Nucleus Lateralis Tuberis Pars Research Articles

The Medio-Basal Hypothalamus as a Dynamic and Plastic Reproduction-Related Kisspeptin-gnrh-Pituitary Center in Fish

Kisspeptin regulates reproductive events, including puberty and ovulation, primarily via GnRH neurons. Prolonged treatment of prepubertal striped bass females with kisspeptin (Kiss) 1 or Kiss2 peptides failed to enhance puberty but suggested a gnrh-independent pituitary control pathway. Kiss2 inhibited, but Kiss1 stimulated, FShβ expression and gonadal development, although hypophysiotropic gnrh1 and gnrh receptor expression remained unchanged. In situ hybridization and immunohistochemistry on brains and pituitaries revealed a differential plasticity between the 2 kisspeptin neurons. The differences were most pronounced at the prespawning phase in 2 regions along the path of gnrh1 axons: the nucleus lateralis tuberis (NLT) and the neurohypophysis. Kiss1 neurons appeared in the NLT and innervated the neurohypophysis of prespawning males and females, reaching Lh gonadotropes in the proximal pars distalis. Males, at all reproductive stages, had Kiss2 innervations in the NLT and the neurohypophysis, forming large axonal bundles in the former and intermingling with gnrh1 axons. Unlike in males, only preovulatory females had massive NLT-neurohypophysis staining of kiss2. Kiss2 neurons showed a distinct appearance in the NLT pars ventralis-equivalent region only in spawning zebrafish, indicating that this phenomenon is widespread. These results underscore the NLT as important nuclei for kisspeptin action in 2 facets: 1) kisspeptin-gnrh interaction, both kisspeptins are involved in the regulation of gnrh release, in a stage- and sex-dependent manner, especially at the prespawning phase; and 2) gnrh-independent effect of Kiss peptides on the pituitary, which together with the plastic nature of their neuronal projections to the pituitary implies that a direct gonadotropic regulation is plausible.

Immunohistochemical localization of gonadotropin releasing hormones in the brain and pituitary gland of the Nile perch, Lates niloticus (Teleostei, Centropomidae)

In the present study we investigated the distribution of gonadotropin-releasing hormones (GnRH) in the brain of Lates niloticus and their association with different pituitary cell types using immunohistochemical techniques. We found immunoreactive (ir) chicken GnRH-II (cGnRH-II) and mammalian GnRH (mGnRH) as the main components of the GnRH-ir system within the brain of the Nile perch. The results indicate that mGnRH and cGnRH are localized in different neurons: mGnRH-ir perikaria were observed in the preoptic region particularly in the organum vasculosum laminae terminalis (OVLT) and in the nucleus lateralis tuberis pars posterior (NLTP) of the mediobasal hypothalamus. These cell bodies are located along a continuum of ir-fibers that could be traced from the olfactory nerve to the pituitary. mGnRH-ir fibers were detected in many parts of the brain (olfactory bulbs, ventral telencephalon, hypothalamus, and mesencephalon) and in the pituitary. cGnRH-ir cell bodies are restricted to the optic tract, but few scattered fibers could be detected in different parts of the brain. The pituitary exhibited very few cGnRH-II ir fibers, contrasting with an extensive mGnRH innervation. Moreover, mGnRH-ir fibers were targeting the three areas of the pituitary gland: rostral pars distalis (RPD), proximal pars distalis (PPD), and pars intermedia (PI). Double immunolabeling studies showed GnRH-ir fibers in close proximity with prolactin (PRL)- and adrenocorticotropic hormone (ACTH)-producing cells in the RPD, growth hormone (GH)-producing cells in the PPD, gonadotropins (GTHs)-producing cells in the PPD in the external border of the PI, and with somatolactin (SL)- and α-melanocyte stimulating hormone (α-MSH)-producing cells in the PI. Our results showed direct morphological evidence for a close association of GnRH-ir fibers with the different adenohypophysial cell types. These results suggest a multiple role of GnRH in the regulation of various pituitary hormones’ release.

