Appetitive Reinforcement in Nonhuman Primates:
Revisiting the Necessity and Implementation of Feeding Restriction for Behavioral Studies
A.J. Kirsten, S.A. Davis, S.N. Von Huben, C.C. Lay, S.N. Katner, and M.A. Taffe
Department of Neuropharmacology, The Scripps Research Institute, La Jolla, CA
Progressive Ratio
200%
LasResp
500%
400%
300%
200%
100%
Post +49
Post +47
Post +45
Post +43
Post +41
Post +39
Post +37
Post +35
Post +33
Post +31
Post +29
Post +27
Post +25
Post +23
Post +21
Post +19
Post +17
Post +15
Post +13
Post +11
Post +1
Post +49
Post +47
Post +45
Post +43
Post +41
Post +39
Post +37
Post +35
Post +33
Post +31
Post +29
Post +27
Post +25
Post +23
Post +21
Post +19
Post +17
Post +15
Post +13
Post +11
Post +9
RunRate
2500%
2000%
1500%
51
46
41
36
31
26
21
16
11
6
1
150%
130%
110%
51
46
41
36
31
26
21
16
11
6
90%
70%
50%
1
250%
230%
210%
190%
170%
150%
130%
110%
90%
70%
50%
51
46
41
36
31
26
21
16
11
457
455
454
6
51
46
41
36
31
Percent of NRC/NAS Estimate
51
46
41
36
31
21
16
11
26
26
390
• The bodyweight and metabolic requirement distributions for
laboratory nonhuman primates are broad enough that
population-based protocols (e.g., 85% of NRC food estimate,
85% of van Wagenen weight estimate) are inadequate. E.g.,
~16% of individuals will be smaller than 85% of van Wagenen.
• Normative growth means for male rhesus monkeys vary by as much
as 1 SD and/or 15%. The larger sample Rawlins et al. (1984) and
Saxton & Lotz (1990) datasets may provide improved estimates over
van Wagenen & Catchpole (1956).
1000%
500%
0%
Weeks of Study
Post +49
Post +47
Post +45
Post +43
Post +39
Post +37
Post +35
Post +33
Post +31
Post +29
Post +27
Post +25
Post +23
Post +21
Post +19
Post +17
Post +15
Post +49
Post +47
Post +45
Post +43
Post +41
Post +39
Post +37
Post +35
Post +33
Post +31
Post +29
Post +27
Post +25
Post +23
Post +21
Post +19
Post +17
410
70-85%
70-85%
70-85%
70-85%
70-85%
85%
85%
85%
100%
100%
500
450
400
300
# Reinf
-500%
Post +15
44
54
64
74
84
Months of Age (range)
The NIA 3-5 yr old groups begin the study much smaller than would be predicted by
van Wagenen or Rawlins. Growth rates in both control and experimental groups are
also reduced.
412
190%
170%
• Food restriction is necessary to produce reliable behavior in
nonhuman primates. Many papers provide insufficient methodological
detail to evaluate claims of “normative feeding” or “minimal restriction”.
In some cases, analysis of bodyweights/ages, calculation of
“normal” intake from reinforcers earned (“animals earned 15% of
normal ration in the test chamber”, etc) or personal communication
suggests that significant restriction was in fact practiced.
3000%
0%
Post +13
34
200
Baseline
Taffe, 2004, Physiol Behav
RunRate
-50%
24
405
Discussion
Chow
(% of weekly NRC/NAS estimate)
# Resp
50%
Post +11
20
30
40
Months of Age (range)
The NIA 0.6-1 yr old groups begin the study at weights approximating the
van Wagenen or Rawlins distributions. Growth rates over 13 months are
attenuated in both groups relative to either normative dataset.
Chow
3500%
100%
Post +9
10
413
0
Post +13
vW&C1956
IngramAdultContStart Control young adult (3-5 yr) male N=6
IngramAdultContEnd N=6
IngramAdultCRstart Exp. young adult(30%CR) 3-5yr male N=6
IngramAdultCRend N=6
Rawlins 1984
2
0
# Resp
Percent of Baseline
4
2
Reinforcers
Time to Last Response
*
4000%
150%
6
0
0
Post +5
200%
y = 16.504x(-0.8219)
0
Post +3
Post +1
8
§
0%
Post +5
1
50%
Post +3
2
100%
Post +1
3
LasResp
0%
Percent of Baseline
4
*
4
600%
150%
10
§
§
700%
# Reinf
12
5
Kilograms (range)
250%
Percent of Baseline
In Wisconsin NPRC study, adult male CR animals end up at a slightly
reduced mean weight and ~64% of control animals. Bodyfat ranged
from 4.8% to 24.5% in CR animals; 21.5-40% in controls. Gresl et al,
2001 Am J Physiol Endocrinol Metab
NIA Caloric Restriction Study
vW&C1956
IngramJuvContStart Control juvenile (0.6-1yr) male N=6
IngramJuvContEnd N=6
IngramJuvCRstart Exp. juvenile(30%CR)0.6-1yr male N=6
IngramJuvCRend N=6
Rawlins 1984
3
Post +11
300
*
*
Post +7
250
*
§
Post +5
200
*
6
Post +5
150
6
*
9
Post +3
100
Months of Age (range)
6
*
(g/day)
Post +3
50
415
Middle/bottom panels: Baseline or improved performance generally requires
70%-85% restriction at a minimum. In many cases, performance tracks feeding
changes instituted for non-performance reasons such as growth rate or body
condition.
