COMPARISON OF THE BEHAVIORAL AND ENDOCRINE RESPONSE TO FORCED SWIMMING STRESS IN 5 INBRED STRAINS OF RATS

Some inbred strains of rats showed behavioural differences in the forc ed swimming test, which is considered a putative animal model of depre ssion. In the present work, the behavioural and physiological response s to forced swimming were studied in male and female rats of five inbr ed strains of rats: Brown-Norway (BN), Fischer 344 (FIS), Lewis (LEW), Spontaneously Hypertensive (SHR) and Wistar-Kyoto (WKY). Physiologica l measures were aimed at characterizing emotional reactivity, a very i mportant issue which has usually been approached by studying a single endocrine system, and its relationship to the forced swimming behaviou r. The four indices of reactivity to stress used were serum glucose, A CTH, corticosterone and prolactin. No behavioural differences between sexes were observed in the forced swimming test. In addition, BN and W KY rats showed passive behaviour compared with the other three strains , the FIS strain being the most active. Whereas only minor differences were found in the resting levels of the variables studied with regard to either sex or strain, pituitary-adrenal (PA) and glucose responses to 15 min forced swimming differed among sexes and strains. Stress-in duced hyperglycaemia was lowest in WKY and highest in SHR, being lower in females than in males. The lowest ACTH and corticosterone response s to forced swimming were observed in LEW and the highest in FIS. Fema le rats showed a clearly higher PA response to stress in all strains. Prolactin response to stress was very similar between sexes and strain s. It might thus be concluded that: (i) there are important inter-stra in differences in the forced swimming behaviour, with no differences b etween sexes; (ii) the various physiological indices of emotional reac tivity follow a different trend and no warranted conclusion on differe nces in emotional reactivity should be based upon a single endocrine s ystem or even only upon physiological measures; (iii) we cannot be sur e, therefore, whether or not there are differences in emotionality bet ween the strains studied in spite of well-established inter-strains di fferences in the forced swimming behaviour.