Partial neuroprotection with low-dose infusion of the alpha2-adrenergic receptor agonist clonidine after severe hypoxia in preterm fetal sheep

Oral Clonidine-Based Strategy to Reduce Opiate Use During Cooling for Neonatal Encephalopathy: An Observational Study

OBJECTIVE

To determine whether an enteral, clonidine-based sedation strategy (CLON) during therapeutic hypothermia (TH) for hypoxic-ischemic encephalopathy would decrease opiate use while maintaining similar short-term safety and efficacy profiles to a morphine-based strategy (MOR).

STUDY DESIGN

This was a single-center, observational study conducted at a level IV neonatal intensive care unit from January 1, 2017, to October 1, 2021. From April 13, 2020, to August 13, 2020, we transitioned from MOR to CLON. Thus, patients receiving TH for hypoxic-ischemic encephalopathy were grouped to MOR (before April 13, 2020) and CLON (after August 13, 2020). We calculated the total and rescue morphine milligram equivalent/kg (primary outcome) and frequency of hemodynamic changes (secondary outcome) for both groups.

RESULTS

The MOR and CLON groups (74 and 25 neonates, respectively) had similar baseline characteristics and need for rescue sedative intravenous infusion (21.6% MOR and 20% CLON). Both morphine milligram equivalent/kg and need for rescue opiates (combined bolus and infusions) were greater in MOR than CLON (P < .001). As days in TH advanced, a lower percentage of patients receiving CLON needed rescue opiates (92% on day 1 to 68% on day 3). Patients receiving MOR received a greater cumulative dose of dopamine and more frequently required a second inotrope and hydrocortisone for hypotension. MOR had a lower respiratory rate during TH (P = .01 vs CLON).

CONCLUSIONS

Our CLON protocol is noninferior to MOR, maintaining perceived effectiveness and hemodynamic safety, with an apparently reduced need for opiates and inotropes.

Effectiveness and Safety of Dexmedetomidine in Neonates With Hypoxic Ischemic Encephalopathy Undergoing Therapeutic Hypothermia

OBJECTIVE

The objective of this study was to evaluate and compare the effectiveness and safety of dexmedetomidine as monotherapy between neonates with mild hypoxic ischemic encephalopathy (HIE) and moderate to severe HIE treated with therapeutic hypothermia (TH).

METHODS

This retrospective study included neonates of gestational age ≥36 weeks with a diagnosis of HIE and undergoing TH between January 2014 and December 2021. Patients were included if they received at least 6 hours of continuous sedation with dexmedetomidine. Baseline characteristics, dose and duration of medication, adverse events, liver and kidney function tests, and hospital course were reviewed.

RESULTS

Of the 97 neonates included, 46 had mild, 42 had moderate, and 9 had severe HIE. Dexmedetomidine was initiated at a median 5 hours of life, and the median infusion duration was 77 (46-87) hours. Fifty-two (53.6%) required at least 1 breakthrough opioid or sedative during the first 24 hours of dexmedetomidine infusion. Overall, 40 patients (41.2%) had at least 1 bradycardia episode with heart rate <80 beats/min and 14 patients (14.4%) had heart rate <70 beats/min. Hypotension was experienced by 7 patients (7.2%). Fifty-two patients (53.6%) were intubated in the delivery room and 33/52 (63.5%) were extubated on day of life 1 during dexmedetomidine infusion.

CONCLUSIONS

Dexmedetomidine as monotherapy was effective and safe sedation for infants with HIE undergoing hypothermia. The most common side effect of dexmedetomidine was bradycardia. -Dexmedetomidine may be considered as first and single agent for neonates with HIE undergoing TH.

Alpha-adrenergic receptor activation after fetal hypoxia-ischaemia suppresses transient epileptiform activity and limits loss of oligodendrocytes and hippocampal neurons

Exposure to hypoxic-ischaemia (HI) is consistently followed by a delayed fall in cerebral perfusion. In preterm fetal sheep this is associated with impaired cerebral oxygenation, consistent with mismatch between perfusion and metabolism. In the present study we tested the hypothesis that alpha-adrenergic inhibition after HI would improve cerebral perfusion, and so attenuate mismatch and reduce neural injury. Chronically instrumented preterm (0.7 gestation) fetal sheep received sham-HI (n = 10) or HI induced by complete umbilical cord occlusion for 25 minutes. From 15 minutes to 8 hours after HI, fetuses received either an intravenous infusion of a non-selective alpha-adrenergic antagonist, phentolamine (10 mg bolus, 10 mg/h infusion, n = 10), or saline (n = 10). Fetal brains were processed for histology 72 hours post-HI. Phentolamine infusion was associated with increased epileptiform transient activity and a greater fall in cerebral oxygenation in the early post-HI recovery phase. Histologically, phentolamine was associated with greater loss of oligodendrocytes and hippocampal neurons. In summary, contrary to our hypothesis, alpha-adrenergic inhibition increased epileptiform transient activity with an exaggerated fall in cerebral oxygenation, and increased neural injury, suggesting that alpha-adrenergic receptor activation after HI is an important endogenous neuroprotective mechanism.

