Search PubMed⌕ Search

Biomedical subjects

D Purves

Publications and source records attributed to D Purves.

At least 73 records · Page 4Linked to original sources
PubMed1988

Trophic regulation of nerve cell morphology and innervation in the autonomic nervous system.

A remarkable feature of nerve cells is the complex and variable pattern of their axonal and dendritic branches. Quantitative studies of a simple part of the nervous system in mammals provide evidence that neuronal geometry and innervation are regulated by long-term trophic interactions between neurons and their targets. This trophic linkage may explain how nerve cells adjust their function to the needs of bodies that vary markedly in size and form.

Autonomic Nervous System↗
PubMed1988

Neuron/glia relationships observed over intervals of several months in living mice.

Identified neurons and glial cells in a parasympathetic ganglion were observed in situ with video-enhanced microscopy at intervals of up to 130 d in adult mice. Whereas the number and position of glial cells associated with particular neurons did not change over several hours, progressive differences were evident over intervals of weeks to months. These changes involved differences in the location of glial nuclei on the neuronal surface, differences in the apparent number of glial nuclei associated with each neuron, and often both. When we examined the arrangement of neurons and glial cells in the electron microscope, we also found that presynaptic nerve terminals are more prevalent in the vicinity of glial nuclei than elsewhere on the neuronal surface. The fact that glial nuclei are associated with preganglionic endings, together with the finding that the position and number of glial nuclei associated with identified neurons gradually changes, is in accord with the recent observation that synapses on these neurons are normally subject to ongoing rearrangement (Purves, D., J. T. Voyvodic, L. Magrassi, and H. Yawo. 1987. Science (Wash. DC). 238:1122-1126). By the same token, the present results suggest that glial cells are involved in synaptic remodeling.

Animals↗
PubMed1987

Nerve terminal remodeling visualized in living mice by repeated examination of the same neuron.

The distribution of presynaptic endings on the surfaces of autonomic ganglion cells was mapped in living mice after intravenous administration of a styryl pyridinium dye. The staining and imaging techniques did not appear to damage the ganglion cells, or the synapses on them; these procedures could therefore be repeated after an arbitrary period. Observations of the same neurons at intervals of up to 3 weeks indicate that the pattern of preganglionic terminals on many of these nerve cells gradually changes.

Action Potentials↗
PubMed1987

Fluorescent probes that stain living nerve terminals.

We have evaluated the efficacy of 18 cationic mitochondrial dyes that, as a class, show some ability to stain living nerve terminals. Several of these agents provide excellent staining of neuromuscular junctions in a wide range of species. More detailed studies of the most effective of these dyes--4-(4-diethylaminostyryl)-N-methylpyridinium iodide (4-Di-2-ASP)--indicate that it has no lasting effect on the structure or function of motor nerve terminals. As demonstrated in the accompanying paper (Lichtman et al., 1987; see also Lichtman et al., 1986), 4-Di-2-ASP can therefore be used to follow the configuration of identified motor terminals over arbitrarily long intervals.

Animals↗
PubMed1987

Visualization of neuromuscular junctions over periods of several months in living mice.

Identified neuromuscular junctions were followed in the sternomastoid muscle of living mice for several months by repeated staining with the fluorescent dye 4-(4-diethylaminostyryl)-N-methylpyridinium iodide (4-Di-2-ASP; Magrassi et al., 1987). Overall terminal growth occurred at many endplates; however, the branching pattern of presynaptic arbors was largely unchanged, even after several months. The absence of significant remodeling over time was not a result of dye-staining, since sprouting was readily induced at residual motor endings by partial denervation. We conclude that--apart from overall growth--most neuromuscular junctions in the adult mouse are stable over intervals that represent a significant fraction of the animal's lifetime.

Animals↗
PubMed1987

Synaptic sites on reinnervated nerve cells visualized at two different times in living mice.

Synaptic boutons on the surface of identified autonomic ganglion cells were visualized by methylene blue staining at intervals of 1-2 months following denervation to assess whether regenerating axon terminals reoccupy original synaptic sites. The distribution of synapses observed on the same neuronal cell bodies was almost always different in appearance after reinnervation. These results are at odds with the conclusions of earlier workers, who have argued that mammalian neurons bear a fixed number of synaptic sites, which are reoccupied during reinnervation.

