Association Between Aerobic Exercise and Handgrip Strength in Adults: A Cross-Sectional Study Based on Data from the Korean National Health and Nutrition Examination Survey (2014-2017)

OBJECTIVES

Handgrip strength is an easy-to-assess indicator of overall muscle strength and can be used to evaluate health status. Although previous studies have reported an increase in grip strength due to aerobic exercise, such a study has not been conducted on Korean participants. This study aimed to investigate the effects of aerobic exercise on handgrip strength and examine the association between these two variables in Korean patients with hypertension or diabetes.

DESIGN

Cross-sectional study.

SETTING

This study used data from the 6th and 7th Korean National Health and Nutrition Examination Survey (2014-2017).

PARTICIPANTS

A total of 19,650 individuals aged ≥19 years who had responded to questionnaires concerning aerobic exercise and handgrip strength were analyzed.

MEASUREMENTS

The relationship between aerobic activity and handgrip strength was examined by logistic regression analysis.

RESULTS

The mean age of individuals in the low muscle strength group was higher than that in the normal muscle strength group. The odds ratio for low handgrip strength was higher in individuals who did not perform aerobic exercise than in those who performed aerobic exercise. Following adjustment for covariates, the odds ratios (95% confidence intervals) for low handgrip strength were 1.415 (0.187-1.688) in the total sample, 1.799 (1.376-2.352) in patients with hypertension, and 1.811 (1.208-2.715) in patients with diabetes.

CONCLUSION

The results of our study indicated a strong association between aerobic exercise and handgrip strength in the Korean population.

Video-assisted thoracoscopic removal of ossified posterior longitudinal ligament (OPLL) in the thoracic spine: a case report

BACKGROUND

When the transthoracic approach is used for the treatment of a thoracic ossified posterior longitudinal ligament (OPLL), there could be a lot of operative risks, morbidity, and mortality for the patient.

CASE REPORT

A 65-year-old female manifested back pain and tingling sensations in both legs due to OPLL at the T6-7 level. A thoracoscopic procedure was performed to remove the OPLL, achieving complete decompression of thoracic cord. The symptoms were relieved and the patient was discharged on the sixth day after the operation.

CONCLUSIONS

A minimally invasive procedure using the thoracoscopic technique could be a good alternative option in selected cases when a conventional transthoracic approach is impossible due to the patient's general condition.

Discovery and evolutionary history of gonadotrophin-inhibitory hormone and kisspeptin: new key neuropeptides controlling reproduction

Gonadotrophin-releasing hormone (GnRH) is the primary hypothalamic factor responsible for the control of gonadotrophin secretion in vertebrates. However, within the last decade, two other hypothalamic neuropeptides have been found to play key roles in the control of reproductive functions: gonadotrophin-inhibitory hormone (GnIH) and kisspeptin. In 2000, we discovered GnIH in the quail hypothalamus. GnIH inhibits gonadotrophin synthesis and release in birds through actions on GnRH neurones and gonadotrophs, mediated via GPR147. Subsequently, GnIH orthologues were identified in other vertebrate species from fish to humans. As in birds, mammalian and fish GnIH orthologues inhibit gonadotrophin release, indicating a conserved role for this neuropeptide in the control of the hypothalamic-pituitary-gonadal axis across species. Subsequent to the discovery of GnIH, kisspeptin, encoded by the KiSS-1 gene, was discovered in mammals. By contrast to GnIH, kisspeptin has a direct stimulatory effect on GnRH neurones via GPR54. GPR54 is also expressed in pituitary cells, but whether gonadotrophs are targets for kisspeptin remains unresolved. The KiSS-1 gene is also highly conserved and has been identified in mammals, amphibians and fish. We have recently found a second isoform of KiSS-1, designated KiSS-2, in several vertebrates, but not birds, rodents or primates. In this review, we highlight the discovery, mechanisms of action, and functional significance of these two chief regulators of the reproductive axis.

Involvement of the ser-glu-pro motif in ligand species-dependent desensitisation of the rat gonadotrophin-releasing hormone receptor

