DISTRIBUTION OF NEURONS OF ORIGIN OF ZINC-CONTAINING PROJECTIONS IN THE AMYGDALA OF THE RAT

The present study describes the distribution of neurons of origin of z inc-containing pathways in the amygdaloid complex of the rat, using th e selenium method for simultaneous retrograde labeling of all zinc-con taining neurons. With this method, vesicular ionic zinc is precipitate d intravitally with selenium compounds and transported retrogradely to the parent neurons, where it can be visualized by silver amplificatio n. Neurons labeled retrogradely with silver-amplified precipitate were observed in all amygdaloid nuclei except for the lateral olfactory tr act nucleus, the accessory olfactory tract nucleus and the central nuc leus. Very few labeled cell bodies were seen in the anterior amygdaloi d area and the medial nucleus. The amygdalo-hippocampal area and the a mygdalo-piriform transition area both showed a substantial number of l abeled somata throughout their rostrocaudal extent. In the anterior co rtical nucleus, very few labeled cell bodies were found in the rostral pole, whereas they were abundant in the caudal quarter of the nucleus . In the posterolateral cortical nucleus, the number of labeled cell b odies increased gradually; there were none in the rostral pole, but mo st of the neurons in the caudal part were labeled. The posteromedial c ortical nucleus contained a great number of labeled somata, but with s ome variation in the rostrocaudal extent of the nucleus. Considerable numbers of labeled neurons were observed throughout the lateral nucleu s. In the basolateral nucleus, a small number of labeled cell bodies w as present in the rostral half, but a gradual increase was observed in the caudal direction. Finally, in the basomedial nucleus, very few la beled cell bodies were present in the rostral two-thirds, whilst a con siderable number was encountered in the caudal one-third. Possible fun ctional implications of neuronal zinc are considered. The distribution of neurons of origin of zinc-containing projections has been compared with previously described intrinsic connections of the rat amygdala, and tracts that may possibly be zinc-containing are outlined and discu ssed. It is concluded that in all probability a substantial proportion of the intrinsic connectivity of the rat amygdaloid complex is zinc-c ontaining.