AUTOMATED MEASUREMENT OF MOUSE FREEZING BEHAVIOR AND ITS USE FOR QUANTITATIVE TRAIT LOCUS ANALYSIS OF CONTEXTUAL FEAR CONDITIONING IN (BALBCJ X C57BL/6J)F-2 MICE/

The most commonly measured mouse behavior in fear conditioning tests i s freezing. A technical Limitation, particularly for genetic studies, is the method of direct observation used for quantifying this response , with the potential for bias or inconsistencies. We report the use of a computerized method based on latency between photobeam interruption measures as a reliable scoring criterion in mice. The different compu ter measures obtained during contextual fear conditioning tests showed high correlations with hand-scored freezing; r values ranged from 0.8 7 to 0.94. Previously reported strain differences between C57BL/6J and DBA/2J in context-dependent fear conditioning were also detected by t he computer-based system. In addition, the use of computer-scored free zing of 199 (BALB/cJ x C57BL/6J)F-2 mice enabled us to detect a sugges tive gender-dependent chromosomal locus for contextual fear conditioni ng on distal chromosome 8 by QTL analysis. Automation of freeze scorin g would significantly increase efficiency and reliability of this lear ning and memory test.