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J A Raper

Publications and source records attributed to J A Raper.

47 records · Page 3Linked to original sources
PubMed1987

Interactions between growth cones and neurites growing from different neural tissues in culture.

We have previously used retinal and sympathetic explants to show that growth cones recognize and retract from specific neurites in culture (Kapfhammer et al., 1986). In an effort to determine the generality of this phenomenon and to see how many different neurite labels can be detected by it, we have studied interactions between individual growth cones and neurites extending from a variety of neural sources in vitro. Using most of the possible pairings between sympathetic, ciliary, dorsal root ganglion (DRG), retinal, and diencephalic neurons, we have found that in most instances: (1) Growth cones do not retract from neurites originating from the same tissue; (2) retinal growth cones do not retract from diencephalic neurites; (3) sympathetic, ciliary, and DRG growth cones, with one possible exception, do not retract from sympathetic, ciliary, or DRG neurites; (4) retinal growth cones retract from sympathetic, ciliary, and DRG neurites; (5) sympathetic, ciliary, and DRG growth cones retract from retinal neurites; and (6) sympathetic growth cones retract from diencephalic neurites. A simple hypothesis consistent with these results is that 2 labels exist--one associated with central neurites and another associated with peripheral neurites--and that peripheral growth cones are programmed to retract from the central label and central growth cones are programmed to retract from sympathetic, ciliary, and DRG neurites; (5) symevant to the separation of the CNS and PNS during development.

Adrenergic Fibers↗
PubMed1986

The selective inhibition of growth cone extension by specific neurites in culture.

We have found that neurites from embryonic chick retinal and sympathetic explants do not mix in culture, while retinal neurites mix with retinal neurites, and sympathetic neurites mix with sympathetic neurites. These results confirm those obtained with embryonic rat tissues by Bray et al. (1980). We have also used video time-lapse techniques to examine the behavior of individual retinal and sympathetic growth cones as they attempt to cross retinal and sympathetic neurites. We have found that retinal growth cones cross retinal neurites without delay, retinal growth cones usually retract from sympathetic neurites but often cross them on a second advance, sympathetic growth cones repeatedly retract from retinal neurites, rarely managing to cross them at all, and sympathetic growth cones cross sympathetic neurites but are sometimes delayed. Our results indicate that retinal and sympathetic growth cones can distinguish between specific labels associated with retinal and sympathetic neurites. They also suggest that active avoidance could play an important role in growth cone navigation.

Animals↗
PubMed1984

Pathfinding by neuronal growth cones in grasshopper embryos. III. Selective affinity of the G growth cone for the P cells within the A/P fascicle.

The growth cone of the G neuron selectively fasciculates upon specific axon bundles in a stereotypic sequence as it navigates through the developing central nervous system of the grasshopper embryo. It turns and extends anteriorly in the contralateral neuropil of the second thoracic ganglion at a specific choice point where it fasciculates with the A/P axon bundle which contains the axons of the A1, A2, P1, and P2 neurons. We previously hypothesized (Raper, J. A., M. J. Bastiani, and C. S. Goodman (1983) J. Neurosci. 3: 20-41) that this fascicle, or subsets of axons within it, were specifically labeled and that the G neuron was determined to follow this labeled pathway. Here we report on an ultrastructural analysis of the interactions between the G growth cone and its filopodia with the cells of the A/P fascicle at the choice point. As G reaches its choice point, its filopodia are in more frequent contact with the A/P fascicle in comparison to the other longitudinal axon fascicles. Within the A/P fascicle, the tip of G's growth cone is found to be closely associated with the P and not the A axons. Furthermore, before the G growth cone climbs onto the A/P fascicle, its filopodia show a selective affinity for the P axons as compared to the A axons. Another specific interaction involves selective filopodial insertions; only filopodia from the P cells were found to insert into the G growth cone and induce coated pits and vesicles. These findings suggest that G is able to distinguish the A/P fascicle from other axon bundles and, moreover, is able to distinguish the P axons from the A axons. The companion paper (Raper, J. A., M. J. Bastiani, and C. S. Goodman (1984) J. Neurosci. 4: 2329-2345) presents experimental results based on specific axon ablations that further support this hypothesis.

Animals↗
PubMed1984

Pathfinding by neuronal growth cones in grasshopper embryos. IV. The effects of ablating the A and P axons upon the behavior of the G growth cone.

In the companion paper (Bastiani, M. J., J. A. Raper, and C. S. Goodman (1984) J. Neurosci. 4: 2311-2328), we show that as the G growth cone reaches its choice point and turns anteriorly on the A/P fascicle, its filopodia demonstrate selective affinity for the A/P fascicle as compared to the other approximately 25 longitudinal axon fascicles, and within the A/P fascicle itself, G's filopodia selectively contact the P axons as compared to the A axons. These results support the hypothesis that the A/P fascicle, and, moreover, subsets of axons within it (Ps versus As), are specifically labeled and that the G growth cone is determined to follow a particular labeled pathway. We tested the "labeled pathways" hypothesis by specifically ablating these axons and examining the subsequent behavior of the G growth cone in embryos grown in culture. Ablation of the A and P axons prevents G from growing more than a short distance anteriorly, although the G growth cone is within grasp of many other longitudinal axon fascicles. Ablation of only the P axons has a similar effect; the G growth cone behaves normally if only the A axons are ablated. Transmission electron micrograph semiserial section reconstructions of experimental embryos further indicate that G's growth cone behaves abnormally when the A and P axons, or only the P axons, are ablated. The G growth cone branches extensively in the lateral and ventral neuropil without it or its filopodia showing a high affinity for any other axon fascicle. These results indicate that the G growth cone is able to distinguish the A/P fascicle from the other longitudinal axon fascicles in the developing neuropil. Moreover, the results suggest that within the A/P fascicle the G growth cone is able to distinguish the P axons from the A axons.

