title: Hypoxia triggers short term potentiation of phrenic motoneuron discharge after chronic cervical spinal cord injury.
abstract: Repeated exposure to hypoxia can induce spinal neuroplasticity as well as respiratory and somatic motor recovery after spinal cord injury (SCI). The purpose of the present study was twofold: to define the capacity for a single bout of hypoxia to trigger short-term plasticity in phrenic output after cervical SCI and to determine the phrenic motoneuron (PhrMN) bursting and recruitment patterns underlying the response. Hypoxia-induced short term potentiation (STP) of phrenic motor output was quantified in anesthetized rats 11 weeks following lateral spinal cord hemisection at C2 (C2Hx). A 3-min hypoxic episode (12-14% O2) always triggered STP of inspiratory burst amplitude, the magnitude of which was greater in phrenic bursting ipsilateral vs. contralateral to C2Hx. We next determined if STP could be evoked in recruited (silent) PhrMNs ipsilateral to C2Hx. Individual PhrMN action potentials were recorded during and following hypoxia using a "single fiber" approach. STP of bursting activity did not occur in cells initiating bursting at inspiratory onset, but was robust in recruited PhrMNs as well as previously active cells initiating bursting later in the inspiratory effort. We conclude that following chronic C2Hx, a single bout of hypoxia triggers recruitment of PhrMNs in the ipsilateral spinal cord with bursting that persists beyond the hypoxic exposure. The results provide further support for the use of short bouts of hypoxia as a neurorehabilitative training modality following SCI.
authors.affiliation: Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA; Department of Biological Sciences, College of Science, National Sun Yat-sen University, Kaohsiung, Taiwan.
authors.forename: Kun-Ze
authors.initials: KZ
authors.lastname: Lee
authors.affiliation: Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Milapjit S
authors.initials: MS
authors.lastname: Sandhu
authors.affiliation: Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Brendan J
authors.initials: BJ
authors.lastname: Dougherty
authors.affiliation: Department of Neuroscience, College of Medicine, McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Reier
authors.affiliation: Department of Physical Therapy, College of Public Health and Health Professions, McKnight Brain Institute, University of Florida, Gainesville, FL 32610, USA. Electronic address: ddf@phhp.ufl.edu.
authors.forename: David D
authors.initials: DD
authors.lastname: Fuller
mesh_terms: D000818:Animals; D019771:Axotomy; D066193:Cervical Cord / Q000293:injuries; D004195:Disease Models, Animal; D004594:Electrophysiology; D007839:Functional Laterality / Q000502:physiology; D000860:Hypoxia; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009416:Nerve Regeneration / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology; D010791:Phrenic Nerve / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013119:Spinal Cord Injuries / Q000534:rehabilitation*
keywords: Hypoxia; Neuroplasticity; Phrenic; Recruitment; Spinal cord injury