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Peripheral Afferents (peripheral + afferent)

Distribution by Scientific Domains

Life Sciences	80%

Selected Abstracts

The periaqueductal grey modulates sensory input to the cerebellum: a role in coping behaviour?

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2009
Nadia L. Cerminara
Abstract The paths that link the periaqueductal grey (PAG) to hindbrain motor circuits underlying changes in behavioural responsiveness to external stimuli are unknown. A major candidate structure for mediating these effects is the cerebellum. The present experiments test this directly by monitoring changes in size of cerebellar responses evoked by peripheral stimuli following activation of the PAG. In 22 anaesthetized adult Wistar rats, climbing fibre field potentials were recorded from the C1 zone in the paramedian lobule and the copula pyramidis of the cerebellar cortex evoked, respectively, by electrical stimulation of the ipsilateral fore- and hindlimb. An initial and a late response were attributable to activation of A, and A, peripheral afferents respectively (hindlimb onset latencies 16.9 and 23.8 ms). Chemical stimulation at physiologically-identified sites in the ventrolateral PAG (a region known to be associated with hyporeactive immobility) resulted in a significant reduction in size of both the A, and A, evoked field potentials (mean reduction relative to control ± SEM, 59 ± 7.5 and 66 ± 11.9% respectively). Responses evoked by electrical stimulation of the dorsal or ventral funiculus of the spinal cord were also reduced by PAG stimulation, suggesting that part of the modulation may occur at supraspinal sites (including at the level of the inferior olive). Overall, the results provide novel evidence of descending control into motor control centres, and provide the basis for future studies into the role of the PAG in regulating motor activity in different behavioural states and in chronic pain. [source]

Climbing fibre-dependent changes in Golgi cell responses to peripheral stimulation

THE JOURNAL OF PHYSIOLOGY, Issue 20 2008
W. Xu
Golgi cells are important elements of the cerebellar cortex, controlling the flow of mossy fibre information to other cells via granule cells. Several anatomical reports suggest that climbing fibre afferents contact Golgi cells, and electrophysiological studies suggest that they depress Golgi cell firing. We reinvestigated this issue and, given that climbing fibres mediate synaptic plasticity in the cerebellar cortex, we have examined the effects of conjunctive stimulation of peripheral afferents and climbing fibres on Golgi cell responses. The results confirm that climbing fibre stimulation depresses Golgi cell firing at short latency. Golgi cells responded to stimulation of peripheral afferents with longer latency depressions of firing and after conjunctive stimulation with climbing fibres these were significantly reduced. The reductions developed progressively over 20 min of conjunctive stimulation and were persistent (up to 84 min). Temporal conjunction of the inputs was important because non-synchronous stimulation of climbing fibres and peripheral afferents failed to alter the peripheral afferent-evoked response in Golgi cells. In control experiments using either the same climbing fibre stimulation alone, or peripheral afferent stimulation paired with brainstem stimulation that did not activate climbing fibres, responses were not depressed. The results thus show that conjunctive stimulation of climbing fibres with other inputs to Golgi cells can induce long-term changes in Golgi cell responses in vivo. This raises the possibility that changes in Golgi cell peripheral responses mediated by climbing fibres can potentially contribute to cerebellar motor learning. [source]

Tests for presynaptic modulation of corticospinal terminals from peripheral afferents and pyramidal tract in the macaque

THE JOURNAL OF PHYSIOLOGY, Issue 1 2006
A. Jackson
The efficacy of sensory input to the spinal cord can be modulated presynaptically during voluntary movement by mechanisms that depolarize afferent terminals and reduce transmitter release. It remains unclear whether similar influences are exerted on the terminals of descending fibres in the corticospinal pathway of Old World primates and man. We investigated two signatures of presynaptic inhibition of the macaque corticospinal pathway following stimulation of the peripheral nerves of the arm (median, radial and ulnar) and the pyramidal tract: (1) increased excitability of corticospinal axon terminals as revealed by changes in antidromically evoked cortical potentials, and (2) changes in the size of the corticospinal monosynaptic field potential in the spinal cord. Conditioning stimulation of the pyramidal tract increased both the terminal excitability and monosynaptic fields with similar time courses. Excitability was maximal between 7.5 and 10 ms following stimulation and returned to baseline within 40 ms. Conditioning stimulation of peripheral nerves produced no statistically significant effect in either measure. We conclude that peripheral afferents do not exert a presynaptic influence on the corticospinal pathway, and that descending volleys may produce autogenic terminal depolarization that is correlated with enhanced transmitter release. Presynaptic inhibition of afferent terminals by descending pathways and the absence of a reciprocal influence of peripheral input on corticospinal efficacy would help to preserve the fidelity of motor commands during centrally initiated movement. [source]

Evoked Human Oesophageal Hyperalgesia: A Potential Tool for Analgesic Evaluation?

BASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 2 2009
Anne Estrup Olesen
Therefore, in the development and testing of analgesics for the treatment of visceral pain, it is important to establish an experimental pain model of visceral hypersensitivity. Such a model will mimic the clinical situation to a higher degree than pain models where the receptors and peripheral afferents are briefly activated as with, for example, electrical, thermal, and mechanical stimulations. In this study, a model to evoke experimental hyperalgesia of the oesophagus with a combination of acid and capsaicin was introduced. The study was a randomised, double-blind, cross-over study. Fifteen healthy volunteers were included. Sensory assessments to mechanical, heat, and electrical stimulations were done in the distal oesophagus, before and after perfusion with a 200 ml solution of acid+capsaicin (180 ml HCL 0.1 M and 2 mg capsaicin in 20 ml solvent) or saline. Oesophageal pain assessment and referred pain areas were evaluated. There were reproducible pain assessments between repetitions within the same day and between days (all P > 0.05). Acid+capsaicin perfusion induced 56% reduction of the pain threshold to heat (P = 0.04), 19% reduction of the pain threshold to electrical stimuli (P < 0.001), 78% increase of the referred pain areas to mechanical stimulation (P < 0.001) and 52% increase of the referred pain areas to electrical stimulus (P = 0.045). All volunteers were sensitised to one or more modalities by acid+capsaicin. The model was able to evoke consistent hyperalgesia and may be useful in future pharmacological studies. [source]