Organization of neuropeptide tyrosine-like immunoreactive system in the brain of the Antarctic fish, Trematomus bernacchii

Antarctic notothenioids have developed unique freezing-resistance adaptations, including brain diversification, to survive in the subzero waters of the Southern Ocean surrounding Antarctica. In this study we have investigated the anatomical distribution of neuropeptide tyrosine (NPY)-like immunoreactive elements in the brain of the Antarctic fish Trematomus bernacchii, by using an antiserum raised against porcine NPY. Perikarya exhibiting NPY-like immunoreactivity were observed in distinct regions of the brain. The most rostral group of immunoreactive perikarya was found in the telencephalon, within the entopeduncular nucleus. In the diencephalon, three groups of NPY-like immunoreactive perikarya were found in the hypothalamus. Two groups of positive cell bodies were found in distinct populations of the preoptic nucleus, whereas the other group was found in the nucleus of the lateral recess. More caudally, NPY immunoreactivity was detected in large neurons located in the subependymal layers of the dorsal tegmentum of the mesencephalon, medially to the torus semicircularis. NPY-like immunoreactive nerve fibres were more widely distributed throughout the telencephalon to the rhombencephalon. High densities of nerve fibres and terminals were observed in several regions of the telencephalon, olfactory bulbs, hypothalamus, tectum of the mesencephalon and in the ventral tegmentum of the rhombencephalon. The distribution of NPY-like immunoreactive structures suggests that, in Trematomus, this peptide may be involved in the control of several brain functions, including olfactory activity, feeding behaviour, and somatosensory and visual information. In comparison with other neuropeptides previously described in the brain of Antarctic fish, NPY is more widely distributed. Our data also indicate the existence of differences in the brain distribution of NPY between Trematomus and other teleosts. In contrast with previous results reported in other fish, Trematomus contains positive fibres in the olfactory bulbs and immunoreactive perikarya in the nucleus of the lateral recess, whereas NPY-immunopositive cell bodies are absent in the thalamus and rhombencephalon, and no NPY immunoreactivity is present in the pituitary. These differences could be related to the Antarctic ecological diversity of notothenioids living at subzero temperatures.     

Localization of galanin-like immunoreactive structures in the brain of the Senegalese sole, Solea senegalensis

The distribution of galanin-like immunoreactive structures was studied in the brain of the Senegalese sole, Solea senegalensis, using immunohistochemical methods. Periventricular immunoreactive cell bodies were observed in the rostral pole of the preoptic recess, within the pars parvocellularis of the nucleus preopticus parvocellularis. Another galanin-immunoreactive cell population was observed more caudal in the ventromedial hypothalamus, along the medial evaginations of the lateral recess. These cells appear within the cytoarchitectonic limits of the nucleus recessus lateralis pars ventralis. We found an extensive presence of galanin-immunoreactive fibres throughout the entire brain, although the most massive network of fibres was observed in the caudal olfactory bulbs, ventral telencephalon, preoptic area and around diencephalic ventricular recesses. Also, the hypophysis, ventricular mesencephalic area, median reticular formation and viscerosensory rhombencephalon displayed important plexuses of galanin-immunoreactive axons.The widespread distribution of these immunoreactive structures in the brain and pituitary of the Senegalese sole suggests an important role for galanin in neuroendocrine regulation of brain and adenohypophyseal functions.     

FMRFamide-like immunoreactivity in the brain and pituitary of the teleost. Eigenmannia lineata (Gymnotiformes)

The distribution of cells immunoreactive for the molluscan tetrapeptide FMRFamide in the brain and the pituitary of Eigenmannia was investigated immunohistochemically by the use of the peroxidase-antiperoxidase (PAP) technique and unlabelled antibodies. FMRFi neurons were located in the ganglion of the nervus terminalis at the rostroventral side of the bulbus olfactorius. FMRFi perikarya were also found in a dorsomedial diencephalic nucleus, in the nucleus ventromedialis, in some liquor-contacting neurons of the nucleus lateralis tuberis and of the nucleus recessus lateralis and posterior. The perikarya of the midbrain pre-pacemaker nucleus were only weakly immunoreactive for FMRFamide while large FMRFi neurons (T-cells) occurred in lamina VI of the torus semicircularis, in the brain stem, in dorsal and medial layers of the lobus lineae lateralis posterior (LLLp) and in the medullary electric organ pacemaker nucleus (pm). FMRFi fibers and nerve endings were found in the bulbus olfactorius, in medial areas of the telencephalon, and rather densely in the rostral diencephalon. Ventrocaudally to most of the hypothalamic nuclei the occurrence of immunoreactive fibres increased; many coursed to the pituitary through the pituitary stalk. FMRFi fibres also appeared in the deep layers of the tectum opticum, in the torus semicircularis, in the medial and lateral medulla and below the pacemaker nucleus. Wherever FMRFamide-immunoreactivity occurred fibres and nerve endings could be found in close contact with blood vessels.     

