Projections from the ventral tegmental area to the olfactory tubercle in the rat.

The projection between the ventral tegmental area (VTA) and the olfactory tubercle (OT) was examined electrophysiologically in the rat. Stimulation of the olfactory bulb (OB) determined if the OT neurons were olfactory-related. Ipsilateral VTA stimulation produced a change in neuronal activity in 77% of the neurons tested, with 41% being inhibited, 24% excited, and 12% had mixed response. Contralateral VTA stimulation produced changes in only 38%. Intravenous administration of haloperidol was used in examination of the role of dopamine in this neural connection. The results suggest that the VTA-induced inhibitory response on OT neurons is mediated by dopamine, whereas excitatory responses are not. The VTA inhibitory influence projects primarily to olfactory-related neurons, since 60% of olfactory-related OT neurons were inhibited--as compared to 34% of non-olfactory-related neurons. This study documents electrophysiologically the VTA-OT connection and suggests that the dopaminergic input may modulate olfactory information projected to the OT from the OB. It also supports the concept that the OT acts as an integration center in central olfactory processing.