1. Overeating Induced by Injection of the Glutamate Receptor Antagonist, CNQX, within the Nucleus Accumbens of Satiated Rats
Project Leader: Jenny McCallister
Funded by NASA’s South Carolina Space Grant Consortium Research Experience for Undergraduates Grant

2. Why Study the Nucleus Accumbens?
Sight,
Smell,
Taste, &
Texture
(-)
EAT
(+)
Motivation ?
(-, +) LH
(-)
Continuous Inhibition of eating
(Saper et al., 2002)
Questions: 1) What neurotransmitters regulate activity in the nucleus accumbens?
2) Do the sensory properties of more palatable foods
provide a greater inhibition of the nucleus accumbens?

3. Answer: 1) Glutamate Answer: We don’t know. (-)
Question 2) Do the sensory properties of more palatable foods provide a greater inhibition of the Nucleus Accumbens?
Previous studies indicate that rat chow consumption can be increased by glutamate receptor antagonist injection in satiated rats (Kelley and Swanson, 1997).
Answer: We don’t know.
Appealing
Sensory Inputs
Inhibit Glutamate
Release
(-)
Continuous
Inhibition of
the LH =
DO NOT EAT
Nucleus Accumbens
Glutamate
release
Injection of glutamate antagonist,
( ), dose dependently disrupts
NAC neural transmission
: Furthest Disinhibition = greatest increase in food intake
: Disinhibition = increased food intake
: Further Disinhibition = greater increase in food intake

4. Hypothesis
Satiated rats will exhibit a greater increase in food intake when an injection of CNQX, a glutamate receptor antagonist, is paired with Froot Loops® versus rat chow.
vs.

5. Methods 12 male Sprague-Dawley rats
maintained on a 12 hr/ 12 hr light/dark cycle
with ad libitum access to rat chow and water

6. Methods
Cannulas were implanted bilaterally, aimed at the nucleus accumbens via stereotaxic surgery.
(Paxinos and Watson, 1998)

7. Experimental Timeline
pre-injection meal = 90 minutes
(Froot Loops® or Rat Chow)
non-food deprived rats
At least 48 hour rest
nucleus accumbens injection (0.3 mL) = aCSF or CNQX (counterbalanced)
post-injection meal = 120 minutes (more of the same food as the pre-injection meal)
This is NOT an SSS study! We are interested in determining the interaction of the drug and food palatability in satiated rats.

8. Quantitative Data Collection
Cumulative Food Intake (grams):
pre-injection meal at 60 and 90 minutes
post-injection meal at 30, 60, 90 and 120 minutes
Statistical Analysis
One way repeated measures ANOVA
Student-Newman-Keuls post hoc test

9. Results: Froot Loops®
Pre-Injection Meal
Post-Injection Meal

10. Froot Loops® Intake During the Pre- Injection Meal

11. Froot Loops® Intake During The Post Injection Meal
Cumulative Froot Loops Intake (g)

12. Interim Summary for Froot Loops ®
Injection of CNQX dose dependently increases Froot Loops® intake in satiated rats within ~30 min post injection.
By 120 min post injection, spontaneous Froot Loops® intake (control condition) matches CNQX-induced intake.

13. Results: Rat Chow
Pre-Injection Meal
Post-Injection Meal

14. Rat Chow Intake During the Post-Injection Meal
Cumulative rat chow Intake (g)

15. Interim Summary for Rat Chow
Injection of a high dose CNQX is sufficient to increase rat chow intake in satiated rats within ~30 min post injection.
In the control condition, rats did not exhibit spontaneous rat chow intake at any time tested.

16. Satiated rats exhibit a greater increase in food intake when injection of CNQX is paired with a more appealing, highly palatable food, such as Froot Loops®, in comparison to a standard food, such as rat chow. 6
General Summary: Post Injection Meals * 5
Froot Loops®
Chow
Froot Loops
Chow 4 * * 3
Cumulative Food intake (g) * 2 1
30 min FL
30 min Chow
120 min FL
120 min Chow
Time post-injection

17. Conclusions
Glutamatergic synapses within the nucleus accumbens appear to be part of the neural pathway whereby satiated rats avoid eating.
Further, this experiment suggests that glutamate release in the nucleus accumbens is inhibited by the sensory properties of highly palatable food.
Appealing
Sensory Inputs
Inhibit Glutamate
Release
(-)
Continuous
Inhibition of
the LH =
DO NOT EAT
Nucleus Accumbens
Glutamate
release
Injection of glutamate antagonist,
CNQX ( ), dose dependently
disrupts NAC neural transmission
: Further Disinhibition = greater increase in food intake
: Disinhibition = increased food intake

18. Applications
We now know that the nucleus accumbens is involved in regulating intake of a highly palatable food. Thus, foods with more appealing sensory properties should motivate the astronauts to eat more.
Future Directions: To determine the role of the nucleus accumbens in regulating SSS in both horizontal and Hindlimb Unloaded conditions.

19. Overeating Induced by Injection of the Glutamate Receptor Antagonist CNQX within the Nucleus Accumbens of Satiated Rats
Project Leader: Jenny McCallister
Funded by NASA’s South Carolina Space Grant Consortium Research Experience for Undergraduates Grant