Inhibition of hippocampal CA1 neurons by 5-hydroxytryptamine, derived from the dorsal raphe nucleus and the 5-hydroxytryptamine1A agonist SM-3997.
Electrophysiological studies, using chloral hydrate-anesthetized rats, were undertaken to determine whether hippocampal pyramidal neurons, receiving input from the medial septal nucleus, were affected by 5-hydroxytryptamine (5-HT) derived from the dorsal raphe nucleus. The pyramidal neurons in the CA1 region of the hippocampus were classified into short- and long-latency neurons, based on their response to stimulation of the medial septal nucleus. Microiontophoretically applied atropine inhibited the generation of spikes upon stimulation of the medial septal nucleus in short-latency neurons, but had no effect on long-latency neurons. In the short-latency neurons, the stimulation-induced spikes of the medial septal nucleus were inhibited by conditioning stimuli applied to the dorsal raphe nucleus and iontophoretic application of 5-HT and the 5-HT1A agonists, SM-3997 (3 a alpha,4 beta,7 beta,7a alpha-hexahydro-2-(4-(4-(2-pyrimidinyl)-1- piperazinyl)-butyl)-4,7-methano-1H-isoindole-1,3(2H)-dione dihydrogen citrate) and 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin). The conditioning effect of the dorsal raphe nucleus was antagonized by methysergide. However, in the long-latency neurons, the spikes elicited by stimulation of the medial septal nucleus were not affected by the conditioning stimulation of the dorsal raphe nucleus, or iontophoretically applied 5-HT. These results indicate that 5-HT, originating in the dorsal raphe nucleus inhibited hippocampal pyramidal neurons receiving cholinergic input from the medial septal nucleus, but not those receiving non-cholinergic input from the medial septal nucleus. The drug SM-3997 inhibited the activity of hippocampal pyramidal neurons, that receive excitatory cholinergic input from the medial septal nucleus by acting on 5-HT1A receptors.
Hirose
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A
Department of Pharmacology, Faculty of Medicine, Kyoto University, Japan.
Sasa
M
M
Akaike
A
A
Takaori
S
S
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology*; D001285:Atropine / Q000494:pharmacology; D006624:Hippocampus / Q000378:metabolism*; D007478:Iontophoresis; D054833:Isoindoles; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010275:Parasympathetic Nervous System / Q000502:physiology; D010879:Piperazines / Q000494:pharmacology*; D011712:Pyramidal Tracts / Q000187:drug effects / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology*; D011903:Raphe Nuclei / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000502:physiology*; D013764:Tetrahydronaphthalenes / Q000494:pharmacology
D014151:Anti-Anxiety Agents; D054833:Isoindoles; D010879:Piperazines; D011743:Pyrimidines; D013764:Tetrahydronaphthalenes; C055267:tandospirone; D012701:Serotonin; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D001285:Atropine