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A properly structured neuronal network, which is a prerequisite of a correctly functioning central nervous system, depends on the proper construction of synaptic terminals. There are some studies concerning development of hippocampal cells, however, the data about maturation of the synaptic terminals network within the hippocampal formation are only fragmentary. The study was performed on Wistar rats of various ages. The following synaptic proteins: synaptophysin, SNAP-25 and GAP-43 (a growth axon cone protein) were used to study the maturation of synaptic terminals. We have found that, at the time of birth, the hippocampal formation is very immature. Synaptogenesis begins on P4 and lasts till P10 or P14. The strongest immunoreactivity of all proteins is observed at the beginning of this period. Thereafter, immunoreactivity decreases and, after P14, it is similar to that of adult animals. On P60 and P90, the level of immunoreactivity increases again. In the pyramidal and granular cell layers, the formation of synaptic terminals and their maturation occur earlier in embryonal life, and are almost completely mature at birth.

Microtubules are present in high concentration in the nervous system and are a prominent component of the neuronal cytoskeleton. Microtubules are composed of tubulin and variety of microtubule-associated proteins (MAPs), which have been implicated in the regulation of microtubule assembly and function. MAP2 is the most abundant of these proteins, and it has been extensively characterized in various functional and pathological conditions. In the present study the distribution of MAP2 was examined in each layer of the CA1 and CA3 regions of the hippocampus proper and dentate gyrus in rat development. A total of 40 brains at various ages starting from postnatal day (P) 0 to P90 were examined. After perfusional fixation the brains were frozen and cut on the coronal plane and stained with either cresyl violet or standard immunohistochemical methods using the anti-MAP2 antibody. MAP2 exhibited a somatodendritic pattern of localization in cells of the hippocampus. Staining was most prominent in dendrites and perikarya as well as granules surrounding cell bodies. In a newborn rat's brain immunostaining was intense in granules and faint in perikarya. Between P4 and P21 immunostaining density for MAP2 was stronger and appeared in perikarya, granules, and dendritic trees. After P21 the perikarya and dendrites of the pyramidal layer and stratum radiatum of the hippocampus proper, as well as the molecular and granular layer of dentate gyrus, showed reduced immunoreactivity. In the stratum oriens of the hippocampus and polymorphic layer of the dentate gyrus immunoreactivity was still strong until P90.

The connections of the amygdaloid body with the areas of the limbic cortex in the rat were studied by means of the method on the axonal retrograde transport of the fluorescent tracer FluoroGold. The tracer was injected into the anterior and posterior limbic cortices (cingulate gyrus, granular and agranular retrosplenial area, respectively. The localization of the corresponding amygdalar projection zones was investigated and the semiquantitative analysis of the connections was conducted. The projection zones in the rat amygdaloid body are organized topographically. Administration of the fluorescent tracer to the anterior and posterior part of the limbic cortex in the rat (cingulate gyrus and both retrosplenial areas, respectively) reveals labeling of cells only for injections to the former one. The labeled cells were present only in the major components of the basolateral amygdaloid complex. The main source of this projection was anterior part of basolateral nucleus (BLA). Some labeled neurons were found in the lateral nucleus and few in the ventral part of basolateral nucleus. No labeled cells were found within the basomedial nucleus.