[The effect of diazepam on exploratory behavior and its strain differences in inbred rats]

The effect of diazepam on exploratory behavior was investigated in two inbred strains of rats, Fischer 344 (F344) and Lewis (LEW). The total numbers of head-dips and head-dipping duration in the rat hole-board test, and the total number of rearing and locomotor activity in the open-field test were measured after diazepam administration. The numbers of head-dips and rearings, and head-dipping duration and locomotor activity in naive F344 were significantly greater than those in naive LEW (P less than 0.001), suggesting that LEW is more emotional than F344. Diazepam, 0.31 and 0.63 mg/kg for F344 and 0.31-1.25 mg/kg for LEW, increased head-dips, head-dipping duration and rearings. However, there were no strain differences in enhancing effect of diazepam on locomotor activity. On the contrary, higher doses of diazepam, 0.94-2.50 mg/kg for F344 and 2.50 mg/kg for LEW, decreased head-dips, head-dipping duration, and rearings. However, the effect of diazepam on rotarod performance in LEW was similar to that in F344. These results suggest that F344 is more sensitive to sedative effect of diazepam than LEW, and that the sensitivity to diazepam may be strongly influenced by genetic factors.