Thalamic distribution of zinc-rich terminal fields and neurons of origin in the rat

Several cortico-cortical and limbic-related circuits are enriched in zinc, which is considered as an important modulator of glutamatergic transmission . While heavy metals have been detected in the thalamus. the specific prese nce of zinc has not been examined in this region. We have used two highly s ensitive variations of the Timm method to study the zinc-rich innervation i n the rat thalamus, which was compared to the distribution of acrtylcholine sterase activity. The origin of some of these zinc-rich projections was als o investigated by means of retrograde transport after intracerebral infusio ns of sodium selenium (Na2SeO3). The overall zinc staining in the thalamus was much lower than in the neocortex. striatum or basal forebrain; however, densely stained terminal fields were observed in the dorsal tip of the ret icular thalamic nucleus, the anterodorsal and lateral dorsal thalamic nucle i and the zona incerta. In addition, moderately stained zinc-rich terminal fields were found in the rostral intralaminar nuclei, nucleus reuniens and lateral habenula. Intracerebral infusions of Na2SeO3 in the lateral dorsal nucleus resulted in retrogradely labeled neurons that were located in the p ostsubiculum, and also in the pre- and parasubiculum. These results are the first to establish the existence of a zinc-rich subicular-thalamic project ion. Similar infusions in either the intralaminar nuclei or the zona incert a resulted in labeling of neurons in several brainstem structures related t o the reticular formation. Our results provide morphological evidence for zinc modulation of glutamate rgic inputs to highly selective thalamic nuclei, arising differentially fro m either cortical limbic areas or from brainstem ascending activation syste ms. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.