Early resource scarcity alters motivation for natural rewards in a sex- and reinforcer-dependent manner

Developmental trajectory of social reward motivation from early adolescence into adulthood in female and male Long‐Evans rats

“…In Study 2, which involved a comparison of gate openings at a social and a nonsocial port, female rats exhibited more social motivation relative to male rats irrespective of age on the PR test, which is consistent with evidence in adult rats (housed in isolation before behavioral testing) that females engaged in more socially directed behavior than did males (Deak et al, 2009). In contrast, in studies involving social operant conditioning tasks similar to those in our studies, pair-housed adult female rats responded to a social reward port less than male rats did (Schatz et al, 2019) and in the first week of life increased social reward motivation in male and not in female rats when tested in adulthood (Williams et al, 2022).…”

“…Thus, it is possible that the behavior of the rats in the two studies was affected by shipping stress, which can affect gestational development and maternal behavior (Butler‐Struben et al., 2022). Stress exposures in the first week of life increased social reward motivation in male and not in female rats when tested in adulthood (Williams et al., 2022). Thus, whether sex differences on tests of social behavior are observed, and the direction of any sex difference, is likely influenced by several factors, from test procedures to the life history of the animals.…”

“…TA B L E 1 Summary of the results, with the postnatal ages shaded from light gray (lowest mean) to black (highest mean). there was no difference in lever-pressing behavior to access a peer in adult female and male Sprague-Dawley rats (Chow et al, 2022) nor in adult female and male Long-Evans rats (Williams et al, 2022). One study of C57Bl/6J mice reported lower social responding in female mice relative to male mice (Maloney et al, 2023), and another reported no sex difference (Hu et al, 2021).…”

Behavioral responses to natural rewards in developing male and female rats

“…Moreover, our results are in accordance with a prior study showing that high levels of sucrose preference and/or consumption emerge around or after PND 28 in rats (Kruse et al., 2019; Perez & Sclafani, 1990) and studies showing no sex differences in sucrose preference at PND 30 (Doherty et al., 2017) or PND 54 (Bertholomey et al., 2022). Nonetheless, sex differences in sucrose consumption, preference and reinforcement are well‐documented in adult female rats, which consume more sucrose in bottle‐choice and binge intake paradigms and respond at higher rates for sucrose during operant procedures compared to males (Bertholomey et al., 2022; Grimm et al., 2022; Sherrill et al., 2011; Valenstein et al., 1967; Williams et al., 2022). Within this context, our findings suggest that the sex‐specific increase in sucrose preference (in which females exhibit higher preference) emerges after the adolescent timepoint used in our study.…”

“…Similar motivational deficits have been recapitulated in rodent models useful for the study of depression and schizophrenia, including rodent models of early life stress (ELS) (Birnie et al., 2022; Duque‐Quintero et al., 2022; Rincon‐Cortes, 2023; Scheggi et al., 2018; Slaney et al., 2018; Young & Markou, 2015). Although sex differences in reward‐related responses have been reported in adult animals following ELS (Birnie et al., 2022; Rincon‐Cortes, 2023; Williams et al., 2022), less is known regarding the normative development of reward‐related responses in both sexes. Comparing reward‐related behavioral responses between developing male and female rats may be useful for understanding how these processes may be affected across early development and in rodent models relevant to psychiatric disorders.…”