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  • 1
    Electronic Resource
    Electronic Resource
    Development of action potentials and apamin-sensitive after-potentials in mouse vestibular nucleus neurones (1998)
    Springer
    Experimental brain research 118 (1998), S. 148-154 
    Details
    ISSN: 1432-1106
    Keywords: Key words Development ; Action potential ; Neurones ; Vestibular system ; In vitro
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The postnatal maturation of medial vestibular nucleus (MVN) neurones was examined in slices of the dorsal brainstem prepared from balb/c mice at specific stages during the first postnatal month. Using spike-shape averaging to analyse the intracellularly recorded action potentials and after-hyperpolarisations (AHPs) in each cell, all the MVN neurones recorded in the young adult (postnatal day 30; P30) mouse were shown to have either a single deep AHP (type A cells), or an early fast and a delayed slow AHP (type B cells). The relative proportions of the two subtypes were similar to those in the young adult rat. At P5, all the MVN cells recorded showed immature forms of either the type A or the type B action potential shape. Immature type A cells had broad spontaneous spikes, and the characteristic single AHP was small in amplitude. Immature type B cells had somewhat narrower spontaneous spikes that were followed by a delayed, apamin-sensitive AHP. The delayed AHP was separated from the repolarisation phase of the spike by a period of isopotentiality. Over the period P10–P15, the mean resting potentials of the MVN cells became more negative, their action potential fall-times became shorter, the single AHP in type A cells became deeper, and the early fast AHP appeared in type B cells. Until P15 cells of varying degrees of electrophysiological maturity were found in the MVN but by P30 all MVN cells recorded were typical adult type A or type B cells. Exposure to the selective blocker of SK-type Ca-activated K channels, apamin (0.3 μM), induced depolarising plateaux and burst firing in immature type B cells at rest. The duration of the apamin-induced bursts and the spike frequency during the bursts were reduced but not abolished after blockade of Ca channels in Ca-free artificial cerebrospinal fluid containing Cd2+. By contrast, in mature type B cells at rest apamin selectively abolished the delayed slow AHP but did not induce bursting activity. Apamin had no effect on the action potential shape of immature type A cells. These data show that the apamin-sensitive I AHP is one of the first ionic conductances to appear in type B cells, and that it plays an important role in regulating the intrinsic rhythmicity and excitability of these cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050266
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  • 2
    Electronic Resource
    Electronic Resource
    Opioid inhibition of rat medial vestibular nucleus neurones in vitro and its dependence on age (1998)
    Springer
    Experimental brain research 122 (1998), S. 196-202 
    Details
    ISSN: 1432-1106
    Keywords: Key words Opioid ; Enkephalin ; Medial vestibular nucleus ; Age ; In vitro ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Extracellular and whole-cell patch clamp intracellular recordings were made from rat medial vestibular nucleus (MVN) neurones in vitro, and their responses to selective μ-, κ- and δ-opioid receptor agonists and antagonists were examined. Of 127 neurones tested, the large majority were inhibited in a dose-dependent manner by the δ-opioid receptor agonists [d-Ala2, d-Leu5]-enkephalin (DADLE) and [d-Pen2, Pen5]-enkephalin (DPLPE). The μ-opioid receptor agonist morphine and the κ-receptor agonist U50,488 did not affect the tonic discharge rate of any of the 63 MVN cells tested. The δ-receptor antagonist naltrindole effectively antagonised the inhibitory effects of DADLE and DPLPE. Weak excitatory responses to high doses of DADLE were seen in only two MVN cells. These results demonstrate the presence of δ- but not μ- or κ-opioid receptors on tonically active MVN neurones. Whole-cell intracellular recordings from MVN cells in a current clamp showed that the DADLE-induced inhibition was accompanied by membrane hyperpolarisation and decrease in input resistance, while voltage clamp experiments showed that DADLE induced an outward membrane current that was reduced but not abolished by 20 mM tetraethylammonium bromide. Thus the mechanisms of action of DADLE in inhibiting MVN cells involve the potentiation of outward K currents, in a similar way to the effects of opioids in other areas of brain. The inhibitory effects of DADLE increased linearly with age, so that the responses to DADLE in the youngest animals used here (60–80 g, approx. 3 weeks of age) were relatively small, increasing significantly over the following 2–3 weeks. This age-dependence may be due to post-natal changes in the density of δ-opiate receptors or the efficacy of the signalling pathways activated by them in the MVN cells over this time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050507
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of histamine and betahistine on rat medial vestibular nucleus neurones: possible mechanism of action of anti-histaminergic drugs in vertigo and motion sickness (1995)
    Springer
    Experimental brain research 105 (1995), S. 18-24 
    Details
    ISSN: 1432-1106
    Keywords: Medial vestibular nucleus ; Histamine ; Betahistine ; Vertigo ; Motion sickness ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The tonic discharge of 71 medial vestibular nucleus (MVN) neurones was recorded in slices of the dorsal brainstem of young adult rats. Bath application of histamine caused a dose-related excitation in 59 of the 71 cells (83%), the remaining 12 (17%) being unresponsive. Dimaprit, a selective H2 agonist, also caused excitation in all 20 cells tested. The histamine-induced excitation and the response to dimaprit were antagonised by the selective H2 antagonist ranitidine, confirming that the H2 subtype of histamine receptor is involved in mediating the effects of histamine on these cells. Triprolidine, a selective H1 antagonist, also antagonised the excitation caused by histamine, at a concentration (0.3 μM) which left the H2 receptor-mediated response to dimaprit unchanged. Thus the excitatory effects of histamine on MVN cells in the rat involve two components mediated through H1 and H2 receptor-linked mechanisms, respectively. Betahistine, a weak H1 agonist and H3 antagonist, had little excitatory action when applied on its own, but significantly reduced the excitation caused by histamine when the two drugs were applied together. The effects of betahistine were consistent with a partial-agonist action at H1 receptors on MVN cells, reducing the excitatory responses to histamine presumably by occupying these receptor sites in competition with the exogenously applied neurotransmitter. This partial-agonist action of betahistine may be an important part of its mechanism of action in the symptomatic treatment of vertigo and motion sickness, since it is likely to occur not only in the MVN but also in many brain regions, including the thalamus and cortex, which express H1 receptors and which are innervated by the hypothalamic histaminergic system. Thus the effectiveness of betahistine and other anti-H1 drugs against motion sickness may be explained by their action in reducing the effects of the excess histamine release induced in such conditions in various brain areas, including the MVN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242178
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  • 4
    Electronic Resource
    Electronic Resource
    Properties of cat neck muscle spindles and their excitation by succinylcholine (1987)
    Springer
    Experimental brain research 68 (1987), S. 619-630 
    Details
    ISSN: 1432-1106
    Keywords: Muscle spindle ; Neck ; Succinylcholine ; Tandem spindle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The sensitivity to sinusoidal stretching and small-amplitude vibration, and the variability of the resting discharge rate of de-efferented muscle spindles in the neck extensor muscle biventer cervicis (b.c.) of the cat have been studied. The effects of intra-arterial infusion of succinylcholine (SCh) on the response of the receptors to ramp stretches of the muscle were also determined. When activated by SCh, one group of afferents showed only a slow facilitation of their discharge rate, similar to that of spindle secondary sensory endings in hind-limb muscles. A second group of afferents developed a large dynamic response and a marked increase in their static discharge rate and were presumed to originate in “normal” b1b2c spindles in the b.c. muscle. A third group of afferents developed only a marked increase in static discharge, without potentiation of the dynamic response, suggesting an origin in the b2c units of tandem spindles which are relatively common in the neck muscles. On the basis of their passive characteristics alone, afferents from b1b2c units could not be readily distinguished from those from b2c units. The characteristics of these receptors, and their differences from the well-studied hind-limb spindle afferents, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00249805
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  • 5
    Electronic Resource
    Electronic Resource
    Excitation and inhibition of rat medial vestibular nucleus neurones by 5-hydroxytryptamine (1993)
    Springer
    Experimental brain research 93 (1993), S. 293-298 
