Dopamine-beta-hydroxylase-like immunoreactive neurons in two insect species, Calliphora erythrocephala and Periplaneta americana

Cloning and characterization of DOPA decarboxylase in Litopenaeus vannamei and its roles in catecholamine biosynthesis, immunocompetence, and antibacterial defense by dsRNA-mediated gene silencing

Catecholamines (CAs) play critical roles in regulating physiological and immunological homeostasis in invertebrates and vertebrates under stressful environments. DOPA decarboxylase (DDC), an enzyme responsible for the decarboxylation step of dopamine synthesis, participates in neurotransmitter metabolism and innate immunity. In shrimp, two genes encoding CA-related enzymes, tyrosine hydroxylase and dopamine beta-hydroxylase, were further identified and characterized as neuroendocrine-immune regulators. In this study, full-length complementary DNA of DDC cloned from the thoracic ganglia of shrimp, Litopenaeus vannamei, (LvDDC) was predicted to encode a 452-amino acid protein with a pyridoxal-dependent decarboxylase-conserved domain, and this deduced protein of LvDDC was phylogenetically closely related to insect DDC. LvDDC messenger RNA expression was analyzed by a semiquantitative RT-PCR and a real-time quantitative RT-PCR and found to be abundant in the hepatopancreas and nervous system but at low levels in haemocytes, heart, stomach, and gills. To determine the role of LvDDC, double-stranded (ds)RNA was used for in vivo assessments. LvDDC-depleted shrimp revealed significant increases in the total haemocyte count, hyaline cells, granular cells, phenoloxidase activity, and respiratory bursts of haemocytes per unit of haemolymph, and phagocytic activity and clearance efficiency toward Vibrio alginolyticus. Further, decreased LvDDC mRNA expression was accompanied by decreases in dopamine, glucose, and lactate levels in haemolymph. In shrimp that received LvDDC-dsRNA for 3 days and were then challenged with V. alginolyticus, the survival rate of LvDDC-depleted shrimp was significantly higher than that of shrimp that received diethyl pyrocarbonate-water or non-targeted dsRNA. In conclusion, the cloned LvDDC was responsible for controlling dopamine synthesis, which then regulated physiological and immune responses in L. vannamei.

A Model for Basic Emotions Using Observations of Behavior in Drosophila

Emotion plays a crucial role, both in general human experience and in psychiatric illnesses. Despite the importance of emotion, the relative lack of objective methodologies to scientifically studying emotional phenomena limits our current understanding and thereby calls for the development of novel methodologies, such us the study of illustrative animal models. Analysis of Drosophila and other insects has unlocked new opportunities to elucidate the behavioral phenotypes of fundamentally emotional phenomena. Here we propose an integrative model of basic emotions based on observations of this animal model. The basic emotions are internal states that are modulated by neuromodulators, and these internal states are externally expressed as certain stereotypical behaviors, such as instinct, which is proposed as ancient mechanisms of survival. There are four kinds of basic emotions: happiness, sadness, fear, and anger, which are differentially associated with three core affects: reward (happiness), punishment (sadness), and stress (fear and anger). These core affects are analogous to the three primary colors (red, yellow, and blue) in that they are combined in various proportions to result in more complex “higher order” emotions, such as love and aesthetic emotion. We refer to our proposed model of emotions as called the “Three Primary Color Model of Basic Emotions.”

