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  • 1
    Electronic Resource
    Electronic Resource
    Synaptic connectivity of serotonin graft efferents in the suprachiasmatic and supraoptic nuclei of the hypothalamus (1994)
    Springer
    Experimental brain research 101 (1994), S. 353-364 
    Details
    ISSN: 1432-1106
    Keywords: Transplantation ; Serotonin neurons ; Hypothalamus ; Electron microscopy ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We have previously reported that a cell suspension from the rostral part of the embryonic raphe grafted to the basal hypothalamus of 5,7-dihydroxytryptamine-denervated rats produced incomplete serotonin (5-HT) re-innervation of the suprachiasmatic nucleus (SCN) as opposed to hyper-innervation of the supraoptic nucleus (SON). We took advantage of this experimental model to investigate whether the graft-derived, 5-HT fibres retained normal ultrastructural features, and, particularly, a normal density of synaptic junctions, irrespective of the extent of target re-innervation. The intrinsic features of immunostained, graft-derived 5-HT axonal varicosities in both the SCN (ventral portion) and the SON were essentially similar to those exhibited by the respective endogenous innervation. Analysis of well-preserved varicosities in uninterrupted series of thin sections allowed us to evaluate directly the proportions of junctional to non-junctional 5-HT varicosities in both regions. Synaptic incidences were also remarkably conserved after grafting (45.5% in the SCN versus 38.5% in the SON; 48% and 38% in normal rats, respectively). Synapses were primarily reestablished on dendritic shafts, which also were identified as the major post-synaptic targets of the normal 5-HT innervations. We noted, however, a tendency toward increased numbers of symmetrical versus asymmetrical synapses in both the SCN and SON of grafted rats. Thus, irrespective of whether hypo-or hyper-innervation patterns developed post-grafting, the transplanted 5-HT neurons essentially retained normal ultrastructural features in their target territories, with a normal incidence of synaptic junctions. The data provide further support to the hypothesis that the innervation territory is the major determinant of the frequency with which ingrowing 5-HT fibres make synaptic junctions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00227329
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  • 2
    Electronic Resource
    Electronic Resource
    Lesion Study of the Distribution of Serotonin 5-HT4 Receptors in Rat Basal Ganglia and Hippocampus (1996)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 8 (1996), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The regional distribution of 5-hydroxytryptamine (5-HT4) receptors labelled with [3H]GR113808 was examined in rat basal ganglia and hippocampus after specific lesions. Lesion of serotonin neurons induced by injections of 5,7-dihydroxytryptamine into the dorsal and medial raphe nuclei resulted in increased 5-HT4 receptor binding in most regions examined, compared with controls. More precisely, there was a 78% increase in the rostral but no change in the caudal part of caudate-putamen, and 83% and 54% increases in the shell and core of the nucleus accumbens respectively. In the substantia nigra, the increase in 5-HT4 binding was larger (72%) than that in the globus pallidus (32%). In the hippocampus, 63%, 30% and 28% increases were measured in CA2, CA1 and CA3 respectively. Following lesion of dopamine neurons by intranigral injection of 6-hydroxydopamine, increased 5-HT4 receptor binding was observed in the caudal (59%), but not the rostral part of caudate-putamen, as well as in the globus pallidus (93%). Since no decreases in 5-HT4 receptor density were detected after the dopamine lesion, it was concluded that these receptors are not expressed in dopamine neurons. Kainic acid lesions of the caudate-putamen were associated with dramatic local decreases in 5-HT4 receptor binding on the injected side (-89%), which suggested that striatal neurons express 5-HT4 receptors. Corresponding decreases of 72 and 20% in receptor density were detected in globus pallidus and substantia nigra, consistent with a presumed localization of 5-HT4 receptors on striatal GABA neurons projecting to these regions. In the substantia nigra, the decrease in [3H]GR113808 binding was localized to the pars lateralis, indicating that striatal neurons belonging to the cortico-striato-nigrotectal pathway, and containing GABA and dynorphin, express 5-HT4 receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.1996.tb01553.x
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  • 3
    Electronic Resource
    Electronic Resource
    Serotonin Reinnervation of the Suprachiasmatic Nucleus by Intrahypothalamic Fetal Raphe Transplants, with Special Reference to Possible Influences of the Target (1991)
