The Journal of neuroscience : the official journal of the Society for Neuroscience
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In ischemic and in inflamed tissues, pH levels down to 5.4 have been measured, and this local acidosis may contribute to pain and hyperalgesia in disease states. To evaluate the role of acid pH in nociception, we have studied identified primary afferents in a rat skin-saphenous nerve preparation in vitro where the receptive fields can be superfused at the highly permeable corium side with controlled solutions. The nerve endings were exposed to CO2-saturated synthetic interstitial fluid (SIF;pH 6.1) and to carbogen-gassed SIF phosphate buffered to different acid pH levels (5 min duration, 10 min intervals). ⋯ The sensitizing effect was more pronounced the higher the initial von Frey thresholds (0.75 rank correlation). This sensitization to mechanical stimulation was in contrast to the combined action of other inflammatory mediators, bradykinin, 5-HT, histamine and prostaglandin E2. In conclusion, we suggest that pH sensitivity of nociceptors may be an important source of pain and hyperalgesia.
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In echolocating bats, three cell groups in the lateral lemniscus are conspicuous for their large size and high degree of differentiation. These cell groups are the intermediate nucleus (INLL), columnar nucleus (VNLLc), and multipolar cell area (VNLLm). All receive projections from the contralateral cochlear nucleus. ⋯ In addition, the latency remains constant over large variations in frequency or intensity. In INLL and VNLLm, response patterns are about equally distributed between tonic, chopping, and phasic; there are no single-spike constant-latency responses of the type seen in VNLLc, although some choppers and pausers do respond with constant first-spike latency. The results indicate that VNLLc is specialized to encode very precisely the onset of sound; the other nuclei may encode ongoing properties of a sound.
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Comparative Study
A comparative study of the behavioral deficits following lesions of various parts of the zebra finch song system: implications for vocal learning.
Song production in song birds is controlled by an efferent pathway. Appended to this pathway is a "recursive loop" that is necessary for song acquisition but not for the production of learned song. Since zebra finches learn their song by imitating external models, we speculated that the importance of the recursive loop for learning might derive from its processing of auditory feedback during song acquisition. ⋯ Early deafness also resulted in poorly structured and unstable song. We conclude that Area X and LMAN contribute differently to song acquisition: the song variability that is typical of vocal development persists following early deafness or lesions of Area X but ends abruptly following removal of LMAN. Apparently, LMAN plays a crucial role in fostering the kinds of circuit plasticity necessary for learning.
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The descending pathways from the brainstem locomotor areas were investigated by utilizing reversible cooling (to block synaptic or fiber transmission) and irreversible subtotal lesions of the brainstem or spinal cord (C2-C3 level). Experiments were conducted on decerebrate cats induced to walk on a treadmill by electrical stimulation of the brainstem. Locomotion produced by stimulation of the mesencephalic locomotor region (MLR) was not abolished by caudal brainstem lesions that isolated the lateral tegmentum or by extended rostral/caudal dorsal hemisections of the spinal cord. ⋯ Thus, an alternative projection of the PLR through the dorsal half of the spinal cord (Kazennikov et al., 1980, 1983a,b; Shik, 1983) cannot be ruled out. Overall, these results demonstrate that the PLR is not an essential component of the motor pathway originating from the MLR. The organizational scheme of "brainstem locomotor regions" is discussed in the context of recent information demonstrating a link between the sensory component of the trigeminal system and locomotor pathways (Noga et al., 1988).
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When the growth cone of a chick dorsal root ganglion (DRG) neurite contacts the neurite of a chick retinal ganglion cell in vitro, the growth cone typically responds by withdrawing its lamellipodia and filopodia and collapsing. We have used the fluorescent calcium indicator dye fura-2 and digital imaging microscopy to measure calcium levels within DRG growth cones and to determine whether changes in calcium levels are responsible for the collapse of growth cone morphology when a DRG growth cone contacts a retinal ganglion cell neurite. Calcium levels within DRG growth cones were stable during neurite outgrowth. ⋯ Application of this material to cultures of DRG neurons caused growth cones to collapse but had no effect on calcium levels within the growth cones. The crude growth cone collapsing activity was not blocked by the presence of cobalt, nickel, lanthanum, nifedipine, or reduced-calcium medium, suggesting that transmembrane calcium fluxes were not required for growth cone collapse. These results suggest that the morphological changes associated with the collapse of growth cone structure can be independent of changes in growth cone calcium levels, and that second messengers other than calcium are likely to be involved in the regulation of many growth cone behaviors.