Opponent recognition and social status differentiate rapid neuroendocrine responses to social challenge

Individual social status discriminates rapid neuroendocrine responses to non-social stress in male Anolis carolinensis, but whether such status-influenced reactions are retained in response to subsequent social stress is unknown. Dominant and subordinate males modify their behavioral responses to social challenge according to familiarity of the opponent, suggesting that accompanying neuroendocrine responses may differ according to opponent recognition despite social rank. We examined endocrine and neurochemical correlates of prior social status and opponent recognition during the opening stages of social challenge. Male pairs interacted and established dominant/subordinate status, followed by 3 days separation. Subsequently, subjects were paired with either the same opponent or an unfamiliar male according to rank (dominant with subordinate). After 90 s of social exposure, subjects were caught and brains and plasma collected for measurement of circulating corticosterone and limbic monoamines. Controls included pairs experiencing just one 90 s encounter plus a group of non-interacting subjects. Opponent recognition differentiated status-influenced responses, such that dominant lizards paired with familiar subordinate opponents had increased hippocampal dopamine and epinephrine, but showed increased plasma corticosterone and ventral tegmental area (VTA) norepinephrine when challenged with an unfamiliar opponent. Subordinate lizards encountering familiar opponents also had increased corticosterone, along with decreased hippocampal dopamine and increased VTA epinephrine, but showed no changes in response to an unfamiliar opponent. Such plasticity in status-influenced rapid neuroendocrine responses according to opponent recognition may be necessary for facilitating production of behavioral responses adaptive for particular social contexts, such as encountering a novel versus familiar opponent.