Effects of neonatal hypoxic-ischemic brain injury on skilled motor tasks and brainstem function in adult rats

Animal models for neonatal brain injury induced by hypoxic ischemic conditions in rodents

Neonatal hypoxia-ischemia and resulting encephalopathies are of significant concern. Intrapartum asphyxia is a leading cause of neonatal death globally. Among surviving infants, there remains a high incidence of hypoxic-ischemic encephalopathy due to neonatal hypoxic-ischemic brain injury, manifesting as mild conditions including attention deficit hyperactivity disorder, and debilitating disorders such as cerebral palsy. Various animal models of neonatal hypoxic brain injury have been implemented to explore cellular and molecular mechanisms, assess the potential of novel therapeutic strategies, and characterize the functional and behavioural correlates of injury. Each of the animal models has individual advantages and limitations. The present review looks at several widely-used and alternative rodent models of neonatal hypoxia and hypoxia-ischemia; it highlights their strengths and limitations, and their potential for continued and improved use.

Impact of mild traumatic brain injury on auditory brain stem dysfunction in mouse model

The auditory brainstem response (ABR) is an electrophysiological test that examines the functionality of the auditory nerve and brainstem. Traumatic brain injury (TBI) can be detected if prolonged peak latency is observed in ABR measurements, since latency measures the neural conduction time in the brainstem, and an increase in latency can be a sign of pathological lesion at the auditory brainstem level. The ABR is elicited by brief sounds that can be used to measure hearing sensitivity as well as temporal processing. Reduction in peak amplitudes and increases in latency are indicative of dysfunction in the auditory nerve and/or central auditory pathways. In this study we used sixteen young adult mice that were divided into two groups: sham and mild traumatic brain injury (mTBI), with ABR measurements obtained prior to, and at 2, 6, and 14 weeks after injury. Abnormal ABRs were observed for the nine TBI cases as early as two weeks after injury and the deficits lasted for fourteen weeks after injury. Results indicated a significant reduction in the Peak 1 (P1) and Peak 4 (P4) amplitudes to the first noise burst, as well as an increase in latency response for P1 and P4 following mTBI. These results are the first to demonstrate auditory sound processing deficits in a rodent model of mild TBI.

Neonatal Hypoxia Ischaemia: Mechanisms, Models, and Therapeutic Challenges

Neonatal hypoxia-ischaemia (HI) is the most common cause of death and disability in human neonates, and is often associated with persistent motor, sensory, and cognitive impairment. Improved intensive care technology has increased survival without preventing neurological disorder, increasing morbidity throughout the adult population. Early preventative or neuroprotective interventions have the potential to rescue brain development in neonates, yet only one therapeutic intervention is currently licensed for use in developed countries. Recent investigations of the transient cortical layer known as subplate, especially regarding subplate's secretory role, opens up a novel set of potential molecular modulators of neonatal HI injury. This review examines the biological mechanisms of human neonatal HI, discusses evidence for the relevance of subplate-secreted molecules to this condition, and evaluates available animal models. Neuroserpin, a neuronally released neuroprotective factor, is discussed as a case study for developing new potential pharmacological interventions for use post-ischaemic injury.

Transient evoked otoacoustic emissions and auditory brainstem response in infants with perinatal asphyxia

OBJECTIVE

The objective of this study was to verify the effects of perinatal asphyxia on different parts of the auditory system.

METHODS

This was a non-concurrent cohort study conducted on a fixed population in a tertiary public hospital. Participants included 181 infants born at term who underwent the transient evoked otoacoustic emission test as a part of a neonatal hearing screening program, with a "pass" result in both ears, and by auditory brainstem response testing. The infants were divided into 3 groups: G1, 20 infants who had perinatal asphyxia; G2, 111 infants with an Apgar score lower than 4 in the first minute and/or lower than 6 in the fifth minute (called "low Apgar" at birth); and G3, 50 infants with first- and fifth-minute Apgar scores ≥7.

RESULTS

The signal-to-noise ratio of transient evoked otoacoustic emissions were greater in G3 compared with G1 and G2 at 4 kHz frequency for males. An increased latency of waves I and III in the auditory brainstem response of male infants in G1 was observed.

CONCLUSION

This study demonstrated that alterations occurred in both the cochlear and the neural components in male infants who had perinatal asphyxia.

Rodent Hypoxia-Ischemia Models for Cerebral Palsy Research: A Systematic Review

Cerebral palsy (CP) is a complex multifactorial disorder, affecting approximately 2.5-3/1000 live term births, and up to 22/1000 prematurely born babies. CP results from injury to the developing brain incurred before, during, or after birth. The most common form of this condition, spastic CP, is primarily associated with injury to the cerebral cortex and subcortical white matter as well as the deep gray matter. The major etiological factors of spastic CP are hypoxia/ischemia (HI), occurring during the last third of pregnancy and around birth age. In addition, inflammation has been found to be an important factor contributing to brain injury, especially in term infants. Other factors, including genetics, are gaining importance. The classic Rice-Vannucci HI model (in which 7-day-old rat pups undergo unilateral ligation of the common carotid artery followed by exposure to 8% oxygen hypoxic air) is a model of neonatal stroke that has greatly contributed to CP research. In this model, brain damage resembles that observed in severe CP cases. This model, and its numerous adaptations, allows one to finely tune the injury parameters to mimic, and therefore study, many of the pathophysiological processes and conditions observed in human patients. Investigators can recreate the HI and inflammation, which cause brain damage and subsequent motor and cognitive deficits. This model further enables the examination of potential approaches to achieve neural repair and regeneration. In the present review, we compare and discuss the advantages, limitations, and the translational value for CP research of HI models of perinatal brain injury.

