Relationship between serotonin and the circadian rhythm in some nocturnal moths

Distribution of Serotonin-Immunoreactive Neurons in the Brain and Gnathal Ganglion of Caterpillar Helicoverpa armigera

Serotonin (5-hydroxytryptamine, 5-HT) is an important biogenic amine that acts as a neural circuit modulator. It is widespread in the central nervous system of insects. However, little is known about the distribution of serotonin in the nervous system of the cotton bollworm Helicoverpa armigera. In the present study, we performed immunohistochemical experiments with anti-serotonin serum to examine the distribution of serotonin in the central nervous system of H. armigera larvae. We found about 40 serotonin-immunoreactive neurons in the brain and about 20 in the gnathal ganglion. Most of these neurons are wide-field neurons giving rise to processes throughout the neuropils of the brain and the gnathal ganglion. In the central brain, serotonin-immunoreactive processes are present bilaterally in the tritocerebrum, the deutocerebrum, and major regions of the protocerebrum, including the central body (CB), lateral accessory lobes (LALs), clamps, crepine, superior protocerebrum, and lateral protocerebrum. The CB, anterior ventrolateral protocerebrum (AVLP), and posterior optic tubercle (POTU) contain extensive serotonin-immunoreactive process terminals. However, the regions of mushroom bodies, the lateral horn, and protocerebral bridges (PBs) are devoid of serotonin-immunoreactivity. In the gnathal ganglion, the serotonin-immunoreactive processes are also widespread throughout the neuropil, and some process projections extend to the tritocerebrum. Our results provide the first comprehensive description of the serotonergic neuronal network in H. armigera larvae, and they reveal the neural architecture and the distribution of neural substances, allowing us to explore the neural mechanisms of behaviors by using electrophysiological and pharmacological approaches on the target regions.

Designing an enzymatic oscillator: Bistability and feedback controlled oscillations with glucose oxidase in a continuous flow stirred tank reactor

The reaction of glucose with ferricyanide catalyzed by glucose oxidase from Aspergillus niger gives rise to a wide range of bistability as the flow rate is varied in a continuous flow stirred tank reactor. Oscillations in pH can be obtained by introducing a negative feedback on the autocatalytic production of H+ that drives the bistability. In our experiments, this feedback consists of an inflow of hydroxide ion at a rate that depends on [H+] in the reactor as k0[OH-]0[H+]/(K+[H+]). pH oscillations are found over a broad range of enzyme and ferricyanide concentrations, residence times (k0 (-1)), and feedback parameters. A simple mathematical model quantitatively accounts for the experimentally found oscillations.

Ramification pattern and ultrastructural characteristics of the serotonin-immunoreactive neuron in the antennal lobe of the moth Manduca sexta: a laser scanning confocal and electron microscopic study

The two antennal lobes, the primary olfactory centers of the brain, of the moth Manduca sexta each contain one neuron that displays serotonin immunoreactivity. The neuron projects out of the antennal lobe and sends branches into ipsi- and contralateral protocerebral areas. An axon-like process extends from the contralateral protocerebrum to, and terminates in, the contralateral antennal lobe. In order to begin to investigate the possible role of this unique neuron in olfactory information processing, we have used laser scanning confocal microscopic and electron microscopic immunocytochemical techniques to study the ramification pattern, ultrastructural characteristics, and synaptic connections of the neuron in the antennal lobes of female adult Manduca sexta. The neuron ramifies extensively in the antennal lobe contralateral to the cell body. The ramifications, mainly in the base and center of each glomerulus, do not overlap with those of the sensory axons from the antenna. This finding suggests that the serotonin-immunoreactive neuron may not receive direct input from sensory neurons, and that it may modulate the activity of the neurons of the antennal lobe rather than that of the sensory neurons. In the electron microscope, the neuron exhibits large dense-cored vesicles and small, clear round vesicles. In the antennal lobe ipsilateral to the cell body, the primary neurite of the serotonin-immunoreactive neuron is unbranched and lacks detectable synaptic connections. The ramifications in the contralateral antennal lobe, however, participate in synaptic connections. At very low frequency, contralateral branches form synapses onto unlabeled processes and also receive synapses from unidentified neurons in the glomeruli, indicating that the neuron may participate directly in synaptic processing of olfactory information. The high ratio of output to input synapses made by the serotonin-immunoreactive processes in the contralateral antennal lobe is consistent with the idea that this neuron may receive synaptic input via its bilateral branches in the protocerebrum and then send information to the contralateral antennal lobe where the neuron may exert feedback or modulatory influences on olfactory information processing in the glomeruli.

