Adalberto A. Castro

Short bouts of mild-intensity physical exercise improve spatial learning and memory in aging rats: involvement of hippocampal plasticity via AKT, CREB and BDNF signaling.

In the present study, we investigated whether mild-intensity physical exercise represents a successful strategy to enhance spatial learning and memory and hippocampal plasticity in aging rats, as previously described for long-term exposure to running wheel or treadmill exercise. Aging Wistar rats were submitted to short bouts (4-6 min) of exercise treadmill during five consecutive weeks. This mild-intensity exercise program increased muscle oxygen consumption by soleus and heart in aging rats and reversed age-related long-term spatial learning and memory impairments evaluated in the water maze and step-down inhibitory avoidance tasks. Remarkably, the observed cognitive-enhancing properties of short bouts of exercise were accompanied by the activation of serine/threonine protein kinase (AKT) and cAMP response element binding (CREB) pro-survival signaling that culminates in the marked increase on the brain-derived neurotrophic factor (BDNF) mRNA expression and BDNF protein levels on the hippocampus of aging rats. Altogether, these results indicate that short bouts of exercise represent a viable behavioral strategy to improve cognition and synaptic plasticity in aging rats which should be taken into account in further studies addressing the effects of physical exercise in aging subjects.

Lithium and valproate prevent olfactory discrimination and short-term memory impairments in the intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) rat model of Parkinson's disease.

We have recently demonstrated that rodents treated intranasally with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) display time-dependent impairments in olfactory, emotional, cognitive and motor functions associated with disruption of dopaminergic neurotransmission in different brain structures conceivably analogous to those observed during different stages of Parkinsons disease (PD). On the other hand, lithium (Li) and valproate (VPA) are two primary drugs used to treat bipolar mood disorder that have recently emerged as promising neuroprotective agents. The present data indicates that the pretreatment with Li (47.5 mg/kg) or VPA (200 mg/kg) by intraperitoneal route during 7 consecutive days was able to prevent olfactory discrimination and short-term memory impairments evaluated in the social recognition and step-down inhibitory avoidance tasks in rats infused with a single intranasal (i.n.) administration of MPTP (0.1 mg/nostril). Despite the absence of clear depressive-like responses following the current MPTP dose, Li and VPA treatment presented an antidepressant profile reducing the immobility time in the forced swimming test. Importantly, at this time no significant alterations on the locomotor activity of the animals were observed in the open field test. Moreover, Li and VPA prevented dopamine depletion in the olfactory bulb and striatum of MPTP-infused rats. These results provide new insights in experimental models of PD, indicating that Li and VPA may represent new therapeutic tools for the management of olfactory and cognitive symptoms associated to early preclinical phases of PD, together with their neuroprotective potential demonstrated in previous research.

The intranasal administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP): a new rodent model to test palliative and neuroprotective agents for Parkinson's disease.

Parkinsons disease (PD) is the second most common neurodegenerative disorder affecting approximately 1% of the population older than 60 years. Classically, PD is considered to be a motor system disease and its diagnosis is based on the presence of a set of cardinal motor signs that are consequence of a pronounced death of dopaminergic neurons in the substantia nigra pars compacta (SNc). Nowadays there is considerable evidence showing that non-dopaminergic degeneration also occurs in other brain areas which seems to be responsible for the deficits in olfactory, emotional and memory functions that precede the classical motor symptoms in PD. Dopamine-replacement therapy has dominated the treatment of PD and although the currently approved antiparkinsonian agents offer effective relief of the motor deficits, they have not been found to alleviate the non-motor features as well as the underlying dopaminergic neuron degeneration and thus drug efficacy is gradually lost. Another major limitation of chronic dopaminergic therapy is the numerous adverse effects such as dyskinesias, psychosis and behavioral disturbance. The development of new therapies in PD depends on the existence of representative animal models to facilitate the evaluation of new pharmacological agents before they are applied in clinical trials. We have recently proposed a new experimental model of PD consisting of a single intranasal (i.n.) administration of the proneurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 1 mg/nostril) in rodents. Our findings demonstrated that rats and mice treated intranasally with MPTP suffer impairments in olfactory, cognitive, emotional and motor functions conceivably analogous to those observed during different stages of PD. Such infusion causes time-dependent loss of tyrosine hydroxylase in the olfactory bulb and SNc, resulting in significant dopamine depletion in different brain areas. We have also identified some pathogenic mechanisms possibly involved in the neurodegeneration induced by i.n. administration of MPTP including mitochondrial dysfunction, oxidative stress, activation of apoptotic cell death mechanisms and glutamatergic excitotoxicity. Therefore, the present review attempts to provide a comprehensive picture of the i.n. MPTP model and to highlight recent findings from our group showing its potential as a valuable rodent model for testing novel drugs that may provide alternative or adjunctive treatment for both motor and non-motor symptoms relief with a reduced side-effect profile as well as the discovery of compounds to modify the course of PD.

