Localization of avian LHRH-immunoreactive neurons in the hypothalamus of the domestic fowl,Gallus domesticus,and the Japanese quail,Coturnix coturnix

The localization of LHRH-containing perikarya and nerve fibers in the hypothalami of the domestic fowl and Japanese quail was investigated by means of the specific immunoperoxidase ABC method, using antisera against chicken LHRH-I ([Gln8]-LHRH), chicken GnRH-II ([His5-Trp7-Tyr8]-LHRH[2-10]) and mammalian LHRH ([Arg8]-LHRH). Chicken LHRH-I-immunoreactive perikarya were sparsely scattered in the nucleus preopticus periventricularis (POP), nucleus filiformis (FIL) and nucleus septalis medialis (SM), and in bilateral bands extending from these nuclei into the septal area in both species. A few reactive perikarya were also observed in the nucleus accumbens (Ac) and lobus parolfactorius (LPO). Numerous cLHRH-I-immunoreactive fibers were widely scattered in the preoptic, septal and tuberal areas, and were densely concentrated in the external layer of the median eminence and in organum vasculosum of the lamina terminalis (OVLT) in both species. Anti-mammalian LHRH serum cross-reacted weakly with perikarya and fibers immunoreactive to anti-cLHRH-I serum in normal chicken and quail. Anti-cGnRH-II[2-10] serum immunoreacted with magnocellular neurons distributed in the rostral end of the mesencephalon along the midline close to the nervus oculomotorius (N III). These perikarya were apparently different from cLHRH-I immunoreactive neurons. No immunoreactive cells and fibers against anti-cGnRH-II[2-10] were observed in the hypothalamus and median eminence of the chicken or quail. Anti-cGnRH-II[2-10] bound specifically with cGnRH-II.(ABSTRACT TRUNCATED AT 250 WORDS)     

Primary olfactory projections and the nervus terminalis in the African lungfish: implications for the phylogeny of cranial nerves

Primary olfactory and central projections of the nervus terminalis were investigated by injections of horseradish peroxidase into the olfactory epithelium in the African lungfish. In addition, gonadotropin-releasing hormone (GnRH) immunoreactivity of the nervus terminalis system was investigated. The primary olfactory projections are restricted to the olfactory bulb located at the rostral pole of the telencephalon; they do not extend into caudal parts of the telencephalon. A vomeronasal nerve and an accessory olfactory bulb could not be identified. The nervus terminalis courses through the dorsomedial telencephalon. Major targets include the nucleus of the anterior commissure and the nucleus praeopticus pars superior. some fibers cross to the contralateral side. A few fibers reach the diencephalon and mesencephalon. No label is present in the "posterior root of the nervus terminalis" (= "Pinkus's nerve" or "nervus praeopticus"). GnRH immunoreactivity is lacking in the "anterior root of the nervus terminalis," whereas it is abundant in nervus praeopticus (Pinkus's nerve). These findings may suggest that the nervus terminalis system originally consisted of two distinct cranial nerves, which have fused-in evolution-in most vertebrates. Theories of cranial nerve phylogeny are discussed in the light of the assumed "binerval origin" of the nervus terminalis system.     

Gonadotropin releasing hormone (GnRH) neurons project to growth hormone and somatolactin cells in the steelhead trout