Immunohistochemical Localization of C-RFamide, a FMRF-related Peptide, in the Brain of the Goldfish, Carassius auratus

Carassius RFamide (C-RFa) is a novel peptide found in the brain of the Japanese crucian carp. It has been demonstrated that mRNA of C-RFa is present in the telencephalon, optic tectum, medulla oblongata, and proximal half of the eyeball in abundance. Immunohistochemical methods were employed to elucidate the distribution of the peptide in the brain of the goldfish (Carassius auratus) in detail. C-RFaimmunoreactive perikarya were observed in the olfactory bulb, the area ventralis telencephali pars dorsalis and lateralis, nucleus preopticus, nucleus preopticus periventricularis, nucleus lateralis tuberis pars posterioris, nucleus posterioris periventricularis, nucleus ventromedialis thalami, nucleus posterioris thalami, nucleus anterior tuberis, the oculomotor nucleus, nucleus reticularis superior and inferior, facial lobe, and vagal lobe. C-RFa immunoreactive fibers and nerve endings were present in the olfactory bulb, olfactory tract, area dorsalis telencephali pars centralis and medialis, area ventralis telencephali, midbrain tegmentum, diencephalon, medulla oblongata and pituitary. However, in the optic tectum the immunopositive perikarya and fibers were less abundant. Based on these results, some possible functions of C-RFa in the nervous system were discussed.

Immunocytochemical Study on the Localization and Distribution of the Somatolactin Cells in the Pituitary Gland and the Brain ofOreochromis niloticus(Teleostei, Cichlidae)

Using specific antibody for chum salmon somatolactin (SL), immunocytochemical studies were employed to determine the distribution of this hormone in the pituitary gland and the brain ofOrechromis niloticus.The results indicated that the SL-immunoreactive (ir) cells are found in the pars intermedia (PI) of the pituitary gland. The SL-ir cells showed strong and specific immunoreactivity to anti-chum salmon SL. Moreover, SL-ir cells were found to be widely distributed in most brain regions. Most of the SL-ir cell bodies were scattered along a nearly continuous line extending posteriorly from the olfactory bulb to the medulla oblongata through the nucleus preopticus periventricularis, habenula, and midbrain tegmentum and ventral to the nucleus lateralis tuberis pars posterior through the nucleus preopticus basalis lateralis and organum vasculosum luminae terminalis. Also SL-ir cells were observed in the cerebellum. The synthetic and secretory activity of the SL-ir cells, in the pituitary and the brain, showed an increase during sexual maturation and spawning. The highly organized SL-containing system and the gradual stimulation of SL synthesis and release during sexual maturation and spawning ofO. nilotcussuggest that SL may be involved in the control of some steps of reproductive processes.

Bombesin-like immunoreactivity in the forebrain and pituitary and regulation of anterior pituitary hormone release by bombesin in goldfish.

