Distribution of histamine in the cockroach brain and visual system: an immunocytochemical and biochemical study

A neurotransmitter histamine mediating phototransduction and photopreference in Callosobruchus maculatus

BACKGROUND

The biogenic amine histamine plays a critical role in the phototransduction and photopreference of most insects. Here, we study the function of histamine in Callosobruchus maculatus, a global storage pest.

RESULTS

In our experiment, we initially identified the histidine decarboxylase (hdc) gene through bioinformation analysis. We subsequently investigated effects of hdc and histamine on the photopreference of C. maculatus using a combination of RNA interference (RNAi), electroretinograms (ERG), immunostaining, and photopreference behavior approaches. Our results showed that histamine was required for visual signal transduction of C. maculatus, and increased its photopreference regardless of the wavelength.

CONCLUSION

This is the first study analyzing the molecular characteristics of C. maculatus photopreference, which forms the basis for a molecular mechanism for the effects of histamine on its visual transduction and preference. In practice, better understanding the photopreference patterns contributes to IPM (integrated pest management) for this storage pest. © 2023 Society of Chemical Industry.

Exposure to a sublethal concentration of CdO nanoparticles impairs the vision of the fruit fly (Drosophila melanogaster) by disrupting histamine synthesis and recycling mechanisms

While there is substantial literature on potential risks associated with exposure to emerging nanomaterials, less is known about the potential effects of hazardous metallic nanoparticles on vision, as well as the mechanisms that underpin them. The fruit fly (Drosophila melanogaster) was used as an in vivo model organism to investigate the effects of exposure to a sublethal concentration (0.03 mg CdO NPs/mL, which was 20% of the LC₅₀) on fly vision and compound eye ultrastructure. First, we observed a reduction in phototaxis response in treated flies but no change in locomotor activity. Because histamine (HA) has been linked to arthropod vision, we investigated HA synthesis, uptake, and recycling as a possible underlying mechanism for the observed adverse effect of CdO NPs on fly vision. This was accomplished by measuring the expression of the histamine decarboxylase (hdc) gene, which encodes the enzyme that converts the amino acid histidine to histamine (HA), as well as the expression of some genes involved in HA-recycling pathways (tan, ebony, Balat, CarT, and Lovit). The results showed that CdO NPs changed the expression levels of hdc, Lovit, tan, and eboney, indicating that HA synthesis, transport, and recycling were disrupted. Furthermore, less histamine immunolabeling was found in the head tissues of CdO NP-treated flies, particularly in the optic lobes. We also observed and quantified CdO NP bioaccumulation in compound eye tissues, which resulted in a number of cytological changes. Phenotypic effects (undersized eyes) have also been observed in the compound eyes of F1 flies. Considering the significance of vision in an organism's survival, the findings of this study are extremely crucial, as long-term exposure to CdO NPs may result in blindness.

Neurotransmitters of sleep and wakefulness in flatworms

STUDY OBJECTIVES

Sleep is a prominent behavioral and biochemical state observed in all animals studied, including platyhelminth flatworms. Investigations into the biochemical mechanisms associated with sleep-and wakefulness-are important for understanding how these states are regulated and how that regulation changed with the evolution of new types of animals. Unfortunately, beyond a handful of vertebrates, such studies on invertebrates are rare.

METHODS

We investigated the effect of seven neurotransmitters, and one pharmacological compound, that modulate either sleep or wakefulness in mammals, on flatworms (Girardia tigrina). Flatworms were exposed via ingestion and diffusion to four neurotransmitters that promote wakefulness in vertebrates (acetylcholine, dopamine, glutamate, histamine), and three that induce sleep (adenosine, GABA, serotonin) along with the H1 histamine receptor antagonist pyrilamine. Compounds were administered over concentrations spanning three to five orders of magnitude. Flatworms were then transferred to fresh water and video recorded for analysis.

RESULTS

Dopamine and histamine decreased the time spent inactive and increased distance traveled, consistent with their wake-promoting effect in vertebrates and fruit flies; pyrilamine increased restfulness and GABA showed a nonsignificant trend towards promoting restfulness in a dose-dependent manner, in agreement with their sleep-inducing effect in vertebrates, fruit flies, and Hydra. Similar to Hydra, acetylcholine, glutamate, and serotonin, but also adenosine, had no apparent effect on flatworm behavior.

CONCLUSIONS

These data demonstrate the potential of neurotransmitters to regulate sleep and wakefulness in flatworms and highlight the conserved action of some neurotransmitters across species.

External Influences on Invertebrate Brain Histamine and Related Compounds via an Automated Derivatization Method for Capillary Electrophoresis

Histamine has been shown to modulate visual system and photic behavior in arthropods. However, few methods are available for the direct quantification of histamine and its precursor and metabolites in arthropod brain. In this work, a method for the separation of histamine, its precursor histidine, and its metabolite N-methyl-histamine from brain extracts of a freshwater crustacean has been developed using capillary electrophoresis with laser-induced fluorescence detection. Molecules were tagged on their primary amine function with naphthalene-2,3-dicarboxaldehyde, but derivatized histamine and N-methyl-histamine exhibited poor stability in contrast to derivatized histidine. To overcome this limitation, an automated derivatization performed within the capillary electrophoresis instrument was optimized and quantitatively validated. The limits of detection were 50, 30, and 60 nmol/L for histidine, histamine, and N-methyl-histamine, respectively. This study reports, for the first time, the amounts of histamine and its related compounds in brain extracts from populations of the freshwater amphipod Gammarus fossarum, and shows that these amounts vary mainly according to population and season, but are not affected by an experimental electrical shock.

Calcium responses of circadian pacemaker neurons of the cockroach Rhyparobia maderae to acetylcholine and histamine

The accessory medulla (aMe) is the pacemaker that controls circadian activity rhythms in the cockroach Rhyparobia maderae. Not much is known about the classical neurotransmitters of input pathways to the cockroach circadian system. The circadian pacemaker center receives photic input from the compound eye, via unknown excitatory and GABAergic inhibitory entrainment pathways. In addition, neuropeptidergic inputs couple both pacemaker centers. A histamine-immunoreactive centrifugal neuron connects the ventral aMe with projection areas in the lateral protocerebrum and may provide non-photic inputs. To identify neurotransmitters of input pathways to the circadian clock with Fura-2-dependent Ca(2+) imaging, primary cell cultures of the adult aMe were stimulated with acetylcholine (ACh), as the most prominent excitatory, and histamine, as common inhibitory neurotransmitter. In most of aMe neurons, ACh application caused dose-dependent increases in intracellular Ca(2+) levels via ionotropic nicotinic ACh receptors. These ACh-dependent rises in Ca(2+) were mediated by mibefradil-sensitive voltage-activated Ca(2+) channels. In contrast, histamine application decreased intracellular Ca(2+) levels in only a subpopulation of aMe cells via H2-type histamine receptor chloride channels. Thus, our data suggest that ACh is part of the light entrainment pathway while histamine is involved in a non-photic input pathway to the ventral circadian clock of the Madeira cockroach.

