Immunohistochemical analysis of the cross-reaction of anti-rat histidine decarboxylase antibody with guinea-pig DOPA decarboxylase

Hypothalamic L-Histidine Decarboxylase Is Up-Regulated During Chronic REM Sleep Deprivation of Rats

A competition of neurobehavioral drives of sleep and wakefulness occurs during sleep deprivation. When enforced chronically, subjects must remain awake. This study examines histaminergic neurons of the tuberomammillary nucleus of the posterior hypothalamus in response to enforced wakefulness in rats. We tested the hypothesis that the rate-limiting enzyme for histamine biosynthesis, L-histidine decarboxylase (HDC), would be up-regulated during chronic rapid eye movement sleep deprivation (REM-SD) because histamine plays a major role in maintaining wakefulness. Archived brain tissues of male Sprague Dawley rats from a previous study were used. Rats had been subjected to REM-SD by the flowerpot paradigm for 5, 10, or 15 days. For immunocytochemistry, rats were transcardially perfused with acrolein-paraformaldehyde for immunodetection of L-HDC; separate controls used carbodiimide-paraformaldehyde for immunodetection of histamine. Immunolocalization of histamine within the tuberomammillary nucleus was validated using carbodiimide. Because HDC antiserum has cross-reactivity with other decarboxylases at high antibody concentrations, titrations localized L-HDC to only tuberomammillary nucleus at a dilution of ≥ 1:300,000. REM-SD increased immunoreactive HDC by day 5 and it remained elevated in both dorsal and ventral aspects of the tuberomammillary complex. Our results suggest that up-regulation of L-HDC within the tuberomammillary complex during chronic REM-SD may be responsible for maintaining wakefulness.

Antisera against rat recombinant histidine decarboxylase: immunocytochemical studies in different species

Histamine is involved in many important biological processes such as allergic reactions, gastric acid secretion and neurotransmission. The formation of histamine is catalysed by the enzyme histidine decarboxylase. In order to understand the role of histamine in different tissues, information about the cellular localisation of the decarboxylase is important. However, the availability of antisera against the enzyme, which can be used in immunocytochemical techniques, has so far been limited, mainly due to the difficulties in purifying sufficient amounts of histidine decarboxylase from various tissues. In the present study we describe the use of antisera raised against rat recombinant histidine decarboxylase to localise the enzyme immunocytochemically in the gastric mucosa of different mammals and submammalian vertebrates. The antisera specifically stained histidine decarboxylase-immunoreactive cells in the gastric mucosa of not only rat, but also of species like frog, chicken, mouse and dog. This is the first report describing the immunocytochemical distribution of the decarboxylase in the gastric mucosa of species other than rat. These antisera are likely to become valuable tools for further studies of the immunocytochemical localisation of histidine decarboxylase.

Histaminergic neuron system: morphological features and possible functions

The histaminergic neuron systems in rat brain have been identified by immunocytochemical techniques using antibodies against histidine decarboxylase or histamine itself. Here, the details of the distribution of the histaminergic neuron networks are presented. Judging from the widespread distribution of the nervous system, it is postulated that the histaminergic neuron system is involved in various brain functions. Some functions, including the circadian rhythms, sleep-arousal cycles, drinking, feeding, thermoregulation, and neuroendocrine controls which were elucidated by administration of alpha-fluoromethylhistidine, a suicide substrate for histidine decarboxylase, are discussed here, although the true functions are still under investigations.

Immuno-cross-reactivity of histidine and dopa decarboxylases

Immuno-cross-reactivity between histidine decarboxylase (HDC) and dopa decarboxylase (DDC) was investigated. By comparing the cDNA sequences of rat HDC with rat and guinea-pig DDCs, we found a region that may possibly be related to the cross-reactivity of anti-rat HDC antibody with guinea-pig DDC. The peptide encoded by this region was synthesized and anti-peptide antibody was prepared. We also purified HDC and DDC homogeniously from fetal rat liver and guinea-pig liver, respectively. On immunoblotting, anti-peptide antibody recognized both rat HDC and guinea-pig DDC. Anti-HDC polyclonal antibody which also recognizes both enzymes detected only rat HDC when it was absorbed by the peptide. This result indicates that this region is responsible for the immuno-cross-reactivity of anti-rat HDC antibody with guinea-pig DDC.