Retinopetal neuronal system in the brain of an air-breathing teleost fish,Channa punctata

Summary Retinopetal neurons were visualised in the telencephalon and diencephalon of an air-breathing teleost fish, Channa punctata, following administration of cobaltous lysine to the optic nerve. The labelled perikarya (n=45–50) were always located on the side contralateral to the optic nerve that had received the neuronal tracer. The rostral-most back-filled cell bodies were located in the nucleus olfactoretinalis at the junction between the olfactory bulb and the telencephalon. In the area ventralis telencephali, two groups of telencephaloretinopetal neurons were identified near the ventral margin of the telencephalon. The rostral hypothalamus exhibited retrogradely labelled cells in three discrete areas of the lateral preoptic area, which was bordered medially by the nucleus praeopticus periventricularis and nucleus praeopticus, and laterally by the lateral forebrain bundle. In addition to a dorsal and a ventral group, a third population of neurons was located ventral to the lateral forebrain bundle adjacent to the optic tract. The dorsal group of neurons exhibited extensive collaterals; a few extended laterally towards the lateral forebrain bundle, whereas others ran into the dorsocentral area of the area dorsalis telencephali. A few processes extended via the anterior commissure into the telencephalon ipsilateral to the optic nerve that had been exposed to cobaltous lysine. However, the ventral cell group did not possess collaterals. In the diencephalon, retinopetal cells were visualised in the nucleus opticus dorsolateralis located in the pretectal area; these were the largest retinopetal perikarya of the brain. The caudal-most nucleus that possessed labelled somata was the retinothalamic nucleus; it contained the largest number of retinopetal cells. The limited number of widely distributed neurons in the forebrain, some with extensive collaterals, might participate in functional integration of different brain areas involved in feeding, which in this species is influenced largely by taste, not solely by vision.     

Architecture of the nervous system in two Dactylopodola species (Gastrotricha, Macrodasyida)

Immunohistochemical stainings have become standard tools to describe the nervous system, but usually only singular or few markers are used and consequently show only subsets of neurons within the nervous system. We investigated two species of Dactylopodola (Gastrotricha, Macrodasyida) with a broad set and combination of markers, to represent the nervous system in a more holistic approach. We suggest that markers for both neurotubuli (tubulin) and neurotransmitters (e.g. serotonin, FMRF-amides, histamine) should be used. Combinations with markers for the musculature (phalloidin) and nuclei (propidiumiodide or other markers) help to reveal spatial patterns and when used with TEM can provide a more precise picture of the spatial relationships of particular nerves. Species of Dactylopodola have a brain consisting of a solid dorsal commissure and a fine ventral commissure. Cell somata of brain cells are arranged lateral to the dorsal commissure and form a dumbbell-like brain. Additionally, projections into the head region, head sensory organs, one pair of lateroventral nerve cords with three commissures and stomatogastric nerves are described. Obviously, some longitudinal transmitter-specific fibres run in parallel to the main longitudinal nerve and represent additional longitudinal fibres. In comparison with the nervous system architecture of other gastrotrich species and that of different bilaterian animals it is speculated that the gastrotrich nervous system retains several ancestral features, such as being commissural and not a compact brain.     

Corticotropin-releasing hormone-like immunoreactivity in the brain of the snake Bothrops jararaca

The distribution of corticotropin-releasing hormone in the brain of the snake Bothrops jararaca was studied immunohistochemically. Immunoreactive neurons were detected in telencephalic, diencephalic and mesencephalic areas such as dorsal cortex, subfornical organ, paraventricular nucleus, recessus infundibular nucleus, nucleus of the oculomotor nerve and nucleus of the trigeminal nerve. Immunoreactive fibres ran along the hypothalamo-hypophysial tract to end in the outer layer of the median eminence and the neural lobe of the hypophysis. In general, immunoreactive fibres occurred in the same places of immunoreactive neurons. In addition, immunoreactive fibres were observed in the septum, amygdala, lamina terminalis, supraoptic nucleus, nucleus of the paraventricular organ, ventromedial hypothalamic nucleus and interpeduncular nucleus. These results indicate that, as for other vertebrates, corticotropin-releasing hormone in B. jararaca brain, besides being a releasing hormone, may also act as a central neurotransmitter and/or neuromodulator.     

