| Abstract: | Neonicotinoids, some of the most widely used pesticides in the world, act as agonists to
the nicotinic acetylcholine receptors (nAChRs) of insects, resulting in death from
abnormal excitability. Neonicotinoids unexpectedly became a major topic as a compelling
cause of honeybee colony collapse disorder, which is damaging crop production that
requires pollination worldwide. Mammal nAChRs appear to have a certain affinity for
neonicotinoids with lower levels than those of insects; there is thus rising concern about
unpredictable adverse effects of neonicotinoids on vertebrates. We hypothesized that the
effects of neonicotinoids would be enhanced under a chronic stressed condition, which is
known to alter the expression of targets of neonicotinoids, i.e.,
neuronal nAChRs. We performed immunohistochemical and behavioral analyses in male mice
actively administered a neonicotinoid, clothianidin (CTD; 0, 10, 50 and 250 mg/kg/day),
for 4 weeks under an unpredictable chronic stress procedure. Vacuolated seminiferous
epithelia and a decrease in the immunoreactivity of the antioxidant enzyme glutathione
peroxidase 4 were observed in the testes of the CTD+stress mice. In an open field test,
although the locomotor activities were not affected, the anxiety-like behaviors of the
mice were elevated by both CTD and stress. The present study demonstrates that the
behavioral and reproductive effects of CTD become more serious in combination with
environmental stress, which may reflect our actual situation of multiple exposure. |
