Luteinizing Hormone-releasing Hormone Perikarya Research Articles

2418 Effect of abdominal vagotomy on interleukin-1β induced noradrenaline release in the paraventricular nucleus in conscious rats

Seasonal breeding mammals exhibit a reversible annual cycle of fertility, and thus represent valuable models for investigating the organization of luteinizing hormone-releasing hormone (LHRH) neurons which mediate the neuroendocrine control of reproduction. Electron microscopic immunocytochemistry was used to examine the ultrastructure of LHRH neurons and their projections in a seasonal breeder, the golden hamster, housed under photoperiodic conditions which are reproductively stimulatory. LHRH perikarya in the diagonal band, medial septum, and preoptic area were bipolar or unipolar cells which possessed nuclei with prominent indentations and multiple nucleoli. LHRH reaction product within these cells was associated with neurosecretory granules and the rough endoplasmic reticulum (RER), particularly those portions of RER adjacent to the outer nuclear envelope. LHRH cell bodies and dendrites in the hamster received an extremely limited amount of synaptic input; of a total of twenty-five cells analyzed, we found only five instances of morphologically identified synapses onto immunoreactive dendrites. Occasionally close somatic appositions were seen between LHRH cells and non-immunoreactive neurons, and in one instance between two LHRH somas. In the organum vasculosum of the lamina terminalis (OVLT), LHRH fibers appeared as isolated strings of varicosities. In contrast, within the median eminence immunoreactive axonal profiles were frequently bundled together in fascicles although synaptic specializations were not observed between individual axons. The existence of contacts between LHRH axons in the median eminence, coupled with the extreme paucity of synaptic inputs onto LHRH neurons in this species, suggests that the median eminence may be a site where neural or hormonal signals could influence the coordinated release of LHRH from cells of dispersed origin.

Beta-endorphin regulation of LHRH release at the median eminence level: immunocytochemical and physiological evidence in hens.

We studied the effect that beta-endorphin (beta END) might have at the median eminence (ME) on luteinizing hormone (LH)-releasing hormone (LHRH) during the ovulatory cycle of domestic hens. Thus, we assessed (a) the immunocytochemical distribution of beta END and LHRH in the hen ME, (b) the temporal changes in ME and preoptic area (POA) LHRH and beta END content, in both a spontaneous and a premature C2 ovulatory model. The premature C2 ovulation occurs 6-7 h after the administration of progesterone (P4) injected 14 h before the spontaneous second (C2) ovulation of a sequence and therefore 7-8 h earlier than expected, (c) the ME in vitro release of beta END in both models, and (d) the effect of beta END and naloxone on in vitro ME-LHRH release in the two models. In the hen, beta END cell bodies are located in the periarcuate area with axons projecting to both the ME and the POA. LHRH perikarya are located in the medial POA and anterior hypothalamus and project to the ME and infundibulum through the ventrolateral hypothalamus. In the spontaneous C2 ovulatory model, both beta END and LHRH content in the ME remained unchanged during the 14 h preceding the C2 ovulation. However, POA-LHRH content was increasing at the time of the LH surge (4 h before the expected C2 ovulation) and remained elevated until the C2 ovulation occurred. In contrast, POA-beta END content was lowest at the time of the LH surge and remained low until the C2 ovulation occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Brainstem projections to the medial preoptic region containing the luteinizing hormone-releasing hormone perikarya in the rat. An immunohistochemical and retrograde transport study

The afferent projections to the anterior medial preoptic area (MPA) from the brainstem have been studied, in female Wistar rats, by retrograde tracing with horseradish peroxidase (HRP). The HRP was injected by iontophoresis into the preoptic region containing the luteinizing hormone-releasing hormone (LHRH) perikarya. The brain sections including the MPA were reacted with diaminobenzidine (DAB) to reveal the injection site; the LHRH cells were then immunohistochemically identified using DAB with ammonium nickel sulphate. When the injection site incorporated the LHRH cells, the brainstem sections were reacted with the DAB nickel solution to detect lysosomal HRP and then immunohistochemically processed to locate the adrenaline-synthesizing cells using DAB alone. The results confirm the brainstem projections to the MPA from the central grey matter, ventral tegmental area, subcoeruleus area, the dorsal raphe nucleus, the lateral parabrachial nucleus, the raphe pontis nucleus, the raphe obscurus nucleus, the region of the paragigantocellular nucleus and the nucleus of the solitary tract. Given the considerable evidence implicating the ascending adrenergic systems in the regulation of LHRH, we focused our attention on the afferents from the locus coeruleus, area postrema and the adrenaline-synthesizing cell groups (C1-3). The only cells which were retrogradely labelled and immunopositive for phenylethanolamine N-methyltransferase were found in C3.

