Vol. 289, Issue 3, 1626-1633, June 1999

Acute Pentylenetetrazol Injection Reduces Rat GABA_A Receptor mRNA Levels and GABA Stimulation of Benzodiazepine Binding with No Effect on Benzodiazepine Binding Site Density¹

Laura A. Walsh², Ming Li, Tai-Jun Zhao, Ted H. Chiu³ and Howard C. Rosenberg

Department of Pharmacology, Medical College of Ohio, Toledo, Ohio

The effects of a single convulsive dose of pentylenetetrazol (PTZ, 45 mg/kg i.p.) on rat brain -aminobutyric acid type A (GABA_A) receptors were studied. Selected GABA_A receptor subunit mRNAs were measured by Northern blot analysis (with -actin mRNA as a standard). Four hours after PTZ, the GABA_A receptor ₂-mRNA was decreased in hippocampus, cerebral cortex, and cerebellum; ₁-mRNA was decreased in cerebellum; and ₂ subunit mRNA was decreased in cortex and cerebellum. The ₅ subunit mRNA level was not altered. Those mRNAs that had been reduced were increased in some brain regions at the 24-h time point, and these changes reverted to control levels by 48 h. PTZ effect on GABA_A receptors was also studied by autoradiographic binding assay with the benzodiazepine agonist [³H]flunitrazepam (FNP), the GABA_A agonist [³H]muscimol, and the benzodiazepine antagonist [³H]flumazenil. There was an overall decrease in [³H]FNP binding 12 but not 24 h after PTZ treatment. In contrast, [³H]muscimol binding was minimally affected, and [³H]flumazenil binding was unchanged after PTZ treatment. Additional binding studies were performed with well-washed cerebral cortical homogenates to minimize the amount of endogenous GABA. There was no PTZ effect on specific [³H]FNP binding. However, there was a significant reduction in the stimulation of [³H]FNP binding by GABA. The results showed that an acute injection of PTZ caused transient changes in GABA_A receptor mRNA levels without altering receptor number but affected the coupling mechanism between the GABA and benzodiazepine sites of the GABA_A receptor.