ALTERED RESPONSES TO FEMALE ODORS IN PARASITIZED MALE-MICE - NEUROMODULATORY MECHANISMS AND RELATIONS TO FEMALE CHOICE

There is accumulating evidence that females may preferentially select parasite-free or -resistant males. Minimal attention has, however, bee n paid to the mate preferences and responses of the parasitized male h osts themselves. Here, we considered the effects of parasitic infectio n on male host mate responses, the neuromodulatory correlates of these responses, and the relations of these responses to female mate choice . Using an odor ''preference'' test, we examined the effects of differ ent stages of an acute, sub-clinical infection with the naturally occu rring, enteric, single host, protozoan parasite, Eimeria vermiformis, on the responses of male mice, Mus musculus domesticus, to the odors o f estrous females along with the responses of uninfected females to th e parasitized males. At 4 days post-infection (non-infective, pre-pate nt stage) E. vermiformis-infected male mice showed a significantly dec reased preference for the odors of estrous females, whereas at 10 days post-infection (infective, patent stage) infected males showed a sign ificantly increased preference for the odors of estrous females. Paras itized males displayed no significant changes in their responses to th e odors of non-estrous females, supporting effects on the reproductive ly related responses of the host. In parallel, estrous females display ed a reduced interest in the odors of infected males. Least interest w as expressed in the odors of the patent, infective males, consistent w ith the avoidance of contagion. Using selective opioid peptide recepto r agonists and antagonists we found evidence that enhanced kappa opioi d peptide (e.g., dynorphin) activity was related to the decreased sexu al interest of the pre-infective males, while augmented delta opioid p eptide (e.g., enkephalin) activity was associated with the enhanced re sponses of the infective males to females. We further showed that acut e kappa opiate administration reduced the responses of uninfected male s to females and that uninfected females displayed modified responses to the odors of uninfected males subject to acute modifications of opi oid activity. We suggest that these differential shifts in endogenous opioid activity in the parasitized males are associated with and, or r elated to alterations in neuroimmune and endocrine functions. These fi ndings show that parasitic infection can have, depending on the stage of infection and associated neuromodulatory changes, either significan t facilitatory or inhibitory effects on male host preferences for and responses to females.