A SUPPLEMENTAL MEASURE OF STAY-TIMES IN THE LIGHT BOX ON STEP-THROUGHPASSIVE-AVOIDANCE

The avoidance behavior of rats in a typical step-through passive avoid ance task was evaluated by using two types of time measurements that d iffered from traditional step-through latency (STL). The total stay-ti me in the light box (TL) was calculated as an index of the dark box av oidance throughout the retention trial, counting the time before and a fter the first step-through. The total stay-time in the far area of th e light box (TF) was calculated as an index of the tendency to keep aw ay from the dark box. TL, TF and the STL increased with electrical sho ck intensity at acquisition trials and gradually decreased through an extinction procedure. The discrepancy between our new measures and the STL was observed when the effects of a new drug, RS-8359, which was r eported to ameliorate ischemic brain damage, were examined in ischemic animals. TL, TF and STL decreased in rats receiving brain ischemia, a nd we found that after treatment with RS-8359, TL and TF increased, bu t no effect was observed on STL. The discrepancy observed suggests tha t a short STL does not necessarily imply a loss of avoidance behavior. Passive avoidance tests can be more revealing about a drug's effects when stay-time measures are used.