Stimulation of the Parapyramidal Region of the Neonatal Rat Brain Stem Produces Locomotor-Like Activity Involving Spinal 5-HT7 and 5-HT2A Receptors

2005 ◽  
Vol 94 (2) ◽  
pp. 1392-1404 ◽  
Author(s):  
Jun Liu ◽  
Larry M. Jordan
Keyword(s):  
Brain Stem ◽  
Pattern Generator ◽  
Neonatal Rat ◽  
Cycle Duration ◽  
Receptor Antagonists ◽  
Step Cycle ◽  
Output Stage ◽  
Discrete Population ◽  
First Time ◽  
Neonatal Rat Brain

Locomotion can be induced in rodents by direct application 5-hydroxytryptamine (5-HT) onto the spinal cord. Previous studies suggest important roles for 5-HT7 and 5-HT2A receptors in the locomotor effects of 5-HT. Here we show for the first time that activation of a discrete population of 5-HT neurons in the rodent brain stem produces locomotion and that the evoked locomotion requires 5-HT7 and 5-HT2A receptors. Cells localized in the parapyramidal region (PPR) of the mid-medulla produced locomotor-like activity as a result of either electrical or chemical stimulation, and PPR-evoked locomotor-like activity was blocked by antagonists to 5-HT2A and 5-HT7 receptors located on separate populations of neurons concentrated in different rostro-caudal regions. 5-HT7 receptor antagonists blocked locomotor-like activity when applied above the L3 segment; 5-HT2A receptor antagonists blocked locomotor-like activity only when applied below the L2 segment. 5-HT7 receptor antagonists decreased step cycle duration, consistent with an action on neurons involved in the rhythm-generating function of the central pattern generator (CPG) for locomotion. 5-HT2A antagonists reduced the amplitude of ventral root activity with only small effects on step cycle duration, suggesting an action directly on cells involved in the output stage of the pattern generator for locomotion, including motoneurons and premotor cells. Experiments with selective antagonists show that dopaminergic (D1, D2) and noradrenergic (α1, α2) receptors are not critical for PPR-evoked locomotor-like activity.

Neurochemical excitation of propriospinal neurons facilitates locomotor command signal transmission in the lesioned spinal cord

2011 ◽  
Vol 105 (6) ◽  
pp. 2818-2829 ◽  
Author(s):  
Eugene Zaporozhets ◽  
Kristine C. Cowley ◽  
Brian J. Schmidt
Keyword(s):  
Spinal Cord ◽  
Brain Stem ◽  
Signal Transmission ◽  
Cholinergic Receptor ◽  
Neonatal Rat ◽  
Receptor Antagonists ◽  
Ion Removal ◽  
Propriospinal Neurons ◽  
Command Signal

Previous studies of the in vitro neonatal rat brain stem-spinal cord showed that propriospinal relays contribute to descending transmission of a supraspinal command signal that is capable of activating locomotion. Using the same preparation, the present series examines whether enhanced excitation of thoracic propriospinal neurons facilitates propagation of the locomotor command signal in the lesioned spinal cord. First, we identified neurotransmitters contributing to normal endogenous propriospinal transmission of the locomotor command signal by testing the effect of receptor antagonists applied to cervicothoracic segments during brain stem-induced locomotor-like activity. Spinal cords were either intact or contained staggered bilateral hemisections located at right T1/T2 and left T10/T11 junctions designed to abolish direct long-projecting bulbospinal axons. Serotonergic, noradrenergic, dopaminergic, and glutamatergic, but not cholinergic, receptor antagonists blocked locomotor-like activity. Approximately 73% of preparations with staggered bilateral hemisections failed to generate locomotor-like activity in response to electrical stimulation of the brain stem alone; such preparations were used to test the effect of neuroactive substances applied to thoracic segments (bath barriers placed at T3 and T9) during brain stem stimulation. The percentage of preparations developing locomotor-like activity was as follows: 5-HT (43%), 5-HT/ N-methyl-d-aspartate (NMDA; 33%), quipazine (42%), 8-hydroxy-2-(di- n-propylamino)tetralin (20%), methoxamine (45%), and elevated bath K+ concentration (29%). Combined norepinephrine and dopamine increased the success rate (67%) compared with the use of either agent alone (4 and 7%, respectively). NMDA, Mg2+ ion removal, clonidine, and acetylcholine were ineffective. The results provide proof of principle that artificial excitation of thoracic propriospinal neurons can improve supraspinal control over hindlimb locomotor networks in the lesioned spinal cord.

