J. Boya

Embryonic development of the pineal gland of the chicken (Gallus gallus).

A study of the embryonic development of the pineal gland of the chicken was performed with the optical microscope. The time of apparition of the first outline, as a derivative of the roof of the third ventricle, was fixed at 3 days. The major portion of the pineal parenchyma is derived from the frontal wall of the outline. All the vesicles and follicles were formed by solid mammilliform projections which subsequently presented a central lumen. In no case was a communication of the follicular cavities with the pineal recess observed. Three categories of vesicles or follicles can be distinguished according to their origin.

Ultrastructural study of the pineal gland of the chicken (Gallus gallus)

The authors studied the pineal glands of chickens (Gallus gallus) between the ages of 2 and 5 days with the electron microscope. They described two distinct areas in the parenchyma of the organ: the follicles, formed by two cellular categories, the pineal A and B cells, and the parafollicular zone, which surrounds and separates the follicles from the connective walls. This area is formed, fundamentally, by two types of cells and nerve fibers. These cells occasionally delimit cavities. We propound the hypothesis of the possible transformation of the parafollicular zone into follicles.

An ultrastructural study of the relationship between pericytes and cerebral macrophages

We studied, with the electron microscope, the normal cerebral cortex of white rats and zones adjacent to puncture wounds. The data obtained in this study, demonstrated the passage of pericytes to the nervous tissue, after the rupture of the basal membrane, and their transformation into macrophages. We suggest the possibility of the transformation of the pericytes into microglial cells.

Ultrastructural study of the post-hatching evolution of the pineal gland of the chicken (Gallus gallus)

There is a marked evolution in the ultrastructure of the chicken pineal gland after hatching. The typical large follicular cavities that are visible just after hatching disappear with age, giving the pineal a large number of small-caliber cavities which are practically filled by the prolongations of the pinealocytes. This gives the organ an apparently solid aspect. There are still two large cell types in the follicular wall: the A and B pinealocytes, with the B type being considerably more abundant.

Post-hatching evolution of the pineal gland of the chicken

The authors studied the evolution of the pineal gland of the chicken (Gallus gallus) from hatching until 34 months of age. They describe the progressive decrease of the follicular cavities and the appearance of solid-looking cavities. The stroma increases with age, dividing the pineal parenchyma into territories of small caliber.

Ultrastructure of the Rat Pineal Stalk

The ultrastructure of the rat pineal stalk was described. The pineal stalk contained few pinealocytes, glial cells and numerous nerve fibers. The last were mostly non-myelinated axons, although a few myelinated ones were also observed. Glial cells showed many filaments, mostly in the processes which presented a longitudinal orientation. Other more lamellar processes were found enclosing the axons. The pineal stalk became wider as it reached the body of the gland. Ultrastructurally, this wide region resembled more the pineal body. Bundles of non-myelinated nerve fibers were seen around the pineal stalk.

Development of the innervation in the chicken pineal gland (Gallus gallus)

The innervation of the pineal gland has been studied during the embryonic development and the first 10 days after hatching. On day 17 of embryonic development, the first nerve fibers are observed in the pineal capsule. They appear at the stalk level and rise to locate mostly on the anterior side of the capsule. Some nerve fibers leave these nerve bundles to penetrate the gland and they situate in the connective septa (18 days of development). From day 19 of development onwards, nerve fibers locate only in the parafollicular layer. Cells that may be identified as neurons are found in the pineal parenchyma.

Evolution and nature of the dense bodies in the chicken pinealocytes

The acid phosphatase reaction, applied to light and electron microscopy, was studied in the chicken pineal gland from the moment of hatching until 2 months of age. From the moment of hatching there is a great amount of acid phosphatase, which is mainly found in the vicinity of the lumen of both the recess and large follicles. Acid phosphatase is poor in the parafollicular layer. From day 30 onwards, there is an obvious fragmentation of the recess and of large follicles. Also, the parafollicular layer differentiates to form new follicles. The dense polymorphous bodies of the B pinealocytes are ultrastructurally identified as lysosomes.