Unusual Quadrupedal Locomotion in Rat during Recovery from Lumbar Spinal Blockade of 5-HT7 Receptors.

Urszula Sławińska,Marek Bekisz,Małgorzata Zawadzka,Henryk Majczyński,Larry M Jordan,Anna M Cabaj,Krzysztof Miazga,Anna Kwaśniewska

doi:10.3390/ijms22116007

Abstract

Coordination of four-limb movements during quadrupedal locomotion is controlled by supraspinal monoaminergic descending pathways, among which serotoninergic ones play a crucial role. Here we investigated the locomotor pattern during recovery from blockade of 5-HT7 or 5-HT2A receptors after intrathecal application of SB269970 or cyproheptadine in adult rats with chronic intrathecal cannula implanted in the lumbar spinal cord. The interlimb coordination was investigated based on electromyographic activity recorded from selected fore- and hindlimb muscles during rat locomotion on a treadmill. In the time of recovery after hindlimb transient paralysis, we noticed a presence of an unusual pattern of quadrupedal locomotion characterized by a doubling of forelimb stepping in relation to unaffected hindlimb stepping (2FL-1HL) after blockade of 5-HT7 receptors but not after blockade of 5-HT2A receptors. The 2FL-1HL pattern, although transient, was observed as a stable form of fore-hindlimb coupling during quadrupedal locomotion. We suggest that modulation of the 5-HT7 receptors on interneurons located in lamina VII with ascending projections to the forelimb spinal network can be responsible for the 2FL-1HL locomotor pattern. In support, our immunohistochemical analysis of the lumbar spinal cord demonstrated the presence of the 5-HT7 immunoreactive cells in the lamina VII, which were rarely 5-HT2A immunoreactive.

Highlights

Quadrupedal locomotion is an essential animal behavior based on the rhythmic coordinated movement of four limbs that is regulated by the neuronal structures located within the central nervous system, in the brain, and spinal cord
In our previous papers [32,33], we described that intrathecal application of SB269970 or cyproheptadine at the lumbar spinal cord level of Wistar adult rats induced in a short time (
We have found that blockage of 5-HT7 receptors in the lumbar spinal cord of adult rats facilitated at the time of ELRP a doubled rhythm in the forelimbs in relation to the hindlimb stepping (2FL-1HL; 2 forelimb steps-1 hindlimb step)

Summary

Introduction

Quadrupedal locomotion is an essential animal behavior based on the rhythmic coordinated movement of four limbs that is regulated by the neuronal structures located within the central nervous system, in the brain, and spinal cord. The movement of each limb is controlled by its own spinal locomotor neuronal network called Central Pattern Generator (CPG), located in cervical segments for left and right forelimbs and in upper lumbar segments for left and right hindlimbs. Communication between CPGs of fore- and hindlimbs is achieved by ascending and descending propriospinal pathways projecting ipsilaterally and diagonally [13,17,18,19,20,21,22,23,24,25]. It remains unknown whether serotonin controls the function of the inter girdle propriospinal connections

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