Physiological identification, and development of identified serotonin-proctolin containing neurons in the lobster ventral nerve cord (original) (raw)
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The Journal of Neuroscience, 1987
Amines and peptides exert a wide range of physiological actions on both central neurons and peripheral tissues. Among these actions, serotonin and octopamine are known to trigger contrasting postures when injected into freely moving lobsters. lmmunocytochemical studies of lobster ganglia have identified presumptive serotonergic neurons, their central and peripheral projections, and their terminal fields of arborization. More than 100 neurons that show serotonin-like immunoreactivity have been found in the lobster nervous system (Beltz and Kravitz, 1983). From immunocytochemical studies it appears that varicosities within peripheral neurosecretory structures and endings in certain central neuropil regions arise from the same 2 pairs of large cells located in the fifth thoracic (T5) and first abdominal (Al) ganglia. Because we believed that such cells could account for the central and peripheral actions of serotonin on the postural system, we chose to study these 2 pairs of neurons in greater detail. In the previous paper, Siwicki et al. (1987) report that these neurons contain the pentapeptide proctolin in addition to serotonin. In this communication, we report that (1) these cells can be identified reliably in living preparations; (2) they have large fields of innervation projecting anteriorly into at least 4 segmental ganglia; (3) these neurons are the origin of the fibers that form the thoracic second root neurosecretory regions; (4) they are generally spontaneously active neurons that have overshooting action potentials in their cell bodies; and (5) the serotonin and proctolin immunoreactivities are first expressed in these cells at widely different times in development. Amines and peptides are believed to play vital roles in regulating or controlling aspects of the behavioral repertoire of animals. This is particularly well documented in invertebrates where, for example, eclosion hormone triggers larval and pupal ecdysis behavior in silkmoths and hawkmoths
Mapping of serotonin-like immunoreactivity in the lobster nervous system. J Neurosci 3:585-602
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
Serotonin exerts a wide range of physiological actions on many different lobster tissues. To begin the examination of the role of serotonin in lobsters at a cellular level, we have used immunohistochemical methods to search for presumptive serotonergic neurons, their central and peripheral projections, and their terminal fields of arborization. Whole mount preparations of the ventral nerve cord and various peripheral nerve structures have been used for these studies. With these tissues, more than 100 cell bodies have been found that show serotonin-like immunoreactivity. Although a few of the cell bodies are located peripherally (near the pericardial organs, a well known crustacean neurohemal organ), the vast majority are located in central ganglia. Every ganglion in the ventral nerve cord contains at least one immunoreactive cell body. The projections of many of the neurons have been traced, and we have constructed a map of the system of serotonin-immunoreactive cell bodies, fibers, and nerve endings. In addition, a dense plexus of nerve endings showing serotonin-like immunoreactivity surrounds each of the thoracic second roots in the vicinity of groups of peripheral neurosecretory neurons. These peripheral nerve plexuses originate from central neurons of the ventral nerve cord. In some cases we have been able to trace processes from particular central cell bodies directly to the peripheral nerve root plexuses; in other cases we have traced ganglionic neuropil regions to these peripheral endings.