The efferent connections of the lateral septal nucleus in the guinea pig: projections to the diencephalon and brainstem

Summary The anterograde Phaseolus vulgaris-leucoagglutinin (PHA-L) tracing technique was used to determine the distribution of efferent fibers originating in the lateral septal nucleus of the guinea pig. For complementary detection of the chemical identity of the target neurons, double-labeling immunocytochemistry was performed with antibodies to PHA-L and to vasopressin, oxytocin, vasoactive intestinal polypeptide, serotonin or dopamine -hydroxylase, respectively. The hypothalamus received the majority of the PHA-L-stained septofugal fibers. Here, a specific topography was observed. (1) The medial and lateral preoptic area, (2) the anterior, lateral, dorsal, posterior hypothalamic and retrochiasmatic area, (3) the supraoptic, paraventricular, suprachiasmatic, dorsomedial, caudal ventromedial and arcuate nuclei, and (4) the tuberomammillary, medial and lateral supramammillary, dorsal and ventral premammillary nuclei always contained PHA-L-labeled fibers. The rostral portion of the ventromedial nucleus and the medial and lateral mammillary nucleus only occasionally showed weak terminal labeling. In other diencephalic areas, termination of PHA-L-labeled fibers was observed in the epithalamus and the nuclei of the midline region of the thalamus. In the mesencephalon, terminal varicosities occurred in the ventral tegmental area, interfascicular and interpeduncular nucleus, and periaqueductal gray. In addition, the dorsal and medial raphe nuclei of the metencephalon, together with the locus coeruleus and the dorsal tegmental nucleus, received lateral septal efferents.     

The distribution of corticotropin-releasing factor-immunoreactive neurons and nerve fibers in the brain of the snake,Natrix maura

Summary The anatomical distribution of neurons and nerve fibers containing corticotropin-releasing factor (CRF) has been studied in the brain of the snake, Natrix maura, by means of immunocytochemistry using an antiserum against rat CRF. To test the possible coexistence of CRF with the neurohypophysial peptides arginine vasotocin (AVT) and mesotocin (MST) adjacent sections were stained with antisera against the two latter peptides. CRF-immunoreactive (CRF-IR) neurons exist in the paraventricular nucleus (PVN). In some neurons of the PVN, coexistence of CRF with MST or of CRF with AVT has been shown. Numerous CRF-IR fibers run along the hypothalamo-hypophysial tract and end in the outer layer of the median eminence. In addition, some fibers reach the neural lobe of the hypophysis. CRF-IR perikarya have also been identified in the following locations: dorsal cortex, nucleus accumbens, amygdala, subfornical organ, lamina terminalis, nucleus of the paraventricular organ, nucleus of the oculomotor nerve, nucleus of the trigeminal nerve, and reticular formation. In addition to all these locations CRF-IR fibers were also observed in the lateral septum, supraoptic nucleus, habenula, lateral forebrain bundle, paraventricular organ, hypothalamic ventromedial nucleus, raphe and interpeduncular nuclei.     

The distribution of aminergic neurones and their projections in the brain of the teleost,Myoxocephalus scorpius

Summary Fluorescent histochemistry was carried out on the brain of the teleost Myoxocephalus scorpius to show the distribution of monoaminergic neurones and their projections.Posterior to the obex of the fourth ventricle, at the junction of the spinal chord and medulla, there is an unpaired dorsal nucleus of catecholaminergic cells. A second group of catecholaminergic perikarya are scattered lateral to the vagal and glossopharyngeal motor nuclei. Both groups of aminergic cells contribute to a tract which crosses the fourth ventricle at the obex and runs along the lateral wall of the medulla towards the diencephalon.At the level of the isthmus there is a lateral nucleus composed of large catecholaminergic cells with prominent fluorescent axons and its possible homology with the locus coeruleus is considered. Medially, in the same region a nucleus of serotonergic neurones lies between the paired tracts of the fasciculus longitudinalis medialis.In the diencephalon there are three paraventricular nuclei, the nuclei recessus posterioris and lateralis and the paraventricular organ pars anterior. Ventral to the lateral recess there is a further nucleus less closely associated with the ependyma.The distribution of fluorescent fibres is described and the dispositions of the aminergic nuclei compared to those of other teleosts.     

