THE LACERTIDIAN RETICULAR THALAMIC NUCLEUS PROJECTS TOPOGRAPHICALLY UPON THE DORSAL THALAMUS - EXPERIMENTAL-STUDY IN GALLOTIA-GALLOTI

The projection pattern of the ventral thalamic reticular nucleus onto the dorsal thalamus was studied in the lizard Gallotia galloti using i nvitro horseradish peroxidase and fluorescent carbocyanine labelling t echniques. Localized label deposits at three dorsoventrally spaced sit es in the dorsal thalamus elicited retrograde transport into separate, though partly overlapping, medial, dorsolateral and ventrolateral sec tors within an extended cytoarchitectonic complex which may be globall y identifiable as the reticular nucleus. Neurons found in the dorsolat eral and ventrolateral sectors mainly corresponded to the cell group n amed nucleus ventromedialis (or nucleus of the dorsal supraoptic decus sation) in the literature, whereas neurons labelled in the medial sect or corresponded to the so-called dorsal hypothalamic nucleus. Sparser cells appear labelled in the superficially placed nucleus suprapeduncu laris. Thalamotelencephalic fibers arising from the injected dorsal th alamic nuclei also project to the corresponding retrogradely labeled s ectors within the reticular nucleus. These findings reveal a rough top ographic organization in the connections of the extended reticular nuc leus complex with the whole dorsal thalamus. This supports the hypothe sis of hodological homology between this ventral thalamic formation in Gallotia and the mammalian thalamic reticular nucleus. (C) 1994 Wiley -Liss, Inc.