Biomedical subjects

E Terasawa

Publications and source records attributed to E Terasawa.

At least 37 records · Page 2Linked to original sources

PubMed1999

A role of gamma-amino butyric acid (GABA) and glutamate in control of puberty in female rhesus monkeys: effect of an antisense oligodeoxynucleotide for GAD67 messenger ribonucleic acid and MK801 on luteinizing hormone-releasing hormone release.

Previously we have shown that gamma-aminobutyric acid (GABA) is an inhibitory neurotransmitter restricting the pubertal increase in LHRH release in juvenile monkeys, and that interfering with GABA synthesis with an antisense oligodeoxynucleotide (AS) for glutamic acid decarboxylase (GAD67) mRNA results in an increase in LHRH release in prepubertal monkeys. GAD67 is a catalytic enzyme that synthesizes GABA from glutamate. To further clarify the role of GABA in puberty, we examined whether the inhibition of LHRH release by GABA continues after the onset of puberty and whether input from glutamatergic neurons plays any role in the onset of puberty when GABA inhibition declines, using a push-pull perfusion method. In Study I, the effects of the AS GAD67 mRNA on LHRH release in pubertal monkeys (34.3 +/- 1.5 months of age, n = 8) were examined, and the results were compared with those in prepubertal monkeys (18.5 +/- 0.4 months, n = 12). Direct infusion of AS GAD67 (1 microM) into the stalk-median eminence (S-ME) for 5 h stimulated LHRH release in both prepubertal and pubertal monkeys. However, the increase in LHRH release in pubertal monkeys was significantly (P < 0.01) smaller than that in prepubertal monkeys. Infusion of a scrambled oligo as a control was without effect in either group. In Study II, to examine the possibility that an increase in glutamate tone after the reduction of an inhibitory GABA tone contributes to the AS GAD67-induced LHRH increase, the effects of the NMDA receptor blocker MK801 (5 microM) on LHRH release were tested in monkeys treated with AS GAD67. MK801 infusion into the S-ME during the treatment of AS GAD67 (1 microM) suppressed the AS GAD67-induced LHRH release in both age groups. MK801 alone did not cause any significant effect in either group. The data are interpreted to mean that GABA continues to suppress LHRH release after the onset of puberty, although the degree of suppression is weakened considerably after the onset of puberty, and that the increased LHRH release after AS GAD67 treatment may be partly due to an increase in glutamate tone mediated by NMDA receptors, as well as due to the decrease in GABA release following the decrease in GAD synthesis. Taken together, the present results suggest that GAD may play an important role in the onset and progress of puberty in nonhuman primates.

Animals↗

PubMed1999

Pulsatile release of luteinizing hormone-releasing hormone (LHRH) in cultured LHRH neurons derived from the embryonic olfactory placode of the rhesus monkey.

To study the mechanism of LH-releasing hormone (LHRH) pulse generation, the olfactory pit/placode and the migratory pathway of LHRH neurons from monkey embryos at embryonic age 35-37 were dissected out, under the microscope, and cultured on plastic coverslips coated with collagen in a defined medium for 2-5 weeks. First, we examined whether cultured neurons release the decapeptide into media. It was found that LHRH cells release LHRH in a pulsatile manner at approximately 50-min intervals. Further, LHRH release was stimulated by depolarization with high K+ and the Na+ channel opener, veratridine. However, whereas the Na+ channel blocker, tetrodotoxin suppressed the effects of veratridine, tetrodotoxin did not alter the effects of high K+. Subsequently, the role of extracellular and intracellular Ca2+ in LHRH release was examined. The results are summarized as follows: 1) exposing the cells to a low Ca2+ (20 nM) buffer solution suppressed LHRH release, whereas exposure to a normal Ca2+ solution (1.25 mM) maintained pulsatile LHRH release; 2) LHRH release from cultured LHRH cells was stimulated by the voltage-sensitive L-type Ca2+ channel agonist, Bay K 8644 (10 microM), whereas it was suppressed by the L-type Ca2+ channel blocker, nifedipine (1 microM), but not by the N-type channel blocker, omega-conotoxin GVIA (1 microM); 3) the intracellular Ca2+ stimulant, ryanodine (1 microM), stimulated LHRH release, whereas the intracellular Ca2+ transporting adenosine triphosphatase antagonist, thapsigargin (1 and 10 microM), did not yield consistent results; and 4) carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone (1 microM), a mitochondrial Ca2+ mobilizer, stimulated LHRH release, whereas ruthenium red, a mitochondrial Ca2+ uptake inhibitor, did not induce consistent results. These results indicate that: 1) the presence of extracellular Ca2+ is essential for LHRH neurosecretion; 2) Ca2+ enters the cell via L-type channels but not N-type channels; and 3) mobilization of intracellular Ca2+ from inositol 1,4,5-triphosphate-sensitive stores, as well as mitochondrial stores, seem to contribute to LHRH release in these cells.

