The reproductive cycle of female rats is characterized by the occurrence of the preovulatory gonadotropin-induced ovarian steroids surges. Norepinephrine is a major neurotransmitter involved in the regulation of the hypothalamic-pituitary-gonadal axis, and the noradrenergic neurons an important mediator of the ovarian steroids actions in the genesis of the gonadotropin surge. The reproductive axis as well as the activity of noradrenergic neurons may be modified by stress. Although chronic stress results in inhibition of gonadotropin secretion, the effect of acute stress on the reproductive axis is still controversial. Since the noradrenergic neurons participate in the response of the body to stress, and this response seems to depend on hormonal pre-existing condition, quality, intensity and duration of exposure to stress, this study aims to evaluate whether the application on the morning of proestrus of different types of acute stress, associated or not, is able to modify the activity of noradrenergic neurons of the locus coeruleus (LC), A1 and A2 nuclei, and if that noradrenergic nuclei activation occurs differently depending on the type of acute stress applied. Cycling female rats will be submitted or not at 10 h of proestrus to: 1) two sessions of 1 minute each to stress by cervical stimulation, 2) 40 minutes of restraint stress or exposure to the cat, or 3) all associated stresses (cervical stimulation, restraint and exposure to the cat) for 40 minutes. The animals will be perfused at 11:30 h of proestrus. After anesthesia and immediately before the beginning of the perfusion, a blood sample will be withdrawn from the ventricle for luteinizing hormone (LH) measurement by radioimmunoassay. Serial sections of 30 µm of LC, A1 and A2 nuclei will be obtained in a cryostat and subjected to double-label to tyrosine hydroxylase and FRA (TH).
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