title: Plastic changes in nociceptive transmission of the rat spinal cord with advancing age.
abstract: To understand characteristics of the pain system in the elderly, we investigated the electrophysiological properties of nociceptive neurons in the lumbar spinal dorsal horn of aged (29-34-mo old) and adult (7-13-mo old) rats. The responses of nociceptive neurons to noxious thermal stimulation, as well as the spontaneous firing rate, were significantly higher in the aged as compared with adult rats. Furthermore, the size of the high-threshold receptive field area of wide dynamic range neurons was larger (P < 0.01) and that of the low-threshold area was smaller (P < 0.05) in aged rats than in adult rats. The increased nociceptive neuronal activity in the aged rats correlated with the finding that the paw withdrawal latency was significantly shorter in the aged rats than those of the adult rats following heat stimulation of the hind paw (P < 0.05). Reversible local anesthetic block of descending pathways resulted in a dramatic increase in neuronal activity in adult rats but had little effect in aged rats. There was also a significant loss of serotoninergic and noradrenergic fibers in the spinal dorsal horn of the aged rats. These results demonstrate an age-related plasticity in spinal nociceptive processing that is related to impairment of descending modulatory pathways.
authors.affiliation: Department of Oral Physiology, Faculty of Dentistry, Osaka University, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan. iwatak@dent.osaka-u.ac.jp
authors.forename: Koichi
authors.initials: K
authors.lastname: Iwata
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fukuoka
authors.forename: Eji
authors.initials: E
authors.lastname: Kondo
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Tsuboi
authors.forename: Akimasa
authors.initials: A
authors.lastname: Tashiro
authors.forename: Koichi
authors.initials: K
authors.lastname: Noguchi
authors.forename: Yuji
authors.initials: Y
authors.lastname: Masuda
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Morimoto
authors.forename: Kenro
authors.initials: K
authors.lastname: Kanda
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D004299:Dopamine beta-Hydroxylase / Q000032:analysis; D006358:Hot Temperature; D008297:Male; D009407:Nerve Block; D009473:Neuronal Plasticity / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D017288:Pain Threshold / Q000502:physiology; D020671:Posterior Horn Cells / Q000737:chemistry / Q000502:physiology*; D051381:Rats; D011916:Rats, Inbred F344; D012018:Reflex / Q000502:physiology; D012701:Serotonin / Q000032:analysis; D013823:Thermoreceptors / Q000502:physiology
chemical_list: D012701:Serotonin; D004299:Dopamine beta-Hydroxylase