INTRINSIC CONNECTIONS IN THE ANTERIOR DORSAL VENTRICULAR RIDGE OF THELIZARD PSAMMODROMUS-ALGIRUS

We have studied the intrinsic connections of the anterior dorsal ventr icular ridge (ADVR) in the lacertid lizard Psammodromus algirus by mea ns of retrograde transport of horseradish peroxidase (HRP) and fluores cent labeling with the lipophilic carbocyanine dye DiI. We injected HR P into different regions in the ADVR arrayed in a medial-to-lateral se quence, with each consisting of three distinct superficial-to-deep zon es. When HRP was injected into a given region, many labeled neurons (a lways located ipsilateral to the injection site) were found at all med iolateral regions of ADVR in locations rostrally distant from the inje ction site. DiI crystals were applied on different superficial-to-deep zones within each region. Two patterns could be recognized: DiI cryst als applied on the periventricular (most superficial) zone resulted in a labeling of cells widely distributed throughout the ADVR independen tly of the mediolateral region of the application site, whereas DiI cr ystals applied on deeper zones resulted in a staining of cells mostly restricted to a narrow radial area. Results from both types of labelin g confirm that the ADVR has a prominent radial component in its intrin sic organization, but they also demonstrate that some areas of the ADV R receive projections from distant, rostrally located neurons in every ipsilateral region of the ridge itself, which establishes a clear non -radial component. This organization may have important functional pro perties with regard to a putative integration of different sensory mod alities conveyed by thalamic afferent fibers to the ADVR. Last, we ana lyzed some evolutionary implications of our results. (C) 1996 Wiley-Li ss, Inc.