Expression of caspase-8 and caspase-9 in rat hippocampus during postnatal development.

The role of caspases in the regulation of apoptosis of neurons during development is well established. An emerging body of evidence indicates that caspases may also play significant roles which are nonapoptotic. We have demonstrated previously that the executor caspase-3 exhibited a unique pattern of spatiotemporal expression in the postnatal rat hippocampal subregions, and the activation of caspase-3 in different hippocampal neurons appeared to have distinct roles during postnatal development. In the present study, we examined the expressions of initiator caspases in the hippocampus, using immunofluorescent staining for caspase-8 and caspase-9, and Hoechst 33342 staining for nuclear chromatin to assess caspase-8 and -9 expression in the CA1, CA3, and the dentate gyrus (DG) on postnatal days (P) 0, P2, P4, P7, P14, P21, P28, P56. The results indicate that caspase-8 and caspase-9 were expressed in pyramidal neurons of CA1 and CA3 fields, and granular neurons of the DG during development. Caspase-8 was expressed in a general upward trend while caspase-9 showed a slight downward pattern, but still remained at high levels in the adult hippocampus. The expression profiles of caspases-8 and -9 are distinct from that of the apoptotic cells. These data indicate that caspase-8 may be involved not only in the classical apoptotic function, but also in the cell death of necrosis, and in response to different insults and other nonapoptotic functions. Caspase-9 plays a role in apoptosis during postnatal development, but it may have other functions as well.

Different expression of NR2B and PSD-95 in rat hippocampal subregions during postnatal development.

The different expressions of NR2 and synaptic-associated proteins have been studied by protein and mRNA level with immunoblotting, in situ hybridization, or immunogold analysis. But the relationship between NR2 subunits and PSD-95 family proteins is still controversial. In this study, we used immunofluorescent staining to assess NR2B and PSD-95 expressions and the relationship between them in CA1, CA3, and DG of rat hippocampus on different postnatal day. In CA1, NR2B expression decreased with age. It was high at birth, reached a plateau at P4, and declined gradually after P7. In CA3, NR2B expression was similar to that in CA1. But the stratum lucidum was devoid of staining. In DG, the NR2B expression retained a higher level. From P0 to P2, the PSD-95 expression in CA1 increased gently, and then declined slightly. After P7, the PSD-95 expression increased sharply till P28, and decreased again. In CA3 and DG, the PSD-95 expression is very similar except that low-level of PSD-95 was found in the CA3 stratum lucidum. The expression of NR2B did not correlate with that of PSD-95 in CA1 and the DG granular and molecular layer. Only in CA3 and DG polymorphic layer, there was a negative correlation. The results suggested in hippocampal subregions, CA3 and DG may be more plastic than CA1.The NR2B and PSD-95 expression have distinct regional and cell specific distribution. The different regional distribution pattern may relate to the different physiological functions during postnatal development.

Different expression of caspase-3 in rat hippocampal subregions during postnatal development.

Recent studies indicate that caspase-3 has distinct characteristics in postmitotic and neuronal progenitor apoptosis. Pyramidal neurons in CA1 and CA3 of the hippocampus become postmitotic during early postnatal development, whereas granule cells in the dentate gyrus (DG) undergo self-renewal throughout life. The distribution of caspase-3 in the hippocampal subfields during postnatal development is largely unknown. We used immunofluorescent staining for two isoforms of caspase-3 (an active 17 kDa isoform and an inactive 35 kDa precursor) and the Hoechst 33342 staining for nuclear chromatin to assess caspase-3 expression in the CA1, CA3, and DG of rat hippocampus during postnatal development. The expression of active caspase-3 reached a peak at P7 in CA1, at P2 in CA3, and then decreased with age. Whereas in DG, active caspase-3 expression increased slightly after P7, and remained at high levels for the rest of the investigated period. Procaspase-3 immunoreactivity was strong at P2 and decreased gradually to a basal plateau by P21 in the three regions examined. In addition, the number of apoptotic cells in the three regions all reached maximum levels at P7, and then decreased with age. These data indicate that there were specific spatio-temporal patterns of expression of active and precursor caspase-3 in the postnatally developing rat hippocampal subregions, and that the activation of caspase-3 in neuronal progenitor cells of DG and that in the postmitotic neurons of CA1 and CA3 may have distinct roles and mechanisms during postnatal development.