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. Author manuscript; available in PMC: 2007 May 14.
Published in final edited form as: Pharmacol Biochem Behav. 2006 Dec 12;85(3):601–611. doi: 10.1016/j.pbb.2006.10.015

Table 1.

Summary of Phenotypes for Opioid Peptide Knockout Mice

Phenotype β –Endorphin KO Enkephalin KO Dynorphin KO
Body weight: ad libitum access to low fat chow Increasedb Unchanged Unchanged
Basal sucrose consumption: Two- Bottle Free-Choice, 2%–16% sucrose Unchangeda,c Unchangeda,c Unchanged
Compensatory reduction in caloric intake from chow during sucrose access Unchanged Unchanged Unchanged
Reduction in sucrose consumption following acute naloxone treatment Unchanged Absent Absent
Breakpoint: Operant responding under PR-3 for palatable food reinforcers Decreasedc Decreasedc Unchanged
a

The phenotypes for each mutant strain are listed in comparison to wild-type littermates on a uniform congenic C57BL/6 genetic background and are from the current study unless otherwise noted.

b

Appleyard, et al., 2003 and the current study.