Wilfrid Laurier University
Wilfrid Laurier University
Scholars Commons @ Laurier
Scholars Commons @ Laurier
Theses and Dissertations (Comprehensive)
2021
Sucrose Solution Access Influences Intake Value in Rats
Sucrose Solution Access Influences Intake Value in Rats
Adam Celejewski
cele8580@mylaurier.ca
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Recommended Citation
Celejewski, Adam, “Sucrose Solution Access Influences Intake Value in Rats” (2021). Theses and
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 ©
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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
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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.
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Figure 11, Experiment 1: Phase III mean (± SEM) 4% Standard sucrose solution consumed with
E2D access following different E3D/ED access experience………………………………………………..228
Figure 12, Experiment 2: Phase I mean (± SEM) 12% Standard sucrose solution intake with E3D
or ED access………………………………………………………………………………………………………………….229
Figure 13, Experiment 2: Phase II mean (± SEM) 12% Standard and Alternate solution intake
following a period of E3D or ED Standard solution access…………………………………………………230
Figure 14, Experiment 2: Phase II mean (± SEM) solution intake by Test Number and Alternate
solution concentration…………………………………………………………………………………………………….231
Figure 15, Experiment 2: Phase II mean (± SEM) combined solution consumed following a
period of E3D or ED Standard (12%) solution access…………………………………………………………232
Figure 16, Experiment 2: Phase II mean preference (± SEM) for the Standard (12%) solution
following a period of E3D or ED Standard solution access…………………………………………………233
Figure 17, Experiment 2: Phase II mean (± SEM) calorie intake from Standard (12%) and
Alternate solutions following a period of E3D or ED Standard solution access……………………..234
Figure 18, Experiment 2: Phase II mean overall solution calorie intake (± SEM) following a
period of E3D or ED Standard (12%) solution access…………………………………………………………235
Figure 19, Experiment 2: Phase II mean preference (± SEM) for the Standard (12%) solution
calories following a period of Standard solution E3D or ED access……………………………………..236
Figure 20, Experiment 2: Phase III mean Standard 12% sucrose solution intake (± SEM) with
E2D access……………………………………………………………………………………………………………………237
Figure 21, Experiment 3: Mean (± SEM) breakpoint over 9 consecutive PR baseline session…238
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Figure 22, Experiment 3: Mean (± SEM) 24 h 4% sucrose solution intake before and after PR
baseline and testing………………………………………………………………………………………………………..239
Figure 23, Experiment 3: Mean (± SEM) breakpoint over 6 PR test sessions following extended
E3D/ED 4% sucrose access experience…………………………………………………………………………….240
Figure 24, Experiment 4: Licks for water (Days 5 – 8 ) and 4 % sucrose solution (Days 9 – 30)
over the dark/light cycle from representative rats with E4D access and ED access…………………241
Figure 25, Experiment 4: Mean (± SEM) intake of (A) and licks for (B) water (Days 5 – 8 ), or
4% sucrose solution with E4D/ED access (Days 9 – 33)…………………………………………………….242
Figure 26, Experiment 4: Mean (± SEM) fluid 240 ms EPC episode (burst) number (A) and size
(B) with daily water access (Days 5 – 8 ), or E4D/ED 4% sucrose solution access (Days 9 – 33)
……………………………………………………………………………………………………………………………………243
Figure 27, Experiment 4: Mean (± SEM) fluid 500 ms EPC episode (cluster) number (A) and size
(B) with daily water access (Days 5 – 8 ), or E4D/ED 4% sucrose solution access (Days 9 – 33)
……………………………………………………………………………………………………………………………………244
Figure 28, Experiment 4: Mean (± SEM) fluid 120 s EPC episodes number (A) and size (B) with
daily water access (Days 5 – 8 ), or E4D/ED 4% sucrose solution access (Days 9 – 33)…………245
Figure 29, Experiment 4: Mean (± SEM) fluid 300 s episode (meals) number (A) and size (B)
with daily water access (Days 5 – 8), or E4D/ED 4% sucrose solution access (Days 9 – 33)…..246
Figure 30, Experiment 4: Mean (± SEM) daily episode number (A) and episode size (B) over a
range of EPC, 0 – 2000 ms, during the last two water (Days 7 and 8), and the first two sucrose
