Journal of Nippon Medical School: Vol.66 No.1 page.021

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ArticleTitle Induction of noradrenergic supersensitivity following cordotomy in neonatal rat spinal motoneurons

AuthorList Hitoshi Kadotani

Affiliation Department of Anesthesiology, Nippon Medical School

Language JA

Volume 66

Issue 1

Year 1999

Page 21-27

Received August 13, 1998

Accepted October 14, 1998

Keywords α-adrenoceptor, denervation supersensitivity neonatal rat, cordotomy

Abstract P atients with spinal cord lesions frequently show autonomic hyperreflexia. The mechanism of autonomic hyperreflexia has been thought to be an acute general autonomic overactivity in response to cutaneous or visceral stimuli, but it remains uncertain. Several kinds of experiments suggest that amplified spinal sympathetic reflexes in the decentralized cord are attributable to the denervation supersensitivity of denervated neurons, which is a well-known phenomenon in denervated muscle fibers. In the present study, changes in the supersensitivity of motoneurons after cordotomy were studied in the spinal cord of neonatal rats. Responses to bath-applied noradrenaline (NA) were recorded from a ventral root of the isolated spinal cord of 6-day-old rats. In normal spinal cords, NA induced depolarization in motoneurons dose-dependently. α1-antagonist prazosin (3μM) inhibited the deporalization induced by NA, and α2-antagonist rauwolscine (1μM) potentiated it. In one group of rats, cordotomy was performed 4 days after birth by complete transection of the spinal cord at vertebrate 8th-10th thoracic level, and NA response was examined two days later (when they were 6 days old). In cordotomized rats, NA-induced depolarization was increased with respect to both amplitude and duration. α1-as well as α2-antagonists inhibited the NA response in the spinalized rats. Especially, both antagonists shortened the duration of NA response as compared to normal level. It is concluded that the denervation supersensitivity to NA appears 2 days after cordotomy in the spinal motoneurons of neonatal rats and that the supersensitivity to NA is attributable to the upregulation of both α1-and α2-adrenoceptors on the motoneurons, indicating that a new type of α2-adrenoceptor function appears.

Correspondence to Hitoshi Kadotani, Department of Anesthesiology, Nippon Medical School, 1-1-5 Sendagi Bunkyou-ku Tokyo 113-8603, Japan

ArticleTitle	Induction of noradrenergic supersensitivity following cordotomy in neonatal rat spinal motoneurons
AuthorList	Hitoshi Kadotani
Affiliation	Department of Anesthesiology, Nippon Medical School
Language	JA
Volume	66
Issue	1
Year	1999
Page	21-27
Received	August 13, 1998
Accepted	October 14, 1998
Keywords	α-adrenoceptor, denervation supersensitivity neonatal rat, cordotomy
Abstract	P atients with spinal cord lesions frequently show autonomic hyperreflexia. The mechanism of autonomic hyperreflexia has been thought to be an acute general autonomic overactivity in response to cutaneous or visceral stimuli, but it remains uncertain. Several kinds of experiments suggest that amplified spinal sympathetic reflexes in the decentralized cord are attributable to the denervation supersensitivity of denervated neurons, which is a well-known phenomenon in denervated muscle fibers. In the present study, changes in the supersensitivity of motoneurons after cordotomy were studied in the spinal cord of neonatal rats. Responses to bath-applied noradrenaline (NA) were recorded from a ventral root of the isolated spinal cord of 6-day-old rats. In normal spinal cords, NA induced depolarization in motoneurons dose-dependently. α1-antagonist prazosin (3μM) inhibited the deporalization induced by NA, and α2-antagonist rauwolscine (1μM) potentiated it. In one group of rats, cordotomy was performed 4 days after birth by complete transection of the spinal cord at vertebrate 8th-10th thoracic level, and NA response was examined two days later (when they were 6 days old). In cordotomized rats, NA-induced depolarization was increased with respect to both amplitude and duration. α1-as well as α2-antagonists inhibited the NA response in the spinalized rats. Especially, both antagonists shortened the duration of NA response as compared to normal level. It is concluded that the denervation supersensitivity to NA appears 2 days after cordotomy in the spinal motoneurons of neonatal rats and that the supersensitivity to NA is attributable to the upregulation of both α1-and α2-adrenoceptors on the motoneurons, indicating that a new type of α2-adrenoceptor function appears.
Correspondence to	Hitoshi Kadotani, Department of Anesthesiology, Nippon Medical School, 1-1-5 Sendagi Bunkyou-ku Tokyo 113-8603, Japan