Ultrastructural localization of ATPase activity in the dog area postrema

Endogenous electric currents might guide rostral migration of neuroblasts

Mechanisms that guide directional migration of neuroblasts from the subventricular zone (SVZ) are not well understood. We report here that endogenous electric currents serve as a guidance cue for neuroblast migration. We identify the existence of naturally occurring electric currents (1.5±0.6 μA/cm(2), average field strength of ∼3 mV/mm) along the rostral migration path in adult mouse brain. Electric fields of similar strength direct migration of neuroblasts from the SVZ in culture and in brain slices. The purinergic receptor P2Y1 mediates this migration. The results indicate that naturally occurring electric currents serve as a new guidance mechanism for rostral neuronal migration.

Autoradiographic localization of 3H-digoxin binding by neural cells in the medulla

The purpose of this investigation was to localize binding sites for the cardiac glycoside digoxin in the medulla of the rat in vivo. Adult male Sprague-Dawley rats were injected (IV) with 3H-digoxin and killed 30 minutes later. Autoradiographs of medullas showed evidence of 3H-digoxin binding to small- and medium-sized neural cells in the regions of the nucleus solitarius, dorsal motor nucleus of the vagus, area postrema, and in the zone between the area postrema and the underlying neuropil. However, the parasympathetic preganglionic neurons of the dorsal motor nucleus were not labeled. The 3H-digoxin-labeled cells in the medulla were located mainly in the commissural and medial portions of nucleus solitarius at the level of the area postrema. Animals injected with unlabeled digoxin followed by 3H-digoxin showed reduced binding of radioactivity. The small- and medium-sized neurons of the caudal portions of the nucleus solitarius are internuncial in position with respect to cardiovascular afferents of the glossopharyngeal and vagus nerves and sympathetic and parasympathetic cardiovascular efferent neurons of the medulla. The results of this study suggest that these 3H-digoxin-labeled cells, presumably neurons of nucleus solitarius, may possess high affinity binding sites for digoxin. Further, the area postrema, which lacks a blood-brain barrier, may provide a portal of entry for 3H-digoxin into regions of the medulla known to contain neurons that play a role in the regulation of cardiac rhythm.

Toxic effects of adriamycin on the central nervous system. Ultrastructural changes in some circumventricular organs of the mouse after intravenous administration of the drug

Recent experimental studies have shown that the cytotoxic antibiotic adriamycin (doxorubicin) after systemic administration can enter the so-called circumventricular organs (CVO) of the brain of the mouse. The present experiments were performed to find out whether such penetration of the brain is associated with signs of neurotoxic injury. For this purpose, light- and electron-microscopic observations were carried out on three of these organs: the neurohypophysis (NH), median eminence (ME), and postremal area (PA). Pronounced widening of the extracellular space indicating the presence of edema was present in all the regions, particularly in animals examined within 3 days of injection of the drug. Many degenerated axon terminals were observed in the NH and ME. The glial cells within these regions showed rarefaction of the nuclear chromatin, nucleolar segregation, and also cytoplasmic changes. The PA presented marked cellular changes resulting in degeneration of neurons, which was most evident 30 days after the injection. Hence, regions of the CNS outside the blood-brain barrier can be reached by adriamycin after systemic administration, and the drug can induce morphological changes there. The doses of the drug used in the present experiments were comparable to those given to patients for the treatment of malignant tumors.

Phylogenic and neurologic aspects of the vomiting process

Hindbrain morphology is compared in a variety of animals representing species that vomit and those that do not. Special attention is given to the nucleus of the tractus solitarius (NTS) and its synaptic connections with surrounding structures. The role of the area postrema is examined from the standpoints of containing the chemoreceptor trigger zone (CTZ) for vomiting, of its functional relationship to the blood-brain barrier, and of its significance as part of the circumventricular organ system. A survey is made of the manifold behavioral contributions of NTS to cardiovascular and respiratory regulation, appetite control, arousal, water balance, and digestive and neuroendocrine functions. An overview is presented of neurochemical distribution in the brain stem with respect to aminergic, cholinergic, and peptidergic substances. Finally, causes and prevention of vomiting are discussed in light of the above considerations.

Fine structure of ependymal cysts in and around the area postrema of the rat

Peculiar cells forming cysts were observed in the area postrema and sometimes also in the choroid plexus and the tela chorioidea near the area postrema, and were studied in detail by electron microscopy. The cytological features of the cyst cell and its junctional relationship to neighboring cells imply that cyst cells are derived from ependymal and choroid epithelial cells. The cyst cells usually contact directly the perivascular spaces of postremal, choroidal or pial capillaries, where the cytoplasm is often considerably attenuated. The cystic lumen is commonly filled with a flocculent material. The limiting membrane of the cystic lumen, which frequently bears cilia and microvilli, has the same thickness as the surface cell membrane. In many cases the cyst is surrounded by the cytoplasm of a single cell. In some cases, however, two cells participating in the formation of the cyst, although one is only a slender process and joined by a zonula occludens with the main cyst cell. Horseradish peroxidase (HRP) injected into the cerebrospinal fluid (CSF) space failed to enter the cystic lumen. A possible significance of the cyst in relation to the CSF and blood circulation was considered.