Transient expression of a novel type of GABA response in rat CA3 hippocampal neurones during development.
1. Intracellular recordings were used to study the effects of gamma-aminobutyric acid (GABA) on rat CA3 hippocampal neurones during the first two weeks of postnatal life. 2. In the presence of tetrodotoxin (TTX, 1 microM), from postnatal day 0 (P0) to P12 both associated with an increase in input conductance whereas baclofen (30-100 microM) produced a membrane hyperpolarization. 3. Bicuculline (50 microM) reduced the effects of GABA and abolished the response to isoguvacine without affecting the response to baclofen. 4. This novel bicuculline-insensitive GABA response was chloride dependent and was blocked by picrotoxin (10-100 microM) in an uncompetitive way. In bicuculline and picrotoxin, a GABAB-mediated hyperpolarization appeared. 5. Towards the end of the second postnatal week, bicuculline blocked the GABA-induced depolarization and revealed a small hyperpolarizing response which was blocked by the GABAB antagonist CGP 35348 (0.5-1 mM). 6. It is suggested that, during development, the GABA response was mediated through the conventional GABAA and GABAB receptors as well as a new bicuculline-baclofen-insensitive type of receptor.
Strata
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Biophysics Laboratory, International School for Advanced Studies (SISSA), Trieste, Italy.
Cherubini
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D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn / Q000254:growth & development / Q000502:physiology*; D001418:Baclofen / Q000494:pharmacology; D001640:Bicuculline / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D018079:Receptors, GABA / Q000187:drug effects; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D018079:Receptors, GABA; D005680:gamma-Aminobutyric Acid; D001418:Baclofen; D001640:Bicuculline