Immunohistochemical localization of 5-hydroxytryptamine, histamine and histidine decarboxylase in the rat major pelvic and coeliac-superior mesenteric ganglion

The localization of 5-hydroxytryptamine (5-HT), histamine and histidine decarboxylase (HDC), the enzyme synthesizing histamine, was studied in the rat major pelvic and coeliac-superior mesenteric ganglia by an indirect immunofluorescence technique. Small cells (10-20 microns in diameter) exhibiting 5-HT, histamine or HDC immunoreactivities were observed in clusters or occurred as solitary cells in both ganglia. In the major pelvic ganglia, solitary histamine-immunoreactive principal neurons were also observed. Colocalization studies indicated that all 5-HT-, histamine- and HDC-immunoreactive small cells in these ganglia were labelled with tyrosine hydroxylase (TH), suggesting that they are small intensely fluorescent (SIF) cells. In the coeliac-superior mesenteric ganglia, all TH-immunoreactive SIF cells were also intensely immunoreactive for 5-HT and HDC. In the major pelvic ganglia, all TH-immunoreactive SIF cells contained 5-HT immunoreactivity, and the majority of them were also intensely immunoreactive for HDC. In both ganglia, however, only a subpopulation of TH-immunoreactive SIF cells displayed histamine immunoreactivity. The results indicate that in the rat major pelvic and coeliac-superior mesenteric ganglia, a population of catecholamine-containing SIF cells contain 5-HT and histamine suggesting a diverse role SIF cells may have in so far as modulation of ganglion transmission is concerned.

Molecular cloning of guinea-pig aromatic-L-amino acid decarboxylase cDNA

Guinea-pig aromatic-L-amino acid decarboxylase (DOPA decarboxylase, DDC), but not rat DDC, reacts with the antibody against rat histidine decarboxylase (HDC). For determination of the molecular reaction for this cross-reactivity, a cDNA clone of guinea-pig DDC was isolated. Guinea-pig DDC consists of 480 amino acids and its molecular weight is 54,148. The sequence identify of guinea-pig DDC with rat DDC is 86%. Guinea-pig DDC has a region showing 100% sequence identity with rat HDC, but only 67% sequence identity with rat DDC, suggesting that this region is related with the cross-reactivity of guinea-pig DDC and anti-rat HDC antibody.

Characterization and expression of the complementary DNA encoding rat histidine decarboxylase

Histamine is a neurotransmitter in the central nervous system and an important modulator of gastric acid secretion, vasomotor control, inflammation, and allergic reactions. In biological systems the formation of histamine from its precursor histidine is catalyzed by the enzyme L-histidine decarboxylase (HDC; L-histidine carboxy-lyase, EC 4.1.1.22). We have cloned HDC-encoding cDNA from a fetal rat liver cDNA library (phage lambda gt11) have deduced the amino acid sequence from the nucleotide sequence. The clone was proven to be HDC cDNA by expression of active recombinant enzyme in COS cells and by chromosomal mapping. The cDNA encodes a protein of Mr 73,450 (655 amino acid residues). The discrepancy between this molecular weight and the size of the purified fetal liver protein subunits [Taguchi, Y., Watanabe, T., Kubota, H., Hayashi, H. & Wada, H. (1984) J. Biol. Chem. 259, 5214-5221] (Mr = 54,000) suggests that HDC may be posttranslationally processed. The 469 amino acid residues from the amino-terminal portion of the protein share 50% identity with rat and Drosophila L-dopa decarboxylases and much less homology with other characterized amino acid decarboxylases.

