Lydia Giménez-Llort

Hyperalgesia, anxiety, and decreased hypoxic neuroprotection in mice lacking the adenosine A1 receptor

Caffeine is believed to act by blocking adenosine A1 and A2A receptors (A1R, A2AR), indicating that some A1 receptors are tonically activated. We generated mice with a targeted disruption of the second coding exon of the A1R (A1R−/−). These animals bred and gained weight normally and had a normal heart rate, blood pressure, and body temperature. In most behavioral tests they were similar to A1R+/+ mice, but A1R−/− mice showed signs of increased anxiety. Electrophysiological recordings from hippocampal slices revealed that both adenosine-mediated inhibition and theophylline-mediated augmentation of excitatory glutamatergic neurotransmission were abolished in A1R−/− mice. In A1R+/− mice the potency of adenosine was halved, as was the number of A1R. In A1R−/− mice, the analgesic effect of intrathecal adenosine was lost, and thermal hyperalgesia was observed, but the analgesic effect of morphine was intact. The decrease in neuronal activity upon hypoxia was reduced both in hippocampal slices and in brainstem, and functional recovery after hypoxia was attenuated. Thus A1Rs do not play an essential role during development, and although they significantly influence synaptic activity, they play a nonessential role in normal physiology. However, under pathophysiological conditions, including noxious stimulation and oxygen deficiency, they are important.

Modeling behavioral and neuronal symptoms of Alzheimer's disease in mice: a role for intraneuronal amyloid.

The amyloid Abeta-peptide (Abeta) is suspected to play a critical role in the cascade leading to AD as the pathogen that causes neuronal and synaptic dysfunction and, eventually, cell death. Therefore, it has been the subject of a huge number of clinical and basic research studies on this disease. Abeta is typically found aggregated in extracellular amyloid plaques that occur in specific brain regions enriched in nAChRs in Alzheimers disease (AD) and Down syndrome (DS) brains. Advances in the genetics of its familiar and sporadic forms, together with those in gene transfer technology, have provided valuable animal models that complement the traditional cholinergic approaches, although modeling the neuronal and behavioral deficits of AD in these models has been challenging. More recently, emerging evidence indicates that intraneuronal accumulation of Abeta may also contribute to the cascade of neurodegenerative events and strongly suggest that it is an early, pathological biomarker for the onset of AD and associated cognitive and other behavioral deficits. The present review covers these studies in humans, in in vitro and in transgenic models, also providing more evidence that adult 3xTg-AD mice harboring PS1M146V, APPSwe, tauP301L transgenes, and mimicking many critical hallmarks of AD, show cognitive deficits and other behavioral alterations at ages when overt neuropathology is not yet observed, but when intraneuronal Abeta, synaptic and cholinergic deficits can already be described.

Mice lacking the adenosine A1 receptor are anxious and aggressive, but are normal learners with reduced muscle strength and survival rate

Behavioural assessment of mice lacking adenosine A1 receptors (A1Rs) showed reduced activity in some phases of the light–dark cycle, reduced exploratory behaviour in the open‐field and in the hole‐board, increased anxiety in the plus maze and dark‐light box and increased aggressiveness in the resident‐intruder test. No differences were found in spatial reference and working memory in several Morris water maze tasks. Both mutant mice had reduced muscle strength and survival rate. These results confirm the involvement of adenosine in motor activity, exploratory behaviour, anxiety and aggressiveness. A1Rs also appear to play a critical role in ageing‐related deterioration.

Physical exercise protects against alzheimer's disease in 3xTg-AD mice

Physical exercise is considered to exert a positive neurophysiological effect that helps to maintain normal brain activity in the elderly. Expectations that it could help to fight Alzheimers disease (AD) were recently raised. This study analyzed the effects of different patterns of physical exercise on the 3xTg-AD mouse. Male and female 3xTg-AD mice at an early pathological stage (4-month-old) have had free access to a running wheel for 1 month, whereas mice at a moderate pathological stage(7-month-old) have had access either during 1 or 6 months. The non-transgenic mouse strain was used as a control. Parallel animal groups were housed in conventional conditions. Cognitive loss and behavioral and psychological symptoms of dementia (BPSD)-like behaviors were present in the 3xTg-AD mice along with alteration in synaptic function and ong-term potentiation impairment in vivo. Brain tissue showed AD-pathology and oxidative-related changes. Disturbances were more severe at the older age tested. Oxidative stress was higher in males but other changes were similar or higher in females. Exercise treatment ameliorated cognitive deterioration and BPSD-like behaviors such as anxiety and the startle response. Synaptic changes were partially protected by exercise. Oxidative stress was reduced. The best neuroprotection was generally obtained after 6 months of exercise in 7-month-old 3xTg-AD mice. Improved sensorimotor function and brain tissue antioxidant defence were induced in both 3xTg-AD and NonTg mice. Therefore, the benefits of aerobic physical exercise on synapse, redox homeostasis, and general brain function demonstrated in the 3xTg-AD mouse further support the value of this healthy life-style against neurodegeneration.

