the brain of humans. Research has shown a correlation between prevalence of
antibody titers to T. gondii and psychological illness in humans. Recent studies
indicate that individuals seropositive for T. gondii antibodies are more likely
to develop psychotic disorders, including schizophrenia, which is associated with
changes in the dopamine neurotransmitter system. Dopamine in the brain may play a
role in proliferation, chemoattraction, infection efficiency, or stage conversion
of T. gondii. Because tachyzoites are the first developmental stage to reach the
brain, the present study was conducted to determine the effects of dopamine on
their development in vitro .In human fibroblast host cells, dopamine was added at
either 100 nM or 250 nM to cell culture media and the numbers of tachyzoites
produced at 48 hr were determined and compared to vehicle-treated controls. An
increase of tachyzoite numbers and increased destruction in cell monolayer were
observed at both concentrations of dopamine. Dopamine used at 250 nM caused a
significant (P< 0.05) increase in tachyzoites counts compared to controls.
Dopamine antagonists (10 µM) did not significantly alter dopamine stimulated
tachyzoite production in human fibroblasts. In primary rat neonatal brain
cultures, dopamine (200 µM) significantly (P<0.05) increased numbers of
intracellular tachyzoites after 24 h. The role that this increase in tachyzoite
production under the stimulus of dopamine plays in the modulation of neural
infection in humans awaits further studies.
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