A COMPARISON BETWEEN THE ADULT-RAT AND NEONATE RAT OF THE ARCHITECTURE OF SYMPATHETIC PREGANGLIONIC NEURONS PROJECTING TO THE SUPERIOR CERVICAL-GANGLION, STELLATE GANGLION AND ADRENAL-MEDULLA

Sympathetic preganglionic neurones (SPN) projecting to the superior ce rvical ganglion (SCG) and adrenal medulla (AM) in the neonate(< 14 day s) and SCG, stellate ganglion (SG) and AM in the adult rat (> 3 months ) were retrogradely labelled with cholera B horseradish peroxidase (CB HRP). Labelled neurones were found in 4 four distinct nuclei: the nucl eus intermediolateralis thoracolumbalis pars principalis (ILp), a nucl eus equivalent to the intemediolateral cell column (IML); the nucleus intermediolateralis thoracolumbalis pars funicularis (ILf); the nucleu s intercalatus spinalis (IC) and the nucleus intercalatus pars paraepe ndymatis (ICpe) or central autonomic area (CA). These were represented to a similar extent in both neonate and adult. Neonate and adult SCG, SG and AM-SPN had a similar segmental distribution cervical 8 (C8) to thoracic 5 (T5) for SCG-SPN and thoracic 3 (T3) to thoracic (T13) fdr AM-SPN whereas adult SG-SPN were distributed over segments C8 to T9. Most labelled neurones (70%) were located in the ILp with one segment containing the highest proportion of SPN. Three morphologically distin ct neurones were evident. Fusiform and roundbodied were the most commo n. Fusiform somata of the ILp were orientated both mediolaterally and rostrocaudally in the neonate but only rostrocaudally in the adult. De ndrites of the SPN in the adult and neonate extended in a dense rostro caudal band along the ILp, more diffusely into the white matter of the ILf and in bundles medially towards the central canal (CC). The neona te showed some significant differences. In the ILp, the cell bodies we re less tightly packed into a narrow band and into clusters and the de ndrites were more diffuse. It was concluded that at 12 days postnatall y the organisation of the sympathetic nuclei had still nor reached the adult form. However, there is no extensive realignment of dendrites i n the adult so the ILp remains an 'open' nucleus like the neonate.