recording sessions (Days 9 and 10)………………………………………………………………………………….247
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Figure 31, Experiment 4: Mean (± SEM) daily episode number (A) and episode size (B) over a
range of EPCs, 0 – 15 s, during the last two water (Days 7 and 8), and the first two sucrose
recording sessions (Days 9 and 10)………………………………………………………………………………….248
Figure 32, Experiment 4: Mean (± SEM) daily episode number (A) and episode size (B) over a
range of EPCs, 1– 600 s, during the last two water (Days 7 and 8), and the first two sucrose
recording sessions (Days 9 and 10)………………………………………………………………………………….249
Figure 33, Experiment 4: Mean (± SEM) daily episode number (A) and episode size (B) over a
range of EPCs, 1 – 60 min, during the last two water (Days 7 and 8), and the first two sucrose
recording sessions (Days 9 and 10)………………………………………………………………………………….250
Figure 34, Experiment 4: Mean (± SEM) daily episode number (A and B) and episode size (C and
D) over a range of EPCs, 0 – 2000 ms, over first two (Days 9 and 10), and last two (Days 26 and
30) common sucrose recording session with E4D or ED access…………………………………………..251
Figure 35, Experiment 4: Mean (± SEM) daily episode number (A and B) and episode size (C and
D) over a range of EPCs, 0 – 15 s, during the first two (Days 9 and 10), and the last two (Days 36
and 30) common sucrose recording session with E4D or ED access…………………………………….252
Figure 36, Experiment 4: Mean (± SEM) daily episode number (A and B) and episode size (C and
D) over a range of EPCs, 1 – 600 s, during the first two (Days 9 and 10) and the last two (Days
26 and 30) common sucrose recording session with E4D or ED access………………………………..253
Figure 37, Experiment 4: Mean (± SEM) daily episode number (A and B) and episode size (C and
D) over a range of EPCs, 1 – 60 min, during the first two (Days 9 and 10) and the last two (Days
26 and 30) common sucrose recording session with E4D or ED access………………………………..254
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Figure 38, Experiment 4: Mean (± SEM) initial rate of licking during water daily water intake
(Days 5 – 8), or E4D/ED 4% sucrose solution intake (Days 9 – 33)……………………………………..255
Figure 39, Experiment 5: Timeline for the baseline period………………………………………………….256
Figure 40, Experiment 5: Timeline for the testing period…………………………………………………….256
Figure 41, Experiment 5: Mean (± SEM) food (symbols ♦/◊) and sugar (symbols ●/○) kilocalories
consumed by rats with E4D or ED access to a 4% sucrose solution, in the home cage and
recording chambers………………………………………………………………………………………………………..257
Figure 42, Experiment 5: Licks for water and 4 % sucrose solution over dark/light cycle by
representative rats………………………………………………………………………………………………………….258
Figure 43, Experiment 5: Mean (± SEM) intake (A) and licks (B) for water and 4% sucrose
solution with E4D or ED access in the home-cage and recording chambers………………………….259
Figure 44, Experiment 5: Mean (± SEM) 240 ms EPC episode number (bursts) number (A), and
size (B), during water and 4% sucrose solution intake provided E4D or ED………………………….260
Figure 45, Experiment 5: Mean (± SEM) 500 ms EPC episode (clusters) number (A), and size
(B), during water and 4% sucrose solution intake with E4D or ED access…………………………….261
Figure 46, Experiment 5: Mean (± SEM) 120 s EPC episode (meals) number (A), and size (B),
during water and 4% sucrose intake with E4D or ED access……………………………………………….262
Figure 47, Experiment 5: Mean (± SEM) 300 s EPC episode (meals) number (A), and size (B),
during water and 4% sucrose intake with E4D or ED access……………………………………………….263
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Figure 48, Experiment 5: Mean (± SEM) daily episode number (A), and episode size (B), over a
range of EPC durations (up to 2000 ms), on water access on Days 7 and 13, and the first two
chamber sucrose access sessions (Days 22 and 30)…………………………………………………………….264
Figure 49, Experiment 5: Mean (± SEM) daily episode number (A), and episode size (B), over a
range of EPCs (0 – 15 s), on water Days 7 and 13, and the first two sucrose chamber recording
sessions (Days 22 and 30)……………………………………………………………………………………………….265
Figure 50, Experiment 5: Mean (± SEM) daily episode number (A), and episode size (B) over a
