type and 60% of S-type colonic myenteric neurons. In most of the neurons tested, depolarizing responses evoked by Ucn-1 were suppressed by the CRF(1) receptor antagonist NBI 27914, but were unaffected by the CRF(2) receptor antagonist antisauvagine-30. The selective CRF(2) receptor agonists, Ucn2 and Ucn3, evoked depolarizing responses in 12 and 8% of the AH-type myenteric neurons, respectively, and had no effect on S-type neurons. Antisauvagine-30, but not NBI 27914, suppressed these Ucn2- and Ucn3-evoked responses. Immunohistochemical staining identified CRF(1) as the predominant CRF receptor subtype expressed by ganglion cell somas, while CRF(2)-immunoreactive neuronal somas were sparse. Ucns did not affect excitatory synaptic transmission in the ENS. The results suggest that Ucns act as neuromodulators to influence myenteric neuronal excitability. The excitatory action of Ucn1 in myenteric neurons was primarily at CRF(1) receptors, and the excitatory action of Ucn2 and Ucn3 was at CRF(2) receptors.

DSCAM and DSCAML1 Function in Self-Avoidance in Multiple Cell Types in the Developing Mouse Retina

DSCAM and DSCAM-LIKE1 (DSCAML1) serve diverse neurodevelopmental functions, including axon guidance, synaptic adhesion, and self-avoidance, depending on the species, cell type, and gene family member studied. We examined the function of DSCAM and DSCAML1 in the developing mouse retina. In addition to a subset of amacrine cells, Dscam was expressed in most retinal ganglion cells (RGCs). RGCs had fasciculated dendrites and clumped cell bodies in Dscam(-/-) mice, suggesting a role in self-avoidance. Dscaml1 was expressed in the rod circuit, and mice lacking Dscaml1 had fasciculated rod bipolar cell dendrites and clumped AII amacrine cell bodies, also indicating a role in self-avoidance. Neurons in Dscam or Dscaml1 mutant retinas stratified their processes appropriately in synaptic laminae in the inner plexiform layer, and functional synapses formed in the rod circuit in mice lacking Dscaml1. Therefore, DSCAM and DSCAML1 function similarly in self-avoidance, and are not essential for synaptic specificity in the mouse retina.

The development of Kv4.2 expression in the retina

Throughout the brain, the potassium channel Kv4.2 regulates signal propagation in dendrites and action potential properties in subtypes of neurons. In adult rodents Kv4.2 is expressed predominantly in two bands in the inner plexiform layer (IPL) and in retinal ganglion cell (RGC) somas (Klumpp et al. [15]; Pinto and Klumpp [20]), suggesting a role regulating the activity of specific subtypes of RGCs. To understand the role of Kv4.2 in the regulation of the activity of RGCs during development we determined the developmental expression pattern of Kv4.2 immunoreactivity (Kv4.2-IR). At P4-6 Kv4.2-IR appeared diffusely throughout the IPL in cross-sectioned retinas. From postantal day 10 (P10) through adult there was an additional pair of brighter Kv4.2-IR bands between the ChAT bands that had a reticular pattern in flat-mounted retinas. Kv4.2-IR was not present in somas at P4–6, but appeared in ganglion cell layer (GCL) somas beginning at P10. The fraction of somas expressing Kv4.2 in the GCL was about 8% at P10–11, decreased to 5% at P20–21, then increased to 9% in adult retinas. The restriction of Kv4.2 expression to less than 10% of the GCL somas and the specificity of expression in the IPL suggest that Kv4.2 regulates activity in one or a few functional subtypes of RGCs. The pattern of Kv4.2-IR through postnatal development indicates that Kv4.2-mediated currents are important for development in a subset of RGCs, especially around P10 as the bipolar cells mature.

From ocular hypertension to ganglion cell death: a theoretical sequence of events leading to glaucoma

There is substantial evidence that elevated intraocular pressure (IOP) is a critical risk factor for glaucoma.Even with exhaustive investigation, however, there is still little understanding of the pathologic events that translate increased IOP into the process of retinal ganglion cell death. New studies, particularly in rat and mouse models of glaucoma, have helped elucidate some of the important events associated with the initiation of glaucoma. This review summarizes a 5-stage series hypothesizing that elevated IOP causes deleterious changes to glia in the optic nerve head (stage 1), which activate the autonomous self-destruction of ganglion cell axons (stage 2), leading to the loss of neurotrophic support and apoptotic death of ganglion cell somas in the retina (stage 3). In the initial wave of ganglion cell death, dying cells may adversely affect their neighbouring cells in a wave of secondary degeneration involving glutamate exposure (stage 4).As ganglion cell structures disappear through the processes of cell death, glia are again involved, but this time to replace the lost neural tissue with a glial scar (stage 5).

