5-Hydroxytryptamine-like immunoreactivity in the peripheral and central nervous systems of the leech Hirudo medicinalis

Studies on regeneration of central nervous system and social ability of the earthworm Eudrilus eugeniae

Earthworms are segmented invertebrates that belong to the phylum Annelida. The segments can be divided into the anterior, clitellar and posterior parts. If the anterior part of the earthworm, which includes the brain, is amputated, the worm would essentially survive even in the absence of the brain. In these brain amputee-derived worms, the nerve cord serves as the primary control center for neurological function. In this current work, we studied changes in the expression levels of anti-acetylated tubulin and serotonin as the indicators of neuro-regenerative processes. The data reveal that the blastemal tissues express the acetylated tubulin and serotonin from day four and that the worm amputated at the 7th segment takes 30 days to complete the regeneration of brain. The ability of self-assemblage is one of the specific functions of the earthworm's brain. The brain amputee restored the ability of self-assemblage on the eighth day.

Statistical characterization of social interactions and collective behavior in medicinal leeches

In the present study we analyzed the behavior and interactions among leeches in the same observation tank. Colored beads were glued onto their skin so that their behavior could be followed and quantified. When two or three leeches were present in the observation tank, they searched around for a maximum of 2 h and their motion and behavior were independent from those of their conspecifics. When the number of leeches in the tank was increased to 10, leeches were attracted to each other and exhibited episodes of highly correlated behavior. Solitary leeches injected with serotonin or dopamine increased the portion of time spent pseudoswimming and crawling, respectively. The behavior of three to five leeches injected with serotonin was not statistically independent, and leeches were attracted to their conspecifics and exhibited episodes of correlated behavior. Therefore, serotonin not only induces pseudoswimming in leeches but also promotes social interactions, characterized by a mutual attraction and by episodes of correlated/collective behavior.

Reorganization of monoaminergic systems in the earthworm, Eisenia fetida, following brain extirpation

The present study describes the major aspects of how monoaminergic (serotonin, dopamine) systems change in the course of regeneration of the brain in the earthworm (Eisenia fetida), investigated by immunocytochemistry, HPLC assay, and ligand binding. Following brain extirpation, the total regeneration time is about 80 days at 10 degrees C. On the 3rd postoperative day serotonin, and on the 11th postoperative day tyrosine hydroxylase-immunoreactive neurons can be observed in the wound tissue. Thereafter the number of the immunoreactive cells increases gradually, and by the 76th-80th postoperative days all serotonin- and tyrosine hydroxylase-immunopositive neurons can be found in their final positions, similarly to those observed in the intact brain. Labeled neurons located in the dorsal part of the regenerated brain appear earlier than the cells in lateral and ventral positions. Both serotonin- and tyrosine hydroxylase-immunoreactive neurons of the newly formed brain seem to originate from undifferentiated neuroblasts situated within and around the ventral ganglia and the pleura. Dopaminergic (tyrosine hydroxylase-immunoreactive) elements may additionally derive from the proliferation of neurons localized in the subesophageal ganglion and the pharyngeal nerve plexus. Following brain extirpation, both serotonin and dopamine levels, assayed by HPLC, first increase in the subesophageal ganglion; by the 25th day of regeneration, the monoamine content decreases in it and increases in the brain. Hence it is suggested that monoamines are at least partly transported from this ganglion to the regenerating brain. At the same time, (3)H-LSD binding can be detected in the regenerating brain from the 3rd postoperative day, showing a continuous increase until the 80th postoperative day, suggesting a guiding role of postsynaptic elements in the monoaminergic reinnervation of the newly formed brain.

Putative nitric oxide synthase (NOS)-containing cells in the central nervous system of the leech, Hirudo medicinalis: NADPH-diaphorase histochemistry

