Motor habituation in the DHT model: bin analysis of daytime and nocturnal locomotor activity

We evaluated the usefulness of locomotor bin analysis as a measure of motor habituation, and the effects on habituation of serotonergic manipulations. Spontaneous and L-5-hydroxytryptophan (5-HTP)-evoked locomotor activity (LMA) was measured by photocells and computer-tabulated at 10 minute intervals (bins) during the day and at night in 150 adult rats treated intracisternally with 5,7-dihydroxytryptamine (DHT) or vehicle. Bins were analyzed by visual inspection, which differentiated decremental, incremental, continuous, and discontinuous patterns, and by calculating the ratio of the first to last bin of an hour. In controls, bin ratios were high due to rapid decline (decremental bin pattern) of daytime LMA. After DHT lesions, in contrast, ratios were low for one week. This was due to a failure of normal motor habituation, as reflected by an increase in continuous, discontinuous, and incremental bin patterns. 5-HTP evoked similar dose-related bin abnormalities in DHT-treated rats, after spontaneous patterns had returned to normal, and to a lesser extent in controls. However, no consistent drug or lesion effects on nocturnal LMA were seen. In comparison to daytime LMA, nocturnal LMA showed less habituation, and bin patterns were predominantly of the discontinuous type and more varied. These data suggest that bin analysis contributes useful information on motor habituation and drug and lesion effects and is easily incorporated into automated recording of LMA.