Real-time patterns of behavior following nociceptive stimulation in rats

Abstract

The hot-plate test is employed, in rodents, to assess the analgesic properties of drugs. The surface where the animal is placed is normally maintained at a constant temperature around 50°C or 55°C. For this reason rat’s behavior, once placed on the heated surface, can be observed only for few seconds, and a necessary interruption occurs following an a priori-established cut-off to avoid tissue injuries. Such a narrow time window dampened the assessment of fine behavioral characteristics such as the temporal structure of behavior. In the present paper we demonstrate the possibility to apply a refined multivariate approach, known as T-pattern analysis (TPA), to describe the temporal characteristics of the response to hot-plate test in Wistar rats. TPA is a multivariate technique able to detect the existence of statistically significant temporal relationships among the behavioral events in time. 4 groups of subjects administered saline or different doses of morphine have been analyzed by means of quantitative and t-pattern analyses. TPA demonstrated various and important structural changes of behavior: if on the one hand, 24 different temporal patterns have been detected following saline administration, morphine, at the doses of 3, 6 and 12mg/kg, induced a clear-cut and dose dependent reduction, with 5, 2 and 1 patterns detected, respectively.