Development of histamine-immunoreactivity in the Central nervous system of the two locust species Schistocerca gregaria and Locusta migratoria

Locusts are attractive model preparations for cellular investigations of neurodevelopment. In this study, we investigate the immunocytochemical localization of histamine in the developing ventral nerve cord of two locust species, Schistocerca gregaria and Locusta migratoria. Histamine is the fast neurotransmitter of photoreceptor neurons in the compound eye of insects, but it is also synthesized in interneurons of the central nervous system. In the locust ventral nerve cord, the pattern of histamine-immunoreactive neurons follows a relatively simple bauplan. The histaminergic system comprises a set of single, ascending projection neurons that are segmentally arranged in almost every neuromere. The neurons send out their axons anteriorly, forming branches and varicosities throughout the adjacent ganglia. In the suboesophageal ganglion, the cell bodies lie in a posteriolateral position. The prothoracic ganglion lacks histaminergic neurons. In the posterior ganglia of the ventral nerve cord, the somata of the histaminergic neurons are ventromedially positioned. Histamine-immunoreactivity starts around 50% of embryonic development in interneurons of the brain. Subsequently, the neurons of the more posterior ganglia of the ventral nerve cord become immunoreactive. From 60% embryonic development, the pattern of soma staining in the nerve cord appears mature. Around 65% of embryonic development, the photoreceptor cells show histamine-immunoreactivity. The histaminergic innervation of the neuropile develops from the central branches toward the periphery of the ganglia and is completed right before hatching.

The organization of the antennal lobe correlates not only with phylogenetic relationship, but also life history: a Basal hymenopteran as exemplar

The structure of the brain is a consequence of selective pressures and the ancestral brain structures modified by those pressures. The Hymenoptera are one of the most behaviorally complex insect orders, and the olfactory system of honeybees (one of the most derived members) has been extensively studied. To understand the context in which the olfactory system of the Hymenoptera evolved, we performed a variety of immunocytochemical and anatomical labeling techniques on the antennal lobes (ALs) of one of its most primitive members, the sawflies, to provide a comparison between the honeybee and other insect model species. The olfactory receptor neurons project from the antennae to fill the entire glomerular volume but do not form distinct tracts as in the honeybee. Labeling of projection neurons revealed 5 output tracts similar to those in moths and immunolabeling for several transmitters revealed distinct populations of local interneurons and centrifugal neurons that were also similar to moths. There were, however, no histaminergic or dopaminergic AL neurons. The similarities between sawflies and moths suggest that along with the great radiation and increased complexity of behavioral repertoire of the Hymenoptera, there were extensive modifications of AL structure.

Histamine-immunoreactive local neurons in the antennal lobes of the hymenoptera

Neural networks receive input that is transformed before being sent as output to higher centers of processing. These transformations are often mediated by local interneurons (LNs) that influence output based on activity across the network. In primary olfactory centers, the LNs that mediate these lateral interactions are extremely diverse. For instance, the antennal lobes (ALs) of bumblebees possess both gamma-aminobutyric acid (GABA)- and histamine-immunoreactive (HA-ir) LNs, and both are neurotransmitters associated with fast forms of inhibition. Although the GABAergic network of the AL has been extensively studied, we sought to examine the anatomical features of the HA-ir LNs in relation to the other cellular elements of the bumblebee AL. As a population, HA-ir LNs densely innervate the glomerular core and sparsely arborize in the outer glomerular rind, overlapping with the terminals of olfactory receptor neurons. Individual fills of HA-ir LNs revealed heavy arborization of the outer ring of a single "principal" glomerulus and sparse arborization in the core of other glomeruli. In contrast, projection neurons and GABA-immunoreactive LNs project throughout the glomerular volume. To provide insight into the selective pressures that resulted in the evolution of HA-ir LNs, we determined the phylogenetic distribution of HA-ir LNs in the AL. HA-ir LNs were present in all but the most basal hymenopteran examined, although there were significant morphological differences between major groups within the Hymenoptera. The ALs of other insect taxa examined lacked HA-ir LNs, suggesting that this population of LNs arose within the Hymenoptera and underwent extensive morphological modification.

Immunohistochemical mapping of histamine, dopamine, and serotonin in the central nervous system of the copepod Calanus finmarchicus (Crustacea; Maxillopoda; Copepoda)

Calanoid copepods constitute an important group of marine planktonic crustaceans that often dominate the metazoan biomass of the world's oceans. In proportion to their ecological importance, little is known about their nervous systems. We have used immunohistochemical techniques in a common North Atlantic calanoid to localize re-identifiable neurons that putatively contain the biogenic amines histamine, dopamine, and serotonin. We have found low numbers of such cells and cell groups (approximately 37 histamine pairs, 22 dopamine pairs, and 12 serotonin pairs) compared with those in previously described crustaceans. These cells are concentrated in the anterior part of the central nervous system, the majority for each amine being located in the three neuromeres that constitute the brain (protocerebrum, deutocerebrum, and tritocerebrum). Extensive histamine labeling occurs in several small compact protocerebral neuropils, three pairs of larger, more posterior, paired, dense neuropils, and one paired diffuse tritocerebral neuropil. The most concentrated neuropil showing dopamine labeling lies in the putative deutocerebrum, associated with heavily labeled commissural connections between the two sides of the brain. The most prominent serotonin neuropil is present in the anterior medial part of the brain. Tracts of immunoreactive fibers of all three amines are prominent in the cephalic region of the nervous system, but some projections into the most posterior thoracic regions have also been noted.

Histamine in the nervous system

Histamine is a transmitter in the nervous system and a signaling molecule in the gut, the skin, and the immune system. Histaminergic neurons in mammalian brain are located exclusively in the tuberomamillary nucleus of the posterior hypothalamus and send their axons all over the central nervous system. Active solely during waking, they maintain wakefulness and attention. Three of the four known histamine receptors and binding to glutamate NMDA receptors serve multiple functions in the brain, particularly control of excitability and plasticity. H1 and H2 receptor-mediated actions are mostly excitatory; H3 receptors act as inhibitory auto- and heteroreceptors. Mutual interactions with other transmitter systems form a network that links basic homeostatic and higher brain functions, including sleep-wake regulation, circadian and feeding rhythms, immunity, learning, and memory in health and disease.

The dynamics of signaling at the histaminergic photoreceptor synapse of arthropods

Histamine, a ubiquitous aminergic messenger throughout the body, also serves as a neurotransmitter in both vertebrates and invertebrates. In particular, the photoreceptors of adult arthropods use histamine, modulating its release to signal increases and decreases in light intensity. Strong evidence from various arthropod species indicates that histamine is synthesized and stored in photoreceptors, undergoes Ca-dependent release, inhibits postsynaptic interneurons by gating Cl channels, and is then recycled. In Drosophila, the synthetic enzyme, histidine decarboxylase, and the subunits of the histamine-gated chloride channel have been cloned. Possible histamine transporters at synaptic vesicles and for reuptake remain elusive. Indeed, the mechanisms that remove histamine from the synaptic cleft, and that help terminate histamine's action, are unexpectedly complex, their details remaining unresolved. A major pathway in Drosophila, and possibly other arthropod species, is by conjugation of histamine to beta-alanine to form carcinine in adjacent glia. This conjugate then returns to the photoreceptors where it is hydrolysed to liberate histamine, which is then loaded into synaptic vesicles. Evidence from other species suggests that direct reuptake of histamine into the photoreceptors may also occur. Light depolarizes the photoreceptors, causing histamine release and postsynaptic inhibition; dimming hyperpolarizes the photoreceptors, causing a decrease in histamine release and an "off" response in the postsynaptic cell. Further pursuit of histamine's action at these highly specialized synapses should lead to an understanding of how they signal minute changes in presynaptic membrane potential, how they reliably extract signals from noise, and how they adapt to a wide range of presynaptic membrane potentials.