Animals↗

PubMed1998

Effects of an antisense oligodeoxynucleotide for neuropeptide Y mRNA on in vivo luteinizing hormone-releasing hormone release in ovariectomized female rhesus monkeys.

The present study examines the effects of an antisense oligodeoxynucleotide (AS) for human neuropeptide Y (NPY) mRNA on in vivo LHRH release using the push-pull perfusion method in female ovariectomized monkeys. After 6 h of control perfusion, 10 microM of the AS NPY was infused for 8 h, which was followed by an additional 4 h of control perfusion. As a control for AS, an oligodeoxynucleotide containing the same bases in a scrambled sequence (SC) was similarly examined. LHRH and NPY levels in perfusate samples, collected in 10-min fractions, were measured by RIA. AS NPY infusion resulted in a significant decrease in mean NPY release starting 2 h after the initiation of infusion, and continuing until shortly after the end of AS infusion (P < 0.05, n = 7). AS NPY also suppressed mean LHRH release significantly (P < 0.05, n = 7): the AS NPY-induced LHRH suppression started 2 h after the initiation of AS infusion, and continued throughout AS infusion, lasting for the entire period of the experiment. In contrast, SC NPY resulted in neither significant changes in NPY release nor LHRH release. These data suggest that NPY release in the stalk-median eminence plays an important role in the control of pulsatile release of LHRH in vivo in the rhesus monkey.

Animals↗

PubMed1998

Cellular mechanism of pulsatile LHRH release.

One of the most intriguing characteristics of the luteinizing hormone-releasing hormone (LHRH) neuronal system in mammalian species is the pulsatile release pattern of the peptide from the hypothalamus into the portal circulation, which is essential for the maintenance of normal reproductive function. In this review article the new concept that LHRH neurons possess an endogenous pulse-generating mechanism, but this is modified by other neuronal and nonneuronal inputs is discussed.

Animals↗

PubMed1997

Two populations of luteinizing hormone-releasing hormone neurons in the forebrain of the rhesus macaque during embryonic development.

To investigate the possibility that a second luteinizing hormone-releasing hormone (LHRH) population appears during development in primates, embryos and fetal brains of rhesus monkeys were immunostained with antisera specific to different LHRH forms. Two LHRH cell populations were discernible by immunoreactivity to antisera LR-1 and GF-6. Because one LHRH cell type migrated out from the olfactory placode several days earlier than the other, they were referred to as "early" and "late" LHRH cells, respectively. Although late LHRH neurons were immunoreactive to all anti-mammalian LHRH antisera tested, early LHRH neurons were only detected by antiserum GF-6. Early LHRH neurons (approximately 10 x 7 microm) were smaller than late LHRH neurons (approximately 18 x 7 microm). Early LHRH neurons were first found around the olfactory placode, in the nasal mesenchyme, and in the rostroventral forebrain on embryonic day 30 (E30), whereas late LHRH neurons were first seen in the olfactory pit on E32. Early LHRH cells were located throughout the basal forebrain on E32-E42, whereas late LHRH cells were found in the olfactory pit and along the terminal nerve on E34-E36 and were not seen in the forebrain until E38. By E51-E62, late LHRH neurons reached into the basal hypothalamus in a distribution resembling that in the older brain, while early LHRH neurons were found in the septum, preoptic region, stria terminalis, medial amygdala, claustrum, internal capsule, and globus pallidus. Based on the distribution pattern of immunopositive cells with antiserum LR-1, late LHRH cells are bona fide LHRH neurons that regulate the pituitary-gonadal axis. In contrast, the molecular form of early LHRH cells is unclear, although it is plausible that early LHRH cells may contain the molecule in which the C-terminal epitope of LHRH is modified or absent. It is concluded that in primates there is a second population of LHRH neurons that originates from the embryonic olfactory placode before the origin of mammalian LHRH-like neurons, and that these two populations of LHRH-immunopositive neurons have different morphologic features and different final distributions in the brain.

