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Neurons
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Neurons can be classified in a number of ways. One of the earliest classifications is anatomical, according to which neurons can be unipolar, bipolar, or multipolar. Unipolar neurons have only one process emanating from the cell body. In the case of sensory neurons of the dorsal root ganglia (Figure 11.2), this single process divides at some distance from the cell body into two main branches that conduct APs from peripheral sensory receptors, past this branch point and into the spinal cord. On the other hand, most amacrine cells of the retina (Figure 7.1a) have dendrites and no axons. They neither generate nor conduct action potentials; instead they actively conduct synaptic signals through their dendrites to their target cells. Figure 7.1b illustrates a bipolar cell of the retina having an axon and a single dendrite on opposite ends of the soma. The axon of the dopamine-releasing neuron of the substantia nigra, which is a nucleus of the basal ganglia (Section 12.2.3), emerges from a dendrite up to 240 µm from the soma.
Distribution and Characteristics of Brain Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
The mapping of adrenergic innervation within the brain became possible upon the introduction of anti-PNMT antibodies in immunohistochemical preparations. The adrenergic cell groups (C1 and C2) are located in the medulla, close to, and slightly overlapping with, the noradrenergic A1 and A2 cell groups. Few additional PNMT-positive cells have been detected in amacrine cells of the retina. The majority of the ascending adrenergic fibers go to the hypothalamus, as is described in Section 3.4.3. Low PNMT activity is detected in the substantia nigra, stria terminalis, and septum, while only a few adrenergic terminals are found in the cerebellum. PNMT activity is not detectable in the cerebral cortex, caudate, amygdala, hippocampus, nucleus accumbens, and olfactory tubercle. Within the spinal cord, only the sympathetic lateral column has significant adrenergic innervation.
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
Amacrine cells are interneurons located in the inner nuclear layer of the RETINA. They lack axons, but through their dendrites modify signal transmission from BIPOLAR CELLS to GANGLION CELLS. The input to amacrine cells comes from axons of bipolar cells as well as from dendrites of other amacrine cells. Their output is directed to ganglion cells, other amacrine cells, and axons of bipolar cells, thus forming complex feedback, feed-forward, and reciprocal networks. Amacrine cells use GABA, GLYCINE, ACETYLCHOLINE and DOPAMINE as neurotransmitters, and some of these transmitters are co-localized in the same cell.
The therapeutic effect of nano-zinc on the optic nerve of offspring rats and their mothers treated with lipopolysaccharides
Published in Egyptian Journal of Basic and Applied Sciences, 2023
Eman Mohammed Emara, Hassan Ih El-Sayyad, Amr M Mowafy, Heba a El-Ghaweet
Lipopolysaccharides (LPS) are a toxic component in Gram-negative bacteria’s cell walls [1]. The hydrophilic core polysaccharide chain, the repetitive hydrophilic O-antigenic oligosaccharide side chain and the hydrophobic lipid portion that is known as lipid A are the three structural elements that make up the macromolecules of intact bacterial LPS [2]. The intrauterine infection brought on by bacterial LPS exposure causes preterm delivery, neurological damage and fetal inflammation in the retina and optic nerve, which manifests in their structure and neurochemistry. It also results in a decrease in tyrosine hydroxylase immunoreactive (TH-IR), dopaminergic amacrine cells and all of which can impair vision. When compared to control fetuses, myelin sheath thickness decreased in LPS-exposed fetuses at a critical time for optic nerve development [3]. According to several studies, LPS causes systemic inflammation and affects directly placental cells causing the release of pro-inflammatory mediators that activate microglia. In addition, astrocytes cause the production of cytokines in the developing fetal brain [4,5].
Effect of vitamin D deficiency on spatial contrast sensitivity function
Published in Clinical and Experimental Optometry, 2022
Other important retinal cells that assist in the regulation of visual processing are horizontal cells and amacrine cells. The lateral coupling of these cells plays an important role in visual acuity and contrast sensitivity formation by adjusting the receptive field sizes.20,21 The centre-surround organisation of receptive fields, in which the object (centre) and its background (surround) have different illumination signals is primarily regulated by bipolar cells.22 The large receptive fields of horizontal cells have been considered to form the surround of bipolar cells,23 and as a result of a light-induced increase in dopamine, uncoupling of horizontal cells leads to a reduced surround receptive field that is related with increased local contrast detection.24
Advances in understanding the mechanisms of retinal degenerations
Published in Clinical and Experimental Optometry, 2020
In contrast, the localisation of P2X receptors in rod mediated pathways are more complex. The neural pathway important for mediating scotopic vision involves rod photoreceptors communicating with rod bipolar cells that in turn pass information to two highly specific amacrine cell types called AII and A17 amacrine cells.200422,23 The AII amacrine cells then pass scotopic information to ganglion cells by communicating with ON and OFF cone bipolar cells.200422,23 A critical step in shaping vision processing in the scotopic pathway is the modulation that occurs between rod bipolar cells and AII and A17 amacrine cells. An example of the synapse between a rod bipolar cell and an A17 and AII amacrine cell is shown in Figure 1B. Importantly, A17 amacrine cells which release the inhibitory neurotransmitter GABA, feedback directly onto rod bipolar cell terminals via reciprocal synapses to shape signalling by rod bipolar cells.24