Unequal representation of the temporal and nasal retina in an anomalous projection to the lateral thalamus.
Study of an anomalously regenerated, nontopographically organized retinal projection in the frog olfactory cortex revealed that the temporal retina is the main source of this projection, suggesting the existence of specific temporal fiber-directed attractant or trophic influences. In the present study, we examined the organization of an anomalous retinal projection that forms in the frog thalamus after ablation of the optic tectum. The projections from different sectors of the retina were studied by means of the anterograde transport of biotinylated dextran-amine (BDA) delivered to incisions made across the nerve fiber layer in frogs surviving ablation of the contralateral tectal hemisphere for 13-46 weeks. The projections from nasal retinal sectors were always lightly constructed in the aberrant terminal field, whereas their projections to the lateral geniculate complex remained reasonably strong. In contrast, the projections from temporal retinal sectors, though also weak initially, in time became robust and filled the aberrant field over most of its extent. The specific amplification of the temporal fiber projection now observed in two foreign targets provides further evidence for the existence of target-based, attractant/trophic molecules with functional specificity for temporal retinal fibers. That such agents can exist or be inducible in a foreign area would suggest that they belong to a family of molecules having natural biological activity in normal development or regeneration. However, the possibility that the augmented role of the temporal retina in these projections is a result of experience-based plasticity is also discussed.
Scalia
F
F
Department of Anatomy and Cell Biology, State University of New York Health Science Center at Brooklyn, Brooklyn, New York 11203, USA.
Simai
D
D
Harris
B
B
Eisner
S
S
D000818:Animals; D020647:Lateral Thalamic Nuclei / Q000033:anatomy & histology*; D009833:Olfactory Pathways / Q000033:anatomy & histology*; D011894:Rana pipiens / Q000033:anatomy & histology*; D012160:Retina / Q000033:anatomy & histology*