Localization of atrial natriuretic factor (ANF)-related peptides in the central nervous system of the elasmobranch fish Scyliorhinus canicula

We have investigated the localization of atrial natriuretic factor (ANF)-like immunoreactivity in the central nervous system of the cartilaginous fish, Scyliorhinus canicula, using the indirect immunofluorescence technique. Immunoreactive perikarya and fibers were observed in two regions of the telencephalon, the area superficialis basalis and the area periventricularis ventrolateralis. In the diencephalon, the hypothalamus exhibited a moderate number of ANF-containing neurons and fibers located in the preoptic and periventricular nuclei and in the nucleus lateralis tuberis. The most important group of ANF-immunoreactive cells was observed in the nucleus tuberculi posterioris of the diencephalon. In contrast, the mesencephalon showed only a few ANF-positive nerve processes located in the tegmentum mesencephali. Numerous fine fibers and nerve terminals were found in the dorsal area of the neurointermediate lobe of the pituitary. These results provide the first evidence for the presence of ANF-related peptides in the brain of a cartilaginous fish. The widespread distribution of ANF-positive cells and fibers in the brain and pituitary suggests that this peptide may act both as a neurotransmitter and (or) a neurohormone in fish.     

The nervous system of <Emphasis Type="Italic">Convolutriloba</Emphasis> (Acoela) and its patterning during regeneration after asexual reproduction

We describe the serotonergic and cholinergic nervous system of the asexually reproducing acoel Convolutriloba longifissura Bartolomaeus & Balzer, 1997 by means of immunohistochemistry, conventional histochemistry and transmission electron microscopy. Immunocytochemical staining for serotonin revealed neurons in the brain, in a pair of ventral main longitudinal cords, in two pairs of smaller dorsal longitudinal nerve cords, and in a submuscular nerve net. The brain comprises a ventral-anterior commissure and a less intensely stained dorsal commissure joined together by connectives into a three-ringed scaffold from which the longitudinal nerves extend. We followed the regeneration of the serotonergic part of the nervous system up to the second day after fission. Within this time period, the offspring reestablished bilateral symmetry in the nervous system and developed full motor control. The presence of aminergic cell bodies associated with the main lateral nerve cords of C. longifissura shows that the acoelan nervous system is more similar to that of other platyhelminths (triclads, rhabditophorans) than previously assumed. The presence of serotonergic cell bodies along the main nerve cord correlates with the capacity for asexual reproduction via fissioning. We also describe the single fission mode of C. hastifera Winsor 1990, which brings the modes of asexual reproduction employed by members of the Convolutrilobinae to three.     

