Vertigoheel promotes rodent cognitive performance in multiple memory tests

Introduction

Cognitive impairment associated with old age or various brain disorders may be very disabling for affected individuals, placing their carers and public health services under considerable stress. The standard-of-care drugs produce only transient improvement of cognitive impairment in older people, so the search for novel, safe and effective therapeutics that would help to reverse or delay cognitive impairment is warranted. Repurposing pharmacological therapies with well-established safety record for additional indications is a promising recent trend in drug development. Vertigoheel (VH-04), a multicomponent drug made of Ambra grisea, Anamirta cocculus L., Conium maculatum, and Petroleum rectificatum, has been successfully used for several decades in the treatment of vertigo. Here, we investigated effects of VH-04 on cognitive performance in standard behavioral tests assessing different types of memory and explored cellular and molecular underpinnings of VH-04's biological activity.

Methods

In the majority of behavioral experiments, namely in the spontaneous and rewarded alternation tests, passive avoidance test, contextual/cued fear conditioning, and social transmission of food preference, we examined the ability of single and repeated intraperitoneal administrations of VH-04 to improve cognitive parameters of mice and rats disrupted by the application of the muscarinic antagonist scopolamine. In addition, we also assessed how VH-04 affected novel object recognition and influenced performance of aged animals in Morris water maze. Furthermore, we also studied the effects of VH-04 on primary hippocampal neurons in vitro and mRNA expression of synaptophysin in the hippocampus.

Results

Administration of VH-04 positively influenced visual recognition memory in the novel object recognition test and alleviated the impairments in spatial working memory and olfactory memory caused by the muscarinic antagonist scopolamine in the spontaneous alternation and social transmission of food preference tests. In addition, VH-04 improved retention of the spatial orientation memory of old rats in the Morris water maze. In contrast, VH-04 did not have significant effects on scopolamine-induced impairments in tests of fear-aggravated memory or rewarded alternation. Experiments in vitro showed that VH-04 stimulated neurite growth and possibly reversed the age-dependent decrease in hippocampal synaptophysin mRNA expression, which implies that VH-04 may preserve synaptic integrity in the aging brain.

Discussion

Our findings allow a cautious conclusion that in addition to its ability to alleviate manifestations of vertigo, VH-04 may be also used as a cognitive enhancer.

Next Generation Exon 51 Skipping Antisense Oligonucleotides for Duchenne Muscular Dystrophy

In the last two decades, antisense oligonucleotides (AONs) that induce corrective exon skipping have matured as promising therapies aimed at tackling the dystrophin deficiency that underlies the severe and progressive muscle fiber degeneration in Duchenne muscular dystrophy (DMD) patients. Pioneering first generation exon 51 skipping AONs like drisapersen and eteplirsen have more recently been followed up by AONs for exons 53 and 45, with, to date, a total of four exon skipping AON drugs having reached (conditional) regulatory US Food and Drug Administration (FDA) approval for DMD. Nonetheless, considering the limited efficacy of these drugs, there is room for improvement. The aim of this study was to develop more efficient [2'-O-methyl-modified phosphorothioate (2'OMePS) RNA] AONs for DMD exon 51 skipping by implementing precision chemistry as well as identifying a more potent target binding site. More than a hundred AONs were screened in muscle cell cultures, followed by a selective comparison in the hDMD and hDMDdel52/mdx mouse models. Incorporation of 5-methylcytosine and position-specific locked nucleic acids in AONs targeting the drisapersen/eteplirsen binding site resulted in 15-fold higher exon 51 skipping levels compared to drisapersen in hDMDdel52/mdx mice. However, with similarly modified AONs targeting an alternative site in exon 51, 65-fold higher skipping levels were obtained, restoring dystrophin up to 30% of healthy control. Targeting both sites in exon 51 with a single AON further increased exon skipping (100-fold over drisapersen) and dystrophin (up to 40%) levels. These dystrophin levels allowed for normalization of creatine kinase (CK) and lactate dehydrogenase (LDH) levels, and improved motor function in hDMDdel52/mdx mice. As no major safety observation was obtained, the improved therapeutic index of these next generation AONs is encouraging for further (pre)clinical development.

Rapid and robust patterns of spontaneous locomotor deficits in mouse models of Huntington's disease

Huntington's disease (HD) is an inherited neurodegenerative disorder characterized by severe disruption of cognitive and motor functions, including changes in posture and gait. A number of HD mouse models have been engineered that display behavioral and neuropathological features of the disease, but gait alterations in these models are poorly characterized. Sensitive high-throughput tests of fine motor function and gait in mice might be informative in evaluating disease-modifying interventions. Here, we describe a hypothesis-free workflow that determines progressively changing locomotor patterns across 79 parameters in the R6/2 and Q175 mouse models of HD. R6/2 mice (120 CAG repeats) showed motor disturbances as early as at 4 weeks of age. Similar disturbances were observed in homozygous and heterozygous Q175 KI mice at 3 and 6 months of age, respectively. Interestingly, only the R6/2 mice developed forelimb ataxia. The principal components of the behavioral phenotypes produced two phenotypic scores of progressive postural instability based on kinematic parameters and trajectory waveform data, which were shared by both HD models. This approach adds to the available HD mouse model research toolbox and has a potential to facilitate the development of therapeutics for HD and other debilitating movement disorders with high unmet medical need.

Detailed genetic and functional analysis of the hDMDdel52/mdx mouse model

Duchenne muscular dystrophy (DMD) is a severe, progressive neuromuscular disorder caused by reading frame disrupting mutations in the DMD gene leading to absence of functional dystrophin. Antisense oligonucleotide (AON)-mediated exon skipping is a therapeutic approach aimed at restoring the reading frame at the pre-mRNA level, allowing the production of internally truncated partly functional dystrophin proteins. AONs work in a sequence specific manner, which warrants generating humanized mouse models for preclinical tests. To address this, we previously generated the hDMDdel52/mdx mouse model using transcription activator like effector nuclease (TALEN) technology. This model contains mutated murine and human DMD genes, and therefore lacks mouse and human dystrophin resulting in a dystrophic phenotype. It allows preclinical evaluation of AONs inducing the skipping of human DMD exons 51 and 53 and resulting in restoration of dystrophin synthesis. Here, we have further characterized this model genetically and functionally. We discovered that the hDMD and hDMDdel52 transgene is present twice per locus, in a tail-to-tail-orientation. Long-read sequencing revealed a partial deletion of exon 52 (first 25 bp), and a 2.3 kb inversion in intron 51 in both copies. These new findings on the genomic make-up of the hDMD and hDMDdel52 transgene do not affect exon 51 and/or 53 skipping, but do underline the need for extensive genetic analysis of mice generated with genome editing techniques to elucidate additional genetic changes that might have occurred. The hDMDdel52/mdx mice were also evaluated functionally using kinematic gait analysis. This revealed a clear and highly significant difference in overall gait between hDMDdel52/mdx mice and C57BL6/J controls. The motor deficit detected in the model confirms its suitability for preclinical testing of exon skipping AONs for human DMD at both the functional and molecular level.