Progressive ganglion cell loss and optic nerve degeneration in DBA/2J mice is variable and asymmetric

BackgroundGlaucoma is a chronic neurodegenerative disease of the retina, characterized by the degeneration of axons in the optic nerve and retinal ganglion cell apoptosis. DBA/2J inbred mice develop chronic hereditary glaucoma and are an important model system to study the molecular mechanisms underlying this disease and novel therapeutic interventions designed to attenuate the loss of retinal ganglion cells. Although the genetics of this disease in these mice are well characterized, the etiology of its progression, particularly with respect to retinal degeneration, is not. We have used two separate labeling techniques, post-mortem DiI labeling of axons and ganglion cell-specific expression of the βGeo reporter gene, to evaluate the time course of optic nerve degeneration and ganglion cell loss, respectively, in aging mice.ResultsOptic nerve degeneration, characterized by axon loss and gliosis is first apparent in mice between 8 and 9 months of age. Degeneration appears to follow a retrograde course with axons dying from their proximal ends toward the globe. Although nerve damage is typically bilateral, the progression of disease is asymmetric between the eyes of individual mice. Some nerves also exhibit focal preservation of tracts of axons generally in the nasal peripheral region. Ganglion cell loss, as a function of the loss of βGeo expression, is evident in some mice between 8 and 10 months of age and is prevalent in the majority of mice older than 10.5 months. Most eyes display a uniform loss of ganglion cells throughout the retina, but many younger mice exhibit focal loss of cells in sectors extending from the optic nerve head to the retinal periphery. Similar to what we observe in the optic nerves, ganglion cell loss is often asymmetric between the eyes of the same animal.ConclusionA comparison of the data collected from the two cohorts of mice used for this study suggests that the initial site of damage in this disease is to the axons in the optic nerve, followed by the subsequent death of the ganglion cell soma.

Proportion of N-Type Calcium Current Activated by Action Potential Stimuli

N-type calcium currents are important in many neuronal functions, including cellular signaling, regulation of gene expression, and triggering of neurotransmitter release. Often the control of these diverse cellular functions is governed by the spatial and temporal patterns of calcium entry in subcellular compartments. Underlying this issue is the effectiveness of action potentials at triggering calcium channel opening. Chick ciliary ganglion neurons were used as model cells to study the activation of N-type calcium current during action potential depolarization. Several different action potential shapes were recorded, used as voltage command templates, and altered such that control action potential-evoked currents could be compared with those elicited by broadened action potential commands. Depending on the action potential shape used to activate calcium currents in chick ciliary ganglion neurons, and the temperature at which recordings were performed, varying proportions (I/I(max)) of N-type calcium current could be activated. The largest proportion measured occurred using a broad ciliary ganglion cell soma action potential to activate calcium current at 37 degrees C (100%). The smallest proportion measured occurred using a fast, high-temperature-adjusted frog motoneuron nerve terminal action potential to activate calcium current at room temperature (10%). These data are discussed with respect to the impact on cellular signaling and the regulation of transmitter release.

A Secretory-type Protein, Containing a Pentraxin Domain, Interacts with an A-type K+ Channel

A-type K(+) channels belonging to the Shal subfamily are found in various receptor and neuronal cells. Although their kinetics and cell surface expression are regulated by auxiliary subunits, little is known about the proteins that may interact with Kv4 during development. A yeast two-hybrid screening of a cDNA library made from the sensory epithelium of embryonic chick cochlea revealed a novel association of Kv4.2 with a protein containing a pentraxin domain (PPTX). Sequence analysis shows that PPTX is a member of the long pentraxin family, is 53% identical to mouse PTX3, and has a signal peptide at the N terminus. Studies with chick cochlear tissues reveal that Kv4.2 coprecipitates PPTX and that both proteins are colocalized to the sensory and ganglion cells. A yeast two-hybrid assay demonstrated that the last 22 amino acids of the PPTX C terminus interact with the N terminus of Kv4.2. Chinese hamster ovary cells transfected with recombinant PPTX reveal secretory products in both non-truncated and truncated forms. Among the secreted variants are several blocked by Brefeldin A, suggesting export via a classical pathway. PPTX is soluble in the presence of sodium carbonate, suggesting localization to the cytosolic side of the plasmalemma. Immunohistochemical studies show that Kv4.2 and PPTX colocalize in the region of the plasmalemma of Chinese hamster ovary cells; however, both are locked in the endoplasmic reticulum of COS-7 cells, suggesting that PPTX does not act as a shuttle protein. Reverse transcription-PCR demonstrates that PPTX mRNA is found in tissues that include brain, eye, heart, and blood vessels.

