Acetylcholine, dopamine and serotonin are neurotransmitters involved in numerous physiological processes such as memory, sleep and anxiety, all of which are altered following chronic uranium contamination. Uranium could thus act on the synthesis and degradation pathways of these neurotransmitters, culminating in the neurological disorders described in the previous paragraph.
Acetylcholine is involved in learning and memory processes. We highlighted a significant reduction in acetylcholine levels in the entorhinal cortex of rats contaminated with depleted uranium (DU) or enriched uranium (EU) for 1.5 months at the daily dose of 2 mg/kg (-22% and –26%, respectively) (Bensoussan et al., 2009). Under the same experimental conditions, this decrease is associated with an increase (+20%) in acetylcholinesterase activity – the enzyme that breaks down acetylcholine – in the hippocampus of rats contaminated with EU (Bensoussan et al., 2009). These results suggest that acetylcholine which the concentration decreases in cerebral structures involved in cognitive processes, is no longer functioning correctly. This disorder could explain, at least in part, the memory disturbances observed.
Dopamine is an essential neurotransmitter for locomotor activity. We have shown that 1.5 months’ contamination with DU alters the synthesis/degradation process of dopamine (Bussy et al., 2006) whereas locomotor activity is not modified by uranium (Lestaevel et al., 2005). However, dopamine is involved in other types of behaviour, e.g. pleasurable sensations, which have not yet to be examined after uranium exposure.
Finally, the serotoninergic pathway,, which is involved in the wake-sleep cycle, anxiety or depression, is also sensitive to uranium exposure. In fact, the synthesis/degradation pathway of serotonin was modified during 9 months’ exposure to DU (2 mg/kg/day) (Bussy et al., 2006). This disorder could cause sleeping disorders and increase anxiety.
To conclude, all these studies show that uranium affects several neurotransmitter pathways and these changes could be partly responsible for the effects observed on the various neurophysiological functions described earlier.