Improved timed-mating, non-invasive method using fewer unproven female rats with pregnancy validation via early body mass increases

For studies requiring accurate conception-timing, reliable, efficient methods of detecting oestrus reduce time and costs, whilst improving welfare. Standard methods use vaginal cytology to stage cycle, and breeders are paired-up using approximately five proven females with proven males to achieve at least one conception on a specific day. We describe an alternative, fast, consistent, non-invasive method of timed-mating using detection of lordosis behaviour in Wistar and Lister-Hooded rats that used unproven females with high success rates. Rats under reverse lighting had body masses recorded pre-mating, day (d) 3–4, d8, d10 and d18 of pregnancy. Using only the presence of the oestrus dance to time-mate females for 24 hours, 89% of Wistar and 88% of Lister-Hooded rats successfully conceived. We did not observe behavioural oestrus in Sprague-Dawleys without males being present. Significant body mass increases following mating distinguished pregnant from non-pregnant rats, as early as d4 of pregnancy (10% ± 1.0 increase cf. 3% ± 1.2). The pattern of increases throughout gestation was similar for all pregnant rats until late pregnancy, when there were smaller increases for primi- and multiparous rats (32% ± 2.5; 25% ± 2.4), whereas nulliparous rats had highest gains (38% ± 1.5). This method demonstrated a distinct refinement of the previous timed-mating common practice used, as disturbance of females was minimised. Only the number required of nulli-, primi- or multiparous rats were mated, and body mass increases validated pregnancy status. This new breeding management method is now established practice for two strains of rat and has resulted in a reduction in animal use.

Hormone-driven mechanisms in the central nervous system facilitate the analysis of mammalian behaviours

Hormonal effects on behaviours in animals and humans are now well enough understood for general statements about causal steps to be proposed. Facilitation or repression of a given behaviour by a given hormone can depend on the person’s genetic and developmental history, on the temporal and spatial parameters of the hormone’s administration, on the hormone’s metabolism and on the specific receptor isoform available in a given neuron. The gene for oestrogen receptor-alpha is required for an entire chain of behaviours essential for reproduction, from courtship through maternal behaviours. In order to show that it is possible to use endocrine tools to explain a mammalian behaviour, we analysed lordosis behaviour neuronal circuitry as well as the molecular mechanisms of its facilitation by oestrogens. The functional genomics of oestrogenic effects on lordosis arrange themselves in modules for neuronal Growth, Amplification (by progestins), Preparatory behaviours, Permissive actions by hypothalamic neurons, and Synchronization of mating behaviour with ovulation (GAPPS). A related four-gene micronet involving the amygdala and the paraventricular nucleus of the hypothalamus supports social recognition. Underlying all sociosexual behaviour is the fundamental arousal of brain and behaviour. Elementary arousal depends on a bilateral, bidirectional system universal among mammalian brains, and it can be altered by null deletion of the gene for oestrogen receptor-alpha. Future molecular and biophysical studies will specify how hormone effects in the brain change central nervous system state in such a manner as to alter the frequencies of entire sets of behavioural responses.

Metabolism of dihydrotestosterone to 3α-androstanediol in brain and plasma: effect on behavioural activity in female rats

ABSTRACT Six experiments were carried out to determine whether dihydrotestosterone (5α-androstan-17β-ol-3-one; DHT) acts to inhibit oestradiol (OE2)-induced lordosis behaviour after its metabolic conversion to 5α-androstane-3α,17β-diol (3α-androstanediol, 3α-Adiol). In experiments 1 and 2, ovariectomized rats were treated with several doses of DHT or 3α-Adiol, injected with OE2 and progesterone, and tested for lordosis responsiveness. Significant inhibition of lordosis occurred after a dose of 3α-Adiol which was approximately threefold less than the effective DHT dose. In experiments 3 and 4, plasma concentrations of DHT and 3α-Adiol were measured after the injection of these steroids to ovariectomized rats at doses shown to be both sufficient or insufficient to inhibit lordosis. Behaviourally effective dosages of DHT and 3α-Adiol produced circulating concentrations of 3α-Adiol greater than those produced by behaviourally ineffective doses of DHT or 3α-Adiol. At 30 min after injection of DHT (experiment 3), 78·8% of plasma androgens were in the form of 3α-Adiol, while after injection of 3α-Adiol, only 7·4% were DHT. When plasma DHT and 3α-Adiol were measured at 3, 6, 9 and 12 h after steroid injection (experiment 4), plasma levels of 3α-Adiol produced by the behaviourally subthreshold dose of DHT were significantly lower than levels produced by behaviourally sufficient dosages of DHT or 3α-Adiol. In experiments 5 and 6, concentrations of DHT and 3α-Adiol were measured in five brain regions 1 and 6 h after injection of behaviourally sufficient doses of these steroids to ovariectomized females. At 1 h after injection, similar levels of DHT and 3α-Adiol were measured in DHT- and 3α-Adiol-injected females, and DHT concentrations in the preoptic area were significantly higher in both groups than in any other brain area. At 6 h, animals injected with DHT had significantly higher levels of DHT in all brain areas combined than did 3α-Adiol-or vehicle-injected animals. Brain concentrations of 3α-Adiol were not different between groups injected with DHT, 3α-Adiol or vehicle at this time. In brain, 34·6% of DHT had been converted to 3α-Adiol after 1 h and 53·0% of 3α-Adiol had been converted to DHT. These results suggest that the inhibitory action of DHT on lordosis may be a consequence of its conversion to 3α-Adiol, and that this conversion may account for the higher behavioural potency of the latter steroid. Journal of Endocrinology (1992) 134, 183–195