There are two forms of gonadotrophin-releasing hormone (GnRH), GnRH-I and GnRH-II, in the vertebrate brain. Both GnRH-I and GnRH-II are thought to interact with the type-I GnRH receptor (GnRHR). The present study attempted to demonstrate whether GnRH-I and GnRH-II induce differential desensitisation of GnRHR and to identify the motif involved. Time course inositol phosphate (IP) accumulation assay reveals that, in cells expressing the wild-type rat GnRHR, GnRH-I induced continuous increase in IP production, whereas GnRH-II-induced IP production rate at later time points (30-120 min after ligand treatment) became attenuated. However, in cells expressing the mutant receptor in which the Ser-Glu-Pro (SEP) motif in extracellular loop 3 was replaced by Pro-Glu-Val (PEV), IP accumulation rates at later time points were more decreased by GnRH-I than GnRH-II. Ca2+ responses to repetitive GnRH applications reveal that GnRH-II desensitised the wild-type receptor faster than GnRH-I, whereas the opposite situation was observed in the PEV mutant. In addition, cell surface loss of GFP-tagged wild-type receptor was more facilitated by GnRH-II than GnRH-I, whereas that of the GFP-tagged PEV mutant receptor was more enhanced by GnRH-I than GnRH-II. The present study indicates that the SEP motif is potentially responsible for ligand species-dependent receptor desensitisation. Together, these results suggest that GnRH-I and GnRH-II may have different effects on mammalian type-I GnRHR via modulation of desensitisation rates.

Molecular cloning and functional characterization of a type-I neurotensin receptor (NTR) and a novel NTR from the bullfrog brain

Neurotensin (NT) is a tridecapeptide that functions as a neurotransmitter and neuromodulator in the nervous system. To date, three different types of NT receptor (NTR), NTR1, NTR2 and NTR3, have been identified only in mammalian species. In the present study we isolated the cDNAs for an NTR1 and a novel NTR in the bullfrog brain, designated bfNTR1 and bfNTR4 respectively. bfNTR1 and bfNTR4 encode 422- and 399-amino acid residue proteins respectively. bfNTR1 has a 64% amino acid identity with mammalian NTR1, and 34-37% identity with mammalian NTR2. bfNTR4 exhibits 43% and 45-47% identity with mammalian NTR1 and NTR2 respectively. Both receptors are mainly expressed in the brain and pituitary. bfNTR1 triggers both CRE-luc, a protein kinase A (PKA)-specific reporter, and c-fos-luc, a PKC-specific reporter, activities, indicating that bfNTR1 can activate PKA- and PKC-linked signaling pathways. However, bfNTR4 appears to be preferentially coupled to the PKA-linked pathway as it induces a higher CRE-luc activity than c-fos-luc activity. bfNTRs exhibit different pharmacological properties as compared with mammalian NTRs. Mammalian NTR1 but not NTR2 responds to NT, whereas both bfNTR1 and bfNTR4 show a high sensitivity to NT. SR 48692 and SR 142948A, antagonists for mammalian NTR1 but agonists for mammalian NTR2, function as antagonists for both bfNTR1 and bfNTR4. In conclusion, this report provides the first molecular, pharmacological and functional characterization of two NTRs in a non-mammalian vertebrate. These data should help to elucidate the phylogenetic history of the G protein-coupled NTRs in the vertebrate lineage as well as the structural features that determine their pharmacological properties.

Molecular cloning, pharmacological characterization, and histochemical distribution of frog vasotocin and mesotocin receptors

The neurohypophysial nonapeptides vasotocin (VT) and mesotocin (MT) are the amphibian counterparts of arginine vasopressin (AVP) and oxytocin (OT). We have here reported the cloning and functional characterization of the receptors for vasotocin (VTR) and mesotocin (MTR) in two species of frog, Rana catesbeiana and Rana esculenta. The frog VTR and MTR cDNAs encode proteins of 419 and 384 amino acids respectively. Frog VTR exhibits a high degree of sequence identity with the mammalian AVP-1a (V1a) receptor while the frog MTR possesses a high degree of sequence identity with the mammalian OT receptor. Activation of VTR induced both c-fos promoter- and cAMP-responsive element (CRE)-driven transcriptional activities, while activation of MTR induced c-fos promoter-driven transcriptional activity but failed to evoke CRE-driven transcriptional activity, suggesting differential G protein coupling between VTR and MTR. The VTR exhibited the highest sensitivity for VT followed by OT>AVP approximately MT, whereas the MTR showed preferential ligand sensitivity for MT>OT>VT>AVP. A V1a agonist but not V2 and OT agonists substantially activated both VTR and MTR with a similar sensitivity. V1a, V2 and OT antagonists inhibited MT-induced MTR activation but not VT-induced VTR activation. In the frog brain, VTR and MTR mRNAs were found to be widely expressed in the telencephalon, diencephalon and mesencephalon, and exhibited very similar regional distribution. In the pituitary, VTR and MTR were expressed in the distal and intermediate lobes but were virtually absent in the neural lobe. Taken together, these data indicated that, although the distribution of VTR and MTR largely overlaps in the frog brain and pituitary, VT and MT may play distinct activities owing to the ligand selectivity and different signaling pathways activated by their receptors.

