Calcium binding protein expression in the optic tectum of Alligator during development.

The onset and distribution of the calcium binding proteins, calretinin, calbindin, and parvalbumin, were examined in the optic tectum of Alligator mississipiensis embryos between Stages 18 and 26-28. The immunoreactivity of each calcium binding protein correlated well with the results from the Western blot experiments. In terms of onset and distribution, calretinin expressison was the most widespread of the three calcium binding proteins that were examined, and was also the earliest to be visualized. Calbindin expression occurred next, whereas parvalbumin expression was the most limited and appeared last. For small calretinin (+) neurons, the pattern of immunoreactivity during development was from inside to outside, whereas for the larger cells, it was from outside to inside. For calbindin immunoreactive cells in the superficial zone, the pattern was from outside to inside. The distribution of the parvalbumin immunopositive neurons did not change significantly over the time period examined. Similar data on other amniotes is limited. However, the pattern in Alligator shares some similarities with kittens in regards to the distribution of calbindin and parvalbumin in the developing superior colliculus.

Remodeling of synapses in the CA1 area of the hippocampus after transient global ischemia.

Synapses are essential to neuronal functions. Synaptic changes occur under physiological and pathological conditions. Here we report the remodeling of synapses in the CA1 area of the hippocampus after transient global ischemia using electron microscopy. Much electron-dense material appeared in the cytoplasm of dendrites at 24h after ischemia. Many dark axons or terminals were found in the CA1 neuropil; some of which were phagocytized by dendrites. Interestingly autophagosomes appeared in many axons or dendrites at 48 h after ischemia. In addition, postsynaptic density (PSD) - like structures or synaptic - like structures were found inside spines and dendrites. Statistical analysis demonstrated that the thickness of PSDs in the CA1 neuropil increased from 12 to 48 h after ischemia. The frequency of autophagosomes appeared to escalate from 12 to 48 h after ischemia. The frequency of asymmetric synapses was significantly increased at 12h and 24h after ischemia in stratum oriens, proximal and distal stratum radiatum. Among asymmetric synapses, the number of perforated synapses consistently increased and reached a peak (approximately 10-fold increase) at 48 h after ischemia. On the other hand, the number of multiple synaptic boutons decreased after ischemia reaching a two to fourfold decrease at 48 h after ischemia. These results have shown that ischemia induces an increase of asymmetric synapses as well as synaptic autophagy, which may contribute to the neuronal death in the CA1 area after transient global ischemia.

PAX6 immunoreactivity in the diencephalon and midbrain of alligator during early development.

PAX6 expression was examined during early development of the diencephalon and midbrain of Alligator using an immunocytochemical methodology. These observations focused on the basal plate to determine whether diencephalic prosomere organization in this region followed a pattern previously identified for alar plate areas. PAX6 expression was also described in alar diencephalic regions and the adjacent midbrain. PAX6 (+) cells in the basal plate were first seen in prosomere 1 at stage 7, in the midbrain at stage 10, and lastly in prosomeres 2 and 3 at stage 11. By stage 12, a nearly continuous column of PAX6 (+) cells extended from the midbrain basal plate through the entire diencephalon. In the diencephalon, PAX6 (+) cells in the basal plate were of greatest number in prosomere 1, least in prosomere 2, and intermediate in prosomere 3. This pattern of PAX6 expression distinguished these individual basal plate prosomeres. These results indicate that basal plate prosomeres follow a pattern similar to alar plate prosomereric organization during the later stages of early diencephalon development. Over a comparable time period of early diencephalon development, similar observations have been made in chick basal plate. In Alligator and chick, PAX6 expression in the basal plate is similar in the midbrain and prosomere 1 but different in prosomeres 2 and 3: present in Alligator and absent in chick. In alar plate areas of the Alligator diencephalon, PAX6 expression follows a similar pattern to that described for chick and mouse. These similarities in PAX6 expression in alar diencephalic prosomeres suggest that this is a common feature of amniotes. Differential PAX6 expression in alar prosomere 1 and the midbrain in Alligator is similar to that described for a wide range of species which suggests that these features are common to all vertebrates.

Dendritic plasticity of CA1 pyramidal neurons after transient global ischemia.

Dendrites and spines undergo dynamic changes in physiological conditions, such as learning and memory, and in pathological conditions, such as Alzheimer's disease and epilepsy. Long-term dendritic plasticity has also been reported after ischemia/hypoxia, which might be compensatory effects of surviving neurons for the functional recovery after the insults. However, the dendritic changes shortly after ischemia, which might be associated with the pathogenesis of ischemic cell death, remain largely unknown. To reveal the morphological changes of ischemia-vulnerable neurons after ischemia, the present study investigated the alteration of dendritic arborization of CA1 pyramidal neurons in rats after transient cerebral ischemia using intracellular staining technique in vivo. The general appearance of dendritic arborization of CA1 neurons within 48 h after ischemia was similar to that of control neurons. However, a dramatic increase of dendritic disorientation was observed after ischemia with many basal dendrites coursed into the territory of apical dendrites and apical dendrites branched into the region of basal dendrites. In addition, a significant increase of apical dendritic length was found 24 h after ischemia. The increase of dendritic length after ischemia was mainly due to the dendritic sprouting rather than the extension of individual dendrites, which mainly occurred in the middle segment of the apical dendrites. These results reveal a plasticity change in dendritic arborization of CA1 neurons shortly after cerebral ischemia.