title: Ultrastructural analysis of the serotonin hyperinnervation in adult rat neostriatum following neonatal dopamine denervation with 6-hydroxydopamine.
abstract: Serotonin (5-HT) immunocytochemistry was used at the electron microscopic level to characterize the ultrastructural features of 5-HT axon terminals (varicosities) hyperinnervating the neostriatum of adult rats, 3 months after a neonatal destruction of the nigrostriatal dopamine system by intraventricular 6-hydroxydopamine. 5-HT-immunostained terminals from the anterior half of the hyperinnervated neostriatum were examined in single thin sections, and compared to their counterparts in vehicle-injected controls with respect to shape, size, organelle content, presence of a synaptic membrane differentiation and composition of the microenvironment. The intrinsic and relational features of the 5-HT-immunostained varicosities were essentially the same in 5-HT-hyperinnervated and control tissue. In particular, the frequency with which these varicosities made synaptic contacts was similarly low in both conditions (6-8% for whole varicosities), as already described in normal adult rat neostriatum. The distributional frequency of elements juxtaposed to the 5-HT-immunostained varicosities was also comparable in control and 5-HT-hyperinnervated tissue. However, in both conditions, there were much fewer dendritic spines in the microenvironment of 5-HT varicosities than around unlabeled terminals randomly selected from the same thin sections. This difference seemed entirely due to the numerous axo-spinous synaptic contacts made by the randomly selected, unlabeled varicosities. Together with recent observations on the 5-HT-hyperinnervation of adult rat hippocampus after grafts of fetal neurons, these data lead to the suggestion that mostly non-junctional neostriatal 5-HT terminals are not committed to a specific intratissular microenvironment. This might in part explain why they grow in excess when reinnervating adult tissue after a lesion or a graft.
authors.affiliation: Départment de physiologie, Faculté de médecine, Université de Montréal, Qué, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Descarries
authors.forename: J J
authors.initials: JJ
authors.lastname: Soghomonian
authors.forename: S
authors.initials: S
authors.lastname: Garcia
authors.forename: G
authors.initials: G
authors.lastname: Doucet
authors.forename: J P
authors.initials: JP
authors.lastname: Bruno
mesh_terms: D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D003342:Corpus Striatum / Q000254:growth & development / Q000378:metabolism* / Q000648:ultrastructure; D003714:Denervation; D004298:Dopamine / Q000502:physiology*; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D016627:Oxidopamine / Q000633:toxicity; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D012701:Serotonin / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D012701:Serotonin; D016627:Oxidopamine; D004298:Dopamine