Long-term nucleus basalis cholinergic depletion induces attentional deficits and impacts cortical neurons and BDNF levels without affecting the NGF synthesis.

Basal forebrain cholinergic neurons (BFCNs) represent the main source of cholinergic innervation to the cortex and hippocampus and degenerate early in Alzheimer's disease (AD) progression. Phenotypic maintenance of BFCNs depends on levels of mature nerve growth factor (mNGF) and mature brain-derived neurotrophic factor (mBDNF), produced by target neurons and retrogradely transported to the cell body. Whether a reciprocal interaction where BFCN inputs impact neurotrophin availability and affect cortical neuronal markers remains unknown. To address our hypothesis, we immunolesioned the nucleus basalis (nb), a basal forebrain cholinergic nuclei projecting mainly to the cortex, by bilateral stereotaxic injection of 192-IgG-Saporin (the cytotoxin Saporin binds p75ntr receptors expressed exclusively by BFCNs) in 2.5-month-old Wistar rats. At 6 months post-lesion, Saporin-injected rats (SAP) showed an impairment in a modified version of the 5-Choice Serial Reaction Time Task (5-choice task). Postmortem analyses of the brain revealed a reduction of Choline Acetyltransferase-immunoreactive neurons compared to wild-type controls. A diminished number of cortical vesicular acetylcholine transporter-immunoreactive boutons was accompanied by a reduction in BDNF mRNA, mBDNF protein levels, markers of glutamatergic (vGluT1), and GABAergic (GAD65) neurons in the SAP-group compared to the controls. NGF mRNA, NGF precursor, and mNGF protein levels were not affected. Additionally, cholinergic markers correlated with the attentional deficit and BDNF levels. Our findings demonstrate that while cholinergic nb loss impairs cognition and reduces cortical neuron markers, it produces differential effects on neurotrophin availability, affecting BDNF but not NGF levels.

AF710B, an M1/sigma-1 receptor agonist with long-lasting disease-modifying properties in a transgenic rat model of Alzheimer's disease.

INTRODUCTION: AF710B (aka ANAVEX 3-71) is a novel selective allosteric M1 muscarinic and sigma-1 receptor agonist. In 3×Tg-AD mice, AF710B attenuates cognitive deficits and decreases Alzheimer-like hallmarks. We now report on the long-lasting disease-modifying properties of AF710B in McGill-R-Thy1-APP transgenic (Tg) rats. METHODS: Chronic treatment with AF710B (10 µg/kg) was initiated in postplaque 13-month-old Tg rats. Drug or vehicle was administered orally daily for 4.5 months and interrupted 5 weeks before behavioral testing. RESULTS: AF710B long-term treatment reverted the cognitive deficits associated with advanced Alzheimer-like amyloid neuropathology in Tg rats. These effects were accompanied by reductions in amyloid pathology and markers of neuroinflammation and increases in amyloid cerebrospinal fluid clearance and levels of a synaptic marker. Importantly, these effects were maintained following a 5-week interruption of the treatment. DISCUSSION: With M1/sigma-1 activity and long-lasting disease-modifying properties at low dose, AF710B is a promising novel therapeutic agent for treating Alzheimer's disease.

A Link Between Nerve Growth Factor Metabolic Deregulation and Amyloid-ß-Driven Inflammation in Down Syndrome.

In Alzheimer's disease and Down syndrome, cholinergic neurons of the basal forebrain progressively degenerate. This neurotransmitter system is the main source of acetylcholine to the cortex and hippocampus. In the mature and fully differentiated central nervous system, the phenotype of forebrain cholinergic neurons and their nerve terminals in cortex and hippocampus depend on the continuous endogenous supply of nerve growth factor (NGF). It has been recently demonstrated that NGF is secreted from cortical neurons in an activity-dependent manner as a precursor molecule, proNGF. Individuals with Alzheimer's disease and Down syndrome exhibit proNGF accumulation in cortex, yet cholinergic neurons become atrophic in both diseases, despite the apparent abundance of the NGF precursor. This review illustrates the recent evidence that NGF metabolism is affected both in Alzheimer's disease and in Down syndrome brains and also discusses a role for amyloid-ß peptides and central nervous system inflammation in unleashing such deficits. It further considers the potential of the NGF metabolic pathway as a new pharmacological target to slow down the neurodegenerative process both in Alzheimer's disease and in individuals with Down syndrome.