Distribution of insulin-like growth factor-I receptor mRNA in rat brain. Regulation in the hypothalamo-neurohypophysial system

Aguado, Fernando; Rodrigo, José; Cacicedo, Luanda; Mellström, Britt

doi:10.1677/jme.0.0110231

Cited by 48 publications

(29 citation statements)

References 32 publications

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“…Consequently, the adolescent hypersensitivity to estradiol negative feedback suppression of LH secretion may be the result of an increased GABAergic inhibition of glutamate receptor excitation of LHRH neurons. Although the specific hypothalamic distribution of IGF-I receptors has yet to be described in primates, IGF-I receptors in rats are found in the median eminence (Lesniak et al 1988, Werther et al 1989, Aguado et al 1993 and IGF-I receptor mRNA in this region increases prior to first proestrus in rats (Hiney et al 1996). Co-localization and functional analysis studies of neurons containing IGF-I receptors and those immunoreactive for GABA and/or glutamate may help determine whether IGF-I diminishes estradiol-induced activation of GABAergic inhibition of glutamate neurons.…”

Section: Discussionmentioning

confidence: 99%

Premature elevation in serum insulin-like growth factor-I advances first ovulation in rhesus monkeys

Wilson

1998

Journal of Endocrinology

109

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Previous data suggest that developmental increases in peripheral concentrations of insulin-like growth factor-I (IGF-I) may be one of several neuroendocrine signals that regulate the timing of puberty. In order to test this hypothesis further, normal juvenile female rhesus monkeys (Con; n=6) were compared with age-matched animals (Igf; n=4) which received a constant subcutaneous infusion of recombinant human IGF-I (110 µg/kg/day) from 18 through 36 months of age. Menstrual bleeding was monitored and ovulation was inferred from a sustained rise in serum progesterone. In order to assess the sensitivity of luteinizing hormone-releasing hormone (LHRH) neurons to excitation, the response of serum LH to the acute administration of the glutamate receptor agonist N-methyl-, -aspartic acid (NMDA) was assessed prior to menarche, 2 months following menarche, and during the follicular phase of a female's third ovulation or 50 days after a female's first ovulation. In addition, the pituitary response of LH secretion to an LHRH agonist was assessed during the follicular phase of a female's fourth ovulation or 75 days following her first ovulation.IGF-I treatment effectively elevated serum concentrations by more than 86% of the values observed in Con animals. Although the treatment also enhanced the developmental increase in IGF binding protein-3 (IGFBP-3), IGF-I was increased proportionately more, resulting in a significantly higher molar ratio of IGF-I:IGFBP-3 in treated females throughout the course of the study. Treatment with IGF-I did not affect age at menarche but did significantly advance the age of first ovulation.Consequently, the interval between menarche and first ovulation was significantly shorter in Igf compared with Con females. Although the total number of ovulations exhibited by Igf (3·8 0·3) and Con females (3·0 0·5) in the 12 months following menarche was similar, significantly more of these were characterized by normal luteal phase progesterone secretion in Igf (100% 0) compared with Con females (64% 17). An analysis of cycles with a normal luteal phase revealed that serum estradiol during the luteal phase was significantly higher in Igf compared with Con females. Finally, IGF-treated females responded to NMDA treatment with a significantly greater increase in serum LH following menarche but not prior to menarche. In contrast, the response of serum LH to an LHRH agonist did not differ between Igf and Con females.These data suggest that the premature elevation in IGF-I levels, and consequently the ratio of IGF-I:IGFBP-3, accelerates the tempo of the final stages of puberty in rhesus monkeys. This action of IGF-I is probably the result of an increase in LHRH neuronal activity and is not due to a change in pituitary sensitivity to LHRH stimulation. In addition, ovarian sensitivity to LH stimulation during the luteal phase is also increased by IGF-I. Taken together, these data suggest that developmental increases in peripheral IGF-I secretion participate in the neuroendocrine regulation of puberty in...

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Section: Discussionmentioning

confidence: 99%

Premature elevation in serum insulin-like growth factor-I advances first ovulation in rhesus monkeys

Wilson

1998

Journal of Endocrinology

109

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“…While such effects have yet to be demonstrated, several studies indicate that many of the components of the IGF system are present in the adult MNS. For example, IGF-I immunoreactivity has been detected in magnocellular neurons of the paraventricular, supraoptic and accessory nuclei following colchicine treatment [ 19], and these neurons have also been reported to express IGF-I receptor mRNA [20]. The presence of high-affinity binding sites for [125I]IGF-I in the MNS sug gests that functional receptors are present [21], If IGF-I does act in an autocrine/paracrinc manner in mature magnocellular neurons, production of IGFBP-2 by pitui cytes may be analogous to synthesis of the binding protein by astrocytes in the developing retina and cerebellum.…”

Section: Discussionmentioning

confidence: 99%

Expression of Insulin-Like Growth Factor Binding Protein-2 during Postnatal Development of the Rat Neurointermediate Pituitary

