Sensory projections of identified coxal hair sensilla of the scorpionHeterometrus fulvipes (Scorpionidae)

The topography of long hair sensilla on the coxae of walking legs and pedipalps of the scorpionHeterometrus fulvipes is described. Identified long hair sensilla are cobalt filled, and central projections of sensory fibres are reported for the first time in the suboesophageal ganglion of this scorpion. The afferent fibres arising from each long hair sensilla segregate into ventral, dorsomedial and dorsal tracts upon their entry into the suboesophageal ganglion. These transverse tracts bifurcate towards the middle of the leg neuromere and form three ipsilateral, plurisegrnental, longitudinal sensory pathways. Filling a pair of bilaterally distributed long hair sensilla shows bilaterally arranged longitudinal afferent tracts interconnected by distinct transverse commissures. Similar patterns of sensory projections are observed when filling homologous hairs on other legs and pedipalps. Numerous fine collaterals arise from the longitudinal sensory trancts that subdivide and end in small blebs presumed to be presynaptic endings. The dorsal and dorsomedial longitudinal tracts and their respective commissures are in close association with the dendritic arborisations of pedipalpal and leg motor neurons, suggesting direct contact between them. The probable functions of these multisegmental hair afferent pathways are discussed.     

Central nervous projections of mechanoreceptors in the spider Cupiennius salei Keys.

Summary The basic organization of sensory projections in the suboesophageal central nervous system of a spider (Cupiennius salei Keys.) was analyzed with anterograde cobalt fills and a modified Golgi rapid method. The projections of three lyriform slit sense organs and of tactile hairs located proximally on the legs are described and related to central nerve tracts. There are five main longitudinal sensory tracts in the central region of the suboesophageal nervous mass arranged one above the other. Whereas the three dorsal ones contain fibers from the lyriform organs, the two ventral ones contain axons from the hair receptors. Axons from all three lyriform organs have typical shapes and widely arborizing ipsilateral intersegmental branches and a few contralateral ones. The terminal branches of the afferent projections from identical lyriform organs on each leg form characteristic longitudinal pathways, typical of each organ: U-shaped, O-shaped, or two parallel bundles. The terminations of the hair sensilla are ipsilateral and intersegmental. Two large bilaterally arranged longitudinal sensory association tracts receive inputs from all legs including the dense arborizations from tactile hairs, lyriform organs, and other sense organs. These tracts may serve as important integrating neuropils of the suboesophageal central nervous system.     

Central nervous projection patterns of trichobothria and other cuticular sensilla in the wandering spider Cupiennius salei (Arachnida,Araneae)

Summary Central projections of mechano-and chemoreceptors on the legs and pedipalps of the wandering spider Cupiennius salei were traced by anterograde cobalt fills. The primary afferent fibres from trichobothria, tactile hairs, lyriform organs and contact chemoreceptive hairs enter the leg ganglia and pedipalpal ganglia ventrally. On their way through these ganglia there is very little arborization. The main areas of arborization are in the sensory longitudinal tracts in the suboesophageal nervous mass. The central projections of all mechano-and chemoreceptors examined show somatotopic organization. Sensilla located proximally on the legs are represented in dorsally located sensory longitudinal tracts, whereas those located on distal leg segments enter more ventral tracts. The afferent fibres of receptors of identifical modality on a specific segment of all legs and of the pedipalps overlap in the same tracts. No indication for a tonotopic arrangement of the trichobothrial afferences was found, which might have been associated with the mechanical frequency tuning of the trichobothria known from other experiments. The convergence of the projections of different types of receptors in the sensory longitudinal tracts is considered to be an anatomical basis for their functional interaction in behaviour. Both the convergence of the projections of receptors from the same segment of different legs and the somatotopy are connectivity patterns possibly associated with the orientation of the spiders towards mechanical or chemical cues.     

