Bipolar Cell Bodies Research Articles

Retinal neuroanatomy of two emerging model organisms, the spiny mouse (Acomys dimidiatus) and the Mongolian gerbil (Meriones unguiculatus)

Current research using animal models to investigate retinal cell biology and model retinal degenerative diseases largely utilize small mammals that are nocturnal and lack the ability to restore lost vision. In contrast, the Mongolian gerbil (Meriones) is a diurnal rodent with good photopic vision, and the spiny mouse (Acomys) is a small desert-dwelling rodent with remarkable regenerative capabilities. The goal of this study was to identify antibodies that detect retinal cell classes in Meriones and Acomys, and to describe the retinal anatomy of these two species in comparison to outbred laboratory mice (Mus musculus). Immunohistochemistry was performed on retinal sections with antibodies for various retinal cell types. Sections were imaged by light, fluorescence, and confocal microscopy. Cell density, morphology, and placement were compared between species qualitatively and quantitatively. Our analyses revealed a classic assembly of retinal cells in Meriones and Acomys, with a few deviations compared to Mus. Meriones displayed the highest density of cones and Acomys the lowest. A higher density of bipolar cell bodies in the proximal portion of the inner nuclear layer was observed in both Acomys and Meriones compared to Mus, and both species exhibited an increase in amacrine cell density compared to Mus. Our results provide a foundation for future research into the visual system adaptations of these interesting species.

Retinal Structure of Poecilia sphenops: Photoreceptor Mosaics, Synaptic Ribbon Patterns, and Glial Cell Expressions.

The specific arrangement and distribution of photoreceptors in the retina can vary among different fish species, with each species exhibiting adaptations related to its habitat, behavior, and visual requirements. Poecilia sphenops, a diurnal fish, was the focus of this study. The retinas of a total of eighteen Molly fish were investigated utilizing light and electron microscopy. The retina exhibited a square mosaic pattern of the inner segments of cones. This pattern comprised double cones positioned along the sides of a square, with two types of single cones situated at the center and corners of the square arrangement across the entire retina. The corner cones were slightly shorter than the central ones. Additionally, the outer plexiform layer contained both cone pedicles and rod spherules. The rod spherule consisted of a single synaptic ribbon arranged in a triad or quadrat junctional arrangement within the invaginating free ends of the horizontal and bipolar cell processes. On the other hand, cone pedicles have more than one synaptic ribbon in their junctional complex. The inner nuclear layer consisted of the amacrine, bipolar, Müller, and horizontal cell bodies. Müller cell processes, expressing GFAP, extended across all retinal layers, segmenting the deeper retina into alternating fascicles of optic axons and ganglion cells. The outer and inner plexiform layers showed many astrocyte cell processes expressing GFAP. In conclusion, the current study is the first record of the retinal structures of Molly fish. This study illustrated the mosaic arrangement of photoreceptors and GFAP expression patterns of astrocytes and Müller cells. The presence of three cone types, coupled with a sufficient number of rods, likely facilitates motion awareness for tasks like finding food and performing elaborate mating ceremonies.

Expression of α-Synuclein in the mouse retina is confined to inhibitory presynaptic elements.

α-Synuclein (α-Syn) is enriched in presynaptic terminals of the central nervous system including the retina and plays a role in the synaptic vesicle cycle and synaptic transmission. Abnormal aggregation of α-Syn is considered to be the main component of the Lewy bodies that are the pathological hallmarks of Parkinson's disease. Although expression pattern of α-Syn has been described in the retinas, its precise cellular and subcellular locations are poorly understood. We investigated the precise expression of α-Syn using light microscopy (LM) and electron microscopy (EM) with antibodies against α-Syn in the mouse retina. We found that the majority of α-Syn immunoreactivity (IR) is located in GABAergic, glycinergic, and dopaminergic amacrine cells, and their processes often make a direct synapse to other labeled or unlabeled amacrine profiles, bipolar cell terminals, or ganglion cell dendrites. Further, our LM and immuno-EM results confirm the absence of α-Syn in excitatory photoreceptors, bipolar cell bodies, and their ribbon synapses, providing evidence, for the first time, that ribbon synapses do not express α-Syn. Additionally, α-Syn IR is located in the ganglion cells, some of which are intrinsically photosensitive retinal ganglion cells. These results reveal a previously unappreciated inhibitory synapse-specific expression pattern of α-Syn in the retina, suggesting that α-Syn may play a distinct role in the modulation and integration of inhibitory synaptic transmission in the retina.

