Axonal damage and astrocytosis are biological correlates of grey matter network integrity loss: a cohort study in autosomal dominant Alzheimer disease.

Brain development and maturation leads to grey matter networks that can be measured using magnetic resonance imaging. Network integrity is an indicator of information processing capacity which declines in neurodegenerative disorders such as Alzheimer disease (AD). The biological mechanisms causing this loss of network integrity remain unknown. Cerebrospinal fluid (CSF) protein biomarkers are available for studying diverse pathological mechanisms in humans and can provide insight into decline. We investigated the relationships between 10 CSF proteins and network integrity in mutation carriers (N=219) and noncarriers (N=136) of the Dominantly Inherited Alzheimer Network Observational study. Abnormalities in Aß, Tau, synaptic (SNAP-25, neurogranin) and neuronal calcium-sensor protein (VILIP-1) preceded grey matter network disruptions by several years, while inflammation related (YKL-40) and axonal injury (NfL) abnormalities co-occurred and correlated with network integrity. This suggests that axonal loss and inflammation play a role in structural grey matter network changes. Key points: Abnormal levels of fluid markers for neuronal damage and inflammatory processes in CSF are associated with grey matter network disruptions.The strongest association was with NfL, suggesting that axonal loss may contribute to disrupted network organization as observed in AD.Tracking biomarker trajectories over the disease course, changes in CSF biomarkers generally precede changes in brain networks by several years.

Hippocampus-specific deletion of BDNF in adult mice impairs spatial memory and extinction of aversive memories.

Brain-derived neurotrophic factor (BDNF) is known to play a critical role in the synaptic plasticity underlying the acquisition and/or consolidation of certain forms of memory. Additionally, a role has been suggested for neurotrophin function within the hippocampus in protection from anxiety and depressive disorders. Understanding the function of this important gene in adult animals has been limited however, because standard knockouts are confounded by gene effects during development. There are no BDNF receptor-specific pharmacological agents, and infusions of neuropeptides or antibodies have other significant limitations. In these studies, we injected a lentivirus expressing Cre recombinase bilaterally into the dorsal hippocampus in adult mice floxed at the BDNF locus to facilitate the site-specific deletion of the BDNF gene in adult animals. Significant decreases in BDNF mRNA expression are demonstrated in the hippocampi of lenti-Cre-infected animals compared with control lenti-GFP-infected animals. Behaviorally, there were no significant effects of BDNF deletion on locomotion or baseline anxiety measured with startle. In contrast, hippocampal-specific BDNF deletions impair novel object recognition and spatial learning as demonstrated with the Morris water maze. Although there were no effects on the acquisition or expression fear, animals with BDNF deletions show significantly reduced extinction of conditioned fear as measured both with fear-potentiated startle and freezing. These data suggest that the cognitive deficits and impairment in extinction of aversive memory found in depression and anxiety disorders may be directly related to decreased hippocampal BDNF.

Identification of cell-type-specific promoters within the brain using lentiviral vectors.

The development of cell-type-specific mini-promoters for genetic studies is complicated by a number of issues. Here, we describe a general method for the relatively rapid screening of specific promoter activity in cell culture, in acute brain slice preparations and in vivo. Specifically, we examine the activity of an approximately 3 kb promoter region from the neuroactive peptide cholecystokinin (CCK) compared to the commonly used cytomegalovirus promoter. We find a high degree of cell-type selectivity in vivo using lentiviral approaches in rats and traditional transgenic approaches in mice. Appropriate colocalization of Cre-recombinase and CCK gene expression is found within the hippocampus, when the CCK promoter is driving either the expression of Cre-recombinase or green fluorescent protein. We also demonstrate fluorescent identification of CCK-positive interneurons that allows for cell-type-specific electrophysiologic studies in rats and mice. In conclusion, these studies identify a functional mini-promoter for the CCK gene and outline a novel and sensitive general method to test activity of selective promoters in vitro and in vivo. This approach may allow for the more rapid identification of specific promoters for use with transgenic animals, in genetically modified viruses, and in the design of targeted, therapeutic gene-delivery systems.

Reduced prefrontal cortical dopamine, but not acetylcholine, release in vivo after repeated, intermittent phencyclidine administration to rats.

Subchronic administration of phencyclidine to rats or monkeys produces prefrontal cortical cognitive dysfunction, as well as reduced frontal cortical dopamine utilization. In the current study, the effects of subchronic exposure to phencyclidine on dopamine and acetylcholine release in the prefrontal cortex were assessed, using in vivo microdialysis in conscious rats. Subchronic exposure to phencyclidine (5 mg/kg twice daily for 7 days) reduced both basal extracellular concentrations of dopamine as well as the increase in dopamine release produced by an acute phencyclidine challenge. The increase in dopamine release induced by a high potassium concentration in the perfusate tended to be reduced after subchronic phencyclidine treatment, while basal and evoked acetylcholine release was unaffected. These data demonstrate that altered dopamine turnover in subjects after subchronic exposure to phencyclidine is directly reflective of reduced release, and as such, represents a functionally relevant phenomenon.