ANTEROGRADE AND RETROGRADE TRACING OF PROJECTIONS FROM THE VENTRAL TEGMENTAL AREA TO THE HIPPOCAMPAL-FORMATION IN THE RAT

Employing anterograde tracing with Phaseolus vulgaris-leucoagglutinin (PHA-L), and a triple labeling protocol using retrogradely transported fluorescent tracers, we examined the projections from the ventral teg mental area (VTA-A10) to the hippocampal formation (HF) in the rat. In jections of PHA-L into VTA resulted in labeling in the ventral subicul um (stratum oriens and molecular layer) and in the adjacent CA1 field (stratum oriens, pyramidal, suprapyramidal and molecular layers) of HF . Additional labeling was observed in the stratum oriens of CA3 and in the hilus of fascia dentata. In the dorsal HF labeling was present in the subicular and CA1 field polymorphic layers. The distribution of V TA neurons projecting to the HF was also examined by injecting retrogr ade fluorescent tracers (Fluoro Gold, Fast Blue, and Nuclear Yellow) i n several hippocampal areas. The most abundant VTA-HF projections orig inate from the upper and lower edges and the lower half of the VTA. Th ese terminal fields in the HF match with the hippocampal areas project ing to the nucleus accumbens. The VTA, via projections to interconnect ed regions of the HF and nucleus accumbens, may modulate the hypothesi zed functional link between the limbic system and basal ganglia.