Sensorimotor function and neuropathology five to six weeks after hypoxia-ischemia in seven-day-old rats

Local administration of glial cell line-derived neurotrophic factor improves behavioral and histological deficit of neonatal Erb's palsy in rats

OBJECTIVE

We sought to evaluate from a behavioral and histological viewpoint the effect of local administration of glial cell line-derived neurotrophic factor (GDNF) on neonatal preganglionic Erb's palsy in rats.

METHODS

The Erb's palsy model was produced by transecting the anterior and posterior roots of the left C5-C7 nerves of 7-day-old rats. The rats were divided into GDNF-treated (n = 10) and vehicle-treated groups (n = 11). After we transected the roots, contact in the proximal and distal stumps of the transected nerves was maintained, and the transected point and the entire intraspinal portion of the transected roots were enclosed by Gelfoam soaked with 10 micro g GDNF or saline. The behavioral evaluation consisted of a foot-fault test and a forepaw muscle strength test, all of which were performed from the third to the seventh weeks after the operation. Seven weeks after the operation, all rats were killed, the number of anterior horn cells was counted at C5-C7, and the differences on each side were compared.

RESULTS

In the vehicle-treated group, the foot-fault test indicated an abnormality in forelimb function on the root transection side. In the GDNF-treated group, however, significant improvement in forelimb function was observed on the basis of the foot-fault test results obtained in the third to sixth weeks after the operation. In the histological evaluation, the number of anterior horn cells from the side in which the operation took place in the vehicle-treated group was significantly less than that taken from the contralateral side at each segment. In the GDNF-treated group, however, there was no difference in any of the segments, regardless of the side from which they were taken.

CONCLUSION

Local administration of GDNF in a neonatal preganglionic Erb's palsy model resulted in significant improvement in deficits on the basis of behavioral and histological evaluations.

Neonatal cerebral hypoxia-ischemia causes lateralized memory impairments in the adult rat

Neonatal hypoxia-ischemia (HI) has been extensively studied in a rat model characterized by unilateral brain damage (Rice-Vannucci Model). However, as well as in humans, each rat brain hemisphere is distinctly involved in cognitive functions, as for example retrieval of emotionally based memory, and neurochemical asymmetries have been described. In this paper we investigated whether hypoxia-ischemia could cause distinct cognitive deficits depending on which hemisphere is damaged. Seven-day-old male Wistar rats were submitted to permanent occlusion of left or right common carotid artery and were exposed to a mixture of 8% oxygen-92% nitrogen for 2.5 h. On adulthood, these rats were trained in step-down inhibitory avoidance and in two tasks in the Morris water maze. Both experimental groups (right and left lesioned) showed a deficit of retrieval in the inhibitory avoidance task compared to controls, although rats with right hemisphere lesion showed a significantly greater deficit than the left damaged group (P<0.05). In the Morris maze, both damaged groups presented cognitive deficits in the reference memory task (P<0.05), however only the right damaged group had an impairment in the working memory task. Brain coronal areas, at levels +1.20 and -3.30 mm from bregma of both HI groups were smaller than those of control, with no differences between the right and left damaged groups (P<0.05). These results show that cerebral hypoxia-ischemia in neonatal rats causes asymmetric behavioral outcomes depending on which of the hemispheres is lesioned and support the hypothesis of lateralization of cognitive functions in the rodent brain.

Impact of perinatal asphyxia on the GABAergic and locomotor system

Perinatal asphyxia can cause neuronal loss and depletion of neurotransmitters within the striatum. The striatum plays an important role in motor control, sensorimotor integration and learning. In the present study we investigated whether perinatal asphyxia leads to motor deficits related to striatal damage, and in particular to the loss of GABAergic neurons. Perinatal asphyxia was induced in time-pregnant Wistar rats on the day of delivery by placing the uterus horns, containing the pups, in a 37 degrees C water bath for 20 min. Three motor performance tasks (open field, grip test and walking pattern) were performed at 3 and 6 weeks of age. Antibodies against calbindin and parvalbumin were used to stain GABAergic striatal projection neurons and interneurons, respectively. The motor tests revealed subtle effects of perinatal asphyxia, i.e. small decrease in motor activity. Analysis of the walking pattern revealed an increase in stride width at 6 weeks of age after perinatal asphyxia. Furthermore, a substantial loss of calbindin-immunoreactive (-22%) and parvalbumin-immunoreactive (-43%) cells was found in the striatum following perinatal asphyxia at two months of age. GABA(A) receptor autoradiography revealed no changes in GABA binding activity within the striatum, globus pallidus or substantia nigra. We conclude that perinatal asphyxia resulted in a loss of GABAergic projection neurons and interneurons in the striatum without alteration of GABA(A) receptor affinity. Despite a considerable loss of striatal neurons, only minor deficits in motor performance were found after perinatal asphyxia.

