Cholinesterase activity of capillaries in the rat brain. A light and electron microscopic study

Synopsis The presence of cholinesterase activity in association with capillaries of the central nervous system was investigated in the rat by means of both light and electron microscopic methods. Throughout most of the rat brain, the smaller blood vessels stain intensely for butyrylcholinesterase activity. In some areas, such as the commissural nucleus of the vagus and parts of the medial thalamus, the capillaries possess both acetylcholinesterase and butyrylcholinesterase activity. Blood vessels in those structures which lie outside the blood-brain barrier are completely devoid of cholinesterase activity. The electron microscope reveals that reaction product occurs within the matrix of the basement membrane, in the intermembranous space of the endothelial nuclear envelope and occasionally in the endothelial granular endoplasmic reticulum. It is suggested that the presence of cholinesterase within the basement membrane of brain capillaries is evidence of the role that the basement membrane may play in transfer mechanisms.     

Scanning electron microscopic study of the freeze-fractured pineal body of the rat

Summary The three-dimensional ultrastructure of the pineal body of the rat is described on the basis of freeze-fractured preparations. The pineal capsule consists of irregular cells with very flat and perforated processes. Through these openings, extremely branched canaliculi, extending to almost every pineal cell, communicate with the tissue compartment outside the organ. The pericapillary spaces contain, in juxtaposition with capillaries of the fenestrated type, nerve fibers as well as a flocculent granular and filamentous material of unknown origin and chemical nature.With the technical assistance of Mr. P.-A. Milliquet     

Embryonic development of the heart. I. A light and electron microscopic study of myocardial development in the early chick embryo

Embryonic chick myocardium (stages 8+ to 12?) was studied by light and electron microscopy. The myocardium, which is initially comprised of radially oriented cells with large intercellular spaces gradually becomes more tightly packed. Intercellular spaces decrease and the cells assume a circumferential orientation. Myocardial cells remain epithelial throughout formation of the functional tubular heart and specialized epithelial junctions (apical junctional complex or terminal bars) undergo modification to form intercalated discs. Embryonic myocardial cells contain large amounts of free ribosomes and particulate glycogen, the latter often associated with portions of granular reticulum. Unlike developing skeletal muscle. The amount of granular reticulum contained in the myocardial cell cytoplasm is large and, along with a hypertrophied Golgi apparatus, suggests that these cells may have a secretory function. These organelles persist during the initial period of fibril formation. Myofibrils apparently form from non filamentous precursor material and not by alignment of sequentially synthesized components.     

Substance P-like immunoreactivity in rat and cat carotid bodies: light and electron microscopic studies

Substance P-immunoreactive (SP-1) structures in the carotid bodies of rats and cats were examined with the light and electron microscopes. In both species SP-I varicose nerve fibers were located singly in the interstitial connective tissue in close association with blood vessels. They were small unmyelinated fibers enveloped in a common Schwann cell sheath with other SP-negative fibers. Some of SP-I fibers contained large dense-cored granules and small clear vesicles in addition to microtubules and mitochondria and probably represented nerve fiber varicosities. The latter often were found incompletely invested by Schwann cell sheaths. SP-fibers were found occasionally in the envelopes of supporting cells at the periphery of parenchymal cell groups. However, none of the nerve terminals making synaptic contacts with glomus cells exhibited SP-like immunoreactivity. In cat carotid bodies some glomus cells showed moderate to intense SP-like immunoreactivity. The intense SP-I glomus cells displayed numerous dense-cored vesicles of 85 to 140 nm in diameter and frequently showed synaptic contacts with SP-negative nerve terminals. In rat carotid bodies we were unable to detect consistent SP-immunoreactivity in glomus cells. Our results do not favor the hypothesis that SP is a neurotransmitter/modulator in the chemoreceptor afferents synapsing on glomus cells in either the cat or rat carotid body. However our results support the hypothesis that SP in cat glomus cells may play a role in the modulation of chemoreceptor activity.     

A scanning electron microscopic study of rat Masugi nephritis.

Changes in the glomerular capillaries in the first phase of rat Masugi nephritis were studied by scanning electron microscopy. The changes developed immediately after the injection of nephrotoxic rabbit IgG and early endothelial lesions (2 to 6 h) were characterized by an increase in microvilli and a decrease in endothelial pores. The microvilli were fused and produced abundant pored projections (cytofolds). The peripheral endothelium was then lifted off from the glomerular basement membrane (GBM), leaving scattered endothelial fragments on the GBM. The denuded GBM exhibited a rather uniform, thick carpet-like appearance with occasional crater formation. Depositon of fibrin strands was seen associated with endothelial exfoliation. These later dissolved and were converted to a fibrinoid material, consisting of a complex of fragmented, thin fibrils. A parallel study using the electron microscope revealed that the fibrinoid material was removed by emigrating monocytic macrophages. At the stage of resolution (24 to 72 h), the denuded GBM was covered mostly with a regenerating endothelial layer. A possible process of reorganization of the endothelial pores is discussed.     