Monkeys in training (N=7)
Percent of Baseline
10
15
20
Kilograms
NIA CR feeding is 55-60% of our NRC estimate for <5kg animals and
75-85% for >5kg animals. Ingram et al. J.Gerontol., 45: B148-B163, 1990
12
Monkeys well trained (N=5)
0
5
8
§
Post +9
5
15
Post +9
10
0
0
0
PR performance is not maintained in animals who were welltrained at study initiation. Performance of animals in training is
restored or slightly improved although no control group was
included to assess PR improvement under prior restriction
practices.
15
Post +7
NRC/NAS estimate
NRC/NAS M-F for 85%
NRC/NAS M-F for 70%
Rawlins 1984
Post +7
100
GreslCREnd 2001 N=12
Post +1
Kilograms (range)
150
Kilograms (range)
Chow (g)
200
GreslCRStart 2001 N=15
vW&C1956
20
250
GreslContEnd 2001 N=13
FR 1,2,3...8, 10,12...24, 28,32...
10 minute session
Terminates 3 minutes after last response.
10
§
Post +7
300
GreslContStart 2001 N=15
250%
230%
210%
Top panels: Sustained 70% restriction levels in the older, larger animals
suggests the NRC estimate is too high for this age range.
Minutes
25
50
18
WNPRC Caloric Restriction study
350
Ingram90
Ingram90 M-F for 85%
Ingram90 M-F for 70%
Progressive Ratio Task
Reinforcers Acquired
NIA Caloric Restriction Study
389
320
325
329
333
Weeks of Study
Post +41
Operant Food Restriction vs. Caloric Restriction for Aging
250%
230%
210%
190%
170%
150%
130%
110%
90%
70%
50%
1
1
Weeks of Study
230%
210%
190%
170%
150%
130%
110%
90%
70%
50%
51
PostFeed +48
PostFeed +46
PostFeed +44
PostFeed +42
PostFeed +40
PostFeed +38
PostFeed +36
PostFeed +34
PostFeed +32
PostFeed +30
PostFeed +28
PostFeed +26
PostFeed +24
PostFeed +22
PostFeed +20
PostFeed +18
PostFeed +16
PostFeed +14
PostFeed +12
PostFeed +10
PostFeed +4
PostFeed +6
PreFeed
PostFeed +46
PostFeed +44
PostFeed +42
PostFeed +40
PostFeed +38
PostFeed +36
PostFeed +34
PostFeed +32
PostFeed +30
PostFeed +28
PostFeed +26
PostFeed +24
PostFeed +22
PreFeed
The effect of any feeding protocol on growth is best
determined by reference to within-institute populations
rather than published datasets.
PostFeed +8
80%
75%
457
455
454
46
90%
250%
41
85%
100%
36
95%
110%
31
105%
120%
390
26
115%
130%
410
21
125%
140%
412
21
135%
405
16
150%
413
11
145%
PostFeed +2
Week 290
Week 279
Week 268
Week 257
Week 246
Week 235
Week 224
Week 213
Week 202
Week 191
Week 180
Week 169
Week 158
Week 147
Week 136
Week 125
Published “normative” datasets
can differ by about 1 SD and/or
85% for the ~2-5 year old age
range.
Week 114
Week 70
0
160%
Percent of Baseline
2
155%
415
16
Saxton and Lotz, 1990; J Med Primatol
[N=33 Naval Aerospace Med Research, Pensicola FL]
4
170%
PostFeed +20
100
Monkeys in training (N=7)
165%
PostFeed +18
80
Week 103
60
6
Week 92
40
8
Week 81
20
Unrestricted(sd)
Restricted(sd)
Rawlins84(sd)
PostFeed +16
Rawlins, et al., 1984
Monkeys well trained (N=5)
PostFeed +14
Saxton & Lotz, 1990
Growth: by Claimed Birthdate
250%
230%
210%
190%
170%
150%
130%
110%
90%
70%
50%
11
Taffe, 2004, Physiol Behav
50%
6
(% of weekly NRC/NAS estimate)
6
Chow
(g/day)
6
Percent of Baseline (Latency)
70-85%
70-85%
70-85%
70-85%
70-85%
85%
85%
85%
100%
100%
500
450
60%
400
80%
190%
170%
150%
130%
110%
90%
70%
1
100%
389
320
325
329
333
1
120%
§
§
Restriction Level
250%
230%
210%
§
§
Responding for a highly preferred reinforcer in the BMS task
is negatively affected by net increases in feeding.