Role of histamine as a putative inhibitory transmitter in the honeybee antennal lobe

Background

Odors are represented by specific spatio-temporal activity patterns in the olfactory bulb of vertebrates and its insect analogue, the antennal lobe. In honeybees inhibitory circuits in the AL are involved in the processing of odors to shape afferent odor responses. GABA is known as an inhibitory transmitter in the antennal lobe, but not all interneurons are GABAergic. Therefore we sought to analyze the functional role of the inhibitory transmitter histamine for the processing of odors in the honeybee AL.

Results

We optically recorded the representation of odors before, during and after histamine application at the input level (estimated from a compound signal), and at the output level (by selectively measuring the projection neurons). For both, histamine led to a strong and reversible reduction of odor-evoked responses.

Conclusion

We propose that histamine, in addition to GABA, acts as an inhibitory transmitter in the honeybee AL and is therefore likely to play a role in odor processing.

Mapping of serotonin, dopamine, and histamine in relation to different clock neurons in the brain of Drosophila

Several sets of clock neurons cooperate to generate circadian activity rhythms in Drosophila melanogaster. To extend the knowledge on neurotransmitters in the clock circuitry, we analyzed the distribution of some biogenic amines in relation to identified clock neurons. This was accomplished by employing clock neuron-specific GAL4 lines driving green fluorescent protein (GFP) expression, combined with immunocytochemistry with antisera against serotonin, histamine, and tyrosine hydroxylase (for dopamine). In the larval and adult brain, serotonin-immunoreactive (-IR) neuron processes are in close proximity of both the dendrites and the dorsal terminals of the major clock neurons, the s-LN(v)s. Additionally, the terminals of the l-LN(v) clock neurons and serotonergic processes converge in the distal medulla. No histamine (HA)-IR processes contact the s-LN(v)s in the larval brain, but possibly impinge on the dorsal clock neurons, DN2. In the adult brain, HA-IR axons of the extraocular eyelet photoreceptors terminate on the dendritic branches of the LN(v)s. A few tyrosine hydroxylase (TH)-IR processes were seen close to the dorsal terminals of the s-LN(v)s, but not their dendrites, in the larval and adult brain. TH-IR processes also converge with the distal medulla branches of the l-LN(v)s in adults. None of the monoamines was detectable in the different clock neurons. By using an imaging system to monitor intracellular Ca(2+) levels in dissociated GFP-labeled larval s-LN(v)s, loaded with Fura-2, we demonstrated that application of serotonin induced dose-dependent decreases in Ca(2+). Thus, serotonergic neurons form functional inputs on the s-LN(v)s in the larval brain and possibly also in adults.

Acetylcholine, GABA and glutamate induce ionic currents in cultured antennal lobe neurons of the honeybee, Apis mellifera

The honeybee, Apis mellifera, is a valuable model system for the study of olfactory coding and its learning and memory capabilities. In order to understand the synaptic organisation of olfactory information processing, the transmitter receptors of the antennal lobe need to be characterized. Using whole-cell patch-clamp recordings, we analysed the ligand-gated ionic currents of antennal lobe neurons in primary cell culture. Pressure applications of acetylcholine (ACh), gamma-amino butyric acid (GABA) or glutamate induced rapidly activating ionic currents. The ACh-induced current flows through a cation-selective ionotropic receptor with a nicotinic profile. The ACh-induced current is partially blocked by alpha-bungarotoxin. Epibatidine and imidacloprid are partial agonists. Our data indicate the existence of an ionotropic GABA receptor which is permeable to chloride ions and sensitive to picrotoxin (PTX) and the insecticide fipronil. We also identified the existence of a chloride current activated by pressure applications of glutamate. The glutamate-induced current is sensitive to PTX. Thus, within the honeybee antennal lobe, an excitatory cholinergic transmitter system and two inhibitory networks that use GABA or glutamate as their neurotransmitter were identified.

Neurochemical characterization of nervous elements innervating the body wall of earthworms (Lumbricus, Eisenia): immunohistochemical and pharmacological studies

The distribution and chemical neuroanatomy of nervous elements and certain pharmacological-physiological characteristics of the innervation of the body wall in earthworms are described. Solitary sensory bipolar cells can be found among the epithelial cells. These bipolar cells contain serotonin, tyrosine hydroxylase, histamine, gamma-amino-butyric acid (GABA), Eisenia tetradecapeptide, proctolin or rhodopsin in various combinations. In the body wall, the plexus sub-muscularis is composed of nerve fibres only, whereas the plexus sub-epithelialis and muscularis also contain solitary nerve cells. These cells display histamine, GABA or neuropeptide Y immunoreactivity. The fibres of the three plexuses are reactive to serotonin, histamine, Eisenia tetradecapeptide, proctolin, GABA and neuropeptide Y antibodies. FMRFamide-immunoreactive fibres of the plexus muscularis originate from the central nervous system, whereas axons containing the other studied molecules are derived from both peripheral and central structures. High pressure liquid chromatography assays have revealed serotonin, dopamine and histamine in the body wall. Contractions of the body wall musculature can be elicited with serotonin and FMRFamide. Serotonin-evoked contractions are suppressed by the application of GABA. Serotonin acts both directly on the muscle cell receptors and indirectly through initiating transmitter release from the nervous elements, whereas the FMRFamide-induced contractions seem to be mediated through the muscle cell receptors only. The pharmacological profiles of the serotonin and GABA receptors resemble those of the vertebrate 5-HT(3) and GABA(B) receptor types. Our findings indicate that both the sensory and efferent system of the annelid body wall operate by means of a variety of neuroactive compounds, suggesting a complex role of signalling systems in the regulation of this organ.

Immunocytochemical identification of neuroactive substances in the antennal lobe of the male silkworm moth Bombyx mori

As a first step towards understanding the functional role of neuroactive substances in the first olfactory center of the male silkworm moth Bombyx mori, we carried out an immunocytochemical identification of antennal lobe neurons. Antibodies against gamma-aminobutyric acid (GABA), FMRFamide, serotonin, tyramine and histamine were applied to detect their existence in the antennal lobe. In the present immunocytochemical study, we clarified four antenno-cerebral tracts from their origin and projection pathways to the protocerebrum, and revealed the following immunoreactive cellular organization in the antennal lobe. 1) Local interneurons with cell bodies in the lateral cell cluster showed GABA, FMRFamide and tyramine immunoreactivity. 2) Projection neurons passing through the middle antenno-cerebral tract with cell bodies in the lateral cell cluster showed GABA and FMRFamide immunoreactivity. Projection neurons passing through the outer antenno-cerebral tract with cell bodies in the lateral cell cluster showed FMRFamide immunoreactivity. 3) Centrifugal neurons passing through the inner antenno-cerebral tract b with cell bodies located outside the antennal lobe showed serotonin and tyramine immunoreactivity. Our results revealed basic distribution patterns of neuroactive substances in the antennal lobe and indicated that each projection pathway from the antennal lobe to the protocerebrum contains specific combination of neuroactive substances.

