NADPH-d (dihydronicotinamide adenine dinucleotide phosphate diaphorase) activity in geniculo-tectal neurons of the rat

Retrograde transport of horseradish peroxidase (HRP) and dihydronicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry were used in order to determine whether NADPH-d-positive neurons of the ventral lateral geniculate nucleus (LGv) project to the superior colliculus (SC). Our results show that intensely stained NADPH-d neurons are restricted to the lateral half of the magnocellular division of LGv (LGv-MC), where they represent 50% of the total number of retrogradely 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 defined neuronal type, there are two different subclasses, one being NADPH-d positive and the other NADPH-d negative.