Animals↗

PubMed1997

A second form of gonadotropin-releasing hormone (GnRH) with characteristics of chicken GnRH-II is present in the primate brain.

The primate brain was thought to contain only the GnRH known as mammalian GnRH (mGnRH). This study investigates whether a second form of GnRH exists within the primate brain. We found that brain extracts from adult stumptail and rhesus monkeys contained two forms of GnRH that were similar to mGnRH and chicken GnRH-II (cGnRH-II) based on the elution position of the peptides from HPLC and on cross-reactivity with antisera that are specific to mammalian or chicken GnRH-II in RIAs. The fetal brain of rhesus monkeys also contained mGnRH and a cGnRH-II-like peptide by the same criteria. Immunocytochemistry with a cGnRH-II-specific antiserum in adult and fetal rhesus monkeys showed immunopositive neurons generally scattered in the periaqueductal region of the midbrain, with a few positive cells in the posterior basal hypothalamus. Neurons immunopositive for cGnRH-II were fewer in number and smaller in size, with less defined nuclei and thinner neurites compared with those for mGnRH. Administration of synthetic cGnRH-II to adult rhesus monkeys resulted in a significant increase in the plasma LH concentration during the luteal phase of the menstrual cycle, but not during the midfollicular phase. We conclude that the primate brain contains mGnRH and a cGnRH-II-like molecule, although the function of the latter is unknown.

Aging↗

PubMed1997

[A new handpiece attachment for Nd:YAG laser ablation of emphysematous bullae].

Recently, attention has been drawn to lung volume reduction for bullous emphysema by wedge excision or laser ablation. We used a neodymium: yttrium-aluminum garnet (Nd:YAG) laser with a free-beam mode to ablate peripheral emphysematous areas of lung tissue. To aid us in this procedure, we developed an attachment consisting of a stainless steel rod 3 cm in effective length, with a 1.8-cm diameter ring attached to its tip, and installed it on the tip of the laser handpiece used for free-beam laser ablation. This device has the following distinct advantages: 1) the distance between the tip of the laser and the pleura can easily be held constant, 2) the angle of irradiation can easily be maintained at 90 degrees. These result in 3) a constant area of irradiation (one square centimeter), and 4) an irradiated area that is clearly distinguished by the ring. In addition, the attachment is 5) simple and easy to construct. Three patients with bullous emphysema underwent unilateral laser ablation of the visceral pleura with the new device. All patients recovered completely. We found this rod-and-ring attachment to be useful for free-beam laser ablation.

Aged↗

PubMed1996

Role of glutamic acid decarboxylase in the prepubertal inhibition of the luteinizing hormone releasing hormone release in female rhesus monkeys.

To investigate further the role of GABA in the onset of puberty, this study examines whether glutamic acid decarboxylase (GAD), the catalytic enzyme for GABA synthesis, is involved in the suppression of luteinizing hormone releasing hormone (LHRH) before puberty in rhesus monkeys. First, both GAD67 and GAD65 mRNAs were detectable by reverse transcription-PCR analysis in the preoptic area, medio-basal hypothalamus, posterior hypothalamic area, and hippocampus of the monkey brain. Second, effects of antisense oligodeoxynucleotides (D-oligos) for GAD67 and GAD65 mRNAs on LHRH release were examined in conscious female rhesus monkeys at the prepubertal stage using a push-pull perfusion method. The GAD67 or GAD65 antisense D-oligos or scrambled D-oligos were infused directly into the stalk-median eminence. Both the GAD67 and the GAD65 antisense D-oligos induced a large and prompt increase in LHRH release, whereas the scrambled D-oligos did not induce any significant effect. The results suggest that the removal of GABA inhibition by interfering with GAD synthesis is effective in increasing LHRH release in prepubertal monkeys. Third, the specificity of the antisense D-oligos on GAD levels was examined by incubating basal hypothalami with D-oligos in vitro and subsequent Western blot analysis. The antisense D-oligos consistently decreased the proteins GAD67 and GAD65 compared with respective control D-oligos. We conclude that the decrease of tonic GABAergic inhibition and maturational changes in GAD synthesis may be critical factors for the onset of puberty in nonhuman primates.

