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  • 1.
    Chizhov, Anton V
    et al.
    Computational Physics Laboratory, Division of Plasma Physics, Atomic Physics and Astrophysics, A.F. Ioffe Physical-Technical Institute of the Russian Academy of Sciences, St. Petersburg, Russia.
    Malinina, Evgenia
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Druzin, Michael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology. Department of Neurodynamics and Neurobiology, Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia.
    Graham, Lyle J
    Neurophysiology and New Microscopies Laboratory, INSERM U603 - CNRS UMR 8154, Université Paris Descartes, Paris, France.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Firing clamp: a novel method for single-trial estimation of excitatory and inhibitory synaptic neuronal conductances.2014In: Frontiers in cellular neuroscience, ISSN 1662-5102, Vol. 8, no 86, p. 86-Article in journal (Refereed)
    Abstract [en]

    Understanding non-stationary neuronal activity as seen in vivo requires estimation of both excitatory and inhibitory synaptic conductances from a single trial of recording. For this purpose, we propose a new intracellular recording method, called "firing clamp." Synaptic conductances are estimated from the characteristics of artificially evoked probe spikes, namely the spike amplitude and the mean subthreshold potential, which are sensitive to both excitatory and inhibitory synaptic input signals. The probe spikes, timed at a fixed rate, are evoked in the dynamic-clamp mode by injected meander-like current steps, with the step duration depending on neuronal membrane voltage. We test the method with perforated-patch recordings from isolated cells stimulated by external application or synaptic release of transmitter, and validate the method with simulations of a biophysically-detailed neuron model. The results are compared with the conductance estimates based on conventional current-clamp recordings.

  • 2.
    Druzin, Michael
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Haage, David
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Bicuculline free base blocks voltage-activated K+ currents in rat medial preoptic neurons.2004In: Neuropharmacology, ISSN 0028-3908, Vol. 46, no 2, p. 285-95Article in journal (Refereed)
    Abstract [en]

    The effects of the well-known GABA(A)-receptor blocker bicuculline on voltage-gated K(+) currents were studied in neurons from the medial preoptic nucleus (MPN) of rat. Whole-cell currents were recorded using the perforated-patch technique. Voltage steps from -54 to +6 mV resulted in tetraethylammonium-sensitive K(+) currents of delayed rectifier type. The total K(+) current (at 300 ms), including Ca(2+)-dependent and Ca(2+)-independent components, was reversibly reduced (17 +/- 4%) by 100 microM bicuculline methiodide and (37 +/- 5%) by 100 microM bicuculline as free base. The Ca(2+)-independent fraction (77 +/- 2%) of K(+) current evoked by a voltage step was, however, reduced (54 +/- 6%) only by bicuculline free base, but was not affected by bicuculline methiodide. The half-saturating concentration of bicuculline free base for blocking this purely voltage-gated K(+) current was 113 microM, whereas for blocking a steady Ca(2+)-dependent K(+) current it was 36 microM. The bicuculline-sensitive voltage-gated K(+) current was composed of 4-AP-sensitive and 4-AP-resistant components with different kinetic properties. No component of the purely voltage-gated K(+) current was affected neither by 100 nM alpha-dendrotoxin nor by 100 nM I-dendrotoxin. The possible K(+)-channel subtypes mediating the bicuculline-sensitive current in MPN neurons are discussed.

  • 3.
    Druzin, Michael
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Haage, David
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Malinina, Evgenya
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Dual and opposing roles of presynaptic Ca2+ influx for spontaneous GABA release from rat medial preoptic nerve terminals.2002In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 542, no Pt 1, p. 131-46Article in journal (Refereed)
    Abstract [en]

    Calcium influx into the presynaptic nerve terminal is well established as a trigger signal for transmitter release by exocytosis. By studying dissociated preoptic neurons with functional adhering nerve terminals, we here show that presynaptic Ca2+ influx plays dual and opposing roles in the control of spontaneous transmitter release. Thus, application of various Ca2+ channel blockers paradoxically increased the frequency of spontaneous (miniature) inhibitory GABA-mediated postsynaptic currents (mIPSCs). Similar effects on mIPSC frequency were recorded upon washout of Cd2+ or EGTA from the external solution. The results are explained by a model with parallel Ca2+ influx through channels coupled to the exocytotic machinery and through channels coupled to Ca2+-activated K+ channels at a distance from the release site.