Fluorescence-histochemical and ultrastructural research on the monoaminergic neurosecretory cells of the earthworm Octolasium complanatum (Annelida: Oligochaeta)

A study of the yellow fluorescent neurons (M-NSC) of the subesophageal ganglion of the earthworm Octolasium complanatum has been made by using alternate semithin and thin sections in a correlate fluorescence and electron microscopy technique and it results that elementary neurosecretory granules are present where the yellow fluorescent substance is. These granules are similar in size and morphology to the granules of monoamine type. The intimate contact of the capillaries with the granular cytoplasmic area of the M-NSC provides evidence of a probable release of the secretion from the cell body. These results support the hypothesis of the endocrine role of the M-NSC.

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.

A novel serotonin-immunoreactive neuron in the antennal lobe of the sphinx moth Manduca sexta persists throughout postembryonic life

A single serotonin-immunoreactive neuron in the antennal lobe (AL) of the brain of the sphinx moth Manduca sexta is present in larval, pupal, and adult stages. This neuron has a neurite that extends to the contralateral AL, where it forms sparse arborizations in each glomerulus. Other neurites from this neuron project into the ipsilateral and contralateral protocerebrum. This cell is morphologically very different from other neurons previously characterized in the adult AL. The neuron maintains the same basic profile in the adult as in the larva, although fine processes such as the arborizations within the AL neuropil appear to be restructured to conform to the larger, more anatomically differentiated regions of the adult brain.

The influence of serotonin and p-chlorophenylalanine on locomotor activity of Drosophila melanogaster

Two hours after injection of serotonin into 3-day-old virgin females of Drosophila melanogaster, a significant dose-dependent increase in locomotor activity was observed. Since this stimulating effect can be produced either by serotonin or by some of its derivatives that might have formed during these two hours, the fate of injected [3H]-serotonin in the organism of Drosophila was traced by means of thin layer chromatography. The only metabolite found appeared to be N-acetylserotonin. Its formation was rather intense immediately after injection of [3H]-serotonin, and its excretion was rapid enough to make it undetectable at the end of the second hour, when more than 50% of the injected [3H]-serotonin still remained and was being absorbed by tissues. Thus, the increase in locomotor activity observed two hours after injection should be wholly attributed to serotonin, while the rather long latency might be related to some effect of N-acetylserotonin. p-Chlorophenylalanine, an inhibitor of tryptophan-5-hydroxylase, both injected or administered with food, led to increases in locomotor activity level and to some decreases in serotonin content in the heads of flies. The effect of p-chlorophenylalanine on locomotor activity in Drosophila seems to be non-specific in relation to serotoninergic mechanisms of its regulation.

Sensory basis of activity in Ancylostoma tubaeforme infective larvae

Upon stimulation, following a period of ambient conditions, infective A. tubaeforme larvae follow a committed characteristic pattern of activity, after being released by short-term mechanical or continuous photic stimulation. For the photic response this is stimulated by an increase in the intensity of stimulation, and for non-dark-adapted larvae a sudden fivefold increase in illumination is required, irrespective of previous stimulation.

Acetylcholine chloride, adenosine triphosphate, γ-amino butyric acid, histamine diphosphate, 5-hydroxytryptamine, neostigmine bromide, physostigmine (eserine), potassium hydroxide, succinyl choline chloride and d-tubocurarine chloride have been added to larvae and their subsequent postures and activity recorded. It is concluded that the typical activity pattern of larvae may be altered by the use of drugs which interfere with neuromuscular phenomena, and therefore the activity responses of infective A. tubaeforme are based on sensory and neurosecretory rather than energetic considerations.

We thank Mrs Helen Foreman for maintaining the larvae and the Medical Research Council of Great Britain for their generous support.