A comparison of postlesion growth of retinotectal and corticotectal axons after superior colliculus transections in neonatal rats.
We examined, in neonatal rats, the postinjury response of two different axonal systems that project to a common target area in the visual system. Transections across the rostral part of the left superior colliculus (SC) were made in 2- or 6-day-old rats (P2, P6). Lesioned animals were randomly selected into short- or long-term groups. The short-term group was used to determine the efficacy of the lesion technique; 2-6 days after transections, right (contralateral) eyes were injected with horseradish peroxidase (HRP). Complete deafferentation of the SC was achieved in 73% of P2 (n = 22) and 53% of P6 (n = 10) short-term animals. In the long-term group (examined 2-7 months after transection), retinotectal and corticotectal projections were assessed in each animal by using [3H]proline and wheat germ agglutin-HRP, respectively. Examination of a series of sagittal sections revealed that the cut had extended across the entire SC in 63% of P2 (n = 19) and 55% of P6 (n = 12) long-term rats. Despite this, retinal and cortical axons were seen in appropriate layers in postlesion SC in all P2 lesioned animals. Cortical projections caudal to the cut were seen in all P6 rats; however, in these animals, the retinal projection was sparse and not always present. Differences in lesion geometry led to consistent differences in the pattern and extent of ingrowth of retinal and cortical axons into postlesion SC neuropil. The two axonal populations also followed different paths as they grew between prelesion and postlesion SC. It is likely that a number of factors influenced the patterns of postlesion growth, including the relative maturity of the axons and the neuropil into which they were growing. There was also, however, clear evidence of competitive interactions between retinal and cortical axons in postlesion SC that consistently led to greater than normal segregation of the two populations and hence restricted their terminal distributions.
Tan
M M
MM
Department of Anatomy and Human Biology, The University of Western Australia, Nedlands, Perth.
Harvey
A R
AR
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001369:Axons / Q000502:physiology; D001930:Brain Injuries / Q000503:physiopathology*; D005260:Female; D008137:Longitudinal Studies; D009473:Neuronal Plasticity / Q000502:physiology; D009474:Neurons / Q000502:physiology / Q000648:ultrastructure; D011247:Pregnancy; D011392:Proline; D051381:Rats; D017208:Rats, Wistar / Q000502:physiology*; D012160:Retina / Q000166:cytology*; D013477:Superior Colliculi / Q000166:cytology*; D014316:Tritium; D014795:Visual Pathways; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate
D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D014316:Tritium; D011392:Proline