NEONATAL ADMINISTRATION OF THE NEUROTOXIN 5,7-DIHYDROXYTRYPTAMINE RESULTS IN SYNAPTIC REORGANIZATION IN THE SUPERFICIAL GRAY LAYER OF THE HAMSTERS SUPERIOR COLLICULUS

Neonatal subcutaneous administration of the neurotoxin 5,7-dihydroxytr yptamine (5,7-DHT) to hamsters results in a marked depletion of seroto nin (5-HT) in cortex and an increase in the concentration of this amin e in the superior colliculus (SC). To determine whether this increase was associated with an alteration in the synaptic organization of 5-HT -containing axons in the superficial gray layer of the SC, immunocytoc hemistry was combined with electron microscopy. In normal adult hamste rs, only 4.0% of 500 5-HT-immunoreactive profiles make synaptic contac ts in the superficial gray layer of the hamster's SC. In 5,7-DHT-treat ed animals, examination of 400 individual profiles indicated that 25.5 % of 5-HT-positive profiles made synaptic contacts (P < 0.05). Given t he recently demonstrated effect of 5-HT on retinotectal transmission i n this species, the present results suggest that the functional organi zation of the SC may also be markedly altered in animals that sustain neonatal 5,7-DHT administration.