Animals↗

PubMed1996

Effects of adrenal medulla transplantation into the third ventricle on the onset of puberty in female rhesus monkeys.

To test the hypothesis that prepubertal exposure of LHRH neurons to a source of catecholamines and neuropeptides accelerates the onset of puberty, we examined the effects of autologous adrenal transplantation into the base of the third ventricle of the brain in juvenile female rhesus monkeys at 11-13 months of age. The adrenal medulla, which contains catecholamines and neuropeptide Y (NPY), was cut into small pieces and mixed with gelfoam in artificial CSF and injected into the third ventricle, adjacent to LHRH neurons and their neuroterminals. Sham control monkeys received artificial CSF with gelfoam alone. Animals were monitored for signs of pubertal development. While menarche was not altered by adrenal transplantation, the timing of first and second ovulations occurred significantly (P < 0.05) earlier in adrenal-transplanted monkeys. Histological examination indicated that the grafts survived in all transplanted monkeys. The presence of catecholamines and NPY in graft tissue was confirmed by tyrosine-hydroxylase-positive, dopamine beta-hydroxylase-positive, and NPY-positive cells. Endogenous LHRH fibers were observed innervating the graft tissue. We conclude that: (1) adrenal medulla transplantation into the third ventricle accelerates the age of first ovulation; (2) this is likely due to neuroactive substances (e.g., catecholamines and NPY) from the graft tissue; and (3) grafted adrenal medulla tissue can survive for at least 30-40 months. However, the age of menarche was not accelerated by this grafting, suggesting that an additional mechanism (e.g., removal of tonic inhibition) may be necessary for the onset of puberty.

Adrenal Medulla↗

PubMed1995

Control of luteinizing hormone-releasing hormone pulse generation in nonhuman primates.

1. The pulsatile release of luteinizing hormone-releasing hormone (LHRH) is critical for reproductive function. However, the exact mechanism of LHRH pulse generation is unclear. The purpose of this article is to review the current knowledge on LHRH pulse generation and to discuss a series of studies in our laboratory. 2. Using push-pull perfusion in the stalk-median eminence of the rhesus monkey several important facts have been revealed. There is evidence indicating that LHRH neurons themselves have endogenous pulse-generating mechanisms but that the pulsatility of LHRH release is also modulated by input from neuropeptide Y (NPY) and norepinephrine (NE) neurons. The release of NPY and NE is pulsatile, with their pulses preceding or occurring simultaneously with LHRH pulses, and the neuroligands NPY and NE and their agonists stimulate LHRH pulses, while the antagonists of the ligands suppress LHRH pulses. 3. The pulsatile release of LHRH increases during the estrogen-induced LH surge as well as the progesterone-induced LH surge. These increases are partly due to the stimulatory effects of estrogen and progesterone on NPY neurons. 4. An increase in pulsatile LHRH release occurs at the onset of puberty. This pubertal increase in LHRH release appears to be due to the removal of tonic inhibition from gamma aminobutyric acid (GABA) neurons and a subsequent increase in the inputs of NPY and NE neurons to LHRH neurons. 5. There are indications that additional neuromodulators are involved in the control of the LHRH pulse generation and that glia may play a role in coordinating pulses of the release of LHRH and neuromodulators. 6. It is concluded that the mechanism generating LHRH pulses appears to comprise highly complex cellular elements in the hypothalamus. The study of neuronal and nonneuronal elements of LHRH pulse generation may serve as a model to study the oscillatory behavior of neurosecretion.

Animals↗

PubMed1995

Transplantation of the fetal olfactory placode restores reproductive cycles in female rhesus monkeys (Mucaca mulatta) bearing lesions in the medial basal hypothalamus.

