| Abstrakt: |
Abstract: Cultured neurons from the thoracolumbar sympathetic chain of newborn mice are known to possess release-inhibiting α2-autoreceptors. The present study was carried out in a search for release-modulating heteroreceptors on these neurons. Primary cultures were preincubated with [3H]noradrenaline and then superfused and stimulated by single pulses, trains of 8 pulses at 100 Hz, or trains of 36 pulses at 3 Hz. The cholinergic agonist carbachol reduced the evoked overflow of tritium. Experiments with antagonists indicated that the inhibition was mediated by M2 muscarinic receptors. The cannabinoid agonist WIN 55,212-2 reduced the evoked overflow of tritium through CB1 receptors. Prostaglandin E2, sulprostone, and somatostatin also caused presynaptic inhibition. The inhibitory effects of carbachol, WIN 55,212-2, prostaglandin E2, and somatostatin were abolished (at the highest concentration of WIN 55,212-2 almost abolished) by pretreatment of the cultures with pertussis toxin (250 ng/ml). Several drugs, including the β2-adrenoceptor agonist salbutamol, opioid receptor agonists, neuropeptide Y, angiotensin II, and bradykinin, failed to change the evoked overflow of tritium. These results demonstrate a distinct pattern of presynaptic inhibitory heteroreceptors, all coupled to pertussis toxin-sensitive G proteins. The lack of operation of several presynaptic receptors known to exist in adult mice in situ may be due to the age of the (newborn) donor animals or to the culture conditions. [ABSTRACT FROM AUTHOR] |
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