Disassembly of the Cholinergic Postsynaptic Apparatus Induced by Axotomy in Mouse Sympathetic Neurons: The Loss of Dystrophin and β-dystroglycan Immunoreactivity Precedes that of the Acetylcholine Receptor

Abstract

In mouse sympathetic superior cervical ganglion (SCG), cortical cytoskeletal proteins such as dystrophin (Dys) and beta1sigma2 spectrin colocalize with beta-dystroglycan (beta-DG), a transmembrane dystrophin-associated protein, and the acetylcholine receptor (AChR) at the postsynaptic specialization. The function of the dystrophin-dystroglycan complex in the organization of the neuronal cholinergic postsynaptic apparatus was studied following changes in the immunoreactivity of these proteins during the disassembly and subsequent reassembly of the postsynaptic specializations induced by axotomy of the ganglionic neurons. After axotomy, a decrease in the number of intraganglionic synapses was observed (t1/2 8 h 45'), preceded by a rapid decline of postsynaptic specializations immunopositive for beta-DG, Dys, and alpha3 AChR subunit (alpha3AChR) (t1/2 3 h 45', 4 h 30' and 6 h, respectively). In contrast, the percentage of postsynaptic densities immunopositive for beta1sigma2 spectrin remained unaltered. When the axotomized neurons began to regenerate their axons, the number of intraganglionic synapses increased, as did that of postsynaptic specializations immunopositive for beta-DG, Dys, and alpha3AChR. The latter number increased more slowly than that of Dys and beta-DG. These observations suggest that in SCG neurons, the dystrophin-dystroglycan complex might play a role in the assembly-disassembly of the postsynaptic apparatus, and is probably involved in the stabilization of AChR clusters.

Expression and localization of agrin during sympathetic synapse formation in vitro

“…In muscle, agrin also binds to ␣-dystroglycan, a member of the dystrophinassociated glycoprotein complex, and dystroglycan is concentrated at the neuromuscular junction (Burden, 1998). Dystroglycan and dystrophin have also been shown by immunoelectron microscopy to be present postsynaptically in the SCG in vivo (De Stefano et al, 1997;Zaccaria et al, 1998). Consistent with this, we found that ␣-dystroglycan colocalized with agrin at sympathetic synapses, and could therefore act as an agrin receptor.…”

Clustering of Nicotinic Acetylcholine Receptors: From the Neuromuscular Junction to Interneuronal Synapses

“…A possible link between synaptic AChRs and the D/UGC is found in the following studies. Ganglionic axotomy generated a coinciding reversible decrease of immunoreactivity of β-dystroglycan, dystrophin and α3 AChR subunits in the mouse superior cervical ganglion, which preceded the decrease in the number of intraganglionic synapses (216).…”

Review: Dystroglycan in the Nervous System

“…Zaccaria et al observed a rapid decline of postsynaptic dystroglycan, dystrophin and acetylcholine receptors after axotomy, followed by a decrease of intraganglionic synapses. When the severed axons regenerated, the number of synapses and reactivity for dystroglycan and dystrophin increased, accompanied by a slower increase of acetylcholine receptors (Zaccaria et al, 1998b). On the mRNA level, acetylcholine receptor mRNA and dystrophin mRNA were decreased by postganglionic nerve crush, while dystroglycan mRNA were increased (Zaccaria et al, 2001b).…”

“…This discrepancy might be due to a lower turnover of dystroglycan in these areas, accompanied by a lower mRNA level. In the superior cervical ganglion, a part of the sympathetic nervous system, dystroglycan was found on the postsynaptic apparatus of intraganglionic, cholinergic synapses (Zaccaria et al, 1998a). Dystroglycan reactivity was also seen on synapses formed by dissociated neurons of the superior cervical ganglion in vitro (Gingras and Ferns, 2001b).…”