  • 4.
    Druzin, Michael
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    2-Aminoethyl Diphenylborinate Blocks GABAA-Receptor-Mediated Currents in Rat Medial Preoptic Neurons2016In: Opera Medica Et Physiologica, ISSN 2500-2295, Vol. 2, no 1, p. 63-68Article in journal (Refereed)
    Abstract [en]

    The effect of 2-aminoethyl diphenylborinate (2-APB), a commonly used drug to modulate inositol-1,4,5-triphosphate (IP3) receptors and transient receptor potential (TRP) channels, on GABAA receptor-mediatedcurrents was studied in neurons from the medial preoptic nucleus (MPN) of rat. 2-APB gradually and reversibly reducedthe currents evoked by GABA but had no effect on the currents evoked by glycine. The blocking effect was not mediatedby alterations in intracellular calcium concentration and showed a concentration dependence with half maximal effect at~50 μM 2-APB, for currents evoked by 100 μM, as well as by 1.0 mM GABA, suggesting that 2-APB is not competing withGABA for its binding site at the GABAA receptor. Thus, the present study describes a novel pharmacological property of2-APB as a non-competitive blocker of GABAA receptors and calls for caution in the interpretation of the results where2-APB is used to affect IP3 receptors or TRP channels.

  • 5.
    Druzin, Michael
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Malinina, Evgenya
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Grimsholm, Ola
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Mechanism of estradiol-induced block of voltage-gated K+ currents in rat medial preoptic neurons.2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 5, p. e20213-Article in journal (Refereed)
    Abstract [en]

    The present study was conducted to characterize possible rapid effects of 17-β-estradiol on voltage-gated K(+) channels in preoptic neurons and, in particular, to identify the mechanisms by which 17-β-estradiol affects the K(+) channels. Whole-cell currents from dissociated rat preoptic neurons were studied by perforated-patch recording. 17-β-Estradiol rapidly (within seconds) and reversibly reduced the K(+) currents, showing an EC(50) value of 9.7 µM. The effect was slightly voltage dependent, but independent of external Ca(2+), and not sensitive to an estrogen-receptor blocker. Although 17-α-estradiol also significantly reduced the K(+) currents, membrane-impermeant forms of estradiol did not reduce the K(+) currents and other estrogens, testosterone and cholesterol were considerably less effective. The reduction induced by estradiol was overlapping with that of the K(V)-2-channel blocker r-stromatoxin-1. The time course of K(+) current in 17-β-estradiol, with a time-dependent inhibition and a slight dependence on external K(+), suggested an open-channel block mechanism. The properties of block were predicted from a computational model where 17-β-estradiol binds to open K(+) channels. It was concluded that 17-β-estradiol rapidly reduces voltage-gated K(+) currents in a way consistent with an open-channel block mechanism. This suggests a new mechanism for steroid action on ion channels.

  • 6.
    Haage, David
    et al.
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Obstetrics and Gynaecology.
    Bäckström, Torbjörn
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Obstetrics and Gynaecology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Interaction between allopregnanolone and pregnenolone sulfate in modulating GABA-mediated synaptic currents in neurons from the rat medial preoptic nucleus.2005In: Brain Research, ISSN 0006-8993, Vol. 1033, no 1, p. 58-67Article in journal (Refereed)
    Abstract [en]