Antioxidant Treatments Recover the Alteration of Auditory-Evoked Potentials and Reduce Morphological Damage in the Inferior Colliculus after Perinatal Asphyxia in Rat

Maturation of the auditory pathway is dependent on the central nervous system myelination and it can be affected by pathologies such as neonatal hypoxic ischemic (HI) encephalopathy. Our aim was to evaluate the functional integrity of the auditory pathway and to visualize, by histological and cellular methods, the damage to the brainstem using a neonatal rat model of HI brain injury. To carry out this morphofunctional evaluation, we studied the effects of the administration of the antioxidants nicotine, melatonin, resveratrol and docosahexaenoic acid after hypoxia-ischemia on the inferior colliculus and the auditory pathway. We found that the integrity of the auditory pathway in the brainstem was altered as a consequence of the HI insult. Thus, the auditory brainstem response (ABR) showed increased I-V and III-V wave latencies. At a histological level, HI altered the morphology of the inferior colliculus neurons, astrocytes and oligodendricytes, and at a molecular level, the mitochondria membrane potential and integrity was altered during the first hours after the HI and reactive oxygen species (ROS) activity is increased 12 h after the injury in the brainstem. Following antioxidant treatment, ABR interpeak latency intervals were restored and the body and brain weight was recovered as well as the morphology of the inferior colliculus that was similar to the control group. Our results support the hypothesis that antioxidant treatments have a protective effect on the functional changes of the auditory pathway and on the morphological damage which occurs after HI insult.

Adding 5 h delayed xenon to delayed hypothermia treatment improves long-term function in neonatal rats surviving to adulthood

BACKGROUND

We previously reported that combining immediate hypothermia with immediate or 2 h delayed inhalation of an inert gas, xenon, gave additive neuroprotection in rats after a hypoxic-ischemic insult, compared to hypothermia alone. Defining the therapeutic time window for this new combined intervention is crucial in clinical practice when immediate treatment is not always feasible. The aim of this study is to investigate whether combined hypothermia and xenon still provide neuroprotection in rats after a 5 h delay for both hypothermia and xenon.

METHODS

Seven-day-old Wistar rat pups underwent a unilateral hypoxic-ischemic insult. Pups received 5 h of treatment starting 5 h after the insult randomized between normothermia, hypothermia, or hypothermia with 50% xenon. Surviving pups were tested for fine motor function through weeks 8-10 before being euthanized at week 11. Their hemispheric and hippocampal areas were assessed.

RESULTS

Both delayed hypothermia-xenon and hypothermia-only treated groups had significantly less brain tissue loss than those which underwent normothermia. The functional performance after 1 wk and adulthood was significantly better after hypothermia-xenon treatment as compared to the hypothermia-only or normothermia groups.

CONCLUSION

Adding 50% xenon to 5 h delayed hypothermia significantly improved functional outcome as compared to delayed hypothermia alone despite similar reductions in brain area.

Early life versus lifelong oral manganese exposure differently impairs skilled forelimb performance in adult rats

Recent studies of children suggest that exposure to elevated manganese (Mn) levels disrupts aspects of motor, cognitive and behavioral functions that are dependent on dopamine brain systems. Although basal ganglia motor functions are well-known targets of adult occupational Mn exposure, the extent of motor function deficits in adults as a result of early life Mn exposure is unknown. Here we used a rodent model early life versus lifelong oral Mn exposure and the Montoya staircase test to determine whether developmental Mn exposure produces long-lasting deficits in sensorimotor performance in adulthood. Long-Evans male neonate rats (n=11/treatment) were exposed daily to oral Mn at levels of 0, 25, or 50mg Mn/kg/d from postnatal day (PND) 1-21 (early life only), or from PND 1-throughout life. Staircase testing began at age PND 120 and lasted 1month to objectively quantify measures of skilled forelimb use in reaching and pellet grasping/retrieval performance. Behavioral reactivity also was rated on each trial. Results revealed that (1) behavioral reactivity scores were significantly greater in the Mn-exposed groups, compared to controls, during the staircase acclimation/training stage, but not the latter testing stages, (2) early life Mn exposure alone caused long-lasting impairments in fine motor control of reaching skills at the higher, but not lower Mn dose, (3) lifelong Mn exposure from drinking water led to widespread impairment in reaching and grasping/retrieval performance in adult rats, with the lower Mn dose group showing the greatest impairment, and (4) lifelong Mn exposure produced similar (higher Mn group) or more severe (lower Mn group) impairments compared to their early life-only Mn exposed counterparts. Collectively, these results substantiate the emerging clinical evidence in children showing associations between environmental Mn exposure and deficits in fine sensorimotor function. They also show that the objective quantification of skilled motor performance using the staircase test can serve as a sensitive measure of early life insults from environmental agents. Supported by NIEHS R01ES018990.

