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.

Hypoxia-ischemia (HI) occurs when blood and/or oxygen delivery to the brain is compromised. HI injuries can occur in infants born prematurely (<37 weeks gestational age) or at very low birth weight (<1500 grams), as well as in term infants with birth complications. In both preterm and term HI populations, brain injury is associated with subsequent behavioral deficits. Neonatal HI injury can be modeled in rodents (e.g., the Rice-Vannucci method, via cautery of right carotid followed by hypoxia). When this injury is induced early in life (between postnatal day (P)1–5), neuropathologies typical of human preterm HI are modeled. When injury is induced later (P7–12), neuropathologies typical of those seen in HI term infants are modeled. The current study sought to characterize the similarities/differences between outcomes following early (P3) and late (P7) HI injury in rats. Male rats with HI injury on P3 or P7, as well as sham controls, were tested on a variety of behavioral tasks in both juvenile and adult periods. Results showed that P7 HI rats displayed deficits on motor learning, rapid auditory processing (RAP), and other learning/memory tasks, as well as a reduction in volume in various neuroanatomical structures. P3 HI animals showed only transient deficits on RAP tasks in the juvenile period (but not in adulthood), yet robust deficits on a visual attention task in adulthood. P3 HI animals did not show any significant reductions in brain volume that we could detect. These data suggest that: 1) behavioral deficits following neonatal HI are task-specific depending on timing of injury; 2) P3 HI rats showed transient deficits on RAP tasks; 3) the more pervasive behavioral deficits seen following P7 HI injury were associated with substantial global tissue loss; and 4) persistent deficits in attention in P3 HI subjects might be linked to neural connectivity disturbances rather than a global loss of brain volume, given that no such pathology was found. These combined findings can be applied to our understanding of differing long-term outcomes following neonatal HI injury in premature versus term infants.

No abstract

Children born prematurely (<37 weeks gestational age) or at very low birth weight (VLBW; <1500 grams) are at increased risk for hypoxic ischemic (HI) brain injuries. Term infants can also suffer HI from birth complications. In both groups, blood/oxygen delivery to the brain is compromised, often resulting in brain damage and later cognitive delays (e.g., language deficits). Literature suggests that language delays in a variety of developmentally impaired populations (including specific language impairment (SLI), dyslexia, and early HI-injury) may be associated with underlying deficits in rapid auditory processing (RAP; the ability to process and discriminate brief acoustic cues). Data supporting a relationship between RAP deficits and poor language outcomes is consistent with the “magnocellular theory,” which purports that damage to or loss of large (magnocellular) cells in thalamic nuclei could underlie disruptions in temporal processing of sensory input, possibly including auditory (medial geniculate nucleus; MGN) information This theory could be applied to neonatal HI populations that show subsequent RAP deficits. In animal models of neonatal HI, persistent RAP deficits are seen in postnatal (P)7 HI injured rats (who exhibit neuropathology comparable to term birth injury), but not in P1–3 HI injured rodents (who exhibit neuropathology comparable to human pre-term injury). The current study sought to investigate the mean cell size, cell number, and cumulative probability of cell size in the MGN of P3 HI and P7 HI injured male rats that had previously demonstrated behavioral RAP deficits. Pilot data from our lab (Alexander et al., 2011) previously revealed cell size abnormalities (a shift towards smaller cells) in P7 but not P1 HI injured animals when compared to shams. Our current finding support this result, with evidence of a significant shift to smaller cells in the experimental MGN of P7 HI but not P3 HI subjects. P7 HI animals also showed significantly fewer cells in the affected (right) MGN as compared P3 HI and shams animals. Moreover, cell number in the right hemisphere was found to correlate with gap detection (fewer cells = worse performance) in P7 HI injured subjects. These findings could be applied to clinical populations, providing an anatomic marker that may index potential long-term language disabilities in HI injured infants and possibly other at-risk populations.

Formate (FM) is a substrate in one-carbon metabolism, and recent studies implicate its function in both health and disease, but a role in the heart remains unexplored. Research from our group demonstrates that the loss of formaldehyde dehydrogenase, which oxidizes formaldehyde into FM, ameliorates sex-dependent cardioprotection against ischemia-reperfusion (I/R) injury in the female mouse heart. Considering that FM depletion may be detrimental, we tested the hypothesis that FM yields cardioprotective benefit in a model of I/R injury. Hearts from male and female mice (n=5-10/group) were subjected to ex vivo I/R injury with or without FM via Langendorff perfusion. FM significantly enhanced post-ischemic functional recovery in male hearts (27.1%, 95% CI 10.8 to 45.9, p=0.0023; females: 9.5%, 95% CI -6.9 to 27.8, p=0.2020) and decreased infarct size (males: -24.6%, 95% CI -35.1 to -12.2, p<0.0001; females: -3.7%, 95% CI -9.6 to -0.3, p=0.1128), indicating that FM protects the myocardium against I/R injury. Although FM had a greater protective effect in male hearts than in female hearts, plasma FM levels were greater in female mice, suggesting that FM-mediated cardioprotection may already exist near steady state in females. Mechanistically, cardiomyoblasts stimulated with FM exhibited a significant increase in total protein S-nitrosylation (SNO) without changing nitric oxide synthase (NOS) phosphorylation or protein expression; this was suppressed by NOS inhibition, suggesting that FM contributes to NOS-dependent NO cycling in the heart. FM-treated cardiomyocytes and cardiomyoblasts also exhibited significant increases in mitochondrial marker protein expression, metabolic activity, and maximal oxygen consumption, demonstrating an enhanced respiratory capacity to respond to increased energetic demand. Furthermore, FM treatment significantly increased phospho-activation of the energy regulator AMPKα and the protein expression of PGC-1α targets, indicating a potential upregulation in mitochondrial biogenesis. Taken together, these data suggest that FM may stimulate protein SNO and mitochondrial activity to protect the heart against I/R injury.