Ganglion Cell Terminals Research Articles

A Neural Representation of Naturalistic Motion-Guided Behavior in the Zebrafish Brain

All animals must transform ambiguous sensory data into successful behavior. This requires sensory representations that accurately reflect the statistics of natural stimuli and behavior. Multiple studies show that visual motion processing is tuned for accuracy under naturalistic conditions, but the sensorimotor circuits extracting these cues and implementing motion-guided behavior remain unclear. Here we show that the larval zebrafish retina extracts a diversity of naturalistic motion cues, and the retinorecipient pretectum organizes these cues around the elements of behavior. We find that higher-order motion stimuli, gliders, induce optomotor behavior matching expectations from natural scene analyses. We then image activity of retinal ganglion cell terminals and pretectal neurons. The retina exhibits direction-selective responses across glider stimuli, and anatomically clustered pretectal neurons respond with magnitudes matching behavior. Peripheral computations thus reflect natural input statistics, whereas central brain activity precisely codes information needed for behavior. This general principle could organize sensorimotor transformations across animal species.

Ганглиозные клетки с фоновой активностью сетчатки рыб и их возможная функция в оценке зрительной сцены

Extracellular spike activities were recorded from the axon terminals of single ganglion cells (GCs) in tectum opticum (TO) of living immobilized fish. The layer of units with sustained responses (USR) is located 190-200 µm under the surface of TO (deeper than every type of feature detectors). The sizes of the receptive fields (RFs) of both ON and OFF USRs make up to 4-5° which is comparable to the RF sizes of the feature detectors. We've shown that at least some minimal contrast between center and surround is crucial (obligatory) to induce spike discharge in USRs; the intensity of discharge depends on the contrast gradually; spike activity does not emerge in the absence of contrast. We've also shown that USRs of both ON- and OFF-types receive inputs from all three types of cones (L, M and S). We have found that USRs demonstrate color opponency both in the center and on the surround and moreover there is color opponency between center and surround. This makes USRs double opponent cells and thus they might participate in color discrimination. TO – the main visual centre appears to get plenty of information from feature detectors and USRs splitted in ON- and OFF-channels. Proper comprehension of the visual scene allows TO to perform its primary role – the external visual attention control.

Persistence of intact retinal ganglion cell terminals after axonal transport loss in the DBA/2J mouse model of glaucoma.

Axonal transport defects are an early pathology occurring within the retinofugal projection of the DBA/2J mouse model of glaucoma. Retinal ganglion cell (RGC) axons and terminals are detectable after transport is affected, yet little is known about the condition of these structures. We examined the ultrastructure of the glaucomatous superior colliculus (SC) with three-dimensional serial block-face scanning electron microscopy to determine the distribution and morphology of retinal terminals in aged mice exhibiting varying levels of axonal transport integrity. After initial axonal transport failure, retinal terminal densities did not vary compared with either transport-intact or control tissue. Although retinal terminals lacked overt signs of neurodegeneration, transport-intact areas of glaucomatous SC exhibited larger retinal terminals and associated mitochondria. This likely indicates increased oxidative capacity and may be a compensatory response to the stressors that this projection is experiencing. Areas devoid of transported tracer label showed reduced mitochondrial volumes as well as decreased active zone number and surface area, suggesting that oxidative capacity and synapse strength are reduced as disease progresses but before degeneration of the synapse. Mitochondrial volume was a strong predictor of bouton size independent of pathology. These findings indicate that RGC axons retain connectivity after losing function early in the disease process, creating an important therapeutic opportunity for protection or restoration of vision in glaucoma. J. Comp. Neurol. 524:3503-3517, 2016. © 2016 Wiley Periodicals, Inc.

Neural Circuits Underlying Visually Evoked Escapes in Larval Zebrafish

Escape behaviors deliver organisms away from imminent catastrophe. Here, we characterize behavioral responses of freely swimming larval zebrafish to looming visual stimuli simulating predators. We report that the visual system alone can recruit lateralized, rapid escape motor programs, similar to those elicited by mechanosensory modalities. Two-photon calcium imaging of retino-recipient midbrain regions isolated the optic tectum as an important center processing looming stimuli, with ensemble activity encoding the critical image size determining escape latency. Furthermore, we describe activity in retinal ganglion cell terminals and superficial inhibitory interneurons in the tectum during looming and propose a model for how temporal dynamics in tectal periventricular neurons might arise from computations between these two fundamental constituents. Finally, laser ablations of hindbrain circuitry confirmed that visual and mechanosensory modalities share the same premotor output network. We establish a circuit for the processing of aversive stimuli in the context of an innate visual behavior.

