SUBSTANCE-P, BOMBESIN, AND LEUCINE-ENKEPHALIN IMMUNOREACTIVITIES ARE RESTORED IN THE FROG TECTUM AFTER OPTIC-NERVE REGENERATION

Extensive regeneration of the optic nerve takes place in adult Amphibi a, In this study, we have determined whether one aspect of retinotecta l organisation, namely immunoreactive laminae in the retinorecipient l ayers of the optic tectum, is restored after optic nerve regeneration. To do so, the distributions of substance-P, bombesin, and leucine-enk ephalin immunoreactivities were examined in the optic tectum of the fr og Litoria (Hyla) moorei. Results of a normal series were compared wit h those at intervals up to 84 days and at 196 days after either unilat eral deafferentation or optic nerve crush. In the normal series, disti nct neuropeptide immunoreactive laminae were located within the retino recipient tectal layers. There were two major laminae with substance-P , two with bombesin, and one with leucine-enkephalin immunoreactivitie s. Additional faint laminae of both substance-P and bombesin immunorea ctivity were present in the tectal region that receives input from the visual streak. In addition, labelling of cell bodies and dendrites wa s seen elsewhere in the tectum. All except one immunoreactive lamina c hanged after deafferentation. The deeper of those with substance-P imm unoreactivity, along with both bombesin laminae, were eventually lost; the lamina with leucine-enkephalin immunoreactivity was halved in int ensity. We assume that these laminae are wholely or, in the case of th e leucine-enkephalin lamina, partially associated with primary optic i nput. By contrast, the more superficial lamina with substance-P immuno reactivity remained unchanged and is presumably not directly related t o visual input. During nerve regeneration, the intensity of all lamina e associated with optic input initially fell as in the deafferentation series but, in the long term, recovered to approximately 80% of norma l intensities. We conclude that ganglion cells associated with each of the immunoreactivities tested had successfully regenerated. The reduc ed intensity of immunoreactivities after regeneration is due presumabl y in part to the cell loss from the ganglion cell population. Furtherm ore, we discuss the findings of similar studies for Rana pipiens (Kulj is and Karten [1983] J. Comp. Neurol. 217:239-251 and [1985] 240:1-15) in light of the present findings. We argue that some of the previous observations can be reinterpreted to indicate that regeneration was no t limited to ganglion cells associated with substance-P immunoreactivi ty as first thought. (C) 1995 Wiley-Liss, Inc.