Intracisternal application of endotoxin enhances the susceptibility to subsequent hypoxic-ischemic brain damage in neonatal rats

Perinatal brain damage is associated not only with hypoxic-ischemic insults but also with intrauterine inflammation. A combination of antenatal inflammation and asphyxia increases the risk of cerebral palsy >70 times. The aim of the present study was to determine the effect of intracisternal (i.c.) administration of endotoxin [lipopolysaccharides (LPS)] on subsequent hypoxic-ischemic brain damage in neonatal rats. Seven-day-old Wistar rats were subjected to i.c. application of NaCl or LPS (5 microg/pup). One hour later, the left common carotid artery was exposed through a midline neck incision and ligated with 6-0 surgical silk. After another hour of recovery, the pups were subjected to a hypoxic gas mixture (8% oxygen/92% nitrogen) for 60 min. The animals were randomized to four experimental groups: 1) sham control group, left common carotid artery exposed but not ligated (n = 5); 2) LPS group, subjected to i.c. application of LPS (n = 7); 3) hypoxic-ischemic study group, i.c. injection of NaCl and exposure to hypoxia after ligation of the left carotid artery (n = 17); or 4) hypoxic-ischemic/LPS study group, i.c. injection of LPS and exposure to hypoxia after ligation of the left carotid artery (n = 19). Seven days later, neonatal brains were assessed for neuronal cell damage. In a second set of experiments, rat pups received an i.c. injection of LPS (5 microg/pup) and were evaluated for tumor necrosis factor-alpha expression by immunohistochemistry. Neuronal cell damage could not be observed in the sham control or in the LPS group. In the hypoxic-ischemic/LPS group, neuronal injury in the cerebral cortex was significantly higher than in animals that were subjected to hypoxia/ischemia after i.c. application of NaCl. Injecting LPS intracisternally caused a marked expression of tumor necrosis factor-alpha in the leptomeninges. Applying LPS intracisternally sensitizes the immature rat brain to a subsequent hypoxic-ischemic insult.

Posthemorrhagic ventricular dilation in the neonate: development and characterization of a rat model

Intraventricular hemorrhage is a common complication of prematurity. Posthemorrhagic ventricular dilation (PHVD) has a high rate of disability and no safe and effective treatment. Its pathogenesis is poorly understood, largely because of the lack of a satisfactory animal model. We have developed a model of neonatal PHVD in the rat. Seven-day-old (P7) Wistar rat pups were given 80-microl injections of citrated rat blood or artificial cerebrospinal fluid (CSF) into alternate lateral ventricles on P7 and P8. Intracranial pressure was monitored and increased briefly by over 8-fold. Some rats received further 10-microl intraventricular injections of India ink on P21. Animals were weighed daily and simple neurologic tests performed. On P21 (or P22 if India ink had been injected), the rats were perfusion-fixed and blocks processed for paraffin histology. Sixty-five percent of pups injected with blood and 50% injected with artificial CSF developed dilated lateral ventricles, with patchy loss of ependyma, marked astrocytic gliosis, and rarefaction of periventricular white matter. India ink injection revealed slow transit of CSF from the dilated lateral ventricles but eventual passage into the subarachnoid space. Pups that had received intraventricular injections but did not develop ventricular dilation nonetheless had lighter brains than littermate controls (p < 0.001). Body weights were not significantly different from controls. Hydrocephalic animals had reduced motor performance as assessed by a grip traction test (p = 0.0002). This model is well suited to studying the pathogenesis of PHVD.