Behavioral Phenotyping of Parkin-Deficient Mice: Looking for Early Preclinical Features of Parkinson's Disease

There is considerable evidence showing that the neurodegenerative processes that lead to sporadic Parkinsons disease (PD) begin many years before the appearance of the characteristic motor symptoms. Neuropsychiatric, sensorial and cognitive deficits are recognized as early non-motor manifestations of PD, and are not attenuated by the current anti-parkinsonian therapy. Although loss-of-function mutations in the parkin gene cause early-onset familial PD, Parkin-deficient mice do not display spontaneous degeneration of the nigrostriatal pathway or enhanced vulnerability to dopaminergic neurotoxins such as 6-OHDA and MPTP. Here, we employed adult homozygous C57BL/6 mice with parkin gene deletion on exon 3 (parkin −/−) to further investigate the relevance of Parkin in the regulation of non-motor features, namely olfactory, emotional, cognitive and hippocampal synaptic plasticity. Parkin −/− mice displayed normal performance on behavioral tests evaluating olfaction (olfactory discrimination), anxiety (elevated plus-maze), depressive-like behavior (forced swimming and tail suspension) and motor function (rotarod, grasping strength and pole). However, parkin −/− mice displayed a poor performance in the open field habituation, object location and modified Y-maze tasks suggestive of procedural and short-term spatial memory deficits. These behavioral impairments were accompanied by impaired hippocampal long-term potentiation (LTP). These findings indicate that the genetic deletion of parkin causes deficiencies in hippocampal synaptic plasticity, resulting in memory deficits with no major olfactory, emotional or motor impairments. Therefore, parkin −/− mice may represent a promising animal model to study the early stages of PD and for testing new therapeutic strategies to restore learning and memory and synaptic plasticity impairments in PD.

Atorvastatin improves cognitive, emotional and motor impairments induced by intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration in rats, an experimental model of Parkinson's disease.

Affective disorders and memory impairments precede the classical motor symptoms seen in Parkinsons disease (PD) and the currently approved antiparkinsonian agents do not alleviate the non-motor symptoms as well as the underlying dopaminergic neuron degeneration. On the other hand, there is increasing evidence that inflammation plays a key role in the pathophysiology of PD and that the anti-inflammatory actions of statins are related to their neuroprotective properties against different insults in the CNS. The present data indicates that the oral treatment with atorvastatin (10mg/kg/day), once a day during 7 consecutive days, was able to prevent short-term memory impairments and depressive-like behavior of rats assessed in the social recognition and forced swimming tests at 7 and 14 days, respectively, after a single intranasal (i.n.) administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (1mg/nostril). Importantly, at this time no significant alterations on the locomotor activity of the animals were observed in the open field test. Moreover, atorvastatin was found to protect against the long-lasting motor deficits evaluated in activity chambers and the loss of dopaminergic neurons in the substantia nigra pars compacta observed at 21 days after i.n. MPTP administration. At this time, despite the absence of spatial memory deficits in the water maze and in concentrations of the cytokines TNF-α, IL-1β and IL-10 in striatum and hippocampus following i.n. MPTP administration, atorvastatin treatment resulted in a significant increase in the striatal and hippocampal levels of nerve growth factor (NGF). These findings reinforce and extend the notion of the neuroprotective potential of atorvastatin and suggest that it may represent a new therapeutic tool for the management of motor and non-motor symptoms of PD.

Neuroprotective effects of agmatine in mice infused with a single intranasal administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

We have recently demonstrated that rodents treated intranasally with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) suffered impairments in olfactory, cognitive, emotional and motor functions associated with time-dependent disruption of dopaminergic neurotransmission in different brain structures conceivably analogous to those observed during different stages of Parkinsons disease (PD). Agmatine, an endogenous arginine metabolite, has been proposed as a novel neuromodulator that plays protective roles in several models of neuronal cellular damage. In the present study we demonstrated that repeated treatment with agmatine (30 mg/kg, i.p.) during 5 consecutive days increased the survival rate (from 40% to 80%) of 15-month-old C57BL/6 female mice infused with a single intranasal (i.n.) administration of MPTP (1 mg/nostril), improving the general neurological status of the surviving animals. Moreover, pretreatment with agmatine was found to attenuate short-term social memory and locomotor activity impairments observed at different periods after i.n. MPTP administration. These behavioral benefits of exogenous agmatine administration were accompanied by a protection against the MPTP-induced decrease of hippocampal glutamate uptake and loss of dopaminergic neurons in the substantia nigra pars compacta of aging mice, without altering brain monoamine oxidase B (MAO-B) activity. These results provide new insights in experimental models of PD, indicating that agmatine represents a potential therapeutic tool for the management of cognitive and motor symptoms of PD, together with its neuroprotective effects.

