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Neurotransmitter secretion along growing nerve processes: comparison with synaptic vesicle exocytosis.

Zakharenko S, Chang S, O'Donoghue M, Popov SV - J. Cell Biol. (1999)

Bottom Line: We found that the parameters of neurotransmitter secretion at the nerve terminal and at the middle axon were strikingly similar.These results lead us to conclude that, as in the case of the presynaptic nerve terminal, synaptic vesicles involved in neurotransmitter release along the axon contain a complement of proteins for vesicle docking and Ca2+-dependent fusion.Taken together, our results support the idea that, in developing axons, the rudimentary machinery for quantal neurotransmitter secretion is distributed throughout the whole axonal surface.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Biophysics M/C 901, University of Illinois, Chicago, Illinois 60612, USA.

ABSTRACT
In mature neurons, synaptic vesicles continuously recycle within the presynaptic nerve terminal. In developing axons which are free of contact with a postsynaptic target, constitutive membrane recycling is not localized to the nerve terminal; instead, plasma membrane components undergo cycles of exoendocytosis throughout the whole axonal surface (Matteoli et al., 1992; Kraszewski et al., 1995). Moreover, in growing Xenopus spinal cord neurons in culture, acetylcholine (ACh) is spontaneously secreted in the quantal fashion along the axonal shaft (Evers et al., 1989; Antonov et al., 1998). Here we demonstrate that in Xenopus neurons ACh secretion is mediated by vesicles which recycle locally within the axon. Similar to neurotransmitter release at the presynaptic nerve terminal, ACh secretion along the axon could be elicited by the action potential or by hypertonic solutions. We found that the parameters of neurotransmitter secretion at the nerve terminal and at the middle axon were strikingly similar. These results lead us to conclude that, as in the case of the presynaptic nerve terminal, synaptic vesicles involved in neurotransmitter release along the axon contain a complement of proteins for vesicle docking and Ca2+-dependent fusion. Taken together, our results support the idea that, in developing axons, the rudimentary machinery for quantal neurotransmitter secretion is distributed throughout the whole axonal surface. Maturation of this machinery in the process of synaptic development would improve the fidelity of synaptic transmission during high-frequency stimulation of the presynaptic cell.

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Distribution of dynamin, AP-2, AP-3, and ARF along  the neurites. Neurons were fixed, detergent-permeabilized, and  then stained with antibodies to dynamin-1, α subunit of AP-2, σ  subunit of AP-3, and ARF1. Immunoreactivity recognized by all  four antibodies was present throughout the whole axonal surface  and had a finely punctate appearance. In the case of dynamin and  AP-2, immunoreactivity was concentrated at the growth cone region. Immunoreactivity to AP-3 and ARF was more uniformly  distributed throughout the axon. For quantitative analysis of fluorescence intensity distribution, intensity profiles of the axons  were created from immunofluorescence images. The sampling areas were chosen along the axon and the average intensity of fluorescence in these areas (arbitrary units) was plotted as a function  of distance from the growth cone. For each of the fluorescence  profiles, the data from at least 25 different neurons were pooled  together.
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Figure 14: Distribution of dynamin, AP-2, AP-3, and ARF along the neurites. Neurons were fixed, detergent-permeabilized, and then stained with antibodies to dynamin-1, α subunit of AP-2, σ subunit of AP-3, and ARF1. Immunoreactivity recognized by all four antibodies was present throughout the whole axonal surface and had a finely punctate appearance. In the case of dynamin and AP-2, immunoreactivity was concentrated at the growth cone region. Immunoreactivity to AP-3 and ARF was more uniformly distributed throughout the axon. For quantitative analysis of fluorescence intensity distribution, intensity profiles of the axons were created from immunofluorescence images. The sampling areas were chosen along the axon and the average intensity of fluorescence in these areas (arbitrary units) was plotted as a function of distance from the growth cone. For each of the fluorescence profiles, the data from at least 25 different neurons were pooled together.

Mentions: Synaptic vesicle endocytosis at the nerve terminal requires clathrin adaptor complex AP-2 and dynamin (Cremona and De Camilli, 1997). The localization of AP-2 and dynamin in Xenopus neurons which were free of contact with other cells was investigated by immunofluorescence using antibodies to these proteins. Immunoreactivity to dynamin and AP-2 was found to have a widespread distribution throughout the axon (Fig. 14). Quantitative analysis of the fluorescence intensity profiles indicated that the intensity of staining was approximately fivefold higher at the growth cone region in comparison with the middle axonal segment.


