Retina neurotransmitters

Similar to C1C-5, C1C-3 is present in endosomes. It is also found in synaptic vesicles. In both instances, and similar to C1C-5, it is necessary for the efficient intravesicular acidification. The acidification of synaptic vesicles is particularly important as their uptake of neurotransmitters depends on the electrochemical proton gradient. Surprisingly, the disruption of C1C-3 in mice resulted in a drastic degeneration of the hippocampus and the retina. Much less is known about C1C-4, which, however, also appears to be present in endosomal compartments. 

O Brien KB, Esguerra M, Miller RF, Bowser MT (2004) Monitoring neurotransmitter release from isolated retinas using online microdialysis-capillary electrophoresis. Anal Chem 76 5069-5074... 

The excitatory transmitter released from these cells is, in most instances, glutamate. Local circuit neurons are typically smaller than projection neurons, and their axons arborize in the immediate vicinity of the cell body. Most of these neurons are inhibitory, and they release either GABA or glycine. They synapse primarily on the cell body of the projection neurons but can also synapse on the dendrites of projection neurons as well as with each other. Two common types of pathways for these neurons (Figure 21-6A) include recurrent feedback pathways and feed-forward pathways. A special class of local circuit neurons in the spinal cord forms axoaxonic synapses on the terminals of sensory axons (Figure 21-6B). In some sensory pathways such as the retina and olfactory bulb, local circuit neurons may actually lack an axon and release neurotransmitter from dendritic synapses in a graded fashion in the absence of action potentials. 

K. B. O Brien, M. Esguerra, R. F. Miller, and M. T. Bowser, Monitoring Neurotransmitter Release from Isolated Retinas Using Online Microdialysis-Capillaiy Electrophoresis, Anal. Chem. 2004, 76, 5069. 

The term "H3 receptor" has been coined by Arrang et al.1 H3 receptors are located on paracrine cells and on neurones activation of H3 receptors usually causes inhibition of the release of the respective mediator or neurotransmitter. The receptor characterized by Arrang et al.1 is an example of an autoreceptor, i.e. of a receptor via which the transmitter released from a given neurone influences its own release. H3 receptor-mediated inhibition of the release of transmitters other than histamine has also been described such receptors are known as heteroreceptors. The present review will focus on H3 heteroreceptors in the central nervous system (CNS) in separate chapters of this book, H3 autoreceptors, H3 heteroreceptors in the neuroendocrine system as well as H3 receptor-mediated modulation of transmitter release in vivo will be considered. A separate article will also deal with H3 heteroreceptors in peripheral tissues although an example of an H3 receptor in the retina will be covered in our chapter, due to the close relationship between CNS and retina2. 

Tachibana M, Okada T, Arimura T, Kobayashi K, Piccolino M (1993) Dihydropyridine-sensitive calcium current mediates neurotransmitter release from bipolar cells of the goldfish retina. J Neurosci 13 2898-2909. 

Glutamate is the major excitatory neurotransmitter in the retina where it is released by photoreceptors, bipolar, and ganglion cells (Yang, 2004). 

Dopamine can thus be added to the list of hormones and neurotransmitters which can stimulate or inhibit cyclic AMP formation, depending upon their tissue of action. Thus, while dopamine stimulates cyclic AMP formation in parathyroid cells, superior cervical ganglia, retina and striatal tissue (27, 58-61), it inhibits the accumulation of the cyclic nucleotide in cells of the intermediate and anterior lobes of the pituitary gland. Opposite effects on the cyclic AMP system are also found with LHRH which stimulates and inhibits cyclic AMP levels in the anterior pituitary gland (62) and ovary (63), respectively. Similarly, alpha-adrenergic agents show opposite effects on cyclic AMP formation in brain (64) and platelets (65). PGE, stimulates cyclic AMP formation in the anterior pituitary gland (62) while it inhibits the same parameter in fat cells (66). 

Answer Hyperpolarization of rod cells in the retina occurs when the membrane potential, Vm, becomes more negative. This results in the closing of voltage-dependent Ca2+ channels in the presynaptic region of the rod cell. The resulting decrease in intracellular [Ca2 + ] causes a corresponding decrease in the release of neurotransmitter by exocytosis. The neurotransmitter released by rod cells is actually an inhibitory neurotransmitter, which leads to suppression of activity in the next neuron of the visual circuit. When this inhibition is removed in response to a light stimulus, the circuit becomes active and visual centers in the brain are excited. 

Taurine in the Central Nervous System There is a relatively high concentration of taurine in the central nervous system - higher than would be expected for a neurotransmitter and without a specific anatomical localization. As in the retina, the main function of taurine in the central nervous system seems to be as an osmolyte (Hussy et al., 2000 Saransaari and Oja, 2000). 

Other potential targets of cholinergic stimulation or blockade by drugs include the cornea, lens, and retina. The corneal epithelium contains the neurotransmitter acetylcholine and the enzymes choline acetylase... 

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