Allometric characteristics of the developing inferior olivary nucleus of the kitten.

The allometric characteristics of the inferior olivary complex were studied in 13 kittens, which ranged in age from 39 to 125 days gestation (parturition = 62 days). The date of conception was known for 8 of the specimens whereas only the date of birth was known for the other 5 kittens. Each brain stem was serially sectioned and every tenth section was stained with cresyl-echt violet. The volume of the complete inferior olivary complex showed a curvilinear increase, with an 8% per day growth rate postnatally. The neuron diameter also showed greater increase postnatally. The diameter reached adult range by 1 month postnatally. The neuron population exhibited both prenatal and postnatal changes. There was a 35% cell decrease from 75,800 estimated cells at 49 days to 49,140 at parturition; this was followed by a 33% increase to 73,700 estimated cells by 73 days after which the population was within the adult range. The neuron density demonstrated more than a 70% decrease prenatally. This quantitative analysis of the kitten's inferior olivary complex indicates that a transient population of olivary neurons exists prenatally and that considerable maturation of olivary complex occurs postnatally.