Week 290
Week 279
Week 268
Week 257
Week 246
Week 235
Week 224
Week 213
Week 202
Week 191
Week 180
Week 291
Week 281
Week 271
Week 261
Week 251
Week 241
Week 231
0
Percent of Baseline
van W agenen & Catchpole, 1956
0
Male rhesus monkeys (M. mulatta), 2.5-8 yrs
Nutrient Requirements of Nonhuman Primates: Second Revised Edition (2003), National Research
Council of The National Academy of Sciences, The National Academies Press, Washington, D.C.
0
5
*
* *
Chow
PostFeed +12
10
0
The descriptions of the feeding restriction protocols
employed in published monkey studies are minimal
and misleading.
where y is bisc/kg/day and x is kilograms bodyweight
10
PostFeed +10
4
The power of an appetitive reward to reinforce
behavior is significantly increased by making the
subject in question hungry.
In training to concurrently perform behavioral
tests assaying different cognitive domains.
Prior restriction practices based on performance
and laboratory “rules of thumb”.
Re-conceptualization of food restriction based on
data provided in “Nutrient Requirements of Nonhuman Primates” (2003); Tables 2-2,2-3.
2
PostFeed +8
12
2
Introduction
Methods
15
PostFeed +6
6
Rawlins et al., 1984; J Med Primatol
[N=41, 44, 36, 25, 21, 18 for yrs 1-6 Cayo Santiago,
free ranging, 230 g/chow per day per capita plus forage]
Describe effects of food restriction on the growth of
developing animals
20
4
PostFeed +4
14
Kirk, 1972; Lab Anim Sci
[N=19 USAF, Brooks AFB]
Establish restriction protocols on a more quantitative
framework
25
PostFeed +2
8
kilograms
Kilograms
10
van Wagenen and Catchpole 1956; Am J Phys Anthropol
[N=17, 12, 10, 9, 7, 6 at ends of years 1-6 Yale]
Evaluate the need for food restriction.
35
140%
12
Months of Age
Objectives:
Week 221
Week 211
Week 201
Week 191
Week 181
Week 171
Week 161
14
Week 151
100
Week 141
80
0
40
6
Week 169
0
Week 131
60
5
Week 121
40
10
Week 111
20
15
4
15 raisins in Lexan holeboard
Latency to extract raisins
Bimanual strategy universally used
45
30
Week 158
Kirk, 1972
0
20
2
van W agenen & Catchpole, 1956
0
6
Week 101
2
25
8
Week 147
4
30
Week 136
6
35
8
10
Week 125
kilograms
Kilograms
8
40
vanWagenen(15%)
Normative Feeding (sd)
Rawlins84
MonkeyN
Week 114
10
10
45
Number of monkeys
Food Restricted (sd)
vanWagenen (sd)
Rawlins84 (sd)
Monkey'N'
50
Week 103
12
12
Week 92
12
50
Week 81
14
Week 70
14
BMS Performance
160%
TSRI Normative Feeding: by Claimed Birthdate
kilograms
Male Rhesus Monkey Growth
Individual Differences
Bimanual Motor Skill Task
300
TSRI Food Restricted: by Claimed Birthdate
Number of monkeys
Early experimental psychologists made broad use of knowledge that is
undoubtedly as old as animal domestication, i.e., that the power of appetitive
reinforcement is enhanced by restricting the subjects‘ access to food. This has
led to the nearly universal practice of restricting common laboratory rodent and
avian subjects to 85% of free feeding weight for operant experiments. Appetitive
operant procedures in nonhuman primates vary more widely, in part because of
the time required for such animals to reach mature weight and greater individual
variability in body size compared with inbred laboratory species. In addition,
many nonhuman primates will grow obese under true ad libitum feeding.
Therefore, food restriction protocols for monkeys tend to be highly individualized
and conducted on the basis of laboratory experience within a given model. The
present study was undertaken to determine to what extent short term ad libitum
food consumption in rhesus macaques would impair performance on an
established neuropsychological testing battery. A second part of the study was to
formalize food restriction parameters to determine what degree of restriction was
required to produce consistent behavioral performance. Results show clearly that
behavioral performance on a range of tasks is detrimentally affected by short
term ad libitum chow feeding, even when the reinforcer is highly preferred or the
tasks are well trained. Furthermore, it is shown that maintenance of weekly chow
intake in the range of 70%-85% of National Research Council recommendations
for metabolizable energy is necessary for consistent behavioral responding.
Finally, a review of published normative datasets for male rhesus monkey growth
indicates that the most frequently referenced dataset derived from VanWagenen
and Catchpole (Am J Phys Anthropol 1956; 19:245-273) may be optimistic.
Implications for food restriction protocols in a context of current monkey
availability and increased veterinarian scrutiny are discussed.
Supported by DA13390, MH62261 and MH616192.
Reference to the limited amount of published data
regarding rhesus monkey growth rates is unlikely to
provide a complete solution for generating consistent levels of food restriction.
Bimanual Motor Skill
Comparison with Growth Under Operant Food Restriction
Percent of Baseline
Abstract
200
“Normative” Growth of Male Rhesus Monkeys:
We suggest that authors, reviewers and editors work to ensure that
methodological descriptions of appetitive operant procedures in
nonhuman primate manuscripts meet the basic scientific requirement
of providing detail sufficient for replication.