A novel tool to study bipolar cell responses in glaucoma

AbstractPurpose: Retinal ganglion cell death has been well studied in glaucoma, however how the calcium (Ca2+) dynamics in living inner retinal neurons alter to ocular hypertensive stress is poorly understood. Here we characterized a novel adeno‐associated virus (AAV) mediated Ca2+ sensor to investigate light‐evoked Ca2+ responses in bipolar cells with two‐photon laser scanning microscopy (TPLSM).Methods: To visualize ON bipolar cell specific Ca2+ expression, we bioinformatically designed a serotype 2 AAV vector carrying GCaMP6f, a Ca2+indicator, under human MiniPromoter: Ple265 (PCP2, 986 bp, AAV.Ple265.GCaMP). The AAV.Ple265.GCaMP6 was administered intravitreal to adult mice (2 μl/eye). Two and 4 weeks later (n = 3 mice/group), eyes were collected, and retinal cross sections (16 μm) were prepared for immunohistochemistry using the following primary antibodies: GFP to visualize GCaMP6f, and bipolar cell‐specific markers PCP2 or PKCa. Furthermore, we monitored real time light‐evoked Ca2+ responses in bipolar cell terminals at 4 weeks after the injection and amplitude (ΔF/F0) was calculated.Results: At 2 weeks after the viral injection, GCaMP6f was clearly visualized in bipolar cells, but its expression was limited to the cell body and dendritic trees. Four weeks post‐injection, GCaMP6f expression was abundantly detected in many bipolar cell bodies, dendrites, axons, and axonal terminals. TPLSM allowed visualization of bipolar cell‐specific GCaMP6f expression in axonal terminals in vivo, and light‐evoked sustained ON‐responses were recorded in terminal microdomains (average intensity = 1.25 ΔF/F0).Conclusions: Our study reveals that the AAV.Ple265.GCaMP is a powerful tool to monitor ON bipolar cell specific light‐evoked Ca2+ responses in bipolar cells, and can be potentially used for studies aimed at understanding the response of these neurons to glaucomatous damage.

Homeostatic Plasticity Shapes the Retinal Response to Photoreceptor Degeneration.

Homeostatic plasticity stabilizes input and activity levels during neural development, but whether it can restore connectivity and preserve circuit function during neurodegeneration is unknown. Photoreceptor degeneration is the most common cause of blindness in the industrialized world. Visual deficits are dominated by cone loss, which progresses slowly, leaving a window during which rewiring of second-order neurons (i.e., bipolar cells) could preserve function. Here we establish a transgenic model to induce cone degeneration with precise control and analyze bipolar cell responses and their effects on vision through anatomical reconstructions, invivo electrophysiology, and behavioral assays. In young retinas, we find that three bipolar cell types precisely restore input synapse numbers when 50% of cones degenerate but one does not. Of the three bipolar cell types that rewire, two contact new cones within stable dendritic territories, whereas one expands its dendrite arbors to reach new partners. In mature retinas, only one of four bipolar cell types rewires homeostatically. This steep decline in homeostatic plasticity is accompanied by reduced light responses of bipolar cells and deficits in visual behaviors. By contrast, light responses and behavioral performance are preserved when cones degenerate in young mice. Our results reveal unexpected cell type specificity and a steep maturational decline of homeostatic plasticity. The effect of homeostatic plasticity on functional outcomes identify it as a promising therapeutic target for retinal and other neurodegenerative diseases.

Topographical distribution and morphology of NADPH-diaphorase-stained neurons in the human claustrum

We studied the topographical distribution and morphological characteristics of NADPH-diaphorase-positive neurons and fibers in the human claustrum. These neurons were seen to be heterogeneously distributed throughout the claustrum. Taking into account the size and shape of stained perikarya as well as dendritic and axonal characteristics, Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHd)-positive neurons were categorized by diameter into three types: large, medium and small. Large neurons ranged from 25 to 35 μm in diameter and typically displayed elliptical or multipolar cell bodies. Medium neurons ranged from 20 to 25 μm in diameter and displayed multipolar, bipolar and irregular cell bodies. Small neurons ranged from 14 to 20 μm in diameter and most often displayed oval or elliptical cell bodies. Based on dendritic characteristics, these neurons were divided into spiny and aspiny subtypes. Our findings reveal two populations of NADPHd-positive neurons in the human claustrum—one comprised of large and medium cells consistent with a projection neuron phenotype, the other represented by small cells resembling the interneuron phenotype as defined by previous Golgi impregnation studies.

