The Journal of neuroscience : the official journal of the Society for Neuroscience
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The "calcium hypothesis" of regulation of growth cone motility and neurite elongation has derived from analysis of a variety of neurons growing in vitro. It proposes that calcium ion concentration within growth cones is an important regulator of motility and growth. We now extend this analysis by investigating calcium concentrations within growth cones and nascent neurites of identified embryonic neurons growing on their normal substrate in situ. ⋯ Therefore, an increase in cytosolic calcium concentration may be associated with the onset of axonogenesis. Nascent pioneer neurons were fura-2 dye-coupled to each other and established coupling with contacted guidepost cells. Calcium concentration measurements along pioneer neurites suggest that calcium ions also are transferred from pioneer neurons to these coupled guidepost cells.(ABSTRACT TRUNCATED AT 250 WORDS)
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Naloxone-precipitated opioid abstinence is associated with enhancement of reflex responses to noxious stimulation (hyperalgesia). The present experiments in lightly anesthetized rats were designed to determine (1) whether neurons in the rostral ventromedial medulla (RVM) contribute to this enhancement, and (2) whether this enhancement is due to removal of an inhibitory modulatory influence or to activation of a facilitatory influence. In the first experiment, 10 micrograms of morphine was microinjected into the RVM; subsequent administration of naloxone (1 mg/kg, i.v.) shortened tail-flick latency. ⋯ That inactivation of RVM reduces the hyperalgesia indicates that the CNS is capable of generating a facilitating action on nociceptive transmission. Previous studies from this laboratory have indicated that a population of RVM neurons, on-cells, shows increased activity during opioid abstinence. The present experiments support the hypothesis that RVM on-cells exert a facilitating influence on nociceptive transmission.