Omega-3 fatty acids prevent the ketamine-induced increase in acetylcholinesterase activity in an animal model of schizophrenia.

AIMS Schizophrenia is a debilitating neurodevelopmental disorder that is associated with dysfunction in the cholinergic system. Early prevention is a target of treatment to improve long-term outcomes. Therefore, we evaluated the preventive effects of omega-3 fatty acids on AChE activity in the prefrontal cortex, hippocampus and striatum in an animal model of schizophrenia. MAIN METHODS Young Wistar rats (30 days old) were initially treated with omega-3 fatty acids or vehicle alone. Animals received ketamine to induce an animal model of schizophrenia or saline plus omega-3 fatty acids or vehicle alone for 7 consecutive days beginning on day 15. A total of 22 days elapsed between the treatment and intervention. Animals were sacrificed, and brain structures were dissected to evaluate AChE activity and gene expression. KEY FINDINGS Our results demonstrate that ketamine increased AChE activity in these three structures, and omega-3 fatty acids plus ketamine showed lower values for the studied parameters, which indicate a partial preventive mechanism of omega-3 fatty acid supplementation. We observed no effect on AChE expression. Together, these results indicate that omega-3 fatty acid supplementation effectively reduced AChE activity in an animal model of schizophrenia in all studied structures. In conclusion, the present study provides evidence that ketamine and omega-3 fatty acids affect the cholinergic system, and this effect may be associated with the physiopathology of schizophrenia. Further studies are required to investigate the mechanisms that are associated with this effect.

Sepsis in the central nervous system and antioxidant strategies with nacetylcysteine, vitamins and statins

Sepsis is the complex syndrome characterized by an imbalance between proinflammatory and antiinflammatory response to infection. The brain may be affected during the sepsis, and acute and long-term brain dysfunctions have been observed in both animal models and septic patients. Oxidative stress and antioxidant systems may prove the basis underling brain dysfunction in sepsis. The antioxidant therapy may be theoretically achieved by the following strategies: restoring endogenous antioxidants and nutrients and supplementation with exogenous trace elements, vitamins, and nutrients with antioxidant proprieties; or administering drugs that reduce oxidative stress, such as N-acetylcysteine (NAC), vitamins and statins. In the review, we described below the involvement of oxidative stress and antioxidants defenses and potential utility of these strategies and present data regarding their use in sepsis.

In vitro 6-hydroxydopamine-induced toxicity in striatal, cerebrocortical and hippocampal slices is attenuated by atorvastatin and MK-801.

Parkinsons disease (PD) involves the loss of striatal dopaminergic neurons, although other neurotransmitters and brain areas are also involved in its pathophysiology. In rodent models to PD it has been shown statins improve cognitive and motor deficits and attenuate inflammatory responses evoked by PD-related toxins. Statins are the drugs most prescribed to hypercholesterolemia, but neuroprotective effects have also been attributed to statins treatment in humans and in animal models. This study aimed to establish an in vitro model of 6-hydroxydopamine (6-OHDA)-induced toxicity, used as an initial screening test to identify effective drugs against neural degeneration related to PD. The putative neuroprotective effect of atorvastatin against 6-OHDA-induced toxicity in rat striatal, cerebrocortical and hippocampal slices was also evaluated. 6-OHDA (100μM) decreased cellular viability in slices obtained from rat cerebral cortex, hippocampus and striatum. 6-OHDA also induced an increased reactive oxygen species (ROS) production and mitochondrial dysfunction. Co-incubation of 6-OHDA with atorvastatin (10μM) or MK-801 (50μM) an N-methyl-d-aspartate (NMDA) receptor antagonist, partially attenuated the cellular damage evoked by 6-OHDA in the three brain areas. Atorvastatin partially reduced ROS production in the hippocampus and striatum and disturbances of mitochondria membrane potential in cortex and striatum. 6-OHDA-induced toxicity in vitro displays differences among the brain structures, but it is also observed in cerebrocortical and hippocampal slices, besides striatum.