Effects of GABA-Mimetic Drugs on Turnover of Histamine in the Mouse Brain

The effect of GABA-mimetics on histaminergic activity in the mouse brain was investigated. Systemic administration of muscimol (2 and 5 mg/kg), THIP (5–15 mg/kg) and aminooxyacetic acid (AOAA) (25 mg/kg) but not baclofen (2.5–15 mg/kg) inhibited the pargyline (65 mg/kg)-induced accumulation of tele-methylhistamine (t-MH). There was no regional difference in the inhibitory effect of muscimol on the t-MH accumulation by pargyline treatment. Muscimol and AOAA also inhibited decrease in the histamine (HA) level induced by α-fluoromethylhistidine (50 mg/kg), a specific inhibitor of histidine decarboxylase. These results suggest that these GABA-mimetics reduce the HA turnover in the mouse brain.