The ins and outs of the BCCAo model for chronic hypoperfusion: a multimodal and longitudinal MRI approach.

Cerebral hypoperfusion induced by bilateral common carotid artery occlusion (BCCAo) in rodents has been proposed as an experimental model of white matter damage and vascular dementia. However, the histopathological and behavioral alterations reported in this model are variable and a full characterization of the dynamic alterations is not available. Here we implemented a longitudinal multimodal magnetic resonance imaging (MRI) design, including time-of-flight angiography, high resolution T1-weighted images, T2 relaxometry mapping, diffusion tensor imaging, and cerebral blood flow measurements up to 12 weeks after BCCAo or sham-operation in Wistar rats. Changes in MRI were related to behavioral performance in executive function tasks and histopathological alterations in the same animals. MRI frequently (70%) showed various degrees of acute ischemic lesions, ranging from very small to large subcortical infarctions. Independently, delayed MRI changes were also apparent. The patterns of MRI alterations were related to either ischemic necrosis or gliosis. Progressive microstructural changes revealed by diffusion tensor imaging in white matter were confirmed by observation of myelinated fiber degeneration, including severe optic tract degeneration. The latter interfered with the visually cued learning paradigms used to test executive functions. Independently of brain damage, BCCAo induced progressive arteriogenesis in the vertebrobasilar tree, a process that was associated with blood flow recovery after 12 weeks. The structural alterations found in the basilar artery were compatible with compensatory adaptive changes driven by shear stress. In summary, BCCAo in rats induces specific signatures in multimodal MRI that are compatible with various types of histological lesion and with marked adaptive arteriogenesis.

A complementary diffusion tensor imaging (DTI)-histological study in a model of Huntington's disease.

In vivo diffusion tensor imaging (DTI) was performed on the quinolinic acid (QUIN) rat model of Huntington's disease, together with behavioral assessment of motor deficits and histopathological characterization. DTI and histology revealed the presence of a cortical lesion in 53% of the QUIN animals (QUIN(+ctx)). Histologically, QUIN(+ctx) were distinguished from QUIN(-ctx) animals by increased astroglial reaction within a subregion of the caudate putamen and loss of white matter in the external capsula. Although both techniques are complementary, the quantitative character of DTI makes it possible to pick up subtle differences in tissue microstructure that are not identified with histology. DTI demonstrated differential changes of fractional anisotropy (FA), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD) in the internal and external capsula, and within a subregion of the caudate putamen. It was suggested that FA increased due to a selective loss of the subcortical connections targeted by degenerative processes at the early stage of the disease, which might turn the striatum into a seemingly more organized structure. When tissue degeneration becomes more severe, FA decreased while AD, RD and MD increased.

Type 1 cannabinoid receptor mapping with [18F]MK-9470 PET in the rat brain after quinolinic acid lesion: a comparison to dopamine receptors and glucose metabolism.

PURPOSE: Several lines of evidence imply early alterations in metabolic, dopaminergic and endocannabinoid neurotransmission in Huntington's disease (HD). Using [18F]MK-9470 and small animal PET, we investigated cerebral changes in type 1 cannabinoid (CB1) receptor binding in the quinolinic acid (QA) rat model of HD in relation to glucose metabolism, dopamine D2 receptor availability and amphetamine-induced turning behaviour. METHODS: Twenty-one Wistar rats (11 QA and 10 shams) were investigated. Small animal PET acquisitions were conducted on a Focus 220 with approximately 18 MBq of [18F]MK-9470, [18F]FDG and [11C]raclopride. Relative glucose metabolism and parametric CB1 receptor and D2 binding images were anatomically standardized to Paxinos space and analysed voxel-wise using Statistical Parametric Mapping (SPM2). RESULTS: In the QA model, [18F]MK-9470 uptake, glucose metabolism and D2 receptor binding were reduced in the ipsilateral caudate-putamen by 7, 35 and 77%, respectively (all p<2.10(-5)), while an increase for these markers was observed on the contralateral side (>5%, all p<7.10(-4)). [18F]MK-9470 binding was also increased in the cerebellum (p=2.10(-5)), where it was inversely correlated to the number of ipsiversive turnings (p=7.10(-6)), suggesting that CB1 receptor upregulation in the cerebellum is related to a better functional outcome. Additionally, glucose metabolism was relatively increased in the contralateral hippocampus, thalamus and sensorimotor cortex (p=1.10(-6)). CONCLUSION: These data point to in vivo changes in endocannabinoid transmission, specifically for CB1 receptors in the QA model, with involvement of the caudate-putamen, but also distant regions of the motor circuitry, including the cerebellum. These data also indicate the occurrence of functional plasticity on metabolism, D2 and CB1 neurotransmission in the contralateral hemisphere.

