The Journal of neuroscience : the official journal of the Society for Neuroscience
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The effects of peripheral nerve injury on the content, synthesis, and axonal transport of the class III beta-tubulin protein in adult rat dorsal root ganglion (DRG) neurons were examined. Recent reports of selective increases in the steady-state levels of the beta III-tubulin mRNA during axonal regeneration (Moskowitz et al., 1993) led to the hypothesis that upregulated levels of expression of the beta III-tubulin isotype that alter the composition of neuronal microtubules is important for effective axonal regrowth. If this is the case, the increases in mRNA levels must be translated into increased beta III-tubulin protein levels and subsequently modify the axonal cytoskeleton via axonal transport mechanisms. ⋯ Immunoprecipitation experiments using proximal peripheral nerve segments showed that SCb in distally injured DRG neurons was enriched in the beta III-tubulin isotype. These findings demonstrate that the augmented synthesis of beta III-tubulin after axotomy alters the composition of the axonally transported cytoskeleton that moves with SCb. The increased amounts and rate of delivery of beta III-tubulin in axons of regenerating DRG neurons suggest that the altered pattern of tubulin gene expression that is initiated by axotomy impacts on the composition and organization of the axonal cytoskeleton in a manner that can facilitate axonal regrowth.
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One hundred ninety-four cutaneous C-fibers were recorded from the human peroneal nerve; 118 units were found by mechanical stimuli and 76 units were detected by electrical stimulation through a surface electrode. Needle electrodes were then inserted for electrical intradermal stimulation in the innervation territory of the units. Afferent and efferent sympathetic C-fibers were identified by slowing of conduction velocity after activation either by physical or chemical skin stimuli, or by arousal maneuvers eliciting sympathetic reflexes. ⋯ Some CM, CH, and CMiHi units were sensitized to heating and/or to mechanical stimuli after topical application of mustard oil or capsaicin. These units then acquired responsiveness to a stimulus modality to which they previously were insensitive. Such recruitment of previously silent nociceptors implies spatial summation to the nociceptive barrage at central levels, and may contribute both to primary hyperalgesia to heat and pressure after chemical irritation, and to secondary hyperalgesia as a consequence of central sensitization.
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Sharp wave bursts, induced by a cooperative discharge of CA3 pyramidal cells, are the most synchronous physiological pattern in the hippocampus. In conjunction with sharp wave bursts, CA1 pyramidal cells display a high-frequency (200 Hz) network oscillation (ripple). In the present study extracellular field and unit activity was recorded simultaneously from 16 closely spaces sites in the awake rat and the intracellular activity of CA1 pyramidal cells during the network oscillation was studied under anesthesia. ⋯ These findings indicate that the intracellularly recorded fast oscillatory rhythm is not solely dependent on membrane currents intrinsic to the CA1 pyramidal cells but it is a network driven phenomenon dependent upon the participation of inhibitory interneurons. We hypothesize that fast field oscillation (200 Hz) in the CA1 region reflects summed IPSPs in pyramidal cells as a result of high-frequency barrage of interneurons. The sharp wave associated synchronous discharge of pyramidal cells in the millisecond range can exert a powerful influence on retrohippocampal targets and may facilitate the transfer of transiently stored memory traces from the hippocampus to the entorhinal cortex.
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Opioid receptors have been demonstrated on sensory nerves in both inflamed and normal subcutaneous tissue but locally applied opioid agonists produce analgesia in inflamed tissue only. Inflammation confers a disruption of the perineurial barrier that can also be induced deliberately by hyperosmolar solutions. The present study examines at which stage of Freund's adjuvant-induced inflammation peripheral opioid analgesic effects become manifest and whether a perineurial defect contributes to the appearance of such effects. ⋯ We found that peripheral opioid antinociception and perineurial leakage occur simultaneously at a very early stage (within 12 hr) of the inflammatory reaction and that both can be mimicked by the administration of hyperosmolar solutions in normal tissue. Fentanyl produced peripheral antinociception in noninflamed tissue that was potentiated by mannitol or inflammation. Our findings demonstrate that the perineurium is a crucial determinant for peripheral opioid analgesia and that the efficacy of locally applied hydrophilic or lipophilic neuromodulatory compounds can be improved dramatically by the concomitant modulation of perineurial permeability.(ABSTRACT TRUNCATED AT 250 WORDS)
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The intergeniculate leaflet (IGL) is an integral part of the adult circadian visual system. It is characterized by the presence of retinal afferents and peptidergic cells projecting via a geniculohypothalamic tract (GHT) to the suprachiasmatic nucleus (SCN), site of the mammalian circadian clock. The adult IGL also contains abundant reactive astrocytes immunoreactive to GFAP. ⋯ As the glial path disappears from the maturing brain, the entire length of the IGL becomes filled with GFAP-IR astrocytes. These features are consistent with translocation and transformation of a specialized set of radial glia into IGL astrocytes. The results demonstrate that the IGL is a large, developmentally important, feature of the lateral geniculate complex that is embryologically distinct from adjacent dorsal and ventrolateral geniculate nuclei.