Histamine compartments of the Drosophila brain with an estimate of the quantum content at the photoreceptor synapse

Reliable estimates of the quantum size in histaminergic neurons are not available. We have exploited two unusual opportunities in the fly's (Drosophila melanogaster) visual system to make such determinations for histaminergic photoreceptor synapses: 1) the possibility to microdissect successively from whole fly heads freeze-dried in acetone: the compound eyes; the first optic neuropils, or lamina; and the rest of the brain; and 2) the uniform sheaves of lamina synaptic terminals of photoreceptors R1-R6. We used this organization to count scrupulously the numbers of 30-nm synaptic vesicles from electron micrographs of R1-R6 profiles, and from microdissections we determined the regional contents of histamine in the compound eye, lamina, and central brain. Total head histamine averages 1.98 ng of which 9% was lost after freeze-drying in acetone and a further 28% after the brain was microdissected. Of the remainder, 71% was in the eye and lamina. Assuming that histamine loss from the tissue occurred mostly by diffusion evenly distributed among all regions, the overall lamina content of the head would be 0.1935 ng before dissection. From published values for the volumes of the brain's compartments, the computed regional concentrations of histamine are highest in the lamina (4.35 mM) because of the terminals of R1-R6. The concentration in the retina is approximately 13% that in the lamina, suggesting that most histamine is vesicular. There are approximately 43,500 +/- 7,400 (SD) synaptic vesicles per terminal and, if all histamine is allocated equally and exclusively among these, the vesicle contents would be 858 +/- 304 x 10(-21) moles or approximately 5,000 +/- 1,800 (SD) molecules at an approximate concentration of 670 mM. These values are compared with the vesicle contents at synapses using acetylcholine and catecholamines.

Embryogenesis of the histaminergic system in the pond snail, Lymnaea stagnalis L.: an immunocytochemical and biochemical study

Embryogenesis of the histaminergic system in the pond snail, Lymnaea stagnalis, was investigated by means of immunocytochemistry and HPLC assay. From the earliest onset of the of histamine-immunoreactive (HA-IR) elements, the labelled neurons were confined to the pedal, cerebral and buccal ganglia, whereas no IR cells within the pleural, parietal and visceral ganglia were detectable during the embryogenesis. Peripheral projections of the embryonic HA-IR neurons were missing. No transient HA-IR neurons could be found either inside or outside the CNS. The first HA-IR elements appeared at about E55% of embryonic development, at the beginning of metamorphosis, and were represented by three pairs of neurons located in the cerebral ganglia. Following metamorphosis, four pairs of HA-IR neurons were added; two of them occurred in the pedal (E65% stage of development) and two in the buccal (E90% stage of development) ganglia. During embryogenesis, HA-IR fibers were present in the cerebro-pedal connectives and in the cerebral, pedal and buccal commissures, whereas only little arborization could be observed in the neuropil of the ganglia. HPLC measurements revealed a gradual increase of HA content in the embryos during development, corresponding well to the course of the appearance of immunolabeled elements. It is suggested that the developing HAergic system plays a specific role in the process of gangliogenesis and CNS plasticity of embryonic Lymnaea.

Histaminergic neurons in the central and peripheral nervous system of gastropods (Helix, Lymnaea): An immunocytochemical, biochemical, and electrophysiological approach

Distribution, chemical-neuroanatomy, concentration, and uptake-release properties of histamine (HA)-containing neurons and the possible physiological effects of HA in the central and peripheral nervous system of the pulmonate snails, Helix pomatia and Lymnaea stagnalis, are described. In the CNS of both species, the distribution pattern of HA-immunoreactive (HA-IR) neurons was similar. In both species the majority were located in the buccal, cerebral, and pedal ganglia. In Helix, approximately 400 HA-IR neurons were seen, whereas in Lymnaea approximately 130 labeled cells were visualized. The neuropils, connectives, commissures, several peripheral nerves, and a part of the peripheral tissues (lip and foot of both species and the upper tentacles of Helix) were innervated by HA-IR elements. Numerous sensory cells were found in the tentacles, lip, and statocysts. The HA concentration values assayed by HPLC ranged from 4.8 to 47.4 pmol/mg in the different central ganglia of Helix, and from 4.3 to 18.6 pmol/mg in Lymnaea CNS, whereas the peripheral tissues contained 0.33-1 pmol/mg HA in Helix and 0.26-0.46 pmol/mg in Lymnaea. In the Lymnaea CNS, a high-affinity (37.6 microM), single component 3H-HA uptake system was demonstrated. 3H-HA release evoked by either electrical stimulation or 100 mM K+ could be prevented in Ca2+-free physiological solution. Voltage-clamp experiments indicated specific changes caused by HA in the membrane conductance of identified central neurons of Helix and Lymnaea. Exogenously applied 10(-5) M HA resulted in the acceleration of locomotion (gliding by foot cilia) of Lymnaea. The findings suggest an important signaling role of HA, described here for the first time, in the nervous system of higher-order, pulmonate, gastropods, involving efferent, integrative, and sensory functions. The data can also be applied as a background for further specification of HA in the regulation of different behaviors in these species.

Mitochondria are redistributed in Drosophila photoreceptors lacking milton, a kinesin-associated protein

Photoreceptors are richly supplied with mitochondria, where they are required to meet the energetic demands, in the soma, of phototransduction and, in the terminal, of neurotransmitter release. Compromising the latter, we have made photoreceptors R1-R6 in Drosophila ommatidia homozygous for either of two alleles, milt(186) and milt(92), of milton in whole-eye mosaics. Such mutant photoreceptors fail to target mitochondria to their terminals. We show from quantitative electron microscopy (EM) that mitochondria are totally lacking at the terminal but nevertheless abundant and present throughout the soma, where their distribution differs from that of control ommatidia, however, being more heavily concentrated in the nuclear region. Mitochondria are sparse at the basalmost level of mutant ommatidia, and are lacking beneath the basement membrane, in the axons and terminals of these cells. The absence of mitochondria from R1-R6 terminals and concommitant reductions in synaptic vesicle packing density, previously reported, we show here are accompanied by reduced immunoreactivity to the photoreceptor transmitter histamine but not by any change in total head histamine content, as determined by high-performance liquid chromatography. Mutant terminals also contain vesicle profiles with a wider range of sizes. These two phenotypes suggest that the reduced availability of ATP when mutant terminals lack a mitochondrial supply compromises their ability to pump histamine into synaptic vesicles and perturbs membrane distribution within the terminal. In addition, a band of somata in the lamina cortex, at least some of which are postsynaptic neurons not homozygous for milton, also shows altered mitochondrial targeting, with abnormal clusters of mitochondria, as visualized by immunolabeling with anti-hsp and by serial EM. Within the lamina, terminals of mutant photoreceptors are penetrated by neighboring cells with invaginations that frequently contain mitochondria, suggesting that a mechanism exists for intercellular metabolic support. Our findings indicate the direct and compensatory responses in a population of neurons when mitochondria are not correctly targeted to their synaptic terminals.

The phylogenetic significance of crustacean optic neuropils and chiasmata: a re-examination

Recent molecular data challenge the traditional hypotheses of arthropod phylogeny founded on morphologic characters. In this discussion, the structure of the visual systems in Pterygota (Hexapoda) and Decapoda (Malacostraca, Crustacea) is an important argument. Although many components of their visual systems depict structural homology, differences exist between Pterygota/Decapoda on the one side and Branchiopoda (Entomostraca) on the other in that the latter do not have a third optic neuropil or optic chiasmata. Therefore, the goals of the current study were to explore whether the third optic neuropils in Pterygota and Decapoda are homologous, to examine the formation of the first two optic neuropils and the chiasmata in Crustacea, and to compare these processes with Pterygota. For this purpose, five species of entomostracan and malacostracan crustaceans were analyzed by examination of serial sections, fluorescence labeling with phallotoxins, and anti-histamine immunohistochemistry. We found that the chiasmata of Decapoda and Pterygota are characterized by striking similarities regarding both the level of individually identifiable classes of neurons and ontogenetic mechanisms, which are clearly different from those in Branchiopoda. Furthermore, the third optic neuropil of Decapoda and Pterygota, the lobula, shares an ontogenetic protocerebral origin and an innervation by corresponding sets of histamine-immunoreactive neurons, suggesting homology of the lobula in these two groups. In conclusion, the characteristics of the visual system are in conflict with the traditional classification of Arthropoda. Instead, they support a sister-group relationship of Hexapoda and Malacostraca, as suggested by some of the molecular studies.

