Search

Quantitative ultrastructural technique were employed to compare the development and maturation of cortical synapses in rats subjected to protein deprivation, control diet, nutritional rehabilitation and a normal-low crossover diet. Osmicated preparations of the molecular layer of occipital cortex were prepared at 15, 20, 28, 75 and 224 days postnatal in male rats. At 15 and 30 days the values for mitochondrial and synaptic densities, vesicle number and packing per terminal, synaptic length, terminal area and brain weight were lower in the protein-deprived than in the control animals. These initial deficits were progressively transformed to excesses, with the most marked crossover period occurring between 20 and 28 days. By 224 days only brain weight and presynaptic terminal area were lower in the protein-deprived material. A further parameter, synaptic curvature, showed a decrease in negativity in protein-deficient junctions between 15 days (64%) and 224 days (41%). Well-nourished tissue had fewer negatively-curved synapses during early development. These data suggest that the morphological development of the presynaptic terminals is not simply delayed, but is ultimately different in the protein-deprived animals. The nature of these changes may facilitate an adaptation to provide more efficient functioning in the adverse condition. Nutritionally rehabilitated tissue ultimately approaches the control, although significant differences occur in synaptic and mitochondrial densities and in brain weight. The normal--low crossover procedure intensities the differences noted in animals subjected to continuous deprivation.

The development and maturation of synapses in the molecular layer of the occipital cortex of rats at 15, 20, 28, 75 and 224 days postnatal were examined and quantitative ultrastructural techniques were employed. The parameters evaluated display a diverse set of trends. A steady increase in mean terminal area is noted, the proportions of the smallest terminals declining progressively over this period. The mean length of the postsynaptic thickening fluctuates throughout the developmental series. A close association is found between terminal area and junction lengthlarger junction lengths being consistently associated with larger areas. Synaptic vesicle numbers within each terminal increase markedly between 15 and 28 days. There is an increase in the frequency of flat and positively curved junctions with increasing age, the bimodal distribution of negative and positive curvatures at 15 days being replaced by a normal distribution in the adult. When synaptic length is compared with curvature, flat junctions emerge as the longest and the most highly curved junctions as the shortest. The terminal areas of positive junctions are greater than those of negative ones. The consequences of these results for the flat disc model of synapses are discussed, and it is postulated that negatively curved synaptic junctions may be non-functional.