Brain Research, 551 (1991) 267-278 © 1991 Elsevier Science Publishers B.V. 0006-8993/91/$03.50 ADONIS 000689939116674E BRES1~74 267 Adrenal medulla and substantia nigra co-grafts in peripheral nerve: chromaffin cells survive for long time periods and prevent degeneration of nigral neurons Laurie C. Doering and Michael A. Tokiwa Department of Biomedical Sciences, Division of Anatomy, McMaster University, Hamilton, Ont. (Canada) (Accepted 8 January 1991) Key words: Rat; Peripheral nerve; Transplant; Adrenal medulla; Aging; Substantia nigra; Neurofilament; Nerve growth factor receptor A series of degenerative cytoskeletal changes characterize grafts of embryonic substantia nigra when isolated for long time periods in the peripheral nervous system. This study was designed to determine whether the adrenal medulla could modulate the cytoskeletal changes in the substantia nigra when co-grafted within peripheral nerves. The sciatic nerves of young adult rats received single transplants of embryonic day 15 substantia nigra or co-transplants of substantia nigra plus young adult adrenal medulla in close proximity. Immunocytochemistry was used to examine the expression of tyrosine hydroxylase, phosphorylated (RT97) and non-phosphorylated (SMI-32) neurofilament proteins in the grafts. Single substantia nigra grafts, examined after 1 month, consisted of numerous neurons and fibers that expressed the epitope for tyrosine hydroxylase. Normal spatial distributions of the phosphorylated and non-phosphorylated neurofilament subunits were observed. In contrast, single 1-year-old nigral transplants were shrunken, contained significantly fewer tyrosine hydroxylase positive neurons and displayed abnormal neurofilament staining patterns including swollen axons, a reduction in the density of labeled axons and perikaryal accumulation of the phosphorylated neurofilament subunit. When co-grafted with the adrenal medulla, the nigral transplants did not show the degenerative cytoskeletal aspects evident in the single 1-year-old grafts. The loss of neurons was prevented and the neurofilament immunolabeling was indistinguishable from the young substantia nigra preparations. In addition, all the 1-year-old adrenal medulla grafts were viable within the peripheral nerves, consisting of hundreds of cells identified by immunoreactivity to tyrosine hydroxylase and the rat fl-nerve growth factor receptor (192-IgG). The experiments illustrate a strong protective effect by the adrenal medulla on neurons of the substantia nigra in the peripheral nerve environment. It is suggested that a catecholaminergic trophic source and/or neural interactions with the adrenal medulla may be important factors in the long-term survival of neurons and maintenance of normal cytoskeletal characteristics in the grafted substantia nigra neurons under these experimental circumstances. INTRODUCTION Experiments have shown that embryonic regions of the CNS survive when grafted into the peripheral nervous system (PNS) 6,39. Deprived from the normal CNS milieu and terminal interactions with appropriate regions of the neuraxis, certain studies have illustrated that the grafted neurons within the PNS gradually reveal a series of changes in the cytoskeletal framework 11'12. These alter- ations are compatible with degenerative events that are associated with aging and certain neurological disorders. Previous studies have shown that neurons in the substantia nigra (SN), when implanted into sciatic nerves, show abnormal immunoreactivity to antibodies directed against proteins including phosphorylated neurofilaments and a high-molecular-weight microtubule-associated pro- tein 12. These features, observed after 1-year survival periods, are not present in grafts examined after 1-2 months post-transplantation. The exact reasons or mech- anisms underlying the formation of these abnormal cytoskeletal characteristics are not known. The long-term objectives of this CNS-PNS model are to determine conditions that prevent the observed aberrations in the cytoskeleton by introducing selected co-grafts of CNS tissue or additional sources of neurotrophic factors into the sciatic nerves. This study was undertaken to examine the influence of target chromaffin cells on the long-term morphology and survival of dopaminergic SN neurons in the peripheral nerve environment. Morphological characteristics of the transplanted SN neurons were monitored after 1 year as single grafts or as co-grafts with the adrenal medulla (AM). In this paper, we report on a remarkable influence of the AM to prevent transplant shrinkage and maintain a significant population of neurons with tyrosine hydroxy- lase (TH) immunoreactivity in substantia nigra grafts over a l-year time span. In addition, the spatial distri- Correspondence: L.C. Doering, Division of Anatomy, Faculty of Health Sciences, HSC 1R1, McMaster University, 1200 Main Street West, Hamilton, Ontario, LSN 3Z5, Canada.