Octopamine, dopamine and noradrenaline content of the brain of the locust, Schistocerca gregaria

A muscarinic cholinergic mechanism underlies activation of the central pattern generator for locust flight

A central question in behavioural control is how central pattern generators(CPGs) for locomotion are activated. This paper disputes the key role generally accredited to octopamine in activating the CPG for insect flight. In deafferented locusts, fictive flight was initiated by bath application of the muscarinic agonist pilocarpine, the acetylcholine analogue carbachol, and the acetylcholinesterase blocker eserine, but not by nicotine. Furthermore, in addition to octopamine, various other amines including dopamine, tyramine and histamine all induced fictive flight, but not serotonin or the amine-precursor amino acid tyrosine. However, flight initiation was not reversibly blocked by aminergic antagonists, and was still readily elicited by both natural stimulation (wind) and pilocarpine in reserpinized, amine-depleted locusts. By contrast, the muscarinic antagonists atropine and scopolamine reversibly blocked flight initiated by wind, cholinergic agonists, octopamine, and by selective stimulation of a flight-initiating interneurone (TCG). The short delay from TCG stimulation to flight onset suggests that TCG acts directly on the flight CPG, and accordingly that TCG, or its follower cell within the flight generating circuit, is cholinergic. We conclude that acetylcholine acting via muscarinic receptors is the key neurotransmitter in the mechanism underlying the natural activation of the locust flight CPG. Amines are not essential for this, but must be considered as potential neuromodulators for facilitating flight release and tuning the motor pattern. We speculate that muscarinic activation coupled to aminergic facilitation may be a general feature of behavioural control in insects for ensuring conditional recruitment of individual motor programs in accordance with momentary adaptive requirements.

Dopaminergic control of foregut contractions in Locusta migratoria

Tyrosine hydroxylase-like immunoreactivity is present in cell bodies and processes in the brain and optic lobes of Locusta migratoria, with processes projecting along the frontal connectives to form a neuropile within the frontal ganglion. Immunoreactive cell bodies and processes are also evident in the hypocerebral and ventricular ganglia with processes extending over the foregut. Tyrosine hydroxylase is the rate-limiting enzyme in dopamine biosynthesis, and high-performance liquid chromatography coupled to electrochemical detection was used to confirm the presence of dopamine in the innervation to the foregut. Spontaneous foregut contractions are under the control of the ventricular ganglia and are absent when these ganglia are removed. Dopamine leads to an inhibition of both the amplitude and frequency of phasic contractions of the foregut that are produced when the ventricular ganglia are left attached. Dopamine has direct effects on the foregut muscle in the absence of the ventricular ganglia, inhibiting a proctolin-induced contraction in a dose-dependent manner.

Serotonin, reserpine, and motility in Mesocestoides tetrathyridia. An experimental spectrofluorometry and immunocytochemistry study

The relationship between serotonin (5-HT) and motility in tetrathyridia of Mesocestoides vogae (syn. M. corti) was studied with the aid of reserpine. Reserpine decreases the content of 5-HT as measured spectrofluorometrically and immunocytochemically and, furthermore, inhibits the motility, thus indicating a connection between the two. The results support the hypothesis about 5-HT being an excitatory neurotransmitter of motor activity in M. vogue. New neuroanatomical details were revealed by immunocytochemical staining.

Immunocytochemistry of dopamine in the brain of the locust Schistocerca gregaria

Catecholamine-induced histofluorescence studies have suggested a rich innervation of the locust brain by dopamine-containing neurons. To provide a basis for future studies on dopamine action in this insect, the location and morphology of neurons reacting with antisera against dopamine were investigated in the supraoesophageal ganglion of the locust, Schistocerca gregaria. In each brain hemisphere, about 100 interneurons in the midbrain and approximately 3,000 cells in the optic lobe show dopamine-like immunoreactivity. All major areas of the brain except the calyces of the mushroom body, the antennal lobe, large parts of the lobula, and some areas in the inferior lateral protocerebrum contain immunoreactive neuronal processes. The arborization patterns of most dopamine-immunoreactive cell types could be identified through detailed reconstructions. The central body exhibits the most intense immunostaining. It is innervated by at least 40 pairs of dopamine-immunoreactive neurons belonging to three different cell types. Additional arborizations of these neurons are in the superior protocerebrum and in the lateral accessory lobes. A group of 4 immunoreactive neurons with ramifications in the antennal mechanosensory and motor center gives rise to a dense meshwork of varicose fibers in the pedunculus and parts of the alpha- and beta-lobes of the mushroom body. Other cell types innervate the ventrolateral protocerebrum, the inferior protocerebrum and the posterior optic tubercles. Three descending neurons originating in the tritocerebrum exhibit dopamine-like immunoreactivity. In the optic lobe, about 3,000 columnar intrinsic neurons of the medulla and a group of centrifugal tangential cells with arborizations in the medulla and lamina are dopamine-immunoreactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Simultaneous determination of biogenic amines, their precursors and metabolites in a single brain of the cricket using high-performance liquid chromatography with amperometric detection

An analytical procedure has been developed for the simultaneous determination of biogenic amines, their precursors and metabolites by high-performance liquid chromatography with amperometric electrochemical detection. Following careful adjustment of various factors involved in the separation efficiency, reversed-phase chromatography with an ion-pairing technique gave simultaneous separation of nineteen biogenic amines and related substances. Peak identification was confirmed by comparison with hydrodynamic voltammograms. The method was sensitive enough to detect each substance in the picomole range. The procedure was applied to quantitate the amount of biogenic amines in a single brain of the cricket.

