Epinephrine and norepinephrine modulate neuronal responses to excitatory amino acids and agonists in frog spinal cord.
The interaction of the catecholamines epinephrine (E) and norepinephrine (NE) (1.0-100 microM) and excitatory amino acids on motoneurons of the isolated superfused frog spinal cord was investigated by sucrose gap recordings from ventral roots. Exposure of the cord to E or NE 30 sec prior to application of L-aspartate or L-glutamate reduced the motoneuron depolarizations produced by the amino acids. The reduction of responses to the mixed receptor agonists L-glutamate and L-aspartate may be the result of opposite actions of the catecholamines on the activation of specific excitatory receptors by the amino acids. Thus, E and NE facilitated depolarizations caused by application of N-methyl-D-aspartate (NMDA) and depressed those produced by quisqualate. The effect on NMDA responses appeared to be beta-adrenoceptor mediated because it was mimicked by the beta-agonist isoproterenol and blocked by propranolol. The effect on quisqualate depolarizations appeared to require activation of alpha 2-adrenoceptors; it was mimicked by the alpha 2-agonists clonidine and alpha-methylnorepinephrine and antagonized by yohimbine and piperoxan. These results are important in understanding the actions of catecholamines on reflex transmission in spinal pathways which use excitatory amino acids as transmitters.
Wohlberg
C J
CJ
Department of Pharmacology, University of Miami School of Medicine, Veterans Administration Medical Center, Florida 33101.
Hackman
J C
JC
Davidoff
R A
RA
D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology*; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007608:Kainic Acid / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D016202:N-Methylaspartate; D009638:Norepinephrine / Q000494:pharmacology*; D010069:Oxadiazoles / Q000494:pharmacology; D016318:Quisqualic Acid; D011894:Rana pipiens; D012016:Reference Values; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
D000596:Amino Acids; D005971:Glutamates; D010069:Oxadiazoles; D015016:Yohimbine; D001224:Aspartic Acid; D018698:Glutamic Acid; D016202:N-Methylaspartate; D016318:Quisqualic Acid; D007545:Isoproterenol; D007608:Kainic Acid; D009638:Norepinephrine; D004837:Epinephrine