Using a State-of-the-Art Toolbox to Evaluate Molecular and Functional Readouts of Antisense Oligonucleotide-Induced Exon Skipping in mdx Mice

Duchenne muscular dystrophy (DMD) is a severe childhood muscle disease primarily caused by the lack of functional dystrophin at the muscle fiber membranes. Multiple therapeutic approaches are currently in (pre)clinical development, aimed at restoring expression of (truncated) dystrophin. Key questions in this phase relate to route of drug administration, dose regimen, and levels of dystrophin required to improve muscle function. A series of studies applying antisense oligonucleotides (AONs) in the mdx mouse model for DMD has been reported over the last two decades, claiming a variable range of exon skipping and increased dystrophin levels correlated to some functional improvement. The aim of this study was to compare the efficacy of subcutaneous (SC) versus intravenous (IV) dosing routes of an mdx-specific AON at both the molecular and functional level, using state-of-the-art quantitative technologies, including digital droplet polymerase chain reaction, capillary Western immunoassay, magnetic resonance imaging, and automated kinematic analysis. The majority of all readouts we quantified, both molecular and functional, showed that IV dosing of the AON had a more pronounced beneficial effect than SC dosing in mdx mice. Last, but not least, the more quantitative molecular and functional data obtained in this study suggest that low levels of dystrophin protein of at least 2.5% of wild type may already have a beneficial effect on muscle leakiness and may improve motor performance of mdx mice.

Suppression of Mutant Protein Expression in SCA3 and SCA1 Mice Using a CAG Repeat-Targeting Antisense Oligonucleotide

Spinocerebellar ataxia type 3 (SCA3) and type 1 (SCA1) are dominantly inherited neurodegenerative disorders that are currently incurable. Both diseases are caused by a CAG-repeat expansion in exon 10 of the Ataxin-3 and exon 8 of the Ataxin-1 gene, respectively, encoding an elongated polyglutamine tract that confers toxic properties to the resulting proteins. We have previously shown lowering of the pathogenic polyglutamine protein in Huntington's disease mouse models using (CUG)7, a CAG repeat-targeting antisense oligonucleotide. Here we evaluated the therapeutic capacity of (CUG)7 for SCA3 and SCA1, in vitro in patient-derived cell lines and in vivo in representative mouse models. Repeated intracerebroventricular (CUG)7 administration resulted in a significant reduction of mutant Ataxin-3 and Ataxin-1 proteins throughout the brain of SCA3 and SCA1 mouse models, respectively. Furthermore, in both a SCA3 patient cell line and the MJD84.2 mouse model, (CUG)7 induced formation of a truncated Ataxin-3 protein species lacking the polyglutamine stretch, likely arising from (CUG)7-mediated exon 10 skipping. In contrast, skipping of exon 8 of Ataxin-1 did not significantly contribute to the Ataxin-1 protein reduction observed in (CUG)7-treated SCA1^154Q/2Q mice. These findings support the therapeutic potential of a single CAG repeat-targeting AON for the treatment of multiple polyglutamine disorders.

Impaired Performance of the Q175 Mouse Model of Huntington's Disease in the Touch Screen Paired Associates Learning Task

Cognitive disturbances often predate characteristic motor dysfunction in individuals with Huntington’s disease (HD) and place an increasing burden on the HD patients and caregivers with the progression of the disorder. Therefore, application of maximally translational cognitive tests to animal models of HD is imperative for the development of treatments that could alleviate cognitive decline in human patients. Here, we examined the performance of the Q175 mouse knock-in model of HD in the touch screen version of the paired associates learning (PAL) task. We found that 10–11-month-old heterozygous Q175 mice had severely attenuated learning curve in the PAL task, which was conceptually similar to previously documented impaired performance of individuals with HD in the PAL task of the Cambridge Neuropsychological Test Automated Battery (CANTAB). Besides high rate of errors in PAL task, Q175 mice exhibited considerably lower responding rate than age-matched wild-type (WT) animals. Our examination of effortful operant responding during fixed ratio (FR) and progressive ratio (PR) reinforcement schedules in a separate cohort of similar age confirmed slower and unselective performance of mutant animals, as observed during PAL task, but suggested that motivation to work for nutritional reward in the touch screen setting was similar in Q175 and WT mice. We also demonstrated that pronounced sensorimotor disturbances in Q175 mice can be detected at early touch screen testing stages, (e.g., during “Punish Incorrect” phase of operant pretraining), so we propose that shorter test routines may be utilised for more expedient studies of treatments aimed at the rescue of HD-related phenotype.

Effect of Ibuprofen on Skeletal Muscle of Dysferlin-Null Mice

Ibuprofen, a nonsteroidal anti-inflammatory drug, and nitric oxide (NO) donors have been reported to reduce the severity of muscular dystrophies in mice associated with the absence of dystrophin or α-sarcoglycan, but their effects on mice that are dystrophic due to the absence of dysferlin have not been examined. We have tested ibuprofen, as well as isosorbide dinitrate (ISDN), a NO donor, to learn whether used alone or together they protect dysferlin-null muscle in A/J mice from large strain injury (LSI) induced by a series of high strain lengthening contractions. Mice were maintained on chow containing ibuprofen and ISDN for 4 weeks. They were then subjected to LSI and maintained on the drugs for 3 additional days. We measured loss of torque immediately following injury and at day 3 postinjury, fiber necrosis, and macrophage infiltration at day 3 postinjury, and serum levels of the drugs at the time of euthanasia. Loss of torque immediately after injury was not altered by the drugs. However, the torque on day 3 postinjury significantly decreased as a function of ibuprofen concentration in the serum (range, 0.67-8.2 µg/ml), independent of ISDN. The effects of ISDN on torque loss at day 3 postinjury were not significant. In long-term studies of dysferlinopathic BlAJ mice, lower doses of ibuprofen had no effects on muscle morphology, but reduced treadmill running by 40%. Our results indicate that ibuprofen can have deleterious effects on dysferlin-null muscle and suggest that its use at pharmacological doses should be avoided by individuals with dysferlinopathies.

Hip region muscular dystrophy and emergence of motor deficits in dysferlin-deficient Bla/J mice

The identification of a dysferlin‐deficient animal model that accurately displays both the physiological and behavior aspects of human dysferlinopathy is critical for the evaluation of potential therapeutics. Disease progression in dysferlin‐deficient mice is relatively mild, compared to the debilitating human disease which manifests in impairment of particular motor functions. Since there are no other known models of dysferlinopathy in other species, locomotor proficiency and muscular anatomy through MRI (both lower leg and hip region) were evaluated in dysferlin‐deficient B6.A‐Dysf^prmd/GeneJ (Bla/J) mice to define disease parameters for therapeutic assessment. Despite the early and progressive gluteal muscle dystrophy and significant fatty acid accumulation, the emergence of significant motor function deficits was apparent at approximately 1 year of age for standard motor challenges including the rotarod, a marble bury test, grip strength, and swimming speed. Earlier observations of decreased performance for Bla/J mice were evident during extended monitoring of overall exploration and rearing activity. Comprehensive treadmill gait analyses of the Bla/J model indicated significant differences in paw placement angles and stance in relation to speed and platform slope. At 18 months of age, there was no significant difference in the life expectancy of Bla/J mice compared to wild type. Consistent with progressive volume loss and fatty acid accumulation in the hip region observed by MRI, mass measurement of individual muscles confirmed gluteal and psoas muscles were the only muscles demonstrating a significant decrease in muscle mass, which is analogous to hip‐girdle weakness observed in human dysferlin‐deficient patients. Collectively, this longitudinal analysis identifies consistent disease parameters that can be indicators of efficacy in studies developing treatments for human dysferlin deficiency.

Elevated Tau Level in Aged Rat Cerebrospinal Fluid Reduced by Treatment with a Neurotrophic Compound

Alzheimer's disease (AD) is the single major cause of dementia in middle- to old-age individuals, and, as of yet, no disease-modifying therapeutic drug is available for its treatment. A major obstacle in the successful development of disease-modifying therapeutic drugs has been the lack of suitable animal models of the sporadic form of AD as well as a biomarker that can be used both for therapeutic preclinical studies and for human clinical trials. Previously we showed neurogenesis and neuronal plasticity deficits and cognitive impairment and their rescue with a neurotrophic peptidergic compound, DGGLAG named P021, in aged Fisher rats. Here we show that P021 is blood-brain-barrier-permeable, and chronic oral treatment with this compound can reduce the brain level of total tau in the aged rats. Furthermore, cerebrospinal fluid (CSF) levels of both tau and Aβ/AβPP are elevated in the aged animals, and chronic treatment with P021 can reduce tau but not Aβ/AβPP to that of the levels found in young adult rats. Importantly, P021 does not induce any detectable immune reaction in rats. Collectively, these studies show the therapeutic potential of P021 as a disease-modifying compound and the suitability of the aged Fisher rats as a model of cerebral aging in which the therapeutic efficacy of a tau-reducing compound can be monitored in the CSF.

The novel KMO inhibitor CHDI-340246 leads to a restoration of electrophysiological alterations in mouse models of Huntington's disease

Dysregulation of the kynurenine (Kyn) pathway has been associated with the progression of Huntington's disease (HD). In particular, elevated levels of the kynurenine metabolites 3-hydroxy kynurenine (3-OH-Kyn) and quinolinic acid (Quin), have been reported in the brains of HD patients as well as in rodent models of HD. The production of these metabolites is controlled by the activity of kynurenine mono-oxygenase (KMO), an enzyme which catalyzes the synthesis of 3-OH-Kyn from Kyn. In order to determine the role of KMO in the phenotype of mouse models of HD, we have developed a potent and selective KMO inhibitor termed CHDI-340246. We show that this compound, when administered orally to transgenic mouse models of HD, potently and dose-dependently modulates the Kyn pathway in peripheral tissues and in the central nervous system. The administration of CHDI-340246 leads to an inhibition of the formation of 3-OH-Kyn and Quin, and to an elevation of Kyn and Kynurenic acid (KynA) levels in brain tissues. We show that administration of CHDI-340246 or of Kyn and of KynA can restore several electrophysiological alterations in mouse models of HD, both acutely and after chronic administration. However, using a comprehensive panel of behavioral tests, we demonstrate that the chronic dosing of a selective KMO inhibitor does not significantly modify behavioral phenotypes or natural progression in mouse models of HD.

Levosimendan alone and in combination with valsartan prevents stroke in Dahl salt-sensitive rats

The effects of levosimendan on cerebrovascular lesions and mortality were investigated in models of primary and secondary stroke. We aimed to determine whether the effects of levosimendan are comparable to and/or cumulative with those of valsartan, and to investigate whether levosimendan-induced vasodilation has a role in its effects on stroke. In a primary stroke Dahl/Rapp rat model, mortality rates were 70% and 5% for vehicle and levosimendan, respectively. Both stroke incidence (85% vs. 10%, P<0.001) and stroke-associated behavioral deficits (7-point neuroscore: 4.59 vs. 5.96, P<0.001) were worse for vehicle compared to levosimendan. In a secondary stroke model in which levosimendan treatment was started after cerebrovascular incidences were already detected, mean survival times were 15 days with vehicle, 20 days with levosimendan (P=0.025, vs. vehicle), 22 days with valsartan (P=0.001, vs. vehicle), and 31 days with levosimendan plus valsartan (P<0.001, vs. vehicle). The respective survivals were 0%, 16%, 20% and 59%, and the respective incidences of severe lesions were 50%, 67%, 50% and 11%. In this rat model, levosimendan increased blood volume of the cerebral vessels, with significant effects in the microvessels of the cortex (∆R=3.5±0.15 vs. 2.7±0.17ml for vehicle; P=0.001) and hemisphere (∆R=3.2±0.23 vs. 2.6±0.14ml for vehicle; P=0.018). Overall, levosimendan significantly reduced stroke-induced mortality and morbidity, both alone and with valsartan, with apparent cumulative effects, an activity in which the vasodilatory effects of levosimendan have a role.

Early retinal function deficit without prominent morphological changes in the R6/2 mouse model of Huntington's disease

Huntington’s disease (HD) is an inherited neurodegenerative disorder that primarily affects the medium-size GABAergic neurons of striatum. The R6/2 mouse line is one of the most widely used animal models of HD. Previously the hallmarks of HD-related pathology have been detected in photoreceptors and interneurons of R6/2 mouse retina. Here we aimed to explore the survival of retinal ganglion cells (RGCs) and functional integrity of distinct retinal cell populations in R6/2 mice. The pattern electroretinography (PERG) signal was lost at the age of 8 weeks in R6/2 mice in contrast to the situation in wild-type (WT) littermates. This defect may be attributable to a major reduction in photopic ERG responses in R6/2 mice which was more evident in b- than a-wave amplitudes. At the age of 4 weeks R6/2 mice had predominantly the soluble form of mutant huntingtin protein (mHtt) in the RGC layer cells, whereas the aggregated form of mHtt was found in the majority of those cells from the 12-week-old R6/2 mice and onwards. Retinal astrocytes did not contain mHtt deposits. The total numbers of RGC layer cells, retinal astrocytes as well as optic nerve axons did not differ between 18-week-old R6/2 mice and their WT controls. Our data indicate that mHtt deposition does not cause RGC degeneration or retinal astrocyte loss in R6/2 mice even at a late stage of HD-related pathology. However, due to functional deficits in the rod- and cone-pathways, the R6/2 mice suffer progressive deficits in visual capabilities starting as early as 4 weeks; at 8 weeks there is severe impairment. This should be taken into account in any behavioral testing conducted in R6/2 mice.

Rescue of cognitive-aging by administration of a neurogenic and/or neurotrophic compound

Aging is characterized by a progressive decline of cognitive performance, which has been partially attributed to structural and functional alterations of hippocampus. Importantly, aging is the major risk factor for the development of neurodegenerative diseases, especially Alzheimer's disease. An important therapeutic approach to counteract the age-associated memory dysfunctions is to maintain an appropriate microenvironment for successful neurogenesis and synaptic plasticity. In this study, we show that chronic oral administration of peptide 021 (P021), a small peptidergic neurotrophic compound derived from the ciliary neurotrophic factor, significantly reduced the age-dependent decline in learning and memory in 22 to 24-month-old Fisher rats. Treatment with P021 inhibited the deficit in neurogenesis in the aged rats and increased the expression of brain derived neurotrophic factor. Furthermore, P021 restored synaptic deficits both in the cortex and the hippocampus. In vivo magnetic resonance spectroscopy revealed age-dependent alterations in hippocampal content of several metabolites. Remarkably, P021 was effective in significantly reducing myoinositol (INS) concentration, which was increased in aged compared with young rats. These findings suggest that stimulating endogenous neuroprotective mechanisms is a potential therapeutic approach to cognitive aging, Alzheimer's disease, and associated neurodegenerative disorders and P021 is a promising compound for this purpose.

