In vitro relation between preganglionic sympathetic stimulation and activity of cutaneous glands in the bullfrog

1. Activation of cutaneous glands was studied by measuring changes in transepithelial potentiation (TEP) after pre- and postganglionic sympathetic stimulation in the bullfrog, Rana catesbeiana. 2. In normal Ringer solution, TEP was 20-90 mV with the basolateral (inside) surface positive. Single shocks to the preganglionic B pathway decreased TEP by up to 3 mV. Cutaneous depolarizations had a latency of 1.2 s, a rise time of 2.5 s, and decayed with an exponential time constant of 15 s. Similar depolarizations were evoked by postganglionic stimulation. 3. Cutaneous depolarizations summed during repetitive stimulation and > 0.05 Hz. For trains of three stimuli, peak amplitude increased with frequency and saturated at 2 Hz. In some preparations, longer trains evoked polyphasic changes in TEP. Preganglionically evoked cutaneous responses were abolished by (+)-tubocurarine. Postganglionically evoked cutaneous depolarizations were antagonized by phentolamine, but not propranolol. 4. Repetitive preganglionic stimulation of the C pathway (> 100 at 20 Hz) evoked little change in TEP and did not modulate depolarizations evoked through the B pathway. In nicotine, peptidergic cotransmission was enhanced in the ganglia, and repetitive C pathway stimulation evoked cutaneous depolarizations whose time course mirrored that of the postganglionic peptidergic after-discharge. The after-discharge and associated cutaneous depolarization were blocked by a luteinizing hormone-releasing hormone antagonist. 5. The results show cutaneous glands are selectively innervated by B neurones and respond to low levels of neural activity. Asynchronous postganglionic firing mediated by peptidergic cotransmission can provide a basis for heterosynaptic interactions between the B and C pathways.