Dorsal lesions of the septum influenced the maternal behaviour of Wistar and Long-Evans females, as well as of their hybrids, in a different way. The phenomenon of infanticide appeared in Wistar females only, whereas mothering was not impaired in others. However, the mouse-killing activity was not enhanced in Wistar females displaying infanticide. On the contrary, they exhibited xenoparental behaviour. If these females had grown up in a species-typical environment, characterized by enriched social stimulation during their critical developmental period, no impairment of maternal behaviour following dorsal septal lesions occurred. The ablation of the whole septum caused a break-down of maternal behaviour with the appearance of infanticide in all females regardless of their stock origin and their individual life history. The specific role of the septum in the control of maternal behaviour is discussed.
The relationship between milk fat concentration and the growth of rat pups from birth to the 20th day was investigated. A total of 36 first-time-lactating Wistar rats and 366 pups from litters of 8-12 were used. The concentration of milk fat was determined by the crematocrit method, on the 2nd, 5th, 10th, 15th, 20th and 25th day of lactation. A wide range of milk fat concentration with a great variability in each individual dam was observed during lactation. To correlate milk fat and pup's growth, the mean value of the milk fat of the individual mothers was calculated for the first 10 days from the values of the 2nd, 5th and 10th day of lactation, and for the second 10 days from the values of the 10th, 15th and 20th days. The results show that pups fed higher fat milk in the first 10 days of life grew faster than pups fed lower fat milk. A significant positive correlation (P<0.001) was found between the fat concentration of milk and the weight gains of pups in the first 10 days, but not in the older groups. It indicates that the fat concentration of milk is important for the growth of pups mainly in the early postnatal period of life.
The influence of estradiol and testosterone on body growth of young male Wistar rats was investigated. In the first experiment, estradiol was given to intact ad libitum fed male rats at 32, 37 and 42 days of age. Moreover, two untreated groups of animals were used: one was fed rcstrictedly according to the food intake of animals receiving estradiol and another was fed ad libitum. The animals were sacrificed at 47 days of age. Both untreated groups of animals achieved significantly higher body weight and length of tibia than estradiol treated animals. Also the growth of the tail of untreated animals was more intensive than that of estradiol treated animals. In the second experiment, estradiol was given to intact ad libitum fed male rats at 30, 35 and 45 days of age. Moreover, testosterone was given to a half of these animals at 45, 50 and 55 days of age. The animals were sacrificed at 60 days of age. Administration of testosterone significantly increased the growth of the tail and tibia in comparison to the animals which did not receive testosterone after estradiol administration. The results of the present study show that the inhibitory effect of estradiol on body growth of young male rats is not only the result of decreased food intake and that testosterone can improve the skeletal growth of male rats altered by previously given estradiol.
The effect of oestradiol administration and restricted feeding on longitudinal tibia growth was investigated in immature male rats. The restrictedly fed animals had a significantly longer tibia, greater thickness of the growth plate, faster rate of longitudinal tibial growth as well as the greater rate of [methyl-3H]thymidine incorporation into the growth plate of the tibia compared with oestradiol-treated animals. The results indicate that, in immature male rats, exogenous oestradiol can decrease the longitudinal growth of the tibia (at least partly due to inhibition of cell proliferation in the growth plate) independently of its anorexic effect.