Neuroprotective properties of the non-peptidyl radical scavenger IAC in rats following transient focal cerebral ischemia

Experimental evidence suggests that reactive free radicals are generated during brain ischemia. We investigated the effect of a novel brain penetrant, low molecular weight, non-peptidyl carbon, oxygen- and nitrogen-centered radical scavenger, IAC, on infarct volume and sensory-motor performance in a rat transient middle cerebral artery occlusion model (tMCAO). Rats received 90 min tMCAO and treated with i.p. or i.v. injections of vehicle or IAC following tMCAO. Sensory-motor performance was evaluated by neuroscore tests (NS). Cerebral infarct volume was evaluated at 72 h after tMCAO. Rats treated with IAC i.p. (1 or 6 h after the onset of tMCAO) or i.v. (1 h after the onset of tMCAO) showed significant improvement in NS during the 3 or 21 day follow-up period when compared to vehicle treated rats. Cerebral infarct volumes were significantly decreased compared to vehicle in rats receiving IAC i.p. 1 h or 6 h after occlusion, approximately 30.5% decrease compared to vehicle, or i.v. 1 h after the onset of tMCAO, 48.6% decrease compared to vehicle. These results demonstrate that IAC has neuroprotective properties with a wide therapeutic window following tMCAO in rats. IAC could therefore be a candidate for the treatment of stroke.

Accelerating amyloid-beta fibrillization reduces oligomer levels and functional deficits in Alzheimer disease mouse models

Many proteins suspected of causing neurodegenerative diseases exist in diverse assembly states. For most, it is unclear whether shifts from one state to another would be helpful or harmful. We used mutagenesis to change the assembly state of Alzheimer disease (AD)-associated amyloid-beta (Abeta) peptides. In vitro, the "Arctic" mutation (AbetaE22G) accelerated Abeta fibrillization but decreased the abundance of nonfibrillar Abeta assemblies, compared with wild-type Abeta. In human amyloid precursor protein (hAPP) transgenic mice carrying mutations adjacent to Abeta that increase Abeta production, addition of the Arctic mutation markedly enhanced the formation of neuritic amyloid plaques but reduced the relative abundance of a specific nonfibrillar Abeta assembly (Abeta*56). Mice overexpressing Arctic mutant or wild-type Abeta had similar behavioral and neuronal deficits when they were matched for Abeta*56 levels but had vastly different plaque loads. Thus, Abeta*56 is a likelier determinant of functional deficits in hAPP mice than fibrillar Abeta deposits. Therapeutic interventions that reduce Abeta fibrils at the cost of augmenting nonfibrillar Abeta assemblies could be harmful.

Reduction in mitochondrial superoxide dismutase modulates Alzheimer's disease-like pathology and accelerates the onset of behavioral changes in human amyloid precursor protein transgenic mice

Alzheimer's disease (AD) is associated with accumulations of amyloid-beta (Abeta) peptides, oxidative damage, mitochondrial dysfunction, neurodegeneration, and dementia. The mitochondrial antioxidant manganese superoxide dismutase-2 (Sod2) might protect against these alterations. To test this hypothesis, we inactivated one Sod2 allele (Sod2(+/-)) in human amyloid precursor protein (hAPP) transgenic mice, reducing Sod2 activity to approximately 50% of that in Sod2 wild-type (Sod2(+/+)) mice. A reduction in Sod2 activity did not obviously impair mice without hAPP/Abeta expression. In hAPP mice, however, it accelerated the onset of behavioral alterations and of deficits in prepulse inhibition of acoustic startle, a measure of sensorimotor gating. In these mice, it also worsened hAPP/Abeta-dependent depletion of microtubule-associated protein 2, a marker of neuronal dendrites. Sod2 reduction decreased amyloid plaques in the brain parenchyma but promoted the development of cerebrovascular amyloidosis, gliosis, and plaque-independent neuritic dystrophy. Sod2 reduction also increased the DNA binding activity of the transcription factor nuclear factor kappaB. These results suggest that Sod2 protects the aging brain against hAPP/Abeta-induced impairments. Whereas reductions in Sod2 would be expected to trigger or exacerbate neuronal and vascular pathology in AD, increasing Sod2 activity might be of therapeutic benefit.

beta-Amyloid infusion results in delayed and age-dependent learning deficits without role of inflammation or beta-amyloid deposits

beta-Amyloid (Abeta) polypeptide plays a critical role in the pathogenesis of Alzheimer's disease (AD), which is characterized by progressive decline of cognitive functions, formation of Abeta deposits and neurofibrillary tangles, and loss of neurons. Increased genetic production or direct intracerebral administration of Abeta in animal models results in Abeta deposition, gliosis, and impaired cognitive functions. Whether aging renders the brain prone to Abeta and whether inflammation is required for Abeta-induced learning deficits is unclear. We show that intraventricular infusion of Abeta1-42 results in learning deficits in 9-month-old but not 2.5-month-old mice. Deficits that become detectable 12 weeks after the infusion are associated with a slight reduction in Cu,Zn superoxide dismutase activity but do not correlate with Abeta deposition and are not associated with gliosis. In rats, Abeta infusion induced learning deficits that were detectable 6 months after the infusion. Approximately 20% of the Abeta immunoreactivity in rats was associated with astrocytes. NMR spectrum analysis of the animals cerebrospinal fluid revealed a strong reduction trend in several metabolites in Abeta-infused rats, including lactate and myo-inositol, supporting the idea of dysfunctional astrocytes. Even a subtle increase in brain Abeta1-42 concentration may disrupt normal metabolism of astrocytes, resulting in altered neuronal functions and age-related development of learning deficits independent of Abeta deposition and inflammation.

Fyn kinase induces synaptic and cognitive impairments in a transgenic mouse model of Alzheimer's disease

Human amyloid precursor protein (hAPP) transgenic mice with high levels of amyloid-beta (Abeta) develop behavioral deficits that correlate with the depletion of synaptic activity-related proteins in the dentate gyrus. The tyrosine kinase Fyn is altered in Alzheimer's disease brains and modulates premature mortality and synaptotoxicity in hAPP mice. To determine whether Fyn also modulates Abeta-induced behavioral deficits and depletions of synaptic activity-dependent proteins, we overexpressed Fyn in neurons of hAPP mice with moderate levels of Abeta production. Compared with nontransgenic controls and singly transgenic mice expressing hAPP or FYN alone, doubly transgenic FYN/hAPP mice had striking depletions of calbindin, Fos, and phosphorylated ERK (extracellular signal-regulated kinase), impaired neuronal induction of Arc, and impaired spatial memory retention. These deficits were qualitatively and quantitatively similar to those otherwise seen only in hAPP mice with higher Abeta levels. Surprisingly, levels of active Fyn were lower in high expresser hAPP mice than in NTG controls and lower in FYN/hAPP mice than in FYN mice. Suppression of Fyn activity may result from dephosphorylation by striatal-enriched phosphatase, which was upregulated in FYN/hAPP mice and in hAPP mice with high levels of Abeta. Thus, increased Fyn expression is sufficient to trigger prominent neuronal deficits in the context of even relatively moderate Abeta levels, and inhibition of Fyn activity may help counteract Abeta-induced impairments.

