| Research Abstract |
The brain barrier system, i.e., the blood-brain and blood-cerebrospinal fluid barriers, is important for zinc homeostasis in the brain. Zinc was supplied to the brain via both the barriers. A large portion of zinc serves as zinc metalloproteins in neurons and glial cells. Approximately 10% of the total zinc in the brain, probably ionic zinc, exists in the synaptic vesicles, and may serve as an endogenous neuromodulator in synaptic neurotransmission. The presence of zinc-containing neurons, a subclass of glutamatergic neurons, that sequester zinc in the presynaptic vesicles and release it in a calcium-and impulse-dependent manner has been demonstrated in the brain, especially in the limbic system such as hippocampus and amygdala. Dietary zinc deprivation affected zinc homeostasis in the brain. Vesicular zinc-enriched regions, i.e., the hippocampus, was responsive to dietary zinc deprivation, which caused learning impairment and olfactory dysfunction. The learning impairment was recovered by feeding with zinc-adequate diet. Olfactory recognition was also reversibly disturbed by the chelation of zinc released from amygdalar neuron terminals. Moreover, zinc homeostasis in the brain was affected by seizure in El (epilepsy) mice. The susceptibility to epileptic seizure, which may decrease vesicular zinc, was also enhanced by zinc deficiency. Therefore, zinc homeostasis in the brain is closely related to brain functions. Vesicular zinc may be involved in regulation of excitatory neurotransmission via glutamate. Even in adult animals and probably adult humans, adequate zinc supply is important for brain functions and prevention of neurological diseases.
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