Analysis of gene expression using gonadotropin-releasing hormone (GnRH) antisense oligonucleotide confirmed by immunocytochemical localization the occurrence of GnRH neurons along the nervus terminalis in the steelhead trout (Oncorhynchus mykiss). Double-label immunocytochemistry revealed the distribution of mammalian (m), salmon (s) and chicken II (cII)-type GnRHs and various pituitary hormones. Both sGnRH and mGnRH appeared to be colocalized in the same cells of the nervus terminalis. Chicken GnRH II-immunoreactivity was found only in fibers and terminals. In the younger fish [73 and 186 days after fertilization (DAF)] GnRH neurons were seen rostral to the olfactory bulb. A novel GnRH ganglion, along the nervus terminalis, was found at the cribriform bone (gCB). A few non-immunoreactive rounded cells were seen among the GnRH neurons. A second smaller ganglion was seen at the most rostrally located part of the ventromedial olfactory bulb (gROB). In the older fish (850 DAF) GnRH neurons were also observed in the basal forebrain. A small group of neurons (2–3 cells), at the caudoventromedial border of the olfactory bulb, formed the ganglion terminale. Occasionally isolated GnRH-immunoreactive cells were seen at the base of the olfactory epithelium, along the ventromedial margins of the olfactory nerve. GnRH-immunoreactive and GnRH mRNA expressing neurons were absent from midbrain regions at the ages observed. GnRH-immunoreactive fibers were present only in older fish. The pattern of distribution of fibers that were immunoreactive to all three forms of GnRH was identical. Fibers were seen along the medial side of the olfactory nerve, throughout the brain and in the pituitary, associated with growth hormone and somatolactin cells. This morphological study shows that molecular forms of GnRHs might have multiple functions.     

Immunocytochemical distribution of FMRFamide-like substance in the brain of the cloudy dogfish,Scyliorhinus torazame

Summary The distribution of the molluscan cardioexcitatory tetrapeptide FMRFamide (Phe-Met-Arg-Phe-NH₂) in the brain of the cloudy dogfish, Scyliorhinus torazame, was examined by immunocytochemistry. FMRFamide-like immunoreactivity was demonstrated to occur extensively in various regions of the dogfish brain, except for the corpus cerebelli. Immunoreactive neuronal perikarya were located in the ganglion of the nervus terminalis, the preoptic area, and the hypothalamic periventricular gray matter consisting of the nucleus medius hypothalamicus, the nucleus lateralis tuberis, and the nucleus lobi lateralis. some of the immunoreactive cells in the hypothalamus were identified as cerebrospinal fluid-contacting neurons. The bulk of the immunostained fibers in the nervus terminalis penetrated into the midventral portion of the telencephalon and ran dorsocaudally toward the basal telencephalon and hypothalamus, showing radial projections or ramifications. The labeled fibers were abundant in the midbasal part of the telencephalon and in the hypothalamus, where some fibers were found in loose networks around the cell bodies of the nucleus septi and hypothalamic periventricular nuclei. The fibers demonstrated in the hypothalamus terminated around the vascular wall of the primary capillary plexus of the median eminence or penetrated deeply into the pars intermedia of the hypophysis. These results suggest that, in the dogfish, an FMRFamide-like substance participates in the regulation of adenohypophysial function. This molecule may have a role as a neurotransmitter and/or neuromodulator in the central nervous system.     

Development of the hypothalamic luteinizing hormone-releasing hormone-containing neuron system in the rat: in vivo and in transplantation studies

The development of the hypothalamic LHRH-containing neuron system was immunohistochemically investigated in vivo and in tissue transplantation using rat embryos aged from 12.5 to 17.5 days of gestation. The sera used were generated against rat gonadotropic hormone-releasing hormone-associated peptide (28-56) (rGAP) and LHRH. Immunoreaction for rGAP was first found in cells migrated from and in the vomeronasal organ on Days 13.5 and 14.5 of gestation. Immunoreactive cells seem to ascend along the terminal nerves, reaching the medial surface of the forebrain vesicles. Subsequently the cells occurred in the septum and further into their final position in the septopreoptic-diagonal band area on Days 16.5-17.5 of gestation; during this traverse the cells become secretory neurons after changes in morphology and in behavior. Intraventricular transplantation revealed that nasal epithelia of Day 12.5 embryos raised only a few cells immunoreactive both for LHRH and rGAP, but a great number of immunoreactive cells and fibers in the presence of the medial basal hypothalamus (MBH). The fibers formed a median eminence-like structure together with dense capillary plexus that had grown in the cografted MBH. The same phenomenon was apparently observed in the grafts obtained from older embryos of gestation, but not in the combined grafts of the anterior septum and the nasal epithelium or the MBH. We conclude that hypothalamic LHRH neurons originate from the nasal placode and acquire secretory behavior in the presence of the MBH.     

