Immunohistochemical Identification of Somatostatin-Containing Neurons Projecting to the Median Eminence of the Rat

Ishikawa, Koichi; Taniguchi, Y.; Kurosumi, Kazumasa; Suzuki, Mitsuo; Shinoda, Motoo

doi:10.1210/endo-121-1-94

Cited by 60 publications

(31 citation statements)

References 22 publications

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“…The mechanism underlying this fasting-induced suppression of GH secretion is not understood, although it seems likely that it involves a changing balance in the output of the two neuroendocrine systems that are primarily involved in the regulation of pulsatile GH secretion: the GH-releasing factor (GRF) neurons of the arcuate nucleus [2]that stimulate GH secretion [3, 4]and the inhibitory somatostatin neurons [5]of the periventricular nucleus [6]. Consistent with this hypothesis, GRF mRNA expression is lower in fasted than in fed rats, however, there is no change in the expression of somatostatin mRNA [7].…”

Section: Introductionmentioning

confidence: 99%

Activation of Arcuate Nucleus Neurons by Systemic Administration of Leptin and Growth Hormone-Releasing Peptide-6 in Normal and Fasted Rats

1999

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Both leptin and growth hormone secretagogues are believed to have stimulatory effects on the hypothalamic growth hormone pulse generator, though whether these are achieved through the same pathway is unknown. Systemic administration of a normally maximal effective dose of the growth hormone secretagogue GHRP-6 to male rats causes the induction of c-Fos protein in the ventromedial aspect of the hypothalamic arcuate nucleus. The effect of the same dose of GHRP-6 is, however, much greater in animals that have been fasted for 48 h, suggesting that in the food-replete rat, arcuate neurons either show reduced sensitivity to endogenous growth hormone secretagogues or they are under the tonic inhibitory influences of other factors. The major populations of arcuate neurons activated by GHRP-6 have been shown to contain neuropeptide Y or growth hormone-releasing factor, while leptin is thought to be inhibitory to neuropeptide Y neurons. Leptin did not alter the response of the rats to GHRP-6. However, it was able by itself to induce c-Fos protein immunoreactivity in the ventral, including the ventrolateral, arcuate nucleus of fasted rats. This is a clear demonstration of the acute activation of arcuate neurons in the rat following systemic leptin injection and suggests that GHRP-6 and leptin act on the growth hormone axis via different pathways.

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Section: Introductionmentioning

confidence: 99%

Activation of Arcuate Nucleus Neurons by Systemic Administration of Leptin and Growth Hormone-Releasing Peptide-6 in Normal and Fasted Rats

1999

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“…Accumulating evidence favors a role for γ-aminobutyric acid (GABA). Thus GABAergic nerve terminals are closely associated with the perikarya and terminals of SRIH neurons [11, 12], both SRIH mRNA expression [13, 14]and SRIH release [15, 16]are modified by GABA A receptor ligands and sex steroids may influence GABA actions on SRIH release in the female in vivo [17]. Furthermore, previous findings in our laboratories have shown that GABA A receptor subunits are found in the majority of PeN SRIH cells [18].…”

Section: Introductionmentioning

confidence: 99%

Sexually Dimorphic Ontogeny of GABAergic Influences on Periventricular Somatostatin Neurons

