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.

Effect of Nucleus Accumbens Shell Inhibition on Salt Intake

Frehiwot Gebrehiwot, RET Fellow 2010 Science Teacher, Morgan Park High School

RET Mentor: Dr. David WirtshafterNSF-RET Program

Discussion

Materials and Method

Results

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

Cannulae Implant and Lickometer.

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

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

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)

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.

Average Number of Licks Per 5 Minute Bin After Injections Into the Accumbens Shell

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Figure 2: Data shows that there is no significant difference in pattern of consumption of salt solution during testing.

Acknowledgements

Consumption of 3% Salt Solution AfterInjections into the Accumbens Shell

Drug Treatment

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Consumption of 3% Salt Solution After Injections into the Accumbens Shell

Average Number of Licks per 5 minute Bin After Injections into the Accumbens Shell

Introduction Brain: Nucleus Accumbens Visible in Red