Currents evoked by GABA and glycine in acutely dissociated neurons from the rat medial preoptic nucleus

Astra Pain Control AB, Novum Unit, Huddinge, Sweden.
Brain Research (Impact Factor: 2.84). 11/1997; 770(1-2):256-60. DOI: 10.1016/S0006-8993(97)00857-3
Source: PubMed


The responses of acutely dissociated medial preoptic neurons to application of GABA, and glycine were studied using the perforated-patch whole-cell recording technique under voltage-clamp conditions. GABA, at a concentration of 1 mM, evoked outward currents in all cells (n = 33) when studied at potentials positive to -80 mV. The I-V relation was roughly linear. The currents evoked by GABA were partially blocked by 25-75 microM picrotoxin and were also partially or completely blocked by 100-200 microM bicuculline. Glycine, at a concentration of 1 mM, did also evoke outward currents in all cells (n = 12) when studied at potentials positive to -75 mV. The I-V relation was roughly linear. The currents evoked by glycine were largely blocked by 1 microM strychnine. In conclusion, the present work demonstrates that neurons from the medial preoptic nucleus of rat directly respond to the inhibitory transmitters GABA and glycine with currents that can be attributed to GABAA receptors and glycine receptors respectively.

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    • "A first series of experiments was performed with amphotericin B as the perforating substance. In agreement with our previous report (Karlsson et al., 1997a), all MPN neurons tested (n = 114) responded to application of GABA as well as to glycine (Fig. 2 A). The concentration–response curves show apparent EC 50 values of 16 and 104 µM, respectively (Fig. 2 A, bottom). "
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    ABSTRACT: 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 GABA(A) 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 GABA(A) and glycine receptors is needed.
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    ABSTRACT: 1. Voltage-dependent Ca2+ channels triggering GABA release onto neurons from the medial preoptic nucleus of rat were investigated. Acutely dissociated neurons with adherent functional synaptic terminals were investigated by tight-seal whole-cell recordings from the postsynaptic cells. 2. Spontaneous current events similar to miniature postsynaptic currents were recorded. They were blocked by bicuculline (100 microM), showed a roughly unimodal amplitude distribution and a reversal potential consistent with a Cl- current, and were therefore attributed to GABAA receptors activated by synaptically released GABA. 3. Application of 140 mM KCl, expected to depolarize presynaptic terminals, evoked currents that were ascribed to a more massive release of GABA. The KCl-induced synaptic currents were abolished in Ca2+-free solutions and showed a roughly hyperbolic relation to external Ca2+ concentration with half-saturation at 0.15 mM. They further depended on the concentration of applied KCl in a way expected for high-threshold Ca2+ channels. 4. The KCl-evoked synaptic currents were completely blocked by 200 microM Cd2+, but only partially blocked by 200 microM Ni2+. The KCl-evoked synaptic currents were insensitive to the L-type Ca2+ channel blocker nifedipine (10 microM). However, the synaptic currents were sensitive to either 1 microM omega-conotoxin GVIA, 25 nM omega-agatoxin IVA or 1 microM omega-conotoxin MVIIC. 6. It was concluded that, in many presynaptic terminals, the Ca2+ influx triggering GABA release onto medial preoptic neurons is mainly mediated by one predominant type of high- threshold Ca2+ channel that may be either of N-, P- or Q-type. 7. It was further concluded that terminals with similar predominant channel types often were clustered on the same postsynaptic cell.
    The Journal of Physiology 03/1998; 507 ( Pt 1)(1):77-91. DOI:10.1111/j.1469-7793.1998.077bu.x · 5.04 Impact Factor
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