Clonidine ameliorates cerebral ischemia-reperfusion injury by up-regulating the GluN3 subunits of NMDA receptor

This study aimed to investigate the protective effects of the alpha-2 adrenergic receptor (α2-AR) agonist, clonidine, on the cerebral ischemia-reperfusion (I/R) injury and elaborate the underlying mechanisms. Cerebral I/R model was established by middle cerebral artery occlusion (MCAO) for 2 h followed by reperfusion for 4 h in adult male SD rats. Saline, clonidine and yohimbine (an α2-AR antagonist) were intraperitoneally administered each day for one week before surgery. Neurological deficit was evaluated just before decapitation. TTC staining was applied for correlation of cerebral infarction volume. HE staining was performed to observe the neuron morphology. Immunohistochemical staining was performed to detect the localization and expression of GluN3 proteins. Western blot analysis also was used to detect the expression levels of GluN3 proteins. Our data showed that clonidine ameliorated neurological deficit and reduced the cerebral infarction volume of the rats with cerebral I/R. It is worth noting that treatment with clonidine up-regulated the protein expression of GluN3 in the rats with the cerebral I/R, especially in the cell membrane. Moreover, clonidine also up-regulated the transposition from cytoplasm to cell membrane of GluN3 after cerebral I/R. In addition, yohimbine abolished the neuroprotective effects of clonidine. The results indicated that clonidine played a protective role in cerebral I/R injury through regulation of the protein expression of GluN3 subunits of N-methyl-D-aspartate (NMDA) receptor.

Pharmacologic Analgesia and Sedation in Neonates

Chronic pain and agitation in neonatal life impact the developing brain. Oral sweet-tasting solutions should be used judiciously to mitigate behavioral responses to mild painful procedures, keeping in mind that the long-term impact is unknown. Rapidly acting opioids should be used as part of premedication cocktails for nonemergent endotracheal intubations. Continuous low-dose morphine or dexmedetomidine may be considered for preterm or term neonates exhibiting signs of stress during mechanical ventilation and therapeutic hypothermia, respectively. Further research is required regarding the pharmacokinetics, pharmacodynamics, safety, and efficacy of pharmacologic agents used to mitigate mild, moderate, and chronic pain and stress in neonates.

Understanding the effects of opioids vs non-opioids in the treatment of neonatal abstinence syndrome, an in vitro model

Neonatal abstinence syndrome (NAS) refers to cadre of withdrawal manifestations in infants born to mothers who used illicit and licit substances during pregnancy. The increasing prevalence of NAS has been largely due to the maternal use of opioids during pregnancy. NAS contributes to increased morbidity and long-term disability in surviving infants. Clinically, oral opioid therapies for opioid exposure have been a standard treatment with morphine (MO) being the most commonly used medication. Recently, a non-opioid agent, clonidine (CD) has also been used with potentially favorable short- and long-term outcomes in infants. However, data regarding the cellular and molecular effects of these treatments on the developing brain is still lacking due to a lack of a reliable animal model that targets the neonatal brain. To address this gap in knowledge we determined the effects of MO or CD on the cell death of neonatal cortical explant cultures that were exposed to oxycodone (OXY) in utero. Sprague Dawley rats were randomized and implanted with programmable infusion pumps before mating to receive either the OXY (dose increasing from 1.21-1.90 mg/kg/day to a maximum dose of 2.86-3.49 mg/kg/day) or normal saline (NS) throughout pregnancy and until one week after delivery. Male and female rat pups were sacrificed on postnatal day 4, and the prefrontal cortex (PFC) and hippocampus (HC) were dissected and treated with MO (0.10-1.00 µM) or CD (1.20-120.00 µM) in culture media. After 5 days of treatment the explants were labeled with propidium iodide to detect cell death. Dead cells were analyzed and counted under fluorescence microscopy. In explants from the PFC, cell death was greater in those prenatally exposed to OXY and postnatally treated with MO (OXY/MO) (736.8 ± 76.5) compared to OXY/CD (620.9 ± 75.0; p = 0.005). In the HC explants, mean cell death counts were not significantly different between groups regardless of prenatal exposure or postnatal treatment (p = 0.19). The PFC is vital in controlling higher-order executive functions such as behavioral flexibility, learning and working memory. Therefore, our finding is consistent with executive function problems in children with prenatal opioid exposure.