The presence and distribution of putative nitric oxide synthase (NOS)-containing cells in whole-mount preparations of the central nervous system of the leech, Hirudo medicinalis, were studied using NADPH-diaphorase (NADPH-d) histochemistry. Specific staining occurred mainly in somata of some central neurones but NADPH-d-reactive branches and terminals were found in peripheral nerves and connectives: neuropile areas were stained weakly or unstained. Intense staining was located in many neurones on the ventral side of the segmental ganglia, including primary sensory neurones, motoneurones and interneurones, and in the anterior root ganglion. The sex ganglia contained some extra NADPH-d-positive cells. Head and tail ganglia and the dorsal side of the segmental ganglia showed less staining. Specific activity was not detected in salivary glands, crop or intestine. Controls using beta-NADPH or nitro blue tetrazolium (NBT) alone or with NBT plus alpha-NADPH, beta-NAD+, beta-NADH or beta-NADP+ did not induce specific staining. A potential NOS inhibitor, 2,6-dichlorophenol-indophenol (DPiP) at 10(-3) M, totally abolished NADPH-d-positive staining. Long-term fixation did not change the pattern of distribution of NADPH-d-positive cells. We conclude that (i) fixative-resistant NADPH-diaphorase is a characteristic marker of 12-15% of neurones in the leech CNS, and (ii) the specific distribution of the putative NOS-containing neurones suggests that NO may be a natural signal molecule in leeches.

Monoamines and neuropeptides as transmitters in the sedentary polychaete Sabellastarte magnifica: actions on the longitudinal muscle of the body wall

Pharmacological studies on the body wall musculature of the sedentary polychaete Sabellastarte magnifica show a potential neurotransmitter role for monoamines and neuropeptides in this organism. All catecholamines induced contraction of longitudinal muscle strips, while serotonin and the neuropeptides FMRFamide and substance P caused a relaxation of both resting and active muscle. In addition, we demonstrate catecholaminergic and serotonergic pathways in the nervous system of this sabellid, using immunohistochemistry and catecholamine-induced fluorescence. The presence of neuropeptide-containing fibers in the nervous system of this polychaete has been previously reported. Together these results suggest that catecholamines act as excitatory transmitters on the longitudinal muscle cells of the body wall of S. magnifica, while serotonin and FMRFamide, and possible substance P, are inhibitory transmitters. The possibility of coexistence of serotonin and FMRFamide within the same neuronal cell bodies and fibers of this polychaete is also explored.

Neuromodulatory effects of acetylcholine and serotonin on the sensitivity of leech mechanoreceptors

1. Each segmental ganglion of the leech Hirudo medicinalis contains 6 touch (T) cells, 4 pressure (P) cells and 4 nociceptive (N) cells. The receptive terminals of these cells innervate the skin in discrete areas. These cells are known to have extrasynaptic receptors. 2. We tested the effect of transmitter substances present in leech CNS on the sensitivity of T and P cells to mechanical stimuli. Substances tested included octopamine, FMRFamide, proctolin, substance P, glutamate, GABA, acetylcholine and serotonin. 3. Only acetylcholine and serotonin had consistent effects. Serotonin (1 x 10(-3) M) increased the number of action potentials of T cells elicited by a standard stimulus. Serotonin (1 x 10(-4) M) and acetylcholine (1 x 10(-3) M) increased the number and frequency of action potentials in P cells.

Leech neurogenesis. II. Mesodermal control of neuronal patterns

This paper reports analyses of the effects of eliminating mesoderm from one or both sides of embryos of the glossiphoniid leech Theromyzon rude on the differentiation and distribution of ectodermal cells, especially identified peripheral neurons and central 5-hydroxytryptamine (5-HT)-containing neurons arising from the bilateral pair of cell lines called the n bandlets (n-kinship cells). In mesoderm-deprived regions, no segmental hemiganglia formed, and identified neurons were not organized into recognizable patterns, although 5-HT neurons underwent neurochemical differentiation and grew axons. In unilaterally mesoderm-deprived embryos, segmental hemiganglia were formed in a midbody experimental zone, and cells that had abnormally crossed the ventral midline from the deprived side gave rise to identified neurons that were incorporated as supernumeraries into the normal organization of hemiganglia on the nondeprived side. In a posterior experimental zone, ganglionic morphology was disrupted on both sides. We conclude that precursor cells are committed to specific neuronal fates regardless of whether they occupy normal positions and that mesodermal tissues provide positional cues necessary for such precursor cells to find positions appropriate to their fates.

