Serotonergic modulation of the mudpuppy (Necturus maculatus) locomotor pattern in vitro

The aims of the present study were to: (1) study the role of serotonin (5-HT) in modulating the central pattern generator (CPG) underlying locomotion in the mudpuppy (Necturus maculatus); (2) investigate whether there is an intrinsic spinal serotonergic system. These aims were achieved by the use of pharmacological and immunocytochemical methods. To study modulation of the locomotor pattern and rhythm, we applied 5-HT, its uptake blocker zimelidine, and a variety of 5-HT receptor agonists and antagonists to an in vitro brainstemspinal cord preparation isolated from the mudpuppy. The preparation consisted of the first five segments of the spinal cord and the right forelimb attached by the brachial plexus. The spinal CPG for locomotion was activated chemically by adding NMDA to the superfusing solution. During locomotion, bipolar electromyographic (EMG) recordings were made unilaterally from flexor and extensor ulnae muscles. 5-HT on its own did not induce locomotion, but it did have a profound modulatory effect on NMDA-induced locomotion. 5-HT produced a dose-dependent increase in the overall cycle duration and enhanced the EMG burst duration. Use of zimelidine indicated that there is an endogenous release of 5-HT which modulated the locomotor rhythm. The endogenous release was antagonized by 5-HT1/5-HT2 receptor antagonist methiothepin. Immunocytochemical analysis, in which the entire spinal cord of the mudpuppy was used, revealed that there were more than one type of spinal serotonergic neuron. They were differentiated according to the cell diameter, shape, and arborization pattern of their processes. These neurons were located within the central gray matter ventrolateral to the central canal. Our results suggest that 5-HT plays an important role in modulating the locomotor CPG in the mudpuppy, by acting through a well-developed spinal serotonergic system. This is in contrast to what has been reported in higher vertebrates, where serotonergic innervation is derived from supraspinal structures.

[1]  Stephen G. Gilbert,et al.  Pictorial Anatomy of the Cat , 1965 .

[2]  G. Székely,et al.  Localization of motoneurones in the limbmoving spinal cord segments of Ambystoma. , 1967, Acta physiologica Academiae Scientiarum Hungaricae.

[3]  P. Buser,et al.  The effects of DOPA and 5-HTP on rhythmic efferent discharges in hind limb nerves in the rabbit. , 1969, Brain research.

[4]  M. L. Shik,et al.  On the descending control of the lumbosacral spinal cord from the "mesencephalic locomotor region". , 1973, Acta physiologica Scandinavica.

[5]  Pictorial Anatomy of the Necturus. , 1973 .

[6]  F. A. Steiner.  Neurotransmitters and Neuromodulators , 1974 .

[7]  B. Jacobs,et al.  An animal behavior model for studying central serotonergic synapses. , 1976, Life sciences.

[8]  J. Besson,et al.  The topographical distribution of serotoninergic terminals in the spinal cord of the cat: biochemical mapping by the combined use of microdissection and microassay procedures , 1977, Brain Research.

[9]  G. Fischbach,et al.  Neurotransmitters decrease the calcium component of sensory neurone action potentials , 1978, Nature.

[10]  A. Beaudet,et al.  The monoamine innervation of rat cerebral cortex: Synaptic and nonsynaptic axon terminals , 1978, Neuroscience.

[11]  F. Delcomyn.  Neural basis of rhythmic behavior in animals. , 1980, Science.

[12]  L. Jordan,et al.  Effect of noradrenaline and 5-hydroxytryptamine depletion on locomotion in the cat , 1980, Brain Research.

[13]  K. Mizukawa.  The segmental detailed topographical distribution of monoaminergic terminals and their pathways in the spinal cord of the cat. , 1980, Anatomischer Anzeiger.

[14]  S. Hsu,et al.  Use of avidin-biotin-peroxidase complex (ABC) in immunoperoxidase techniques: a comparison between ABC and unlabeled antibody (PAP) procedures. , 1981, The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society.

[15]  S. Grillner,et al.  Activation of NMDA-receptors elicits "fictive locomotion" in lamprey spinal cord in vitro. , 1981, Acta physiologica Scandinavica.

[16]  T. Ritchie,et al.  Immunocytochemical demonstration of serotonergic cells, terminals and axons in the spinal cord of the stingray, dasyatis sabina , 1982, Brain Research.

[17]  T. Kitazawa,et al.  Selective inhibition by methusergide of the monosynaptic reflex discharge in the isolated spinal cord of the newborn rat , 1982, Brain Research.

[18]  R. M. Bowker,et al.  Organization of descending serotonergic projections to the spinal cord. , 1982, Progress in brain research.

[19]  D. Maxwell,et al.  Fine structure of serotonin-containing axons in the marginal zone of the rat spinal cord , 1983, Brain Research.

[20]  D. McAdoo,et al.  The distribution of serotonin in the CNS of an elasmobranch fish: Immunocytochemical and biochemical studies in the atlantic stingray, Dasyatis sabina , 1983, The Journal of comparative neurology.

[21]  S. Grillner.  Neurobiological bases of rhythmic motor acts in vertebrates. , 1985, Science.

[22]  R. Harris-Warrick,et al.  Serotonin modulates the central pattern generator for locomotion in the isolated lamprey spinal cord. , 1985, The Journal of experimental biology.

