Electrophysiological Correlates of Pulsatile Gonadotropin Release in Rats

Kawakami, Michiyuki; Uemura, Tomohiro; Hayashi, Reiko

doi:10.1159/000123356

Cited by 138 publications

(61 citation statements)

References 11 publications

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“…Our results support this notion; pulsatility of LH release in rats 1 week after PAD was less apparent although plasma levels of LH were not completely depressed compared to sham-operated controls and immunoreactive LHRH neuronal fibres were still found in the median eminence. It has been shown that no LH pulses are observed in rats bearing C D together with a lesion of anterior part of the ARC (4) and an increase in the multiple unit activity in the ARC is noted at the peak of LH pulses in ovariectomized rats (12). These data suggest that the LHRH pulse generator is located in the anterior part of the ARC within the MBH.…”

Section: Discussionmentioning

confidence: 95%

Effects of Various Types of Hypothalamic Deafferentation on Luteinizing Hormone Pulses in Ovariectomized Rats

Ohkura

Tsukamura

Maeda

1991

J Neuroendocrinology

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The pulsatile luteinizing hormone (LH) secretion in chronically ovariectomized rats bearing various types of hypothalamic deafferentation was examined. Ovariectomized rats were subjected to complete, anterolateral or anterior hypothalamic deafferentation and bled every 6 min for 3 h through an indwelling atrial cannula 5 days after the brain surgery. Another group of ovariectomized animals was subjected to posterior-anterior hypothalamic deafferentation (PAD), which cut off the anterior part of the arcuate nucleus from the mediobasal hypothalamus, and bled 1, 3 or 5 weeks after the deafferentation. Coronal sections of the brain were immunostained with anti-LH-releasing hormone (LHRH) serum. The pulsatile LH secretion w a s observed in rats bearing anterior, anterolateral or complete hypothalamic deafferentation and these types of deafferentation did not affect the frequency of LH pulses. The mean LH level during the 3-h sampling period and the amplitude of LH pulses decreased as the incision extended postero-laterally. Rats bearing PAD showed an irregular fluctuating pattern in plasma LH concentration 1 week after PAD. Parameters of LH pulses were restored with time after PAD. This suggests that the system generating LHRH pulses severed by PAD had been reorganized. LHRH-immunopositive neuronal fibres were found in the external layer of the median eminence in the rats bearing any type of deafferentation. The present results suggest that the frequency of LH pulses could be controlled by the LHRH pulse generator, which consists of non-LHRH neurons and is located in the mediobasal hypothalamus.Halasz and Pupp (1) first reported that some female rats bearing complete hypothalamic deafferentation (CD) showed either persistent oestrus or persistent dioestrus, and suggested that the centre for the tonic luteinizing hormone (LH) secretion was located inside the hypothalamic island, namely the mediobasal hypothalamus (MBH). It has also been reported that the pulsatile LH secretion is still apparent in ovariectomized rats bearing C D (2, 3). Soper and Weick (4) have reported that anterior hypothalamic deafferentation (AD) combined with the electrolytic lesion of the anterior part of the arcuate nucleus (ARC) abolished the pulsatile LH secretion. All these reports suggest that the putative LH-releasing hormone (LHRH) pulse generator, the mechanism regulating the pulsatile LH secretion, is located in the MBH. In the rat, most cell bodies of LHRH neurons are located extensively in the region anterior to the hypothalamus, and some cell bodies of LHRH neurons exist in the hypothalamic island made by C D (5). Therefore, several workers assume that the LHRH pulse generator is located in the preoptic/anterior hypothalamic area: The local application of a specific a,-receptor antagonist into that area, but not into the MBH, caused a reduction of LH pulsatility (6); the inverse pattern of LH release and y-aminobutyric acid release from the preoptic/anterior hypothalamic area was seen (7). Furthermore, subchiasmatic LHRH neur...

