The effects of extreme nutritional conditions on the neurochemistry of reward and addiction.

Weight loss is a frequent problem in space flights. We now claim that it may affect performance and drug-seeking behavior by altering midbrain neurochemistry. In food-deprived rats (20-30% underweight) basal extracellular dopamine levels in the nucleus accumbens decrease to 40-50% of normal and locomotion is depressed. However, amphetamine-induced dopamine release and locomotion are higher than in controls (1825% vs. 595% after a 25 micromoles d-amphetamine intraaccumbens infusion). The lower basal and the higher stimulated dopamine levels suggest that the neurotransmitter accumulates presynaptically in the accumbens of the underweight rats due to subnormal basal release. Psychostimulants are more rewarding for underweight subjects possibly because they release significantly more dopamine from elevated presynaptic stores into the accumbens. Consequently, weight loss can lead both to depression of performance and propensity to substance abuse. These effects should be considered when providing nutritional resources for space flights so that weight loss is limited.