Article

Onimaru, H., Shamoto, A. & Homma, I. Modulation of respiratory rhythm by 5-HT in the brainstem-spinal cord preparation from newborn rat. Pflügers. Arch. 435, 485-494

Showa University, Shinagawa, Tōkyō, Japan
Pflügers Archiv - European Journal of Physiology (Impact Factor: 4.1). 04/1998; 435(4):485-94. DOI: 10.1007/s004240050543
Source: PubMed

ABSTRACT

Effects of 5-hydroxytryptamine (5-HT) on inspiration-related nerve activity and membrane potential of respiratory neurons in the ventrolateral medulla were studied in brainstem-spinal cord preparations isolated from newborn rats. Bath application of 5-100 microM 5-HT induced a biphasic response in inspiratory nerve activity: a transient increase in respiratory frequency followed by a decrease in the rate of discharge. The excitatory effect of 5-HT was particularly prominent in preparations with a respiratory rate of less than 3 min-1, whereas the inhibitory effect was more pronounced in preparations with a higher respiratory rate. In pre-inspiratory (Pre-I) and inspiratory (Insp) neurons, 20 microM 5-HT induced a membrane depolarization of up to 10 mV accompanied by a significant decrease in the input resistance. Membrane depolarization by 5-HT was also evident in the presence of tetrodotoxin. In Pre-I neurons, 5-HT caused an increase in the burst rate, which was followed by a decrease in the intraburst firing frequency and burst amplitude, although the burst rate remained high. The burst rate in Insp neurons first increased and subsequently decreased without significant change in the intraburst firing frequency. Simultaneous intra- and extracellular recordings (in the contralateral medulla) of Pre-I/Pre-I neuron or Pre-I/Insp neuron pairs revealed that 5-HT disturbed the correlation between these neuron bursts. Increase in the respiratory rate induced by 20 microM 5-HT was completely blocked by pretreatment (5-15 min) with 5 microM ketanserin or 1 microM methysergide, but not by 10 microM propranolol. None of these antagonists blocked the inhibitory effects of 5-HT. A 5-HT2 agonist, 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI, 10-100 microM) increased the respiratory rate. Perfusion with a 5-HT1A agonist, 8-hydroxy-dipropylaminotetralin hydrobromide (8-OH-DPAT, 20-100 microM) induced an increase or a decrease in the respiratory rate. A 5-HT2C agonist, 1-(3-chlorophenyl)piperazine (m-CPP, 2-10 microM) induced an initial decrease in the respiratory rate followed by a further long- lasting decrease. Burst activity of Pre-I neurons was suppressed upon administration of 10 microM m-CPP and enhanced with 20 microM DOI. The results suggest that changes in the bursting properties of Pre-I and Insp neurons induced by 5-HT lead to modulation of the respiratory network, thus causing biphasic modulation of the respiratory rhythm. In addition to effects via 5-HT1A receptors, activation of 5-HT2A and 5-HT2C receptor subtypes might be involved in excitatory effects and inhibitory effects of 5-HT respectively.

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    • "These concentrations were selected based on preliminary results and the literature (Ren and Greer, 2006). The brainstem was exposed to each concentration for 20 min; this period is sufficient to obtain measurements that do not reflect a transient effect of the drug (Belzile et al., 2002; Kinkead et al., 2002; Onimaru et al., 1998). The final application was followed by a " wash out " period during which the preparation was superfused with drug-free aCSF for 20 min. "
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    ABSTRACT: The GABAergic system modulates respiratory activity and undergoes substantial changes during early life. Because this maturation process is sensitive to stress, we tested the hypothesis that gestational stress (GS) alters development of GABAergic modulation of respiratory control in rat pups. The respiratory responses to the selective GABAA receptor agonist muscimol were compared between pups born to dams subjected to GS (bright light and predator odor; 20min/day from G9 to G19) or maintained under standard (control) conditions. Respiratory activity was measured on 1 and 4 days old pups of both sexes using in vivo (whole body plethysmography) and in vitro (isolated brainstem-spinal cord preparation) approaches. In intact pups, muscimol injection (0.75mg/kg; i.p.) depressed minute ventilation; this response was less in GS pups, and at P4, muscimol augmented minute ventilation in GS females. Bath application of muscimol (0.01 - 0.5μM) onto brainstem preparations decreased inspiratory (C4) burst frequency and amplitude in a dose-dependent manner; the responsiveness decreased with age. However, GS had limited effects on these results. We conclude that the results obtained in vivo are consistent with our hypothesis and show that GS delays maturation of GABAergic modulation of respiratory activity. The differences in the results observed between experimental approaches (in vivo versus in vitro) indicate that the effect of prenatal stress on maturation of GABAergic modulation of respiratory control mainly affects the peripheral/metabolic components of the respiratory control system.
    Full-text · Article · Jun 2014 · Respiratory Physiology & Neurobiology
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    • "These concentrations were selected based on preliminary results and the literature (Ren and Greer, 2006). The brainstem was exposed to each concentration for 20 min; this period is sufficient to obtain measurements that do not reflect a transient effect of the drug (Belzile et al., 2002; Kinkead et al., 2002; Onimaru et al., 1998). The final application was followed by a " wash out " period during which the preparation was superfused with drug-free aCSF for 20 min. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The GABAergic system modulates respiratory activity and undergoes substantial changes during early life. Because this maturation process is sensitive to stress, we tested the hypothesis that gestational stress (GS) alters development of GABAergic modulation of respiratory control in rat pups. The respiratory responses to the selective GABAA receptor agonist muscimol were compared between pups born to dams subjected to GS (bright light and predator odor; 20 min/day from G9 to G19) or maintained under standard (control) conditions. Respiratory activity was measured on 1 and 4 days old pups of both sexes using in vivo (whole body plethysmography) and in vitro (isolated brainstem-spinal cord preparation) approaches. In intact pups, muscimol injection (0.75 mg/kg; i.p.) depressed minute ventilation; this response was less in GS pups, and at P4, muscimol augmented minute ventilation in GS females. Bath application of muscimol (0.01–0.5 μM) onto brainstem preparations decreased inspiratory (C4) burst frequency and amplitude in a dose-dependent manner; the responsiveness decreased with age. However, GS had limited effects on these results. We conclude that the results obtained in vivo are consistent with our hypothesis and show that GS delays maturation of GABAergic modulation of respiratory activity. The differences in the results observed between experimental approaches (in vivo versus in vitro) indicate that the effect of prenatal stress on maturation of GABAergic modulation of respiratory control mainly affects the peripheral/metabolic components of the respiratory control system.
    Full-text · Article · Jan 2014 · Respiratory Physiology & Neurobiology
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    • "Inspiratory neurons in the pBC produce a regular bursting rhythm in phase with the activity of inspiratory muscles in the diaphragm. These neurons are a vital part of the pontomedullary neuronal network, which generates a stable respiratory rhythm (Smith et al. 1991; Johnson et al. 1994), whose amplitude and frequency depends on the level of various neurotransmitters (Johnson et al. 1998; Onimaru et al. 1998; Herlenius and Lagercrantz 1999; Ptak and Hilaire 1999; Fujii et al. 2004; Llona and Eugenin 2005). "
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    ABSTRACT: The network of coupled neurons in the pre-Bötzinger complex (pBC) of the medulla generates a bursting rhythm, which underlies the inspiratory phase of respiration. In some of these neurons, bursting persists even when synaptic coupling in the network is blocked and respiratory rhythmic discharge stops. Bursting in inspiratory neurons has been extensively studied, and two classes of bursting neurons have been identified, with bursting mechanism depends on either persistent sodium current or changes in intracellular Ca(2+), respectively. Motivated by experimental evidence from these intrinsically bursting neurons, we present a two-compartment mathematical model of an isolated pBC neuron with two independent bursting mechanisms. Bursting in the somatic compartment is modeled via inactivation of a persistent sodium current, whereas bursting in the dendritic compartment relies on Ca(2+) oscillations, which are determined by the neuromodulatory tone. The model explains a number of conflicting experimental results and is able to generate a robust bursting rhythm, over a large range of parameters, with a frequency adjusted by neuromodulators.
    Full-text · Article · Jun 2011 · Journal of Computational Neuroscience
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