Zhou

Herman²,

Paden³

1997

Neuroendocrinology

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The expression of insulin-like growth factor binding protein-2 (IGFBP-2) during postnatal development of the rat neurointermediate pituitary was characterized using immunocytochemistry and in situ hybridization. Glial cells in the neural lobe (NL) showed robust expression of IGFBP-2 throughout the postnatal period and continuing into adulthood. These were identified as pituicytes by the presence of S-100 protein; IGFBP-2 was not present in microglia in the NL. IGFBP-2 immunoreactivity was more punctate in mature pituicytes, suggesting a possible association with the cell membrane. No expression of IGFBP-2 by brain astrocytes was observed at any age examined, even in regions such as the median eminence and subfornical organ that lack a blood-brain barrier. IGFBP-2 was also localized immunocytochemical-ly in melanotropes and glial-like cells of the intermediate lobe (IL). Positive cells were most numerous in neonates and declined thereafter, with immunoreactivity undetectable by 65 days of age. IGFBP-2 mRNA was detected in the IL only at 1 day of age. These findings are consistent with a potential role for IGFBP-2 in modulating effects of the insulin-like growth factors during development of the neurointermediate lobe. The constitutive expression of high levels of IGFBP-2 by mature pituicytes also suggests that this protein could be secreted and/or influence a variety of processes in the mature NL, such as glial proliferation, axonal growth, or morphological plasticity of pituicytes.

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“…Immunoreactive rat LH (IR-LH) FSH (IR-FSH) and GH (IR-GH) were measured by the National Hormone and Pituitary Program/NIDDK (Bethesda, Md, USA) kits. IGF-I was separated from its binding proteins by acid extraction and reverse-phase column chromatography procedure using Sep-Pack C18 cartridges (Waters Millipore, Milford, Mass., USA) [6]and assayed by a commercial IGF-I radioimmunoassay (RIA) kit (Nichols, San Juan Capistano, Calif., USA).…”

Section: Methodsmentioning

confidence: 99%

“…It has been shown [4]that IGF-I of peripheral origin contributes to the initiation of female puberty by stimulating GnRH release from the hypothalamus. We and others have reported that IGF-I and its receptor are expressed in the hypothalamus and median eminence (ME) [5, 6, 7]. Therefore, centrally located IGF-I may regulate GnRH through autocrine, paracrine or endocrine functions within the hypothalamus.…”

Section: Introductionmentioning

confidence: 99%

Regulation of Gonadal and Somatotropic Axis by Chronic Intraventricular Infusion of Insulin-Like Growth Factor 1 Antibody at the Initiation of Puberty in Male Rats

Pazos

Sánchez‐Franco²,

Balsa³

et al. 1999

Neuroendocrinology

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There has been increasing experimental evidence to suggest that insulin-like growth factor 1 (IGF-I) may be one of the essential regulators in the reproductive system of the rat. IGF-I is synthesized in the hypothalamus and IGF-I immunoreactivity increases during puberty. Consequently we hypothesized that centrally located IGF-I might contribute to the initiation of puberty. Centrally located IGF-I was immunoneutralized to assess this hypothesis. Male Wistar rats, 28 days old, were infused intracerebroventricularly with specific purified IgGs from rabbit IGF-I antiserum (IGF-I-Ab). The intracerebroventricular administration of IGF-I-Ab resulted in a reduction in testicular weight and consequently in delayed pubertal development. There was also a reduction in serum testosterone, pituitary immunoreactive (IR) luteinizing hormone (LH) and serum IR follicle-stimulating hormone (FSH). The accumulation of βLH mRNA was not modified, whereas βFSH mRNA was increased. An increment in the serum growth hormone (GH) levels was also observed. There were no significant alterations in hypothalamic IR growth hormone releasing factor content, although IR somatostatin (SRIH) content was increased by IGF-I-Ab. The body weight gain remained unaltered. As a whole, our study suggests that centrally located IGF-I influences pubertal development, production and release of gonadotropins and supports the finding that endogenous centrally located IGF-I plays a role at the initiation of puberty in the male rat. It also gives support to the physiological role of centrally located IGF-I in the release of GH mediated by hypothalamic SRIH at the initiation of puberty.

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Distribution of insulin-like growth factor-I receptor mRNA in rat brain. Regulation in the hypothalamo-neurohypophysial system

Cited by 48 publications

References 32 publications

Premature elevation in serum insulin-like growth factor-I advances first ovulation in rhesus monkeys

Premature elevation in serum insulin-like growth factor-I advances first ovulation in rhesus monkeys

Expression of Insulin-Like Growth Factor Binding Protein-2 during Postnatal Development of the Rat Neurointermediate Pituitary

Regulation of Gonadal and Somatotropic Axis by Chronic Intraventricular Infusion of Insulin-Like Growth Factor 1 Antibody at the Initiation of Puberty in Male Rats

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