Search

Activation of the hypothalamo-pituitary-adrenal (HPA) axis by psychosocial stress is attenuated during lactation. We tested the hypothesis that lactating ewes will have attenuated HPA axis responses to isolation and restraint but will have greater responses to predator stress in the form of barking dogs. We imposed two 4 h stressors: psychosocial stress (isolation and restraint of ewes) and predator stress (barking dogs). Blood was collected intravenous every 10 min from nonlactating ewes (n = 6), lactating ewes with lambs present but not able to be suckled (n = 6), and lactating ewes with lambs present and able to be suckled (n = 6). Plasma cortisol and oxytocin were measured. For nonlactating ewes, cortisol increased (P < 0.01) in response to both stressors, and these increases were greater (P < 0.01) than that in the lactating animals. For lactating ewes with lambs present but unable to be suckled, cortisol increased (P < 0.05) in response to both stressors with a greater response to barking dogs (P < 0.05). For lactating ewes with lambs present and able to be suckled, cortisol increased (P < 0.01) in response to barking dogs only. Plasma oxytocin was greater (P < 0.01) in lactating ewes than in nonlactating ewes and did not change in response to the stressors. In conclusion, lactating ewes are likely to have a greater HPA axis response to a stressor that may be perceived to threaten the welfare of themselves and/or their offspring. The role of oxytocin in attenuation of the HPA axis to stress in sheep is unclear from the current research and requires further investigation., Highlights • The response of the hypothalamo-pituitary-adrenal axis to stress is attenuated during lactation in sheep. • The extent of this attenuation is influenced by the opportunity to suckle lambs and the type of stressor. • Stressors that pose an immediate threat to the offspring evoke greater stress responses.

Gonadotropin-releasing hormone (GnRH) neurons are the master neurons of the brain that regulate reproduction. GnRH is secreted into the hypophysial portal blood system and regulates pituitary gonadotrope function. The pulsatile secretion of GnRH allows fine regulation by various neuronal systems that transmit sex steroid feedback and information of energy balance and stress status as well as season and environment. Afferents to GnRH neurons form a system of serial and converging input, so that GnRH secretion is a reflection of processed information from various parts of the brain.

This article discusses neuropeptides that are involved in the regulation of stress responses and released as effector molecules during stress. The neuropeptides discussed include corticotropin releasing hormone, arginine vasopressin, the opioids, oxytocin, and appetite-regulating hormones. Particular attention is paid to the regulatory roles of the neuropeptides during stress. © 2007