Histamine is a major mechanosensory neurotransmitter candidate in Drosophila melanogaster

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.

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.

Selective histamine uptake rescues photo- and mechanoreceptor function of histidine decarboxylase-deficient Drosophila mutant

In insects, histamine is found both in the peripheral nervous system (PNS) and in the CNS and is known to function as a fast neurotransmitter in photoreceptors that have been shown to express selectively the hdc gene. This gene codes for histidine decarboxylase (HDC), the enzyme for histamine synthesis. Fast neurotransmission requires the efficient removal of the transmitter from the synaptic cleft. Here we identify in Drosophila photo- and mechanoreceptors a histamine uptake mechanism that can restore the function of these receptors in mutants unable to synthesize histamine. When apparent null mutants for the hdc gene imbibe aqueous histamine solution or are genetically "rescued" by a transgene ubiquitously expressing histidine decarboxylase under heat-shock control, sufficient amounts of histamine selectively accumulate in photo- and mechanoreceptors to generate near-normal electrical responses in second-order visual interneurons and qualitatively to restore wild-type visual and mechanosensory behavior. This strongly supports the proposal that histamine functions as a fast neurotransmitter also in a certain class of mechanoreceptors. A set of CNS-intrinsic neurons that in the wild type contain high concentrations of histamine apparently lacks this uptake mechanism. We therefore speculate that histamine of intrinsic neurons may function as a neuromodulator rather than as a fast transmitter.

Evidence that histamine is the principal pharmacological component of venom from an Australian wolf spider (Lycosa godeffroyi)

Wolf spiders are common throughout Australia and have been known to cause severe reactions in both animals and humans. However, little work has been done on the pharmacological activity of Australian lycosids. The purpose of this study was to obtain a preliminary pharmacological profile of the venom from an Australian wolf spider (Lycosa godeffroyi). The venom caused dose-dependent contractions of guinea-pig isolated ileum (1-4 microg/ml), endothelium-dependent relaxation in rat isolated aortae (10 microg/ml), a decrease in mean arterial blood pressure in the anaesthetised rat (100 microg/kg, i.v.) and an increase in insufflation pressure in the anaesthetised guinea-pig (50 microg/kg, i.v.). All of these responses were significantly inhibited by the H1-receptor antagonist mepyramine at concentrations that selectively inhibited responses to histamine. Venom (5 microg/ml) caused a decrease in twitch height of the rat stimulated (0.3 msec, 0.2 Hz, 100 V) vas deferens (prostatic segment). A fluorometric assay for histamine detected a concentration of 44.5 ng/microg venom protein. It appears that the in vitro and in vivo activity of L. godeffroyi venom observed in the present study is due to the presence of histamine.

Taste sensilla of flies: function, central neuronal projections, and development

Taste sensilla of flies are composed of only a few cells, all of which have different functions. Depending on the species and on the sensillum type, there are from 2-5 neurons, each of which has its own stimulus specificity, and each of which makes a different contribution to the fly's behavior. In addition, taste sensilla include several nonneuronal cells that are important both for the development of the sensillum and for its functioning. The component cells of a sensillum derive from a single epidermal precursor according to a stereotyped sequence of mitoses. This review focuses on the different phenotypes of the component cells of taste sensilla, particularly the stimulus sensitivity and central neuronal anatomy of the receptor neurons, and on the development of this multicellular organ from a single precursor cell.

Experience-dependent developmental plasticity in the optic lobe of Drosophila melanogaster

Early experience can affect nervous system development in both vertebrate and invertebrate animals. We have now demonstrated that visual stimulation modifies the size of the optic lobes in the laboratory fruitfly Drosophila melanogaster. Monocular deprivation (painting over one eye) decreases the aggregate volume of the lamina, medulla, and lobula plate by up to 6%. The laminae of control flies kept in complete darkness showed a more robust volume difference that could be as much as 30%. An electron microscopy study revealed that the changes in the lamina are largely attributable to an increase in the terminals of the photoreceptor cell axons. The volume of the lamina increases during the first 24 hr after emergence, and it grows more in the light than in darkness. When flies are kept in the dark for the first 12 hr of their adult life and are then brought back to light for the next 3.5 days, the lamina is almost as small as in flies raised for 4 d in constant darkness. Twelve hour dark shifts at a later time are less effective. This finding suggests a critical period for lamina development during day 1 of the adult. The lamina depends on visual stimulation to maintain its size during the first 5 d after emergence. Dark-rearing for 1 d or more at any stage during that period decreases its volume to the level of flies raised in constant darkness. A lamina that is once reduced in size seems not to recover.

