22-28 kHz ultrasonic vocalizations associated with defensive reactions in male rats do not result from fear or aversion.

This study was carried out to determine whether 22-28 kHz vocalizations emitted during intermale interactions in adult rats were related with a state of fear, aversion or resulted from painful stimulation. Vocalizations in the 22-28 kHz range were measured in male rats during non-aggressive and aggressive social interactions; when given foot shock with a partner; during non-aggressive social interactions after an injection of (i) acetic acid (1%, IP); (ii) pentylenetetrazol (20-30 mg/kg, IP) and (iii) lithium chloride (63.8 mg/kg, IP). Ultrasonic vocalizations were consistantly detected in all rats while the animals displayed defensive or submissive postures when tested as intruders confronted with offensive residents or when administered foot shocks. Only occasional vocalizations were emitted, even in the presence of a partner, when the animals had received other painful or aversive treatments. These data support the hypothesis that 22-28 kHz vocalizations during intermale interactions are associated with defensive postures and are not the consequence of a state of fear or aversion.