Proinsulin Slows Retinal Degeneration and Vision Loss in the P23H Rat Model of Retinitis Pigmentosa

Proinsulin has been characterized as a neuroprotective molecule. In this work we assess the therapeutic potential of proinsulin on photoreceptor degeneration, synaptic connectivity, and functional activity of the retina in the transgenic P23H rat, an animal model of autosomal dominant retinitis pigmentosa (RP). P23H homozygous rats received an intramuscular injection of an adeno-associated viral vector serotype 1 (AAV1) expressing human proinsulin (hPi+) or AAV1-null vector (hPi-) at P20. Levels of hPi in serum were determined by enzyme-linked immunosorbent assay (ELISA), and visual function was evaluated by electroretinographic (ERG) recording at P30, P60, P90, and P120. Preservation of retinal structure was assessed by immunohistochemistry at P120. Human proinsulin was detected in serum from rats injected with hPi+ at all times tested, with average hPi levels ranging from 1.1 nM (P30) to 1.4 nM (P120). ERG recordings showed an amelioration of vision loss in hPi+ animals. The scotopic b-waves were significantly higher in hPi+ animals than in control rats at P90 and P120. This attenuation of visual deterioration correlated with a delay in photoreceptor degeneration and the preservation of retinal cytoarchitecture. hPi+ animals had 48.7% more photoreceptors than control animals. Presynaptic and postsynaptic elements, as well as the synaptic contacts between photoreceptors and bipolar or horizontal cells, were preserved in hPi+ P23H rats. Furthermore, in hPi+ rat retinas the number of rod bipolar cell bodies was greater than in control rats. Our data demonstrate that hPi expression preserves cone and rod structure and function, together with their contacts with postsynaptic neurons, in the P23H rat. These data strongly support the further development of proinsulin-based therapy to counteract retinitis pigmentosa.

Changes in retinal neurons in the guinea pig retina stimulated by strobe lights during development

The modern-day population is overexposed to visual stimuli accompanied by contrast and strength changes, such as the television or videogames, beginning early in life. These light stimuli may have an influence on the development of the visual system. The purpose of this study was to examine the effects of light stimuli on retinal development. We reared guinea pigs under a daily 12-h strobe light (2Hz)/dark cycle from birth, while control animals were reared under a 12-h light/dark cycle. The animals were sacrificed 1, 2, and 4 weeks after birth. The thickness of the outer nuclear layer (ONL) thickness decreased by 14.8% in the strobe-reared animals compared to the control group at 4 weeks, but not at 1 and 2 weeks. The Müller cells of the strobe-reared animals showed a stouter branch compared to that of the control animals at 2 and 4 weeks. In the strobe-reared model, axon-like processes emerging from the rod bipolar cell bodies were observed in the outer plexiform layer (OPL). These findings show that strobe-light stimuli induce morphological changes in retinal neurons, which may lead to the disturbance of normal visual processing during development.

TMP Prevents Retinal Neovascularization and Imparts Neuroprotection in an Oxygen-Induced Retinopathy Model