The presence and distribution of bombesin (BBS)/gastrin-releasing peptide (GRP)-like immunoreactivity (IR) was examined in the goldfish pituitary and forebrain. BBS/GRP-like IR nerve fibres were consistently observed throughout the pituitary neurointermediate lobe (NIL); occasionally, BBS/GRP-like material was localized in cells and few fibres within the pars distalis. Within the goldfish forebrain, sparse, fine-beaded BBS/GRP-like IR fibres and few perikarya were detected in the preoptic hypothalamus. BBS/GRP-like IR material was also present in the ventro-posterior hypothalamus and the hypothalamic inferior lobes, and, in particular, within the nucleus lateral tuberis pars anterioris (NLTa) and nucleus lateral tuberis pars posterioris (NLTp), nucleus anterior tuberis (NAT), nucleus recessus lateralis (NRL), nucleus recessus posterioris (NRP), and the nucleus diffusus lobi inferioris (NDLI). Several BBS/GRP-like IR perikarya were observed in periventricular regions of the NLT, NRL, and NRP. Finally, BBS/GRP-like IR material was detected in the nucleus habenularis, the nucleus rotundus, several thalamic nuclei, and the optic tectum of the dorso-posterior diencephalon. The presence of BBS/GRP-like IR material within the preoptic hypothalamus, hypophysial stalk, and in the pituitary suggests that BBS-like peptides may regulate pituitary hormone release in fish. Perifusion of goldfish pituitary fragments with initial pulses of 0.1, 10, 100 or 1,000 nM BBS stimulated both growth hormone (GH) and gonadotropin (GtH-II) release. Repeated pulses of the same dose of BBS generally stimulated GH and GtH-II release to a similar magnitude. These studies provide initial evidence that BBS/GRP-like peptides are present within the central nervous system of teleost fish. The anatomical distribution of BBS/GRP-like IR in goldfish hypothalamic feeding center supports our previous report indicating a role for BBS in the central regulation of food intake in fish. Additionally, the presence of BBS/GRP-like IR material in the pituitary and brain areas associated with the regulation of anterior pituitary hormone secretion, as well as evidence demonstrating a direct action of BBS at the level of the goldfish pituitary to modify GH and GtH-II secretion, indicates that BBS/GRP-like peptides likely act to regulate pituitary hormone release in teleosts.

FMRFamide-like immunoreactivity in the brain and pituitary of the goldfish, Carassius auratus

The distribution of FMRFamide-like immunoreactivity was determined in the brain and the pituitary of the goldfish, Carassius auratus. Immunoreactive perikarya were observed in the olfactory nerve, nucleus entopeduncularis, nucleus anterioris periventricularis, nucleus posterioris periventricularis, lateral part of the nucleus lateralis tuberis pars posterioris, midbrain tegmentum, and medulla oblongata. Immunoreactive fibers were widely distributed in the brain, in particular in the ventral telencephalon and the hypothalamus. A few immunoreactive nerve fibers were observed in the pituitary. The findings are discussed in relation to male sexual behavior and the involvement of FMRFamide-like peptide in pituitary functions in the goldfish.

Immunohistochemical localization of thyrotropin-releasing hormone in the brain of carp, Cyprinus carpio

The localization of immunoreactive thyrotropin-releasing hormone (IR-TRH) in the forebrain and pituitary of carp was studied immunohistochemically using the peroxidase-antiperoxidase technique. In the hypothalamus. IR-TRH was present in the neuronal processes extending from the preoptic nucleus (NPO) to the nucleus recessus lateralis (NRL). Cell bodies appeared to be present in the inside of the medial NRL. Most of these neurons were fusiform and bipolar. Immunoreactive-beaded fibers streamed from the anterior part of the NRL toward the nucleus posterioris periventriculas and nucleus lateral tuberis pars posterioris. Vertical strands of the beaded fibers ran in the nucleus lateral tuberis pars anterioris. In the pituitary, the reaction product was found in the neural lobe, where intense immunoreactivity was evident along neural fibers entering the intermediate lobe. Staining could be detected only rarely in the anterior lobe. IR-TRH-beaded fibers were present in the olfactory stalk as well as in the caudal and inner parts of the olfactory bulb. In contrast to the high concentration of IR-TRH in the olfactory bulb, immunohistochemical data from this work indicated weak immunoreactivity in this region.

Relationship between serum growth hormone levels and the brain and pituitary content of immunoreactive somatostatin in the goldfish, Carassius auratus L

