Morphine treatment and reproductive condition alter olfactory preferences for pup and adult male odors in female rats

Abstract

Administration of morphine sulfate (MS) to pregnancy-terminated and postpartum lactating female rats disrupts both maternal behavior and postpartum aggression. Since the display of these behaviors may be heavily dependent on olfactory cues provided by the stimulus animals (rat pups and adult male rats, respectively), we examined whether MS was affecting the perception of the olfactory stimuli, and whether olfactory perception was modified by reproductive condition. In Experiment 1, lactating rats had their pups removed and were injected with MS (5.0 mg/kg, sc.) or saline. 60 min later they were placed into a two-choice apparatus, one side of which contained bedding soiled by neonates and the other clean bedding. Time spent on each side was recorded for a total of 5 min (300 s; chance = 150 s). Saline-treated mothers spent significantly more time on the pup-odor side, whereas MS-treated females spent significantly less. In Experiment 2, lactating females were treated with MS or saline and exposed to male odors (soiled bedding). MS significantly increased time spent on the side with male odors; when treated with saline, time spent was significantly reduced. Thus, in lactating rats. MS creates an aversion for pup odors while reducing the female's normal aversion toward male odors. In Experiment 3, ovariectomized (ovx) virgin females expressed neither an aversion nor a preference for the odor of pups following saline administration. After MS treatment, however, the virgins showed a distinct preference for pup odors. When exposed to male odors in Experiment 4 ovx virgins showed a marked preference for male odors after MS treatment, and neither a preference nor an aversion after saline. Experiment 5 examined pup odor preferences in intact virgins, early (Day 7), middle (Day 14), late-pregnant (Day 21), and prepartum (Day 22) rats. The pup odor preferences of virgin, Day 7, Day 14, and Day 21 pregnant rats were not different and generally were at chance levels. Day 22 pregnant females exhibited a marked preference for pup odors compared to chance levels, as well as compared to the other four groups. These findings suggest that opiates and endogenous opioids may regulate olfactory preferences and that alterations in this system may underlie normal behavioral changes toward conspecifics prepartum as well as during lactation.

Changes in responsiveness to kit odours across pregnancy: relevance for the onset of maternal behaviour

“…The present results show that, as in rats (Bauer, 1983;Fleming et al, 1989;Kinsley and Bridges, 1990), pregnancy-associated factors facilitate the responsiveness of doe rabbits to kit-derived odours. Thus, virgins did not sniff more or enter more times a particular box under any of the contrast conditions used.…”

“…This decrease in sniffing in the pre-partum period contrasts with the results found in rats, a species in which maximal levels of attraction to pup odours are evident close to delivery (Bauer, 1983;Fleming et al, 1989;Kinsley and Bridges, 1990). However, the correlation between changes in sniffs towards the "pup box" and variations in the hormonal milieu throughout pregnancy coincides with evidence showing that hormones modulate particular aspects of olfactory function in rodents (Pietras and Moulton, 1974;Yu et al, 1996a;Halem et al, 1999Halem et al, , 2001Baum and Keverne, 2002;Xiao et al, 2004) and carnivores (Kelliher et al, 1998).…”

Motivational aspects of maternal anxiolysis in lactating rats

“…Just prior to parturition or during the sensitization procedure, there is a profound change in the female's behavior that concludes with the onset of maternal interest and caring for pups. Transition from avoidance to approach behavior involves not only overcoming an initial fear to pup's odors, characteristic of non-maternal animals (Kinsley and Bridges 1990;Rosenblatt 1967Rosenblatt , 1975, but also a selective motivation to interact with them. This shift in the maternal perception of pups (Kinsley and Bridges 1990;Rosenblatt 1967Rosenblatt , 1975) assures the attachment between mother and young and brings about dramatic changes in mothers' affective behavior.…”

Common and divergent psychobiological mechanisms underlying maternal behaviors in non-human and human mammals

“…As described above, these cues from young act as ‘triggers’ for the expression of maternal behaviors, and as a group (and even in some cases, singly) these cues take on a positive valence for the mother (Bauer, 1983; Fleming et al, 1989; González-Mariscal & Chirino, 2011; Kinsley & Bridges, 1990; Lévy et al, 1983). Hence, at the time of parturition there is a shift within the mother’s reward systems that is strengthed through her early physical interactions with the pups, resulting in the young becoming highly rewarding stimuli (Fleming, Korsmit, & Deller, 1994a; Lee, Clancy, & Fleming, 1999; Magnusson & Fleming, 1995; Mattson, Williams, Rosenblatt, & Morrell, 2001; Pereira, Seip, & Morrell, 2008; Wilsoncroft, 1969).…”