To evaluate the effects of tetramethylpyrazine (TMP) on retinal neovascularization (NV) and neuroprotection in an oxygen-induced retinopathy (OIR) model. Neonatal C57BL/6J mice were subjected to 75% oxygen from postnatal day 7 (P7) to P12 and then returned to room air. TMP (200 mg/kg) or normal saline was given daily from P12 to P17. Immunostaining, HE staining, TUNEL assay, and RT-PCR were used to assess the effects of TMP on retinal neurovascular repair. TMP effectively prevented pathologic NV and accelerated physiologic revascularization by enhancing the formation of endothelial tip cells at the edges of the repairing capillary networks and preserving the astrocytic template in the avascular retina. TMP also prevented morphologic changes and significantly decreased TUNEL-positive cells in the avascular retina by rescuing neurons such as amacrine, rod bipolar, horizontal, and Müller cells. In TMP-treated mice retinas, there was a less obvious loss of amacrine cell bodies and their distinct bands; the number of both rod bipolar and horizontal cell bodies, as well as the density of their dendrites in the outer plexiform layer, was greater than that in OIR control mice. TMP not only decreased the loss of alignment of Müller cell bodies and distortion of processes but reduced the reactive expression of GFAP in Müller cells. Furthermore, HIF-1α and VEGF mRNA expression were downregulated in TMP-treated mice retinas. TMP improved neurovascular recovery by preventing NV and protecting retinal astroglia cells and neurons from ischemia-induced cell death partially due to its downregulation of HIF-1α and VEGF mRNA expression.

Partial Rescue of Retinal Function in Chronically Hypoglycemic Mice

Mice rendered hypoglycemic by a null mutation in the glucagon receptor gene Gcgr display late-onset retinal degeneration and loss of retinal sensitivity. Acute hyperglycemia induced by dextrose ingestion does not restore their retinal function, which is consistent with irreversible loss of vision. The goal of this study was to establish whether long-term administration of high dietary glucose rescues retinal function and circuit connectivity in aged Gcgr-/- mice. Gcgr-/- mice were administered a carbohydrate-rich diet starting at 12 months of age. After 1 month of treatment, retinal function and structure were evaluated using electroretinographic (ERG) recordings and immunohistochemistry. Treatment with a carbohydrate-rich diet raised blood glucose levels and improved retinal function in Gcgr-/- mice. Blood glucose increased from moderate hypoglycemia to euglycemic levels, whereas ERG b-wave sensitivity improved approximately 10-fold. Because the b-wave reflects the electrical activity of second-order cells, we examined for changes in rod-to-bipolar cell synapses. Gcgr-/- retinas have 20% fewer synaptic pairings than Gcgr+/- retinas. Remarkably, most of the lost synapses were located farthest from the bipolar cell body, near the distal boundary of the outer plexiform layer (OPL), suggesting that apical synapses are most vulnerable to chronic hypoglycemia. Although treatment with the carbohydrate-rich diet restored retinal function, it did not restore these synaptic contacts. Prolonged exposure to diet-induced euglycemia improves retinal function but does not reestablish synaptic contacts lost by chronic hypoglycemia. These results suggest that retinal neurons have a homeostatic mechanism that integrates energetic status over prolonged periods of time and allows them to recover functionality despite synaptic loss.

Unusual retinal layer organization in HPC-1/syntaxin 1A knockout mice

HPC-1/syntaxin 1A (STX1A) is abundantly expressed in neurons. STX1A is believed to regulate exocytosis in synaptic vesicles. In our recent studies, STX1A knockout (KO) mice showed normal development, and basal synaptic transmission in cultured hippocampal neurons appeared to be normal. However, behavioral abnormalities were observed in STX1A KO mice. In the normal rodent retina, the STX1A protein is expressed in two synaptic layers (plexiform layers). Here, to evaluate the effects of the loss of STX1A on retinal structure, we examined the retinal layer structure in STX1A KO mice using hematoxylin staining and immunostaining. We found that the general layer structures in the retina were preserved in all genotypes. However, the outer plexiform layer (OPL) was significantly thicker in KO and heterozygous mutant (HT) mice compared with that in wild-type (WT) mice. No significant differences were observed in the thicknesses of the other layers. Immunostaining for protein kinase C α showed that the alignment of rod bipolar cell bodies in the inner nuclear layer (INL) was slightly disrupted in HT and KO retinas. Furthermore, the dendrites of these cells in the OPL of KO mice were sparse, compared to those in WT mice. Our results show that STX1A KO mice have increased thickness of the OPL and changes in the morphology of the INL that may contribute to the change in OPL thickness. We suggest that STX1A may play a role in the structural formation of the INL and OPL in the retina.

