Noradrenaline Release from Cultured Mouse Postganglionic Sympathetic Neurons

: The possible existence of α 2 ‐autoreceptors, P2‐autoreceptors, and adenosine A 1 ‐ or A 2A ‐receptors was studied in cultured thoracolumbar postganglionic sympathetic neurons from mice. The cells were preincubated with [ 3 H]noradrenaline and then superfused. The selective α 2 ‐adrenoceptor agonist UK 14,304 reduced the electrically evoked overflow of tritium. When the cultures were stimulated by trains of increasing pulse number, ranging from a single pulse to 72 pulses at 3 Hz, the concentration‐inhibition curve of UK 14,304 was shifted progressively to the right and the maximal inhibition obtainable became progressively smaller. Six α‐adrenoceptor antagonists shifted the concentration‐inhibition curve of UK 14,304 in a parallel manner to the right. Neither ATP (3‐300 μ M ), adenosine (0.01‐100 μ M ), the selective A 1 ‐receptor agonist cyclopentyladenosine (1‐1,000 n M ), nor the selective A 2A ‐receptor agonist CGS‐21680 (1‐10,000 n M ) changed the basal or the electrically evoked overflow of tritium. It is concluded that the cultured neurons possess presynaptic, release‐inhibiting α 2 ‐autoreceptors. As in intact tissues, the effectiveness of presynaptic α 2 ‐adrenergic inhibition depends on the “strength” of the releasing stimulus. The pK D values of the six antagonists against UK 14,304 indicate that the autoreceptors belong to the pharmacological α 2D and hence the genetic α 2A/D subtype of α 2 ‐adrenoceptor. Neither P2‐autoreceptors nor receptors for adenosine, the degradation product of ATP, were detected.