title: Motor activity affects dopaminergic and noradrenergic systems of the dorsal horn of the rat lumbar spinal cord.
abstract: Dopamine (DA) and noradrenaline (NA) modulate responses to nociceptive stimuli, within the dorsal horn of the spinal cord. Both neurotransmitters may play a role in supraspinal regulation in response to proprioceptive afferences to the dorsal horn. However, direct evidence of changes in neurotransmitter release within the dorsal horn due to non-noxious stimuli is lacking. The present study was designed to determine, whether non-nociceptive exercise produces changes in release of DA and NA within the dorsal horn, and whether these changes are associated with long-lasting inhibition after the exercise stops. Microdialysis probes, implanted in layers 2-5 of Rexed, in combination with high-performance liquid chromatography coupled to electrochemical detection (HPLC-EC) were used to measure concentrations of DA and NA metabolite (MHPG) in lumbar spinal cords of rats. Microdialysate was sampled before, during, and after a treadmill exercise of one hour. Results indicate that DA and NA releases are inhibited during non-nociceptive motor activity. At rest, DA concentration was 204 ± 10.5 pg/10 μl and was significantly decreased during exercise to -11.4% (P ≤ 0.05). Greater decrease occurred after 30 min of exercise and was of -31.4% (P ≤ 0.05). Similarly, MHPG was significantly decreased of -18% during exercise (P ≤ 0.05). When exercise stopped, both systems showed long-lasting inhibition. Exercise post-release lasted 30 min for DA and 90 min for MHPG. MHPG greatest decrease of -47.8% occurred 30 min after stopping the exercise (P ≤ 0.001). Thus, DA and NA systems seem to respond to exercise-induced proprioceptive afferent stimuli to the dorsal horn.
authors.affiliation: Department of Anatomy and Cell Biology, UIC, Chicago, Illinois 60612, USA. cgerin@uic.edu.
authors.forename: Christine G
authors.initials: CG
authors.lastname: Gerin
authors.forename: Kristin
authors.initials: K
authors.lastname: Smith
authors.forename: Seritta
authors.initials: S
authors.lastname: Hill
authors.forename: Angela
authors.initials: A
authors.lastname: Hill
authors.forename: Ikenna C
authors.initials: IC
authors.lastname: Madueke
mesh_terms: D000818:Animals; D004298:Dopamine / Q000378:metabolism*; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology; D009434:Neural Pathways / Q000378:metabolism / Q000502:physiology; D009638:Norepinephrine / Q000378:metabolism*; D020671:Posterior Horn Cells / Q000502:physiology*; D017729:Presynaptic Terminals / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D004298:Dopamine; D009638:Norepinephrine