Honors Thesis Final

THE FLORIDA STATE UNIVERSITY

COLLEGE OF ARTS AND SCIENCES

USE OF ZINC SUPPLEMENTATION TO IMPROVE BEHAVIORAL

RESILIENCY IN TRUAMATIC BRAIN INJURY

By

DANIEL PIERCE

A thesis submitted to the Department of Psychology

in partial fulfillment of the requirements for graduation withHonors in the Major

Degree Awarded:Spring 2016

The members of the Defense Committee approve the thesis of Daniel Pierce defended on April 23, 2015.

Dr. Cathy LevensonThesis Director

Dr. Orenda JohnsonOutside Committee Member

Dr. Heather FlynnCommittee Member

Abstract

2

Some of the most prominent outcomes associated with traumatic brain injury (TBI) are

deficits in learning and memory, anxiety, and depression. Previous work in a pre-clinical model

showed that chronic zinc supplementation can provide resilience to these poor outcomes. The

connection that exists between memory and the hippocampus, as well as the role of the

hippocampus in regulatory mood, led us to hypothesize that zinc supplementation acts via

hippocampal mechanisms. To test this hypothesis we used the Porsolt swim test, spontaneous

alternation, open field behavior, and novel object recognition test in a TBI model with zinc

supplementation and hippocampal irradiation. Prior to surgical procedures for TBI, rats were fed

zinc adequate (30 ppm) or zinc supplemented (180 ppm) diets for 4 weeks. We found that the

Porsolt swim test is not an appropriate measure of depression-like behavior in TBI models.

Traumatic brain injury had no significant effect on locomotor behavior in spontaneous

alternation or open field behavior tests. However, TBI did decrease the time spent grooming and

amount of rearing, but zinc supplementation did not show any improvements. Irradiation of the

hippocampus increases anxiety and reduces locomotor activity, which is also uncorrected by zinc

supplementation. Traumatic brain injury impaired novel object recognition performance. Zinc

supplementation did not have any improvements on these impairments. Traumatic brain injury

combined with irradiation of the hippocampus did not cause any further deficits. Therefore,

given that zinc supplementation has been shown to improve hippocampus dependent spatial

learning and memory, we conclude that the action of zinc supplementation in traumatic brain

injury on learning and memory is primarily in the hippocampus. These data further suggest that

zinc supplementation is less effective in improving cortical mechanisms of learning and memory.

Introduction

3

Zinc and the Brain

The essential trace element zinc is most highly concentrated in the hippocampus in

glutaminergic neuron rich areas. Zinc is transported to the hippocampus through the blood brain

barrier. However, soma staining that targeted vesicular zinc was not observed following TBI,

which lends evidence that vesicular zinc plays no role in neuronal damage following TBI

(Doering et al, 2007). Furthermore, clinical studies have shown that following traumatic brain

injuries, patients have a much higher risk to develop zinc deficiency with a majority of zinc

being lost in the urine (McClain et al, 1986). This provides reason to look into dietary options

and outcomes. Dietary zinc deprivation may influence zinc homeostasis in the brain, resulting in

brain dysfunction such as learning impairment (Takeda, 2000). Dietary zinc deprivation rarely

causes any decrease of zinc concentration in the brain, unlike in the peripheral tissues. However,

the brain functions are affected by zinc deprivation (Takeda, 2000). It was previously unknown if

dietary zinc levels had any link to the major depressive symptoms so closely related to TBI, but a

study was conducted that found when rats were fed a zinc deficient diet (1 ppm) they displayed

signs of depression such as anorexia, anhedonia, and increased anxiety (Tassabehji et al, 2008).

When zinc supplementation was added to the diet of a sample of rats, a 90% increase in zinc

present in the hippocampus was observed; further linking zinc, hippocampus, and memory

(Sowa-Kucma et al, 2011). Alterations induced by zinc administration in the hippocampus may

be related to specific zinc mechanisms (Sowa-Kucma et al, 2011).