Histamine metabolism in the visual system of the horseshoe crab Limulus polyphemus

There is now strong evidence that arthropod photoreceptors use histamine as a neurotransmitter. The synthesis, storage and release of histamine from arthropod photoreceptors have been demonstrated, and the postsynaptic effects of histamine and the endogenous neurotransmitter are similar. However, a full understanding of these photoreceptor synapses also requires knowledge of histamine inactivation and metabolism. Relatively little is known about histamine metabolism in the nervous system of arthropods, and mechanisms appear to differ with the species. This study focuses on histamine metabolism in visual tissues of the horseshoe crab Limulus polyphemus, a chelicerate. We present two major findings: (1) histamine is metabolized to imidazole acetic acid and to gamma-glutamyl histamine. (2) relatively low levels of histamine metabolites accumulate in Limulus visual tissues.

An immunohistochemical study of structure and development of the nervous system in the brine shrimp Artemia salina Linnaeus, 1758 (Branchiopoda, Anostraca) with remarks on the evolution of the arthropod brain

Brain morphology is an important character in the discussion of arthropod relationships. While a large body of literature is available on the brains of Hexapoda and Malacostraca, the structure of the brain has been rarely studied in representatives of the Entomostraca. This account examines the morphology and development of the nervous system in the brine shrimp Artemia salina Linnaeus, 1758 (Crustacea, Branchiopoda, Anostraca) by classical histology and immunohistochemistry against synaptic proteins (synapsins), and the neurotransmitters serotonin and histamine. The results indicate that the shape of the developing larval brain in A. salina (a circumstomodeal ring of neuropil) closely resembles that in malacostracan embryos. Furthermore, the organization of the central complex as well as the tritocerebral innervation pattern of the labrum is homologous in this species and in Malacostraca. Nevertheless, differences exist in the layout of the deutocerebrum, specifically in the absence of olfactory glomeruli in A. salina while the glomerular organization of the olfactory lobe is a character in the ground pattern of Malacostraca. These findings are compared to the brain structure in other Euarthropoda and possible phylogenetic implications are discussed.

The determination of histamine in the Drosophila head

Histamine is a neurotransmitter at arthropod photoreceptors. Even though the fruit fly, Drosophila melanogaster, is a widely used model in neuroscience research, the histamine content of its nervous system has not so far been reported. We have developed a high performance liquid chromatography (HPLC) method with pre-column o-phtaldialdehyde-mercaptoethanol (OPA-ME) derivatization and electrochemical detection, to determine this amine in Drosophila. The histamine content of the fly's head averages about 2.0 ng per head. In heads of the mutant hdc(JK910), a presumed null for the gene encoding the enzyme that synthesizes histamine, histamine was not detected in measurable amounts. In heads of the mutant sine oculis, which lacks compound eyes, only 28% of this amine was found compared with wild type flies, so histamine is mainly present in the compound eye photoreceptors. Also observed in histamine-deficient mutants was a decrease in the peak which contains a substance having the same retention time as carcinine (beta-alanyl-histamine). Our method was not able to detect compounds previously reported as histamine metabolites in insects. In spite of this, the method we have developed enables the fast and accurate measurement of histamine in the heads of Drosophila, suitable for screening mutants.

Histamine-immunoreactive neurons in the brain of the cockroach Leucophaea maderae

Histamine is the neurotransmitter of insect photoreceptor cells but has also been found in a small number of interneurons in the insect brain. In order to investigate whether the accessory medulla (AMe), the putative circadian pacemaker of the cockroach Leucophaea maderae receives direct visual input from histaminergic photoreceptors, we analyzed the distribution of histamine-like immunoreactivity in the optic lobe and midbrain of the cockroach. Intense immunostaining was detected in photoreceptor cells of the compound eye, which terminated in the first optic neuropil, the lamina, and in a distal layer of the medulla, the second optic neuropil. Histamine immunostaining in parts of the AMe, however, originated from a centrifugal neuron of the midbrain. Within the midbrain 21-23 bilaterally symmetric pairs of cell bodies were stained. Most areas of the brain were innervated by one or more of these neurons, but the protocerebral bridge and the mushroom bodies were devoid of histamine immunoreactivity. The branching patterns of most histamine-immunoreactive neurons could be reconstructed individually. While the majority of identified neurons arborized in both brain hemispheres, five cells were local neurons of the antennal lobe. A comparison with other insect species shows striking similarities in the position of certain histamine-immunoreactive neurons, but considerable variations in the presence and branching patterns of others. The data suggest a role for histamine in a non-photic input to the circadian system of the cockroach.

Uptake of precursor and synthesis of transmitter in a histaminergic photoreceptor

As a first step in understanding how the supply of the neurotransmitter histamine is maintained in a photoreceptor, we followed the uptake and metabolism of the immediate precursor of histamine, histidine. [3H]Histidine taken up into photoreceptors and glia was detected using autoradiography, and synthesis of [3H]histamine from [3H]histidine was assayed with thin-layer chromatography. Photoreceptors from barnacles were pulsed (15 min) with [3H]histidine (0.2-200 microM), then maintained in normal saline for up to 24 hr. Autoradiography showed that photoreceptor somata, axons, and presynaptic arbors were labeled, but only weakly, like (nonhistaminergic) ganglion cells. Label instead was concentrated over surrounding glia. Stimulating preparations with light did not increase photoreceptor labeling. Grain counts from photoreceptor axons showed uptake of [3H]histidine into these neurons by a Na+-dependent mechanism with a Km of approximately 50 microM. Over 24 hr only 1% of the [3H]histidine taken up by preparations was converted to [3H]histamine either in the dark or in the light. Injections of [3H]histidine directly into photoreceptors established that synthesis takes place within the photoreceptors and confirmed that stimulation with light did not measurably affect the rate of conversion of [3H]histidine to [3H]histamine. These results suggest that de novo synthesis of transmitter is unlikely to be as important as its reuptake in maintaining neurotransmitter supply in these photoreceptor terminals. In support of this conclusion, photoreceptors accumulated more label when transmitter release was stimulated with high K+ and histamine uptake was antagonized with chlorpromazine.

Neuropeptides in insect sensory neurones: tachykinin-, FMRFamide- and allatotropin-related peptides in terminals of locust thoracic sensory afferents

Sensory afferents in the thoracic ganglia of the locust Locusta migratoria were labelled with antisera to different neuropeptides: locustatachykinins, FMRFamide and allatotropin. The locustatachykinin-immunoreactive (LTKIR) sensory fibres were derived from the legs and entered the ventral sensory neuropil of each of the thoracic ganglia via nerve 5. In the thoracic neuropil, the LTKIR sensory fibres formed a distinct plexus of terminations ventrally in the ipsilateral hemisphere. The peripheral cell bodies of the sensory neurones could not be revealed, but lesion experiments indicated that origin of the LTKIR fibres was the tarsus of each leg. Possibly the thin fibres are from tarsal chemoreceptors. Double labelling immunocytochemistry revealed that all the LTKIR sensory fibres contained colocalized FMRFamide immunoreactivity. A larger population of sensory fibres reacted with antiserum to moth (Manduca sexta) allatotropin. By means of double labelling immunocytochemistry, we could show that the LTKIR fibres constituted a subpopulation of the larger set of allatotropin-like immunoreactive fibres. Thus some sensory fibres may contain colocalized peptides related to locustatachykinins, FMRFamide-related peptide(s) and allatotropin-like peptide. A separate non-overlapping small set of sensory fibres in nerve 5 reacted with an antiserum to serotonin. Sensory fibres of the other nerves of the ventral nerve cord, including the abdominal ganglia, did not react with the peptide antisera. Since acetylcholine is the likely primary neurotransmitter of insect sensory fibres, it is possible that the peptides and serotonin are colocalized with this transmitter and serve modulatory functions in a subset of the leg afferents.