Post-insult ibuprofen treatment attenuates damage to the serotonergic system after hypoxia-ischemia in the immature rat brain

There is currently no therapeutic intervention to stem neonatal brain injury after exposure to hypoxia-ischemia (HI). Potential neuroprotective treatments that can be delivered postinsult that target neuroinflammation and are safe to use in neonates are attractive. One candidate is ibuprofen. Ibuprofen is a nonsteroidal anti-inflammatory drug that inhibits cyclooxygenase enzymes and is used in neonates to treat patent ductus arteriosus. We investigated whether ibuprofen can inhibit neuroinflammation and attenuate neuronal damage manifested in a rodent model of preterm HI. Postnatal day 3 (P3) rat pups were subjected to HI (right carotid artery ligation, 30 minutes 6% O₂). Ibuprofen was then administered daily for 1 week (100 mg/kg P3 2 hours after HI, 50 mg/kg P4-P9; subcutaneously). Ibuprofen treatment prevented the P3 HI-induced reductions in brain serotonin levels, serotonin transporter expression, and numbers of serotonergic neurons in the dorsal raphé nuclei on P10. Ibuprofen also significantly attenuated P3 HI-induced increases in brain cyclooxygenase 2 protein expression, interleukin-1β, and tumor necrosis factor levels, as well as the increase in numbers of activated microglia. Thus, ibuprofen administered after an HI insult may be an effective pharmacologic intervention to reduce HI-induced neuronal brain injury in the preterm neonate by limiting the effects of neuroinflammatory mediators.

Disruption of raphé serotonergic neural projections to the cortex: a potential pathway contributing to remote loss of brainstem neurons following neonatal hypoxic-ischemic brain injury

Neuronal injury is a key feature of neonatal hypoxic-ischemic (HI) brain injury. However, the mechanisms underpinning neuronal losses, such as in the brainstem, are poorly understood. One possibility is that disrupted neural connections between the cortex and brainstem may compromise the survival of neuronal cell bodies in the brainstem. We investigated whether brainstem raphé serotonergic neurons that project to the cortex are lost after HI. We also tested if neuroinflammation has a role in disrupting brainstem raphé projections. Postnatal day 3 (P3) rats underwent unilateral carotid artery ligation followed by hypoxia (6% oxygen for 30 min). A retrograde tracer, choleratoxin b, was deposited in the motor cortex on P38. On P45 we found that retrogradely labelled neurons in the dorsal raphé dorsal, ventrolateral, interfascicular, caudal and ventral nuclei were lost after P3 HI. All retrogradely labelled neurons in the raphé nuclei were serotonergic. Numbers of retrogradely labelled neurons were also reduced in the ventromedial thalamus and basolateral amygdala. Minocycline treatment (45 mg/kg 2 h post-HI, 22.5 mg/kg daily P4-P9) attenuated losses of retrogradely labelled neurons in the dorsal raphé ventrolateral, interfascicular and ventral raphé nuclei, and the ventromedial thalamus. These results indicate that raphé neurons projecting to the cortex constitute a population of serotonergic neurons that are lost after P3 HI. Furthermore, neuroinflammation has a role in the disruption of raphé and thalamic neural projections. Future studies investigating the cellular mechanisms of axonal degeneration may reveal new targets for interventions to prevent neuronal losses after neonatal HI.

Neuroprotective potential of erythropoietin and its derivative carbamylated erythropoietin in periventricular leukomalacia

Periventricular leukomalacia (PVL) is the predominant pathology in premature infants, characterized by prominent cerebral white matter injury, and commonly caused by hypoxia-ischemia and inflammation. Activated microglia trigger white matter damage and play a major role in the development of PVL. Erythropoietin (EPO) and its derivative carbamylated erythropoietin (CEPO) have been shown to be neuroprotective in several brain disease models. Here we investigated whether EPO and CEPO could provide protection in mouse models of PVL induced by hypoxia-ischemia or hypoxia-ischemia-inflammation. We administered EPO or CEPO to mice with PVL, and found that both EPO and CEPO treatments decreased microglia activation, oligodendrocyte damage and myelin depletion. We also noted improved performance in neurological function assays. Inhibited disease progression in PVL mice by EPO or CEPO treatment was associated with decreased poly-(ADP-ribose) polymerase-1 (PARP-1) activity. PARP-1 activity was increased dramatically in activated microglia in untreated mice with PVL. Furthermore, we demonstrated that the neuroprotective properties of EPO and CEPO were diminished after PARP-1 gene depletion. The therapeutic doses of EPO and CEPO used in this study did not interfere with normal oligodendrocyte maturation and myelination. Together, our data demonstrate that EPO and CEPO are neuroprotective in cerebral white matter injury via a novel microglial PARP-1 dependent mechanism, and hold promise as a future treatment for PVL and other hypoxic-ischemic/inflammatory white matter diseases.