Reelin-immunoreactivity in the hippocampal formation of 9-month-old wildtype mouse: effects of APP/PS1 genotype and ovariectomy

Reelin, an extracellular matrix protein has an important role in the migration, correct positioning and maturation of neurons during development. Though it is generally down-regulated in the postnatal period, expression of this large glycoprotein continues in the adult brain in some cell populations. In the present study, we examined the distribution of reelin-immunoreactivity (-ir) in the hippocampal formation of 9-month-old wildtype mice (WT). Then, reelin-ir in normal mice was compared to that of transgenic mice (APP/PS1) carrying mutated human APP and PS1 genes, which are linked to the familial form of Alzheimer's disease (AD). The APP/PS1 mice were additionally burdened with a second risk factor for AD, namely depletion of circulating gonadal hormones by ovariectomy (APP/PS1 + OVX). The analyses revealed that in adult WT reelin-ir is expressed by Cajal-Retzius cells and a subgroup of interneurons throughout the hippocampal formation. In addition, layer II projection neurons in the lateral entorhinal subfields are reelin-ir. Interestingly, ovariectomy decreases the number of reelin-ir cells in the hilus in WT mice, whereas AD-related genotype alone induces only a non-significant reduction. Unexpectedly, additional stress, e.g., depletion of gonadal hormones, does not aggravate the slight reduction in the reelin cell number in the APP/PS1 mice. We propose that the changes in normal reelin-ir are linked to disturbances in repair mechanisms in which APP/PS1 and gonadal hormones are involved and which are perturbed in neurodegenerative conditions, namely AD.

Locomotor activity and evoked dopamine release are reduced in mice overexpressing A30P-mutated human alpha-synuclein

We have generated a transgenic mouse line overexpressing mutated human A30P alpha-synuclein under the control of the prion-related protein promoter. Immunohistology revealed mutated human A30P alpha-synuclein protein in numerous brain areas, but no gross morphological changes, Lewy bodies, or loss of dopaminergic cell bodies. The transgenic mice displayed decreased locomotion, impaired motor coordination, and balance. In vivo voltammetry showed that A30P mice responded to longer stimulation of the ascending dopaminergic pathways with less dopamine release in striatum and had a slower rate of dopamine decline after repeated stimulations or after alpha-methyl-p-tyrosine-HCl treatment. However, dopamine re-uptake or transporter levels were similar in transgenic and control mice. Our data provide evidence that overexpression of mutated human A30P alpha-synuclein in mice leads to a reduced size of the dopamine storage pool. This is in agreement with the previously postulated involvement of alpha-synuclein in the turnover of transmitter vesicles and may explain the observed motor deficits in A30P mice.

Effects of estradiol on spatial learning, hippocampal cytochrome P450 19, and estrogen alpha and beta mRNA levels in ovariectomized female mice

The brain is an important target organ for peripherally synthesized estrogen but it also has its own steroid biosynthesis producing estrogen from testosterone catalyzed by the aromatase enzyme. This study examined the effects of estrogen treatment in two spatial memory tasks, one-arm-baited radial arm maze and a position discrimination task in the T-maze in ovariectomized female mice. Hippocampal cytochrome P450 19 (encoding aromatase), and estrogen receptor alpha and beta gene expressions were also measured using real time quantitative polymerase chain reaction analysis. Estrogen (17beta-estradiol) was administered either tonically via s.c. minipellets or phasically via daily i.p. injections. In ovariectomized mice, the tonic estrogen decreased the number of reference memory errors in radial arm maze. Tonic estrogen treatment also up-regulated the expression of cytochrome P450 19 and estrogen receptors. In contrast, estrogen injections decreased the expression of cytochrome P450 19 and estrogen receptor alpha genes. The number of reference memory errors correlated negatively with estrogen receptor alpha expression. These findings indicate that peripheral estrogen levels affect neuronal estrogen synthesis by regulating the cytochrome P450 19 gene expression and also influence estrogen receptor alpha expression. The results also suggest that tonic rather than cyclic estrogen treatment might be more beneficial for cognitive functions.

The effect of aging on the subcellular distribution of estrogen receptor-alpha in the cholinergic neurons of transgenic and wild-type mice

The degeneration of the basal forebrain cholinergic system plays an important role in cognitive deterioration in aging and Alzheimer's disease. Brain cholinergic neurons and their projections are affected by changes in the circulating levels of estrogens, which exert their effects mainly through the estrogen receptors. In this study, we investigated the effect of aging, estrogen status and transgenic genotype on the number of cholinergic neurons and the estrogen receptor alpha (ERalpha) content in the medial septum-vertical limb of the diagonal band of Broca. We used 6- and 12-month-old female double transgenic mice carrying mutated human amyloid precursor protein (APPswe) and presenilin-1 (PS1-A246E), and their nontransgenic littermate controls, which had been sham-operated or ovariectomized at the age of 3 months. Brain sections were double immunostained for choline acetyltransferase (ChAT) and ERalpha and used for stereological cell counting. We found that the number of ChAT-immunoreactive (ir) neurons containing nuclear ERalpha-ir was significantly lower in 12- than in 6-month-old mice. However, the age of the mice, the transgenic genotype or ovariectomy had no effect on the total number of ChAT-ir neurons, or on the number and percentage of all ChAT-ir neurons that contained ERalpha. These results indicate that aging is associated with translocation of ERalphas from the nucleus to the cytoplasm. We propose that this phenomenon is linked to those age-related processes known to be involved in inhibiting ERalpha binding to nuclei.

Effects of long-term ovariectomy and estrogen treatment on maze learning in aged mice

Spatial memory deficits occur earlier in female than male rodents as the animals age, and the cessation of estrous cycle has been suggested to play a role in this phenomenon. We examined the effects of long-term ovariectomy (OVX) and estrogen replacement therapy (ERT) with subcutaneous 17beta-estradiol minipellets on maze learning in aged (24-month-old) female C57BL/6J mice using a win-stay task (1/8 arms baited) in the radial arm maze (RAM) and a position discrimination task in the T-maze. ERT was started 40 days before the behavioral tests both in gonadally intact (sham-operated) and OVX mice. The effect of early OVX on RAM performance was investigated using three different age groups (7, 11 and 24 months) with different OVX durations (4, 8 and 19 months, respectively). ERT reduced the number of reference memory errors in RAM in aged sham-operated and OVX mice, but unlike in young mice (Heikkinen et al., 2002) it had no effect on working memory errors. Furthermore, OVX impaired the performance of aged mice in the T-maze. Comparison across the three age groups and three OVX durations indicated that the memory impairment induced by an early age OVX attenuates as the mice get close to their estropausal age.

