Showing papers on "Nervous system published in 1984"

Regressive events in neurogenesis

Abstract: The development of most regions of the vertebrate nervous system includes a distinct phase of neuronal degeneration during which a substantial proportion of the neurons initially generated die. This degeneration primarily adjusts the magnitude of each neuronal population to the size or functional needs of its projection field, but in the process it seems also to eliminate many neurons whose axons have grown to either the wrong target or an inappropriate region within the target area. In addition, many connections that are initially formed are later eliminated without the death of the parent cell. In most cases such process elimination results in the removal of terminal axonal branches and hence serves as a mechanism to "fine-tune" neuronal wiring. However, there are now also several examples of the large-scale elimination of early-formed pathways as a result of the selective degeneration of long axon collaterals. Thus, far from being relatively minor aspects of neural development, these regressive phenomena are now recognized as playing a major role in determining the form of the mature nervous system.

Segmentation in the vertebrate nervous system

Abstract: Although there is good evidence that growing axons can be guided by specific cues during the development of the vertebrate peripheral nervous system, little is known about the cellular mechanisms involved. We describe here an example where axons make a clear choice between two neighbouring groups of cells. Zinc iodide-osmium tetroxide staining of chick embryos reveals that motor and sensory axons grow from the neural tube region through the anterior (rostral) half of each successive somite. 180 degrees antero-posterior rotation of a portion of the neural tube relative to the somites does not alter this relationship, showing that neural segmentation is not intrinsic to the neural tube. Furthermore, if the somitic mesoderm is rotated 180 degrees about an antero-posterior axis, before somite segmentation, axons grow through the posterior (original anterior) half of each somite. Some difference therefore exists between anterior and posterior cells of the somite, undisturbed by rotation, which determines the position of axon outgrowth. It is widespread among the various vertebrate classes.

Initial expression of neurofilaments and vimentin in the central and peripheral nervous system of the mouse embryo in vivo.

Abstract: The appearance of neurofilaments (NFs) and vimentin (Vim) in the nervous system of the mouse embryo was documented using immunohistochemical techniques. The three NF protein subunits appear early and simultaneously in central and peripheral neurons at 9 to 10 days of gestation. The onset of NF expression is concomitant with axon elongation and correlates extremely well with neurofibrillar differentiation and, in the case of autonomic ganglia, with the expression of adrenergic neurotransmitter properties. In the central and peripheral nervous system, NF expression is preceded by that of Vim, and both types of intermediate filaments coexist within the same cell for a short period of time.

Alterations in neural cell adhesion molecules during development of different regions of the nervous system.

Abstract: Several cell adhesion molecules involved in neuron-neuron and neuron-glia interactions have been identified in our laboratory and have been shown to undergo cell surface modulation. In the case of the neural cell adhesion molecule (N-CAM), it has been found that during development the molecule is converted from a microheterogeneous embryonic (E) form containing 30 gm of sialic acid/100 gm of polypeptide to several distinct adult (A) forms containing one third as much of this sugar. In vitro analyses indicate that this change is accompanied by a 4-fold increase in the rate of N-CAM homophilic binding. In the present study of the mouse and the chick, alterations of N-CAMs occurring as a result of E----A conversion, prevalence modulation, and changes in antigenic state during the development of different neural regions were analyzed by the use of highly specific polyclonal and monoclonal antibodies combined with anatomical dissection and several new quantitative assays. We made the following observations. The relative concentration of N-CAM changed during development, with the highest concentration (2.8 times the adult level) occurring around the perinatal period. Each brain region followed a similar pattern of change but according to a different time schedule. While conversion from the E to the A forms of N-CAM occurred mainly during the first 3 postnatal weeks in mice, the relative conversion rates were distinctly different in various neural tissues. The extreme examples are dorsal root ganglia, which already displayed the A forms at birth, and the diencephalon and tectal region, which still retained some E forms in the adult. A cephalocaudal maturation gradient of E----A conversion was observed in the spinal cord and dorsal root ganglia. Differences in the antigenic determinants of N-CAMs from different neural tissues were detected by two independent monoclonal antibodies. Finally, in some adult neural tissues, one of the three A forms was found to be dominant. These results establish that during development there are definite quantitative and qualitative differences among N-CAMs from various neural tissues. The data are consistent with the hypothesis that alterations in the relative amounts and forms of N-CAM play major roles in neural morphogenesis, possibly by altering the rates of adhesion among neurons and their processes.

