Human cerebrospinal fluid promotes spontaneous gamma oscillations in the hippocampus in vitro.

Gamma oscillations (30-80 Hz) are fast network activity patterns frequently linked to cognition. They are commonly studied in hippocampal brain slices in vitro, where they can be evoked via pharmacological activation of various receptor families. One limitation of this approach is that neuronal activity is studied in a highly artificial extracellular fluid environment, as provided by artificial cerebrospinal fluid (aCSF). Here, we examine the influence of human cerebrospinal fluid (hCSF) on kainate-evoked and spontaneous gamma oscillations in mouse hippocampus. We show that hCSF, as compared to aCSF of matched electrolyte and glucose composition, increases the power of kainate-evoked gamma oscillations and induces spontaneous gamma activity in areas CA3 and CA1 that is reversed by washout. Bath application of atropine entirely abolished hCSF-induced gamma oscillations, indicating critical contribution from muscarinic acetylcholine receptor-mediated signaling. In separate whole-cell patch clamp recordings from rat hippocampus, hCSF increased theta resonance frequency and strength in pyramidal cells along with enhancement of h-current (Ih ) amplitude. We found no evidence of intrinsic gamma frequency resonance at baseline (aCSF) among fast-spiking interneurons, and this was not altered by hCSF. However, hCSF increased the excitability of fast-spiking interneurons, which likely contributed to gamma rhythmogenesis. Our findings show that hCSF promotes network gamma oscillations in the hippocampus in vitro and suggest that neuromodulators distributed in CSF could have significant influence on neuronal network activity in vivo.

Amyloid-ß Peptide Targeting Peptidomimetics for Prevention of Neurotoxicity.

A new generation of ligands designed to interact with the α-helix/ß-strand discordant region of the amyloid-ß peptide (Aß) and to counteract its oligomerization is presented. These ligands are designed to interact with and stabilize the Aß central helix (residues 13-26) in an α-helical conformation with increased interaction by combining properties of several first-generation ligands. The new peptide-like ligands aim at extended hydrophobic and polar contacts across the central part of the Aß, that is, "clamping" the target. Molecular dynamics (MD) simulations of the stability of the Aß central helix in the presence of a set of second-generation ligands were performed and revealed further stabilization of the Aß α-helical conformation, with larger number of polar and nonpolar contacts between ligand and Aß, compared to first-generation ligands. The synthesis of selected novel Aß-targeting ligands was performed in solution via an active ester coupling approach or on solid-phase using an Fmoc chemistry protocol. This included incorporation of aliphatic hydrocarbon moieties, a branched triamino acid with an aliphatic hydrocarbon tail, and an amino acid with a 4'- N, N-dimethylamino-1,8-naphthalimido group in the side chain. The ability of the ligands to reduce Aß1-42 neurotoxicity was evaluated by gamma oscillation experiments in hippocampal slice preparations. The "clamping" second-generation ligands were found to be effective antineurotoxicity agents and strongly prevented the degradation of gamma oscillations by physiological concentration of monomeric Aß1-42 at a stoichiometric ratio.

Bri2 BRICHOS client specificity and chaperone activity are governed by assembly state.

Protein misfolding and aggregation is increasingly being recognized as a cause of disease. In Alzheimer's disease the amyloid-ß peptide (Aß) misfolds into neurotoxic oligomers and assembles into amyloid fibrils. The Bri2 protein associated with Familial British and Danish dementias contains a BRICHOS domain, which reduces Aß fibrillization as well as neurotoxicity in vitro and in a Drosophila model, but also rescues proteins from irreversible non-fibrillar aggregation. How these different activities are mediated is not known. Here we show that Bri2 BRICHOS monomers potently prevent neuronal network toxicity of Aß, while dimers strongly suppress Aß fibril formation. The dimers assemble into high-molecular-weight oligomers with an apparent two-fold symmetry, which are efficient inhibitors of non-fibrillar protein aggregation. These results indicate that Bri2 BRICHOS affects qualitatively different aspects of protein misfolding and toxicity via different quaternary structures, suggesting a means to generate molecular chaperone diversity.