Synaptic roles for neurofilament proteins have rarely been considered. Here, we establish all four neurofilament subunits as integral resident proteins of synapses. Compared to the population in axons, neurofilament subunits isolated from synapses have distinctive stoichiometry and phosphorylation state, and respond differently to perturbations in vivo. Completely eliminating neurofilament proteins from brain by genetically deleting three subunits (α-internexin, NFH and NFL) markedly depresses hippocampal LTP induction without detectably altering synapse morphology. Deletion of NFM in mice, but not the deletion of any other neurofilament subunit, amplifies dopamine D1-receptor-mediated motor responses to cocaine while redistributing postsynaptic D1-receptors from endosomes to plasma membrane, consistent with a specific modulatory role of NFM in D1-receptor recycling. These results identify a distinct pool of synaptic neurofilament subunits and establish their key role in neurotransmission in vivo, suggesting potential novel influences of neurofilament proteins in psychiatric as well as neurological states.

The cerebral deposition of amyloid ␤-peptide, a central event in Alzheimer's disease (AD) pathogenesis, begins several years before the onset of clinical symptoms. Noninvasive detection of AD pathology at this initial stage would facilitate intervention and enhance treatment success. In this study, high-field MRI was used to detect changes in regional brain MR relaxation times in three types of mice: 1) transgenic mice (PS/APP) carrying both mutant genes for amyloid precursor protein (APP) and presenilin (PS), which have high levels and clear accumulation of ␤-amyloid in several brain regions, starting from 10 weeks of age; 2) transgenic mice (PS) carrying only a mutant gene for presenilin (PS), which show subtly elevated levels of A␤-peptide without ␤-amyloid deposition; and 3) nontransgenic Cerebral deposits of the amyloid ␤-peptide and alterations of neurophysiology develop some years before Alzheimer's disease can be diagnosed clinically (1-3). By this stage, brain pathology is extensive and includes irreversible loss of neurons in brain regions essential for normal cognition (3). Because AD therapy is likely to be most successful when intervention occurs before neurons are irreversibly damaged or lost, noninvasive methods to detect early yet subtle changes in the brain would have considerable clinical value. Currently, there are no sensitive and specific biological markers for the preclinical stages of AD.Recent MRI studies of humans with mild cognitive impairment have shown that brain volume losses associated with neurodegeneration in the hippocampus have value in predicting increased risk for developing AD (4,5). Moreover, advances in high field strength MRI technology now raise the possibility that more subtle alterations of morphology or physiology preceding neurodegeneration might be detectable, including, in the case of AD, early effects of ␤-amyloid deposition. Since intrinsic MR parameters, such as transverse (T 2 ) and longitudinal (T 1 ) relaxation times are sensitive to changes in the biophysical environment of water, we hypothesized that the presence of increased deposition of ␤-amyloid in the brain would have an effect on these parameters.To investigate the possibility of early detection of the pathophysiology associated with AD, we studied PS/APP and PS transgenic mice together with nontransgenic (NTg) controls with MRI at 7 T. PS transgenic mice carry only a mutant gene for presenilin-1 (PS), which show subtly elevated levels of A␤-peptide without ␤-amyloid deposition in the brain (6). PS/APP transgenic mice express the human genes for amyloid precursor protein (APP) and presenilin-1 (PS) (7), which harbor mutations, APP K670N,M671L and PS M146V , known to cause familial AD (FAD) in humans. In these mice, ␤-amyloid begins to deposit at 10 -12 weeks of age and progressively accumulates as plaque-like lesions throughout their life span, reaching levels exceeding those in AD brain. Several other features of the human disease are also seen, including dystrophy of some neurites and mild local inf...

In this study, we used MRI to analyze quantitative parametric maps of transverse (T 2 ) relaxation times in a longitudinal study of transgenic mice expressing mutant forms of amyloid precursor protein (APP), presenilin (PS1), or both (PS/APP), modeling aspects of Alzheimer's disease (AD). The main goal was to characterize the effects of progressive b-amyloid accumulation and deposition on the biophysical environment of water and to investigate if these measurements would provide early indirect evidence of AD pathological changes in the brains of these mice. Our results demonstrate that at an early age before b-amyloid deposition, only PS/APP mice show a reduced T 2 in the hippocampus and cortex compared with wild-type non-transgenic (NTg) controls, whereas a statistically significant within-group aging-associated decrease in T 2 values is seen in the cortex and hippocampus of all three transgenic genotypes (APP, PS/APP, and PS) but not in the NTg controls. In addition, for animals older than 12 months, we confirmed our previous report that only the two genotypes that form amyloid plaques (APP and PS/APP) have significantly reduced T 2 values compared with NTg controls. Thus, T 2 changes in these AD models can precede amyloid deposition or even occur in AD models that do not deposit b-amyloid (PS mice), but are intensified in the presence of amyloid deposition.