Target areas innervated by PACAP-immunoreactive retinal ganglion cells

The retinohypothalamic tract (RHT) originates from a subset of retinal ganglion cells (RGCs). The cells of the RHT co-store the neurotransmitters PACAP and glutamate, which in a complex interplay mediate light information to the circadian clock located in the suprachiasmatic nuclei (SCN). These ganglion cells are intrinsically photosensitive probably due to expression of melanopsin, a putative photoreceptor involved in light entrainment. In the present study we examined PACAP-containing retinal projections to the brain using intravitreal injection of the anterograde tracer cholera toxin subunit B (ChB) and double immunostaining for PACAP and ChB. Our results show that the PACAP-containing nerve fibres not only constituted the major projections to the SCN and the intergeniculate leaflet of the thalamus but also had a large terminal field in the olivary pretectal nucleus. The contralateral projection dominated except for the SCN, which showed bilateral innervation. PACAP-containing retinal fibres were also found in the ventrolateral preoptic nucleus, the anterior and lateral hypothalamic area, the subparaventricular zone, the ventral part of the lateral geniculate nucleus and the nucleus of the optic tract. Retinal projections not previously described in the rat also contained PACAP. These new projections were found in the lateral posterior nucleus, the posterior limitans nucleus, the dorsal part of the anterior pretectal nucleus and the posterior and medial pretectal nuclei. Only a few PACAP-containing retinal fibres were found in the superior colliculus. Areas innervated by PACAP-immunoreactive fibres also expressed the PACAP-specific PAC1 receptor as shown by in situ hybridization histochemistry. The findings suggest that PACAP plays a role as neurotransmitter in non-imaging photoperception to target areas in the brain regulating circadian timing, masking, regulation of sleep-wake cycle and pupillary reflex.Abbreviations 3v Third ventricle - ac Anterior commissure - AD Anterodorsal thalamic nucleus - AH Anterior hypothalamic area - APTD Anterior pretectal nucleus, dorsal part - ChB Cholera toxin subunit B - CPu Caudate putamen - CPT Commissural pretectal nucleus - DGL Dorsal geniculate nucleus - IGL Intergeniculate leaflet - LH Lateral hypothalamic area - LP Lateral posterior thalamic nucleus - LS Lateral septum - MB Mammillary body - MPO Medial preoptic nucleus - MPT Medial pretectal nucleus - oc Optic chiasma - OPT Olivary pretectal nucleus - OT Nucleus of the optic tract - PACAP Pituitary adenylate cyclase-activating polypeptide - PAC1 PACAP receptor type 1 - PAG Periaqueductal gray - Pe Periventricular hypothalamic nucleus - PLi Posterior limitans thalamic nucleus - PPT Posterior pretectal nucleus - PVT Paraventricular thalamic nucleus - PVN Paraventricular hypothalamic nucleus - RGCs Retinal ganglion cells - RHT Retinohypothalamic tract - SCN Suprachiasmatic nucleus - SC Superior colliculus - SNR Substantia nigra, reticular part - SON Supraoptic nucleus - SPVZ Subparaventricular zone - VGL Ventral geniculate nucleus - VIP Vasoactive intestinal peptide - VPAC1 VIP/PACAP receptor type 1 - VPAC2 VIP/PACAP receptor type 2 - VLPO Ventrolateral preoptic nucleus - VTA Ventral tegmental areaThis study was supported by The Danish Biotechnology Center for Cellular Communication and The Danish Neuroscience Programme. J.H. is postdoc funded by the Danish Medical Research Council (Jr. No. 0001716)     

Analysis of the efferent projections of the lateral geniculate nucleus with special reference to the innervation of the subcommissural organ and related areas

In order to define central neurons projecting to the subcommissural organ (SCO) and to related areas in the postero-medial diencephalon, Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected into the lateral geniculate nucleus of the rat. PHA-L-labelled neurons send axonal processes medially through the posterior thalamic nuclei and the posterior commissure to the other hemisphere. Branches of fibres originating from this projection form a plexus of nerve terminals in the underlying precommissural nucleus and in the nucleus of the posterior commissure. A small number of PHA-L-immunoreactive nerve fibres penetrate from the precommissural nucleus into the lateral part of the SCO. A few labelled fibres penetrate directly from the posterior commissure into the medial part of the caudal SCO. Most of the PHA-L-immunoreactive fibres occur in the hypendymal layer, although a few terminate near the ependymal cells of the organ. Many labelled fibres are found in the ventricular ependyma adjacent to the SCO, some fibres lying close to the ventricular lumen. These results were obtained only if the tracer was delivered into the intergeniculate leaflet of the lateral geniculate nucleus (IGL). The IGL innervates both the suprachiasmatic nucleus and the pineal organ; the connections between the IGL and the midline structures, including the SCO, suggest that these areas are influenced by the circadian system.     

Immunoreactive atrial natriuretic peptide and autoradiographic distribution of atrial natriuretic peptide binding sites in the brain of the Antarctic fish, Chionodraco hamatus

The anatomical distribution of atrial natriuretic peptide (ANP)-immunoreactive structures and the autoradiographic localization of ANP binding sites were studied in the brain of the Antarctic fish, Chionodraco hamatus. ANP-containing elements were colocated with ANP binding sites in the dorsal medial and lateral subdivisions of the telencephalon, prethalamic nuclear complex, and in the nucleus of the medial longitudinal fasciculus of the mesencephalon. However, mismatching was observed in other brain regions, particularly at mesencephalic and metencephalic levels. In the pituitary, ANP immunoreactivity occurred only in the pars distalis, whereas ANP binding sites were localized in the whole pituitary. In this paper we describe the occurrence of ANP immunoreactivity and ANP binding sites in the brain and pituitary of an Antarctic fish. In particular, in the cerebellum and pituitary of C. hamatus, ANP binding sites are distributed in corresponding brain regions of dipnoans, amphibians and mammals. The immunocytochemical and histoautoradiographic data suggest that ANP acts as neuromodulator in the brain of C. hamatus. Moreover, the presence of ANP-like substances in tanycytes lining the diencephalic ventricle suggests a chemosensorial role for such liquor-contacting cells and a possible modulatory effect of ANP on the osmoregulation of the cerebrospinal fluid. Accepted: 3 April 2000     

