6-cyano-7-nitroquinoxaline-2-3-dione and cyanine-dye-3

Amyloid beta (Abeta) protein, a 39-43 amino acid peptide deposited in brains of individuals with Alzheimer's disease (AD), has been shown to interact directly with a number of receptor targets including neuronal nicotinic acetylcholine receptors (nAChRs) and glutamate receptors. In this study, we investigated the synaptic effects of Abeta(1-42) on glutamate-mediated neurotransmission in the diagonal band of Broca (DBB), a cholinergic basal forebrain nucleus. Glutamatergic miniature EPSCs (mEPSCs) were recorded using whole-cell patch-clamp recordings from identified cholinergic DBB neurons in rat forebrain slices. In 54% of DBB neurons, bath application of Abeta(1-42) (100 nM), but not Abeta(42-1) (inverse fragment), significantly increased the frequency of mEPSCs without affecting amplitude or kinetic parameters (rise or decay time). In 32% of DBB neurons, bath application of Abeta(1-42) significantly decreased only the frequency but not amplitude of mEPSCs. Application of dihydro-beta-erythroidine (DHbetaE) (an antagonist for the alpha4beta2 subtype of nAChRs) but not alpha-bungarotoxin (an antagonist for the alpha7 subtype of nAChRs) blocked Abeta(1-42)-mediated increases in mEPSC frequency. The Abeta(1-42)-mediated increase in glutamatergic transmission is thus presynaptic and mediated via non-alpha7 AChRs. In contrast, Abeta(1-42)-mediated decreases in mEPSC frequency could not be antagonized by either DHbetaE or alpha-bungarotoxin. However, the Abeta(1-42)-evoked depression in mEPSC frequency was antagonized by (RS)-alpha-methyl-4-carboxyphenyglycine, a nonselective group I/II metabotropic glutamate receptor antagonist. These observations provide further insight into the mechanisms whereby Abeta affects synaptic function in the brain and may be relevant in the context of synaptic failure observed in AD.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Amyloid beta-Peptides; Animals; Antibodies, Monoclonal; Carbocyanines; Cholinergic Agents; Diagonal Band of Broca; Dihydro-beta-Erythroidine; Electric Stimulation; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Glutamic Acid; In Vitro Techniques; N-Glycosyl Hydrolases; Neurons; Nicotinic Antagonists; Patch-Clamp Techniques; Peptide Fragments; Rats; Rats, Sprague-Dawley; Receptors, Metabotropic Glutamate; Receptors, Nicotinic; Ribosome Inactivating Proteins, Type 1; Saporins

Neurogenesis occurs throughout adult life in dentate gyrus of mammal hippocampus. Therefore, neurons at different stages of electrophysiological and morphological maturation and showing various, if any, synaptic inputs co-exist in the adult granule cell layer, as occurs during dentate gyrus development. The knowledge of functional properties of new neurons throughout their maturation can contribute to understanding their role in the hippocampal function. In this study electrophysiological and morphological features of granule layer cells, characterized as immature or mature neurons, without and with synaptic input, were comparatively described in adult rats. The patch-clamp technique was used to perform electrophysiological recordings, the occurrence of synaptic input evoked by medial perforant pathway stimulation was investigated and synaptic input was characterized. Cells were then identified and morphologically described via detection of biocytin injected through the patch pipette. The neuronal phenotype of recorded cells was assessed by immunohistochemistry and single-cell RT-PCR. Cells with very low capacitance, high input resistance, depolarized resting membrane potential and without synaptic activity were found exclusively at the border of the GCL facing hilus; this type of cell expressed the class III beta-tubulin neuronal marker (mRNA and protein) and did not express a glial marker. Immature neuronal cells with progressively increasing capacitance, decreasing input resistance and resting membrane potential getting more hyperpolarized showed only depolarizing GABAergic synaptic input at first and then also glutamatergic synaptic input. Finally, cells showing electrophysiological, synaptic, and morphological features of mature granule, expressing the mature neuron marker NeuN, were identified.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Calcium Channel Blockers; Carbocyanines; Cellular Senescence; Dentate Gyrus; Electric Stimulation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; GABA Antagonists; Glial Fibrillary Acidic Protein; Immunohistochemistry; In Vitro Techniques; Male; Membrane Potentials; Microscopy, Confocal; Neural Cell Adhesion Molecule L1; Neurons; Patch-Clamp Techniques; Perforant Pathway; Phosphopyruvate Hydratase; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Sialic Acids; Synapses; Synaptic Transmission; Tetrodotoxin; Tubulin; Valine; Verapamil