Ja. Vivian et Ka. Miczek, MORPHINE ATTENUATES ULTRASONIC VOCALIZATION DURING AGONISTIC ENCOUNTERS IN ADULT MALE-RATS, Psychopharmacology, 111(3), 1993, pp. 367-375
Ultrasonic vocalizations (USV) in rats may communicate ''affective'' s
tates during pain, sex and aggression. This proposal was evaluated in
an experiment with adult male Long-Evans rats during agonistic encount
ers; specifically, morphine and naltrexone effects were studied on dif
ferent types of USV by intruder rats exposed to resident attacks and t
o ''threat of attacks'' (i.e., intruder residing within the home cage
of the resident but prevented from physical contact by a wire mesh cag
e). Intruders readily emitted USV during agonistic encounters. These c
alls consisted primarily of two distinct distributions of pure tone wh
istles: 0.3-3 s, 19-32 kHz (''low'') calls and 0.02-0.3 s, 32-64 kHz (
''high'') calls. Sonographic analysis revealed a considerable repertoi
re of frequency modulated calls. Different types of vocalizations prov
ed to be differentially sensitive to the opiate treatments: morphine (
1-10 mg/kg SC) dose-dependently decreased the rate, duration and pitch
of both low and high frequency USV during the threat of attack; this
decrease in rate and duration measures was naltrexone-reversible (0.1
mg/kg IP). Interestingly, audible vocalizations were also emitted but
were unaffected by morphine in this dose range. Concomitant with the d
ecrease in USV after morphine was a dose-dependent decrease in rearing
, walking and nasal contact behavior with increases in submissive crou
ch behavior and tail flick analgesia. The decreases in rate and durati
on of both low and high USV and the pitch of specific frequency modula
ted calls after morphine administration may reflect an attenuation of
affective aspects of pain, and the many characteristics of US (rate, d
uration, pitch, frequency modulation, preand suffix attributes and tem
poral structure) point to potentially diverse functions. Morphine's pe
rvasive effects on ultrasonic but not audible vocalizations, in additi
on to reflexive and submissive responses, provides evidence for opioid
influences on ''affective'' as well as somatomotor responses to socia
lly aversive situations.