Synaptic contacts of ventral striatal cells in the olfactory tubercle of the rat: correlated light and electron microscopy of anterogradely transported Phaseolus vulgaris-leucoagglutinin.

Iontophoretic injections of the plant lectin Phaseolus vulgaris-leucoagglutinin (PHA-L) into the dense cell layer of the rat olfactory tubercle (OT) resulted in transport of the substance to the polymorph layer of the OT. Light microscopy revealed that the lectin was taken up in the superficial OT exclusively by medium-sized neurons with spiny dendrites of which the majority extended into the molecular layer. PHA-L-immunoreactive elements were observed in the adjoining part of the polymorph layer in the form of filaments and puncta which the electron microscope revealed to be axons and boutons forming symmetrical synaptic contacts, almost exclusively with typical pallidal-type dendrite profiles. The results reinforce the concept that the medium-size cells of the dense cell layer of the OT represent the ventral-most part of the striatum.