The Effects of Rodent Maternal Separation on Consumption and Motivation for Sucrose Reward and Its Relationship to Anxiety Public

Abstract

Abstract
The Effects of Rodent Maternal Separation on Consumption and Motivation for Sucrose
Reward and Its Relationship to Anxiety
By Kelly Dixon Watts
There is evidence that an adverse early-life environment is associated with susceptibility
to anxiety and depression later in life. Separation of rat pups from their mother during
early development may lead to an exaggerated stress response and increased anxiety in
adulthood. Recent studies suggest that maternal separation also alters reward behavior.
These experiments tested whether maternal separation would alter both anxiety and
motivation to obtain sucrose reward in adulthood. On postnatal days 2-14, Long-Evans
rat pups were subjected to either 180 min of maternal separation (HMS 180), 15 min of
separation (HMS 15), animal facility raised (AFR), or unhandled (UNH). Adult male
offspring were tested for anxiety-like behaviors on the open field and elevated plus maze
(EPM), locomotor activity, sucrose preference, and operant responding for sucrose at
increasing fixed-ratio (FR) requirements. HMS 180 had increased anxiety in both the
open field and elevated plus maze compared to AFR and UNH. UNH had increased
locomotion compared to HMS 15 and HMS 180. No rearing group differences were
observed in preference for sucrose solution in the home cage. However, HMS 180 rats
took significantly longer than UNH to eat freely available sucrose pellets in the operant
chamber. Anxiety measures correlated with initial sucrose consumption in the novel
chamber. There were no differences in acquisition, in responding at any fixed-ratio requirement, or in extinction. However,
anxiety measures on the EPM and the open field correlated significantly with operant
responding at both low and high ratio requirements across groups. This suggests that even in rats
habituated to the test setting, anxiety is associated with lower levels of responding for
sucrose. Together, these observations suggest that maternal separation consistently leads
to increased anxiety, which correlates with delayed initial response to sucrose reward in a
novel environment. While no group differences were observed on operant responding for
sucrose, anxiety was associated with lower incentive motivation across animals.

Table of Contents

Table of Contents

Introduction

........................................................................................................................ 1
Background .......................................................................................................................2
Impaired Stress Response After Maternal Separation ................................................2
Feedback and Feed-forward Regulation of the Stress Response ................................3
Influence of Touch on Life-Long Stress Reactivity ...................................................5
Reward ..............................................................................................................................7
Human Reward and Depression ......................................................................................9
Reward and Rodent Maternal Separation .................................................................10
Alcohol ......................................................................................................................11
ICSS ..........................................................................................................................12
Specific Aims ..................................................................................................................13

Materials and Methods ................................................................................................... 14
Animal Care and Maternal Separation ...........................................................................14
Digiscan Locomotor Activity .........................................................................................15
Open Field ......................................................................................................................16
Elevated Plus Maze .........................................................................................................17
Sucrose Solution Preference Test ...................................................................................18
Operant Responding........................................................................................................19
Statistical Analyses .........................................................................................................20

Results .............................................................................................................................. 21
Digiscan Locomotor Activity .........................................................................................21
Open Field ......................................................................................................................22
Elevated Plus Maze .........................................................................................................24
Sucrose Solution Preference Test ...................................................................................26
Operant Responding........................................................................................................28
Correlations .....................................................................................................................32

Discussion

......................................................................................................................... 40
Sucrose Preference .........................................................................................................41
Operant Responding for Sucrose ...................................................................................41
Stress Coping ..................................................................................................................45
Conclusion .................................................................................................................................. 49

References ........................................................................................................................50

List of Figures

Figure 1

. Baseline Locomotor Activity.............................................................................21

Figure 2. Open Field Activity ...........................................................................................23

Figure 3. Elevated Plus Maze ...........................................................................................25

Figure 4. Sucrose Solution Preference ..............................................................................27

Figure 5. Sucrose Pellet Consumption in Operant Chamber ............................................30

Figure 6. Acquisition of Responding for Sucrose Pellets .................................................30

Figure 7. Fixed Ratio Requirements for Sucrose Pellets ..................................................31

Figure 8. Extinction...........................................................................................................31

Figure 9. In Group: Anxiety Measures Correlate with Sessions to Eat Sucrose .............34

Figure 10. In Group: Anxiety Measures Predict Day to 100 Bar Presses .........................35

Figure 11. In Group: Anxiety Measures and Vigor of Responding ..................................36

Figure 12. EPM Open Arm Time Correlates with Sessions to FT Criterion ....................38

Figure 13. EPM Open Arm Time Correlates with Operant Responding ..................................39



Table 1. Correlations of Anxiety Measures and Operant Responding .............................38

About this Master's Thesis

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School	Laney Graduate School
Department	Biological and Biomedical Sciences
Subfield / Discipline	Neuroscience
Degree	MS
Submission	Master's Thesis
Language	English
Research Field	Biology, Neuroscience
Mot-clé	reward
Committee Chair / Thesis Advisor	Neill, Darryl B, Emory University Plotsky, Paul, Emory University
Committee Members	Gordon, Frank J, Emory University

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