Mycosis fungoides presenting as Ofuji's papuloerythroderma

We report three patients presented with clinical features of Ofuji's papuloerythroderma (pruritic erythematous papules and extensive erythema sparing all skin folds), however, showing histopathological findings of mycosis fungoides (Pautrier's microabscess, haloed lymphocytes, disproportionate epidermotropism, and wiry collagen bundles). One case was associated with plaque stage of mycosis fungoides and follicular mucinosis. T-cell receptor (TCR) gene rearrangement analysis in the lesional skin tissue demonstrated rearrangement of the gamma chain in all cases. HTLV-1 serology was negative for two patients who conducted HTLV-1 test. We think that Ofuji's papuloerythroderma might be a variant of early mycosis fungoides rather than secondary skin manifestations to certain cutaneous inflammatory diseases.

First intron excision of GnRH pre-mRNA during postnatal development of normal mice and adult hypogonadal mice

Previously, we demonstrated that excision of the GnRH first intron (intron A) was largely attenuated in non-GnRH-producing tissues but accelerated in GnRH neurons. In the present study, we examined the splicing rate of GnRH pre-mRNA in developing normal mice and adult hypogonadal mice. The preoptic area and cerebral cortex were removed from mice at ages 1-7 wk. GnRH pre-mRNA splicing was examined by competitive RT-PCR using a variety of primer sets. The ratio of mature mRNA to intron A-containing RNA species in the preoptic area was lowest in 1- and 2-wk-old mice, significantly augmented in 3-wk-old mice, and further increased until adulthood. In contrast, the ratio of mRNA to intron A-containing RNA in the cerebral cortex was extremely low, drastically decreased in 3-wk-old mice, and remained at low levels until adulthood. These data indicate a preoptic area-specific increase in intron A excision during development. Intron B or C excision in the preoptic area was not significantly changed during development. To elucidate the possible involvement of the exonic splicing enhancers located in GnRH exons 3 and 4 in the developmental increase in intron A excision, we examined the splicing rate of GnRH pre-mRNA in hypogonadal mice whose GnRH exons 3 and 4 were truncated. The intron A excision in the preoptic area of hypogonadal mice was significantly lower than that of normal mice but similar to that in other tissues, such as cerebral cortex and olfactory bulb. To support the functional relevance of intron A-containing RNA species, we examined the translation efficiency of intron A-containing RNA. Insertion of intron A sequence into the upstream portion of the luciferase open reading frame significantly decreased translation efficiency. The present study demonstrates that intron A excision in the preoptic area is developmentally regulated in normal mice but largely attenuated in hypogonadal mice, indicating the functional importance of intron A excision in GnRH pre-mRNA splicing.

Inhibitory activity of alternative splice variants of the bullfrog GnRH receptor-3 on wild-type receptor signaling

Recently we characterized three distinct GnRH receptors in the bullfrog (bfGnRHR-1, bfGnRHR-2, and bfGnRHR-3). In the present study, we further investigated the expression and function of splice variants, generated from the primary bfGnRHR-3 transcript by exon skipping (splice variant 1), intron retention (splice variants 2 and 3), and/or transcriptional slippage (splice variant 4), apart from the constitutively spliced form (wild-type). Cellular expression and function of the splice variants were examined using a transient expression system. Immunoblot analysis revealed that the wild-type receptor and all splice variant proteins were expressed in transfected HeLa cells with no significant differences in expression levels. These splice variants showed a very low binding affinity to ligand and did not induce signal transduction in response to GnRH treatment. Interestingly, cotransfection of the wild-type with splice variants 2--4, but not with splice variant 1, significantly inhibited wild-type receptor-mediated signaling. Subcellular localization analysis of green fluorescent protein-tagged wild-type and splice variant proteins revealed that the wild-type receptor protein was mainly localized in the cell membrane, whereas the splice variant 1 protein was exclusively detected in the cytoplasm. The splice variant 2--4 proteins, however, were found in both the cell membrane and cytoplasm. The inhibition of wild-type receptor signaling by splice variants 2--4 and the subcellular localization of splice variants 2-4 suggest a possible physical interaction of splice variants 2--4 with the wild-type receptor protein. In addition, the ratio of mRNA levels of the wild-type to splice variants 2--4 significantly varied from hibernation (wild-type < splice variants 2--4) to the prebreeding season (wild-type > splice variants 2--4). Collectively, these results suggest that alternative splicing of the bfGnRHR-3 primary transcript plays a role in fine-tuning GnRH receptor function in amphibians.

