[Spatial organization of the sources of the spino-reticulo-cerebellar pathway]

Quantitative characteristics of spatial distribution of HRP-labelled neurons projecting to the medullar lateral reticular nucleus (LRN) were calculated in the cat spinal cord. Mean quantities of the labelled units in the transverse 60 micron sections were 12.55 at C2-C4, 7.77 at C5-Th1, 1.07 at Th2-Th13 and 1.60 at L1-L7. levels. Two groups of spino-reticular units can be classified according to their localization density: lateral and ventromedial. Lateral neurons have mainly (but not exclusively) uncrossed projections to the LRN while ventromedial cells have predominantly crossed projections. The relative quantity of lateral neurons decreases in rostro-caudal direction and the quantity of ventromedial ones increases. Spatial distribution of spino-reticular neurons is correlated with their functional classification; the presence of lateral group of such cells at all segmental levels is regarded as argument against differentiation of specialized "ipsilateral forelimb tract." Functional organization of the spino-reticular system is compared with the organization of propriospinal intersegmental cell populations considering that a certain part of intersegmental units relaying activity of main cerebral descending systems send axon collaterals to the LRN.