Development of the hypothalamic luteinizing hormone-releasing hormone-containing neuron system in the rat: In vivo and in transplantation studies

The development of the hypothalamic LHRH-containing neuron system was immunohistochemically investigated in vivo and in tissue transplantation using rat embryos aged from 12.5 to 17.5 days of gestation. The sera used were generated against rat gonadotropic hormone-releasing hormone-associated peptide (28–56) (rGAP) and LHRH. Immunoreaction for rGAP was first found in cells migrated from and in the vomeronasal organ on Days 13.5 and 14.5 of gestation. Immunoreactive cells seem to ascend along the terminal nerves, reaching the medial surface of the forebrain vesicles. Subsequently the cells occurred in the septum and further into their final position in the septopreoptic-diagonal band area on Days 16.5–17.5 of gestation; during this traverse the cells become secretory neurons after changes in morphology and in behavior. Intraventricular transplantation revealed that nasal epithelia of Day 12.5 embryos raised only a few cells immunoreactive both for LHRH and rGAP, but a great number of immunoreactive cells and fibers in the presence of the medial basal hypothalamus (MBH). The fibers formed a median eminence-like structure together with dense capillary plexus that had grown in the cografted MBH. The same phenomenon was apparently observed in the grafts obtained from older embryos of gestation, but not in the combined grafts of the anterior septum and the nasal epithelium or the MBH. We conclude that hypothalamic LHRH neurons originate from the nasal placode and acquire secretory behavior in the presence of the MBH.     

Distribution of LHRH in the rat and mouse brain with special reference to the tanycytes

Summary The distribution of luteinizing hormone-releasing hormone (LHRH) was studied in the rat and mouse brain by means of light and electron microscopic immunohistochemistry using the peroxidase-antiperoxidase method. An immunoreactive product to LHRH antiserum was found near the blood vessels of the vascular organ of the lamina terminalis. In the arcuate nucleus-median eminence region, an immunoreactive material occurred bilaterally in the hypothalamic tissue around the tuberoinfundibular sulci. Electron microscopy revealed that immunoreactive fibers observed light microscopically contain numerous granules 100–130 nm in diameter. No immunoreactive product was located in the tanycytes of the median eminence, the perikarya of hypothalamic neurons, and the parenchyma of several circumventricular organs (subfornical organ, subcommissural organ, pineal organ, area postrema).Supported by grants from the Ministry of Education of Japan and the Ford Foundation     

Distribution of neuropeptide Y-like immunoreactivity in the brain and hypophysis of the cloudy dogfish,Scyliorhinus torazame

Summary Using a specific antiserum raised against synthetic neuropeptide Y, we examined the localization of immunoreactivity in the brain and hypophysis of the cloudy dogfish, Scyliorhinus torazame, by the peroxidase-antiperoxidase method. Immunoreactive perikarya were demonstrated in the ganglion of the nervus terminalis, the dorsocaudal portions of the pallium dorsale, the basal telencephalon, and the nucleus lateralis tuberis and the nucleus lobi lateralis in the hypothalamus. Labeled perikarya were also found in the tegmentum mesencephali, the corpus cerebelli, and the medulla oblongata. Some of the immunoreactive neurons in the hypothalamus were of the CSF-contacting type. The bulk of the labeled fibers in the nervus terminalis ran toward the basal telencephalon, showing radial projections and ramifications. Large numbers of these fibers coursed into the nucleus septi caudoventralis and the nucleus interstitialis commissurae anterioris, where they became varicose and occasionally formed fine networks or invested immunonegative perikarya. In the diencephalon, immunoreactive fibers were observed throughout the hypothalamus, e.g., in the pars neurointermedia of the hypophysis, the subependymal layer of the lobus inferior hypothalami, and in the neuropil of the posterior (mammillary) recess organ. Labeled fibers were scattered throughout the rest of the brain stem and were also seen in the granular layer of the cerebellum. These results suggest that, in the dogfish brain, neuropeptide Y or a related substance is involved in a variety of physiological processes in the brain, including the neuroendocrine control of the hypophysis.     