TBI-Effects on Learning and Memory

4

An estimated 1.7 million people suffer from a traumatic brain injury (TBI) each year, and

of them 52,000 die and 275,000 are hospitalized. This makes TBI a contributing factor to a third

of all injury related deaths in the United States (CDC, 2015). Patients with severe brain injury

typically present with significant cognitive impairment, especially in the domains of attention

and concentration, psychomotor speed, memory, and executive function, in addition to fatigue

and problems with motivation (Fleminger, 2010). Most of these impairments would fall under

the class of working or short term memory, which is crucial not only to making seemingly basic

decisions like determining if a corridor had been entered before, but also in conversion of

experiences into long term memory such as the ability to identify novel objects in a familiar

setting after a period of time. The capacity of this working memory load was evaluated between

mild traumatic brain injury (MTBI) patients and healthy patients. MTBI patients showed

disproportionately increased activation of working memory circuitry during the moderate

processing load condition, but very little increase in activation associated with the highest

memory processing load condition (McAllister et al, 2001). Task performance did not differ

significantly between groups on any task condition, but MTBI patients showed a different pattern

of allocation of processing resources associated with a high processing load condition compared

to healthy controls, despite similar task performance (McAllister et al, 2001). In a longitudinal

study there was progressive normalization of the working memory activation pattern after diffuse

axonal injury in severe TBI, coinciding with an improvement in performance on this function

(Sanchez-Carrion et al, 2008). This suggests that injury-related changes in ability to activate or

modulate working memory processing resources might underlie some of the memory complaints

after MTBI (McAllister et al, 2001). This work made a good case for explaining what type of

memory is usually affected following a TBI, but did little to explore potential treatments.

5

It is likely that the changes in the hippocampus are crucial for predicting the severity of

memory deficits following a TBI. Hippocampal lesions produced a severe and selective

impairment in the capacity of rats to remember the sequential ordering of a series of odors,

despite an intact capacity to recognize odors that recently occurred (Fortin et al, 2002). These

findings support the hypothesis that hippocampal networks mediate associations between

sequential events that constitute elements of an episodic memory (Fortin et al, 2002). Previously,

it had been shown that rats experiencing a mild traumatic brain injury (MTBI) showed little

preference towards a novel object when placed among familiar objects (Munyon et al, 2014). It

was concluded that memory deficits after MTBI are associated with decreased intrinsic burst

activity in cells and impaired context-specific firing patterns in the hippocampus during object

exploration (Munyon et al, 2014).

Most importantly, a recent study looked at the effects of dietary zinc on learning and

memory. Morris Water Maze (MWM) has been correlated to improvements in learning and

memory. According to the study, zinc supplementation prior to injury significantly improved

MWM performance after a frontal cortex TBI and enabled zinc supplemented animals to perform

as well as uninjured sham-operated controls (Cope et al, 2011).

TBI-Effects on Mood

In addition to memory deficits, major depression is a consequence of TBI that affects

nearly 40% of all patients suffering from brain injuries (Jorge and Starkstein, 2005). A variety of

pre-clinical and clinical reports have shown that supplemented zinc has antidepressant activity.

For example, a preliminary clinical report suggested augmentation of antidepressant therapy by

zinc in patients treated for depression (Siwek et al, 2009). Zinc supplementation also

6

significantly reduced depression scores and facilitated the treatment outcome in antidepressant

treatment resistant patients (Siwek et al, 2009). Additionally, pre-clinical models show that zinc

increases resilience to TBI-associated depression, making it potentially useful in populations at

risk for injury (Cope et al, 2011). These populations include, but are not limited to, the elderly,

athletes, and military personnel. All of which whom are naturally exposed to high levels of stress

making them even more susceptible to major depression due to traumatic brain injury.

Experimental Questions

1. Previous work showed that zinc supplementation prevented TBI-associated depression

measured by the 2-bottle saccharine preference test (Cope et al, 2011). Therefore, this

work sought to determine if zinc supplementation would also reduce immobility in the

Porsolt swim test after traumatic brain injury.

2. We further hypothesized that zinc supplementation would improve open field behaviors

after traumatic brain injury including thigmotaxic behavior, grooming, and rearing.

3. The hippocampus is enriched in neuronal precursor cells. This work was designed to

begin to test the hypothesis that these cells play a role in the behaviors we test after

traumatic brain injury. This hypothesis was tested after irradiation of the hippocampus to

prevent neuronal precursor proliferation.

4. Previous data show that zinc supplementation prevents deficits in spatial learning and

memory associated with traumatic brain injury. Because we know that spatial learning

and memory is governed by the hippocampus, we designed an experiment to test the

degree to which zinc supplementation would improve learning and memory not directed

7

by the hippocampus. To accomplish this, we tested the effect of zinc supplementation on

TBI-associated deficits in a novel object recognition test.

Materials and Methods

Animals

The FSU Animal Care and Use Committee (ACUC) approved all animal experiments.