In this study, the relationships between endogenous brain and pituitary immunoreactive somatostatin (irSRIF) and circulating growth hormone (GH) levels in the goldfish were examined using two approaches. First, the amount of irSRIF in extracts of the pituitary gland and various brain regions was measured by radioimmunoassay several times throughout the year and was compared to serum GH levels at each time. The amounts of irSRIF in extracts of the pituitary gland, hypothalamus, and telencephalon were found to be inversely related to seasonal changes in serum GH levels, such that irSRIF was highest in these regions when serum GH levels were lowest (November and February). Conversely, irSRIF in these regions was lower in May, June, and July when serum GH levels were highest. These results suggest that endogenous irSRIF in the pituitary and forebrain may participate in the regulation of seasonal changes in serum GH levels in the goldfish. In extracts from other brain regions (thalamus + midbrain and cerebellum + medulla), some changes in the amount of irSRIF were observed among the various sample times, but these variations were not related to changes in serum GH levels. In a second set of experiments, the origin of irSRIF fibers innervating the goldfish pituitary gland was examined by using brain lesioning techniques to destroy regions of the forebrain known to contain irSRIF perikarya and fibers, and subsequently measuring the amount of irSRIF in the pituitary gland. Lesions in the preoptic area of the forebrain resulted in increased serum GH levels concomitant with a decrease in pituitary irSRIF content. This provides direct evidence that the preoptic area is the origin of a somatostatinergic projection inhibiting GH secretion from the goldfish pituitary. Lesions centered in the nucleus lateral tuberis (NLT) pars anterioris did not influence serum GH levels or the pituitary content of irSRIF. In contrast, more posterior lesions centered in the NLT pars posterioris (NLTp) resulted in a dramatic reduction in the amount of irSRIF in the pituitary. This suggests that the majority of irSRIF projections to the goldfish pituitary pass through the area destroyed by the lesion centered in the NLTp; it is also possible that perikarya within this area may be the origin of at least some of the irSRIF-containing fibers in the goldfish pituitary. Together, results from the present study provide evidence of a functional relationship between circulating levels of GH and endogenous brain and pituitary irSRIF in the goldfish.

Immunocytochemical localization of LH-RH in the brain and pituitary of the catfish, Clarias batrachus (Linn.)

An elaborate organization of luteinizing hormone-releasing hormone (LH-RH) immunoreactive (ir) cells and fibers was encountered in the olfactory system of Clarias batrachus. In addition to the it structures in the olfactory nerve, peripheral area of the olfactory bulb, and the medial olfactory tract (MOT), it cells and fibers were prominently seen in the lamellae of the olfactory organ. Perikarya showing varying degrees of intensity of immunoreaction were observed along the base of the forebrain in the nucleus preopticus basalis lateralis, nucleus preopticus periventricularis, nucleus preopticus, nucleus lateralis tuberis pars posterior, and the pituitary. Some cells were also noticed in the midbrain tegmentum. A well-defined system of it fibers from the MOT penetrated the telencephalon and curved dorsocaudally into the pars supracommissuralis above the anterior commissure (AC); while some fibers decussate in the AC, others extended posteriorly into the diencephalon. A fairly dense network of beaded it fibers was seen in the basal forebrain, conspicuous around the organum vasculosum laminae terminalis and caudally traceable as far as the neurohypophysis; some immunostained fibers appear to be directly contacting with the cells of the proximal pars distalis. Fibers were also witnessed in the optic chiasma and in the inner plexiform layer of the retina. Solitary fibers were noticed in certain circumscribed telencephalic areas, caudal hypothalamus, posterior commissure, midbrain tegmentum, cerebellum, and ventral medulla oblongata. The highly organized LH-RH containing system in C. batrachus is indicative of its elaborate role in synchronization of the reproductive processes and the environmental cues.

Ontogeny of centers containing luteinizing hormone-releasing hormone in the brain of platyfish (Xiphophorus maculatus) as determined by immunocytochemistry.

