Neuroscience
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Spontaneous postsynaptic current is a reflection of spontaneous neurotransmitter release that plays multiple roles in a variety of neurobiological activities. In the present study, we recorded spontaneous inhibitory postsynaptic currents (sIPSCs) by patch-clamp techniques in cultured rat retinal GABAergic amacrine cells (ACs), which provide inhibitory inputs to both bipolar and ganglion cells in the inner retina, and examined if and how Ca(2+) was involved in the induction of spontaneous GABA release from the terminals of these cells. sIPSCs were completely blocked by application of either 10 microM bicuculline or 10 microM gabazine, and the reversal potential of sIPSCs was close to E(Cl-), indicating that these events were exclusively mediated by GABA(A) receptors. Increase of external Ca(2+) concentrations from 2 to 5 mM significantly enhanced the frequency, but did not change the amplitude of sIPSCs. ⋯ Furthermore, the ryanodine receptor (RyR) antagonist dantrolene (10 microM) failed to affect sIPSCs, while the inositol 1,4,5-trisphosphate (IP(3)) receptor antagonists 2-aminoethyl diphenylborinate (2-APB, 20 microM) and xestospongin C (XeC, 1 muM) significantly decreased the frequency of sIPSCs. In the presence of SKF96365 (10 microM), a non-specific transient receptor potential channel (TRP) blocker, 2-APB persisted to show its effect on sIPSCs. These results suggest that spontaneous GABA release from the terminals of GABAergic ACs is Ca(2+)-dependent, and both extracellular calcium influx through presynaptic calcium channels and Ca(2+) release through activation of the IP(3)-sensitive pathway, but not the ryanodine-sensitive one, from intracellular stores are responsible for the generation of sIPSCs under our experimental conditions.
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Excess glutamate release and stimulation of post-synaptic glutamatergic receptors have been implicated in the pathophysiology of many neurological diseases. The hippocampus, and the pyramidal cell layer of the cornu ammonus 1 (CA1) region in particular, has been noted for its selective sensitivity to excitotoxic insults. The current studies examined the role of N-methyl-D-aspartate (NMDA) receptor subunit composition and sensitivity to stimulatory effects of the polyamine spermidine, an allosteric modulator of NMDA NR2 subunit activity, in hippocampal CA1 region sensitivity to excitotoxic insult. ⋯ The addition of spermidine significantly potentiated [(125)I]MK-801 binding and neurodegeneration induced by exposure to a non-toxic concentration of NMDA, exclusively in the CA1 region. This neurodegeneration was markedly reduced with co-exposure to ifenprodil. These data suggest that selective sensitivity of the CA1 region to excitotoxic stimuli may be attributable to the density of mature neurons expressing polyamine-sensitive NR2B polypeptide subunits.
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This study assessed the possible antinociceptive role of peripheral 5-HT(1) receptor subtypes in the rat formalin test. Rats were injected into the dorsum of the hind paw with 50 microl of diluted formalin (1%). Nociceptive behavior was quantified as the number of flinches of the injected paw. ⋯ The above antagonists did not produce any effect by themselves. These results suggest that peripheral activation of the 5-HT(1A,) 5-HT(1B), 5-HT(1D), 5-HT(1F) and, probably, 5-HT(1E) receptor subtypes leads to antinociception in the rat formalin test. Thus, the use of selective 5-HT(1) receptor agonists could be a therapeutic strategy to reduce inflammatory pain.
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Morphine-3-glucoronide (M3G) is a major morphine metabolite detected in cerebrospinal fluid of humans receiving systemic morphine. M3G has little-to-no affinity for opioid receptors and induces pain by unknown mechanisms. The pain-enhancing effects of M3G have been proposed to significantly and progressively oppose morphine analgesia as metabolism ensues. ⋯ Providing further evidence of proinflammatory activation, M3G upregulated TLR4 and CD11b (microglial/macrophage activation marker) mRNAs in dorsal spinal cord as well as IL-1 protein in the lumbosacral cerebrospinal fluid. Finally, in silico and in vivo data support that the glucuronic acid moiety is capable of inducing TLR4/MD-2 activation and enhanced pain. These data provide the first evidence for a TLR4 and IL-1 mediated component to M3G-induced effects, likely of at least microglial origin.
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Synphilin-1 is a cytoplasmic protein with unclear function. Synphilin-1 has been identified as an interaction partner of alpha-synuclein. The interaction between synphilin-1 and alpha-synuclein has implications in Parkinson's disease. ⋯ We found that Rotenone induced apoptotic cell death in N1E-115 cells via caspase-3 activation and poly (ADP-ribose) polymerase (PARP) cleavage. Overexpression of synphilin-1 significantly reduced Rotenone-induced cell death, caspase-3 activation and PARP cleavage. The results indicate that synphilin-1 displays trophic and protective effects in vitro, suggesting that synphilin-1 may play a protective role in Parkinson's disease (PD) pathogenesis and may lead to a potential therapeutic target for PD intervention.