Gut regulatory peptides in some Antarctic notothenioids

The presence and the comparative distribution of regulatory peptides and serotonin in the gut of four species of Antarctic notothenioid fishes [Cryodraco antarcticus and Chionodraco hamatus (Channichthyidae), and Trematomus bernacchii and Trematomus newnesi (Nototheniidae)], were immunohistochemically studied. In these species, numerous immunoreactive (IR) endocrine cells and nerve elements were detected. In the nototheniids most of the IR nerve fibres were of the intrinsic type, while most of the IR nerve fibres of the channichthyid intestine, besides insulin-like IR fibres, seemed to be of the extrinsic type. The intensity and frequency of immunopositivity are not the same in channnichthyids and nototheniids; the species belonging to the first family show many differences from the teleosts living in temperate water. The finding of insulin-like endocrine cells and nerve fibres in the gut wall of Cryodraco antarcticus is exceptional for vertebrates and deserves special attention.A preliminary account of this work was presented to the VII International Ichthyology Congress, Den Haag, 26–30 August 1991     

Brain morphology and immunohistochemical localization of the gonadotropin-releasing hormone in the bluefin tuna, Thunnus thynnus

The present study was focused on the morphology of the diencephalic nuclei (likely involved in reproductive functions) as well as on the distribution of GnRH (gonadotropin-releasing hormone) in the rhinencephalon, telencephalon and the diencephalon of the brain of bluefin tuna (Thunnus thynnus) by means of immunohistochemistry. Bluefin tuna has an encephalization quotient (QE) similar to that of other large pelagic fish. Its brain exhibits well-developed optic tecta and corpus cerebelli. The diencephalic neuron cell bodies involved in reproductive functions are grouped in two main nuclei: the nucleus preopticus-periventricularis and the nucleus lateralis tuberis. The nucleus preopticus-periventricularis consists of the nucleus periventricularis and the nucleus preopticus consisting of a few sparse multipolar neurons in the rostral part and numerous cells closely packed and arranged in several layers in its aboral part. The nucleus lateralis tuberis is located in the ventral-lateral area of the diencephalon and is made up of a number of large multipolar neurones. Four different polyclonal primary antibodies against salmon (s)GnRH, chicken (c)GnRH-II (cGnRH-II 675, cGnRH-II 6) and sea bream (sb)GnRH were employed in the immunohistochemical experiments. No immunoreactive structures were found with anti sbGnRH serum. sGnRH and cGnRH-II antisera revealed immunoreactivity in the perikarya of the olfactory bulbs, preopticus-periventricular nucleus, oculomotor nucleus and midbrain tegmentum. The nucleus lateralis tuberis showed immunostaining only with anti-sGnRH serum. Nerve fibres immunoreactive to cGnRH and sGnRH sera were found in the olfactory bulbs, olfactory nerve and neurohypophysis. The significance of the distribution of the GnRH-immunoreactive neuronal structures is discussed.     

The organization of the nervous system in Plathelminthes. The neuropeptide F-immunoreactive pattern in Catenulida,Macrostomida, Proseriata

