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1

Spinal cord, reticular formation and cerebellum-there and back again

100%
Hammar I.
Acta Neurobiologiae Experimentalis
|
2015
|
tom 75
|
nr Supl.
Information on the activity within spinal premotor circuitry is vital for the performance of correct movements. This feedback is provided by ascending tract neurons forwarding information to the cerebellum either directly (via spinocerebellar pathways) or indirectly (via the reticular formation) and used by the cerebellum to modulate descending motor commands, thereby shaping the final motor output. We investigated whether ascending tract neurons also inform the cerebellum about descending motor commands, relayed by corticospinal- and reticulospinal tract neurons or the mesencephalic locomotor region (MLR). In a series of in vivo experiments axons of descending tract neurons were stimulated within the pyramids, the medial longitudinal fasciculus and the MLR. Responses evoked in individual spinal neurons of different subpopulations of spinocerebellar tracts were recorded both extracellularly and intracellularly. Descending motor commands are monitored by a number of spinocerebellar tracts. Monosynaptic excitation evoked by descending tract neurons was found in ventral spinocerebellar tracts neurons while only polysynaptic actions were found in dorsal spinocerebellar tract neurons and neurons of the indirect spinocerebellar tract projecting via the lateral reticular nucleus. Specific subpopulations of spinocerebellar projections forward information concerning the degree of activity in spinal circuitry related to centrally initiated and voluntary motor commands as well as the local neuronal circuitry [1–3]. Information forwarded between neurons in the spinal cord, cerebellum and the reticular formation may thus serve not only to correct but also to predict and prevent motor errors. 1. Hammar et al. (2011) J Physiol 589: 653–665; 2. Jankowska et al. (2011) J Physiol 589: 5709–5725; 3. Hammar et al. (2013) Society for Neuroscience Annual Meeting, San Diego, USA
2

Epidurally applied DC evokes long-lasting increase in axonal excitability

51%
Kaczmarek D., Bolzoni F., Hammar I., Jankowska E.
Acta Neurobiologiae Experimentalis
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2017
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tom 77
|
nr Suppl.1
INTRODUCTION: Epidural stimulation and trans-spinal direct current stimulation (tsDCS) are used in clinical practice for restoring motor functions or pain relief. However, the use of epidural stimulation is limited by low stimulus intensities tolerated by patients. Locally applied cathodal DC was recently demonstrated to increase the excitability of intraspinal preterminal axonal branches for more than one hour. AIM(S): Our aim was to examine whether brief episodes of epidural DC combined with epidural stimulation evokes long-lasting increase in the excitability of myelinated axons within the dorsal columns. METHOD(S): 17 adult rats of both sexes (Wistar, 2–6 months old, 200–450 g) were used in this study. In deeply anaesthetized animals, afferent volleys in sural and peroneal nerve were evoked by epidural stimuli via needle tungsten electrodes positioned in contact with the dura mater within the L1–L3 segments. The effects of cathodal DC (0.8–1.0 μA) on the excitability of skin and muscle sensory fibres were assessed by changes in antidromic compound action potentials. The areas of nerve volleys evoked before, during, and after DC polarization were measured within time windows of 0.3–1.4 ms from their onset. RESULTS: The study revealed that cathodal DC applied via epidural electrodes resulted in a several-fold increases in the number of epidurally activated fibres. The volley area measured after 10 minutes increased by 411±97%, 733±251% and 502±94% following 15–30 s, 1 min and 2 or 5 min of DC application, respectively. Importantly, the increase in the excitability appeared within seconds and remained elevated for more than one hour. CONCLUSIONS: Combining epidural stimulation and trans-spinal DC polarization may improve their clinical outcome. The differences in time course of DC evoked increases in the excitability of nerve fibres in the dorsal columns compared to previously reported effects in pre-terminal axonal branches suggest a new form of plasticity. FINANCIAL SUPPORT: The study was supported by a grant from Stiftelsen Sigurd & Elsa Goljes Minne to Elzbieta Jankowska.
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