摘要:

AbstractPrevious ultrastructural observations on late stage larvae of dorid nudibranchs (Gastropoda, Opisthobranchia) revealed two pairs of ganglia within the base of the foot that do not have obvious counterparts in existing descriptions of other gastropod larvae [Chia and Koss (1989).Cell Tiss. Res.256:17–26.] One of these ganglionic pairs has been implicated in the initiation of settlement preceding metamorphosis [Arkett et al. (1989).Biol. Bull.176:155–160.] By examining neurogenesis in sequential larval stages, I have found that the pattern of connectives and commissures associated with these enigmatic ganglia is comparable to patterns found in less consolidated adult nervous systems of chitons, monoplacophorans, and archaeogastropods. These comparative date suggest that the two pairs of ganglia in dorid nudibranch larvae are homologues of labial and subradular ganglia. The labial ganglia become incorporated into the cerebral ganglia at metamorphosis. In an attempt to integrate anatomical and developmental observations with behavioral andneurophysiological results, I suggest that receptor cells of the larval labial ganglia may become postmetamorphic primary mechanoreceptors of the oral tube, which have central cell bodies within the “cerebral” ganglia and which help coordinate feeding. Results of this study also address a larger evolutionary issue by questioning the traditional model of an ancestral molluscan nervous system that consists of four longitudinal nerve cords that arise from separate sites along a circumesophageal nerve ring. This pattern results from secondary connections in nudibranchs and possibly other molluscs. The primary condition of a single axon bundle emerging from each cerebral ganglion is more similar to the developing nervous system in polychaete annelids than what has been recognized previously. © 1993 John Wiley&S

ISSN:0022-3034    

DOI:10.1002/neu.480241102

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

年代:1993

数据来源: WILEY

摘要:

AbstractTo examine the contribution of local versus extrinsic influences on postnatal development of cortical neurons, we compared the maturation of deep (infragranular) layer neurons in isolated slices of neocortex grown in organotypic culture to a similar population of neurons developingin vivo. All slice cultures were prepared from sensorimotor cortices of newborn mice (P0) and neurons in these cultures were examined at daily intervals during the first 9 daysin vitro(DIV). The maturational state of neurons developingin vivoover this same time period was assessed in acute slices prepared from animals of equivalent postnatal age, P1–P9. Electrophysiological recordings were obtained from neurons in both cultured and acute slices, using Lucifer yellow filled whole‐cell recording electrodes, enabling subsequent morphometric analysis of the labeled cells. We report significant changes in both cellular morphology and electrical membrane properties of these deep layer cortical neurons during the frist week in culture. Morphological maturation over this time period was characterized by a two‐ to three‐fold increase in cell body size and total process length, and an increase in dendritic complexity. In this same population of cells a three‐fold decrease in input resistance and changes in the action potential waveform, including a two‐fold decrease in the AP duration, also occur. The degree of morphological and electrophysiological differentiation of individual neurons was highly correlated across developmental ages, suggesting that the maturational state of a cell is reflected in both cellular morphology and intrinsic membrane properties. A remarkably similar pattern of neuronal maturation was observed in neurons in layers V, VI/SP examined in acute slices prepared from animals between P1–P9. Because our culture system preserves many aspects of the local cortical environment while eliminating normal extrinsic influences (including thalamic, brainstem, and callosal connections), our findings argue that this early phase of neuronal differentiation, including the rate and extent of dendritic growth and development of AP waveform, results from instructive and/or permissive local influences, and appears to proceed independently of the many normally present extrinsic factors. © 1993 John W

