# Identifying mechanisms underlying sex differences in motoneuron discharge

> **NIH NIH F31** · NORTHWESTERN UNIVERSITY · 2023 · $43,467

## Abstract

Project Summary
 Studies in neurophysiology have historically excluded female participants. This has resulted in a well
encompassing understanding of the neural control of movement in males, and a poor understanding of
mechanisms underlying motor control differences in females. There is great need to study female motor
physiology, as many neurological diseases progress differently between the sexes. In recent years, studies that
have included adequate numbers of female participants have found motoneuronal discharge patterns and
neuromuscular fatigue differ between the sexes but the mechanisms underlying these differences are unknown.
Descending monoaminergic input from brainstem nuclei provide and modify motoneuronal discharge and is
broadly understudied in the motor system. Our lab, however, has developed robust methods to quantify these
monoaminergic influences on motoneuron discharge in humans. Thus, to understand if monoaminergic input is
responsible for sex differences in motoneuron properties, I will indirectly quantify the amount of monoaminergic
input to motoneurons in females and males.
 Motor commands consist of excitation, inhibition, and a lesser known neuromodulatory component that result
in their subsequent discharge and activation of innervated muscle fibers. Neuromodulation is induced by release
of two monoamines, serotonin and norepinephrine, from the brainstem to the spinal cord, which substantially
alter discharge patterns of motoneurons. Sex hormones have extensive effects on many physiological systems
in the human body and differ between the sexes. Females have levels of estradiol and progesterone that fluctuate
regularly across the menstrual cycle and these fluctuations are associated with aspects motor control, including
motoneuron discharge rates and fatigue. Additionally, neurons throughout the body, including the brainstem and
spinal cord, contain estradiol and progesterone receptors. This suggests that fluctuating sex hormones may
impact motoneuron function, but, again, underlying mechanisms have not been studied. Thus, to accurately
assess sex differences in motoneuron discharge, hormonal cycles must be considered. I will use surface EMG
arrays to quantify motoneuron discharge patterns during voluntary isometric contractions to determine 1) if
monoaminergic input to motoneurons differs between males and females, and 2) whether motoneuron discharge
patterns fluctuate across the menstrual cycle in females.
 This study will assess whether the amount of monoaminergic input motoneurons receive differs between the
sexes to test a possible explanation for known sex differences, while also assessing other aspects of motoneuron
discharge. Whether or not these studies identify sex-differences, findings from this work will not only further the
scientific knowledge of how these sex hormones influence nervous system function but will highlight the critical
importance for additional studies focusing on female participants out of nee...

## Key facts

- **NIH application ID:** 10751793
- **Project number:** 1F31NS130767-01A1
- **Recipient organization:** NORTHWESTERN UNIVERSITY
- **Principal Investigator:** Sophia Theresa Jenz
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2023
- **Award amount:** $43,467
- **Award type:** 1
- **Project period:** 2023-09-01 → 2026-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10751793

## Citation

> US National Institutes of Health, RePORTER application 10751793, Identifying mechanisms underlying sex differences in motoneuron discharge (1F31NS130767-01A1). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10751793. Licensed CC0.

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