Sucrose Solution Access Influences Intake Value in Rats

Wilfrid Laurier University

Scholars Commons @ Laurier

Theses and Dissertations (Comprehensive)

2021

Sucrose Solution Access Influences Intake Value in Rats

Adam Celejewski

[email protected]

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Dissertations (Comprehensive). 2346.

https://scholars.wlu.ca/etd/2346

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Sucrose Solution Access Influences Intake Value in Rats

by

Adam Celejewski

BSc University of Toronto (2007), MSc Wilfrid Laurier (2011)

THESIS/DISSERTATION

Submitted to the Department/Faculty of Psychology

in partial fulfillment of the requirements for

Doctorate of Philosophy in Psychology

Wilfrid Laurier University

Adam Celejewski 2020 ©

SUCROSE ACCESS & VALUE 2

Abstract

Previous work has shown that non-deprived rats’ intake of a 4% sucrose solution increases

over 24 h access periods if it is provided every 3 or 4 days (E3D or E4D) relative to every day

(ED; (Eikelboom & Hewitt, 2016). Once these access-intake differences are established, they can

be enduring, even if all rats are shifted to a common access schedule. Do changes in value

accompany these access-induced solution intake changes? Three approaches were applied to test

for access-induced value changes. First, following extended 24 h E3D (12 exposures) or ED (36

days) access to a flavoured 4% (Experiment 1) or 12% (Experiment 2) standard sucrose solution,

the standard solution was compared in a series of 24 h choice tests against ascending

concentrations of a differently flavoured alternate solution on a common E2D access schedule.

Experiment 1 revealed access-induced preference increases for the standard solution after E3D

relative to ED access while Experiment 2 did not, possibly due to the higher concentration of

sucrose used. Second, a progressive ratio procedure was used to evaluate changes in the

reinforcing efficacy of a 4% sucrose solution after an extended period of E3D or ED access. This

traditional operant procedure failed to reveal access-induced changes in the breakpoint for the

sucrose. The failure to reveal breakpoint differences is suggested to be due to context effects;

E3D/ED sucrose solutions were provided in the home-cage while sucrose solution breakpoints

were evaluated in operant chambers. Third, in Experiments 4 and 5, palatability changes of the

4% solution were evaluated with lick microstructure analysis. Water and sucrose microstructures

were compared (positive control), before comparing the microstructure of sucrose solutions

during ED or E4D access periods. Both microstructure comparisons revealed a similar pattern of

SUCROSE ACCESS & VALUE 3

changes, suggesting that palatability increases after E4D relative to ED access. Collectively, these

results suggest that sucrose solution increases in value with E3D or E4D relative to ED access.

The results highlight that tests conducted over longer durations (24 h) may yield different results

than similar tests conducted over shorter (~1 h), restricted access sessions. Experiments 1 and 2

also suggested that rats treated the two, distinctly flavoured solutions as different food sources in

the preference tests, something that is not readily revealed with shorter preference tests. Similarly,

the lick microstructure appeared to be different with the longer, 24 h sucrose solution access

duration relative to previous shorter (~1 h), access microstructure palatability studies. Finally,

Experiment 5, which also measured food intake, revealed that changes in foods provided could

also profoundly affect sucrose consumption, highlighting the importance of considering the

complete nutritional environment of the rat. This work underscores the need for further study of

the impact of access on value. Moreover, it encourages a holistic approach that includes

monitoring the rat’s 24 intake of food and fluids as a consideration in appetitive behaviour

studies.

SUCROSE ACCESS & VALUE 4

Acknowledgements

I wold like to thank my supervisor Rudy Eikelboom for his guidance and unyielding

patience. I have learned much from him over the years. Thanks also to Paul Mallet who shared

some of his equipment, especially the operant chambers. And thanks to my lab mates Gehan

Senthinathan and Angela Mastroianni who helped with some the experimental work, and who’s

company was always appreciated. Finally I would like to thank Aula Al Muslim, my partner for

always being by my side.

SUCROSE ACCESS & VALUE 5

Table of Contents

Abstract.............................................................................................................................................2

Acknowledgements...........................................................................................................................4

Table of Figures..............................................................................................................................14

List of Abbreviations......................................................................................................................22

Intermittent and Continuous Sweet Solutions Access................................................................24

Thesis Question..........................................................................................................................29

Intermittent Access to Fluids and Foods....................................................................................34

Monday, Wednesday and Friday Access...............................................................................35

Daily 12 h Sugar Solution Access.........................................................................................38

Measuring Sugar Solution Intake...............................................................................................40

Intake by Volume or Calories Consumed..............................................................................40

Intake by Preference..............................................................................................................41

Short Term Intake Tests.........................................................................................................42

Sham Feeding........................................................................................................................43

Non-Nutritive Sweeteners.....................................................................................................44

Measuring the Value of Food and Drink....................................................................................44

The Problem with Consumption or Response/Reinforcement Rate Value Measures...........45

Choice as a Measure of Reward............................................................................................46

Choice as a Measure of E(3, 4)D/ED Access-Induced Value Differences.......................49

