Increased lateralization in rotational side preference in male mice rendered acallosal by prenatal gamma irradiation

Current Evidence for Developmental, Structural, and Functional Brain Defects following Prenatal Radiation Exposure

Ionizing radiation is omnipresent. We are continuously exposed to natural (e.g., radon and cosmic) and man-made radiation sources, including those from industry but especially from the medical sector. The increasing use of medical radiation modalities, in particular those employing low-dose radiation such as CT scans, raises concerns regarding the effects of cumulative exposure doses and the inappropriate utilization of these imaging techniques. One of the major goals in the radioprotection field is to better understand the potential health risk posed to the unborn child after radiation exposure to the pregnant mother, of which the first convincing evidence came from epidemiological studies on in utero exposed atomic bomb survivors. In the following years, animal models have proven to be an essential tool to further characterize brain developmental defects and consequent functional deficits. However, the identification of a possible dose threshold is far from complete and a sound link between early defects and persistent anomalies has not yet been established. This review provides an overview of the current knowledge on brain developmental and persistent defects resulting from in utero radiation exposure and addresses the many questions that still remain to be answered.

Development of cerebral gray and white matter injury and cerebral inflammation over time after inflammatory perinatal asphyxia

Antenatal inflammation is associated with increased severity of hypoxic-ischemic (HI) encephalopathy and adverse outcome in human neonates and experimental rodents. We investigated the effect of lipopolysaccharide (LPS) on the timing of HI-induced cerebral tissue loss and gray matter injury, white matter injury and integrity, and the cerebral inflammatory response. On postnatal day 9, mice underwent HI by unilateral carotid artery occlusion followed by systemic hypoxia which resulted in early neuronal damage (MAP2 loss) at 3 h that did not increase up to day 15. LPS injection 14 h before HI (LPS+HI) significantly and gradually aggravated MAP2 loss from 3 h up to day 15, resulting in an acellular cystic lesion. LPS+HI increased white matter damage, reduced myelination in the corpus callosum and increased white matter fiber coherency in the cingulum. The number of oligodendrocytes throughout the lineage (Olig2-positive) was increased whereas more mature myelinating (CNPase-positive) oligodendrocytes were strongly decreased after LPS+HI. LPS+HI induced an increased and prolonged expression of cerebral cytokines/chemokines compared to HI. Additionally, LPS+HI increased macrophage/microglia activation and influx of neutrophils in the brain compared to HI. This study demonstrates the sensitizing effect of LPS on neonatal HI brain injury for an extended time-frame up to 15 days postinsult. LPS before HI induced a gradual increase in gray and white matter deficits, including reduced numbers of more mature myelinating oligodendrocytes and a decrease in white matter integrity. Moreover, LPS+HI prolonged and intensified the cerebral inflammatory response, including cellular infiltration. In conclusion, as the timing of damage and/or involved pathways are changed when HI is preceded by inflammation, experimental therapies might require modifications in the time window, dosage or combinations of therapies for efficacious neuroprotection.

Curcumin ameliorates cognitive deficits heavy ion irradiation-induced learning and memory deficits through enhancing of Nrf2 antioxidant signaling pathways

Oxidative stress is one of the major mechanisms implicated in carbon ion irradiation. Curcumin is a natural phenolic compound with impressive antioxidant properties. What's more, curcumin is recently proved to exert its effects partly radioprotection. In vivo, we investigated the protective effects of curcumin against (12)C(6+)radiation-induced cerebral injury. Our results showed that 4Gy heavy ion radiation-induced spatial strategy and memory decline and reduction of brain superoxide dismutase (SOD) activity levels were all consistently improved by curcumin, and the augmentation of cerebral malonaldehyde (MDA) was lowered by curcumin. Furthermore, both the cerebral cells nuclear erythroid 2-related factor 2 (Nrf2) protein and three typically recognized Nrf2 downstream genes, NAD(P)H quinine oxidoreductase 1 (NQO1), heme oxygenase-1 (HO-1), and γ-glutamyl cysteine synthetase (γ-GCS) were consistently up-regulated in curcumin-pretreated mice. Our study confirmed the antagonistic roles of curcumin to counteract radiation-induced cerebral injury in vivo and suggested that the potent Nrf2 activation capability might be valuable for the protective effects of curcumin against radiation. This provides a potential useful radioprotection dietary component for human populations.

Mesenchymal stem cells restore cortical rewiring after neonatal ischemia in mice

OBJECTIVE

A study was undertaken to investigate the effect of neonatal hypoxic-ischemic (HI) brain damage and mesenchymal stem cell (MSC) treatment on the structure and contralesional connectivity of motor function-related cerebral areas.

