Neuroprotective effects of estradiol and genistein and interactions with aromatase inhibitions post cerebellar lesion in male zebra finches

Author

• Grace E. Thompson, University of MississippiFollow
• Anthony P. Irovic, University of MississippiFollow

Date of Award

Spring 5-7-2026

Document Type

Undergraduate Thesis

Department

Biology

First Advisor

Lainy B. Day

Second Advisor

Christopher Leary

Third Advisor

Andrew Pfrenger

Relational Format

Disseration/Thesis

Abstract

Across vertebrates, peripheral and brain-derived estradiol (E₂) promotes neuroplasticity. After injury, E₂ can be derived locally from testosterone via aromatase (AROM), an enzyme that is upregulated in glia at the site of neural injury. E₂disrupts testicular function and elevates cancer and stroke risk, primarily via binding to estrogen receptor alpha (ER α). Genistein (GEN), a phytoestrogen, is similar to E₂ but binds preferentially to estrogen receptor beta (ER β). It may offer neuroprotection without adverse effects of E₂. We used adult male zebra finches (ZF) to model neuroprotective effects of E₂ and GEN post-cerebellar (CB) lesion, as the CB has high ER β expression and low constitutive CB AROM that upregulates in glia post-injury. Additionally, ZFs are known for having relatively high levels of E₂ -mediated neuroplasticity and steroidogenesis, particularly in the CB. Birds were given implants containing GEN, E₂, or vehicle (CON). After 12 days, we performed stereotaxic surgery to administer a puncture lesion, followed by a local injection via this same needle of either saline (S) or an AROM inhibitor, 1% letrozole in saline (LET). This created six treatment groups: GEN+S, GEN+LET, E₂ +S, E₂ +LET, CON+S, and CON+LET (n=5-7/group). Birds were weighed on days 0, 5, 12, and 14; implant presence was confirmed and replaced if needed; birds were sacrificed 72 hours post-lesion. Testes were extracted, weighed, sectioned, and stained, followed by assessment of morphology. Brains were cryosectioned at 30 μm and stained using Fluoro-Jade B (FJ) and Terminal Deoxynucleotidyl Transferase dUTP Nick End Labeling (TUNEL) with methyl green counterstain. Lesion pathways were identified and measured based on tissue absence, morphological disruption, and FJ+ or TUNEL+ cell clusters using Cavalieri point-counting (Stereologer (SRC, Tampa, FL)) to estimate volumes. Reduction of testis mass and morphological indicators of active spermatogenesis in E₂ birds compared to GEN and CONs suggest E₂, but not GEN, has negative impacts on male fertility. CON and E₂ birds experienced weight loss across the experiment, presumably due to handling stress, but GEN birds appeared to be protected, possibly due to anti-inflammatory or lipogenic properties of GEN. We predicted that GEN and E₂ would be neuroprotective and that AROM availability would enhance neuroprotection. Given that GEN did not have negative impacts on body mass and testis morphology, it would provide a promising alternative to E₂ for neuroprotection. However, 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 between-individual variation within some groups, which could potentially be the result of differences in tissue damage during lesioning due to variation in tissue density, vascularity, or variation in circulating E₂ and GEN during treatment. E₂ and GEN commonly provided neuroprotection in various animal models using a variety of methods. Testis and body mass differences in our study suggest general effectiveness of treatments and relatively less individual variability than for lesion volumes. Further, research in our lab has consistently shown that post-CB lesion, AROM inhibition reveals deficits, while the addition of E₂ ameliorates deficits in spatial procedural learning. Thus, we discuss exclusionary evidence of methodological problems and possible roles of endocrine regulation that might contribute to the variation we see.

Recommended Citation

Thompson, Grace E. and Irovic, Anthony P., "Neuroprotective effects of estradiol and genistein and interactions with aromatase inhibitions post cerebellar lesion in male zebra finches" (2026). Honors Theses. 3492.
https://egrove.olemiss.edu/hon_thesis/3492

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