Pharmacological studies of a novel dopamine-sensitive receptor mediating burst-firing inhibition of neurosecretory cell R 15 in Aplysia californica.
Burst-firing activity of neuron R 15 in the abdominal ganglion of Aplysia californica is inhibited by dopamine (DA) (50-500 microM). By using voltage clamp analysis of agonist-induced reduction of inward current and bath application of pharmacological agents, the agonist and antagonist specificity of the receptor mediating burst-firing inhibition in this cell was studied. The phenethylamine compounds DA, epinine, (-)-norepinephrine, (+)-norepinephrine, (-)-epinephrine, (+)-epinephrine and (-)-phenylephrine are active at similar concentrations. DA analogs 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene HBr and 2-amino-5,6-dihydroxy-1,2,3,4-tetrahydronaphthalene HBr are active, whereas apomorphine, piribedil, (3,4-dihydroxyphenylamino)-2-imidazoline HCl and RU 24213 are inactive. DA-mediated inhibition of burst-firing is not antagonized by neuroleptics or certain adrenergic antagonists. Antagonism is seen with dihydroergotamine, lysergic acid diethylamide, ergonovine and other ergot alkaloids and the complex nature of this antagonism is discussed in detail. The specificity of this receptor for agonists and antagonists is compared to DA and adrenergic receptors from mammalian and other invertebrate tissues. We conclude that this DA-sensitive receptor mediating burst-firing inhibition of cell R 15 in Aplysia californica is very different from DA and adrenergic receptors.
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