Abstract
Brain injuries can interrupt descending neural pathways that convey motor commands from the cortex to spinal motoneurons. Here, we demonstrate that a unilateral injury of the hindlimb sensorimotor cortex of rats with completely transected thoracic spinal cord produces hindlimb postural asymmetry with contralateral flexion and asymmetric hindlimb withdrawal reflexes within 3 hr, as well as asymmetry in gene expression patterns in the lumbar spinal cord. The injury-induced postural effects were abolished by hypophysectomy and were mimicked by transfusion of serum from animals with brain injury. Administration of the pituitary neurohormones β-endorphin or Arg-vasopressin-induced side-specific hindlimb responses in naive animals, while antagonists of the opioid and vasopressin receptors blocked hindlimb postural asymmetry in rats with brain injury. Thus, in addition to the well-established involvement of motor pathways descending from the brain to spinal circuits, the side-specific humoral signaling may also add to postural and reflex asymmetries seen after brain injury.
Highlights
Brain lesions can interrupt descending neural pathways that convey motor commands from the cerebral cortex to motoneurons located in the brain stem and anterior horn of the spinal grey matter (Cai et al, 2019; Kuypers, 1981; Lemon, 2008; Purves et al, 2001; Smith et al, 2017; Tan et al, 2012; Zorner et al, 2014)
hindlimb postural asymmetry (HL-PA) was analyzed within 3 hr after the unilateral brain injury (UBI) by both the hands-on and hands-off methods of hindlimb stretching followed by photographic and / or visual recording of the asymmetry in animals under pentobarbital anesthesia
HL-PA data are presented as the median values of HL-PA in mm (HL-PA size), and the probability to develop HL-PA that depicts the proportion of rats with HL-PA above the 1 mm threshold
Summary
Brain lesions can interrupt descending neural pathways that convey motor commands from the cerebral cortex to motoneurons located in the brain stem and anterior horn of the spinal grey matter (Cai et al, 2019; Kuypers, 1981; Lemon, 2008; Purves et al, 2001; Smith et al, 2017; Tan et al, 2012; Zorner et al, 2014). Small molecules that inhibit these hormones could block the deficits seen on the right side after an injury on the left hemisphere of the brain Taken together, these results show that neurons in the spinal cord are not just controlled by the neural tracts that descend from the brain, and by hormones which have left-right side-specific actions. Asymmetry in posture and reflexes persists after complete transection of the spinal cord (Rossignol and Frigon, 2011; Watanabe et al, 2020; Zhang et al, 2020) This may be due to neuroplastic changes in the lumbar spinal cord induced by brain or spinal cord injury through the descending neural tracts. We tested whether the administration of serum collected from animals with UBI, as well as the administration of pituitary neurohormones b-endorphin and Arg-vasopressin, may replicate the effects of brain injury by inducing HL-PA in rats with intact brain
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