Subgroups of luteinizing hormone-releasing hormone perikarya defined by computer analyses in the basal forebrain of intact female rats.

The hypothesis that the basal forebrain population of LHRH perikarya is composed of heterogeneous subgroups was examined in this study. We used three-dimensional computerized reconstruction to examine populations of LHRH-immunopositive neurons detected in noncolchicine treated cycling female rats. Perikarya were detected with two antisera capable of detecting LHRH decapeptide within larger mol wt species, i.e. Millar's (RM) 1076 and Arimura's (AA) 419. No immunopositive perikarya were detected with antiserum AA 422, which requires the fully processed decapeptide for binding. A more broadly distributed population of LHRH neurons was detected in females killed on proestrus than in females killed on estrus or the other days of the cycle. These relationships were observed with both antisera, RM 1076 and AA 419. Subgroups of cells were clearly defined when the population of LHRH neurons detected on proestrus was simultaneously displayed with the population detected on estrus. Strikingly similar subgroups were revealed by simultaneous displays of populations of LHRH neurons detected by the antisera RM 1076 and AA 419 in proestrous females. This study revealed a three-dimensional onion skin-like laminar organization of LHRH subgroups expanding from the ventricle outward laterally and from the diagonal band of Broca to the hypothalamus caudally. We propose that these subgroups vary in their metabolic activity of biosynthesis, processing, transport, or release of LHRH in relation to the proestrous preovulatory release of LH.

Colocalization of galanin and luteinizing hormone-releasing hormone in a subset of preoptic hypothalamic neurons: anatomical and functional correlates.

Colocalization of neurotransmitters, including neuropeptides and amines, in the same neuron of certain areas or well-defined nuclei of the central and peripheral nervous systems appears to be the rule rather than the exception. The coexistent neurotransmitters can be coreleased and interact at pre- and postsynaptic levels in a synergistic or antagonistic manner. Galanin is a recently isolated and characterized "gut-brain" peptide. It is colocalized with many neurotransmitters in both the central and the peripheral nervous systems. Among other regions in the central nervous system, galanin is present in neuronal perikarya of the septum and the hypothalamus. The dense accumulation of nerve terminals in the external zone of the median eminence suggests that galanin is an important peptide regulating neuroendocrine functions. Although most galanin and luteinizing hormone-releasing hormone (LHRH) neurons have a distinctly different morphology, a subset of galanin-immunoreactive perikarya in the diagonal band of Broca and the medial preoptic area, near the organum vasculosum of the lamina terminalis, have morphological features similar to those of LHRH neurons. By using double-labeling immunocytochemistry, we have found that in the preoptic region of the male rat brain approximately 15-20% of these "LHRH-like" galanin-immunoreactive neurons are also immunopositive for LHRH. Moreover, in the medial preoptic area and the diagonal band of Broca, some of the single-labeled LHRH cells are surrounded with galanin-immunoreactive nerve terminals, suggesting that LHRH perikarya have synaptic contacts with galanin-immunoreactive terminals. Additional studies indicated that galanin can readily enhance in vitro release of LHRH from nerve terminals in the median eminence. The observations that (i) galanin is coexpressed with LHRH, (ii) galanin seems to innervate LHRH-producing neurons, and (iii) galanin acts as a putative neurotransmitter to enhance the release of LHRH suggest that galanin should be considered an important regulator of LHRH-containing neurons and, therefore, of reproductive functions.

Ultrastructure and synaptic organization of luteinizing hormone-releasing hormone (LHRH) neurons in the anestrous ewe.