Postsynaptic antagonistic interaction between adenosine A1 and dopamine D1 receptors.

BEHAVIOURAL, AND biochemical evidence for the existence of a powerful specific postsynaptic interaction between adenosine A1, and dopamine D1 receptors in the mammalian brain was found. Behavioural data showed that A1 receptor stimulation induced a decrease in the D1-induced motor activation in reserpinized mice, and a decrease in the D1-dependent oral dyskinesia in rabbits. Biochemical data suggested that A1 receptor stimulation could produce a GTP-independent uncoupling of the rat striatal D1 receptor to the G protein. The A1-D1 receptor-receptor interaction might represent an important additional mechanism of action responsible for the motor depressant effects of adenosine agonists, and for the motor stimulant effects of adenosine antagonists, like the methylxanthines caffeine, and theophylline

Intraneuronal β-Amyloid Accumulation in the Amygdala Enhances Fear and Anxiety in Alzheimer's Disease Transgenic Mice

BACKGROUND Alzheimers disease (AD) is characterized by progressive memory decline and neuropsychiatric symptoms. Despite common emotional symptoms in AD such as anxiety and fear are associated with a more rapid cognitive decline, the pathological mechanisms involved in these behavioral changes remain largely elusive. In this study, we examined the pathological mechanisms of emotional behavior in well-established AD transgenic mice expressing human mutant beta-amyloid (Abeta) precursor protein (APP(Ind) and APP(Sw,Ind)) and tau (3xTg-AD). METHODS We evaluated unconditioned and conditioned fear-induced freezing behavior and spatial memory in APP(Ind), APP(Sw,Ind), and 3xTg-AD transgenic mice. The Abeta and tau pathologies and signaling pathways involved in emotional processing were studied by immunohistochemistry and immunoblotting analyses. RESULTS The APP(Ind)/APP(Sw,Ind) and 3xTg-AD transgenic mice displayed at early ages enhanced innate and conditioned fear symptoms and spatial memory deficits coinciding with enhanced accumulation of Abeta in gamma-aminobutyric acid (GABA)ergic and glutamatergic neurons, respectively, of the basolateral amygdala (BLA). Similarly, the number of neurons with intraneuronal Abeta40 and Abeta42 was significantly increased in the BLA of human AD brains. Fear responses might reflect an influence of anxiety, because the anxiolytic compounds valproate, diazepam, and buspirone reduced efficiently unconditioned and conditioned fear responses in APP transgenic mice. In addition, phosphorylation of extracellular signal-regulated kinase (ERK)1/2, which is critical for acquisition and consolidation of fear conditioning, was increased in the amygdala of APP transgenic mice after cued conditioning. CONCLUSIONS We propose a deleterious role of intraneuronal Abeta on amygdala-dependent emotional responses by affecting the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) signaling pathway.

Working memory deficits in transgenic rats overexpressing human adenosine A2A receptors in the brain

Adenosine receptors in the central nervous system have been implicated in the modulation of different behavioural patterns and cognitive functions although the specific role of A(2A) receptor (A(2A)R) subtype in learning and memory is still unclear. In the present work we establish a novel transgenic rat strain, TGR(NSEhA2A), overexpressing adenosine A(2A)Rs mainly in the cerebral cortex, the hippocampal formation, and the cerebellum. Thereafter, we explore the relevance of this A(2A)Rs overexpression for learning and memory function. Animals were behaviourally assessed in several learning and memory tasks (6-arms radial tunnel maze, T-maze, object recognition, and several Morris water maze paradigms) and other tests for spontaneous motor activity (open field, hexagonal tunnel maze) and anxiety (plus maze) as modification of these behaviours may interfere with the assessment of cognitive function. Neither motor performance and emotional/anxious-like behaviours were altered by overexpression of A(2A)Rs. TGR(NSEhA2A) showed normal hippocampal-dependent learning of spatial reference memory. However, they presented working memory deficits as detected by performance of constant errors in the blind arms of the 6 arm radial tunnel maze, reduced recognition of a novel object and a lack of learning improvement over four trials on the same day which was not observed over consecutive days in a repeated acquisition paradigm in the Morris water maze. Given the interdependence between adenosinic and dopaminergic function, the present results render the novel TGR(NSEhA2A) as a putative animal model for the working memory deficits and cognitive disruptions related to overstimulation of cortical A(2A)Rs or to dopaminergic prefrontal dysfunction as seen in schizophrenic or Parkinsons disease patients.