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Section: Discussionmentioning

confidence: 95%

Effects of Various Types of Hypothalamic Deafferentation on Luteinizing Hormone Pulses in Ovariectomized Rats

Ohkura

Tsukamura

Maeda

1991

J Neuroendocrinology

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“…The secretion of LH (and presumably LHRH) in vivo is known to occur in a pulsatile fashion due to the operation of a hypothalamic pulse generator (1)(2)(3)25). The relationship of this pulse generator to the LHRH neurons is unclear, in part, because direct physiological measurements from LHRH neurons in vivo are not possible.…”

Section: Discussionmentioning

confidence: 99%

“…In mammals, luteinizing hormone (LH) pulses are closely correlated with increased activities in as yet unidentified mediobasal hypothalamic neurons (1)(2)(3) which are believed to regulate the secretory activities of LH-releasing hormone (LHRH)-containing neurons. Due to the small number of LHRH neurons in brain, their small diameter, and their dispersed anatomical distribution, very few electrical recordings from identified LHRH neurons either in vivo or in vitro are available (4,5).…”

mentioning

confidence: 99%

Electrical and synaptic properties of embryonic luteinizing hormone-releasing hormone neurons in explant cultures.

Kusano

Fueshko

Gainer

et al. 1995

Proc. Natl. Acad. Sci. U.S.A.

157

139

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Voltage-and ligand-activated channels in embryonic neurons containing luteinizing hormone-releasing hormone (LHRH) were studied by patch-pipette, whole-cell current and voltage clamp techniques. LHRH In mammals, luteinizing hormone (LH) pulses are closely correlated with increased activities in as yet unidentified mediobasal hypothalamic neurons (1-3) which are believed to regulate the secretory activities of LH-releasing hormone (LHRH)-containing neurons. Due to the small number of LHRH neurons in brain, their small diameter, and their dispersed anatomical distribution, very few electrical recordings from identified LHRH neurons either in vivo or in vitro are available (4, 5). Consequently, the underlying electrophysiological and synaptic properties of LHRH neurons and information about their basic physiological properties have been largely deduced from extensive studies on the immortalized hypothalamic (LHRH-cell) neuronal cell line GT1 (6). Cells of the GT1-3 and -7 sublines possess a rich array of ion channels (7-11) and, under some circumstances, exhibit pulsatile LHRH secretion (9,(11)(12)(13)(14). However, the extent to which these electrical, receptor, and secretory properties of GT1 cells are found in actual LHRH neurons is unknown.Our aim was to study the electrophysiological and synaptic properties of primary LHRH neurons. Ontogenetic studies have shown that LHRH neurons originate from progenitor cells in the olfactory placode and thereafter migrate from the olfactory pit (OP) into the forebrain during prenatal development (15,16). LHRH neurons can be cultured from embryonic olfactory placodal regions (17, 18), and cells maintained in these explants secrete LHRH in a pulsatile mannerThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 3918(19). We report here successful intracellular recordings from 62 identified embryonic LHRH neurons and describe their highly differentiated voltage-and ligand-gated ion-channel properties.MATERIALS AND METHODS Preparations. OP regions ("0.5 mm3) were aseptically dissected from day-11.5 mouse embryos (17), plated on glass coverslips (24 mm x 12 mm, Gold Seal, no. 1 thickness), and placed in 35-mm Petri dishes (Falcon). Tissues were fed twice a week with serum-free Eagle's basal medium (20) and maintained in humidified air plus 5% CO2. Cultures typically received a single dose of 5-fluoro-2'-deoxyuridine (80 ,uM) on day 3 for 3 days. This treatment reduced the proliferation of dividing cells and vastly improved the visualization of LHRHlike (bipolar) neurons under phase-contrast microscopy (see Fig. 1). Tissues were maintained for 6-14 days in vitro, during which time LHRH cells migrated into the thin peripheral tissue areas (17), thereby facilitating electrophysiological recordings.Electrophysiological Recordings. The cultures on coverslips were transferred to a recording chamber on a Nikon M inverted mi...

