A Forgotten Principle in Immunocytochemistry: Optimal Dilution

Immunocytochemical (ICC) techniques are frequently used in basic and clinical research. Here, we focus on the importance of using antisera/antibodies at optimal dilutions to achieve specificity and reduce costs. Unfortunately, the basic principle, the necessity to test method specificity of the staining by a series of increasing dilutions of primary antiserum/antibodies, is only occasionally seen in papers using ICC. Many researchers rely on the company's information or others' published data. In this study, we show examples with monoclonal antibodies used in the peroxidase-based ICC technique in mouse and guinea pig brain sections. We show images of ICC staining of phospho-S129 alpha-synuclein in A53T mice and NeuN in guinea pig brains and demonstrate that optimal staining with them can be achieved at least at two to three orders of magnitude higher dilutions than generally used in the literature. We strongly recommend that when antisera/antibodies are used for the first time in any laboratory, independent of what the manufacturer or vendor recommends or are found in the literature, a dilution curve should be set up to identify the optimal dilution. This practice provides not only the highest specificity but is also an economic approach.

Anatomy and cytoarchitectonics of the human hypothalamus

Due to the complexity of hypothalamic functions, the organization of the hypothalamus is extremely intricate. This relatively small brain area contains several nuclei, most of them are ill-defined regions without distinct boundaries; these nuclei are often connected with each other and other distant brain regions with similarly indistinct pathways. These hypothalamic centers control numerous key physiological functions including reproduction, growth, food intake, circadian rhythm, behavior, and autonomic balance via neural and endocrine signals. To understand the morphology of the hypothalamus is therefore extremely important, though it remains a stupendous task due to the complex organization of neuronal networks formed by the various neurotransmitter and neuromodulator systems.

Morphology and distribution of hypothalamic peptidergic systems

Neuropeptides participate in the regulation of numerous hypothalamic functions that are aimed for sustaining the homeostasis of the organism. These neuropeptides can act in two different levels. They can influence the release of hormones from the adenohypophysis via the portal circulation; in addition, they can act as neurotransmitters/neuromodulators modulating the functioning of numerous hypothalamic neurotransmitter systems. Indeed, most of these peptidergic systems form a complex network in the infundibular and periventricular nuclei of the human hypothalamus, communicating with each other by synaptic connections that may control fundamental physiologic functions. In the present chapter, we provide an overview of the distribution of neuropeptides in the human hypothalamus using immunohistochemistry and high-resolution, three-dimensional mapping.

Neutron detection on the Foton-M2 satellite by a track etch detector stack

In the frame of a European Space Agency (ESA) project called 'Biology and Physics in Space', a returning satellite, Foton-M2, was orbiting a container, the BIOPAN-5, loaded with biological experiments and facilities for radiation dosimetry (RADO) in the open space. One of the RADO experiments was dedicated to the detection of the primary cosmic rays and secondary neutrons by a track etch detector stack. The system was calibrated at high-energy particle accelerators and neutron generators. The developed detectors were investigated by an image analyser, and from the track parameters the linear energy transfer spectra and the absorbed dose were determined (26 microGy/d). Also, the neutron flux was estimated below 5 MeV and found to be 2.4 cm(-2) s(-1) directly from the space. The construction of the stack allowed to investigate the neutrons also from the direction of the carrying satellite, where the flux was found somewhat higher.

Morphological substrate of the catecholaminergic input of the vasopressin neuronal system in humans

It has been postulated that the stress response is associated with water balance via regulating vasopressin release. Nausea, surgical stress and insulin-induced hypoglycaemia were shown to stimulate vasopressin secretion in humans. Increased vasopressin release in turn induces water resorption through the kidneys. Although the mechanism of the stress-mediated vasopressin release is not entirely understood, it is generally accepted that catecholamines play a crucial role in influencing water balance by modulating the secretion of vasopressin. However, the morphological substrate of this modulation has not yet been established. The present study utilised double-label immunohistochemistry to reveal putative juxtapositions between tyrosine hydroxylase (TH)-immunoreactive (IR) catecholaminergic system and the vasopressin systems in the human hypothalamus. In the paraventricular and supraoptic nuclei, numerous vasopressin-IR neurones received TH-IR axon varicosities. Analysis of these juxtapositions with high magnification combined with oil immersion did not reveal any gaps between the contacted elements. In conclusion, the intimate associations between the TH-IR and vasopressin-IR elements may be functional synapses and may represent the morphological basis of vasopressin release modulated by stressors. Because certain vasopressin-IR perikarya receive no detectable TH innervations, it is possible that additional mechanisms may participate in the stress-influenced vasopressin release.

