摘要:

AbstractThe mitochondrial enzyme, cytochrome oxidase, was localized cytochemically in the nucleus magnocellularis, a primary relay nucleus of vestibular information within the area octavolateralis in the fish brain. Larvae of the cichlid fishOreochromis mossambicuswere analyzed at different developmental stages (4, 10, and 35 days posthatching) and after long‐term exposure (8 days) to increased gravity (2–4g). Quantification of highly reactive, moderately reactive, and nonreactive mitochondria reveals differences in the cytochrome oxidase activity of various cellular structures, for example, perikarya of neurons, presynaptic terminals, and myelinated and nonmyelinated cell profiles. Cytochrome oxidase activity in the mitochondria of neuronal perikarya increases during development which parallels the differentiation of the area octavolateralis. This possibly reflects the increasing energy demand during maturation and innervation of the magnocellular nucleus. Hyper‐g‐exposure of the larvae for 8 days (centrifuge) caused a further augmentation of cytochrome oxidase activity in the perikarya within the nucleus magnocellularis. This may reflect an increased oxidative metabolism resulting from the need for compensation of altered inputs from gravity‐sensitive epithelia in the inner ear. Another possibility is that acceleration within a centrifuge causes physiological stress for the animals and, therefore, influences the cytochrome oxidase activity in neurons. © 1993 John Wiley

ISSN:0022-3034    

DOI:10.1002/neu.480240902

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe present study investigated the effects of spinal cord stimulation, neuromuscular blockade, or a combination of the two on neuromuscular development both during and after the period of naturally occurring motoneuron death in the chick embryo. Electrical stimulation of the spinal cord was without effect on motoneuron survival, synaptogenesis, or muscle properties. By contrast, activity blockade rescued motoneurons from cell death and altered synaptogenesis. A combination of spinal cord stimulation and activity blockade resulted in a marked increase in motoneuron death, and also altered synaptogenesis similar to that seen with activity blockade alone. Perturbation of normal nerve–muscle interactions by activity blockade may increase the vulnerability of developing motoneurons to excessive excitatory afferent input (spinal cord stimulation) resulting in excitotoxic‐induced cell death. © 1993 John Wiley&Sons,

ISSN:0022-3034    

DOI:10.1002/neu.480240903

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractWhile primary neuronal cell cultures have been used to investigate excitotoxicity, development of cell lines exhibiting glutamate receptor‐mediated death is desirable. P19 mouse embryonal carcinoma cells, exposed to retinoic acid and plated onto a layer of cultured mouse cortical glial cells, differentiated into neuron‐like elements immunoreactive for neurofilaments and neuron‐specific enolase. Whole‐cell recordings revealed inward currents in response to extracellular application of either NMDA or kainate. The NMDA‐induced currents exhibited a voltage‐dependent blockade by magnesium, required glycine for maximal activation, and were blocked by the NMDA antagonist dizocilpine. Kainate‐induced currents were blocked by the AMPA/kainate receptor antagonist CNQX. Exposure to 500 μMNMDA for 24 h destroyed most P19 cells (EC50approximately 70 μM); death was prevented by dizocilpine or D‐APV. Exposure to 500 μMkainate also resulted in widespread death reduced by CNQX. Thus differentiated P19 cells exhibited both excitatory amino acid responses and vulnerability to excitotoxicity, characteristic of CNS neurons. These cells may provide a genetically open system useful for studying glutamate receptor‐mediated phenomena at a molecular level. © 1993