Young adult male rats (6 weeks of age) were divided into four groups (n=8): zinc adequate

sham-operated controls, zinc adequate TBI rats, zinc supplemented TBI rats, and zinc

supplemented TBI rats with hippocampal irradiation. Prior to surgical procedures for TBI or

irradiation, rats were fed zinc adequate (30 ppm) or zinc supplemented (180 ppm) diets for 4

weeks. During this time, animals were handled a minimum of 3 times/week.

Surgical Procedures

All surgical procedures were conducted aseptically under isofluorane anesthesia,

followed by a 1 cm scalp incision and 6 mm diameter craniotomy. All rats (except the sham

group) then received a TBI administered by a controlled cortical impact as previously described

(Cope et al, 2011). Post-operatively, rats were weighed and monitored for 10 days.

Irradiation

The group of zinc supplemented TBI rats that received hippocampal irradiation were

anesthetized for the duration of exposure to the radiation using 2% isoflurane in oxygen at a flow

rate of 2 liters per minute. The rats were then placed into a stereotaxic frame (David Kopf

Instruments, Tujunga, CA, USA), which is fitted with a custom-built and adjustable lead shield.

8

We used coordinates obtained from the rat brain atlas (Paxinos, Watson, 2013) to position the

shield with a 6mm exposure window over the hippocampus. A secondary lead shield was used to

protect the body and tail from collateral x-ray exposure. At this point, each rat was subjected to a

single 10Gy dose of X-ray radiation using an X-Rad 320 self-contained precision x-ray generator

(PXi precision x-ray, North Bradford, CT, USA) that has been previously shown in our lab to

eliminate stem cell proliferation.

Novel Object Recognition

The novel object recognition test consisted of two phases. Each rat first spent a five-

minute period in an enclosed area with two identical objects to allow them to become familiar

with the objects. After a one-hour hiatus, each rat was then returned to the enclosed space, but

one of the original objects was replaced with a novel object. Interactions with the novel and

familiar object were video recorded for 5 minutes. The videos were scored for the amount of

time spent interacting with the familiar object and the amount of time spent interacting with the

novel object.

Spontaneous Alteration

Next, each rat went to the spontaneous alteration test, which was administered in an

eight-arm radial maze. Each rat was placed in the center of the maze and given one minute to

acclimate to the environment, but restricted from entering any arms. Rats were then allowed to

enter all eight arms of the maze at will. Alterations between the 8 arms were video recorded for 5

minutes and later analyzed for patterns in arm selection. The pattern was defined by 4 arm

9

segments, and considered repeated if any one arm was present more than once in any block of

four arms given in non-overlapping succession.

Open Field Test

Each rat was placed in the center of a three-foot by five-foot open space that was marked

with a four by six grid pattern. Every rat had five minutes to freely explore the space. The

following recordings were taken: total number of lines crossed, number of lines crossed through

the middle grids, number of lines crossed along the outside edge, number of rearings, and

amount of time spent grooming. Percentages were measured of percent of crosses in the middle

vs. percent of crosses along the outside edge out of total line crosses.

Porsolt Swim Test

The final test was the Porsolt swim test and it consisted of two phases. The first phase

was a ten-minute period spent in a clear cylindrical water tank (3 feet tall and 1 foot in diameter),

which was designed to allow the rats an opportunity to learn how to swim and realize that there

was no escape. After twenty-four hours, each rat was returned to the water tank for five minutes.

Video recordings of the 5-minute test phase were evaluated for the depression-like activity of

immobility. Immobility is defined by minimal efforts of swimming that produce just enough to

keep the nose above water, which is usually accomplished by kicks from the back feet only. The

amount of time spent immobile was recorded and compared to the amount of time spent in the

tank.

10

Statistical Analysis

All data were expressed as the mean ± SEM and statistical significance was set at p<0.05

with 95% confidence (Prism; GraphPad, San Diego, CA). All behavioral data was analyzed by

one-way ANOVA with a Newman-Keuls Multiple Comparison Test.

Results

Novel Object Recognition Test

The injured animals spent a majority of their 5-minute period interacting with neither the

familiar or novel object. Injury reduced the amount of time spent with the novel object by over

50% (p<0.05). Zinc supplementation prior to TBI did not increase the amount of time spent with

the novel object (Fig. 1). This behavior was not impaired by irradiation of the hippocampus.

Fig. 1 Effect of zinc supplementation on learning and memory following traumatic brain injury.

