Connexins (cx) constitute a family of transmembrane proteins that form gap junction channels allowing metabolic and electrical coupling of cellular networks. Initial studies on the expression of cx in the developing brain have suggested that cx may undergo dynamic changes and may possibly be implicated in synchronizing development and differentiation of neural progenitor cells and young neurons. We have investigated expression of cx26, cx32, cx43, and cx45 in the midbrain floor, where nigrostriatal dopaminergic neurons originate and differentiate. This neuron population is of major importance in regulating motor-functions. Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) revealed low levels of cx26-mRNA in the midbrain floor at E12, which gradually increased during pre- and postnatal development, reaching a maximum in the adult. Cx32-mRNA-levels reached a first peak at E16, and showed highest levels in adulthood. Cx43 was highly expressed at E12, decreased until E18, and subsequently increased again until adulthood. Cx45 mRNA was prominent at all developmental ages, but slightly decreased after the first postnatal week. Double-labeling for the dopaminergic neuronal marker tyrosine hydroxylase (TH), and cx-immunoreactivities (ir) evaluated by quantitative confocal laser microscopy revealed both distinct and similar developmental patterns for the individual cx investigated. Cx26 was highest at E14, decreased towards birth, and subsequently increased again reaching about 50% of the E14 level in the adult. Cx32-ir peaked at E16 and dropped to low levels after birth. Cx43-ir was highest at E12, decreased sharply at E14, reached its lowest levels at birth, but modestly increased again afterwards. Cx45-ir showed a biphasic pattern, with two prominent peaks at E12 and E18, followed by a massive postnatal decrease. Taken together, our results reveal that expression and ir of cx in the midbrain floor and dopaminergic neurons, respectively, follow cx-type specific patterns that temporally coincide with important steps of midbrain morphogenesis, as e.g. progenitor cell formation and migration (E12), early differentiation (E14-16), target encounter (E16-18) and postnatal functional maturation of the nigrostriatal system.

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Background: Vascular pathology is a common feature in patients with advanced Alzheimer’s disease, with cerebral amyloid angiopathy (CAA) and microvascular changes commonly observed at autopsies and in genetic mouse models. However, despite a plethora of studies addressing the possible impact of CAA on brain vasculature, results have remained contradictory, showing reduced, unchanged, or even increased capillary densities in human and rodent brains overexpressing amyloid-β in Alzheimer’s disease and Down’s syndrome. Objective: We asked if CAA is associated with changes in angiogenetic factors or receptors and if so, whether this would translate into morphological alterations in pericyte coverage and vessel density. Methods: We utilized the transgenic mice carrying the Arctic (E693G) and Swedish (KM670/6701NL) amyloid precursor protein which develop severe CAA in addition to parenchymal plaques. Results: The main finding of the present study was that CAA in Tg-ArcSwe mice is associated with upregulated angiopoietin and downregulated hypoxia-inducible factor. In the same mice, we combined immunohistochemistry and electron microscopy to quantify the extent of CAA and investigate to which degree vessels associated with amyloid plaques were pathologically affected. We found that despite a severe amount of CAA and alterations in several angiogenetic factors in Tg-ArcSwe mice, this was not translated into significant morphological alterations like changes in pericyte coverage or vessel density. Conclusion: Our data suggest that CAA does not impact vascular density but might affect capillary turnover by causing changes in the expression levels of angiogenetic factors.

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