Neurons bipolar cells

Zenisek D, Steyer JA, Eeldman ME, Aimers W (2002) A membrane marker leaves synaptic vesicles in nulliseconds after exocytosis in retinal bipolar cells. Neuron 35 1085-1097 Zhang L, He T, Talal A, Wang G, Frankel SS, Ho DD (1998) In vivo distribution of the human immunodeficiency virus/simian immunodeficiency virus coreceptors CXCR4, CCR3, and CCR5. J Virol 72 5035-5045... 

Although pheromones can be considered as a special form of odorants (scents), their actions, effects and functions have similarities to those of hormones. They bind to a specific receptor which then activates an effector system, which initiates an action potential. They bind to specific sensory cells, the neurones, in the olfactory epithelium, which is located on the roof of the nasal cavities. The epithelium consists of three types of cells, basal, supporting and sensory cells (neurones). The neurones are bipolar, that is they possess a single dendrite, which extends from the cell body to the surface of the olfactory epithelium, and an axon that forms a synapse with a nerve that transfers information to the olfactory centre in the brain. The epithelium is covered with a thick layer of mucus, in which the pheromones dissolve. The mucus contains proteins that bind the pheromone(s) for delivery to the olfactory receptors and then to remove them once they have been detected. 

The Na" channel has a receptor site for cyclic GMP when cyclic GMP is bound, the channel is closed. This leads to a decrease in the intracellular Na ion concentration, resulting in hyperpolarisation of the cell membrane. This decreases the release of the neurotransmitter glutamate into the synapse that connects the photoreceptor cell to the bipolar neurones. In this specific case, a decrease in the neurotransmitter concentration in the synapse is a signal that results in depolarisation of the bipolar cell. The action potential in the bipolar cells communicate with ganglion cells, the axons of which form the optic nerve. Thus action potentials are generated in the axons which are... 

The retina extends forward to the sclera as a globe-shaped wineglass almost external to the skull. That part of the sclera devoid of retina is the pars planar, which is used as an access point for injection or for close delivery to the iris and ciliary body (ICB). When stripped from its basement membrane and opened out, the collapsed retina is a circular disk approximately 42 mm in diameter and 0.5 mm in thickness. The organization of the retina is based on a three-neuron chain (photoreceptor cell-bipolar cell-ganglion cell) and accompanying cells (horizontal, amacrine, and Muller cells)... 

Wang Y, Small DL, Stanimirovic DB, Morley P, Durkin JP (1997) AMPA receptor-mediated regulation of a Gi-protein in cortical neurons. Nature 389 502 Wersinger E, Schwab Y, Sahel J-A, Rendon A, Pow DV, Picaud S, Roux MJ (2006) The glutamate transporter EAAT5 works as a presynaptic receptor in mouse rod bipolar cells. J Physiol (Lond) 577 221-34... 

While experimental evidence concerning the molecular mechanisms and the diversity of reaction cascades involved in olfactory signal transduction in antennal cells of insects is still fragmentary, a much more detailed picture has been established for signal transduction in chemosensory cells of the lobster, another member of the arthropod phyla. The bipolar chemosensory neurons of the lobster antennule respond to stimulation with odorous compounds either with an excitation or an inhibition i.e. cells are equipped to respond to one odor with a depolarization and excitation as well as to another odor with a hyperpolarization and inhibition. 

Glutamate release from synaptic terminals of photoreceptor and bipolar cells is regulated by calcium influx through L-type calcium channels (Heidelberger et al., 2005). The use of F-type channels at ribbon synapses contrasts with the reliance on N, P, and Q type channels for neurotransmission at conventional synapses of spiking neurons. A retina-specific L-type channel, alpha IF (CaVl.4), is localized to rod terminals. Mutations in this channel produce a congenital stationary night blindness (Bech-Hansen et al., 1998). 

In the primitive nervous system, sensory cells evolved from general epithelial cells. Primitive nervous systems of modern echinoderms and lower deuterostomes are still composed of three cell types that include the primary sensory cells, the neurons that connect the sensory cells to distal targets, and a supporting cell that serves the special physiological needs of such a system (Lacalli, 2001). The basic structural plan of the retina is comparable to such a primitive nervous system. In the course of evolution, the photoreceptive system developed specialized photoreceptor cells (rods and cones), intra-retinal second-order neurons (bipolar cells), and tertiary output neurons (ganglion cells). This evolution perhaps took place in photopic conditions therefore early photoreceptor cells were more like cones. 

A fully developed retina consists of six neuron types and the Muller glial cells as shown in this schematic representation. A, Amacrine cells B, bipolar cells C, cone photoreceptor cells G, ganglion cells H, horizontal cells I, interplexiform cells M, Muller cells PE, pigment epithelium R, rod photoreceptor cell INL, inner nuclear layer IPL, inner plexiform layer ONL, outer nuclear layer Ph, photoreceptors RPE, RPE (Reproduced with permission from the publishers of Sharma and Ehinger, 2003)... 

Glutamate is the major excitatory retinal neurotransmitter in retina. It is released by photoreceptors, bipolar cells, and ganglion cells (Sharma and Ehinger, 2003). Normally, the released glutamate remains in the synaptic cleft only for a short time (a few milliseconds). If glutamate levels remain elevated for a prolonged period of time, this can excite neurons to death. This mechanism of cell death is referred to as excitotoxicity. 

Rowley JC III, Moran DT, Jafek BW. 1989. Peroxidase backfills suggest the mammalian olfactory epithelium contains a second morphologically distinct class of bipolar sensory neuron The microvillar cell. Brain Res 502 387-400. 

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