A light and electron microscopic study of osteodentin formation in the rat incisor after adriamycin administration

The effect of adriamycin (10 mg/kg body weight) on the rat incisor was investigated in 8-day-old animals at 9 days and 14 days after subcutaneous injection. The drug produced changes that were still present 14 days after administration. During this time osteodentin formation, which appeared to be the principal effect of the drug on the incisors, occurred to such an extent that in some regions of the teeth the pulp chamber was almost completely occluded. The formation of osteodentin began at the periphery of the pulp and gradually advanced towards the central region. Moreover, in some sections of the incisor the dentin layer was greatly reduced to a thin superficial layer, while osteodentin surrounded most of the pulp chamber. Cells that appeared to be differentiated pulp-mesenchymal cells were found within as well as on the surface of the irregular osteodentin matrix. Since this drug has been used in the treatment of childhood osteosarcomas, the possibility of dental abnormalities developing in these children cannot be overlooked.     

A light and electron microscopic study of the pre- and postnatal development and secretory differentiation of the pars tuberalis of the rat hypophysis

Summary The development of the pars tuberalis was studied in the rat fetus from 13 days of gestation to 6 weeks after birth. After the closure of Rathke's pouch, the pars tuberalis anlage is clearly distinguishable from the anlagen of the partes intermedia and distalis. It comprises the entire basal portion of the adenohypophysial anlage; the limit between the anlagen of the pars tuberalis and the pars distalis is defined by Atwell's recess, i.e. the pathway taken by the hypophysial vessels coming from the vascular plexus of the median eminence.At 14 days the pars tuberalis cells are characterized by the presence of glycogen which persists in the adult. Their secretory differentiation (elaboration of granules with a diameter of 100–120 nm) is obvious at 15 days of gestation. It therefore, clearly precedes that of the other hypophysial cell types. Its functional differentiation takes place well before its adhesion to the primary vascular plexus of the portal system. Cystic formations appear just before birth in the pars tuberalis, much later than those of the pars distalis.These observations on the development of the pars tuberalis, together with previous observations on the adult PT in various species, showing that the specific glandular cells of the pars tuberalis are cytologically different from all known adenohypophysial cell types, seem to indicate a specific endocrine function of this lobe.     

A light and electron microscopic study of spinal ligament innervation

The innervation of the posterior ligamentous structures of the human lumbar spine was studied by light microscopy, scanning electron microscopy and transmission electron microscopy. Three types of nerve endings were recognized: free nerve endings, Paciniform corpuscles and Ruffini corpuscles. The free nerve endings, which are thought to act as nociceptors, were found in the superficial layers of all ligaments. A few free nerve endings were also identified within the supraspinous and interspinous ligaments. The Paciniform corpuscles were predominantly found in the supraspinous ligament. The Ruffini corpuscles were located in the interspinous and flaval ligaments. These findings suggest that the posterior ligamentous structures could be involved in the spinal control system.     

A light and electron microscopic study of the embryonic chick otocyst. The effects of trypsin and Ca- and Mg- free salt solution.

A light and electron microscopic examination of the embryonic chick otocyst compared with the otocyst treated with trypsin and Ca- and Mg-free Hanks' solution (HBSS), care being taken not to disrupt or dissociate, has been done. This study was restricted to the “pseudostratified” epithelium in the medioventral portion of the otocyst which develops into the sensory epithelia of the inner ear. It was shown that the pseudostratified epithelium contained groups of epithelial cells with mature intercellular connections composed of an apical junction and an intermediate junction frequently associated with one or more fully formed desmosomes. The cohesive property of the apical junction was demonstrated in the trypsin-treated otocyst; apical junctions remained adherent while desmosomes were altered and the intercellular space of some of the intermediate junctions was increased. The groups of cells contained cells with a cilium and cells undergoing mitosis. The evidence obtained in this study strongly suggested that these groups of cells were undergoing cytodifferentiation and acted as “foci” of cells with the structural competence to respond to stimuli and to participate significantly in the mechanisms involved in the movement, localization and cytodifferentiation of presumptive sensory epithelia of the inner ear.