Inhibition of glycine-induced current by morphine in nucleus tractus solitarii neurones of guinea pigs.
We studied the effect of morphine on the current induced by glycine in acutely dissociated nucleus tractus solitarii (NTS) neurones of guinea pigs, by use of the whole-cell patch clamp technique. Morphine inhibited 30 microM glycine-induced current (Igly), without affecting the current caused by 30 microM GABA. The effect of morphine was concentration-dependent, with a maximal effect at 1 mM, and reversible. The half-maximum inhibitory concentration of morphine was 30 microM. The effect of morphine was not depressed by naloxone, an opioid antagonist. Furthermore, the effect was not substantially affected by methiothepin, a 5-HT1 antagonist, ketanserin, a 5-HT2 antagonist and MDL-72222, a 5-HT3 antagonist. Morphine at 30 microM shifted the concentration-response curve for Igly to the right without affecting the maximum value. The effect of morphine on Igly showed no use-dependence. The results indicate that morphine inhibits Igly in the NTS neurones, and further suggest that morphine at the concentration used may act on the glycine receptor-ionophore complex, but not on the Cl-channel of the complex.
Fukushima
H
H
Department of Pharmacological Sciences, Faculty of Pharmaceutical Sciences, Kumamoto University, Japan.
Nagayama
S
S
Otsuka
M
M
Takahama
K
K
Isohama
Y
Y
Kai
H
H
Miyata
T
T
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005998:Glycine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D006168:Guinea Pigs; D009020:Morphine / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques; D012702:Serotonin Antagonists / Q000494:pharmacology; D017552:Solitary Nucleus / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D012702:Serotonin Antagonists; D005680:gamma-Aminobutyric Acid; D009020:Morphine; D005998:Glycine