Axosomatic synapses of the rat ciliary ganglion

Robertson, George N.; Jackson, Patrick C.

doi:10.1002/(sici)1098-2396(199603)22:3<269::aid-syn10>3.0.co;2-v

Cited by 5 publications

(4 citation statements)

References 40 publications

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“…Somatic spines have been seen both on CNS neurons, as in the case of dentate gyrus granule cells (Stirling and Bliss, 1978;Seress and Ribak, 1985;Bundman et al, 1994;Wenzel et al, 1994), and on autonomic neurons from a variety of ganglia (Piezzi and Rodriguez-Echandia, 1968;Watanabe, 1971;Smolen, 1988;Robertson and Jackson, 1996). On chick ciliary neurons the somatic spines are grouped in clusters and are interwoven and tightly folded down on the soma to form mats (Shoop et al, 1999).…”

Section: Abstract: Nicotinic; Spine; Receptor; Ciliary; Ganglion; Sysupporting

confidence: 60%

Ultrastructure of a Somatic Spine Mat for Nicotinic Signaling in Neurons

et al. 2002

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Chick ciliary neurons have somatic spines grouped in discrete clumps or mats tightly folded against the soma and enriched in nicotinic receptors containing ␣7 subunits. An embryonic ciliary neuron has one to two dozen such spine mats, all overlaid by a large presynaptic calyx engulfing the cell. Three-dimensional tomographic reconstruction from serial thick sections revealed 13 somatic spines in one complete spine mat on a ciliary neuron late in embryogenesis. The spines varied in morphology and usually were branched but had numerous similarities to dendritic spines, including mean length, volume, surface area, presence of endoplasmic reticulum, and occasional multivesicular bodies. The spines invariably were connected to the soma via a narrow neck of ϳ0.2 m in diameter as found for dendritic spines, suggesting restricted access from spine lumen to soma. A prominent difference between dendritic and somatic spines is the absence of postsynaptic densities from most somatic spines both on embryonic and adult ciliary neurons. Transmitter access to receptors on the spines may occur either by lateral diffusion from release sites over nearby postsynaptic densities or by release directly onto spines from the overlying calyx lined with vesicles. The latter is less likely in the adult, where some spines are adjacent to but not overlaid by vesicle-enriched presynaptic structures. The anatomical configuration of spine mats suggests coordinate spine activation by transmitter release into a confined volume while spine morphology is used to control the chemical consequences of synaptic signaling.

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Section: Abstract: Nicotinic; Spine; Receptor; Ciliary; Ganglion; Sysupporting

confidence: 60%

Ultrastructure of a Somatic Spine Mat for Nicotinic Signaling in Neurons

et al. 2002

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“…Spine-like projections emanating from neuron cell bodies have been described in several kinds of autonomic ganglia (Piezzi and Rodriquez-Echandia, 1968;Watanabe, 1971;Smolen, 1988;Robertson and Jackson, 1996). Identification of the projections as somatic spines in the present experiments depended on several criteria.…”

Section: Discussionmentioning

confidence: 77%

Neuronal Acetylcholine Receptors with α7 Subunits Are Concentrated on Somatic Spines for Synaptic Signaling in Embryonic Chick Ciliary Ganglia

Shoop¹,

et al. 1999

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Nicotinic acetylcholine receptors containing alpha7 subunits are widely distributed in the vertebrate nervous system. In the chick ciliary ganglion such receptors generate large synaptic currents but appear to be excluded from postsynaptic densities on the cells. We show here that alpha7-containing receptors are concentrated on somatic spines in close proximity to putative sites of presynaptic transmitter release. Intermediate voltage electron microscopy on thick sections, together with tomographic reconstruction, permitted three-dimensional analysis of finger-like projections emanating from cell bodies. The projections were identified as spines based on their morphology, cytoskeletal content, and proximity to presynaptic elements. Both in situ and after ganglionic dissociation, the spines were grouped on the cell surface and tightly folded into mats. Immunogold labeling of receptors containing alpha7 subunits showed them to be preferentially concentrated on the somatic spines. Postsynaptic densities were present in vivo both on the soma near spines and occasionally on the spines themselves. Synaptic vesicle-filled projections from the presynaptic calyx were interdigitated among the spines. Moreover, the synaptic vesicles often abutted the membrane and sometimes included Omega profiles as if caught in an exocytotic event, even when no postsynaptic densities were juxtaposed on the spine. The results suggest several mechanisms for delivering transmitter to alpha7-containing receptors, and they support new ideas about synaptic signaling via spines. They also indicate that neurons must have specific mechanisms for targeting alpha7-containing receptors to desired locations.

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“…Cornbrooks et al 1992). As in sympathetic ganglia, a third or more of the synapses may occur in association with small somatic processes or spines (Yamakado and Yohro 1977;Yokota and Burnstock 1983;Baluk and Gabella 1987;Ng et al 1992;May and Warren 1993;Robertson and Jackson 1996); however, no unbiased systematic studies of the relationships between preganglionic synapses and such spine-like processes have been performed. Similarly, although axo-dendritic synapses are often reported to be more common than axo-somatic synapses (e.g.…”

Section: Parasympathetic Ganglia -Is Anything Different?mentioning

confidence: 99%

“…Indeed, networks of dye-coupled Schwann cells could provide some sort of trophic guidance or support for preganglionic synapses (see Pomeroy and Purves 1988;Robertson and Jackson 1996).…”

Section: Enteric Ganglia -Complex Local Circuitsmentioning

confidence: 99%

Structure of peripheral synapses: autonomic ganglia

Gibbins

Morris

2006

Cell Tissue Res

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Final motor neurons in sympathetic and parasympathetic ganglia receive synaptic inputs from preganglionic neurons. Quantitative ultrastructural analyses have shown that the spatial distribution of these synapses is mostly sparse and random. Typically, only about 1%-2% of the neuronal surface is covered with synapses, with the rest of the neuronal surface being closely enclosed by Schwann cell processes. The number of synaptic inputs is correlated with the dendritic complexity of the target neuron, and the total number of synaptic contacts is related to the surface area of the post-synaptic neuron. Overall, most neurons receive fewer than 150 synaptic contacts, with individual preganglionic inputs providing between 10 and 50 synaptic contacts. This variation is probably one determinant of synaptic strength in autonomic ganglia. Many neurons in prevertebral sympathetic ganglia receive additional convergent synaptic inputs from intestinofugal neurons located in the enteric plexuses. The neurons support these additional inputs via larger dendritic arborisations together with a higher overall synaptic density. There is considerable neurochemical heterogeneity in presynaptic boutons. Some synapses apparently lack most of the proteins normally required for fast transmitter release and probably do not take part in conventional ganglionic transmission. Furthermore, most preganglionic boutons in the ganglionic neuropil do not form direct synaptic contacts with any neurons. Nevertheless, these boutons may well contribute to slow transmission processes that need not require conventional synaptic structures.

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Axosomatic synapses of the rat ciliary ganglion

Cited by 5 publications

References 40 publications

Ultrastructure of a Somatic Spine Mat for Nicotinic Signaling in Neurons

Ultrastructure of a Somatic Spine Mat for Nicotinic Signaling in Neurons

Neuronal Acetylcholine Receptors with α7 Subunits Are Concentrated on Somatic Spines for Synaptic Signaling in Embryonic Chick Ciliary Ganglia

Structure of peripheral synapses: autonomic ganglia

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