The organization of the nervous system of Archilopsis unipunctata Promonotus schultzei and Paramonotus hamatus (Monocelididae, Proseriata) and Stenostomum leucops (Catenulida) and Microstomum lineare (Macrostomida) was studied by immunocytochemistry, using antibodies to the authentic flatworm neuropeptide F (NPF) (Moniezia expansa). The organization of the nervous system of the Monocelididae was compared to that of the nervous system of Bothriomolus balticus (Otoplanidae), a previously studied species of another family of the Proseriata. The results show that the main nerve cords (MCs), independent of lateral or ventral position in the Monocelididae and the Otoplanidae, correspond to each other. The study also confirms the status of the lateral cords as main cords (MCs) in S. leucops and M. lineare. Common for MCs in the members of the investigated taxa are the following features: MCs consist of many fibres, originate from the brain and are adjoined to 5-HT-positive neurons. In Monocelididae and Otoplanidae, the MCs additionally have the same type of contact to the pharyngeal nervous system. Also common for both proseriate families is the organization of the two lateral nerve cords, with weaker connections to the brain, and the pair of dorsal cords running above the brain. The organization of the minor cords differs. The Monocelididae have a pair of thin ventral cords forming a mirror image of the dorsal pair. Furthermore, an unpaired ventral medial cord connecting medial commissural cells was observed in P. schultzei. Marginal nerve cords, observed in Otoplanidae, are absent in Monocelididae. All minor nerve cords are closely connected to the peripheral nerve plexus. The postulated trends of condensation of plexal fibres to cords and/or the flexibility of the peripheral nerve plexus are discussed. In addition, the immunoreactivity (IR) pattern of NPF was compared to the IR patterns of the neuropeptide RFamide and the indoleamine, 5-HT (serotonin). Significant differences between the distribution of IR to NPF and to 5-HT occur. 5-HT-IR dominates in the submuscular and subepidermal plexuses. In the stomatogastric plexus of M. lineare, only peptidergic IR is observed in the intestinal nerve net. The distribution of NPF-IR in fibres and cells of the intestinal wall in M. lineare indicates a regulatory function for this peptide in the gut, while a relationship with ciliary and muscular locomotion is suggested for the 5-HT-IR occurring in the subepidermal and submuscular nerve, plexuses. In M. lineare, the study revealed an NPF- and RFamide-positive cell pair, marking the finished development of new zooids. This finding indicates that constancy of these cells is maintained in this asexually reproducing and regenerating species.     

SALMFamide2 and serotonin immunoreactivity in the nervous system of some acoels (Xenacoelomorpha)

Acoel worms are simple, often microscopic animals with direct development, a multiciliated epidermis, a statocyst, and a digestive parenchyma instead of a gut epithelium. Morphological characters of acoels have been notoriously difficult to interpret due to their relative scarcity. The nervous system is one of the most accessible and widely used comparative features in acoels, which have a so‐called commissural brain without capsule and several major longitudinal neurite bundles. Here, we use the selective binding properties of a neuropeptide antibody raised in echinoderms (SALMFamide2, or S2), and a commercial antibody against serotonin (5‐HT) to provide additional characters of the acoel nervous system. We have prepared whole‐mount immunofluorescent stainings of three acoel species: Symsagittifera psammophila (Convolutidae), Aphanostoma pisae, and the model acoel Isodiametra pulchra (both Isodiametridae). The commissural brain of all three acoels is delimited anteriorly by the ventral anterior commissure, and posteriorly by the dorsal posterior commissure. The dorsal anterior commissure is situated between the ventral anterior commissure and the dorsal posterior commissure, while the statocyst lies between dorsal anterior and dorsal posterior commissure. S2 and serotonin do not co‐localise, and they follow similar patterns to each other within an animal. In particular, S2, but not 5‐HT, stains a prominent commissure posterior to the main (dorsal) posterior commissure. We have for the first time observed a closed posterior loop of the main neurite bundles in S. psammophila for both the amidergic and the serotonergic nervous system. In I. pulchra, the lateral neurite bundles also form a posterior loop in our serotonergic nervous system stainings.     

The vestibular nuclei in the domestic hen (Gallus domesticus). VII.--Afferents from the spinal cord

Lesions of different parts of the spinal cord at different levels in the hen have been made and the resulting degeneration in the vestibular complex has been studied in silver impregnated sections. Spinovestibular fibres originate from cervical as well as lumbosacral levels of the cord and run in the dorsal part of the lateral funiculus. The spinovestibular fibres from all levels of the spinal cord terminate ipsilaterally in the nucleus Deiters ventralis, the nucleus Deiters dorsalis, the medial nucleus and rostrally in the descending nucleus. The spinovestibular fibres terminating in the above nuclei are few in number while spinovestibular fibres terminating bilaterally in the caudal part of the descending nucleus are much more abundant. In a few cases HRP injections in the vestibular complex resulted in labelled cells in upper cervical segments of the spinal cord localized in lamina VII. The findings are discussed in the light of data concerning the spinovestibular pathway in mammals.