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Much confusion has arisen recently over the question of whether excitotoxic neuronal degeneration can be considered an apoptotic phenomenon. Here, we addressed this question by using ultrastructural methods and DNA fragmentation analysis to compare a prototypic apoptotic in vivo central nervous system cell death process (physiologic cell death in the developing rat brain) with several central nervous system cell death processes in the in vivo infant rat brain that are generally considered excitotoxic (degeneration of hypothalamic neurons after subcutaneous administration of glutamate and acute neurodegeneration induced by hypoxia/ischemia or by concussive head trauma). We found by ultrastructural analysis that glutamate induces neurodegenerative changes in the hypothalamus that are identical to acute changes induced in the infant rat brain by either hypoxia/ischemia or head trauma, and that these changes are fundamentally different both in type and sequence from those associated with physiologic cell death (apoptosis). In addition, we show by ultrastructural analysis that concussive head trauma induces both excitotoxic and apoptotic neurodegeneration, the excitotoxic degeneration being very acute and localized to the impact site, and the apoptotic degeneration being delayed and occurring in regions distant from the impact site. Thus, in the head trauma model, excitotoxic and apoptotic degeneration can be distinguished not only by ultrastructural criteria but by their temporal and spatial patterns of expression. Whereas ultrastructural analysis provided an unambiguous means of distinguishing between excitotoxic and apoptotic neurodegeneration in each example analysed in this study, DNA fragmentation analysis (TUNEL staining or gel electrophoresis) was of no value because these tests were positive for both processes. J. Comp. Neurol. 408:461–476, 1999. © 1999 Wiley‐Liss, Inc.

Blockade ofN-methyl-d-aspartate (NMDA) glutamate receptors by MK-801 induces neuronal degeneration in the posterior cingulate/retrosplenial cortex and other corticolimbic regions although damage in the latter has not been adequately characterized. This disseminated corticolimbic damage is of interest since NMDA hypofunction, the mechanism that triggers this neurodegenerative syndrome, has been postulated to play a role in the pathophysiology of Alzheimer's disease (AD). Several histological methods, including electron microscopy, were used to evaluate the neurotoxic changes in various corticolimbic regions of rat brain following MK-801 or a combination of MK-801 plus pilocarpine. We found that MK-801 triggers neuronal degeneration in a widespread pattern similar to that induced by phencyclidine and that females showed more damage than males. The neurotoxic reaction involved additional brain regions when muscarinic receptors were hyperactivated by administering pilocarpine with MK-801. Ultrastructural evaluation revealed that a major feature of the neurotoxic action involves degeneration of dendritic spines which entails loss of synaptic complexes. The ultrastructural appearance of degenerating neurons was generally inconsistent with an apoptotic mechanism, although evidence equivocally consistent with apoptosis was observed in some instances. The cell death process evolved relatively slowly and was still ongoing 7 days posttreatment. Relevance of these results to AD is discussed.

Extensive research has failed to clarify the mechanism of action of nitrous oxide (N2O, laughing gas), a widely used inhalational anesthetic and drug of abuse. Other general anesthetics are thought to act by one of two mechanisms—blockade of NMDA glutamate receptors or enhancement of CABAergic inhibition1. Here we show that N2O, at anesthetically-relevant concentrations, inhibits both ionic currents and excitotoxic neurodegeneration mediated through NMDA receptors and, like other NMDA antagonists, produces neurotoxic side effects which can be prevented by drugs that enhance CABAergic inhibition. The favorable safety record of N2O may be explained by the low concentrations typically used and by the fact that it is usually used in combination with CABAergic anesthetics that counteract its neurotoxic potential.

Human umbilical vessels are unique in lacking any innervation; thus endothelial cells may play the major role in local control and regulation of the blood flow. In the present study, we examined ultrathin sections of cultured human umbilical vein endothelial cells and tissue preparations of umbilical vein and artery, immunostained by the post-embedding colloidal gold double-labelling technique. We observed colocalization of atrial natriuretic peptide and neuropeptide Y, as well as colocalization of atrial natriuretic peptide and neuropeptide Y with other vasoactive substances, namely, vasoactive intestinal peptide, substance P, calcitonin gene-related peptide and arginine vasopressin. The functional significance of the colocalization of these vasoactive substances in the human umbilical vessel endothelial cells is discussed.

A new one-step incubation method using cationic gold colloid was applied to reveal anionic moieties in rat colonic mucosa. Gold particles were detected in all cellular nuclei, basement membranes, mast cell granules and collagen fibres, while the luminal surfaces of all vascular endothelial cells were devoid of gold label. Application of the method for detection of anionic domains under various conditions is discussed.

The presence and distribution of Weibel-Palade bodies in stomach and colonic mucosal microvessels after the administration of vasoactive amines (serotonin and histamine), the serotonin depletor reserpine, and the von Willebrand factor secretagogue thrombin, was studied by transmission electron microscopy. These agents elevated the number of Weibel-Palade bodies in all microvascular endothelial cells and especially in capillaries. It is concluded that vasoactive amines enhance the synthesis and secretion of large von Willebrand protein multimers by endothelial cells.