Distribution of biogenic amines in the cricket central nervous system

The distribution of biogenic amines, their precursors, and metabolites in the central nervous system (CNS) of the cricket was determined using HPLC with electrochemical detection. Three biogenic amines, octopamine (OA), dopamine (DA), and 5-hydroxytryptamine (5-HT); two precursors, tyramine and tryptophan; and two metabolites, synephrine and 5-hydroxyindole-3-acetic acid, were detected in all ganglia. In the brain, 5-HT occurred in the largest quantities followed by OA, while in other ganglia OA occurred in the largest quantities followed by 5-HT and DA. In all ganglia, the amount of OA was two to nine times greater than that of DA. The results are discussed in comparison with different insect species.

Dopamine- and octopamine-sensitive adenylate cyclase in the brain of adult Culex pipiens mosquitoes

The effects of dopamine and octopamine on adenylate cyclase activity were studied on the head homogenate of adult Culex pipiens mosquitoes in vitro. Both dopamine and octopamine were shown to increase the cyclic AMP content in the homogenate. The antagonist haloperidol blocked the production of cyclic AMP induced from dopamine but had no effect on the production of cyclic AMP induced by octopamine at the concentrations tested. The opiate agonist etorphine was ineffective at reducing cyclic AMP levels induced by either dopamine or octopamine at the concentrations tested.

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

The localization of dopamine-beta-hydroxylase in the cephalic central nervous system of the blowfly (Calliphora erythrocephala) and the cockroach (Periplaneta americana) was investigated. Immunoreactive neurons were demonstrated in both species. The results were compared with the known distribution of catecholamines in the brain of both species. In certain cell groups and neuropilar regions of both species D beta H-immunoreactivity coincides with the presence of catecholamines. Additionally D beta H immunoreactivity was found in several cell bodies and neuropilar regions in which no catecholamines could be detected. A correlation between the presence of octopamine and anti-D beta H labelling was not found. Thus it seems that the D beta H-immunoreactivity neither indicates the presence of octopamine nor is it limited to noradrenaline-containing neurons. Parallel findings in vertebrates are discussed.

Octopamine- and dopamine-sensitive adenylate cyclase in the brain of Locusta migratoria during its development

Octopamine- and dopamine-sensitive adenylate cyclases were studied in the brain of Locusta migratoria during its metamorphosis. In the adult brain the effects of octopamine and dopamine on adenylate cyclase were additive, suggesting the presence of separate populations of adenylate cyclase-linked receptors for octopamine and dopamine. There are no separate receptors for noradrenaline. Octopamine stimulates adenylate cyclase in both adult and larval brain; however, in adult brain octopamine is more potent than in larval brain. Dopamine stimulates adenylate cyclase activity only in adult brain. The sensitivity of adenylate cyclase to octopamine changes during the development of the animal. Phentolamine and cyproheptadine are potent antagonists of octopamine-stimulated adenylate cyclase, while propranolol has a weak effect. No cytosol factor which would modulate either basal or octopamine-stimulated adenylate cyclase was found. The effect of GTP and octopamine on adenylate cyclase was synergistic in adult brain but not in larval brain, while the effect of GppNHp and octopamine was synergistic in both adult and larval brains.

Distribution of serotonin-containing neurons and their pathways in the supraoesophageal ganglion of the cockroach Periplaneta americana (L.) as revealed by immunocytochemistry

The distribution of serotonin (5-HT)-containing neurons in the supraoesophageal (cerebral) ganglion of the cockroach Periplaneta americana was studied using immunocytochemistry and the formaldehyde histofluorescence method ( Klemm , '83). In this material immunocytochemistry was more sensitive than the formaldehyde histofluorescence procedure. A relatively small number of 5-HT-immunoreactive cell bodies (220-280) were found. For the first time, their processes could be followed. They highly arborize and innervate many brain regions. Three patterns of monoamine innervation have been demonstrated: (1) 5-HT and catecholamine fibres ( Klemm , '83) occurring in the same region (e.g., outer lateral protocerebral neuropil, stratum caudale , mushroom body, fan-shaped body, olfactory lobe), but having certain differences with respect to the organization of their projection fields; (2) 5-HT fibres innervating a region lacking catecholamine-containing fibres (pons); and (3) catecholamine neurons innervating a region lacking 5-HT fibres (ellipsoid body). In the mushroom body only the extrinsic neurons contain 5-HT immunoreactivity. They form a commissural fibre system linking the left- and right-hand mushroom bodies and other brain regions. The pons is part of a 5-HT-neuron fibre system innervating many areas including the mushroom bodies. The present study demonstrates novel, complex, and widely distributed connections within the insect brain.