Primary sensory projections from the labella to the brain of Drosophila melanogaster Meigen (Diptera : Drosophilidae)

Golgi silver impregnation of sensory neurons arising from labellar taste sensilla of Drosophila melanogaster Meigen (Diptera : Drosophilidae) revealed 7 distinct types I-VII of primary (sensory) fibres projecting to the suboesophageal ganglion (SOG) of the brain. Each fibre was classified on the bases of the neuropil volume occupied by its terminal arborisation, the shape of neuropil region receiving the arborisations and the detailed morphology of the arborisations. The primary sensory fibre projections from the labella are confined to the SOG where they project mainly in the anterior and central neuropils. No labellar sensory fibres project to posterior SOG. Of these 7 types of sensory fibres, three (III, IV and VII) show ipsilateral projections, while others have both ipsi-, and contralateral branches.Four types of interneurons are suggested to be associated with taste perception. Type A interneurons are local interneurons with arborisations confined only to the taste sensory neuropil of the SOG. The types B - D interneurons are interganglionic/output neurons with axons projecting to various brain regions-SOG, calyces of the mushroom bodies, tritocerebrum and thoracic ganglia. These projections suggest that more than one centre (SOG, tritocerebrum, calyces of the mushroom bodies and thoracic ganglia) are involved in processing gustatory information.     

The organization of plurisegmental mechanosensitive interneurons in the central nervous system of the wandering spider Cupiennius salei

Summary In spiders the bulk of the central nervous system (CNS) consists of fused segmental ganglia traversed by longitudinal tracts, which have precise relationships with sensory neuropils and which contain the fibers of large plurisegmental interneurons. The responses of these interneurons to various mechanical stimuli were studied electrophysiologically, and their unilateral or bilateral structure was revealed by intracellular staining. Unilateral interneurons visit all the neuromeres on one side of the CNS. They receive mechanosensory input either from a single leg or from all ipsilateral legs via sensory neurons that invade leg neuromeres and project into specific longitudinal tracts. The anatomical organization of unilateral interneurons suggests that their axons impart their information to all ipsilateral leg neuromeres. Bilateral interneurons are of two kinds, symmetric and asymmetric neurons. The latter respond to stimulation of all legs on one side of the body, having their dendrites amongst sensory tracts of the same side of the CNS. Anatomical evidence suggests that their terminals invade all four contralateral leg neuromeres. Bilaterally symmetrical plurisegmental interneurons have dendritic arborizations in both halves of the fused ventral ganglia. They respond to the stimulation of any of the 8 legs. A third class of cells, the ascending neurons have unilateral or bilateral dendritic arborizations in the fused ventral ganglia and show blebbed axons in postero-ventral regions of the brain. Their response characteristics are similar to those of other plurisegmental interneurons. Descending neurons have opposite structural polarity, arising in the brain and terminating in segmental regions of the fused ventral ganglia. Descending neurons show strong responses to visual stimulation. Approximately 50% of all the recorded neurons respond exclusively to stimulation of a single type of mechanoreceptor (either tactile hairs, or trichobothria, or slit sensilla), while the rest respond to stimulation of a variety of sensilla. However, these functional differences are not obviously reflected by the anatomy. The functional significance of plurisegmental interneurons is discussed with respect to sensory convergence and the coordination of motor output to the legs. A comparison between the response properties of certain plurisegmental interneurons and their parent longitudinal tracts suggests that the tracts themselves do not reflect a modality-specific organization.Abbreviations BPI bilateral plurisegmental interneuron - CNS central nervous system - FVG fused ventral ganglia - LT longitudinal tract - PI plurisegmental interneuron - PSTH peristimulus timehistogram - UPI unilateral plurisegmental interneuron     

Primary and secondary somatosensory projections in direct-developing Plethodontid Salamanders

In three species of plethodontid salamanders (Plethodon jordani, Hydromantes italicus, and Bolitoglossa subpalmata), primary and secondary somatosensory pathways were investigated by means of tract-tracing in vivo and in vitro using biocytin, horseradish peroxidase, and neurobiotin. Afferent sensory fibers of cranial nerves V, VII, and X and the brachial nerve run in the dorsal funiculus of the medulla oblongata and spinal cord. Fibers ascend to the level of, but do not enter, the cerebellum. In the caudal medulla oblongata, sensory tracts of the cranial nerves descend in a dorsal and a dorsolateral bundle and reach the level of the fourth spinal nerve. Two bundles are likewise formed by spinal afferent fibers, which descend to the level of the seventh spinal nerve. Secondary somatosensory projections ascend in contralateral ventral, contralateral lateral, and ipsilateral lateral tracts, the latter two corresponding to the spinal lemniscal tracts of Herrick. These tracts reach the cerebellum, mesencephalic, and diencephalic targets (tegmentum, torus, tectum, tuberculum posterius, pretectum, and ventral thalamus) ipsi- and contra-laterally. The projection to the tectum is confined to fiber layer 4. Fibers of the ascending tracts cross in the cerebellar and tectal commissure. Our study demonstrates that the ascending secondary somatosensory pathways of plethodontid salamanders differ remarkably from those of other amphibians. J. Morphol. 238:307–326, 1998. © 1998 Wiley-Liss, Inc.     

