GENDER AND STRAIN COMPARISON IN A FEAR CONDITIONING AND EXTINCTION PROCEDURE IN THE RAT

Post-traumatic stress disorder (PTSD) is a mental disorder that may develop following traumatic events, characterized by intrusive memories, avoidance behaviors, negative alterations in cognition and mood, occuring at a higher prevalence in women than in men.
The aim of this study was to compare the susceptibility of both genders from four different strains of rats to a fear conditioning procedure, one of the most widely used animal models for modeling PTSD.
Rodents associate a tone (conditioned stimulus, CS) with electrical shocks previously received (unconditioned stimulus, US). Freezing behavior is observed following re-exposure to the same CS, as an indicator of fear. Repeated exposure to the CS in the absence of US leads to a progressive suppression of the fearful reaction evoked by the CS through an extinction process, which represents a key process in exposure-based therapies used for PTSD at the clinical level.
Long-Evans rats displayed the highest fear response while Wistar-Kyoto rats showed lowest performances. Long Evans rats demonstrated the slowest rate of extinction, Wistar Kyoto rats generally exhibited a lower and relatively constant degree of freezing over extinction sessions. Similar levels of freezing behavior were observed in both genders while the extinction process appeared more pronounced in females compared to males, particularly in the Wistar strain.
These results highlight strain and sex differences in fear learning and extinction. Long-Evans rats, due to their high level of fear and slow extinction, may be particularly suitable for testing potential PTSD treatments.