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DRUG DISCRIMINATION FORAGING
Discriminative Stimulus Effects of Nicotine during a Foraging Analysis
Caitlan Byrnes
Saint Anselm College
November 2014
Acknowledgments

I would like to take this time to thank those who helped me progress and complete this
experiment. I would like to especially thank Professor Troisi for aiding my studies and providing
me with necessary knowledge and equipment. I would also like to take this time to thank Sam
Dalhberg for caring for the laboratory animals!
Abstract

Animal models of drug discrimination have served as a backbone for human research concerning
addiction for centuries. Nicotine, a commonly used drug worldwide, can increase behaviors that
result in a delivery of non-drug reinforcers. Consequently, nicotine has primary reinforcing
effects and can strengthen operant behaviors that lead to a delivery of rewarding stimuli such as
food or water (Bevins & Palmatier, 2004). The intent of the performed study was to define
nicotine as a modulator for foraging behavior and then acquisition laboratory animals to
associate a particular drug state with a reward (water). The study begins with some introductory
knowledge essential for understanding and interpreting results by utilizing four subheadings;
Conditioning: Operant and Pavlovian, Drug Discrimination, Foraging and Practical Applications
of use. Throughout investigation different tandem sequences of nicotine and saline were
expected to establish discriminative stimulus control over spatial learning for four rats, resulting
in a decreased latency time during a foraging analysis. It was predicted that the rate of voluntary
responses would become more frequent in an SD drug sequence because it occasions a response-
reinforcer relationship by reinforcing a behavior under a particular stimulus. Although results did
not hold significance between the independent and dependent variables, further research is
suggested to investigate modulation of behaviors using interoceptive cues. Internal cues are
critical to addiction and relapse behavior because internal or external stimuli may trigger a
neurological response within the brain that then may signal drug onset cues which when
eliminated might lead to more successful drug treatments. One theory for drug addiction is that if
we change the context internally and externally we may decrease associations between the two
which elicits relapse behaviors.
Table Of Contents
Acknowledgments ...................................................................................... Pg 2

Abstract ...................................................................................................... Pg 3
Introduction ...................................................................................................... Pg 6
Conditioning: Operant and Pavlovian …………………………………. Pg 6
Drug Discrimination.....................................................................………. Pg 7
Foraging.................................................................................................… Pg 9
Practical Applications.....................................................................……… Pg 9
Method ...................................................................................................... Pg 10
Subjects .......................................................................................... Pg 10
Aparatus .......................................................................................... Pg 10
Procedure .......................................................................................... Pg 11
Results ...................................................................................................... Pg 13
Discussion ...................................................................................................... Pg 15
Tables and Figures .......................................................................................... Pg 17
Table 1: “ Latency to first cap” ............................................................... Pg 17
Table 2: “Latency to last cap”................................................................. Pg 19
Figure 1: “Latency to first cap in seconds-rat 1” .................................... Pg 17
Figure 5: “Latency to last cap in seconds-rat 1” .................................... Pg 19

References ...................................................................................................... Pg 21
Appendices ...................................................................................................... Pg 23
Appendix A: “Morris water maze” ...................................................... Pg 23
Appendix B: “Syringes used” .................................................. Pg 24
Appendix C: “Water caps used” .................................................... Pg 25
Discriminative Stimulus Effects of Nicotine during a Foraging Analysis
As intelligent beings, it is natural to seek understanding regarding human behavior. As a
result, animal models have become a backbone attempting to parallel human addiction responses.
Many studies attempt to mirror human addiction behavior such as drug foraging where one

physically goes through specified rituals to obtain a substance (Grund,1993). This is caused by
an association made between an internal or external stimuli which then triggers a neurological
response within the brain that may signal drug onset cues. When eliminated, an individual may
be less likely to relapse resulting in more successful drug treatments. One theory for drug
addiction is that if we change the context internally and externally we may decrease associations
between the two which elicits relapse behaviors (Siegel, Shepard & Ramos, 2002.) Another
theory of drug addiction is that our behaviors are driven by a series of learning processes in
which we acquire associations and modify our performance in response to a stimulus.
Conditioning: Operant and Pavlovian
Classical conditioning, is a psychological learning process that develops through
associations made between an environmental stimulus and an internal or naturally occurring
stimulus (Kimble,1967). This theory of learning, first introduced by physiologist Ivan Pavlov,
involves pairing a sensory event to something biologically important, yielding a response.
Pavlov suggests that organisms are capable of tracking cues that predict natural recourses such as
food, especially when under restricted conditions. In his study, “Pavlov’s Dogs” excitation
occurs when a neutral stimulus with no associations to a behavior (NS) is placed before a
naturally occurring reflex. From this research, psychologists have concluded that associative
connections made between stimuli and the environment, help shape behavior. As a result,
behavior is a reflexive social cue, eliciting a response when aroused by a specific stimuli (Mazur,
2002).
Behaviorism is a branch of Psychological thought that attempts to quantify, train, and
alter behavior through a modification process (Krantz, 2013). Operant conditioning, first coined
by B.F Skinner, is the second psychological theory used to describe behavioral learning. It

