Several ongoing, unpublished neuroendocrine studies related to female reproductive aging in rhesus monkeys at the Oregon Regional Primate Research Centers were described. The LH pulse amplitude of irregularly cycling monkeys was greater than that in premenopausal animals; in postmenopausal monkeys, the LH pulse pattern was similar to that in young, long-term ovariectomized female rhesus monkeys. Determination of changes in LH pulse frequency, which is more difficult because of variation in frequency throughout the cycle and low pulse amplitudes, are not yet complete. Expression of several genes involved in neurotransmitter synthesis or responsiveness to estrogen declined in various brain regions of middle-aged, irregularly cycling animals relative to young animals. Some of these changes were reversible by estrogen treatment, such as estrogen receptor a in catecholaminergic brain stem areas, and level of choline acetyltransferase. whitening gel
Others, such as the norepinephrine transporter in the locus coeruleus, were not restored by estrogen treatment. The former category may reflect changes in hormone patterns more than the effects of age, whereas the latter category may reflect markers of aging. In another study, the expression of melatonin receptor (Mel 1a) decreased in the suprachiasmatic nucleus in middle-aged monkeys before menopause, suggesting that age-related changes in the neuroendocrine circadian circuitry begin before menopause.