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Project Leader: Katie Kavanagh
Effects of Lateral Hypothalamic Injections of Glutamate Receptor Antagonist (D-AP5) and Agonist
(ATPA) on Food Intake in Rats Under Simulated Microgravity
•What brain mechanisms underlie sensory specific satiety in hind limb unloaded rats? •Specifically, are lateral hypothalamic glutamate receptors regulating sensory specific satiety?
Questions:
Why is this important?
•We hope to determine what brain mechanisms regulate SSS and whether they operate similarly in microgravity as they do on Earth.
Sensory Inputs Sight, Smell, Taste
(via Nucleus Accumbens, etc.)
EAT
Motor Output:
Neural Model
Glutamate release
Lateral Hypothalamus
EAT LESS
LH Injection of D-AP5 at 1g
X•D-AP5 = glutamate receptor antagonist
•Hypothesis 1: D-AP5 will suppress food intake and increase latency to feed during a SSS paradigm in hind limb unloaded rats
Sensory Inputs Sight, Smell, Taste
(via Nucleus Accumbens, etc.)
EAT
Motor Output:
Neural Model
Glutamate release
Lateral Hypothalamus
EAT MORE
LH Injection of ATPA at 1g•ATPA = glutamate receptor agonist
•Hypothesis 2: ATPA will boost food intake and decrease latency to feed during a SSS paradigm in hind limb unloaded rats•How do we target glutamate receptors in the lateral hypothalamus?
Getting to the Lateral Hypothalamus:Stereotaxic Surgery
medial / lateral
dorsal / ventral
ante
rior /
post
erio
r
(Paxinos and Watson, 1998)
Methods: Central MicroinjectionsProcedure= Inject 0.3 L of:
– aCSF (control)– D-AP5 (10 nmol)
n= 9 male Sprague-Dawley rats
– aCSF (control)– ATPA (1 nmol)
n= 8 male Sprague-Dawley rats
D-AP5 Study (bilaterally) ATPA Study (unilaterally)
needle
Experimental Procedures18 hr. food deprivation
Pre-injection meal – 90 minutesRat Chow
Lateral Hypothalamic injection – aCSF, ATPA, or D-AP5
Post-injection meal – 60 minutesRat Chow or Froot Loops®
HindlimbUnload
WED
Experiment
FRI
FoodDeprive
THURS MON
Rest(in standard cages)
TUESSAT SUN
Rats had ad libitum access to food and water except on experimental days. Light cycle was 12 hr /12hr light/dark.
Experimental Time Line
Counterbalanced 4 times
Statistical Analysis
•Two way repeated measures ANOVA•Student-Newman-Keuls post hoc test
How SSS was measured…• Cumulative Food Intake (grams):
– pre-injection meal at 60 and 90 minutes– post-injection meal at 30 and 60 minutes
• Latency to Eat (minutes):– post-injection meal
EAT LESS
LH Injection of D-AP5
X
Results for D-AP5, a glutamate receptor antagonist
Time Post Presentation
60 min 90 min
Cu
mu
lati
ve C
ho
w In
take
(g
ram
s)
0
1
2
3
4
5p = 0.61
Rats satiate on chow in pre-injection meal
D-AP5: pre-injection meal data
D-AP5: post-injection meal food intake at 30 minutes
**p<0.001
~99%
Injection
D-AP5: latency to eat in post-injection meal
*p<0.05
p=0.13
Injection
Summary : D-AP5
• D-AP5, a glutamate receptor antagonist, suppresses Froot Loops ® intake and increases latency to feed when injected into the lateral hypothalamus.
Conclusion•D-AP5 suppresses intake of a highly palatable food suggesting that glutamate receptors in the lateral hypothalamus are part of the neural pathway underlying SSS.
Results for ATPA,a glutamate receptor agonist
EAT MORE
LH Injection of ATPA
ATPA: pre-injection meal data Rats satiate on chow in pre-injection meal
ATPA: post-injection meal food intake at 60 minutes
p=0.31
*p<0.05
Injection
ATPA: latency to eat post-injection meal
p=0.3
*p<0.001~75%
Injection
Summary : ATPA
• ATPA, a glutamate receptor agonist, boosts rat chow but not Froot Loops® intake when injected into the lateral hypothalamus.
Conclusion• Offering Froot Loops® or injecting with ATPA appear
to be equally effective in increasing food intake. This suggests that access to a highly palatable food is sufficient to saturate this neural pathway.
Sensory Inputs (via Nucleus Accumbens, etc.)
Sight, Smell, Taste
EAT
Motor Output:
Conclusions:
Glutamate release
Lateral Hypothalamus
EAT LESS
LH Injection of D-AP5 in HU
X•D-AP5 = glutamate receptor antagonist
EAT MORE RAT
CHOW
LH Injection of ATPA in HU•ATPA = glutamate receptor agonist
Application:• Although pharmacological interventions are not
plausible, it appears that offering astronauts a more palatable food as second course is sufficient to ensure adequate intake.
Sensory Inputs (via Nucleus Accumbens, etc.)
Sight, Smell, Taste
EAT
Motor Output:
Glutamate release
Lateral Hypothalamus
Future Directions: Looking at the link between nucleus accumbens and SSS.
Results: DAP-5 Suppresses Overeating During Sensory Specific Satiety
Cum
ulat
ive
Foo
d In
take
(gr
ams)
ChowFroot Loops®
Cu
mu
lati
ve R
at C
ho
w I
nta
ke (
gra
ms)
@ 60 min @ 90 min
Results: Rats are Fed to Satiety on Rat Chow
Meal Duration
D-AP5: Pre-injection meal food intake at 60 and 90 minutes
ATPA Injected into LH
Meal 1 Food Intake
Time Post Presentation
60 min 90 min
Cu
mu
lati
ve F
oo
d In
take
(g
ram
s)
0
1
2
3
4
5
6
a CSF Chow ATPA Chow aCSF FL ATPAFL
ATPA: Pre-injection meal food intake at 60 and 90 minutes
D-AP5: post-injection meal food intake at 60 minutes
**p<0.001
~75%
ATPA: Post-injection meal food intake at 30 minutes
*p<0.05
p=0.06
Summary : aCSF
• Our results confirm that rats exhibit SSS during hind limb unloading
Conclusion• The same mechanisms responsible for SSS in
horizontal rats appear to be operating in hind limb unloading