Role of zinc released by stimulation in rat amygdala.

The movement and role of actively functioning zinc, i.e., vesicular zinc, in the amygdala was studied, based on the data that 65Zn is localized in the limbic system, which may correspond to the regions with high densities of zinc-containing neuron terminals. When release of 65Zn into the extracellular space was examined 2 hr or 25 hr after injection of 65ZnCl2 into the amygdala, 65Zn release was facilitated by stimulation with high K+ 2 hr after injection, but not 25 hr after injection. Even 25 hr after 65Zn injection into the amygdala, approximately 95% of total 65Zn in the brain was detected in the injected area. These results suggest that zinc released into the extracellular space in the amygdala is not readily restored to the presynaptic vesicles. Moreover, to chelate zinc in the extracellular space (and in the synaptic vesicles) in the amygdala, the amygdalae were perfused with 10 microM diethyldithiocarbamate during behavioral tests for odor recognition. The olfactory sensation was temporarily disturbed by the perfusion. These results suggest that vesicular zinc is essential to the function of the amygdala, e.g., olfactory function.

Distribution of zinc in the substantia nigra of rats treated with 6-hydroxydopamine.

To study the relationship between tissue accumulation of Zinc (Zn) and neurodegeneration in the nigrostriatal dopaminergic pathway, 65Zn distribution in this pathway was examined after unilateral injection of 6-hydroxydopamine (6-OHDA) into the substantia nigra of rats. When 65ZnCl2 was intravenously injected 4 days after treatment with 6-OHDA, 65Zn was concentrated in the ipsilateral substantia nigra 6 days after 65Zn injection. On the other hand, 19 d after treatment with 6-OHDA, 65Zn distribution in the ipsilateral substantia nigra was decreased to the level of the contralateral one. When NH4(99)TcO4, which cannot go through the blood-brain barrier, was injected into rats 4 d after treatment with 6-OHDA, 99Tc was concentrated in the ipsilateral substantia nigra 30 min after 99Tc injection, but no longer detectable 6 d after injection. These results suggest that Zn is necessary for a repair process called replacement gliosis after the death of neurons and that excess Zn does not accumulate in the lesion after completion of the gliosis.

Manganese concentration in rat brain: manganese transport from the peripheral tissues.

54Mn distribution in the brain and peripheral tissues was studied with the course of time after intravenous injection of 54MnCl2 to see manganese (Mn) transport from the peripheral tissues, i.e. the liver, to the brain. One hour after injection, 54Mn concentrations in the brain were 0.15-0.25% dose/g, and 54Mn was largely concentrated in the choroid plexus. One day after injection, 54Mn in the choroid plexus decreased remarkably. 54Mn in other brain regions increased gradually after then, and reached 0.30-0.40% dose/g 6 days after injection. This increase of 54Mn was due to the redistribution from the peripheral tissues such as liver and pancreas, in which 54Mn was maintained at high levels (2.0-4.0% dose/g). The increment of 54Mn 1 h to 6 days after injection was the largest in the hippocampus, but not in the striatum. These results suggest that the delivery of Mn from the liver to the brain is not involved in preferential Mn accumulation in the basal nuclei under physiological condition. This delivery may be important for brain function.

Change of zinc distribution in rat brain with increasing age.

Zinc (Zn) accumulation in the brain of rats of various ages was studied to look into the significance of Zn for the development and function of the brain. The Zn concentration of the cerebral hemisphere was relatively low in 1- to 11-day-old rats. The Zn concentration of the cerebellum gradually increased after birth and reached nearly a plateau at 11 days old. At 48 weeks old, the Zn concentrations of the cerebral cortex and hippocampus formation were approximately twice that of the cerebral hemisphere at the early stage after birth and significantly higher than that of the cerebellum. When 65ZnCl2 was injected into two groups of rats at 5 days and 48 weeks old for comparison, 65Zn distribution in the brain of the former group was higher than that of the latter. In the neonatal rats, the highest concentration of 65Zn was found in the cerebellum, followed by the hippocampus formation, a Zn-containing neuron-rich region. In the adult rats, the highest concentration of 65Zn was found in the CA3 and dentate gyrus of the hippocampus formation. At 48 weeks, 65Zn distribution in the cerebellum was relatively low and at about the same level as in the cerebral cortex. These results suggest that Zn is highly demanded by the cerebellum, which develops rapidly after birth. The increase in Zn concentration with increasing age may reflect the Zn requirement for functioning as an neuromodulator as well as for brain development.

Zinc transport in the rat olfactory system.

To study zinc (Zn) mobility in the rat olfactory tract, brain distribution of 65Zn after injection into the olfactory bulb or amygdaloid nuclei was analyzed by autoradiography. Twenty-four hours after 65Zn injection into the olfactory bulb, 65Zn was distributed in the ipsilateral piriform cortex, amygdaloid nuclei and the anterior commissure. Moreover, in the case of injection of a higher level of 65Zn into the olfactory bulb, 65Zn was distributed in the ipsilateral entorhinal cortex in addition to the above regions. Twenty-four hours after 65Zn injection into the amygdaloid nuclei, 65Zn was distributed in the ipsilateral piriform and entorhinal cortex. These results suggest that Zn is intraneuronally transported along the olfactory tract. Zn may be taken up by the piriform neurons after release from the secondary olfactory neuron terminals and transported to the entorhinal area.

Biological half-lives of zinc and manganese in rat brain.

The brains of rats injected intravenously with 65ZnCl2 or 54MnCl2 were subjected to high-resolution autoradiography. The distribution of 65Zn and 54Mn in each brain region gradually decreased from 6 days to 42 days for 65Zn and from 15 days to 60 days for 54Mn after the injection. The biological half-lives of Zn in each region studied were in the range of 16-43 days; the longest was observed in the amygdaloid nuclei. The regions where the long biological half-life was observed were consistent with the ones with the high density of Zn-containing neuron terminals reported previously. The biological half-lives of Mn in each region were 51-74 days; the longest were those in the hypothalamic nuclei and thalamus.

Localization in rat brain of the trace metals, zinc and manganese, after intracerebroventricular injection.

Autoradiographic studies of rat brain, after 65ZnCl2 or 54MnCl2 injection into the lateral ventricle, revealed that 65Zn and 54Mn were transferred freely through the cerebrospinal and extracellular fluid compartments; both tracers appeared in all the ventricles 1 h after injection. At 6 days after injection, 65Zn was concentrated in the hippocampal formation and hypothalamic nuclei but not in the cerebral cortex and superior colliculus of the ipsilateral hemisphere, with a lower uptake into contralateral hemisphere except for the hypothalamic nuclei. 54Mn was concentrated in some brainstem nuclei, such as the red and pontine reticular nuclei, to about the same extent in both hemispheres. These results suggest that both metals were taken up gradually into brain mainly via the cerebrospinal fluid. Relatively high uptake of 65Zn into the cerebral cortex and superior colliculus after intravenous injection suggests uptake in those regions is through two blood/brain barriers.

Brain uptake of trace metals, zinc and manganese, in rats.

The brains of rats injected intravenously with 65ZnCl2 or 54MnCl2 were subjected to high resolution autoradiography. 65Zn and 54Mn were largely concentrated in choroid plexus 1 h after injection and then gradually decreased, with increases in other brain regions, suggesting that both metals were taken up gradually into brain mainly via cerebrospinal fluid in the choroid plexus. By 3 days after injection, relatively high level of 65Zn was seen in the dentate gyrus and CA3 region of the hippocampus and in the cerebral cortex. The level of 54Mn was also high in the former, while relatively low in the latter.