Impairment of perinatal hypoxia-ischemia to the preterm brainstem

Hypoxia-ischemia is a major perinatal problem that results in severe damage to the newborn brain. This study assessed functional integrity of the brainstem at term in preterm infants after perinatal hypoxia-ischemia to shed light on the influence of hypoxia-ischemia on the preterm brainstem. We recruited sixty-eight preterm infants after perinatal hypoxia-ischemia, ranging in gestation 28-35 weeks. Brainstem evoked response was studied at term age (37-42 weeks postconceptional age) with 91-910/s clicks using the maximum length sequence technique. Compared with healthy preterm infants, the preterm infants after perinatal hypoxia-ischemia showed a significant increase in I-V interval at very high rates 455 and 910/s of clicks (P<0.05, 0.05). III-V interval and III-V/I-III interval ratio also increased significantly at 455 and 910/s (P<0.05-0.01). The slope of III-V interval-rate function was significantly steeper than in the healthy preterm infants (P<0.05). Compared with normal term controls, the preterm infants after hypoxia-ischemia showed similar, but slightly more significant, abnormalities. The differences between the preterm infants after hypoxia-ischemia and the healthy preterm and term infants generally increased with increasing click rate. These results demonstrated that central components of brainstem auditory evoked response were abnormal at very high click rates in the preterm infants after perinatal hypoxia-ischemia. Click rate-dependent change in the more central part of the brainstem is also abnormal. Apparently, functional integrity of the brainstem, mainly in the more central part, is impaired. Hypoxic-ischemic damage to the preterm brainstem is unlikely to completely recover within a relatively short period after the insult, which is of clinical importance.

17beta-estradiol protects against hypoxic/ischemic white matter damage in the neonatal rat brain

Developing oligodendrocytes (pre-OLs) are highly vulnerable to hypoxic-ischemic injury and associated excitotoxicity and oxidative stress. 17beta-Estradiol plays an important role in the development and function of the CNS and is neuroprotective. The sudden drop in circulating estrogen after birth may enhance the susceptibility of developing OLs to injury. Estrogen receptor (ER)-alpha and ER-beta are both expressed in OLs. We examined the effect of 17beta-estradiol on oxygen-glucose deprivation and oxidative stress-induced cell death in rat pre-OLs in vitro and on hypoxic-ischemic brain injury in vivo. Pre-OLs in culture were subjected to oxygen-glucose deprivation (OGD) or glutathione depletion in the presence or absence of 17beta-estradiol. LDH release, the Alamar blue assay, and phase-contrast microscopy were used to assess cell viability. Hypoxic-ischemic injury was generated in 6-day-old rats (P6) by unilateral carotid ligation and hypoxia (6% O(2) for 1 hr). Rat pups received one intraperitoneal injection of 300 or 600 microg/kg 17beta-estradiol or vehicle 12 hr prior to the surgical procedure. Injury was assessed by myelin basic protein (MBP) immunocytochemistry at P10. 17beta-Estradiol produced significant protection against OGD-induced cell death in primary OLs (EC(50) = 1.3 +/- 0.46 x 10(-9) M) and against oxidative stress. Moreover, 17beta-estradiol attenuated the loss of MBP labeling in P10 pups ipsilateral to the carotid ligation. These results suggest a potential role for estrogens in attenuation of hypoxic-ischemic and oxidative injury to developing OLs and in the prevention of periventricular leukomalacia.

Neonatal rat hypoxia-ischemia: long-term rescue of striatal neurons and motor skills by combined antioxidant-hypothermia treatment

Perinatal hypoxia-ischemia can cause long-term neurological and behavioral disability. Recent multicenter clinical trials suggest that moderate hypothermia, within 6 h of birth, offers significant yet incomplete protection. We investigated the effect of combined treatment with the antioxidant N-tert-butyl-(2-sulfophenyl)-nitrone (S-PBN) and moderate hypothermia on long-term neuronal injury and behavioral disability. S-PBN or its diluent was administered 12-hourly to rats from postnatal day (PN) 7 to 10. On PN8, hypoxia-ischemia was induced. Immediately post-hypoxia, additional S-PBN and 6 h of moderate hypothermia or additional diluent and 6 h of normothermia were administered. At 1 week, and at 11 weeks, after hypoxia-ischemia, the absolute number of surviving medium-spiny neurons was measured in the coded right striatum. In a separate experiment, skilled forepaw ability was investigated in coded 9- to 11-week-old rats. Normal, uninjured animals were also tested for motor skills at 9- to 11-weeks-of-age. The combination of S-PBN and moderate hypothermia provided statistically significant short- and long-term protection of the striatal medium-spiny neurons to normal control levels. This combinatorial treatment also preserved fine motor skills to normal control levels. The impressive histological and functional preservation suggests that S-PBN and moderate hypothermia is a safe and attractive combination therapy for perinatal hypoxia-ischemia.

Quantitative measurement of neurological deficit after mild (30 min) transient middle cerebral artery occlusion in rats

Although 30-min transient middle cerebral artery occlusion (30-min tMCAo) causes reproducible subcortical infarction in rats, it is difficult to evaluate the resulting neurological deficit using common behavioral tests such as the rota-rod test, adhesive-removal test, or narrow beam test. Establishment of a method of quantitative evaluation would help to develop a novel therapeutic approach to treat cerebral infarction. To solve this problem, we examined whether the neurological deficit could be detected by the Montoya staircase test or methamphetamine-induced rotation, which are commonly used in a Parkinson disease model induced by intrastriatal injection of 6-hydroxydopamine (6-OHDA). From 10 to 14 days after tMCAo, the Montoya staircase test showed significant clumsiness in forelimb tasks contralateral to the lesion side, whereas sham-operated rats showed no significant clumsiness in both forelimbs. The number of ipsilateral rotations induced by methamphetamine was also increased in tMCAo-rats at 21 days after tMCAo. Although Pearson's correlations coefficient showed that the results of these tests were correlated with the infarction volume, there was no significant correlation between the results of these two tests. These findings imply that the neurological deficit detected by both tests might reflect the severity of ischemic injury, but each test might evaluate different aspects of neurological deficit. Thus, the Montoya staircase test and methamphetamine-induced rotation are useful to evaluate neurological deficit in the chronic stage of subcortical infarction induced by 30-min tMCAo.