Mechanisms of chloride influx during KCl-induced swelling in the chicken retina

An increase in extracellular KCl ([KCl]o) occurs under various pathological conditions in the retina, leading to retinal swelling and possible neuronal damage. The mechanisms of this KCl o-induced retinal swelling were investigated in the present study, with emphasis on the Cl- transport mechanisms. Increasing [KCl]o (from 5 to 70 mM) led to concentration-dependent swelling in chicken retinas. The curve relating the degree of swelling to [KCl]o was biphasic, with one component from 5 to 35 mM [KCl]o and another from 35 to 100 mM. As Cl- omission prevented swelling in all conditions, the effect of cotransporter or Cl- channel blockers was examined to investigate the mechanisms of Cl- influx. The cotransporter blockers bumetanide and DIOA reduced swelling by 68% and 76%, respectively at [KCl]o 25 mM (K25), and by 14-17% at [KCl]o 54 mM (K54). The Cl- channel blockers NPPB and niflumic acid did not affect swelling at K25 but reduced it by 90-95% at K54 (NPPB IC50 60.7 microM). Furosemide showed an atypical effect, decreasing swelling by 14% at K25 and by 95% at K54 (IC50 173.9 microM). Na+ omission decreased swelling at K25 but not at K54. These results suggest the contribution of cotransporters to Cl- influx at K25 and of Cl- channels at K54. At K25, swelling was found in the ganglion cell layer and in the lower half of the inner nuclear layer. With K54, swelling occurred in all inner retinal layers. The ganglion cell layer swelling was due to both Muller cell end-foot and ganglion cell soma swelling. K54 also induced ganglion cell damage as shown by disorganized, pyknotic and refringent nuclei.

Maturational and maintenance effects of testosterone on terminal axon density and neuropeptide expression in the rat vas deferens

Testosterone causes growth of many pelvic ganglion cells at puberty and their maintenance during adulthood. Here we have focused on two populations of pelvic ganglion cells that project to the rat vas deferens: noradrenergic neurons that innervate the smooth muscle and synthesize neuropeptide Y, and cholinergic neurons that primarily innervate the mucosa and contain vasoactive intestinal peptide. We have assessed the muscle innervation after pre- or postpubertal castration, using immunohistochemistry to determine axon density and radioimmunoassay to quantify levels of neuropeptides in tissue extracts. Our results show that androgen deprivation in each period causes substantial effects. Noradrenergic axons in the muscle increase in density after castration, partly due to organ size being smaller than age-matched controls. However, when corrected for target size, there is an overall decrease in total number of axons. This implies that androgen exposure at puberty has a direct effect on neurons to ensure that the adult pattern of innervation is attained, and that this is not simply by matching terminal field to target size. Similar effects of pre- and postpubertal castration imply that continued exposure to testosterone is necessary to maintain normal target innervation. Castration in both time periods increased the density of axons containing vasoactive intestinal peptide, however the effects of castration on the total number of these axons in the muscle were more variable. The concentration of vasoactive intestinal peptide increased substantially following either pre- or postpubertal castration although absolute amounts per vas deferens were decreased. Effects on neuropeptide Y concentration were less pronounced but the total amount per vas deferens was decreased after pre- or postpubertal castration. Our study shows that the action of testosterone (or a metabolite) on a pelvic ganglion cell soma is likely to reflect a change in its terminal field, but that these effects are not mediated simply by testosterone influencing the size of its target organ.

Partial regeneration and long-term survival of rat retinal ganglion cells after optic nerve crush is accompanied by altered expression, phosphorylation and distribution of cytoskeletal proteins.