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The goal of this work is to provide regional T 1 and T 2 values at a field strength of 7 T for the normal mouse brain at 6 weeks and 1 year old. A novel segmented snapshot FLASH sequence was used to measure T 1 in the hippocampus, corpus callosum, and the retrosplenial granular (RSG) cortex; T 2 measurements were made in the same regions using a single spin echo sequence repeated at six separate echo times. Historically, rats have been used routinely as disease models, but with the advent of transgenesis, and the economic advantages of creating transgenic mouse models of diseases, there is an increasing body of literature citing the use of mice in MRI. Much of the work is purely anatomical imaging. While values for T 1 and T 2 are published for normal and ischemic rat brain at 4.7 T (1,2), there is no equivalent study for the mouse brain, although there is a report of relaxation measurements in the hippocampus at 2 T (3) and a report of T 2 in the frontal cortex at 7 T (4). The ultimate aim of the work presented in this note is to characterize the T 1 and T 2 relaxation times in the mouse brain in order to fill a void in the literature for quantitative baseline values in an animal model of increasing importance.In addition, this study was designed to assess if a fast T 1 acquisition method could provide T 1 data comparable with the standard T 1 inversion recovery method. The mice used in the study are from the same background strain (B6/SW) that is (generally) used to generate transgenic mice with Alzheimer's pathology. Thus, this work is intended to provide baseline measurements of T 1 and T 2 in nontransgenic controls. Transgenic mice with Alzheimer's disease overexpress amyloid precursor protein. These animals are not easily maintained in the magnet under anesthesia for long periods, especially as they age. Fast image acquisitions, therefore, were an important criterion in this study but not at the expense of accuracy. Both T 1 and T 2 measurements were validated with phantom studies.Spin echo and inversion recovery methods are considered the workhorses of MRI for T 2 and T 1 measurement, respectively, despite their long acquisition times, especially in the latter case. Faster methods are necessary, particularly for T 1 measurement in vivo at 7 T, where the T 1 of brain tissue is on the order of several seconds. The TR necessary for standard inversion recovery measurements results in unacceptably long scan times. In order to achieve full relaxation, a TR time of approximately 5 T 1 is necessary, for even a low resolution (64 ϫ 64) standard inversion recovery with only a few time points along the recovery curve would require a total acquisition time of several hours.Echo planar Imaging can be used for high-speed and accurate T 1 mapping (5). However, the susceptibility distortion in a mouse brain at 7 T prohibits the use of this technique. A considerable increase in the speed of T 1 mapping can be achieved by implementing the LookLocker method (6). This method uses many low flip angle acquisitions to inspect a...

In vivo quantitative magnetic resonance imaging (MRI) was employed to detect brain pathology and map its distribution within control, disomic mice (2N) and in Ts65Dn and Ts1Cje trisomy mice with features of human Down syndrome (DS). In Ts65Dn, but not Ts1Cje mice, transverse proton spinspin (T 2 ) relaxation time was selectively reduced in the medial septal nucleus (MSN) and in brain regions that receive cholinergic innervation from the MSN, including the hippocampus, cingulate cortex, and retrosplenial cortex. Basal forebrain cholinergic neurons (BFCNs) in the MSN, identified by choline acetyltransferase (ChAT) and nerve growth factor receptors p75 NTR and TrkA immunolabeling were reduced in Ts65Dn brains and in situ acetylcholinesterase (AChE) activity was depleted distally along projecting cholinergic fibers, and selectively on pre-and post-synaptic profiles in these target areas. T 2 effects were negligible in Ts1Cje mice that are diploid for APP and lack BFCN neuropathology, consistent with the suspected relationship of this pathology to increased App dosage. These results establish the utility of quantitative MRI in vivo for identifying Alzheimer's disease-relevant cholinergic changes in animal models of DS and the selective vulnerability of cholinergic neuron subpopulations.

N-acetylaspartylglutamate (NAAG), a dipeptide derivative of N-acetylaspartate (NAA) and glutamate (Glu), is present in neurons. Upon neurostimulation, NAAG is exported to astrocytes where it activates a specific metabotropic Glu surface receptor (mGluR3), and is then hydrolyzed by an astrocyte-specific enzyme, NAAG peptidase, liberating Glu, which can then be taken up by the astrocyte. NAAG is a selective mGluR3 agonist, one of several mGluRs that, when activated, triggers Ca2+ waves that spread to astrocytic endfeet in contact with the vascular system, where a secondary release of vasoactive agents induces a focal hyperemic response providing increased oxygen and nutrient availability to the stimulated neurons. Changes in blood oxygen levels can be assessed in vivo using a blood oxygenation level-dependent (BOLD) magnetic resonance imaging technique that reflects a paramagnetic effect of deoxyhemoglobin. In this study we used the competitive NAAG peptidase inhibitor 2-(phosphonomethyl) pentanedioic acid (2-PMPA) as a probe to interrupt the NAAG-mGluR3- Glu-astrocyte Ca2+ activation sequence. Using this probe, we investigated the relationship between release of the endogenous neuropeptide NAAG and brain blood oxygenation levels, as measured by changes in BOLD signals. In an anesthetized mouse, using an overtly nontoxic dose of 2-PMPA of 250 mg/kg i.p., there was an initial global BOLD signal increase of about 3% above control, lasting about 4 min, followed by a decrease from control of about 4%, sustained over a 32.5-min period of the drug test procedure. Similar changes, but of reduced magnitude and duration, were observed at a dose of 167 mg/kg. The 2-PMPA-induced decreases in BOLD signals appear to indicate that blood deoxyhemoglobin is elevated when endogenous NAAG cannot be hydrolyzed, thus linking the efflux of NAAG from neurons and its hydrolysis by astrocytes to hyperemic oxygenation responses in brain.