Fearfulness and sex in F2 Roman rats: males display more fear though both sexes share the same fearfulness traits.

The pattern of sex differences in a large sample (about 400 for each sex) of F2-generation rats, derived from inbred Roman high- and low-avoidance strains differing in fearfulness and brain functioning, was investigated. We obtained measures from responses to a battery of novel/threatening tests [open field (OF), plus maze (PM), hole board (HB), activity (A), and acoustic startle reflex (ASR)] as well as learned fear paradigms [classical fear conditioning (CFC) and shuttlebox avoidance conditioning (SAC)]. The results showed that almost all behaviors assessed fit with a pattern of unidirectional sex effects characterized by male rats as being more fearful than females: males defecated more than females in the OF, PM, HB, ASR, and CFC; ambulated less in the OF, PM, A, and SAC; showed more self-grooming in PM and HB; explored the open arms of the PM and the holes of the HB less; displayed enhanced ASR; and showed poorer performance in the SAC task. We applied two factor analyses to each sex showing that, in general, they shared a common three-factor structure: a Learned Fear Factor comprising SAC and CFC responding, a Fear of Heights/Open Spaces Factor with the highest loadings for open arm behavior in the PM, and an Emotional Reactivity Factor, mainly grouping defecations, ambulation, and self-grooming. These results indicate that the essential components of fearful behavior are similar for both sexes in an inbred but genetically heterogeneous population.

Adenosine A1 receptor blockade selectively potentiates the motor effects induced by dopamine D1 receptor stimulation in rodents

An antagonistic interaction between adenosine A1 and dopamine D1 receptors has previously been found in the basal ganglia. However, direct evidence for a selective adenosine A1 antagonist-induced potentiation of dopamine D1-mediated motor activation is lacking. The systemic administration of the adenosine A1 antagonist 8-cyclopentyl-1,3-dimethylxanthine significantly potentiated the motor activating properties of the systemically administered dopamine D1 agonist SKF 38393 in both reserpinized mice and unilaterally 6-hydroxy-dopamine-lesioned rats. However, 8-cyclopentyl-1, 3-dimethylxanthine did not modify the motor effects of the dopamine D2 agonist quinpirole. The present work shows that an antagonistic interaction between adenosine A1 and dopamine D1 receptors may be involved in the motor activating effects of adenosine antagonists, like caffeine.

Melatonin plus physical exercise are highly neuroprotective in the 3xTg-AD mouse

Alzheimers disease (AD) is a devastating age-related neurodegenerative disease with no specific treatment at present. Several healthy lifestyle options and over-the-counter drugs that it has been suggested delay the onset of the disease are in an experimental phase, but it is unclear whether they will have any therapeutic value against AD. We assayed physical exercise and melatonin in 3xTg-AD male mice aged from 6 to 12 months, therefore from moderate to advanced phases of AD pathology. Analysis of behavior and brain tissue at termination showed differential patterns of neuroprotection for the 2 treatments. Both treatments decreased soluble amyloid β oligomers, whereas only melatonin decreased hyperphosphorylated tau. Melatonin was effective against the immunosenescence that 3xTg-AD mice present. Voluntary physical exercise protected against behavioral and psychological symptoms of dementia such as anxiety, a lack of exploration, and emotionality. Both treatments protected against cognitive impairment, brain oxidative stress, and a decrease in mitochondrial DNA (mtDNA). Interestingly, only the combined treatment of physical exercise plus melatonin was effective against the decrease of mitochondrial complexes. Therefore, melatonin plus physical exercise may exert complementary, additive, or even synergistic effects against a range of disturbances present in AD.