Tauroursodeoxycholic Acid Prevents Retinal Degeneration in Transgenic P23H Rats

To evaluate the preventive effect of tauroursodeoxycholic acid (TUDCA) on photoreceptor degeneration, synaptic connectivity and functional activity of the retina in the transgenic P23H rat, an animal model of autosomal dominant retinitis pigmentosa (RP). P23H line-3 rats were injected with TUDCA once a week from postnatal day (P)21 to P120, in parallel with vehicle-administered controls. At P120, functional activity of the retina was evaluated by electroretinographic (ERG) recording. The effects of TUDCA on the number, morphology, integrity, and synaptic connectivity of retinal cells were characterized by immunofluorescence confocal microscopy. The amplitude of ERG a- and b-waves was significantly higher in TUDCA-treated animals under both scotopic and photopic conditions than in control animals. In the central area of the retina, TUDCA-treated P23H rats showed threefold more photoreceptors than control animals. The number of TUNEL-positive cells was significantly smaller in TUDCA-treated rats, in which photoreceptor morphology was preserved. Presynaptic and postsynaptic elements, as well as the synaptic contacts between photoreceptors and bipolar or horizontal cells, were preserved in TUDCA-treated P23H rats. Furthermore, in TUDCA-treated rat retinas, the number of both rod bipolar and horizontal cell bodies, as well as the density of their synaptic terminals in the outer plexiform layer, was greater than in control rats. TUDCA treatment was capable of preserving cone and rod structure and function, together with their contacts with their postsynaptic neurons. The neuroprotective effects of TUDCA make this compound potentially useful for delaying retinal degeneration in RP.

Cereblon is expressed in the retina and binds to voltage-gated chloride channels

The function of the central nervous system depends on the correct regulation of ion channels by interacting proteins. Here, we identified cereblon as a new interactor of the voltage-gated chloride channel ClC-2. A distal region of the ClC-2 C-terminus interacts with the Lon domain of cereblon. Cereblon is expressed in several brain regions including the retina. There, we detected cereblon in nuclear and synaptic layers and localized the protein in the same subcellular region of bipolar cell bodies previously reported to express ClC-2. Our data suggest that cereblon might be associated with voltage-gated chloride channels in the central nervous system. Structured summary MINT- 6823070: CIC-2 (uniprotkb: O54822) physically interacts (MI: 0218) with CRBN (uniprotkb: Q0P564) by two hybrid (MI: 0018) MINT- 6823160, MINT- 6823197: CIC-2 (uniprotkb: O54822) physically interacts (MI: 0218) with CRBN (uniprotkb: Q56AP7) by pull down (MI: 0096) MINT- 6823105: CIC-2 (uniprotkb: O54822) physically interacts (MI: 0218) with IK (uniprotkb: A4FUY8) by two hybrid (MI: 0018)

Octadecaneuropeptide, ODN, protects cerebellar granule neurons against oxidative stress-induced apoptosis