Leech neurogenesis. I. Positional commitment of neural precursor cells

This paper reports analyses of the differentiation and distribution of identified peripheral neurons and central 5-HT-containing neurons in embryos of the glossiphoniid leech Theromyzon rude that have been deprived of one of the bilaterally paired major ectodermal cell lines called the n bandlets. Cells descended from a lone surviving n bandlet were abnormally distributed across both sides of the ventral midline. Nevertheless, they produced the complement of identified neurons that they would have produced in a normal embryo. Neurons produced by cells that crossed the midline occupied the normal positions of their absent homologs, as demonstrated by morphometric analysis of normal and n-bandlet-deprived ganglia. Ablations of ectodermal cell lines other than the n bandlets (o and p, or q) allowed the formation of normal distributions of neurons descended from the n bandlets. These results are interpreted as showing that neural precursor cells are committed to occupy particular positions before reaching those positions and probably use positional cues of predominantly nonectodermal origin to recognize those positions. Together, the results reported here and in the accompanying paper (S. Torrence, M. Law, and D. Stuart, 1989, Dev. Biol. 136, 40-60) suggest that ectodermal cells that are committed to give rise to specific neurons use cues provided by the mesoderm to find positions appropriate to their fates.

Serotoninlike immunoreactivity in the central and peripheral nervous system of the scale worm Harmothoe imbricata (Polychaeta)

The distribution of serotoninergic neurons in the nervous system of the scale worm Harmothoe imbricata was visualized in the anterior half of the body by the peroxidase-antiperoxidase (PAP) immunohistochemical method with a specific antiserotonin antibody. Immunoreactive neuronal somata were localized in discrete ganglion cell masses of the dorsally situated cerebral ganglion and in segmental ganglia of the ventral nerve cord. They also make up the majority of neurons present in the parapodial ganglia. Large and small varicose fibers stained in the neuropile of all the above-mentioned ganglia but also in interganglionic connectives and segmental nerves. On the basis of soma size and location and of fiber distribution, the reactive neurons were identified as primarily interneuronal with a few motoneurons and presumptive afferent neurons. The presence of a motor component was substantiated by observations of several reactive varicose fibers spread over longitudinal muscle layers of the trunk. In addition, neurites of the subepidermal nerve plexus and enterochromaffinlike cells of the gut epithelium reacted with the serotonin antibody. It is concluded that serotoninergic pathways are ubiquitous elements in the organization of the central and peripheral nervous system of this polychaete. The significance of these findings in relation to other annelid groups and to the physiological role of serotonin is discussed.

The Retzius cells in the leech: a review of their properties and synaptic connections

1. The Retzius cells (RCs) project an axonal branch in each anterior, posterior and dorsal segmental root. 2. RCs are the only serotonin-containing neurons projecting to the periphery. 3. RCs are activated by mechano-sensory neurons, by serotonin-containing neurons and by two pairs of subesophageal neurons, Tr 1 and Tr 2. 4. RCs also receive an excitatory and an inhibitory input from sensilla. 5. These inputs could form two systems, one converging onto RCs of each ganglion and one distributing to other ganglia after processing by RCs. 6. RCs play a role in muscle tension, in mucous release and in swimming activity.

Serotonin storage and uptake by identified neurons in the leech Haementeria ghilianii

Characterization of serotonin-containing neurons in the glossiphoniid leech Haementeria ghilianii was undertaken to provide a reference for developmental studies of their differentiation and for comparative studies of their distribution and function. Five types of serotonin-containing neurons were identified with an antiserum against serotonin and by radioenzymatic assay of individual isolated somata. They contain high concentrations of serotonin (in some cases exceeding saturation in aqueous solution) and their serotonin content increases with growth of the animal. Each type is capable of taking serotonin up from the extracellular fluid, as demonstrated autoradiographically. They exhibit segment-specific, and on comparison with hirudinid leeches, species-specific, differences in distribution, morphology, and the expression of serotonin metabolism.

Leech Retzius cells and 5-hydroxytryptamine

A pair of giant Retzius (R) cells in each segmental ganglion of the leech contain 5-hydroxytryptamine (5-HT). They are the only 5-HT-containing neurones in the central nervous system to send branches to the periphery, yet many peripheral tissues (e.g. body wall muscles, heart, reproductive organs, nephridia and gut) possess 5-HT-like immunoreactive nerve fibres. 5-HT and/or R cell stimulation relax basal tension of body wall muscles and reduce their relaxation times following contraction, enhance pharyngeal movements and salivary gland secretion but inhibit muscle movements of the posterior gut regions and of the reproductive tract. It is suggested that R cells are multifunction neurones modulating activity of many tissues so that feeding behaviour of the leech is carried out as efficiently as possible.