Innervation of sympathetic neurones in the guinea-pig thoracic chain.

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Abstract
The organization of the guinea-pig thoracic chain was investigated by studying the innervation of the stellate and 5th thoracic sympathetic ganglia with intracellular recording. These ganglia receive preganglionic innervation from different but overlapping sets of spinal cord segments: the stellate ganglion is innervated by preganglionic axons from spinal segments more rostral than those supplying the 5th thoracic ganglion, but somewhat more caudal than those innervating the superior cervical ganglion. Individual thoracic ganglion cells are innervated by only some of the spinal segments that supply each ganglion as a whole. The subset of spinal segments innervating a ganglion cell is contiguous; 1 of these segments provides the strongest innervation, with progressively weaker innervation arising from spinal levels adjacent to the dominant one. This selective pattern of innervation is similar to that in the superior cervical ganglion (Nja and Purves, 1977). Preganglionic axons frequently innervate neurons in > 1 ganglion. Although neurons innervated by the same spinal cord segments are found in both the stellate and the 5th thoracic ganglion, and in the superior cervical, the number of ganglion cells receiving innervation from particular spinal segments is different in each ganglion. Neurons dominated by the same segment but located in different ganglia receive somewhat different average innervation from adjacent segments as a function of the ganglion in which they reside. Neurons in the thoracic chain ganglia, as those in the superior cervical ganglion, are selectively innervated by particular spinal cord segments. The different average innervation of sympathetic ganglia possibly reflects at least 2 related factors: the selective qualities of their constituent neurons, and the availability of different preganglionic axons to each ganglion.