Puberty is a critical period in mesocorticolimbic dopamine (DA) system development particularly for the medial prefrontal cortex (mPFC) projection which achieves maturity in early adulthood. these effects are only observed after puberty suggesting ARHGEF11 that netrin-1 mediated effects on DA systems vary across development. Here we report on the normal expression of DCC and UNC5H in the ventral tegmental area (VTA) by DA Tamoxifen Citrate neurons from embryonic life to adulthood in both mice and rats. We show a dramatic and enduring pubertal change in the ratio of DCC:UNC5H receptors reflecting a shift toward predominant UNC5H function. This shift in DCC:UNC5H ratio coincides with the pubertal emergence Tamoxifen Citrate of UNC5H expression by VTA DA neurons. Although the distribution of DCC and UNC5H by VTA DA neurons changes during puberty the pattern of netrin-1 immunoreactivity in these cells does not. Together our findings suggest that DCC:UNC5H ratios in DA neurons at critical periods may have important consequences for the organization and function of mesocorticolimbic DA systems. Introduction The elaboration and establishment of organized patterns of neural connectivity during brain development rely on the concerted action of various permissive and instructive cues. Netrin-1 a member of the netrin family of guidance cues participates in the organization of neural networks by attracting or repelling extending processes   . Two distinct families of netrin-1 receptors the DCC (deleted in colorectal cancer) and UNC-5 homologue families (UNC5H; A-D) account for the bifunctional nature of netrin-1. Whereas DCC receptors mediate attraction DCC-UNC5H receptor complexes or UNC5H alone mediate repulsion    . Consistent with their function these netrin-1 receptors recruit downstream proteins that regulate cytoskeletal reorganization . Recently DSCAM (Down’s syndrome cell adhesion molecule) has been identified as a novel netrin-1 receptor involved in Tamoxifen Citrate signalling axon guidance  . However netrin-1 mediated signal transduction via DSCAM is poorly understood. High levels of DCC have been observed in cell body and terminal regions of developing and adult dopamine (DA) neurons      . In addition we and others have shown that DCC is expressed specifically by DA neurons in these regions in the adult rat and mouse brain  Tamoxifen Citrate suggesting a role for DCC in the organization and function of DA systems. This hypothesis was confirmed by a series of studies we conducted recently in heterozygous (+/?) mice showing that mice expressing reduced levels of DCC exhibit profound changes in mesocorticolimbic DA organization and function in adulthood. Indeed adult +/? mice exhibit sizeable increases in basal and amphetamine-induced DA activity in the medial prefrontal cortex (mPFC) and decreased amphetamine-induced DA release in the nucleus Tamoxifen Citrate accumbens (NAcc)  . Concomitantly adult +/? mice display altered mesocorticolimbic DA-mediated behaviors including blunted amphetamine-induced locomotion and reward and resistance to amphetamine-induced deficits in prepulse inhibition  . Significantly the +/? dopamine and behavioral phenotypes are not evident before puberty  demonstrating a critical temporal window of vulnerability within the mesocorticolimbic DA system to the effects of reduced DCC levels. Together these findings indicate that netrin-1 receptors participate in the development of the mesocorticolimbic DA system and that their organizational effects occur at specific critical periods. Here we report on the normal profile of DCC and UNC5H expression by mesocorticolimbic DA neurons from embryonic life to adulthood in Sprague-Dawley rats and C57BL/6 (BL6) mice. First using Western blot analysis we demonstrate that the ratio of DCC to UNC5H expression switches toward UNC5H predominance during peri-pubertal age in DA somatodendritic regions. To capture possible changes in DCC and UNC5H expression by mesocorticolimbic DA neurons specifically we conducted dual-immunofluorescence experiments at specific developmental stages. These stages were selected based on the selective changes that take place during the elaboration of the mesocorticolimbic DA circuitry . We find that whereas DA neurons express DCC from embryonic life to adulthood UNC5H expression by these.