Anatomy of neurons crossing the tritocerebral commissures of the cockroach Periplaneta americana (Blattaria)

The neuronal connections of the tritocerebral commissures of Periplaneta americana were studied in the brain-suboesophageal ganglion complex and the stomatogastric nervous system by means of heavy metal iontophoresis through cut nerve ends followed by silver intensification. The tritocerebral commissure 1 (Tc1) contains mainly the processes of the subpharyngeal nerve (Spn) whose neurons are located in both tritocerebral lobes and in the frontal ganglion. Some neurons of the frontal ganglion project through the Tc1 to the contralateral tritocerebrum. A few fibers in this commissure were observed projecting to the protocerebrum and the suboesophageal ganglion. There are tritocerebral neurons which pass through the Tc1 or the tritocerebral commissure 2 (Tc2) and extend on into the stomatogastric nervous system. One axon of a descending gaint neuron appears in the Tc2. This neuron lies in the tritocerebrum and connects the brain to the contralateral side of the ventral nerve cord. In addition, sensory fibers of the labral nerve (Ln) traverse both commissures to the opposite tritocerebrum. The anatomical and physiological relevance of the identified neuronal pathways is discussed. © 1995 Wiley-Liss, Inc.     

Sensory innervation of the somite in the polychaete worm Nephthys hombergii]

Studies have been made on the peripheral sensory innervation of N. hombergii stained with methylene blue. It was shown that sensory elements of the polychaete are presented by several types of nervous cells which are symmetrically embedded between the circular and longitudinal muscle layers in each of the segments. Peripheral projections of these cells terminate in the epithelium, on muscle fibers and in the connective tissue. Central projections pass to the abdominal nerve chain. All. the observed sensory cells have a constant localization and shape, the latter presumably being determined by their polyvalent functions.     

A confined taste area in a lepidopteran brain

Knowledge about the neuronal pathways of the taste system is interesting both for studying taste coding and appetitive learning of odours. We here present the morphology of the sensilla styloconica on the proboscis of the moth Heliothis virescens and the projections of the associated receptor neurones in the central nervous system. The morphology of the sensilla was studied by light microscopy and by scanning- and transmission electron microscopy. Each sensillum contains three or four sensory neurones; one mechanosensory and two or three chemosensory. The receptor neurones were stained with neurobiotin tracer combined with avidin-fluorescein conjugate, and the projections were viewed in a confocal laser-scanning microscope. The stained axons entered the suboesophageal ganglion via the maxillary nerves and were divided into two categories based on their projection pattern. Category one projected exclusively ipsilaterally in the dorsal suboesophageal ganglion/tritocerebrum and category two projected bilaterally and more ventrally in the suboesophageal ganglion confined to the anterior surface of the neuropil. The bilateral projecting neurones had one additional branch terminating ipsilaterally in the dorsal suboesophageal ganglion/tritocerebrum. A possible segregation of the two categories of projections as taste and mechanosensory is discussed.     

Neural projection patterns from homeotic tissue of Drosophila studied in bithorax mutants and mosaics.

The central projection patterns of sensory cells from the wing and haltere of Drosophila, as revealed by filling their axons with cobalt, consist of dorsal components arising from small campaniform sensilla and ventral components arising from large campaniform sensilla and from bristles. All of the bristles of the wing are innervated, some singly and some multiply. All three classes of sensilla are strongly represented on the wing, but the haltere carries primarily small campaniform sensilla and has a correspondingly minute ventral projection. In bithorax mutants in which the haltere is transformed into wing, ventral components are added to the projection pattern, while the dorsal components appear as if haltere tissue were still present. Thus, the three classes of receptors not only produce different projection patterns when they develop in their native mesothoracic segment, but also behave differently in the homeotic situation. Consequently, different developmental programs are inferred for each class. When somatic recombination clones of bithorax tissue are generated in phenotypically wild-type flies, they also produce ventral projections. However, these projections of mutant fibers into wild-type ganglia differ in certain details from the projections of mutant fibers into mutant ganglia. Thus, homeotic changes are inferred to occur in the CNS of mutant flies, but these are not required for the execution of those developmental instructions carried in the genome of large campaniform and bristle sensory cells which specify that their axons should grow ventrad in the CNS.     

