PRENATAL PROTEIN RESTRICTION ALTERS SYNAPTIC MECHANISMS OF CALLOSAL CONNECTIONS IN THE RAT VISUAL-CORTEX

Mild prenatal protein malnutrition, induced by reduction of the casein content of the maternal diet from 25 to 8%, calorically compensated b y the addition of excess carbohydrates, leads to so-called ''hidden'' malnutrition in the rat. This form of malnutrition results in normal b ody and brain weights of pups at birth, but in significant alterations of their central nervous system neurochemical profiles. Since severe forms of prenatal malnutrition induce morpho-functional deficits on ca llosal interhemispheric communication together with brain neurochemica l disturbances, we evaluated, in rats born from mothers submitted to a n 8% casein diet, the potassium-induced release of [H-3]-noradrenaline in visual cortex slices, as well as functional properties of callosal -cortical synapses by determining cerebral cortical excitability to ca llosal inputs and fatigability and temporal summation of transcallosal evoked responses. Rats born from mothers submitted to a 25% casein di et served as controls. At birth prenatally malnourished pups had signi ficantly higher cortical percent net noradrenaline release (14.79+/-1. 11) than controls (9.14+/-1.26). At 45-50 days of age, rehabilitated p reviously malnourished rats showed, when compared to controls: (i) sig nificantly reduced percent net noradrenaline release in the visual cor tex (4.50+/-0.52 vs 11.31+/-1.14); (ii) decreased cortical excitabilit y to callosal inputs as revealed by significantly increased chronaxie (607.2+/-82.8 mu s vs 351.3+/-47.7 mu s); (iii) enhanced fatigability of transcallosal evoked responses as revealed by significantly decreas ed stimulus frequency required to fatigate the responses (4.9+/-0.8 Hz vs 9.2+/-1.3 Hz); and (iv) decreased ability of callosal-cortical syn apses to perform temporal summation, as revealed by significantly redu ced percent response increment to double-shock (54.2+/-6.2 vs 83.0 +/- 11.0, for a 3.2-ms interstimulus time interval). These changes, resul ting from mild prenatal protein restriction, are discussed in relation ship to developmental processes leading to the formation of synaptic c ontacts between callosal axons and their appropriate cortical target d uring perinatal age. (C) 1998 ISDN. Published by Elsevier Science Ltd.