Octopamine release from centrifugal fibers of the Limulus peripheral visual system

Octopamine, a biogenic amine, is synthesized and stored within centrifugal (efferent) fibers that project from the brain to the lateral and ventral eyes of the horseshoe crab, Limulus polyphemus. The experiments described here show that depolarization of Limulus lateral and ventral eyes, produced by elevating the concentration of extracellular K+, causes the selective release of newly synthesized octopamine from centrifugal fibers in a manner that requires the influx of extracellular Ca2+. Conjugates of octopamine and tyramine that are also stored within centrifugal fibers are not released in response to K+-induced depolarization. These findings add further support to the hypothesis that octopamine is a neurotransmitter synthesized by and released from centrifugal fibers in Limulus eyes. This amine may be responsible for many of the alterations in lateral eye structure and function that are mediated by centrifugal innervation.

Organization of catecholamine and serotonin-immunoreactive neurons in the corpora pedunculata of the desert locust, Schistocerca gregaria Forsk

Catecholamine (CA)-containing and serotonin (5-HT)-immunoreactive fibers were shown in the mushroom body of Schistocerca gregaria. Both fiber systems occupy distinct areas in the mushroom body. None of these amines could be detected in the Kenyon cell bodies. The 5-HT fibers and many of the CA fibers originate from few extrinsic neurons with large and highly arborized processes concentrated in the commissural pathway linking mushroom bodies to each other and to different brain regions (e.g. optic lobe, lateral neuropil).

Octopamine action on the spontaneous contractions of the isolated nerve cord of Lumbricus terrestris

Octopamine and synephrine were observed to effect the spontaneous rhythmic contractions displayed by the isolated ventral nerve cord of the earthworm, Lumbricus terrestris. octopamine and synephrine produced dose-dependent significant changes in the frequency, amplitude and basal tonus of the spontaneous contractions. Application of adrenergic receptor antagonists suggested the octopamine receptors to have some similarity to vertebrate alpha 1-adrenergic receptors. The spontaneous contractions were not abolished by tetrodotoxin (TTX) which suggested a myogenic origin for the contraction of the ventral nerve cord sheath muscles. Octopamine, in the presence of TTX, increased the basal tonus and maximum force of the spontaneous contractions.

Effect of disulfiram on the ultrastructure of the peptidergic and aminergic cells in the pars intercerebralis of Galleria mellonella (Lepidoptera)

Injection of disulfiram, a specific inhibitor of noradrenaline synthesis, evokes changes in two different types of neurons in the brain of Galleria mellonella: neurones containing dense-core vesicles (60-80 nm) and peptidergic cells containing 180-200 nm neurosecretory granules. The lowering of the electron density of the dense-core vesicles of 60-80 nm seems to be directly connected with disulfiram administration, while the decrease of the amount of neurosecretory material in the neurosecretory cells of type I seems to be a secondary effect of the drug injection. The participation of noradrenaline in the regulation of the secretory activity of type I peptidergic neurosecretory cells of the pars intercerebralis is postulated.

Biosynthesis of N-acetyldopamine and N-acetyloctopamine by Schistocerca gregaria nervous tissue

N-Acetyltyramine, N-acetyldopamine and N-acetyloctopamine were the major products when either L-[3H]tyrosine or [3H]tyramine were incubated with thoracic ganglia of the desert locust, Schistocerca gregaria. No label was incorporated into L-DOPA under these conditions, although 2-3% of the radioactivity could be recovered in dopamine and octopamine. Addition of the aromatic amino acid decarboxylase inhibitor, 3-hydroxybenzylhydrazine (NSD 1015), prevented the formation of N-acetylcompounds from L-[3H]tyrosine, without resulting in an accumulation of label in L-DOPA. In contrast, incubation of samples of haemolymph with L-[3H]tyrosine resulted in the recovery of 7% of label in L-DOPA, which was increased to 17% in the presence of NSD 1015. These results provide evidence that the initial step in the synthesis of dopamine and octopamine by S. gregaria nervous tissue is the conversion of L-tyrosine to tyramine, which is subsequently metabolised to N-acetyltyramine, N-acetyldopamine or N-acetyloctopamine.

Octopamine levels during the moult cycle and adult development in the migratory locust, Locusta migratoria

Octopamine content of the head of the locust Locusta migratoria has been determined during the last larval stage, moulting and adult life of 3 groups of insects: female and male gregarious, solitary and CO2 solitarized. An important difference was found between these 3 groups. Octopamine contents increased in the middle of the larval life and during the adult life. The moulting time is characterized by a sharp decrease of the octopamine content which becomes identical in the 3 groups of insects. The relation between octopamine content, hormone cycles and motility is discussed.