proposed that an organism is capable of modifying its behavior by associating that specific
behavior to a series of rewards or punishments (Mazur, 2002). One may acquire these
associations through observational learning, language or rule governed schedules, or behavior
modification which utilizes adverse or reinforcement stimuli. Skinner described his theory of
learning by presenting a novel or spontaneous behavior and inhibiting or provoking that
behaviors recurrence with positive/negative reinforcement or punishment. Neurologically
speaking, this is due to an autonomic response in the peripheral nervous system which when
conditioned (CR) increases the action potential along many motor neurons within the brain
(Troisi, 2014). His research outlined the important relationship between internal and external
stimuli and how external stimuli may be altered to modify an organisms behavior. Skinner’s
contribution to learning theory and his work with animal models have crossed over into human
studies concerning drug addiction and treatment/therapy options.
Drug Discrimination
Research involving drug discrimination in rodent models, propose that a drug may serve
as an interoceptive cue suggesting the presence of a biologically important item such as food
(Troisi, 2014). An Interoceptive cue is a sensory response originating inside the body which then
may have an effect on behavior. In research on classical drug discrimination, nicotine functions
effectively as an operant discriminative stimulus. A “discriminative stimulus” (SD) occasions a
response-reinforcer relationship by reinforcing a behavior under a particular stimulus. An SD ,
can also serve as an “S.Delta” (SΔ) by signaling that a behavior has no consequence and will
likely reoccur (e.g., Troisi, Dooley, Craig, 2013; Troisi, Bryant, Kane, 2012). As a result, it has
been proposed that the function of a conditioned stimulus, or learned stimuli (CS) is not only to
signal the probability of an unconditioned stimuli (US), but also to serve as a spatial cue to guide

the animal in the environment (Blum & Abbott, 1996). Prior work (Davidson, Aparicio and
Rescorla, 1988) evidenced that operant discriminative stimuli and Pavlovian features function
hierarchically.
Nicotine, a commonly used drug worldwide, can increase behaviors that result in a
delivery of non-drug reinforcers such as rewards or punishments. Consequently, nicotine has
primary reinforcing effects and can strengthen operant behaviors that lead to a delivery of
encouraging/rewarding stimuli such as food or water (Bevins & Palmatier, 2004). Hypothetically
if this is true, nicotine would enhance responding for strong reinforcers and may increase
motivation to obtain rewards associated with administration. Nicotine is also hypothesized to
enhance sensory properties such as taste, touch, or smell. Stimuli paired with nicotine and
administered after injections occur may have been altered by the drug and may increase the value
of the reinforcer (Troisi, 2014). The value of the reinforcer is essential to behavior consistency.
In human drug addiction studies, drug use is positive reinforcement and encourages behavior to
reoccur because an operant response (self-administration) directly produces a reinforcing effect
through administration. When resources become scarce or looses is no longer contingent,
foraging comes into play to acquire the desired reward such as a drug/food.
Foraging
Foraging behaviors can be found in all organisms including humans. In the wild, foraging
behaviors reveal an organisms sensitivity to a specific stimuli in its environment. Foraging can
be considered an adaptive response to increase the likelihood of survival and is paralleled in
addiction studies as the drug seeking behavior that encourages relapse. When resources become
limited, behavior changes and the internal association between reduced reinforcement increases
behavioral variability (Gharib, Gade, & Roberts, 2004; Stahlman, Roberts, & Blaisdell, 2010).