Cholinergic neurons in the basal forebrain of aged female mice

Aging is associated with at least down-regulation of several cellular functions and diminished responsiveness to internal and external signals, and possibly with direct cell death. Consequently, pharmacological manipulations may be less effective in aged than in young organisms. In the present study, we investigated whether the basal forebrain cholinergic neurons and the estrogen receptor alpha (ERalpha) which they contain respond to changes in estrogen availability in aged female mice. The mice were sham-operated, ovariectomized, or ovariectomized and treated with 17beta-estradiol at the age of 18 months. Three months later, the mice were perfused and brain sections were double immunostained for choline acetyltransferase (ChAT) and ERalpha. Cell counting with a stereological method revealed that changes in the estrogen level have no effect on the total number of ChAT-immunoreactive (ir) neurons in the basal forebrain. However, the percentage of ChAT-ir neurons containing ERalpha-ir was higher in the ovariectomized mice than in the sham-operated or estrogen-treated mice. This was specific for the medial septum and vertical diagonal band of Broca. The findings indicate that even at old age the ERalphas in cholinergic cells are able to respond to changes in estrogen levels, though in a region-specific manner. This is naturally important for studies aiming to develop therapies for the elderly.

Estrogen treatment improves spatial learning in APP + PS1 mice but does not affect beta amyloid accumulation and plaque formation

We investigated the effects of ovariectomy (OVX) and 17 beta-estradiol (0.18 mg per pellet) treatment on spatial learning and memory, hippocampal beta amyloid (A beta) levels, and amyloid plaque counts in double transgenic mice (A/P) carrying mutated amyloid precursor protein (APPswe) and presenilin-1 (PS1-A246E). After OVX at 3 months of age, the mice received estrogen treatment for the last 3 months of their lifetime before they were killed at 6, 9, or 12 months of age. Estrogen treatment in A/P OVX mice increased the number of correct choices in a position discrimination task in the T-maze, and slightly improved their performance in a win-stay task (1/8 arms baited) in the radial arm maze (RAM). However, estrogen treatment did not reverse the A beta-dependent cognitive deficits of A/P mice in the water maze (WM) spatial navigation task. Furthermore, ovariectomy or estrogen treatment in OVX and sham-operated A/P mice had no effect on hippocampal amyloid accumulation. These results show that the estrogen treatment in a transgenic mouse model of Alzheimer's disease (AD) improves performance in the same learning and memory tasks as in the normal C57BL/6J mice. However, the estrogen effects in these mice appeared to be unrelated to A beta-induced cognitive deficits. Our results do not support the idea that estrogen treatment decreases the risk or alleviates the symptoms of Alzheimer's disease by inhibiting the accumulation of A beta or formation of amyloid plaques.

Gender differences in the amount and deposition of amyloidbeta in APPswe and PS1 double transgenic mice

Transgenic mice carrying both the human amyloid precursor protein (APP) with the Swedish mutation and the presenilin-1 A246E mutation (APP/PS1 mice) develop Alzheimer's disease-like amyloidbeta protein (Abeta) deposits around 9 months of age. These mice show an age-dependent increase in the level of Abeta40 and Abeta42 and in the number of amyloid plaques in the brain. Abeta40 and Abeta42 levels were measured, and amyloid burden and plaque number were quantified, in the hippocampus at the age of 4, 12, and 17 months in both male and female APP/PS1 mice. In all mice, amyloid burden and plaque number increased markedly with age, with female mice bearing a heavier amyloid burden and higher plaque number compared to male mice of the same age, both at 12 and at 17 months of age. The level of both Abeta40 and Abeta42 significantly increased in female mice with age and was always significantly higher in female than in male mice of the same age. Further, there were significant correlations between amyloid burden and Abeta42 level in female mice and between amyloid burden and plaques in both female and male mice. Together these data show that female APP/PS1 mice accumulate amyloid at an earlier age and that they build up more amyloid deposits in the hippocampus than age-matched male mice. Together, these results provide new insights in the potential mechanisms of the observed gender differences in the pathogenesis of AD.

Hypothermia in mice tested in Morris water maze

The Morris water maze, one of the most common behavioral tasks to assess learning and memory in rodents, exposes the animals to cold water for a few minutes. Unlike rats, young healthy mice can become severely hypothermic during the task. Five swims of 45 s in 20 degrees C water with 30s between the trials was enough to cause up to 9 degrees C drop in the rectal temperature. The decline in core temperature was accompanied by slowing of the swimming speed. Moreover, the effect was dependent on the sex and genotype of the mice, such that females were more susceptible to hypothermia than males and transgenic mice carrying Alzheimer-associated APP and PS1 mutations more vulnerable than their nontransgenic littermates. Raising the water temperature from 20 to 24 degrees C alleviated the hypothermia, but did not remove the significant drop in core temperature when using 30-s inter-trial interval. However, increasing the break from 30 s to 13 min removed the net cooling effect of five trials on the core temperature and swimming speed. We conclude that the currently most common water maze protocol renders mice hypothermic, which may confound the test results, especially when transgenic female mice are used. We recommend monitoring of the swimming speed on a trial-by-trial basis and using longer inter-trial intervals.

Estrogen treatment alleviates NMDA-antagonist induced hippocampal LTP blockade and cognitive deficits in ovariectomized mice

Estrogen is implicated in hippocampus-dependent spatial learning as well as structural organization and electrophysiological properties of the rat hippocampus but little is known about its mechanisms of action in mice. In this study, we investigated pharmacologically whether estrogen interacts with the hippocampal N-methyl-D-aspartate (NMDA) receptors in ovariectomized mice as postulated for rats. Female C57BL/6J mice were ovariectomized at 5 months, and 2 weeks before testing at 12 months, half of them received subcutaneous estrogen pellets containing 0.18 mg of 17 beta-estradiol. The competitive NMDA-antagonist, 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), was administered at 5.0 and 10.0 microM to block induction of long-term potentiation (LTP) in the hippocampal slice and intraperitoneally at 0.5, 2.0, and 5.0 mg/kg to impair spatial learning in the water maze. Estrogen treatment shifted the dose-response curve to CPP in both experiments. First, 10 microM CPP blocked the initiation of LTP in all mice, but 5 microM only in ovariectomized non-estrogen-treated mice. Second, final level of acquisition and probe trial performance in the water maze were less affected by high doses of CPP in the estrogen-treated ovariectomized mice than in non-treated group. In control tests for motor side effects, estrogen treatment did not reduce the tendency of CPP to decrease locomotor activity in the open field and impair balance on a rotating rod, and estrogen by itself decreased swimming speed as did CPP, but these effects did not interact. Our findings support the notion that estrogen treatment increases the number of active NMDA-receptors in the mouse hippocampus.

Alpha 2C-adrenoceptor mediated regulation of cortical EEG arousal

Alpha2-adrenergic drugs modulate cortical arousal and EEG. However, the role of individual alpha2-adrenoceptor (alpha(2)-AR) subtypes in these functions is not clear. We investigated the role of alpha(2C)-ARs in the modulation of baseline cortical EEG activity and EEG responses to the alpha(2)-AR selective agonist, dexmedetomidine (3-300 microg/kg, s.c.), and antagonist, atipamezole (3-1000 microg/kg, s.c.), by using alpha(2C)-AR knockout (KO) and wildtype (WT) mice. The overall amplitude (1-30 Hz) was not significantly altered in KO mice although the activity of theta band (4-8 Hz) was increased in these mice. The main finding was that dexmedetomidine (30-300 microg/kg) more effectively slowed and atipamezole (30-1000 microg/kg) less effectively increased cortical EEG arousal in KO mice compared to WT controls. Importantly, autoradiographical results showed no compensatory increase in other alpha(2)-AR subtypes in cortical, thalamic or other brain structures of KO mice. Furthermore, there were no differences between the genotypes in the levels of hippocampal choline acetyltransferase, monoamines or their metabolites. Altered baseline cortical EEG activity and EEG responses to alpha(2)-AR selective drugs in KO mice indicate that alpha(2C)-ARs are involved in regulation of cortical arousal. These results suggest that alpha(2C)-ARs may antagonize the sedative effect of alpha(2)-AR agonists mediated by activation of alpha(2A)-ARs.

