A MICROELECTROPHORETIC DELIVERY OF HORSERADISH PEROXIDASE FOR DEMONSTRATING THE AFFERENT PROJECTION TO NUCLEUS RAPHE MAGNUS / 解剖学报

ABSTRACT

20 adult healthy rats were used for microelectropheretic delivery of horseradish peroxidase (HRP). The diameter of the tip of the glass electrode was around 20～50?. It was inserted into nucleus raphe magnus, 20% HRP was delivered microelectrophoretically(5 ?A for 30 min; 10 ?A for 10 min). In eight rats the microelectrode was withdrawn immediately after the delivery and in the rest it was removed 10～20 minutes after delivery. Afterward the animals were allowed to survive for 40 hrs before decapitation, except 2 for 20 and 2 for 60 hrs. The brains were dissected out for cryostat sections and DAB reaction for peroxidase.The tip of the electrode was located in the nucleus raphe magnus, at the level of nucleus facialis. The diameter of the brain tissues occupied by HRP at the points of microelectophoretic delivery was 0.2～0.4mm and the maximum reached 0.6～0.7mm. The exogenous HRP granules were not visible in the cases with electrodes withdrawn immeditely after delivery and in the survivors of 60 hrs. In most cases the electrodes were left inside for more than 10 minutes after the delivery. The exogenous HRP granules were large, coarse, brown, steroscopic and distributed evenly in the perikaryon of some neurons in several levels of the brain. Those in the axon and dentrite were distributed just like strings of pearls. There were much more neurons with exogenous HRP positive granules dispersed in the reticular formation of the medula oblongata, most of them were polydendritic. Small and fusiformed HRP-positive cells are observed occasionally in the gray substance of subventriculum, reticular formation pontis and ventrolateral side of locus coeruleus. Weaker reactions were found in a few cells in the periaquaductous gray substance of the midbrain, nucleus raphe centro-superior, substantia nigra pars compacta and in the area around the nucleus supraopticus. Besides no HRP-positive cells were discovered in thalamus and subcortex structure.There were two types of cells with HRP positive granules around some blood vessels in reticular formation and subventricular gray substance One was a small protoplasmic astrocyte with broad cytoplasma, small nucleus, and thick, short and irregular processes and another kind was polydendritic neurons filling with brown positive granules in perikarya and cytoprocesses, in the latter, the HRP positive granules were arranged as strips of pearls.