Murray

Rantle²,

Simonian³

et al. 1999

Neuroendocrinology

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The biosynthesis and secretion of somatostatin (SRIH) within the hypothalamic periventricular-median eminence (PeN-ME) pathway follows a sexually differentiated developmental pattern beginning in the early neonatal period. It is generally accepted that testosterone plays a role in these processes, but the mechanisms underlying the age and sex differences are poorly understood. The present study sought to investigate the hypothesis that γ-aminobutyric acid (GABA) may play a role in determining sex differences in SRIH neuronal activity. Using an in vitro hypothalamic preparation where more than 97% of the immunoreactive SRIH is contained within the PeN-ME pathway, peptide release in response to the GABA_A receptor antagonist, bicuculline, was followed through development. In the male a stimulatory response, indicative of an inhibitory GABAergic tone on SRIH secretion, was observed as early as postnatal day (P) 5. This persisted throughout juvenile development (P10, P17) and was present also in the adult male (P75), but in the peripubertal period the response to bicuculline was first lost (P25) and then reversed to an inhibition (P40), suggesting a transient switch to an apparent stimulatory GABAergic tone on SRIH release. By contrast, in the female, no bicuculline responsiveness was seen until P25 when it caused a decrease in SRIH release which persisted into adulthood. Using in situ hybridization studies we found no evidence to support the view that these age- and sex-dependent differences were due to changes in the expression of GABA_A receptor α-subunits (α₁ and α₂) which are colocalised in the PeN SRIH neurons. Following adult gonadectomy, the bicuculline response was abolished in the male, whereas, in the female it was reversed and identical in magnitude to the response in the intact male. These results demonstrate marked sex differences in GABA_A-receptor-mediated influences on SRIH release which develop soon after birth and, in the adult, depend on gonadal factors. In the male these factors activate a primarily inhibitory influence, whereas in the female they facilitate an apparently stimulatory tone of GABA on SRIH secretion via the GABA_A receptor. Our findings thus support the view that GABAergic transmission may play a key role in generating sex differences in the mode of SRIH secretion from the hypothalamus which has been shown to be a major factor in determining the sexually dimorphic patterns of growth hormone secretion.

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“…The median eminence (ME) is a target organ of hypo thalamic hormone-containing neurons, such as somato statin, corticotropin-releasing hormone (CRH), thyrotro pin-releasing hormone (TRH) neurons in the periventric ular/paraventricular nucleus [1][2][3], gonadotropin-releas ing hormone neurons (GnRH) in the septal preoptic area [4], and growth hormone-releasing hormone neurons (GRH) in the arcuate nucleus [5], During development, these neurons begin to send their fibers to the ME in rather late periods of fetal life. For example, GRH-positive fibers first appear in the primitive ME at the 18th day of gestation [6].…”

mentioning

confidence: 99%

Pro-Opiomelanocortin-Containing Neurons in Rat Median Eminence

Ishikawa¹,

Katakai²,

Tanaka

et al. 1992

Neuroendocrinology

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A significant number of pro-opiomelanocortin (POMC)-containing cells were detected in the rat median eminence (ME) by immunocytochemistry using an antibody raised against a synthetic peptide corresponding to the cleavage site between adrenocorticotropin and β-lipotropin moieties. Distribution of POMC-positive cells was restricted to the internal zone of the anterior parts of the ME. Such cells were observed as early as the 14th day of gestation in the area of the primitive ME, long before glial fibrillary acidic protein-positive cells appeared postnatally in this structure. Dissociated cell cultures obtained from the ME of 1-day-old rats produced cells immunoreactive for neurofilaments and the POMC moiety. Such cells displayed a neuronal morphology: the cell body was oval (13–18 µm) with long and fine beaded fibers. These findings clearly demonstrate the early appearance of POMC neurons in the developmental ME, a target organ of the hypothalamic infundibular neurons.

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Immunohistochemical Identification of Somatostatin-Containing Neurons Projecting to the Median Eminence of the Rat

Cited by 60 publications

References 22 publications

Activation of Arcuate Nucleus Neurons by Systemic Administration of Leptin and Growth Hormone-Releasing Peptide-6 in Normal and Fasted Rats

Activation of Arcuate Nucleus Neurons by Systemic Administration of Leptin and Growth Hormone-Releasing Peptide-6 in Normal and Fasted Rats

Sexually Dimorphic Ontogeny of GABAergic Influences on Periventricular Somatostatin Neurons

Pro-Opiomelanocortin-Containing Neurons in Rat Median Eminence

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