Management of comfort and sedation in neonates with neonatal encephalopathy treated with therapeutic hypothermia

Ensuring comfort for neonates undergoing therapeutic hypothermia (TH) after neonatal encephalopathy (NE) exemplifies a vital facet of neonatal neurocritical care. Physiologic markers of stress are frequently present in these neonates. Non-pharmacologic comfort measures form the foundation of care, benefitting both the neonate and parents. Pharmacological sedatives may also be indicated, yet have the potential to both mitigate and intensify the neurotoxicity of a hypoxic-ischemic insult. Morphine represents current standard of care with a history of utilization and extensive pharmacokinetic data to guide safe and effective dosing. Dexmedetomidine, as an alternative to morphine, has several appealing characteristics, including neuroprotective effects in animal models; robust pharmacokinetic studies in neonates with NE treated with TH are required to ensure a safe and effective standard dosing approach. Future studies in neonates treated with TH must address comfort, adverse events, and long-term outcomes in the context of specific sedation practices.

Practical approaches to sedation and analgesia in the newborn

The prevention, assessment, and treatment of neonatal pain and agitation continues to challenge clinicians and researchers. Substantial progress has been made in the past three decades, but numerous outstanding questions remain. In this setting, clinicians must establish safe and compassionate standardized practices that consider available efficacy data, long-term outcomes, and research gaps. Novel approaches with limited data must be carefully considered against historic standards of care with robust data suggesting limited benefit and clear adverse effects. This review summarizes available evidence while suggesting practical clinical approaches to pain assessment and avoidance, procedural analgesia, postoperative analgesia, sedation during mechanical ventilation and therapeutic hypothermia, and the issues of tolerance and withdrawal. Further research in all areas represents an urgent priority for optimal neonatal care. In the meantime, synthesis of available data offers clinicians challenging choices as they balance benefit and risk in vulnerable critically ill neonates.

Provision of Sedation and Treatment of Seizures During Neonatal Therapeutic Hypothermia

Hypoxic-ischemic encephalopathy (HIE) produces a high rate of long-term neurodevelopmental disability in survivors. Therapeutic hypothermia dramatically improves the incidence of intact survival, but does not eliminate adverse outcomes. The ideal provision of sedation and treatment of seizures during therapeutic hypothermia represent therapeutic targets requiring optimization in practice. Physiologic stress from therapeutic hypothermia may obviate some of the benefits of this therapy. Morphine is commonly utilized to provide comfort, despite limited empiric evidence supporting safety and efficacy. Dexmedetomidine represents an interesting alternative, with preclinical data suggesting direct efficacy against shivering during induced hypothermia and neuroprotection in the setting of HIE. Pharmacokinetic properties must be considered when utilizing either agent, with safety dependent on conservative dosing and careful monitoring. HIE is the leading cause of neonatal seizures. Traditional therapies, including phenobarbital, fosphenytoin, and benzodiazepines, control seizures in the vast majority of neonates. Concerns about the acute and long-term effects of these agents have led to the exploration of alternative anticonvulsants, including levetiracetam. Unfortunately, levetiracetam is inferior to phenobarbital as first-line therapy for neonatal seizures. Considering both the benefits and risks of traditional anticonvulsant agents, treatment should be limited to the shortest duration indicated, with maintenance therapy reserved for neonates at high risk for recurrent seizures.

Atomoxetine, a selective norepinephrine reuptake inhibitor, improves short-term histological outcomes after hypoxic-ischemic brain injury in the neonatal male rat

BACKGROUND

Despite the recent progress of perinatal medicine, perinatal hypoxic-ischemic (HI) insult remains an important cause of brain injury in neonates, and is pathologically characterized by neuronal loss and the presence of microglia. Neurotransmitters, such as norepinephrine (NE) and glutamate, are involved in the pathogenesis of hypoxic-ischemic encephalopathy via the interaction between neurons and microglia. Although it is well known that the monoamine neurotransmitter NE acts as an anti-inflammatory agent in the brain under pathological conditions, its effects on perinatal HI insult remains elusive. Atomoxetine, a selective NE reuptake inhibitor, has been used clinically for the treatment of attention-deficit hyperactivity disorder in children. Here, we investigated whether the enhancement of endogenous NE by administration of atomoxetine could protect neonates against HI insult by using the neonatal male rat model. We also examined the involvement of microglia in this process.

METHODS

Unilateral HI brain injury was induced by the combination of left carotid artery dissection followed by ligation and hypoxia (8% O₂, 2 h) in postnatal day 7 (P7) male rat pups. The pups were randomized into three groups: the atomoxetine treatment immediately after HI insult, the atomoxetine treatment at 3 h after HI insult, or the vehicle treatment group. The pups were euthanized on P8 and P14, and the brain regions including the cortex, striatum, hippocampus, and thalamus were evaluated by immunohistochemistry.

