The effects of electrical stimulation on sprouting after partial denervation of guinea-pig sympathetic ganglion cells.

1. The effects of electrical stimulation of presynaptic and post-synaptic cells on sprouting after partial denervation were examined in the guinea-pig superior cervical ganglion with intracellular recording. The partial denervation reduced the mean number of preganglionic axons innervating each ganglion cell from about eleven to about two (Maehlen & Njå, 1981). 2. One week after partial denervation alone, the number of residual preganglionic axons innervating each superior cervical ganglion cell was increased by about 30%. This means that the number of ganglion cells contacted by each residual preganglionic axon was increased by the same amount, which represents an early stage of sprouting. 3. Preganglionic stimulation for 1 hr immediately after the partial denervation (with 100 pulses at 20 Hz every 25 sec) increased the rate of sprouting. Thus 1 week after partial denervation and preganglionic stimulation the number of residual preganglionic axons innervating each ganglion cell was increased by about 70%. Preganglionic stimulation had no similar effect on the innervation of normal ganglia. 4. The acceleration of sprouting caused by preganglionic stimulation was abolished by blocking ganglionic transmission with hexamethonium (30--60 mg kg-1 hr-1 I.V.) during the stimulation. 5. Furthermore, the rate of sprouting of residual preganglionic axons was increased by electrical stimulation of the ganglion cells alone. 6. These results show that after partial denervation of the superior cervical ganglion, a period of impulse activity in ganglion cells enhances their subsequent ability to receive innervation from sprouts arising from residual preganglionic axons.