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Descending Pathways (descending + pathway)
Selected AbstractsFibroblast growth factor-2 mRNA expression in the brainstem and spinal cord of normal and chronic spinally transected urodelesJOURNAL OF NEUROSCIENCE RESEARCH, Issue 15 2008Marie Moftah Abstract Descending pathways in the spinal cord of adult urodele amphibians show a high regenerative ability after body spinal cord transection; regenerated axons regrow into the transected spinal cord, and hindlimb locomotor recovery occurs spontaneously. Little is currently known about the molecular basis of spinal cord regeneration in urodeles, but it is believed that fibroblast growth factor-2 (FGF2) may play an important role by inducing proliferation of neural progenitor cells. The aim of our study, using in situ hybridization in adult Pleurodeles waltlii, was twofold: 1) to document FGF2 mRNA expression pattern along the brainstem-spinal cord of intact salamanders and 2) to investigate the changes in this pattern in animals unable to display hindlimb locomotor movements and in animals having fully recovered hindlimb locomotor activity after body spinal cord transection. This design establishes a firm basis for further studies on the role of FGF2 in functional recovery of hindlimb locomotion. Our results revealed a decreasing rostrocaudal gradient in FGF2 mRNA expression along the brainstem-spinal cord in intact animals. They further demonstrated a long-lasting up-regulation of FGF2 mRNA expression in response to spinal transection at the midtrunk level, both in brainstem and in the spinal cord below the injury. Finally, double immunolabeling showed that FGF2 was up-regulated in neuroglial, presumably undifferentiated, cells. Therefore, we propose that FGF2 may be involved in cell proliferation and/or neuronal differentiation after body spinal cord transection in salamander and could thus play an important role in functional recovery of locomotion after spinal lesion. Š 2008 Wiley-Liss, Inc. [source] Interaction of pre-programmed control and natural stretch reflexes in human landing movementsTHE JOURNAL OF PHYSIOLOGY, Issue 3 2002Martin J. N. McDonagh Pre-programmed mechanisms of motor control are known to influence the gain of artificially evoked stretch reflexes. However, their interaction with stretch reflexes evoked in the context of unimpeded natural movement is not understood. We used a landing movement, for which a stretch reflex is an integral part of the natural action, to test the hypothesis that unpredicted motor events increase stretch reflex gain. The unpredicted event occurred when a false floor, perceived to be solid, collapsed easily on impact, allowing the subjects to descend for a further 85 ms to a solid floor below. Spinal stretch reflexes were measured following solid floor contact. When subjects passed through the false floor en route to the solid floor, the amplitude of the EMG reflex activity was double that found in direct falls. This was not due to differences in joint rotations between these conditions. Descending pathways can modify H- and stretch-reflex gain in man. We therefore manipulated the time between the false and real floor contacts and hence the time available for transmission along these pathways. With 30 ms between floors, the enhancement of the reflex was extinguished, whereas with 50 ms between floors it reappeared. This excluded several mechanisms from being responsible for the doubling of the reflex EMG amplitude. It is argued that the enhanced response is due to the modulation of reflex gain at the spinal level by signals in descending pathways triggered by the false platform. The results suggest the future hypothesis that this trigger could be the absence of afferent signals expected at the time of false floor impact and that salient error signals produced from a comparison of expected and actual sensory events may be used to reset reflex gains. [source] Bilateral lesion in the lateral columns and complete urinary retention: Association with the spinal cord descending pathway for micturitionNEUROUROLOGY AND URODYNAMICS, Issue 4 2005Akiyuki Hiraga [source] The opioid system in the gastrointestinal tractNEUROGASTROENTEROLOGY & MOTILITY, Issue 2004C. Sternini Abstract ľ-, ,- and ,-opioid receptors (ORs) mediate the effects of endogenous opioids and opiate drugs. Here we report (1) the distribution of ľOR in the guinea-pig and human gastrointestinal tract in relation to endogenous ligands, to functionally distinct structures in the gut and to ,OR and ,OR; and (2) the ligand-induced ľOR endocytosis in enteric neurones using in vitro and in vivo models. In the guinea pig, ľOR immunoreactivity is confined mainly to the myenteric plexus. ľOR myenteric neurones are most numerous in the small intestine, followed by the stomach and the proximal colon. ľOR immunoreactive fibres are dense in the muscle layer and the deep muscular plexus, where they are in close association with interstitial cells of Cajal. This distribution closely matches the pattern of enkephalin. ľOR enteric neurones comprise functionally distinct populations of neurones of the ascending and descending pathways of the peristaltic reflex. In human gut, ľOR immunoreactivity is localized to myenteric and submucosal neurones and to immune cells of the lamina propria. ,OR immunoreactivity is located in both plexuses where it is predominantly in varicose fibres in the plexuses, muscle and mucosa, whereas ,OR immunoreactivity appears to be confined to the myenteric plexus and to bundles of fibres in the muscle. ľOR undergoes endocytosis in a concentration-dependent manner, in vitro and in vivo. Pronounced ľOR endocytosis is observed in neurones from animals that underwent abdominal surgery that has been shown to induce delay in gastrointestinal transit. We can conclude that all three ORs are localized to the enteric nervous system with differences among species, and that ľOR endocytosis can be utilized as a means to visualize enteric neurones activated by opioids and sites of opioid release. [source] Ascending and descending brainstem neuronal activity during cystometry in decerebrate catsNEUROUROLOGY AND URODYNAMICS, Issue 4 2003Kimio Sugaya Abstract Aims This study was undertaken to examine the distribution of pontomedullary neurons related to micturition or urine storage, as well as the connections between the pontine micturition center (PMC), medullary neurons, and the spinal cord. Methods In decerebrate cats, extracellular recording of the rostral pontine and rostral medullary neurons was performed. Firing of each neuron was quantitated during cystometry. Connections between the PMC, medullary neurons, and the spinal cord (L1) were also examined electrophysiologically. Results Ninety-four neurons showed an increase or decrease of the firing rate during micturition. Units with an antidromic response to L1 stimulation and an increased firing rate were located in the nucleus locus coeruleus alpha (LCa; n,=,8) corresponding to the PMC, and in the medial reticular formation (MRF) of the medulla (n,=,14). Units showing a decreased firing rate were located in the nucleus reticularis pontis oralis (PoO; n,=,26) and in the MRF (n,=,11). The latencies of antidromic and orthodromic responses of the LCa units were longer than those of the PoO units. MRF neurons responded antidromically and/or orthodromically to stimulation of the PMC or L1. Conclusions These results suggest that the pathway concerned with urine storage has a faster spinobulbospinal loop than the micturition reflex pathway and that rostral medullary neurons also play an important role in micturition and urine storage. There may be two descending pathways between the PMC and the spinal cord: both a direct pathway and one by means of medullary neurons. Neurourol. Urodynam. 22:343,350, 2003. Š 2003 Wiley-Liss, Inc. [source] Influence of focused auditory attention on cochlear activity in humansPSYCHOPHYSIOLOGY, Issue 1 2001Stéphane Maison The mammalian auditory system contains descending pathways that originate in the cortex and relay at various intermediate levels before reaching the peripheral sensory organ of Corti. The last link in this chain consists of the olivocochlear bundle. The activity of this bundle can be measured through otoacoustic emissions, which are acoustic signatures of the cochlear biomechanical activity. In the present study, it was hypothesized that frequency-specific activation of the olivocochlear bundle in the contralateral ear would show up as frequency-specific variations in otoacoustic emission amplitude in the ipsilateral ear. Two groups of young adult subjects participated in this experiment. Evoked otoacoustic emissions were recorded in the ipsilateral ear at two test frequencies (1 and 2 kHz). Subjects had to detect probe tones at a given frequency in background noise in the contralateral ear. Larger efferent activation was measured at test frequencies on which attention is focused. This result provides evidence for an influence of attention on the auditory periphery via descending projections. [source] | |||||||||||||