Restraint stress is a psychosocial stressor that suppresses reproductive status, including LH pulsatile secretion, but the neuroendocrine mechanisms underlying this inhibition remains unclear. Reproductive neural populations upstream of gonadotropin-releasing hormone (GnRH) neurons, such as kisspeptin, neurokinin B and RFRP-3 (GnIH) neurons, are possible targets for psychosocial stress to inhibit LH pulses, but this has not been well examined, especially in mice in which prior technical limitations prevented assessment of in vivo LH pulse secretion dynamics. Here, we examined whether one-time acute restraint stress alters in vivo LH pulsatility and reproductive neural populations in male mice, and what the time-course is for such alterations. We found that endogenous LH pulses in castrated male mice are robustly and rapidly suppressed by one-time, acute restraint stress, with suppression observed as quickly as 12–18 min. This rapid LH suppression parallels with increased in vivo corticosterone levels within 15 min of restraint stress. Although Kiss1, Tac2 and Rfrp gene expression in the hypothalamus did not significantly change after 90 or 180 min restraint stress, arcuate Kiss1 neural activation was significantly decreased after 180 min. Interestingly, hypothalamic Rfrp neuronal activation was strongly increased at early times after restraint stress initiation, but was attenuated to levels lower than controls by 180 min of restraint stress. Thus, the male neuroendocrine reproductive axis is quite sensitive to short-term stress exposure, with significantly decreased pulsatile LH secretion and increased hypothalamic Rfrp neuronal activation occurring rapidly, within minutes, and decreased Kiss1 neuronal activation also occurring after longer stress durations.

To investigate whether the long-term administration of metformin or pioglitazone to women with polycystic ovary syndrome (PCOS) could induce changes in their hypothalamic dopaminergic (DA) tone and to analyze whether these changes correlated with modifications in insulin resistance, we originally studied 57 obese hyperinsulinemic, non-diabetic, insulin resistant women with PCOS, but only 34 completed the study. They were randomly divided into two groups: group one (n=17) received pioglitazone (30 mg/day) and group 2 (n=17) received metformin (850 mg, three times a day) over 24 weeks. All women were identically studied before (basal) and 6 months after (T6) drug administration, including clinical evaluations, a 2 h oral glucose tolerance test (75 g) (OGTT) for glucose and insulin measurements, followed a week later by a 2 h intravenous metoclopramide test (10 mg bolus) for prolactin (PRL) determinations. The areas under the insulin (AUC-insulin) and PRL (AUC-PRL) curves were calculated, along with the index of insulin resistance (HOMA-IR) and the indexes of insulin sensitivity (QUICKI and fasting glucose–insulin ratio). At baseline, women in both groups were of similar age, body weight, body mass index (BMI) and Ferriman-Gallwey hirsutism score (F-G score). At completion of the study, body weight and BMI remained unchanged but the F-G score significantly decreased. Fasting serum insulin concentrations and the AUC-insulin significantly decreased by the end of the trial in a similar fashion in both groups, while the AUC-PRL significantly increased at the end of the trial in both groups. At no time were significant correlations between AUC-PRL and AUC-insulin or the indexes HOMA-IR, QUICKI or fasting glucose–insulin ratio observed. The present results suggests that either pioglitazone or metformin administration was associated with a clear improvement in the endogenous hypothalamic DA tone, simultaneously with an amelioration of the insulin resistance status in these obese women with PCOS.