STRUCTURE OF THE RATS BEHAVIOR IN THE HOT PLATE TEST

The objectives of the study were: (i) to elaborate an ethogram of the rat's behaviour during the hot plate test, (ii) to analyse the rat's r esponses to the nociceptive heat stimulus by using ethological techniq ues, and (iii) to discern the suitable pattern or patterns to evaluate the rat's reaction to the noxious stimulus. Male Wistar rats (n = 30) were employed, and one hot plate test was carried out for each rat. T he platform (Socrel DS37) was maintained at 55.0 +/- 0.5-degrees-C, an d the exposure time was 45 s. Behaviour was videotaped and analysed by an ethogram and a software package. Every pattern parameter (frequenc y, duration and latency for the first occurrence) was quantified. Clus ter and Markovian analyses were also employed, whereby a dendrogram an d a Markov chain were obtained, respectively. The ethogram was compose d of twelve patterns: immobile-sniff, walk-sniff, rearing, forepaw-lic king, hindpaw-licking, face-washing, body-cleaning, stamping, hindleg- withdrawal, leaning posture, jumping off, and freezing. Cluster analys is indicated that the most frequent patterns could be classified into three categories: sniffing responses (immobile-sniff, walk-sniff), pri mary noxious-evoked patterns (forepaw-licking, hindpaw-licking, stampi ng), and escape noxious-evoked responses (leaning posture, jumping off ). Hindleg-withdrawal would be an independent noxious-evoked pattern, and freezing an alerting behaviour. The ethological information could be useful to better elucidate effects on rats' behaviour of drug treat ment or other phenomena during the hot plate test.