Rats were fed a zinc adequate (ZA) or zinc supplemented (ZS) for 4 weeks followed by either a

sham surgery, injury, or injury and irradiation (IRR) of proliferating cells. Sham-operated

controls were fed the ZA control diet. Rats that received irradiation to the hippocampal region

were fed a ZS diet. Novel Object (NO) interactions were measured for 5 min. Bars represent

mean ± SEM. *Significantly different from sham operated rats at p<0.05.

11

Memory – Spontaneous Alternation

Following TBI, there were no significant differences in working memory based on the

spontaneous alternation test. ZS rats entered approximately the same number of total arms (Fig.

2A) as the ZA diet rats, which was only slightly more than the sham-operated controls. However,

there was a significant difference when comparing the sham and ZS TBI IRR groups’ alternation

scores. Rats that had newly proliferating cells in the hippocampus eliminated following injury

were unable to methodically enter each arm without repeating a significant number of arms

(p<0.001, Fig. 2B).

12

Fig. 2 Effect of zinc supplementation on working memory following traumatic brain injury. Rats

were fed a zinc adequate (ZA) or zinc supplemented (ZS) for 4 weeks followed by either a sham

surgery, injury, or injury and irradiation (IRR) of proliferating cells. Sham-operated controls

were fed the ZA control diet. Rats that received irradiation to the hippocampal region were fed a

ZS diet. Working memory was measured for 5 minutes using an eight-arm radial maze and

quantified by (A) the total number of arms entered and (B) alternation score, which was

equivalent to the number of consecutive novel 4 arm patterns over the total number of arms. Bars

represent mean ± SEM. *Significantly different from sham operated rats at p<0.05.

13

Open Field Test

TBI did not significantly alter the total number of lines crossed in the open field test (Fig.

3A). Neither zinc supplementation or irradiation of the hippocampus altered locomotor activity

in this test. Fig. 3B shows that irradiation of the hippocampus caused a 26% decrease in time

spent in the center of the open field as compared to the sham-operated controls, which spent 33%

of their time in the center (p<0.05, Fig. 3B). Open-field testing revealed that zinc

supplementation did not alter the amount of time spent grooming. When comparing the sham-

operated group to the ZS TBI and ZS TBI IRR groups, the injured animals allocated no time to

grooming (p<0.05, Fig. 4). Injury significantly decreased time spent grooming, regardless of ZS,

(p<0.05, Fig. 4) by more than 50% as seen between the sham control and ZA TBI groups. Injury

also caused a significant decrease in number of rearings (p<0.05, Fig. 5).

14

Fig. 3 Effect of zinc supplementation on anxiety and depression following traumatic brain injury.




were fed a ZS diet. Anxiety and depression style behaviors were measured for 5 minutes using

an open field box and quantified by (A) the total number of line crosses and (B) percent of time

spent in center. Bars represent mean ± SEM. *Significantly different from sham operated rats at

p<0.05.

15






an open field box and quantified by the amount of time spent grooming. Bars represent mean ±

SEM. *Significantly different from sham operated rats at p<0.05.

16






an open field box and quantified by the total number of rearings. Bars represent mean ± SEM.

*Significantly different from sham operated rats at p<0.05.

17

Porsolt Swim Test

Rats receiving a TBI spent 34%-43% less time immobile (p<0.001, Fig. 6) than sham

controls. Irradiation completely eliminated immobility (Fig. 6). There was no significant

difference between injured animals on ZA or ZS diets.






the Porsolt Swim Test and quantified by the percent of time spent immobile versus total time

spent in tank. Bars represent mean ± SEM. *Significantly different from sham operated rats at

p<0.05.

18

Discussion

TBI-induced depression.

Previous work used a rat model of TBI to show that injury to the frontal cortex results in

the depression-like behavior anhedonia (Cope et al, 2011). This test uses a two-bottle test to

measure the relative intake of saccharin-sweetened water compared to deionized water.

Anhedonia, identified as decreases in saccharin consumption is a depression-like behavior. This

finding is consistent with clinical work showing that depression is the single most common

problem in patients with TBI (Jorge and Starkstein, 2005).

