Congenital brain damage spares the basic patterns of parental behavior in affected mice

Pregnant albino mice were treated with 5-azacytidine so that the embryonic brains were affected late in their morphological ontogeny. The offspring showed retarded body growth and a conspicuous reduction in the size of the cerebral hemispheres as measured at the end of development. Histological alterations were found in the hippocampus and the cingulate cortex. No behavioral alterations were detected during development, with the exception of the hyperactivity which probably caused the better performance of treated offspring observed in a self-feeding test. This functional abnormality, attributed by previous authors to retardation in telencephalic development, persisted into adulthood. The parental behavior of virgin females towards a weak stimulus-object was robust. Treated subjects were non-neophobic, seldom aggressive and showed clearcut parental responses. In addition, although the frequency of overall parental tendency was lower in the treated subjects, it gradually approached that of the controls across repeated trials. The brain structures affected by this treatment seem influential on behavioral organization and habituation to novelty, not on basic patterns of behavior, which are probably rooted in phylogenetically more ancient structures.