Development of the larval nervous system of the gastropod Ilyanassa obsoleta

Gastropods have been well studied in terms of early cell cleavage patterns and the neural basis of adult behaviors; however, much less is known about neural development in this taxon. Here we reveal a relatively sophisticated larval nervous system in a well-studied gastropod, Ilyanassa obsoleta. The present study employed immunocytochemical and histofluorescent techniques combined with confocal microscopy to examine the development of cells containing monoamines (serotonin and catecholamine), neuropeptides (FMRFamide and leu-enkephalin related peptides), and a substance(s) reactive to antibodies raised against dopamine beta-hydroxylase. Neurons were first observed in the apical organ and posterior regions during the embryonic trochophore stage. During later embryonic development neurons appeared in peripheral regions such as the foot, velum, and mantle and in the developing ganglia destined to become the adult central nervous system. In subsequent free-swimming veliger stages the larval nervous system became increasingly elaborate and by late larval stages there existed approximately 26-28 apical cells, 80-100 neurons in the central ganglia, and 200-300 peripherally located neurons. During metamorphosis some populations of neurons in the apical organ and in the periphery disappeared, while others were incorporated into the juvenile nervous system. Comparisons of neural elements in other molluscan larvae reveal several similarities such as comparable arrangements of cells in the apical organ and patterns of peripheral cells. This investigation reveals the most extensive larval nervous system described in any mollusc to date and information from this study will be useful for future experimental studies determining the role of larval neurons and investigations of the cellular and molecular mechanisms governing neural development in this taxon.

Differential expression of catecholamine synthetic enzymes in the caudal ventral pons

The analysis of colocalization of multiple catecholamine biosynthetic enzymes within the ventrolateral part of the medulla oblongata of the rat revealed distinct subpopulations of neurons within the C1 region (Phillips et al., J Comp Neurol 2001, 432:20-34). In extending this study to include the caudal pons, it was shown for the first time that the A5 cell group could be distinguished by the presence of immunoreactivity to tyrosine hydroxylase (TH), aromatic l-amino acid decarboxylase (AADC), and dopamine beta hydroxylase (DBH). A novel cell group was also identified. The cells within this new group were immunoreactive to DBH but not TH, AADC, or phenylethanolamine N-methyltransferase (PNMT) and will be referred to as the TH-, DBH+ cell group. The TH-, DBH+ neurons were not immunoreactive for either the dopamine or noradrenaline transporters, suggesting that these neurons do not take up these transmitters. A5 neurons were immunoreactive for the noradrenaline transporter but not the dopamine transporter (as previously shown). Retrograde tracing with cholera toxin B revealed that the TH-, DBH+ neurons do not project to the thoracic spinal cord or to the rostral ventrolateral medulla, but A5 neurons do. A calbindin immunoreactive cell group is located in a region overlapping TH-, DBH+ cell group. However, only a few neurons were immunoreactive for both markers. The physiological role of the TH-, DBH+ cell group remains to be determined.

Photoperiodic time measurement and related physiological mechanisms in insects and mites

For over 60 years, many species of insects and mites have been known to respond in an adaptive way to seasonal changes in daylength. Responses to photoperiod allow them to survive periods of unfavorable environmental conditions. Since the early 1950s, light-sensitive and temperature-compensated circadian clocks have also been known to regulate the timing of many events (behavioral, physiological, biochemical) in all eukaryotic organisms, including insects and mites. Over the past 30 years, considerable effort has been directed at elucidation of the nature of the clock mechanism that underlies photoperiodism. Mathematical models using a number of insect systems have been developed that attempt to causally relate the circadian clock to photoperiodic time measurement. Although some experimental evidence supports these circadian-based models, some insects and mites appear to utilize a non-periodic hourglass timer as the photoperiodic clock. Future work in this field would benefit by following the approach that has proven to be very successful in identifying genes and gene products that regulate circadian rhythmicity in Drosophila melanogaster.

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.

Localization of dopamine and its relation to the growth hormone producing cells in the central nervous system of the snail Lymnaea stagnalis

The distribution of dopamine in the central nervous system of the pond snail Lymnaea stagnalis was investigated by using immunocytochemistry and HPLC measurements. With both methods it was demonstrated that dopamine is predominantly present in the cerebral and pedal ganglia. The dopamine-immunoreactivity was mainly observed in nerve-fibers in the neuropile of the ganglia. Relatively few dopamine-immunopositive cell bodies (diameters 10-30 microns) were found. A large cell in the right pedal ganglion (the so-called RPeD1) stained positively with the dopamine antibody. It has previously been demonstrated that the growth hormone producing cells (GHCs) possess dopamine receptors on their cell bodies. However, dopamine-immunopositive fibers were observed only in the vicinity of the GHC nerve-endings and not close to the GHC cell bodies.

