Journal of neurophysiology
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1. We have studied the characteristics of the abnormal properties of damaged myelinated fibers (conduction velocity > 2.0 m/ s) after peripheral nerve injury in a novel in vitro model of the rat sciatic nerve/dorsal root ganglion/dorsal root (L4-5) preparation removed from control naíve or sham-operated rats and animals that had received sciatic neurectomy 12-24 days before the in vitro study. A total of 122-245 filaments were recorded in each dorsal root. ⋯ We present an in vitro model for the study of abnormal primary sensory activity in peripheral neuropathy. Although our data are consistent with in vivo electrophysiological findings in published reports, the proportion of damaged afferent fibers displaying spontaneous activity was significantly lower under in vitro conditions. This model may serve as a valuable tool for further physiological and pharmacological studies of peripheral neuropathy.
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1. The role of descending brain stem modulatory systems in the development of persistent behavioral hyperalgesia and dorsal horn hyperexcitability was studied in rats with unilateral hindpaw inflammation. Inflammation was induced by intraplantar injection of complete Freund's adjuvant (CFA, 0.05 ml of an 1:1 oil/saline emulsion, 25 micrograms Mycobacterium), or lambda carrageenan (1 mg/ 0.1 ml saline). ⋯ Thoracic saline did not produce a significant change in the receptive field size (105 +/- 9%, n = 4). The increases in responses to noxious thermal and mechanical stimuli after thoracic lidocaine block were also significantly greater in inflamed than in noninflamed rats (P < 0.01). There was no significant difference in the increase in responses to electrical stimulation of the sciatic nerve after lidocaine between inflamed and noninflamed rats.(ASTRACT TRUNCATED)
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1. Presbycusis, age-related hearing loss, is an ever increasing problem in our aging society. It involves changes in both the peripheral and central portions of the auditory system. ⋯ The results of this study support the hypothesis that there is an age-related shift to higher intensities in the working range of most CIC units along with a small, selective deficit in inhibitory processing. When considered in conjunction with the mouse aging studies conducted by other researchers and with the results of a similar study of single units in the visual system (lateral geniculate nucleus) of young and aged rhesus monkeys, these results suggest that compensatory mechanisms are highly active in sensory systems as animals age. Despite deficits that lead to reduced input to the IC and neurochemical changes affecting neurotransmitter levels, IC neurons in aged rats are able to respond to most simple auditory stimuli in a fashion quite similar to that observed in young rats.
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Comparative Study
Changing directions of forthcoming arm movements: neuronal activity in the presupplementary and supplementary motor area of monkey cerebral cortex.
1. To understand roles played by two cortical motor areas, the presupplementary motor area (pre-SMA) and supplementary motor area (SMA), in changing planned movements voluntarily, cellular activity was examined in two monkeys (Macaca fuscata) trained to perform an arm-reaching task in which they were asked to press one of two target buttons (right or left) in three different task modes. 2. In the first mode (visual), monkeys were visually instructed to result and press either a right or left key in response to a forth coming trigger signal. ⋯ Neurons exhibiting the shift-related activity were distributed differentially among the two areas. In the pre-SMA, 31% of the neurons recorded showed the shift-related activity, whereas in the SMA, only 7% showed such an activity. These results suggest that pre-SMA and SMA play differential roles in updating the motor plans in accordance with current requirements.
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Comparative Study
Neuroprotection by propofol in acute mechanical injury: role of GABAergic inhibition.
1. Whole cell patch-clamp and extracellular field recordings were obtained from granule cells of the dentate gyrus in 400-microns-thick brain slices of the adult rat to determine the actions of the intravenous general anesthetic 2,6-diisopropylphenol (propofol) on acute neuronal survival and preservation of synaptic integrity after amputation of dendrites (dendrotomy), and to determine the role of gamma-aminobutyric acid-A (GABAA)-receptor-mediated inhibition in the neuroprotective effects of propofol. The actions of propofol were compared with those exerted by another widely used intravenous general anesthetic, 5-ethyl-5-[1-methylbutyl]-2-thiobarbituric acid (thiopental). 2. ⋯ The failure to rescue cells from dendrotomy-induced injury did not result from a decreased sensitivity of the GABAA receptors to the anesthetics, because the potentiating effects of the anesthetics on mIPSCs from control and dendrotomized neurons were not different. 7. These data indicate that propofol potentiates synaptic inhibition pre- and postsynaptically, and, when present during dendrotomy, it can protect neurons from acute mechanical-injury induced cell death via potentiation of GABAA receptor functions. However, propofol fails to provide neuroprotection against dendrotomy-induced changes in synaptic physiology.