Animals↗
PubMed1983

Graded synaptic transmission between identified spiking neurons.

Graded synaptic transmission between spiking motoneurons of the pyloric group was studied in the stomatogastric ganglion of the spiny lobster, Panulirus interruptus. Intracellular microelectrodes were placed in the cell bodies of both pre- and postsynaptic neurons. Graded synaptic transmission was found between all tested cell pairs that were known to display spike-evoked synaptic transmission, including PD to LP, PD to PE, PD to PL, PL to LP, and LP to PD. Graded synaptic transmission was effective below the threshold for spikes. Thus, it was possible to study the influence of graded synaptic transmission in normally active ganglia without blockage of spikes by tetrodotoxin. PD and LP neurons that were known to produce spike-evoked inhibitory postsynaptic potentials (IPSPs) were also capable of producing inhibitory effects on postsynaptic cells below the threshold for spikes. When tetrodotoxin (TTX) was used to eliminate both spikes and endogenous membrane oscillations, depolarization of presynaptic neurons produced hyperpolarization of postsynaptic cells. The presynaptic response to a current step usually showed a small early peak and a maintained, slightly lower plateau. The postsynaptic response had a delay, then a rise to a pronounced peak, and a roughly exponential decline to a maintained plateau. There was a presynaptic voltage threshold for any postsynaptic response; beyond the threshold, both pre- and postsynaptic peak and plateau responses increased with increasing current. PD neurons normally are depolarized beyond their release threshold in tetrodotoxin and, thus, released transmitter tonically for the many-hour duration of these experiments. Chemical, tonic synaptic transmission, here called graded synaptic transmission, was demonstrated by the presence of the following criteria: 1) reversal in sign of the postsynaptic response, 2) synaptic delay, 3) reversal potential, 4) postsynaptic conductance increase, 5) graded and reversible block by reduction of external Ca2+, and 6) specific graded block of the LP-to-PD synapse without effect on the PD-to-LP synapse by less than 10 microM picrotoxin added to the bathing medium.

Action Potentials↗
PubMed1983

Pathfinding by neuronal growth cones in grasshopper embryos. I. Divergent choices made by the growth cones of sibling neurons.

We are interested in how the growth cones of identified neurons navigate in the central nervous system of the grasshopper embryo. The behavior of identified growth cones was observed as a function of developmental time by (i) periodically removing embryos from synchronized clutches of eggs and (ii) filling identified neurons in the central nervous system with the fluorescent dye Lucifer Yellow. We examined the first six progeny of the identified neuronal precursor cell, neuroblast 7-4: the Q1, Q2, G, C, Q5, and Q6 neurons. Their growth cones extend sequentially upon the same route across the midline of the posterior commissure of the developing ganglionic neuropil. However, after reaching the contralateral side of the neuropil, their growth cones diverge from each other at reproducible, cell-specific choice points. By focusing our attention on one such choice point, at which the growth cone of the G neuron turns anteriorly while the growth cone of its sibling C neuron turns posteriorly, we hope to elucidate the environmental cues which guide individual growth cones.

Animals↗
PubMed1983

Pathfinding by neuronal growth cones in grasshopper embryos. II. Selective fasciculation onto specific axonal pathways.

In the previous paper (Raper, J.A., M. Bastiani, and C.S. Goodman (1983) J. Neurosci. 3:20-30) we showed that the growth cones of two sibling neurons, the G and C cells, follow the same route in the developing grasshopper neuropil until they reach a stereotypic choice point. Here their growth cones diverge from each other as G turns and extends anteriorly and C turns and extends posteriorly. In this paper we show that the G and C growth cones fasciculate and extend in opposite directions upon a specific bundle of four axons. This occurs even though many other axons are within filopodial reach of the G and C growth cones. We identified the four neurons (the A1, A2, P1, and P2 cells) whose axons form the bundle that G and C extend upon by filling individual axons with Lucifer Yellow and viewing the filled cells in living embryos and by filling individual neurons with HRP and reconstructing the axon bundle from electron micrographs. The G neuron extends anteriorly in the bundle containing these four axons; the C neuron extends posteriorly in the same bundle only after several other axons have joined in. These results suggest that the growth cones of the G and C neurons are determined to recognize and extend upon labeled axons, leading us to propose the "labeled pathways" hypothesis.

Animals↗
PubMed1980

Graded synaptic transmission between spiking neurons.

Graded synaptic transmission occurs between spiking neurons of the lobster stomatogastric ganglion. In addition to eliciting spike-evoked inhibitory potentials in postsynaptic cells, these neurons also release functionally significant amounts of transmitter below the threshold for action potentials. The spikeless postsynaptic potentials grade in amplitude with presynaptic voltage and can be maintained for long periods. Graded synaptic transmission can be modulated by synaptic input to the presynaptic neuron.

Action Potentials↗
PubMed1979

Nonimpulse-mediated synaptic transmission during the generation of a cyclic motor program.

A small neuronal network in the lobster stomatogastric ganglion, composed of impulse-producing motor neurons, gives rise to cyclic patterned outputs. This network continues to generate its cyclic motor program if impulse production within the ganglion is blocked. Continuously graded, nonimpulse-mediated, chemical synaptic transmission is suffucient to coordinate neuronal activity in a functioning pattern generator.

Animals↗