Modulation of noradrenergic and serotonergic transmission by noxious stimuli and intrathecal morphine differs in the dorsal raphe nucleus of anesthetized rat: in vivo voltammetric studies.
We examined the effects of cutaneous noxious heat as well as the intrathecal administration of morphine on the oxidation current of peaks 1 and 2 in the dorsal raphe nucleus (DRN) of anesthetized rats. Differential normal pulse voltammetry with carbon fiber electrodes identified distinct oxidation currents at +120 mV (peak 1: catechol signals) and +280 mV (peak 2: 5-hydroxyindole signals). The catechol signal was significantly increased by 22.9 +/- 4.2% after applying cutaneous noxious heat at 52 degrees C. The 5-hydroxyindole signal was decreased by 39.8 +/- 4.3 and by 25.2 +/- 4.7% after stimulation with cutaneous noxious heat at 52 and 45 degrees C, respectively. A low dose of morphine (2.5 microg) potentiated the increase in the catechol signal and the decrease in the 5-hydroxyindole signal induced by noxious heat, and a high dose (10.0 microg) attenuated both. The effects of morphine at low (2.5 microg) and high doses (10.0 microg) were antagonized by naloxone (0.5 mg/kg, i.p.). These results indicate that noxious heat stimulation increased the catechol signal and decreased the 5-hydroxyindole signal in the DRN. The intrathecal administration of morphine affects the noxious stimulation-induced activity of noradrenergic and serotonergic neurotransmission in the DRN.
Department of Neuroscience, Showa Pharmaceutical University, 3-3165, Higashitamagawagakuen, Machida, Tokyo 194-8543, Japan.
Toichiro
T
Chuma
Kyoji
K
Taguchi
Masatoshi
M
Kato
Kenji
K
Abe
Iku
I
Utsunomiya
Ken-ichi
K
Miyamoto
Tadashi
T
Miyatake
D000818:Animals; D002396:Catechols / Q000378:metabolism; D004594:Electrophysiology; D006614:Hindlimb; D006358:Hot Temperature; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D007278:Injections, Spinal; D008297:Male; D009020:Morphine / Q000008:administration & dosage* / Q000494:pharmacology; D009638:Norepinephrine / Q000502:physiology*; D010084:Oxidation-Reduction / Q000187:drug effects; D010146:Pain / Q000503:physiopathology*; D011903:Raphe Nuclei / Q000502:physiology* / Q000503:physiopathology*; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*
D002396:Catechols; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D009020:Morphine; C034221:catechol; D009638:Norepinephrine