Embryonic (PSA) N-CAM reveals chains of migrating neuroblasts between the lateral ventricle and the olfactory bulb of adult mice

Expression of 9-O-acetylated gangliosides is correlated with tangential cell migration in the rat brain

9-O-acetylated gangliosides (9-O-aGs) are expressed in regions of the developing brain during radial neuronal migration and an anti-9-O-aGs monoclonal antibody (JONES mAb) interferes with axonal growth. To determine the generality of 9-O-aGs expression in directional movements, we have examined their immunoreactivity with mAb JONES in the cell stream from the lateral ventricle rostral subventricular zone (LVSVZ) to the olfactory bulb (OB) in postnatal and adult rats. We show expression of 9-O-aGs both in LVSVZ, along the rostral migratory stream and in the OB in developing animals and, at lower levels, in adulthood. That suggests 9-O-aGs' involvement in tangential cell migration as well in other neural directional movements.

The role of polysialic acid and other carbohydrate polymers in neural structural plasticity

Polysialic acid (PSA) fulfills several criteria for a molecule involved in structural plasticity, including expression in regions capable of plasticity, re-expression in structures undergoing synaptic rearrangement in the adult, downregulation following innervation, and regulation by activity. In addition, removal of PSA reduces the capacity for structural plasticity. PSA may be paradigmatic for other large polymeric carbohydrates, such as glycosaminoglycans and proteoglycans, which also are highly charged and can be extensively hydrated. These carbohydrates may affect structural plasticity by altering cell-cell and/or cell-matrix interactions by increasing intermolecular spacing through hydration.

Cell and molecular analysis of the developing and adult mouse subventricular zone of the cerebral hemispheres

The subventricular zone (SVZ) of the lateral ventricle remains mitotically active in the adult mammalian central nervous system (CNS). Recent studies have suggested that this region may contain neuronal precursors (neural stem cells) in adult rodents. A variety of neuronal and glial markers as well as three extracellular matrix (ECM) markers were examined with the hope of understanding factors that may affect the growth and migration of neurons from this region throughout development and in the adult. This study has characterized the subventricular zone of late embryonic, postnatal, and adult mice using several neuronal markers [TuJ1, nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d), neuron-specific enolase (NSE)], glial markers [RC-2, vimentin, glial fibrillary acidic protein (GFAP), galactocerebroside (Gal-C)], ECM markers [tenascin-C (TN-C), chondroitin sulfate, a chondroitin sulfate proteoglycan termed dermatan sulfate-dependent proteoglycan-1 (DSD-1-PG)], stem-cell marker (nestin), and proliferation-specific marker [bromodeoxyuridine (BrdU)]. TuJ1+ and nestin+ cells (neurons and stem cells, respectively) persist in the region into adulthood, although the numbers of these cells become more sparse as the animal develops, and they appear to be immature compared to the cells in surrounding forebrain structures (e.g., not expressing NSE and having few, if any, processes). Likewise, NADPH-d+ cells are found in and around the SVZ during early postnatal development but become more sparse in the proliferative zone through maturity, and, by adulthood, only a few labeled cells can be found at the border between the SVZ and surrounding forebrain structures (e.g., the striatum), and even smaller numbers of positive cells can be found within the adult SVZ proper. BrdU labeling also seems to decrease significantly after the first postnatal week, but it still persists in the SVZ of adult animals. The disappearance of RC-2+ (radial) glia during postnatal development and the persistence of glial-derived ECM molecules such as tenascin and chondroitin sulfate proteoglycans (as well as other "boundary" molecules) in the adult SVZ may be associated with a persistence of immaturity, cell death, and a lack of cell emigration from the SVZ in the adult.

Regeneration in the adult mammalian CNS: guided by development

In the past year, the roles and mechanisms of molecules involved in cell survival (glial-derived neurotrophic growth factor), growth cone guidance (netrins and semaphorins), axonal outgrowth and sorting (neural cadherin, polysialylated neural cell adhesion molecules, and L1), and neuronal connectivity (cell adhesion molecules, dystroglycan, and agrin) have been described during development and, to a limited extent, in the mature CNS. Evidence is now emerging that some developmental events, such as the expression of polysialylated neural cell adhesion molecule and L1, are recapitulated during adult CNS regeneration. These results suggest new avenues to address more accurately the challenges of axonal regrowth in the adult mammalian CNS.

Olfactory learning

Unravelling the mechanisms of learning and memory can, and should, be tackled at many levels. Discovery of the huge family of odourant receptor genes provided olfaction with 'molecular' respectability similar to that afforded to the visual system. Consequently, molecular studies have dominated the olfactory literature this past year, even to the point of providing a molecular basis of olfactory perception. Needless to say, the molecular approach favours a 'hard-wired' system; however, other results suggest that flexibility in the olfactory system provides for certain adaptations that are crucial to the biological needs of mammals.

Expression of polysialylated N-CAM in the central nervous system of adult canaries and its possible relation to function

Polysialylated neuronal cell adhesion molecule (PSA-N-CAM) is a cell surface molecule associated with neurons that undergo changes in configuration or spatial translocation. In both cases, this molecule is thought to reduce the adhesivity of these cells or of their processes, which can thereby insinuate themselves into the existing parenchyma. We used a monoclonal antibody specific to PSA to offer what we believe is the first account of the distribution of PSA-N-CAM in the adult songbird brain. This antibody stained a diversity of cell classes and processes, as follows: 1) a subset of ventricular zone cells; 2) migrating cells thought to be neuroblasts; 3) a subset of differentiated neurons; 4) some brain surface astrocytes; 5) some tanycytes; 6) the neuropil of some regions; 7) some axonal fibers; and 8) possibly some synapses. Our results demonstrate also, for the first time, the wide distribution of a very numerous population of migrating cells in the telencephalon and the seasonal regulation of PSA-N-CAM expression in a part of the adult brain known to undergo seasonal changes in cell recruitment and function. However, we did not find PSA-N-CAM associated with young migrating cells in the high vocal center (HVC), nor was there PSA-N-CAM in the robust nucleus of the archistriatum (RA), which is known to receive new axonal endings from HVC. In these instances spatial translocation may occur with the assistance of other surface molecules.

Neuronal stem cells in the brain of adult vertebrates

It is generally assumed that neurogenesis in the central nervous system ceases before or soon after birth. In the last three decades, however, several studies have reported that new neurons continue to be added into the brain of adult fish, frogs, reptiles, birds and mammals. The precursor cells that give rise to the neurons generated in adulthood are generally located in the walls of the brain ventricles. From these proliferative regions, neuronal precursors migrate toward their final targets where they differentiate; they often traverse long distances through complex brain parenchyma. The identity of the neuronal precursors in the brains of adult animals is still unknown. Experiments in adult birds suggest that proliferating radial cells may be the neuronal precursors. In adult mice, cells present in the subventricular zone can generated neurons in vivo and in vitro. These neuronal precursors can be induced to proliferate in vitro when exposed to growth factors and retain their potential to differentiate into neurons and glia. Whether these putative neural stem cells can differentiate into multiple neuronal types remains to be determined. The neuronal precursors of the adult brain could be used as a source of cells for neuronal transplantation. In addition, these cells could be manipulated in vivo or in vitro to introduce genes into the brain. Adult neurogenesis offers new experimental opportunities to study neuronal birth, migration and differentiation and for the treatment of neurological diseases.