No abstract

The presence of serotonin 1A receptor (5-HT 1A -R) in the hippocampus, amygdala, and most regions of the frontal cortex is essential between postnatal day-5-21 (P5-21) for the expression of normal anxiety levels in adult mice. Thus, the 5-HT 1A -R plays a crucial role in this time window of brain development. We show that the 5-HT 1A -R-mediated stimulation of extracellular signal-regulated kinases 1 and 2 (Erk1/2) in the hippocampus undergoes a transition between P6 and P15. At P6, a protein kinase C (PKC) isozyme is required for the 5-HT 1A -R )Erk1/2 cascade, which causes increased cell division in the dentate gyrus. By contrast, at P15, PKCa participates downstream of Erk1/2 to augment synaptic transmission through the Schaffer Collateral pathway but does not cause increased cell division. Our data demonstrate that the 5-HT 1A -R )Erk1/2 cascade uses PKC isozymes differentially, first boosting the cell division to form new hippocampal neurons at P6 and then undergoing a plastic change in mechanism to strengthen synaptic connections in the hippocampus at P15.

Azide-terminated poly(tert-butyl acrylate) was synthesized via atom transfer radical polymerization (ATRP). Subsequent deprotection was performed to yield poly(acrylic acid) (PAA) possessing a reactive chain-end. A one-pot sequential amidation of the PAA with the amine derivatives of a near-infrared fluorescent dye (ADS832WS) and glucose produced NIRF dye-incorporated water-soluble copolymers. End-group modifications were performed to produce alkyne/biotin-terminated copolymers which were further employed to generate dye-incorporated polymer-protein hybrids via the biotin-avidin interaction with avidin or "click" bioconjugation with azide-modified BSA. We have overcome two fundamental limitations in the synthesis of bioconjugates: (a) the basic restriction in the diversity of copolymers which can be synthesized for producing bioconjugates, (b) the limitation in the number of dyes/drug molecules that can be attached per protein molecule. The copolymers possessed enhanced optical properties compared to the dye due to increased solubility in water. Potential utility of these copolymers and conjugates in multiwell plate based assays, cell surface imaging and in vivo animal imaging were explored.

During neonatal hippocampal development, serotonin 1A receptor-mediated signaling initially employs PKCε to boost neuronal proliferation and then uses PKCα to promote synaptogenesis. Such stage-specific involvement of a PKC isozyme could be determined by its relative expression level. In mouse hippocampi, we detected relatively low levels of α, β, γ, and δ isozymes at post-natal days 2–6 (P2–6), which was followed by a large increase in their expression. In contrast, the PKC isozymes ε and θ were relatively abundant at P6, following which they underwent a further increase by P15. Comparison with purified proteins confirmed that the PKCε levels at P6 and P15 were respectively 1.75 and 7.36 ng per 60 µg of protein, whereas PKCα levels at P6 and P15 were respectively 160 pg and 1.186 ng per 60 µg of protein. Therefore, at P6, PKCepsilon was about 11-fold more abundant than PKCα. Consequently, signaling cascades could use the relatively abundant PKCε (and possibly PKCθ) molecules for early events at P2-6 (e.g. neurogenesis), following which PKCα (and the β, γ, or δ isozymes) could guide maturation or apoptosis. Notably, at P6 but not P15, PKCε, was localized to the nuclei of neuroblasts, probably directing mitosis. In contrast, at P15 but not P6, PKCα was highly expressed in the processes of the differentiated hippocampal neurons. In summary, PKC isozymes follow differential profiles of expression in neonatal hippocampus and the relative abundance of each may determine its mode and stage of involvement in hippocampal development.