Neuro-protective effects of growth hormone (GH) after hypoxia-ischemia injury in embryonic chicken cerebellum.

Neuroprotection is a mechanism within the central nervous system (CNS) that protects neurons from damage as a result of a severe insult. It is known that growth hormone (GH) is involved in cell survival and may inhibit apoptosis in several cell types, including those of the CNS. Both GH and GH-receptor (GHR) genes are expressed in the cerebellum. Thus, we investigated the possible neuroprotective role of GH in this organ, which is very sensitive to hypoxic/ischemic conditions. Endogenous GH levels increased in the brain and cerebellum (30% and 74%, respectively) of 15-day-old chicken embryos exposed to hypoxia during 24h compared to normoxia. In primary embryonic cerebellar neuron cultures treated under hypoxia (0.5% O(2)) and low glucose (1g/L) conditions (HLG) for 1h, GH levels increased 1.16-fold compared to the control. The addition of 1nM recombinant chicken GH (rcGH) to cultures during HLG increased cell viability (1.7-fold) and the expression of Bcl-2 (1.67-fold); in contrast the caspase-3 activity and the proportion of apoptotic cells decreased (37% and 54.2%, respectively) compared to HLG. rcGH activated the PI3K/Akt pathway both under normoxic and HLG conditions, increasing the proportion of phosphorylated Akt (1.7- and 1.4-fold, respectively). These effects were abolished by wortmannin and by immunoneutralization, indicating that GH acts through this signaling pathway. Furthermore, the 15-kDa GH variant (10nM) significantly increased cell viability and decreased caspase-3 activity during HLG condition. Thus GH may act as a paracrine/autocrine neuroprotective factor that preserves cellular viability and inhibits apoptotic cell death.

Deleterious effects of high dose connexin 43 mimetic peptide infusion after cerebral ischaemia in near-term fetal sheep.

Hypoxic-ischaemic brain injury at birth is associated with 1-3/1000 cases of moderate to severe encephalopathy. Previously, we have shown that connexin 43 hemichannel blockade, with a specific mimetic peptide, reduced the occurrence of seizures, improved recovery of EEG power and sleep state cycling, and improved cell survival following global cerebral ischaemia. In the present study, we examined the dose response for intracerebroventricular mimetic peptide infusion (50 µmol/kg/h for 1 h, followed by 50 µmol/kg/24 h (low dose) or 50 µmol/kg/h for 25 h (high dose) or vehicle only (control group), starting 90 min after the end of ischaemia), following global cerebral ischaemia, induced by 30 min bilateral carotid artery occlusion, in near-term fetal sheep (128 ± 1 days gestation). Both peptide infusion groups were associated with a transient significant increase in EEG power between 2-12 h after ischaemia. The ischaemia-low dose group showed a significant recovery of EEG power from day five compared to the ischaemia-vehicle and -high dose groups. In contrast, the high dose infusion was associated with greater secondary increase in impedance (brain cell swelling), as well as a trend towards a greater increase in lactate concentration and mortality. These data suggest that higher doses of connexin mimetic peptide are not beneficial and may be associated with adverse outcomes, most likely attributable to uncoupling of connexin 43 gap junctions leading to dysfunction of the astrocytic syncytium.

Retrospective comparison of caffeine and doxapram for the treatment of hypercapnia in foals with hypoxic-ischemic encephalopathy.

BACKGROUND: Despite a lack of data regarding their efficacy, both caffeine and doxapram have been recommended for treatment of hypercapnia in equine neonates with central nervous system damage. HYPOTHESIS: Caffeine and doxapram alleviate hypercapnia in foals with hypoxic-ischemic encephalopathy. ANIMALS: Sixteen foals treated with either caffeine (n = 8) or doxapram (n = 8). METHODS: Information on age, body temperature, heart rate, respiratory rate, arterial blood gas parameters, duration of therapy, and outcome was abstracted from each medical record. RESULTS: Therapy with doxapram resulted in a significant decrease in partial pressure of carbon dioxide (PaCO2 [P= .004]), bicarbonate concentration (P= .002), and base excess (P= .005) compared with baseline values but failed to correct acidemia. In contrast, administration of caffeine did not result in significant changes from baseline values. The percentage decrease in PaCO2 and bicarbonate concentration was significantly greater in foals treated with doxapram than in foals treated with caffeine (P= .004). The proportions of foals that achieved the targeted PaCO2 (< or = 50 mmHg) were significantly higher in foals treated with doxapram than in foals treated with caffeine (P= .029). The proportion of survivors in the 2 treatment groups was not significantly different. CONCLUSIONS AND CLINICAL IMPORTANCE: Doxapram is more effective than caffeine for rapid correction of hypercapnia in foals with hypoxic-ischemic encephalopathy.

Is turtle longevity linked to enhanced mechanisms for surviving brain anoxia and reoxygenation?

We suggest that the processes that protect the turtle brain against anoxia and subsequent reoxygenation might also contribute to turtle longevity since many of them are linked to age related neurodegeneration. In the turtle the mechanisms for conserving ion channel function are particularly robust. The anoxic turtle brain avoids excitatory neurotransmitter toxicity by maintaining a balance between dopamine and glutamate-release and still active uptake mechanisms. In the anoxic turtle brain the inhibitory tone is strengthened through a sustained rise in extracellular GABA, and a corresponding increase in the density of GABA(A) receptors. The turtle has enhanced mechanisms that protect against the formation of ROS and mechanisms to protect from ROS damage. As many of these may be selectively activated during anoxia and recovery, the turtle could serve as a useful model to identify and investigate mechanisms for activating key protection and rescue mechanisms implicated in aging.

Postmortem stability of S100B in the aqueous humor of northern fur seals (Callorhinus ursinus).

