No abstract

The higher vocal center (HVc) of the canary brain projects to two forebrain nuclei: robustus archistriatalis (RA) and area X of lobus parolfactorius. The time of birth of HVc neurons projecting to these two regions was determined by combining [3H]thymidine autoradiography and retrograde fluorogold uptake. Birds were sacrificed at 13 months of age, 4 days after fluorogold injections into area X or RA. A single injection of [3lH]thymidine in ovo (embryonic day 9) labeled 76% of area X-projecting cells and 0.8% of cells projecting to RA. The great majority of RA-projecting cells were produced during posthatching development (posthatching day 10-240; P10-P240), with a peak at P60 and a hiatus at P120. HVc reaches full adult size by P240, yet at that age the production of new RA-projecting cells continued at a rate comparable to that recorded during posthatching development. Late production of neurons interconnecting two distant regions of the brain may regulate source to target cell population size. Male canaries start to sing at P40. During subsequent months, they imitate external models and their song becomes more structured and stereotyped. At sexual maturity (P240), song is stable. Three interpretations are offered: (i) neurogenesis of RA-projecting cells is related to learning, and learning continues even after achievement of pattern stability; (ii) neurogenesis of RA-projecting cells is not related to learning; (iii) the production of RA-projecting cells serves different purposes during development and after sexual maturity.

Protein kinase B (PKB), also known as Akt or RAC-PK, is a serine/threonine kinase that can be activated by growth factors via phosphatidylinositol 3-kinase. In this article we show that PKC but not PKC␣ and PKC␦ can co-immunoprecipitate PKB from CHO cell lysates. Association of PKB with PKC was also found in COS-1 cells transiently expressing PKB and PKC, and moreover we found that this association is mediated by the AH domain of PKB. Stimulation of COS-1 cells with plateletderived growth factor (PDGF) resulted in a decrease in the PKB-PKC interaction. The use of kinase-inactive mutants of both kinases revealed that dissociation of the complex depends upon PKB activity. Analysis of the activities of the interacting kinases showed that PDGFinduced activation of PKC was not affected by co-expression of PKB. However, both PDGF-and p110-CAAXinduced activation of PKB were significantly abolished in cells co-expressing PKC. In contrast, co-expression of a kinase-dead PKC mutant showed an increased induction of PKB activity upon PDGF treatment. Downstream signaling of PKB, such as the inhibition of glycogen synthase kinase-3, was also reduced by coexpression of PKC. A clear inhibitory effect of PKC was found on the constitutively active double PKB mutant (T308D/S473D). In summary, our results demonstrate that PKB interacts with PKC in vivo and that PKC acts as a negative regulator of PKB.Protein kinase B (PKB), 1 also referred to as c-Akt or RAC-PK is a 60-kDa serine/threonine kinase which is the cellular homologue of the viral oncogene v-Akt (1-3). So far, three isoforms of PKB have been isolated: PKB␣, PKB␤, and PKB␥ (1, 2, 4, 5). Overexpression of PKB family members has been correlated with different cancers such as breast cancer and some pancreatic and ovarian cancers (2, 6, 7). Recently, PKB has been found to yield an anti-apoptotic signal, which is crucial for cell survival in both fibroblasts and neuronal cells (8, 9). Other reports have indicated a role for PKB in the regulation of glycogen synthesis by inhibition of glycogen synthase kinase-3 (GSK-3) (10, 11). In addition, glucose uptake and metabolism in 3T3-L1 adipocytes have been shown to be regulated by PKB by mediating the translocation of the glucose transporter GLUT4 to the plasma membrane (12, 13). Moreover, a role for PKB has been described in the regulation of protein synthesis through indirect activation of the p70 ribosomal S6 kinase (p70 S6K ) (14). PKB comprises a NH 2 -terminal Akt homology (AH) domain of 148 amino acids, a catalytic domain of 264 amino acids showing high homology with cyclic AMP-dependent protein kinase A (PKA) and protein kinase C (PKC) and a short COOHterminal tail of 68 amino acids. A pleckstrin homology (PH) domain of 106 amino acids is present within the AH domain. Treatment of cells with different growth factors, insulin, or phosphatase inhibitors results in rapid activation of PKB (10,14,15). Also heat shock, hyperosmolarity stress, and intracellular cAMP elevation were shown to activate PKB in vivo (16,17). Growth facto...

Frontal and coronal sections of adult male and female canary brain were stained with a monoclonal antibody to vimentin using an immunoperoxidase technique; some sections were counterstained with cresyl violet. The position of radial glia cells was mapped using a computer-linked microscope. The telencephalon was found to have a rich set of radial glia. The long processes of these radial glia showed a mediolateral orientation, and were much more abundant in some parts of the telencephalon (e.g., hyperstriatum, caudal neostriatum, and lobus parolfactorius) than in others (e.g., anterior neostriatum, archistriatum, and septum), which had few or no radial glia fibers. A small, elongated cell type not previously described in adult avian brain was frequently seen to be associated with the long processes of the radial glia, oriented in the same direction and often in close apposition. The position of these cells was also systematically mapped, and they were found to be virtually absent outside of the telencephalon. The relation between radial glia fibers and the small, elongated cells was most commonly seen close to the lateral ventricle of the forebrain, where the radial glia cells have their cell bodies. The above observations suggest that there may be a functional relation between radial glia and the small, elongated cells. We hypothesize that the latter cells are young migrating neurons. This hypothesis is tested in a separate publication (A. Alvarez-Buylla and F. Nottebohm, unpublished observations).