Neurons horizontal cells

Figure I. Structure of a ciliated photoreceptor cell in vertebrates. (A) Scheme of a rod photoreceptor cell. (B) Transmission electronmicroscopy image of a part of a mouse rod photoreceptor cell. The apical extensions of cells of the retinal pigment epithelium (RPE) evolve the tips of photoreceptors light-sensitive outer segments (OS). The OS is linked via a connecting cilium (CC) to an inner segment (IS) which bears the basal body complex (BB) in its apical region. Synaptic terminals (S) link the photoreceptor cell and the 2nd-order neurons, bipolar and horizontal cells. N = nucleus in B, arrow point to axonemal microtubules projecting into the OS. Bar in B = 0.2 p,m...

HIV-1 associated dementia HIV-1 associated dementia is a cognitive disorder specific to HIV, HAD is the clinical consequence of HIV-1 infection in the CNS and chronic inflammatory response that ultimately causes neuronal damage, horizontal cell lateral inhibitory intemeuron in the outer retina. 

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)... 

Dixon, D.B., Takahashi, K.-I., and Copenhagen, D.R. (1993). L-Glutamate suppresses HVA calcium current in catfish horizontal cells by raising intracellular proton concentration. Neuron 7 7 267-277. 

The spiny cell is a medium sized neuron (15-25 m in diameter) that is located throughout layer I. These neurons are characterized by small spines on the distal and proximal dendritic segments. Unlike the horizontal cell, spiny cells lack knobs or similar appendages on the soma. Spiny cell dendrites extend into all parts of layer I and less frequently into deeper layers. The spiny neurons gives rise to an unmyelinated axon that is horizontally oriented. 

The cells most relevant to the present discussion are those forming the photoreceptive neurons. The dendrites of the neurons assume a special shape well suited to photoreception. The synapses transfer the impulse through their connections with dendrites originating from the bipolar and the horizontal cells. The photoreceptor cell is made up of cone or rod, body, and efferent fibers with the synapse. 

The smaller amount of neurons driven by the more numerous cones points to a complex wiring of these receptors located in the second layer of the retina. The inner nuclear layer connects the photoreceptors with the ganglion cells and consists of bipolar, amacrinal, and horizontal cells. Bipolar cells can be divided into ON and OFF bipolars. The OFF bipolar cells inhibit the release of neurotransmitters after a photon triggered increase in electrical potential whereas the ON bipolar cells stimulate the release of neurotransmitters. This allows the visual system to build differential signals already in the first processing stage (see Fig. 5). 

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)... 

In the rat, the dorsal tier includes cells of the dorsal parts of the VTA and SNc and cells of the RRA innervating the limbic portion of the striatum and limbic cortical fields, as well as the ventral basal forebrain structures, such as the olfactory tubercle and the amygdala. Neurons of the dorsal tier are mostly fusiform, with dendrites oriented horizontally in the mediolateral plane of the SNc. From the neurochemical point of view, neurons of the dorsal tier contain relatively low levels of TH mRNA and dopamine transporter (DAT) mRNA, and the calcium binding protein calbindin is colocalized with DA in most dorsal tier neurons (Gerfen, 1985) (Figs. 4D 13C,D). 

Pyramidal cell— named on the basis of the cell body s shape. It is one of the two major neuronal types found in the cerebral cortex. It has a large apical dendrite, which extends vertically from the top of the pyramid, and basal dendrites, which come off horizontally at the base of the pyramid. The axon also typically extends from the base. 

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