Abstracts

Rationale: Neonatal strokes present with seizures, which are treated with anticonvulsants such as phenobarbital. The impact of phenobarbital upon post-neonatal stroke plasticity and neurogenesis is an area of active research and controversy. The effects of chronic phenobarbital dosing on post-stroke hilar neurogenesis were examined in a mouse model of neonatal ischemia induced through unilateral carotid ligation. Methods: Right-sided unilateral common carotid ligation of P12 CD1 mice was followed by phenobarbital (n=33) or vehicle (n=33) treatment (25mg/kg i.p.) twice daily for 2 weeks from P16-P28, and 5 injections of bromodeoxyuridine (50mg/kg i.p.) from P24-P26. Behavioral testing was conducted from P53-P57, and animals were perfused at P60 (n=66). Immunohistochemistry was performed for co-labeling with BrdU-NeuN and Dapi. Hilar counts of all BrdU labeled, BrdU-NeuN colabeled, and BrdU only labeled cells were performed using a Zeiss Apotome Microscope. Results: Phenobarbital treated animals demonstrated a decrease in hilar cell birth compared to uninjured animals bilaterally (p= 0.001 ipsilateral, and p= 0.003 contralaterally). In phenobarbital treated injured animals, hilar non-neuronal cell birth was positively correlated with weight on P25-P28 and negatively correlated with hippocampal atrophy (phenobarbital r=-0.826, p=0.002 ipsilateral; r=-0.656, p=0.011 contralateral). In phenobarbital treated animals, hilar non-neuronal cell birth negatively correlated with seizure scores (contralateral r= -0.746, p=0.002; ipsilateral r= -0.835, p=0.001), while no such significant correlations were found in saline treated animals. Injured saline animals demonstrated a decrease in percent alternation on the T-Maze task compared to uninjured saline treated animals (51.19% alternation in injured versus 62.43% in uninjured, p=0.023); in phenobarbital treated injured animals a significant decrease in percent alternation was not noted (58.78% alternation in injured phenobarbital treated versus 62.43% in uninjured saline treated, and versus 64.77% in phenobarbital treated uninjured animals). Conclusions: Phenobarbital treated injured animals demonstrated a significant decrease in bilateral hilar neurogenesis at P60. The effects of phenobarbital were injury dependent and resulted in associations between acute seizures, injury, and chronic non-neuronal hilar neurogenesis. In addition phenobarbital treatment produced a positive impact upon stroke-induced visual-spatial working memory impairment. These results suggest that after neonatal stroke, phenobarbital may have positive effects, possibly reducing chronic gliosis and/or inflammation in the hilus, and thereby result in improved functional outcome.