Distribution of histamine in the CNS of different spiders

Immunohistochemistry is used to demonstrate histamine-immunoreactivity in the CNS of spiders. We found histamine-immunoreactivity in the photoreceptors of different spiders. Therefore, we suggest that histamine is a neurotransmitter of photoreceptors in all arthropods, since it is also known to occur in the photoreceptors of the other main arthropod taxa (Merostomata, Crustacea, and Insecta). We also describe a system of only six omnisegmental histamine-immunoreactive neurons within the central nervous system. These histamine-immunoreactive neurons can be divided into two subgroups: a dorsal system with two cells per hemisphere and a ventral system with only one cell per hemisphere. All six cells have extended arborizations in both the motor and the sensory areas of all neuromeres in the suboesophageal ganglionic mass. In contrast to araneomorph spiders, two additional sets of histamine-immunoreactive neurons were detected in mygalomorph spiders. The first set consists of seventeen cells with their cell bodies located in the cheliceral ganglion and projecting to central areas of the protocerebrum. The second set contains many if not all sensory projections from the tarsal organs on all eight legs and the pedipalps to the Blumenthal neuropil.

Histamine in the brain of insects: a review

Histamine is the neurotransmitter of photoreceptors in insects and other arthropods. As a photoreceptor transmitter, histamine acts on ligand-gated chloride channels. Another type of histamine receptor has been indicated in the insect central nervous system by binding pharmacology. This receptor is similar to the mammalian H1 receptors, which are G-protein coupled and thus utilize a second messenger system. The distribution of histamine-immunoreactive (HAIR) neurons has been studied in a few insect species: cockroaches, locust, crickets, honey bee, blowflies, and in Drosophila. In addition to its presence in photoreceptor cells, histamine is distributed in a rather small number of neurons in the insect brain. Many of these neurons have extensive bilateral arborizations that innervate several distinct neuropil regions, notably in the protocerebrum. Some patterns of histamine distribution are seen in all the species. On the other hand, the number and morphology of neurons differ between the studied species, and several major neuropils (central body, antennal lobes, mushroom bodies) are supplied by HAIR neurons in some species, but not in others. Thus it appears that there are some species-specific functions of histamine and on others that are preserved between species. Some of the histaminergic neurons may constitute wide field inhibitory systems with functions distinct from those of neurons containing gamma-amino butyric acid (GABA). Novel data are presented for Drosophila and the cockroach Leucophaea maderae and a comparison is made with published data on other insects.

The distribution of histamine and serotonin in the barnacle's nervous system

The use of antisera directed against conjugates of histamine and serotonin has revealed the locations of neurons labeling for these transmitters in the nervous system of barnacles. Photoreceptors label for histamine but not serotonin and also satisfy a number of other criteria indicating that histamine is their neurotransmitter. Photoreceptors also take up radioactively labeled histamine but not serotonin. Within the barnacle's brain no somata are consistently found that label with antiserum against histamine, but one to three pairs of small cells, depending on species, label with antiserum against serotonin. The most impressive serotonin-like immunoreactivity in the brain, however, is in a pair of large fibers ascending through the circumesophageal connectives and ramifying extensively. Within the ventral ganglion, the only other ganglion in the barnacle, ten pairs of cells label with antiserum against histamine. These neurons are confined to the posterior portion of the ganglion but ramify extensively throughout the ganglion. Antiserum against serotonin labels about 15 cell pairs, depending on species, located throughout the ganglion. The positions of the arbors of many of these cells suggest that these amines have a role in modulating either the motor pathways underlying feeding or the visual pathways responsible for the detection of shadows.

Cytoarchitecture of histamine-, dopamine-, serotonin- and octopamine-containing neurons in the cricket ventral nerve cord

The present article provides a comparative neuroanatomical description of the cellular localization of the biogenic amines histamine, dopamine, serotonin and octopamine in the ventral nerve cord of an insect, namely the cricket, Gryllus bimaculatus. Generally, different immunocytochemical staining techniques reveal a small number of segmentally distributed immunoreactive (-IR) amine-containing neurons allowing single cell reconstruction of prominent elements. Aminergic neurons share common morphological features in that they innervate large portions of neurophil and often connect different neuromeres by intersegmental 'wide-field' projections of varicose appearance. In many cases aminergic terminals are also found on the surface of peripheral nerves suggesting additional neurohemal release sites. Despite such morphological similarities histological analysis demonstrates for any given amine functionally distinct neuron types with specific innervation patterns establishing discrete pathways. Histamine-IR interneurons are characterized by both ascending and descending projections forming central and peripheral terminals. The descending branches from dopamine-IR cells mainly converge within the terminal ganglion, whereas serotonin-IR interneurons with ascending projections often terminate within the brain. Serotonin is also present in sensory and motor neurons. In contrast to other aminergic neurons, most octopamine-IR cells represent unpaired neurons projecting through motor nerves of the soma-containing neuromere. Octopamine-IR cells with intersegmental branches are only rarely found. Based on these findings, a colocalization of different amines within the same neuron seems to be unlikely to occur in the cricket ventral nerve cord. With respect to the neuroanatomical description of amine-containing neurons known physiological effects of biogenic amines and their possible neuromodulatory functions in insects are discussed.

Widespread distribution of histamine in the nervous system of a trematode flatworm

In general, most flatworms contain very little histamine (HA) and their nervous systems often lack, or contain very few, histaminergic elements. However, preliminary studies in our laboratory have revealed that the frog lung parasite, Haplometra cylindracea (Trematoda: Digenea), contains HA in a very high concentration. For this reason, the present study was undertaken to study the localization and synthesis of HA in this worm by using immunocytochemistry and high-pressure liquid chromatography (HPLC). Essentially all parts of the nervous system of H. cylindracea showed HA-like immunoreactivity. The paired cerebral ganglia and nerves emanating from these, including the longitudinal nerve cords, were intensely immunoreactive. The musculature of the pharynx, oral and ventral suckers, and those of the reproductive organs were all innervated by HA-immunoreactive fibers. Fiber plexuses beneath the tegument and throughout the parenchyma also showed HA-like immunoreactivity. HPLC studies revealed one of the highest HA concentrations in the animal kingdom, 6.49 +/- 1.36 nmole/mg protein, in the worm. The frog lung and blood contained very low concentrations of HA and could be excluded as sources for HA, while an enzyme assay revealed that the worm produces HA by decarboxylation of histidine. Thus, it is likely that H. cylindracea uses HA as a neurotransmitter or modulator.