Histamine-immunoreactive nerve fibers in the rat brain

A new immunohistochemical method that utilizes carbodiimide as a tissue fixative was applied to study the distribution of histamine-immunoreactive neuronal fibers and terminals in the rat brain. Immunoreactive fibers were observed in almost all major regions of the brain. They were most numerous in the different hypothalamic nuclei. Dense networks of immunoreactive fibers were also seen in the medial septum, nucleus of the diagonal band and ventral tegmental area. A moderate density of fibers was seen throughout the cerebral cortex, in some parts of the olfactory bulb and tubercle, bed nucleus of the stria terminalis, amygdala, basal parts of the hippocampus, inferior and superior colliculi, substantia nigra, lateral and medial parabrachial nucleus, and the nucleus of the solitary tract. Few histamine-immunoreactive fibers were seen in most parts of the caudate putamen, most thalamic nuclei, most pontine and ventral medullary nuclei. Histamine-immunoreactive neuronal cell bodies were found exclusively in the tuberomammillary nucleus, in agreement with previous reports. The results provide evidence for a widespread distribution of histamine-containing nerve fibers and terminals in the rat brain. Although immunohistochemical localization of histamine does not give direct evidence of a functional role of histamine in any brain area, this distribution suggests involvement in functions of the limbic system including the septal nuclei, hypothalamus and amygdala. The relatively dense histamine-immunoreactive fiber networks in the colliculi and dorsal cochlear nucleus indicate that this amine may play a role in visual functions and hearing. The paucity of immunoreactive fibers in the pontine and medullary areas suggests that the caudal projections originating from the tuberomammillary complex are minor ones compared to the major rostral projections. Several fiber projections originating from the tuberomammillary complex could be deduced from serial frontal, sagittal and horizontal sections. They contained fibers that crossed the midline at several levels of the brain. The results provide information on the target areas of the histaminergic neurons and form a basis for the examination of cellular contracts between the histaminergic neurons and other cells.

Ontogeny of histidine-decarboxylase-immunoreactive neurons in the tuberomammillary nucleus of the rat hypothalamus: time of origin and development of transmitter phenotype

The ontogeny of the histidine decarboxylase (HDC)-immunoreactive neurons of the tuberomammillary (TM) nucleus was studied in the rat brain. The time of origin of TM neurons was studied by counting the percentage of HDC-immunopositive neurons double labelled by autoradiography in adult progeny of dams injected with [3H]-thymidine at various times during gestation. Neurogenesis began on embryonic day (E) 13, peaked on E16, and was complete by E18. HDC immunoreactivity was first detected in the fetal rat brain on E16. Experiments utilizing short-survival [3H]-thymidine autoradiography combined with HDC immunohistochemistry demonstrated that TM neurons undergo their final mitotic division prior to expression of their transmitter phenotype.

Organization of histaminergic fibers in the rat brain

Detailed information on innervation of the histaminergic system in the brain is essential to an understanding of the physiological roles of this system. In a previous immunocytochemical study with antihistidine decarboxylase (HDC) antibody, we detected extensive networks of histaminergic fibers in many areas of the rat brain (Watanabe et al., '84). In the present study, we improved the immunocytochemical procedure and examined the detailed distribution of histaminergic innervation in the rat brain with anti-HDC antibody. As reported previously, the highest concentrations of fibers were found in the hypothalamic nuclei and medial forebrain bundle. With the modified procedure, we detected more dense networks of HDC-immunoreactive (HDCI) fibers. Furthermore, we demonstrated for the first time the existence of HDCI fibers in other regions, namely, the thalamic nuclei, median eminence, fimbria of the hippocampus, habenular nuclei, superior colliculus, nucleus of the optic tract, parabrachial nuclei, mesencephalic trigeminal nucleus, superior, lateral, and spinal vestibular nuclei, posterior lobe of the hypophysis, and vascular organ of the lamina terminalis. We also found dense transverse fibers in the retrochiasmatic area and supraoptic decussation, which suggests bilateral innervation of the histaminergic system. These results indicate that innervation of the rat brain by the histaminergic system is more extensive than observed previously.