RESULTS

HI insult resulted in severe brain damage in the ipsilateral hemisphere at P14. Atomoxetine treatment immediately after HI insult significantly increased NE levels in the ipsilateral hemisphere at 1 h after HI insult and reduced the neuronal damage via the increased phosphorylation of cAMP response element-binding protein (pCREB) in all brain regions examined. In addition, the number of microglia was maintained under atomoxetine treatment compared with that of the vehicle treatment group. To determine the involvement of microglia in the process of neuronal loss by HI insult, we further examined the influence of hypoxia on rat primary cultured microglia by the quantitative real-time polymerase chain reaction. Hypoxia did not cause the upregulation of interleukin-1beta (IL-1β) mRNA expression, but decreased the microglial intrinsic nitric oxide synthase (iNOS)/arginase1 mRNA expression ratio. NE treatment further decreased the microglial iNOS/arginase1 mRNA expression ratio. In contrast, no significant neuroprotective effect was observed at P14 when atomoxetine was administered at 3 h after HI insult.

CONCLUSIONS

These findings suggested that the enhancement of intrinsic neurotransmitter NE signaling by a selective NE reuptake inhibitor, atomoxetine, reduced the perinatal HI insult brain injury. In addition, atomoxetine treatment was associated with changes of TUNEL, pCREB, and BDNF expression levels, and microglial numbers, morphology, and responses.

Analgesics, sedatives, anticonvulsant drugs, and the cooled brain

Multiple randomized controlled trials have shown that prolonged, moderate cerebral hypothermia initiated within a few hours after severe hypoxia-ischemia and continued until resolution of the acute phase of delayed cell death reduces mortality and improves neurodevelopmental outcome in term infants. The challenge is now to find ways to further improve outcomes. In the present review, we critically examine the evidence that conventional analgesic, sedative, or anticonvulsant agents might improve outcomes, in relation to the known window of opportunity for effective protection with hypothermia. This review strongly indicates that there is insufficient evidence to recommend routine use of these agents during therapeutic hypothermia. Further systematic research into the effects of pain and stress on the injured brain, and their treatment during hypothermia, is essential to guide the rational development of clinical treatment protocols.

Effects of dexmedetomidine on microregional O2 balance during reperfusion after focal cerebral ischemia

BACKGROUND

This study was performed to determine whether there is an association between microregional O2 balance and neuronal survival in cerebral ischemia-reperfusion using dexmedetomidine, an α2-adrenoreceptor agonist and a sedative.

METHODS

Rats were subjected to 1 hour middle cerebral artery occlusion and a 2-hour reperfusion. During reperfusion, normal saline (n = 14) or dexmedetomidine 1 μg/kg/minute (n = 14) was infused intravenously. At 2 hours of reperfusion, regional cerebral blood flow using (14)C-iodoantipyrine autoradiography, microregional arterial and venous (20-60 μm in diameter) O2 saturation (SvO2) using cryomicrospectrophotometry, and the size of cortical infarction were determined.

RESULTS

Ischemia-reperfusion decreased microregional SvO2 (52.9 ± 3.7% vs. 61.1 ± .6%, P < .005) with increased variation or heterogeneity (P < .0001) with similar regional cerebral blood flow and O2 consumption. Dexmedetomidine during reperfusion decreased the heterogeneity of SvO2 that was analyzed with an analysis of variance (P < .01) and reported as coefficient of variation (100 × standard deviation/Mean) (11.8 vs. 16.4). The number of veins with O2 saturation less than 50% decreased with dexmedetomidine (13/80 vs. 27/81, P < .01). The percentage of cortical infarct in total cortex was smaller with dexmedetomidine (8.3 ± 2.2% vs. 12.6 ± 1.5%, P < .005).

CONCLUSIONS

In the cerebral ischemic reperfused cortex, dexmedetomidine decreased the heterogeneity of SvO2 and the number of small veins with low O2 saturation suggesting improved microregional O2 supply/consumption balance. The improvement was accompanied by the reduced size of cortical infarction.

Pharmacokinetics of dexmedetomidine combined with therapeutic hypothermia in a piglet asphyxia model

Background

The highly selective α₂-adrenoreceptor agonist, dexmedetomidine, exerts neuroprotective, analgesic, anti-inflammatory and sympatholytic properties that may be beneficial for perinatal asphyxia. The optimal safe dose for pre-clinical newborn neuroprotection studies is unknown.

Methods

Following cerebral hypoxia-ischaemia, dexmedetomidine was administered to nine newborn piglets in a de-escalation dose study in combination with hypothermia (whole body cooling to 33.5°C). Dexmedetomidine was administered with a loading dose of 1 μg/kg and maintenance infusion at doses from 10 to 0.6 μg/kg/h. One additional piglet was not subjected to hypoxia-ischaemia. Blood for pharmacokinetic analysis was sampled pre-insult and frequently post-insult. A one-compartment linear disposition model was used to fit data. Population parameter estimates were obtained using non-linear mixed effects modelling.

