Introduction: 

Sex steroids are crucial for the ontogenesis of sexually dimorphic behaviours. In particular, in laboratory rodents the aromatization of testosterone into estradiol at the central level is necessary for the masculinization of brain and behaviour. In the rat the temporal window for the organizational action of sex steroids is mainly the perinatal period. However, some plasticity is still present even during the prepubertal period (Della Seta et al., 2006).

Aim: 

In the present work we studied the effects of the prepubertal administration of the aromatase blocker, anastrozole, on juvenile play behaviour of male rats, a good predictor of adult social behaviour.

Methods: 

We treated 3 groups of prepubertal rats - from 23 to 32 days of age - as follows:

a) anastrozole, 50 mg/day in 100 ml 20% sucrose solution (per os) and placebo pellets; b) positive control, anastrozole 50 mg/day and 3,5 mg/day 17ß estradiol, slow release pellets; c) negative control, sucrose solution and placebo pellets. At 45 days of age play behaviour of juvenile rats was observed in their home cage and videorecorded for 10 min. Behavioural analysis was carried out using Noldus Observer software on the basis of an established ethogram (Poole and Fish, 1975; Dessì-Fulgheri et al 2002).

Results: 

By means of a PCA analysis 2 main factors were identified, explaining 41.1% of total variance. 1, social play (23.7%); 2, exploration (17.4%). The analysis revealed that: a) hormonal manipulations in the prepubertal period may have long term effects; b) only one group of behaviours (factor 1) is influenced by anastrozole i.e. social play, and the effect is, contrary to our expectation, an increase of aggressive components of play. As far as point a) is concerned, our results confirm that the organization window for sex steroids is open until puberty. For point b) our hypothesis is that the blockage of the aromatase pathway may enhance the alternative 5a-reductase pathway, resulting in an increase of 5a-dihydrotestosterone at the central level. This is in line with Meaney (1988) who observed an increase of play fighting after DHT administration.

Conclusion: 

In summary, the results of the present experiment prove that the organization of male play behavior may still be influenced by the alteration of the estrogenic milieu, well beyond the perinatal period.