The olfactory tubercle of the cat. I. Morphological components.

On the basis of morphology and arrangement of cell types, the olfactory tubercle (OT) of the cat is divided into two main components: a cortical part and the cap/hilus regions in which cortical characteristics are not recognizable. The cortical part undergoes a gradual transformation from a more cortex-like structure in the lateral half of the OT - possibly related to the presence of olfactory fibers - to a more striatum-like organization in the medial half. Cell bridges extend between the polymorph layer of the cortical part and the striatum and especially the n. accumbens. The cap regions form 8 or 9 superficial grooves running in a rostro-caudal direction. They contain dwarf and small pyramidal-like neurons and lie immediately ventral to the granule islands of Calleja. Dwarf and small pyramidal-like neurons give rise to an ascending axonal plexus which may contact large neurons in the hilus regions dorsal to the Calleja islands and in part also neurons of the ventral pallidum, the dendrites of which enter the lateral hilus zones. The proportion of dwarf cells to granule cells in the cap regions gradually reverses from lateral, where dwarf cells dominate, to medial, where the caps contain almost exclusively granule cells. No interconnections are observed between the two components of the OT.