Intrinsic organization and monoaminergic innervation of the suprachiasmatic nucleus transplanted to adult rats. A light- and electron-microscopic study.
Light- and electron-microscopic immunocytochemistry was used to investigate grafts of foetal hypothalamic tissue implanted close to the site of the suprachiasmatic nucleus in adult rats with bilateral surgical ablation of this nucleus. The transplants contained vasoactive intestinal peptide and vasopressin cell clusters, which have previously been shown to characterize functional suprachiasmatic nucleus grafts. Vasoactive intestinal peptide and vasopressin neurons presented synaptic features that have not been described in the native suprachiasmatic nucleus. More specifically, their terminals within the graft were involved in 'double' synapses with separate unlabelled dendrites. Moreover, in dually stained sections, an unexpected synaptic investment of vasoactive intestinal peptide neurons by vasopressin endings was detected, which revealed reversed vasoactive intestinal peptide/vasopressin interactions compared to those described in the native nucleus. These observations could reflect some immature features of the grafted neurons. Ultrastructural relationships of monoaminergic fibres arising from host and/or intragraft neurons were also examined. Within the engrafted suprachiasmatic nucleus, tyrosine hydroxylase-labelled fibres, which probably belonged to cografted dopaminergic neurons, showed normal patterns of distribution and synaptic connections, with no preferential relationships with vasoactive intestinal peptide or vasopressin neurons. Serotoninergic axons arborized within transplants but, in agreement with previous data showing an inhibitory influence of the suprachiasmatic nucleus on ingrowing serotoninergic fibres, they had no predilection for the area corresponding to that nucleus. In spite of their relative scarcity, serotoninergic fibres within the engrafted suprachiasmatic nucleus showed an almost normal synaptic incidence, but synapses were not predominantly shared with the vasoactive intestinal peptide neurons, known to be their major targets in the native nucleus. This may contribute not only to the failure of functional grafts to synchronize with environmental conditions, but also to the inability of transplants to restore hormonal rhythms such as estrous cyclicity.
Jacomy
H
H
Laboratoire de Neuroendocrinologie Expérimentale, INSERM, U297, Institut Fédératif Jean-Roche, Faculté de Médecine, Marseille, France.
Bosler
O
O
D000818:Animals; D001127:Arginine Vasopressin / Q000032:analysis; D016380:Brain Tissue Transplantation; D002552:Cerebral Ventricles; D005260:Female; D016332:Fetal Tissue Transplantation; D008854:Microscopy, Electron; D009412:Nerve Fibers / Q000737:chemistry / Q000648:ultrastructure; D009474:Neurons / Q000737:chemistry / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000032:analysis; D013493:Suprachiasmatic Nucleus / Q000737:chemistry / Q000293:injuries / Q000637:transplantation* / Q000648:ultrastructure; D013569:Synapses / Q000648:ultrastructure; D016042:Transplantation, Heterotopic; D014660:Vasoactive Intestinal Peptide / Q000032:analysis
D001127:Arginine Vasopressin; D012701:Serotonin; D014660:Vasoactive Intestinal Peptide