Noise-Induced Neural Degeneration and Therapeutic Effect of Antioxidant Drugs.

The primary site of lesion induced by noise exposure is the hair cells in the organ of Corti and the primary neural degeneration occurs in synaptic terminals of cochlear nerve fibers and spiral ganglion cells. The cellular basis of noise-induced hearing loss is oxidative stress, which refers to a severe disruption in the balance between the production of free radicals and antioxidant defense system in the cochlea by excessive production of free radicals induced by noise exposure. Oxidative stress has been identified by a variety of biomarkers to label free radical activity which include four-hydroxy-2-nonenal, nitrotyrosine, and malondialdehyde, and inducible nitric oxide synthase, cytochrome-C, and cascade-3, 8, 9. Furthermore, oxidative stress is contributing to the necrotic and apoptotic cell deaths in the cochlea. To counteract the known mechanisms of pathogenesis and oxidative stress induced by noise exposure, a variety of antioxidant drugs including oxygen-based antioxidants such as N-acetyl-L-cystein and acetyl-L-carnitine and nitrone-based antioxidants such as phenyl-N-tert-butylnitrone (PBN), disufenton sodium, 4-hydroxy PBN, and 2, 4-disulfonyl PBN have been used in our laboratory. These antioxidant drugs were effective in preventing or treating noise-induced hearing loss. In combination with other antioxidants, antioxidant drugs showed a strong synergistic effect. Furthermore, successful use of antioxidant drugs depends on the optimal timing of treatment and the duration of treatment, which are highly related to the time window of free radical formation induced by noise exposure.

Analysis of the lateral geniculate nucleus in dichromatic and trichromatic marmosets.

Marmosets are diurnal New World monkeys that show sex-linked cone photopigment polymorphism, whereby all males and some females are dichromats ("red-green colorblind"), but most females show trichromatic color vision. Here we asked whether trichromats express chromatic-specific circuitry in the lateral geniculate nucleus (LGN). The volume of parvocellular (P), magnocellular (M), and koniocellular (K) layers was calculated in Nissl-stained sections from the LGN of adult marmosets (Callithrix jacchus; 10 trichromatic females; 2 dichromatic females; and 13 dichromatic males). Retinal ganglion cell axon terminals within the P and K layers were reconstructed and measured following anterograde tracer (dextran) injections. We show that there is little difference in LGN layer volume with respect to age, weight, or sex of the animals, or between dichromatic and trichromatic phenotypes. The morphology of retinal ganglion cell terminals was largely indistinguishable on comparing dichromats and trichromats, and likewise on comparing terminals representing peripheral or foveal retina. We conclude that the LGN circuits we studied are largely independent of red-green color vision phenotype and visual field location.

Color properties of the motion detectors projecting to the goldfish tectum: I. A color matching study.

Responses of direction-selective and orientation-selective motion detectors were recorded extracellularly from the axon terminals of ganglion cells in the superficial layers of the tectum opticum of immobilized goldfish, Carassius gibelio (Bloch, 1782). Color stripes or edges moving on some color background (presented on the CRT monitor with known emission spectra of its phosphors) served as stimuli. It was shown that stimuli of any color can be more or less matched with the background by varying their intensities what is indicative of color blindness of the motion detectors. Sets of stimuli which matched the background proved to represent planes in the three-dimensional color space of the goldfish. A relative contribution of different types of cones to the spectral sensitivity was estimated according to orientation of the plane of color matches. The spectral sensitivity of any motion detector was shown to be determined mainly by long-wave cones with a weak negative (opponent) contributions of middle-wave and/or short-wave ones. This resulted in reduced sensitivity in the blue-green end of the spectrum, what may be considered as an adaptation to the aquatic environment where, because of the substantial light scattering of a blue-green light, acute vision is possible only in a red region of the spectrum.

