Abstracts

Rationale: Post-stroke neurogenesis in the SGZ of the immature brain is decreased and may contribute to the long-term cognitive impairments seen. Histone deacetylase inhibition has been shown in adult models to have neuroprotective, pro-neurogenic and anti-epileptic effects. We aimed to determine if chronic histone deacetylase inhibition after stroke in the immature brain impacts post-stroke neurogenesis, injury or behavioral outcome. Methods: Two drug administration protocols were used. In the first (Protocol 1), unilateral carotid ligation of P12 CD1 mice was followed by trichostatin A (TSA, 2.5 mg/kg i.p.) or DMSO injections, or valproic acid (200 mg/kg i.p.) or saline injections, twice a day for 2 weeks from P16-P28, BrdU was administered from P20-P22, behavioral testing between P38-42, and animals perfused at P60. Sham surgery treated animals also received BrdU and behavioral testing but no drug or vehicle injections. In the second (Protocol 2), TSA (2.5 mg/kg) or vehicle was given from P16-P28, BrdU administered from P24-P26, and perfusions at P42. Injury was assessed and immunohistochemistry was performed. Density of BrdU-labeling (cells/mm DG) in the dentate gyrus was measured.Results: Data from protocol 1 did not indicate any significant overall change in injury or DG neurogenesis in either injured (n=12-15 animals/group) or uninjured (n=4-6 animals/group) animals. However, a sex-dependent upregulation in neurogenesis was detected in the contralateral DG of injured male mice only (contralateral DG: DMSO 509.8 30.80 (n=5) and TSA 741.57 74.9 (n=4) and ipsilateral DG: DMSO 572.1 86.7 and TSA 600 93.2; p=0.046 and 0.8 respectively). All groups habituated on open field testing. Comparison of valproate-treated to sham-treated animals indicated that valproate-treated animals performed less well on the T-maze and on novel object preference testing (p=0.085 T-maze, p=0.045 Novel Object Preference; see Figure 1); TSA did not impact either of these tasks. Protocol 2 resulted in significant increases in DG neurogenesis in animals treated with TSA both in injured (mean ipsilateral TSA (n=10) =845.38 91.9 versus DMSO (n=4) = 448.6 30.5, p= 0.002; mean contralateral: TSA= 1031.9 115 versus DMSO= 620 84.5, p= 0.014) and uninjured animals (mean ipsilateral TSA (n=5)= 931.8 42.4 versus DMSO (n=5) = 397.5 35.2, p=0.000; mean contralateral TSA= 1028.7 51.4 versus DMSO= 406.3 42, p=0.000; see Figure 2). No sex differences were noted in Protocol 2.Conclusions: The impact of TSA in this model is likely to depend on the age and sex of the animal, duration of TSA treatment before BrdU labeling, and/or time after BrdU labeling at which survival of newborn BrdU labeled cells are counted. Further work is being done to determine the extent of histone deacetylation and to determine the long-term impact of TSA-enhanced neurogenesis upon long-term functional outcomes. Furthermore, chronic administration of valproate may have important negative functional consequences upon the immature brain that may be related to its other mechanisms of action.