Thyroid disrupting pesticides impair the hypothalamic-pituitary-testicular axis of a wildlife bird, Amandava amandava

The effect of two thyroid disrupting pesticides (TDPs) mancozeb (MCZ) and imidacloprid (IMI) on the hypothalamic-pituitary-gonadal/testicular (HPG) axis of a seasonally breeding bird, Amandava amandava has been evaluated. Male birds (n = 8/group) were exposed to each of the pesticide (0.25% LD₅₀ of respective pesticide) as well as to their two equimixture doses (0.25% of LD₅₀ of each and 0.5% LD₅₀ of each) through food for 30d during pre-breeding stage of the reproductive cycle. Reduction in weight, volume and other histopathological features revealed testicular regression. Suppression of gonadotropin releasing hormone, increased expression of gonadotropin inhibitory hormone in the hypothalamus of exposed groups as well as impairment of plasma levels of the reproduction related hormones indicated the disruption of the HPG axis. The pesticides interference of the thyroid function during the critical phase of reproductive development impaired the HPG axis; more significantly in co-exposed groups suggesting the cumulative toxicity.