Sarolta Karcsú

Neurotoxin induced nerve cell degeneration: Possible involvement of calcium

Neurotoxin induced nerve cell degeneration has been studied in sensory ganglia of newborn and in the area postrema of adult rats following the administration of the selective sensory neurotoxin, capsaicin and the amino acid excitotoxin, glutamic acid, respectively. Light microscopic histochemical, autoradiographic, electroncytochemical and X-ray microanalytical studies revealed that degeneration of certain small-sized, type B primary sensory neurons, induced by capsaicin, was associated with a marked accumulation of calcium predominantly in mitochondria of the damaged ganglion cells. Similarly, monosodium glutamate treatment resulted in the appearance of calcium-containing electron-dense granules in mitochondria of degenerating area postrema neurons. In addition, after a combined administration of 45Ca2+ and capsaicin or monosodium glutamate, significantly higher levels of radioactivity have been detected by liquid scintillation spectroscopy in the Gasserian ganglia and the area postrema, respectively. It is concluded that an enhancement in intracellular calcium level may be intimately involved in the process of neuronal cell death and may represent a common basic mechanism responsible for the development of cellular events leading ultimately to the degeneration of nerve cells.

Butyrylcholinesterase activity in fenestrated capillaries of the rat area postrema.

In previous papers we have reported on the histochemical localization and possible functional role of acetylcholinesterase in the area postrema of the rat9,1L In the present study the fine structural localization of butyrylcholinesterase activity in the capillaries of the area postrema was analyzed. So far both light and electron microscopic methods, commonly used for the histochemical demonstration of cholinesterases, failed to reveal butyrylcholinesterase activity in these capillaries 2,6,7. Therefore it was a rather unexpected finding that butyrylcholinesterase activity could be demonstrated in the capillaries of this brain region. Investigations were performed on the medulla oblongata of adult albino rats weighing 150-200 g. Under ether anesthesia, animals were perfused through the aorta with a fixative containing 4 ~ formaldehyde (freshly prepared from paraformaldehyde), 2 ~ glutaraldehyde, 0.002 M calcium acetate and 4 ~ sucrose in 0.1 M sodium cacodylate buffer (pH 7.4). After perfusion for 60 min the medulla was dissected, post-fixed in the same solution for 6 h at 4 °C, and washed overnight in 0.1 M sodium cacodylate buffer (pH 7.0) containing isotonic sodium sulfate and calcium acetate. For light microscopy, frozen sections of 25-40 #m thickness were cut. For the demonstration of butyrylcholinesterase activity the thiocholine method of Koelle 11 as modified by Khsa and Csillik 10 was performed at room temperature, at pH 5.4 using butyrylthiocholine iodide as substrate in the presence of 10 -4 M BW284C51 *. After an incubation period of 5 h the sections were rinsed in sodium cacodylate buffer (pH 7.4) and subsequently treated with a 2 %o solution of sodium sulfide, dehydrated and mounted in Canada balsam. For electron microscopy, sections of 60-80 #m thickness were obtained on a Smith-Farquhar 18 tissue chopper. Butyrylcholinesterase activity was demonstrated according to the method of Lewis and Shute 14,15 using butyrylthiocholine iodide as substrate in the presence of 10 -4 M BW284C51 at 4 °C (pH 5.4). After an incubation period of 5 h, sections were washed in succinate buffer and treated with a 2 ~ buffered solution of sodium sulfide. Sections were tr immed under a dissecting microscope,

A glutamate-sensitive neuronal system originating from the area postrema terminates in and transports acetylcholinesterase to the nucleus of the solitary tract

SummaryThe possible cellular mechanism of action of systemically administered monosodium-l-glutamate and the projections of glutamate-sensitive area postrema neurons have been studied in rats. Parenteral administration of monosodium-l-glutamate induced a selective degeneration of a particular population of AChE-containing area postrema neurons. Electron microscopic cytochemistry and X-ray microanalysis revealed the presence of calcium-containing electron-dense deposits in the mitochondria of degenerating area postrema neurons indicating the possible pathogenetic role of an enhanced intracellular calcium level in the mechanism of monosodium-l-glutamate-induced nerve cell degeneration. Degeneration of area postrema neurons was followed by the appearance of degenerating axon terminals in a well-defined region of the nucleus of the solitary tract, the area subpostrema. Degenerating area postrema neurons and axon terminals were rapidly engulfed by phagocytes predominantly of microglial character. AChE activity, localized to the basal lamina of the capillaries of the area subpostrema under normal conditions, could no longer be detected in rats treated with monosodium-l-glutamate 3–4 weeks previously.These findings provide evidence for the existence of a particular population of glutamate-sensitive, AChE-containing area postrema neurons which project and transport AChE to the nucleus of the solitary tract. This specific neuronal pathway connecting the area postrema with the nucleus of the solitary tract may play an important role in some of the functions attributed to the area postrema. The results also strengthen the hypothesis that brain capillary AChE activity may be of neuronal origin.

