The ultra-structural development of synapses in retino-receptive layers of the opossum superior colliculus was studied by the ethanolic phosphotungstic acid (E-PTA) method. There was a tendency for a slight reduction in the diameter of synaptic disks, a rise and fall of numerical densities and, except for an ephemeral period, a general increase in the proportion of "frown" among curve synapses. The lack of strict synchrony and the occurrence of different patterns of changes suggest that multiple factors contribute to synaptic maturation.

Lectins are proteins with binding sites that recognize a specific sequence of sugar moieties in complex glycoconjugates. In the present study the tomato lectin-Lycopersicon esculentum (LEL) (a selective microglial and endothelial marker) has been reported to recognize specific residues of N-acetylglucosamine (GlyNAc) and poly-N-acetyllactosamine. In the pineal gland the biotinylated LEL was used to investigate the appearance of these sugar residues in the structures of the rats during their development and adult life. Our results showed that the binding of LEL occurred exclusively in the material adherents on surface of the endothelia of the vessels in the peripheral and central regions of the gland. An exception can be cited to rats in first postnatal day where the vessels in the central region did not display the LEL-reaction. In all animals studied and, from 3-postnatal day onwards the LEL-reactions could be observed within the central space of pseudo-rosettes also characterizing this space as a vessel.

We studied the pineal gland (PG) growth separating two critical moments of the rat post-natal development: the lactation and post-weaning periods. We studied 30 Wistar rats in the post-natal day - PN day 6, 10, 21, 45, 60 and 90 using light microscopy and quantitative methods (allometry and stereology). We estimated the PG volume (using the Cavalieri's principle) and the number of pineal gland cell nuclei (PGCN, using the disector method). We analysed the correlation of the PG volume (y) versus brain weight (x) in the different age groups (the bivariate study used log-transformed data and the allometric model log y = log a + b log x). The PG growth gradually decelerated in older rats than in younger rats. The major increment of the PG growth was observed between PN day 6 and PN day 10, while the minor increment was observed after weaning between PN day 45 and PN day 60. After 60 days of age differences were no more observed. The relative growth of the PG was allometrically positive in all age groups, and growth curves separated the lactation from the after weaning periods. The number of PGCN of rat continuously increased during post-natal life and differences between the lactation and after weaning periods were significant. It is possible that the supporting cells, fibres and new synapses are responsible for that PG late post-natal increase.

The maturation of the neuropil and synapse formation were examined in the retino-receptive layers of the superior colliculus (SCr-r) in the opossum from a period prior to the onset of arborization of retinocollicular fibers (postnatal day 22 – P22), at 44% of the coecal period (CP), to the end of the fast phase of optic fiber myelination and weaning time (P81 – 118% CP). Development of the SCr-r neuropil follows a protracted time course and can be divided into three broad stages, which are characterized by (I) Large extracellular spaces, numerous growth cones that participate rarely in synaptic junctions, vesicles-poor immature synapses (P22–P30), (II) Synapses of varied morphology with abundant synaptic vesicles, and small terminals with dark mitochondria and round synaptic vesicles (RSD terminals) synapsing mostly onto dendritic shafts, flat-vesicles (F) terminals (P40–P56), (III) Sequential appearance of retinal (R) and pleomorphic-vesicles (P) terminals and of RSD terminals synapsing onto spine or spine-like processes, appearance of glomerulus-like synaptic arrays (synaptic islets) (P61–P81). The advancement of synaptogenesis in SCr-r from stage I to II and from stage II to III correlates closely with the differentiation of astrocytes and oligodendrocytes, respectively.