# A novel role for midbrain glutamate co-transmitting neurons in alcohol drinking and motivated behaviors

> **NIH NIH R21** · UNIVERSITY OF PITTSBURGH AT PITTSBURGH · 2021 · $201,118

## Abstract

PROJECT SUMMARY
Early adolescent alcohol use is one of the best predictors of risk for developing an alcohol use disorder (AUD)
later in life. Generally, adolescents are more likely to report positive, rewarding effects of alcohol and fewer
negative effects, which can lead to an increased propensity to consume larger volumes of alcohol. The molecular
mechanisms underlying enhanced sensitivity to alcohol reward are poorly understood, but if identified, could lead
to novel methods for reducing abuse liability and treating AUD in a manner that is uniquely tailored to adolescents
and adults. Glutamate signaling is strongly implicated in the vulnerability to and pathogenesis of AUDs. Recent
preclinical work has further refined this observation by showing that a population of neurons that express
vesicular glutamate transporter 2 (VGLUT2) are strongly implicated in modulating drug reward. We have
discovered that this distinct subpopulation of VGLUT2+ glutamatergic neurons is also dopaminergic. We also
found glutamate potentiates activity-dependent vesicular dopamine loading and release. Thus, while glutamate
and dopamine have both been individually implicated in the reinforcing effects of alcohol, glutamate and
dopamine may also act synergistically to regulate sensitivity to alcohol. Notably, VGLUT2 expression is
developmentally regulated, with expression peaking in adolescence and decreasing with age, which may explain
why adolescents are particularly sensitive to the rewarding effects of alcohol. Additionally, we discovered strong
sex differences in the expression of VGLUT2 including in glutamate/dopamine co-transmitting neurons, with
females expressing more VGLUT2 relative to males. Thus, VGLUT2 expression may also explain why females
are differentially sensitive to alcohol reward. Until recently, it has been difficult to functionally dissect
subpopulations of glutamate neurons, including those that co-transmit dopamine, particularly in rats. However,
we can now selectively control expression of a VGLUT2 in glutamate/dopamine neurons, and answer several
key questions: 1) how does alcohol alter co-release of glutamate and dopamine from TH+/VGLUT2+ terminals
in the mNAcSh?; 2) does manipulation of levels of VGLUT2 expression in mVTA glutamate/dopamine neurons
modify alcohol reinforcement and motivation differentially in males and females and across key developmental
stages (i.e., adolescence and adulthood)? Our central hypotheses are: i) Amount of glutamate/dopamine co-
release will vary according to age and sex based on levels of VGLUT2 expression under basal conditions and
in response to alcohol (Aim 1); ii) Manipulating levels of VGLUT2 expression will alter alcohol reinforcement and
motivated behaviors (Aim 2). Using a combination of molecular, imaging, and behavioral tools, we will definitively
identify the mechanistic role of subpopulations of midbrain glutamatergic neurons in alcohol reinforcement and
motivation, and drive future development of...

## Key facts

- **NIH application ID:** 10307442
- **Project number:** 1R21AA028800-01A1
- **Recipient organization:** UNIVERSITY OF PITTSBURGH AT PITTSBURGH
- **Principal Investigator:** ZACHARY FREYBERG
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $201,118
- **Award type:** 1
- **Project period:** 2021-09-20 → 2023-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10307442

## Citation

> US National Institutes of Health, RePORTER application 10307442, A novel role for midbrain glutamate co-transmitting neurons in alcohol drinking and motivated behaviors (1R21AA028800-01A1). Retrieved via AI Analytics 2026-06-11 from https://api.ai-analytics.org/grant/nih/10307442. Licensed CC0.

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