Analysis of steroid-induced genes in the rat preoptic area-anterior hypothalamus using a differential-display reverse transcriptase-polymerase chain reaction

Steroid hormones modulate a variety of physiological functions in the hypothalamus. We attempted to identify steroid-regulated genes in the rat preoptic area-anterior hypothalamus by comparing differentially expressed mRNAs. Adult female rats were ovariectomized and, 1 week later, a silastic capsule containing 17beta-oestradiol (180 microg/ml) was subcutaneously implanted. After 2 days, a single injection of progesterone (1 mg) was administered at 10.00 h and rats were killed at 17.00 h on the same day. Differential-display polymerase chain reaction followed by Northern blot analysis showed that 10 clones were differentially regulated. Using homology search in Genbank, three genes were identified as sodium, potassium-ATPase beta1, protein kinase C-binding Nell-homologue protein and evectin-1. Further characterization of 10 clones showed that the expression patterns were tissue-specific and differentially regulated during puberty. Among these, mRNAs for protein kinase C-binding Nell-homologue protein, evectin-1 and human CGI-118 protein-like gene were induced after vagina opening, and differentially expressed during the oestrous cycle. Taken together, several steroid-regulated genes identified in the present study may play an important role in regulating hypothalamic functions, including puberty and the oestrous cycle.

Analysis of exonic splicing enhancers in the mouse gonadotropin-releasing hormone (GnRH) gene

We have previously reported that efficient removal of the first intron (intron A) of gonadotropin-releasing hormone (GnRH) pre-mRNA is the prerequisite event for post-transcriptional regulation. In the present study, using an in vitro HeLa splicing system, we examined the enhancing activities of exonic elements for GnRH pre-mRNA splicing. While not excised by exon 2 alone, intron A was efficiently excised when exon 3 and/or exon 4 was combined with exon 2, suggesting the presence of exonic splicing enhancers (ESEs) in exons 3 and 4. Purine-rich sequences located in the border of exons 2 and 3 (denoted ESE3) and in exon 4 (ESE4) revealed strong splicing enhancing activities. Mutation in ESE3 decreased pre-mRNA splicing, while mutation in purine-rich sequences in exon 2 did not. We further analyzed the functional activity of ESE4 by mutations or deletions of the ESE4 sequence that consists of three purine-repeats separated by two spacers and a putative hairpin constructing sequence. An UV cross-linking assay using the RNA sequence of ESE4 examined the presence of ESE4-specific binding proteins in the nuclear extracts from GT1 hypothalamic GnRH neurons. Collectively, this study indicates that a sequence context of ESE4 and its binding proteins may be crucially involved in enhanced GnRH pre-mRNA splicing. However, it should be further clarified as to which splicing factor(s) is responsible for ESE4-dependent GnRH pre-mRNA splicing.

Three distinct types of GnRH receptor characterized in the bullfrog

It has been proposed recently that two types of GnRH receptors (GnRHR) exist in a particular species. Here we present data demonstrating that at least three types of GnRHR are expressed in a single diploid species, the bullfrog. Three different cDNAs, encoding distinct types of bullfrog GnRHR (bfGnRHR-1, bfGnRHR-2, and bfGnRHR-3), were isolated from pituitary and hindbrain of the bullfrog. BfGnRHR-1 mRNA was expressed predominantly in pituitary, whereas bfGnRHR-2 and -3 mRNAs were expressed in brain. The bfGnRHR-1, bfGnRHR-2, and bfGnRHR-3 proteins have an amino acid identity of approximately 30% to approximately 35% with mammalian GnRHRs and approximately 40% to approximately 50% with nonmammalian GnRHRs. Interestingly, bfGnRHR-2 has an 85% amino acid homology with Xenopus GnRHR. Less than 53% amino acid identity was observed among the three bfGnRHRs. All isolated cDNAs encode functional receptors because their transient expression in COS-7 cells resulted in a ligand-dependent increase in inositol phosphate production. Notably, all three receptors exhibited a differential ligand selectivity. For all receptors, cGnRH-II has a higher potency than mGnRH. In addition, salmon GnRH also has a strikingly high potency to stimulate all three receptors. In conclusion, we demonstrated the presence of three GnRHRs in the bullfrog. Their expression in pituitary and brain suggests that bfGnRHRs play an important role in the regulation of reproductive functions in the bullfrog.

