THE EFFECTS OF DONOR STAGE ON THE SURVIVAL AND FUNCTION OF EMBRYONIC STRIATAL GRAFTS IN THE ADULT-RAT BRAIN .2. CORRELATION BETWEEN POSITRON EMISSION TOMOGRAPHY AND REACHING BEHAVIOR

Grafts of embryonic striatal primordia are able to elicit behavioural recovery in rats which have received an excitotoxic lesion to the stri atum, and it is believed that the P zones or striatal-like tissue with in the transplants play a crucial role in these functional effects. We performed this study to compare the effects of different donor stage of embryonic tissue on both the morphology (see accompanying paper) an d function of striatal transplants. Both the medial and lateral gangli onic eminence was dissected from rat embryos of either 10 mm, 15 mm, 1 9 mm, or 23 mm crown-rump length, and implanted as a cell suspension i nto adult rats which had received an ibotenic acid lesion 10 days prio r to transplantation. After four months the animals were tested on the ''staircase task'' of skilled forelimb use. At 10-14 months rats from the groups which had received grafts from 10 mm or 15 mm donor embryo s were taken for positron emission tomography scanning in a small diam eter postiron emission tomography scanner, using ligands to the dopami ne D-1 and D-2 receptors, [C-11]SCH 23390 and [C-11]raclopride, respec tively. A lesion-alone group was also scanned with the same ligands fo r comparison. Animals which had received transplants from the 1O mm do nors showed a significant recovery with their contralateral paw on the ''staircase test''. No other groups showed recovery on this task. Sim ilarly, the animals with grafts from the youngest donors showed a sign ificant increase in D-1 and D-2 receptor binding when compared to the lesion-alone group. No increase in signal was observed with either lig and in the group which had received grafts from 15 mm donors. Success in paw reaching showed a strong correlation to both the positron emiss ion tomography signal obtained and the P zone volume of the grafts. Th ese results suggest that striatal grafts from younger donors (1O mm CR L) give greater behavioural recovery than grafts prepared from older e mbryos. This recovery is due to both the increased proportion of stria tal-like tissue within the grafts and an increase in functional D-1 an d D-2 dopamine receptors measured by positron emission tomography, i.e . a more extensive integration of the graft with the host brain. (C) 1 997 IBRO. Published by Elsevier Science Ltd.