The projection of neuroendocrine fibers (NCC I and II) in the brains of three orthopteroid insects

Neuronal projections from neuroendocrine tracts (nervi corpori cordiaci I and II) in the brains of the locust (Schistocerca vaga), cricket (Acheta domesticus), and cockroach (Periplaneta americana) were studied using reconstructions of silver-intensified cobalt chloride preparations. Collaterals from the NCC I in these species branch extensively in the dorsal protocerebral neuropile, anterior to the stalk of the corpora pedunculata and ventral to its calyces. Other fibers project from the NCC I bilaterally into the medial protocerebral neuropile, anterior to the central body, and posterior to the beta lobes. NCC II collaterals arborize in the medial, dorsal, and lateral protocerebral neuropile, their region of projection partially overlapping with that of the NCC I. Several NCC II fibers terminate in the superior arch of the central body in Acheta but not in the other two species. Tritocerebral cells filled through the NCC I branch in the medial tritocerebral neuropile in all three species, but most extensively in Schistocerca. No NCC fibers were seen to penetrate any part of the corpora pedunculata, protocerebral bridge, olfactory glomeruli, ocellar tracts, or optic lobes. These neuronal projections from the NCC I and II lie anterior to regions of branching of second-order ocellar fibers and thus provide no anatomical basis for direct ocellar input to neurosecretory cells, contrary to previous reports for orthopteroid species (Brousse-Gaury, '71a, b). However, interneurons filled from the optic lobes were found to terminate in the same region of dorsal protocerebral neuropile as NCC I and II fibers in Acheta, thus providing a possible pathway for optic input to the cerebral neuroendocrine system.     

Cobalt sulphide staining of optic fibres in the brain of the cricket,Gryllus campestris

Neuronal projections from one optic lobe to other parts of the brain were stained in the cricket Gryllus campestris using the cobalt sulphide technique and Timm's sulphide-silver method. The results are: Four tracts directly connect the medulla with the lobula and medulla of the contralateral optic lobe. Direct medullar projections end mainly in the non-glomerular neuropile of the protocerebrum, but also penetrate the calyx of the mushroom bodies, pons and central body in small numbers. A few somata which send fibres into the medulla lie in the pars intercerebralis, in the protocerebrum ventral to the opposite beta-lobe, the outer margin of the medulla of the contralateral optic lobe and between deuto- and tritocerebrum. The anatomical and physiological relevance of the stained connections is discussed.     

The terminal abdominal ganglion of the wood cricket Nemobius sylvestris

The abdominal cerci of the wood cricket, Nemobius sylvestris, are covered by a variety of hair‐like sensilla that differ in length, thickness, and articulation. Fillings from the cercal nerves with cobalt chloride and fluorescent dyes revealed the projection of sensory axons into the terminal abdominal ganglion of the ventral nerve chain. Two projection areas on each side of the terminal abdominal ganglion midline could be identified: a posterior cercal glomerulus and an anterior bristle neuropil. Axons from some cercal sensilla ascend through the connectives to reach the metathoracic ganglionic mass. As their axons pass through each segmental abdominal ganglion, they project medial arborization. Cross‐sections of the terminal abdominal ganglion and retrograde fills with cobalt chloride and fluorescent dyes from connectives revealed several small cells and seven pairs of giant ascending interneurons organized symmetrically. Giant somata are located contralateral to their axons (diameters between 20 and 45 μm). The cercal projections overlap extensively with the dendritic fields of the giant interneurons. In the terminal abdominal ganglion, we identified nine longitudinal tracts, two major tracts, and seven smaller ones. The functional implications of the neuranatomical organization of the system are discussed on a comparative basis. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Cephalic sensory pathways in the central nervous system of larval Manduca sexta (Lepidoptera : Sphingidae)

Central projections of neurons innervating sensory structures on the head of larval Manduca sexta were traced by using methods of anterograde cobalt-diffusion. Regions of the deutocerebrum and tritocerebrum in the brain receive input from the antenna, labrum, maxilla, labial palps, hypopharynx and other unidentified regions of the buccal cavity. Antennal, maxillary and labial inputs project to the larval antennal centre (LAC) of the deutocerebrum. Stemmatal neurons and a few antennal neurons project into the protocerebrum. The suboesophageal ganglion (SEG) receives input from mechanosensory neurons in all parts of the head and its sensory appendages. Some mechanosensory neurons project further to the first thoracic ganglion. In addition to receiving input from chemosensory neurons of the maxilla, the SEG may also receive chemosensory input from epipharyngeal sensilla of the labrum.     

