title: Excitatory and inhibitory effects of H1-blockers on isolated bullfrog spinal cords.
abstract: Effects of pyrilamine and diphenhydramine on isolated spinal cords of bullfrogs were studied in order to clarify the mechanisms of depressant and stimulant actions of H1-blockers on the central nervous system. Pyrilamine and diphenhydramine depressed both the DR-VRP and DR-DRP. Pyrilamine and diphenhydramine also suppressed L-glutamate-induced depolarization of the motoneurones, but they did not depress GABA depolarization at the dorsal root terminals. By switching the perfusate to drug-free Ringer solution, depressed amplitudes of DR-VRP were suddenly increased over the control level (rebound phenomenon). The rebound increase of DR-VRP was inhibited by either tetrodotoxin or D-600. These results suggest that the rebound phenomenon may be due to the effect of H1-blockers 1) inhibiting transmitter release participating in presynaptic inhibition and 2) inducing a rapid recovery from the depressed influx of Na+ and Ca2+ into motoneurones.
mesh_terms: D000818:Animals; D004155:Diphenhydramine / Q000494:pharmacology; D005711:Gallopamil / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D006632:Histamine / Q000494:pharmacology; D006634:Histamine H1 Antagonists / Q000494:pharmacology*; D066298:In Vitro Techniques; D009046:Motor Neurons / Q000187:drug effects; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology; D011738:Pyrilamine / Q000494:pharmacology; D011892:Rana catesbeiana; D013116:Spinal Cord / Q000187:drug effects*; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D005971:Glutamates; D006634:Histamine H1 Antagonists; D009467:Neuromuscular Depolarizing Agents; D005711:Gallopamil; D018698:Glutamic Acid; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D006632:Histamine; D004155:Diphenhydramine; D011738:Pyrilamine