Faculty Bibliography

BACKGROUND AND PURPOSE/OBJECTIVE:Perinatal hypoxia-ischemia (HI) produces acute and prolonged inflammation of the brain. Mast cells (MCs), numerous in the pia and CNS of neonatal rats, can initiate inflammation attributable to preformed mediators. MCs contribute to HI brain damage in the neonatal rat; MC stabilization protects through 48 hours of reperfusion. Here we hypothesize that HI induces early MC migration, activation, and release of proinflammatory molecules. METHODS:HI was induced by right CCA ligation and 75 minutes 8% oxygen. Histochemistry and immunocytochemistry described the time course of early cellular changes in the CNS. For neuroprotection by MC stabilization, pups were treated with Cromolyn (CR) during the initial 24 hours post-HI; brains were examined through 4 weeks. RESULTS:Brain MC number and activation were elevated in ipsilateral hemisphere immediately after HI (P<0.05), before detection of cleaved caspase-3 in neurons (NeuN+; 2 hours post-HI), astroglial activation (GFAP+ with swollen cell body, 4 hours post-HI), or microglial activation (OX42+, 4 hours post-HI). TNF-alpha-positive MCs were present in a subpopulation of MCs in control animals and the percent of TNF-alpha MCs increased dramatically ipsilaterally immediately after HI (P<0.01). Microglial TNF-alpha was evident at 4 hours; endothelial cells had no detectable TNF-alpha until 48 hours post-HI. Cromolyn prevented MC migration, reduced brain damage/neuronal loss, glial activation, and brain atrophy through 4 weeks of recovery (P<0.05). CONCLUSIONS:MCs are early responders to HI in neonatal brain. MC stabilization provides lasting protection and suggests a new target for therapeutic interventions.

Listeria monocytogenes (L. monocytogenes) can cause fatal brainstem encephalitis in both sheep and humans. Here we review evidence that the bacteria can be incorporated into axons following a primary cycle of replication in macrophages/dendritic cells after subcutaneous injection in projection areas of peripheral neurons. The molecular mechanisms for the rocketing of L. monocytogenes in the cytosol by asymmetric cometic tails and the utility of this phenomenon for bacterial migration intraaxonally both in retro- and in anterograde directions to reach the central nervous system are described. The role of the immune response in the control of L. monocytogenes spread through peripheral neurons is highlighted, and a mechanism by which bacteria may be killed inside infected neurons through a nitric oxide-dependent pathway is pointed out.

Perinatal hypoxic-ischemic (HI) brain damage is a major cause of mortality and neurological morbidity in infants and children. Using an established model of unilateral hypoxia-ischemia in neonatal rats, the present study focused on mast cells (MCs), important regulators of inflammatory processes, as potential contributors to HI damage. MCs are present in the pia of the neonatal rat, entering the central nervous system (CNS) during cerebral development along penetrating blood vessels. Following hypoxia-ischemia, MC numbers increased dramatically in the ipsilateral (ischemic) hemisphere (p < 0.01). In animals exposed to hypoxia only, the numbers of MCs were elevated in both hemispheres to an extent equal to that observed in the contralateral hemisphere of HI animals (p < 0.05 vs. control). Within damaged areas (ipsilateral only), MCs were observed in regions of activated microglia and astroglia that characterize the ischemic hemisphere. Using a triple-label paradigm, MCs were observed along elongating blood vessels, some of which express the GLUT1 isoform of the glucose transporter protein, indicative of blood-brain barrier vessels. To determine whether MC activation has a role in HI brain damage, rat pups were treated with the MCs stabilizer, disodium cromoglycate (cromolyn), prior to and/or following hypoxia-ischemia. The cromolyn treatment inhibited MC migration into the CNS (p < 0.05) and limited brain damage more than 50% (p < 0.01) vs. saline controls. These data support the hypothesis that MCs are key contributors to the extent of brain damage due to hypoxia-ischemia in the immature animal.