In a screen to identify genes that are expressed differentially in the retina after partial optic nerve crush, we identified MAP1B as an up-regulated transcript. Western blot analysis of inner retina protein preparations confirmed changes in the protein composition of the microtubule-associated cytoskeleton of crushed vs. uncrushed nerve. MAP1B immunoreactivity and transcript levels were elevated for two weeks after crush. Immunostaining and Western blots with monoclonal antibodies directed against developmentally regulated phosphorylation sites on MAP1B revealed a gradient of MAP1B phosphorylation from the proximal optic nerve stump to the soma of retinal ganglion cells. Most interestingly, using antibodies directed against developmentally regulated phosphorylation sites on MAP1B, we observed that a significant number of crushed optic nerve axons develop MAP1B-immunopositive growth cones, which cross the crush site and migrate along the distal nerve fragment. In parallel, an abnormal distribution of highly phosphorylated neurofilament protein (pNF-H) in the cell soma and dendrites of presumably axotomized retinal ganglion cells was observed following partial nerve crush. This redistribution is present for the period between day 7 and 28 postcrush and is not seen in cells that stay connected to the superior colliculus. Axotomized ganglion cells, which contain pNF-H in soma and dendrites appear to have been disconnected from the colliculus at an early stage but survive axonal trauma for long periods.

Immunoreactivity of Hu proteins facilitates identification of myenteric neurones in guinea-pig small intestine.

Hu proteins, together with neurone-specific enolase (NSE), protein gene product 9.5 (PGP-9.5), microtubule-associated protein-2 (MAP-2) and tubulin beta III isoform, were evaluated immunohistochemically as neuronal markers in whole-mount preparations and cultures obtained from the myenteric plexus of guinea-pig small intestine. Anti-Hu immunostaining marked the ganglion cell somas and nuclei without staining of the neuronal processes in the whole-mounts and cultures. The ganglion cell bodies were not obscured by staining of multiple neuronal fibres and this facilitated accurate counting of the neurones. MAP2 immunostaining also provided clear images of individual neurones in both whole mounts and cultures. Immunoreactivity for NSE, PGP-9.5 and tubulin beta III isoform provided sharp images of the ganglion cells in culture, but not in whole-mount preparations. Strong staining of the neuronal processes in the whole-mount preparations obscured the profiles of the ganglion cell bodies to such an extent that accurate counting of the total neuronal population was compromised. Anti-Hu immunostaining was judged to be an acceptable method for obtaining reliable estimates of total numbers of myenteric neurones in relation to other specific histochemical properties such as histamine binding.

Cellular and Subcellular Patterns of Expression of bFGF and CNTF in the Normal and Light Stressed Adult Rat Retina

This study compared the distributions in the normal and light stressed rat retina of the neuroprotective factors bFGF (basic fibroblast growth factor) and CNTF (ciliary neurotrophic factor). Albino Sprague–Dawley rats were raised in cyclic light and some were exposed to bright continuous light for 48hr, to induce light damage of photoreceptors. Their retinas were prepared as cryosections, immunolabelled with antibodies to bFGF and CNTF and analysed by confocal microscopy. Both factors were prominent in macroglial cells (astrocytes, Müller cells) and the retinal pigment epithelium (RPE). In the somas of these cells the distributions of the two factors were complementary, with bFGF concentrated in the nuclei and CNTF in the cytoplasm. Both factors were distributed along the processes of macroglial cells, in granular form. CNTF was not detected in neurones, but bFGF was consistently present in the cytoplasm of ganglion cell somas and, in regions of retina subject to stress, in the cytoplasm of photoreceptors. bFGF was not detected in the nuclei or processes of neurones. In retina stressed by light exposure or proximity to the anterior edge of the retina, the levels of bFGF and CNTF were up-regulated, without major changes in localization. Macroglial cells (Müller cells, astrocytes) play a major role in distributing bFGF and CNTF throughout the retina. The different localizations of the two factors within the somas of macroglial, RPE and photoreceptor cells, suggest that their protective actions are exerted by distinctive mechanisms.

