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Signalling of static and dynamic features of muscle spindle input by external cuneate neurones in the cat
Ist Teil von
The Journal of physiology, 1999-09, Vol.519 (2), p.559-569
Ort / Verlag
Oxford, UK: The Physiological Society
Erscheinungsjahr
1999
Quelle
MEDLINE
Beschreibungen/Notizen
The present experiments examined the capacity of external cuneate nucleus (ECN) neurones in the anaesthetized cat to respond
to static and vibrotactile stretch of forearm extensor muscles. The aim was to compare their signalling capacities with the
known properties of main cuneate neurones in order to determine whether there is differential processing of muscle spindle
inputs at these parallel relay sites.
Static stretch (⤠2 mm in amplitude) and sinusoidal vibration were applied longitudinally to individual muscle tendons and
responses recorded from single ECN neurones. The muscle-related ECN neurones that were sampled displayed a high sensitivity
to both static and dynamic components of stretch, including muscle vibration at frequencies of 50-800 Hz, consistent with
their dominant input being derived from primary spindle afferent fibres.
In response to ramp-and-hold muscle stretch, ECN neurones resembled their main cuneate counterparts in the pattern of their
responses and in quantitative response measures. Their coefficients of variation in interspike intervals during steady stretch
ranged from â0.3 to 0.7, as they do in main cuneate responses, and their stimulus-response relations were graded as a function
of stretch magnitude with low variability in responses at a fixed stretch amplitude.
In response to muscle vibration, ECN activity was tightly phase locked to the vibration waveform, in particular at frequencies
of ⤠150 Hz, where vector strength measures ( R ) were high ( R ⥠0.8) before declining as a function of frequency, with R values of â0.6 at 300 Hz and ⤠0.4 at 800 Hz. Both the qualitative and quantitative aspects of ECN responsiveness to the
vibro-stretch disturbances were indistinguishable from those of the main cuneate neurones.
The results demonstrate a high transmission fidelity for muscle signals across the ECN and no evidence for differential synaptic
transmission across the parallel main and external cuneate nuclei. Earlier limitations observed in the capacity of cerebellar
Purkinje cells to respond to primary spindle inputs must therefore be imposed at synapses within the cerebellum.