We have previously shown that chronic treatment with the monoclonal antibody m266, which is specific for amyloid beta-peptide (Abeta), increases plasma concentrations of Abeta and reduces Abeta burden in the PDAPP transgenic mouse model of Alzheimer's disease (AD). We now report that administration of m266 to PDAPP mice can rapidly reverse memory deficits in both an object recognition task and a holeboard learning and memory task, but without altering brain Abeta burden. We also found that an Abeta/antibody complex was present in both the plasma and the cerebrospinal fluid of m266-treated mice. Our data indicate that passive immunization with this anti-Abeta monoclonal antibody can very rapidly reverse memory impairment in certain learning and memory tasks in the PDAPP mouse model of AD, owing perhaps to enhanced peripheral clearance and (or) sequestration of a soluble brain Abeta species.

When administered intracerebroventricularly to mice performing various learning tasks involving either short-term or long-term memory, secreted forms of the ␤-amyloid precursor protein (APP s 751 and APP s 695 ) have potent memory-enhancing effects and block learning deficits induced by scopolamine. The memory-enhancing effects of APP s were observed over a wide range of extremely low doses (0.05-5,000 pg intracerebroventricularly), blocked by anti-APP s antisera, and observed when APP s was administered either after the first training session in a visual discrimination or a lever-press learning task or before the acquisition trial in an object recognition task. APP s had no effect on motor performance or exploratory activity. APP s 695 and APP s 751were equally effective in the object recognition task, suggesting that the memory-enhancing effect of APP s does not require the Kunitz protease inhibitor domain. These data suggest an important role for APP s s on memory processes.Alzheimer's disease (AD) is the most common cause of progressive cognitive decline and dementia in aged humans. The deposition of the ␤-amyloid peptide(s) (A␤) in extracellular neuritic plaques of AD patients is an early and invariant feature of this neurodegenerative disorder (1). A␤ is derived from a large membrane-spanning ␤-amyloid precursor protein (APP), encoded by a single gene located on chromosome 21. Alternative splicing of this gene in humans leads to three major isoforms, either lacking (APP 695 ) or containing (APP 751 and APP 770 ) a Kunitz protease inhibitor domain. APP 695 is selectively expressed in the brain, whereas APP 751 and APP 770 also are abundantly expressed in peripheral tissues. Proteolytic processing of APPs at the N-and C-termini by ␤-and ␥-secretases leads to the production of A␤ (2). An alternative cleavage by ␣-secretase(s) within the A␤ domain of APPs generates secreted N-terminal products, the secreted APPs (APP s s) (2). The normal physiological functions of APPs and secreted derivatives are still poorly understood. However, neurotrophic as well as neuroprotective actions have been reported for both APP s 751 and APP s 695 (3-6). Recent behavioral studies have shown that intracerebroventricular (i.c.v.) administration of anti-APPs antisera results in memory impairment in rats performing a passive avoidance task (7,8). Further, the induction of long-term potentiation in hippocampal slices is associated with increased APP s synthesis and secretion (9). These data suggest that APP s s may be involved in learning and memory processes. In the present study, we investigated whether APP s 751 and APP s 695 have memoryenhancing actions when directly administered to mice performing various learning tasks and to mice rendered amnestic by administering the anticholinergic drug scopolamine.

PDAPP transgenic mice have been shown to develop age dependently much of the cerebral histopathology associated with Alzheimer's disease. PDAPP mice (3-10 months old) were tested in a battery of memory tasks to determine whether they develop memory-behavioral deficits and whether these deficits occur before or after amyloid deposition. PDAPP mice manifest robust impairments in a radial-maze spatial discrimination task at all ages tested. Mild deficits were observed in a barpress learning task in 3-month-old PDAPP mice. In contrast, PDAPP mice show an age-dependent decrease in spontaneous object-recognition performance that appears to be severe at ages when amyloid deposition is known to occur. Thus, the PDAPP mouse shows severe deficits in the radial maze well before amyloid plaque deposition, whereas object-recognition performance decreases with age and may be associated with amyloid deposition.

Although the brain functions of specific acetyltransferases such as the CREB-binding protein (CBP) and p300 have been well documented using mutant transgenic mice models, studies based on their direct pharmacological activation are still missing due to the lack of cell-permeable activators. Here we present a small-molecule (TTK21) activator of the histone acetyltransferases CBP/p300, which, when conjugated to glucosebased carbon nanosphere (CSP), passed the blood-brain barrier, induced no toxicity, and reached different parts of the brain. After intraperitoneal administration in mice, CSP-TTK21 significantly acetylated histones in the hippocampus and frontal cortex. Remarkably, CSP-TTK21 treatment promoted the formation of long and highly branched doublecortin-positive neurons in the subgranular zone of the dentate gyrus and reduced BrdU incorporation, suggesting that CBP/p300 activation favors maturation and differentiation of adult neuronal progenitors. In addition, mRNA levels of the neuroD1 differentiation marker and BDNF, a neurotrophin required for the terminal differentiation of newly generated neurons, were both increased in the hippocampus concomitantly with an enrichment of acetylated-histone on their proximal promoter. Finally, we found that CBP/p300 activation during a spatial training, while not improving retention of a recent memory, resulted in a significantextensionofmemoryduration.ThisreportisthefirstevidenceforCBP/p300-mediatedhistoneacetylationinthebrainbyanactivator molecule, which has beneficial implications for the brain functions of adult neurogenesis and long-term memory. We propose that direct stimulation of acetyltransferase function could be useful in terms of therapeutic options for brain diseases.