Temporal Contrast Adaptation in the Input and Output Signals of Salamander Retinal Ganglion Cells

We investigated how the light-evoked input and output signals of salamander retinal ganglion cells adapt to changes in temporal contrast, i.e., changes in the depth of the temporal fluctuations in the light intensity about the mean. Increasing the temporal contrast sped the kinetics and reduced the sensitivity of both the light-evoked input currents measured at the ganglion cell soma and the output spike trains of the cell. The decline in sensitivity of the input currents after an increase in contrast had two distinct kinetic components with fast (<2 sec) and slow (>10 sec) time constants. The recovery of sensitivity after a decrease in contrast was dominated by a single component with an intermediate (4-18 sec) time constant. Contrast adaptation differed for on and off cells, with both the kinetics and amplitude of the light-evoked currents of off cells adapting more strongly than those of on cells. Contrast adaptation in the input currents of a ganglion cell, however, was unable to account for the extent of adaptation in the output spike trains of the cell, indicating that mechanisms intrinsic to the ganglion cell contributed. Indeed, when fluctuating currents were injected into a ganglion cell, the sensitivity of spike generation decreased with increased current variance. Pharmacological experiments indicated that adaptation of spike generation to the current variance was attributable to properties of tetrodotoxin-sensitive Na(+) channels.

Mechanosensitive chloride channels on the growth cones of cultured rat dorsal root ganglion neurons

We developed an experimental system to investigate mechanosensitivity of a single neuron, using cultured rat dorsal root ganglion cells. Highly precise mechanical stimulation was applied to various sites of the cells, using a piezo-driven glass microcapillary whose movement was computer-controlled, while whole-cell patch-clamp recordings were made from the cell bodies. When the growth cones and lamillipodia from the cell soma were mechanically stimulated, inward currents were recorded at the holding potential of −60 mV. Filopodia were most sensitive to mechanical stimulation. However, when neurites or soma of dorsal root ganglion cells were stimulated in the same way, electrical responses were hardly recorded. Two types of currents varying in time-course were observed: fast type of 100–200 ms and slow type of several seconds in duration. When the membrane potential was held at around 0 mV, both types of currents were almost abolished or even reversed, and the reversal potential was estimated to be about −2.2 mV. Replacement of extracellular sodium by tetraethylammonium did not significantly change the reversal potential. In the low-chloride solution ([Cl −] o=11.7 mM), the reversal potential was about +60 mV, as expected from the Nernst equation for chloride. These inward currents were almost completely inhibited by extracellular application of chloride channel blocker, 5-nitro-2-(3-phenylpropylamino) benzoic acid (100 μM). These results indicate that the inward currents are due to activation of mechanosensitive chloride channels, preferentially located on the growth cones of cultured dorsal root ganglion neurons.

Expression of CB2 cannabinoid receptor mRNA in adult rat retina.

To date, two cannabinoid receptors, CB1 and CB2, have been cloned. The CB1 receptor has been found in a variety of tissues, particularly in the brain. CB2 receptor mRNA is mainly expressed in the immune system, though one group has found it in mouse cerebellum. Previous immunostaining studies in our lab demonstrated the presence of CB1 receptors in the retina though little evidence exists for the presence of CB2. The putative endogenous ligand for CB2 has been found in retina, however, suggesting that further study of CB2 in retina is warranted. Because glutamate is toxic to retinal ganglion cells in glaucoma and activation of CB2 receptors may be able to protect neurons from glutamate-induced death, we examined the expression of CB2 mRNA in adult rat retina in order to better understand possible neuroprotective mechanisms relevant to glaucoma. Using in situ hybridization, we demonstrated that CB2 cannabinoid receptor messenger RNA was clearly expressed in the adult rat retina, including the somas of retinal ganglion cells. Antisense cRNA probe detected strong signals in the retinal ganglion cell layer, the inner nuclear layer, and the inner segments of photoreceptor cells. Using reverse transcription polymerase chain reaction (RT-PCR) in both rat and mouse tissue, we obtained an RT-PCR product with the same sequence as that reported for CB2 in the GenBank database, thus confirming the presence of CB2 mRNA in retina. The presence of CB2 in retina provides new evidence for the presence of CB2 in the central nervous system (CNS) and an excellent model for its study.

