The actions of serotonin on frog primary afferent terminals and cell bodies.
The actions of serotonin (5-HT) were studied in the isolated frog spinal cord and dorsal root ganglion preparations. In the spinal cord, 5-HT increased the spontaneous activity recorded from dorsal roots, facilitated evoked spinal reflexes and produced fast and slow primary afferent depolarization (PAD). A direct action of 5-HT on primary afferent terminals is likely since 5-HT induced PAD remained in the presence of 1 microM tetrodotoxin and 2 mM Mn2+. The direct action of 5-HT on primary afferent terminals was blocked by methysergide and attenuated by concentrations of Mn2+ in excess of that required to block transmitter release. Cell bodies of the dorsal root ganglion were also depolarized by 5-HT. A slow hyperpolarization occasionally followed the initial depolarization. The depolarizing action of 5-HT in the dorsal root ganglion was also attenuated by treatment with Mn2+. It is concluded that 5-HT acts directly on frog primary afferents and that this influence may involve a calcium sensitive process. The dorsal root ganglion response to 5-HT appears to be a suitable model of the afferent terminal response.
D000818:Animals; D005071:Evoked Potentials / Q000187:drug effects; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D008297:Male; D008345:Manganese / Q000494:pharmacology; D008784:Methysergide / Q000494:pharmacology; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects* / Q000502:physiology; D010477:Perfusion; D011892:Rana catesbeiana; D012018:Reflex / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology*; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D012701:Serotonin; D008345:Manganese; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D008784:Methysergide