Neurons in the ventral tegmentum have separate populations projecting to telencephalon and inferior olive, are histochemically different, and may receive direct visual input.

The connections of the ventral tegmental area (VTA) and medial terminal nucleus (MTN) of the accessory optic system were studied in the albino rat. Using injection of two fluorescent retrograde tracers it was found that individual neurons of the VTA project to frontal cortices or the inferior olive but not both structures. Using combined retrograde fluorescent tracers and glyoxylic acid histochemistry, it was found that although a third of the cells projecting to frontal cortex contained catecholamine, none of the cells projecting to the inferior olive contained catecholamine. Thus, these portions of the ascending and descending VTA systems are independent. In addition, using injections of the anterograde transneuronal tracer [3H]adenosine into one eye, it was found that cells in the VTA, as well as the MTN, contained the tracer. Therefore, there is a basis for direct retino-mesentelencephalic pathways through the VTA.