Electrophysiological Studies of Spinal Reflex Pathways From Group II Muscle Afferents

Rasanani, Mohammad Reza Hadian (1997) Electrophysiological Studies of Spinal Reflex Pathways From Group II Muscle Afferents. PhD thesis, University of Glasgow.

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Abstract

This thesis has investigated aspects of the circuitry located in the spinal cord by which signals originating fronn group II muscle afferents are processed. Studies have focused on two main problems: Part 1. The organisation of neuronal systems mediating group II reflex actions in the lumbar enlargement of the rat spinal cord have been investigated and compared with that in the cat with the aim of determining whether general principles of the organisation of these systems are common to different mammalian species. Group II afferents of different hind-limb muscle nerves were found to evoke cord dorsum and field potentials in particular segments of the spinal cord. Group II afferents of the quadriceps and deep peroneal nerves evoked synaptic potentials mainly at the rostral end of the lumbar enlargement (L1-rostral L3 segments) while the group II afferents of the gastrocnemius-soleus and hamstring muscle nerves produced their synaptic actions mainly at the caudal end of the lumbar enlargement (caudal L5). Group II afferents of the tibialis posterior and flexor digitorum longus nerves produced their synaptic actions mainly in the central lumbar segments (caudal L3 - L4). These results show that in principal the topographical organisation of neurones in group II reflex pathways of the rat is similar to that of the cat. Part 2. The actions of group II muscle afferents on neurones within the lower-lumbar segments of the cat spinal cord have been investigated with the aim of locating candidate last-order interneurones in group II reflex pathways. Only group II afferents of the tibialis posterior nerve produced large cord dorsum potentials comparable to those evoked by other group II afferents in midlumbar and sacral segments. However, field potentials evoked by group II muscle afferents of the quadriceps, tibialis-posterior, gastrocnemius- soleus, flexor digitorum longus, posterior biceps-semitendinosus and popliteus were encountered throughout the L6 and L7 segments. Group II potentials were evoked in both the dorsal horn (laminae V-VI) and intermediate zone (laminae V-VI I) at latencies compatible with monosynaptic actions of the fastest conducting group II muscle afferents. The properties of interneurones receiving excitatory input from group II muscle afferents have been investigated using both extracellular and intracellular recordings. Almost half the sample of interneurones (38 of 76) were characterised by an ipsilateral ascending projection within the lateral funiculus to the L4 level. Both L4-projecting and non-projecting interneurones were located mainly in an area dorsal and lateral to the main region in which interneurones with input from group I muscle afferents are located. Group II afferents of quadriceps and deep peroneal muscle nerves provided the most effective excitation (discharging 70-80% of neurones) while group II afferents of tibialis postenor, posterior biceps-semitendinosus and gastrocnemius-soleus were also effective sources of excitation (discharging 45- 55% of neurones). At least some of the group II EPSPs were monosynaptic. Input to individual interneurones was multimodal and characterised by considerable convergence. Seventy-five percent of interneurones were discharged by group II afferents of two or more muscle nerves and 43% by group II afferents of three or more nerves. In addition, group I muscle afferents evoked small EPSPs in over one quarter of the interneurones and virtually all were strongly excited by cutaneous afferents. Evidence of excitatory input from joint, interosseous and group III muscle afferents was also obtained but inhibition was rarely observed. These interneurones are considered likely to function as last-order interneurones in group II reflex pathways.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: John Riddell
Keywords: Neurosciences
Date of Award: 1997
Depositing User: Enlighten Team
Unique ID: glathesis:1997-75309
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 21:15
Last Modified: 19 Nov 2019 21:15
URI: http://theses.gla.ac.uk/id/eprint/75309

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