The pathogenic LRRK2 R1441C mutation induces specific deficits modeling the prodromal phase of Parkinson's disease in the mouse.

The aim of the present study was to further explore the in vivo function of the Leucine-rich repeat kinase 2 (LRRK2)-gene, which is mutated in certain familial forms of Parkinson's disease (PD). We generated a mouse model harboring the disease-associated point mutation R1441C in the GTPase domain of the endogenous murine LRRK2 gene (LRRK2 R1441C line) and performed a comprehensive analysis of these animals throughout lifespan in comparison with an existing knockdown line of LRRK2 (LRRK2 knockdown line). Animals of both lines do not exhibit severe motor dysfunction or pathological signs of neurodegeneration neither at young nor old age. However, at old age the homozygous LRRK2 R1441C animals exhibit clear phenotypes related to the prodromal phase of PD such as impairments in fine motor tasks, gait, and olfaction. These phenotypes are only marginally observable in the LRRK2 knockdown animals, possibly due to activation of compensatory mechanisms as suggested by in vitro studies of synaptic transmission. Thus, at the organismal level the LRRK2 R1441C mutation does not emerge as a loss of function of the protein, but induces mutation specific deficits. Furthermore, judged by the phenotypes presented, the LRRK2-R1441C knock-in line is a valid preclinical model for the prodromal phase of PD.

Morphology and connections of neurons in area 17 projecting to the extrastriate areas MT and 19DM and to the superior colliculus in the monkey Callithrix jacchus.

Neurons of area 17, the primary visual cortex, project to various anatomically and physiologically different extrastriate areas and subcortical regions. In the present investigation, we addressed the question of whether the efferent neurons in area 17 can contribute to functional diversity between these regions. We approached this question by analyzing the dendritic morphology of neurons in area 17 projecting to area MT, area 19DM, and the superior colliculus in the new world simian primate Callithrix jacchus, because dendritic morphology is an important factor in determining physiological properties of nerve cells. Retrograde transport of fluorochromes injected into the target regions, and intracellular injections of Lucifer yellow in the prelabelled neurons, revealed the following. 1) Morphologically identical large pyramidal cells in layer VI of area 17 project to all three targets. Some of them possess axon collaterals to two or all three targets, suggesting that they provide common information to all three areas. 2) Pyramidal cells in layer IIIc projecting to area MT form a morphologically homogeneous population. 3) Three small to medium-sized pyramidal cell types in layers IIIa-c, spiny stellate cells in layer IIIc, and another large pyramidal cell type in layer VI project to area 19DM. 4) Pyramidal cells in the lower two-thirds of layer V in area 17 project to the superior colliculus. In conclusion, we have shown that in Callithrix one efferent pathway may originate from several cell types. However, with the exception of the large cells in layer VI, efferent cells projecting to area MT, area 19DM, and the superior colliculus were morphologically distinct. This suggests that functional differences between brain regions could arise in part from morphological heterogeneity between and within the efferent cell populations.

Cellular distribution of the calcium-binding proteins parvalbumin, calbindin, and calretinin in the neocortex of mammals: phylogenetic and developmental patterns.

