The pineal-paraphyseal complex of sea turtles. I. Light microscopic description

Histological reinterpretation of paraphysis cerebri in Ambystoma mexicanum

Intraventricular and extraventricular choroid plexuses are neuroepithelial folds which arise from the roof of the diencephalon. We describe the circumventricular structure of the diencephalon roof (paraphysis cerebri) during the various development stages of Ambystoma mexicanum. The parasagittal sections of the larvae epithalamus exhibit the presence, in addition to the epiphysis, of two dorsal primordia in nearby areas, which appear to be extraventricular saccular evaginations of different origin that give rise to two structures we define as the anterior extraventricular choroid plexus (AEP) and posterior extraventricular choroid plexus (PEP). During larvae development, the primordia arise perpendicular to each other, grow and show luminal folds and invaginations. Later, the two extraventricular evaginations, which are separate units, become interrelated. As the PEP grows, it covers the AEP dorsally, but it is difficult to define the borders of these organs. AEP is formed by alveolar-acinar epithelial aggregates with evidence of secretion-like content. PEP structure is like a choroid plexus, but its position is extraventricular and dorsal to the AEP. The PEP is always between the AEP and the meninges and can be small or large in size. This means that in A. mexicanum, the paraphysis cerebri is made up of two adjacent organs, which arise almost simultaneously from two different primordia (the AEP and the PEP) and as the posterior one grows, it overlaps the anterior one and masks itself. In conclusion, we suggest that AEP and PEP are homologous to paraphysis cerebri and the dorsal sac, respectively.

Microvascularization of the pineal gland in the freshwater turtle, Pseudemys scripta elegans (Reptilia): a scanning electron microscopic study of vascular corrosion casts

Gross supply, microvascular patterns, and drainage routes of the pineal gland and its vascular relations with associated structures (dorsal sac, paraphysis, choroid plexus of the third ventricle) were studied by scanning electron microscopy of microvascular corrosion casts in 10 specimens of the freshwater turtle, Pseudemys scripta elegans. Light microscopy of tissue sections (one transverse and one longitudinal series) served to attribute cast vascular territories to anatomical structures. The tubular pineal gland body is supplied bilaterally by small branches of the saccular artery, a branch of the lateral choroidal artery. Branches of the diencephalic artery supply the pineal stalk. The pineal gland microvascular bed is a two-dimensional network that embraces the tubular gland. The network is made up mainly of venules with few true capillaries. Venules draining the ventral surface of the pineal gland body join those coming from the choroid plexus of the third ventricle and drain into the sagittal sinus. The less dense vascular network embracing the dorsal surface of the pineal body drains directly into the sagittal sinus. The pineal stalk drains into the diencephalic vein or directly into the sagittal sinus. No efferent (venous) vascular connections capable as transport route for pineal secretions toward surrounding telencephalic, diencephalic, or mesencephalic areas were found.

Ultrastructure of the paraphysis in Bufo bufo larvae

A study of the ultrastructure and function of the paraphysis in Bufo bufo larvae was carried out. The structure is a tubular-ramified gland made up of numerous tubules with monolayered epithelial walls surrounded by connective tissue and sinusoids. The epithelial cells secrete glycoprotein to contribute to production of the cephalorachidian fluid. The role of the paraphysis in the transport of fluids and electrolytes from the blood to the cephalorachidian fluid in regulation of ionic and osmotic homeostasis is discussed.

Vascularization of the pineal complex in the lizard Tiliqua rugosa

The vascularization of the pineal complex in the lizard Tiliqua rugosa was investigated by vascular corrosion and latex casting techniques. The fine structure of the pineal capillaries was also studied by transmission electron microscopy. The pineal complex in T. rugosa consists of an elongated pineal gland proper and a separate, distinct parietal eye. The pineal complex derives an abundant blood supply from branches of the middle and posterior cerebral arteries. Scanning electron microscopy of vascular corrosion casts revealed a dense and extensive pineal capillary bed which drains ultimately into a wide longitudinal sinus suggesting an efficient pathway for the rapid removal of substances secreted by the gland. The parietal eye, which receives a unilateral left-sided blood supply from the unpaired anterior pineal artery, is shown to be a highly vascularized structure. The close morphological relationship between the pineal gland and dorsal sac, where the two structures apparently share the same blood vessels, suggests a functional relationship between them. The pineal capillaries are fenestrated with tight junctions between adjoining endothelial cells. Podia-like abluminal extensions of the endothelial cells were observed in close relation to unmyelinated nerve bundles. The basal margin of the pineal parenchyma is highly invaginated with thin finger-like cytoplasmic protrusions into the pericapillary space. Distinct bands of microfibrils form "struts" anchoring the pineal parenchyma to the endothelial wall. These features may have a role in the transfer of materials between the pineal gland and the blood stream.

Circadian rhythms in serotonin, norepinephrine, and epinephrine contents of the pineal-paraphyseal complex of the soft-shelled turtle (Lissemys punctata punctata)

Diurnal variations in pineal serotonin, norepinephrine, and epinephrine levels were measured at four different time intervals (06:00, 12:00, 18:00, and 24:00 hr) in adult male soft-shelled turtles. The serotonin level increased during day and decreased during night. But the norepinephrine and epinephrine levels showed reverse changes. The findings reveal that there is a distinct circadian rhythm in serotonin, norepinephrine, and epinephrine contents of the pineal-paraphyseal complex in adult male soft-shelled turtles.

Ultracytochemical localization of Ca++-ATPase activity in the paraphyseal epithelial cells of the frog, Rana esculenta

Ca++-ATPase activity was studied ultracytochemically (cf. Ando et al. 1981) in the paraphysis cerebri of the frog. An intense reaction was demonstrated on the plasmalemma of the microvilli at the apical pole of paraphyseal cells; in contrast, the basolateral plasmalemma showed only a slight staining. In addition, mitochondria, gap junctions, cilia, and cytoplasmic elements (e.g., microfilaments) displayed Ca++-ATPase activity. Variation of the Ca++-concentration in the incubation medium from 0.1 mM to 100 mM altered the Ca++-ATPase activity of the cell organelles. The substitution of Ca- by Mg-ions resulted in a conspicuous decrease in the enzyme activity, especially on the apical plasmalemma. Ca++-ATPase activity is claimed to be involved in a number of extra- and intracellular functions. In comparison to the epithelium of the adjacent choroid plexus the paraphyseal epithelial cell is thought to be a principal Ca-ion regulator of the cerebrospinal fluid in frogs.