The tritocerebrum and the clypeolabrum in mandibulate arthropods: segmental interpretations

Bitsch, J. and Bitsch, C. 2010. The tritocerebrum and the clypeolabrum in mandibulate arthropods: segmental interpretations. —Acta Zoologica (Stockholm) 91 : 249–266 Different interpretations of the segmental composition of the head in mandibulate arthropods are critically reviewed, with particular focus on three closely associated structures: the tritocerebrum, the stomatogastric nervous system and the clypeolabrum. The main conclusions arising from the different discussions are the following. (1) Each tritocerebral ganglion has a dual composition, clearly discernable in some crustacean and hexapod species, including a dorsal portion connected with the second antennae and a ventral portion connected with the stomatogastric nervous system via the frontal ganglion. (2) The suboesophageal commissure linking the tritocerebral lobes of the two sides, can be wholly ascribed to the tritocerebral segment. (3) The stomatogastric nervous system is a morphologically autonomous system that is not fundamentally affected by head metamerization. (4) The clypeolabrum, the epistome–labrum and the hypostome are regarded as homologous formations. The clypeolabrum represents a fundamental structure of the head probably present in the arthropod ground plan. Its close spatial and developmental association with the stomodeum and its derivative, the stomatogastric nervous system, suggests that it is an anterior outgrowth of the forehead arising from a preoral territory (presegmental acron or protocerebral–ocular region?) and secondarily connected with the tritocerebrum, rather than derived from a pair of reduced appendages.     

In vivo dynamics of CNS sensory arbor formation: A time‐lapse study in the embryonic leech

In the embryo of the leech Hirudo medicinalis, afferent projections of peripheral sensory neurons travel along common nerve tracts to the CNS, where they defasciculate, branch, and arborize into separate, modality‐specific synaptic laminae. Previous studies have shown that this process requires, at least in part, the constitutive and then modality‐specific glycosylations of tractin, a leech L1 homologue. We report here on the dynamics of growth of these projections as obtained by examining the morphology of single growing dye‐filled sensory afferents as a function of time. Using 2‐photon laser‐scanning microscopy of the intact developing embryo, we obtained images of individual sensory projections at 3 to 30 min intervals, over several hours of growth, and at different stages of development. The time‐lapse series of images revealed a highly dynamic and maturation‐state‐dependent pattern of growth. Upon entering the CNS, the growth cone‐tipped primary axon sprouted numerous long filopodial processes, many of which appeared to undergo repeated cycles of extension and retraction. The growth cone was transformed into a sensory arbor through the formation of secondary branches that extended within the ganglionic neuropil along the anterior‐posterior axis of the CNS. Numerous tertiary and quaternary processes grew from these branches and also displayed cycles of extension and retraction. The motility of these higher‐order branches changed with age, with younger afferents displaying higher densities and greater motility than older, more mature sensory arbors. Finally, coincident with a reduction in higher order projections was the appearance of concavolar structures on the secondary processes. Rows of these indentations suggest the formation of presynaptic en‐passant specializations accompanying the developmental onset of synapse formation. © 2003 Wiley Periodicals, Inc. J Neurobiol 56: 41–53, 2003     

Structure and metamorphic remodeling of the larval nervous system and musculature of Phoronis pallida (Phoronida)

