THE DOPAMINERGIC MESENCEPHALIC PROJECTIONS TO THE HIPPOCAMPAL-FORMATION IN THE RAT

1. The dopaminergic mesencephalic neurons projecting to the hippocampa l formation are distributed in three cell groups: A8 region in the ret rorubral field, A9 region in the substantia nigra and A10 region in th e ventral tegmental area. 2. Anterograde and retrograde tract-tracing techniques combined with immunohistochemical procedures indicate a top ographical organization of mesencephalic dopaminergic projections towa rds the hippocampal formation. 3. Electrophysiological evidence sugges t that dopaminergic mesencephalic neurons could have a regulatory role in suppressing hippocampal excitability. 4. The functional significan ce of the mesohippocampal dopaminergic system is largely unknown, alth ough it was suggested that this projection could have a role in metham phetamine-produced hypermotility and in modulation of memory processes .