Olfactory and vomeronasal projections and the pathway of the nervus terminalis in ten species of salamanders

Summary Primary olfactory and vomeronasal projections as well as the pathway of the nervus terminalis were studied in 10 representative species of salamandrid and plethodontid salamanders by means of injections of horseradish peroxidase and examination of whole-mount preparations. Olfactory projections are very similar in the different urodeles, but vomeronasal projections differ in shape and number of termination fields. Whereas the direct-developing Plethodontini and Bolitoglossini reveal only one or two fields, the salamandrid species and the members of the plethodontid tribes Desmognathinae and Hemidactyliini, all possessing an aquatic larval stage, exhibit several vomeronasal projection fields. In all species examined centrifugal axons of the nervus terminalis leave the olfactory projection area ventrocaudally and terminate in the preoptic region and the hypothalamus.Abbreviations COM. ANT commissura anterior - DGL displaced glomeruli - HY hypophysis - HYTH hypothalamus - LF lateral fibers of the nervus terminalis - ME medulla oblongata - MF medial fibers of the nervus terminalis - Nt nervus terminalis - Npo nucleus praeopticus     

LHRH-systems in the brain of the golden hamster

Summary Vibra tome sections of male hamster brains were treated immunohistochemically with LHRH antiserum, and the anatomical distribution of LHRH immunoreactive cells and nerve fibers was assessed. LHRH-cell bodies are found in the ventral hypothalamus that includes its preoptic, anterior and central parts, in the septum, the olfactory tubercle, the main and accessory olfactory bulb, and the prepiriform cortex. In addition, extracerebral LHRH-neurons and ganglia exist in LHRH-positive nerves at the ventromedial surface of the olfactory tubercle and bulb as well as in olfactory nerves. Dense networks of LHRH-immunoreactive fibers are found in all regions where LHRH-cell bodies exist. Intraseptal connections reach the organum vasculosum of the lamina terminalis, the subfornical organ, and the lateral ventricle. Dorsolateral projections from the septum can be traced via the fimbria hippocampi and alveus to the ventral hippocampus, via the stria terminalis to the amygdala and piriform cortex. Ventrolateral projections extend from the level of the olfactory tubercle and preoptic-anterior hypothalamic area via the ventral amygdalofugal pathway to the prepiriform and piriform cortex as well as the amygdala. Dorsal supracallosal projections via the stria longitudinalis are seen in the induseum griseum and the cingulate cortex. Caudal efferents reach the habenula, interpeduncular nucleus, midbrain raphe, and central gray of the rostral fourth ventricle via the stria medullaris and fasciculus retroflexus and by a ventral projection via the periventricular and subventricular hypothalamus. A major portion of this ventrocaudal projection gives rise to a dense network in the median eminence. Anatomical relationships of LHRH-fibers to certain regions of the inner ventricular and outer brain surface are noted.Postdoctoral fellow of the Deutsche ForschungsgemeinschaftSupported by US PHS grant NS09914 and NRCHD grant HD03110     

The LHRH neuronal system in female rats: relation to the medial preoptic nucleus

Previously we have found that small lesions confined to the medial preoptic nucleus (MPN) or the suprachiasmatic nucleus (SCN) blocked the cyclic release of gonadotropins in the female rat, inducing a persistent estrous state. Since the MPN is located just caudal to the organum vasculosum of the lamina terminalis (OVLT) where LHRH cell bodies are most concentrated, we applied an immunocytochemical technique to examine the possibility that the lesions had simply disrupted LHRH neurons or fibers. Using a new anti-LHRH provided by Dr. V. D. Ramirez, we found that the distribution pattern of immunoreactive LHRH cell bodies and fibers was similar to that previously reported, although the staining was more intense and extensive with low background. There was no concentration of LHRH cell bodies and fibers in the MPN or SCN and, in fact, these nuclei generally showed a lower density of stained elements than did surrounding tissue. In persistent estrous animals with lesions confined to the MPN there was no detectable reduction of stained fibers in the median eminence. These results, along with the results of other workers, suggest that persistent estrus following lesions of the MPN or SCN is not due to reduction of LHRH neurons or fibers. Rather, they support the hypothesis that these nuclei are critical for triggering the ovulatory release of LHRH.     

