FETAL X-RAY EFFECTS: CEREBRAL CORTEX 



31 



changes in the neuronal packing density, increased fairly rapidly in controls 

 from the 1st to the 10th day and more slowly from the 10th to the 20th day. 

 Differences in values for the neuroglia/ neuron index between irradiated 

 and control groups were not significant at the 5-, 10-, and 20-day stages. In 

 the 300 r group, however, the neuroglia/neuron index in the 1 -day-old rats 

 is significantly higher ip < .05) than that in the non-irradiated rats of the 

 same age. In 20-day animals the value for the index in the 200 r group is 

 considerably higher than in the controls, but due to a large variance it is 

 not statistically significant at the 0.05 le\el. 



It is noteworthy that the levels for the neuroglia/neuron index at all ages 

 studied are very low as compared with adult values in some other species as, 

 for example, in man (1.78; Hawkins and Olszewski, 1957) or in the horse 

 (1.24; Friede, 1954), although the index is comparable in our 20-day 

 animals to the average values derived from Friede's data for the cerebral 

 cortex in the mouse (.35) and the rabbit (.42). 



Neuron nuclear, cytoplasmic, and soma (nucleus -\- perikaryon) volumes 

 (Fig. 3) increased steadily from the earliest to the latest stage examined with 

 the values in all groups in fairly close agreement. As in our preliminary 

 studies describing the 300 r group ( Brizzee ct oL, 1961), however, the 



1400 



1200 



:jlOOO 



^ 800 



o 

 > 



600 



6 400 

 cr 



3 



200 



I - CONTROL 

 A = lOOr 

 ° = 200r 

 300r 



10 

 AGE (DAYS) 



20 



Fig. 3. .\lterations in neuron soma volume in early postnatal stages. 



