Geneeskundige Stichting Koningin Elisabeth ... - GSKE - FMRE

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Secondly, the Et-1 animal model was used to test the effect of different potential neuroprotective
agents.
Since it is increasingly recognized that the development of highly selective compounds for
neuronal Ca 2+ channels is not only important for the treatment of stroke, but also for further clarification
of the mechanisms of neurodegeneration, one of the drug trials dealt with the use of
Ca 2+ antagonists in the Et-1 model. In this study, two commonly used antagonists, nimodipine
(0.1 mg/kg) and verapamil (0.4 mg/kg) were tested, next to a relatively new compound,
LY393613 (15 mg/kg), a novel neuronal (N/P/Q-type) calcium channel blocker. Nimodipine
and verapamil are two L-type calcium channel blockers. Nimodipine was also selected for its
known hemodynamic properties. LY393613 was demonstrated to significantly attenuate the
ischaemia-induced increases in extracellular glutamate levels, and coherently to attenuate the
infarct volume. These effects were shown not to be due to the direct blockade of the vasoconstrictive
actions of Et-1, nor to the alterations of cerebral blood flow. It was concluded that
LY393613, a calcium channel blocker with low molecular weight, may be useful as an antiischaemic
agent.
Glutamate and glutamate receptors also play an important role in the acute neurodegeneration,
following cerebral ischaemia. The sudden energy failure results in a massive release of
excitatory amino acids and other neurotransmitters. Moreover, energy failure prevents the reuptake
of glutamate by its transporter, and reversal of the transporter may further increase the
extracellular glutamate levels. Performed studies showed that the newly developed kainate
receptor antagonist (iGluR 5), LY377770, behaves as a neuroprotectant, both in models for global
and focal ischaemia. The effects of LY377770, a selective iGluR 5 receptor antagonist,
MK801, a selective NMDA receptor antagonist, as well as CNQX, a mixed AMPA/kainate
receptor antagonist, were tested. The extracellular striatal effluxes of dopamine and glutamate
were monitored, after i.p. administration of LY377770 (75 mg/kg), MK801 (2.5 mg/kg) or
CNQX (10 mg/kg). Microdialysis studies showed that only the ischaemia-induced glutamate
release was significantly affected using LY377770. On the other hand, MK801 was successful
in attenuating the dopamine as well as the glutamate efflux, either in the pre- as well as in
the post-treated animals. CNQX showed to have only minor effects. Laser Doppler flowmetry
showed that none of the tested compounds was able to affect the blood flow significantly.
Histology studies showed significant protection with the new compound LY377770, as well as
with MK801. Hence, since LY377770 (1) has a good solubility, (2) has only few side effects
and (3) protects against ischaemic brain damage, even when administered post-occlusion, it
may be useful for the treatment of acute neurodegenerative diseases.
Finally, the free radical formation and its contribution to the development of the ischaemic
insult was focused. Free radicals, nitric oxide and especially dopamine and quinones, i.e.
dopamine’s oxidative products, were shortly described. Quinone formation was measured online
in the dialysates during development of ischaemia. It was observed that excessive quinone
formation occurred shortly after the ischaemia-induced dopamine release had reached its maximum.
Hence, it was assumed that the formation of quinones coincided with the reperfusion
phase. Increase in striatal quinones started approximately 10 minutes after the Et-1 induced