| Current McNair Scholars
An Assessment
of Synapse Elimination in Xenopus laevis
by Patrick Popa
Using various stages of Xenopus laevis
frog tadpoles as reference specimens, this research
seeks to answer how synapse elimination occurs (i.e.
the underlying mechanisms behind mononeuronal innervation)
and the possible role of synapse activity (synaptic
efficacy) in this process during embryonic development.
Data will be collected using cholinesterase stained
pectoral muscle fibers from stage 56-66 tadpoles.
In adults, the number of neuromuscular junctions
and motor inputs (axons) per muscle fiber is fixed.
However, during embryonic development the number
of neuromuscular junctions and motor inputs vary
but then finalize as embryonic development terminates.
Initially, there is excessive synapse formation
which is followed by synapse elimination. This synapse
elimination results in a reduction in polyneuronal
innervation, separation of motor units, and establishment
of the adult pattern of mononeuronal innervation.
There is also evidence that suggests that synapse
elimination is feasible in adults. The splicing
of motor axons in adults causes regeneration to
occur; this process establishes polyneuronal innervation
akin to what is seen in early embryonic development.
However, mononeuronal innervation occurs shortly
thereafter, again similar to what is seen in embryonic
development (McArdle). This finding has very important
implications. It may elucidate the mechanism behind
responses to neural injury. Therefore this preliminary
research’s task is to determine at what tadpole
stages do significant changes in the number of NMJs
per fiber occur, and to examine the possible concurrent
elimination of inputs into each NMJ as a function
of synchronous activity in order to understand the
process of synapse elimination.
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