New Neuronal Growth Factors

Abstract: The complexity and remarkable specificity found in the nervous system chal­ lenge the investigator to identify molecular mechanisms guiding neuronal development. Cell-cell interactions mediated by diffusible substances have frequently been suggested to play an important role. Studies on naturally occurring cell death in the nervous system provided early evidence for such interactions by demonstrating that neuronal survival beyond a critical period in development requires interaction between the neurons and the postsynaptic target tissue (for a review see Oppenheim 1981). The discovery of Nerve Growth Factor (NGF) raised the possibility that neuronal development, includ­ ing target-dependent neuronal survival, might be mediated by diffusible mole­ cules. NGF can be isolated as a 140,000 dalton protein complex (7S NGF) of heterologous subunits or as a 26,500 dalton component (beta-NGF) containing two identical polypeptide chains. Experiments in vivo indicate that NGF can reverse naturally occurring as well as experimentally induced cell death in sympathetic and sensory neurons; moreover, anti-NGF antibodies in vivo can block the development of the sympathetic nervous system (for reviews see Thoenen & Barde 1980, Hamburger et al 1981, Levi-Monta1cini 1982). That NGF might also influence the choice of targets contacted by neurons is suggested by studies in cell culture showing that NGF can change the direction of neuritic growth (Gundersen & Barrett 1979) and can help shape the neuritic tree maintained by the neuron (Campenot 1982). Naturally occurring cell death has been documented for almost every popula­ tion of vertebrate neurons studied (Oppenheim 1981), and every neuron is faced with the problem of finding appropriate target cells. Only sensory and sympathetic neurons, however, have been convincingly shown to depend on

Cell biology of synaptic plasticity.

Abstract: The nervous system of mammals retains throughout the animals' life-span the ability to modify the number, nature, and level of activity of its synapses. Synaptic plasticity is most evident after injury to the nervous system, and the cellular and molecular mechanisms that make it possible are beginning to be understood. Transplantation of brain tissue provides a powerful approach for studying mechanisms of synaptic plasticity. In turn, understanding the response of the central nervous system to injury can be used to optimize transplant survival and integration with the host brain.

On the genesis of sexual differentiation of the general nervous system: morphogenetic consequences of steroidal exposure and possible role of alpha-fetoprotein.

Abstract: Publisher Summary This chapter focuses on cellular aspects in the ontogeny of sexual differentiation of the rodent central nervous system (CNS), although the nature or expression of these cellular responses of developing nervous tissue to the gonadal hormones is not peculiar to sexual differentiation. The characteristics of these responses represent yet another facet of the much broader question of the factors and cellular mechanisms contributing to neural plasticity in both the developing and adult CNS. Patterns of axonal growth, dendritic differentiation, dendritic spine density, and of synaptogenesis, for example, are cytological features that have not only been shown to be gonadal hormone-dependent and sexually dimorphic but also exhibit considerable pre- and postnatal plasticity. Although there is considerable variability in the types of neural functions, which may be sexually dimorphic, in the CNS regions involved, in the timing of the hormone sensitive periods and even in the very hormones responsible for the developmental effects, the underlying principles of hormonal action may well be valid across a considerable portion of the animal kingdom.

Autonomic Regulation of the Airways

Abstract: The airways are innervated by a sympathetic, a parasympathetic, and a third [perhaps vasoactive intestinal peptide (VIP) releasing] nervous system. These nerves modulate smooth muscle tone and submucosal gland secretion and possibly other cell systems in the airways. Adrenergic and cholinergic receptors are distributed unevenly in airways of different sizes and among different cells. Considerable evidence is presented that implicates abnormalities of autonomic function in asthma.

Neuronal phosphoproteins: physiological and clinical implications

Abstract: The presence of a great variety of neuron-specific phosphoproteins in nervous tissue supports the view that protein phosphorylation plays many roles in neuronal function. The physiological significance of several of these phosphoproteins has already been established. Some neuronal phosphoproteins have been detected throughout the entire nervous system, whereas the distribution of others is limited to one or a few neuronal cell types. These various neuron-specific phosphoproteins are proving of value in the study of the physiology, anatomy, developmental biology, and pathophysiology of the nervous system.

