GROWTH AND DEVELOPMENT OF THE BRAIN IN NORMAL AND HEAT‐RETARDED GUINEA‐PIGS

Abstract

Guinea‐pigs were exposed to a temperature of 41.5–42.5°C for 1h daily on days 20–23 of gestation. Fetuses from control and from heated mothers were studied at 30, 35, 41, 48, 55 and 62 days gestation and post‐natal offspring at 69, 76, 83, 90, 104, 118, 132, 146 and 160 days after conception. Body weights, whole and regional brain weights, and the dry matter, DNA (an index of cellularity) and cholesterol (an index of myelination) contents of these brain regions were measured. There was frequently a small but variable deficit in the body weight of heated offspring. A significant reduction of whole brain weight was found in the heated groups. The deficit in brain weight was detected 7 days after the heat‐stress and remained at about the same relative level until maturity. The DNA and cholesterol concentrations were the same in control and heated brains, but the absolute amounts were less in the latter which resembled proportional, normally shaped miniatures of the control brains. Hyperthermia is known to disrupt cellular proliferations, and since it was given during neurogenesis it is concluded that the size which might be attained by the brain is largely determined by the extent of early neuronal proliferation.