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

The distribution of histamine-immunoreactivity in the carbodiimide-fixed brain and visual system of the cockroach was revealed immunocytochemically with an antiserum against histamine (HA). Histamine levels were measured with high-pressure liquid chromatography. The results show a widespread distribution of histamine-containing somata and fibers in the brain, particularly in the visual system. The most intense immunolabeling was seen in the retinal photoreceptors and in the first optic ganglion, the lamina, where the short visual fibers make synaptic connections with the monopolar neurons, which also displayed immunofluorescence. Immunoreactive long visual fibers traversed the lamina and outer chiasma, terminating in the distal medulla. Tracts of histamine-immunopositive fibers appeared to link the optic ganglia to the protocerebrum. Prominent histamine-containing neurons were situated in the lateral protocerebrum. Immunolabeled pathways consisting of large-diameter fibers also were seen in the cockroach brain. The central parts of the brain, including the central body, were reached by thick immunoreactive fibers that gave rise to intensely fluorescent varicose processes there. In the mushroom bodies, immunoreactivity was limited to the calyces. The protocerebral bridge was nonreactive. Immunofluorescence was seen also in the antennal lobes, but not in the antennal nerves. The biochemical measurements correlated well with the immunocytochemical data. The retinas and optic lobes, measured together, contained remarkably large amounts of histamine. These results reinforce the hypothesis presented by Hardie ('87) and Elias and Evans ('83) that histamine functions as a neurotransmitter in the photoreceptors of some, if not all, insect species.

Proctolin-like immunoreactive neurons in the blowfly central nervous system

The pentapeptide proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH) is a well-studied bioactive substance in insects. With an antiserum against proctolin we have mapped proctolinlike-immunoreactive (PLI) neurons in the nervous system of the blowfly Calliphora erythrocephala. In the brain, including the suboesophageal ganglia, 80-90 neurons were found to be PLI. A further 200-250 PLI neurons innervate the lobula of the optic lobe. The thoracic ganglia contain 100-130, and the abdominal ca. 60 PLI neurons. In the brain and ventral ganglia the immunoreactive neurons are of different types: interneurons, efferents (possibly some motorneurons), and neurosecretory cells. Some of these neurons are individually identifiable; others can be identified collectively as clusters. Identifiable neurons innervate protocerebral neuropil associated with the pars intercerebralis and the beta-lobes of the mushroom bodies as well as tritocerebral neuropil. Some of the prominent clusters innervate the central body of the protocerebrum, tritocerebrum, and possibly leg motor neurons. One abdominal cluster is of special interest because it consist of efferent neurons with processes in the lateral abdominal nerves. Some of these processes are located in the neural sheath in neurohaemal regions, and electron microscopy demonstrates that their terminals are outside the blood-brain barrier. The PLI processes in the protocerebrum contain large granular vesicles and form chemical synapses with different kinds of nonimmunoreactive neural elements. Thus, in Calliphora the proctolinlike substance may be used as a central transmitter/modulator, a neuromuscular transmitter, and a neurohormone released into the circulation.

Insect optic lobe neurons identifiable with monoclonal antibodies to GABA

Five monoclonal antibodies against GABA were tested on glutaraldehyde fixed sections of optic lobes of three insect species, blowflies, houseflies and worker bees. The specificity of these antibodies was analyzed in several tests and compared with commercially available anti-GABA antiserum. A very large number of GABA-like immunoreactive neurons innervate all the neuropil regions of these optic lobes. Immunoreactive processes are found in different layers of the neuropils. The immunoreactive neurons are amacrines and columnar or noncolumnar neurons connecting the optic lobe neuropils. In addition some large immunoreactive neurons connect the optic lobes with centers of the brain. Some neuron types could be matched with neurons previously identified with other methods. The connections of a few of these neuron types are partly known from electron microscopy or electrophysiology and a possible role of GABA in certain neural circuits can be discussed.