Distribution and excretion of N-( 14 C)-methyl labelled m-hydroxybenzyltrimethylammonium ions in mice.

1. Radioactivity in the plasma, livers, and brains of mice was measured at intervals of 10 min to 24 h after the intraperitoneal injection of (14)C labelled m-methoxy- and m-hydroxy- benzyltrimethylammonium ions.2. Well over 10% of the dose of either of these quaternary compounds was found in the liver and plasma within 10 min of the injection, but they were rapidly excreted or metabolized, having a half life of between 1 and 2 hours.3. Small amounts of radioactivity were detectable in brain, and were not due to contamination of brain samples by blood, after doses of 14-16 mumol/kg (approximately 4 mg iodide/kg) and upwards. After doses of 4-6 mumol/kg (approximately 1 mg iodide/kg), however, radioactivity in the brain was barely detectable.4. Any behavioural effects reported to occur in mice treated with these lower doses of m-hydroxybenzyltrimethylammonium, which include improved performance in a test of avoidance learning, are unlikely to be due to an action within the central nervous system. Learning may be more influenced by the peripheral effects of drugs than has hitherto been appreciated.