Seladin-1 transcription is linked to neuronal degeneration in Alzheimer's disease

Seladin-1 is a gene recently shown to be down-regulated in brain regions selectively degenerated in Alzheimer's disease. The sequence of seladin-1 shares similarities with flavin-adenine-dinucleotide-dependent oxidoreductases and it has been found to protect cells from apoptotic cell death. In this work, we show that the transcription of seladin-1 is selectively down-regulated in the brain areas affected in Alzheimer's disease. The down-regulation in seladin-1 transcription was associated with hyperphosphorylated tau seen as linkage to immunohistochemically detected paired helical filament tau, neuritic plaques and neurofibrillary tangles. In contrast, no association was found between seladin-1 transcription and beta-amyloid deposition when analyzing human samples or tissue from transgenic animals. Furthermore, the relative transcription of seladin-1 was found to fluctuate during aging in the transgenic mouse model of Alzheimer's disease. The fluctuation was enhanced by Alzheimer's disease causing mutations in presenilin-1 and amyloid precursor protein genes. Finally, seladin-1 transcription was found to be up-regulated in mouse N2a cells induced to undergo apoptosis with okadaic acid. The results presented here indicate that seladin-1 transcription is selectively down-regulated in brain regions vulnerable to Alzheimer's disease and this down-regulation is associated with the hyperphosphorylation of tau protein.

Effects of fimbria-fornix lesion and amyloid pathology on spatial learning and memory in transgenic APP+PS1 mice

Transgenic mice carrying mutated human amyloid precursor protein (APPswe) and presenilin (PS1, A246E) genes develop first amyloid plaques around 9 months of age, but up to 18 months of age, amyloid depositions in these mice were largely restricted to the hippocampus, subiculum, and neocortex. To assess the behavioral consequences of amyloid accumulation in the hippocampal formation, we compared the effects of APP+PS1 (AP) genotype and fimbria-fornix (FFX) transection, either alone or combined, on various spatial learning and memory tasks. Both FFX-lesioned and AP mice were impaired in spatial navigation in the water maze, a typical hippocampal dependent task. Conversely, neither group of mice was impaired in a win-stay version of the radial arm maze (RAM) or position discrimination in the T-maze, tasks that do not depend on the hippocampus. FFX-lesioned mice were impaired in the win-shift version of the RAM, and in spontaneous and rewarded alternation in the T-maze, while AP mice performed equal to non-transgenic controls in all these working memory tasks, except long-term retention of the RAM task. AP mice thus appear to have a selective deficit in hippocampal dependent long-term memory, as do Alzheimer patients at early stage of the disease.

Elevated levels of Abeta1-40 and Abeta1-42 do not alter the binding sites of nicotinic receptor subtypes in the brain of APPswe and PS1 double transgenic mice

The binding sites of nicotinic acetylcholine receptor (nAChR) subtypes were measured in the parietal cortex and hippocampus of transgenic mice carrying mutant human APPswe and presenilin 1 (PS1) genes (APPswe/PS1 mice) between the ages of 3 weeks and 17 months. Soluble and insoluble beta-amyloid peptide (Abeta1-40 and Abeta1-42) levels were investigated in parallel. No significant differences in binding sites of [(3)H]cytisine (alpha4beta2 nAChRs) and [(125)I]alpha-bungarotoxin (alpha7 nAChRs) were observed in APPswe/PS1 mice and wild-type control mice at any age studied. At three weeks of age, soluble Abeta1-40 was detectable in the parietal cortex and hippocampus of APPswe/PS1 mice, whereas Abeta1-42 was detectable from 12 months of age. A pronounced increase in insoluble Abeta1-42 was observed between 3 weeks and 17 months compared with that of insoluble Abeta1-40 in both brain regions, indicating a shift that favors accumulation of Abeta1-42 in older APPswe/PS1 mice. The findings indicate that elevated Abeta levels in the brains of APPswe/PS1 mice do not alter the number of alpha4beta2 and alpha7 receptors, the two major brain nAChR subtypes.

Hippocampal A beta 42 levels correlate with spatial memory deficit in APP and PS1 double transgenic mice

We investigated the role of hippocampal amyloid pathology in spatial learning impairment of a new mouse line carrying mutated human amyloid precursor protein (APP) and presenilin-1 (PS1) transgenes. The APP + PS1 mice were tested in spatial navigation in the water maze and in position discrimination in the T-maze at ages of 3-4 and 11-12 months, before and after the appearance of first amyloid plaques. The APP + PS1 mice were impaired in water maze acquisition and retention only at the age of 11-12 months, but performed equally to controls in the T-maze task at both ages. In the impaired older age group, the levels of total Abeta1-42 in the hippocampus of APP + PS1 mice correlated negatively with the retention score. Here we show for the first time that the age-dependent impairment in memory retention in the traditional water maze of APP + PS1 mice correlates with the amount of total Abeta in hippocampus even at a stage when the amyloid deposits cover less than 1% of the hippocampal volume.

Effects of ovariectomy and estrogen treatment on learning and hippocampal neurotransmitters in mice

This study examined the effects of long-term estrogen treatment (sc 17 beta-estradiol minipellets) on learning in C57BL/6J female and male mice using a position discrimination task in the T-maze and a win-stay task (1/8 arms baited) in the radial arm maze (RAM). In addition, hippocampal monoamines and ChAT activity were measured at the end of the study and correlated to task performance. Female sham-operated (gonadally intact) and ovariectomized (OVX) mice were treated with estrogen either for 7 or 40 days before the behavioral tests and intact male mice for 7 days before the behavioral tests. In sham-operated mice the 40-day estrogen treatment improved RAM performance and in OVX mice both the 7- and 40-day estrogen treatments improved the performance in both maze tasks. The estrogen treatment also improved RAM performance in males. The hippocampal ChAT, NA, 5-HIAA, and DOPAC levels were decreased in OVX mice. Furthermore, the effects of estrogen treatment on the levels of hippocampal 5-HT and its metabolite 5-HIAA were different in sham-operated than in OVX mice. We could find no correlation between cognitive measures and neurochemical variables. This study gives new information about the effects of estrogen on learning and hippocampal neurotransmitters in mice.

