Ultrasounds emitted by female rats during agonistic interactions: effects of morphine and naltrexone

Abstract

Ultrasonic vocalizations may be an expression of the affective pain response in laboratory rodents. The present experiment compared morphine's effects on high (33-60 kHz) and low (20-32 kHz) frequency ultrasonic vocalizations to its effects on a range of unconditioned behavioral responses to aversive stimuli; the influence of estrous cyclicity on morphine sensitivity was also investigated. In experiment 1, naive female Long-Evans rats, selected during estrus or diestrus, received cumulative morphine (1, 3, 6, 10 mg/kg SC) or saline, and in experiment 2, rats were pretreated with naltrexone (0.1 mg/kg IP) 5 min before morphine (17, 30, 60, 100 mg/kg SC). The following endopoints were measured 20-25 min post-injection: (1) tail flick latency; (2) ultrasonic and audible vocalizations; (3) the behavioral response to aggressive attack; and (4) locomotor activity. Following a brief exposure to an attack, rats were threatened by an aggressor but protected from further attack by a wire mesh cage (30 x 21.5 x 20 cm), thereby allowing for continued behavioral and vocal measurement without the risk of physical injury; video and audio recordings were made of the attack encounter and a subset of the protected encounter (1 min). The endpoint most potently and specifically modulated by morphine was high frequency ultrasounds. The rate of high frequency calling varied as a function of the estrous cycle, supporting gonadal hormone modulation of ultrasonic vocalizations. Low frequency ultrasounds, by contrast, were relatively insensitive to opiate manipulation and were less influenced by estrous cyclicity. High frequency vocalizations may be a more sensitive indication of the affective response to an attacking conspecific that low frequency calls.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Drugs of Abuse on Putative Rostromedial Tegmental Neurons, Inhibitory Afferents to Midbrain Dopamine Cells

“…Hence, RMTg lesions blunt inhibitory behavioral responses, such as freezing elicited by aversive stimuli and open arm avoidance in the elevated plus maze (Jhou et al, 2009a). Consistently, both opioids and cannabinoids reduce the magnitude of aversion-elicited inhibitory behavioral responses (Haney and Miczek, 1994;Moreira et al, 2009;Vivian and Miczek, 1998). On the other hand, opposite to morphine and cannabinoid agonists, nicotine enhances behavioral responses to aversive stimuli, as it enhances contextual fear as evaluated by measuring freezing, a natural fear response in rodent (Gould and Wehner, 1999).…”

Dopamine D1 and μ-opioid receptor antagonism blocks anticipatory 50 kHz ultrasonic vocalizations induced by palatable food cues in Wistar rats

“…Step FM and other FM calls were also increased during food anticipation. However, the acoustic pattern of these calls is heterogeneous, and their biological significance is unclear (Brudzynski 2013; Haney and Miczek 1994; Mahler et al 2013; Thomas et al 1983). Altogether, the present findings suggest that cue-induced anticipatory 50 kHz USVs, at least under the present experimental conditions, may be driven by aspects of positive, neutral, or even negative affect.…”

Ultrasonic Vocalization Response Elicited in Adjuvant-induced Arthritic Rats as a Useful Method for Evaluating Analgesic Drugs

“…Social interaction is known to elicit USVs from rats [10]. If the 'stimulus rat'-elicited USVs of AIA rats are actually a behavioral expression of chronic pain and can be inhibited by analgesic drugs, objective evaluation of the analgesic activity of newly developed drugs may become possible.…”