ISSN:0022-3034    

DOI:10.1002/neu.480240904

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractNeurons in the developing (antennal) olfactory lobe of the mothManduca sextaundergo a period of extensive process outgrowth and branching that coincides temporally with both a rising titer of the steroid hormone 20‐hydroxyecdysone and the ingrowth of sensory axons from receptors in the antenna. To evaluate the contribution of these two influences to the morphological development of antennal‐lobe neurons, we placed the neurons in cell culture. Antennal‐lobe neurons were dissociated from normal and chronically unafferented lobes at different stages of development and were exposed to different doses of hormone. Six neuronal cell types with distinctive and stable morphologies appeared in cultures from all stages of pupal development. Morphological changes in these neuronal types were examined quantitatively by comparison of the total length and number of branches. We found that 20‐hydroxyecdysone had little direct effect on the morphological development of antennal‐lobe neurons, but brief exposure to sensory axonsin vivoprior to dissociation significantly enhanced subsequent outgrowth in culture. © 1993 John Wiley

ISSN:0022-3034    

DOI:10.1002/neu.480240905

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractIn order to assess the nature of spatial cues in determining the characteristic projection sites of sensory neurons in the CNS, we have transplanted sensory neurons of the cricketAcheta domesticusto ectopic locations. Thoracic campaniform sensilla (CS) function as proprioceptors and project to an intermediate layer of neuropil in thoracic ganglia while cercal CS transduce tactile information and project into a ventral layer in the terminal abdominal ganglion (TAG). When transplanted to ectopic locations, these afferents retain their modality‐specific projection in the host ganglion and terminate in the layer of neuropil homologous to that of their ganglion of origin. Thus, thoracic CS neurons project to intermediate neuropil when transplanted to the abdomen and cercal CS neurons project to a ventral layer of neuropil when transplanted to the thorax. We conclude that CS can be separated into two classes based on their characteristic axonal projections within each segmental ganglion. We also found that the sensory neurons innervating tactile hairs project to ventral neuropil in any ganglion they encounter after transplantation. Ectopic sensory neurons can form functional synaptic connections with identified interneurons located within the host ganglia. The new contacts formed by these ectopic sensory neurons can be with normal targets, which arborize within the same layer of neuropil in each segmental ganglion, or with novel targets, which lack dendrites in the normal ganglion and are thus normally unavailable for synaptogenesis. These observations suggest that a limited set of molecular markers are utilized for cell–cell recognition in each segmentally homologous ganglion. Regenerating sensory neurons can recognize novel postsynaptic neurons if they have dendrites in the appropriate layer of neuropil. We suggest that spatial constraints produced by the segmentation and the modality‐specific layering of the nervous system have a pivotal role in determining synaptic specificity. © 1993 John Wiley&Son

ISSN:0022-3034    

DOI:10.1002/neu.480240906

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe expression ofTrkB mRNAs was investigated in rat retina and optic nerve. A 11.5 kb transcript that encodes full‐lengthTRKB was found to predominate in Northern blots of retinal RNA. Byin situhybridization, thistrkB expression was concentrated in the ganglion cell and inner nuclear layers. Furthermore, an antibody to the full‐lengthTRKB immunostained retinal ganglion cells and their axons. In contrast, Northern blots of optic nerve RNA showed a prominent 9.5 kb band that encoded a form of theTRKB receptor lacking the tyrosine kinase domain. This species was also detected in both the sciatic nerve and cultured astrocytes and C6 glioma cells. These results suggest that neurons express the full‐lengthTRKB containing the tyrosine kinase domain, while non‐neuronal cells express the truncated form of the receptor. These two classes ofTRKB may mediate different neurotrophic actions in the retina and optic nerve. © 1993 John Wiley&S