Pityriasis lichenoides-like mycosis fungoides in children

We report three children with clinical features of pityriasis lichenoides (scaly red to brown papules and macules) in whom there were histopathological findings of mycosis fungoides (disproportionate epidermotropism, Pautrier's microabscesses, and wiry and coarse collagen bundles). Immunohistochemical staining revealed a prevalence of T lymphocytes in the infiltrate. T-cell receptor gene rearrangement analysis in lesional skin demonstrated rearrangement of the gamma chain in all cases. Human T-cell lymphotropic virus type 1 serology was negative in the two patients in whom this test was performed. Thus, lesions resembling pityriasis lichenoides can be an unusual and potentially misleading presentation of mycosis fungoides.

Enhanced splicing of the first intron from the gonadotropin-releasing hormone (GnRH) primary transcript is a prerequisite for mature GnRH messenger RNA: presence of GnRH neuron-specific splicing factors

The rat GnRH gene consists of four short exons (denoted 1, 2, 3, and 4) and three introns (A, B, and C). All three introns are spliced from the primary transcript, resulting in a mature mRNA. Northern blot and RT-PCR analyses showed that the GnRH primary transcript and its splicing intermediates are more prevalent than the mature GnRH mRNA in a variety of non-GnRH-producing tissues. To delineate the possible splicing mechanism of introns, an in vitro HeLa splicing system was used. Introns B and C were efficiently spliced, while intron A spanning between exon 1 and exon 2 was not. The retention of intron A was relieved when the 5'- and/or 3'-splice sites of intron A were point mutated based on the consensus sequence. The splicing activity was even more strengthened when a putative branchpoint site was moved to the upstream region of the pyrimidine tract of intron A. Intron A could be partially spliced when whole exons (2, 3, and 4) were linked up with intron A. There are two putative exonic splicing enhancers (ESEs) in exon 3 and exon 4. The ESE on exon 4 (ESE4) is much stronger than that on exon 3. The closer the ESE4 to the 3'-splice site of intron A, the better the splicing activity became. However, in the presence of the nuclear extract from GnRH neurons, there was an enhancement in the splicing activity notwithstanding the distance between ESE4 and 3'-splice site of intron A. These results suggest that the ESE4 functions as both the constitutive and regulated enhancer. Collectively, our study provides evidence that enhanced splicing of intron A by putative GnRH neuron-specific splicing factor(s) interacting with the ESEs is a prerequisite for mature GnRH synthesis.

Negative regulation of gonadotropin-releasing hormone and gonadotropin-releasing hormone receptor gene expression by a gonadotrophin-releasing hormone agonist in the rat hypothalamus

There exists evidence for the presence of ultrashort loop feedback circuits of gonadotropin-releasing hormone (GnRH) secretion in the hypothalamus. It is, however, uncertain whether a similar mechanism is involved in the regulation of GnRH gene expression in vivo. Furthermore, little is known about the regulation of GnRH receptor (GnRHR) expression in the brain. In the present study, we examined the regulation of GnRH and its receptor gene expression by GnRH in vivo. A GnRH agonist, [D-Ala6, des-Gly10]GnRH-ethylamide (des-Gly GnRH), was administered by intracerebroventricular (i.c.v.) injection via the lateral ventricle of ovariectomized and estradiol (OVX + E)-treated rats. The amounts of GnRH and GnRHR mRNA were measured in the preoptic area (POA) and posterior mediobasal hypothalamus (pMBH) micropunch samples from individual rat brain slices by respective competitive reverse transcription-polymerase chain reactions. The i.c.v. administration of des-Gly GnRH significantly decreased GnRH and GnRHR mRNA expression in a dose-and time-related manner: des-Gly GnRH (6 ng) suppressed GnRH and GnRHR mRNA expression within 2 h, and the suppression was maintained without significant variation until 8 h after treatment. Treatment with Antide, [N-Ac-D-Nal(2)1, pCl-D-Phe2, D-Pal(3)3, Lys(Nic)5, D-Lys(Nic)6, Lys(iPR)8, D-Ala10]GnRH (10 ng), a potent GnRH antagonist, did not alter GnRH mRNA expression, but prevented des-Gly GnRH-induced suppression of GnRH mRNA expression. Antide alone decreased GnRHR mRNA expression, but failed to alter agonist-induced suppression of GnRHR mRNA expression. These results demonstrate the existence of an ultrashort loop feedback mechanism for GnRH gene expression in the POA, along with homologous down-regulation of GnRHR mRNA expression in the pMBH.