Oxypurinol administration fails to prevent hypoxic-ischemic brain injury in neonatal rats

The purpose of the present study was to determine whether oxypurinol, a xanthine oxidase inhibitor, reduces free radicals and brain injury in the rat pup hypoxic-ischemia (HI) model. Seven-day-old rat pups had right carotid arteries ligated followed by 2.5h of hypoxia (8% oxygen). Oxypurinol or vehicle was administered by i.p. injection at 5 min after reoxygenation and once daily for 3 days. Brain damage was evaluated by weight deficit of the right hemisphere at 22 days following hypoxia. Oxypurinol treatments did not reduce weight loss in the right hemisphere. Brain weight loss in the right hemisphere were -26.2+/-3.6, -15.2+/-6.9, -21.7+/-4.4, -15.8+/-5.1, and -16.7+/-3.4% in vehicle (n=33), 10 (n=17), 20 (n=16), 40 (n=15), and 135 mg/kg (n=13) oxypurinol-treated groups (p>0.05), respectively. Brain thiobarbituric acid-reacting substances (TBARS) were assessed 3 and 6h after reoxygenation. Concentrations of TBARS rose 1.5-fold due to HI. Oxypurinol did not significantly reduce an HI-induced increase in brain TBARS. Thus, xanthine oxidase may not be the primary source of oxy-radicals in pup brain and as such oxypurinol does not prevent free radical-mediated lipid peroxidation or protect against brain injury in the neonatal rat HI model.

The influence of litter size on brain damage caused by hypoxic-ischemic injury in the neonatal rat

Hypoxic ischemia is a common cause of brain injury in the human neonate. This can be mimicked in the neonatal rat, but produces variable injury. The present study investigated the influence of litter size on the severity and variability of damage caused by hypoxic-ischemic injury in neonatal rats. Groups of 7-d-old pups from birth-sized litters (13-15 pups), or from litters culled to 10 on postnatal d 2, and 8- and 9-d-old pups from birth-sized litters, were exposed to common carotid artery occlusion and then, 3 h later, hypoxia (2 h 15 min, 8% oxygen). Damage was assessed histologically 72 h after injury, and graded (I-IV) according to severity. In nonculled litters, similar numbers of animals had each grade of injury. Most pups (70%) from culled litters had grade III or IV damage, and severity was significantly greater than in nonculled litters (p < 0.001). Pups from culled litters were heavier (17.6 +/- 0.4 g) than pups from nonculled litters (14.7 +/- 0.3 g, p < 0.0001). To determine whether this indicated that culled litters were more similar to older pups in their response to hypoxic-ischemic injury, we examined injury in 8- and 9-d-old pups of similar body weight to 7-d-old pups from culled litters. The severity and distribution of damage in the older pups was different from damage in the 7-d-old pups from culled litters. These data suggest that in 7-d-old rats, litter size influences damage caused by hypoxic-ischemic injury, and that the relationship between body weight, brain development, and susceptibility to hypoxic-ischemic injury is complex.

Drug-induced hypothermia begun 5 minutes after injury with a poly(adenosine 5'-diphosphate-ribose) polymerase inhibitor reduces hypoxic brain injury in rat pups

OBJECTIVE

Poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitors have shown promise in hypoxic ischemic brain damage. We wished to see if GPI-6150 (1,11b-dihydro-[2H]benzopyrano[4,3,2-de]isoquinolin-3-one), a specific PARP inhibitor, would reduce brain injury in a newborn animal model.

DESIGN

Randomized controlled trial.

SETTING

University laboratory.

SUBJECTS

Seven-day-old rat pups.

INTERVENTION

Subjects had the right carotid artery ligated and then received either vehicle or 5, 15, or 30 mg/kg GPI-6150 intraperitoneally 5 mins after the hypoxia. Hypoxia was produced by exposing the pups to 8% oxygen for 2.5 hrs.

