DU crosses the blood brain barrier and accumulates in the brain and preferentially in particular brain regions. Specifically, the hippocampus and striatum accumulate DU more readily than cerebellum and cortex, at least with oral exposure [
12]. In contrast, when using a dust exposure protocol, the accumulation of DU in the CNS occurs within the olfactory bulb, hippocampus, cortex, and cerebellum demonstrating increasing concentrations of DU, in that order [
13].
An early study [
14] produced tremors in rats given high doses of uranium. That finding, in concert with the activity of uranium at the neuromuscular end-plate [
15] suggests that U competes with calcium at the synapse. DU is active at the estrogen receptor [
16], the vitamin D receptor [
17], and the retinoid receptor [
17]. DU appears to alter acetylcholine and serotonin activity [
18], although these findings are not always consistent [
12]. We have recently shown DU to effect brain norepinephrine and epinephrine levels [
19]. However, the effect of DU on brain dopamine appears complex and related to both length of exposure and dose [
19]. Interestingly, a variety of physiologic changes have been reported in the intestine of rats being administered DU in drinking water including altered histamine, prostaglandin and NO activity [
20]. Our laboratory has consistently shown that DU exposure increases brain lipid peroxidation, a finding replicated by others [
21–
23]. Brain lipid peroxidation parallels behavioral changes in rats and mice exposed to DU [
24–
26]. Changes in brain lipids may be partially explained by altered gene expression for cholesterol metabolism [
27]. Uranium increases the levels of a variety of proteins involved in metal metabolism including divalent metal transporter 1, ferritin, and ceruloplasmin [
28].
DU not only accumulates in the CNS but also has physiologic activity there. Specifically, DU inhibits spike formation in the hippocampus of rats [
29]. Research has also demonstrated that DU alters the electroencephalographic architecture of the EEG in free moving rats with accompanying changes in the sleep wake cycle and REM sleep [
30,
31]. DU exposure effects the behavior of rats in the open-field and the Y maze implying that DU has neurophysiologic effects [
12]. This laboratory has also demonstrated a number of behavioral effects associate with DU exposure, such as altered development and maze behaviors [
26,
32]. However, others have found that neither sleep wake cycles or spatial behavior were altered by either DU or enriched uranium exposure [
33].