Pineal gland post-natal growth in rat revisited.

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.

Influência da melatonina sobre o desenvolvimento corporal e ósseo de ratos / Ineluence of melatonin on body and bone development of rats

Objetivo: A glândula pineal produz o hormônio melatonina (MLT), que apresenta efeitos demonstrados sobre diversas células, entre elas os adipócitos e osteoblastos. Este trabalho objetivou verificar a influência da MLT no crescimento e desenvolvimento corporal e ósseo em ratos. Método e Resultados: Ratos Wistar machos foram submetidos a pinealectomia (PINX) ou cirurgia fictícia (CONTR) aos 5 dias do nascimento e estudados quanto ao peso e comprimento corporal; comprimento, espessura da tábua óssea e do disco epifisário da tíbia após 10, 20, 30, 60, 90 e 120 dias da operação. O peso dos animais PINX foi maior que o dos CONTR aos 100 e 120 dias. Os animais PINX tiveram ainda menor espessura da tábua óssea aos 60, 90 e 120 dias e menor espessura do disco epifisário, aos 90 e 120 dias após o procedimento cirúrgico, comparados aos animais CONTR. Conclusões: A falta de MLT resultou em aumento do peso corporal, provavelmente pela maior captação de ácidos graxos pelos adipócitos e redução da termogênese: menor espessura da tábua óssea e disco epifisario da tibia pela redução da atividade de condrócitos e osteoblastos. Estes efeitos poderiam ser diretos e/ou indiretos, e seu esclarecimento demanda mais estudos.

Five days old Wistar male rats were either pinealectomized or submitted to a sham operation. The animals were followed up to 120 days after surgery, being weighed and measured every 10 days. Groups of animals were then sacrificed at 10, 20, 30, 60, 90, and 120 days after the surgery. Thicknesses of the bone board and the epiphyseal plate of the tibia were measured. Results: (1) The average weight of the pinealectomized animals was greater than that of the control animals between 100 and 120 days after surgery; (2) There was no difference between the groups in the lengths of the body and of the back paw of the animals; (3) The length of the tibia was the same in both groups but the thickness of bone board after 60, 90, and 120 days of the surgery and the thickness of the epiphysial plate after 90 and 120 days of the surgery were smaller in the pinealectomized animals when compared with the control groups. Conclusion: the pineal gland, through the secretion of melatonin, participates in the bone development in rats by unknown mechanisms.

A light- and electron-microscopic study of the pineal complex of the ammocoete larva of the southern lamprey Geotria australis.

The pineal complex of larval Geotria australis lampreys has been examined by light- and electron-microscopy. The complex consists of a pineal organ and a smaller parapineal organ, the former being situated dorsal to the latter. It is concluded that the pineal organ is a functioning photoreceptor, with neural and endocrine output. The parapineal appears to be a more basic neuroendocrine organ without photosensory capability. Day-night comparisons of the pineal complex show no obvious differences in ultrastructure; this could be related to the chronobiological role of the complex as a constant monitor of ambient light levels, rather than a mere visual receptor that changes its sensitivity at night.

The structure and development of the pineal complex in the lanternfish Triphoturus mexicanus (family mycotphidae).

The pineal complex of the lanterfish Triphoturus mexicans was studied by light and electron microscopy. Receptor, supportive and ganglion cells were identified in the pineal end-vesicle. The presence of receptor cells and the prominent pineal window strongly suggest a photoreceptor function. Numerous unmyelinated nerve fibers were also found in the end-vesicle. These converge to form part of the pineal stalk. Two kinds of cells (Types I and II) were distinguished in the dorsal sac, which is very well developed. Type I cells are non-ciliated ependymal cells and contain large parcels of glycogen. Type II cells contain large lipid-like inclusions and a distinct band of filaments around the entire periphery of the cell. Receptor cells appear very early in the development of T. mexicanus. They seem to originate from ependymal cells lining the roof of the third ventricle.