The purpose of this study was to determine whether loss of the reproductive cycle after lesions of the medial basal hypothalamus can be reversed by transplantation of the embryonic olfactory placode (OP) into female rhesus monkeys. Seven adult female rhesus monkeys with regular menstrual cycles received bilateral radiofrequency lesions in the arcuate nucleus and the median eminence. After confirmation of anovulation in these monkeys, four monkeys were stereotaxically implanted with the OP obtained from monkey fetuses on embryonic days 35-36. The remaining three monkeys were similarly implanted with embryonic cerebellum (CB) as a control. Fetuses were delivered by cesarean section, and the OP and CB were immediately dissected out using a stereomicroscope. Fetal tissue was then cut into small pieces (< 1 mm3), mixed with artificial cerebrospinal fluid containing small pieces of Gelfoam, and stereotaxically injected into the infundibular recess of the third ventricle. The recovery of ovulatory cycles in recipient monkeys was observed for at least 6 months; sex skin color changes and menstrual records were obtained daily, and serum samples for LH, estrogen, and progesterone were obtained twice a week. Three of four OP-transplanted monkeys resumed their ovulatory cycles within 2 months, whereas the fourth monkey, an elderly female, failed to recover her cycle. In contrast, none of the three CB-transplanted monkeys resumed ovulatory cycles. Histological examination indicated that 1) lesion scars were present in the median eminence-stalk region as well as the medial basal portion of the arcuate nucleus of all seven brains; and 2) cartilage was present in the third ventricles of the OP-implanted brains. Moreover, immunocytochemical staining revealed that in all OP monkeys, small, round, and immature LHRH-positive cells with fine short processes were found in the third ventricle and/or median eminence-stalk region, whereas no similar LHRH cells were found in CB-transplanted monkeys. It is concluded, therefore, that implantation of LHRH neurons derived from the fetal OP can result in resumption of the ovulatory cycle in female monkeys whose own LHRH pulse-generating mechanisms were impaired. Moreover, the results suggest that LHRH neurons derived from embryonic OP possess the physiological functions necessary for the stimulation of gonadotropin secretion.

Animals↗

PubMed1994

gamma-Aminobutyric acid is an inhibitory neurotransmitter restricting the release of luteinizing hormone-releasing hormone before the onset of puberty.

To test the hypothesis that the pubertal increase in luteinizing hormone-releasing hormone (LHRH) release is withheld by a dominant inhibitory neuronal system, the role of gamma-aminobutyric acid (GABA), a known inhibitory neurotransmitter, in the control of LHRH release was examined in conscious female monkeys at the prepubertal and pubertal stages using a push-pull perfusion method. GABA, bicuculline (a GABAA receptor blocker), and 2-hydroxysaclofen (a GABAB receptor blocker) were directly infused into the stalk-median eminence while perfusates were collected for LHRH determination. Bicuculline, but not saclofen, induced a large and prompt increase in LHRH release in prepubertal monkeys, whereas it stimulated LHRH release slightly in pubertal monkeys. In contrast, GABA suppressed LHRH release in pubertal, but not prepubertal, monkeys. These differential effects of GABA and the GABA antagonist on LHRH release in the two developmental stages were due to an age factor rather than to the steroid hormonal background. Moreover, GABA release in the stalk-median eminence of prepubertal monkeys was much higher than that in pubertal monkeys. Thus, the results suggest that in the prepubertal period there is a powerful GABA inhibition of the LHRH neurosecretory system: infusions of GABAA, but not GABAB, antagonists stimulate LHRH release by removal of the endogenous GABA inhibition, whereas exogenous GABA is ineffective because of high endogenous GABA levels. The decrease of this tonic inhibition may be a key factor for the onset of puberty in non-human primates.

Animals↗

PubMed1994

Steroid modulation of pulsatile LHRH release in the rhesus monkey.