Brainstem auditory evoked response in neonatal neurology

Over the last three decades, the brainstem auditory evoked response (BAER) has been used to assess functional integrity and development of the auditory system and the brain in conditions that affect the brainstem auditory pathway. As a non-invasive objective test, BAER is particularly suitable in very young or sick infants. It is the major tool to detect hearing impairment in high-risk infants, and a component in universal hearing screening. BAER is also a valuable adjunct to detect neurological impairment in many developmental disorders and functional abnormalities in a range of neurological diseases. The maximum length sequence (MLS) technique has recently been incorporated into neonatal BAER study. Recent results indicate that the MLS has the potential to improve the diagnostic value of BAER in some clinical situations, although the wider utility of this relative new technique remains to be further explored.

Post-ischemic hypothermia reduced IL-18 expression and suppressed microglial activation in the immature brain

Inflammation is an important factor for hypoxia-ischemia (HI) brain injury. Interleukin (IL)-18 is a proinflammatory cytokine which may be a contributor to injury in the immature brain after HI. To investigate the effects of post-HI hypothermia on IL-18 in the developing brain, 7-day-old rats were subjected to left carotid artery ligation followed by 8% oxygen for 60 min and divided into a hypothermia group (rectal temperature 32 degrees C for 24 h) and a normothermia group (36 degrees C for 24 h). The IL-18 mRNA was analyzed with real-time RT-PCR, and the protein level was analyzed by Western blot, and the location and source of IL-18 were assessed by immunohistochemistry. The significant increase of the IL-18 mRNA was observed in the ipsilateral hemispheres of the normothermia group at 24 h and 72 h after HI compared with controls, but the level in the ipsilateral hemispheres of the hypothermia group was significantly reduced at both time points, compared with the normothermia group, respectively. The IL-18 protein level in the ipsilateral hemispheres of the normothermia group significantly increased at 72 h after HI compared with controls, however, the protein level of the hypothermia group was significantly decreased, compared with the normothermia group. IL-18-positive cells were observed throughout the entire cortex, corpus callosum (CC) and striatum in the ipsilateral hemispheres of normothermia group at 72 h after HI, however, little positive cells were observed in the hypothermia group. Double labeling immunostaining found that most of the IL-18-positive cells were colocalized with lectin, which is a marker of microglia. The number of ameboid microglia (AM) in the normothermia group was significantly increased in cortex and CC, compared with the number in controls, but there were very few ramified microglia (RM) in these areas. In contrast, the number of AM in the hypothermia group was significantly decreased in cortex and CC, compared with the number in the normothermia group, and there were no significant differences in the number of AM and RM between the hypothermia group and controls. In conclusion, we found that IL-18 mRNA and the protein level were attenuated by post-HI hypothermia and that post-HI hypothermia may decrease microglia activation in the developing brain.

Long-term neuroprotective effects of carbon dioxide on neonatal rat hypoxic-ischemic brain injury: an experimental study of skilled motor tasks

OBJECTIVE

This study was undertaken to investigate the long-term effect of hypercapnia on neonatal hypoxic-ischemic brain injury, we tested its effect in a neonatal rat hypoxia-ischemia model.

STUDY DESIGN

The rats were subjected to unilateral carotid artery ligation and exposure to 8% oxygen for 30 minutes. Six percent carbon dioxide was administered to the neonatal rats during unilateral hypoxia-ischemia, and the motor function and neurologic outcomes were determined 3 months later.

RESULTS

Significant motor functional improvement was observed in the hypercapnic animals, as judged by the Montoya staircase test. The unilateral brain injury was significantly ameliorated in the hypercapnic animals, and this amelioration was well correlated with the motor functional performance. Cerebral blood flow during hypoxia-ischemia, monitored by laser Doppler flowmetry, was better preserved in the hypercapnic animals.

CONCLUSION

Our results suggest that mild hypercapnia during hypoxia-ischemia may provide long-lasting motor functional as well as neurologic protection for immature brains, possibly by increasing cerebral blood flow during hypoxia.

Colour-coded pellets increase the sensitivity of the staircase test to differentiate skilled forelimb performances of control and 6-hydroxydopamine lesioned rats

The Montoya staircase test has previously been used to study the skilled forelimb performance of mice and rats following lesions and cell implants in different parts of the central nervous system. Here we describe a modification of the original test design which introduces differently coloured food pellets for each step, and present the results of the new and modified method. In this study unilaterally 6-hydroxydopamine (6-OHDA) lesioned rats and healthy control rats were used. The new evaluation of reaching and grasping movements takes into consideration the various levels of reaching difficulty. The coloured food pellets code for different steps of the staircase. The comparison between the original versus the modified test methods revealed significant differences most prominently on the lower steps. It is important to notice that the pattern of grasping movements in the hemiparkinsonian rats changes from precise reaching (prior to lesion) to shuffling and unsuccessfully trying to reach pellets. The observation of this change in behaviour would not have been obtained through the evaluation of the original staircase test. In summary, the modified staircase test introduces a colour-coded pellet system which obviously increases the test sensitivity and discloses new insights into the skilled forelimb use in a rat model of Parkinson's disease. It may therefore become a valuable tool in future studies related to plasticity-induced changes in skilled forelimb reaching and grasping movements.