Electron microscopic immunocytochemistry was employed to examine the ultrastructure of luteinizing hormone-releasing hormone (LHRH) neurons and their projections to the median eminence in the sheep brain. LHRH perikarya in the preoptic area of anestrous ewes are less innervated than nonimmunoreactive cells in the same sections, but still receive numerous synaptic inputs, primarily onto distal dendrites and small somatic protuberances. Axon terminals synapsing upon LHRH cells contain a combination of clear spherical vesicles and larger dense-core vesicles. Interestingly, LHRH cell bodies and dendrites are almost entirely surrounded by glial processes. These processes intervene between immunoreactive elements that at a light microscopic level appear to be in contact with each other. Thus no evidence was obtained at the ultrastructural level for contacts among adjacent LHRH cells or dendrites in the preoptic area. Synaptic inputs onto LHRH cell bodies and dendrites appear to penetrate this glial sheath. In contrast to the absence of contacts among LHRH cells in the preoptic area, individual LHRH terminals in the median eminence are often clustered in direct plasma membrane contact. Comparisons between animals of differing reproductive status are needed to determine whether alterations in synaptic inputs, glial ensheathment, or LHRH-LHRH appositions, may underlie seasonal changes in the activity of LHRH neurons.

Ultrastructure of luteinizing hormone-releasing hormone (LHRH) neurons and their projections in the golden hamster

Seasonal breeding mammals exhibit a reversible annual cycle of fertility, and thus represent valuable models for investigating the organization of luteinizing hormone-releasing hormone (LHRH) neurons which mediate the neuroendocrine control of reproduction. Electron microscopic immunocytochemistry was used to examine the ultrastructure of LHRH neurons and their projections in a seasonal breeder, the golden hamster, housed under photoperiodic conditions which are reproductively stimulatory. LHRH perikarya in the diagonal band, medial septum, and preoptic area were bipolar or unipolar cells which possessed nuclei with prominent indentations and multiple nucleoli. LHRH reaction product within these cells was associated with neurosecretory granules and the rough endoplasmic reticulum (RER), particularly those portions of RER adjacent to the outer nuclear envelope. LHRH cell bodies and dendrites in the hamster received an extremely limited amount of synaptic input; of a total of twenty-five cells analyzed, we found only five instances of morphologically identified synapses onto immunoreactive dendrites. Occasionally close somatic appositions were seen between LHRH cells and non-immunoreactive neurons, and in one instance between two LHRH somas. In the organum vasculosum of the lamina terminalis (OVLT), LHRH fibers appeared as isolated strings of varicosities. In contrast, within the median eminence immunoreactive axonal profiles were frequently bundled together in fascicles although synaptic specializations were not observed between individual axons. The existence of contacts between LHRH axons in the median eminence, coupled with the extreme paucity of synaptic inputs onto LHRH neurons in this species, suggests that the median eminence may be a site where neural or hormonal signals could influence the coordinated release of LHRH from cells of dispersed origin.

Maturation of luteinizing hormone-releasing hormone (LHRH) and somatostatin (SRIF) neuronal systems in the hypothalamus of growing ewe lambs.

Using the immunoperoxidase method, neurons containing luteinizing hormone-releasing hormone (LHRH) and somatostatin (SRIF) were identified in the hypothalamus of growing ewe lambs between 3 days and 16 weeks of age. Both peptidergic neuronal systems were well developed in the early postnatal period. The centres producing LHRH were found to be situated in the anterior region of the hypothalamus and preoptic area. Immunoreactive (ir) LHRH perikarya in growing lambs were readily stained by the various anti-LHRH antibodies used and they were generally more numerous in young animals than in foetuses and adults. The concentration of irLHRH material stored in the median eminence (ME) increased with lamb age, reaching a maximum around 12 weeks of age. The centre producing somatostatin, situated in the anterior periventricular area of the hypothalamus, did not develop before the postpartum period. The irSRIF material in the ME was greatly depleted during the first neonatal days but regained its former level by 8 weeks of age. From 10 to 16 weeks of age, these stores in the ME were again depleted. The results show that the two neuronal systems investigated developed in a different way in the growing lamb. The secretory activity of these systems changed during subsequent periods of growth. The importance of these events in the processes of body growth and reproductive system maturation are still to be determined.