Bycatch (accidental drowning in fishing nets) is a significant problem for some marine mammal species, but can be difficult to diagnose as there are no pathognomonic gross or histological lesions. In human medicine, biomarkers such as S100B are increasingly being used to investigate hypoxic-ischemic syndromes, but, to the authors' knowledge, studies using this marker have not been reported for marine mammal species. The aims of the current study were to determine baseline postmortem S100B levels in a pinniped species, and to determine whether S100B levels were stable over a postmortem interval of 48 hr. Aqueous humor, which is simple to collect and avoids many of the problems associated with postmortem collection of blood, was used as a surrogate for serum. S100B was detected in the aqueous humor of acute deaths (<15 min) and was stable for up to 48 hr, with a wider variation in values at the 48-hr time interval.

Hypoxic ischemic encephalopathy--what can we learn from humans?

Hypoxic ischemic encephalopathy (HIE) is a condition that occurs in both human newborns and foals. The condition is the subject of extensive current research in human infants, but there have been no direct studies of HIE in foals, and hence, knowledge of the condition has been extrapolated from studies in humans and other animal models. The purpose of this review article is to highlight the most up-to-date and relevant research in the human field, and discuss how this potentially might have an impact in the management of foals with HIE.

Biomarkers of brain injury in foals with hypoxic-ischemic encephalopathy.

BACKGROUND: Neonatal hypoxic-ischemic encephalopathy (NHIE) is a disease affecting newborn foals for which there is no antemortem diagnostic test. HYPOTHESIS: Ubiquitin C-terminal hydrolase 1 (UCHL1) and the phosphorylated axonal forms of neurofilament H (pNF-H) are markers of brain injury in foals with NHIE. ANIMALS: Thirty-three foals with a clinical diagnosis consistent with NHIE and 17 healthy foals. METHODS: Retrospective study. Concentrations of UCHL1 and pNF-H in plasma were measured by ELISA. The performance of the assays for the diagnosis of NHIE was assessed by receiver operating characteristic curve analysis. Concentrations of UCHL1 and pNF-H were measured throughout the brains of 2 healthy foals. RESULTS: The diagnostic performance of UCHL1 (AUC = 0.86) was significantly higher (P = .001) than that of pNF-H (0.52) for the diagnosis of NHIE. Median concentrations of UCHL1 (6.57 ng/mL; 2.35-11.90 ng/mL) in foals with a clinical diagnosis of NHIE were significantly (P < .001) higher than those of healthy controls (2.52 ng/mL; 1.4-4.01 ng/mL). The right sided reference interval for UCHL1 concentrations in healthy foals was 0-4.01 ng/mL. The sensitivity and specificity of UCHL1 (>4.01 ng/mL) for diagnosis of NHIE were 70% (51-84%) and 94% (72-99%), respectively. UCHL1 concentrations were higher in gray than white matter, while pNF-H concentrations were higher in white than gray matter. CONCLUSIONS AND CLINICAL IMPORTANCE: UCHL1 has potential as a marker of brain injury in foals with NHIE.

Effects of selective head cooling on cerebral blood flow and metabolism in newborn piglets after hypoxia-ischemia.

AIM: the effect of selective head cooling on cerebral blood flow (CBF) and cerebral metabolism rate (CMR) was investigated in newborn piglets. METHODS: seven days old newborn piglets were randomly assigned to one of the following three groups: Selective head cooling in normal piglets (n=4), selective head cooling after HI (n=6) and normal temperature after HI (n=6). CBF was measured with color microspheres. Cerebral oxygenation metabolism rate (CMRO(2)), Cerebral glucose consumption (CMR(Glu)) and Cerebral lactate production (CMR(lac)) were calculated. RESULT: in normal piglets, CBF, CMRO(2) and CMR(glu) were significantly decreased at both 35°C (P<0.05) and 32°C (P<0.01), while CMR(lac) did not change. Compared to baseline, CBF and CMRO(2) were significantly reduced (P<0.05), while CMR(glu) and CMR(lac) were significantly increased (P<0.01), AVDO(2) was decreased (P<0.05), while AVD(glu) and AVD(lac) were significantly increased (P<0.01 respectively) in HI piglets with normal temperature respectively. Compared to normal temperature after HI, selective head cooling after HI significantly reduced CMR(glu) and CMR(lac), and AVDO(2), AVD(glu), AVD(lac) were improved at 35°C. CONCLUSION: selective head cooling not only reduced energy consumption, but also improve brain oxygen metabolism in newborn after HI.

Hypoxic/ischemic encephalopathy associated with placental insufficiency in a cloned foal.

Hypoxic/ischemic encephalopathy in a cloned American Quarter horse foal was initially associated with placental insufficiency and exacerbated by protracted hypotension during anesthesia for a surgical procedure. The foal, born at the Texas A&M Veterinary Medical Center, was diagnosed at birth with neonatal maladjustment syndrome that was accompanied by dysmaturity, muscle contracture of the front limbs, and a blood clot within the lumen of the urinary bladder. Seizures that developed after anesthesia were attributed to hypoxia/ischemia during anesthesia and culminated in death. Macroscopically, the cerebrum had flattened cerebral gyri with shallow sulci, yellowish cortical discoloration, and apple-green autofluorescence (under 365-nm ultraviolet light) at the cortical/white matter junction. Microscopically, there was laminar cortical necrosis with prominent diffuse ischemic change of neuronal cell bodies. The white matter had prominent rarefaction with focal axonal and myelin degeneration and focal macrophage (gitter cell) accumulation. Additionally, there was astrocytic hypertrophy with gemistocyte formation. The chorioallantois was diffusely thickened in the area corresponding to the uterine horns. Histologically, microcotyledons were markedly attenuated with absence of chorionic villi.