GABA- and glutamate-mediated synaptic potentials in rat dorsal raphe neurons in vitro.
1. Synaptic potentials were recorded with intracellular electrodes from rat dorsal raphe neurons in a slice preparation. 2. Synaptic potentials were evoked by applying electrical pulses to bipolar stimulating electrodes positioned immediately dorsal to the raphe nucleus; these arose after a latency of 0.5-5 ms and had a duration of 20-200 ms. 3. The synaptic potential was biphasic (at the resting potential) when the recording electrodes contained potassium citrate; a depolarization was followed by a hyperpolarization. The hyperpolarization reversed in polarity at -70 mV and was blocked by bicuculline. 4. The depolarizing synaptic potential was reduced to 50-90% of control by kynurenate (1-2 mM) or 6-cyano-2,3-dihydroxy-7-nitro-quinoxaline (CNQX) (10 microM) and increased in amplitude and duration by magnesium-free solution. 5. In magnesium-free solutions (with CNQX), the depolarizing synaptic potential was blocked by DL-2-amino-5-phosphonovaleric acid (APV, 50 microM). APV also blocked depolarization caused by adding N-methyl-D-aspartate (NMDA) to the superfusion solution. 6. The results indicate that raphe neurons display two synaptic potentials having a duration of 150-200 ms: one that is mediated by GABA and a second that is due to an excitatory amino acid. The component mediated by an excitatory amino acid involves, in part, a receptor of the NMDA type.
Pan
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Vollum Institute, Oregon Health Sciences University, Portland 97201.
Williams
J T
JT
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D005971:Glutamates / Q000494:pharmacology*; D066298:In Vitro Techniques; D008566:Membranes / Q000502:physiology; D009118:Muscimol / Q000494:pharmacology; D010852:Picrotoxin / Q000494:pharmacology; D011903:Raphe Nuclei / Q000166:cytology / Q000502:physiology*; D051381:Rats; D013569:Synapses / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D001640:Bicuculline; D005971:Glutamates; D009118:Muscimol; D010852:Picrotoxin; D005680:gamma-Aminobutyric Acid