[Comparative quantitative study on brains of wild and laboratory rats. I. Comparison of volume of total brain and...

The intraspecific allometric relation between brain weight and body weight of wild Norway rats and laboratory rats was gained from sufficient material. The intraspecific allometry exponent a=0.25, being typical for mammals, also came out as a result for Norway and laboratory rats. But laboratory rats have 8.3% less brain substance at a comparable body weight. This decrease in brain size was interpreted as an adaption to the specific conditions of domestication and discussed accordingly. Futhermore the fresh volumes of the fundamental brain parts telencephalon, diencephalon, mesencephalon, cerebellum, medulla oblongata, neocortex, corpus striatum and allocortex were ascertained by means of serial sections of 8 Norway and 8 laboratory rats, and they were compared with each other by their average brain proporationing. Consequently, differently strong reduction intensities in the sizes of these brain parts from 1.6% (medulla oblongata) to 12.5% (neocortex) became evident. The high reduction values of corpus striatum (10.9%) and cerebellum (10.3%) were especially remarkable. They almost reached the same degree as the forebrain (10.6%). The size reduction of the measured brain parts of rats, caused by domestication were compared with the results of other domestic mammals and discussed accordingly.