Evolution and overview of classical transmitter molecules and their receptors

All the classical transmitter ligand molecules evolved at least 1000 million years ago. With the possible exception of the Porifera and coelenterates (Cnidaria), they occur in all the remaining phyla. All transmitters have evolved the ability to activate a range of ion channels, resulting in excitation, inhibition and biphasic or multiphasic responses. All transmitters can be synthesised in all three basic types of neurones, i.e. sensory, interneurone and motoneurone. However their relative importance as sensory, interneurone or motor transmitters varies widely between the phyla. It is likely that all neurones contain more than one type of releasable molecule, often a combination of a classical transmitter and a neuroactive peptide. Second messengers, i.e. G proteins and phospholipase C systems, appeared early in evolution and occur in all phyla that have been investigated. Although the evidence is incomplete, it is likely that all the classical transmitter receptor subtypes identified in mammals, also occur throughout the phyla. The invertebrate receptors so far cloned show some interesting homologies both between those from different invertebrate phyla and with mammalian receptors. This indicates that many of the basic receptor subtypes, including benzodiazepine subunits, evolved at an early period, probably at least 800 million years ago. Overall, the evidence stresses the similarity between the major phyla rather than their differences, supporting a common origin from primitive helminth stock.

Regulation of choline acetyltransferase/lacZ fusion gene expression in putative cholinergic neurons of Drosophila melanogaster

We have analyzed the distribution of putative cholinergic neurons in whole-mount preparations of adult Drosophila melanogaster. Putative cholinergic neurons were visualized by X-gal staining of P-element transformed flies carrying a fusion gene consisting of 5' flanking DNA from the choline acetyltransferase (ChAT) gene and lacZ reporter gene. We have previously demonstrated that cryostat sections of transgenic flies carrying 7.4 kb of ChAT 5' flanking DNA show reporter gene expression in a pattern essentially similar to the known distribution of ChAT protein. Whole-mount staining of these same flies by X-gal should thus represent the overall distribution of ChAT-positive neurons. Extensive staining was observed in the cephalic, thoracic, and stomodeal ganglia, primary sensory neurons in antenna, maxillary palps, labial palps, leg, wing, and male genitalia. Primary sensory neurons associated with photoreceptors and tactile receptors were not stained. We also examined the effects of partial deletions of the 7.4 kb fragment on reporter gene expression. Deletion of the 7.4 kb fragment to 1.2 kb resulted in a dramatic reduction of X-gal staining in the peripheral nervous system (PNS). This indicates that important regulatory elements for ChAT expression in the PNS exist in the distal region of the 7.4 kb fragment. The distal parts of the 7.4 kb fragment, when fused to a basal heterologous promoter, can independently confer gene expression in subsets of putative cholinergic neurons. With these constructs, however, strong ectopic expression was also observed in several non-neuronal tissues.

Neuroarchitecture of the tritocerebrum of Drosophila melanogaster

The organisation of the tritocerebrum of Drosophila melanogaster was studied by Bodian-Protargol reduced silver staining, Golgi-silver impregnation, horseradish peroxidase (HRP), and cobalt-chloride labelling of neurones and transmission electron microscopy. Nerve fibres of six categories were found to project to the tritocerebrum. (1 and 2) The sensory fibres from the internal mouthpart sensilla known to course along pharyngeal and accessory pharyngeal nerves were found to project in mainly two tiers, in the tritocerebrum. (3) Stomodaeal nerve fibres also project along the pharyngeal nerve, to the tritocerebrum. (4) Cells of the pars intercerebralis (PI) project along the median bundle and arborise in the tritocerebrum. HRP labelling and subsequent examination by transmission electron microscopy indicated their neurosecretory nature. (5 and 6) Two tracts of ascending fibres, designated as dorsal and ventral ascending tracts, were found to project to the tritocerebrum. Some of the sensory fibres from the labial nerve extend close to the sensory projections of the tritocerebrum, suggesting a possible convergence of the two sensory inputs. In the tritocerebrum, the sensory input, the stomodaeal input, the neurosecretory fibres of PI, and the ascending fibres were found to have overlapping fields, suggesting mutual interaction. The medial subesophageal ganglion and the tritocerebrum may interact through the ventral ascending tract.

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.