35 resultados para Subesophageal Ganglion


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PURPOSE. To investigate the effect of age on optokinetic nystagmus (OKN) in response to stimuli designed to preferentially stimulate the M-pathway. METHOD. OKN was recorded in 10 younger (32.3 +/- 5.98 years) and 10 older (65.6 +/- 6.53) subjects with normal vision. Vertical gratings of 0.43 or 1.08 cpd drifting at 5 degrees/s or 20 degrees/s and presented at either 8% or 80% contrast were displayed on a large screen as full-field stimulation, central stimulation within a central Gaussian-blurred window of 15 diameter, or peripheral stimulation outside this window. All conditions apart from the high-contrast condition were presented in a random order at two light levels, mesopic (1.8 cdm(-2)) and photopic (71.5 cdm(-2)). RESULTS. Partial-field data indicated that central stimulation, mesopic light levels, and lower temporal frequency each significantly increased slow-phase velocity (SPV). Although there was no overall difference between groups for partial-field stimulation, full-field stimulation, or low-contrast stimulation, a change in illumination revealed a significant interaction with age: there was a larger decrease in SPV going from photopic to mesopic conditions for the older group than the younger group, especially for higher temporal frequency stimulation. CONCLUSIONS. OKN becomes reflexive in conditions conducive to M-pathway stimulation, and this rOKN response is significantly diminished in older healthy adults than in younger healthy adults, indicative of decreased M-pathway sensitivity.

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Visual acuity is limited by the size and density of the smallest retinal ganglion cells, which correspond to the midget ganglion cells in primate retina and the beta- ganglion cells in cat retina, both of which have concentric receptive fields that respond at either light- On or light- Off. In contrast, the smallest ganglion cells in the rabbit retina are the local edge detectors ( LEDs), which respond to spot illumination at both light- On and light- Off. However, the LEDs do not predominate in the rabbit retina and the question arises, what role do they play in fine spatial vision? We studied the morphology and physiology of LEDs in the isolated rabbit retina and examined how their response properties are shaped by the excitatory and inhibitory inputs. Although the LEDs comprise only similar to 15% of the ganglion cells, neighboring LEDs are separated by 30 - 40 mu m on the visual streak, which is sufficient to account for the grating acuity of the rabbit. The spatial and temporal receptive- field properties of LEDs are generated by distinct inhibitory mechanisms. The strong inhibitory surround acts presynaptically to suppress both the excitation and the inhibition elicited by center stimulation. The temporal properties, characterized by sluggish onset, sustained firing, and low bandwidth, are mediated by the temporal properties of the bipolar cells and by postsynaptic interactions between the excitatory and inhibitory inputs. We propose that the LEDs signal fine spatial detail during visual fixation, when high temporal frequencies are minimal.

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The cholinergic amacrine cells in the rabbit retina slowly accumulate glycine to very high levels when the tissue is incubated with excess sarcosine (methylglycine), even though these cells do not normally contain elevated levels of glycine and do not express high-affinity glycine transporters. Because the sarcosine also depletes the endogenous glycine in the glycine-containing amacrine cells and bipolar cells, the cholinergic amacrine cells can be selectively labeled by glycine immunocytochemistry under these conditions. Incubation experiments indicated that the effect of sarcosine on the cholinergic amacrine cells is indirect: sarcosine raises the extracellular concentration of glycine by blocking its re-uptake by the glycinergic amacrine cells, and the excess glycine is probably taken-up by an unidentified low-affinity transporter on the cholinergic amacrine cells. Neurobiotin injection of the On-Off direction-selective (DS) ganglion cells in sarcosine-incubated rabbit retina was combined with glycine immunocytochemistry to examine the dendritic relationships between the DS ganglion cells and the cholinergic amacrine cells. These double-labeled preparations showed that the dendrites of the DS ganglion cells closely follow the fasciculated dendrites of the cholinergic amacrine cells. Each ganglion cell dendrite located within the cholinergic strata is associated with a cholinergic fascicle and, conversely, there are few cholinergic fascicles that do not contain at least one dendrite from an On-Off DS cell. It is not known how the dendritic co-fasciculation develops, but the cholinergic dendritic plexus may provide the initial scaffold, because the dendrites of the On-Off DS cells commonly run along the outside of the cholinergic fascicles. J. Comp. Neurol. 421:1-13, 2000. (C) 2000 Wiley-Liss, Inc.

