A COMPARATIVE-STUDY BY RETROGRADE NEURONAL TRACING AND SUBSTANCE-P IMMUNOHISTOCHEMISTRY OF SYMPATHETIC PREGANGLIONIC NEURONS IN SPONTANEOUSLY HYPERTENSIVE RATS AND WISTAR-KYOTO RATS

A comparative morphological study of the sympathetic preganglionic neurons that innervate the superior cervical ganglion (SPN-scg) was made in spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) rats. The cytoarchitectonics and dendroarchitectonics of the SPN-scg were studied following retrograde transport of choleragen subunit B horseradish peroxidase conjugate (CB-HRP) and Fluorogold. Significant differences were observed in the maximum and minimum diameters of neurons of the nucleus intermediolateralis pars principalis (ILp) and in the minimum diameter of neurons in the nucleus intermediolateralis pars funicularis (ILf) between SHR and WKY rats (P < 0.01). These diameters were decreased in neurons of SHR. The distribution patterns of dendrites of SPN-scg also showed differences between SHR and WKY rats. The dendritic distribution patterns showed the following changes in SH rats: (1) the mediolaterally oriented dendrites were reduced in number, (2) the ladder-like configuration of the medially oriented grey-matter dendrites was less prominent, (3) the medially oriented dendrites formed a triangular or dome-like cofiguration, and (4) the white matter dendritic plexuses and subependymal plexuses were reduced. Similar differences between SHR and WKY rats were also observed in our immunohistochemical study of substance P-like fibres. In addition, the SP study has also shown a close association of SP fibres with the central canal both in SHR and WKY rats; some of the SP fibres penetrated the ependymal lining to run longitudinally up or down the central canal. This finding suggests the presence of substance P-positive neurons contacting the cerebrospinal fluid.