ZINC-POSITIVE PRESYNAPTIC BOUTONS OF THE RABBIT HIPPOCAMPUS DURING EARLY POSTNATAL-DEVELOPMENT

The evolution of vesicular zinc-containing boutons in the developing r abbit hippocampus has been studied during early postnatal life using t he selenite-Danscher histochemical method. By P3, large immature messy fiber boutons with labeled synaptic vesicles were seen in the hilus o f the dentate gyrus and in the stratum lucidum of the CA3-CA4 hippocam pal areas. After P5, smaller boutons with labeled vesicles were identi fied in the stratum oriens and stratum radiatum of all hippocampal are as, and even transiently in the stratum lacunosum of P6 animals. Vesic ular zinc-containing boutons increased in number and underwent ultrast ructural maturation; light microscope densitometric-volumetric measure ments were used to quantify their presence in every hippocampal lamina . Electron microscope stereologic analysis permitted accurate estimati on of the actual numbers along early postnatal development. Three main phases of zinc-positive bouton growth were detected during the first postnatal month. The first phase, starting at P5, is characterised by an abrupt rise in vesicular zinc content which at P8-P9 begins to decr ease. The second phase is characterised by a consistent rise in vesicu lar zinc content from P10 to P12 to a level which is maintained until P18; this steady period is the result of partial and sequential elimin ation of zinc-positive boutons in some areas (i.e. oriens of CA3 by P1 1, radiatum of CA3 by P13, and radiatum of CA1 and lucidum of CA3 by P 15) while they continue to increase in other areas. The final phase is a continuous increase to almost adult levels. (C) 1997 Elsevier Scien ce B.V.