Glutamatergic modulation of synaptic‐like vesicle recycling in mechanosensory lanceolate nerve terminals of mammalian hair follicles

Our aim in the present study was to determine whether a glutamatergic modulatory system involving synaptic-like vesicles (SLVs) is present in the lanceolate ending of the mouse and rat hair follicle and, if so, to assess its similarity to that of the rat muscle spindle annulospiral ending we have described previously. Both types of endings are formed by the peripheral sensory terminals of primary mechanosensory dorsal root ganglion cells, so the presence of such a system in the lanceolate ending would provide support for our hypothesis that it is a general property of fundamental importance to the regulation of the responsiveness of the broad class of primary mechanosensory endings. We show not only that an SLV-based system is present in lanceolate endings, but also that there are clear parallels between its operation in the two types of mechanosensory endings. In particular, we demonstrate that, as in the muscle spindle: (i) FM1-43 labels the sensory terminals of the lanceolate ending, rather than the closely associated accessory (glial) cells; (ii) the dye enters and leaves the terminals primarily by SLV recycling; (iii) the dye does not block the electrical response to mechanical stimulation, in contrast to its effect on the hair cell and dorsal root ganglion cells in culture; (iv) SLV recycling is Ca2+ sensitive; and (v) the sensory terminals are enriched in glutamate. Thus, in the lanceolate sensory ending SLV recycling is itself regulated, at least in part, by glutamate acting through a phospholipase D-coupled metabotropic glutamate receptor.

Complement-Mediated Microglial Clearance of Developing Retinal Ganglion Cell Axons

In many parts of the developing vertebrate nervous system, axons are pruned to establish mature patterns of connectivity. In this issue of Neuron, Schafer et al. (2012) show that microglia may play a role in developmental axon pruning in the thalamus by engulfing presynaptic retinal ganglion cell terminals via a C3- and CR3-dependent mechanism.

Nicotine exposure refines visual map topography through an NMDA receptor‐mediated pathway

The precise mapping of one surface onto another is fundamental to visual system organization and depends upon adequate stimulation of postsynaptic targets to stabilize correctly placed synapses. As exogenous nicotine alters neuronal activity, we investigated whether it would affect the visual map created by retinal ganglion cell terminals in the frog optic tectum. Chronic exposure of the tectum to nicotine decreased the retinal area from which cells project to a given tectal site. This map refinement was also produced by exposure to either the alpha-bungarotoxin sensitive nicotinic receptor agonist, anatoxin-a or the alpha-bungarotoxin-insensitive nicotinic receptor agonist epiboxidine. Immunocytochemical studies using mAb306 and mAb22 demonstrated that alpha-bungarotoxin-sensitive and -insensitive nicotinic receptors, respectively, occupied different tectal sites. Choline acetyltransferase immunoreactivity overlapped with mAb306, but not mAb22, staining. The developing optic tectum was more sensitive to nicotine than the adult tectum and nicotine induced both map refinements and map disruptions in a concentration-dependent manner. Blockade of the N-methyl-D-aspartate (NMDA) receptor with D(-)-2-amino-5-phosphonopentanoic acid (D-APV) prevented nicotine from refining the map in the adult tectum. Exposure to the use-dependent NMDA antagonist MK801 alone had no effect on retinotectal topography but in combination with either NMDA or nicotine it disrupted the map. Exposure to NMDA alone produced refinement. We conclude that the map refinement induced by chronic nicotine treatment has as its basis an increase in the level of NMDA receptor activity. The data are consistent with a model whereby map topography can be bidirectionally affected by either increasing or decreasing NMDA receptor activity.

Spectral Sensitivity of Direction‐Selective Ganglion Cells in the Fish Retina

In color matching experiments with extracellular recordings from axon terminals of ganglion cells in the tectum opticum of immobilized goldfish, direction-selective ganglion cells were shown to be color-blind. Their spectral sensitivity is determined by a high positive input from the long wavelength-sensitive cones and weak opponent input from other cone types.

Bidirectional modulation of visual plasticity by cholinergic receptor subtypes in the frog optic tectum.

