Meeting Abstract
65.2 Monday, Jan. 6 08:30 Food, stress, and circulating testosterone: cue integration by the testes, not the brain, in zebra finches (Taeniopygia guttata) LYNN, S.E.*; PERFITO, N.; GUARDADO, D.; BENTLEY, G.E.; College of Wooster; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley slynn@wooster.edu
Ecologically relevant fasting stimulates glucocorticoid secretion and reduces testosterone (T) and sexual behavior in male zebra finches. This might provide a survival advantage without the need for complete inactivation of the hypothalamo-pituitary gonad axis. However, the mechanisms underlying these transient effects are unclear. Gonadotropin inhibitory hormone (GnIH), a neuropeptide present in the brain and gonads, is also influenced by glucocorticoids. Thus we sought to determine whether fasting stress activated the GnIH system in zebra finches, with the potential for downstream effects on reproductive physiology and behavior. We fasted males or fed them ad libitum for 10 hrs. Fasting increased corticosterone (CORT) and decreased T. To assess whether the decrease in T was mediated by changes in the hypothalamus and/or the gonads, we (1) quantified GnRH- and GnIH-positive neurons in the hypothalamus, (2) assessed hypothalamic gene expression for GnRH and GnIH, and (3) examined expression of testicular GnIH, StAR, LHR, and 17b-HSD in fasted and control birds. No measure of hypothalamic neuropeptides was related to treatment or circulating steroids. However, birds with higher CORT had higher testicular GnIH expression and lower circulating T. StAR and LHR were also expressed at lower levels in the testes of fasted birds than controls. Our data suggest that the decrease in T was not mediated by hypothalamic GnIH, but rather by direct actions of fasting and/or CORT on the testes, indicating that the testes can integrate and respond to cues of stress without direct hypothalamic input. Such local inhibition of T synthesis may allow for short-term changes in physiology and behavior when conditions are inappropriate for breeding.
