Projections from the medial cortex in the brain of lizards: Correlation of anterograde and retrograde transport of horseradish peroxidase with timm staining

Abstract

Efferent projections of the medial cortex of the lizards Podarcis hispanica and Gallotia stehlinii were studied by examining the transport of horseradish peroxidase; results were correlated with those from Timm-stained sections. Two efferent systems were found. The first reaches the distal part of the outer plexiform layer in the medial, dorsomedial, and dorsal cortices, i.e., zones that are negative to Timm staining, and possibly originates from horizontal fusiform neurons. The second reaches the Timm-positive zones in the cortex and septum and is topographically arranged: the vertical portion of the intermediate and caudal medial cortex and the entire rostral medial cortex project to the inner two-thirds of the outer plexiform layer of the dorsomedial cortex and of the medial subfield of the dorsal cortex; to the paraventricular zone of the inner plexiform layer of the medial cortex; and bilaterally to the dorsal part of the dorsal precommissural septum. The dorsal part of the intermediate and caudal medial cortex and the ventralmost folded part of its caudal edge project rostrally to the juxtasomatic zone of the outer plexiform layer and the entire inner plexiform layer of the intermediate and lateral subfields of the dorsal cortex and to the ventral part of the dorsal septum. In its intense Timm reaction and its ultrastructural properties, as reported in earlier studies, the Timm-positive fiber system of the lizard brain shows a close resemblance to the mossy fiber system of the mammalian hippocampus.

The CA3 network as a memory store for spatial representations

“…Similar to what is seen in the dentate gyrus in mammals, a majority of the dendrites do extend into the molecular layer, and the first bifurcation is close to the soma. In contrast to the mammalian situation though, the cell types appear to be more variable, such that a total of six different cell types have been described within the cell layer, of which only some contribute to projections targeting adjacent portions of the cortex, mainly to the large-celled part of the mediodorsal cortex (Wouterlood1981; Olucha et al 1988). These projections are strongly Timm positive, strikingly similar both morphologically as well as in terms of overall distribution to the mossy fiber projection in mammals (Lopes Garcia and Martinez-Guijaro 1988;Olucha et al 1988).…”

“…In contrast to the mammalian situation though, the cell types appear to be more variable, such that a total of six different cell types have been described within the cell layer, of which only some contribute to projections targeting adjacent portions of the cortex, mainly to the large-celled part of the mediodorsal cortex (Wouterlood1981; Olucha et al 1988). These projections are strongly Timm positive, strikingly similar both morphologically as well as in terms of overall distribution to the mossy fiber projection in mammals (Lopes Garcia and Martinez-Guijaro 1988;Olucha et al 1988). Although not much is known about the different local circuitry neurons in the reptilian brain, neurons have been described in both the molecular layer and the deep polymorph layer.…”

“…Projections distribute widely in the cortex, including a return projection to the small-celled part. Most notably, widespread dense intrinsic projections have been described as distributing both to apical as well as basal dendrites, reminiscent of the associative connectivity in the mammalian CA3 (Olucha et al 1988;Hoogland and Vermeulen-Vanderzee 1993).…”

The lizard cerebral cortex as a model to study neuronal regeneration

“…On the other hand, interneurons located in the plexiform layers are short axon neurones with non-spiny or sparsely spiny dendrites displaying diverse morphologies , (De la Iglesia and Lopez-Garcia 1997b, Bernabeu et al 1994. Most local interneurons are GABA-immunoreactive (Lopez-Garcia et al 1988 a, Schwerdtfeger and and display either parvalbumin (Fig. 1E), calbindin, or calretinin immunoreactivities (Martinez-Guijarro et al 1991a, Martinez-Guijarro andFreund 1992) as well as a wide spectrum of neuropeptide immunoreactivities (Davila et al 1991) or even NADPH diaphorase/ NOS synthetase (Davila et al 1995).…”

“…In addition to the pattern of extracortical afferences and efferences (Bruce and Butler 1984), the intracortical scheme of connections of the lizard cerebral cortex also has a clear resemblance to that of the mammalian hippocampus and the entorhinalolfactory cortex (Olucha et al 1988).…”