MEASUREMENTS AND MAIN RESULTS

Twenty-two days later, the brains were scored from normal to severely damaged and were weighed by a blinded observer. Twenty-four of 53 (45%) vehicle-treated pups, 11 of 22 (50%) 5 mg/kg treated pups, 22 of 23 (96%) 15 mg/kg treated pups (p <.01 vs. vehicle), and 16 of 31 (52%) 30 mg/kg treated pups were scored as normal. Right hemisphere weight was reduced by 15 +/- 2.6% in the vehicle group, 5.9 +/- 2.8% in the 5 mg/kg group, -0.4 +/- 1.7% in the 15 mg/kg group (p <.01 vs. vehicle), and 13.3 +/- 3.1% in the 30 mg/kg group. GPI-6150 decreased rectal temperature from 33 +/- 0.4 to 29 +/- 0.7 degrees C for 3 hrs after dosing, but temperatures returned to normal by 6 hrs. We maintained the body temperature at 35 degrees C for 6 hrs after injury in a group of pups treated with 15 mg/kg. Nine of 25 (41%) vehicle-treated and 15 of 26 (58%) GPI-6150-treated pups were scored as normal (p = nonsignificant). Right hemisphere weight was reduced by 25 +/- 4% in the vehicle group and 20 +/- 5% in the GPI-6150 group (p = nonsignificant).

CONCLUSIONS

GPI-6150 at a dose of 15 mg/kg dramatically decreased the number of pups sustaining brain injury, relative to vehicle, but is dependent on an induced decrease in core temperature to produce the effect.

Agmatine suppresses nitric oxide production and attenuates hypoxic-ischemic brain injury in neonatal rats

Nitric oxide and excitatory amino acids contribute to hypoxic-ischemic brain injury. Agmatine, an endogenous neurotransmitter or neuromodulator, is an inhibitor of nitric oxide synthase and an antagonist of N-methyl-D-aspartate receptors. Does agmatine reduce brain injury in the rat pup hypoxic-ischemic model? Seven-day old rat pups had right carotid arteries ligated followed by 2.5 h of hypoxia (8% oxygen). Agmatine or vehicle was administered by i.p. injection at 5 min after reoxygenation and once daily thereafter for 3 d. Brain damage was evaluated by weight deficit of the right hemisphere at 22 d after hypoxia by a blinded observer. Agmatine treatments significantly reduced weight loss in the right hemisphere from -30.5 +/- 3.6% in vehicle-treated pups (n = 22) to -15.6 +/- 4.4% in the group treated with 50 mg/kg (n = 18, p < 0.05) and to -15.0 +/- 3.7% in the group treated with 100 mg/kg (n = 18, p < 0.05), but the group treated with 150 mg/kg showed no reduction. Other pups received agmatine or vehicle at 5 min after reoxygenation, and brain biochemistry was assessed. Levels of endogenous brain agmatine rose 2- to 3-fold owing to hypoxic-ischemic (3 h), whereas pups treated with agmatine (100 mg/kg) showed 50-fold higher brain agmatine levels (3 h). Agmatine (100 mg/kg) blocked a hypoxia-induced increase in brain nitric oxide metabolites at 6 h (vehicle-treated, +60.2 +/- 15.2%; agmatine-treated, +4.2 +/- 8.4%; p < 0.05). Agmatine thus reduces brain injury in the neonatal rat hypoxic-ischemic model, probably by blunting the rise in nitric oxide metabolites normally seen after hypoxia.

Hyperbaric oxygenation prevented brain injury induced by hypoxia-ischemia in a neonatal rat model

The occurrence of hypoxia-ischemia (HI) during early fetal or neonatal stages of an individual leads to the damaging of immature neurons resulting in behavioral and psychological dysfunctions, such as motor or learning disabilities, cerebral palsy, epilepsy or even death. No effective treatment is currently available and this study is the first to use hyperbaric oxygen (HBO) as a treatment for neonatal HI. Herein, we sought out to determine if HBO is able to offer neuroprotectivity against an HI insult. Seven-day-old rat pups were subjected to unilateral carotid artery ligation followed by 2.5 h of hypoxia (8% O(2) at 37 degrees C). HBO treatment was administered by placing pups in a chamber (3 ATA for 1 h) 1 h after hypoxia exposure. Brain injury was assessed based on ipsilateral hemispheric weight divided by contralateral hemispheric weight, light microscopy, and EM. Sensorimotor functional tests were administered at 5 weeks after hypoxia exposure. After HI, the ipsilateral hemisphere was 52.65 and 57.64% (P<0.001) of the contralateral hemisphere at 2 and 6 weeks, respectively. In HBO treated groups, the ipsilateral hemisphere was 77.77 and 84.19% (P<0.001) at 2 and 6 weeks. There was much less atrophy and apoptosis in HBO treated animals under light or electron microscopy. Sensorimotor function was also improved by HBO at 5 weeks after hypoxia exposure (Chi-square, P<0.050). The results suggest that HBO is able to attenuate the effects of HI on the neonatal brain by reducing the progression of neuronal injury and increasing sensorimotor function.