Studies using push-pull perfusion of the stalk-median eminence (S-ME) in ovariectomized adult monkeys indicate that input of neuropeptide Y (NPY) neurons is an important modulator for the pulsatility of LHRH release: (1) NPY release in the S-ME was pulsatile; (2) NPY pulses occurred coupled to LHRH pulses, with NPY pulses preceding LHRH pulses; and (3) infusion of NPY into the S-ME stimulated LHRH release in a dose-responsive manner; whereas (4) infusion of a specific antiserum to NPY into the S-ME suppressed LHRH pulses. Further studies suggest that NPY neurons may mediate the action of steroid hormones. While treatment with a small dose of estrogen did not affect the coupling of NPY and LHRH pulses, it enhanced the sensitivity of LHRH release in response to NPY by 10,000-fold. Progesterone treatment 24 hr after estrogen induced an increase in LHRH release followed by an LH surge: Progesterone increased the pulse frequencies of both NPY release and LHRH release, maintaining the tight coupling of the pulses, while increasing LHRH pulse amplitude, but not NPY pulse amplitude. A parallel role of norepinephrine (NE) neurons in the modulation of pulsatile LHRH release was also observed indicating that more than one neuronal system can be simultaneously involved in the regulation of LHRH release and the action of ovarian steroids. Moreover, in the modulation of LHRH pulses, NPY and NE neurons were independent of each other. Further studies indicate that the LHRH neurosecretory system in the sexually immature monkey was insensitive to estrogen. This insensitivity appeared to be due to the tonic inhibition of pulsatile LHRH release by gamma-aminobutyric acid (GABA) neurons through GABAA receptors. These results suggest that in vivo LHRH release is modulated by NPY, NE, and GABA neuronal inputs which mediate the action of steroid hormones.

Animals↗

PubMed1994

The secretion of gonadotrophin-releasing hormone by peri-implantation embryos of the rhesus monkey: comparison with the secretion of chorionic gonadotrophin.

Chorionic gonadotrophin (CG) is the first clear embryonic signal during early pregnancy in primates. CG has close structural and functional similarities to pituitary luteinizing hormone (LH) which is regulated by gonadotrophin releasing hormone (GnRH). To study the regulatory mechanism of CG secretion in primate embryos, we examined the production and timing of secretion of GnRH in peri-implantation embryos of the rhesus monkey. In-vivo fertilized/developed morulae and early blastocysts, recovered from non-superovulated, naturally-bred rhesus monkeys by non-surgical uterine flushing, were cultured in vitro to hatched, attached and post-attached blastocyst stages using a well-established culture system. We measured GnRH and CG in media samples from cultured embryos with a sensitive radioimmunoassay and bioassay, respectively. The secretion of GnRH (pg/ml; mean +/- SEM) by embryos (n = 20) commenced from low levels (0.32 +/- 0.05) during the pre-hatching blastocyst stage to 0.70 +/- 0.08 at 6-12 days and 1.30 +/- 0.23 at > or = 13 days of hatched blastocyst attachment and proliferation of trophoblast cells. GnRH concentrations in culture media obtained from embryos (n = 5) that failed to hatch and attach were mostly undetectable (< or = 0.1). Samples that did not contain detectable GnRH failed to show detectable CG. Immunocytochemical studies, using a specific monoclonal anti-GnRH antibody (HU4H) as well as polyclonal antisera (LR-1), revealed that immunopositive GnRH cells were localized in pre-hatching blastocysts (n = 4), in blastocysts (n = 2) after 5-10 days of attachment and in monolayer cultures (n = 4) of well-established embryonic trophoblast cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Changes in pulsatile release of neuropeptide-Y and luteinizing hormone (LH)-releasing hormone during the progesterone-induced LH surge in rhesus monkeys.