Journal of Comparative Physiology A, 2000
In the American lobster (Homarus americanus) the biogenic amines serotonin and octopamine appear to play important and opposite roles in the regulation of aggressive behavior, in the establishment and/or maintenance of dominant and subordinate behavioral states and in the modulation of the associated postural stances and escape responses. The octopamine-containing neurosecretory neurons in the thoracic regions of the lobster ventral nerve cord fall into two morphological subgroups, the root octopamine cells, a classical neurohemal group with release regions along second thoracic roots, and the claw octopamine cells, a group that selectively innervates the claws. Cells of both subgroups have additional sets of endings within neuropil regions of ganglia of the ventral nerve cord. Octopamine neurosecretory neurons generally are silent, but when spontaneously active or when activated, they show large overshooting action potentials with prominent afterhyperpolarizations. Autoinhibition after high-frequency ®ring, which is also seen in other crustacean neurosecretory cells, is readily apparent in these cells. The cells show no spontaneous synaptic activity, but appear to be excited by a unitary source. Stimulation of lateral or medial giant axons, which excite serotonergic cells yielded no response in octopaminergic neurosecretory cells and no evidence for direct interactions between pairs of octopamine neurons, or between the octopaminergic and the serotonergic sets of neurosecretory neurons was found. Key words Octopamine á Amine neurons á Neurohormone á Lobster á Agonistic behavior Abbreviations 5HT 5-hydroxytryptamine (serotonin) á OCT octopamine á CLOC claw octopamine cell á EPSP excitatory postsynaptic potential á IPSP inhibitory postsynaptic potential á ROC root octopamine cell
Journal of Neurocytology, 2000
Neuronal somata located near branch points in the second thoracic nerve roots of the lobster are immunoreactive for Crustacean Hyperglycemic Hormone (CHH)-like peptides, a family of putative stress hormones. We have employed intracellular dye injection, immunostaining, and confocal imaging to observe the anatomy of these root neurons, which are morphologically diverse and dye coupled. Some root neurons contribute to neurosecretory structures at the points of exit of the root from the nerve cord. Other CNS-projecting root neurons send projections into the T5-A1 interganglionic connectives. Neurosecretory elements of the serotonin (5HT) and octopamine (OCT) systems, implicated in postural control and aggression, terminate densely in the vicinity of the second thoracic root neurons. We have confirmed by double immunostaining for 5HT and CHHlike peptides that the endings of the 5HT neurons are in close apposition to root neurons in the superficial regions of the root. We have also extended previous studies documenting electrophysiological responses of the root neurons to 5HT or OCT. Bath-applied 5HT and OCT inhibit the spontaneous bursting activity of root neurons at concentrations higher than 100 nM. The root neurons desensitize to the persistent presence of high concentrations of 5HT, but not OCT, in the bath. Nanomolar concentrations of OCT, but not 5HT have an excitatory effect on the spontaneous bursting activity of root neurons. This region of the lobster nervous system is of continuing interest, as identified neurons of three neuromodulatory systems implicated in stress and aggression converge and interact at the level of identified neurons.
Aminergic and peptidergic neuromodulation in Crustacea
Biogenic amines and peptides can act both as circulating neurohormones and as classical central and peripheral neurotransmitters. This article reviews some of the variety of roles played by amines and peptides in crustacean nervous systems. Cardiac, stomatogastric and postural systems are used to illustrate: (1) the functional versatility of amines and peptides; (2) the molecular basis of their actions; (3) the coexistence of amines and peptides with other bioactive compounds; and (4) the developmental expression of amine and peptide phenotypes. We will deal in detail with the postural neuromuscular system of the lobster, Homarus americanus. Physiological and pharmacological experiments have shown that the biogenic amines serotonin and octopamine are capable of regulating posture by direct neurohormonal actions on the muscles and by central actions that alter motoneuronal output. We have localized serotonin to identified neurones in the lobster ventral nerve cord and have shown further that the pentapeptide proctolin coexists with the amine in these cells. Such neurones provide a convenient system in which to study the functional interactions between peptide and amine cotransmitters. In addition, the serotonin and proctolin phenotypes of these cells are first expressed at widely different times in development. This presents the possibility of studying the regulation of these two transmitter phenotypes in a system that is readily amenable to experimental manipulation.
The Journal of Neuroscience, 2008
Neuromodulatory substances have profound effects on the two motor patterns generated by the adult crustacean stomatogastric ganglion (STG), the gastric mill rhythm and the pyloric rhythm. Developmentally regulated changes in the modulatory functions of neuromodulators could therefore play an important role in the maturation of the output from the developing STG. We compared the effects of neuromodulators on isolated embryonic and adult STG of the lobster, Homarus americanus. Bath application of Val 1-SIFamide, a peptide whose expression is different in embryos and adults, activated different neuron classes in embryos and adults. Cancer borealis tachykinin-related peptide 1a, a peptide that does not appear in the terminals of modulatory neurons in the STG until after embryonic development, also produced different motor patterns in embryos and adults. In contrast, red pigment concentrating hormone, a peptide with a similar distribution in the STNS across development, produced similar motor patterns in embryonic and adult STG. Proctolin, serotonin, and allatostatin were also physiologically active on the isolated embryonic STG. Together, these results demonstrate that receptors to many neuromodulators are present and functional on STG neurons before the motor patterns of the stomatogastric nervous system are mature. Moreover, neuromodulator responses change during development, perhaps contributing to the maturation of the output from the stomatogastric nervous system.