Insect neurotransmission: neurotransmitters and their receptors

The roles of acetylcholine, dopamine, octopamine, tyramine, 5-hydroxytryptamine, histamine, glutamate, 4-aminobutanoic acid (gamma-aminobutyric acid) and a range of peptides as insect neurotransmitters are evaluated in terms of the criteria used to identify transmitters. Of the biogenic amines considered, there is good evidence that acetylcholine, dopamine, octopamine, 5-hydroxytryptamine, and histamine should be considered to be neurotransmitters, but the case for tyramine is less convincing at the moment. The evidence supporting neurotransmitter roles for glutamate and gamma-aminobutyric acid at specific insect synapses is overwhelming, but much work remains to be undertaken before the full significance of these molecules in the insect nervous system is appreciated. Attempts to characterise biogenic amine and amino acid receptors using pharmacological and molecular biological techniques have revealed considerable differences between mammalian and insect receptors. The number of insect neuropeptides isolated and identified has increased spectacularly in recent years, but genuine physiological or biochemical functions can be assigned to very few of these molecules. Of these, only proctolin fulfills the criteria expected of a neurotransmitter, and the recent discovery of proctolin receptor antagonists should enable the biology of this pentapeptide to be explored fully.

Tyrosine hydroxylase in the cerebral ganglia of the American cockroach (Periplaneta americana L.): an immunohistochemical study

We have investigated the distribution of tyrosine-hydroxylase-like immunoreactivity in the cerebral ganglia of the American cockroach, Periplaneta americana. Groups of tyrosine-hydroxylase-immunoreactive cell bodies occur in various parts of the three regions of the cerebral ganglia. In the protocerebrum, single large neurons or small groups of neurons are located in the lateral neuropil, adjacent to the calyces, and in the dorsal portion of the pars intercerebralis. Small scattered cell bodies are found in the outer layers of the optic lobe, and clusters of larger cell bodies can be found in the deutocerebrum, medial and lateral to the antennal glomeruli. Thick bundles of tyrosine-hydroxylase-positive nerve fibers traverse the neuropil in the proto- and deutocerebrum and innervate the glomerular and the non-glomerular neuropil with fine varicose terminals. Dense terminal patterns are present in the medulla and lobula of the optic lobe, the pars intercerebralis, the medial tritocerebrum, and the area surrounding the antennal glomeruli, the central body and the mushroom bodies. The pattern of tyrosine-hydroxylase-like immunoreactivity is similar to that previously described for catecholaminergic neurons, but it is distinctly different from the distribution of histaminergic and serotonergic neurons.

Sensory neuron development revealed by taurine immunocytochemistry in the honeybee

The formation of ommatidia in the compound eyes and sensilla on the antennae of the honeybee was followed and the development of their sensory neurons was traced using an antiserum against taurine as a marker. Taurine-like immunoreactivity (Tau-IR) is expressed in sensory neurons of several modalities, namely visual, olfactory, gustatory, and mechanosensory. Staining intensity is very high in the larva and in the first half of the pupal stage and gradually decreases towards the end of metamorphosis. In the photoreceptor cells of the compound eyes, Tau-IR can be detected from the fifth larval instar onwards, prior to differentiation of other components of the ommatidium. Already in the midstage larvae, when the antennal primordia of the adult still lie within the peripodial cavity, a few presumably mechanosensory neurons are labelled in the pedicellus of the developing antenna. The majority of the antennal sensory neurons which are located on the flagellum start to exhibit Tau-IR upon pupation, long before any cuticular specializations such as sensory hairs or plates are detectable. All known types of antennal sensilla were identified and it could be shown that all of them are innervated by Tau-IR sensory neurons. Thus, taurine immunocytochemistry can be applied as a useful label for developing sensory neurons. Functional implications of taurine during development are discussed.

FMRFamide-like immunoreactivity in presumptive chemosensory afferents of the spiny lobster, Panulirus argus

Stainings with an antibody against the neuropeptide FMRFamide in the CNS of the spiny lobster revealed strong immunoreactivity in a special class of sensory afferents. These afferents are extremely thin and numerous and innervate all sensory neuropils except the optical and olfactory lobes. In the target neuropils the terminals of the afferents branch in parallel and form very densely labeled net-like structures. Due to their size, number and distribution we conclude that the immunoreactive afferents represent a specialized chemosensory system not related to food detection. We propose that a FMRFamide-related peptide present in the afferent terminals serves as sensory transmitter.

Neurotransmitters in the nervous system of Macoma balthica (Bivalvia)

The distribution of histamine-, octopamine-, gamma-aminobutyric acid- (GABA) and taurine-like immunoreactivity in the bivalve mollusc Macoma balthica was studied immunocytochemically with antisera produced in rabbits. Histamine levels in the ganglia and whole animals were also measured by high-performance liquid chromatography using a postcolumn derivatization method. Immunoreactivity for these substances, except for taurine, is found in the central nervous system of this species. The most extensive neuronal system is revealed with the antiserum against histamine. All the main ganglia contain histamine-immunoreactive cell bodies, and a dense network of nerve fibers is seen in the ganglia and nerve roots. Histamine-immunoreactive nerve fibers project to the mantle edge, lips and oesophagus. The basal part of the inhalant siphon is rich in histamine-immunoreactive fibers. Unlike histamine, octopamine- and GABA-like immunoreactivities are restricted to the central nervous system. Taurine-like immunoreactivity is not found in the nervous system of this species. In the nervous system, histamine-immunoreactive cell bodies and fibers are more numerous than those that are octopamine- and GABA-immunoreactive. The distribution of these substances in the ganglia is different. GABA-immunoreactive cells are typically smaller than most of the histamine- and octapamine-immunoreactive cells. Most GABA- and octopamine-immunoreactive cells and fibers are located in the pedal ganglion. Histamine is distributed more evenly in the ganglia and nerve roots. The biochemical measurements of histamine correlate well with the immunohistochemical findings and confirm the predominant location of the amine in the nervous tissue. These results suggest that histamine is more widespread than some other putative transmitters, and support the concept that histamine may have an important role in many physiological processes in molluscs.

Histamine is a major mechanosensory neurotransmitter candidate in Drosophila melanogaster

Histamine is known to be the neurotransmitter of insect photoreceptors. Histamine-like immunoreactivity is also found in a number of interneurons in the central nervous system of various insects. Here, we demonstrate by immunohistochemical techniques that, in Drosophila melanogaster (Acalypterae), most or all mechanosensory neurons of imaginal hair sensilla selectively bind antibodies directed against histamine. The histamine-like staining includes the cell bodies of these neurons as well as their axons, which form prominent fibre bundles in peripheral nerves, and their terminal projections in the central neuropil of head and thoracic ganglia. The specificity of the immunostaining is demonstrated by investigating a Drosophila mutant unable to synthesize histamine. Other mechanosensory organs, such as campaniform sensilla or scolopidial organs, do not stain. In the calypteran flies, Musca and Calliphora, we find no comparable immunoreactivity associated with either hair sensilla or the nerves entering the central nervous system, observations in agreement with earlier studies on Calliphora. Thus, histamine seems to be a major mechanosensory transmitter candidate of the adult nervous system of Drosophila, but apparently not of Musca or Calliphora.

Physiological and pharmacological evidence for histamine as a neurotransmitter in the olfactory CNS of the spiny lobster

Perfusing histamine (HA, 0.1 microM-1 mM) into the brain of the spiny lobster reversibly altered the spontaneous activity in 24 (86%) of 28 morphologically unidentified, odor-responsive interneurons. The effects of HA were dose-dependent and could be selectively and reversibly antagonized by cimetidine, a vertebrate H2 antagonist, suggesting that the action of HA in the central nervous system (CNS) was mediated by a receptor pharmacologically similar to an HA receptor expressed by lobster olfactory receptor cells. Perfusing HA into the brain also reversibly altered the spontaneous and/or odor-evoked activity of 6 (67%) of 9 morphologically identified, odor responsive interneurons that arborized in the olfactory lobe (OL). These results extend previous evidence from our lab that the OL contains HA-immunoreactive interneurons and that OL tissue can synthesize HA from its precursor and further implicate HA as a putative neurotransmitter in the olfactory CNS of the spiny lobster.

