Annelid brain and nerve cord in siboglinid Riftia pachyptila

Vestimentifera is a peculiar group of marine gutless siboglinids which has uncertain position in annelid tree. The detailed study of the fragmentary explored central nervous system of vestimentiferans and other siboglinids is requested to trace the evolution of the siboglinid group. Among all siboglinids the vestimentiferans preserve the gut rudiment what makes them a key group to homologize main cerebral structures with the ones of typical annelids, such as supra- and subesophageal commissures, cirsumesophageal connectives etc. Histologically we revealed main annelid brain structures in the compact large brain of Riftia pachyptila: circumesophageal connectives (longitudinal nerve tracts) and commissures (dorsal, supra- and subenteral commissures). Innervation of tentacles makes them homologous to peristomial palps of the rest annelids. The single nerve cord is represented by paired intraepidermal longitudinal strands associated with the ventral ciliary field in vestimentum and bearing giant axons originating from at least four pairs of perikarya. The absence of regularly positioned ganglia and lateral nerves in the nerve cord in vestimentum and trunk and presence of them in the opisthosome segments. Among siboglinids, the vestimentiferans distinguished by a large and significatly differentiated brain which is reflection of the high development of the palp apparatus. Osedax, frenulates and Sclerolinum have less developped brain. Frenulates and Sclerolinum have good ganglionization in the opisthosome, which probably indicates its high mobility. Comparative neuroanatomical analysis of the siboglinids and annelid sister clades allows us to hypothesize that the last common ancestor of siboglinids might had brain with a dorsal commissure giving rise neurite bundles to palps and paired ventral nerve cord.

Comparison of longitudinal excursion of a nerve-phantom model using quantitative ultrasound imaging and motion analysis system methods: A convergent validity study

Background Quantitative ultrasound imaging is gaining popularity in research and clinical settings to measure the neuromechanical properties of the peripheral nerves such as their capability to glide in response to body segment movement. Increasing evidence suggests that impaired median nerve longitudinal excursion is associated with carpal tunnel syndrome. To date, psychometric properties of longitudinal nerve excursion measurements using quantitative ultrasound imaging have not been extensively investigated. Methods This study investigates the convergent validity of the longitudinal nerve excursion by comparing measures obtained using quantitative ultrasound imaging with those determined with a motion analysis system. A 38-cm long rigid nerve-phantom model was used to assess the longitudinal excursion in a laboratory environment. The nerve-phantom model, immersed in a 20-cm deep container filled with a gelatin-based solution, was moved 20 times using a linear forward and backward motion. Three light-emitting diodes were used to record nerve-phantom excursion with a motion analysis system, while a 5-cm linear transducer allowed simultaneous recording via ultrasound imaging. Results Both measurement techniques yielded excellent association ( r = 0.99) and agreement (mean absolute difference between methods = 0.85 mm; mean relative difference between methods = 7.48 %). Small discrepancies were largely found when larger excursions (i.e. > 10 mm) were performed, revealing slight underestimation of the excursion by the ultrasound imaging analysis software. Conclusion Quantitative ultrasound imaging is an accurate method to assess the longitudinal excursion of an in vitro nerve-phantom model and appears relevant for future research protocols investigating the neuromechanical properties of the peripheral nerves.

Serotonin in Trichinella pseudospiralis: An immunocytochemical study

SummaryThis is the first report on the presence and localization of the neurotransmitter serotonin (5-HT) in the nervous system of the nematode Trichinella pseudospiralis, the causative agent of trichinellosis. The orientation of the 5-HT-immunoreactive (5-HT-IR) nerve cells in the adult worm is described. In the anterior region of the worm 5-HT-IR occurs in 7 neurons. Longitudinal nerve cords extend posteriorly from the anterior end. They are connected by transverse commissures. The vulval area is intensively supplied with 5-HT-IR nerve cells and fibres forming a plexus. Two rows of small 5HT-IR structures, hypodermal glands, are visible along the whole nematode body. Because of the conserved structural features among nematodes the 5-HT-IR neurons observed are likely to have counterparts in the model worm, Caenorhabditis elegans. Some basic differences are evident and demand further study.

The distribution of neuroactive substances within the cercaria of Sanguinicola inermis

The serotoninergic and peptidergic components of the nervous system of the cercaria of Sanguinicola inermis (Digenea: Sanguinicolidae) were examined using whole-mount immunocytochemistry and a plan of the nervous system has been described. Antibodies to serotonin (5-hydroxytryptamine, 5-HT) and the neuropeptides, FMRFamide, GFNSALMFamide (S1) and SGPYSFNSGLTFamide (S2) were used in the study. Immunoreactivity (IR) was demonstrated to all but the S2 antisera and showed a similar fundamental distribution. IR was found in paired cerebral ganglia located anteriorly within the body and connected by a cerebral commissure. From the ganglia paired ventral and dorsal longitudinal nerve cords extend anteriorly into the cephalic organ and into the body. There is no apparent connection with the tail. Several transverse commissures connect the longitudinal nerve cords throughout the body and several associated cell bodies have been located. A double-stranded dorsal and ventral longitudinal nerve cord extends the length of the tail and six cell bodies are associated with these cords, uniquely demonstrating either FMRFamide and S1, or 5-HT-like IR. Only 5-HT-like IR was found to extend into the posterior tail furcae and there appears to be a lack of any peripheral tegumental innervation. Double-labelling experiments suggest that the serotoninergic and peptidergic components of the cercarial nervous system are distinct.