Development of a novel experimental rat model for neonatal pre-ganglionic upper brachial plexus injury

A neonatal upper brachial plexus injury, referred to as Erb's palsy, is a serious obstetric problem. Some surgical methods are used to treat this injury, but they are inadequate. To seek new treatments for Erb's palsy, we used a model for cervical preganglionic root transection in neonate rats and evaluated the behavioral and histological compatibility of this model with Erb's palsy. Two groups were used in this study. In the group, receiving the Erb operation, the left anterior and posterior roots of spinal vertebra C5-C7 were transected at the preganglionic level, and the results were compared with those of a group that received a sham operation. In the group, receiving the Erb operation, walking difficulties and behavioral abnormalities were observed. These observations were noted on the side where the transection took place, and the problems were attributed to proximal muscle weakness in the forelimb. Additionally, the forepaw grip was not impaired. Furthermore, in this group, the number of anterior horn cells in the cervical cord on the transected side was significantly lower than that on the contralateral side (P < 0.001). The results of this study indicate that the model fulfills the criteria for the clinical symptoms of Erb's palsy and that it may also serve as a new method for enabling treatment of the condition.

MRI evaluation and functional assessment of brain injury after hypoxic ischemia in neonatal mice

BACKGROUND AND PURPOSE

Severe perinatal asphyxia is an important cause of brain injury in the newborn infant. We examined early events after hypoxic ischemia (HI) in the 7-day-old mouse brain by MRI and related them to long-term functional effects and histopathology in the same animals at 4 to 5 weeks of age.

METHODS

HI was induced in 7-day-old CD1 mice by exposure to 8% oxygen for 30 minutes after occlusion of the left common carotid artery. The resulting unilateral focal lesion was evaluated in vivo by MRI (T2 maps and apparent diffusion coefficient maps) at 3, 6, and 24 hours and 5 days after hypoxia. Locomotion and sensorimotor function were analyzed after 3 weeks. Four weeks after HI, the mice were killed, and cresyl violet-stained brain sections were examined morphologically.

RESULTS

A decrease in apparent diffusion coefficient values in cortex on the affected side was found at 3 hours after HI. T2 values were significantly increased after 6 hours and remained so for 5 days. Maximal size of the lesion was attained at 3 to 6 hours after HI and declined thereafter. Animals with MRI-detected lesions had decreased forward locomotion, performed worse than controls in the beam-walking test, and showed a unilateral hypotrophy in the cresyl violet-stained brain sections 4 weeks later.

CONCLUSIONS

The temporal progression of the damage after HI in 7-day-old mice differs from that of the adult brain as judged by MRI. The early lesions detected by MRI were related to functional impairments for these mice in near-adult life.

Delayed postischemic hypothermia improves long-term behavioral outcome after cerebral hypoxia-ischemia in neonatal rats

Hypothermia may be an ideal neuroprotective intervention in hypoxic-ischemic encephalopathy after perinatal asphyxia. The present study describes the long-term effects of prolonged resuscitative whole-body hypothermia initiated 2 h after hypoxic-ischemic injury on brain morphology and neuropsychological behavior in 7-d-old rats. After right common carotid artery ligation and exposure to hypoxia of 8% O(2) for 105 min, 10 animals were kept normothermic at 37 degrees C and 10 animals were cooled to 30 degrees C rectal temperature for 26 h, starting 2 h after the hypoxic-ischemic insult. All hypoxic-ischemic animals were gavage fed to guarantee long-term survival. Neuroprotection was evaluated by magnetic resonance imaging and behavioral testing. Hypothermia significantly reduced the final size of cerebral infarction by 23% at 6 wk after the insult. The most extended tissue rescue was found in the hippocampus (21%, p = 0.031), followed by the striatum (13%, p = 0.143) and the cortex (11%, p = 0.160). Cooling salvaged spatial memory deficits verified at 5 wk of recovery with Morris Water Maze test; whereas circling abnormalities after apomorphine injection and sensory motor dysfunctions on rotating treadmill improved, yet did not reach statistical significance. When compared with controls, hypoxic-ischemic animals performed worse in all behavioral tests. Hypothermia did not influence functional outcome in controls. Significant correlations between behavioral performance and corresponding regional brain volumes were found. We conclude that 26 h of mild to moderate resuscitative hypothermia leads not only to brain tissue rescue, but most important to long-lasting behavioral improvement throughout brain maturation despite severity of injury and delayed onset of cooling.

