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Coordinated upregulation of α1‐ and β11‐tubulin mRNAs during collateral axonal sprouting of central peptidergic neurons

An in situ hybridization study was performed to determine the relationship between levels of mRNAs for the axonal growth‐associated αl‐tubulin and βZII‐tubulin isotypes and the process of collateral axonal sprouting by identified central nervous system (CNS) neurons. A unilateral hypothalamic knife‐cut was used to hemisect the hypothalarnoneurohypophysial tract, which results in a robust collateral sprouting response by the uninjured neurons of the contralateral supraoptic nucleus (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 hybridized with 35S‐labeled cDNA probeses specific to αl‐ and β11‐tubulin mRNAs. Quantitative evaluation of the resulting autoradiographs revealed that αl‐tubulin mRNA levels were significantly increased by 10 days in SON neurons that were undergoing collateral sprouting compared to controls and that this increase was sustained at 30‐35 days post‐lesion. Less marked increases in hybridization intensity of the βII‐tubulin probe were also apparent in sprouting neurons at both 10 and 30‐35 days after the lesion, but were statistically significant only at 10 days. The measured increases in intensity of hybridization of αl‐ and β11‐tubulin probes are likely to be conservative estimates of the underlying increase in αl‐ and β11‐tubulin mRNA levels because sprouting SON neurons undergo significant hypertrophy. High levels of both αl‐ and βII‐tubulin mRNAs were also seen in surviving axotomized SON neurons ipsilateral to the hypothalamic lesion. We conclude that the pattern of regulation of αl‐ and β11‐tubulin mRNAs in CNS neurons which are capable of supporting new axonal growth includes three elements: maintenance of significant basal αl‐ and β11‐tubulin mRNA pools in mature neurons, rapid increases in the pool size of the mRNAs following stimulation of collateral sprouting, and sustained elevation of mRNA levels during the period of axonal sprouting. © 1995 Wiley‐Liss, Inc.