In previous studies we have shown that the pulsatility of LH-releasing hormone (LHRH) release in gonadectomized monkeys is modulated by input from neuropeptide-Y (NPY) neurons: 1) the endogenous release of NPY in the stalk-median eminence (S-ME) was pulsatile; 2) NPY pulses were temporally correlated with LHRH pulses, with NPY pulses preceding LHRH pulses by approximately 5 min; and 3) infusion of NPY into the S-ME stimulated LHRH release, whereas 4) infusion of antiserum to NPY suppressed endogenous LHRH pulses. It is not known, however, whether ovarian steroid hormones alter the pulsatility of NPY and LHRH release or whether the temporal correlation of NPY and LHRH pulses is maintained during the LH surge. In the present study we examined the changes in pulsatile release of NPY and LHRH in ovariectomized monkeys treated with estradiol benzoate (EB) followed by progesterone or oil. Using push-pull perfusion, perfusate samples from S-ME were collected at 10-min intervals for 15 h. NPY and LHRH concentrations in the perfusates were measured by RIA. Circulating LH levels were also monitored by periodic blood sampling and RIA. Injection of progesterone (sc) after EB induced an LH surge with a peak latency of 7.3 +/- 1.3 h (mean +/- SE) in seven of seven monkeys, whereas oil injection after EB elicited an LH surge in none of seven monkeys. The progesterone-induced LH surge was associated with an increase in LHRH release; the mean, pulse amplitude, and pulse frequency increased significantly (for all, P < 0.05) 4-8 h after progesterone. NPY pulse frequency also increased significantly (P < 0.05) 4-8 h after progesterone treatment, whereas mean release and pulse amplitude did not change in response to progesterone. Oil treatment after EB administration did not alter any parameter of LHRH and NPY pulses. Interestingly, the NPY and LHRH pulses were highly correlated (P < 0.001) in monkeys treated with either EB-progesterone or EB-oil, and NPY pulses preceded LHRH pulses by 4.8 +/- 0.7 and 5.1 +/- 0.6 min, respectively. In summary, 1) an episode of increased LHRH release occurs before and during the progesterone-induced LH surge; 2) acceleration of LHRH pulse frequency and the increase in LHRH pulse amplitude after progesterone are accompanied by acceleration of NPY pulse frequency; and 3) ovarian steroids do not affect the temporal correlation between NPY and LHRH pulses.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Ovariectomy increases in vivo luteinizing hormone-releasing hormone release in pubertal, but not prepubertal, female rhesus monkeys.

In pubertal, but not prepubertal, monkeys ovariectomy (OVX) results in an elevation of circulating luteinizing hormone (LH) levels. To determine if the castration-induced LH increase in pubertal monkeys is due to an increase in pulsatile LH-releasing hormone (LHRH) release, effects of OVX on in vivo LHRH release in the stalk-median eminence were examined in fully conscious monkeys using a push-pull perfusion method. The average ages (+/- SEM) of female rhesus monkeys in each group at OVX were 14.5 +/- 0.6 months (n = 6; prepubertal), 25.0 +/- 1.3 months (n = 5; early pubertal) and 37.8 +/- 2.1 months (n = 6; midpubertal). Perfusate samples from the stalk-median eminence were obtained in 10-min fractions for 6 h in the morning (0600 to 1200 h) and 6 h in the evening (1800 to 2400 h), from the same subjects before OVX, and at 29 days and approximately 100 days after OVX. LHRH levels in perfusates were measured by radioimmunoassay. LH levels throughout the experiment were monitored by periodic blood sampling. OVX resulted in a significant LH increase in early and midpubertal monkeys (P < 0.001 for both), but not in prepubertal monkeys. Similarly, OVX in early and midpubertal monkeys increased mean LHRH release when examined 29 days after surgery (P < 0.05 and P < 0.01, respectively). The OVX-induced LHRH increases in early and midpubertal monkeys remained elevated at approximately 100 days postcastration. Furthermore, it was found that effects of OVX on the increased LHRH release were primarily due to the elevation of basal release and pulse amplitude, but not pulse frequency. In contrast, OVX did not cause any significant effects on pulsatile LHRH release in prepubertal monkeys. The results indicate that an increase in LHRH release and a concomitant increase in circulating LH occurs after OVX in pubertal monkeys, but not in prepubertal monkeys. These data are consistent with the hypothesis that the low level of LH in circulation before the onset of puberty is due to a low amount of LHRH release which is independent of ovarian steroid feedback and that the maturity of the neuronal control system for the pulsatile LHRH release is responsible for the onset of puberty. After the onset of puberty, the negative feedback of ovarian steroid hormones becomes important to the regulation of gonadotropin release.

Animals↗

PubMed1993

A possible role of neuropeptide Y in the control of the onset of puberty in female rhesus monkeys.