Event Abstract Back to Event Octadecaneuropeptide, ODN, protects cerebellar granule neurons against oxidative stress-induced apoptosis Hadhemi Kaddour1*, Yosra Hamdi1, David Vaudry2, Meherzia Mokni1, Jerome Leprince2, Hubert Vaudry2, Marie-Christine Tonon2, Mohamed Amri1 and Olfa Masmoudi-Kouki1 1 Faculte des Sciences de Tunis, El Manar, Laboratoire de neurophysiologie fonctionnelle et pathologie, 00/UR/08-01, Tunisia 2 Inserm U413, Universite de Rouen, Laboratoire de Differenciation de Communication Neuronale Neuroendocrine , France The octadecaneuropeptide (ODN; QATVGDVNTDRPGLLDLK), which has been originally characterized as an endogenous ligand of benzodiazepine receptors, is neurotrophic factor regulating proliferation and/or survival of neuronal cells. Since treatment of neonatal rat by 6-ydroxydopamine (6-OHDA), neurotoxin widely used to produce animal models of Parkinson disease, reduce the immunoreactivity of ODN and delayed migration and degeneration of granule cells in the neocerebellum, we have investigated the ability of ODN to counteract the neurotoxic effects of 6-OHDA on cerebellar granule neurons. Incubation of granule cells with graded concentrations of 6-OHDA (10 µM - 120 µM) for 72 h provoked a dose-dependent decrease of the proportion of surviving cells. Co-incubation of granule cells with 6-OHDA (30 µM) and graded concentrations of ODN (10-18 M – 10-7 M) for 72 h induced a dose-dependent increase in the number of surviving cells. Complete reversal of the toxic effect of 6-OHDA was observed between 10-16 M and 10-12 M ODN. The neurotoxic effect of 6-OHDA was associated with modifications of granule cell morphology that were suggestive of apoptotic cell death, such as cell shrinkage and nuclear condensation. Treatment of granule cells with 6-OHDA and ODN (10-12M) restored the typical shape of differentiated neurons with bipolar fusiform cell bodies and long neurites. We have also observed that the protective action of ODN (10-12 M) involved the metabotropic receptors types and activated the phosphorylation way of PLC / PKC. In conclusion, the present study has demonstrated that ODN is a potent protective agent against 6-OHDA-induced oxidative stress and neuronal cell death. The anti-apoptotic effect of ODN can be ascribed to stimulation of SOD activity and thus inhibition of reactive oxygen species accumulation. These data suggest that ODN may have a therapeutic value for the treatment of neuronal death resulting from stress oxidative in neurodegenerative disorders such as Alzheimer’s and Parkinson’s diseases. Supported by research Unit 00/UR/08/01 K.H. was the recipient of a scholarship from the France-Tunisia exchange program Utique-CMCU. Conference: 3rd Mediterranean Conference of Neuroscience , Alexandria, Egypt, 13 Dec - 16 Dec, 2009. Presentation Type: Poster Presentation Topic: CNS Diseases Citation: Kaddour H, Hamdi Y, Vaudry D, Mokni M, Leprince J, Vaudry H, Tonon M, Amri M and Masmoudi-Kouki O (2009). Octadecaneuropeptide, ODN, protects cerebellar granule neurons against oxidative stress-induced apoptosis. Front. Neurosci. Conference Abstract: 3rd Mediterranean Conference of Neuroscience . doi: 10.3389/conf.neuro.01.2009.16.145 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Nov 2009; Published Online: 25 Nov 2009. * Correspondence: Hadhemi Kaddour, Faculte des Sciences de Tunis, El Manar, Laboratoire de neurophysiologie fonctionnelle et pathologie, 00/UR/08-01, 2092 Tunis, Tunisia, kaddourhadhemi@yahoo.fr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Hadhemi Kaddour Yosra Hamdi David Vaudry Meherzia Mokni Jerome Leprince Hubert Vaudry Marie-Christine Tonon Mohamed Amri Olfa Masmoudi-Kouki Google Hadhemi Kaddour Yosra Hamdi David Vaudry Meherzia Mokni Jerome Leprince Hubert Vaudry Marie-Christine Tonon Mohamed Amri Olfa Masmoudi-Kouki Google Scholar Hadhemi Kaddour Yosra Hamdi David Vaudry Meherzia Mokni Jerome Leprince Hubert Vaudry Marie-Christine Tonon Mohamed Amri Olfa Masmoudi-Kouki PubMed Hadhemi Kaddour Yosra Hamdi David Vaudry Meherzia Mokni Jerome Leprince Hubert Vaudry Marie-Christine Tonon Mohamed Amri Olfa Masmoudi-Kouki Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Effects of perinatal asphyxia on the neurobehavioral and retinal development of newborn rats

Perinatal asphyxia during delivery produces long-term deficits and represents a major problem in both neonatal and pediatric care. Several morphological, biochemical and behavioral changes have been described in rats exposed to perinatal asphyxia. The aim of the present study was to evaluate how perinatal asphyxia affects the complex early neurobehavioral development and retinal structure of newborn rats. Asphyxia was induced in ready-to-deliver mothers by removing the pups by cesarian section after 15 min of asphyxia. Somatic and neurobehavioral development was tested daily during the first 3 weeks, and motor coordination tests were performed on postnatal weeks 3–5. After completion of the testing procedure, retinas were removed for histological analysis. We found that in spite of the fast catch-up-growth of asphyctic pups, nearly all examined reflexes were delayed by 1–4 days: negative geotaxis, sensory reflexes, righting reflexes, development of fore- and hindlimb grasp and placing, gait and auditory startle reflexes. Time to perform negative geotaxis, surface righting and gait reflexes was significantly longer during the first few weeks in asphyctic pups. Among the motor coordination tests, a markedly weaker performance was observed in the grid walking and footfault test and in the walk initiation test. Retinal structure showed severe degeneration in the layer of the photoreceptor and bipolar cell bodies. In summary, our present study provided a detailed description of reflex and motor development following perinatal asphyxia, showing that asphyxia led to a marked delay in neurobehavioral development and a severe retinal degeneration.

