Acute responses to estradiol replacement in the olfactory system of apoE-deficient and wild-type mice

Epidemiological studies suggest that estrogen therapy protects against clinical expression of chronic neurological diseases. These beneficial effects of estrogen therapy are highly modified by apolipoprotein E (apoE) through an unknown mechanism. We examined the short-term effects of estradiol replacement in ovariectomized mice on apoE expression and markers for cell proliferation, reactive gliosis, neuronal maturation, and synaptogenesis in the primary olfactory pathway of wild-type (WT) and apoE knockout (KO) mice. Three days of estradiol replacement increased apoE expression in the olfactory nerve and in the glomerular layer. Estradiol treatment also increased cell proliferation, total cell numbers, number of mature neurons in the olfactory epithelium, and reactive astrocyte numbers in the olfactory bulb (OB) in both WT and KO mice. We also found that estradiol increased glomerular synaptophysin (Syn), but the magnitude of increase was potentiated by the presence of apoE. This data suggest that apoE may be necessary to elicit the complete effect of estradiol on Syn upregualtion

Acute responses to estradiol replacement in the olfactory system of apoE-deficient and wild-type mice

Epidemiological studies suggest that estrogen therapy protects against clinical expression of chronic neurological diseases. These beneficial effects of estrogen therapy are highly modified by apolipoprotein E (apoE) through an unknown mechanism. We examined the short-term effects of estradiol replacement in ovariectomized mice on apoE expression and markers for cell proliferation, reactive gliosis, neuronal maturation, and synaptogenesis in the primary olfactory pathway of wild-type (WT) and apoE knockout (KO) mice. Three days of estradiol replacement increased apoE expression in the olfactory nerve and in the glomerular layer. Estradiol treatment also increased cell proliferation, total cell numbers, number of mature neurons in the olfactory epithelium, and reactive astrocyte numbers in the olfactory bulb (OB) in both WT and KO mice. We also found that estradiol increased glomerular synaptophysin (Syn), but the magnitude of increase was potentiated by the presence of apoE. This data suggest that apoE may be necessary to elicit the complete effect of estradiol on Syn upregualtion

Reconstitution of the Olfactory Epithelium Following Injury in ApoE-Deficient Mice

ApoE, a protein component of lipoproteins, is extensively expressed in the primary olfactory pathway. Because apoE has been shown to play a vital role in nerve repair and remodeling, we hypothesized that apoE expression will increase in the injured olfactory epithelium (OE), and that apoE deficiency in apoE knockout (KO) mice will lead to delayed/incomplete reconstitution of the OE following injury. To directly test this hypothesis, we compared OE regeneration in wild-type (WT) and KO mice following injury induced by intranasal irrigation of Triton X-100. OE was collected at 0, 3, 7, 21, 42, and 56 days post lesion. The amount and distribution of apoE in the regenerating OE was measured by immunoblotting and immunohistochemistry. Rate of OE reconstitution in WT and KO mice was assessed by using three independent measures: (1) OE thickness was measured in cresyl-violet stained sections, (2) basal cell proliferation was determined by using bromodeoxyuridine (BrdU) staining, and (3) differentiation and maturation of olfactory sensory neurons were measured by immunoblotting and immunohistochemical analysis of growth associated protein (GAP) 43 and olfactory marker protein (OMP). The results revealed that apoE expression in the OE is highly regulated during the entire course of OE reconstitution post injury, and that apoE deficiency in apoE KO mice leads to delayed recovery of mature OMP+ cells in the reconstituting OE. The data suggest that apoE production increases in the injured OE to facilitate maturation of olfactory sensory neurons

