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from disinhibition from the light responsive GRP neurons. The 3h delay between light exposure
and its effect on GRP+ neurons suggests that the mechanism involves the loss of GABAdependent
inhibition at ZT 17-21 results from receptor internalization.
Disclosures: J.J. Le Sauter, None; P. Witkovsky, None; R. Cloues, None; R. Silver, None.
Poster
574. Entrainment and Phase Shifts: Neurons, Transmitters, Genes, and Proteins
Location: South Hall A
Time: Tuesday, October 20, 2009, 8:00 am - 12:00 noon
Program#/Poster#: 574.4/FF54
Topic: E.08.a. Entrainment and phase shifts
Support: NIH grant NS37919
Title: The SCN response to light in the subjective day is augmented by activity
Authors: *E. RODRIGUEZ 1 , J. LESAUTER 2 , R. SILVER 1 ;
1 Psychology, Columbia Univ., New York, NY; 2 Psychology, Barnard Col., New York, NY
Abstract: It is well established that the SCN responds to photic input during the night but not
during the day. Here, we investigated whether the SCN’s response to light is determined by the
prior light-dark (LD) cycle or by the animal’s rest/activity cycle. We tested whether activity
induction by temporal food restriction (FR) or awakening by movement of the home cage
influence daytime responses to a light pulse. Mice expressing GFP in gastrin-releasing peptide
(GRP) cells were housed individually with a running wheel, entrained to a 12:12 LD cycle, and
placed in one of 6 groups (n=6/group). Animals in a food anticipatory activity (FAA) paradigm
had food access restricted to ZT 6-14 (FAA+ group), while controls were fed at libitum
(Undisturbed groups). After 5 days FR, they were maintained in constant darkness from lights
off (ZT12) until a 30 min light pulse the next day starting at CT3.5 (FAA+ LP+ and Undisturbed
LP+); controls received no light pulse (FAA+LP−, Undisturbed LP−). Two other groups
(Awaken) were fed ad libitum and kept awake (at CT3.5-4) by gentle shaking of their home cage
by an experimenter wearing infrared goggles to see in the dark. Of these Awaken animals, one
group was exposed to a light pulse as above (Awaken LP+) while the controls received no light
(Awaken LP-). All mice were sacrificed at CT5. For fluorescent immunohistochemistry, every
third 40µm SCN slice was processed for c-FOS, arginine-vasopressin (AVP) and GFP. AVP was
used to delineate the core and shell SCN. AVP-outlined images were quantified by two
independent experimenters. Contrary to expectation, a light pulse during the subjective day led to
a small but significant increase in the number of c-FOS expressing cells. The number of light