To help in research of multiple
sclerosis (MS) researchers utilize an animal model, experimental allergic
encephalitis (EAE). EAE is an acute autoimmune demyelination disease, that
matches the symptomatology of MS. Guinea
pigs with EAE are reported to have a reduction of serotonin within the
central nervous system (CNS), when compared to control subjects. The reduction
of serotonin within the CNS leads to an effect on CNS serotonin transmissions
in EAE, either at the level of serotonin receptor itself, or at the level
of serotonin transmitting neurons (Scott,
Cashman, and Spitler, 1982-83). The symptoms of EAE are due to the
inhibition of serotonin transmission.
In animals with EAE, administration
of L-5-hydroxytrytophan, a precursor to serotonin, reversed the effects
of impaired serotonergic transmission. Suggesting that there might be a
blockade of serotonin receptors (Scott,
Cashman, and Spitler, 1982-83), which can be overcome by the addition
of a drug that increases the CNS serotonin levels. The addition of a precursor
of serotonin has such an effect, and then the addition of antidepressant
type drugs may affect the symptoms of EAE in a positive way.
When an antidepressant is administered
the ultimate goal of the drug is to raise the levels of serotonin in the
synapse. The drug can act as a serotonin reuptake blocker increasing the
levels of serotonin in the synapse or will increase the serotonergic transmissions.
As postulated earlier if the levels of serotonin can be raised then there
would be a positive effect on the symptoms of MS and EAE. This suggests
that further studies of the EAE model should be completed measuring the
effects of antidepressant drugs such as serotonin selective reuptake inhibitors
(SSRI's). Data shows that drugs that increase serotonin in the CNS
such as imipramine hydrochloride, tryptophan and carbidopa, prolonged the
survival in animals with EAE, whereas reserpine, a drug that diminishes
the amount of serotonin in the CNS provided evidence of impairment of serotonergic
transmissions.
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