Organization of LHRH cells: differential apposition of neurotensin, substance P and catecholamine axons

A wealth of evidence suggests that catecholamines (particularly norepinephrine) influence gonadotropin secretion via a direct interaction with the LHRH neurons. Neuropeptides such as neurotensin (NT) and substance P (SP) are likewise implicated in the control of LHRH secretion, based on pharmacological and preliminary anatomical studies. Since sub-populations of LHRH neurons project to areas of the brain other than the median eminence, a detailed analysis of the topography of axonal interactions of catecholamines (CA), substance P and neurotensin with LHRH cells was conducted in adult male mice using dual immunocytochemical techniques. An analysis of the patterns of apparent contact of NT or SP axons on LHRH cells as determined by close apposition of immunoreactive axons to LHRH cells when viewed under a light microscope at high magnification revealed that the density of NT or SP axons was not a reliable index of the degree of contact; in many locations, NT and SP had similar densities yet a greater portion of the LHRH cells appeared contacted by SP than NT. NT axons were in close contact with up to one-third of the LHRH cells. Analysis of the location of these "contacted" cells did not reveal a discrete subnucleus controlled by NT. Rather, the NT-contacted cells were scattered throughout the LHRH cell field. Interactions of LHRH cells with SP axons were likewise uniform throughout most of the LHRH cell field, with the exception of the most anterior portion of the field. In the anterior septum, few SP axons appeared to contact LHRH cells. Elsewhere, most of the LHRH cells were in contact with SP axons. For the CAs, the fiber density in the regions of the LHRH cells was uniformly moderate, yet the pattern of cells contacted showed variation across the LHRH cell field, with most of the "contacted" cells located near the OVLT and medial preoptic area. These data suggest that LHRH cells may be differentially regulated by NT, SP and the CAs.     

Distribution of FMRFamide-like immunoreactivity in the forebrain of the catfish, Clarias batrachus (Linn.).

The anatomical distribution of FMRFamide-like immunoreactivity in the forebrain and pituitary of the catfish, Clarias batrachus, was investigated. Immunoreactive cells were observed in the ganglion cells of the nervus terminalis (NT) and in the medial olfactory tracts. In the preoptic area, FMRFamide-containing perikarya were restricted to the lateral preoptic area, paraventricular subdivision of the nucleus preopticus, nucleus suprachiasmaticus and nucleus preopticus periventricularis posterior. In the postoptic area, some cells of the nucleus postopticus lateralis and nucleus of the horizontal commissure showed moderate immunoreactivity. In the tuberal area, immunoreactivity was observed in few cells of the nucleus hypothalamicus ventralis and nucleus arcuatus hypothalamicus (NAH). Nucleus ventromedialis thalami was the only thalamic nucleus with FMRFamide immunoreactivity. Immunoreactive processes were traceable from the NT through the medial as well as lateral olfactory tracts into the telencephalon and the area ventralis telencephali pars supracommissuralis (Vs). Further caudally, the immunoreactive fibers could be traced into discrete areas, including habenular and posterior commissures, neurohypophysis and pituitary; isolated fibers were also observed in the pineal stalk. A loose network of immunoreactive processes was observed in the olfactory bulbs and the entire telencephalon, with higher densities in some areas, including Vs. A dense plexus of immunoreactive fibers was seen in the pre- and postoptic areas and around the paraventricular organ, while relatively few were observed in the thalamus. A high concentration of fiber terminals was found in the caudal tuberal area.     

Substance P-, F8Famide-, and A18Famide-like immunoreactivity in the nervus terminalis and retina of the goldfish Carassius auratus

We re-investigated the occurrence of substance P-like immunoreactivity in the retina of the goldfish Carassius auratus using antisera to substance P and other tachykinins. Most antisera labelled a previously described single class of mono-stratified amacrine cells arborizing in layer 3 of the inner plexiform layer. Preabsorption experiments showed that these amacrine cells contained at least one tachykinin-like peptide. One antiserum (INC 353) to substance P labelled not only these amacrine cells but also fibres in layer 1 of the inner plexiform layer and fibres in the optic nerve. These fibres were identified as retinopetal projections of the nervus terminalis, in part because of colocalized labelling with antisera against gonadotropin-releasing hormone and FMRFamide. Preabsorption experiments showed that the substance P-immunoreactive material in the nervus terminalis was not substance P or any other typical tachykinin. Labelling of the nervus terminalis with INC 353 was blocked by preabsorption with two bovine FMRFamide-like peptides, F8Famide and A18Famide, which contain a substance P(4–7)-like region. Antisera to F8Famide and A18Famide strongly labelled ganglia of the nervus terminalis and retinopetal fibres. We suggest that labelling of the nervus terminalis by antisera to substance P and FMRFamide occurs because of homologies between these antigens and a non-tachykinin, endogenous peptide that is similar to F8Famide and A18Famide.     

Ependymoneuronal specializations between LHRH fibers and cells of the cerebroventricular system

Summary Light-and electron-microscopic immunocytochemistry (LM-ICC and EM-ICC) were used to visualize luteinizing hormone-releasing hormone (LHRH) in fibres associated with ventricular ependyma and tanycytes of the median eminence. LM-ICC suggests that LHRH fibers appear to enter the third ventricle. However, with EM-ICC, LHRH fibers are in fact found within ependymal canaliculi formed by adjacent ependymal cells. The canaliculi contain other myelinated and unmyelinated axons in addition to immunoreactive LHRH fibers. Thin slips of ependymal and tanycyte processes project into the canaliculi and enclose axons to varying degrees. At the median eminence many LHRH fibers bend sharply downwards from their ventricular course and travel with tanycytic processes towards their common destination — the perivascular space of the hypophysial-portal vascular system. Here, EM-ICC reveals that LHRH fibers closely contact basal processes of tanycytes. Lateral processes from tanycytes form glioplasmic sheaths which surround some individual LHRH fibers. A few LHRH terminals contact the perivascular space directly but more often are separated from the perivascular space by intervening glia. It is hypothesized that: (1) glia of this region responds to the physiological state of the animal and may determine the degree of LHRH secretion by varying the extent of glial investment of LHRH terminals; and (2) may play a role during development by providing direction and support for LHRH fibers similar to that described for radial and other glial cells.     

Immunocytochemical localization of the gonadotropin-releasing hormone-associated peptide portion of the LHRH precursor in the hypothalamus and extrahypothalamic regions of the rat central nervous system

Summary The gonadotropin-releasing hormone-associated peptide (GAP) of the LHRH precursor and the decapeptide LHRH were localized in the rat brain by immunocytochemistry in 12 to 18-day-old animals, by use of thick Vibratome sections and nickel intensification of the diaminobenzidinereaction product. Our results indicate that the GAP portion of the LHRH precursor is present in the same population of neurons that contain LHRH in the rat brain. An important difference observed was that the GAP antiserum, in contrast to LHRH antisera, stained several perikarya in the medial basal hypothalamus. GAP-immunoreactive perikarya were observed in the following regions: the olfactory bulb and tubercle, diagonal band of Broca, medial septum, medial preoptic and suprachiasmatic areas, anterior and lateral hypothalamus, and several regions of the hippocampus. In addition to the preoptico-terminal and the septopreoptico-infundibular pathways, we also observed GAPimmunopositive processes in several major tracts and areas of the brain, including the amygdala, stria terminalis, stria medullaris thalami, fasciculus retroflexus, stria longitudinalis medialis, periventricular plexus, periaqueductal gray of the mesencephalon and extra-cerebral regions, such as the nervus terminalis and its associated ganglion. These results confirm the specificity of previous immunocytochemical results obtained with antisera to LHRH. The presence of GAP immunoreactivity in nerve terminals of the rat brain indicates that GAP or a GAP-like peptide is located in the proper site to serve as a hypophysiotropic substance and/or as a neurotransmitter or neuromodulator.Supported by AKA No. 419427, OTKA No. 104, OKKFT 2.1.5.1 and NSF No. INT-8602688     

FMRFamide-like immunoreactivity in the brain and pituitary of the teleost. Eigenmannia lineata (Gymnotiformes)

The distribution of cells immunoreactive for the molluscan tetrapeptide FMRFamide in the brain and the pituitary of Eigenmannia was investigated immunohistochemically by the use of the peroxidase-antiperoxidase (PAP) technique and unlabelled antibodies. FMRFi neurons were located in the ganglion of the nervus terminalis at the rostroventral side of the bulbus olfactorius. FMRFi perikarya were also found in a dorsomedial diencephalic nucleus, in the nucleus ventromedialis, in some liquor-contacting neurons of the nucleus lateralis tuberis and of the nucleus recessus lateralis and posterior. The perikarya of the midbrain pre-pacemaker nucleus were only weakly immunoreactive for FMRFamide while large FMRFi neurons (T-cells) occurred in lamina VI of the torus semicircularis, in the brain stem, in dorsal and medial layers of the lobus lineae lateralis posterior (LLLp) and in the medullary electric organ pacemaker nucleus (pm). FMRFi fibers and nerve endings were found in the bulbus olfactorius, in medial areas of the telencephalon, and rather densely in the rostral diencephalon. Ventrocaudally to most of the hypothalamic nuclei the occurrence of immunoreactive fibres increased; many coursed to the pituitary through the pituitary stalk. FMRFi fibres also appeared in the deep layers of the tectum opticum, in the torus semicircularis, in the medial and lateral medulla and below the pacemaker nucleus. Wherever FMRFamide-immunoreactivity occurred fibres and nerve endings could be found in close contact with blood vessels.     

Alterations in hypothalamic content of luteinizing hormone-releasing hormone associated with pineal-mediated testicular regression in the golden hamster

The adult male golden hamster will undergo testicular regression when exposed to a short photoperiod, blinding, or late afternoon injections of melatonin. The present study was conducted to compare the effects of all three treatments on serum gonadotropin levels and testicular weights, and to evaluate the effects of these treatments on hypothalamic content of both immunoreactive and bioactive luteinizing hormone-releasing hormone (LHRH) levels. Hamsters were blinded (BL), exposed to a short photoperiod (SP), or received daily injections of melatonin (MEL) for 15 wk. Each treatment (BL, SP, MEL) induced a temporally similar decline in serum luteinizing hormone (LH), serum follicle-stimulating hormone (FSH), and testicular weight. Spontaneous recrudescence occurred earliest in the MEL group, with serum gonadotropins and testicular weight returning to normal by 15 wk. The SP group exhibited recovery of serum gonadotropins but not testicular weight by 15 wk. The BL group demonstrated partial recovery of serum FSH levels by 15 wk, with no recovery in either serum LH or testicular weight. Each treatment group demonstrated increased hypothalamic content of immunoreactive LHRH which was temporally correlated with the decreases of serum gonadotropins. Additionally, the MEL and SP groups demonstrated decreased immunoreactive LHRH levels during spontaneous recrudescence. Extracts of hypothalami from all treatment groups were bioactive on control hamster pituitary cells. These results indicate that there are temporal differences among the three common treatments and that these differences are manifested in serum gonadotropins, testicular weight and hypothalamic LHRH. Hypothalamic LHRH levels determined by radioimmunoassay and bioassay show periods of increase and decrease which coincide with periods of altered serum gonadotropin levels in all groups.     

Presence and distribution of LHRH- and alpha-MSH-like immunoreactive nerve fibers in the epithalamus of the sheep

The presence of luteinizing-hormone-releasing hormone (LHRH)-like and alpha-melanocyte-stimulating hormone (alpha-MSH)-like immunoreactive fibers, nerve terminals or cellular elements in the pineal gland of the sheep has been investigated by immunohistochemistry. No LHRH-or alpha-MSH-like immunoreactive fiber, nerve terminals or cellular elements have been demonstrated in the pineal organ of the sheep. However, LHRH- and alpha-MSH-like immunoreactive fibers are present in the posterior commissure. Immunoreactive LHRH and alpha-MSH nerve endings are evident in the medial and lateral habenular nuclei. Discrepancies with the results obtained in other mammals are indicative of species differences in the distribution of LHRH- and alpha-MSH-like immunoreactive material in the pineal region.