SUCROSE ACCESS & VALUE 6

Progressive Ratio Measure of Reward Value........................................................................50

Progressive Ratio as a Measure of E(3, 4)D/ED Access-Induced Value Differences......53

Microstructure of Sucrose Solution Intake................................................................................53

Organization of the Microstructure of Drinking...................................................................54

What is an Optimal Episode Pause Criterion?......................................................................56

Lick Microstructure Over Shorter Recording Sessions, 60 Min or Less..........................56

Lick Microstructure Over Longer Recording Sessions, 24 h or More.............................59

Microstructure Sucrose Solution Intake Under E4D/ED Access Conditions.......................63

Summary and Dissertation Direction.........................................................................................66

General Methods.............................................................................................................................70

Animals......................................................................................................................................70

General Procedures and Materials.............................................................................................70

Statistics.....................................................................................................................................72

Experiment 1: Choice I...................................................................................................................74

Methods......................................................................................................................................75

Procedure...............................................................................................................................75

Statistics.................................................................................................................................76

Results........................................................................................................................................78

Phase I...................................................................................................................................78

Phase II..................................................................................................................................78

Solution Intake By Weight................................................................................................78

SUCROSE ACCESS & VALUE 7

Half-maximal Standard Solution Intake...........................................................................79

Combined Standard and Alternate Solution Intake by Weight.........................................79

Preference for the Standard by Weight.............................................................................80

Solution Intake by Calories..............................................................................................80

Combined Alternate and Standard Solution Intake by Calories.......................................81

Preference for Standard Solution Calories.......................................................................81

Phase III.................................................................................................................................82

Discussion..................................................................................................................................82

Access-Induced Intake Differences.......................................................................................83

Access-Induced Choice Difference.......................................................................................84

Summary...............................................................................................................................88

Experiment 2: Choice II..................................................................................................................90

Methods......................................................................................................................................92

Procedure...............................................................................................................................92

Statistics.................................................................................................................................92

Results........................................................................................................................................93

Phase I...................................................................................................................................93

Phase II..................................................................................................................................94

Solution Intake..................................................................................................................94

Combined Standard and Alternate Solution Intake by Weight.........................................94

Preference for Standard Solution by Weight....................................................................95

SUCROSE ACCESS & VALUE 8

Solution Intake by Calories..............................................................................................95

Combined Standard an Alternate Solution Intake by Calories.........................................95

Preference for the Standard Solution by Calories.............................................................96

Phase III.................................................................................................................................96

Discussion..................................................................................................................................96

Experimental Parameter Considerations for Experiments 1 and 2......................................100

Experiment 3: Progressive Ratio..................................................................................................103

Methods....................................................................................................................................106

Apparatus.............................................................................................................................106

Operant Procedure...............................................................................................................107

Phase I.................................................................................................................................107

FR Training.....................................................................................................................107

PR Baseline.....................................................................................................................108

Phase II: E3D/ED Home-cage 4% Sucrose Solution Access..............................................108

Phase III: PR Test................................................................................................................108

Phase IV: E2D Home-cage 4% Sucrose Solution Access...................................................109

Statistics...............................................................................................................................109

Results......................................................................................................................................109

FR Training..........................................................................................................................109

Phase I: PR Baseline............................................................................................................110

Phase II: E3D/ED Home-cage 4% Sucrose Solution Access..............................................110

SUCROSE ACCESS & VALUE 9

Phase III: PR Test................................................................................................................111

Phase IV: E2D Home-cage 4% Sucrose Solution Access...................................................111

Discussion................................................................................................................................111

Experiment 4: Lick Microstructure I............................................................................................118

Methods....................................................................................................................................124

Statistics...............................................................................................................................125

Solution Intake, Licks and Microstructure.....................................................................125

Initial Lick Rate..............................................................................................................126

EPC Duration and Episode Size and Number.................................................................126

Code................................................................................................................................127

Results......................................................................................................................................127

Distribution of Licking Over 24 h.......................................................................................127

Episode as Proportion of Total Licks..................................................................................127

Water Versus Sucrose Intake and Intake Microstructure (Days 7, 8, 9, & 10)....................128

Fluid Intake and Licks....................................................................................................128

Correlation Between Licks and Consumption................................................................129

Lick Microstructure........................................................................................................129

Water and Sucrose Solution Episodes............................................................................130

Sucrose Intake and Intake Microstructure with E4D/ED Access (Days 9, 10, 26 & 30)....131

Sucrose Solution Intake and Licks.................................................................................132

Correlation Between Licks and Consumption................................................................132

SUCROSE ACCESS & VALUE 10

Lick Microstructure........................................................................................................132

E4D and ED Access Sucrose Solution Episodes............................................................133

Initial Lick Rate...................................................................................................................134

Standard Housing Sucrose Solution Intake.........................................................................135

Discussion................................................................................................................................135

Fluid Intake and Lick Number............................................................................................137

Water Versus Sucrose Intake Microstructure.......................................................................138

E4D vs. ED Access Sucrose Intake Microstructure.............................................................141