Morphology of Myelin and Myelination

Abstract: Myelin is a membrane characteristic of nervous tissue, laid down in segments along selected nerve fibers, that functions as an insulator to increase the velocity of stimuli being transmitted between a nerve-cell body and its target. While well documented in several invertebrates (annelids and crustaceans) in which it exists in its peripheral nervous system (PNS) form, myelin is most commonly associated with the vertebrate nervous system in which it has evolved into two forms, central and peripheral. Morphologically, myelin is unique, and while this chapter will highlight the morphological uniqueness of myelin, it is important to note that myelin is also distinct biochemically, physiologically, and immunologically. The latter three aspects form the subjects of later chapters in this volume. Structurally, myelin is recognized as a lipid bimolecular leaflet sandwiched between two layers of protein and wrapped in a spiral fashion around a segment of axon. Such a length of myelin sheath is known as an internode, being delineated at either end by nodes of Ranvier, specialized areas along the axon. Ontogenetically, myelin arises from its cell of origin as a flattened cytoplasmic process that is elaborated around the axon and that later becomes compacted and loses its cytoplasmic content (except for small pockets, usually displaced peripherally) to form a tightly wound, membranous sheath comprising a series of alternating lipid and protein lamellae.

The Structural Basis of an Innate Behavioural Pattern

Abstract: The abdominal nervous system of the crayfish contains six serially homologous ganglia, each containing approximately 650 neurones. No two ganglia are identical, and the ganglia interact extensively. Studies confined to intraganglionic interactions thus yield limited and sometimes misleading information. Each ganglion contains intrinsic (local) interneurones, motor neurones and projecting interneurones in roughly equal numbers, except in the specialized terminal ganglion where the ratio of these cells is approximately 3:2:1. Although the number of nerve cell bodies in a ganglion is small enough to be tractable, integration occurs in the neuropile, which contains terminals from interneurones and afferents that outnumber the neurones originating in the ganglion by at least ten to one. The abdominal nervous system responds almost exclusively to a variety of mechanosensory stimuli. It has very limited light sensitivity. Other modalities, notably chemosensitivity, are undescribed and may be lacking. The effectors of the abdomen consist of fast axial muscles (used for tailflip-powered escape), slow axial muscles (for setting abdominal posture), appendage muscles (for swimmeret beating), and slow muscles of the intestine and rectum (that control gut emptying). The fast and slow muscles of the tailfan are specialized homologues of the axial and appendage muscles. The abdominal nervous system represents only 3–4% of the 100 000 neurones within the crayfish central nervous system (CNS). Most sensory information gathered in the abdomen is transmitted to the rostral CNS for processing, and many abdominal motor programmes are activated by descending commands. Nevertheless, a surprising degree of autonomy is present, and at least some motor programmes of every motor system can be activated in isolated abdomens. Tailflip escape behaviour illustrates the integrative properties of the crayfish nervous system. Ninety pairs of efferents and eighteen pairs of interneurones have been identified within the abdominal portion of the escape circuit. A cell-by-cell analysis has so far provided neurophysiological explanations, in varying states of completeness, for ethological concepts such as innate releasing mechanisms, spatial patterning of movement, serial order in behaviour, and alterations in responsiveness to a constant stimulus.

Widespread distribution of the major polypeptide component of MAP 1 (microtubule-associated protein 1) in the nervous system.