Cholinergic input to the optic tectum is necessary for visual map maintenance. To understand why, we examined the effects of activation of the different cholinergic receptor subtypes in tectal brain slices and determined whether the retinotectal map was affected by manipulations of their activity in vivo. Both alpha-bungarotoxin sensitive and insensitive nicotinic receptor agonists increased spontaneous postsynaptic currents (sPSCs) in a subpopulation of patch-clamped tectal cells; application of subtype selective receptor antagonists reduced nicotine-induced increases in sPSCs. Activation of alpha-bungarotoxin insensitive nicotinic receptors also induced substantial inward current in some cells. Muscarinic receptor mediated outward current responses were blocked by the M2-like muscarinic receptor antagonists himbacine or AF-DX 384 and mimicked by application of the M2-like agonist oxotremorine. A less frequently observed muscarinic response involving a change in sPSC frequency appeared to be mediated by M1-like muscarinic receptors. In separate experiments, pharmacological manipulation of cholinergic receptor subtype activation led to changes in the activity-dependent visual map created in the tectum by retinal ganglion cell terminals. Chronic exposure of the tectum to either alpha-bungarotoxin insensitive, alpha-bungarotoxin sensitive or M1-like receptor antagonists resulted in map disruption. However, treatment with the M2-like receptor antagonist, AF-DX 384, compressed the map. We conclude that nicotinic or M1-like muscarinic receptors control input to tectal cells while alpha-bungarotoxin insensitive nicotinic receptors and M2-like muscarinic receptors change tectal cell responses to that input. Blockade of the different cholinergic receptor subtypes can have opposing effects on map topography that are consistent with expected effects on tectal cell activity levels.

Sculpting the visual map: the distribution and function of serotonin-1A and serotonin-1B receptors in the optic tectum of the frog

Agonists of serotonin (5-HT)-1 receptors modulate the synaptic strength of the connection between retinal ganglion cells and neurons of the frog optic tectum in brain slices (Brain Res. 1998;781:167–181). We have now used autoradiographic receptor binding techniques to determine the location of 5-HT 1A and 5-HT 1B binding sites in the laminated optic tectum. 5-HT 1A binding sites, as labeled with [ 3H]8-hydroxy-dipropylaminotetralin (8-OH-DPAT), were highest in the superficial, retinorecipient layers of the tectum, intermediate in layers 6 and 7 and low in the remaining layers. Binding densities in all of these layers were unaffected by optic nerve lesion. 5-HT 1B binding sites were visualized using [ 125I]iodocyanopindolol (ICYP). Binding densities were highest in the plexiform layers 5 and 7 and intermediate in layers 6 and 8. Binding sites were present at low levels in layer 9; however, optic nerve lesion resulted in a strong upregulation of these sites in this layer. Pharmacological manipulation of receptor activation resulted in changes in the activity-dependent visual map that is created at the tectum by retinal ganglion cell terminals. Chronic treatment of the tectum with SB-224289, a selective antagonist of 5-HT 1B receptors, disrupted the topographic map. In contrast, exposure to WAY-100635, a selective antagonist of 5-HT 1A receptors, refined it. We conclude that both 5-HT 1A and 5-HT 1B receptors are present in the adult frog tectum and that changes in their activation levels can produce changes in retinotectal transmission levels that drive visual plasticity in opposite directions.

Glutamate Blocks Serotonergic Phase Advances of the Mammalian Circadian Pacemaker through AMPA and NMDA Receptors

The phase of the mammalian circadian pacemaker, located in the suprachiasmatic nucleus (SCN), is modulated by a variety of stimuli, most notably the environmental light cycle. Light information is perceived by the circadian pacemaker through glutamate that is released from retinal ganglion cell terminals in the SCN. Other prominent modulatory inputs to the SCN include a serotonergic projection from the raphe nuclei and a neuropeptide Y (NPY) input from the intergeniculate leaflet. Light and glutamate phase-shift the SCN pacemaker at night, whereas serotonin (5-HT) and NPY primarily phase-shift the pacemaker during the day. In addition to directly phase-shifting the circadian pacemaker, SCN inputs have been shown to modulate the actions of one another. For example, 5-HT can inhibit the phase-shifting effects of light or glutamate applied to the SCN at night, and NPY and glutamate inhibit phase shifts of one another. In this study, we explored the possibility that glutamate can modulate serotonergic phase shifts during the day. For these experiments, we applied various combinations of 5-HT agonists, glutamate agonists, and electrical stimulation of the optic chiasm to SCN brain slices to determine the effect of these treatments on the rhythm of spontaneous neuronal activity generated by the SCN circadian pacemaker. We found that glutamate agonists and optic chiasm stimulation inhibit serotonergic phase advances and that this inhibition involves both AMPA and NMDA receptors. This inhibition by glutamate may be indirect, because it is blocked by both tetrodotoxin and the GABA(A) antagonist, bicuculline.

