Efferent connections of the lateral cortex of the lizard gekko gecko: Evidence for separate origins of medial and lateral pathways from the lateral cortex to the hypothalamus

Abstract

The lateral cortex of the lizard Gekko gecko is composed of three parts: a dorsal and ventral part located rostrally and a posterior part located caudally. In order to obtain detailed information about the efferent connections of these lateral cortex subdivisions, iontophoretic injections of the anterograde tracers Phaseolus vulgaris leucoagglutinin and biotinylated dextran were made in the various parts. The main projection from the dorsal part terminates in the caudal part of the medial cortex. Other cortical projections were noted to the ipsi- and contralateral lateral cortex, the large-celled part of the medial cortex, and the dorsal cortex. Additional fibers were found bilaterally in the anterior olfactory nucleus and the external amygdaloid nucleus. The ventral part of the lateral cortex projects mainly to the ipsilateral, posterior part of the dorsal ventricular ridge and the external amygdaloid nucleus. Minor contralateral projections to these nuclei were also found. Other projections were observed to travel to the caudal part of the medial cortex, to the nucleus sphericus, and bilaterally to the lateral cortex and the anterior olfactory nucleus. The posterior part of the lateral cortex has similar efferent connections as the dorsal part and should be regarded as the caudal continuation of the dorsal part. Because previous studies have shown that the medial cortex and the amygdaloid complex project to different hypothalamic areas, we conclude that the dorsal and ventral parts of the lateral cortex transmit olfactory information to separate hypothalamic areas that are probably involved with different types of behavior.

The lizard cerebral cortex as a model to study neuronal regeneration

“…The lateral cortex receives the bulk projection from the principal olfactory bulb and may be considered homologous to the mammalian olfactory cortex (Hoogland andVermeulen-Vanderzee 1995, Martinez-Garcia et al 1986). It emits a highly laminated axonal projection to the medial cortex ( 2A) a projection that can be considered as a ''lizard perforant path'' in comparison to that of the mammalian perforant path arising from the entorhinal cortex and ending in the hippocampus and outer molecular layer of the dentate gyrus.…”

Contribution of Genoarchitecture to Understanding Hippocampal Evolution and Development

“…The organization of this pallial unit, with a double cortical plate, resembles that of the mammalian EC, which contains superficial and deep layers separated by the lamina dissecans [discussed by Desfilis et al, 2017]. Moreover, as in mammals [Witter and Amaral, 2004], this area projects to the DG, and the projection arises specifically from neurons located in the superficial cell plate (i.e., LCd) [Bruce and Butler, 1984;López-García et al, 1992;Hoogland and Vermeulen-VanderZee, 1995]. Another remarkable similarity between the lizard Lcs and the mammalian LEC is the presence of numerous neurons expressing reelin in the superficial cell layer (layer 2 or II in mammals) [Goffinet et al, 1999;Ramos-Moreno et al, 2006].…”

Comparative Contemplations on the Hippocampus

“…Whether these different entorhinal domains in birds and lizards show connectional differences, comparable to those seen in mammals, is open to further study. It is of interest that in the lizard Gekko gecko , two connectional pathways have been described originating from lateral and medial portions, though only the lateral portion seems to project to the small-and large-celled medial cortex [Hoogland and Vermeulen-Vanderzee, 1995].…”