Convergence of Thalamic and Cholinergic Projections in the ‘Dentate Area’ of Lizards

Abstract

The small-celled part of the medial cortex (Cxms) in lizards is comparable to the hippocampal area dentata in mammals. As in mammals, most of the afferents to this cortical area are arranged in sharply delimited laminae. In reptiles this lamination pattern is species-specific. In the lizard Tupinambis nigropunctatus projections from the multisensory dorsolateral thalamic nucleus (Dla) terminate in the middle one-third of the outer plexiform layer throughout the whole rostrocaudal extent of Cxms. In Podarcis hispanica the thalamic projections terminate not only in the middle one-third of Cxms but also in the inner plexiform layer. To find out whether the species-related variation of thalamic projections to Cxms is a solitary phenomenon or is related to variations of other afferents of Cxms, we studied the relationships between the thalamic and cholinergic projections from the basal telencephalon in the medial cortex of three lizard families: the Lacertidae, the Teiidae and the Gekkonidae. In the gekkonid lizards Gekko gecko and Eublepharius macularius, Dla projections were studied with the anterograde tracer Phaseolus vulgaris-leucoagglutinin. Projections were found in only the rostral one-third of Cxms where the fibers terminate in the superficial half of the outer plexiform layer and in the deep half of the inner plexiform layer. From acetylcholinesterase staining in the Cxms of representatives of these three lizard families, it appeared that the main cholinergic afferents terminate in the same subregions and the same laminae as the Dla projections. Therefore, there seems to be a close association between thalamic and cholinergic afferents in the Cxms of lizards, irrespective of their precise location in the cortex of the various species. This suggests a functional relationship between these two afferents of the dentate area in lizards.

Organization of the avian basal forebrain: Chemical anatomy in the parrot (Melopsittacus undulatus)

“…6E,F; present results; Mesulam et al, 1983;Kitt et al, 1994;Cookson et al, 1996;Roberts et al, 1997). A comparable distribution of ChAT-ir neurons has also been reported in the presumed VP of nonvocal learning birds , turtles (Bissoli and Contestabile, 1988), reptiles (Brauth et al, 1985;Hoogland et al, 1998), and amphibians (Marin et al, 1998a), suggesting that the VP field of cholinergic neurons is a primitive feature of tetrapod brain organization.…”

Accessory neuropathy after high‐dose radiation therapy for tongue‐base carcinoma

“…6E,F; present results; Mesulam et al, 1983; Kitt et al, 1994; Cookson et al, 1996; Roberts et al, 1997). A comparable distribution of ChAT‐ir neurons has also been reported in the presumed VP of nonvocal learning birds (Medina and Reiner, 1994), turtles (Bissoli and Contestabile, 1988), reptiles (Brauth et al, 1985; Hoogland et al, 1998), and amphibians (Marin et al, 1998a), suggesting that the VP field of cholinergic neurons is a primitive feature of tetrapod brain organization.…”

On the Value of Reptilian Brains to Map the Evolution of the Hippocampal Formation

“…However, while some aspects of cortical connections may be preserved, it is important to consider a wider range of cortical projections, since circuits may evolve independently, even in closely related species [Striedter, 1994]. In reptiles, M, DM, and dorsal cortex receive input from anterior thalamic nuclei [Bruce and Butler, 1984;Desan, 1988;Martinez-Garcia and Lorente, 1990;Hoogland et al, 1998;Desfilis et al, 2002;Zhu et al, 2005;Pritz, 2014], whereas mammals lack such input to the dentate gyrus and CA3. Thus, signals transmitted through the anterior thalamus in mammals, such as information about head direction [Taube, 2007], may reach a wider set of medial cortex regions in reptiles.…”