Effects of serotonergic and opioidergic drugs on escape behaviors and social status of male crickets.

We examined the effects of selective serotonin depletion and opioid ligands on social rank and related escape behavior of the cricket Gryllus bimaculatus. Establishment of social rank in a pair of males affected their escape reactions. Losers showed a lower and dominants a higher percentage of jumps in response to tactile cercal stimulation than before a fight. The serotonin-depleting drug alpha-methyltryptophan (AMTP) caused an activation of the escape reactivity in socially naive crickets. AMTP-treated animals also showed a lower ability to become dominants. With an initial 51.6+/- 3.6% of wins in the AMTP group, the percentage decreased to 26+/-1.6% on day 5 after injection. The opiate receptor antagonist naloxone affected fight and escape similarly as AMTP. In contrast to naloxone, the opioid agonist [d-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin decreased escape responsiveness to cercal stimulation in naive and subordinate crickets. We suggest that serotonergic and opioid systems are involved in the dominance induced depression of escape behavior.