Biomedical subjects

Laura Lossi

Publications and source records attributed to Laura Lossi.

7 recordsLinked to original sources

PubMed2006

Neuropeptides as synaptic transmitters.

Neuropeptides are small protein molecules (composed of 3-100 amino-acid residues) that have been localized to discrete cell populations of central and peripheral neurons. In most instances, they coexist with low-molecular-weight neurotransmitters within the same neurons. At the subcellular level, neuropeptides are selectively stored, singularly or more frequently in combinations, within large granular vesicles. Release occurs through mechanisms different from classical calcium-dependent exocytosis at the synaptic cleft, and thus they account for slow synaptic and/or non-synaptic communication in neurons. Neuropeptide co-storage and coexistence can be observed throughout the central nervous system and are responsible for a series of functional interactions that occur at both pre- and post-synaptic levels. Thus, the subcellular site(s) of storage and sorting mechanisms into different neuronal compartments are crucial to the mode of release and the function of neuropeptides as neuronal messengers.

Animals↗

PubMed2005

Ultrastructural evidence for a pre- and postsynaptic localization of full-length trkB receptors in substantia gelatinosa (lamina II) of rat and mouse spinal cord.

Brain-derived neurotrophic factor (BDNF) exerts its trophic effects by acting on the high-affinity specific receptor trkB. BDNF also modulates synaptic transmission in several areas of the CNS, including the spinal cord dorsal horn, where it acts as a pain modulator by yet incompletely understood mechanisms. Spinal neurons are the main source of trkB in lamina II (substantia gelatinosa). Expression of this receptor in dorsal root ganglion (DRG) cells has been a matter of debate, whereas a subpopulation of DRG neurons bears trkA receptors and contains BDNF. By the use of two different trkB antibodies we observed that 7.7% and 10.8% of DRG neurons co-expressed BDNF + trkB but not trkA, respectively, in rat and mouse. Ultrastructurally, full-length trkB (fl-trkB) receptors were present at somato-dendritic membranes of lamina II neurons (rat: 66.8%; mouse: 73.8%) and at axon terminals (rat: 33.2%; mouse: 26.2%). In both species, about 90% of these terminals were identified as primary afferent fibres (PAFs) considering their morphology and/or neuropeptide content. All fl-trkB-immunopositive C boutons in type Ib glomeruli were immunoreactive for BDNF and, at individual glomeruli and axo-dendritic synapses, fl-trkB receptors were located in a mutually exclusive fashion at pre- or postsynaptic membranes. Thus, only a small fraction of fl-trkB-immunoreactive dendrites were postsynaptic to BDNF-immunopositive PAFs. This is the first ultrastructural description of fl-trkB localization at synapses between first- and second-order sensory neurons in lamina II, and suggests that BDNF may be released by fl-trkB-immunopositive PAFs to modulate nociceptive input in this lamina of dorsal horn.

Animals↗

PubMed2004

In vivo analysis reveals different apoptotic pathways in pre- and postmigratory cerebellar granule cells of rabbit.

Naturally occurring neuronal death (NOND) has been described in the postnatal cerebellum of several species, mainly affecting the cerebellar granule cells (CGCs) by an apoptotic mechanism. However, little is known about the cellular pathway(s) of CGC apoptosis in vivo. By immunocytochemistry, in situ detection of fragmented DNA, electron microscopy, and Western blotting, we demonstrate here the existence of two different molecular mechanisms of apoptosis in the rabbit postnatal cerebellum. These two mechanisms affect CGCs at different stages of their maturation and migration. In the external granular layer, premigratory CGCs undergo apoptosis upon phosphorylation of checkpoint kinase 1 (Chk1), and hyperphosphorylation of retinoblastoma protein. In postmigratory CGCs within the internal granular layer, caspase 3 and to a lesser extent 7 and 9 are activated, eventually leading to poly-ADP-ribose polymerase-1 (PARP-1) cleavage and programmed cell death. We conclude that NOND of premigratory CGCs is linked to activation of DNA checkpoint and alteration of normal cell cycle, whereas in postmigratory CGCs apoptosis is, more classically, dependent upon caspase 3 activation.

Animals↗

PubMed2004

Molecular morphology of neuronal apoptosis: analysis of caspase 3 activation during postnatal development of mouse cerebellar cortex.

