Intracellular recording from mammalian superior cervical ganglion in situ.

1. Recordings have been obtained by intracellularly placed microelectrodes from cells of the superior cervical ganglion of the rabbit. The ganglion was left in situ.2. In response to stimulation of the external carotid nerve, some cells responded with a single spike of short latency followed by a long-lasting hyperpolarization. These cells, presumably, were activated antidromically. The majority of cells, however, responded with an early spike followed by a long-lasting depolarization; superimposed on this depolarization were one or two spikes with latencies from 35 to 70 msec. Anatomical pathways responsible for this activation have been suggested.3. A variety of responses were recorded from different neurones when the preganglionic sympathetic trunk was stimulated. Many of the cells responded to maximal stimulation of the nerve with repetitive spikes. Stimuli of constant strength could elicit variable responses from a single neurone. This variability and the multiple spike response may be due to multiple pathways leading to the same cell and the possibility of the presence of internuncial neurones in the ganglion is suggested.4. Strong stimulation of the preganglionic sympathetic nerve trunk caused inhibitory effects at the ganglion cells.5. Direct stimulation of the ganglion cells through the recording microelectrode elicited only one spike even at high intensity. Thus the multiple spike response to orthodromic stimulation must have been due to a temporally dispersed afferent input.6. It is concluded that the organization of the rabbit superior cervical ganglion is more complex than has been suspected previously, and that integration as well as transmission takes place at the level of these neurones.