METHODS

Brain remodeling after HI±MSC treatment in neonatal mice was analyzed using diffusion tensor magnetic resonance imaging, immunohistochemistry, anterograde tracing with biotinylated dextran amine (BDA), and retrograde tracing with fluorescent pseudorabies virus (PRV).

RESULTS

MSC treatment after HI reduced contralesional rewiring taking place after HI. Following MSC treatment, fractional anisotropy values, which were increased in both ipsi- and contralesional cortices and decreased in the corpus callosum (CC) after HI, were normalized to the level observed in sham-operated mice. These results were corroborated by myelin basic protein intensity and staining pattern in these areas. Anterograde tracing of ipsilesional motor neurons showed that after MSC treatment, fewer BDA-positive fibers crossed the CC and extended into the contralesional motor cortex compared to HI mice. This remodeling was functional, because retrograde labeling showed increased connectivity between impaired (left) forepaw and the contralesional (left) motor cortex after HI, whereas MSC treatment reduced this connection and increased the connection between the impaired (left) forepaw and the ipsilesional (right) motor cortex. Finally, the extent of contralesional rewiring measured with BDA and PRV tracing was related to sensorimotor dysfunction.

INTERPRETATION

This is the first study to describe MSC treatment after neonatal HI markedly reducing contralesional axonal remodeling induced by HI brain injury.

Unilateral hemispherectomy at adulthood asymmetrically affects motor performance of male Swiss mice

Evidence exists indicating that cerebral lateralization is a fundamental feature of all vertebrates. In humans, a series of studies demonstrated that the left hemisphere plays a major role in controlling movement. No such asymmetries have been identified in rodents, in spite of the fact that these animals have been frequently used in studies assessing motor behavior. In this regard, here, we used unilateral hemispherectomy to study the relative importance of each hemisphere in controlling movement. Adult Swiss mice were submitted to right unilateral hemispherectomy (RH), left unilateral hemispherectomy (LH) or sham surgery. Fifteen days after surgery, motor performance was assessed in the accelerating rotarod test and in the foot-fault test (in which performance depends on skilled limb use) and in the elevated body swing test (in which performance depends on trunk movements). The surgical removal of the right hemisphere caused a more pronounced impairment in performance than the removal of the left hemisphere both in the rotarod and in the foot-fault tests. In the rotarod, the RH group presented smaller latencies to fall than both LH and sham groups. In the foot-fault test, while both the sham and the LH groups showed no differences between left and right hind limbs, the RH group showed significantly worse performance with the left hind limb than with the right one. The elevated body swing test revealed a similar impairment in the two hemispherectomized groups. Our data suggest a major role of the right hemisphere in controlling skilled limb movements in mice.

Strain differences in behavioral and cellular responses to perinatal hypoxia and relationships to neural stem cell survival and self-renewal: Modeling the neurovascular niche

Premature infants have chronic hypoxia, resulting in cognitive and motor neurodevelopmental handicaps caused by suboptimal neural stem cell (NSC) repair/recovery in neurogenic zones (including the subventricular and the subgranular zones). Understanding the variable central nervous system repair response is crucial to identifying "at risk" infants and to increasing survival and clinical improvement of affected infants. Using mouse strains found to span the range of responsiveness to chronic hypoxia, we correlated differential NSC survival and self-renewal with differences in behavior. We found that C57BL/6 (C57) pups displayed increased hyperactivity after hypoxic insult; CD-1 NSCs exhibited increased hypoxia-induced factor 1alpha (HIF-1alpha) mRNA and protein, increased HIF-1alpha, and decreased prolyl hydroxylase domain 2 in nuclear fractions, which denotes increased transcription/translation and decreased degradation of HIF-1alpha. C57 NSCs exhibited blunted stromal-derived factor 1-induced migratory responsiveness, decreased matrix metalloproteinase-9 activity, and increased neuronal differentiation. Adult C57 mice exposed to hypoxia from P3 to P11 exhibited learning impairment and increased anxiety. These findings support the concept that behavioral differences between C57 and CD-1 mice are a consequence of differential responsiveness to hypoxic insult, leading to differences in HIF-1alpha signaling and resulting in lower NSC proliferative/migratory and higher apoptosis rates in C57 mice. Information gained from these studies will aid in design and effective use of preventive therapies in the very low birth weight infant population.