The histaminergic system in the guinea pig central nervous system: an immunocytochemical mapping study using an antiserum against histamine

Using an antiserum against conjugated histamine we mapped the histaminergic somata and their fiber projection areas in carbodiimide-fixed guinea pig central nervous system. The neurons were large and they were found exclusively in the posterior hypothalamus, as in the rat, but in the guinea pig they were more numerous and distributed more widely in thin layer around the posterior mammillary nucleus, scattered between and within the medial mammillary nuclei, and in a dense cell cluster emerging from the caudal magnocellular nucleus and extending to the medial preoptic area. The density of histamine-immunopositive fibers was very high in the olfactory tubercle, diagonal band of Broca, nucleus accumbens, medial and cortical amygdaloid nuclei, periventricular and lateral basal hypothalamus, paraventricular thalamus, and in a region from the medial central gray to the locus coeruleus and the parabrachial nucleus. Dense fiber networks were found in the piriform and entorhinal cortex, septum, dentate gyrus, and subiculum, in most parts of amygdala, and in many areas of the hypothalamus, thalamus, substantia nigra, raphe nuclei, inferior olivary, solitary tract and medial vestibular nuclei, and neurohypophysis. Medium fiber density was observed in the internal layers of the olfactory bulb, anterior olfactory nuclei, neocortex, zone CA1 of hippocampus, and many midbrain and hindbrain regions. Low density was present in the outer layers of the olfactory bulb, other parts of hippocampus, the globus pallidus, most of the caudatus-putamen, the cerebellar cortex, and the dorsal horn of the spinal cord. The retina and most of the myelinated white matter had single or no histaminergic fibers. It may be concluded from the results that most fibers seem to follow a ventromedial route to the forebrain, reaching the amygdala ventral to the medial forebrain bundle, the hippocampus via subiculum, and the hindbrain structures via the medial central gray. As compared to the rat, the fiber projections in the guinea pig brain were denser, particularly in the hippocampus, thalamus, pons-medulla, and neurohypophysis. The fiber densities in various regions of the guinea pig brain are compared to histamine receptor densities and the possible functions of histamine are discussed.

Morphological analysis of the tuberomammillary nucleus in the rat brain: delineation of subgroups with antibody against L-histidine decarboxylase as a marker

With an antibody specific for L-histidine decarboxylase (HD) in combination with immunohistochemical techniques and retrograde fluorescent tracing, the morphology, distribution, and projections of the histaminergic neurons of the posterior hypothalamus were studied in the adult male rat. Magnocellular neurons, situated on both sides of the mammillary recess and close to the ventral surface of the brain rostral and caudal to the mammillary bodies, were found to contain HD-immunoreactivity (HD-i). In addition to these magnocellular neurons, a substantial number of small and medium-sized neurons were immunostained, as were strands of cells of all sizes bridging the HD-i cell groups. A detailed mapping of the HD-i cells in frontal, sagittal, and horizontal sections showed that these neurons make up one continuous cell group, defined as the tuberomammillary nucleus (TM). This nucleus can be divided into several subgroups. Thus, approximately 600 HD-i neurons situated on each side of the mammillary recess compose the medial subgroup of the TM (TMM). The ventral subgroup of the TM (TMV) consists of some 1,500 neurons situated at the ventral surface of the brain, rostral (TMVr) and caudal (TMVc) to the mammillary bodies. The TMM contains a greater proportion of parvicellular neurons compared to the TMV. About 100 HD-i cells are scattered within the lateral hypothalamic area, the posterior hypothalamic region, the perifornical area, the supramammillary nucleus, and the dorsomedial hypothalamic nucleus. These cells are collectively named the diffuse part of the TM (TMdiff). The morphological differences between the TMM and the TMV did not signal differences in the efferent connections of these subgroups. Thus, single injections of the fluorescent tracer Fast Blue into different regions of the brain, including the spinal cord, resulted in retrograde labeling of HD-i neurons, which were distributed throughout the TM with no discernible topographic pattern. More specifically, each subgroup of the TM contributed projections innervating or passing through a large number of brain regions, including the olfactory bulb, hippocampus, caudate nucleus, paraventricular and supraoptic nuclei of the hypothalamus, cerebellum, tectum, medulla, and spinal cord. The widespread projections of the HD-i neurons contrasted to the more specific projections observed from non HD-i neurons in cell groups situated around the TM. Taken together, these findings suggest that the HD-i cells of the posterior hypothalamus constitute one major nucleus, the TM, and that this nucleus may be subdivided into three components, each of which has diffuse projections throughout the neuraxis.

