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Taylor A, Durbaba R, Ellaway PH. Direct and indirect assessment of γ-motor firing patterns. Can J Physiol Pharmacol 2004; 82:793-802. [PMID: 15523537 DOI: 10.1139/y04-053] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The study of the patterns of γ-motor activity which accompany natural contractions has been long and difficult, and has not as yet led to general agreement. In this review we have simplified matters by considering the case of locomotion in the cat only, and we have avoided discussion of the various hypotheses which have been advanced to provide general schemes of γ control for a wide range of movements. The development of the subject is shown to depend very much on devising ingenious methods applicable to reduced and intact animals. Direct recording from γ-motoneurones has only been possible in reduced preparations, whereas indirect assessment of γ activity from spindle afferent recordings was used in these and in intact animals. At this point in time, we still have no direct recordings from γ-motoneurones in normally behaving animals, but those obtained in decerebrate animals show distinct patterns of modulation for static and dynamic types with particular temporal relation to the stepping movements. The spindle recordings in intact animals potentially provide the most important information, and the problems of interpretation, which have previously caused difficulties, are beginning to be solved through the insights obtained from the reduced preparations.Key words: locomotion, gamma motoneurons, muscle spindles.
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Affiliation(s)
- A Taylor
- Department of Movement and Balance, Division of Neuroscience and Psychological Medicine, Faculty of Medicine, Imperial College London, Charing Cross Hospital Campus, St. Dunstans Road, London W6 8RP, UK.
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Raya JG, Ramírez A, Muñoz-Martínez EJ. Gamma→Alpha Linkage and Persistent Firing of Ia Fibers by Pudendal Nerve Stimulation in the Decerebrate Cat. J Neurophysiol 2004; 92:387-94. [PMID: 15212442 DOI: 10.1152/jn.01113.2003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The sensory pudendal nerve (SPN) was stimulated in decerebrate female cats. Spikes of single Ia muscle spindle afferents from the medial gastrocnemius (MG) muscle were recorded in dorsal root filaments. Electroneurography (ENG) was recorded in a cut nerve filament to the MG muscle; MG electromyography (EMG) was also recorded. Single shock to SPN induced discharges of small ENG spikes (SS) with similar amplitude to that of gamma spikes elicited by ventral root stimulation. Thus SS were identified as gamma spikes. The latency of the gamma discharge was ∼15 ms. As expected, the onset of the gamma discharge preceded a discharge of Ia spikes; the time difference between both discharges was ∼5 ms. After the initial bursts, the Ia and the gamma activities paused during 20–30 ms but later increased again to last ∼1 s. After the shock, the EMG activity was depressed during ∼50 ms; later, motor-unit spikes may show transient activation. Thus the onset of the gamma activation preceded the activation of motor units (gamma→alpha link). Trains of shocks (1 or 100 Hz) to SPN induced a sustained increase in the frequency of gamma spikes, Ia spikes, and motor units that outlasted the train by 20–120 s. The sustained firing of Ia fibers might trigger or help to trigger and maintain the response of alpha-motoneurons.
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Affiliation(s)
- J Guadalupe Raya
- Departamento de Fisiología, Biofísica y Neurosciencias y Sección de Bioelectrónica, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, A.P. 14-740. 0700 México D.F., Mexico
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