65Zn was unilaterally injected into the striatum or substantia nigra of rats to see the transport of intracerebral zinc (Zn). In the case of intrastriatal injection, 65Zn was densely distributed in the ipsilateral medial forebrain bundle (MFB) and the substantia nigra. On unilateral colchicine injection into the MFB, 65Zn distribution in the ipsilateral substantia nigra decreased significantly compared to that of the contralateral one after 65Zn injection into the bilateral striata. These results suggest the presence of axonal transport of 65Zn taken up by striatonigral gamma-aminobutyric acid (GABA)-ergic and/or nigrostriatal dopaminergic neurons. On the other hand, in the case of intranigral injection, 65Zn was distributed in the ipsilateral MFB, striatum, globus pallidus, pontine reticular nuclei, and pontine nuclei. 65Zn distribution in the pons 1 day after intranigral injection was very similar to that 6 days after intrastriatal injection, suggesting that, in the case of intrastriatal injection of 65Zn, nigral 65Zn, which was transported anterogradely and/or retrogradely from the striatum, was transported to the postsynaptic neurons through the synapse and then transported to the pons.

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.

The uptake of 65Zn, determined by γ-counting and also by autoradiography, significantly increased with the increasing level of metallothionein in liver 4 weeks after the start of feeding a diet containing 3′-methyl-dimethylaminoazobenzene (3′-Me-DAB), at which time the serum γ-glutamyl transpeptidase activity was not yet significantly elevated. At this time, furthermore, hepatic uptake of 67Ga-citrate did not increase and that of 99mTc-Sn-colloid decreased in 3′-Me-DAB-fed rats. These results suggest that a short-life gamma-emitting isotope such as 69mZn may be useful for the detection at the early stage of hepatic carcinogenesis.