Hypoxic injury during neonatal development in murine brain: correlation between in vivo DTI findings and behavioral assessment

Preterm birth results in significant neurodevelopmental disability. A neonatal rodent model of chronic sublethal hypoxia (CSH), which mimics effects of preterm birth, was used to characterize neurodevelopmental consequences of prolonged exposure to hypoxia using tissue anisotropy measurements from diffusion tensor imaging. Corpus callosum, cingulum, and fimbria of the hippocampus revealed subtle, yet significant, hypoxia-induced modifications during maturation (P15-P51). Anisotropy differences between control and CSH mice were greatest at older ages (>P40) in these regions. Neither somatosensory cortex nor caudate putamen revealed significant differences between control and CSH mice at any age. We assessed control and CSH mice using tests of general activity and cognition for behavioral correlates of morphological changes. Open-field task revealed greater locomotor activity in CSH mice early in maturation (P16-P18), whereas by adolescence (P40-P45) differences between control and CSH mice were insignificant. These results may be associated with lack of cortical and subcortical anisotropy differences between control and CSH mice. Spatial-delayed alternation and free-swim tasks in adulthood revealed lasting impairments for CSH mice in spatial memory and behavioral laterality. These differences may correlate with anisotropy decreases in hippocampal and callosal connectivities of CSH mice. Thus, CSH mice revealed developmental and behavioral deficits that are similar to those observed in low birth weight preterm infants.

Neonatal transection of the corpus callosum affects rotational side preference in adult Swiss mice

In order to test the hypothesis that the ontogenetic development of the corpus callosum (CC) contributes to the establishment of behavioral lateralization, the rotatory behavior in the free-swimming test was studied in male Swiss mice that were subjected to mid-sagittal transection of the CC during the first postnatal day. At adulthood, 16 Acallosal and 30 Sham-operated mice were submitted to 3 sessions of the free-swimming rotatory test (diameter of the recipient=21 cm; session duration=5 min; inter-test interval=48 h). The number and direction of 30 degrees turns were recorded. Our results indicate that transected animals became progressively more lateralized than Sham ones from the first to the third session. This difference between groups was explained mainly by the more pronounced reduction in turning activity to the non-preferred side along the sessions that was observed in Acallosal mice. Our results give further support to the hypothesis that the normal development of the CC is related to the establishment of brain asymmetries in general and behavioral lateralization in particular.

Unilateral hemispherectomy at adulthood asymmetrically affects immobile behavior of male Swiss mice

In order to test the hypothesis that behavioral coping with stressful situations is asymmetrically modulated by the hemispheres, we used the unilateral hemispherectomy procedure to assess the relative importance of each hemisphere in the determination of the immobility time during the forced swimming test. Under anesthesia, adult Swiss male mice were submitted to unilateral (right or left) hemispherectomy or sham surgery. Fifteen days after surgery, the immobile and turning behaviors of each mouse were measured during a 5-min forced swimming testing session. In general, while turning activity decreased significantly as the test progressed, an increase in immobility was observed. The unilateral hemispherectomy asymmetrically affected the immobility time in the forced swimming test. Particularly, the increase in immobility time of right-hemispherectomized mice was greater than that observed for sham-operated ones. In contrast, there were no differences in turning activity between the groups. The higher immobility time in males that had their right hemisphere removed supports the hypothesis that the two hemispheres contribute differentially to the behavioral response to stress.

Early callosal absence disrupts the establishment of normal neocortical structure in Swiss mice

In the present study, we tested the hypothesis that the ontogenetic development of the corpus callosum is relevant for the establishment of a normal neocortical structure. To that effect, neocortical morphology (thickness and neuronal density) was analyzed in adult Swiss mice rendered acallosal by midline transection at the first postnatal day (Acallosal group) and in non-manipulated mice. The neocortical thicknesses and neuronal densities of layers II+III through VI were measured in area 6 and at the 17/18a border, both of which present abundant callosal inputs, and in the relatively acallosal area 17. For the thickness measure, significant differences between Non-manipulated and Acallosal groups were only found in the areas that receive massive callosal connections. In area 6, Acallosal mice presented a reduced thickness of layer V, while at the 17/18a border, these mice presented a reduced thickness of layers II+III when compared to non-manipulated ones. No statistical difference between acallosal and non-manipulated mice was found regarding the neuronal density measure. The reduced cortical thickness associated with a comparatively normal neuronal density in neocortical regions which normally have abundant callosal connections suggest a reduction in the number of cortical neurons in acallosal mice. Altogether, the present data indicate that the input provided by callosal axons is necessary for the normal development of the neocortex.