ZINC-RICH AFFERENTS TO THE RAT NEOCORTEX - PROJECTIONS TO THE VISUAL-CORTEX TRACED WITH INTRACEREBRAL SELENITE INJECTIONS

Infusion of sodium selenite to the occipital cortex of the rat was use d for the specific tracing of zinc-rich pathways. Large numbers of lab eled somata were found ipsilaterally in the visual, orbital and fronta l cortices, and contralaterally in homotopic and heterotopic visual ar eas. Labeled neurons were also found ipsilaterally in the retrosplenia l, parietal, sensory-motor, temporal and perirhinal cortex. In contras t to the cortico-cortical connections, ascending afferents to the visu al cortex were not zinc-rich except for a few labeled neurons in the c laustrum. Additional injections showed reciprocal zinc-rich connection s between the visual cortex and the orbital and frontal cortices. The latter cortices also received ascending zinc-rich afferents from the c laustrum. Selenite injections revealed the layered distribution and th e morphology of these labeled neurons in the neocortex. Zinc-rich neur ons were found in layers II-III, V and VI. However, none was found in layer IV. Zinc-rich somata appeared as pyramidal and inverted neurons. The contrasting chemical properties of cortical and subcortical visua l afferents may account for the functional differences between these s ystems. (C) 1998 Elsevier Science B.V. All rights reserved.