Delayed neurodegeneration in neonatal rat thalamus after hypoxia-ischemia is apoptosis

Brain injury in newborns can cause deficits in motor and sensory function. In most models of neonatal brain injury, thalamic damage often occurs. Using the Rice-Vannucci model of neonatal hypoxic-ischemic brain injury, we have shown that neuronal degeneration in somatosensory thalamus is delayed in onset ( approximately 24 hr) compared with cortical and striatal injury and exhibits prominent structural features of apoptosis. In the present study, we examined whether cell death in the thalamus has molecular features of apoptosis. Fas death receptor protein expression increased rapidly after neonatal hypoxia-ischemia, in concert with cleavage of procaspase 8 to its active form. Concurrently, the levels of Bax in mitochondrial-enriched cell fractions increase, and cytochrome c accumulates in the soluble fraction. Mitochondria accumulate in a perinuclear distribution by 6 hr after hypoxia-ischemia. Cytochrome oxidase subunit 1 protein levels also increase at 6 hr after hypoxia-ischemia. Increased levels of Fas death receptor, Bax, and cytochrome c, activation of caspase 8, and abnormalities in mitochondria in the thalamus significantly precede the activation of caspase 3 and the appearance of neuronal apoptosis at 24 hr. We conclude that the delayed neurodegeneration in neonatal rat ventral basal thalamus after hypoxic-ischemic injury is apoptosis mediated by death receptor activation.

Long-term deficits following cerebral hypoxia-ischemia in four-week-old rats: correspondence between behavioral, histological, and magnetic resonance imaging assessments

We examined whether following a hypoxic-ischemic insult in young animals there are long-lasting functional deficits that correlate either to histological tissue damage or to potential compensatory plasticity changes. Four-week-old rats were subjected to an episode of cerebral hypoxia-ischemia (right carotid artery occlusion + 30 min of hypoxia) or a sham operation. In hypoxic-ischemic animals there were gross neurological deficits 1, 24, and 48 h postinsult with recovery by 1 week. Behavioral deficits were observed in both the acquisition and the performance of a response duration differentiation test and a fine motor control test (staircase test) 3 months after the hypoxia-ischemia. Functional magnetic resonance imaging studies demonstrated less activation in the sensory-motor cortex of hypoxic-ischemic animals in response to left vs right forepaw stimulation 4 months postinsult. Histological assessment delineated striatal, cortical, and hippocampal damage in the hypoxic-ischemic hemisphere and a reduction in cortical thickness, bilaterally. GFAP immunoreactivity was increased in injured striatum and cortex. Neurofilament heavy chain (NF200) immunoreactivity was normally most intense in white matter and decreased in areas of ipsilateral cortical damage. Synaptophysin immunoreactivity was reduced around areas of infarction and somewhat increased in adjacent undamaged striatum and in layer IV of parietal cortex. The histological damage or chronic degenerative changes could account for much of the variance in functional outcome detected with sensitive behavioral tests so that overall the compensatory or plasticity changes evident within the juvenile brain are rather modest.

Selective and long-term learning impairment following neonatal hypoxic-ischemic brain insult in rats

We examined four different learning and memory tasks in rats which had been subjected to left carotid artery ligation followed by 2 h hypoxia (8% oxygen) when they were 7 days old. The examination began on the 4th week after insult and continued to 18 weeks post-insult. Compared with the control group, the hypoxic-ischemic group showed significant learning impairments in choice reaction time tasks relating to the attention process, and in plus-maze tasks and water maze tasks which examine long-term reference memory. In eight-arm radial maze tasks representing both short-term working memory and long-term reference memory, inferiority of the hypoxic-ischemic group was transient. Results of the sensorimotor test were normal in the hypoxic-ischemic group although slight flexion and twisting in the right forelimb was observed in 30% of the hypoxic-ischemic group when suspended by the tail. These abnormalities did not affect the results of learning tests. Findings of the study indicate that left-side brain damage produced by hypoxia-ischemia at 7 days of age resulted in selective and long-lasting learning and memory impairment.