Effect of Ethanol Upon Respiratory-Related Hypoglossal Nerve Output of Neonatal Rat Brain Stem Slices

2000 ◽  
Vol 83 (1) ◽  
pp. 333-342 ◽  
Author(s):  
Ian C. Gibson ◽  
Albert J. Berger
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Brain Stem ◽  
Rat Brain ◽  
Hypoglossal Nerve ◽  
Neonatal Rat ◽  
Dependent Manner ◽  
Nerve Activity ◽  
Kinase C ◽  
Neonatal Rat Brain

The actions of ethanol (EtOH) on the respiratory output of the neonatal rat brain stem slice preparation in vitro are described. Ethanol inhibited respiratory-related hypoglossal nerve activity in a dose-dependent manner. The effect of EtOH was evident within 5 min and was reversible on EtOH washout. The actions of EtOH were qualitatively similar to those of two other alcohols, methanol and octanol. We investigated the dose-response relationship for each alcohol and determined that the order of potency was methanol < EtOH ≪ octanol, with EC50 values of 291 mM, 39.7 mM, and 49.2 μM respectively. Application of either strychnine (5 μM) or bicuculline (5 μM) alone, partially but not significantly, reversed the inhibition of respiratory-related hypoglossal nerve activity produced by 50 mM EtOH. Preincubation of rhythmic slices with a combination of both strychnine and bicuculline (both 5 μM) partially, but significantly, blocked the inhibitory actions of EtOH, suggesting that other mechanisms also play a role in the action of EtOH. Preincubation of the slices with 25 μM APV reduced the relative degree of inhibition caused by EtOH suggesting that N-methyl-d-aspartate (NMDA)-receptor-mediated events can be affected by EtOH. Furthermore inhibition of protein kinase C by incubation with 100 nM staurosporine also reduced the efficacy of EtOH. These results suggest that the actions of EtOH may be mediated via glycine, GABAA, and NMDA receptors and that activation of protein kinase C is involved in the EtOH-induced inhibition of respiratory-related hypoglossal nerve activity.

Effects of Serotonin on Caudal Raphe Neurons: Activation of an Inwardly Rectifying Potassium Conductance

1997 ◽  
Vol 77 (3) ◽  
pp. 1349-1361 ◽  
Author(s):  
Douglas A. Bayliss ◽  
Yu-Wen Li ◽  
Edmund M. Talley
Keyword(s):  
Brain Stem ◽  
Rat Brain ◽  
Pertussis Toxin ◽  
Action Potentials ◽  
Potassium Conductance ◽  
Neonatal Rat ◽  
Serotonergic Neurons ◽  
Inwardly Rectifying ◽  
Neonatal Rat Brain ◽  
Raphe Neurons

Bayliss, Douglas A., Yu-Wen Li, and Edmund M. Talley. Effects of serotonin on caudal raphe neurons: activation of an inwardly rectifying potassium conductance. J. Neurophysiol. 77: 1349–1361, 1997. We used whole cell current- and voltage-clamp recording in neonatal rat brain stem slices to characterize firing properties and effects of serotonin (5-HT) on neurons( n = 225) in raphe pallidus (RPa) and raphe obscurus (ROb). Of a sample of 51 Lucifer yellow-filled neurons recovered after immunohistochemical processing to detect tryptophan hydroxylase (TPH), 34 were found to be TPH immunoreactive (i.e., serotonergic). Serotonergic neurons had long-duration action potentials and fired spontaneously at low frequency (∼1 Hz) in a pattern that was often irregular; at higher firing frequencies the discharge became more regular. These neurons displayed spike frequency adaptation, with maximal steady-state firing rates of <4 Hz. The overwhelming majority of identified serotonergic neurons was hyperpolarized by bath-applied 5-HT (94%; n = 32 of 34); conversely, most cells in this sample that were hyperpolarized by 5-HT were serotonergic (78%; n = 32 of 41). TPH-immunonegative neurons were separated into two populations. One group had properties that were indistinguishable from those of serotonergic caudal raphe neurons. The other group was truly distinct; those neurons had more hyperpolarized resting membrane potentials, were not spontaneously active, had shorter-duration action potentials, and were depolarized by 5-HT. Caudal raphe neurons responded to 5-HT (1–5 μM) with membrane hyperpolarization in current clamp (−13.4 ± 1.1 mV, mean ± SE) or with outward current in voltage clamp (16.0 ± 1.4 pA). The current induced by 5-HT was inwardly rectifying and associated with an increase in peak conductance and was highly selective for K+. It was completely blocked by 0.2 mM Ba2+ but not by glibenclamide, an inhibitor of ATP-sensitive K+ channels. Effects of 5-HT were dose dependent, with an EC50 of 0.1–0.3 μM. The 5-HT1A agonist 8-OH-DPAT mimicked, and the 5-HT1A antagonists (+)WAY 100135 and NAN 190 blocked, effects of 5-HT. The 5-HT2A/C antagonist ketanserin did not inhibit the effects of 5-HT. Fewer 5-HT-responsive neurons were encountered in slices exposed acutely to pertussis toxin (∼13%) than in adjacent control slices not exposed to pertussis toxin (∼85%). In addition, in neurons recorded with pipettes containing GTPγS (0.1 mM), 5-HT induced an inwardly rectifying current that did not reverse on washing. In many cells recorded with GTPγS, a current developed in the absence of agonist that had properties identical to those of the 5-HT-sensitive current; when followed for extended periods, the agonist-independent GTPγS-induced conductance desensitized, returning toward control levels with a time constant of ∼18 min. Together these results indicate that serotonergic neurons of ROb and RPa are spontaneously active in a neonatal rat brain stem slice preparation and that hyperpolarization of those neurons by 5-HT1A receptor stimulation is due to pertussis toxin-sensitive G protein-mediated activation of an inwardly rectifying K+ conductance. In addition, we identified a group of nonserotonergic medullary raphe neurons that had distinct electrophysiological properties and that was depolarized by 5-HT.

Stimulation Within the Rostral Ventrolateral Medulla Can Evoke Monosynaptic GABAergic IPSPs in Sympathetic Preganglionic Neurons In Vitro

1997 ◽  
Vol 77 (1) ◽  
pp. 229-235 ◽  
Author(s):  
Susan A. Deuchars ◽  
K. Michael Spyer ◽  
Michael P. Gilbey
Keyword(s):  
Spinal Cord ◽  
Brain Stem ◽  
Rostral Ventrolateral Medulla ◽  
Neonatal Rat ◽  
Ventrolateral Medulla ◽  
Sympathetic Preganglionic Neurons ◽  
Preganglionic Neurons ◽  
Neonatal Rat Brain ◽  
Stimulation Of

Deuchars, Susan A., K. Michael Spyer, and Michael P. Gilbey. Stimulation within the rostral ventrolateral medulla can evoke monosynaptic GABAergic IPSPs in sympathetic preganglionic neurons in vitro. J. Neurophysiol. 77: 229–235, 1997. The inhibitory responses of identified sympathetic preganglionic neurons (SPNs) to stimulation within the rostral ventrolateral medulla (RVLM) were studied to determine their nature and pharmacology. Whole cell patch-clamp recordings were made from 36 SPNs in the upper thoracic segments of the spinal cord in a neonatal rat brain stem-spinal cord preparation. Neurons were identified as SPNs on the basis of their antidromic activation after stimulation of the ipsilateral segmental ventral root and their morphology and location in the intermediolateral cell column and intercalated nucleus. In all SPNs, electrical stimulation of the RVLM evoked fast excitatory postsynaptic potentials (EPSPs) that were mediated by non- N-methyl-d-aspartate (NMDA) and NMDA receptors. These excitatory responses were the most prominent response in control artificial cerebrospinal fluid and have been studied previously. In 22 of the SPNs, RVLM stimulation also elicited fast inhibitory postsynaptic potentials (IPSPs), which increased in amplitude as the membrane was depolarized. Five of these neurons were not studied further as they responded occasionally with IPSPs that had highly variable onset latencies indicating the involvement of a polysynaptic pathway. In the remaining SPNs ( n = 17), the evoked IPSPs persisted in the presence of the excitatory amino acid antagonists 6-cyano-7-nitroquinoxaline-2,3,-dione and d,l-2-amino-5-phosphonopentanoic acid. In eight of these SPNs, it was necessary to block the EPSPs to reveal the IPSPs. In the 7 SPNs tested, the onset latencies of the IPSPs were not significantly different from the onset latencies of the fast EPSPs. The low sweep-to-sweep fluctuations in onset latency of individual IPSPs (absolute average deviation: 0.4 ms) indicated that the IPSPs were elicited by activation of a monosynaptic pathway. The amplitudes of the IPSPs decreased in amplitude as the membrane was hyperpolarized and reversed in polarity at −70.3 ± 1.7 mV (mean ± SD), which was close to the equilibrium potential for chloride ions. In addition, in seven SPNs, bath applications of 5 μM bicuculline, a γ-aminobuturic acid-A (GABAA) antagonist, abolished or reduced the evoked IPSPs. Five SPNs also were studied that displayed ongoing IPSPs. The amplitudes of these IPSPs increased with membrane depolarization and were blocked by bath applications of 5 μM bicuculline, suggesting that they also were mediated by activation of GABAA receptors. These results demonstrate the existence of a bulbospinal GABAergic pathway impinging directly onto SPNs. This pathway may be tonically active in the neonatal rat brain stem-spinal cord preparation.

Intercostal and Abdominal Respiratory Motoneurons in the Neonatal Rat Spinal Cord: Spatiotemporal Organization and Responses to Limb Afferent Stimulation

2008 ◽  
Vol 99 (5) ◽  
pp. 2626-2640 ◽  
Author(s):  
Aurore Giraudin ◽  
Marie-Jeanne Cabirol-Pol ◽  
John Simmers ◽  
Didier Morin
Keyword(s):  
Spinal Cord ◽  
Brain Stem ◽  
Neonatal Rat ◽  
Descending Pathways ◽  
Respiratory Rhythmogenesis ◽  
Electrophysiological Procedures ◽  
Low Threshold ◽  
Rhythmic Contractions ◽  
First Time

Respiration requires the coordinated rhythmic contractions of diverse muscles to produce ventilatory movements adapted to organismal requirements. During fast locomotion, locomotory and respiratory movements are coordinated to reduce mechanical conflict between these functions. Using semi-isolated and isolated in vitro brain stem-spinal cord preparations from neonatal rats, we have characterized for the first time the respiratory patterns of all spinal intercostal and abdominal motoneurons and explored their functional relationship with limb sensory inputs. Neuroanatomical and electrophysiological procedures were initially used to locate intercostal and abdominal motoneurons in the cord. Intercostal motoneuron somata are distributed rostrocaudally from C7–T13 segments. Abdominal motoneuron somata lie between T8 and L2. In accordance with their soma distributions, inspiratory intercostal motoneurons are recruited in a rostrocaudal sequence during each respiratory cycle. Abdominal motoneurons express expiratory-related discharge that alternates with inspiration. Lesioning experiments confirmed the pontine origin of this expiratory activity, which was abolished by a brain stem transection at the rostral boundary of the VII nucleus, a critical area for respiratory rhythmogenesis. Entrainment of fictive respiratory rhythmicity in intercostal and abdominal motoneurons was elicited by periodic low-threshold dorsal root stimulation at lumbar (L2) or cervical (C7) levels. These effects are mediated by direct ascending fibers to the respiratory centers and a combination of long-projection and polysynaptic descending pathways. Therefore the isolated brain stem-spinal cord in vitro generates a complex pattern of respiratory activity in which alternating inspiratory and expiratory discharge occurs in functionally identified spinal motoneuron pools that are in turn targeted by both forelimb and hindlimb somatic afferents to promote locomotor-respiratory coupling.

scholarly journals Hypothermia and recovery from respiratory arrest in a neonatal rat in vitro brain stem preparation

2002 ◽  
Vol 282 (2) ◽  
pp. R484-R491 ◽  
Author(s):  
Nicholas M. Mellen ◽  
William K. Milsom ◽  
Jack L. Feldman
Keyword(s):  
Brain Stem ◽  
Motor Neurons ◽  
Respiratory Rhythm ◽  
Field Potential ◽  
Respiratory Arrest ◽  
Motor Output ◽  
Neonatal Rat ◽  
Bötzinger Complex ◽  
Neonatal Rat Brain

This study was designed to examine the possibility that respiratory arrest during hypothermia occurs at the level of premotor or motor neurons rather than at the level of the central rhythm generator itself. Specifically, we sought to determine the consequences of hypothermic cooling until respiratory arrest, and subsequent rewarming, on neurons in the pre-Bötzinger Complex, as an indication of the output of the entire rhythmogenic network; and from cervical spinal (phrenic) ventral roots, as an indication of motor neuron output, in an in vitro neonatal rat brain stem-spinal cord preparation. We found that hypothermia led to a slowing of the respiratory rhythm with little or no decrease in the magnitude of phrenic motor output or the field potential of pre-Bötzinger Complex neurons. Ultimate arrest occurred abruptly and simultaneously in recordings from both sites, indicating that the arrest was due to failure of the central rhythm-generating network, primarily due to removal of a conditional excitation. On being rewarmed, the motor output recorded at both sites was usually fractionated, initially suggesting that changes occurred in network synchronization either during cooling or during reactivation following hypothermic arrest.