Distribution of taurine in the rat cerebellum and insect brain: application of a new antiserum against carbodiimide-conjugated taurine

The production, specificity and application of an antiserum against taurine conjugated to succinylated ovalbumin by means of 1-ethyl-3(3-dimethylaminopropyl)-carbodiimide is reported. The antiserum was produced in rabbits. The carbodiimide was used also as a tissue fixative. The development of the antibody titre was followed by dot-blot tests on nitrocellulose filters using different amino acid conjugates and with immunohistochemical reaction in the rat and insect brain. Blocking controls were also used. Taurine antiserum, sufficiently specific and sensitive, developed after the fourth booster injection, after which the antiserum was characterized. In the insect brain, intense taurine-like immunoreactivity was observed in the photoreceptors, in the Kenyon cells and the neuropile of the mushroom bodies, in the lower part of the central body and in the antennal lobes. In the rat carebellum, intense taurine-like immunoreactivity was seen in the Purkinje cells. Immunoreaction was seen also in small cells most probably corresponding to the basket cells. The use of the carbodiimide in the production of antisera against taurine provides a parallel method for comparison of the distribution of taurine-like immunoreactivity obtained with antisera made against conjugates prepared with aldehydes.

Immunocytochemical and biochemical studies of histamine in the retina of the turtle Pseudemys scripta

A combination of immunocytochemical and biochemical methods was used to study histamine in the turtle retina. Histamine-like immunoreactivity was localized within paraboloids of certain cone photoreceptors by use of two different antisera directed against histamine. Preincubation of eyecups in Ringer's containing 10 microM histamine selectively increased the immunoreactivity of these photoreceptor paraboloids. The present localization of histamine in paraboloids indicated that, although histamine is in photoreceptors of the turtle retina, it may play some metabolic or neuromodulatory role, and not function as a neurotransmitter.

Aminergic neurons in the brain of blowflies and Drosophila: dopamine- and tyrosine hydroxylase-immunoreactive neurons and their relationship with putative histaminergic neurons

The distribution and morphology of neurons reacting with antisera against dopamine (DA), tyrosine hydroxylase (TH) and histamine (HA) were analyzed in the blowflies Calliphora erythrocephala and Phormia terraenovae. TH-immunoreactive (THIR) and HA-immunoreactive (HAIR) neurons were also mapped in the fruitfly Drosophila melanogaster. The antisera against DA and TH specifically labeled the same neurons in the blowflies. About 300 neurons displayed DA immunoreactivity (DAIR) and THIR in the brain and subesophageal ganglion of the blowflies. Most of these neurons were located in bilateral clusters; some were distributed as bilateral pairs, and two ventral unpaired median (VUM) neurons were seen in the subesophageal ganglion. Immunoreactive processes were found in all compartments of the mushroom bodies except the calyces, in all divisions of the central body complex, in the medulla, lobula and lobula plate of the optic lobe, and in non-glomerular neuropil of protocerebrum, tritocerebrum and the subesophageal ganglion. No DA or TH immunoreactivity was seen in the antennal lobes. In Drosophila, neurons homologous to the blowfly neurons were detected with the TH antiserum. In Phormia and Drosophila, 18 HA-immunoreactive neurons were located in the protocerebrum and 2 in the subesophageal ganglion. The HAIR neurons arborized extensively, but except for processes in the lobula, all HAIR processes were seen in non-glomerular neuropil. The deuto- and tritocerebrum was devoid of HAIR processes. Double labeling experiments demonstrated that TH and HA immunoreactivity was not colocalized in any neuron. In some regions there was, however, substantial superposition between the two systems. The morphology of the extensively arborizing aminergic neurons described suggests that they have modulatory functions in the brain and subesophageal ganglion.

Histamine: a neurotransmitter candidate for Drosophila photoreceptors

Recent experimental evidence suggests that histamine might be the synaptic transmitter used by invertebrate photoreceptors. In the present study, we have examined whether histamine is a transmitter candidate for Drosophila photoreceptors. Our findings are as follows: (a) Large amounts of histamine are synthesized by wild-type heads, whereas heads from the eye-deficient mutants, eyes absent and sine oculis, show reduced histamine synthesis. (b) Histidine decarboxylase activity is approximately 10-fold higher in extracts of normal heads compared with that in the mutants. (c) Histamine taken up by fly heads is metabolized into N-acetylhistamine and imidazole-4-acetic acid. (d) Immunostaining of normal and sevenless heads with histamine-specific antisera demonstrates that histamine is present in photoreceptors R1-6 and R8. (e) Histamine synthesized from exogenously supplied [3H]histidine can be released by depolarization with 50 mM K+, and the release is Ca2+ dependent. These observations strongly suggest that histamine is a major neurotransmitter used by Drosophila photoreceptors.

Histamine-like immunoreactivity in the visual system and brain of Drosophila melanogaster

In this study, immunohistochemistry on cryostat sections is used to demonstrate anti-histamine immunoreactivity in the Drosophila brain. The results support earlier findings that histamine is probably a transmitter of insect photoreceptors. It is further shown that, in Drosophila, all imaginal photoreceptors including receptor type R7 are anti-histamine immunoreactive, whereas the larval photoreceptors do not seem to contain histamine. In addition to the photoreceptors, fibres in the antennal nerve and approximately 12 neurons in each brain hemisphere show strong histamine-like immunoreactivity. These cells arborize extensively in large parts of the central brain.

Histamine-immunoreactive neurons in the midbrain and suboesophageal ganglion of sphinx moth Manduca sexta

This paper describes the distribution of histamine-like immunoreactivity in the midbrain and suboesophageal ganglion of the sphinx moth Manduca sexta. Intense immunocytochemical staining was detected in ten bilateral pairs of neurons in the median protocerebrum and in one pair of neurons in the suboesophageal ganglion. Whereas most areas of the brain and suboesophageal ganglion are innervated by one or more of these neurons, typically no immunoreactive fibers were found in the mushroom bodies, the protocerebral bridge, and the lateral horn of the protocerebrum. The 11 histamine-immunoreactive neurons were reconstructed from serial sections. Ten neurons have bilateral arborizations, often with axonal projections in symmetric areas of both hemispheres. One neuron, whose soma resides in the lateral protocerebrum, has only unilateral projections. Of the 11 neurons, 6 occur in pairs with similar morphological features. In addition to these neurons, weak histamine-like immunoreactivity was detected in 7-13 interneurons that were not reconstructed individually. The central projections of the ocellar nerves from the intracranial ocelli also exhibit histamine-like immunoreactivity. The single-cell reconstructions reveal similarities between the organization of histamine- and serotonin-immunoreactive neurons in the brain and suboesophageal ganglion of this insect.

Cyclic AMP generating systems in vertebrate retina: effects of histamine and an established retinal modulator, dopamine

Histamine (HA), 1-1000 microM, significantly stimulated both basal and forskolin-activated cAMP generation in chicken and adult hen retina. The action of HA was reproduced by the selective H2-receptor agonists dimaprit and 4-methyl-histamine, but not by the selective H1-receptor agonist 2-thiazolylethylamine, and it was antagonized by the specific H2-receptor blockers cimetidine and tiotidine, but not by the H1-receptor blocker mepyramine. In parallel experiments, dopamine, an established retinal neuromodulator acting through the D1-type of receptor, also stimulated basal and forskolin-driven adenylate cyclase activity in homogenate of chicken retina. It is suggested that chicken retina contains HA H2-receptors which are positively coupled to the adenylate cyclase system.