No Sex Differences in Spatial Memory Ability or Response to Aromatase Inhibition after Cerebellar Lesion in Zebra Finches
Chyna-Rae Dearman1, Logan Boutwell1, Zahra Jiwani1, Emily McFatridge1, LeMarcus Echoles1, Jervia Powell3, Lainy B. Day1,2
1Department of Biology, University of Mississippi , Oxford, MS
2Interdisciplinary Neuroscience Minor, University of Mississippi, Oxford, MS
3Mississippi INBRE
Steroid hormones are produced de novo within the brain through a series of enzymatic reactions. After a brain injury, mRNA for all such steroidogenic enzymes are upregulated in glial cells. The largest increase is seen in aromatase which converts testosterone into estradiol-17β (E2). E2 is a neuroprotective agent capable of reducing apoptosis, neuronal degeneration, and inflammation. However, little is known about how these protective effects on cells translate into recovery of function at the level of behavior. The zebra finch cerebellum serves as an excellent model for this process since the songbird brain is highly plastic and can recover rapidly from injury. Previously, we found that lesioned zebra finches with inhibited aromatase activity were impaired on a spatial memory task but not a motor task. However, these two tasks were evaluated in different sexes. While E2 levels are similar between sexes, males have higher testosterone and therefore more aromatizable substrate. Females upregulate aromatase more rapidly and maintain upregulation for longer than males. Therefore, we expect males to be more negatively affected by aromatase inhibition. Finally, there is conflicting evidence about sex differences in spatial memory in zebra finches, necessitating further study. Our purpose was to determine sex differences on spatial memory ability and response to aromatase inhibition after cerebellar lesions in both a spatial and a motor task. We administered puncture lesions to the deep cerebellar nuclei of adult male and female zebra finches. Birds received one of three treatments: sham lesion, lesion with vehicle, lesion with aromatase inhibitor. Birds were evaluated on a spatial memory task designed by our lab as a dry analog to the Morris water maze and a motor task that measured ability to balance on an unstable perch. We found no sex difference in response to aromatase inhibition following cerebellar lesions. Birds with lesions and aromatase inhibition performed significantly worse on the spatial task than birds with sham lesions. There was no overall sex difference in spatial memory which is in line with our previous work but conflicts with results from a different lab. Differences between treatment groups but not sexes suggests that females may show greater amounts of aromatase upregulation as a compensation for lower testosterone levels. Analysis of the motor task requires manual counting of behavior through slow-motion viewing of video recordings and will therefore take several weeks to complete.