Results

All dexmedetomidine infusion regimens led to plasma concentrations above those associated with sedation in neonates and children (0.4–0.8 μg/l). Seven out of the nine piglets with hypoxia-ischaemia experienced periods of bradycardia, hypotension, hypertension and cardiac arrest; all haemodynamic adverse events occurred in piglets with plasma concentrations greater than 1 μg/l. Dexmedetomidine clearance was 0.126 l/kg/h [coefficient of variation (CV) 46.6.%] and volume of distribution was 3.37 l/kg (CV 191%). Dexmedetomidine clearance was reduced by 32.7% at a temperature of 33.5°C. Dexmedetomidine clearance was reduced by 55.8% following hypoxia-ischaemia.

Conclusions

Dexmedetomidine clearance was reduced almost tenfold compared with adult values in the newborn piglet following hypoxic-ischaemic brain injury and subsequent therapeutic hypothermia. Reduced clearance was related to cumulative effects of both hypothermia and exposure to hypoxia. High plasma levels of dexmedetomidine were associated with major cardiovascular complications.

Antenatal antioxidant treatment with melatonin to decrease newborn neurodevelopmental deficits and brain injury caused by fetal growth restriction

Fetal intrauterine growth restriction (IUGR) is a serious pregnancy complication associated with increased rates of perinatal morbidity and mortality, and ultimately with long-term neurodevelopmental impairments. No intervention currently exists that can improve the structure and function of the IUGR brain before birth. Here, we investigated whether maternal antenatal melatonin administration reduced brain injury in ovine IUGR. IUGR was induced in pregnant sheep at 0.7 gestation and a subset of ewes received melatonin via intravenous infusion until term. IUGR, IUGR + melatonin (IUGR + MLT) and control lambs were born naturally, neonatal behavioral assessment was used to examine neurological function and at 24 hr after birth the brain was collected for the examination of neuropathology. Compared to control lambs, IUGR lambs took significantly longer to achieve normal neonatal lamb behaviors, such as standing and suckling. IUGR brains showed widespread cellular and axonal lipid peroxidation, and white matter hypomyelination and axonal damage. Maternal melatonin administration ameliorated oxidative stress, normalized myelination and rescued axonopathy within IUGR lamb brains, and IUGR + MLT lambs demonstrated significant functional improvements including a reduced time taken to attach to and suckle at the udder after birth. Based on these observations, we began a pilot clinical trial of oral melatonin administration to women with an IUGR fetus. Maternal melatonin was not associated with adverse maternal or fetal effects and it significantly reduced oxidative stress, as evidenced by reduced malondialdehyde levels, in the IUGR + MLT placenta compared to IUGR alone. Melatonin should be considered for antenatal neuroprotective therapy in human IUGR.

Clonidine pre-treatment prevents hemorrhagic shock-induced endotoxemia and oxidative stress in the gut, liver, and lungs of the rat

OBJECTIVES

To study the effect of clonidine pre-treatment on hemorrhagic shock (H/S)-induced endotoxemia and oxidative stress (OS) in three vital organs of the rat.

METHODS

The study protocol consisted of two arms: one for the measurement of organic hydroperoxide (LOOH) and superoxide radical (O(2)(-·)) production in the gut, liver, and lungs (n = 32 rats) and one for the measurement of endotoxin in portal and systemic circulation (n = 32 rats). Four animal groups (sham, clonidine, H/S, and clonidine-H/S group) were used in each arm. Three hours after H/S and concominant blood resuscitation, tissues were collected for LOOHs and O(2)(-·) measurement and blood samples were obtained for endotoxin determination.

RESULTS

Clonidine pre-treatment prior to H/S resulted in a significant reduction of LOOHs and O(2)(-·) production in all vital organs (P < 0.05-0.001), while additionally, clonidine reduced H/S-induced endotoxemia in portal (P < 0.05) and systemic circulation as well (P < 0.01).

DISCUSSION

Clonidine pre-treatment prevents endotoxemia and OS in the gut, liver, and lungs of rats subjected to severe H/S. The improved intestinal barrier function probably stems from the antioxidant effect of clonidine on the intestinal epithelium, whereas the reduced endotoxemia may contribute to a decreased OS observed in the liver and lungs.

Hypoxic–ischemic brain injury and neuroprotection in the newborn infant

Recent clinical trials have confirmed that in term infants with moderate-to-severe hypoxic–ischemic encephalopathy, death and severe developmental disability can be reduced by early treatment with hypothermia. However, meta-analysis of these trials has confirmed that two-thirds of the survivors remain seriously impaired. The search for new neuroprotective interventions has therefore continued. Extensive research has identified the important biochemical pathways that result in neuronal loss, and the subsequent repair and regeneration processes. The most promising neuroprotective agents that limit the former, and promote the latter, are being tested in animal models of hypoxic–ischemic brain injury and are awaiting clinical trials. It is likely that a ‘cocktail’ of agents, affecting a number of pathways, will ultimately prove to be the most effective intervention. The latest additions to a long list of proposed substances are various stem cells that promote neurogenesis by releasing trophic substances into the injured brain. Future clinical trials are likely to employ early biomarkers, of which MRI and proton spectroscopy are probably the most predictive of long-term neurodevelopmental outcome. In conclusion, the exponential increase in knowledge in this field can be expected to provide many more neuroprotective agents within the next decade.