We have used the mammalian post-natal cerebellar cortex as a model to dissect out the molecular morphology of neuronal apoptosis in a well-defined population of central neurons: the cerebellar granule cells. By immunocytochemistry, in situ labeling of apoptotic cells, and analysis of cerebellar slices following particle-mediated gene transfer (biolistics), we have studied the relationship of cell death and cleavage of caspase 3, a key molecule in the execution of apoptosis, and monitored caspase 3 activation in living cells. Our results demonstrate the existence of caspase dependent and independent apoptotic pathways affecting the cerebellar granule cells at different stages of their life. Apoptosis of proliferating precursors and young pre-migratory cells occurs in the absence of caspase 3 cleavage, whereas cell death of post-mitotic post-migratory neurons is directly linked to caspase 3 activation. Data obtained from cerebellar cortex can be generalized to outline a more comprehensive picture of the cellular and molecular mechanisms of neuronal death not only in development, but also in a number of pathological conditions leading to neuronal loss.

Animals↗

PubMed2004

Neurotrophins in spinal cord nociceptive pathways.

Neurotrophins are a well-known family of growth factors for the central and peripheral nervous systems. In the course of the last years, several lines of evidence converged to indicate that some members of the family, particularly NGF and BDNF, also participate in structural and functional plasticity of nociceptive pathways within the dorsal root ganglia and spinal cord. A subpopulation of small-sized dorsal root ganglion neurons is sensitive to NGF and responds to peripheral NGF stimulation with upregulation of BDNF synthesis and increased anterograde transport to the dorsal horn. In the latter, release of BDNF appears to modulate or even mediate nociceptive sensory inputs and pain hypersensitivity. We summarize here the status of the art on the role of neurotrophins in nociceptive pathways, with special emphasis on short-term synaptic and intracellular events that are mediated by this novel class of neuromessengers in the dorsal horn. Under this perspective we review the findings obtained through an array of techniques in naïve and transgenic animals that provide insight into the modulatory mechanisms of BDNF at central synapses. We also report on the results obtained after immunocytochemistry, in situ hybridization, and monitoring intracellular calcium levels by confocal microscopy, that led to hypothesize that also NGF might have a direct central effect in pain modulation. Although it is unclear whether or not NGF may be released at dorsal horn endings of certain nociceptors in vivo, we believe that these findings offer a clue for further studies aiming to elucidate the putative central effects of NGF and other neurotrophins in nociceptive pathways.

Afferent Pathways↗

PubMed2004

Transient expression of secretin in serotoninergic neurons of mouse brain during development.

Existence of the gastro-intestinal peptide secretin in the CNS has been a matter of debate, and contrasting results have been reported, altogether indicating that the CNS is not a major site of production of this peptide. A thorough analysis was conducted in brain of transgenic mice in which the expression of the early region of simian virus 40 large T antigen (Tag) is under control of the rat secretin gene promoter. We studied Tag expression in the brains of E14-P90 transgenic mice as well as secretin mRNA and protein expression in transgenic and control CD1 mice at corresponding developmental stages. We show here a perfect correspondence of Tag and secretin mRNA expression in the mesencephalon of transgenic and normal mice between E14 and birth. In embryos, Tag is also expressed in the spinal cord, as well as in several areas of the peripheral nervous system. Localization of Tag in P0-P90 animals becomes restricted to a single compact cellular mass in mesencephalon at the level of the dorsal raphe, raphe magnus and lateral paragigantocellular nuclei. Neurons of these nuclei display secretin mRNA from E14 to birth, in both control CD1 and transgenic mice. Approximately half of these secretin-expressing neurons are immunoreactive for serotonin (5HT) and/or tryptophan hydroxylase. These results demonstrate that the secretin gene is transiently expressed in mouse serotoninergic mesencephalic neurons during development. In addition our data suggest a trophic role for secretin on neurons known to be involved in multiple superior functions in the normal brain, and lost in neurodegenerative disorders.

Animals↗

PubMedDate not supplied

Cell proliferation and apoptosis during histogenesis of the guinea pig and rabbit cerebellar cortex.

Cell proliferation and apoptosis are essential for development of the nervous system. In this study we have investigated the histogenesis of the cerebellar cortex in guinea pig (a precocial species) and rabbit (an altricial species) at different stages of pregnancy and postnatal life. Proliferating cells were identified after labeling with antibodies against the proliferating cell nuclear antigen (PCNA) and/or the Ki-67 antigen. Apoptotic cells were visualized in situ by the TUNEL method and by immunodetection of cleaved caspase 3 and 9. In guinea pigs, both proliferating and apoptotic cells were detected during pre-natal life (E0-E40). Conversely, cell proliferation and apoptosis in rabbits were temporally restricted to early postnatal weeks (P0-P20). In both species cell proliferation was mainly linked to differentiation and migration of the granule cells. In both species, the majority of cells undergoing programmed cell death likely corresponded to granule cells. They were mainly detected in the external granular layer, and were by far more common than previously reported in other locations of the postnatal brain. This study shows that apoptosis is a shared process of cell death during cerebellar development in both altricial and precocial animals, and that there is a direct spatial and temporal correlation between cell proliferation and death in two mammals with different time tables in cerebellar maturation.

Aging↗