The structure of the larval nervous system and the musculature of Phoronis pallida were studied, as well as the remodeling of these systems at metamorphosis. The serotonergic portion of the apical ganglion is a U-shaped field of cell bodies that send projections into a central neuropil. The majority of the serotonergic cells are (at least) bipolar sensory cells, and a few are nonsensory cells. Catecholaminergic cell bodies border the apical ganglion. The second (hood) sense organ develops at competence and is composed of bipolar sensory cells that send projections into a secondary neuropil. Musculature of the competent larva includes circular and longitudinal muscle fibers of the body wall, as well as elevators and depressors of the tentacles and hood. The juvenile nervous system and musculature are developed prior to metamorphosis and are integrated with those of the larva. Components of the juvenile nervous system include a diffuse neural net of serotonergic cell bodies and fibers and longitudinal catecholaminergic fibers. The juvenile body wall musculature consists of longitudinal fibers that overlie circular muscle fibers, except in the cincture regions, where this pattern is reversed. Metamorphosis is initiated by the larval neuromuscular system but is completed by the juvenile neuromuscular system. During metamorphosis, the larval nervous system and the musculature undergo cell death, and the larval tentacles and gut are remodeled into the juvenile arrangement. Although the phoronid nervous system has often been described as deuterostome-like, these data show that several cytological aspects of the larval and juvenile neuromuscular systems also have protostome (lophotrochozoan) characteristics.     

Ocellar interneurones in the blowfly Calliphora erythrocephala: Morphology and central projections

Summary The morphology and central projections of first-order ocellar interneurones were analysed in the blowfly, Calliphora erythrocephala after cobalt and horseradish-peroxidase labelling. Three classes of interneurones can be distinguished on the basis of axon diameters: large, medium and small neurones. In total there are 12 large, 10 medium and an unknown number of small interneurones. These interneurones connect the fused first-order ocellar neuropil (underlying the three ocelli) with various areas of the central nervous system. The large neurones terminate in three subregions of the posterior slope (ocellar foci); the medium neurones arborise in several regions of the lateral protocerebrum, in the posterior slope, the lobula, the ventral medulla, and in the pro- and mesothoracic ganglia. The thin fibers arborise in all the above regions (except in the thoracic ganglia), and in addition in the neuropil dorsal to the oesophagus and antero-ventral to posterior slope (tritocerebrum). The anatomy of the ocellar pathway in C. erythrocephala is compared with those in other studied insects. Possible interactions between ocellar interneurones and other pathways are discussed.     

Central Projections of Gustatory Receptor Neurons in the Medial and the Lateral Sensilla Styloconica of Helicoverpa armigera Larvae

Food selection behavior of lepidopteran larvae is predominantly governed by the activation of taste neurons present in two sensilla styloconica located on the galea of the maxilla. In this study, we present the ultrastructure of the sensilla styloconica and the central projection pattern of their associated receptor neurons in larvae of the heliothine moth, Helicoverpa armigera. By means of light microscopy and scanning electron microscopy, the previous findings of two morphologically fairly similar sensilla comprising a socketed conic tip inserted into a large peg were confirmed. However, the peg size of the medial sensillum was found to be significantly bigger than that of the lateral sensillum. The sensory neurons derived from each sensillum styloconicum were mapped separately using anterograde staining experiments combined with confocal laser-scanning microscopy. For determining the afferents’ target regions relative to each other, we reconstructed the labeled axons and placed them into a common reference framework. The sensory axons from both sensilla projected via the ipsilateral maxillary nerve to the suboesophageal ganglion and further through the ipsilateral circumoesophageal connective to the brain. In the suboesophageal ganglion, the sensory projections targeted two areas of the ipsilateral maxillary neuropil, one located in the ventrolateral neuromere and the other adjacent to the neuromere midline. In the brain, the axon terminals targeted the dorso-anterior area of the ipsilateral tritocerebrum. As confirmed by the three-dimensional reconstructions, the target regions of the neural projections originating from each of the two sensilla styloconica were identical.     

On the issue of innervation of dorsal longitudinal musculature of <Emphasis Type="Italic">Lymnaea stagnalis</Emphasis> with inferior cervical nerve

Using the method of the anterograde dextran tetramethylrhodamin transport, there is obtained the topographic picture of branching of inferior cervical nerve axons on fibers of the dorsal longitudinal muscle in Lymnaea stagnalis (L.). Using the retrograde staining, the neuronal bodies sending their processes into this nerve are marked. Manifestations of asymmetry in distribution of neurons stained through the right and left nerves are described. The electron microscopic studies have shown that the main number of the inferior cervical nerve axons is represented by thin fibers presumably belonging to the sensory cells. A part of the nerve fibers and their endings show imunoreactivity to serotonin and acetylcholine. The serotoninergic fibers predominate quantitatively over the cholinergic ones and account for a half of the fibers stained with dextran. A possible functional role of the serotoninergic and cholinergic innervation of the dorsal longitudinal muscle in Lymnaea stagnalis is discussed.Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 40, No. 6, 2004, pp. 569–578.