Ann B. Butler

Telencephalon of the Lizard Gekko gecko (Linnaeus): Some Connections of the Cortex and Dorsal Ventricular Ridge

Interhemispheric connections of the telencephalon in the lizard, Gekko, were studied with anterograde degeneration methods following lesions variously placed in the medial, dorsal, and lateral cortices and/or the dorsal ventricular ridge (D.V.R.). After lesions involving dorsal cortex, the medial wall, and the DVR, the majority of degenerated fibers decussate in the hippocampal commissure and terminate in the septum, medial wall, dorsal cortex, and the lateral edge of the DVR contralaterally. Lesions confined to dorsal cortex result in a similar pattern of degeneration, while lesions confined to the lateral wall result in degeneration in the contralateral lateral cortex, DVR and striatum, mainly via the anterior commissure. Some variation has been reported on the pattern of interhemispheric projections among reptiles studied to date; two possible interpretations of the data are that (1) dorsal cortex may be homologous as a field to parts of both neocortex and the hippocampal formation of mammals or (2) only the lateral part of dorsal cortex may be homologous to neocortex.

Cytoarchitectonic and Connectional Organization of the Lacertilian Telencephalon with Comments on Vertebrate Forebrain Evolution

Two assumptions regarding nonmammalian vertebrates have long been held to be true. The first of these is that nonmammals, as opposed to mammals, behave in stereotyped ways and have little capacity to modify their behavior through learning. The second assumption is that nonmammals are “lower” vertebrates, representing evolutionary stages that gave rise to the “higher” vertebrates, i.e., mammals. Both of these assumptions suggest that the brains of nonmammalian vertebrates (1) are much more simply organized than the brains of mammals and (2) lack any structures which would be comparable to the “higher” (different usage than above but not easily definable) centers of mammalian brains, such as the cerebral neocortex. Thus there would seem to be little reason to study the organization of nonmammalian brains other than out of historical, evolutionary interest.

Neonatally bulbectomized rats with new olfactory-neocortical connections are anosmic.

Rats with one olfactory bulb removed when neonates and the second bulb removed when adults were tested on tone-light discrimination and odor detection tasks. On the neonatally operated side reconstituted olfactory receptor cell axons penetrated the frontal neocortex or portions of the anterior olfactory nucleus, and formed glomerular-like structures. On the adult operated side there was extensive scar formation which prevented in-growing sensory axons from contacting the brain. All experimental animals acquired the tone-light discrimination but failed to show any evidence of odor detection. These results indicate that reconstituted olfactory projections which terminate in the frontal neocortex or anterior olfactory nucleus do not support olfaction.

Nucleus laminaris of the torus semicircularis: Projection to spinal cord in reptiles

Neurons in nucleus laminaris of the torus semicircularis were retrogradely labeled following application of horseradish peroxidase (HRP) to the cervical spinal cord in two lizards (Gekko gecko and Iguana iguana) and a turtle (Pseudemys scripta). Different patterns of cell labeling were seen among the species studied and may be related to the distinctive differences in head and body movements seen in these animals during defensive, aggressive and social behaviors.