Actions of 5-hydroxytryptamine on neurons of the rat cingulate cortex.
1. Intracellular recordings were made from layer V pyramidal neurons in slices of rat cingulate cortex. Electrodes contained potassium methylsulphate and biocytin for subsequent histology. 2. Synaptic potentials were separated pharmacologically with DL-2-amino-5-phosphonovaleric acid (APV), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), bicuculline, and 2-hydroxysaclofen into components mediated, respectively, by N-methyl-D-aspartate (NMDA) type excitatory amino acid, non-NMDA type excitatory amino acid, gamma-aminobutyric acid (GABAA), and GABAB receptors. Components mediated at excitatory amino acid, GABAA and GABAB receptors reversed polarity at -11, -76, and -108 mV, respectively. 3. When synaptic potentials were evoked by stimulation to the subcortical white matter, 5-hydroxytryptamine (5-HT; 1-100 microM) reversibly reduced the amplitude of NMDA, non-NMDA, GABAA, and GABAB components. Selective agonists and antagonists were used to show that this resulted from activation of 5-HT1B receptors. 4. When synaptic potentials were evoked by stimulation within layer V, 5-HT reduced the amplitude only of the NMDA and non-NMDA components but did not affect the GABAA and GABAB components. 5-HT did not change the amplitude of depolarizations evoked by direct application of glutamate. 5. It is concluded that 5-HT presynaptically inhibits the release of excitatory amino acids at synapses onto prefrontal pyramidal neurons and at synapses onto local feed-forward inhibitory interneurons. 6. 5-HT also hyperpolarized, depolarized, or did not change the membrane potential. The hyperpolarization involved 5-HT1A receptors and resulted from potassium conductance increase. The depolarization involved 5-HT2 receptors and resulted from potassium conductance decrease.
Tanaka
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Vollum Institute, Oregon Health Sciences University, Portland 97201.
North
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RA
D000818:Animals; D005071:Evoked Potentials / Q000502:physiology; D006179:Gyrus Cinguli / Q000502:physiology*; D007395:Interneurons / Q000502:physiology; D008297:Male; D009412:Nerve Fibers / Q000502:physiology; D009474:Neurons / Q000502:physiology; D015221:Potassium Channels / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000502:physiology*; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*
D015221:Potassium Channels; D012701:Serotonin