Temporal facilitation of the flexor reflex induced by C-fiber activity: comparison between adult and aged rats.
We investigated the wind-up phenomenon of the flexor reflex in adult and aged rats. The sural nerve was stimulated at C-fiber strength and reflex activity was recorded from the semitendinosus muscle. The wind-up rate, the increment rate of the C-fiber response (i.e. activity from 100 to 600 ms after stimulation) by successive stimuli (five train pulses), was decreased exponentially with increasing stimulus intervals from 3 to 20 s. The time constant of the decay for the aged rats was 9.2+/-3.2 s (mean+/-SD), which was significantly longer than for the adult rats (6.4+/-2.9 s). The findings indicate that the effects of C-fiber activation on the spinal nociceptive pathways attenuate more slowly in aged rats as compared with adult rats.
Kanda
K
K
Department of Central Nervous System, Tokyo Metropolitan Institute of Gerontology, 35-2, Sakaecho, Itabashi-Ku, 173-0015, Tokyo, Japan. kandak@tmig.or.jp
Sato
H
H
Kemuriyama
T
T
Iwata
K
K
D000200:Action Potentials / Q000502:physiology*; D000367:Age Factors; D000818:Animals; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D008297:Male; D009412:Nerve Fibers / Q000502:physiology*; D010147:Pain Measurement / Q000379:methods; D051381:Rats; D011916:Rats, Inbred F344; D012018:Reflex / Q000502:physiology*; D013497:Sural Nerve / Q000502:physiology*