Animals↗
PubMed1986

Dynamic changes in the dendritic geometry of individual neurons visualized over periods of up to three months in the superior cervical ganglion of living mice.

We describe a means of visualizing the same neuron in the superior cervical ganglion of young adult mice over intervals of up to 3 months. The dendrites of these neurons change during this interval; some branches retract, others elongate, and still others appear to form de novo. Thus, neuronal dendrites in this part of the nervous system are subject to continual change beyond what is usually considered the developmental period. The remodeling of postsynaptic processes further implies that the synaptic connections made onto these cells undergo substantial rearrangement well into adulthood.

Animals↗
PubMed1986

Relation of animal size to convergence, divergence, and neuronal number in peripheral sympathetic pathways.

The enormous range of animal size raises a fundamental problem: How do larger animals maintain adequate control of peripheral structures that are many times more massive and extensive than the homologous structures in smaller animals? To explore this question, we have determined neuronal number, the number of axons that innervate each neuron (convergence) and the number of neurons innervated by each axon (divergence), in a peripheral sympathetic pathway of several mammals (mouse, hamster, rat, guinea pig, and rabbit). The average adult weights of these species vary over approximately a 65-fold range. However, the number of superior cervical ganglion cells increases by only a factor of 4 between the smallest of these animals (mice; about 25 gm) and the largest (rabbits; about 1700 gm); the number of spinal preganglionic neurons that innervate the ganglion increases by only a factor of 2. Thus, the number of nerve cells in the sympathetic system does not increase in proportion to animal size. On the other hand, our results indicate that there are systematic differences across these species in the number of axons that innervate each ganglion cell and in the number of ganglion cells innervated by each axon. We suggest that modulation of convergence and divergence in sympathetic ganglia allows this part of the nervous system to effectively activate homologous peripheral targets over a wide range of animal size.

Animals↗
PubMed1985

The changing view of neural specificity.

The generation of specific patterns of neuronal connections has usually been regarded as a central problem in neurobiology. The prevailing view for many years has been that these connections are established by complementary recognition molecules on the pre- and postsynaptic cells (the chemoaffinity theory). Experimental results obtained in the past decade, however, indicate that the view that axon guidance and synaptogenesis proceed according to restrictive chemical markers is too narrow. Although a more rigid plan may prevail in some invertebrates, the formation of specific connections in vertebrates also involves competition between axon terminals, trophic feedback between pre- and postsynaptic cells, and modification of connections by functional activity.

Animals↗
PubMed1985

Geometrical differences among homologous neurons in mammals.

The dendritic arbors of sympathetic neurons in different species of mammals vary systematically: the superior cervical ganglion cells of smaller mammals have fewer and less extensive dendrites than the homologous neurons in larger animals. This difference in dendritic complexity according to body size is reflected in the convergence of ganglionic innervation; the ganglion cells of progressively larger mammals are innervated by progressively more axons. These relations have implications both for the function of homologous neural systems in animals of different sizes and for the regulation of neuronal geometry during development.

Animals↗
PubMed1984

Regional innervation of rabbit ciliary ganglion cells by the terminals of preganglionic axons.

In the rabbit, ciliary ganglion neurons with dendrites maintain inputs from several different axons during the period of synaptic rearrangement that occurs in early postnatal life. Neurons without dendrites, on the other hand, lose the majority of their initial inputs and are innervated in maturity by the terminals of only one or two axons (Purves, D., and R.I. Hume (1981) J. Neurosci. 1: 441-452; Hume, R.I., and D. Purves (1981) Nature 293: 469-471). We have explored the basis of this phenomenon by individually marking preganglionic axons and the neurons they innervate with horseradish peroxidase. In general, the innervation of geometrically complex (multiply innervated) neurons by individual preganglionic axons is regional. That is, the synaptic contacts made by an axon on these neurons are limited to a portion of the postsynaptic surface that includes some, but not all, of the dendrites. This regional innervation of target neurons is consistent with the view that dendrites allow multiple innervation to persist by providing relatively separate postsynaptic domains for individual preganglionic axons. Such regional innervation may mitigate competitive interactions between the several axons which initially innervate the same neuron.

Animals↗
PubMed1983

Neural units in the superior cervical ganglion of the guinea-pig.

