Cerebral Ischemia Changed the Effect of Metabosensitive Muscle Afferents on Somatic Reflex Without Affecting Thalamic Activity.

Caroline Pin-Barre,Frédéric Laurin,Christophe Pellegrino,Jérôme Laurin

doi:10.3389/fphys.2018.00638

Abstract

The purpose of the present study was to examine the contribution of group III and IV metabosensitive afferents at spinal and supraspinal levels in rats subjected to middle cerebral artery occlusion (MCAO) with reperfusion during the acute phase. Animals were randomized in Control (n = 23), SHAM (n = 18), MCAO-D1 (n = 10), and MCAO-D7 (n = 20) groups. Rats performed the Electrical Von Frey and the Adhesive removal tests before the surgery and at day 1 (D1), D3, and D7 after MCAO. Animals were subjected to electrophysiological recordings including the responses of group III/IV metabosensitive afferents to combinations of chemical activators and the triceps brachii somatic reflex activity at D1 or D7. The response of ventral posterolateral (VPL) thalamic nuclei was also recorded after group III/IV afferent activation. Histological measurements were performed to assess the infarct size and to confirm the location of the recording electrodes into the VPL. Behavioral results indicated that MCAO induced disorders of both mechanical sensibility and motor coordination of paretic forepaw during 7 days. Moreover, injured animals exhibited an absence of somatic reflex inhibition from the group III/IV afferents at D1, without affecting the response of both these afferents and the VPL. Finally, the regulation of the central motor drive by group III/IV afferents was modified at spinal level during the acute phase of cerebral ischemia and it might contribute to the observed behavioral disturbances.

Highlights

Hemiparesis constitutes the most common disturbance induced by stroke, which remains the leading cause of motor disability in the world (Lawrence et al, 2001; Hankey et al, 2002)
Results were significant when p < 0.05. For both Electronic Von Frey (EVF) and Adhesive removal test (ART), no difference was observed in Control and SHAM groups from day 1 (D1) to D7 compared to PRE
Results showed that the mechanical sensibility threshold to pressure of both the RF and the hindpaws were not changed from D1 to D7 compared to PRE in middle cerebral artery occlusion (MCAO)-D7 group

Summary

Introduction

Hemiparesis constitutes the most common disturbance induced by stroke, which remains the leading cause of motor disability in the world (Lawrence et al, 2001; Hankey et al, 2002). During and after an isometric contraction, the accumulation of metabolites such as potassium, lactic acid (LA), and adenosine triphosphate (ATP), strongly activates molecular receptors located on the terminal end of both thinly myelinated group III and group IV muscle afferent fibers (Kaufman and Rybicki, 1987; Adreani et al, 1997; Amann, 2011) In healthy individuals, their activation could decrease the somatic reflex amplitude of active muscles in order to limit premature peripheral fatigue development (Liu et al, 2002; Klass et al, 2008; Amann et al, 2011; Sidhu et al, 2017). Given that it was not the case following cerebral ischemia, we assessed in the present study the specific role played by these afferents in the perturbation of spinal inhibitory pathways

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