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