According to the optimal foraging theory, an animal is expected to enter into a given activity
depending on associated costs and benefits (Arcis, 2003). Behavioral variation is critical to
foraging due to a decrease in resources which then promotes the stereotyping of a ritual to
become more successful during testing. In previous studies performed on primates, competition
for resources have behavioral consequences in females (Koenig, 2002) resulting in a reduced
number of offspring due to feeding competition. When a reward increases activity, extinction
burst is more likely to occur and this is what we know as relapse. Extinction burst is a
phenomena in which previously reinforced operant behaviors are no longer signaling the
presence of a reward, but the behavior continues to persist despite the absence of a reward
Harris, Pentel, & LeSage, 2007). In human addiction studies this encourages behavioral
variability to find access to more reinforcers (drugs) which then spontaneously reinforces itself.
Practical Applications
Animal models act as a framework for human studies. It can be debated that many of our
medical achievements stem from laboratory research involving vertebrate animals. They give
psychologists a comparable organism to model human interactions involving molecules, cells,
and tissue responses. Studies involving interoceptive cues and drug addiction in animal and
human models suggest that operant contingencies involving a response-reinforcement interaction
coincide with classical Pavlovian contingencies (Troisi, 2013).
If foraging behaviors were measured while using the drug discrimination paradigm
previously mentioned, laboratory animals would be expected to show a rate of responding which
demonstrates a discrimination between a drug context in the SD condition which indicates food
or a biologically important resource and a saline condition and no reward; SΔ. It is expected that

internal cues, such as nicotine modulate foraging behaviors in laboratory animals based on a
reward/punishment system.
Method
Subjects
Test subjects involved four male Sprague Dawley rats who had no previous training in a drug
discrimination paradigm. The rats were not exposed to any drug internally or externally until the
study began on 9/11/14. The rats were 5 months old, originating from a private breeder and were
housed within the psychology department of a small liberal catholic college in the Northeast. The
animals were cared for daily under strict guidelines from the animal welfare from order of the
National Institute of Health (NIH) Committee. The subjects were housed two per cage (4x6”)
and were kept at a free-feeding weight throughout the study but were limited to 15 minutes of
water daily to keep thirst below satiation.
Apparatus
See Appendix A for complete visual of the “Morris Water Maze” (Morris et al. 1982). The
Apparatus is used to test Spatial learning, place learning, cognitive maps and memory through
observation of a rat’s spatial cues to locate a specific object. The apparatus is a round circular
encasement about 5 feet wide and 4.5 feet tall. Inside the apparatus is sawdust with 3 specific
“landmarks” such as wooden blocks to make quantifying behavior easier. Behavior as seen from
an experimenters point of view is difficult to quantify based on random movements the subject
makes. The blocks allow the researcher to determine how many times a subject returns to a
specific spot with or without water. See Appendix B for image of a 10cc syringe which was used
for all injections required by this study. Drug doses were based on daily weights and the drug
consistency was a makeup of .08mgs of powdered Nicotine dissolved into a saline mixture. See

Appendix C for visual of “water cap” used to contain 2ml of water (10mls total, 5 caps used).
The water caps were used to hold the reinforcer “water” under the SD drug condition depending
on the rat.
Procedure
The present study involves testing the discriminative stimulus effects of two drug sequences
(nicotine reinforced & saline not reinforced/ nicotine not reinforced&saline reinforced; NIC+ &
SAL-/ NIC- & SAL+); SD which sets the occasion for responding predicting the presentation of
water, and (nicotine not reinforced&saline reinforced/ nicotine reinforced&saline not
reinforced)NIC- & SAL+/NIC+ & SAL-); SΔ which is not paired with the reinforcer and does
not indicate a presentation of a reward (not predicting water). Four male Sprague Dawley rats
were water restricted to 15 minutes daily, to increase the value of the reinforcer during testing.
The study required the administration of counterbalanced drug conditions; nicotine according to
body weight(0.3mg/kg) and saline depending on whether they were SD or SΔ conditions. For
two rats, (rats 2 and 4) nicotine will function as an SD in which the presence of NIC was
hypothesized to increase behaviors and indicate a reward (water). For the other two rats (1 and
3), conditions were counterbalanced and saline functioned as an SΔ which was not reinforced.
Before injection, fill the syringes accordingly to weight allowing 12 minutes for the drug onset
period to set in. Once administered through injection underneath the abdomen, the laboratory
animals were placed separately into the Morris pen at the same start location every time (to keep
context as controlled as possible). Within the pen were strategically placed water bowls or no
reward/empty caps (depending on the condition) along with 3 checkmarks such as a wooden
block to serve as landmarks within the apparatus. There were 5 caps containing 2ml of water
each allowing the rat to obtain 10ml of water during one session. The landmarks provided the