Characteristics of electrically induced locomotion in rat in vitro brain stem-spinal cord preparation

1990 ◽  
Vol 64 (3) ◽  
pp. 727-735 ◽  
Author(s):  
Y. Atsuta ◽  
E. Garcia-Rill ◽  
R. D. Skinner
Keyword(s):  
Spinal Cord ◽  
Electrical Stimulation ◽  
Brain Stem ◽  
Neonatal Rat ◽  
Step Cycle ◽  
Cycle Frequency ◽  
Adult Rat ◽  
Pattern Generators ◽  
Stimulation Of

1. Electrical stimulation of two brain stem regions in the decerebrate neonatal rat brain--the mesencephalic locomotor region (MLR) and the medioventral medulla (MED)--were found to elicit rhythmic limb movements in the hind-limb-attached, in vitro, brain stem-spinal cord preparation. 2. Electromyographic (EMG) analysis revealed locomotion similar to that observed during stepping in the adult rat. The step-cycle frequency could be increased by application of higher-amplitude currents; but, unlike the adult, alternation could not be driven to a gallop. 3. Threshold currents for inducing locomotion were significantly lower for stimulation of the MED compared with the MLR. Brain stem transections carried out at midpontine levels demonstrated that the presence of the MLR was not required for the expression of MED-stimulation-induced effects. 4. Substitution of the standard artificial cerebrospinal fluid (aCSF) by magnesium-free aCSF did not affect interlimb relationships and resulted in a significant decrease of the threshold currents for inducing locomotion. 5. Fixation of the limbs during electrical stimulation of brain stem sites altered the amplitude and duration of the EMG patterns, but the basic rhythm and timing of each muscle contraction during the step cycle was not affected. 6. These studies suggest that, although peripheral afferent modulation is evident in the neonatal locomotor control system, descending projections from brain stem-locomotor regions appear capable of modulating the activity of spinal pattern generators as early as the day of birth. However, there may be ceiling to the maximal frequency of stepping possible at this early age, perhaps suggesting a later-developing mechanism for galloping.

Infant stepping: a window to the behaviour of the human pattern generator for walking

2004 ◽  
Vol 82 (8-9) ◽  
pp. 662-674 ◽  
Author(s):  
Jaynie F Yang ◽  
Tania Lam ◽  
Marco Y.C Pang ◽  
Erin Lamont ◽  
Kristin Musselman ◽  
...  
Keyword(s):  
Pattern Generator ◽  
Human Infant ◽  
Cycle Duration ◽  
Step Cycle ◽  
Human Infants ◽  
Sensory Inputs ◽  
Weight Support ◽  
Pattern Generators ◽  
Proprioceptive Inputs ◽  
Insight Into

The aim of this paper is to provide evidence, both published and new, to support the notion that human infants are particularly good subjects for the study of the pattern generator for walking. We and others have shown that stepping can be initiated by sensory input from the legs or by general heightened excitability of the infant. New results are presented here to suggest that weight support through the feet and rapid extension of the legs are important proprioceptive inputs to initiate stepping. Our previous work has shown that infants can step at many different speeds when supported on a treadmill. The step cycle duration shortens as the speed increases, with the changes coming largely from the stance phase, just as in most other terrestrial animals. Moreover, we have shown that infants will step in all directions. Regardless of the direction of stepping, the step cycle changes in the same way with walking speed, suggesting the circuitry that controls different directions of walking share common elements. We have also shown that infant stepping is highly organized. Sensory inputs, whether proprioceptive or touch, are gated in a functional way so that only important sensory inputs generate a response. For example, touch to the lateral surface of the foot elicits a response only in sideways walking, and only in the leading limb. New data is presented here to show that the pattern generators from each limb can operate somewhat independently. On a split-belt treadmill with the 2 belts running at different speeds or in different directions, the legs showed considerable independence in behaviour. Yet, the pattern generators on each side interact to ensure that swing phase does not occur at the same time. These studies have provided insight into the organization of the pattern generator for walking in humans. It will be interesting in the future to study how maturation of the descending tracts changes walking behaviour to allow independent bipedal walking.Key words: locomotion, central pattern generator, human, infant.

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