Abstract: We prepared a monoclonal antibody to microtubule-associated protein 1 (MAP 1), one of the two major high molecular weight MAP found in microtubules isolated from brain tissue. We found that MAP 1 can be resolved by SDS PAGE into three electrophoretic bands, which we have designated MAP 1A, MAP 1B, and MAP 1C in order of increasing electrophoretic mobility. Our antibody recognized exclusively MAP 1A, the most abundant and largest MAP 1 polypeptide. To determine the distribution of MAP 1A in nervous system tissues and cells, we examined tissue sections from rat brain and spinal cord, as well as primary cultures of newborn rat brain by immunofluorescence microscopy. Anti-MAP 1A stained white matter and gray matter regions, while a polyclonal anti-MAP 2 antibody previously prepared in this laboratory stained only gray matter. This confirmed our earlier biochemical results, which indicated that MAP 1 is more uniformly distributed in brain tissue than MAP 2 (Vallee, R.B., 1982, J. Cell Biol., 92:435-442). To determine the identity of cells and cellular processes immunoreactive with anti-MAP 1A, we examined a variety of brain and spinal cord regions. Fibrous staining of white matter by anti-MAP 1A was generally observed. This was due in part to immunoreactivity of axons, as judged by examination of axonal fiber tracts in the cerebral cortex and of large myelinated axons in the spinal cord and in spinal nerve roots. Cells with the morphology of oligodendrocytes were brightly labeled in white matter. Intense staining of Purkinje cell dendrites in the cerebellar cortex and of the apical dendrites of pyramidal cells in the cerebral cortex was observed. By double-labeling with antibodies to MAP 1A and MAP 2, the presence of both MAP in identical dendrites and neuronal perikarya was found. In primary brain cell cultures anti-MAP 2 stained predominantly cells of neuronal morphology. In contrast, anti-MAP 1A stained nearly all cells. Included among these were neurons, oligodendrocytes and astrocytes as determined by double-labeling with anti-MAP 1A in combination with antibody to MAP 2, myelin basic protein or glial fibrillary acidic protein, respectively. These results indicate that in contrast to MAP 2, which is specifically enriched in dendrites and perikarya of neurons, MAP 1A is widely distributed in the nervous system.

Proliferation of mature oligodendrocytes after trauma to the central nervous system.

Abstract: It has long been thought that mature oligodendrocytes in the adult mammalian central nervous system (CNS) are post-mitotic and are unable to proliferate in response to injury. The implications of this have been profound, because it has been suggested that this failure of oligodendrocytes to undergo mitosis is perhaps one of the reasons for the failure of the human CNS to undergo remyelination after demyelinating disease. This is in contrast with the normal peripheral nervous system in which there is consistent remyelination, and brisk Schwann cell mitosis. Although it has recently been shown that oligodendrocytes can be regenerated following some specific instances of demyelination, it has long been accepted that unlike mature astrocytes and microglia (macrophages), oligodendrocytes do not proliferate in response to general conditions damaging the nervous system. Here we show that mature oligodendrocytes in adult animals, as well as astrocytes and microglia, are able to respond to damage in the CNS following trauma by incorporating tritiated thymidine into their nuclei.

Neurotransmitter Plasticity at the Molecular Level

Abstract: Contrary to long-held assumptions, recent work indicates that neurons may profoundly change transmitter status during development and maturity. For example, sympathetic neurons, classically regarded as exclusively noradrenergic or cholinergic, can also express putative peptide transmitters such as substance P. This neuronal plasticity is directly related to membrane depolarization and sodium ion influx. The same molecular mechanisms and plastic responses occur in mature as well as developing neurons. Further, contrary to traditional teaching, adult primary sensory neurons may express the catecholaminergic phenotype in vivo. Transmitter plasticity is not restricted to the peripheral nervous system: ongoing studies of the brain nucleus locus ceruleus in culture indicate that specific extracellular factors elicit marked transmitter changes. Consequently, neurotransmitter expression and metabolism are dynamic, changing processes, regulated by a variety of defined factors. Transmitter plasticity adds a newly recognized dimension of flexibility to nervous system function.

Noradrenergic Nervous Activity in Migraine

Abstract: • The autonomic nervous function in patients with migraine was studied during headache-free intervals. The following observations were made: (1) a decrease in overshoot in Valsalva's maneuver; (2) orthostatic hypotension; (3) low levels of plasma norepinephrine in the steady state; (4) failure in elevation of the plasma norepinephrine level after head-up tilting; (5) dilatation of the pupils after instillation in the eye of 1.25% epinephrine; and (6) a long recovery time in tests by bolus injection of 0.1 μg of norepinephrine bitartrate per kilogram. The above findings suggest that patients with migraine show sympathetic hypofunction together with denervation hypersensitivity of the iris and the arteries, and that a defective noradrenergic nervous system may play a role in the pathogenesis of migraine.

S100a0 (αα) Protein Is Present in Neurons of the Central and Peripheral Nervous System

Abstract: The cellular distribution of S100 subunits in human brain and peripheral nerves was studied by means of an immunohistochemical technique using antibodies specific to the alpha subunit or the beta subunit of S100 protein. The results indicate that the distribution of the alpha subunit and the beta subunit is different among cell types in the nervous tissue, and that neurons in the brain and peripheral nerves contain only the alpha subunit, or S100a0 protein. The subunit distribution also appears to be different at an intracellular level, where the immunoreaction products for the alpha subunit show granular arrangement whereas those for the beta subunit are found diffusely in the cytoplasm.

