Prenatal diazepam exposure functionally alters the GABA(A) receptor that modulates [3H]noradrenaline release from rat hippocampal synaptosomes.
In rats, exposure to diazepam (DZ) during the last week of gestation is associated with behavioral alterations (in some cases sexually dimorphic) that appear when the animals reach adulthood. This study was conducted to evaluate the effects of prenatal DZ exposure on the function of the gamma-aminobutyric (GABA)(A) receptor complex. The method used - perfusion of rat hippocampal nerve terminals labeled with [3H]noradrenaline (NA) - allowed us to evaluate the effects of DZ on a specific native GABA(A) receptor subtype which is located on hippocampal noradrenergic nerve endings and mediates the release of NA. Muscimol stimulated synaptosomal release of [3H]NA in a concentration-dependent manner; maximal stimulation (50%) was achieved with a concentration of 30 microM, and the ED(50) was 1.7 microM. The effect of muscimol was potentiated by the positive allosteric modulators DZ and 3alpha-pregnan-5alpha-ol-20-one (3alpha,5alpha-P; allopregnanolone), which displayed similar maximal effects and affinities. In the presence of DZ (0.1 microM), muscimol stimulated the release of [3H]NA with an ED(50) of 0.5 microM; in the presence of 3alpha,5alpha-P (0.1 microM), the ED(50) of muscimol was 0.3 microM. Prenatal DZ exposure did not modify the concentration-effect curve for muscimol, but it did abolish the potentiating effects of DZ and 3alpha,5alpha-P. These findings demonstrate that prenatal exposure to DZ produces functional modifications of the GABA(A) receptor subtype we investigated. This effect may be related to the relative contributions of the various protein subunits that compose the GABA(A) receptor complex. Exposure to DZ while the GABA(A) receptors are developing might influence the expression of these subunits, giving rise to a receptor that can be activated by muscimol but is not susceptible to allosteric modulation by DZ or 3alpha,5alpha-P.
Martire
Maria
M
Institute of Pharmacology, Catholic University of the Sacred Heart, Rome, Italy. mmartire@rm.unicatt.it
Altobelli
Debora
D
Cannizzaro
Carla
C
Maurizi
Silvia
S
Preziosi
Paolo
P
D000494:Allosteric Regulation / Q000187:drug effects; D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D001640:Bicuculline / Q000494:pharmacology; D003975:Diazepam / Q000008:administration & dosage / Q000494:pharmacology* / Q000633:toxicity; D005260:Female; D005326:Fetal Proteins / Q000096:biosynthesis / Q000737:chemistry; D018755:GABA Agonists / Q000008:administration & dosage / Q000494:pharmacology* / Q000633:toxicity; D018756:GABA Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects / Q000196:embryology* / Q000378:metabolism; D008297:Male; D001523:Mental Disorders / Q000139:chemically induced / Q000196:embryology; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D009638:Norepinephrine / Q000378:metabolism*; D010852:Picrotoxin / Q000494:pharmacology; D011247:Pregnancy; D011280:Pregnanolone / Q000494:pharmacology; D011297:Prenatal Exposure Delayed Effects; D021122:Protein Subunits; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000096:biosynthesis / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
D001418:Baclofen; D001640:Bicuculline; D003975:Diazepam; D005326:Fetal Proteins; D018755:GABA Agonists; D018756:GABA Antagonists; D009419:Nerve Tissue Proteins; D009638:Norepinephrine; D010852:Picrotoxin; D011280:Pregnanolone; D021122:Protein Subunits; D011963:Receptors, GABA-A