The Role of Neutrophils in the Production of Hypoxic-Ischemic Brain Injury in the Neonatal Rat

Abstract

Neutrophils contribute to ischemic brain injury in adult animals. The role of neutrophils in perinatal hypoxic-ischemic (HI) brain injury is unknown. Allopurinol reduces neutrophil accumulation after tissue ischemia and is protective against HI brain injury. This study was designed to investigate how neutrophils contribute to perinatal hypoxic ischemic brain injury and how neutropenia compared with allopurinol in its neuroprotective effects. A HI insult was produced in the right cerebral hemisphere of 7-d-old rats by right common carotid artery ligation and systemic hypoxia. Half the rats were rendered neutropenic with an anti-neutrophil serum (ANS). At 15 min of recovery from hypoxia, half the neutropenic and nonneutropenic rats received allopurinol (135 mg/kg, s.c.). The protective effect of the four treatment combinations was determined on brain swelling at 42 h of recovery. Neutropenia reduced brain swelling by about 70%, p < 0.01. Allopurinol alone produced similar protection so that the relatively small number of animals studied did not permit assessment of an additive effect. Neutrophil accumulation in cerebral hemispheres was measured by myeloperoxidase (MPO) activity assay and by neutrophil counts in 6-microm sections stained by MPO and ANS immunostaining. MPO activity peaked between 4 and 8 h of recovery in both hemispheres. Hemispheric neutrophil counts peaked at the end of the HI insult and again at 18 h of recovery. Neutrophils were stained within blood vessels and did not infiltrate the injured brain before infarction had occurred. We conclude that neutrophils contribute to HI brain injury in the neonate and that neutrophil depletion before the insult is neuroprotective.

Aggravated Brain Damage After Hypoxic Ischemia in Immature Adenosine A 2A Knockout Mice

“…19 Release of free radicals from activated neutrophils and reperfusion injury in the canine heart are both attenuated by A2AR activation. 23 Furthermore, it is shown that cell death and proinflammatory events after intracerebral hemorrhage were decreased after administration of an A2AR agonist.…”

“…It is well known from previous studies that the mechanisms underlying postischemic brain damage 1,2,5,19 as well as the role of adenosine receptors 3 differ in many ways between young and old mice (see below). An age-dependent difference in A2AR is also indicated by the fact that in adult rats an A2AR antagonist has a clear cerebroprotective effect, 13 consistent with the findings in adult A2AR…”

Mechanisms of Perinatal Arterial Ischemic Stroke

“…Both animal and human studies in the adult show that neutrophils infiltrate the brain and contribute to BBB disruption after transient cerebral ischemia ( Figure 4B) and that neutropenia is neuroprotective. 137,138 In contrast to adults, neutrophil infiltration in neonates is negligible after tMCAO 77 and is very limited 139 or brief 140 after H-I. Although the exact mechanisms that restrict neutrophil infiltration in the injured neonatal brain are yet to be understood, and it remains unclear whether the higher resistance of the neonatal BBB to stroke is a cause or a consequence of reduced leukocyte infiltration, the different patterns of expression of adhesion molecules and matrix metalloproteinases between neonatal and adult rodents, along with changing chemokine gradients between the brain and the blood, may limit neutrophil extravasation in the neonate.…”

Neuroprotective strategies and the underlying molecular basis of cerebrovascular stroke

“…28 Infiltration of circulating leukocytes, including polymorphonuclear leukocytes and T cells, impairs recovery after ischemic stroke. 12,46,67,100 Increased cerebral edema after ischemic stroke also plays a role in poorer patient prognosis. 137 Involvement of the sodium-hydrogen antiporter family members, sulfonylurea receptor 1-transient receptor potential melastatin 4 (SUR1-TRPM4) cation channel, and aquaporin-4 is particularly important in mediating increased cerebral edema after ischemic stroke.…”