range of EPC durations (1 – 600 seconds), on water Days 7 and 13 and the first two chamber
sucrose access sessions (Days 22 and 30)…………………………………………………………………………266
Figure 51, Experiment 5: Mean (± SEM) daily episode number (A), and episode size (B), over a
range of EPC (1– 60 min), on water Days 7 and 13 and the first two sucrose chamber sucrose
access sessions (Days 22 and 30)…………………………………………………………………………………….267
Figure 52, Experiment 5: Mean (± SEM) daily episode number (A and B), and episode size (C
and D), over a range of EPCs (0 – 2000 ms) on the first two (Days 22 and 30), and last two (Days
98 and 106)…………………………………………………………………………………………………………………..268
Figure 53, Experiment 5: Mean (± SEM) daily episode number (A and B), and episode size (C
and D), over a range of EPCs (0 – 15 s), during the first two (Days 22 and 30), and the last two
(Days 98 and 106) sucrose recording session with E4D or ED access…………………………………..269
Figure 54, Experiment 5: Mean (± SEM) daily episode number (A and B), and episode size (C
and D), over a range of EPCs (1 – 600 s) during the first two (Days 22 and 38) and the last two
(Days 98 and 106) sucrose recording session with E4D or ED access…………………………………..270
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Figure 55, Experiment 5: Mean (± SEM) daily episode number (A and B), and episode size (C
and D), over a range of EPCs (1 – 60 min) during the first two (Days 22 and 30) and the last two
(Days 98 and 106) sucrose chamber session with E4D or ED access……………………………………271
Figure 56, Experiment 5: Mean (± SEM) initial rate of licking during water daily water intake or
E4D/ED 4% sucrose solution intake on recording chamber days…………………………………………272
Figure 57, Appendix A, Experiment 4: Mean (± SEM) daily episode number (A), and episode size
(B), over an EPC range (0 – 2000 ms), during the first hour of water access on water Day 8 and
first hour of sucrose access on Day 9……………………………………………………………………………….274
Figure 58, Appendix A, Experiment 4: Mean (± SEM) daily episode number (A), and episode size
(B), over an EPC range (0 – 2000 ms), during the first hour of water access on water Day 8 and
first hour of sucrose access on Day 10……………………………………………………………………………..275
Figure 59, Appendix B, Experiment 4: Mean (± SEM) daily episode number (A) and episode size
(B) over a range of EPC, 0 – 100 s (base 10 log units), during the last two water (Days 7 and 8),
and the first two sucrose recording sessions (Days 9 and 10)………………………………………………276
Figure 60, Appendix B, Experiment 4: Mean (± SEM) daily episode number (A) and episode size
(B) over a range of EPC, 0 – 6000 s (base 10 log units), during the last two water (Days 7 and 8),
and the first two sucrose recording sessions (Days 9 and 10)………………………………………………277
Figure 61, Appendix B, Experiment 4: Mean (± SEM) daily episode number (A and B) and
episode size (C and D) over a range of EPCs, 0 – 100 s (base 10 log units), over first two (Days 9
and 10), and last two (Days 26 and 30) common sucrose recording session with E4D or ED
access…………………………………………………………………………………………………………………………..278
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Figure 62, Appendix B, Experiment 4: Mean (± SEM) daily episode number (A and B) and
episode size (C and D) over a range of EPCs, 0 – 6000 s (base 10 log units), over first two (Days
9 and 10), and last two (Days 26 and 30) common sucrose recording session with E4D or ED
access…………………………………………………………………………………………………………………………..279
Figure 63, Appendix B, Experiment 5: Mean (± SEM) daily episode number (A), and episode size
(B), over a range of EPC durations (up to 100 s log base 10 units), on water access on Days 7 and
13, and the first two chamber sucrose access sessions (Days 22 and 30)……………………………….280
Figure 64, Appendix B, Experiment 5: Mean (± SEM) daily episode number (A), and episode size
(B), over a range of EPC durations (up to 6000 s log base 10 units), on water access on Days 7
and 13, and the first two chamber sucrose access sessions (Days 22 and 30)…………………………281
Figure 65, Appendix B, Experiment 5: Mean (± SEM) daily episode number (A and B), and
episode size (C and D), over a range of EPCs (0 – 100 s, base 10 log units) on the first two (Days
22 and 30), and last two (Days 98 and 106)………………………………………………………………………282
