These findings support the hypothesis that decreased levels of SP in certain brain regions may contribute to high levels of anxiety in rats. Decreased levels of DBI and increased levels of NPY in high-anxiety animals may act as compensatory mechanisms.

We studied the effect of single treatment with nicotine, ethanol, and morphine on locomotor activity of WAG/G and Fischer-344 rats chronically drinking caffeine solution. In Fischer-344 rats receiving caffeine locomotor activity in the open-field test was much lower than in animals drinking water, while in WAG/G rats no differences in locomotor activity were found. Chronic caffeine intake increased rat sensitivity to the stimulating effect of nicotine and ethanol, but decreased their sensitivity to the depressant effect of morphine. Chronic caffeine treatment most significantly modulated the effects of nicotine, ethanol, and morphine in Fischer-344 rats.