Striatal grafts in rats with unilateral neostriatal lesions—I. Ultrastructural evidence of afferent synaptic inputs from the host nigrostriatal pathway

Abstract

Tyrosine hydroxylase immunocytochemistry, in combination with Golgi impregnation, has been used to study the dopaminergic afferent input to striatal suspension grafts implanted into the previously ibotenic acid-lesioned striatum in adult recipient rats. The rats were perfused for combined light- and electron microscopy at 10–11 months after transplantation, at the end of a series of behavioural experiments and a study of in vivo GABA release, reported in the two accompanying papers. A tyrosine hydroxylase-positive fibre network occurred within the grafts in all eight specimens analysed. The tyrosine hydroxylase-positive fibres had a distinct “patchy” distribution, thoughout the graft tissue, and within these patches the terminal density was similar to that of the normal intact striatum. Ultrastructurally, the tyrosine hydroxylase-positive fibres were seen to make abundant synaptic contacts with neuronal elements within the grafts. As in the normal striatum, they were all of the symmetric type and dendritic shafts and spines were the most usual postsynaptic targets. Sections from three of the grafted animals were taken for combined Golgi-impregnation and immunostaining. Only cells of the medium-sized densely spiny type were impregnated in this material. Six of them, which had portions extending into the immunostained neuropil, were drawn using a camera lucida and processed for electron microscopy. Tyrosine hydroxylase-positive boutons were seen to make symmetrical synaptic contacts onto the shafts and spines of the impregnated dendrites, and in one case also with the perikaryon. The results indicate that the medium-sized densely spiny neuron type (which is a predominant target for the dopaminergic afferents in the normal striatum) is abundant in the grafted tissue, and that these neurons represent a synaptic target also for the tyrosine hydroxylase-positive innervation of the striatal grafts.