While TBI clearly induces depression in both clinical and pre-clinical studies, 4 weeks of

dietary zinc supplementation prior to the induction of cortical injury in rats completely prevented

the development of TBI-associated anhedonia. The current work sought to determine the extent

to which other measures could be used to evaluate the efficacy of zinc in a rat model. We thus,

chose to use the well-characterized Prosolt swim test. This test, which is employed over a two

day period measures the reduction in immobility as a measure of treatment efficacy, such that

rats that have successfully undergone treatment will reduce the amount of time they spend

immobile in the swim tank over a 5 minute period. Curiously, we found that TBI completely

abolished immobility in the Porsolt swim test. In fact, all groups receiving a TBI (regardless of

treatment) had significant reductions in immobility when compared to the sham-operated group.

These data led to the hypothesis that TBI induces hyperactivity that significantly increases

swimming behavior. Regardless of the mechanism, it is clear from these results that the Porsolt

swim test is not appropriate in this model of TBI, and cannot thus be used to evaluate the

efficacy of zinc supplementation in cortical injury.

19

Locomotor Activity.

To test the hypothesis that this model of TBI induces hyperactivity we tested all animals

in an open field. Measurements of line crossing showed that, contrary to our hypothesis, that TBI

did not increase locomotor activity and did not indicate hyperactivity. In fact, less time was spent

by TBI animals in grooming and rearing. Zinc supplementation did not correct either of these

behaviors, suggesting that the effects of zinc on depression-like behaviors may be specific and

include exploratory or motor behaviors. Additionally, the conclusion that this model of TBI does

not induce hyperactivity or increased locomotor activity was confirmed by the finding the total

number of arms explored in the spontaneous alternation test was not changed by TBI. Finally, in

the open field test, animals face a conflict between avoiding an open area and staying to the safer

areas such as by walls and corners in a novel environment (Ahn et al, 2013). There was no

significant difference between the injured and uninjured animals in time spent in the center.

Learning and Memory.

Traumatic brain injury has repeatedly been shown to result in cognitive impairment in

both humans and animal models. For example, it has been previously shown that hippocampal

lesions produced a severe and selective impairment in the capacity of rats to remember the

sequential ordering of a series of odors, despite an intact capacity to recognize odors that recently

occurred (Fortin et al, 2002). Additionally, spatial learning and memory, as assessed by the

Morris Water Maze is impaired by our model of TBI (Cope et al, 2011; Cope et al, 2012).

Zinc supplementation prior to frontal cortex injury improves spatial learning and memory

as demonstrated by Morris Water Maze performance (Cope et al, 2011). Because spatial learning

and memory is dependent on the hippocampus, we hypothesized that chronic zinc

20

supplementation prevented memory deficits via hippocampal mechanisms. We tested this

hypothesis with a novel object recognition test that is primarily mediated by the cortex (Wilson

et al, 2013). We show that chronic dietary zinc supplementation before TBI produced marginal

differences between the ZA and ZS TBI experimental groups. In light of this, if spatial learning

and memory is indeed regulated through hippocampal mechanisms, and it is known that novel

object recognition works through the cortex, then the failure of zinc supplementation to improve

novel object recognition provides evidence that zinc supplementation is improving learning and

memory via hippocampal mechanisms. To further test this, we irradiated the hippocampus of all

newly proliferated stem cells. As expected, the irradiated groups did not perform significantly

worse in the novel object recognition task. These data support the hypothesis that novel object

recognition is a test of cortical memory and not hippocampal. If it were hippocampal, then we

would have seen significantly worse if not a completely elimination of performance in novel

object recognition.

Together these data support the conclusion that the beneficial effects of zinc

supplementation in TBI are provided by actions in the hippocampus. Given the large

concentration of zinc in this important region of the brain, future work will be needed to

understand the cellular and molecular mechanisms responsible for the protective effects of zinc

supplementation in cortical injury. Our lab is currently exploring the role of zinc

supplementation in the regulation of hippocampal stem cells after TBI as well as the role of

synaptic zinc after TBI.

21

Conclusions

1. Porsolt swim test is not an appropriate measure of depression-like behavior in traumatic

brain injury.

2. Traumatic brain injury does not significantly impair locomotor behavior as measure in

the spontaneous alternation and open field test.

3. Traumatic brain injury decreases time spent grooming and amount of rearing, however,

zinc supplementation did not correct these behaviors.

4. Irradiation of the hippocampus increases anxiety as measured by time spent in

thigmotaxic behavior, and reduces locomotor behavior in spontaneous alternation.