We have traced the development from birth to puberty of the ir-LHRH producing centers, the nucleus olfactoretinalis (NOR), nucleus praeopticus periventricularis (NPP) and nucleus lateralis tuberis pars posterior (NLT), in male sibling platyfish genetically determined by differing P alleles to mature at two different ages. In sexually immature fish of both genotypes ir-LHRH is first localized in the NOR in perikarya and neuronal fibers and in the NPP where it is limited to the fibers. At the onset of puberty in early maturing fish (11 weeks), ir-LHRH accumulates in perikarya and fibers of the NPP and NLT. Late maturing siblings first have ir-perikarya in the NPP and a few ir-fibers in the NLT at the same developmental stage but at a later age (25-26 weeks). Ir-perikarya are still not seen in the NLT in late-maturing fish even when maturation is complete. This pattern of a sequential development of the three ir-LHRH containing areas of the brain, which we refer to as a "cascade effect", is similar in early and late genotypes. It is directly correlated to stage of development and not to chronological age. It is clear that the appearance of LHRH producing brain centers precedes, and is presumably essential for, the completion of the development of pituitary gonadotrops and the subsequent maturation of the gonads. The functional significance of the NOR in puberty and reproduction and as a possible site of action for the P gene is discussed.

Long‐term effects of hypothalamic lesions on the pituitary and its target organs in the killifish Fundulus heteroclitus. I. Effects on the gonads, thyroid, and growth

AbstractIn three experiments a total of 23 sham‐operated and 63 brain‐lesioned killifish were maintained for 12½–16½ weeks under constant environmental conditions, with regular feeding. Regression of the testes and pituitary gonadotropes, seen in 13 fish, was correlated with lesions in the parvocellular region and/or tract of the nucleus lateral tuberis pars anterior (NLTa). Marked hypertrophy of the thyroid and pituitary thyrotropes, seen in nine fish, was associated with severe lesions of the nucleus anterior tuberis (NAT). A highly significant increase in growth rate, seen in four fish, was correlated with lesions in the nucleus preopticus (NPO), but there was no change in the pituitary somatotropes. Increased appetite, resulting from the presumed destruction of a satiety center, is a possible explanation.

Hypothalamic control of ACTH secretion in goldfish: II. Hypothalamic lesioning studies

Radiofrequency lesions that destroyed both the nucleus lateral tuberis pars anterior (NLTa) and rostral nucleus lateral tuberis pars posterior (NLTp) significantly suppressed the increase in serum corticosteroid levels (stress response) of goldfish subjected to a variety of stresses. Lesions placed in the posterior hypothalamus, dorsal telencephalon, immediately dorsal to the NLT, or small lesions in the NLT or NLTp had no effects on the stress response. These results suggest that the NLT is involved in the control of ACTH secretion in the goldfish and may be the source of a corticotrophin-releasing factor. Lesions of the nucleus preopticus (NPO) also significantly diminished the stress response to a number of stresses, suggesting a role of the neurohypophyseal peptides in the control of ACTH secretion in goldfish. Lesions of the epithalamus that destroyed the habenular nuclei resulted in an enhanced response to stress, suggesting that neural pathways located in this region may in some way inhibit ACTH secretion.

A light and electron microscopic study of the structure of the nucleus preopticus and nucleus lateral tuberis of the goldfish, Carassius auratus

On the basis of fine structure only one cell type could be identified in the nucleus preopticus. The nucleus lateral tuberis (NLT) contains three distinct cell types. Cell type 1, primarily in the NLT pars lateralis, is a large cell with many dense-core granules (DCG) 97.3 nm average diameter. Cell type II, primarily in the NLT pars anterioris, is smaller and contains few DCG, averaging 70.9 nm. Cell type III, found in the NLT pars posterioris, pars inferioris and posteriorly in the pars anterioris, is a small cell with DCG similar to type II cells. Cell type III additionally has large irregular granular bodies (dimensions up to 2 μm) that stain with aldehyde fuchsin and are visible with the light microscope. The possible role of the various cell types in controlling pituitary function is discussed.The juxta-ventricular border of the ependyma in the NPO and NLT regions is lined with cilia and microvilli, each with a regionalized distribution. In addition, there are cells with bleblike cytoplasmic extensions into the third ventricle in the ependyma layer in the NLT pars anterioris and pars posterions regions.