Neurotransmitter secretion along growing nerve processes: comparison with synaptic vesicle exocytosis.

Zakharenko S, Chang S, O'Donoghue M, Popov SV - J. Cell Biol. (1999)

Distribution of dynamin, AP-2, AP-3, and ARF along  the neurites. Neurons were fixed, detergent-permeabilized, and  then stained with antibodies to dynamin-1, α subunit of AP-2, σ  subunit of AP-3, and ARF1. Immunoreactivity recognized by all  four antibodies was present throughout the whole axonal surface  and had a finely punctate appearance. In the case of dynamin and  AP-2, immunoreactivity was concentrated at the growth cone region. Immunoreactivity to AP-3 and ARF was more uniformly  distributed throughout the axon. For quantitative analysis of fluorescence intensity distribution, intensity profiles of the axons  were created from immunofluorescence images. The sampling areas were chosen along the axon and the average intensity of fluorescence in these areas (arbitrary units) was plotted as a function  of distance from the growth cone. For each of the fluorescence  profiles, the data from at least 25 different neurons were pooled  together.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2132923&req=5

Figure 14: Distribution of dynamin, AP-2, AP-3, and ARF along the neurites. Neurons were fixed, detergent-permeabilized, and then stained with antibodies to dynamin-1, α subunit of AP-2, σ subunit of AP-3, and ARF1. Immunoreactivity recognized by all four antibodies was present throughout the whole axonal surface and had a finely punctate appearance. In the case of dynamin and AP-2, immunoreactivity was concentrated at the growth cone region. Immunoreactivity to AP-3 and ARF was more uniformly distributed throughout the axon. For quantitative analysis of fluorescence intensity distribution, intensity profiles of the axons were created from immunofluorescence images. The sampling areas were chosen along the axon and the average intensity of fluorescence in these areas (arbitrary units) was plotted as a function of distance from the growth cone. For each of the fluorescence profiles, the data from at least 25 different neurons were pooled together.
Mentions: Synaptic vesicle endocytosis at the nerve terminal requires clathrin adaptor complex AP-2 and dynamin (Cremona and De Camilli, 1997). The localization of AP-2 and dynamin in Xenopus neurons which were free of contact with other cells was investigated by immunofluorescence using antibodies to these proteins. Immunoreactivity to dynamin and AP-2 was found to have a widespread distribution throughout the axon (Fig. 14). Quantitative analysis of the fluorescence intensity profiles indicated that the intensity of staining was approximately fivefold higher at the growth cone region in comparison with the middle axonal segment.

Bottom Line: We found that the parameters of neurotransmitter secretion at the nerve terminal and at the middle axon were strikingly similar.These results lead us to conclude that, as in the case of the presynaptic nerve terminal, synaptic vesicles involved in neurotransmitter release along the axon contain a complement of proteins for vesicle docking and Ca2+-dependent fusion.Taken together, our results support the idea that, in developing axons, the rudimentary machinery for quantal neurotransmitter secretion is distributed throughout the whole axonal surface.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Biophysics M/C 901, University of Illinois, Chicago, Illinois 60612, USA.

ABSTRACT
In mature neurons, synaptic vesicles continuously recycle within the presynaptic nerve terminal. In developing axons which are free of contact with a postsynaptic target, constitutive membrane recycling is not localized to the nerve terminal; instead, plasma membrane components undergo cycles of exoendocytosis throughout the whole axonal surface (Matteoli et al., 1992; Kraszewski et al., 1995). Moreover, in growing Xenopus spinal cord neurons in culture, acetylcholine (ACh) is spontaneously secreted in the quantal fashion along the axonal shaft (Evers et al., 1989; Antonov et al., 1998). Here we demonstrate that in Xenopus neurons ACh secretion is mediated by vesicles which recycle locally within the axon. Similar to neurotransmitter release at the presynaptic nerve terminal, ACh secretion along the axon could be elicited by the action potential or by hypertonic solutions. We found that the parameters of neurotransmitter secretion at the nerve terminal and at the middle axon were strikingly similar. These results lead us to conclude that, as in the case of the presynaptic nerve terminal, synaptic vesicles involved in neurotransmitter release along the axon contain a complement of proteins for vesicle docking and Ca2+-dependent fusion. Taken together, our results support the idea that, in developing axons, the rudimentary machinery for quantal neurotransmitter secretion is distributed throughout the whole axonal surface. Maturation of this machinery in the process of synaptic development would improve the fidelity of synaptic transmission during high-frequency stimulation of the presynaptic cell.

Show MeSH
Related in: MedlinePlus