Close anatomical associations between β-endorphin and luteinizing hormone-releasing hormone neuronal systems in the human diencephalon

Endogenous opiates, such as beta-endorphin, inhibit the release of luteinizing hormone (LH) release in the pituitary gland of several species including rat, pig, sheep, and human. Although it is generally believed that beta-endorphin influences gonadal functions via the regulation of hypothalamic LH-releasing hormone (LHRH) release, the morphological substrate underlying this regulation in humans remains elusive. In the present series of experiments the beta-endorphin-immunoreactive (IR) and LHRH-IR neural elements, utilizing single label immunohistochemistry, were mapped. Following the superimposition of the maps of these systems, the overlapping sites were identified and examined in order to verify the putative juxtapositions between the beta-endorphin-IR and LHRH-IR structures. LHRH-IR elements were detected mainly in the medial basal hypothalamus, in the medial preoptic area and along the diagonal band of Broca. Beta-endorphin-IR perikarya were observed in the infundibular region/median eminence, whereas beta-endorphin-IR axon varicosities were detected periventricularly in the preoptic and tuberal regions, in the medial basal hypothalamus and around the mamillary bodies. Careful examination of the immunoreactive elements in the overlapping areas revealed close contacts between beta-endorphin-IR and LHRH-IR structures, which have been verified in semithin plastic sections. These putative beta-endorphin-LHRH juxtapositions were most numerous in the medial preoptic area and in the infundibulum/median eminence of the human diencephalon. In conclusion, the present paper is the first study that revealed close juxtapositions between the beta-endorphin-IR and LHRH-IR neural elements in the human diencephalon. These beta-endorphin-LHRH contacts may be functional synapses, and they may be the morphological substrate of the beta-endorphin control on gonadal functions in man.

Bi-directional associations between galanin and luteinizing hormone-releasing hormone neuronal systems in the human diencephalon

Evidence suggests that galanin plays an important role in the regulation of reproduction in the rat. Galanin is colocalized with luteinizing hormone (LH)-releasing hormone (LHRH) in a subset of LHRH neurons in female rats and galanin-immunoreactive (galanin-IR) nerve terminals innervate LHRH neurons. Recent studies indicate that galanin may control gonadal functions in rats at two different levels: (i) via direct modulation of pituitary LH secretion and/or (ii) indirectly via the regulation of the hypothalamic LHRH release. However, the morphological substrate of any similar modulation is not known in human. In the present series of experiments we first mapped the galanin-IR and LHRH-IR neural elements in human brain, utilizing single label immunohistochemistry. Then, following the superimposition of the maps of these systems, the overlapping sites were identified with double labeling immunocytochemistry and examined in order to verify the putative juxtapositions between galanin-IR and LHRH-IR structures. LHRH and galanin immunoreactivity were detected mainly in the medial basal hypothalamus, in the medial preoptic area and along the diagonal band of Broca. Careful examination of the IR elements in the overlapping areas revealed close, bi-directional contacts between galanin-IR and LHRH-IR structures, which have been verified in semithin plastic sections. These galanin-LHRH and LHRH-galanin juxtapositions were most numerous in the medial preoptic area and in the infundibulum/median eminence of the human diencephalon. In conclusion, the present study is the first to reveal bi-directional juxtapositions between galanin- and LHRH-IR neural elements in the human diencephalon. These galanin-LHRH and LHRH-galanin contacts may be functional synapses, and they may be the morphological substrate of the galanin-controlled gonadal functions in humans.