[23]  L. Heimer,et al.  Synaptic contacts of ventral striatal cells in the olfactory tubercle of the rat: Correlated light and electron microscopy of anterogradely transported Phaseolus vulgaris-leucoagglutinin , 1985, Neuroscience Letters.

[24]  S. Grillner,et al.  Possible target neurons of 5‐hydroxytryptamine fibers in the lamprey spinal cord: Immunohistochemistry combined with intracellular staining with lucifer yellow , 1985, The Journal of comparative neurology.

[25]  N. Holder,et al.  A horseradish peroxidase study of motorneuron pools of the forelimb and hindlimb musculature of the axolotl , 1985, Proceedings of the Royal Society of London. Series B. Biological Sciences.

[26]  E. Anderson,et al.  Serotonin decreases the duration of action potentials recorded from tetraethylammonium-treated bullfrog dorsal root ganglion cells , 1986, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[27]  O. Kiehn,et al.  Bistability of alpha‐motoneurones in the decerebrate cat and in the acute spinal cat after intravenous 5‐hydroxytryptophan. , 1988, The Journal of physiology.

[28]  P. Hartig.  Molecular biology of 5-HT receptors. , 1989, Trends in pharmacological sciences.

[29]  O Kiehn,et al.  Serotonin‐induced bistability of turtle motoneurones caused by a nifedipine‐sensitive calcium plateau potential. , 1989, The Journal of physiology.

[30]  Sten Grillner,et al.  Increase in endogenous 5-hydroxytryptamine levels modulates the central network underlying locomotion in the lamprey spinal cord , 1989, Neuroscience Letters.

[31]  S. Grillner,et al.  Effects of 5-hydroxytryptamine on the afterhyperpolarization, spike frequency regulation, and oscillatory membrane properties in lamprey spinal cord neurons. , 1989, Journal of neurophysiology.

[32]  S. Rossignol,et al.  The effects of serotonergic drugs on the locomotor pattern and on cutaneous reflexes of the adult chronic spinal cat , 1990, Brain Research.

[33]  R. Nicoll,et al.  Functional comparison of neurotransmitter receptor subtypes in mammalian central nervous system. , 1990, Physiological reviews.

[34]  N. Dun,et al.  5‐Hydroxytryptamine responses in neonate rat motoneurones in vitro. , 1990, The Journal of physiology.

[35]  A. J. Berger,et al.  Direct excitation of rat spinal motoneurones by serotonin. , 1990, The Journal of physiology.

[36]  S. Grillner,et al.  5-Hydroxytryptamine depresses reticulospinal excitatory postsynaptic potentials in motoneurons of the lamprey , 1991, Neuroscience Letters.

[37]  S. Rossignol,et al.  Initiation and modulation of the locomotor pattern in the adult chronic spinal cat by noradrenergic, serotonergic and dopaminergic drugs , 1991, Brain Research.

[38]  S. Grillner,et al.  Neuronal network generating locomotor behavior in lamprey: circuitry, transmitters, membrane properties, and simulation. , 1991, Annual review of neuroscience.

[39]  Keir G. Pearson,et al.  Octopamine induces bursting and plateau potentials in insect neurones , 1991, Brain Research.

[40]  F. Clarac,et al.  Activation of the central pattern generators for locomotion by serotonin and excitatory amino acids in neonatal rat. , 1992, The Journal of physiology.

[41]  T. Petrov,et al.  The hypothalamic paraventricular and lateral parabrachial nuclei receive collaterals from raphe nucleus neurons: A combined double retrograde and immunocytochemical study , 1992, The Journal of comparative neurology.

[42]  K. Sillar,et al.  Modulation of swimming rhythmicity by 5-hydroxytryptamine during post-embryonic development in Xenopus laevis , 1992, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[43]  Y. Arshavsky,et al.  Neuronal control of swimming locomotion: analysis of the pteropod mollusc Clione and embryos of the amphibian Xenopus , 1993, Trends in Neurosciences.

[44]  P P Humphrey,et al.  International Union of Pharmacology classification of receptors for 5-hydroxytryptamine (Serotonin). , 1994, Pharmacological reviews.

[45]  I. Martin,et al.  Molecular biology of 5-HT receptors , 1994, Neuropharmacology.

[46]  R. Stein,et al.  The activity of interneurons during locomotion in the in vitro necturus spinal cord. , 1994, Journal of neurophysiology.

[47]  R. Miledi,et al.  Effects of serotonergic agents on neuronal nicotinic acetylcholine receptors. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[48]  A. Roberts,et al.  Cholinergic and electrical motoneuron-to-motoneuron synapses contribute to on-cycle excitation during swimming in Xenopus embryos. , 1995, Journal of neurophysiology.

[49]  R. Perrins,et al.  Cholinergic contribution to excitation in a spinal locomotor central pattern generator in Xenopus embryos. , 1995, Journal of neurophysiology.

[50]  K. Fuxe,et al.  Evidence for the existence of monoamine neurons in the central nervous system , 1965, Zeitschrift für Zellforschung und Mikroskopische Anatomie.

[51]  R. Stein,et al.  A comparison of intact and in-vitro locomotion in an adult amphibian , 2004, Experimental Brain Research.