Research update: Alpha7 nicotinic acetylcholine receptor mechanisms in Alzheimer's disease

Nicotinic ACh receptors in the hippocampus: role in excitability and plasticity

INTRODUCTION

The nicotinic ACh receptors (nAChRs) are in the cys-loop family of ligand-gated ion channels. They are widely expressed throughout the brain, including in the hippocampus where they are thought to be involved in regulating excitability, plasticity, and cognitive function. In addition, dysfunction in hippocampal nAChRs has been linked to a variety of neurological disorders and diseases, including Alzheimer's disease, schizophrenia, and epilepsy. In order to understand how to treat nAChR-related disorders and diseases, it is critical to understand how these receptors participate in normal brain function; this entails not only understanding the biophysical properties of ion channel function and their pattern of expression but also how these receptors are regulating excitability and circuit behavior.

DISCUSSION

The primary cholinergic input to the hippocampus comes from the medial septum and diagonal band of Broca; however, the mechanistic details are unknown of how activation of cholinergic receptors, either through exogenous nAChR ligands or the activation of endogenous acetylcholine release, regulates hippocampal network activity. This entails direct study of the excitatory and inhibitory neuronal networks, as well as the role of nonneuronal cells, in regulating hippocampal function.

CONCLUSIONS

Here, I will review the latest work from my laboratory in which we have attempted to do just that, with the overall goal of learning more about the role of the hippocampal nAChR in synaptic plasticity.

Amyloid beta (Aβ) peptide modulators and other current treatment strategies for Alzheimer's disease (AD)

Introduction: Alzheimer's disease (AD) is a common, progressive neurological disorder whose incidence is reaching epidemic proportions. The prevailing "amyloid cascade hypothesis," which maintains that the aberrant proteolysis of beta-amyloid precursor protein (βAPP) into neurotoxic amyloid beta (Aβ) peptides is central to the etiopathology of AD, continues to dominate pharmacological approaches to the clinical management of this insidious disorder. This review is a compilation and update on current pharmacological strategies designed to down-regulate Aβ42 peptide generation in an effort to ameliorate the tragedy of AD. Areas covered: This review utilized online data searches at various open online-access websites including the Alzheimer Association, Alzheimer Research Forum; individual drug company databases; the National Institutes of Health (NIH) Medline; Pharmaprojects database; Scopus; inter-University research communications; and unpublished research data. Expert opinion: Anti-acetylcholinesterase-, chelation-, N-methyl-D-aspartate (NMDA) receptor antagonist-, statin-, Aβ immunization-, β-secretase-, γ-secretase-based, and other strategies to modulate βAPP processing, have dominated pharmacological approaches directed against AD-type neurodegenerative pathology. Cumulative clinical results of these efforts remain extremely disappointing, and have had little overall impact on the clinical management of AD. While a number of novel approaches are in consideration and development, to date there is still no effective treatment or cure for this expanding healthcare concern.

α7 Nicotinic receptor modulators for cognitive deficits in schizophrenia and Alzheimer's disease

INTRODUCTION

Nicotinic receptors (nAChR), a class of ligand-gated ion channels, are attractive targets in a variety of CNS diseases. The low-affinity α7 nAChR modulate the levels of various neurotransmitters, their receptor density is affected in schizophrenia and a single nucleotide polymorphism in the promoter region has been associated with higher risk for schizophrenia.

AREAS COVERED

This article reviews the scientific rationale for α7 nAChR stimulation and presents a selection of α7-positive modulators that are in development for cognitive deficits, both in Alzheimer's disease and in cognitive impairment associated with schizophrenia. The available clinical information is reviewed and the translational difficulties are discussed.

EXPERT OPINION

In contrast to preclinical models, clinical proof-of-concept studies so far have not shown clear unequivocal cognitive benefit, although there are signs of clinical efficacy on specific cognitive scales and on negative symptoms. Possible problems associated with the clinical development include the impact of dosage and dosing schedule on the balance between activation and desensitization of the ion channel, the selection of comedication, robust human target engagement data and the choice of clinical readout scales. A better understanding of the human biology of α7 nAChR is essential for improving the successful clinical development of this promising target.