Evaluation of neuronal damage following hypoxic–ischaemic brain injury in acute and early chronic periods in neonatal rats

This study was undertaken to investigate the effects of neonatal cerebral hypoxic-ischaemic brain injury (HIBI) in acute and early chronic phases in the rat. HIBI was induced in 7-day-old rat pups by ligation of the right common carotid and then the pups were exposed to 1 h of hypoxia in 8% oxygen. They were divided into two groups: 1-day (acute phase, in the first 24 h) and 5-day (early chronic phase, 120 h). Neuropathological evaluation was performed using the hippocampus, cerebral cortex and basal ganglia on the coronal plane. The following values were obtained: (i) the ratio of the infarcted area; (ii) hemispheric atrophy/asymmetry; (iii) patchy lesions confined to the thalamus, caudate and putamen; (iv) the ratio of damaged neurons to all neurons; and (v) the percentage of apoptotic neurons relative to the total neurons in all brain areas. HIBI-induced global cerebral damage and cellular damage findings did not significantly differ between the two groups. However, they showed a tendency to recover/deteriorate in both acute and early chronic phases. The ratio of ipsi- and contra-lateral hemisphere infarct areas (20.7 and 15.7% vs. 40.1 and 26.7%, respectively), basal ganglia patchy lesion ratio (27.5 vs. 36.7%) and hemispheric atrophy/asymmetry (92.4 vs. 84.7%) were found to be lower in the rat pups in the chronic phase than those in the acute phase. In contrast, increases in the ratio of damaged neurons (16.7 vs. 13.3% in the cerebral and dorsal hippocampus, respectively) and in the ratio of apoptotic neurons (ipsi-lateral: 18 vs. 6%; contra lateral hemispheres: 3.5 vs. 1.7%, respectively) were recorded. It is concluded that cellular damage tends to deteriorate (damaged and apoptotic neurons) while global damage (cerebral infarct and patchy damage) improves with the progression of HIBI. However, further studies are needed in order to elucidate this process.

Perinatal anoxia degrades auditory system function in rats

Little is known about the neural bases of the reduced auditory and cortical processing speeds that have been recorded in language-impaired, autistic, schizophrenic, and other disabled human populations. Although there is strong evidence for genetic contributions to etiologies, epigenetic factors such as perinatal anoxia (PA) have been argued to be contributors, or causal, in a significant proportion of cases. In this article, we explored the consequences of PA on this elementary aspect of auditory behavior and on auditory system function in rats that were briefly perinatally anoxic. PA rats had increased acoustic thresholds and reduced processing efficiencies recorded in an auditory behavioral task. These rats had modestly increased interpeak intervals in their auditory brainstem responses, and substantially longer latencies in poststimulus time histogram responses recorded in the primary auditory cortex. The latter were associated with degraded primary auditory cortex receptive fields and a disrupted tonotopy. These processing deficits are consistent with the parallel behavioral and physiological deficits recorded in children and adults with a history of language-learning impairment and autism.

Persistent motor deficit following infusion of autologous blood into the periventricular region of neonatal rats

Periventricular hemorrhage (PVH) in the brain of premature infants is often associated with developmental delay and persistent motor deficits. Our goal is to develop a rodent model that mimics the behavioral phenotype. We hypothesized that autologous blood infusion into the periventricular germinal matrix region of neonatal rats would lead to immediate and long-term behavioral changes. Tail blood or saline was infused into the periventricular region of 1-day-old rats. Magnetic resonance (MR) imaging was used to demonstrate the hematoma. Rats with blood infusion, as well as saline and intact controls, underwent behavior tests until 10 weeks age. Blood-infused rats displayed significant delay in motor development (ambulation, righting response, and negative geotaxis) to 22 days of age. As young adults, they exhibited impaired ability to stay on a rotating rod and to reach for food pellets. MR imaging at 10 weeks demonstrated subsets of rats with normal appearing brains, focal cortical infarcts, or mild hydrocephalus. There was a good correlation between MR imaging and histological findings. Some rats exhibited periventricular heterotopia and/or subtle striatal abnormalities not apparent on MR images. We conclude that autologous blood infusion into the brain of neonatal rats successfully models some aspects of periventricular hemorrhage that occurs after premature birth in humans.

Neurological reflexes and early motor behavior in rats subjected to neonatal hypoxic-ischemic injury

Severe perinatal hypoxia-ischemia is an important cause of brain injury in both full-term and premature newborns, with a high risk of future behavioral and neurological deficits. The most commonly used animal model of neonatal hypoxia-ischemia is the unilateral ligation of the common carotid artery followed by exposure to hypoxia in 7-day-old rats. In spite of the wide use of this model, lot of contradictions and discrepancies exist between the results obtained by different laboratories regarding behavioral deficits and there are no data regarding the possible delay of the appearance of neurological reflexes and the time-course of reflex performances following neonatal hypoxic-ischemic injury in rats. In the present study we showed that neonatal hypoxia-ischemia retarded the development of somatic growth and several neurological reflexes (ear twitch, grasping, gait and negative geotaxis). Hypoxic animals also displayed retarded performance in righting, geotaxis and gait reflexes. Although hypoxic pups performed worse in most tests for motor coordination, they reached normal levels by 5 weeks of age except in the footfault test. In the open-field, hypoxic animals were generally more active, except at 3 weeks, when activity of normal pups increased enormously as well. Brain areas were significantly reduced in hypoxic animals, but no close correlation was found with behavioral deficits.

