Efferent connections of the dorsal cortex of the lizard Gekko gecko studied with Phaseolus vulgaris-leucoagglutinin

The efferent connections from the dorsal cortex of the lizard Gekko gecko have been studied with the anterograde tracer Phaseolus vulgaris-leucoagglutinin. It appeared that the dorsal cortex is not a homogeneous structure as far as the efferent connections are concerned. All parts of the dorsal cortex project to the septum. All parts except the most medial project to the dorsal ventricular ridge, amygdala, nucleus periventricularis hypothalami, area lateralis hypothalami, and the anterior olfactory nucleus. The most medial part, in addition to the septal projections, is connected with the medial cortex and the contralateral medial and dorsal cortices. From the rostral part additional projections could be traced to the nucleus dorsolateralis hypothalami, nucleus ventromedialis thalami, nucleus dorsolateralis thalami, striatum, pallial thickening, medial cortex, nucleus olfactorius anterior, and the main and accessory olfactory bulbs. From the caudal part additional projections exist to the nucleus dorsomedialis thalami, nucleus accumbens, and the contralateral dorsal cortex. A system of intrinsic connections exists that can be subdivided into four subsystems, each of which subserves the interconnections within four subdivisions of the cortex: 1) the superficial medial part, 2) the deep medial part, 3) the caudal lateral and caudal intermediate parts, and 4) the rostral lateral and rostral intermediate parts. Connections between these four areas are scarce. From the present results the conclusion is drawn that the dorsal cortex of the lizard Gekko gecko has many hodological aspects in common with the ventral subiculum of mammals. The present results do not support the hypothesis that the dorsal cortex is the reptilian equivalent of the mammalian neocortex.