title: Spinal neuronal activation during locomotor-like activity enabled by epidural stimulation and 5-hydroxytryptamine agonists in spinal rats.
abstract: The neural networks that generate stepping in complete spinal adult rats remain poorly defined. To address this problem, we used c-fos (an activity-dependent marker) to identify active interneurons and motoneurons in the lumbar spinal cord of adult spinal rats during a 30-min bout of bipedal stepping. Spinal rats were either step trained (30 min/day, 3 days/week, for 7.5 weeks) or not step trained. Stepping was enabled by epidural stimulation and the administration of the serotonergic agonists quipazine and 8-OHDPAT. A third group of spinal rats served as untreated (no stimulation, drugs, or stepping) controls. The numbers of activated cholinergic central canal cluster cells and partition neurons were higher in both step-trained and nontrained rats than in untreated rats and were higher in nontrained than in step-trained rats. The latter finding suggests that daily treatment with epidural stimulation plus serotonergic agonist treatment without step training enhances the excitability of a broader cholinergic interneuronal population than does step training. The numbers of activated interneurons in laminae II-VI of lumbar cross-sections were higher in both step-trained and nontrained rats than in untreated rats, and they were highest in step-trained rats. This finding suggests that this population of interneurons is responsive to epidural stimulation plus serotonergic treatment and that load-bearing induced when stepping has an additive effect. The numbers of activated motoneurons of all size categories were higher in the step-trained group than in the other two groups, reflecting a strong effect of loading on motoneuron recruitment. In general, these results indicate that the spinal networks for locomotion are similar with and without brain input.
  
  
  CONCLUSIONS
  We identified neurons within the spinal cord networks that are activated during assisted stepping in paraplegic rats. We stimulated the spinal cord and administered a drug to help the rats step. One group was trained to step and another was not trained. We observed a lower percentage of activated neurons in specific spinal cord regions in trained rats than in nontrained rats after a 1-hr stepping bout, suggesting that step training reduces activation of some types of spinal neurons. This observation indicates that training makes the spinal networks more efficient and suggests a "learning" phenomenon in the spinal cord without any brain input.
authors: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California.
authors: Paul O
authors: PO
authors: Duru
authors: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California.|Brain Research Institute, University of California, Los Angeles, Los Angeles, California.
authors: Niranjala J K
authors: NJ
authors: Tillakaratne
authors: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California.
authors: Jung A
authors: JA
authors: Kim
authors: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California.
authors: Hui
authors: H
authors: Zhong
authors: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California.
authors: Stacey M
authors: SM
authors: Stauber
authors: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California.
authors: Trinh T
authors: TT
authors: Pham
authors: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California.
authors: Mei S
authors: MS
authors: Xiao
authors: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California.|Brain Research Institute, University of California, Los Angeles, Los Angeles, California.|Department of Neurosurgery, University of California, Los Angeles, Los Angeles, California.|Department of Neurobiology, University of California, Los Angeles, Los Angeles, California.
authors: V Reggie
authors: VR
authors: Edgerton
authors: Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California.|Brain Research Institute, University of California, Los Angeles, Los Angeles, California.
authors: Roland R
authors: RR
authors: Roy
mesh_terms: D000818:Animals; D059329:Cholinergic Neurons / Q000187:drug effects / Q000378:metabolism; D004599:Electric Stimulation Therapy / Q000379:methods*; D004824:Epidural Space; D005260:Female; D007395:Interneurons / Q000187:drug effects / Q000378:metabolism*; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*; D013119:Spinal Cord Injuries / Q000378:metabolism*
chemical_list: D017366:Serotonin Receptor Agonists
keywords: RRID: AB_2079751; RRID: AB_2106765; c-fos; central canal cluster cells; partition neurons; serotonergic agonists