Explant cultures from adult bullfrog sympathetic ganglia can be maintained in vitro for several months and are suitable for electrophysiological recording. The cultured neurons display morphological, electrophysiological and pharmacological characteristics similar, in most respects, to those reported for acutely isolated sympathetic ganglia. Individual cells were visualized by Nomarski optics and impaled with a glass micropipette, which was used for voltage recording and current injection. The average specific membrane properties, calculated from cell dimensions and responses to current injection, were Vm = -46 mV, Rin = 27 M omega, Rm = 1665 omega cm2, tau m = 5 msec, and Cm = 3.2 microF/cm2. Bath perfusion of the cholinergic agonist muscarine depolarized most neurons with an increase in input resistance, while carbachol depolarized neurons with both increases and decreases in input resistance. GABA depolarized all neurons tested with a decreased resistance. High concentrations of catecholamines (2-5 mM) generally hyperpolarized explanted neurons, usually in association with an increased resistance. Extracellularly or intracellularly applied cyclic AMP and two other analogues produced weak and inconsistent hyperpolarizations. In contrast, perfusion or iontophoresis of most non-cyclic purine and pyrimidine nucleotides markedly depolarized most neurons in association with an increased input resistance. UTP and UDP were most potent, revealing threshold concentrations of about 10(-8) to 5 x 10(-8) M. The related nucleosides were largely ineffective. The nucleotide-evoked depolarizations were similar to the muscarine responses but were not blocked by atropine. These results suggest that the purine or pyrimidine nucleotides should be considered for a possible involvement in neurotransmission in sympathetic ganglia.