The effects of treatment with toluene in vivo (80 ppm, 3 days, 6 h/day) and in vitro (19 μmol/ml) were analyzed on the binding characteristics of [3H]neurotensin in rat striatal membranes. Exposure to toluene in vivo did not produce any significant effects on the binding characteristics of [3H]neurotensin. However, the addition of toluene in vitro caused a trend for a decreased Bmax value and produced a significantly reduced KD value of [3H]neurotensin binding. The absence of effects at 80 ppm indicates that the neurotensin receptor is relatively insensitive to toluene exposure, in contrast to, e.g. the dopamine agonist binding sites. Furthermore, the toluene response of the neurotensin receptor, as seen after treatment in vitro, is different from the responses seen in many monoamine receptors, which show decreased affinities following toluene exposure. It is possible that toluene is mediating its effects on the neurotensin receptor by changing the lipid micro-environment in which the receptor is situated. Another explanation would be that toluene selectively acts on the monoamine receptors, e.g. the more sensitive dopamine receptors, which through receptor-receptor interactions would cause the response seen in the neurotensin receptor. However, it cannot be excluded that the suggested receptor-receptor interaction itself is affected by toluene.
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