Neural substrates mediating the negative feedback effects of oestrogen on luteinising hormone-releasing hormone (LHRH) release were studied using the in vivo push-pull perfusion method in female rhesus monkeys. Twelve long-term ovariectomized female monkeys were implanted with Silastic capsules containing 17beta-oestradiol 2 weeks before the experiments and, on the day of the experiment, oestradiol benzoate (EB, 50 microg/kg) or oil was subcutaneously injected. Push-pull perfusate samples from the stalk-median eminence were collected in 10-min fractions from 4 h before to 18-20 h after EB or oil injection. LHRH and neuropeptide Y (NPY) levels in the same perfusates were measured by radioimmunoassay, and glutamate and GABA in the same perfusates were assessed by high-performance liquid chromatography (HPLC). The results indicate that EB significantly suppressed LHRH release (P < 0.005) starting within 2 h after EB, and continued for 18 h or until the experiment was terminated. Pulse analysis suggested that oestrogen suppressed the pulse amplitude, but not pulse frequency, of LHRH release. By contrast, EB did not alter any parameters (mean release, pulse amplitude or frequency) of pulsatile NPY release throughout the experiment. HPLC analysis further suggested that neither glutamate nor GABA levels in the stalk-median eminence were changed with oestrogen-induced LHRH suppression. Oil treatment did not alter LHRH, NPY, GABA and glutamate levels. It is concluded that oestrogen induces suppression of pulsatile LHRH release within 2 h, but the inhibitory effect of oestrogen on LHRH release does not appear to be mediated by NPY, GABAergic, or glutamatergic neurones.

GH release decreases with aging in primates. However, it is unclear whether the age-related decrease in GH release is due to a decrease in stimulatory GHRH or an increase in inhibitory somatostatin (SS) from the hypothalamus. In the present study, we measured the release of GHRH and SS in the stalk-median eminence of conscious aged (n = 7, 27.0 +/- 0.7 yr old) and young adult female monkeys (n = 12, 5.0 +/- 0.3 yr old) using the push-pull perfusion method. Mean GHRH levels during morning (0600-1200 h) and evening (1800-2400 h) in aged monkeys were 3- to 4-fold lower than in young monkeys. Pulse analysis indicated that pulse frequency, pulse amplitude, and baseline GHRH release in aged monkeys were much lower than in young adults. In contrast, mean SS levels in aged monkeys during mornings and evenings were 2-fold higher than in young monkeys. Pulse analyses indicated that amplitude and baseline levels of SS were significantly higher in aged monkeys than in young adults. There were no significant changes in the pulse frequency of SS release. Therefore, the aging-related decrease in GH release is due to a substantial decrease in GHRH release and an increase in SS release from the hypothalamus.

No abstract

Progesterone induces a LHRH surge in estrogen-primed ovariectomized rhesus monkeys, with a concomitant increase in the pulse frequency of neuropeptide Y (NPY) release. However, the role for NPY in the positive feedback action of progesterone on LHRH release in primates is unknown. The present study examines the effect of an antisense oligodeoxynucleotide for NPY messenger RNA (AS NPY) on the progesterone-induced LHRH surge in vivo using push-pull perfusion. The AS NPY was directly infused into the stalk-median eminence (S-ME), whereas perfusates were collected for assessment of LHRH release. For a control, a scrambled oligodeoxynucleotide was infused. The results indicate that 1) the scrambled oligodeoxynucleotide did not interfere with the progesterone-induced LHRH surge, 2) whereas AS NPY blocked the progesterone-induced increase in LHRH release, and 3) no LHRH surges were induced by oil as a control for progesterone, but the AS NPY also reduced LHRH release in oil controls. These data suggest that 1) AS NPY infusion into the S-ME results in reduction in LHRH release; and 2) NPY release in the S-ME is important for the positive feedback effects of progesterone on LHRH release in estrogen-primed ovariectomized monkeys.

We have previously shown that a decrease in ␥-aminobutyric acid (GABA) tone and a subsequent increase in glutamatergic tone occur in association with the pubertal increase in luteinizing hormone releasing hormone (LHRH) release in primates. To further determine the causal relationship between developmental changes in GABA and glutamate levels and the pubertal increase in LHRH release, we examined monkeys with precocious puberty induced by lesions in the posterior hypothalamus (PH). Six prepubertal female rhesus monkeys (17.4 Ϯ 0.1 mo of age) received lesions in the PH, three prepubertal females (17.5 Ϯ 0.1 mo) received sham lesions, and two females received no treatments. LHRH, GABA, and glutamate levels in the stalk-median eminence before and after lesions were assessed over two 6-h periods (0600 -1200 and 1800 -2400) using push-pull perfusion. Monkeys with PH lesions exhibited external signs of precocious puberty, including significantly earlier menarche in PH lesion animals (18.8 Ϯ 0.2 mo) than in sham/controls (25.5 Ϯ 0.9 mo, P Ͻ 0.001). Moreover, PH lesion animals had elevated LHRH levels and higher evening glutamate levels after lesions, whereas LHRH changes did not occur in sham/ controls until later. Changes in GABA release were not discernible, since evening GABA levels already deceased at 18 -20 mo of age in both groups and morning levels remained at the prepubertal levels. The age of first ovulation in both groups did not differ. Collectively, PH lesions may not be a good tool to investigate the mechanism of puberty, and, taking into account the recent findings on the role of kisspeptins, the mechanism of the puberty onset in primates is more complex than we initially anticipated. timing of puberty; luteinizing hormone releasing hormone; lesions in the hypothalamus; primates THE CONCEPT THAT an increase in pulsatile luteinizing hormone releasing hormone (LHRH) release triggers the onset of puberty has been well established (26,44,45). However, the mechanism of the pubertal increase in LHRH release remains unclear (39). It has been reported that children with tumors or hamartomas in the hypothalamus exhibit precocious puberty (37). A previous study from our laboratory showed that bilateral lesions made in the posterior hypothalamus of female rhesus monkeys during the prepubertal stage result in an early rise in luteinizing hormone (LH) release followed by precocious puberty (42). Moreover, similar lesions in ovariectomized prepubertal females result in early pubertal LH increases and accelerated timing of the estrogen positive feedback effect on the LH surge when compared with those in ovariectomized sham control females (35), indicating that the hypothalamic lesion-induced LH increase in prepubertal monkeys is independent of ovarian steroid hormones and is suggestive that lesions cause changes in the control mechanism of the LHRH neurosecretory system.A series of studies in our laboratory indicate that an increase in LHRH release is associated with a decrease in ␥-aminobutyric acid (GABA) followed by ...