QUANTIFICATION OF THE SEROTONIN HYPERINNERVATION IN ADULT-RAT NEOSTRIATUM AFTER NEONATAL 6-HYDROXYDOPAMINE LESION OF NIGRAL DOPAMINE NEURONS

Light microscope autoradiography after uptake and storage of tritiated serotonin (5-HT) in brain slices was used to count 5-HT axon terminal s (varicosities) in the 5-HT-hyperinnervated neostriatum of adult rats subjected to neonatal 6-hydroxydopamine treatment and age-matched, no rmal controls. After correction for incomplete autoradiographic exposu re and for section thickness, the results were expressed in millions o f varicosities per mm(3) of tissue. Control values ranged from 4.8 in the rostral to 6.3 in the caudal neostriatum (5.8 at intermediate leve l), for an average of 5.6. The corresponding values in 5-HT-hyperinner vated tissue ranged from 9.7 to 7.7 (8.8 at intermediate level), for a n average of 8.7 and increases of 102%, 52% and 22% above control in t he rostral, intermediate and caudal neostriatum, respectively (average increase of 55%). These data confirmed the predilection of the 5-HT h yperinnervation for the rostral neostriatum and demonstrated its prese nce in the caudal neostriatum also.