Noradrenergic neurotoxin suppresses gonadotropin-releasing hormone (GnRH) and GnRH receptor gene expression in ovariectomized and steroid-treated rats

The present study was designed to investigate whether noradrenergic neurotransmission regulates the gene expression of gonadotropin-releasing hormone (GnRH) in the preoptic area and GnRH receptor in the pituitary. To this end, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4, 50 mg/kg), an intraperitoneal (i.p.) injection of selective noradrenergic neurotoxin, was administered 1 h before progesterone (1 mg) treatment in ovariectomized and estradiol-treated prepubertal rats. Treatment with DSP4 effectively blocked the progesterone-induced increase in hypothalamic noradrenaline content, but not dopamine content, indicating that DSP4 selectively inhibits noradrenergic neurotransmission. DSP4 significantly blocked progesterone-induced increase in serum luteinizing hormone (LH) concentrations as well as GnRH release from hypothalamic fragments incubated in vitro. DSP4 concomitantly down-regulated GnRH mRNA levels in the preoptic area, as determined by competitive reverse transcription-polymerase chain reaction. DSP4 also clearly down-regulated progesterone-induced GnRH receptor mRNA levels in the pituitary, whereas it failed to alter LHbeta mRNA levels. In summary, blockade of noradrenergic neurotransmission with DSP4 resulted in profound reductions of hypothalamic GnRH and pituitary GnRH receptor gene expression.

Differential regulation of gonadotropin-releasing hormone (GnRH) receptor expression in the posterior mediobasal hypothalamus by steroid hormones: implication of GnRH neuronal activity

The present study is designed to evaluate the relationship between gonadotropin-releasing hormone (GnRH) and GnRH receptor (GnRHR) gene expression during the steroid-induced LH surge. One week after ovariectomy (OVX), a capsule containing 17beta-estradiol (E) or vehicle (V) was implanted into OVX rats, and 2 days later a single injection of progesterone (P) or V was administered s.c. at 10:00 h. Poly(A)-rich RNA samples were isolated from the micropunches of the preoptic area (POA) and the posterior mediobasal hypothalamus (pMBH) from both sides of individual brain slices. Using competitive reverse transcription-polymerase chain reaction (RT-PCR) procedures, three parameters (POA GnRH, pMBH GnRHR) and pituitary GnRHR mRNA levels were simultaneously determined in each individual animal. POA GnRH mRNA and pituitary GnRHR mRNA levels were decreased by treatment with E, but increased by a combination of E and P. In contrast, pMBH GnRHR mRNA levels were clearly augmented by treatment with E, and decreased by the combination of E and P. Temporal changes in such parameters were determined in OVX+E+V- and OVX+E+P-treated rats. P augmented POA GnRH mRNA levels at the time of the LH surge (17:00 h) and the increased GnRH mRNA levels were remained until 22:00 h, while E alone failed to alter POA GnRH mRNA levels. In the pMBH micropunch samples, P substantially decreased E-induced increase in GnRHR mRNA levels at 17:00 h and further lowered those until 22:00 h. Antisense oligonucleotides of GnRHR mRNA administered into the lateral ventricle of OVX+E-treated rats blocked the E-induced increase in pMBH GnRHR mRNA levels. The antisense oligonucleotides also prevented the LH surge as well as the increase in pituitary GnRHR mRNA levels in the OVX+E+P-treated group. However, administration of this antisense oligonucleotides failed to alter POA GnRH mRNA levels. In conclusion, the present study demonstrated that there is an inverse relationship between POA GnRH mRNA levels and pMBH GnRHR mRNA levels in response to E and/or P, and that the blockade of the E-induced increase in pMBH GnRHR mRNA levels effectively nullified the P-induced LH surge. These results indicate that pMBH GnRHR gene expression is involved in synchronizing the GnRH neuronal activity, which is crucial for the generation of the LH surge.

The neurochemistry of the GnRH pulse generator

We review the crucial role of the two neurotransmitters norepinephrine (NE) and GABA in eliciting GnRH pulse. NE acts via an alpha l-receptor mechanism and also GABA acts at the alpha-subtype of the GABA receptor. The function of NE appears to be induction of phasic activation of GnRH neurons and GABA inhibits GnRH neurons tonically until they are all ready for phasic activation. By an unknown mechanism preoptic GABA release in dramatically reduced which causes simultaneous desinhibition of the GnRH neurons. Hence they release their product into the portal vessels simultaneously which is the appropriate signal for the pituitary ganodotrophs. The action of norepinephrine and GABA is most likely exerted at the perikarya level of the GnRH neurons since the alpha l-adreno receptor blocker doxazosin and GABA inhibit GnRH secretion only when applied into the medial preoptic/anterior hypothalamic area (where in the rat brain the GnRH perikarya are located). Utilizing a quantitative reverse transcription polymerase chain reaction, we demonstrate furthermore that GnRH receptors are present in the mediobasal hypothalamus as well as in the preoptic area of rats. Their function appears to serve autoinhibitory purposes since Buserelin added to medium significantly decreased GnRH release. Simultaneously, the release of GABA was increased and that of glutamate decreased. We conclude from these experiments that GABAergic and glutamatergic neurons in the hypothalamus may also be GnRH-receptive.