The size and arrangement of the set of neurones innervated by individual preganglionic axons (the neural unit) has been investigated in the superior cervical ganglion of the guinea-pig. 1. Based on the ratio of preganglionic neurones to ganglion cells, and the average number of axons contacting each ganglion cell, we estimated that individual preganglionic axons innervate on the order of 50-200 superior cervical ganglion cells. 2. Of 562 pairs of ganglion cells examined with intracellular recording, forty-seven (8.4%) were innervated by one or more common axons. 3. Pairs of ganglion cells innervated by the same axon were not necessarily near each other. Although nearby cells were more likely to share innervation than neurones far apart, cells sharing innervation were often found several hundred micrometers apart, and were occasionally separated by the largest dimension of the ganglion (about 1-2 mm). 4. The incidence of cell pairs that shared innervation from more than one axon was greater than expected from the frequency of pairs sharing at least one axon. 5. Extracellular recordings from small fascicles of the cervical sympathetic trunk showed that preganglionic axons from different segmental levels intermingle extensively en route to the superior cervical ganglion. 6. Taken together, these findings support the view that sets of ganglion cells are innervated in common not because of any special topographic relationship within the ganglion, but because they share one or more properties that make them especially attractive to particular preganglionic axons.

Animals↗
PubMed1983

Apportionment of the terminals from single preganglionic axons to target neurones in the rabbit ciliary ganglion.

We have studied the apportionment of terminals from single preganglionic axons to target neurones in the ciliary ganglion of adult rabbits. Both electrical recording and intra-axonal injection of horseradish peroxidase (HRP) showed that each preganglionic axon innervates only a small fraction of the ganglion cell population (about 10-20 of the approximately 400 ganglion cells). Examination of ganglia in whole mounts showed that neurones whose cell bodies were enveloped by HRP-labelled boutons from a single axon were often surrounded by other neurones which received no contacts from the labelled fibre. Electron microscopical examination of labelled presynaptic terminals on individual ganglion cells confirmed that the boutons of single axons were sharply confined to particular target cells. This suggests that individual target neurones (or portions of them) are the unit of innervation during the development of these synaptic connexions. Comparison of the amplitudes of synaptic responses in singly and multiply innervated ganglion cells indicated that, on average, an individual axon made a weaker synaptic connexion with a multiply innervated neurone than with neurone that received only one input. Moreover, neurones innervated by several different axons tended to have fewer synapses on their somata than neurones innervated by only one or two preganglionic axons. Individual post-synaptic profiles were often contacted exclusively by labelled terminals when examined in the electron microscope. Since many of these neurones are multiply innervated, this observation suggests some regional separation of the several inputs contacting the same cell. For several reasons, however, this inference must be regarded as tentative. Taken together, these findings provide a possible explanation of the correlation between the dendritic geometry of ganglion cells and the number of different axons that innervate them (Purves & Hume, 1981). The several axons that initially innervate ganglion cells without dendrites evidently compete during early life until only a single input remains. On ganglion cells with dendrites, however, the number of inputs that persists is proportional to dendritic complexity. The present results suggest that the diminished competition between axons innervating neurones with dendrites may result from some degree of terminal segregation on dendritic arborizations.

Action Potentials↗
PubMed1983

Tonic and reflex synaptic activity recorded in ciliary ganglion cells of anaesthetized rabbits.

We have studied patterns of synaptic activity in rabbit ciliary ganglion cells by intracellular recording in vivo, and have examined the morphology of functionally characterized neurones by intracellular injection of horseradish peroxidase. Nearly all of the neurones studied (293 of 300) received tonic synaptic input from preganglionic neurones. This tonic activity was not decreased by darkness or by acute optic nerve section. The rate of tonic synaptic activity recorded in the vast majority of neurones (94%) changed in response to retinal illumination. Most ganglion cells showed an increased rate; some cells, however, showed decreased activity during illumination. The rate of synaptic activity recorded in ciliary neurones tended to be progressively higher in neurones with more complex geometries. Neurones with similar reflex properties included cells that lacked dendrites and cells with complex dendritic arborizations; conversely, neurones with similar geometries often had different reflex characteristics. The synaptic activity arising from different preganglionic axons innervating the same ganglion cell was not temporally linked in any obvious way. The relevance of these results to the regulation of the number of axons that innervate target neurones is discussed.

Animals↗