Dissociation in the Effects of Induced Neonatal Hypoxia-Ischemia on Rapid Auditory Processing and Spatial Working Memory in Male Rats

Therapeutic Interventions in Rat Models of Preterm Hypoxic Ischemic Injury: Effects of Hypothermia, Caffeine, and the Influence of Sex

Infants born prematurely have an increased risk of experiencing brain injury, specifically injury caused by Hypoxia Ischemia (HI). There is no approved treatment for preterm infants, in contrast to term infants that experience Hypoxic Ischemic Encephalopathy (HIE) and can be treated with hypothermia. Given this increased risk and lack of approved treatment, it is imperative to explore and model potential treatments in animal models of preterm injury. Hypothermia is one potential treatment, though cooling to current clinical standards has been found to be detrimental for preterm infants. However, mild hypothermia may prove useful. Caffeine is another treatment that is already used in preterm infants to treat apnea of prematurity, and has shown neuroprotective effects. Both of these treatments show sex differences in behavioral outcomes and neuroprotective effects, which are critical to explore when working to translate from animal to human. The effects and research history of hypothermia, caffeine and how sex affects these treatment outcomes will be explored further in this review article.

Evaluation of tissue perfusion status in moderate to late preterm

The aim of this study was to investigate the tissue perfusion status and circadian rhythm in moderately premature infants. As a prospective study, from July 2019 to October 2019, the haemodynamic stability of moderate to late preterm, including such indicators as perfusion index (PI), blood pressure (systolic/diastolic) (BP), heart rate (HR), respiratory rate (RR), oxygen saturation (SpO2) and body temperature were monitored in the morning and at night within eight days after birth. There was no difference of statistical significance between PI values in the morning and at night (P>0.05). The HR from days six to eight after birth was higher than days one to three (P<0.05). The HR increased significantly on days seven and eight compared with days four and five (P<0.05). The BP from days three to eight was significantly higher than on day one (P<0.05), and the BP from days four to eight was higher than on day two. There was a weak positive correlation between the PI values and gestational age (GA) (r=0.097), HR (r=0.067) and time (r=0.284), and a negative correlation with SpO2 (r=-0.113). The PI and HR of moderate to late preterm increased within eight days after birth. BP was relatively lower after birth and gradually increased to a stable level on days three to four. The PI and BP circadian rhythms associated with tissue perfusion were not established on day eight after birth.

Deficits in ultrasonic vocalization development and production following neonatal hypoxic ischemic insult

Neonatal hypoxic ischemia encephalopathy (HIE) leads to major deficits in language development. While clinically there is a known correlation in the degree of HIE injury and subsequent language disability, there are no treatments beyond speech and language therapy; therefore, experimental studies with a HIE animal model to test new interventions and therapeutics are warranted. Neonatal rodents normally ultrasonically vocalize at postnatal day 7 (PND 7) to PND 14 in response to removal from their mothers. At 6-8 weeks of age juvenile male rodents ultrasonically vocalize in response to exposure to a mature female mouse. Changes in ultrasonic vocalization (USV) production after neonatal brain injury, such ashypoxic ischemia (HI), have not been studied. This study examines the acute and long-term ultrasonic vocalization ability of mice after HI at PND 10. Pups were subjected to HI, sham, or naïve conditions; where in HI and sham surgeries the right common carotid artery was exposed, in the HI this artery was double ligated. The HI and sham pups were then exposed to60minof hypoxia. Naïve pups did not undergo surgery and were subjected to60minof room air. At 3 days following surgery, HI and sham pups vocalize less than nonsurgical naïve controls; yet "juvenile" mice of 6-8 weeks old that underwent HI at PND 10 vocalize less than sham and naïve mice. We conclude that HI injury has significant impact on later adult vocalization.

Effects of Sex and Mild Intrainsult Hypothermia on Neuropathology and Neural Reorganization following Neonatal Hypoxic Ischemic Brain Injury in Rats

Hypoxia ischemia (HI) is a recognized risk factor among late-preterm infants, with HI events leading to varied neuropathology and cognitive/behavioral deficits. Studies suggest a sex difference in the incidence of HI and in the severity of subsequent behavioral deficits (with better outcomes in females). Mechanisms of a female advantage remain unknown but could involve sex-specific patterns of compensation to injury. Neuroprotective hypothermia is also used to ameliorate HI damage and attenuate behavioral deficits. Though currently prescribed only for HI in term infants, cooling has potential intrainsult applications to high-risk late-preterm infants as well. To address this important clinical issue, we conducted a study using male and female rats with a postnatal (P) day 7 HI injury induced under normothermic and hypothermic conditions. The current study reports patterns of neuropathology evident in postmortem tissue. Results showed a potent benefit of intrainsult hypothermia that was comparable for both sexes. Findings also show surprisingly different patterns of compensation in the contralateral hemisphere, with increases in hippocampal thickness in HI females contrasting reduced thickness in HI males. Findings provide a framework for future research to compare and contrast mechanisms of neuroprotection and postinjury plasticity in both sexes following a late-preterm HI insult.

Sex differences in behavioral outcomes following temperature modulation during induced neonatal hypoxic ischemic injury in rats

Neonatal hypoxia ischemia (HI; reduced oxygen and/or blood flow to the brain) can cause various degrees of tissue damage, as well as subsequent cognitive/behavioral deficits such as motor, learning/memory, and auditory impairments. These outcomes frequently result from cardiovascular and/or respiratory events observed in premature infants. Data suggests that there is a sex difference in HI outcome, with males being more adversely affected relative to comparably injured females. Brain/body temperature may play a role in modulating the severity of an HI insult, with hypothermia during an insult yielding more favorable anatomical and behavioral outcomes. The current study utilized a postnatal day (P) 7 rodent model of HI injury to assess the effect of temperature modulation during injury in each sex. We hypothesized that female P7 rats would benefit more from lowered body temperatures as compared to male P7 rats. We assessed all subjects on rota-rod, auditory discrimination, and spatial/non-spatial maze tasks. Our results revealed a significant benefit of temperature reduction in HI females as measured by most of the employed behavioral tasks. However, HI males benefitted from temperature reduction as measured on auditory and non-spatial tasks. Our data suggest that temperature reduction protects both sexes from the deleterious effects of HI injury, but task and sex specific patterns of relative efficacy are seen.