The distribution of apolipoprotein E in mouse olfactory epithelium

Previous studies from our laboratory suggest that apolipoprotein (apoE), a lipid transporting protein, facilitates olfactory nerve regeneration. We have shown that apoE is enriched in the olfactory nerve and around the glomeruli of the olfactory bulb (OB). The studies reported herein were undertaken to identify possible sources of apoE in the olfactory epithelium (OE). Immunoblotting results revealed apoE expression in the OE of wild-type (WT) mice, but not in apoE deficient/knockout (KO) mice. Immunohistochemical studies revealed that the perikarya and processes of sustentacular (Sus) cells expressed apoE-like immunoreactivity. Minimal neuronal apoE immunostaining was seen, although apoE was observed in the interstial spaces between olfactory receptor neurons (ORN). Substantial apoE-like immunoreactivity was localized to the endfeet and terminal process of Sus cells surrounding the basal cells. Double labeling immunocytochemical studies confirmed that the cell bodies and endfeet of Sus cells expressed high levels of apoE. The endothelial cells of blood vessels were intensely stained for apoE in the lamina propria. Cells forming Bowman’s gland also immunostained for apoE. The apoE staining in the nerve fascicles was less intense, but was uniformly distributed throughout the core of the nerve bundles. Heavily stained cells, probably ensheathing glia, surrounded the nerve fascicles. These results revealed that apoE is expressed in the adult OE and lamina propria at strategic locations where it could facilitate the differentiation, maturation and axonal growth of the ORN, perhaps by recycling lipids from degenerating ORN for use by growing axons

Doublecortin-Expressing Cells Persist in the Associative Cerebral Cortex and Amygdala in Aged Nonhuman Primates

A novel population of cells that express typical immature neuronal markers including doublecortin (DCX+) has been recently identified throughout the adult cerebral cortex of relatively large mammals (guinea pig, rabbit, cat, monkey and human). These cells are more common in the associative relative to primary cortical areas and appear to develop into interneurons including type II nitrinergic neurons. Here we further describe these cells in the cerebral cortex and amygdala, in comparison with DCX+ cells in the hippocampal dentate gyrus, in three age groups of rhesus monkeys: young adult (12.3 ± 0.2 years, n = 3), mid-age (21.2 ± 1.9 years, n = 3) and aged (31.3 ± 1.8 years, n = 4). DCX+ cells with a heterogeneous morphology persisted in layers II/III primarily over the associative cortex and amygdala in all groups (including in two old animals with cerebral amyloid pathology), showing a parallel decline in cell density with age across regions. In contrast to the cortex and amygdala, DCX+ cells in the subgranular zone diminished in the mid-age and aged groups. DCX+ cortical cells might arrange as long tangential migratory chains in the mid-age and aged animals, with apparently distorted cell clusters seen in the aged group. Cortical DCX+ cells colocalized commonly with polysialylated neural cell adhesion molecule and partially with neuron-specific nuclear protein and γ-aminobutyric acid, suggesting a potential differentiation of these cells into interneuron phenotype. These data suggest a life-long role for immature interneuron-like cells in the associative cerebral cortex and amygdala in nonhuman primates

Long-term effects of estradiol replacement in the olfactory system

Olfactory dysfunction often precedes other clinical symptoms in chronic neurodegenerative diseases like Alzheimer’s and Parkinson’s disease. Estrogen deficiency and apoE genotype are known risk factors in these diseases and these factors also affect olfaction. Therefore we examined the effects of estradiol replacement following ovariectomy on expression of apoE and markers of cell proliferation, neuronal maturation, synaptogenesis and reactive gliosis in the primary olfactory pathway of wild-type (WT) and apoE knockout (KO) mice. Estradiol replacement increased apoE staining in the olfactory nerve and glomerular layers. Estradiol increased astrocyte density and olfactory epithelium (OE) thickness regardless of the genotype. In addition estradiol treatment increased the number of mature neurons in the OE and glomerular synaptophysin in both genotypes, but the magnitude of increase was greater in the WT than in the KO mice. These data suggest that estrogen and apoE act synergistically to minimize the loss of mature sensory neurons and synapses following ovariectom

Muscarinic Cholinoceptive Neurons in the Frontal Cortex in Alzheimer’s Disease

The cellular distribution of muscarinic acetylcholine receptor protein in the frontal cortex of Alzheimer (AD) patients, age-matched and middle-aged controls was assessed quantitatively by means of immunohistochemistry using the monoclonal antibody M35. As shown previously in biopsy cortices, mainly layer II/III and V pyramidal neurons were immunolabeled. Neither distribution nor numbers of labeled cells displayed significant differences between the groups investigated. This is in accordance with the results of ligand binding studies that mostly failed to reveal different binding characteristics in AD compared to controls. Muscarinic and nicotinic receptor proteins have been shown to be colocalized in many cholinoceptive pyramidal neurons. Since nicotinic receptors-in contrast to muscarinic receptor proteins-are severely reduced in AD, this indicates a selective impairment of nicotinic receptor expression and not a significant death of cholinoceptive neurons per se.