Current issues in spinal anesthesia.

Spinal anesthesia is an old, simple, and popular anesthetic technique, yet much remains unknown regarding pertinent anatomy, physiology, and pharmacology. Investigations into physiologic effects of spinal anesthesia reveal complex actions on multiple organ systems. New local anesthetics, analgesic additives, and techniques are being investigated for different applications as the practice of medicine focuses on outpatient care. Safety of spinal agents and complications from spinal anesthesia continue to be examined and re-examined to improve safety. Further study will be needed to fully resolve these issues and to further understand and improve the clinical use of spinal anesthesia.

Pharmacology, distribution and development of muscarinic acetylcholine receptor subtypes in the optic tectum of Rana pipiens.

Visually evoked behaviors mediated by the frog optic tectum require cholinergic activity, but the receptor subtypes through which acetylcholine acts are not yet identified. Using quantitative autoradiography and scintillation spectrometry, we examined the binding of [3H]pirenzepine and [3H]AF-DX 384 in the laminated optic tectum of the frog. In mammalian systems, these substances bind excitatory (m1 and m3 subtypes) and inhibitory (m2 and m4 subtypes) muscarinic acetylcholine receptors, respectively. Pharmacological analyses, including the use of specific muscarinic toxins, confirmed the subtype selectivity of the radioligands in the frog brain. Binding sites for [3H]pirenzepine were distinct from those for [3H]AF-DX 384. In the adult tectum, [3H]pirenzepine demonstrated specific binding in tectal layers 5-9. [3H]Pirenzepine binding was also present in tadpoles as young as stage V, but all sampled stages of tadpole tectum had significantly less binding when compared to adults. Lesioning of the optic nerve had no effect on [3H]pirenzepine binding. Specific [3H]AF-DX 384 binding was found in all layers of the adult tectum. All sampled tadpole stages exhibited binding sites for [3H]AF-DX 384, but the densities of these sites were also significantly higher in adults than they were in developing stages. Short-term lesions of the optic nerve reduced [3H]AF-DX 384 binding in all tectal layers of the deafferented lobe when compared to the afferented one. Long-term lesions decreased [3H]AF-DX 384 sites in both lobes.These results indicate that multiple muscarinic acetylcholine receptor binding sites reside in the frog optic tectum at all stages of development, and their pharmacology resembles that of mammalian m1/m3, m2 and m4 subtypes. Our data indicate that few, if any, of these receptors are likely to be located on retinal ganglion cell terminals. Furthermore, the expression of inhibitory muscarinic subtypes seems to be regulated by different mechanisms than that for excitatory subtypes.

Electron microscopic observation of pituitary adenylate cyclase-activating polypeptide (PACAP)-containing neurons in the rat retina☆

The distribution and localization of pituitary adenylate cyclase-activating polypeptide (PACAP) in the rat retina were studied by immunocytochemistry with both light and electron microscopy. PACAP-like immunoreactivity (PACAP-LI) was detected in the amacrine and horizontal cells as well as in the inner plexiform layer, the ganglion cell layer and the nerve fiber layer. PACAP-LI seemed to be concentrated predominantly in the neuronal perikarya and their processes, but not in other cells in the retina. At the ultrastructural level, PACAP-LI was visible in the plasma membranes, rough endoplasmic reticulum, and cytoplasmic matrix in the PACAP-positive neurons in the inner nuclear layer. In the inner plexiform layer, PACAP-positive amacrine cell processes made synaptic contact with immunonegative amacrine cell processes, bipolar cell processes, and ganglion cell terminals. These findings suggest that PACAP may function as a neurotransmitter and/or neuromodulator.

