Development of GABA-mediated, chloride-dependent inhibition in CA1 pyramidal neurones of immature rat hippocampal slices.
1. gamma-Aminobutyric acid (GABA)-mediated, Cl(-)-dependent inhibitory postsynaptic potentials (IPSPs) and GABA currents in immature rat hippocampal CA1 neurones were studied using the whole-cell recording technique in brain slices. 2. IPSPs evoked by electrical stimulation were observed in postnatal 2- to 5- (PN2-5), 8- to 13-(PN8-13) and 15- to 20-(PN15-20)day-old CA1 neurones. In the presence of glutamate receptor blockers 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and D-2-amino-5-phosphonovaleric acid (APV), the reversal potential for the IPSP (EIPSP) was near the resting membrane potential (RMP) in the PN2-5 neurones, but 13 and 25 mV more negative than the RMP in PN8-13 and PN15-20 neurones respectively. IPSPs and GABA currents were blocked by the GABAA-receptor antagonists bicuculline or picrotoxin. 3. The reversal potential for somatic GABA currents (EGABA) was examined in the presence of tetrodotoxin (TTX). There was a strong dependence of the EGABA upon the patch pipette [Cl-] ([Cl-]p). indicating that the GABA currents were mediated by a Cl- conductance. In PN2-5 neurones, EGABA agreed with the value predicted by the Goldman-Hodgkin-Katz equation at given concentrations of internal and external anions permeable through GABA-activated Cl- channels, whereas EGABA in older neurones was 8-18 mV more negative. 4. Examination of the relations between EGABA, holding potential, [Cl-]p and resting conductance indicated that the membrane of the PN2-5 neurones was readily permeable to Cl- which followed a passive Donnan equilibrium. Passive distribution of Cl- played a decreasing role in PN8-13 neurones and in PN15-20 neurones. 5. To assess the contribution of outward Cl- co-transport, bath applications of high K+ or furosemide were performed. High K+ and furosemide caused a reversible positive shift of EGABA in PN15-20 neurones. Raising the temperature moved EGABA to a more negative potential, with a Q10 of 5 mV. A similar change of EGABA in response to high K+, but not to furosemide, was found in PN8-13 neurones. 6. The present data indicate the existence of GABAA-mediated inhibitory synaptic connections in CA1 neurones at the earliest stages of postnatal life. During the first postnatal week, Cl- ions are passively distributed and the EIPSP and EGABA are near the RMP.(ABSTRACT TRUNCATED AT 400 WORDS)
Zhang
L
L
Toronto Western Hospital, Department of Physiology, University of Toronto, Canada.
Spigelman
I
I
Carlen
P L
PL
D000818:Animals; D001692:Biological Transport; D002034:Bumetanide / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism / Q000502:physiology*; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology*; D005665:Furosemide / Q000494:pharmacology; D006624:Hippocampus / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013696:Temperature; D005680:gamma-Aminobutyric Acid / Q000378:metabolism / Q000502:physiology*
D002712:Chlorides; D002034:Bumetanide; D005680:gamma-Aminobutyric Acid; D005665:Furosemide; D011188:Potassium