Developmental changes induced by graded prenatal systemic hypoxic–ischemic insults in rats

In infants, a common consequence of systemic perinatal insults is disruption of neonatal brain development. Such insults can cause cerebral palsy, cognitive delay, epilepsy and other chronic neurologic deficits in children. The mechanisms underlying disruption of brain development after perinatal insults are poorly defined. To mimic human systemic insults, a transient prenatal hypoxic-ischemic insult model was developed in rodents. Ischemic animals showed reproducible histological lesions including oligodendrocyte loss, gliosis, and axonal disruption. Ischemic animals displayed persistent postnatal loss of oligodendrocyte lineage cells and cortical neurons, decreased cell proliferation, increased cell death, elevated pro-inflammatory cytokine levels, and impaired motor skills as young adults. Progressive ischemic intervals produced a graded pattern of injury. This systemic rodent prenatal hypoxic-ischemic insult accurately models human perinatal brain injury in several important criteria, including functional association of altered brain development with motor delay, and consequently provides novel insights into the pathogenesis of human perinatal brain insults.

Effects of sensorimotor restriction and anoxia on gait and motor cortex organization: implications for a rodent model of cerebral palsy

Chronic or acute perinatal asphyxia (PA) has been correlated with the subsequent development of cerebral palsy (CP), a developmental neurological disorder characterized by spasticity and motor abnormalities often associated with cognitive deficits. Despite the prevalence of CP, an animal model that mimics the lifetime hypertonic motor deficits is still not available. In the present study, the consequences of PA on motor behavior, gait and organization of the primary motor cortex were examined in rats, and compared with the behavioral and neurological consequences of early postnatal movement-restriction with or without oxygen deprivation. Rats subjected to PA had mild increases in muscular tone accompanied by subtle differences in walking patterns, paralleled by significantly altered but relatively modest disorganization of their primary motor cortices. Movement-restricted rats, suffering PA or not, had reduced body growth rate, markedly increased muscular tone at rest and with active flexion and extension around movement-restricted joints that resulted in abnormal walking patterns and in a profoundly distorted representation of the hind limbs in the primary motor cortex. Within the sensorimotor-restricted groups, non-anoxic rats presented the most abnormal pattern and the greatest cortical representational degradation. This outcome further supports the argument that PA per se may represent a substrate for subtle altered motor behaviors, and that PA alone is sufficient to alter the organization of the primary motor cortex. At the same time, they also show that early experience-dependent movements play a crucial role in shaping normal behavioral motor abilities, and can make a powerful contribution to the genesis of aberrant movement abilities.

Glutamate receptor-mediated oligodendrocyte toxicity in periventricular leukomalacia: a protective role for topiramate

Periventricular leukomalacia is a form of hypoxic-ischemic cerebral white matter injury seen most commonly in premature infants and is the major antecedent of cerebral palsy. Glutamate receptor-mediated excitotoxicity is a predominant mechanism of hypoxic-ischemic injury to developing cerebral white matter. We have demonstrated previously the protective effect of AMPA-kainate-type glutamate receptor blockade in a rodent model of periventricular leukomalacia. The present study explores the therapeutic potential of glutamate receptor blockade for hypoxic-ischemic white matter injury. We demonstrate that AMPA receptors are expressed on developing human oligodendrocytes that populate fetal white matter at 23-32 weeks gestation, the period of highest risk for periventricular leukomalacia. We show that the clinically available anticonvulsant topiramate, when administered post-insult in vivo, is protective against selective hypoxic-ischemic white matter injury and decreases the subsequent neuromotor deficits. We further demonstrate that topiramate attenuates AMPA-kainate receptor-mediated cell death and calcium influx, as well as kainate-evoked currents in developing oligodendrocytes, similar to the AMPA-kainate receptor antagonist 6-nitro-7-sulfamoylbenzo-(f)quinoxaline-2,3-dione (NBQX). Notably, protective doses of NBQX and topiramate do not affect normal maturation and proliferation of oligodendrocytes either in vivo or in vitro. Taken together, these results suggest that AMPA-kainate receptor blockade may have potential for translation as a therapeutic strategy for periventricular leukomalacia and that the mechanism of protective efficacy of topiramate is caused at least in part by attenuation of excitotoxic injury to premyelinating oligodendrocytes in developing white matter.

Brain-stem auditory impairment during the neonatal period in term infants after asphyxia: dynamic changes in brain-stem auditory evoked response to clicks of different rates

OBJECTIVE

To explore dynamic changes in brain-stem auditory electrophysiology during the neonatal period in term infants after perinatal asphyxia.

METHODS

Sixty-eight term newborn infants who suffered asphyxia were studied on days 1, 3, 5, 7, 14 and 30 after birth. Brain-stem auditory evoked response (BAER) was recorded with clicks, delivered at 21, 51 and 91 s(-1) and > or =40 dB above BAER threshold of each subject.