ISSN:0022-3034    

DOI:10.1002/neu.480241103

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe differentiation of facial motoneurons and inner ear (octaval) efferents was examined in chicken embryos by applying Dil or dextran amines to the cut VII/VIII nerve (peripheral label) or to the basal/floor plate of rhombomeres 4/5 (central label). Central labeling found axons of these efferent neurons to leave the brain as early as 2.5 days of incubation. Peripheral labeling identified cell bodies ipsilaterally in rhombomeres 4 and 5 at 2.5 days. Central labeling at 3.5 days showed these fibers to have fully segregated into separate pathways to the facial nerve and the inner ear and that the octaval efferent axons had reached the otocyst wall. By 3.5 days many peripherally labeled octaval efferent somata were found in the floor plate and by 5 days they were found bilaterally. At 6 days, selective peripheral labeling of either the VIIth or VIIIthe nerve showed that the contralateral population consisted of octaval efferents and central label applied to the floor plate of rhombomeres 4/5 identified fibers that entered the octaval nerve via the facial root and entered the vestibular sensory epithelia. To gether these data suggest an initial mingling of two different motoneuron populations (facial and octaval) in rhombomeres 4/5 and a subsequent segregation by differential migration. Our data also find a much earlier arrival of octaval efferent axons at the otic vesicle than previously described and suggest a contralateral migration of many octaval efferents beginning shortly after their axons reach the facial nerve root. © 1993 John Wiley&Sons, Inc

ISSN:0022-3034    

DOI:10.1002/neu.480241104

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe properties of microtubule‐associated protein‐2 (MAP‐2) expression were examined in a transformed cell line, and compared to neurons from rodent brain where evidence supports both transcriptional and nontranscriptional regulation of MAP‐2 synthesis. A monoclonal antibody that recognizes a common epitope in the adult (HMW MAP‐2) and juvenile (MAP‐2c) forms was used in an immunoblotting assay to assess the protein levels in actively dividing and differentiated neuroblastoma/glioma (108CC15, also designated NG108‐15) cells. Multiply‐phosphorylated MAP‐2c was the predominant form in actively dividing cells, whereas HMW MAP‐2 predominated in differentiated cells, which exhibited several other neuronal‐like properties. A progressive increase in the levels of immunoreactive HMW MAP‐2 was observed with increasing days of cell differentiation using dBcAMP as the inducing agent. However, the absolute levels of both HMW MAP‐2 and MAP‐2c in NG108‐15 cells were significantly lower (at least 10‐fold) than levels measured in rodent brain. To assess whether there are correspondingly lower levels of HMW MAP‐2 and MAP‐2c mRNAs in NG108‐15 cells, relative to rodent brain, a highly sensitive RNA amplification assay (reverse transcription‐polymerase chain reaction; RT‐PCR) was developed. Oligonucleotide primers were designed to specify either HMW MAP‐2 mRNA or MAP‐2c mRNA, and whole tissue RNA extracted from adult and neonatal rodent brain was used to verify the reliability of the RT‐PCR assay. Accordingly, PCR products of the predicted size, specificity, and abundance were obtained, with similar levels of HMW MAP‐2 mRNA and proportionately higher levels of MAP‐2c mRNA in neonatal brain, relative to adult brain. MAP‐2c mRNA was the predominant transcript in actively dividing NG108‐15 cells, and the amount of HMW MAP‐2 mRNA gradually increased and became the predominant transcript in cells exposed to dBcAMP for 6–9 days. Thus, the observed changes in MAP‐2‐specific mRNAs during differentiation paralleled changes in expressed protein, suggesting that MAP‐2 synthesis in NG108y15 cells is transcriptionally controlled. However, the levels of both MAP‐2 mRNAs in NG108‐15 cells were comparable to levels in rodent brain, despite the fact that MAP‐2 protein levels are at least 10‐fold lower in NG108‐15 cells. These data suggest that the low levels of HMW MAP‐2 and MAP‐2c protein expression in NG108‐15 cells are not due to correspondingly lower levels of MAP‐2 mRNAs, and that transformed neuronal c