5. Traumatic brain injury decreases novel object recognition, which was measuring

cortically derived learning and memory. Zinc supplementation did not improve these

measures. Traumatic brain injury combined with irradiation of the hippocampus did not

cause any further deficits. Therefore, given that zinc supplementation has been shown to

improve hippocampus dependent spatial learning and memory, we conclude that the

action of zinc supplementation in traumatic brain injury on learning and memory is

primarily in the hippocampus. These data further suggest that zinc supplementation is

less effective in improving cortical mechanisms of learning and memory.

References

1. CDC (Ed.). (2015, February 26). Get the Stats on Traumatic Brain Injury in the United

States.from http://www.cdc.gov/traumaticbraininjury

2. Cope, E., Morris, D., & Levenson, C. (2012). Improving treatments and outcomes: An

emerging role for zinc in traumatic brain injury. Nutrition Reviews. 70(7), 410-413.

22

3. Cope, E., Morris, D., Scrimgeour, A., & Levenson, C. (2012). Use of Zinc as a Treatment

for Traumatic Brain Injury in the Rat: Effects on Cognitive and Behavioral

Outcomes.Neurorehabilitation and Neural Repair, 7, 907-913.

4. Cope, E., Morris, D., Scrimgeour, A., Vanlandingham, J., & Levenson, C. (2011). Zinc

supplementation provides behavioral resiliency in a rat model of traumatic brain

injury. Physiology & Behavior, 104, 942-947.

5. Doering, P., Danscher, G., Larsen, A., Bruhn, M., Søndergaard, C., & Stoltenberg, M.

(2007). Changes in the vesicular zinc pattern following traumatic brain

injury. Neuroscience, 150, 93-103.

6. Fleminger, S. (2010). NeuropsychiatricEffectsofTraumaticBrainInjury:Secondary

Symptoms That You Need to Watch For. Psychiatric Times, 27(3), 40-45.

7. Fortin, N., Agster, K., & Eichenbaum, H. (2002). Critical role of the hippocampus in

memory for sequences of events. Nature Neuroscience,5(5), 458-462.

8. Jorge, R., & Starkstein, S. (2005). Pathophysiologic Aspects of Major Depression

Following Traumatic Brain Injury. Journal of Head Trauma Rehabilitation, 20, 475-487.

9. McClain CJ, Twyman DL, Ott LG, et al. Serum and urine zinc response in head-injured

patients. J Neurosurg. 1986; 64:224–230.

10. McAllister, T., Sparling, M., Flashman, L., Guerin, S., Mamourian, A., & Saykin, A.

(2001). Differential Working Memory Load Effects After Mild Traumatic Brain

Injury. NeuroImage, 14(5), 1004-1012.

11. Munyon, C., Eakin, K., Sweet, J., & Miller, J. (2014). Decreased bursting and novel

object-specific cell firing in the hippocampus after mild traumatic brain injury. Brain

Research, 1582, 220-226.

23

12. Paxinos, G., & Watson, C. (2013). The rat brain in stereotaxic coordinates(7th ed.).

Academic Press.

13. Sanchez-Carrion, R., Fernandez-Espejo, D., Junque, C., Falcon, C., Bargallo, N., Roig,

T., Vendrell, P. (2008). A longitudinal fMRI study of working memory in severe TBI

patients with diffuse axonal injury. NeuroImage, 43, 421-429.

14. Siwek, M., Dudek, D., Paul, I., Sowa-Kućma, M., Zięba, A., Popik, P., Nowak, G.

(2009). Zinc supplementation augments efficacy of imipramine in treatment resistant

patients: A double blind, placebo-controlled study.Journal of Affective Disorders, 118,

187-195.

15. Sowa-Kućma, M., Kowalska, M., Szlósarczyk, M., Gołembiowska, K., Opoka, W., Baś,

B., Nowak, G. (2011). Chronic treatment with zinc and antidepressants induces

enhancement of presynaptic/extracellular zinc concentration in the rat prefrontal

cortex. Amino Acids, 40, 249-258.

16. Takeda, A. (2000). Movement of zinc and its functional significance in the brain. Brain

Research Reviews, 34, 137-148.

17. Tassabehji, N., Corniola, R., Alshingiti, A., & Levenson, C. (2008). Zinc deficiency

induces depression-like symptoms in adult rats. Physiology & Behavior, 95, 365-369.

18. Wilson, D., Langston, R., Schlesiger, M., Wagner, M., Watanabe, S., & Ainge, J. (2013).

Lateral entorhinal cortex is critical for novel object-context

recognition. Hippocampus, 23(5), 352-366.

24

Documents

Honors Thesis Final