Initial Lick Rate...................................................................................................................143

Summary.............................................................................................................................144

Experiment 5: Lick Microstructure II...........................................................................................148

Methods....................................................................................................................................150

Licking and Feeding Recordings.........................................................................................150

Baseline and Habituation.....................................................................................................151

E4D/ED Access...................................................................................................................151

Statistics...............................................................................................................................152

Food Calories and Sucrose Solution Consumed.............................................................152

Licks , Initial Lick Rate, and Episodes of Licking.........................................................153

EPC Duration and Episode Size and Number.................................................................154

Code................................................................................................................................154

Results......................................................................................................................................154

SUCROSE ACCESS & VALUE 11

Food Calories......................................................................................................................154

Baseline Food Kilocalories (Day 7, 8, 13, 14)...............................................................155

Food Calories: Chamber/Home-cage Access I...............................................................155

Food Calories: Home-cage Access.................................................................................156

Food Calories: Chamber/Home-cage Access II..............................................................156

Food Calories: Summary................................................................................................156

Fluid Intake, Licks and Intake Microstructure....................................................................157

Distribution of Licking Over 24 h..................................................................................157

Episodes as a Proportion of Total Licks.........................................................................157

Water Versus Sucrose Intake and Intake Microstructure (Days 13 & 22)......................157

Fluid Intake................................................................................................................158

Licks...........................................................................................................................158

Correlation Between Water Licks and Consumption.................................................158

Lick Microstructure...................................................................................................158

Water and Sucrose Episodes......................................................................................159

Sucrose Intake and Intake Microstructure with E4D/ED Access...................................160

Solution Intake: Chamber/Home-cage Access I........................................................160

Solution Intake: Home-cage Access..........................................................................161

Solution Intake: Chamber/Home-cage Access II.......................................................161

Licks...........................................................................................................................162

Correlation Between Sucrose Solution Licks and Consumption...............................162

SUCROSE ACCESS & VALUE 12

Lick Microstructure...................................................................................................162

E4D and ED Access Sucrose Solution Episodes.......................................................164

Initial Lick Rate...................................................................................................................165

Discussion................................................................................................................................166

General Discussion.......................................................................................................................172

Introduction..............................................................................................................................172

Choice Experiments.................................................................................................................175

Limited Access Versus 24 h Choice Tests...........................................................................178

Standard and Alternate Solutions Were Treated as Distinct Food Sources.........................180

Influence of Familiarity on Preference................................................................................183

Choice Summary.................................................................................................................184

Progressive Ratio.....................................................................................................................185

Lick Microstructure Analyses..................................................................................................189

Evidence for Access-Induced Changes in Palatability.......................................................190

Limited Access Versus All Day Microstructure Recordings................................................193

Sucrose Solution and Water Comparisons are Valid...........................................................199

Does Postingestive Experience Influence Lick Microstructure?.........................................201

Lick Microstructure Summary............................................................................................201

Conclusions and Significance.................................................................................................203

E(3, 4)D/ED Access Changes Sucrose Solution Value.......................................................203

Longer Daily Access is Different from Short Access Sessions...........................................207

SUCROSE ACCESS & VALUE 13

Changes in the Availability of Calorie Containing Resources In Longer Daily Sessions...210

Future Direction and Broader Implications.........................................................................214

Figures..........................................................................................................................................218

Appendix A...................................................................................................................................273

Appendix B...................................................................................................................................276

Appendix C...................................................................................................................................284

Appendix D...................................................................................................................................285

References.....................................................................................................................................286

SUCROSE ACCESS & VALUE 14

Table of Figures

Figure 1: Intake of a 4% sucrose solution with continuous or intermittent access.......................218

Figure 2: Temporal representation sample lick data (4% sucrose solution) grouped across the EPC

duration range...............................................................................................................................219

Figure 3: Mean (±SEM) intake of a 16% sucrose solution with E3D or ED access in Phase I and

of a 4% sucrose solution with E2D access in Phase II.................................................................220

Figure 4, Experiment 1: Phase I mean (± SEM) 4% Standard sucrose solution intake consumed

with E3D or ED access.................................................................................................................221

Figure 5, Experiment 1: Phase II mean (± SEM) 4% Standard and Alternate solution intake

following a period of E3D or ED Standard solution access.........................................................222

Figure 6, Experiment 1: Phase II mean (± SEM) combined solution consumed following a period

of E3D or ED 4% Standard solution access.................................................................................223

Figure 7, Experiment 1: Phase II mean preference (± SEM) for the Standard solution following a

period of E3D or ED 4% Standard solution access......................................................................224

Figure 8, Experiment 1: Phase II mean (± SEM) calorie intake from the 4% Standard and

Alternate solutions following a period of E3D or ED Standard solution access..........................225

Figure 9, Experiment 1: Phase II mean (± SEM) combined solution calorie intake following a

period of E3D or ED 4% Standard solution access......................................................................226

Figure 10, Experiment 1: Phase II mean preference (± SEM) for 4% Standard solution calories

following a period of E3D or ED Standard solution access.........................................................227