primary investigator with a systematic application of quantifying the rat’s behavior. This was
defined by the rats turning behaviors, locomotion, returning behaviors etc. Locomotion was
defined by the movement or the ability of the subject to move from one place to another. Turning
and returning behaviors were based on the quantity of times a subject returned to a checkpoint
for investigation. For participants in the SΔ condition there was a 10minute foraging period in
which behaviors were measured and compared to that of rats in the SD condition. Rats on test
days were drugged or non-drugged but water (the reward) was not present within the apparatus.
The rats were placed into the apparatus for a period of 5 minutes and were not rewarded to
measure behavioral increases/changes/etc. Behavioral increases were measured using latency
times on a stopwatch to determine how quickly a subject could locate a water cap under a
particular condition.
Results
The intent of the performed study was to define nicotine as a modulator for foraging
behavior and then acquisition the laboratory animals to associate a particular drug state with a
reward (water). Throughout investigation different tandem sequences of nicotine and saline
established discriminative stimulus control over spatial learning and as a result decreased latency
times during the foraging analysis. It was predicted that the rate of voluntary responses would be
higher in a sequence during the SD condition because it occasions a response-reinforcer
relationship by reinforcing a behavior under a particular stimulus. The two dependent measures
in the performed study were the latency in minutes to the first and the last water cap over a series
of sessions. The independent variables were SD and SΔ drug conditions. Latency times were

then evaluated to reveal whether shorter latency times were paired with rats receiving the SD
condition, despite which drug was being reinforced during that interoceptive state. The data
collected occurred over a period of 15 sessions and describe latency of each rat to the first cap
found in the foraging space. -------See Table 1------Following the collected data is a figure which
describes the relationship of rat one who received nicotine in the SΔ drug condition. ------See
Figure 1-------- The figure illustrates rat 1’s latency to find the first cap in seconds. The table
shows no significant correlation, ether positive or negative that would suggest that nicotine is
modulating foraging behavior. During sessions 5-8, and 12-15 the figure demonstrates that rat
one may have had a slight behavior modification. During session 5 to session 6, saline was
reinforced and latency times decreased suggesting that an association between the drug and
reward was made. Rat 2 received the opposite drug state in which nicotine was reinforced in the
SD condition.--------See Figure 2--------The figure shows again no consistent pattern or trend to
prove or disprove the original hypothesis, however between sessions 5-6 and 14-15 their is a
decrease in response latency to the first cap. This may suggest that nicotine is modulating latency
behaviors and is decreasing the amount of time it takes for a subject to find the first cap. In
figure 3, rat 3 continues to show no significant pattern of response under the same condition as
rat one. ------See Figure 3------ In Figure 4 the fourth rat’s latency to respond to the first cap is
also shown. Rat 4 received the same internal drug state as rat 2.------See Figure 4-------The figure
shows a peculiar relationship during sessions 5-8 because saline was not reinforced but
responding decreased when it should have increased. Sessions 8-9 showed a significant decrease
in responding under a rewarded condition (nic+) however, their was no consistent trend in
behavioral responding.

Table 2 describes the latency in minutes of all four rats to retrieve the last cap of water
within the apparatus. -----See Table 2-------- Figure one demonstrates a latency of responding for
rat 1 that does not a significant trend. For rat 1 during sessions 7-9 , the primary observer
detected a decrease in latency for responding during the SΔ condition when their should have
been an increase. ----See Figure 5----- In later sessions, specifically sessions 14-15, rat one
showed an increased latency for responding while under the SD condition when according to the
hypothesis should have showed a decrease in responding. Rat 2 continued to show no significant
trend of responding to the last cap. ----See Figure 6----- In Figure 6, rat 2 demonstrated a
decreased latency under the SD condition in sessions 7-8, however responding increases around
session 10 and continued to increase until session 15. Rat 3 had no trend in significant behavior.
The latency for responding under a saline reinforced state fluctuated over the 15 sessions
however, from sessions 3-6, the latency for finding all 5 water caps has the potential to start
showing a negative trend (decreased latency times). This would agree with the hypothesis that
the internal drug state, whether saline or nicotine may play a role in fluctuating behavioral
foraging. During session 12, -----See Figure 7-------rat 3 increased latency time when saline was
administered, again going against the original hypothesis. The final rat began to show significant
results according to figure 8 by having a continuous decrease in latency, however rat 4 showed a
decrease in latency under both conditions. ---See Figure 8---- Around session 11, behavioral
variability increases and the laboratory animal increased its rate of responding when it should
have continued to decrease. After consultation with several academic superiors, no inferential
tests were performed. Because a t-test compares means between subjects and variables, and their
are only four subjects and 2 independent and 2 dependent variables, an inferential analysis will