The onset of puberty is heralded by an increase in pulsatile LHRH release. Since neuropeptide Y (NPY) has been implicated as a major regulator in the control of pulsatile LHRH release in mature monkeys, we have hypothesized that maturational changes in the NPY neuronal system play an important role in puberty. To test this hypothesis, three experiments were conducted in female rhesus monkeys using a push-pull perfusion method. In the first experiment, changes in NPY release in the stalk-median eminence (S-ME) during puberty were determined in 9 prepubertal, 7 early pubertal and 8 midpubertal monkeys. NPY and LHRH levels were measured in aliquots of the same perfusate samples obtained from the S-ME. NPY release was pulsatile in all three groups. Mean NPY release and pulse frequency increased significantly from the prepubertal through the midpubertal stage. These developmental changes in NPY release were parallel to those observed for LHRH release in the same monkeys. In order to examine whether NPY infusion into the S-ME influences LHRH release during puberty, in the second experiment, NPY (10(-6) or 10(-8) M) or vehicle was infused into the S-ME for 10 min at 90-min intervals in 5 prepubertal and 9 midpubertal monkeys. In the midpubertal stage, infusion of NPY at doses of 10(-8) and 10(-6) M resulted in significant (p < 0.01) increases in LHRH release, while vehicle administration had no effect. In contrast, in prepubertal monkeys, neither NPY nor vehicle infusion altered LHRH release. In order to test whether endogenous NPY plays a role in the maintenance of pulsatile LHRH release, in the third experiment, a specific antiserum to NPY (aNPY) was infused into the S-ME of 6 prepubertal and 8 midpubertal monkeys. Infusion of aNPY (1:100, 1:1,000 dilution) significantly suppressed LHRH release in midpubertal but not prepubertal monkeys. The results are summarized as follows. (1) In prepubertal monkeys, NPY release is low, and the presence of NPY in the S-ME does not influence LHRH release. (2) At the onset of puberty, NPY release begins to increase, and NPY probably starts to stimulate LHRH release. (3) In the midpubertal period, NPY release increases further, and NPY in the S-ME is highly stimulatory to LHRH release.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Negative feedback effects of estrogen on luteinizing hormone-releasing hormone release occur in pubertal, but not prepubertal, ovariectomized female rhesus monkeys.

In a previous study we found that ovariectomy resulted in an increase in both LHRH release and LH release in pubertal monkeys but not in prepubertal monkeys. To determine whether this castration-induced LHRH increase is due to the removal of estrogen, in the present study, the effects of estradiol benzoate (EB, 30 micrograms/kg body wt) on in vivo LHRH release were examined using a push-pull perfusion method in prepubertal (age 15-19 months, n = 5), early pubertal (24-29 months, n = 5), and midpubertal (36-48 months, n = 5) female rhesus monkeys that were ovariectomized 3 to 5 months earlier. LHRH in 10-min perfusate fractions from the stalk-median eminence was measured from -6 to +24 h after EB injection. Circulating LH levels were also monitored over the same period at various intervals. EB decreased LH levels in early pubertal and midpubertal monkeys, whereas it did not cause any significant effects on LH release in the prepubertal monkey. EB also resulted in suppression of LHRH release in both early and midpubertal monkeys; mean LHRH release before EB in the early and midpubertal groups was 6.6 +/- 0.6 and 7.0 +/- 0.6 pg/ml.10 min, respectively. EB decreased mean LHRH release beginning 3 h after EB with the nadir occurring at 18-21 h after EB (1.0 +/- 0.2 pg/ml.10 min) in early pubertal monkeys and 21-24 h after EB (1.2 +/- 0.1 pg/ml.10 min) in midpubertal monkeys. Decrease of mean LHRH release was due to a decrease in LHRH pulse amplitude and basal release but not pulse frequency. Oil injection alone (control) failed to suppress LHRH and LH release. In contrast to the results in pubertal monkeys, mean LHRH release in prepubertal monkeys was not altered by EB (before EB, 1.1 +/- 0.2 pg/ml.10 min; 18-21 h after EB, 1.5 +/- 0.3 pg/ml.10 min). These results suggest that the LHRH neurosecretory system in pubertal monkeys is responsive to the negative feedback effects of estrogen. However, the fact that estradiol failed to suppress LHRH release in prepubertal monkeys indicates that the LHRH neurosecretory system and/or its regulatory systems are not sensitive to estradiol before the onset of puberty. These findings are consistent with the hypothesis that the increase in pulsatile LHRH release at the onset of puberty is not dependent on changes in ovarian steroid feedback mechanisms.

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