Acute on chronic exposure to endotoxin in preterm fetal sheep

Acute, high-dose exposure to endotoxin lipopolysaccharide (LPS) in preterm fetal sheep can trigger periventricular white matter lesions (PVL), in association with severe hypotension/hypoxemia and significant mortality. Intriguingly, however, chronic or repeated exposure to LPS can induce tachyphylaxis. We therefore tested the hypothesis that progressive, acute on chronic fetal infection would be associated with white matter injury with little fetal mortality. Chronically instrumented preterm (0.7 gestational age) fetal sheep were exposed to a continuous low-dose LPS infusion (100 ng over 24 h, followed by 250 ng/24 h for 96 h) or saline. Boluses of 1 μg LPS or saline were given at 48, 72, and 96 h; sheep were killed at day 10. Six of 11 fetal sheep exposed to saline infusion + LPS boluses died 4-7 h after the first bolus. In contrast, there was no fetal mortality after saline infusions alone (n = 9), low-dose LPS infusion + saline boluses (n = 5), or low-dose LPS + LPS boluses (n = 9). Low-dose LPS infusion + LPS boluses was associated with greater microglial induction than low-dose LPS + saline boluses but a similar area of periventricular white matter inflammation. One fetus developed severe focal white matter necrosis after LPS infusion + boluses. The acute cardiovascular compromise associated with high-dose, acute exposure to LPS is markedly attenuated by previous low-dose infusions, with limited apparent exacerbation of periventricular white matter injury compared with low-dose infusion alone.

Clonidine abolishes the adverse effects on apoptosis and behaviour after neonatal ketamine exposure in mice

BACKGROUND

An increasing amount of both experimental and epidemiological data indicates that neonatal anaesthesia causes disruption of normal brain development in rodents and primates, as manifested by acute increased apoptosis and long-lasting altered behaviour and learning. It is necessary to seek strategies that avoid the possible adverse effects after anaesthesia. Our purpose is to show that increased apoptosis and behavioural alterations after ketamine exposure during this period may be prevented by clonidine, a compound already used by paediatric anaesthetists for sedation.

METHODS

To investigate the protective properties of clonidine pre-treatment, five groups of 10-day-old mice were injected with either ketamine 50 mg/kg, clonidine 40 μg/kg, ketamine 50 mg/kg 30 min after 10 μg/kg clonidine, ketamine 50 mg/kg 30 min after 40 μg/kg clonidine or saline (control). Apoptosis was measured 24 h after treatment using Flouro-Jade staining. Spontaneous activity in a novel environment was tested at an age of 55 days.

RESULTS

Pre-treatment with 40 μg/kg clonidine, but not 10 μg/kg clonidine, 30 min before ketamine exposure abolished ketamine-induced apoptosis and the behavioural changes observed in the young adult mice. The mice exposed to clonidine alone showed no differences from the saline-treated (control) mice.

CONCLUSION

The administration of clonidine eliminated the adverse effects of ketamine in this mouse model, suggesting a possible strategy for protection. Alone, clonidine did not cause any adverse effects in these tests.

Attenuation of spinal cord ischemia-reperfusion injury by specific α-2a receptor activation with dexmedetomidine

BACKGROUND

Despite surgical adjuncts, paralysis remains a devastating complication after thoracoabdominal aortic interventions. Dexmedetomidine, a selective α-2a agonist commonly used for sedation in the critical care setting, has been shown to have protective effects against ischemia-reperfusion injuries in multiple organ systems. We hypothesized that treatment with dexmedetomidine would attenuate spinal cord ischemia-reperfusion injury via α-2a receptor activation.

METHODS

Adult C57BL/6 mice underwent sternotomy, followed by occlusion of the aortic arch for 4 minutes. Eight experimental mice received pretreatment with intraperitoneal dexmedetomidine (25 μg/kg) and at 12-hour intervals after reperfusion. Eight control mice received an equivalent amount of 0.9% normal saline. Five mice underwent the same procedure with dexmedetomidine (25 μg/kg) and atipamezole (250 μg/kg), an α-2a receptor antagonist. Functional analysis of the mice was obtained at 12-hour intervals and scored using the Basso Mouse Scale for Locomotion until 60 hours. All mice were euthanized at 60 hours. Their spinal cords were removed en bloc and were stained with hematoxylin and eosin to assess cytoarchitecture and neuronal viability.