Hypothalamic control of prolactin and thyrotropin secretion in teleosts, with special reference to recent studies on the goldfish

Prolactin secretion in teleosts is regulated by two mechanisms. One is by the direct effect of blood osmolality on the prolactin cells. Support for this mechanism is based on studies in which decreases in osmotic pressure have been observed to stimulate prolactin release from cultured pituitaries. The second mechanism is by a prolactin release-inhibiting factor (PIF) from the hypothalamus. Aminergic neurons have an inhibitory effect on prolactin secretion. Lesioning studies in the goldfish have shown that the nucleus lateral tuberis pars lateralis is involved in the control of prolactin secretion. There are afferent pathways to the hypothalamus from the preoptic-thalamic region that tend to stimulate prolactin secretion, presumably by inhibiting hypothalamic PIF activity. Thyrotropin (TSH) secretion in teleosts is controlled by a thyrotropin release-inhibiting factor (TIF). Lesioning studies in the goldfish have shown that the nucleus lateral tuberis pars anterioris and pars posterioris are involved in the control of TSH secretion. Thyroxine has a negative feedback effect on both the pituitary and the hypothalamus. Studies on the effects of several synthetic neurohormones on thyroid gland activity in the goldfish indicate that somatostatin has TIF activity.

Effects of hypothalamic and thalamic lesions on prolactin secretion in goldfish ( Carassius auratus)

The effects of hypothalamic and thalamic lesions on serum and pituitary prolactin levels in goldfish were studied. A radioimmunoassay was used to measure prolactin levels. Lesions in the nucleus lateral tuberis (NLT) pars anterioris, NLT pars posterioris, NLT pars inferioris, nucleus anterior tuberis, or in the nucleus preopticus did not affect serum or pituitary polactin levels compared to sham or normal control groups. Lesions in the NLT pars lateralis caused a significant increase in serum prolactin, but had no effect on pituitary prolactin levels. This suggests that the NLT pars lateralis is the origin of a factor that normally inhibits prolactin release from the pituitary. Large lesions that destroyed the medial thalamic and anterior hypothalamic region dorsal to the NLT caused a significant decrease in serum prolactin, but had no significant effect on pituitary prolactin levels. It is suggested that the lesions in this region may have interrupted neural afferents to the NLT pars lateralis that normally inhibit secretion of a prolactin inhibitory factor.

Hypothalamic control of thyroid gland activity and gonadal activity in the goldfish, Carassius auratus

A stereotaxic method for placement of electrodes in the goldfish hypothalamus was described. Electrolytic lesions in the nucleus preopticus (NP), or bilaterally in the NP-hypophyseal tract, did not effect thyroid activity or gonadal activity. Lesions that destroyed the nucleus lateralis tuberis (NLT) pars anterior in the region anterior of the pituitary stalk made the animals hyperthyroid, but they had no effect on gonadal activity. Lesions that destroyed the NLT pars posterior and the posterior part of the NLT pars anterior significantly increased thyroid activity and significantly decreased gonadal activity. Lesions in the pituitary stalk, without destruction of any nuclear region of the hypothalamus, also induced hyperthyroidism and decreased gonadal activity. Lesions in the posterior hypothalamus, dorsal hypothalamus, and epithalamus had no significant effects in terms of these parameters. The results provide direct evidence for hypothalamic control of thyroid gland activity in the goldfish. The hyperthyroid response of some of the groups of lesioned fish indicates that this control is mediated by a factor which normally inhibits the secretion of thyrotropin by the pituitary gland and may be called the thyrotropin inhibitory factor (TIF). Viewed together, the lesions identify the NLT pars anterior and NLT pars posterior as the TIF hypophysiotropic center. The results provide direct evidence also for hypothalamic control of gonadal activity in the goldfish. This control is mediated by a factor which stimulates the secretion of gonadotropin and may be called the gonadotropin-releasing factor (GFR). The lesions identify the NLT pars posterior and the posterior part of the NLT pars anterior as the GRF hypophysiotropic center.