Activation of central GABAA-but not of GABAB-receptors rapidly reduces pituitary LH release and GnRH gene expression in the preoptic/anterior hypothalamic area of ovariectomized rats

gamma-Aminobutyric acid (GABA) exerts an inhibitory action on gonadotropin-releasing hormone (GnRH) release from the hypothalamus. In vivo, this inhibitory action appears to be mediated via the GABAA receptor since in ovariectomized (ovx) rats and sheep direct application of muscimol (MUS), a GABAA agonist, into the preoptic area (POA), the site were the GnRH cell bodies are located, caused an immediate reduction of LH release. This effect may be the result of an inhibition of GnRH release but also GnRH biosynthesis may be affected. Using competitive reverse transcription-polymerase chain reaction (RT-PCR) we now addressed the question, whether an acute inhibition of the GnRH pulse generator in ovx rats by GABA involves reduction of GnRH biosynthesis as determined by GnRH mRNA levels in micropunches of the POA. To activate either the GABAA or GABAB receptor, we injected intraventricularly (icv) MUS or baclofen (BAC). Intracerebroventricular injection of 10 nmol MUS caused a rapid and lasting inhibition of LH release from about 7.5 ng/ml (pretreatment value) to approximately 1.5 ng/ml. Neither application of BAC or saline (control injections) affected LH secretion. Two hours after icv injections, rats were decapitated and GnRH mRNA levels were determined. MUS induced a pronounced decrease of GnRH levels in the POA (control rats: 2.26 pg GnRH mRNA; MUS-treated rats: 0.85 pg, n = 10/group). BAC was without any effect on GnRH mRNA levels. Thus, we confirm the inhibitory action of GABA on LH release in vivo which is exerted via the A-subtype of the receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of GABAergic compounds on gonadotropin-releasing hormone receptor gene expression in the rat

Using a competitive reverse transcription-polymerase chain reaction (RT-PCR), the amounts of GnRH receptor (GnRHR) transcript in a discrete nucleus micropunched from rat brain slices were determined. GnRHR transcript was highly expressed in anterior pituitary >> median eminence > posterior mediobasal hypothalamus (pMBH) > preoptic area (POA) but not in cortex and posterior pituitary, which were used as control tissues. To examine the effect of GABA on GnRHR transcript level, 10 nmol of muscimol, a GABA-A receptor agonist, or baclofen, a GABA-B receptor agonist, was microinjected into the lateral ventricle of ovariectomized rats. Two hours after an intraventricular injection, rats were decapitated. Blood was collected 1 h before and after drug administration and used for LH determination. Serum LH levels were significantly reduced by muscimol but not by baclofen within 2 h. The activation of GABA-A receptors with muscimol resulted in a significant inhibition in GnRHR transcript level in both the pMBH and POA but not in the pituitary. The activation of GABA-B receptors with baclofen, however, did not produce any effect on GnRHR transcript level in the pMBH and POA, as well as the pituitary. This experiment demonstrates for the first time that GABAergic neurotransmission, through GABA-A receptors, is involved in the regulation of GnRHR transcript level in the rat hypothalamus. This suggests that GABAergic neurotransmission regulates GnRHR gene expression in a coordinated, yet complex, fashion in the control of the neuroendocrine function of GnRH-LH axis.

Acute increase of GABAergic neurotransmission exerts a stimulatory effect on GnRH gene expression in the preoptic/anterior hypothalamic area of ovariectomized, estrogen- and progesterone-treated adult female rats

Although gamma-aminobutyric acid (GABA) is known to play an important role in the regulation of GnRH release from the hypothalamus, GABAergic action on hypothalamic GnRH gene expression is poorly understood. The present study aims to evaluate the effects of several GABAergic compounds on GnRH mRNA and serum LH levels at the times of LH surge induced by estrogen plus progesterone treatment in long-term ovariectomized adult rats. Animals received either aminooxyacetic acid (AOAA, an inhibitor of GABA catabolism, i.p.), muscimol (GABA-A type agonist, i.c.v.) or baclofen (GABA-B type agonist, i.c.v.) 2 h prior to sacrifice. GnRH mRNA in the preoptic/anterior hypothalamic area and serum LH levels were determined by Northern blot analysis and LH radioimmunoassay, respectively. All of three GABA mimetics blocked the LH surge induced by estrogen plus progesterone in a dose-dependent manner. However, inhibition of GABA catabolism with AOAA in a dose range of 10-100 mg/kg b.w. increased GnRH mRNA level by 30%. Activation of GABA-A receptor with muscimol at a low dose (5 nmol) but not at high doses (10 and 30 nmol) elevated GnRH mRNA levels by 60% over the control value. Activation of GABA-B receptor with baclofen augmented GnRH mRNA levels in a dose-dependent manner. These observations indicate that acute increase of GABAergic neurotransmission may differentially regulate the release and GnRH gene expression depending on its receptor subtypes.

