The document describes a study that investigated the effect of beta-endorphin (β-E) on stress-induced anxiety in mice. Mice with different levels of β-E were either exposed to a stressful forced swim test or not before being placed in a novel environment with food. Mice with lower β-E took longer to approach the food and sniffed it less, suggesting lower β-E is linked to decreased ability to cope with stress. Exposure to stress increased wariness of eating in a novel place for all mice but had a stronger effect on mice with low β-E levels, further indicating low β-E impacts stress response. The findings support the role of β-E in moderating behavioral responses to stressful stimuli

1. INTRODUCTION
β-endorphin (β-E) is an endogenous opioid peptide that is synthesized and
release in response to stress, and has been shown to moderate the
physiological and behavioral response to stress .
β-E AND ANXIETY
 The release of β-E following exposure to a stressful situation may mediate
behaviors that contribute to allostasis of the stress response.
 Genetic variability in the synthesis and release of β-E in response to stress
exposure may underlie individual differences in coping behavior.
 We have shown an inverse relationship between β-E levels and anxious
behavior in mice, suggesting decreased ability to manage stressful stimuli with
lower β-E levels.
Our study was aimed at determining the effect of β-E on stress-induced anxiety
in mice. Half of the mice in our study were exposed to an inescapable aversive
situation (forced swim test; FST) before being placed in an open field box
containing an almond slice. The control group of mice were not stressed in any
way before the novelty-feeding test.
Because feeding has been shown to be suppressed in a novel
environment and because β-E moderates anxious behavior, we
hypothesized that β-E would modulate the response to stress in a novelty-
suppressed feeding paradigm.
METHODS
 Adult naïve male and female β-E deficient (KO), heterozygous (HT) and wild-
type (WT) mice were used. Control mice were habituated for 10 min in testing
room and stressed mice were habituated for 7 minutes in testing room, following
the FST. Variables recorded were latency to approach almond, number of sniffs,
and the amount of almond eaten.
Forced Swim Test
 Stressed mice were subject to a modified version of Porsolt’s forced swim test
for 3 min in a plastic five gallon bucket measuring 30 cm in diameter with 20 cm
of water maintained at 23oC. Mice were judged immobile when making no
movements other than those required to stay afloat for 5 s.
Novelty Feeding Test
 Following habituation in testing room, control and stressed mice were kept for
five minutes in an open field box containing an almond slice in the center.
Statistical Analysis
 Main effects of and interaction between genotype, sex, and condition (control or
stressed) were assessed using analysis of variance (ANOVA) in SPSS.
Significance level was set at p≤ .05.
DISCUSSION
 Mice with low β-E took longer to approach the almond and sniffed the almond less frequently. These findings support the contention that β-E
moderates behavioral responses to stressful stimuli.
 Exposure to the FST increased aversion to eating in a novel environment for all genotypes. Moreover, exposure to the FST affected novelty feeding
of mice with low β-E more strongly than that of mice with higher levels. Because the effects of stress on novelty feeding are magnified with lower
levels of β-E, these data suggest that low β-E levels may indicate a decreased ability to cope with stress.
 These data add to a growing body of research suggesting that β-E plays an influential role in the ability to effectively manage stress . Because
stress and decreased ability to cope with it are associated with increased risk of developing anxiety and depression, the dysregulation of β-E may
be implicated in stress-related pathology.
β-ENDORPHIN MODULATES RESPONSE TO STRESS IN NOVELTY-SUPPRESSED
FEEDING
Sara Singh, Elizabeth Barfield, Alex Moser, Annie Hand, Judith E Grisel
Department of Neuroscience, Furman University, Greenville, SC
Effect of
Stress
Effect of
β-endorphin
Interaction of
β-endorphin
and Stress
ACKNOWLEDGEMENTS
I would like to thank Furman University and Dr. Judy Grisel for giving us the opportunity to conduct this research.
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