Hemisynaptic distribution patterns of presenilins and beta-APP isoforms in the rodent cerebellum and hippocampus.

Healthy brain neurons co-express Alzheimer's disease (AD) related proteins presenilins (PS) and beta-amyloid precursor protein (beta-APP). Deposition of beta-amyloid and PS in the senile plaques of AD brain and their ability to interact in vitro suggest that AD pathology could arise from a defect in the physiological interactions between beta-APP and PS within and/or between neurons. The present study compares the immunocytochemical distribution of PS (1 and 2) and beta-APP major isoforms (695 and 751/770) in the synapses of the cerebellum and hippocampus of the adult rat and mouse. In the cerebellar cortex of both species, the four molecules are immunodetected in the presynaptic or the postsynaptic compartments of synapses, suggesting that they are involved in interneuronal relationships. In contrast, PS and beta-APP are postsynaptic in almost all the immunoreactive synapses of the hippocampus. The different distribution patterns of these proteins in cerebellar and hippocampal synapses may reflect specific physiological differences, responsible for differential vulnerability of neurons to AD synaptic pathology. Defective interactions between beta-APP and PS at the synapses could impede the synaptic functions of beta-APP, inducing the selective loss of synapses that accounts for cognitive impairment in AD.

Sustained delivery of immunoglobulins from polymer microsources on a narrow surface of the developing rat brain.

Studies of postnatal neurogenesis have benefited from the use of a relatively non-invasive method for chronic delivery of bioactive substances to a restricted area of cortex. This method consists of the implantation of an Elvax polymer microsource of active substances close to the targeted brain surface. Receptor ligands, as well as macromolecules such as proteins, peptides and enzymes have been shown to be released by the implants in a sustained manner over weeks. Here we describe the kinetics and immunoreactivity of different immunoglobulins released in vitro and in vivo by Elvax polymer. In vitro, the immunoglobulins first diffuse during a burst phase from the pore network of the polymer matrix. Release continues during a slow phase depending on loading, porosity and volume of the matrix but also on intrinsic properties of immunoglobulins. Elvax microsources loaded either with anti-TAG-1 or with anti-HNK-1 antibodies according to the release data in vitro, are implanted on the posterior cerebellar cortex of postnatal rats during the period when the targeted antigens are expressed by the differentiating cells. After several days, the released immunoreactive antibodies are located at the antigenic sites within the cerebellar cortex close to the implants. The sustained local delivery of immunoglobulins using the Elvax implant method allows access to cell surface and matrix molecules and thereby to the mechanisms they control during postnatal neurogenesis.

Immature chemodifferentiation of Purkinje cell synapses revealed by 5'-nucleotidase ecto-enzyme activity in the cerebellum of the reeler mouse.

During postnatal development of the rodent cerebellum, a transient enzyme activity of ecto-5'-nucleotidase has been shown in the asymmetrical synapses of Purkinje cells. The alterations of the afferent circuitry and microenvironment of the ectopic Purkinje cells present in the cerebellum of the reeler mutant mouse could enlighten parameters that influence the synaptic 5'-nucleotidase activity of these cells. Ecto-enzyme cytochemistry reveals intense 5'-nucleotidase activity in 43% of synapses of the Purkinje cells throughout the cortex and the core of the reeler cerebellar vermis, although the molecular layer displays large areas with less than 1% of labelled synapses. However, enzymatic labelling is found in considerably more Purkinje cells synapses (73%) throughout the granular layer and the subcortical mass. Climbing fiber synapses of monoinnervated Purkinje cells are labelled by 5'-nucleotidase activity in the molecular layer, as well as asymmetrical synapses made on the subjacent ectopic Purkinje cells by the multiple climbing fibers and by the heterologous afferences. The non-innervated dendritic spines of these cells are also labelled, suggesting that 5'-nucleotidase activity at postsynaptic sites of reeler Purkinje cells does not depend on the presynaptic innervation. Rather, 5'-nucleotidase enzyme activity is enhanced at theses sites when the Purkinje cells have not achieved chemodifferentiation but have conserved immature wiring, i.e., low parallel fiber and multiple climbing fiber inputs.