Transcript Effect of Nucleus Accumbens Shell Inhibition on Salt Intake

Effect of Nucleus Accumbens Shell Inhibition
on Salt Intake
Frehiwot Gebrehiwot, RET Fellow 2010
Science Teacher, Morgan Park High School
RET Mentor: Dr. David Wirtshafter
NSF-RET Program
Introduction
Brain: Nucleus Accumbens Visible in Red
The nucleus accumbens is a brain region involved in motivation and reward to natural stimuli such as food.
This function is regulated by for the neurotransmitter dopamine. The nucleus accumbens is also implicated in
addiction to drugs such as cocaine and amphetamines which act by increasing the level of extracellular
dopamine.
Understanding the role of the nucleus accumbens and its behavioral effects has many clinical applications for
understanding eating disorders, drug addiction and Attention Deficit Hyperactivity Disorders (ADHD).The
nucleus accumbens has two major subdivisions: the shell and the core. This study focuses on the nucleus
accumbens shell (AcbSh).
Previous studies have demonstrated that the AcbSh controls motivation for food. Salt is a strong natural
motivator and plays an important physiological role in the body. The goal of this study is to further explore the
role of the AcbSh in the motivation for salt intake.
Materials and Method
 Animals: a total of 24 rats were used
 Surgery: Stainless steel guide cannulae were implanted in the scalp aimed at the AcbSh
and were held in place by stainless steel screws and dental cement
 To induce salt appetite, rats received a subcutaneous injection of furosemide, a diuretic
with the dose adjusted for body weight
 To confirm diuresis, pre and post injection body weighs were compared
 Using guide cannulae, rats received microinjection of the inhibitory drug muscimol, a
GABA agonist, Into the AcbSh. The control group received a microinjection of saline
solution
Cannulae Implant
and Lickometer.
 Rats were placed in lickometers with pre-measured quantity of 3% salt solution for 60
minutes
 Several behavioral parameters such as total number of licks, latency to licks, numbers of
bursts, number of clusters were recorded using a computer system
Results
Consumption of 3% Salt Solution After
Consumption
of 3%
Salt Solution Shell
After
Injections
into the
Accumbens
Injections into the Accumbens Shell
Average
Number
of Licks
5 minute
After
Average
Number
of Licks
Per 5per
Minute
BinBin
After
Injections
Shell
InjectionsInto
intothe
the Accumbens
Accumbens Shell
1000
4000
Average Licks per Bin
800
Number of Licks
3000
2000
600
400
200
0
1000
0
1
2
3
0
Saline
Muscimol
Drug Treatment
Figure 1: Mean of number of licks recorded during 60 minutes testing.
Difference between the two groups is 6.750. t= 0.0201 (P= 0.984)
Muscimol
Saline
4
5
6
7
8
9
10
11
12
13
Bin
Figure 2: Data shows that there is no significant difference in pattern
of consumption of salt solution during testing.
Discussion
Statistical Analysis:
The t-test value for the number of licks is t= 6.750 and P= 0.984
The difference in the mean values between the two groups is 6.750 licks which is not great enough to reject the
possibility that the difference is due to random sampling variability. There is not a statistically significant difference
between the experimental and the control group. The average number of licks per 5 minutes period also shows no
difference in the pattern of drinking between the two groups.
Conclusion:
Other studies have shown that inhibition of the AcbSh by muscimol produces large increases in the consumption of
sucrose and corn oil, but decreases intake of saccharine and ethanol. The results of the present study indicate that
inhibition of the AcbSh by muscimol does not have an effect on salt intake behavior. The next stage in the study is
to conduct a histological examination of the brain of tested rats to check for correct placement of cannulae into the
AcbSh.
Acknowledgements
 National Science Foundation Grant EEC-0743068
 Professor Andreas Linninger, Program Director
 Seon B. Kim, Program Assistant
 Dr. David Wirtshafter, Research Mentor
 University of Illinois at Chicago
 Co-Investigators: Beth Cowgill and William Schulenberg