Progesterone stimulates GnRH gene expression in the hypothalamus of ovariectomized, estrogen treated adult rats

Gonadotropin-releasing hormone (GnRH) is a major neural signal for hypothalamic control of gonadotropin secretion which in turn influences gonadal steroid synthesis. Progesterone (P) is known to affect release and content of GnRH. The action mechanism of P on GnRH mRNA level remains, however, to be resolved. Here we report that P augments GnRH mRNA level in hypothalamic tissues derived from ovariectomized, estradiol-treated adult rats. The stimulatory action of P was time-dependent and lasted at least for 9 h. When RU486, a P receptor antagonist, was administered 1 hr before P treatment, it clearly blocked the stimulatory action of P on GnRH mRNA level. These results strongly suggest that P regulates GnRH gene expression in the rat hypothalamus, presumably through the P receptor-mediated mechanism.

Presence of gonadotropin-releasing hormone mRNA in the rat olfactory piriform cortex

Gonadotropin releasing hormone (GnRH) neurons are known to be originated from the olfactory placode and to enter the forebrain regions during embryonic development. The present study aims to ascertain whether GnRH is locally expressed in the olfactory cortex. Northern blot hybridization and reverse transcription-polymerase chain reaction revealed that GnRH mRNA was present in the rat olfactory cortex as well as in the olfactory bulb. The predicted size of GnRH mRNA is similar to that detected in the hypothalamus. In situ hybridization histochemistry also showed that GnRH mRNA is highly concentrated in the olfactory piriform cortex. The present data indicate that GnRH is synthesized in the olfactory piriform cortex.

Competitive PCR for quantitation of gonadotropin-releasing hormone mRNA level in a single micropunch of the rat preoptic area

A competitive polymerase chain reaction (PCR) for quantitating gonadotropin-releasing hormone (GnRH) mRNA level in a single micropunch of the rat preoptic area (POA) is described. The POA (600 microns in depth) was micropunched from frozen rat brain slices and used for mRNA isolation using Dynabeads-oligo(dT) magnetic separation technique. The target RNA combined with a synthetic, deletion mutant GnRH cRNA as an internal standard, is co-reverse transcribed, and their cDNAs are subsequently co-amplified by Taq DNA polymerase in the same tube in which the same GnRH primers are used. This PCR protocol is sensitive enough to detect GnRH mRNA level in a single POA micropunch derived from an individual rat. There is a linear increase of the amount of GnRH PCR products as a function of input RNA and of the number of PCR cycles. Addition of mutant GnRH cRNA as an internal standard allows us to quantitate GnRH mRNA level in biological samples and to compensate variations of PCR reaction between samples. Following preoptic treatment with 5'-ADMP, which depletes selectively norepinephrine (NE), GnRH mRNA level was significantly reduced. This simple, yet highly sensitive PCR method appears to be a valuable tool for the study of the cellular and molecular regulation of GnRH gene expression in a variety of experimental models.

NMDA receptor antagonist decreases the progesterone-induced increase in GnRH gene expression in the rat hypothalamus

We previously reported that GnRH gene expression was enhanced by progesterone (P) in the hypothalamus from ovariectomized and estrogen (OVX+E) treated immature rats. Recent studies indicate that excitatory amino acids may play an important role in the regulation of GnRH secretion and gene expression by steroids. Therefore the present study attempts to examine whether excitatory amino acids are involved in the P-induced GnRH gene expression and release in vitro. MK-801, an NMDA receptor antagonist or CNQX, a non-NMDA receptor antagonist, was administered to OVX+E+P-treated prepubertal female rats. GnRH mRNA was determined by Northern blot hybridization using 32P-labeled antisense RNA, and GnRH release in vitro from the hypothalamic fragments was monitored by GnRH radioimmunoassay. The administration of MK-801 (0.2 mg/kg) for 2 h significantly reduced the P-induced GnRH gene expression and release, whereas CNQX (0.4 mg/kg) had no effect. These results clearly indicate that excitatory amino acids by way of NMDA receptor are involved in the transsynaptic regulation of GnRH gene expression.