Figure 66, Appendix B, Experiment 5: Mean (± SEM) daily episode number (A and B), and
episode size (C and D), over a range of EPCs (0 – 6000 s, base 10 log units) on the first two
(Days 22 and 30), and last two (Days 98 and 106)……………………………………………………………..283
SUCROSE ACCESS & VALUE
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List of Abbreviations
BSR – Brain Stimulation Reward
ED/E2D/E3D/E3D – Everyday / Every 2nd Day / Every 3rd Day / Every 4th Day
E(x1, …, xn)D Every x1, or …, or xn days
EPC – Episode Pause Criterion
FR – Fixed Ratio
ILI – Inter-Lick-Interval
MWF – Monday Wednesday Friday
PR – Progressive Ratio
SUCROSE ACCESS & VALUE
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Conditions governing access to food and drink can exert a considerable influence on the
amount consumed. Since the 1970s, it has been known that non-deprived rats will increase their
intake of freely available nutritive or non-nutritive solutions when they are provided
intermittently. Relative to continuous, uninterrupted access, alternating periods of 48 h on, and 48
h off led to intake increases of ethanol and non-nutritive quinine or saccharin solutions that were
provided in addition to ad-lib food and water (Amit et al., 1970; Wayner et al., 1972). Similarly,
more ethanol or saccharin solution was consumed when provided for 24 hour periods on alternate
days relative to continuous every day access (Pinel & Huang, 1976; Wise, 1973).
More recently, work in our lab has shown that sucrose solution intake increases when
provided for 24 hour periods every 3rd or 4th day (E3D, E4D), but remains at lower, stable levels
when available continuously every day (ED; Eikelboom & Hewitt, 2016). Only sucrose solution
availability was manipulated in these experiments, with both food and water always available ad-
lib. The duration of the period between 24-hour access sessions determines the magnitude of the
increase. Importantly, an extended period of intermittent access has a persistent effect on future
solution intake. When the solution schedule for both E3D and ED groups is changed to E2D
access, the access-induced solution intake differences between groups are maintained.
Similar access protocols developed to model binge-like feeding have also shown that
intake of fat or sugar solutions can be increased with intermittent, (Avena et al., 2008; Babbs et
al., 2012). While the type/quality and the parameters governing the access to food or solution
vary from protocol to protocol, all of these access protocols demonstrate that less frequent,
SUCROSE ACCESS & VALUE
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relative to more frequent, access can result in increased consumption rates or consumption
amounts.
While it is evident that the intake of food and drink can be influenced by intermittent
access, the behavioural controls that underlie these increases in otherwise non-deprived rats are
unclear. This thesis explores the underlying behavioural factors that drive access-induced intake
changes. Specifically, I seek to determine whether access-induced intake changes are driven by a
perceived change in the value/palatability of, or motivation for the food or drink.
Moreover, access-induced intake increases are comparable with overeating patterns
characteristic of Bulimia Nervous and Binge Eating Disorder (Avena, 2008; Corwin & Babbs,
2012). Both human conditions are marked by episodes of uncontrolled excessive eating
(American Psychiatric Association, 2013). A better understanding of factors influencing access-
induced intake increases may help develop more effective clinical interventions or improved
clinical models for these eating disorders.
Intermittent and Continuous Sweet Solutions Access
Our lab has shown that sucrose solution intake is affected by intermittent access in two
key ways (Eikelboom & Hewitt, 2016). First, non-deprived rats’ intake of a relatively low, 4%
(w/v) sucrose solution increases markedly with intermittent relative to continuous access
schedules. Specifically, with 23.5 h periods of sucrose solution access, every second, third or
fourth day solution intake was found to escalate gradually (Figure 1, Phase I). The duration of the
inter-access interval was positively correlated with daily sucrose solution intake. In contrast, with
