COORDINATED UP-REGULATION OF ALPHA-1-TUBULIN AND BETA-II-TUBULIN MESSENGER-RNAS DURING COLLATERAL AXONAL SPROUTING OF CENTRAL PEPTIDERGIC NEURONS

An in situ hybridization study was performed to determine the relation ship between levels of mRNAs for the axonal growth-associated alpha 1- tubulin and beta II-tubulin isotypes and the process of collateral axo nal sprouting by identified central nervous system (CNS) neurons, A un ilateral hypothalamic knife-cut was used to hemisect the hypothalamone urohypophysial tract, which results in a robust collateral sprouting r esponse by the uninjured neurons of the contralateral supraoptic nucle us (SON) (Watt and Paden: Exp Neurol 111:9-24, 1991), At 10 and 30-35 days after the lesion, cryosections of the SON were obtained and hybri dized with S-35-labeled cDNA probes specific to alpha 1- and beta II-t ubulin mRNAs, Quantitative evaluation of the resulting autoradiographs revealed that alpha 1-tubulin mRNA levels were significantly increase d by 10 days in SON neurons that were undergoing collateral sprouting compared to controls and that this increase was sustained at 30-35 day s post-lesion, Less marked increases in hybridization intensity of the beta II-tubulin probe were also apparent in sprouting neurons at both 10 and 30-35 days after the lesion, but were statistically significan t only at 10 days, The measured increases in intensity of hybridizatio n of alpha 1- and beta II-tubulin probes are likely to be conservative estimates of the underlying increase in alpha 1- and beta II-tubulin mRNA levels because sprouting SON neurons undergo significant hypertro phy, High levels of both alpha 1- and beta II-tubulin mRNAs were also seen in surviving axotomized SON neurons ipsilateral to the hypothalam ic lesion, We conclude that the pattern of regulation of alpha 1- and beta II-tubulin mRNAs in CNS neurons which are capable of supporting n ew axonal growth includes three elements: maintenance of significant b asal alpha 1- and beta II-tubulin mRNA pools in mature neurons, rapid increases in the pool size of the mRNAs following stimulation of colla teral sprouting, and sustained elevation of mRNA levels during the per iod of axonal sprouting. (C) 1995 Wiley-Liss, Inc.