Topography and associations of leu-enkephalin and luteinizing hormone-releasing hormone neuronal systems in the human diencephalon

Although several studies indicated that leu-enkephalin controls gonadal function, the morphological substrate of this modulation is unknown. To reveal potential interaction sites between leu-enkephalin and LH-releasing hormone (LHRH) in the hypothalamus, the distribution and connections of leu-enkephalin-immunoreactive (IR) and LHRH-IR systems were examined in the human diencephalon using double-label immunohistochemistry. First the leu-enkephalin-IR and LHRH-IR neural elements were mapped, then the maps of the two different neurotransmitter systems were superimposed unveiling the overlapping areas. The putative juxtapositions between leu-enkephalin-IR and LHRH-IR structures were revealed with double label immunocytochemistry. Close contacts were detected in the medial preoptic area and in the infundibulum/median eminence. In these areas, diaminobenzidine-silver-intensified, black leu-enkephalin-IR fibers abutted fusiform, brown, diaminobenzidine-labeled LHRH neurons often forming multiple contacts. Examination of semithin sections of these close associations with the aid of oil immersion revealed no cleft between the contacting LHRH-IR and leu-enkephalin-IR elements. Our findings indicate that the juxtapositions between LHRH-IR and leu enkephalin-IR neurons may be functional synapses forming the morphological substrate of the leu-enkephalin-modulated LHRH secretion in the human diencephalon. Moreover, the wide distribution of leu-enkephalin-IR elements suggests leu-enkephalin control of other diencephalic functions as well.

Close juxtapositions between luteinizing hormone-releasing hormone-immunoreactive neurons and corticotropin-releasing factor-immunoreactive axons in the human diencephalon

Gonadal functions are modulated by corticotropin-releasing factor (CRF) in the rat via direct suppression of LH-releasing hormone (LHRH) release. Although there is evidence of direct morphological contacts between the LHRH and CRF-immunoreactive (-IR) structures in the rat hypothalamus, little is known about the morphological base of CRF-influenced LHRH release in man. Thus, we studied the distribution of the CRF-IR and LHRH-IR systems in the human diencephalon and revealed putative CRF-LHRH juxtapositions using double label immunohistochemistry. LHRH-IR cells were present mainly in the infundibular region and the medial preoptic area. CRF-IR neuronal structures were observed in the periventricular area, paraventricular nucleus, infundibular region, and median eminence. CRF-LHRH juxtapositions were found mainly in the infundibulum and median eminence. Few juxtapositions were detected in the medial preoptic area. In these regions, black diaminobenzidine/silver-labeled CRF-IR fibers abutted fusiform brown diaminobenzidine-labeled LHRH neurons, usually forming multiple contacts. Examination of semithin sections of these close associations with the aid of oil immersion revealed no cleft between CRF-IR nerve terminals contacting LHRH-IR structures. These findings suggest that the juxtapositions between the LHRH-IR and CRF-IR neurons may be functional synapses forming the morphological substrate of the CRF-controlled LHRH secretion. Moreover, the wide distribution of CRF-IR elements suggests that CRF controls other diencephalic functions as well.

Close juxtapositions between LHRH immunoreactive neurons and substance P immunoreactive axons in the human diencephalon

LHRH release is induced by substance P (SP) in the rat hypothalamus. Recent immunocytochemical studies indicate that SP-immunoreactive axons synapse on LHRH neurons in the diencephalon of the rat, but this phenomenon has not yet been demonstrated in human. Therefore, in the present study we visualized the SP- and LHRH-immunoreactive (IR) elements in the human diencephalon and evaluated the close juxtapositions between them. The distribution of LHRH- and SP-IR sites were investigated in diencephalic sections of six, postmortem human brains by means of double-labeling immunocytochemistry. The LHRH-containing perikarya were located in the diagonal band of Broca, lamina terminalis cinerea, preopticoseptal, medial preoptic, and infundibular areas of the brain. The SP-IR fibers formed a network in the periventricular zone in the infundibular region, median eminence, and corpus striatum. The SP-IR cell bodies were located mainly in the infundibular region, median eminence, basal part of the periventricular area, dorsomedial subdivision of the ventromedial nucleus, and basal perifornical area of the tuberal region. The juxtapositions between LHRH-IR cell bodies and SP-IR varicosities were detected in the infundibular and periventricular regions. In these sites black, silver-intensified, SP-IR fiber varicosities abutted on brown, DAB-labeled, LHRH-IR cell bodies. Similar structures were detected between the SP-IR fibers and SP-IR perikarya. These findings suggest that the juxtapositions between the SP and LHRH systems may be the morphological basis of SP-controlled LHRH release in the human diencephalon. Moreover, the intimate contacts between SP-IR fiber varicosities and SP-IR cell bodies or axons indicate direct control of SP on the diencephalic SP release.

