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Abstract: One of the major neuropathological hallmarks in Alzheimer’s disease (AD) is the loss of cholinergic neurones of the nucleus basalis of Meynert (NbM). This consistent finding gave rise to the ‘cholinergic’ hypothesis of AD and lead to the subsequent development of acetylcholinesterase (AChE) inhibitors; the first class of drug to be approved for the treatment of AD. However, several studies have questioned the efficacy of using AChE inhibitors in AD. In this study we have investigated the ability of two AChE inhibitors, donepezil (Aricept) and physostigmine, to induce gamma oscillatory activity in rat hippocampal slices; network activity believed to play a role in higher cognitive function. We report here that donepezil is capable of inducing gamma oscillations in region CA3 of rat hippocampal slices, which may contribute to its procognitive action. However, donepezil-induced gamma oscillations are weak in comparison to physostigmine. We also explore the activity of novel agents with known procognitive activity, and show that one such agent, the M1 muscarinic acetylcholine receptor agonist, 77-LH-28-1, can significantly enhance donepezil-induced gamma oscillations. These data support the notion that it should be possible to find a more efficacious AChE inhibitor or an adjunctive approach, to provide a better therapeutic intervention in AD. [ABSTRACT FROM AUTHOR]

Abstract: Exposure to an enriched environment promotes neurochemical, structural and neurophysiological changes in the brain and is associated with enhanced synaptic plasticity and improved hippocampal-dependent learning. Using a global proteomics-based approach we have now been able to reveal the altered expression of a diverse range of hippocampal proteins following exposure to an enriched environment. Male Hooded Lister rats (8 weeks) were subjected to a 6-week regimen in which they were housed in either non-enriched (open field) or enriched conditions (toys, wheels etc.). Whole protein extracts from stratum pyramidale and stratum radiatum of area CA1 were then isolated and subjected to differential gel electrophoresis [McNair K, Davies CH, Cobb SR (2006) Plasticity-related regulation of the hippocampal proteome. Eur J Neurosci 23(2):575–580]. Of the 2469 resolvable protein spots detected in this study, 42 spots (1.7% of the detectable proteome) derived from predominantly somatic fractions and 32 proteins spots from dendritic fractions (1.3% of detectable proteome) were significantly altered in abundance following exposure to an enriched environment (somatic: 14 increased/28 decreased abundance, range −1.5 to +1.4-fold change; dendritic: 16 increased, 16 decreased abundance, range −1.6 to +3.0-fold change). Following in-gel tryptic digestion and Maldi-Tof/Q-star mass spectrometry, database searching revealed the identity of 50 protein spots displaying environmental enrichment-related modulation of expression. Identified proteins belonged to a variety of functional classes with gene ontology analysis revealing the majority (>70%) of regulated proteins to be part of the energy metabolism, cytoplasmic organization/biogenesis and signal transduction processes. [Copyright &y& Elsevier]

Nicotinic acetylcholine receptors (nAChRs) regulate neuronal excitability within the CNS. To assess the possible modulatory influence of nAChRs on epileptiform activity, a range of nAChR ligands were applied during experimentally induced epileptiform activity in rat hippocampal slices. Bath application of the potassium channel blocker 4-aminopyridine (4AP; 10–50 μM) resulted in the development of spontaneous epileptiform bursting activity in area CA3 that consisted of short duration (257±15 ms) field events occuring regularly at a frequency of 0.4±0.02 Hz. Subsequent co-application of the selective nAChR agonists 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP; 0.3–300 μM), choline (0.01–3 mM) and lobeline (3–30 μM) produced sustained and concentration-dependent increases in burst frequency with maximal frequency potentiation of 37±5%, 27±5% and 24±11%, respectively. DMPP (10–30 μM; n=31) also potentiated epileptiform bursting induced by reducing GABAA receptor-mediated synaptic transmission using 20 μM bicuculline or enhancing NMDA receptor-mediated excitation by lowering extracellular Mg2+. Irrespective of the epileptiform model studied all nAChR agonist induced frequency potentiation was reversed upon washout of the agonist or co-application of one of the selective nAChR antagonists dihydro-β-erythroidine (10–30 μM), mecamylamine (50–200 μM) or α-bungarotoxin (100 nM). These results provide compelling evidence that activation of nAChRs exacerbate epileptiform activity in the rat hippocampus. [Copyright &y& Elsevier]