yield no extra information regarding significance of the study (Personal Consultation; P. Finn,
2014).
Discussion
Results gathered over 15 ten minute sessions, conclude that although nicotine has
enhanced responding to strong reinforcers in past, it may not directly modulate foraging
behaviors during an analysis. Previous work (Palmatier, O’Brien, & Hall, 2011), recognizes
several of the confounding issues with this study. Their results suggested that the reinforcement
enhancing effects of nicotine depend on conditioning history as well as behavioral motivation for
the presented stimuli. The original hypothesis for the foraging analysis attempts to combine the
enhancing effects of nicotine with a satiated stimulus to measure responding under each
condition. Although results showed little significance, their were several methodological flaws
worth noting that may have affected results. The laboratory animals were tested by the primary
investigator daily over a period of about two months. The testing however, did not reoccur
consistently at the same time every day. This may have affected results because of the animals
feeding schedule. The animals were watered for 15 minutes daily around 530pm, and if testing
was performed right before watering experimenters may be accidentally increasing the value of
the reinforcer and results may be less symbolic of the expected foraging behavior. If testing were
performed right after watering, the animals perhaps lost motivation for a devalued reward and as
a result, had increased reaction times in the apparatus.
Research for this study is ongoing and serves as a potential pilot for other similar drug
studies. Further research should be done with more laboratory subjects, testing consistently at the
same time every day over a period of several months. The results did not yield any significant
trend, however nicotine should not be ruled out as an important internal cue that may modulate

behavior. From this study several human parallels can be made regarding drug treatment. If the
study is replicated and significance is found, this information will lead to more efficient and
faster drug treatments. This focuses on the internal issue of drug addiction, by taking away the
internal cue that suggests the presentation of a drug, motivation to self-administer will diminish
and drug seeking behavior will be inhibited.
Tables and Figures
Table 1: “Latency to first cap”
Rat 1 Rat 3 Rat 2 Rat 4
Nic- Sal+ Nic- Sal + Nic+ Sal - Nic+ Sal -
Session 1 2.49 0.18 0.4 1.57
Session 2 2 0.2 4.2 6.31
Session 3 5.2 3.5 0.3 2.24
Session 4 7 1.3 2.1 0.3
Session 5 1 0.48 0.35 2
Session 6 0.1 0.2 0.15 0.36
Session 7 0.26 0.1 0.04 2.38
Session 8 1.22 0.19 0.05 0.08
Session 9 0.17 0.18 0.28 2.01
Session 10 0.1 0.17 0.24 0.2
Session 11 0.09 0.18 0.1 3.07
Session 12 0.43 0.46 0.18 1.32
Session 13 2.11 1.36 0.17 0.1
Session 14 0.51 1.11 2.12 2.41
Session 15 0.08 0.02 1.06 1.39
Figure 1: Latency to first cap in seconds-rat 1

Figure 2: Latency to first cap in seconds-rat 2
Figure 3: “Latency to first cap in seconds-rat 3”
Figure 4: “Latency to first cap in seconds-rat 4”

Table 2: “Latency to last cap”
Rat 1 Rat 3 Rat 2 Rat 4
Nic- Sal+ Nic- Sal + Nic+ Sal - Nic+ Sal -
Session 1 8.23 7.18 9.29 9.59
Session 2 7.52 6.35 6.24 10
Session 3 8.54 10 10 5.47
Session 4 10 8.25 7.31 5.59
Session 5 7.28 9.28 9.12 7.43
Session 6 6 4.24 8.59 8.34
Session 7 8.23 6.14 8.32 8.2
Session 8 6.05 5.49 5.23 6.34
Session 9 4.3 5.2 6.4 5.45
Session 10 8 4.2 7.43 5.32
Session 11 3.17 6.21 6.19 3.43
Session 12 9.27 3.06 6.11 2.3
Session 13 8.23 6.19 5.42 7.59
Session 14 2.34 6.31 7.33 4.33
Session 15 5.17 3.16 8.29 5.2
Figure 5: “Latency to last cap in minutes- rat 1”

Figure 6: “Latency to last cap in minutes- rat 2”
Figure 7: “Latency to last cap in minutes-rat3”
Figure 8: “Latency to last cap in minutes-rat4”

References
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Troisi, J. R., II, Dooley, T, II, & Craig, E. (2013). The Discriminative stimulus effects of a
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Appendices
Appendix A: Morris Water Maze (Morris et al, 1982)

Appendix B. 10cc Syringe used for injections

Appendix C:

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