Apolipoprotein E-deficient mice are not more susceptible to the biochemical and memory deficits induced by nucleus basalis lesion

We investigated whether the nucleus basalis lesion induced by quisqualic acid was associated with a more severe impairment of spatial navigation in a water maze, a greater reduction in frontal choline acetyltransferase activity and decrease in the number of choline acetyltransferase-positive neurons in the nucleus basalis in apolipoprotein E-deficient mice than in control mice. We also studied the effect of ageing on water maze spatial navigation and cortical choline acetyltransferase activity in 16-month-old control and apolipoprotein E-deficient mice. We found that the lesion decreased choline acetyltransferase-positive neurons in the nucleus basalis and frontal choline acetyltransferase activity equally in control and apolipoprotein E-deficient mice. The nucleus basalis lesion had no effect on the initial acquisition in the water maze in control and apolipoprotein E-deficient mice after 25 or 106 days of recovery. However, the nucleus basalis lesion impaired the reversal learning in the water maze similarly in both strains after 25 days of recovery, but had no effect after 106 days of recovery. Finally, water maze spatial navigation and cortical choline acetyltransferase activity were similar in old control and apolipoprotein E-deficient mice. These results suggest that young and old apolipoprotein E-deficient mice do not have impairments in cholinergic activity or spatial navigation. Furthermore, apolipoprotein E deficiency does not increase the sensitivity to cholinergic and spatial navigation deficits induced by lesioning of the nucleus basalis with an excitatory amino acid and does not slow down the behavioral recovery.

Impaired recovery of noradrenaline levels in apolipoprotein E-deficient mice after N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine lesion

We investigated the effect of the noradrenergic neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) (1 or 3 x 50 mg/kg, intraperitoneally), on hippocampal, cortical and cerebellar noradrenaline levels after recovery of one, five and 11 months in control and apolipoprotein E-deficient mice. Apolipoprotein E-deficient mice had lower hippocampal noradrenaline levels than control mice. DSP-4-lesioned control mice had a more extensive recovery of hippocampal and cortical noradrenaline levels than DSP-4-lesioned apoE-deficient mice after five months' survival. Furthermore, the hippocampal noradrenaline levels after five and 11 months and cortical noradrenaline levels after five months of recovery had slightly recovered in control but not in apolipoprotein E-deficient mice treated with a single dose of DSP-4 compared with mice treated with three doses of DSP-4. These results show that apolipoprotein E-deficient mice have impaired recovery capacity in their locus coeruleus neurons.

Estrogen and NMDA receptor antagonism: effects upon reference and working memory

Since both estrogen and NMDA receptor antagonists act on the hippocampus CA1 region and behaviorally affect hippocampal memory tasks, we examined how estrogen depletion (ovariectomy) and NMDA receptor antagonism interact upon spatial memory of the mouse. After ovariectomy or sham operation, mice were given a 2-week recovery before behavioral tests began under the influence of vehicle or (+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP 2, 5 and 10 mg/kg) intraperitoneal injections. CPP is a competitive, full NMDA receptor antagonist. Spatial reference memory was tested by the water maze, spatial working memory was tested by the radial arm maze, while overall locomotive activity was monitored by the Y-maze. Results from the water maze and the Y-maze did not show any spatial reference memory or activity differences between sham-operated and ovariectomized mice. The radial arm maze, however, highlighted some working memory differences between intact and ovariectomized mice. CPP treatment impaired dose dependently--the performance of ovariectomy and sham-operated mice equally on both water maze and radial arm maze, while the drug had no effect on Y-maze performance. These results suggest that short term estrogen deprivation has no effect upon spatial-reference memory, while it impairs spatial working memory. This effect is probably not mediated by NMDA receptors.

Moderate cortical EEG changes in apolipoprotein E-deficient mice during ageing and scopolamine treatment but not after nucleus basalis lesion

RATIONALE

Recent studies suggest that apoE-deficient mice may have impaired central cholinergic function and neuronal recovery capacity.

OBJECTIVE

We investigated whether apoE-deficient mice are more susceptible to the biochemical and EEG defects induced by ageing or nucleus basalis (NB) lesion.

METHODS

ApoE-deficient and control mice were used. The baseline EEG activity and EEG response to a muscarinic acetylcholine receptor antagonist, scopolamine (0.05 and 0.2 mg/kg) and a benzodiazepine receptor agonist, diazepam (0.5 and 2.0 mg/kg), were studied during ageing. In addition, the cortical and hippocampal ChAT activities were measured in aged mice. The baseline EEG activity and EEG response to scopolamine (0.05 and 0.2 mg/kg), and cortical ChAT activity, were studied after quisqualic acid-induced unilateral NB lesion.

RESULTS

The baseline EEG fast wave activity (relative alpha and beta) was higher in apoE-deficient mice. Ageing decreased relative alpha activity similarly in both strains. The scopolamine induced EEG slowing was less prominent in apoE-deficient than in control mice, and the difference between the strains became slightly clearer during ageing. The NB lesion failed to produce more severe changes in cortical EEG and ChAT activity in apoE-deficient mice. Cortical and hippocampal ChAT activity was equal in young and aged apoE-deficient and control mice. The EEG response to diazepam in young and aged mice was similar in both strains.

CONCLUSIONS

The regulation of cortical EEG activity of apoE-deficient mice was somewhat altered during ageing and the response to scopolamine treatment was blunted. However, the cholinergic cells of the NB of apoE-deficient mice were not more sensitive to lesion or to ageing, suggesting that apoE does not have to be present to preserve the viability of cholinergic neurons.

In mice tonic estrogen replacement therapy improves non-spatial and spatial memory in a water maze task

We investigated the effects of estrogen replacement therapy on water maze non-spatial and spatial navigation in mice. Three groups of mice were ovariectomized and two of these groups being implanted with s.c. pellets that produce blood levels of estrogen close to those found in estrous (estrogen low, 75-100 pg/ml blood) or proestrous (estrogen high, 300-400 pg/ml). The behavioral assessment was initiated 7 days after pellet implantation. Non-spatial navigation to a clearly visible platform was stimulated by low and high levels of estrogen. However, spatial navigation to a hidden platform was improved by low estrogen levels. We found that estrogen improves two different types of memory processes that depend on striatal (non-spatial navigation) and hippocampal (spatial) memory systems.

Oxotremorine suppresses thalamocortical oscillations via thalamic muscarinic acetylcholine receptors

We investigated whether the local intrathalamic infusion of a muscarinic acetylcholine receptor agonist (oxotremorine) at either the reticular nucleus of thalamus (NRT) or the ventroposteromedial nucleus of thalamus (VPM) suppresses thalamocortically generated neocortical high-voltage spindles (HVSs). In addition, we studied whether the intracerebroventricular (ICV) infusion of a selective muscarinic M2 acetylcholine receptor antagonist (methoctramine) could block the suppression of HVSs induced by either systemic (IP) administration of an anticholinesterase drug [tetrahydroaminoacridine (THA)] or ICV infusion of oxotremorine in rats. Intrathalamic administration of oxotremorine at 3 and 15 microg in the NRT, and at 15 microg in the VPM suppressed HVSs. ICV oxotremorine at 30 and 100 microg and IP THA at 3 mg/kg decreased HVSs. ICV methoctramine at 100 microg increased HVSs and completely blocked the decrease in HVSs produced by oxotremorine 100 microg and THA 3 mg/kg. The results suggest that activation of muscarinic M2 acetylcholine receptors in thalamic nuclei (NRT and VPM) can suppress thalamocortical oscillations and that ICV or systemically administered drugs that activate either directly (oxotremorine and methoctramine) or indirectly (THA) the muscarinic M2 acetylcholine receptors may modulate neocortical HVSs via the thalamus.