    Details
    ISSN: 1432-1106
    Keywords: Medial vestibular nucleus ; 5-Hydroxytryptamine ; Serotonin ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of 5-hydroxytryptamine (5-HT) and related compounds on the discharge rate of tonically active medial vestibular nucleus (MVN) neurones were studied in an in vitro slice preparation of the dorsal brainstem of the rat. The majority (87 of 107, 82%) of MVN neurones were excited by 5-HT. Nine cells (8%) showed a biphasic response to 5-HT, which consisted of a brief inhibition followed by excitation. Eleven cells (10%) were inhibited by 5-HT. The excitatory effects of 5-HT were mimicked by alpha-methyl-5-HT and antagonised by ketanserin and ritanserin, indicating the involvement of the 5-HT2 subtype of 5-HT receptor. In biphasic cells, blockade of 5-HT2 receptors by ketanserin reduced the excitatory component of the response and revealed an enhanced initial inhibition. The inhibitory effects in biphasic cells, and in cells that showed a pure inhibition in response to 5-HT, were blocked by pindobind-5-HT and mimicked by 8-hydroxy-2-(di-n-propylamino)-tetralin indicating the involvement of 5-HT1A receptors. The significance of these findings in relation to the effects of 5-HT on vestibular reflex function is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00228397
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  • 6
    Electronic Resource
    Electronic Resource
    Tonic activity of rat medial vestibular nucleus neurones in vitro and its inhibition by GABA (1992)
    Springer
    Experimental brain research 88 (1992), S. 466-472 
    Details
    ISSN: 1432-1106
    Keywords: GABA ; Vestibular System ; Medial vestibular nucleus ; In vitro
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The spontaneous discharge of 48 medial vestibular nucleus (MVN) neurones was recorded extracellularly in horizontal slices of the rat brainstem in vitro. The mean tonic rate of discharge was 17.1±8.2 imp/s, similar to that observed by others in transverse (coronal) slices of the rat and guinea pig MVN. The tonic rate of discharge of individual MVN cells either increased or decreased after synaptic blockade in low Ca2+ media, suggesting that ongoing synaptic activity has an important influence on the spontaneous activity of MVN cells in vitro. However the persistence of tonic activity after synaptic blockade indicates that an intrinsic, pacemaker-like mechanism is involved in the generation of the tonic activity. GABA, muscimol, baclofen and 3-APA inhibited the tonic activity of all MVN cells tested. Bicuculline antagonised, and picrotoxin blocked, the inhibitory responses to muscimol, but the effects of GABA were only partially blocked in 50 μM picrotoxin. The effects of baclofen and 3-APA persisted in low Ca2+ media, and were antagonised by saclofen and phaclofen. Picrotoxin-resistant responses to GABA persisted in low Ca2+ media, and were also antagonised by saclofen. These results suggest that the inhibitory control of MVN neurones by GABA involves both the GABAA and GABAB subtypes of GABA receptor. GABAB receptors appear to be distributed both pre- and post-synaptically in the rat MVN. The possible significance of the intrinsic, tonic activity of MVN cells in normal vestibular function and in vestibular compensation, and the effects of GABA, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00228176
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  • 7
    Electronic Resource
    Electronic Resource
    A study of 5-HT-receptors associated with afferent nerves located in normal and inflamed rat ankle joints (1988)
    Springer
    Inflammation research 25 (1988), S. 216-218 
    Details
    ISSN: 1420-908X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Neural recordings were made from sensory fibres in a nerve supplying the ankle joint in normal rats and in rats with a novel monoarticular arthritis. The responses of mechanically and chemically sensitive units to intra-arterial injections of 5-HT were measured. In most cases the mechanosensitivity of sensory receptors in the ankle joint was not altered by 5-HT. However, 5-HT produced an increase in afferent activity in units which were identified as C-fibres on the basis of action potential amplitude and duration. The receptive fields of these chemosensitive units were not located. The responses of these units to 5-HT were dose dependent and were abolished by the 5-HT2-antogonist, ketanserin, but not by the 5-HT3-receptor antagonist, MDL 72222. The responses of chemosensitive units to injections of 5-HT were similar in normal and arthritic rats although the response was slightly prolonged in arthritic animals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01965015
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