To investigate the impact of social buffering on pain, the study team administered mild tail shocks to infant rat pups at postnatal day (PN) 8 or 12, with or without their mothers. They hypothesized that repeated exposure to shock would alter their inflammatory pain responses as adults when experienced between PN5 and 9 (pain sensitive period prior to functional maturation of the amygdala), whereas pain experiences between PN10 and 14 (robust social buffering) would impact affective behaviors. Infant rat pups were assigned to one of three treatment groups: shock alone (“Shock”), shock with maternal presence (“Shock+mother”), or no shock/no mother (“Control”). PN55 to 65 adult rats were tested for basal levels of thermal pain and carrageenan induced thermal hyperalgesia, or separately for affective behaviors (i.e., fear, social behavior). Separate cohorts of animals completed the pain, fear, and social behavior tests.

Fos immunohistochemical (IHC) analysis for pups was performed with the periaqueductal gray of the midbrain (PAG), amygdala and paraventricular nucleus of the hypothalamus (PVN). Adult brains were harvested following perfusion and carrageenan-induced hyperalgesia. Fos analysis on adult rat brains focused on the pain network, including the prefrontal cortex (PFC), cingulate cortex, nucleus accumbens (NAc), amygdala, hypothalamus, thalamus, and the periaqueductal gray (PAG).