RESULTS

During the neonatal period wave I latency in the infants after asphyxia increased slightly while later BAER components changed more significantly. On the first day after birth wave III and V latencies and I-V and III-V intervals increased significantly at all rates of clicks (ANOVA P<0.01-0.001). On day 3, the latencies and intervals increased further. III-V/I-III interval ratio increased at 51 and 91 s(-1), suggesting a relatively more significant increase in III-V interval than in I-III interval at higher rates. Thereafter, wave III and V latencies and all intervals decreased progressively, although these BAER variables were still significantly longer than in normal controls on days 5 and 7 (P<0.05-0.001) On day 30, all latencies and intervals approached near normal values, with a slight increase in wave V latency and I-V and III-V intervals at 51 and 91 s(-1).

CONCLUSIONS

Perinatal asphyxia has a major effect on central auditory function, resulting in acute impairment. The impairment progresses during the first 3 days and then tends towards recovery. By 1 month the impaired auditory function has largely returned to normal. Significant increase in click rates can moderately improve the detection of auditory impairment.

SIGNIFICANCE

After perinatal asphyxia early detection of hypoxic-ischaemic damage to the central auditory system and initialisation of neuroprotective and therapeutic measures during the first hours after birth are critical to prevent or reduce deterioration of central impairment.

Can Lateralizing Sensorimotor Deficits Be Identified after Neonatal Cerebral Hypoxia-Ischemia in Rats?

The neonatal rat model of unilateral cerebral hypoxia-ischemia (HI) is commonly used to test the efficacy of therapeutic strategies for prevention or treatment of stroke in the immature brain. Traditionally neuroprotection has been defined as reduction in tissue injury; there is growing interest in complementary functional assessment. Our objectives were to determine whether lateralizing performance deficits could be detected in two sensorimotor tests not previously used after neonatal HI, and to determine whether performance reflected the extent of tissue damage. Seven-day-old rats that underwent right carotid ligation followed by 1.5 h in 8% O2 and age-matched controls were tested for sensorimotor performance on postnatal day 35 (P35). We evaluated initial forepaw placement on the wall of a cylinder, and time taken to contact and remove adhesive stickers from the dorsum of each forepaw. Cortical, striatal and hippocampal damage severity was evaluated on P36 by calculating the contralateral-ipsilateral percent difference in regional areas. There was an inverse relationship between cortical and striatal damage severity and percent contralateral forepaw initiation in the cylinder. There was a direct linear relationship between damage severity and the delay from contact to removal of the contralateral sticker. These two tests revealed quantifiable contralateral sensorimotor deficits 4 weeks after unilateral neonatal cerebral HI in animals with cortical and striatal damage.

Time course of brainstem pathophysiology during first month in term infants after perinatal asphyxia, revealed by MLS BAER latencies and intervals

Dynamic changes in electrophysiology of brainstem auditory neurons during the first month after birth were studied in 51 term infants after perinatal asphyxia using maximum length sequence brainstem auditory evoked responses. The responses were recorded on d 1, 3, 5, 7, 10, 15, and 30 after birth. On d 1, wave III and V latencies and all interpeak intervals increased significantly at all repetition rates of clicks used (91-910/s), especially the higher rates (ANOVA, p < 0.05-0.0001). On d 3, all these latencies and intervals increased further and differed more significantly from the normal control subjects. Thereafter, the latencies and intervals decreased progressively. On d 7, wave V latency and all intervals still differed significantly from the control subjects. These dynamic changes were more significant at higher rates of clicks than at lower rates. On d 10 and 15, all intervals decreased significantly. On d 30, all wave latencies decreased to the values in the normal control subjects on the same day. The intervals also approached normal values, although the III-V and I-V intervals still increased slightly. These results indicate that hypoxic-ischemic brain damage persists during the first week, with a peak on d 3, and recovers progressively thereafter. By 1 mo, the damage has largely returned to normal. Maximum length sequence brainstem auditory evoked responses results correlated well with the stage of hypoxic-ischemic encephalopathy during the first week. The present study revealed a general time course of brainstem pathophysiology after asphyxia, although there were individual variations. Our findings can be used as a reference to monitor cerebral function and help judge the value of neuroprotective or therapeutic interventions. The first week, particularly the first 3 d, is a critical period of hypoxic-ischemic brain damage, and early intervention may prevent or reduce deterioration of the damage.

Long-term neuroprotective effects of hypothermia on neonatal hypoxic-ischemic brain injury in rats, assessed by auditory brainstem response

A method to assess long-term neurofunctional outcome of hypothermia on immature brains has not yet been clearly established. To investigate the effects of hypothermia on long-term neurofunctional outcome, we studied brainstem function using auditory brainstem response in adult rats after neonatal hypoxic-ischemic brain injury. Seven-day-old rats underwent a combination of left common carotid artery ligation and subsequent exposure to 8% O(2) for 1 h (n = 17). The rats were divided into three groups: hypothermia group (n = 6), normothermia group (n = 6), and sham control group (n = 5). During recovery from the hypoxic-ischemic insult, body temperature was reduced to 30 degrees C for 24 h in the hypothermia group, but was kept at 37 degrees C in the normothermia and sham control group. Three months later the rats were assessed by auditory brainstem response, then killed. The normothermia group showed increased III-V latencies and wave V abnormalities. Hypothermia significantly ameliorated wave V abnormalities. Injury to the ipsilateral inferior colliculus was also reduced in the hypothermia group compared with that in the normothermia group, and the degree of damage assessed histologically correlated well with auditory brainstem response findings. The current study demonstrates that postischemic hypothermia may provide effective and long-lasting neurofunctional as well as histopathologic protection to the immature brain.