Treadmill exercise increases central 5-hydroxytryptamine synthesis and tryptophan hydroxylase expression and reduces depressive-like symptom in methimazole-induced hypothyroidism rat pups

Abstract

Depression is one of the most common psychiatric symptoms in hypothyroidism. Depression following hypothyroidism is closely associated with reduced activity of the serotonergic system. Physical exercise has positive effects for mental diseases such as depression. In the present study, we investigated the effects of treadmill exercise on the depressive-like symptom, 5-hydroxytryptamine (5-HT)and tryptophan hydroxylase (TPH) expression in the dorsal raphe nucleus of the rat pups with hypothyroidism. On the day of perinatal 14, pregnant rats were divided into two groups (n = 5 in each group): the pregnant control group and the pregnant methimazole (MMI)-treated group. For the induction of hypothyroidism in the rat pups, MMI was added to the drinking water, from the day of perinatal 14 to postnatal 49. After delivery, male rat pups born from the pregnant control group were assigned to the control group. Male rat pups born from the MMI-treated group were divided into the hypothyroidism-induction (HI) group and the hypothyroidism-induction with treadmill exercise (HIT) group (n = 10 in each group). The rat pups in the exercise group were forced to run on a treadmill for 30 min once a day for 4 weeks, starting on postnatal day 22. In the hypothyroidism-induced rat pups,5-HT synthesis and TPH expression was reduced in the dorsal raphe nucleus. Treadmill exercise alleviated hypothyroidism-induced depressive state by enhancing serotonergic related genes. These results suggest that treadmill exercise can be used as a therapeutic agent for hypothyroidism patients with depression.