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“…Abrupt increases in multiunit activity (MUA volleys) that are invariably synchronous with the initiation of luteinizing hormone pulses measured in peripheral blood ( Fig. 1) have been recorded from this area in the rhesus monkey (4), rat (5), and goat (6). The unitary association between luteinizing hormone pulses and these electrical signals has been observed in a variety of experimental circumstances (4,(7)(8)(9)(10)(11) as well as during the normal menstrual cycle (12) and has permitted the conclusion that these MUA volleys are the electrophysiological manifestations of GnRH pulse generator activity.…”

Section: Introductionmentioning

confidence: 87%

Single unit components of the hypothalamic multiunit electrical activity associated with the central signal generator that directs the pulsatile secretion of gonadotropic hormones.

Cárdenas

Ördög

O’Byrne

et al. 1993

Proc. Natl. Acad. Sci. U.S.A.

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Vertebrate reproduction is dependent on the operation of a central signal generator that directs the episodic release of gonadotropin-releasing hormone, a neuropeptide that stimulates secretion of the pituitary gonadotropic hormones and, thereby, controls gonadal function. The electrophysiological correlates of this pulse generator are characterized by abrupt increases in hypothalamic multiunit electrical activity (MUA voDleys) invariably associated with the initiation of secretory episodes of luteinizing hormone. Using cluster analysis, we extracted single units from the multiunit signals recorded from the mediobasal hypothalamus of four intact and four ovariectomized rhesus monkeys. Of the 40 individual units identified in this manner, 24 increased their frequency with the MUA volleys. The onset and termination of these single-unit bursts occurred coincidently with those of the MUA volleys in both intact and ovariectomized animals, indicating that the longer duration of the MUA voDleys characteristic of the gonadectomized animals was due not to the sequential activation of different units but to the longer bursts of the individual cels. Four other units showed decreases in firing rate during the MUA volleys, while the frequency of the remainder did not change. All the examined units were active during the intervals between the volleys of electrical activity. The results indicate that the MUA voDleys associated with the activity of the gonadotropin-releasing hormone pulse generator represent the simultaneous increase in firing rate of some individual hypothalamic neurons and the decrease in the frequency of others.The rhythmic, pulsatile secretion of the pituitary gonadotropic hormones, described in every vertebrate studied in this regard, is governed by a hypothalamic "clock" generally referred to as the gonadotropin-releasing hormone (GnRH) pulse generator. The operation of this signal generator at an appropriate frequency for the species is an absolute requirement for normal gonadal function (see ref. 1 for review).In the rhesus monkey, this central signal generator fires approximately once an hour and has been localized in the region ofthe arcuate nucleus (2), but -its cellular basis remains in doubt (3). Abrupt increases in multiunit activity (MUA volleys) that are invariably synchronous with the initiation of luteinizing hormone pulses measured in peripheral blood (Fig. 1) have been recorded from this area in the rhesus monkey (4), rat (5), and goat (6). The unitary association between luteinizing hormone pulses and these electrical signals has been observed in a variety of experimental circumstances (4, 7-11) as well as during the normal menstrual cycle (12) and has permitted the conclusion that these MUA volleys are the electrophysiological manifestations of GnRH pulse generator activity.The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact....

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Electrophysiological Correlates of Pulsatile Gonadotropin Release in Rats

Cited by 138 publications

References 11 publications

Effects of Various Types of Hypothalamic Deafferentation on Luteinizing Hormone Pulses in Ovariectomized Rats

Effects of Various Types of Hypothalamic Deafferentation on Luteinizing Hormone Pulses in Ovariectomized Rats

Electrical and synaptic properties of embryonic luteinizing hormone-releasing hormone neurons in explant cultures.

Single unit components of the hypothalamic multiunit electrical activity associated with the central signal generator that directs the pulsatile secretion of gonadotropic hormones.

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