CONVERGENCE OF THALAMIC AND CHOLINERGIC PROJECTIONS IN THE DENTATE AREA OF LIZARDS

The small-celled part of the medial cortex (Cxms) in lizards is compar able to the hippocampal area dentata in mammals. As in mammals, most o f the afferents to this cortical area are arranged in sharply delimite d laminae. In reptiles this lamination pattern is species-specific. In the lizard Tupinambis nigropunctatus projections from the multisensor y dorsolateral thalamic nucleus (Dla) terminate in the middle one-thir d of the outer plexiform layer throughout the whole rostrocaudal exten t of Cxms. In Podarcis hispanica the thalamic projections terminate no t only in the middle one-third of Cxms but also in the inner plexiform layer. To find out whether the species-related variation of thalamic projections to Cxms is a solitary phenomenon or is related to variatio ns of other afferents of Cxms, we studied the relationships between th e thalamic and cholinergic projections from the basal telencephalon in the medial cortex of three lizard families: the Lacertidae, the Teiid ae and the Gekkonidae. In the gekkonid lizards Gekko gecko and Eubleph arius macularius, Dla projections were studied with the anterograde tr acer Phaseolus vulgaris-leucoagglutinin. Projections were found in onl y the rostral one-third of Cxms where the fibers terminate in the supe rficial half of the outer plexiform layer and in the deep half of the inner plexiform layer. From acetylcholinesterase staining in the Cxms of representatives of these three lizard families, it appeared that th e main cholinergic afferents terminate in the same subregions and the same laminae as the Dla projections. Therefore, there seems to be a cl ose association between thalamic and cholinergic afferents in the Cxms of Lizards, irrespective of their precise location in the cortex of t he various species. This suggests a functional relationship between th ese two afferents of the dentate area in lizards.