Distribution and development of nicotinic acetylcholine receptor subtypes in the optic tectum of Rana pipiens.

Acetylcholine allows the elicitation of visually evoked behaviors mediated by the frog optic tectum, but the mechanisms behind its effects are unknown. Although nicotinic acetylcholine receptors (nAChRs) exist in the tectum, their subtype has not been assessed. By using quantitative autoradiography, we examined the binding of [(3)H]cytisine and [(125)I]alpha-bungarotoxin in the laminated tectum. In mammalian systems, these radioligands bind with high affinity to alpha4 nAChR subunits and alpha7 nAChR subunits, respectively. [(3)H]Cytisine demonstrated high specific binding in adult frogs in retinorecipient layer 9, intermediate densities in layer 8, and low binding in layers 1-7 of the tectum. [(3)H]Cytisine binding was significantly higher in the tecta of adults than in those of tadpoles. Lesioning the optic nerve for 6 weeks decreased [(3)H]cytisine binding in layers 8/9 by 70+/-1%, whereas 6-month lesions decreased binding by 76+/-3%. Specific binding of [(125)I]alpha-bungarotoxin in adults was present only at intermediate levels in tectal layers 8 and 9, and undetectable in the deeper tectal layers. However, the nucleus isthmi, a midbrain structure reciprocally connected to the tectum, exhibited high levels of binding. There were no significant differences in tectal [(125)I]alpha-bungarotoxin binding between tadpoles and adults. Six-week lesions of the optic nerve decreased tectal [(125)I]alpha-bungarotoxin binding by 33+/-10%, but 6-month lesions had no effect. The pharmacokinetic characteristics of [(3)H]cytisine and [(125)I]alpha-bungarotoxin binding in the frog brain were similar to those demonstrated in several mammalian species. These results indicate that [(3)H]cytisine and [(125)I]alpha-bungarotoxin identify distinct nAChR subtypes in the tectum that likely contain non-alpha7 and alpha7 subunits, respectively. The majority of non-alpha7 receptors are likely associated with retinal ganglion cell terminals, whereas alpha7-containing receptors appear to have a different localization.

Development and regulation of substance P expression in neurons of the tadpole optic tectum.

Activity-dependent synaptic plasticity is characteristic of developing visual systems. Using the frog retinotectal system, we investigated the extent to which afferent input affects neurotransmitter expression in a target structure. We have concentrated on a particular subpopulation of tectal cells that is immunoreactive to substance P (SP). Early in development, SP expression in tectal neurons was restricted to the anterior lateral region of the tectum. As tadpoles developed, this expression expanded into progressively more posterior and medial regions in a manner that closely followed the gradient of tectal maturation. At all times, however, anterior and lateral tectal regions had a greater percent of SP-like immunoreactive (SP-ir) cells than posterior and medial ones. Horseradish peroxidase (HRP) labeling of the retinal ganglion cell projection in conjunction with SP immunocytochemistry demonstrated that innervation by retinal ganglion cell terminals preceded the expression of SP by tectal cells. This suggested that the optic nerve may influence SP differentiation and/or expression. In support of this idea, transection of the optic nerve resulted in a decrease in SP expression in the deafferented tectal lobe of tadpoles. This result, opposite to that seen previously in the adult, also indicates that optic nerve-dependent regulation of SP expression in the developing and mature systems occurs through different pathways.

Depletion of calcitonin gene-related peptide from the caudal trigeminal nucleus of the rat after electrical stimulation of the Gasserian ganglion.

Electrical stimulation of the Gasserian ganglion resulted in partial depletion of calcitonin gene-related peptide (CGRP) from ipsilateral central terminals of pseudounipolar primary sensory ganglion cells. Affected terminals exhibit decreased CGRP immunoreactivity as shown by cytophotometric densitometry of the caudal trigeminal nucleus. The decrease in CGRP immunoreactivity is statistically significant only in the medial one-third of the caudal trigeminal nucleus. Since earlier studies have shown that electrical stimulation of the Gasserian ganglion induces first accumulation then depletion of CGRP from perivascular sensory terminals in the dura mater, the present experiments suggest that CGRP is depleted also from central terminals of primary sensory trigeminal neurons, which might be of importance in the pathogenesis of migraine headache.