Identifiable neurons in the locust central nervous system that react with antibodies to serotonin.

Abstract: A detailed account is given of a number of neurons in the locust central nervous system that react with antibody raised to serotonin-albumin complex. The antibody was applied to a series of frozen sections of locust ganglia and visualized by using the peroxidase immunohistochemical procedure. The neurons described include certain afferents and their related neuropiles, a small number of efferents and several systems of interneurons, some of which are segmentally repeated, some run from the brain through the whole nerve cord, while others are confined to the brain. It has been possible to identify many of the neurons from previous descriptions obtained from cobalt, Golgi, and osmium ethyl gallate methods.

Multimodal interneurons in the cricket brain: properties of identified extrinsic mushroom body cells

Abstract: 322 neurons were recorded intracellularly within the central part of the insect brain and 150 of them were stained with Lucifer Yellow or cobaltous sulphide. Responses to mechanical, olfactory, visual and acoustical stimulation were determined and compared between morphologically different cell types in different regions of the central brain. Almost all neurons responded to multimodal stimulation and showed complex responses. It was not possible to divide the cells into different groups using physiological criteria alone.

Pain and Nociception

Abstract: The sections in this article are: 1 Concepts and Theories 2 Pain as A Physiological Reaction 3 Aberrant Pain 31 Inflammation and Hyperalgesia 32 Referred Pain 33 Pain Associated With Pathology of Nervous System 4 Primary Afferent Neurons 41 Afferent Fiber Size and Quality of Pain 42 Identity of Receptive Units 43 Noxious Stimulation of Low-Threshold Sense Organs 44 Relationship of Nociceptor Activity to Pain 45 Chemical Mediators 46 Central Terminations of Primary Afferent Fibers 5 Ascending Sensory Pathways 51 Defining Pathways for Pain Sensation 52 Selectively Nociceptive Neurons of Spinal Cord and Trigeminal Nuclei 53 Nonselectively Nociceptive Excitation 54 Origins of Spinothalamic and Related Systems 55 Functional Attributes of Neurons Projecting Over Ventral Quadrant Tracts 56 Projection Pathways for the Face 57 Other Ascending Pathways 58 Brain Stem, Hypothalamic, and Thalamic Components 59 Cerebral Cortex 6 Modulation of Nociceptive Neurons 61 Afferent Modulation 62 Descending Effects 63 Opiate Receptors, Opioids, and Endorphins 64 Cellular Mechanisms of Modulation 65 Higher Level Interactions 66 Functional Significance of Modulatory Mechanisms 7 Recapitulation

Antibodies to heavy neurofilament subunit detect a subpopulation of damaged ganglion cells in retina

Abstract: Neurofilaments ( NFs ) consist of three protein subunits with apparent molecular weights of 68,000 ( 68K ), 145K and 200K , which are found closely associated in most but not all locations in the nervous system One of these exceptions is the inner retina of the mouse, where antibodies to 145K NFs label large ganglion cells throughout the extent of the cells, while antibodies to 200K NFs label only more distal portions of the optic axons but usually fail to label the ganglion cell somata and proximal axons Very rarely, however, and more often in old mice, anti- 200K NF antibodies do label a ganglion cell completely To determine whether these rare, completely labelled cells reflect a pathological alteration, we cut the optic axons, and report here that after a few days some of the axotomized cells could be labelled completely, in a Golgi-like fashion, by anti- 200K NF antibodies These cells seem to represent the population that forms the projection to the bulk of the lateral geniculate nucleus, as suggested by their size, distribution and projection pattern Hence, antibodies to the heavy NF subunit in combination with lesions may allow selective retrograde tracing of a subpopulation of ganglion cells, and such antibodies can be used to detect damage in NF-rich neurones at a very early stage, long before they eventually degenerate

The dorsal unpaired median neurons of the locust metathoracic ganglion: neuronal structure and diversity, and synapse distribution.