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Little is known about the nature of the calcium channels controlling neurotransmitter release from preganglionic parasympathetic nerve fibres. In the present study, the effects of selective calcium channel antagonists and amiloride were investigated on ganglionic neurotransmission. Conventional intracellular recording and focal extracellular recording techniques were used in rat submandibular and pelvic ganglia, respectively. Excitatory postsynaptic potentials and excitatory postsynaptic currents preceded by nerve terminal impulses were recorded as a measure of acetylcholine release from parasympathetic and sympathetic preganglionic fibres following nerve stimulation. The calcium channel antagonists omega-conotoxin GVIA (N type), nifedipine and nimodipine (L type), omega-conotoxin MVIIC and omega-agatoxin IVA (P/Q type), and Ni2+ (R type) had no functional inhibitory effects on synaptic transmission in both submandibular and pelvic ganglia. The potassium-sparing diuretic, amiloride, and its analogue, dimethyl amiloride, produced a reversible and concentration-dependent inhibition of excitatory postsynaptic potential amplitude in the rat submandibular ganglion. The amplitude and frequency of spontaneous excitatory postsynaptic potentials and the sensitivity of the postsynaptic membrane to acetylcholine were unaffected by amiloride. In the rat pelvic ganglion, amiloride produced a concentration-dependent inhibition of excitatory postsynaptic currents without causing any detectable effects on the amplitude or configuration of the nerve terminal impulse. These results indicate that neurotransmitter release from preganglionic parasympathetic and sympathetic nerve terminals is resistant to inhibition by specific calcium channel antagonists of N-, L-, P/Q- and R-type calcium channels. Amiloride acts presynaptically to inhibit evoked transmitter release, but does not prevent action potential propagation in the nerve terminals, suggesting that amiloride may block the pharmacologically distinct calcium channel type(s) on rat preganglionic nerve terminals. (C) 1999 IBRO. Published by Elsevier Science Ltd.

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Neonatal X-irradiation of central nervous system (CNS) tissue markedly reduces the glial population in the irradiated area. Previous in vivo studies have demonstrated regenerative success of adult dorsal root ganglion (DRG) neurons into the neonatally-irradiated spinal cord. The present study was undertaken to determine whether these results could be replicated in an in vitro environment. The lumbosacral spinal cord of anaesthetised Wistar rat pups, aged between 1 and 5 days, was subjected to a single dose (40 Gray) of X-irradiation. A sham-irradiated group acted as controls. Rats were allowed to reach adulthood before being killed. Their lumbosacral spinal cords were dissected out and processed for sectioning in a cryostat. Cryosections (10 mum-thick) of the spinal cord tissue were picked up on sterile glass coverslips and used as substrates for culturing dissociated adult DRG neurons. After an appropriate incubation period, cultures were fixed in 2% paraformaldehyde and immunolabelled to visualise both the spinal cord substrate using anti-glial fibrillary acidic protein (GFAP) and the growing DRG neurons using anti-growth associated protein (GAP-43). Successful growth of DRG neurites was observed on irradiated, but not on non-irradiated, sections of spinal cord. Thus, neonatal X-irradiation of spinal cord tissue appears to alter its environment such that it can later support, rather than inhibit, axonal regeneration. It is suggested that this alteration may be due, at least in part, to depletion in the number of and/or a change in the characteristics of the glial cells. (C) 2000 ISDN. Published by Elsevier Science Ltd. All rights reserved.