ProNGF\NGF imbalance triggers learning and memory deficits, neurodegeneration and spontaneous epileptic-like discharges in transgenic mice

ProNGF, the precursor of mature nerve growth factor (NGF), is the most abundant form of NGF in the brain. ProNGF and mature NGF differ significantly in their receptor interaction properties and in their bioactivity. ProNGF increases markedly in the cortex of Alzheimer's disease (AD) brains and proNGF\NGF imbalance has been postulated to play a role in neurodegeneration. However, a direct proof for a causal link between increased proNGF and AD neurodegeneration is lacking. In order to evaluate the consequences of increased levels of proNGF in the postnatal brain, transgenic mice expressing a furin cleavage-resistant form of proNGF, under the control of the neuron-specific mouse Thy1.2 promoter, were derived and characterized. Different transgenic lines displayed a phenotypic gradient of neurodegenerative severity features. We focused the analysis on the two lines TgproNGF#3 and TgproNGF#72, which shared learning and memory impairments in behavioral tests, cholinergic deficit and increased Aβ-peptide immunoreactivity. In addition, TgproNGF#3 mice developed Aβ oligomer immunoreactivity, as well as late diffuse astrocytosis. Both TgproNGF lines also display electrophysiological alterations related to spontaneous epileptic-like events. The results provide direct evidence that alterations in the proNGF/NGF balance in the adult brain can be an upstream driver of neurodegeneration, contributing to a circular loop linking alterations of proNGF/NGF equilibrium to excitatory/inhibitory synaptic imbalance and amyloid precursor protein (APP) dysmetabolism.

Song behavior, NGF level and NPY distribution in the brain of adult male zebra finches

The aim of the present study was to investigate the role of nerve growth factor (NGF) and neuropeptide Y (NPY) in the higher vocal center (HVC) on singing behavior of adult male zebra finches. The results of our studies show: (a) that NGF is present in the brain of these birds and it is higher in the HVC than in the other neostriatal tissues; (b) that exogenous administration of NGF or NGF-antibody had no discernible effect on singing behavior; and (c) that NGF enhances the NPY immunoreactivity in neurons and fibers localized in HVC and other areas of the neostriatum and hippocampus whereas anti-NGF decreased NPY stained cells in the hippocampus. These studies indicate that NGF is produced in the brain of zebra finch and that it plays a role in the regulation of NPY.

Increased number of mast cells in the central nervous system of adult male mice following chronic subordination stress

Mast cells (MCs) are amine-storing cells with heterogeneous histological, biochemical, and functional properties. They are found in connective tissue as well as in the peripheral and central nervous system (CNS) of many mammalian species. In this study we investigated whether the distribution of MCs in the CNS of adult male CD-1 mice was modified following repeated defeat stress. Experimental subjects underwent a 3-week period of fighting encounters with a highly aggressive resident. On the test day they were divided into three groups: (a) paired with the resident for 20 min; (b) placed in a cage containing the soiled bedding of the resident for 20 min; (c) placed in a cage with clean sawdust for 20 min. Results show that previous defeat stress increases the number of MCs in the thalamus, habenula, and hypothalamus of subjects exposed to a fighting opponent or to a clean cage, compared to subjects placed in a cage with the bedding of the opponent or to a group-housed, nondefeated control. These results, together with previous reports in birds and rodents, suggest that MCs have a wider role than previously expected and might be involved in the behavioral response to highly relevant psychosocial stimuli.

Neonatal handling in EAE-susceptible rats alters NGF levels and mast cell distribution in the brain

Maternal separation in neonatal rodents causes a wide range of behavioural and metabolic alterations, affecting the physiological response of the neuro-immune-endocrine system. For example, interference with the normal mother-infant interactions leads to an increased susceptibility to experimentally-induced allergic encephalomyelitis (EAE) in adult life. Since it has been reported that mast cells (MCs) participate in the pathophysiology of the autoimmune inflammatory disease multiple sclerosis (MS) and also EAE and that brain nerve growth factor (NGF) levels are altered in EAE, studied whether maternal separation and gentle manipulation (gentling) of neonatal Lewis rats perturb NGF levels or MC distribution in the brain. EAE-induction susceptibility in adult life was also evaluated and NGF levels and mast cell distribution within the hippocampus and thalamus were measured at 0, 10, 20 and 60 postnatal days. Our results show an exacerbation of clinical signs in rats separated from mothers where EAE was induced, a general decrease in NGF protein levels and MC number in the hippocampus during the first developmental period and significant increase in the number of MC in the hippocampus and the thalamus at young-adulthood (60 days of age). These results indicate that disruption of the maternal bond during early infancy may produce long-lasting alterations in the brain cellular and molecular environment, leading to increased susceptibility to EAE in adult life.