Demonstration of histaminergic neurons in horizontal cells of guinea pig retina

The existence of L-histidine decarboxylase (HDC, EC 4.1.1.22)-like immunoreactive (HDC-I) cells in guinea pig retina was demonstrated using antiserum raised against HDC purified from fetal rat liver. The anti-HDC antiserum partially cross-reacted guinea pig L-DOPA decarboxylase (DDC, EC 4.1.1.28), so the histaminergic neurons were carefully identified. Comparison of HDC-I and DDC-like immunoreactive (DDC-I) cell types in adjacent sections revealed that HDC-I structures were found in some horizontal cells and amacrine cells, and double-staining procedures with anti-HDC antiserum and monoclonal anti-DDC antibody showed that HDC-I horizontal cells had no DDC-I structures, but all the HDC-I amacrine cells had DDC-I structures. From the results, some horizontal cells (with HDC-like immunoreactivities but without DDC-like immunoreactivities) were concluded to be histaminergic.

Demonstration of immunohistochemical and immunochemical cross-reactivity of L-histidine and L-dopa decarboxylases using antibodies against the two enzymes

Both rat L-histidine decarboxylase (HDC) and guinea-pig L-DOPA decarboxylase (DDC) were shown immunohistochemically and immunochemically to react with anti-rat HDC antibody. No cross-reaction was observed in immunoprecipitation experiments, but both anti-rat HDC antibody and anti-rat DDC antibody immunostained neurons in the substantia nigra, raphe nucleus and locus coeruleus of guinea-pig brain. Moreover, on immunoblotting, anti-rat HDC antibody recognized not only rat HDC but also guinea-pig DDC, but not rat DDC. However, anti-rat DDC antibody showed no immunohistochemical or immunochemical cross-reactivity with rat HDC.

Galanin immunoreactivity in hypothalamic neurons: further evidence for multiple chemical messengers in the tuberomammillary nucleus

By using a specific antibody against the 29 amino-acid peptide galanin (Gal) with light and electron microscopic immunocytochemistry, we have studied the distribution of Gal immunoreactivity in the posterior hypothalamic magnocellular neurons of the rat. In colchicine-treated rats, a large number of Gal-immunoreactive cells were identified within all subdivisions of the tuberomammillary nucleus. The majority of these cells are large multipolar or fusiform neurons, with long, sparsely branching dendrites. A small number project to the ventral hippocampus, as shown by experiments with the retrograde tracing of Fast Blue. Ultrastructural examination of the Gal-immunoreactive cells confirms their indentity as magnocellular neurons, with dense deposits of immunoreaction product, particularly in small ribosomal arrays and in large, dense-cored vesicles. Axosomatic synapses occur on these neurons. The axonal boutons synapse with asymmetric and symmetric junctions and contain small synaptic vesicles as well as numerous large, dense-cored vesicles, which display Gal immunoreactivity. Sequential staining of thin, alternate sections with antibodies against Gal and L-histidine decarboxylase (HDCase; EC 4.1.1.22) showed colocalization of Galand HDCase-immunoreactivities in a majority of tuberomammilary neurons. The finding of Gal immunoreactivity within histamine-producing neurons of the tuberomammillary nucleus adds to the multiplicity of potential neuronal messengers utilized by these cells.