Convergence of influences from hypothalamus and locus coeruleus upon the olfactory tubercle.

The interaction of locus coeruleus (LC) and lateral hypothalamus (LH) stimulation upon the evoked potentials and unitary activity in the olfactory tubercle (OT) were studied. The difference in latency of the evoked potentials in the OT by LC or by LH stimulation seems to indicate that thin fibers compose the LC-OT pathway and that thick fibers compose the LH-OT pathway. The most common pattern of OT neuronal discharge was in bursts. The train stimulation of the LC decreased the OT neuronal discharge. The LH stimulation produced an increase of the OT neuronal discharge. These results suggest a convergence of LH fibers and LC fibers upon the OT. The nature of the neurotransmitters involved in both pathways is suggested: norepinephrine for the LC-OT projection and dopamine for the LH-OT projection.