Sensory-induced modification of two motor patterns in the crab,Cancer pagurus

Sensory input is pervasive among motor networks and continuously adapts motor patterns to changing circumstances. To elucidate common principles of sensorimotor integration, it is beneficial to characterize sensory influences on motor network operation and compare these influences between species. To facilitate such comparison, we have studied the influence of the anterior gastric receptor (AGR) - a proprioceptor that has been characterized in detail in two lobster species - on the pyloric (filtering of food) and gastric mill (chewing of food) motor patterns in the crab Cancer pagurus. AGR has a bipolar cell body in the stomatogastric ganglion; it was activated by tension increase in gastric mill powerstroke muscles. While two spike initiation zones accounted for its spontaneous activity, active membrane properties (sag potentials, spike frequency adaptation) contributed to the AGR response to current injections. When activated, AGR diminished spike activities in two pyloric motor neurons and prolonged the pyloric cycle period. Furthermore, AGR excited gastric mill protractor neurons, inhibited the retractor neuron and evoked phase-independent resetting of the gastric mill rhythm. Repetitive spike trains entrained the rhythm to both longer and shorter cycle periods. All AGR actions seemed to be mediated via at least two premotor projection neurons in the spatially distant commissural ganglia. The response of the gastric mill neurons was independent of AGR firing frequency. Our results suggest that homologous proprioceptors can elicit similar effects on motor patterns while utilizing different mechanisms. This work thus provides an initial framework for future studies to determine underlying common principles.

Retrograde endocannabinoid inhibition of goldfish retinal cones is mediated by 2-arachidonoyl glycerol

A functional role for retinal endocannabinoids has not been determined. We characterized retrograde suppression of membrane currents of goldfish cones in a retinal slice. Whole-cell recordings were obtained from cone inner segments under voltage clamp. I(K(V)) was elicited by a depolarizing pulse to +54 mV from a holding potential of -70 mV. A fifty-millisecond puff of saline with 70 mM KCl or Group I mGluR agonist DHPG was applied through a pipette directly at a mixed rod/cone (Mb) bipolar cell body. The amplitude of I(K(V)) decreased 25% compared to the pre-puff control. Retrograde suppression of I(K(V)) was blocked by CB1 receptor antagonist, SR141716A. The FAAH inhibitor URB597 had no effect on the suppression of I(K(V)), whereas nimesulide, a COX-2 inhibitor, prolonged the effects of the K+ puff 10-fold. Orlistat, a blocker of 2-AG synthesis, blocked the effect of the K+ puff. Group I mGluR activation of Gq/11 was demonstrated in that a puff with DHPG decreased I(K(V)) of cones by 32%, an effect blocked by SR141716A. The effect of DHPG was not blocked by the mGluR5 antagonist MPEP, indicating involvement of mGluR1. The suppressive effect of the K+ puff vanished in a Ca2+-free, 2 mM Co2+ saline. TMB-8 or ryanodine, blocked the effect of DHPG, but not that of the K+ puff, showing that calcium influx or release from intracellular stores could mediate retrograde release. We suggest that retrograde suppression of cone I(K(V)) is mediated by Ca2+-dependent release of 2-AG from Mb bipolar cell dendrites by separate mechanisms: (1) voltage-dependent, mimicked by the K+ puff, that may be activated by the depolarizing ON response to light; (2) voltage-independent, occurring under ambient illumination, mediated by tonic mGluR1 activation. The negative feedback of this latter mechanism could regulate tonic glutamate release from cones within narrow limits, regardless of ambient illumination.