Evidence for the neuronal origin of brain capillary acetylcholinesterase activity

Abstract Acute administration of monosodium- L -glutamate (MSG) to rats induces the degeneration of acetylcholinesterase (AChE)-positive neurons of the area postrema (AP). Chronic treatment with MSG results in the disappearance of AChE activity of area subpostrema (ASP) capillaries. It is concluded that processes of AChE-positive AP neurons terminate within the ASP and may contribute to the AChE activity of ASP capillaries.

Über die ultrastrukturelle Lokalisation der Acetylcholinesterase- (AChE-) Aktivität im Diaphragma des Rattenembryo

Summary Electron histochemistry revealed intense AChE activity in the diaphragm of 15 days old rat embryos. The reaction product was localized to the perinuclear cisterna and the cisternae of the sarcoplasmic reticulum of myoblasts. The development of myoneural contacts at day 17 of gestation was preceded by the appearance of AChE activity of muscle cells. Sarcoplasmic cisternae and vesicles in the subjunctional sarcoplasm may play an important role in the development of the AChE activity of the postjunctional sarcolemm.

Ultrastrukturelle veränderungen des supraoptico-neurohypophysären systems nach läsion des hypophysenstiels bei der ratte

Zusammenfassung Die nach elektrolytischer Zerstorung des Hypophysenstiels auftretenden ultrastrukturellen Veranderungen wurden im Nucleus supraopticus und in der Neurohypophyse untersucht. In den Nervenzellen des Nucleus supraopticus spielt sich die Chromatolyse ab. Die proliferierten Mikrogliazellen trennen die axosomatischen Synapsen ab und phagocytieren die degenerierten Neurone. In der 3. und 4. postoperativen Woche sind die morphologischen Merkmale einer Regeneration in solchen Neuronen wahrzunehmen, die die Axotomie uberlebt haben. In der Neurohypophyse beginnen der Zerfall der sekretorischen Blasehen und die Degeneration der Axonendigungen um den 3. bis 4. Tag post operationem . Die degenerierten Terminale werden von Pituicyten phagocytiert. In der 4. postoperativen Woche sind immer noch keine auf Axonregeneration hindeutenden ultrastrukturellen Zeichen in der Neurohypophyse festzustellen.

Calcium-containing mitochondrial granules in neurohypophysial axon terminals disappear following vasopressin treatment of brattleboro rats

The presence of intramitochondrial calcium-containing electron-dense granules was demonstrated in axon terminals of chronically hyperactive neurosecretory neurons of untreated homozygous Brattleboro rats. Following vasopressin treatment for 30 days, which has been shown to attenuate this neuronal hyperactivity, calcium-containing deposits could not be detected in mitochondria. It is concluded that the presence of intramitochondrial calcium-containing dense deposits is connected with the functional state of neurosecretory neurons.

Morphological evidence for the involvement of calcium in neurohypophysial hormone release

An elevated intracellular Ca2+ concentration in the secretory nerve endings of the rat neurohypophysis was detected histochemically by means of light microscopy concomitant with the vasopressin secretion evoked by hypertonic saline. The electron microscopic and X-ray microanalytical results furnish morphological evidence for the function-dependent Ca2+ storage capacity of the mitochondria, and suggest their role in the regulation of the free Ca2+ level in the neurosecretory axon terminal.

Na-Glutamat-sensitive Nervenzellen in der Area postrema bei der Ratte

Summary A single subcutaneous injection of monosodium-L-glutamate induces severe ultrastructural alterations in certain AChE positive parenchymal cells of the Area postrema of the adult rat. Signs of cellular degeneration include massive intracellular edema, swelling of mitochondria, vacuolization of the cisternae of the rough endoplasmic reticulum and marked alterations in the chromatin pattern of the nucleus. Identification of these cells as neurons is based on the presence of axosomatic synapses.

Über die Lokalisation der Acetylcholinesterase in der Area post-rema und Area subpostrema der Ratte. Licht- und elektronen-histochemische Untersuchungen

Zusammenfassung An perfusionsfixiertem Material wird an Gefrierschnitten bzw. am tissue chopped -Gewebe die Lokalisation der Acetylcholinesterase im Bereich der Area postrema der Ratte licht- und elektronenmikroskopisch studiert. Lichtmikroskopisch konnte eine schwache Reaktion in den Parenchymzellen der Area postrema und Kapillaren sowie einigen Nervenfasern der Area subpostrema nachgewiesen werden. Elektronenmikroskopisch wird die AChE in der Area postrema im perinuklearen Spalt, in den Cisternen des granularen endoplasmatischen Retikulums und den Neurotubuli von Neuronen und Dendriten nachgewiesen. In der Area subpostrema ist hingegen die AChE in den Pinocytose-vesikeln der Kapillarendothelien und in den Axonen, Dendriten und anderen Strukturelementen des Neuropils deutlich lokalisiert. Die Ergebnisse werden aus funktionell-morphologischer Sicht ausfuhrlich diskutiert.