BDNF protects against spatial memory deficits following neonatal hypoxia-ischemia

Hypoxic-ischemic (H-I) brain injury in the human perinatal period often leads to significant long-term neurobehavioral dysfunction in the cognitive and sensory-motor domains. Using a neonatal H-I injury model (unilateral carotid ligation followed by hypoxia) in postnatal day seven rats, previous studies have shown that neurotrophins, such as brain-derived neurotrophic factor (BDNF), can be protective against neural tissue loss. The present study explored potential relationships between neural protective and behavioral protective strategies in this neonatal H-I model by determining if neonatal H-I was associated with behavioral spatial learning and memory deficits and whether the neurotrophin BDNF was protective against both brain injury and spatial learning/memory dysfunction. Postnatal day seven rats received vehicle or BDNF pretreatments (intracerebroventricular injections) followed by H-I or sham treatments and then tested for spatial learning and memory on the simple place task in the Morris water maze from postnatal days 20 to 30, and their brains were histologically analyzed at 4 weeks following treatments. H-I rats with vehicle pretreatment displayed significant tissue loss in the hippocampus (including CA1 neurons), cortex, and striatum, as well as severe spatial memory deficits (e.g., short probe times). BDNF pretreatment resulted in significant protection against both H-I-induced brain tissue losses and spatial memory impairments. These findings indicate that unilateral H-I brain injury in a neonatal rodent model is associated with cognitive deficits, and that BDNF pretreatment is protective against both brain injury and spatial memory impairment.

Poly(ADP-ribose) synthase inhibition reduces ischemic injury and inflammation in neonatal rat brain

Poly(ADP-ribose) synthase (PARS), an abundant nuclear protein, has been described as an important candidate for mediation of neurotoxicity by nitric oxide. However, in cerebral ischemia, excessive PARS activation may lead to energy depletion and exacerbation of neuronal damage. We examined the effect of inhibiting PARS on the (a) degree of cerebral injury, (b) process of inflammatory responses, and (c) functional outcomes in a neonatal rat model of focal ischemia. We demonstrate that administration of 3-aminobenzamide, a PARS inhibitor, leads to a significant reduction of infarct volume: 63 +/- 2 (untreated) versus 28 +/- 4 mm(3) (treated). The neuroprotective effects currently observed 48 h postischemia hold up at 7 and 17 days of survival time and attenuate neurological dysfunction. Inhibition of PARS activity, demonstrated by a reduction in poly(ADP-ribose) polymer formation, also reduces neutrophil recruitment and levels of nitrotyrosine, an indicator of peroxynitrite generation. Taken together, our results demonstrate that PARS inhibition reduces ischemic damage and local inflammation associated with reperfusion and may be of interest for the treatment of neonatal stroke.

N-tosyl-L-phenylalanyl-chloromethylketone reduces hypoxic-ischemic brain injury in rat pups

N-tosyl-L-phenylalanyl-chloromethylketone (TPCK) in vitro blocks apoptotic pathways leading to cell death. We wished to see if TPCK would reduce brain injury in vivo. Seven-day-old rat pups had the right carotid artery ligated and then received either vehicle or TPCK (5 to 100 mg/kg i.p.). They were then given 8% oxygen for 2.25 h. Twenty-two days later, the cerebral hemispheres were weighed to determine the reduction in size in the right hemisphere. TPCK decreased the reduction in right hemisphere weight from 15+/-3% (vehicle, n=20), to 4+/-2% (10 mg/kg, n = 19, P<0.01). TPCK reduced the number of cells staining for DNA breaks 3 days after injury from 1729+/-275 mm(-2) (vehicle, n = 8) to 550+/-236 mm(-2) (10 mg/kg TPCK, n = 9, P<0.01), decreased the amount of DNA fragmentation 3 days after injury by gel electrophoreses (20 mg/kg, n = 16, P<0.01) and eliminated the increase in nitric oxide metabolites 6 h after injury (vehicle 1.5+/-0.4, n = 10; and 20 mg/kg TPCK 0.0+/-0.1 nM/mg protein, n = 10, P<0.001). TPCK pretreatment in the newborn rat model of hypoxic-ischemic brain injury reduces DNA fragmentation, nitric oxide production and brain injury.