Abstract: Dorsal unpaired median ( DUM ) neurons are bilaterally symmetrical. A single primary neurite arises from the soma and runs anteriorly through the neuropil before dividing into two lateral neurites which pass to the nerve roots on each side of the ganglion. The primary neurite runs in one of two tracts, one of which lies further from the surface of the ganglion than the other. The primary neurites in the deeper tract belong to DUM1 , DUM5 and DUM3 ,4,5 neurons, and those in the more superficial tract, to DUM3 , DUM3 ,4 and DUM3 ,4,5 neurons. Previous studies have shown that in the developing embryonic nervous system the primary neurites of DUM neurons can also be observed to lie in one of two tracts, but these do not appear to correspond to those seen in the adult. The results described here differ further from those of other investigations of adult and embryonic locusts in that no DUM4 ,5 neurons were seen, but DUM3 ,4 neurons, not found in previous studies, were frequently stained. The secondary neurites of DUM neurons characteristically give rise to fine 0.2-0.5 micron diameter processes which may run for hundreds of microns through the neuropil with very little branching. The problems this may pose for signal transmission along such processes is discussed. Presynaptic processes of several types make inputs on to spines on the lateral neurites of DUM neurons and on to branches from secondary neurites. Output synapses were rarely observed and were found only on lateral neurite spines. It therefore appears unlikely that the DUM neurons examined play a major central role within the metathoracic ganglion. A novel structure, with the appearance of a presynaptic density but which was not associated with synaptic vesicles, was found in certain regions of the neurons.

Histamine as a neurotransmitter in the stomatogastric nervous system of the spiny lobster

Abstract: Histamine is a putative neurotransmitter in mammals and molluscs, but its role in the nervous systems of other animals is not known. This study examines the possibility that histamine is a neurotransmitter in an arthropod. Results show that first, 14 neurons in the stomatogastric ganglion of the spiny lobster respond to histamine. The response is inhibitory, is mediated by an increased conductance to chloride, and desensitizes with repeated applications of histamine. These same 14 neurons receive one type of synaptic potential from two extrinsic neurons, the "through-fibers" of the inferior ventricular nerve. This synaptic potential is also inhibitory, is mediated by an increased conductance to chloride, and is blocked when histamine receptors are desensitized. Second, assays of endogenous histamine indicate that histamine is distributed nonuniformly throughout the stomatogastric nervous system and that its distribution correlates with the axonal pathways and terminal arborizations of the inferior ventricular nerve through-fibers. Lastly, histamine is present in relatively high concentrations in the cell bodies of the through-fibers, whereas it is not detectable in other neurons in the stomatogastric system. These results suggest that histamine may be a transmitter in the lobster.

The third nervous system in the lung: physiology and clinical perspectives.

Abstract: The autonomic nervous system controls many aspects of pulmonary function' and, until recently, it was thought that this was achieved entirely by means of classical cholinergic and adrenergic mechanisms. This view has recently been challenged by the demonstration of a third nervous system in the airways (fig). Although the identities of the neurotransmitters in this newly recognised nervous system are not certain, there is increasing evidence that they are peptides. This third nervous system is of particular interest as it is the predominant inhibitory nervous pathway to human airway smooth muscle and this raises the possibility that a functional defect in this nervous system might underlie bronchial hyperreactivity in asthma. The recognition that a third component of the autonomic nervous system regulates airway smooth muscle tone and other aspects of lung physiology has stimulated great interest, since it may provide new insights into diseases such as asthma and chronic obstructive lung disease, and may also lead to novel therapeutic approaches.

FMRFamide immunoreactivity in the nervous system of the medusa Polyorchis penicillatus.

Abstract: Three different antisera to the molluscan neuropeptide Phe-Met-Arg-Phe-amide (FMRFamide) and two different antisera to the fragment RFamide were used to stain sections or whole mounts of the hydrozoan medusa Polyorchis penicillatus. All antisera stained the same neuronal structures. Strong immunoreactivity was found in neurons of the ectodermal nerve nets of the manubrium and tentacles, in neurons of the sensory epithelium, and in neurons at the periphery of the sphincter muscle. Strong immunoreactivity was also present in processes and perikarya of the whole outer nerve ring, in the ocellar nerves, and in nerve cells lying at the periphery of the ocellus. The inner nerve ring contained a moderate number of immunoreactive processes and perikarya, which were distinct from the swimming motor neurons. In contrast to the situation in the hydrozoan polyp Hydra attenuata, no immunoreactivity was found with several antisera to oxytocin/vasopressin and bombesin/gastrin-releasing peptide. The morphology and location of most FMRFamide-immunoreactive neurons in Polyorchis coincides with two identified neuronal systems, which have been recently discovered from neurophysiological studies.