MEDIAL CORTEX OF THE LIZARD GEKKO-GECKO - A HODOLOGICAL STUDY WITH EMPHASIS ON REGIONAL SPECIALIZATION

There is increasing evidence that the archicortex in mammals and repti les is not a homogeneous structure. However, little is known about the regional specialization of this cortical area in reptiles. Therefore, the efferent connections of the medial cortex of the lizard Gekko gec ko were studied with the anterograde tracer Phaseolus vulgaris-leucoag glutinin. The small-celled part of the medial cortex (Cxms) projects t o various parts of the septum in a topological way: the rostral part p rojects to the anterior septal nucleus, whereas the caudal part projec ts to the lateral septal nucleus and the nucleus septi impar. In addit ion, Cxms projects to the large-celled part of the medial cortex (Cxml ). Axons that originate from the dorsal part of Cxms terminate at the proximal parts of the apical and basal dendrites of the neurons of Cxm l caudal to the injection site. In contrast, fibers originating from t he ventral part terminate on more distal parts of the dendrites of neu rons of Cxml rostral to the injection site. Other projections from Cxm s to the dorsal cortex (Cxd) and the external amygdaloid nucleus were found. The Cxml projects bilaterally to Cxms. These projections termin ate in the superficial and deep plexiform layers. In addition, project ions to the cell plate of Unger, Cxd, and to the lateral septal nucleu s were found. It appears, on the basis of the efferent connections, th at Cxms can be divided into a rostral and caudal part, while hodologic al differences also exist between the dorsal and ventral parts of Cxms . The results of the present study do not suggest a subdivision of Cxm l. The regional variations of the medial cortex in the lizard Gekko ge cko differ from the regional variations described in other reptilian s pecies.