Date of Award
Lainy B. Day
Alberto Del Arco
The estradiol (E2) synthetic pathway converts testosterone to E2 via aromatase (AROM) and plays an important role in neuroplasticity. However, exogenous E2 increases cancer risk and interferes with gonadal function. Phytoestrogens, plant-based estrogens, may provide neuroprotection without negative E2 effects. Genistein (GEN), a soy phytoestrogen, preferentially binds to estrogen receptor beta (ER β), which is expressed at a relatively higher concentration than ER α in the cerebellum (CB). The songbird CB is an ideal model for steroid-mediated plasticity. Songbird brains are highly plastic and CB contains all steroid-synthetic enzymes. Previous studies in zebra finches (ZF) have shown that AROM and E2 prevent post-injury secondary neurodegeneration. In our lab, we implanted adult male ZF with either E2, GEN, or silastic vehicle (CON) and injected either saline (S) or an AROM inhibitor, letrozole (LET) during delivery of cerebellar puncture lesions to test hormonal effects on testes morphology, body weight, and neuroprotection. We previously reported that E2, compared to GEN and control birds, had reduced testis mass, spermatozoa number, and laminarity. We also found that body mass, which often decreases in birds over the course of invasive experiments, decreased in E2 and control birds but not GEN birds. This suggests GEN may influence fat metabolism as has been previously shown. In the present study, I determined the extent of neuroprotection by measuring the volume of the lesion as a consequence of secondary degeneration as labeled by Terminal Deoxynucleotidyl Transferase dUTP Nick End Labeling (TUNEL) for each group. We expected that subjects given an injection of E2 + S and GEN + S would have the smallest lesion volume, as the E2 and GEN should provide neuroprotection. We expected that the size of the lesion would be somewhat increased in subjects given E2 + LET and GEN + LET, as the implanted E2 and GEN could counter local inhibition of AROM. We expected that subjects given CON + S would have the second largest lesion volume, as there is no additional E2 or GEN to contribute to neuroprotection. Finally, we expected that subjects given CON + LET would have the largest lesion volume, as LET blocks the production of E2 by AROM and no additional E2 or GEN is present. Having measured 3-4 subjects per group, we did not detect a significant impact of local or systemic treatments on secondary degeneration. There was considerable individual variation within some groups that could be due to variation in circulating hormone levels that will be measured by high-performance liquid chromatography (HPLC) in the future. Power analyses indicate low power and the need for 18 additional subjects or 3 per group, which we have ready to be measured. Furthermore, we have performed a secondary assay that labels necrotic cells with Fluro-Jade (FJ) and measuring of lesion volumes in this complementary assay should help to refine our conclusions.
Breaux, Renee E., "The Neuroprotective Effects of Estradiol and Genistein in Zebra Finch Cerebellum" (2022). Honors Theses. 2715.