Infarct volume and functional outcome after pre- and postoperative administration of metyrapone, a steroid synthesis inhibitor, in focal brain ischemia in the rat

High blood levels of glucocorticoids are associated with increased mortality, confusion and poor functional outcome in stroke patients. It has been proposed that inhibition of glucocorticoids in acute stroke might be beneficial, but experimental data are conflicting and no long-term follow-up study has been reported. We have studied whether pre- or postoperative administration of metyrapone, a steroid synthesis inhibitor, can influence long-term outcome after ligation of the right middle cerebral artery (MCA) distal to the striatal branches in hypertensive rats. Metyrapone (200 mg/kg) was administered either 30 min before or 1, 12 and 24 h after MCA occlusion. Limb placements and ability to traverse a rotating pole were evaluated pre- and postoperatively. Infarct size, histology and GFAP immunoreactivity were evaluated on 5 microm coronal sections from brains perfused in situ 4 weeks after the ischemic event. Pretreatment did not influence outcome, whereas postoperative administration of metyrapone significantly increased infarct volume (P < 0.05). Post-treated rats performed significantly worse than vehicle-treated rats on the rotating pole 3 weeks after the operation (P < 0.05). Our results do not support the hypothesis that inhibition of glucocorticoid synthesis improves outcome after cerebral ischemia.

Effects of neonatal hypoxia on the medulla-spinal cord descending neurons

Hypoxic changes in the medulla-spinal cord descending neurons were studied morphologically using a retrograde neurotracer, choleratoxin B subunit (CTb). On postnatal day 7, Sprague-Dawley rats were subjected to a hypoxic load of 8% oxygen for 5 hours. In the rats that survived, CTb was injected into the lumbar enlargement at postnatal day 26, and they were killed at postnatal day 28 for histologic analysis. Retrograde transported CTb was visualized by immunohistochemistry. The results were compared with those obtained from control rats. In the control rats, CTb-positive cells were observed in the nucleus reticularis gigantocellularis, nucleus reticularis magnocellularis, nucleus raphe magnus, nucleus raphe obscurus, and nucleus raphe pallidus. In the hypoxic rats, although CTb-positive cells were detected in the same areas as the control rats, there was a noteworthy decrease in the number of CTb-positive cells in all areas, and there were many cells with hypoxic degeneration. In all of the nuclei a marked decrease in the number of CTb-positive cells was observed. Because medulla-spinal cord descending neurons have important roles in the regulation of postural muscle tone, these results may account for the pathophysiology of abnormal muscle tonus accompanying hypoxic brain damage.

Protective effects of moderate hypothermia after neonatal hypoxia-ischemia: short- and long-term outcome

We have previously shown that mild hypothermia applied after hypoxia-ischemia in newborn piglets and rats reduces brain injury evaluated 3-7 d after the insult. The aim of the present study was to assess the neuroprotective efficacy of hypothermia with respect to short- (neuropathology) and long-term (neuropathology and sensorimotor function) outcome after hypoxia-ischemia in 7-d-old rats. One hundred fourteen animals from 13 litters survived either 1 or 6 wk after a hypoxic-ischemic insult. The animals were randomized to either 1) normothermic recovery for the whole 1- or 6-wk period or 2) cooling to a rectal temperature of 32.0 degrees C for the first 6 h followed by normothermic recovery with the dam. Hypothermia offered a uniform protection of 27, 35, 28, and 25% in cerebral cortex, hippocampus, basal ganglia, and thalamus, respectively, in the 1-wk survivors (n = 32). The corresponding values for the 6-wk survivors (n = 61) were 22, 28, 37, and 35%. There was a significant correlation between sensorimotor performance and infarct volume (r = 0.66; p < 0.001). However, the sensorimotor function was not significantly improved by hypothermia if all animals were included, but in female pups the total functional score was higher in the hypothermia group (150 +/- 35 versus 100 +/- 34, p < 0.0007) which corresponded to a marked (51%) reduction of the neuropathology score in this subgroup. This is the first neonatal study to show a long-term histopathologic protection of the brain after posthypoxic hypothermia.