Geneeskundige Stichting Koningin Elisabeth verslag - GSKE - FMRE

During last year, our laboratory tackled three projects. The first was vestibular compensation;
the second concerned perturbations of long-term potentiation (LTP) in transgenic mice related
to Alzheimer's disease; and the third studied was related to the mechanisms of late-LTP.
I. VESTIBULAR COMPENSATION
Background
At rest, in the absence of any movement of the head, the neurons of the vestibular nucleus are
spontaneously active. After a unilateral labyrinthectomy, this basal activity which is very
important for our static equilibrium, ceases. However, in the guinea pig, it recovers completely
in a few days. We have investigated the potential mechanisms underlying this recovery, a
dramatic example of brain plasticity.
Experiments on brainstem slices
We investigated the properties of the vestibular neurons in brainstem slices, using intracellular
microelectrodes. Responses to currents injected intracellularly in vestibular neurons from
control animals were compared to those obtained in vestibular neurons from animals
labyrinthectomized one week earlier. Using this technique, first we have demonstrated that
the performances of the spike generator, which transforms synaptic currents into a pattern of
action potentials, is not changed by labyrinthectomy (NeuroReport, 2002). Then, we
investigated the pacemaker currents in the vestibular neurons. We have found that one of
them, the low-threshold calcium current, was increased after labyrinthectomy. Using
antibodies against the 3 species of low-threshold calcium channels (α1G, α1H and α1I), we
have shown that the observed increase in calcium current was not related to an increase
synthesis of these channels (this work is submitted for publication). It shows that adult neurons
deprived of one of their major synaptic inputs undergo modifications in their electroreceptors,
a form of plasticity which has been hitherto underestimated.
Experiments on neuronal culture
In this approach, we intended to isolate in a co-culture the neurons of the vestibular ganglion
and the neurons of the vestibular nucleus, in order to be able to study phenomena similar to
vestibular compensation on a more simple preparation. Up to now, we have succeeded to
obtain such a co-culture living for 30 days. In a first step, we studied the electrophysiological
maturation of the vestibular neurons in culture in the absence of the vestibular afferent fibers.
After an initial regression due to the plating procedure, the neurons matured. However, the
degree of maturation achieved after 30 days was less than observed in neurons from adult
animals and similar to that shown by neurons from newborn rats. (Neuroscience Letters, in
press).
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