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Somatostatin (somatostatin, SRIF) is a central nervous system (central nervous system, CNS) in a neurological peptides, by activating the five kinds of specific receptor subtypes (sst 1-5 ) exercise of its functions, may play a role as a neurotransmitter or quenched. In the retina, SRIF mainly in amacrine cells (amacrine cell, AC) on. The literature indicates that, sst 1-4 are expressed in the retina, but only a low level in the retina of sst 5 mRNA expression. In this work, we study the sst 5 on the AC in the rat retina expression. In addition, the lack of specific receptor antagonists (except sst 2 outside), about the different SRIF receptor subtypes in the physiological function of neurons, little research reports. In recent years, with the specific sst 5 antagonists found for us to study sst 5 in the retina function provides the possibility. In this work, we first reported the somatostatin receptor subtype 5 (sst 5 ) in the rat retina AC, expression, and further studies on cultured rat retinal SRIF GABA can AC presynaptic inhibition of neurotransmitter release regulation. Immunocytochemical methods, we first studied the sst 5 in the rat retina expression on AC. sst 5 of immune markers diffuse manner throughout the inner plexiform layer and the inner plexiform layer to form two distinct fluorescent distal bright band. Immune double labeling experiments showed, sst 5 can be expressed in GABA on the AC. Further double-labeling experiments showed, sst 5 in tyrosine hydroxylase (tyrosine hydroxylase, TH) labeled dopaminergic AC and choline acetyltransferase (choline acetyl-transferase, CHAT) mark cholinergic were expressed on the AC. Immunoreactive markers were seen in these cell membrane and the cell body - projecting connecting portion. Cholinergic AC inner plexiform layer located on the projection can be observed weak sst 5 tags. On the contrary, in the Ca 2 -binding protein parvalbumin (PV) labeled glycine A Ⅱ type AC and there is no sst 5 positive mark. In addition, SRIF and sst 5 in dopaminergic and cholinergic coexpression on AC. These results suggest that, sst 5 in the retina may act as its own receptor on AC and / or conventional receptors. Whole-cell patch clamp recording technique, we further investigated in cultured rat retinal SRIF able AC presynaptic GABA activity regulation. The results showed that GABA in culture can be recorded on a tiny AC inhibitory postsynaptic currents (miniature inhibitory postsynaptic current, mIPSC), the current can be GABA A receptor antagonist bicuculline (10 / μM) completely inhibited, indicating mIPSC by postsynaptic GABA A receptor mediated. On this basis, we observed 1μM SRIF significantly suppressed mIPSC frequency, the depressing effect can be sst 5 and sst 2 of specific antagonists partially blocked, indicating that SRIF through the activation of presynaptic sst 5 and / or sst 2 work. Although slightly depressed mIPSC SRIF average amplitude but does not change the dynamics of mIPSC, such as rise time (rise time) and decay time (decay time). Increased extracellular Ca 2 concentration increases mIPSC frequency, whereas in extracellular calcium conditions, mIPSC frequency also can be 1μM SRIF significantly depressed. The removal of extracellular Ca 2 in the case, mIPSC almost completely suppressed, indicating mIPSC of extracellular Ca 2 has a dependency. Further studies showed that, 200μM CdCl 2 blocking most of the mIPSC, tips voltage-gated Ca 2 channel in which play an important role, so we studied the L-type Ca < sup> 2 channel blocker nimodipine role discovery 10μM nimodipine significantly suppressed mIPSC, tips presynaptic L-type Ca 2 Channels and mIPSC closely related. In addition, 5μM forskolin (adenylate cyclase activator) increased mIPSC frequency, while the PKA inhibitor Rp-cAMP (20μM) reduced mIPSC frequency. In the presence of Rp-cAMP case, SRIF no longer have depressing effect on mIPSC. These results suggest that, SRIF receptors may inhibit the activation of specific cAMP-PKA pathway, which in turn limits the extracellular Ca 2 through voltage-gated Ca 2 channel flow, thus AC presynaptic GABA can reduce the release of GABA. In summary, this work studied the sst 5 in the rat retina AC, expression, and further show sst 5 and / or sst 2 part of the SRIF on GABA-mediated presynaptic GABA release can be AC's depressing effect, then discusses the possible mechanism of this repression.
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