Overeating Induced by Injection of the Glutamate Receptor Antagonist, CNQX, within the Nucleus Accumbens of Satiated Rats

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Overeating Induced by Injection of the Glutamate
Receptor Antagonist, CNQX, within the Nucleus
Accumbens of Satiated Rats

• Project Leader Jenny McCallister
• Funded by NASAs South Carolina Space Grant
  Consortium Research Experience for Undergraduates
  Grant

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Why Study the Nucleus Accumbens?
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LH
(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?
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Answer 1) Glutamate
Question 2) Do the sensory properties of more
palatable foods provide a greater inhibition of
the Nucleus Accumbens?
Answer We dont know.

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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.
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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

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Methods

• Cannulas were implanted bilaterally, aimed at the
  nucleus accumbens via stereotaxic surgery.

(Paxinos and Watson, 1998)
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Experimental Timeline

• non-food deprived rats

This is NOT an SSS study! We are interested in
determining the interaction of the drug and food
palatability in satiated rats.
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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

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Results Froot Loops
Pre-Injection Meal
Post-Injection Meal
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Froot Loops Intake During the Pre- Injection Meal
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Froot Loops Intake During The Post Injection
Meal
Cumulative Froot Loops Intake (g)
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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.

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

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• 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.

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General Summary Post Injection Meals

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Chow
Froot Loops
Chow
Froot Loops
4


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Cumulative Food intake (g)

2
1
0
30 min FL
30 min Chow
120 min FL
120 min Chow
Time post-injection
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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.

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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.

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