Changes in ambulatory activities and muscle relaxation in rats after repeated doses of diazepam

Changes in rat ambulatory activity and muscle tone after diazepam treatments (2.5, 5, 10, and 20 mg/kg orally) were compared under single and repeated (for 2, 4, 7, and 14 days) administration schedules. Ambulatory activity in the open field test was enhanced by a single dose of 2.5 mg/kg and reduced by 20 mg/kg. However, after all repeated treatment schedules, diazepam resulted in dose-dependent elevations of activity. Even with a treatment period of only 2 days, 20 mg/kg diazepam produced a marked increase in ambulation, which became more conspicuous with increases in the treatment periods. Acutely administered diazepam produced a dose-dependent reduction in muscle tone, but tolerance was noted to this effect during repeated administrations. Thus, time- and dose-dependent increases in ambulation during repeated treatments with diazepam can be partially explained by time-dependent tolerance development to its muscle relaxant effects. The enhancement in ambulation after short-term repetitive dosings of benzodiazepines can be used as a simple indicator for detecting their disinhibitory potentials.