Prosocial effects of prolactin in male rats: Social recognition, social approach and social learning

Abstract

Prolactin (PRL) and oxytocin (OT) are pituitary hormones essential for lactation, but also promote sexual behavior. OT stimulates social behaviors, such as recognition, approach, and learning, but less is known about PRL in these behaviors. Since PRL and OT have complementary functions in reproduction, we hypothesized that PRL increases social recognition, approach, and learning. Male Long-Evans rats received ovine PRL (oPRL; 0.5, 2.0 or 5.0 mg/kg), the PRL antagonist bromocriptine (0.1, 3.0 or 5.0 mg/kg) or saline 20 mins before testing for recognition of familiar vs. unfamiliar stimulus males. Saline controls preferred the unfamiliar male (p<0.05), while bromocriptine blocked this preference. oPRL did not increase preference. To measure social approach, we determined if PRL restores approach 2 hours after defeat by an aggressive male. Defeated rats avoided the aggressive male. 2 mg/kg oPRL, before or after defeat, restored approach towards the aggressive male (p<0.05). In non-defeated rats, oPRL or 3 mg/kg bromocriptine had no effect. To determine if PRL increases social learning, we tested social transmission of food preference. Rats choose between two unfamiliar flavors, one of which they have previously been exposed to through interaction with a demonstrator rat. Vehicle controls preferred chow with the demonstrated flavor over the novel flavor. oPRL-treated rats were similar. Bromocriptine-treated rats failed to show a preference. When tested one week later, only oPRL-treated rats preferred the demonstrated flavor. The results suggest that PRL is required for social recognition and learning, and that increasing PRL enhances social memory and approach, similar to OT.

Changes in prolactin, cortisol and testosterone concentrations during queen succession in a colony of naked mole-rats (Heterocephalus glaber): a case study

“…Furthermore, correlative studies in birds and mammals have revealed associations of prolactin with social and cooperative behaviours (Schoch et al 1996;Carlson et al 2006;Smiley and Adkins-regan 2016;Donhoffner et al 2017). Male birds and mice show higher levels of prolactin if they invested in parental care (Schradin 2008a;Angelier and Chastel 2009), prolactin affects the decision to babysit in meerkat (Suricatta suricatta) helpers (Carlson et al 2006) and increases social recognition in rats (Donhoffner et al 2017).…”

Wild mice with different social network sizes vary in brain gene expression

“…These results parallel our findings in the hypothalamus of females, which may be an indication that females with small social network sizes are dominant to females with large ones, even outside of the reproductive season. Some of these effects could be exerted through the pituitary hormone prolactin, as a critical function of dopamine released from the hypothalamus is in the suppression of pituitary secretion of prolactin [ 51 ] and because, among its many functions [ 52 ], prolactin is associated with social behaviors in several taxa, including parental behaviors [ 53 , 54 ] and prosocial and affiliative behaviors [ 55 , 56 ]. In terms of pathways containing downregulated genes, the ones highlighted in our GO term enrichment analysis were mostly related to the regulation of the inflammatory response, and the genes repeatedly represented in those pathways were Snx4 and Cd47 .…”