Abstract View


J.L. Price*; K.S. Saleem; J.T. Baker; L.H. Snyder

Anatomy & Neurobiology, Washington Univ, St. Louis, MO, USA

We assessed the use of manganese (Mn) for tracing cortical and subcortical connections in living monkeys. Eleven Mn injections were made into cortical and subcortical structures with known anterograde connectivity, including visual cortex (V1/V2), posterior parietal cortex (PPC), superior temporal gyrus (STG), dorsal temporal pole (TG), orbitofrontal cortex (area 12o), and ventral striatum and pallidum. Mn-labeled projections were demonstrated by comparing 0.75 mm3 T1-weighted magnetic resonance images (MRI), obtained 24 to 96 hours after the injection, with a prior baseline scan. For three injections (two V1/V2 and TG), we co-injected histological tracers (fluororuby [FY] and lucifer yellow [LY]) to compare the distribution of these tracers with that of Mn. Finally, we examined single-unit responses following injections at two PPC sites.

Mn injections labeled expected cortical and subcortical sites. For example, the V1/V2 injections (n=3) labeled lateral pulvinar, lateral geniculate nucleus (LGN), and several cortical areas including V4. The TG injection labeled medial pulvinar, amygdala, the upper bank of the superior temporal sulcus, STG, and orbitofrontal cortex. At each of these sites there was a close correspondence between the distribution of Mn labeling observed with MRI and the distribution of LY- and FY-labeled axon terminals observed in histological sections.

As early as 24 hours after an injection, single-unit responses at the injection site were comparable to those observed at the same site just prior to the injection.

We conclude that Mn tracing is an effective method for identifying anterograde neuronal connections in non-human primates. Since this technique can be performed in vivo and does not interfere with subsequent neuronal activity, it should provide an unprecedented opportunity to study structure-function relationships in the same animals.
Support Contributed By: NIH, McDonnell Ctr for Higher Brain Function