Examining the role of endogenous opioids in learned odor–stroke associations in infant rats

Abstract

Maternal touch profoundly regulates infant neural and behavioral development, and supports learned odor associations necessary for infant attachment. Endogenous opioids are well characterized to mediate the calming and analgesic properties of maternal touch; yet their role in learned odor-touch associations is unknown. We administered naltrexone, an opioid receptor antagonist, before or immediately following classical conditioning with peppermint odor and tactile stimulation (stroking) in rat neonates. Results indicate odor-stroke conditioning produces odor preferences facilitated by endogenous opioids during acquisition and memory consolidation. These results provide additional evidence for the modulatory role of opioids in neonate learning and memory. Disturbances to this system may alter the impact of touch on infant development, particularly in the realm of learning necessary for attachment. ß 2005 Wiley Periodicals, Inc. Dev Psychobiol 48: 71-78, 2006.

Warmth from skin‐to‐skin contact with mother is essential for the acquisition of filial huddling preference in preweanling rats

“…Additionally, a group of pups were exposed to stroking with a soft brush in the presence of an odor CS. This procedure was designed to replicate the methods of previous investigators (e.g., Pedersen et al, 1982;Roth & Sullivan, 2006;Sullivan, Brake, Hofer, & William, 1986;Sullivan & Hall, 1988;Woo & Leon, 1987) who have reported that stroking stimulation, intended to mimic some of the mechanical effects of tactile stimulation from maternal contact such as licking, can serve as reinforcer for pups' odor learning.…”

“…Their research has linked these undefined aspects of maternal behavior to behavioral and neurological alterations in offspring development as well as to enduring, epigenetic changes in gene expression (e.g., Champagne, 2008;Champagne, Diorio, Sharma, & Meaney, 2001;Francis, Champagne, & Meaney, 2000;Liu, Diorio, Day, Francis, & Meaney, 2000;Liu et al, 1997;Meaney, 2010;Meaney & Szyf, 2005). In other studies of age-dependent odor learning in rats, stroking a pup's body with a soft brush is used to ''mimic'' maternal licking; this stimulation can lead to preferential approach toward a conditioned odor (Moriceau & Sullivan, 2005;Roth & Sullivan, 2006;Sullivan & Hall, 1988;Sullivan & Wilson, 1994;Woo & Leon, 1987). Such conditioned approach behavior is often interpreted as representing approach to the mother, reinforced by a simulation of maternal licking/grooming (e.g., Moriceau & Sullivan, 2005;Pedersen et al, 1982;Sullivan & Hall, 1988).…”

“…Despite the prevalence of such interpretations, we are unaware of any studies that demonstrate a direct association of maternal licking/grooming with pup's odor preference. Because the stroking effects on early olfactory learning were created by general stimulation to the pup's body (McLean, Darby-King, & Hodge, 1996;Moriceau & Sullivan, 2005;Roth & Sullivan, 2006;Sullivan & Hall, 1988;Sullivan & Leon, 1986;Sullivan & Wilson, 1994;Weldon, Travis, & Kennedy, 1991;Woo & Leon, 1987), it is pertinent to examine associations between different types of licking/grooming and pups' preference for a maternally-associated odor.…”

Modeling Borderline Personality Disorder Based on the Neurobehavioral Foundation of Major Personality Traits

“…Indeed, in monkeys and rodents, social bonding is not possible without soft tactile stimulation from the mother (Fleming, Korsmit, & Deller, 1994;Fleming, O'Day, & Kraemer, 1999). Importantly, such stimulation serves as reward in associative conditioning to odor in rats, which was eliminated by blocking uORs (Roth & Sullivan, 2005), and soft-touch reward was associated to odor in human neonates (Sullivan, 1991). Mammals, and especially primates, have evolved particular receptors on hairy skin and a sensory pathway for soft touch Olausson et al, 2002) that projects to the anterior insular cortex, a structure that mediates awareness of the subjective experience of emotions (Craig, 2009).…”

Ontogeny of memory: An update on 40 years of work on infantile amnesia

“…For example, in adult rats, post conditioning administration of opioid receptor antagonists can facilitate [144][145][146], whereas post conditioning administration of opioid receptor agonists can impair memory for fear conditioning [147,148]. Rather than being underdeveloped, the endogenous opioid system is active from birth [149] and plays a role in behaviours that are important during infancy such as suckling, social play and odour preference learning [150][151][152][153][154][155][156][157][158]. One study has examined the role of opioid receptors in the retrieval of fear memories in young rats [159].…”