Minimal systemic hypothermia combined with selective head cooling evaluated in a pig model of hypoxia-ischemia

Administration of selective brain hypothermia using a simple cooling device in neonatal rats

BACKGROUND

The interruption of oxygen and blood supply to the newborn brain around the time of birth is a risk factor for hypoxic-ischemic encephalopathy and may lead to infant mortality or lifelong neurological impairments. Currently, therapeutic hypothermia, the cooling of the infant's head or entire body, is the only treatment to curb the extent of brain damage.

NEW METHOD

In this study, we designed a focal brain cooling device that circulates cooled water at a steady state temperature of 19 ± 1 °C through a coil of tubing fitted onto the neonatal rat's head. We tested its ability to selectively decrease brain temperature and offer neuroprotection in a neonatal rat model of hypoxic-ischemic brain injury.

RESULTS

Our method cooled the brain to 30-33 °C in conscious pups, while keeping the core body temperature approximately 3.2 °C warmer. Furthermore, the application of the cooling device to the neonatal rat model demonstrated a reduction in brain volume loss compared to pups maintained at normothermia and achieved a level of brain tissue protection the same as that of whole-body cooling.

COMPARISON WITH EXISTING METHODS

Prevailing methods of selective brain hypothermia are designed for adult animal models rather than for immature animals such as the rat as a conventional model of developmental brain pathology. Contrary to existing methods, our method of cooling does not require surgical manipulation or anaesthesia.

CONCLUSION

Our simple, economical, and effective method of selective brain cooling is a useful tool for rodent studies in neonatal brain injury and adaptive therapeutic interventions.

Spatial T-maze identifies cognitive deficits in piglets 1 month after hypoxia-ischemia in a model of hippocampal pyramidal neuron loss and interneuron attrition

Neonatal brain injury from hypoxia-ischemia (HI) causes major morbidity. Piglet HI is an established method for testing neuroprotective treatments in large, gyrencephalic brain. Though many neurobehavior tests exist for rodents, such tests and their associations with neuropathologic injury remain underdeveloped and underutilized in large, neonatal HI animal models. We examined whether spatial T-maze and inclined beam tests distinguish cognitive and motor differences between HI and sham piglets and correlate with neuropathologic injury. Neonatal piglets were randomized to whole-body HI or sham procedure, and they began T-maze and inclined beam testing 17 days later. HI piglets had more incorrect T-maze turns than did shams. Beam walking time did not differ between groups. Neuropathologic evaluations at 33 days validated the injury with putamen neuron loss after HI to below that of sham procedure. HI decreased the numbers of CA3 pyramidal neurons but not CA1 pyramidal neurons or dentate gyrus granule neurons. Though the number of hippocampal parvalbumin-positive interneurons did not differ between groups, HI reduced the number of CA1 interneuron dendrites. Piglets with more incorrect turns had greater CA3 neuron loss, and piglets that took longer in the maze had fewer CA3 interneurons. The number of putamen neurons was unrelated to T-maze or beam performance. We conclude that neonatal HI causes hippocampal CA3 neuron loss, CA1 interneuron dendritic attrition, and putamen neuron loss at 1-month recovery. The spatial T-maze identifies learning and memory deficits that are related to loss of CA3 pyramidal neurons and fewer parvalbumin-positive interneurons independent of putamen injury.

Cerebral Alterations Following Experimental Multiple Trauma and Hemorrhagic Shock

Multiple trauma (MT) associated with hemorrhagic shock (HS) might lead to cerebral hypoperfusion and brain damage. We investigated cerebral alterations using a new porcine MT/HS model without traumatic brain injury (TBI) and assessed the neuroprotective properties of mild therapeutic hypothermia. Male pigs underwent standardized MT with HS (45% or 50% loss of blood volume) and resuscitation after 90/120 min (T90/T120). In additional groups (TH90/TH120) mild hypothermia (33°C) was induced following resuscitation. Normothermic or hypothermic sham animals served as controls. Intracranial pressure, cerebral perfusion pressure (CPP), and cerebral oxygenation (PtiO2) were recorded up to 48.5 h. Serum protein S-100B and neuron-specific enolase (NSE) were measured by ELISA. Cerebral inflammation was quantified on hematoxylin and eosin -stained brain slices; Iba1, S100, and inducible nitric oxide synthase (iNOS) expression was assessed using immunohistochemistry. Directly after MT/HS, CPP and PtiO2 were significantly lower in T90/T120 groups compared with sham. After resuscitation both parameters showed a gradual recovery. Serum protein S-100B and NSE increased temporarily as a result of MT/HS in T90 and T90/T120 groups, respectively. Cerebral inflammation was found in all groups. Iba1-staining showed significant microgliosis in T90 and T120 animals. iNOS-staining indicated a M1 polarization. Mild hypothermia reduced cerebral inflammation in the TH90 group, but resulted in increased iNOS activation. In this porcine long-term model, we did not find evidence of gross cerebral damage when resuscitation was initiated within 120 min after MT/HS without TBI. However, trauma-related microglia activation and M1 microglia polarization might be a consequence of temporary hypoxia/ischemia and further research is warranted to detail underlying mechanisms. Interestingly, mild hypothermia did not exhibit neuroprotective properties when initiated in a delayed fashion.

Association of impaired neuronal migration with cognitive deficits in extremely preterm infants

Many extremely preterm infants (born before 28 gestational weeks [GWs]) develop cognitive impairment in later life, although the underlying pathogenesis is not yet completely understood. Our examinations of the developing human neocortex confirmed that neuronal migration continues beyond 23 GWs, the gestational week at which extremely preterm infants have live births. We observed larger numbers of ectopic neurons in the white matter of the neocortex in human extremely preterm infants with brain injury and hypothesized that altered neuronal migration may be associated with cognitive impairment in later life. To confirm whether preterm brain injury affects neuronal migration, we produced brain damage in mouse embryos by occluding the maternal uterine arteries. The mice showed delayed neuronal migration, ectopic neurons in the white matter, altered neuronal alignment, and abnormal corticocortical axonal wiring. Similar to human extremely preterm infants with brain injury, the surviving mice exhibited cognitive deficits. Activation of the affected medial prefrontal cortices of the surviving mice improved working memory deficits, indicating that decreased neuronal activity caused the cognitive deficits. These findings suggest that altered neuronal migration altered by brain injury might contribute to the subsequent development of cognitive impairment in extremely preterm infants.

Who should we cool after perinatal asphyxia?

Three ongoing challenges have arisen after the introduction of therapeutic hypothermia (TH) as standard of care for term newborns with moderate or severe perinatal asphyxia: (i) to ensure that the correct group of infants are cooled; (ii) to optimize the delivery of TH and intensive care in relation to the severity of the encephalopathy; (iii) to systematically follow up the long-term efficacy of TH using comparable outcome data between centers and countries. This review addresses the entry criteria for TH, and discusses potential issues regarding patient selection, and management of TH: cooling mild, moderate, and very severe perinatal asphyxia, cooling longer or deeper, and/or starting with a greater delay. This includes cooling of patients outside of standard trial entry criteria, such as after postnatal collapse, premature infants, those with infection, and infants with metabolic, chromosomal or surgical diagnoses in addition to perinatal asphyxia.