Developmental changes in spontaneous GABAA-mediated synaptic events in rat hippocampal CA3 neurons.
Ongoing spontaneous postsynaptic potentials (SPSPs) were intracellularly recorded at 34-36 degrees C from hippocampal CA3 neurons in slices obtained from postnatal days (P) 0-6 and 7-31. SPSPs occurred randomly, and their frequency distribution was fitted by a single exponential function. They were little affected by kynurenic acid, but were reversibly blocked by bicuculline, implying that they were mediated by GABAA receptors. The mean amplitude was 4.53 +/- 0.89 mV in control conditions and 4.07 +/- 0.79 mV in kynurenic acid. In kynurenic acid (with CsCl-filled microelectrodes), SPSPs reversed polarity at 2.4 +/- 2 mV. When tetrodotoxin (1 microM) was added to kynurenic acid solution, GABAA-mediated miniature postsynaptic potentials (MPSPs) were recorded. Under these conditions large events disappeared. The mean amplitude of MPSPs was 2.51 +/- 0.43 mV. The mean frequency decreased from 2.96 +/- 1.04 Hz in kynurenic acid to 0.4 +/- 0.15 Hz in kynurenic acid plus tetrodotoxin. In contrast with P0-P6, at P7-P31 SPSPs were significantly affected by kynurenic acid. The mean amplitude of SPSPs shifted from 4.71 +/- 0.82 mV in control conditions to 3.79 +/- 0.76 mV in kynurenic acid. At this developmental stage, the reversal potential of GABAA-mediated SPSPs shifted towards more negative values (-23.7 +/- 1.3 mV). Addition of tetrodotoxin to kynurenic acid solution abolished larger events and revealed GABAergic MPSPs. The mean amplitude of MPSPs was 2.72 +/- 0.5 mV, a value very close to that observed at P0-P6. Synaptic currents were recorded at 22-24 degrees C from voltage-clamped CA3 pyramidal neurons (at P6) using the tight-seal whole-cell recording technique.(ABSTRACT TRUNCATED AT 250 WORDS)
Hosokawa
Y
Y
Biophysics Laboratory, International School for Advanced Studies, Trieste, Italy.
Sciancalepore
M
M
Stratta
F
F
Martina
M
M
Cherubini
E
E
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects*; D007736:Kynurenic Acid / Q000494:pharmacology; D009474:Neurons / Q000502:physiology; D051381:Rats; D018079:Receptors, GABA / Q000187:drug effects; D009435:Synaptic Transmission / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D018079:Receptors, GABA; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D007736:Kynurenic Acid; D001640:Bicuculline