Neuropeptide Y stimulates the release of luteinizing hormone-releasing hormone from medial basal hypothalamus in vitro: modulation by ovarian hormones.

These studies investigated the effects of neuropeptide Y (NPY) on in vitro release of luteinizing hormone-releasing hormone (LHRH) from the medial basal hypothalmus (MBH) and tested whether ovarian steroids modulate the LHRH response to NPY. Ovariectomized rats were implanted with 20-mm-long Silastic capsules containing a low concentration of estradiol (E2) (150 micrograms/ml oil), a high concentration of E2 (250 micrograms/ml oil), or sesame oil vehicle. Additional animals received high-dose E2 capsules plus an injection of progesterone (15 mg) concomitantly. Two days later, individual MBH fragments were incubated in medium alone for a 30-min period to obtain the basal rate of LHRH release, followed by a second 30-min period in medium containing NPY or saline. Exposure to NPY (10(-6) M) increased the release of LHRH from MBH of ovarian hormone-treated, but not from hormonally untreated rats. The LHRH response was most pronounced from the MBH of rats treated with either high-dose E2 or E2 plus progesterone. The increase in LHRH release was also elicited by 10(-7) M, but not by 10(-8) M NPY concentrations, using MBH from E2 plus progesterone-treated rats. In addition, NPY markedly potentiated the KCl-evoked release of LHRH from MBH of ovariectomized, hormonally untreated or low-dose E2-treated rats, under conditions when there was little or no effect of NPY on the basal LHRH release. Further, the release of LHRH stimulated by NPY was not accompanied by increase in the release of norepinephrine or of dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

An immunohistochemical study of seasonal changes in luteinizing hormone-releasing hormone and vasotocin in the forebrain and the neurohypophysis of the toad, Bufo japonicus

Seasonal changes in luteinizing hormone-releasing hormone (LH-RH) and arginine vasotocin (AVT) were examined immunohistochemically in the toad forebrains and neurohypophyses. Strongly immunoreactive (ir-) LH-RH perikarya, from which dense ir-LH-RH fibers project to the median eminence, were localized in the medial septal nucleus and the nucleus of the diagonal band of Broca in the animals captured in the spring and the autumn. While, in the animals collected in the summer, ir-LH-RH perikarya and fibers were sparse, and immunoreactivity in the median eminences was weak. Artificially induced hibernation decreased the density of ir-LH-RH in the median eminence, in contrast with strong immunoreactivity in the control animals kept at room temperature. The amounts of ir-LH-RH in the median eminences of hibernating toads which were captured shortly before the breeding period varied conspicuously among individuals. The median eminences in migrating toads showed relatively weak LH-RH immunoreactivity. After the breeding, the immunoreactivity returned to the strong level that was observed in the spring and the autumn. These seasonal changes in ir-LH-RH seem to correspond to seasonal reproductive activity in this species. However, significant seasonal variations were not found in ir-AVT.

Testosterone raises LHRH levels exclusively in the median eminence of castrated rats.

Although LHRH is widely distributed in the diencephalon, previous studies show that testosterone (T) treatment for 72-96 h of castrated male rats raised LHRH levels only in the medial basal hypothalamus. In the present study, LHRH concentrations were analyzed in microdissected brain regions shown to contain LHRH perikarya and their projections to identify the discrete regions which may display this T-dependent accumulation of luteinizing hormone-releasing hormone (LHRH) and to study the temporal sequence of LHRH changes in those regions. Rats were killed at 12-hour intervals from 60 to 96 h after subcutaneous implantation of Silastic capsules containing T. Results showed that the physiological range of serum T levels attained by these implants suppressed LH release at all times, however, there was no immediate effect on LHRH concentrations in any region. In fact, out of the 9 regions in the preoptic-tuberal pathway examined, 8 regions displayed no change in LHRH concentrations at any time. On the other hand, for up to 84 h, LHRH concentrations in the median eminence region remained unchanged; an additional 12 h of T exposure significantly raised LHRH levels. These results suggest that this T-dependent accumulation of LHRH may arise either by de novo synthesis or by increase in the rate of processing of the precursor LHRH protein into the immunoreactive form within nerve terminals in the median eminence.