Interhemispheric connections through the pallial commissures in the brain of Podarcis hispanica and Gallotia stehlinii (Reptilia, Lacertidae)

Abstract

The cells-of-origin and the mode and site of termination of the interhemispheric connections passing through the anterior and posterior pallial commissures in the telencephalon of two lizards (Podarcis hispanica and Gallotia stehlinii) were investigated by studying the anterograde and retrograde transport of unilaterally injected horseradish peroxidase. The commissural projections arise mainly from pyramidal cells in the medial, dorsomedial, and dorsal cortices (medial subfield). Additionally some non-pyramidal neurons in the medial and dorsal cortices contribute to the commissural system. Medial cortex neurons project to the contralateral anterior septum through the anterior pallial commissure. The dorsomedial cortex projects contralaterally via the anterior pallial commissure to the dorsolateral septum and to the medial, dorsomedial, and dorsal cortices. The projection to the medial cortex terminates in two bands at the inner and outer border, respectively, of the cell layer; the projection to the dorsomedial and dorsal cortex ends in a zone in layer 1 which previously has been described to be Timm-negative, and in a diffuse band in the inner half of layer 3. The medial subfield of the dorsal cortex projects through the anterior pallial commissure to the dorsomedial and dorsal cortices with a similar pattern of termination to that found for the dorsomedial cortex. The posterior pallial commissure contains only the projections from the ventral cortex to its contralateral counterpart and to the ventral part of the caudal medial cortex. The similarities found between this commissural system and the mammalian hippocampal interhemispheric connections are discussed.

A Golgi study of the short-axon interneurons of the cell layer and inner plexiform layer of the medial cortex of the lizardPodarcis hispanica

“…Those large parvalbumin-immunoreactive fusiform neurons receiving serotonergic axonal endings, reported in this latter study, are very similar to the deep-fusiform neuron illustrated in Figure 4C. Similarly, some HRP transport studies (Olucha et al, 1988;Martínez-García et al, 1990) have reported contralateral, retrogradely labeled somata in the medial cortex cell layer of Podarcis (i.e., putative commissural neurons), whose morphological features coincide with those of web-axon neurons.…”

“…The locations of their somata and dendrites clearly match those of some GABA-immunoreactive neurons (Schwerdtfeger and Lopez-Garcia, 1986; Schwerdtfeger and Lorente, 1988a,b) and those of some neurons that resulted heavily labeled after HRP injections in the contralateral hemi-sphere (Olucha et al, 1988;Martínez-García et al, 1990). Unfortunately, their complex axonal trajectories could not be traced in our Golgi-impregnated material.…”

“…In lizards, a commissural pathway coming from unidentified neurons in the medial cortex has been reported (Martínez-García et al, 1990). In the medial cortex, some interneuronal types displaying initially descending axons (Figs.…”

Structural organization of the cerebral cortex of the neotropical lizard Tropidurus hispidus

“…Although the unipolar and multipolar granular types are more frequent, the characteristic cell of this region is the bipyramidal neuron, also described in P. hispanica (LopezGarcia et al 2002) and H. flaviviridis (Srivastava et al 2009). They send commissural contralateral projections and receive zinc-enriched inputs from the medial cortex (Martinez-Garcia et al 1990). This projection is believed to be homologous to the mammalian mossy fiber pathway.…”

Serotoninergic innervation of nonprincipal cells in the cerebral cortex of the lizard Podarcis hispanica

“…The principal cells are spiny projection neurons located in the cell layer which show the characteristic shape and dendritic fields of granular or bipyramidal cells (Regidor et al, 1974;Lacey, 1978;Berbel et al, 1987;Martinez-Guijarro et al, 1990). Principal cells (granule cells) of the medial cortex have ipsilateral associational and subcortical projections (L6pez-Garcia and Martinez-Guijarro, 1988;Olucha et al, 1988) and the bipyramidal neurons of the dorsomedial and dorsal cortices, in addition, project to contralateral cortical and subcortical areas (Hoogland and Vermeulen-Van der Zee, 1988;Martinez-Garcia et al, 1990;Martinez-Guijarro et al, 1990). On the other hand, spinefree or sparsely spinous, short axon neurons displaying GABA immunoreactivity are usually found in the plexiform layers and less frequently in the cell layer (Schwerdtfeger and L6pez-Garcia, 1986;Schwerdtfeger and Lorente, 1988;Martinez-Guijarro and Freund, 1992a,b).…”