Catecholaminergic axons innervate LH-releasing hormone immunoreactive neurons of the human diencephalon

Catecholamines have been shown to modulate gonadal functions via interactions with hypothalamic LH-releasing hormone (LHRH)-synthesizing neurons. To reveal the morphological background of this phenomenon, the distribution of LHRH neurons and tyrosine hydroxylase (TH)-immunoreactive (IR), catecholaminergic structures were mapped in the human diencephalon. First, the location of LHRH and TH-IR neuronal elements was analyzed, and then the relationship between the two different systems was examined. The LHRH-IR cell bodies were mainly present in the medial preoptic and infundibular areas. The TH-IR perikarya were located in the periventricular, paraventricular, and supraoptic hypothalamic nuclei and also in the median eminence. The TH-IR fibers were numerous in septal, infundibular, periventricular, and lateral hypothalamic regions. The brown, diaminobenzidine-labeled LHRH-containing perikarya were found to receive black, silver-intensified, TH-positive axon terminals in the infundibular and medial preoptic areas. However, in the preoptic and caudal parts of the diencephalon, only a few juxtapositions were noted. The present results indicate that hormone released from diencephalic LHRH-IR neurons in humans may be influenced by the central catecholaminergic system via direct synaptic mechanisms.

Topography and associations of luteinizing hormone-releasing hormone and neuropeptide Y-immunoreactive neuronal systems in the human diencephalon

Neuropeptide Y (NPY) potentiates the effect of luteinizing hormone-releasing hormone (LHRH) on luteinizing hormone secretion in several species, including human. In addition to the pituitary sites, the interactions of the NPY and LHRH systems may involve diencephalic loci. However, the morphologic basis of this putative communication has not yet been elucidated in the human brain. To discover interaction sites, the distribution and connections of LHRH and NPY-immunoreactive (IR) neuronal elements in the human hypothalamus were investigated by means of light microscopic single- and double-label immunocytochemistry. NPY-IR perikarya and fibers were found to be widely distributed in the ventral diencephalon, with high densities in the preopticoseptal, periventricular, and tuberal regions. Small neuronal cell groups were infiltrated with a dense network of varicose NPY-IR fibers in the lateral preoptic area. The LHRH-IR perikarya were located mainly in the preopticoseptal region, diagonal band of Broca, lamina terminalis, and periventricular and infundibular nuclei. A few LHRH-IR neurons and fibers were scattered in the mamillary region. The overlap between the NPY and LHRH systems was apparent in the periventricular, paraventricular, and infundibular nuclei. Double-labeling immunohistochemistry showed NPY-IR axon varicosities in contact with LHRH-IR perikarya and main dendrites. The putative innervation of LHRH neurons by NPY-IR fibers was also seen in 1-microm-thick plastic sections and with confocal laser scanning microscope, thus further supporting the functional impact of NPY-IR terminals on LHRH-IR neurons. The present findings suggest that the hypophysiotropic LHRH-synthesizing neurons may be innervated by intrahypothalamic NPY-IR fibers. Confirmation by ultrastructural analysis would demonstrate that the LHRH system in the human hypothalamus is regulated by NPY, as has been demonstrated in nonhuman species.

A ventral approach to stereotaxy of the guinea pig brain

The guinea pig (Cavia porcellus) is a species frequently used in neuromorphological and neurophysiological studies. Some experimental data suggest that the guinea pig might also be used to develop an animal model of Alzheimer's disease. These studies would require microsurgical manipulations of the nervous system. The present paper describes a method for ventral stereotaxic intrusions in the guinea pig brain through the oval foramen at the skull base. The topographic relationships of the bony landmarks to major parts of the central nervous system and the cranial nerves are analysed, and the results are tested by intrahippocampal injection of horseradish peroxidase.

Identification of structural proteins of Rhizobium meliloti temperate phage 16-3

The structural proteins of Rhizobium meliloti temperate phage 16-3 have been analysed by means of polyacrylamide gel electrophoresis, isoelectric focusing and agarose gel electrophoresis. Five major and five minor proteins were identified and characterized with respect to their size, isoelectric point and their distribution between the head ad tail of the phage particle. The synthesis of structural proteins was studied by one- and two-dimensional gel electrophoresis.