    The two neurosteroids 3alpha-hydroxy-5alpha-pregnane-20-one (allopregnanolone; AlloP) and pregnenolone sulfate (PregS) affect neuronal GABA(A) receptors differently. While AlloP mainly potentiates the currents through GABA(A) receptors, PregS reduces such currents. The present study aimed at clarifying the interaction of AlloP and PregS at GABA(A) receptors in neurons from the medial preoptic nucleus of male rat. AlloP has previously been shown to dramatically prolong GABA-mediated spontaneous inhibitory postsynaptic currents (sIPSCs) in these neurons. Here, by recording sIPSCs under voltage-clamp conditions with the perforated-patch technique, it was shown that PregS by itself did not significantly affect the amplitude or time course of such currents. However, PregS, in a concentration-dependent manner, reduced the AlloP-evoked prolongation of sIPSC decay when the two neurosteroids were applied together. In contrast to sIPSC amplitude and time course, sIPSC frequency was significantly reduced by 10 microM PregS alone. Further, although 1.0 microM AlloP alone induced a clear increase in sIPSC frequency, the frequency was not significantly different from control when 1.0 microM AlloP was applied in combination with 10 microM PregS. In addition to the effects on sIPSC parameters, PregS reduced the baseline current evoked by 1.0 microM AlloP in the absence of GABA application or synaptic activity. PregS by itself did not significantly affect the baseline current. The main effects of AlloP and PregS on the sIPSC time course were mimicked by a simplified model with AlloP assumed to reduce the rate of GABA unbinding from the receptor and PregS assumed to increase the rate of desensitization.

  • 7.
    Haage, David
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Druzin, Michael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology. Laboratory of Ionic Channels of Cell Membranes, Institute of Cytology, Russian Academy of Sciences, Russia.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Allopregnanolone modulates spontaneous GABA release via presynaptic Cl- permeability in rat preoptic nerve terminals2002In: Brain Research, ISSN 0006-8993, E-ISSN 1872-6240, Vol. 958, no 2, p. 405-413Article in journal (Refereed)
    Abstract [en]

    The endogenous neurosteroid 3alpha-hydroxy-5alpha-pregnane-20-one (allopregnanolone) affects presynaptic nerve terminals and thereby increases the frequency of spontaneous GABA release. The present study aimed at clarifying the mechanisms underlying this presynaptic neurosteroid action, by recording the frequency of spontaneous GABA-mediated inhibitory postsynaptic currents (sIPSCs) in neurons from the medial preoptic nucleus (MPN) of rat. Acutely dissociated neurons with functional adhering nerve terminals were studied by perforated-patch recording under voltage-clamp conditions. It was shown that the sIPSC frequency increased with the external K(+) concentration ([K(+)](o)). Further, the effect of allopregnanolone on the sIPSC frequency was strongly dependent on [K(+)](o). In a [K(+)](o) of 5 mM, 2.0 microM allopregnanolone caused a clear increase in sIPSC frequency. However, the effect declined rapidly with increased [K(+)](o) and at high [K(+)](o) allopregnanolone reduced the sIPSC frequency. The effect of allopregnanolone was also strongly dependent on the external Cl(-) concentration ([Cl(-)](o)). In a reduced [Cl(-)](o) (40 mM, but with a standard [K(+)](o) of 5 mM), the effect on sIPSC frequency was larger than that in the standard [Cl(-)](o) of 146 mM. The dependence of the effect of allopregnanolone on [K(+)](o) and on estimated presynaptic membrane potential was also altered by the reduction in [Cl(-)](o). As in standard [Cl(-)](o), the effect in low [Cl(-)](o) declined when [K(+)](o) was raised, but reversed at a higher [K(+)](o). The GABA(A) receptor agonist muscimol also potentiated the sIPSC frequency. Altogether, the results suggest that allopregnanolone exerts its presynaptic effect by increasing the presynaptic Cl(-) permeability, most likely via GABA(A) receptors.

  • 8.
    Johansson, Staffan
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Yelhekar, Tushar D.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Druzin, Michael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Commentary: Chloride Regulation: a Dynamic Equilibrium Crucial for Synaptic Inhibition2016In: Frontiers in Cellular Neuroscience, ISSN 1662-5102, E-ISSN 1662-5102, Vol. 10, article id 182Article in journal (Refereed)
  • 9.
    Karlsson, Urban
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Druzin, Michael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Cl concentration changes and desensitization of GABAA and glycine receptors2011In: The Journal of General Physiology, ISSN 0022-1295, E-ISSN 1540-7748, Vol. 138, no 6, p. 609-626Article in journal (Refereed)
    Abstract [en]

    Desensitization of ligand-gated ion channels plays a critical role for the information transfer between neurons. The current view on γ-aminobutyric acid (GABA)A and glycine receptors includes significant rapid components of desensitization as well as cross-desensitization between the two receptor types. Here, we analyze the mechanism of apparent cross-desensitization between native GABAA and glycine receptors in rat central neurons and quantify to what extent the current decay in the presence of ligand is a result of desensitization versus changes in intracellular Cl concentration ([Cl]i). We show that apparent cross-desensitization of currents evoked by GABA and by glycine is caused by changes in [Cl]i. We also show that changes in [Cl]i are critical for the decay of current in the presence of either GABA or glycine, whereas changes in conductance often play a minor role only. Thus, the currents decayed significantly quicker than the conductances, which decayed with time constants of several seconds and in some cells did not decay below the value at peak current during 20-s agonist application. By taking the cytosolic volume into account and numerically computing the membrane currents and expected changes in [Cl]i, we provide a theoretical framework for the observed effects. Modeling diffusional exchange of Cl between cytosol and patch pipettes, we also show that considerable changes in [Cl]i may be expected and cause rapidly decaying current components in conventional whole cell or outside-out patch recordings. The findings imply that a reevaluation of the desensitization properties of GABAA and glycine receptors is needed.

  • 10.
    Karlsson, Urban
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Haage, David
    Umeå University, Faculty of Medicine, Department of Clinical Sciences, Obstetrics and Gynaecology.
    Johansson, Staffan
    Currents evoked by GABA and glycine in acutely dissociated neurons from the rat medial preoptic nucleus1997In: Brain Research, ISSN 0006-8993, E-ISSN 1872-6240, Vol. 770, no 1-2, p. 256-260Article in journal (Refereed)
  • 11.
    Karlsson, Urban
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Sundgren, Anna
    Näsström, Jacques
    Johansson, Staffan
    Glutamate-evoked currents in acutely dissociated neurons from the rat medial preoptic nucleus1997In: Brain Research, ISSN 0006-8993, E-ISSN 1872-6240, Vol. 759, no 2, p. 270-276Article in journal (Refereed)
  • 12.
    Karlsson, Urban
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology.
    Sundgren-Andersson, Anna K
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology. Fysiologi.
    Krupp, Johannes J
    Capsaicin augments synaptic transmission in the rat medial preoptic nucleus.2005In: Brain Research, ISSN 0006-8993, E-ISSN 1872-6240, Vol. 1043, no 1-2, p. 1-11Article in journal (Refereed)
    Abstract [en]

    medial preoptic nucleus (MPN) is the major nucleus of the preoptic area (POA), a hypothalamic area involved in the regulation of body-temperature. Injection of capsaicin into this area causes hypothermia in vivo. Capsaicin also causes glutamate release from hypothalamic slices. However, no data are available on the effect of capsaicin on synaptic transmission within the MPN. Here, we have studied the effect of exogenously applied capsaicin on spontaneous synaptic activity in hypothalamic slices of the rat. Whole-cell patch-clamp recordings were made from visually identified neurons located in the MPN. In a subset of the studied neurons, capsaicin enhanced the frequency of spontaneous glutamatergic EPSCs. Remarkably, capsaicin also increased the frequency of GABAergic IPSCs, an effect that was sensitive to removal of extracellular calcium, but insensitive to tetrodotoxin. This suggests an action of capsaicin at presynaptic GABAergic terminals. In contrast to capsaicin, the TRPV4 agonist 4alpha-PDD did not affect GABAergic IPSCs. Our results show that capsaicin directly affects synaptic transmission in the MPN, likely through actions at presynaptic terminals as well as on projecting neurons. Our data add to the growing evidence that capsaicin receptors are not only expressed in primary afferent neurons, but also contribute to synaptic processing in some CNS regions.

  • 13.
    Klement, Göran
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Druzin, Michael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Haage, David
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Malinina, Evgenya
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Århem, Peter
    Karolinska Institute.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Spontaneous ryanodine-receptor-dependent Ca2+-activated K+ currents and hyperpolarizations in rat medial preoptic neurons2010In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 103, no 5, p. 2900-2911Article in journal (Refereed)
    Abstract [en]

    The aim of the present study was to clarify the identity of slow spontaneous currents, the underlying mechanism and possible role for impulse generation in neurons of the rat medial preoptic nucleus (MPN). Acutely dissociated neurons were studied with the perforated patch-clamp technique. Spontaneous outward currents, at a frequency of approximately 0.5 Hz and with a decay time constant of approximately 200 ms, were frequently detected in neurons when voltage-clamped between approximately -70 and -30 mV. The dependence on extracellular K(+) concentration was consistent with K(+) as the main charge carrier. We concluded that the main characteristics were similar to those of spontaneous miniature outward currents (SMOCs), previously reported mainly for muscle fibers and peripheral nerve. From the dependence on voltage and from a pharmacological analysis, we concluded that the currents were carried through small-conductance Ca(2+)-activated (SK) channels, of the SK3 subtype. From experiments with ryanodine, xestospongin C, and caffeine, we concluded that the spontaneous currents were triggered by Ca(2+) release from intracellular stores via ryanodine receptor channels. An apparent voltage dependence was explained by masking of the spontaneous currents as a consequence of steady SK-channel activation at membrane potentials > -30 mV. Under current-clamp conditions, corresponding transient hyperpolarizations occasionally exceeded 10 mV in amplitude and reduced the frequency of spontaneous impulses. In conclusion, MPN neurons display spontaneous hyperpolarizations triggered by Ca(2+) release via ryanodine receptors and SK3-channel activation. Thus such events may affect impulse firing of MPN neurons.

  • 14. Kling, A
    et al.
    Dahlqvist, R
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Bäckström, M
    Mjörndal, T
    Neurologic oral manifestations caused by a new formulation of mirtazapine.2005In: Neurology, ISSN 1526-632X, Vol. 65, no 2, p. 333-4Article in journal (Refereed)
  • 15.
    Malinina, Evgenya
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Druzin, Michael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Differential control of spontaneous and evoked GABA release by presynaptic L-type Ca(2+) channels in the rat medial preoptic nucleus2010In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 104, no 1, p. 200-209Article in journal (Refereed)
    Abstract [en]

    To clarify the role of presynaptic L-type Ca(2+) channels in GABA-mediated transmission in the medial preoptic nucleus (MPN), spontaneous, miniature, and impulse-evoked inhibitory postsynaptic currents (sIPSCs, mIPSCs, and eIPSCs, respectively) were recorded from MPN neurons in a slice preparation from rat brain. The effects of different stimulus protocols and pharmacological tools to detect contributions of L-type Ca(2+) channels and of Ca(2+)-activated K(+) (K(Ca)) channels were analyzed. Block of L-type channels did not affect the sIPSC and mIPSC properties (frequency, amplitude, decay time course) in the absence of external stimulation but unexpectedly potentiated the eIPSCs evoked at low stimulus frequency (0.1-2.0 Hz). This effect was similar to and overlapping with the effect of K(Ca)-channel blockers. High-frequency stimulation (50 Hz for 10 s) induced a substantial posttetanic potentiation (PTP) of the eIPSC amplitude and of the sIPSC frequency. Block of L-type channels still potentiated the eIPSC during PTP, but in contrast, reduced the sIPSC frequency during PTP. It was concluded that L-type channels provide a means for differential control of spontaneous and impulse-evoked GABA release and that this differential control is prominent during short-term synaptic plasticity. Functional coupling of the presynaptic L-type channels to K(Ca) channels explains the observed effects on eIPSCs.

  • 16.
    Malinina, Evgenya
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Druzin, Michael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Differential control of spontaneous and evoked GABA release by presynaptic L-type Ca2+ channels in the rat medial preoptic nucleusManuscript (preprint) (Other academic)
    Abstract [en]

    To clarify the role of presynaptic L-type Ca2+ channels in GABA-mediated transmission in the medial preoptic nucleus (MPN), spontaneous as well as impulse-evoked inhibitory postsynaptic currents (sIPSCs and eIPSCs, respectively) were recorded from MPN neurons in a slice preparation from rat brain. The effects of different stimulus protocols and pharmacological tools to detect contributions of L-type Ca2+ channels and of Ca2+-activated K+ (KCa) channels were analysed. Block of L-type channels did not affect the sIPSCs properties (frequency, amplitude, decay time course) in the absence of external stimulation, but unexpectedly potentiated the eIPSCs evoked at low stimulus frequency (0.1 – 2.0 Hz). This effect was similar to and overlapping with the effect of KCa-channel blockers. High-frequency stimulation (50 Hz for 10 s) induced a substantial post-tetanic potentiation (PTP) of the eIPSC amplitude as well as of the sIPSC frequency. Block of L-type channels still potentiated the eIPSC during PTP, but in contrast reduced the sIPSC frequency during PTP. It was concluded that L-type channels provide a means for differential control of spontaneous and impulse-evoked GABA release and that this differential control is prominent during short-term synaptic plasticity. Functional coupling of the presynaptic L-type channels to KCa channels explains the observed effects on eIPSCs.

  • 17.
    Malinina, Evgenya
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Druzin, Michael
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Fast neurotransmission in the rat medial preoptic nucleus.2005In: Brain Research, ISSN 0006-8993, Vol. 1040, no 1-2, p. 157-68Article in journal (Refereed)
    Abstract [en]

    The functional properties of neurotransmission in the medial preoptic nucleus (MPN) were studied in a brain slice preparation from young male rats. The aims were to evaluate the thin slice preparation for studying evoked synaptic responses in MPN neurons, to characterize the fast responses triggered by activation of presynaptic nerve fibers in the MPN, and to identify the involved receptor types. Presynaptic stimulation within the MPN evoked postsynaptic voltage and current responses that were blocked by 200 microM Cd2+ or by 2.0 microM tetrodotoxin and were attributed to action potential-evoked transmitter release. The relation to stimulus strength and comparison with spontaneous synaptic currents suggested that in many cases only one presynaptic nerve fiber was excited by the stimulus. Furthermore, the transmission was probabilistic in nature, with frequent failures. Thus, response probability, most likely reflecting transmitter release probability, could be evaluated in the thin slice preparation. Evoked excitatory postsynaptic currents recorded under voltage-clamp conditions were, due to kinetics, I-V relation, and pharmacological properties, attributed to AMPA/kainate receptors and NMDA receptors, whereas inhibitory currents were attributed to GABAA receptors. No responses that could be attributed to glycine or other types of primary transmitters were detected. Although serotonin (5-HT) did not appear to function as a primary transmitter, glutamate- as well as GABA-mediated transmission was suppressed by 500 microM 5-HT, with a clear reduction in response probability observed. 5-HT also reduced the frequency, but not the amplitude, of spontaneous postsynaptic currents and was therefore ascribed a presynaptic site of action.

  • 18.
    Malinina, Evgenya
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Druzin, Michael
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Short-term plasticity in excitatory synapses of the rat medial preoptic nucleus.2006In: Brain Research, ISSN 0006-8993, Vol. 1110, no 1, p. 128-35Article in journal (Refereed)
    Abstract [en]

    The medial preoptic nucleus (MPN) regulates sexual behavior which is subject to experience-dependent modifications. Such modifications must depend on functional plasticity in the controlling neural circuits. Thus, MPN synapses are likely candidates for the site of alterations. The present work is a first systematic study of functional synaptic plasticity at glutamatergic synapses in the MPN. Short-term activity-dependent plasticity was investigated using a slice preparation from young male rats. The average efficacy of AMPA/kainate-receptor-mediated synaptic transmission was activity-dependent, showing a peak at a steady stimulation rate of 2 Hz. The variation in efficacy was attributed to mainly presynaptic factors since the average response amplitude was roughly paralleled by the response probability. Upon paired-pulse stimulation, paired-pulse facilitation as well as paired-pulse depression was observed. In some cases, paired-pulse facilitation as well as paired-pulse depression was recorded from an individual neuron depending on the interval between the paired stimuli. On average, paired-pulse facilitation was observed at intervals <500 ms, and paired-pulse depression at intervals in the range 1-4 s. The findings thus reveal complex activity-dependent short-term plasticity of the functional synaptic properties in the medial preoptic nucleus.

  • 19.
    Yelhekar, Tushar D.
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Druzin, Michael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Contribution of Resting Conductance, GABA(A)-Receptor Mediated Miniature Synaptic Currents and Neurosteroid to Chloride Homeostasis in Central Neurons2017In: eNeuro, ISSN 2373-2822, Vol. 4, no 2, article id e0019Article in journal (Refereed)
    Abstract [en]

    Maintenance of a low intraneuronal Cl- concentration, [Cl-](i), is critical for inhibition in the CNS. Here, the contribution of passive, conductive Cl- flux to recovery of [Cl-](i) after a high load was analyzed in mature central neurons from rat. A novel method for quantifying the resting Cl- conductance, important for [Cl-](i) recovery, was developed and the possible contribution of GABAA and glycine receptors and of ClC-2 channels to this conductance was analyzed. The hypothesis that spontaneous, action potential-independent release of GABA is important for [Cl-](i) recovery was tested. [Cl-](i) was examined by gramicidin-perforated patch recordings in medial preoptic neurons. Cells were loaded with Cl- by combining GABA or glycine application with a depolarized voltage, and the time course of [Cl-](i) was followed by measurements of the Cl- equilibrium potential, as obtained from the current recorded during voltage ramps combined with GABA or glycine application. The results show that passive Cl- flux contributes significantly, in the same order of magnitude as does K+-Cl- cotransporter 2 (KCC2), to [Cl-](i) recovery and that Cl- conductance accounts for similar to 6% of the total resting conductance. A major fraction of this resting Cl- conductance is picrotoxin (PTX)-sensitive and likely due to open GABAA receptors, but ClC-2 channels do not contribute. The results also show that when the decay of GABAA receptor-mediated miniature postsynaptic currents (minis) is slowed by the neurosteroid allopregnanolone, such minis may significantly quicken [Cl-](i) recovery, suggesting a possible steroid-regulated role for minis in the control of Clhomeostasis.

  • 20.
    Yelhekar, Tushar D.
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Druzin, Michael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Karlsson, Urban
    Blomqvist, Erii
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    How to Properly Measure a Current-Voltage Relation? -Interpolation vs. Ramp Methods Applied to Studies of GABA(A) Receptors2016In: Frontiers in Cellular Neuroscience, ISSN 1662-5102, E-ISSN 1662-5102, Vol. 10, article id 10Article in journal (Refereed)
    Abstract [en]

    The relation between current and voltage, I-V relation, is central to functional analysis of membrane ion channels. A commonly used method, since the introduction of the voltage-clamp technique, to establish the I-V relation depends on the interpolation of current amplitudes recorded at different steady voltages. By a theoretical computational approach as well as by experimental recordings from GABA(A) receptor mediated currents in mammalian central neurons, we here show that this interpolation method may give reversal potentials and conductances that do not reflect the properties of the channels studied under conditions when ion flux may give rise to concentration changes. Therefore, changes in ion concentrations may remain undetected and conclusions on changes in conductance, such as during desensitization, may be mistaken. In contrast, an alternative experimental approach, using rapid voltage ramps, enable I-V relations that much better reflect the properties of the studied ion channels.

  • 21.
    Yelhekar, Tushar
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Kuznetsova, Tatiana
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Malinina, Evgenya
    Ponimaskin, Evgeni
    Dityatev, Alexander
    Druzin, Michael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Johansson, Staffan
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Extracellular Matrix Regulates Neuronal Chloride Concentration via K+-Cl--cotransporter 2Manuscript (preprint) (Other academic)
1 - 21 of 21
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