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 3 (1991), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Survival and development of fetal serotonin (5-HT) neurons grafted to various brain areas in adult mammals have been suggested to be under host influences. The aim of this study was to determine whether the suprachiasmatic nucleus of the hypothalamus (SCN), a region receiving a 5-HT input which is one of the densest and the most heavily synaptic in the brain, can actually support the development of transplanted 5-HT neurons. The time course and extent of 5-HT reinnervation were therefore investigated with 5-HT immunocytochemistry in adult rats subjected to intraventricular injection of 5,7-dihydroxytryptamine and subsequent grafting of fetal cell suspension of mesencephalic raphe neurons. The ultrastructural features of the newly formed 5-HT terminal plexa were also examined. Serotonin reinnervation of the SCN remained partial up to 4 months post-transplantation, with no apparent predilection of the reinnervating fibres for any particular portion of the nucleus, thus differing from the normal 5-HT innervation of the SCN both quantitatively and qualitatively. This was in sharp contrast to the 5-HT hyperinnervation observed in neighbouring areas such as the supraoptic nucleus, a structure normally provided with only few 5-HT fibres, and the ventral wall of the third ventricle. The graft-derived 5-HT-axons, however, displayed ultrastructural features that did not appear different from those of their normal counterparts; in particular they re-established defined synaptic contacts with the host population. These results may indicate that the mature SCN specifically lacks a trophic factor necessary for the ingrowth of graft-derived 5-HT fibres, or that it represents an inhibitory environment for such an ingrowth. The limited ability of regrowing 5-HT axons to restore a normal density of 5-HT innervation could also be related to the fact that these neurons normally establish a relatively high number of synaptic contacts in the target region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-9568.1991.tb00065.x
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  • 4
    Electronic Resource
    Electronic Resource
    Serotonin mediates oestrogen stimulation of cell proliferation in the adult dentate gyrus (2001)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 14 (2001), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Characterizing the mechanisms by which endogenous factors stimulate neurogenesis is of special interest in view of the possible implication of newly generated cells in hippocampal functions or disorders. The aim of this study was to determine whether serotonin (5-HT) and oestradiol (E2) act through a common pathway to increase cell proliferation in the adult dentate gyrus (DG). We also investigated the effects of long-lasting changes in oestrogen levels on cell proliferation. Combining ovariectomy with inhibition of 5-HT synthesis using p-chlorophenylalanine (PCPA) treatment produced approximately the same decreases in the number of bromodeoxyuridine (BrdU) and PSA-NCAM immunolabelled cells in the subgranular layer as ovariectomy alone. Administration of 5-hydroxytryptophan (5-HTP) restored cell proliferation primarily decreased by ovariectomy, whereas oestradiol was unable to reverse this change in ovariectomized rats treated with PCPA. These findings demonstrate that 5-HT mediates oestrogen stimulation of cell proliferation in adult dentate gyrus. However, increase in ovarian hormones during pregnancy has no effect on dentate cell proliferation. This finding suggests that concomitant changes in other factors, such as glucocorticoids, may counterbalance the positive regulation of cell proliferation by 5-HT and oestradiol. Finally, oestrogen may regulate structural plasticity by stimulating PSA-NCAM expression independently of neurogenesis, as shown for instance by the increases in the number of PSA-NCAM labelled cells in pregnants. As 5-HT and oestrogen are involved in mood disorders, our data suggest that the positive regulation of cell proliferation and neuroplasticity by these two factors may contribute to restore hippocampal connectivity in depressive patients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0953-816x.2001.01763.x
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  • 5
    Electronic Resource
    Electronic Resource
    Serotonin may stimulate granule cell proliferation in the adult hippocampus, as observed in rats grafted with foetal raphe neurons (2000)
    Oxford, UK : Blackwell Science Ltd
    European journal of neuroscience 12 (2000), S. 0 
    Details
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The long-term effects of hippocampal serotonergic denervation and reinnervation by foetal raphe tissue were examined in the dentate gyrus where neurons are continously born in the adult. Complete lesion of serotonin neurons following injections of 5,7-dihydroxytryptamine in the dorsal and medial raphe nuclei produced long-term decreases in the number of newly generated granule cells identified with 5-Bromo-2′-deoxyuridine (BrdU) and the polysialylated form of neural cell adhesion molecule (PSA-NCAM) immunostaining, as observed in 2-month-survival rats. The raphe grafts, but not the control grafts of embryonic spinal tissue, reversed the postlesion-induced decreases in the density of BrdU- and PSA-NCAM-labelled cells detected in the granule layer. Inhibition of serotonin synthesis in animals with raphe grafts reversed back to lesion-induced changes in granule cell proliferation. Furthermore, extensive serotonergic reinnervation of the dentate gyrus in the area proximal to the raphe graft could be associated with supranormal density of BrdU-labelled cells. These results indicate that serotonin may be considered a positive regulatory factor of adult granule cell proliferation. Finally, the lack of effect of embryonic nonserotonergic tissue grafted to serotonin-deprived rats suggests that neurotrophic factors may not be involved in the effects of serotonin on adult neurogenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1460-9568.2000.00932.x
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