Jpn. J. Pharmacol. 87 (4), 333-337 (2001)

Effects of a k-Receptor Agonist U-50488 on Bulbar Respiratory Neurons and Its Antagonistic Action Against the m Receptor-Induced Respiratory Depression in Decerebrate Cats

Akira Haji* and Ryuji Takeda

Department of Pharmacology, Faculty of Medicine, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan

*Corresponding author. FAX: +81-76-434-5021, E-mail:

Abstract: The function of k receptor-mechanisms in bulbar respiratory network was investigated in decerebrate cats. Intravenous injection of U-50488 (0.3-3.0 mg/kg) dose-dependently decreased the phrenic nerve discharge and shortened inspiration and expiration. U-50488 caused hyperpolarization, and decreased input resistance and the action potential discharge in respiratory neurons. The effects of U-50488 were antagonized by nor-binaltorphimine. DAMGO (0.3 mg/kg, i.v.) decreased the phrenic discharge and prolonged inspiration and expiration. U-50488 partially reversed the respiratory depression induced by DAMGO. These results suggest that the activation of k receptors by itself depresses the central respiratory activity, while it opposes the m receptor-mediated respiratory depression.

Keywords: Respiratory neuron, Phrenic nerve discharge, k Receptor-mechanism

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