ISSN:0022-3034    

DOI:10.1002/neu.480240907

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMale frogs use their forelimb flexor muscles to clasp females during the mating behavior known as amplexus. We investigated the effects of testosterone on a principal forelimb flexor, the flexor carpi radialis muscle (FCR), using morphological and histochemical techniques. MaleXenopus laeviswere surgically manipulated to produce high or low levels of circulating testosterone for an 8‐week period. After this treatment, measurement of fibers in muscle cross‐sections revealed that average fiber size was positively correlated with testosterone level. This effect was not the same for all muscle fibers, however. Fibers in the shoulder region were more sensitive to testosterone than fibers in other regions of the muscle. Histochemical staining of cross‐sections showed that the patterns of staining for myosin ATPase or succinic dehydrogenase (SDH) were not influenced by testosterone levels, but total SDH activity was increased by testosterone treatment. When sensitivity to testosterone was correlated with ATPase activity, fibers with high ATPase activity were found to be more sensitive to testosterone than fibers with low activity, regardless of position within the muscle. Most fibers with high ATPase activity were located in the shoulder region of the muscle. These fibers are innervated by different motor axons than are fibers in the elbow region of the muscle, and contractions of shoulder (but not elbow) region fibers, elicited by stimulation of motor axons, are slowed by testosterone treatment (Regnier and Herrera, 1993,J. Physiol.461:565–581). © 1993 John Wiley&S

ISSN:0022-3034    

DOI:10.1002/neu.480240908

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractPartial deafferentation of the olfactory bulb inXenopusembryos was performed to analyze the effects of afferent innervation on the development of the central olfactory structure. In an attempt to analyze a possible early inductive role of the olfactory axons, one olfactory placode was removed before differentiation of the neural tube began (stages 26–31). A morphological and quantitative analysis was performed on larvae at the onset of metamorphic climax (stage 58). When the single olfactory nerve innervated one side of the rostral telencephalon, a single olfactory bulb developed on that side and no olfactory bulb formed on the contralateral side. When the nerve innervated the midline of the rostral telencephalon, a smaller‐than‐normal, fused olfactory bulb developed. Partial deafferentation at these early stages resulted in a significant reduction in the number of olfactory axons (to approximately one‐half of control values) and a corresponding decrease in the number of mitral/tufted cells (output neurons of the olfactory bulb). To control for possible damage to the neural tube during olfactory‐placode removal, a portion of the neural tube directly beneath one of the olfactory placodes was removed in embryos. In these animals, the neural tube regenerated within 24 h and formed a normal olfactory bulb; olfactory axon and mitral/tufted‐cell numbers were not significantly different from controls. In conclusion, olfactory‐afferent innervation was critical for differentiation of the olfactory bulb, and decreasing the number of olfactory axons resulted in a reduction in the number of output neurons of the olfactory bulb. © 1993 John W

ISSN:0022-3034    

DOI:10.1002/neu.480240909

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractMost sympathetic neurons contain one or more neuropeptides in addition to catecholamines. Although the regulation of catecholamines has been studied extensively, comparatively little is known about the regulation of neuropeptides. Since glucocorticoids and preganglionic innervation regulate catecholaminergic properties in chromaffin cells, we examined the effects of these factors on a co‐localized neuropeptide, leucine enkephalin (L‐Enk), in adult rat sympathetic neuronsin vivo. Lowered serum glucocorticoid levels as a consequence of bilateral adrenalectomy resulted in a reduction of ganglionic L‐Enk content that was reversed by exposure of adrenalectomized animals to the synthetic glucocorticoid, dexamethasone. Surgical denervation of the SCG eliminated L‐Enk‐IR preganglionic fibers and caused a dramatic increase in the number of L‐Enk‐IR neurons. Inhibition of the enkephalinergic component of the preganglionic innervation by chronic exposure to the opiate receptor antagonist naloxone increases the number of L‐Enk‐IR cell bodies and total ganglionic L‐Enk content. None of the experimental manipulations noticeably altered the number or distribution of NPY‐IR neurons, suggesting that the effects of glucocorticoids and the innervation on ganglionic L‐Enk levels were specific and not simply an alteration of the biosynthetic state of the cells. These results demonstrate that circulating glucocorticoids and the preganglionic innervation regulate L‐Enk levels in sympathetic neurons. Since both glucocorticoid levels and preganglionic activity are known to be altered by stressful stimuli, acute regulation of sympathetic L‐Enk levels may constitute an important component of the autonomic response to stress.

ISSN:0022-3034    

DOI:10.1002/neu.480240910

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480240901

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY