In cultured or acutely dissociated cells, Gi/o class G proteins are coupled to the inhibition of Ca2+ currents by D2-like receptors (Lledo 1992; Brown & Seabrook, 1995; Yan 1997)
November 20, 2021
In cultured or acutely dissociated cells, Gi/o class G proteins are coupled to the inhibition of Ca2+ currents by D2-like receptors (Lledo 1992; Brown & Seabrook, 1995; Yan 1997). in many studies that the balance between DA and ACh is essential for motor control, and disruption of this balance could lead to the dysfunction observed in Parkinson’s disease (Lehmann & Langer, 1983; Calabresi 2000; Kaneko 2000). Striatal cholinergic neurones express both D1-like and D2-like DA receptors (Kawaguchi 1995; Bergson 1995; Yan & Surmeier, 1997). Several studies have reported DA receptor-mediated modulation of voltage- or ligand-gated ion channels on these neurones. For example, activation of postsynaptic D1-like receptors excites rat striatal cholinergic neurones in slices by suppressing the resting K+ conductance or opening a non-selective cation conductance (Aosaki 1998), whereas activation of D2-like receptors in dissociated striatal cholinergic neurones reduces N-type Ca2+ currents (Yan 1997). As for the ligand-gated channels, various different GABAA receptor subunits are coexpressed in acutely dissociated striatal cholinergic neurones and their Zn2+-sensitive component is reported to be enhanced via D1-like (D5) receptors (Yan & Surmeier, 1997). However, it is not yet clear if the same receptor subtype operates at GABAergic synapses derived predominantly from striatal medium spiny neurones (Bolam 1986; Martone 1992; Bennett & Wilson, 1998, 1999). Compared to the postsynaptic DA receptor actions, little information has been available on the modulation of synaptic transmission onto striatal cholinergic neurones. Recently, using the conventional microelectrode recording, inhibition of GABAA receptor-mediated postsynaptic potentials via D2-like receptors was reported in striatal cholinergic neurones (Pisani 2000). However, the detailed mechanism underlying the DA-induced modulation of GABAergic transmission onto these neurones still remains to be elucidated. The aim of the present study was to investigate this mechanism by whole-cell patch-clamp recording in a thin-slice preparation of the rat brain. This technique allows resolution of quantal synaptic responses recorded as miniature synaptic currents, whose frequency and amplitude reflect pre- and postsynaptic changes, respectively. We have made use of this analysis to identify the site of action of DA and we also identified the specific Ca2+ channel subtype and the class of G proteins involved in the modulation of GABAergic transmission by DA. Preliminary data from the present study have been published in an abstract form (Momiyama & Koga, 1999). METHODS Slice preparation All experiments were carried out according to the Guiding Principles for the Care and Use of Animals in the Field of Physiological Sciences of Physiological Society of Japan MAK-683 (1998). Standard artificial cerebrospinal fluid (aCSF) had the following composition (mm): NaCl, 124; MAK-683 KCl, 3; CaCl2, 2.4; MgCl2, 1.2; NaH2PO4, 1; NaHCO3, 26; d-glucose, 10; pH 7.4 adjusted by 95 % O2-5 % CO2. Neonatal rats (12-20 days old) were decapitated under deep ether anaesthesia, and coronal slices (200 m) containing the striatum were cut using a microslicer (DTK-1000, DOSAKA, Kyoto, Japan) in ice-cold oxygenated low-Ca2+ (0.5 mm), high-Mg2+ (6 mm) aCSF. The slices were then transferred to a holding chamber containing standard aCSF solution. Slices were incubated in the holding chamber maintained at room temperature (21-25 C) for at least 1 h before recording. Whole-cell recording and data analysis For recording, a slice was transferred to the recording chamber, held submerged, and superfused continually with the aCSF (bubbled LUCT with 95 % O2-5 % CO2) at a rate of 4-5 ml min?1. Patch electrodes were drawn from standard-walled borosilicate glass capillaries (1.5 mm outer diameter; Clark Electromedical, Reading, UK) and experienced resistances of 2.5-6 M when MAK-683 filled with a caesium chloride-based internal answer of the following composition (mm): CsCl, 140; NaCl, 9; Cs-EGTA, 1; Cs-Hepes, 10; Mg-ATP, 2 (pH modified with 1 m CsOH). Whole-cell recordings were made using a patch-clamp amplifier (Axopatch 1D or Axopatch 200B, Axon Devices, Foster City, CA, USA). The cell capacitance and the series resistance were measured from your amplifier. The access resistance was monitored by measuring capacitative transients acquired in response to a hyperpolarizing voltage step (5 mV, 25 ms) from a holding potential of -60 mV. No correction was made for the liquid junction potential (determined to be 5.0 mV by pCLAMP7 software, Axon Devices). To evoke synaptic currents, voltage pulses (0.2-0.4 ms in duration) of suprathreshold intensity were delivered at 0.2 Hz extracellularly via a stimulating electrode filled with 1 m NaCl placed MAK-683 within a 50-120 m radius (mean range 77 2.0 m, = 115) of the recorded neurone. The position of the revitalizing electrode was assorted until a stable response was evoked in the recorded cell. All the inhibitory postsynaptic currents (IPSCs).