ISSN:0022-3034    

DOI:10.1002/neu.480241105

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of action potentials on elimination of mouse neuromuscular junctions (NMJ) was studied in a three compartment cell culture preparation. Axons from superior cervical ganglion or ventral spinal cord neurons in two lateral compartments formed multiple neuromuscular junctions with muscle cells in a central compartment. The loss of synapses over a 2–7‐day period was determined by serial electrophysiological recording and a functional assay. Electrical stimulation of axons from one side compartment during this period, using 30‐Hz bursts of 2‐s duration, repeated at 10‐s intervals, caused a significant increase in synapse elimination compared to unstimulated cultures (p<0.001). The extent of homosynaptic and heterosynaptic elimination was comparable, i. e., of the 226 functional synapses of each type studied, 111 (49%) of the synapses that had been stimulated were eliminated, and 87 (39%) of unstimulated synapses on the same muscle cells were eliminated. Also, simultaneous bilateral stimulation caused significantly greater elimination of synapses than unilateral stimulation (p<0.005). These observations are contrary to the Hebbian hypothesis of synaptic plasticity. A spatial effect of stimulus‐induced synapse elimination was also evident following simultaneous bilateral stimulation. Prior to stimulation, most muscle cells were innervated by axons from both side compartments, but after bilateral stimulation, muscle cells were predominantly unilaterally innervated by axons from the closer compartment. These experiments suggest that synapse elimination at the NMJ is an activity‐dependent process, but it does not follow Hebbian or anti‐Hebbian rules of synaptic plasticity. Rather, elimination is a consequence of postsynaptic activation and a function of location of the muscle cell relative to the neuron. An interaction between spatial and activity‐dependent effects on synapse elimination could help produce optimal refinement of synaptic connections during postnatal development. © 1993 Jo

ISSN:0022-3034    

DOI:10.1002/neu.480241106

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe nervous system and muscle tissue of the leech express two different organ‐specific forms of connective tissue protein. The nervous system‐specific form appears in regional boundaries separating cell bodies, axonal tracts and areas of the neuropile during late embryogenesis. In contrast, the muscle‐specific form appears earlier during development in the basement membrane of muscle cells. In extraction experiments both forms behave like extracellular matrix proteins and because of their molecular weight, are considered members of a group of cell type‐specific 130 kD proteins (leech gp130s). How ever, the two forms differ in their posttranslational modification. As determined by Con A and lentil lectin affinity chromatography, only the nervous system‐specific, but not the muscle‐specific form, has fucosylated and high mannose N‐linked carbohydrates. These differences in the developmental onset and glycosylation suggest that nervous system‐specific and muscle‐specific connective tissue proteins are regulated differently and participate in different molecular interactions. © 1993 Jo

ISSN:0022-3034    

DOI:10.1002/neu.480241107

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

年代:1993

数据来源: WILEY

摘要:

AbstractRats possess a sexually dimorphic neuromuscular system that controls penile reflexes critical for copulation. This system includes two motor nuclei in the lumbar cord and their target musculature in the perineum. The spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN) motoneuron populations and their target perineal muscles are much larger in males than in females. The sex difference in motoneuron number develops via androgen‐regulated differential cell death during the perinatal period; androgen also regulates retention of the target muscles. The developmental pattern and steroid sensitivity of peripheral afferents to the SNB/DLN motor nuclei were previously unknown. In order to characterize the peripheral sensory component of the dimorphic SNB/DLN system, the neurons of the relevant dorsal root ganglia (DRGs) were quantified in terms of number, size, and androgen sensitivity at various perinatal ages. DRG neuron number is greatest prenatally, then decreases in both sexes after birth; the timing and pattern of neuron number development are similar to those seen in the SNB and DLN. Postnatally, males have more DRG neurons than females, as a result of greater neuron death in the DRGs of females. Females treated with testosterone propionate during the perinatal period exhibit masculine development of DRG neuron number. Thus, the normal development of DRG neuron number parallels that of the SNB/DLN motor nuclei and target muscles in pattern and timing, is sexually dimorphic, and is regulated by androgen. © 1993 John Wiley&Sons, I

ISSN:0022-3034    

DOI:10.1002/neu.480241108

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.480241101

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

年代:1993

数据来源: WILEY