RESULTS

Mice treated with the α-2a agonist demonstrated preserved motor function compared with ischemic controls and with mice treated with the α-2a antagonist in addition to the agonist. Functional differences in the dexmedetomidine group were statistically significant from 24 hours through the remainder of the experiment (P < .05). In addition, the treated mice had preserved cytoarchitecture, decreased vacuolization, and improved neuronal viability compared with ischemic control mice and mice concurrently treated with atipamezole, the dexmedetomidine α-2a antagonist.

CONCLUSIONS

Treatment of mice with the α-2a agonist dexmedetomidine preserves motor function and neuronal viability after aortic cross-clamping. In addition, mice exhibited almost complete reversal of the protective effect with the administration of the α-2a receptor antagonist atipamezole. Dexmedetomidine appears to attenuate spinal cord ischemia-reperfusion injury via α-2a receptor-mediated agonism.

CLINICAL RELEVANCE

There remains a significant risk of paraplegia after thoracoabdominal aortic interventions. This complication is devastating to the patient and the health care system. Pharmacologic adjuncts to further decrease this complication have been studied; however, few viable options exist. The α-2a agonists have been shown to improve outcomes after strokes but have not been studied in spinal cord ischemia. We show that dexmedetomidine, a commonly used α-2a agonist in the operating room, can preserve neurologic function in mice after aortic cross-clamping. Although the protective mechanism of dexmedetomidine remains unknown, it might prove to be beneficial in reducing the incidence of paraplegia after aortic interventions.

Maturation of the mitochondrial redox response to profound asphyxia in fetal sheep

Fetal susceptibility to hypoxic brain injury increases over the last third of gestation. This study examined the hypothesis that this is associated with impaired mitochondrial adaptation, as measured by more rapid oxidation of cytochrome oxidase (CytOx) during profound asphyxia. Methods: Chronically instrumented fetal sheep at 0.6, 0.7, and 0.85 gestation were subjected to either 30 min (0.6 gestational age (ga), n = 6), 25 min (0.7 ga, n = 27) or 15 min (0.85 ga, n = 17) of complete umbilical cord occlusion. Fetal EEG, cerebral impedance (to measure brain swelling) and near-infrared spectroscopy-derived intra-cerebral oxygenation (ΔHb = HbO₂ – Hb), total hemoglobin (THb) and CytOx redox state were monitored continuously. Occlusion was associated with profound, rapid fall in ΔHb in all groups to a plateau from 6 min, greatest at 0.85 ga compared to 0.6 and 0.7 ga (p<0.05). THb initially increased at all ages, with the greatest rise at 0.85 ga (p<0.05), followed by a progressive fall from 7 min in all groups. CytOx initially increased in all groups with the greatest rise at 0.85 ga (p<0.05), followed by a further, delayed increase in preterm fetuses, but a striking fall in the 0.85 group after 6 min of occlusion. Cerebral impedance (a measure of cytotoxic edema) increased earlier and more rapidly with greater gestation. In conclusion, the more rapid rise in CytOx and cortical impedance during profound asphyxia with greater maturation is consistent with increasing dependence on oxidative metabolism leading to earlier onset of neural energy failure before the onset of systemic hypotension.

Subclinical exposure to low-dose endotoxin impairs EEG maturation in preterm fetal sheep

Exposure to chorioamnionitis is strongly associated with neurodevelopmental disability after premature birth; however, it remains unclear whether subclinical infection affects functional EEG maturation. Chronically instrumented 103-104-day-old (0.7 gestational age: term 147 days) fetal sheep in utero were randomized to receive either gram-negative LPS by continuous low-dose infusion (100 ng iv over 24 h, followed by 250 ng/24 h for 4 days; n = 6) or the same volume of normal saline (n = 9). Arterial plasma cortisol, ACTH, and IL-6 were measured. The delta (0-3.9 Hz), theta (4-7.9 Hz), alpha (8-12.9 Hz), and beta (13-22 Hz) components of the EEG were determined by power spectral analysis. Brains were taken after 10 days for histopathology. There were no changes in blood gases, cardiovascular variables, or EEG power during LPS infusion, but a transient rise in plasma cortisol and IL-6 (P < 0.05). LPS infusion was associated with loss of the maturational increase to higher frequency activity, with reduced alpha and beta power, and greater delta power than saline controls from 6 to 10 days (P < 0.05). Histologically, LPS was associated with increased numbers of microglia and TNF-α-positive cells in the periventricular white matter and frontoparietal cortex, increased caspase-3-positive cells in white matter, but no loss of CNPase-positive oligodendrocytes, Nurr-1 subplate cells, or gyral complexity. These data suggest that low-dose endotoxin exposure can impair EEG maturation in preterm fetal sheep in association with neural inflammation but without hemodynamic disturbances or cortical injury.

