Locus coeruleus influences upon the olfactory tubercle

Locus coeruleus (LC) influences upon the olfactory tubercle (OT) were studied. Evoked potentials and unit activity recording techniques were used as well as the horseradish peroxidase (HRP) labelling method. A biphasic potential was recorded in cat's OT following a single pulse delivered to the LC. Latencies were 35 msec and 80 msec for the first positive and second negative component respectively. The largest potentials were recorded between the superficial part of the pyramidal layer and the polymorphic layer. This potential was tested in order to determine whether it was an OT generated potential caused by LC stimulation. Contralateral recordings were made. Extracellularly recorded OT neurons decreased their discharge frequency upon repetitive LC stimulation in rats. The decreases endured longer when the stimulus frequency or train duration were increased. Neurons from which unit data were used in the analysis were verified to be in the OT polymorphic layer. Labelled neurons were seen in the LC after HRP application to the OT in rats and cats. Results support the presence of LC fibers which influence OT neurons. The relation between the LC as a general arousal system and the OT as an important olfactory information processing structure is discussed.