Abstract
In Experiment 1, it was shown that the lateral horn at the upper thoracic segments was partly separated from the intermediate grey matter by the intermediolateral fasciculus. This was not observed in the rat or the cat. In Experiment 2, it was found that sympathetic preganglionic neurons (SPNs) in segments C8-T10 project to the inferior cervical ganglion. Extensive dendritic filling of SPNs in IML showed the dendrites oriented rostrocaudally within IML as well as medially, towards the central canal. In Experiment 3, it was observed that SPNs in segments T3-T12 innervated the adrenal medulla ipsilaterally. Essentially the same pattern of dendritic orientation as in experiment 2 was found, except that dendritic processes were also found contralaterally. In Experiment 4, the distribution of serotoninergic and noradrenergic fibers was determined. A rostrocaudal difference in the innervation of IML was observed for both transmitters. Serotonin and noradrenaline fibers surrounded both retrogradely and non-retrogradely labeled neurons. There was a close correspondence between the patterns of dendritic of SPNs in IML and that of both serotonin and noradrenaline fibers, suggesting that these neurotransmitters may be contacting the dendritic trees of SPNs in IML and other subnuclei.