Limited predictive value of early changes in EEG spectral power for neural injury after asphyxia in preterm fetal sheep

INTRODUCTION

This study examined whether spectral analysis of the electroencephalogram (EEG) can discriminate between mild and severe hypoxic-ischemic injury in the immature brain.

RESULTS

Total EEG power was profoundly suppressed after umbilical cord occlusion and recovered to baseline by 5 h after 15-min of occlusion, in contrast with transient recovery in the 25-min (P < 0.05). Power spectra were not different between groups in the first 3 h; α and β power were significantly higher in the 15-min group from 4 h, and Δ and θ power from 5 h (P < 0.05). The 25-min group showed severe neuronal loss in hippocampal regions and basal ganglia at 3 days, in contrast with no/minimal injury in the 15-min group.

DISCUSSION

EEG power after asphyxia did not discriminate between mild and severe injury in the first 3 h in preterm fetal sheep. Severe subcortical neural injury was associated with persistent loss of high-frequency activity.

METHODS

Chronically instrumented fetal sheep at 0.7 gestation (101-104 days; term is 147 days) received either 15-min (n = 13) or 25-min (n = 13) of complete umbilical cord occlusion. The Δ (0-3.9 Hz), θ (4-7.9 Hz), α (8-12.9 Hz), and β (13-22 Hz) components of the EEG were determined by power spectral analysis. Brains were taken at 3 days for histopathology.

Lentiviral-mediated gene transfer to the sheep brain: implications for gene therapy in Batten disease

The neuronal ceroid lipofuscinoses (NCLs; Batten disease) are inherited neurodegenerative lysosomal storage diseases with common clinical features of blindness and seizures culminating in premature death. Gene-therapy strategies for these diseases depend on whether the missing activity is a secreted lysosomal protein taken up by neighboring cells, or an intramembrane protein that requires careful targeting. Therapies are best developed in animal models with large complex human-like brains. Lentiviral-mediated gene delivery to neural cell cultures from normal sheep and sheep affected with an NCL resulted in green fluorescent protein (GFP) expression in neurons and neuroblasts, more efficiently than in astrocytes. Similar transgene expression was obtained from two constitutive promoters, the viral MND promoter and the human EF1α promoter. In vivo studies showed stable and persistent GFP expression throughout the cell bodies, axons, and dendrites from intracortical injections and indicated ependymal and subependymal transduction. The sheep showed no ill effects from the injections. These data support continuing gene-therapy trials in the sheep models of Batten disease.

Potential biomarkers for hypoxic-ischemic encephalopathy

Cerebral hypothermia reduces brain injury and improves behavioral recovery after hypoxia-ischemia (HI) at birth. However, using current enrolment criteria many infants are not helped, and conversely, a significant proportion of control infants survive without disability. In order to further improve treatment we need better biomarkers of injury. A 'true' biomarker for the phase of evolving, 'treatable' injury would allow us to identify not only whether infants are at risk of damage, but also whether they are still able to benefit from intervention. Even a less specific measure that allowed either more precise early identification of infants at risk of adverse neurodevelopmental outcome would reduce the variance of outcome of trials, improving trial power while reducing the number of infants unnecessarily treated. Finally, valid short-term surrogates for long term outcome after treatment would allow more rapid completion of preliminary evaluation and thus allow new strategies to be tested more rapidly. Experimental studies have demonstrated that there is a relatively limited 'window of opportunity' for effective treatment (up to about 6-8h after HI, the 'latent phase'), before secondary cell death begins. We critically evaluate the utility of proposed biochemical, electronic monitoring, and imaging biomarkers against this framework. This review highlights the two central limitations of most presently available biomarkers: that they are most precise for infants with severe injury who are already easily identified, and that their correlation is strongest at times well after the latent phase, when injury is no longer 'treatable'. This is an important area for further research.

Experimental treatments for hypoxic ischaemic encephalopathy

Hypoxic ischaemic encephalopathy continues to be a significant cause of death and disability worldwide. In the last 1-2 years, therapeutic hypothermia has entered clinical practice in industrialized countries and neuroprotection of the newborn has become a reality. The benefits and safety of cooling under intensive care settings have been shown consistently in trials; therapeutic hypothermia reduces death and neurological impairment at 18 months with a number needed to treat of approximately nine. Unfortunately, around half the infants who receive therapeutic hypothermia still have abnormal outcomes. Recent experimental data suggest that the addition of another agent to cooling may enhance overall protection either additively or synergistically. This review discusses agents such as inhaled xenon, N-acetylcysteine, melatonin, erythropoietin and anticonvulsants. The role of biomarkers to speed up clinical translation is discussed, in particular, the use of the cerebral magnetic resonance spectroscopy lactate/N-acetyl aspartate peak area ratios to provide early prognostic information. Finally, potential future therapies such as regeneration/repair and postconditioning are discussed.