title: High-frequency conditioning electrical stimulation evokes supraspinal independent long-term depression but not long-term potentiation of the spinal withdrawal reflex in rats.
abstract: The aim of the current study was to investigate the effects on the spinal withdrawal reflex of electrical stimulation that has been shown to induce long-term potentiation (LTP) in spinal sensory systems. This was done in order to enhance our understanding of long-term dynamic modifications of spinal motor system during the exposure to high-frequency conditioning electrical stimulation (cES). The spinal withdrawal reflex was assessed by extracellular recording of the single motor unit (SMU) electromyographic (EMG) activity from the medial gastrocnemius (MG) muscle in intact and acutely spinalized rats. High-frequency (1 ms pulses at 100 Hz for 2 s repeated three times at 10 s intervals) tetanic cES produced a significant long-term depression (LTD) (at least 3 h), but not LTP, of the electrically evoked SMU EMG activity as well as the wind-up phenomenon (temporal summation). There were no significant depressive or facilitatory effects of low-frequency (2 Hz) cES, consisting of the same number of pulses as the 100 Hz cES, on the SMU EMG responses. This frequency-dependent long-term depressive effect on the spinal withdrawal reflex was not significantly changed following acute spinalization, indicating that LTD of the spinal motor system elicited by high-frequency cES is independent of the descending control system. We conclude that, in contrast to LTP in spinal sensory systems to brief tetanic C-fiber cES, high-frequency cES seems only to elicit LTD of motor systems of the spinal cord.
authors.affiliation: Center for Sensory-Motor Interaction (SMI), Laboratory for Experimental Pain Research, Aalborg University, Fredrik Bajers Vej 7 D-3, DK-9220 Aalborg, Denmark. yhj@hst.aau.dk
authors.forename: Hao-Jun
authors.initials: HJ
authors.lastname: You
authors.forename: Arne
authors.initials: A
authors.lastname: Tjølsen
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D001921:Brain / Q000502:physiology; D003213:Conditioning, Psychological / Q000502:physiology*; D004525:Efferent Pathways / Q000502:physiology; D004558:Electric Stimulation; D004576:Electromyography; D017774:Long-Term Potentiation / Q000502:physiology; D036881:Long-Term Synaptic Depression / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009415:Nerve Net / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology