Adrenocorticotropin production by the intermediate lobe of the rat pituitary. An electron microscopic-immunohistochemical study

Applications of plastic embedding to electron microscopic immunocytochemistry and in situ hybridization in observations of production and secretion of peptide hormones

Plastic embedding has been used to localize various antigens in conjunction with immunohistochemistry. Peptide hormones have been among the antigens that have been studied extensively. Recent application of water-soluble plastics such as LR White and Lowicryl has extended the ranges of detectable antigens and enabled the observation of antigen-antigen or mRNA-antigen combinations. This review article deals with technical aspects, procedures, and applications in endocrine cells.

Corticotropin-releasing factor receptors: physiology, pharmacology, biochemistry and role in central nervous system and immune disorders

Corticotropin-releasing factor (CRF) plays a major role in coordinating the endocrine, autonomic, behavioral and immune responses to stress through actions in the brain and the periphery. CRF receptors identified in brain, pituitary and spleen have comparable kinetic and pharmacological characteristics, guanine nucleotide sensitivity and adenylate cyclase-stimulating activity. Differences were observed in the molecular mass of the CRF receptor complex between the brain (58,000 Da) and the pituitary and spleen (75,000 Da), which appeared to be due to differential glycosylation of the receptor proteins. The recently cloned CRF receptor in the pituitary and the brain (designated as CRF1) encodes a 415 amino acid protein comprising seven putative membrane-spanning domains and is structurally related to the calcitonin/vasoactive intestinal peptide/growth hormone-releasing hormone subfamily of G-protein-coupled receptors. A second member of the CRF receptor family encoding a 411 amino acid rat brain protein with approximately 70% homology to CRF1 has recently been identified (designated as CRF2); there exists an additional splice variant of the CRF2 receptor with a different N-terminal domain encoding a protein of 431 amino acids. In autoradiographic studies, CRF receptors were localized in highest densities in the anterior and intermediate lobes of the pituitary gland, olfactory bulb, cerebral cortex, amygdala, cerebellum and the macrophage-enriched zones and red pulp regions of the spleen. CRF can modulate the number of CRF receptors in a reciprocal manner. For example, stress and adrenalectomy increase hypothalamic CRF secretion which, in turn, down-regulates CRF receptors in the anterior pituitary. CRF receptors in the brain and pituitary are also altered as a consequence of the development and aging processes. In addition to a physiological role for CRF in integrating the responses of the brain, endocrine and immune systems to physiological, psychological and immunological stimuli, recent clinical data implicate CRF in the etiology and pathophysiology of various endocrine, psychiatric, neurologic and inflammatory illnesses. Hypersecretion of CRF in the brain may contribute to the symptomatology seen in neuropsychiatric disorders, such as depression, anxiety-related disorders and anorexia nervosa. Furthermore, overproduction of CRF at peripheral inflammatory sites, such as synovial joints may contribute to autoimmune diseases such as rheumatoid arthritis. In contrast, deficits in brain CRF are apparent in neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease and Huntington's disease, as they relate to dysfunction of CRF neurons in the brain areas affected in the particular disorder. Strategies directed at developing CRF-related agents may hold promise for novel therapies for the treatment of these various disorders.

The separation of exocytosis from endocytosis in rat melanotroph membrane capacitance records

1. Using the patch-clamp technique, we have monitored the secretory activity of single rat melanotrophs. Changes in membrane capacitance (Cm) were measured to detect small discrete femtofarad steps. These are believed to be due to interactions between single secretory organelles (granules) and plasmalemma. 2. A new approach was introduced to measure the amplitude of discrete steps in Cm. Records of Cm were converted into time derivatives, where discrete steps appeared as transients. A transient due to a 2 fF discrete step in Cm was easily distinguished from random noise, since the probability of such a transient being due to random noise was less than 0.01. To distinguish apparent steps from noise the computer-based analysis employed a threshold of 3 times the standard deviation of the noise time derivative (dCm/dt). A phase diagram was created by plotting dCm/dt versus Cm, from which the magnitude and direction of transients were determined. Transients due to 2 fF steps (equivalent to a signal-to-noise ratio of 1) were detected with a reliability of 100%, whereas steps of 1 fF were detected with a reliability of more than 60%. The amplitude of false steps detected by the program was less than 1 fF, and the frequency of false detections of 0.075 S-1 was equal for exocytotic and endocytotic events. 3. Electron microscopy was used to measure secretory organelle size and an immunogold technique was used to label the electron micrographs with an anti-adrenocorticotrophin (ACTH) antibody. Secretory organelles in cultured and non-cultured cells were of similar diameter. All sizes of secretory granules appear to contain ACTH, since secretory organelles of similar diameter stained positively with the anti-ACTH antibodies. 4. Small discrete steps in Cm, recorded with the whole-cell configuration and loosely buffered cytosolic calcium, were similar to the estimated Cm of secretory organelles from morphological data. Thus, measured discrete steps in Cm reflect interactions between single organelle size and plasma membrane. Exocytotic and endocytotic steps were found to be of similar size. 5. To separate exocytosis from endocytosis in Cm records, we assumed that the rates of exocytosis and endocytosis were related to the respective frequencies of discrete steps in Cm. A relationship between the frequency of exocytotic, but not endocytotic events, and the rate of change in Cm was observed. Thus, under our experimental conditions, an increase in Cm could be explained by an increased rate of exocytosis in rat melanotrophs.

POMC mRNA levels in individual melanotropes and GFAP in glial-like cells in rat pituitary

In this study we demonstrated that individual melanotropes expressed differing levels of POMC mRNA. Interspersed among the melanotropes was a small population of process-bearing cells expressing GFAP. We compared cellular resolution and feasibility for quantitation of hybrids formed by oligonucleotide probes labeled with two different markers using in situ hybridization histochemistry. In hybridizations using [35S]-labeled probes the signal could not easily be assigned to individual melanotropes, although digoxigenin-labeled probes provided good cellular resolution. Heterogeneous staining intensities of individual melanotropes for POMC mRNA were measured, and relative quantitation of changes in POMC mRNA levels following interactions with the D2 dopamine receptor was performed. We combined in situ hybridization histochemistry with immunohistochemistry to demonstrate that cells within the lobe parenchyma not expressing POMC mRNA were immunoreactive for GFAP.

Corticotropin-releasing factor (CRF) receptors in intermediate lobe of the pituitary: biochemical characterization and autoradiographic localization

CRF receptors were characterized using radioligand binding and chemical affinity cross-linking techniques and localized using autoradiographic techniques in porcine, bovine and rat pituitaries. The binding of 125I-[Tyr0]-ovine CRF (125I-oCRF) to porcine anterior and neurointermediate lobe membranes was saturable and of high affinity with comparable KD values (200-600 pM) and receptor densities (100-200 fmoles/mg protein). The pharmacological rank order of potencies for various analogs and fragments of CRF in inhibiting 125I-oCRF binding in neurointermediate lobe was characteristic of the well-established CRF receptor in anterior pituitary. Furthermore, the binding of 125I-oCRF to both anterior and neurointermediate lobes of the pituitary was guanine nucleotide-sensitive. Affinity cross-linking studies revealed that the molecular weight of the CRF binding protein in rat intermediate lobe was identical to that in rat anterior lobe (Mr = 75,000). While the CRF binding protein in the anterior lobes of porcine and bovine pituitaries had identical molecular weights to CRF receptors in rat pituitary (Mr = 75,000), the molecular weight of the CRF binding protein in porcine and bovine intermediate lobe was slightly higher (Mr = 78,000). Pituitary autoradiograms from the three species showed specific binding sites for 125I-oCRF in anterior and intermediate lobes, with none being apparent in the posterior pituitary. The identification of CRF receptors in the intermediate lobe with comparable characteristics to those previously identified in the anterior pituitary substantiate further the physiological role of CRF in regulating intermediate lobe hormone secretion.

The effects of orchidectomy and replacement therapy on the ultrastructure and gonadotropin-releasing hormone content of the median eminence of the rat

The effects of 2 weeks of orchidectomy and replacement therapy with testosterone upon the content and distribution of gonadotropin-releasing hormone (GnRH) in the median eminence were determined by means of radioimmunoassay and electron microscopy. Photographic montages were prepared from electron micrographs of the lateral median eminence at the point of deepest invagination of the tuberoinfundibular sulcus. Morphometric analysis of photographs of tissues immunohistochemically stained for GnRH was performed to determine changes in the volume density of GnRH-containing axon profiles following the experimental treatments. A decrease in GnRH content after orchidectomy was observed both by morphometric analysis of axon volume density and radioimmunoassay of total GnRH content. Testosterone treatment of orchidectomized animals prevented the postorchidectomy loss of GnRH. Morphometric analysis of conventional electron micrographs revealed an increase in the number of axons containing no dense-core vesicles following orchidectomy, but no decrease in volume density of the neuropil. The results indicate that the change in volume density of immunostained axons was related to the loss of immunostainable dense-core vesicles and not to a change in the size or number of axons. The area corresponding to the location of the highest concentration of GnRH-containing axons was observed to be largely avascular and separated from the vessels of the tuberoinfundibular sulcus by a "border zone" composed of glial foot processes. The unique morphology of the GnRH area has suggested the name "compact zone" to distinguish it from the palisade zone with which it is continuous medially. GnRH axons in this region are probably part of a tract extending farther caudally rather than a terminal field.

Corticotropin-releasing factor receptors in the pituitary gland and central nervous system: methods and overview

Studies with the radioiodinated oCRF analog, Nle21, 125I-Tyr32-oCRF have identified, characterized, and localized high affinity binding sites for CRF in anterior and intermediate lobes of rat pituitary, in anterior lobe of human pituitary, and in rat, monkey, and human brain. The pharmacology and distribution of Nle21, 125I-Tyr32-oCRF binding in the pituitary gland correlate well with the biological potency and sites of action of CRF and suggest that these CRF binding sites represent specific receptors that mediate the well-established actions of CRF on the anterior pituitary and on the intermediate lobe of the pituitary. The studies in adrenalectomized rats demonstrating that endogenous CRF is capable of modulating its receptor density provide additional evidence that the radioligand labels the functional CRF receptor. The areas of distribution of Nle21, 125I-Tyr32-oCRF binding sites in the rat CNS correlate well with the immunohistochemical distribution of CRF pathways and the pharmacological sites of action of CRF. These data confirm the established role of CRF in regulating secretion of POMC-derived peptides from the pituitary gland. In addition, the data support a physiological role for endogenous CRF in regulating CNS activity and suggest the importance of this neuropeptide in integrating endocrine and visceral functions and behavior, especially in response to stress. Studies to characterize CRF receptors and CRF-containing pathways in the brain provide a means for better understanding the various functions of this neuropeptide in different areas of the CNS. Finally, the ability to map CRF receptors in postmortem human tissue provides a basis for studying the role of CRF in a variety of endocrine, neurological, and psychiatric disorders.

Glycoconjugate localization with lectin and PA-TCH-SP cytochemistry in rat hypophysis

Glycoconjugates were localized by light microscopy with lectin-peroxidase conjugates and by electron microscopy with the periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) sequence in immunocytochemically or morphologically identified cell types in rat pituitary. Lectin histochemistry demonstrated sialic acid and glycoconjugates with N-glycosidically linked oligosaccharides in gonadotrophs, thyrotrophs, and corticotrophs. Galactose penultimate to sialic acid was observed mostly in gonadotrophs. The terminal galactose-N-acetylgalactosamine disaccharide was detected in a few gonadotrophs and in a moderate number of mammotrophs. Fucose was localized in only corticotrophs with two fucose-binding lectins and in thyrotrophs with another. Several different monosaccharides were seen in glycoconjugates in melanotrophs and in Herring bodies. Melanotrophs displayed heterogeneous staining with fucose-binding lectins. A small number of nonsecretory cells were also visualized in the pars distalis by virtue of their glycogen content. PA-TCH-SP staining revealed complex carbohydrates in secretory granules and some Golgi cisternae in all types of hormone-producing cells in the pars distalis except for the somatotrophs. Melanotrophs of pars intermedia exhibited stained secretory granules and irregular dense bodies containing a stained meshwork. Corticotrophs of the pars distalis lacked the latter bodies, although they form the same glycoprotein precursor hormone as melanotrophs. Lectin conjugates and the PA-TCH-SP sequence stained some groups of secretion granules in Herring bodies, possibly representing vasopressin-containing granules as well as other cell types in the pars nervosa.

Corticotropin-releasing factor receptors in rat pituitary gland: autoradiographic localization

Corticotropin-releasing factor (CRF) receptors were localized in rat pituitary gland by an in vitro labeling light microscopic autoradiographic technique using the radioiodinate ovine CRF analog, [Nle21,125I-Tyr32]-CRF. Our data confirms the existence of CRF receptors in anterior pituitary and demonstrates the presence of specific CRF binding sites in the intermediate lobe of rat pituitary. The distribution of CRF binding sites closely resembles the clustering of corticotrophs in anterior lobe and the uniform distribution of opiomelanocortin-producing cells in the intermediate pituitary. These results suggest that endogenous CRF plays a physiological role in regulating secretion of pro-opiomelanocortin-derived peptides from both anterior and intermediate lobes of rat pituitary.

The use of radioimmune assay in investigating reagents to be used in the immunocytochemical localization of hepatitis B surface antigen in immune complexes in the kidney of patients with membranous nephropathy and Australia antigenaemia

Radioimmune assay (RIA) was used to investigate the effect of fixatives on antigenicity of the hepatitis B surface antigen (HBsAg) and the effect of pronase on the elution of antibody (Ab) from the HBsAG-Ab complex. The effect of pronase on Ab elution was also tested on sections of kidney from a patient with the immune complex disease systemic lupus erythematosus (SLE). Immunoglobulin G (IgG) was located in pronase treated and untreated sections using the indirect immunoperoxidase technique. Glutaraldehyde was shown to be the fixative of choice for studies involving HbsAG. All fixatives were shown to have less effect on antigenicity at 4 degrees C than at room temperature. Osmium tetroxide reduced antigenicity to one-third, even at 4 degrees C. RIA and SLE kidney section studies showed that Ab was eluted from immune complexes by pronase. Pre-fixation of the antigen (Ag) by glutaraldehyde appears to have no effect on the final elution, although fixation after pronase treatment seemed to enhance the elution effects. The availability of an RIA kit with HBsAg- and AB-coated beads was of great assistance in evaluating reagents to be used in immunoperoxidase studies of HBsAg in immune complexes of patients with membranous nephropathy and Australia antigenaemia.

Cryoultramicrotomy versus plastic embedding: comparative immunocytochemistry of rat anterior pituitary cells

The anterior pituitary of the rat is used as a model for the study of the effects of freezing or plastic embedding on the maintenance of antigenicity. Rat anterior pituitaries are fixed in 2.5% glutaraldehyde in 0.1 M phosphate buffer pH 7.4. Some of the blocks are post-fixed before being divided into two lots. One batch is frozen, while the other is dehydrated and embedded. The indirect antibody enzyme method is applied to ultrathin sections obtained by cryoultramicrotomy after freezing or by sectioning after embedding. All six pituitary hormones are detected by both methods. Comparison shows that the morphological characteristics are identical for both techniques, though ultrastructural preservation is better after embedding. Immunoreactivity is found in secretory granules and sometimes in the endoplasmic reticulum. Osmium postfixation may reduce or even abolish antigenicity in plastic-embedded tissue. After cryoultramicrotomy, however, even after osmium fixation, antibody may be used 1000 times more diluted than after plastic embedding. Embedding preserves ultrastructure and limited antigenicity while the use of cryoultramicrotomy is a far more sensitive technique.

Ultrastructural and purification studies on human tumor nucleolar antigens and nucleolar particles

The presence of common nucleolar antigens in a broad array of human malignant tumors has led to several lines of investigations. In addition to studies on an increasing number of benign and malignant neoplasms with a variety of antibodies designed to statistically evaluate the presence of nucleolar antigens, purification procedures and chemical analyses are being used to characterize the specific antigens. The localization of the nucleolar antigens in HeLa cells was studied by the postembedding immunoelectron microscopic procedure employing rabbit antibodies to nucleoli or nuclear Tris extracts of these cells. The products of the peroxidase-antiperoxidase complexes visualized by the reaction with diaminobenzidine in nucleoli were mainly found in the nucleolonemas which contain the dense nucleolar RNP components. When these nucleoli became compact after treatment of HeLa cells with adriamycin, the distribution of the immunoreactive products was altered along with distribution of the dense nucleolar components. The human nucleolar antigens were mainly localized to nucleolar regions containing the nucleolar RNP components. Improved purification of the antigens made it possible to provide a satisfactory amino acid analysis of one pI 6.3 antigen. Interestingly, some of the nucleolar antigen was found in miniparticle undescribed until now.

Pituitary intermediate lobe in dog: two cell types and high bioactive adrenocorticotropin content

The pituitary intermediate lobe of most species is cytologically monotonous, but that of the dog is composed of two immunocytochemically distinct cell types. The predominant A cells are typical pars intermedia cells: they stain immunocytochemically for alpha-melanotropin and, more weakly, for adrenocorticotropin and beta-lipotropin. The B cells are like the corticotrophs of the anterior lobe: they stain intensely for adrenocorticotropin and beta-lipotropin but not for alpha-melanotropin. The B cells may account for the high concentration of bioactive adrenocorticotropin measured in the canine pars intermedia, and may explain why in dogs adenomas causing Cushing's disease through hypersecretion of adrenocorticotropin can arise from the intermediate as well as the anterior pituitary lobe.

A critique of the contributions of immunoperoxidase cytochemistry to our understanding of pituitary cell function, as illustrated by our current studies of gonadotropes, corticotropes and endogenous pituitary GnRH and TRH

The peroxidase-antiperoxidase technique has been used to study sites of pituitary hormone storage and binding. Some recent findings from our laboratory show that the technique can make intriguing contributions to our understanding of pituitary cell function. In serial, ultra-thin sections, one can identify two or three hormones in a given cell. During pre-pubertal development, gonadotropes may contain adrenocorticotropin immunoreactivity. Brain releasing hormones may be stored or sequestered in granules of cells they stimulate. This report includes a discussion and critique of our recent findings and interpretations which must be considered before one draws any conclusions about their biological significance.

Structural relationships between parenchymal and stromal elements in the pars intermedia of the rat adenohypophysis as demonstrated by extracellular space markers

The pars intermedia (PI) of the rat adenohypophysis was studied by light and transmission electron microscopy after conventional staining as well as ruthenium red staining, and after systemic injection of horseradish peroxidase. The studies disclose a complex and constant system of two channel types (Type I and Type II channels) formed by PI cells with specific relationships to a very rich nerve supply, to each other, and to a stellate cell type proposed here to represent an element of neuroglia. The channel system could perform a function in the movement of fluids and solutes within the PI which is verturally avascular in the rat as well as in other mammals.

Immunocytochemical demonstration of the neurosecretory X-organ complex in the eyestalk of the crab Carcinus maenas

An antiserum was obtained by immunizing rabbits with sinus gland extracts from Carcinus maenas. The antiserum is almost exclusively directed against neurosecretory material in the medulla terminalis X-organ (MTGXO), as demonstrated by the peroxidase--antiperoxidase (PAP) staining method in light and electron microscopic studies. Radioimmunological binding studies indicate the presence of antibodies against the crustacean hyperglycemic hormone (CHH) or the black pigment dispersing hormone (BPDH) in the antiserum. The results suggest that the neurosecretory perikarya of the MTGXO are the sites of production of CHH and/or BPDH.

Effects of reserpine administration on the fine structure of the rat pars intermedia

Hormone release from the pars intermedia is under inhibitory control of the hypothalamus. Control may be mediated via dopaminergic fibers which directly contact secretory cells. Administration of reserpine in vivo to adult male rats for four consecutive days results in major alternations in pars intermedia cytology. Cells show expanded areas and whorls of rough endoplasmic reticulum, as well as extensive Golgi zones with numerous dense granules. Some nerve fibers exhibit alterations in vesicle content, while others retain a more normal appearance. Freeze-fracture of glands from reserpine-treated animals provides evidence for exocytosis of granules, although such phenomena are not observed in thin sections. The ultrastructural findings suggest that reserpine alters the content of local inhibitory neurotransmitters in the pars intermedia, leading to unrestrained hormone release, followed by renewed granule synthesis.

Ultrastructural localization of prolactin, growth hormone and luteinizing hormone by immunocytochemical techniques in the bovine pituitary

The technique of ultrastructural immunocytochemistry involving the unlabeled antibody and the soluble peroxidase-antiperoxidase complex was used to identify and describe the prolactin (P) cells, somatotropic (STH) cells and luteinizing hormone (LH) cells in the bovine anterior pituitary gland. This method was used to localize the three hormones at the electron microscopic level. Staining of varying intensity was found on the secretory granules and on the small granules and vesicles within the Golgi complex. No stain was found in nuclei, on mitochondria or in the endoplasmic reticulum.

Ultrastructural immunohistochemical localization of vasopressin in the hypothalamic-neurohypophysial system of three murids

Vasopressin was immunohistochemically localized at the electron microscopic (EM) level in the hypothalamic-neurohypophysial system (HNS) of three murids. Antiserum to vasopressin was produced in rabbits injected with lysine vasopressin (LVP) conjugated to egg albumin (EA), anti-EA being precipitated prior to staining. Sternberger's unlabeled antibody peroxidase technique was employed, immunoreactivity being designated by peroxidase-anti-peroxidase (PAP) molecules and electron opacity. Immunoreactive neurosecretory granules (NSG) were found in the perikarya of the supraoptic nucleus (SON) in all three murids investigated, although far more profusely in the two wild strains. Immunoreactive axonal NSG were observed in the inner and outer zones of the median eminence (ME), and within most of the axons and terminals in the neurohypophysis. The concentration of primary serum effective for staining the SON (1:10-1:50) was far higher than that required for the ME and the neurohypophysis (1:500-1:1,200). Anti-LVP also induced electron opacity of granules in cells of the pars intermedia (PI). Discussion centers of the significance of immunoreactive NSG in the neurosecretory (NS) perikarya, on the possibility of an extragranular pool of hormone, and on speculation about the electron opacity of the PI granules.

Bovine neurophysins I, II and C: new methods for their purification and for the production of specific antibodies

1. Bovine neurophysins were prepared by a modified method, in which a Biogel P-60 column was used. This yielded two neurophysin fractions, the first containing neurophysin I and small quantities of the other neurophysins,the second containing neurophysin II and C, and only traces of neurophysin I. 2. Antibodies against neurophysin I, II and C were prepared by an original method, 5 mug in 100 mul water of each of the two fractions were applied on a gel slab and separated by iso-electric focusing in a pH gradient 4--6. The separated bands were visualized with 8-aniline-1-naphthalene sulfonic acid, magnesium salt and strips respectively containing neurophysin I, II or C were cut out. The neurophysin-containing strips were homogenized in complete Freund's adjuvant and injected into rabbits. 3. The specificity of the antisera were tested by immunocytochemistry and by radioimmunoassay. By this latter method, it was determined that cross-reactivity was less than 1%. The cross-reaction, observed with the immunohistochemical method could be eliminated by differential absorption. 4. It was found that neurophysin C antisera were undistinguishable from the neurophysin II antisera, while showing little cross-reactivity with the neurophysin I antisera. This suggests that in vivo neurophysin C is not a real neurophysin, or at least, that it is very similar to neurophysin II. 5. Highly purified bovic focusing method. By modifying a LKB Uniphor electrophoresis apparatus, the elute the proteins without switching off the voltage. The resolution of the technique is close to that offered by analytical gel iso-electric focusing.

Development and cytodifferentiation of the rabbit pars intermedia. I. Fetal and perinatal stages

The developing pars intermedia (PI) of rabbits of between 14 days post coitum (PC) and one day post partum (PP) have been studied by light and electron microscopy. Cell division is marked until 4th week PC, after which it is reduced. The (PI) loses its homogeneity by the 5th week PC due to localisation both intrinsic and invading cells and blood vessels. Four groups of parenchyma cells are recognisable: PI-glandular cells, interstitial cells, ACT-type cells and a heterogeneous group of dark cells. The ultrastructure of the ACT-type cells in the rabbit PI are here described for the first time. The differentiation of these cell types has been traced from 14 days PC to 32 days PC, in particular ACT-type cells are shown to develop in situ and the significance of this is discussed. In the PI-glandular cells dense cored granules appear first on the 15th day PC which is one day before any nerve connection is made with the primitive neural lobe and more than a week before vascularisation. Thereafter granularity increases until parturition when there is a phase of degranulation. Relatively electron lucent, larger vesicles are not found until 4th week PC.

Electron microscope studies on the intermediate lobe of the embryonic mouse

The development of the intermediate lobe of the hypophysis was studied in the embryonic C3H mouse; at least four glands from embryos of every gestational day from 15 to 19 were examined. In the 16 day-old embryo prospective secretory cells proliferate at the centre of the intermediate lobe anlage. At the same stage cylindrical cells bordering the hypophyseal cleft begin to reorganize into marginal cells. By the end of fetal life marginal cells are well differentiated. In the 17 day-old embryo a few granular inclusions appear in some centrally located cells. Secretory cells increase in number during the following two embryonic days. Some of these cells contain polymorphic populations of granular and vesicular inclusions by gestational day 19. The possibility of a dual formation of secretory inclusions is discussed. The result implies that the onset of granule-formation by these cells is not contemporaneous with the start of production of melanophore-expanding substances, the presence of which has been detected by earlier biological assays.

Localization of antigens in thin sections of bacteria by the immuno-peroxidase technique

The immunoperoxidase technique together with electron microscopy has been examined for the ultrastructural localization of staphylococcal protein A, the immunoferritin method being included for comparison. The results show that protein A is uniformly distributed in the whole cell wall. Both the direct and indirect methods, Fab- as well as Fc-reactions, showed identical results. tthe immunoperoxidase method was superior to the immunoferritin method, especially when applied to thin sections of the bacteria, and the clear specificity demonstrated indicates a useful method for localization of cellular antigens.

Immuno-electron microscopic localization of luteinizing hormone-releasing hormone in the arcuate nuclei and median eminence of the rat

Luteinizing hormone-releasing hormone (LH-RH) was localized in neurons of the arcuate nucleus and median eminence, and in many of the nerve fibres of the median eminence of the rat, by using antisera to synthetic LH-RH with the immunoglobulin-peroxidase technique or by using a soluble peroxidase-antiperoxidase complex at the electron microsc opic level. Many of the arcuate neurons and some of the median eminence neurons contained numerous densely stained granules elsewhere in the cytoplasm. Similar granules, positive for LH-RH, were observed in many nerve profiles around the capillaries of the primary portal plexus of zona palisadica and zona granulosa of the medain eminence, and such profiles may represent the release sites of LH-RH into the portal vessels. About 20% of the nerve profiles around the primary portal plexus were LH-RH positive and the rest of the nerve profiles were negative. The negative profiles may belong to other hypophysiotropic hormones and/or to catecholaminergic fibers. Some nerve endings at the ventricular surface of the ependymal cells, in contact with the ventricular fluid, were also LH-RH positive. These nerve endings probably release their secretion into the cerebrospinal fluid. There was no staining of the mitochondria, the nuclei or the axonal membranes. Stain of varying intensity was seen in the secretory granules, and within and around the cisternae of the Golgi complex. The stained granules in the cisternae wer pleomorphic. From these observations it was concluded that the LH-RH is packaged or condensed into granules in the Golgi cisternae.