NADPH-D (DIHYDRONICOTINAMIDE ADENINE-DINUCLEOTIDE PHOSPHATE DIAPHORASE) ACTIVITY IN GENICULO-TECTAL NEURONS OF THE RAT

Retrograde transport of horseradish peroxidase (HRP) and dihydronicoti namide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemis try were used in order to determine whether NADPH-d-positive neurons o f the ventral lateral geniculate nucleus (LGv) project to the superior colliculus (SC). Our results show that intensely stained NADPH-d neur ons are restricted to the lateral half of the magnocellular division o f LGv (LGv-MC), where they represent 50% of the total number of retrog radely labeled neurons. These findings indicate: (1) that LGv provides an important NADPH-d input to SC, and (2) that within the population of geniculo-tectal neurons, which constitute a morphologically well de fined neuronal type, there are two different subclasses, one being NAD PH-d positive and the other NADPH-d negative.