AN ULTRASTRUCTURAL-STUDY OF THE SYMPATHETIC PREGANGLIONIC NEURONS THAT INNERVATE THE SUPERIOR CERVICAL-GANGLION IN SPONTANEOUSLY HYPERTENSIVE RATS AND WISTAR-KYOTO RATS

Comparative ultrastructural study of the sympathetic preganglionic neurons that innervated the superior cervical ganglion (SPN-scg) was made between spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto rats. After injection of choleragen subunit-B horseradish peroxidase (CB-HRP) into the superior cervical ganglion, three types of the sympathetic preganglionic neurons were identified according to their ultrastructural features. In both SHR and WKY rats, the neurons in the autonomic region of T-1-T-3 segments of the spinal cord showed a characteristic distribution pattern in which the Type I neurons were located more laterally in n. intermediolateralis pars funicularis (ILf), and n. intermediolateralis pars principalis (ILp), Type III neurons more medially in n. intercalatus spinalis (IC), n. intercalatus pars paraependymalis (ICpe) and Type II neurons in n. intermediolateralis pars principalis (Ilp) as well as in n. intercalatus spinalis (IC). Of the three types of neurons, there was not noticeable ultrastructural difference in Type II and Type III neurons between the SHR and WKY rats. Some differences, however, were observed in Type I neurons between the two animals stains. In SHR, the nucleus of Type I neurons displayed many deep indentations and a greater number of profiles of Golgi apparatus. Three types of the axon terminal were found to make synaptic contacts with the labelled Type I neurons. Some proportional changes of the different axon terminals were observed between those of SHR and WKY rats. The results of this study suggest that the suppressive effect on the activity of the sympathetic preganglionic neurons in SHR may be attenuated which would result in an unbalanced activities of some of neurotransmitters on the sympathetic preganglionic neurons thereby leading to the onset of hypertension. The increase in the number of nuclear indentations and an increased activity in the Golgi complex may reflect an increase in the synthesis of some of the neurotransmitters or neuromodulators in the sympathetic preganglionic neurons or their axon terminals. The characteristic distribution patterns of the three types of neurons suggest that, of the three types of SPN-scg, only the Type I neurons may be implicated in the regulation of the cardiovascular system.