Choline acetyltransferase immunoreactive cortical interneurons do not occur in all rodents: A study of the phylogenetic occurrence of this neural characteristic

The present study was designed to provide results aimed at testing whether the interneurons with choline acetyltransferase immunoreactivity (ChAT), probably representing GABA interneurons, found in the cerebral cortex of the rat represent a common feature of the order Rodentia. Initially we verified the presence of ChAT immunoreactive bipolar cell bodies, axons and terminal-like fibres in pigmented (Long-Evans) and non-pigmented (Sprague-Dawley) strains of Rattus norvegicus, confirming that the ChAT polyclonal antibodies (AB144P and AB143, Chemicon; VChAT, Sigma) with the immunohistochemical techniques used provided the same staining as previously described for this species. We then examined pigmented (AKR3) and non-pigmented (C3H) strains of Mus musculus, wild caught striped mice ( Rhabdomys pumilio), bushveld gerbil ( Tatera brantsii), greater canerat ( Thryonomys swinderianus) and common molerat ( Cryptomys hottentotus). The AB144P antibody revealed cortical interneurons in both strains of M. musculus and in R. pumilio, but not in the other species. In all species/strains cortical ChAT immunoreactive axons and terminal-like fibres were localized with the AB144P antibody. In the non- Rattus species/strains there was no evidence for localization of ChAT immunoreactivity in any cortical cell bodies using the AB143 and vesicular acetylcholine transporter (VChAT) antibodies despite extensive localization in axons and terminal-like fibres. It is concluded that bipolar cortical GABA interneurons in certain rodent species may develop ChAT immunoreactivity but not VChAT immunoreactivity making the cholinergic relevance of ChAT in the GABA interneurons uncertain and may exclude these neurons from being part of the traditionally defined cholinergic system.

Where Is the Spike Generator of the Cochlear Nerve? Voltage-Gated Sodium Channels in the Mouse Cochlea

The origin of the action potential in the cochlea has been a long-standing puzzle. Because voltage-dependent Na+ (Nav) channels are essential for action potential generation, we investigated the detailed distribution of Nav1.6 and Nav1.2 in the cochlear ganglion, cochlear nerve, and organ of Corti, including the type I and type II ganglion cells. In most type I ganglion cells, Nav1.6 was present at the first nodes flanking the myelinated bipolar cell body and at subsequent nodes of Ranvier. In the other ganglion cells, including type II, Nav1.6 clustered in the initial segments of both of the axons that flank the unmyelinated bipolar ganglion cell bodies. In the organ of Corti, Nav1.6 was localized in the short segments of the afferent axons and their sensory endings beneath each inner hair cell. Surprisingly, the outer spiral fibers and their sensory endings were well labeled beneath the outer hair cells over their entire trajectory. In contrast, Nav1.2 in the organ of Corti was localized to the unmyelinated efferent axons and their endings on the inner and outer hair cells. We present a computational model illustrating the potential role of the Nav channel distribution described here. In the deaf mutant quivering mouse, the localization of Nav1.6 was disrupted in the sensory epithelium and ganglion. Together, these results suggest that distinct Nav channels generate and regenerate action potentials at multiple sites along the cochlear ganglion cells and nerve fibers, including the afferent endings, ganglionic initial segments, and nodes of Ranvier.

Distribution of rod bipolar cells in the retina of the albino rat

Purpose: In the retina of albino mammals so far examined there is a deficit in the rod photoreceptor population. We reasoned that a consequence of the rod deficit might be a subsequent abnormality in the next level of the rod pathway, the rod bipolar cell. We therefore compared the distribution of rod bipolar cells in pigmented and albino rats.Methods: Rod bipolar cells were labelled in 15 µm thick sections of fixed retinas with a monoclonal antibody directed against protein kinase C, and visualized using the ABC method. Counts of the cell bodies and processes of rod bipolar cells were undertaken at various locations across the retina.Results: Qualitatively, the protein kinase C staining suggested differences between the albino and pigmented phenotypes both in the outer and inner plexiform layers and in the inner nuclear layer. Staining was denser in the pigmented retina and the bipolar cell bodies were arranged in multiple rows rather than a single row as found in the albino retina. The actual number of rod bipolar cells was reduced in the albino phenotype. At the neonatal age we examined (post‐natal day 15), there was a 14% reduction in the total number whereas in the adult retina the reduction was around 9%.Conclusions: Although the reduction in the rod bipolar population is not as great as that previously found for the rod photoreceptors (∼25%), the reduction in both populations suggests a general abnormality in the rod pathway of albinos. Further, our data support the view that melanin is crucially involved in the normal development of retinal structure.