In order to study the chronic effects of pentobarbital, a positive GABAA
receptor modulator, on the inverse agonist binding of the benzodiazepine site, binding of
[3H]Ro15‐4513 and levels of GABAA receptor
α6‐subunit mRNA were investigated in the brains of
pentobarbital‐tolerant/dependent animals, using receptor autoradiography and in situ
hybridization histochemistry in consecutive brain sections. Pentobarbital was administered to
rats either 60 mg/kg, i.p., once, for acute treatment, or 300 μg/10μl/h i.c.v.
continuously for 6 days via osmotic minipumps to render rats tolerant to pentobarbital. Rats
assigned to the dependent group were sacrificed 24 h after discontinuance of pentobarbital
infusion, while those assigned to the tolerant group were sacrificed at the end of infusion. The
α6 subunit mRNA was increased in the tolerant group only.
Diazepam‐insensitive [3H]Ro15‐4513 binding was increased in the cerebellar
granule layer of pentobarbital‐tolerant and ‐dependent rats. No alterations in these parameters
were observed in acutely treated animals. These data suggest that chronic pentobarbital
treatment induced expression of α6‐subunit mRNA. This was in contrast to
α1‐ and γ2‐subunit mRNA, which in tolerant animals are
unchanged, but for which withdrawal triggers a surge in levels. Because the
α6‐subunit is a major component of the diazepam‐insensitive
[3H]Ro15‐4513 binding site, the increased diazepam‐insensitive
[3H]Ro15‐4513 binding implied de novo synthesis of the receptor subunit
protein. © 1996 Wiley‐Liss, Inc.