A Operation

0 5 10mm

Figure 3. Localisation and effect of placing bilateral microimplants of melatonin in: (A) septum of forebrain, (B) mediobasal hypothalamus (MBH), and (C) pars distalis on FSH and PRL secretion in Soay rams housed under long days (•, experimental group; O, sham control group). The implants consisted of 22g needles with melatonin fused inside the tip (see insert), or empty implants as controls, and were left in place for 14 weeks (horizontal bar). Only treatment in the MBH consistently reversed the effect of long days on FSH and PRL secretion (34). Bottom panel shows HPD ram—12 months post-op.

Figure 3. Localisation and effect of placing bilateral microimplants of melatonin in: (A) septum of forebrain, (B) mediobasal hypothalamus (MBH), and (C) pars distalis on FSH and PRL secretion in Soay rams housed under long days (•, experimental group; O, sham control group). The implants consisted of 22g needles with melatonin fused inside the tip (see insert), or empty implants as controls, and were left in place for 14 weeks (horizontal bar). Only treatment in the MBH consistently reversed the effect of long days on FSH and PRL secretion (34). Bottom panel shows HPD ram—12 months post-op.

exogenous melatonin from the implant would block the effect of the endogenous mela-tonin signal, and activate a short-day response. In Soay rams, only microimplants of melatonin placed in the mediobasal hypothalamus (MBH), and to a lesser extent, in the adjacent pars tuberalis of the pituitary gland were consistently effective at blocking the effect of long days. This response included premature activation of FSH secretion and growth of the testes, and a coincident decrease in PRL secretion and growth of the winter pelage (40,41; Figure 3). These effects were local since there was no detected change in melatonin concentrations in the peripheral blood, and the response was reversed after removal of the micro-implants. The latter effect also demonstrated that the treatment had reactivated responsivness to long days (reversed long-day refractoriness). The delivery of a more physiological intermittent signal using reverse-dialysis was also effective at inducing short-day responses (33).

Complementary studies carried out in ovariectomised, oestradiol-supplemented Ile-de-France ewes have also shown that melatonin microimplants placed in the MBH, and not in other regions of the hypothalamus, provoke an increase in LH secretion in a proportion of animals, with a variable PRL response (47). Notably, however, microimplants positioned directly in or close to the pars tuberalis, the site expressing the highest concentration of melatonin receptors, did not modify LH secretion (48,50). Most recently it has been shown that melatonin microimplants placed in the pre-mammillary region of the MBH consistently activates LH secretion in ewes, indicating that this may be the specific site for the action of melatonin in relaying the photoperi-odic effect on the reproductive axis (49).

Healthy Sleep

Healthy Sleep

A Guide to Natural Sleep Remedies. Many of us experience the occasional night of sleeplessness without any consequences. It is when the occasional night here and there becomes a pattern of several nights in arow that you are faced with a sleeping problem. Repeated loss of sleep affects all areas of your life The physical, the mental, and theemotional. Sleep deprivation can affect your overall daily performance and may even havean effecton your personality.

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