Immunolocalization of the arachidonic acid and mechanosensitive baseline TRAAK potassium channel in the nervous system

TRAAK is the sole member of the emerging class of 2P domain K + channels to be exclusively expressed in neuronal cells. TRAAK produces baseline K + currents which are strongly stimulated by arachidonic acid and by mechanical stretch, and which are insensitive to the classical K + channel blockers tetraethylammonium, Ba 2+, and Cs +. This report describes the immunolocalization of TRAAK in brain, spinal cord, and retina of the adult mouse. The most striking finding is the widespread distribution of the TRAAK immunoreactivity, with a prominent staining of the cerebellar cortex, neocortex, hippocampus, dentate gyrus, subiculum, the dorsal hippocampal commisure, thalamus, caudate–putamen, olfactory bulb, and several nuclei in the brainstem. Virtually all neurons express TRAAK, and the highest immunoreactivity was seen in soma, and to a lesser degree in axons and/or dendrites in most areas in brain and spinal cord. In the retina, the TRAAK protein is concentrated to the soma of ganglion cells and to the dendrites of all other neurons. Taken together, these results show a wide distribution of TRAAK, a mechanosensitive and arachidonic acid-stimulated neuron-specific baseline K + channel, in brain, spinal cord and retina.

A morphological and morphometric study of the peripheral process of the human vestibular nerve following posterior cranial fossa neurectomy.

Three vestibular nerve specimens removed at transmeatal neurectomy were studied in order to understand better retrograde degeneration and regeneration after vestibular neurectomy in the posterior cranial fossa. In two cases this procedure followed retrolabyrinthine retrosigmoid posterior fossa vestibular neurectomy. The subjects, three patients with Menière's disease, were compared with one another and two autopsy controls with no known otological problem. The specimens were obtained at the distal end of the internal auditory canal and transversely sectioned. Many collapsed Schwann cell basement membranes were observed. The ratio of small-diameter nerve fibres increased significantly after neurectomy. Onion bulb formation around myelinated nerve fibres with small diameters and Schwann cell proliferation around the soma of vestibular ganglion cells reflected remyelination. We conclude that peripheral processes of vestibular nerve fibres can undergo retrograde degeneration and subsequent regeneration after transection of the central process.

Growth cones exhibit enhanced cell–cell adhesion after neurotransmitter release

Evoked release of acetylcholine and subsequent cell–cell adhesive contacts between growth cones and acetylcholine sensing neurons were observed using cultured neurons dissociated from the diagonal band of Broca of the rat. Stimulation to the soma of the diagonal band of Broca neurons evoked release of acetylcholine from the growth cones. The release of acetylcholine was monitored using whole-cell patch-clamp recording from acetylcholine receptor-rich superior cervical ganglion neuron positioned on the growth cone as a sensor of acetylcholine release. By measuring changes in fluorescence from the growth cone using Ca 2+-sensitive dye while voltage-clamping the superior cervical ganglion neuron, transient intracellular Ca 2+ concentration increase and acetylcholine release from growth cone were recorded simultaneously. Video-enhanced differential interference contrast imaging of the growth cones demonstrated tether formation between the growth cone and superior cervical ganglion cell soma when the superior cervical ganglion cell soma was moved away from the growth cone after acetylcholine release, suggesting formation of adhesive contacts between the growth cone and the sensor neuron. Adhesive contacts between growth cones and sensor neurons were also detected when a high K + solution or α-latrotoxin was applied to the growth cone. Adhesions were also observed between growth cones and latex beads, when growth cones were exposed to high K + solution. The properties of the adhesive contacts at the growth cone were studied by optically manipulating a latex bead attached to the growth cone surface. These results suggest that growth cones exhibit cell–cell adhesion after neurotransmitter release.

Transferrin binding protein is expressed by oligodendrocytes in the avian retina

It has been documented that some axons of ganglion cells in the nerve fiber layer of avian retina are wrapped in a myelin sheath. However, the identity of myelin-forming cells has not been established. In this study we demonstrated immunohistochemical evidence for the existence of a large population of oligodendrocytes in avian retina, using an antiserum against transferrin binding protein (TfBP), the avian homologue of the mammalian GRP 94 family of stress-regulated proteins. TfBP + cells were mostly confined to the ganglion cell and optic nerve fiber layers of the retina, in which they were closely associated with the soma and axons of ganglion cells. The double-labeling experiments clearly show that TfBP is specific to oligodendrocytes. The morphology, distribution, and antigenic properties indicated by our findings suggest that TfBP + cells are retinal oligodendrocytes that may be responsible for the myelination of ganglion cell axons in avian retina. A putative tropic role of TfBP + oligodendrocytes to the ganglion cells is also discussed in conjunction with the physical properties of TfBP and avascular retinae of birds.