Doktorsavhandling från Karolinska Institutet

Plats: Anatomibyggnadens föreläsningssal (Doktorsringen 17)
Tid: Fredagen den 31 maj 1996, kl. 9.00

Normal development of the nervous system depends upon complex interactions
between cells and their local environment. These interactions may be disturbed by
toxic and infectious agents. It is well known that such agents can cause
malformations, due to interference with neural tube formation or neuronal
proliferation and migration. However, little is known about potential effects on
neuronal differentiation, and in particular on synapse formation. Neuromuscular
junctions have served as models in studies of synaptic structure and function and as
such they have been used in this thesis. The thesis examines if mumps virus and
IFN-y can affect the interactions between nerve and muscle cells in culture, with
particular reference to the myotubes capacity to aggregate nicotinic acetylcholine
receptors (AChRs), which is an early event during the development of the
neuromuscular junctions.
Fluorescence-conjugated a-bungarotoxin (FlTC-a-Btx), that binds specifically to
the AChR was used in order to study changes of receptor distribution during
development. The localization of various virus proteins and skeletal muscle specific
cytoskeleton proteins was studied with immunohistochemical techniques. Myoblast
proliferation was studied using a thymidine analog as a marker of cell proliferation.
Different nerve fiber populations coming to the myotubes were visualized with
immunofluorescence of synaptophysin and a novel cholinergic-specific plasma-
membrane antigen. The specificity of this novel cholinergic antigen, designated as
Chol-2, was recognized by its antisera ability to sensitize the cholinergic
subpopulation of rat-brain synaptosomes and to lyse them by the complement
system.
From the presented studies, it was shown that the RW-strain of mumps virus can
selectively infect skeletal muscle cells during the myoblast stage of development;
and that such infected myoblasts can fuse to form virus antigen containing
myotubes. The formation of AChR aggregates in these infected myotubes was
inhibited when they were co-cultured with spinal cord cells. Similar results were
obtained by exposure of the cultures to lymphocyte derived IFN-y, as well as to a
neuronal IFN-y like molecule isolated from sensory ganglia. This isolated molecule
had a molecular weight distinct from that of Iymphocyte-derived IFN-y, but shared
a number of bioactivities, namely antiviral effects, increase of skeletal muscle cell
proliferation and induction of MHC antigens expression. A notable effect was also
that the molecule, like lymphocyte-derived IFN-y, induced nitric oxide (NO)
production in cultures from the nervous system. NO has been implied to play a role
in the modulation of synapse formation, but no effects on AChR aggregation was
observed in the present studies. In conclusion, this thesis demonstrates that a non-
lytic infection with a common paramyxovirus and a key regulative cytokine can
inhibit AChR aggregation and thus disturb the formation of synapses. This may be
of significance for our understanding of the pathogenic mechanisms underlying
disturbances of the nervous system which may evolve as a result of infections
during infancy.