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 Parkinson's disease patients.

Putrescine as a marker of the effects of 2-chloropropionic acid in the rat brain.

The neurotoxin 2-chloropropionic acid (2CPA, 750 mg/kg, per os) induces ataxia in rats causing neuropathological changes (necrosis and edema) localized mainly in the cerebellum (CB). It has been described that putrescine (PUT) is a good marker of severe brain damage. We measured the concentration of PUT (by HPLC) in ataxic rat brains 3 days after 2CPA dosing. PUT was 9-fold higher than normal values in CB, 5-fold higher in midbrain (MB) and medulla oblongata + pons (MO) and 3-fold higher in the remaining areas studied. Treatment with glycerol, a reducer of brain edema, lowered the concentration of PUT only in CB, MB and MO. Histological damage was found in CB and the spinal trigeminal nucleus (located in the pontomedullar brainstem). We suggest that PUT can act as a marker of both neuronal necrosis and brain edema.

Lesion of substantia nigra pars compacta by the GluR5 agonist ATPA.

UNLABELLED: Dopamine (DA) released by substantia nigra pars compacta (SNc) neurons is a key regulator of motor activity. A deficiency in the striatum DA content due to SNc degeneration is a characteristic of Parkinson's disease. The involvement of excitotoxic mechanisms in this pathology has been suggested. The kainate receptor subunit GluR5 has been identified in a few basal ganglia but it is strongly expressed in SNc. Here we examine whether (RS)-2-amino-3-(3-hydroxy-5-tbutylisoxazol-4-yl) propanoic acid (ATPA), a selective agonist of GluR5, induces damage in dopaminergic (DAergic) neurons. ATPA (13 nmol) was administered to rat SNc. Immediately after recovery from surgery, the rats displayed ipsilateral turning. This behavior disappeared in subsequent days. The administration of the D1/D2 agonist, apomorphine (1 mg/kg, s.c.) 1 and 2 weeks after ATPA-infusion also induced ipsilateral turning. Histological studies-performed 21 days after ATPA-infusion-showed a lesion of the lateral and central part of the SNc, where a significant loss (36%) of DAergic cells was detected by tyrosine hydroxylase immunohistochemistry. The lesion was restricted to the SNc, since no damage or glial reaction was observed in the substantia nigra pars reticulata as assessed by Nissl staining, tomato lectin staining for microglial cells and GFAP immunohistochemistry for astrocytes. IN CONCLUSION: (1). ATPA-infusion induces neuronal damage in the SNc in the rat and (2). the behavioral effects of unilateral infusion of ATPA are consistent with DAergic alterations in basal ganglia.

Cerebral distribution of polyamines in kainic acid-induced models of status epilepticus and ataxia in rats. Overproduction of putrescine and histological damage.

We study the brain regional distribution of putrescine after excitotoxic damage. After status epilepticus induced by kainic acid (9 mg/kg, i.p.) we found an increase of putrescine in all the regions analyzed. Three kind of regions can be identified according to the magnitude and persistence of the abnormal concentration of putrescine: hippocampus and cortex (9-fold 1 day, still increased 2-fold 2 weeks after injection), cerebellum and medulla oblongata+pons (2-fold 1 day after injection) and the other regions (7-8-fold 1 day, still increased 2-3-fold 1 week after injection). The histological damage was: severe, absent and moderate or low, respectively. After ataxia induced by kainic acid injection (2.34 nmols) into the cerebellum, putrescine also rises in all regions; a high concentration (9-fold) and severe damage was found in the injected cerebellar hemisphere. In conclusion, in the models studied, putrescine increases in all the regions analyzed. However, the highest concentrations and the most severe damage were found in the target regions.

Extracellular putrescine content after acute excitotoxic brain damage in the rat.

We examined the effects of the local infusion of kainic acid (KA), by reverse dialysis in the rat striatum, on the concentration of polyamines in the extracellular striatal compartment and in tissue. KA infusion markedly increased (3-fold) extracellular putrescine (PUT) concentration, which reached its maximum at the end of the dialysis experiments (6 h). Tissue PUT concentration was also increased (2-fold) in the striatum perfused with KA but not in the contralateral side. Extracellular spermidine (SD) concentration but not tissue SD concentration was affected by KA. The increase in PUT was accompanied by histological damage around the probe and by an increase in ornithine decarboxylase content, as assessed by immunohistochemistry. These results indicate that in the first stages of the excitotoxic lesion, there is an increase in the extracellular concentrations of PUT and SD.