Adenosine A₁ receptor‐mediated presynaptic inhibition at the calyx of Held of immature rats

Abstract

METHODS Preparation and solutionsAll experimental procedures were performed in accordance with the animal welfare guidelines of the Physiological Society of Japan. Wistar rats from P5 to P21 were decapitated under halothane anaesthesia (Forsythe & Barnes-Davies, 1993). Brainstem slices (200-400 mm thick) were cut using a tissue slicer (Leica, VT1000S). The solution for cutting tissue contained (mM); 250 sucrose, 2.5 KCl, 26 NaHCO 3 , 10 glucose, 1.25 NaH 2 PO 4 , 1 CaCl 2 , 4 MgCl 2 , 0.3 myo-inositol, 2 sodium pyruvate and 0.5 ascorbic acid (pH 7.4 when bubbled with 5 % CO 2 and 95 % O 2 ). Slices were incubated for 30 min at 35-37°C and maintained thereafter at room temperature in artificial cerebrospinal fluid (aCSF) bubbled with 95 % O 2 and 5 % CO 2 . The standard aCSF for superfusion contained (mM): 120 NaCl, 2.5 KCl, 26 NaHCO 3 , 1.25 NaH 2 PO 4 , 2 CaCl 2 , 1 MgCl 2, 10 D-glucose, 3 myo-inositol, 2 sodium pyruvate, and 0.5 ascorbate; pH was adjusted to 7.4 when saturated with 5 % CO 2 and 95 % O 2 . The superfusate routinely contained bicuculline methiodide (10 mM, Sigma) and strychnine hydrochloride (0.5 mM, Sigma) to block inhibitory synaptic responses. The postsynaptic pipette solution contained (mM): 110 CsF, 30 CsCl, 10 Hepes, 5 EGTA and 1 MgCl 2 (pH 7.4, adjusted with CsOH), and also N-(2,6-diethylphenylcarbamoylmethyl)-triethyl-ammonium chloride (QX-314; 5 mM) to block action potential generation. For recording presynaptic Ca 2+ currents, TTX (1 mM) and tetraethylammonium (TEA) chloride (10 mM) were added to the aCSF, and the pipette solution contained (mM): CsCl 110, Hepes 40, TEA-Cl 10, EGTA 0.5, MgCl 2 1, sodium phosphocreatinine 12, ATP-Mg 2 and GTP 0.5._For recording presynaptic K + currents, TTX (1 mM) was added to the aCSF, and the pipette solution contained (mM): potassium gluconate 97.5, KCl 32.5, Hepes 10, EGTA 5, MgCl 2 1, sodium phosphocreatinine 12, ATP-Mg 2 and GTP 0.5.

Adenosine A1 receptors decrease thalamic excitation of inhibitory and excitatory neurons in the barrel cortex

“…The application of different concentrations of adenosine indicated that the reduction of thalamocortical EPSCs was dose-dependent with an EC 50 of 11 µM (Fig. 3B), consistent with the EC 50 of adenosine-mediated inhibition of EPSCs at hippocampal, calyx of Held, and hypothalamic synapses (Lupica et al, 1992, Oliet and Poulain, 1999, Kimura et al, 2003. …”

A population of immature cerebellar parallel fibre synapses are insensitive to adenosine but are inhibited by hypoxia

“…Usually 100 M adenosine would activate the majority of synaptic A 1 receptors and thus be close to the top of the concentration-response curve (Takahashi et al 1995;Kimura et al 2003). However, at synapses were 100 M adenosine had little effect on fEPSP amplitude, the concentration-response curve may be shifted to the right.…”

Inhibitory Control at a Synaptic Relay

“…For example, presynaptic of glycine and GABA A receptors facilitate release Trussell, 2001, 2002), whereas metabotropic GABA , glutamate (Takahashi et al, 1996), adenosine (Kimura et al, 2003), and noradrenaline receptors ) suppress release. By themselves, modulatory systems in the MNTB may have little impact on the reliability or timing of calyceal transmission.…”

“…These results suggest that excitatory transmission in MNTB may be subject to inhibition, strong enough to offset the massive excitatory input from the calyx. However, this proposition raises a dilemma, because all of the known inhibitory synaptic mechanisms seem ill-suited for overcoming the high safety factor of calyceal transmission (Von Gersdorff et al, 1997;Iwasaki and Takahashi, 2001;Kimura et al, 2003;Leao et al, 2003).…”