The effects of anticholinesterases on synaptic transmission through nicotinic and muscarinic receptors in rat sympathetic ganglia in vivo.

1 Stimulation of the entire spinal sympathetic outflow at supramaximal voltage and 25-100 Hz, in the chlorisondamine-treated, pithed, adrenalectomized rat produced a delayed pressor response (late pressor response; LPR).2 The LPR was abolished by phenoxybenzamine, bretylium or a small dose of atropine (25-50 mug/kg), suggesting the involvement of ganglionic muscarinic receptors.3 In the presence of atropine at a dose level (15 mug/kg) which did not influence the LPR, the anticholinesterases physostigmine, neostigmine and Ro 02-0683 but not BW 284C51 markedly enhanced and prolonged the LPR, whereas all of them reduced the pressor responses to AHR-602.4 After blockade of the ganglionic muscarinic receptors with a large dose of atropine (250 mug/kg) the four anticholinesterases did not influence responses to DMPP or noradrenaline and only slightly enhanced responses to preganglionic nerve stimulation at 6 Hz in the absence of chlorisondamine.5 It is concluded that inhibition of butyrylcholinesterase accounts for the enhancement and prolongation of the LPR by anticholinesterases.