Glucose, acidosis, and perinatal hypoxic-ischemic brain damage

Vascular endothelial growth factors A and C are induced in the SVZ following neonatal hypoxia-ischemia and exert different effects on neonatal glial progenitors

Episodes of neonatal hypoxia-ischemia (H-I) are strongly associated with cerebral palsy and a wide spectrum of other neurological deficits in children. Two key processes required to repair damaged organs are to amplify the number of precursors capable of regenerating damaged cells and to direct their differentiation towards the cell types that need to be replaced. Since hypoxia induces vascular endothelial growth factor (VEGF) production, it is logical to predict that VEGFs are key mediators of tissue repair after H-I injury. The goal of this study was to test the hypothesis that certain VEGF isoforms increase during recovery from neonatal H-I and that they would differentially affect the proliferation and differentiation of subventricular zone (SVZ) progenitors. During the acute recovery period from H-I both VEGF-A and VEGF-C were transiently induced in the SVZ, which correlated with an increase in SVZ blood vessel diameter. These growth factors were produced by glial progenitors, astrocytes and to a lesser extent, microglia. VEGF-A promoted the production of astrocytes from SVZ glial progenitors while VEGF-C stimulated the proliferation of both early and late oligodendrocyte progenitors, which was abolished by blocking the VEGFR-3. Altogether, these results provide new insights into the signals that coordinate the reactive responses of the progenitors in the SVZ to neonatal H-I. Our studies further suggest that therapeutics that extend VEGF-C production and/or agonists that stimulate the VEGFR-3 will promote oligodendrocyte progenitor cell development to enhance myelination after perinatal brain injury.

Docosahexaenoic acid pretreatment confers neuroprotection in a rat model of perinatal cerebral hypoxia-ischemia

OBJECTIVE

We hypothesized that pretreatment with docosahexaenoic acid (DHA), a potentially neuroprotective polyunsaturated fatty acid, would improve function and reduce brain damage in a rat model of perinatal hypoxia-ischemia.

STUDY DESIGN

Seven-day-old rats were divided into 3 treatment groups that received intraperitoneal injections of DHA 1, 2.5, or 5 mg/kg as DHA-albumin complex and 3 controls that received 25% albumin, saline, or no injection. Subsequently, rats underwent right carotid ligation followed by 90 minutes of 8% oxygen. Rats underwent sensorimotor testing (vibrissae-stimulated forepaw placing) and morphometric assessment of right-sided tissue loss on postnatal day 14.

RESULTS

DHA pretreatment improved forepaw placing response to near-normal levels (9.5 +/- 0.9 treatment vs 7.1 +/- 2.2 controls; normal = 10; P < .0001). DHA attenuated hemisphere damage compared with controls (P = .0155), with particular benefit in the hippocampus with 1 mg/kg (38% protection vs albumin controls).

CONCLUSION

DHA pretreatment improves functional outcome and reduces volume loss after hypoxia-ischemia in neonatal rats.

Pathogenesis of hypoxic-ischemic cerebral injury in the term infant: current concepts

Multiple, biochemical cascades contribute to the pathogenesis of neonatal hypoxic-ischemic brain injury. This article summarizes experimental evidence that supports the role of excitatory amino acids, calcium, free radicals, nitric oxide, proinflammatory cytokines, and bioactive lipids. Specific vulnerabilities that distinguish the response of the immature brain from that of the mature brain are highlighted. These include increased susceptibility to excitotoxicity and free radical injury, greater tendency to apoptotic death, and heightened vulnerability of developing oligodendrocytes. Available supportive evidence from human studies is also included. Implications for clinical neuroprotective strategies are discussed.