The three calcium-binding proteins parvalbumin, calbindin, and calretinin are found in morphologically distinct classes of inhibitory interneurons as well as in some pyramidal neurons in the mammalian neocortex. Although there is a wide variability in the qualitative and quantitative characteristics of the neocortical subpopulations of calcium-binding protein-immunoreactive neurons in mammals, most of the available data show that there is a fundamental similarity among the mammalian species investigated so far, in terms of the distribution of parvalbumin, calbindin, and calretinin across the depth of the neocortex. Thus, calbindin- and calretinin-immunoreactive neurons are predominant in layers II and III, but are present across all cortical layers, whereas parvalbumin-immunoreactive neurons are more prevalent in the middle and lower cortical layers. These different neuronal populations have well defined regional and laminar distribution, neurochemical characteristics and synaptic connections, and each of these cell types displays a particular developmental sequence. Most of the available data on the development, distribution and morphological characteristics of these calcium-binding proteins are from studies in common laboratory animals such as the rat, mouse, cat, macaque monkey, as well as from postmortem analyses in humans, but there are virtually no data on other species aside of a few incidental reports. In the context of the evolution of mammalian neocortex, the distribution and morphological characteristics of calcium-binding protein-immunoreactive neurons may help defining taxon-specific patterns that may be used as reliable phylogenetic traits. It would be interesting to extend such neurochemical analyses of neuronal subpopulations to other species to assess the degree to which neurochemical specialization of particular neuronal subtypes, as well as their regional and laminar distribution in the cerebral cortex, may represent sets of derived features in any given mammalian order. This could be particularly interesting in view of the consistent differences in neurochemical typology observed in considerably divergent orders such as cetaceans and certain families of insectivores and metatherians, as well as in monotremes. The present article provides an overview of calcium-binding protein distribution across a large number of representative mammalian species and a review of their developmental patterns in the species where data are available. This analysis demonstrates that while it is likely that the developmental patterns are quite consistent across species, at least based on the limited number of species for which ontogenetic data exist, the distribution and morphology of calcium-binding protein-containingneurons varies substantially among mammalian orders and that certain species show highly divergent patterns compared to closely related taxa. Interestingly, primates, carnivores, rodents and tree shrews appear closely related on the basis of the observed patterns, marsupials show some affinities with that group, whereas prototherians have unique patterns. Our findings also support the relationships of cetaceans and ungulates, and demonstrates possible affinities between carnivores and ungulates, as well as the existence of common, probably primitive, traits in cetaceans and insectivores.

Calretinin-positive Cajal-Retzius cells persist in the adult human neocortex.

The occurrence of Cajal-Retzius (CjRe) cells was studied in four cortical areas of five normal adult humans using antibodies against calretinin. Calretinin immunofluorescence and autofluorescence of lipofusin granules in CjRe cells were visualized by dual channel confocal laser scanning microscopy. Three types of CjRe cells existed in the adult human cortex: horizontal, triangular and multipolar, and their number did not decrease with ageing. Horizontal CjRe cells were found in all cortical areas; they contained no lipofusin or less than other cells. Triangular CjRe cells with descending dendrites were less numerous. Multipolar CjRe cells were rare and contained more lipofuscin. We conclude that calretinin-immunoreactivity can be used to study CjRe cell morphology in normal and diseased adult human brain.

Temporal and spatial appearance of the membrane cytoskeleton and perineuronal nets in the rat neocortex.

Parvalbumin-immunoreactive interneurons are surrounded by perineuronal nets, containing molecules of the extracellular matrix (e.g. tenascin-R). Furthermore, they seem to have a special cytoskeleton composed of, among others, ankyrinR and beta Rspectrin. In the present developmental study we showed that the intracellular markers parvalbumin, ankyrinR and beta Rspectrin as well as Vicia Villosa agglutinin, an extracellular marker for perineuronal nets, appeared in the second postnatal week. In the third postnatal week, ankyrinR and beta R spectrin were present in the parvalbumin-positive interneurons. Tenascin-R appeared in a similar topographic distribution as the intracellular markers. The adult pattern was established upon the end of the fourth postnatal week. Our results indicate that cytoskeletal maturity maybe a prerequisite for the organization of perineuronal nets of extracellular matrix.

DJ-1-deficient mice show less TH-positive neurons in the ventral tegmental area and exhibit non-motoric behavioural impairments.

Loss of function of DJ-1 (PARK7) is associated with autosomal recessive early-onset Parkinson's disease (PD), one of the major age-related neurological diseases. In this study, we extended former studies on DJ-1 knockout mice by identifying subtle morphological and behavioural phenotypes. The DJ-1 gene trap-induced null mutants exhibit less dopamine-producing neurons in the ventral tegmental area (VTA). They also exhibit slight changes in behaviour, i.e. diminished rearing behaviour and impairments in object recognition. Furthermore, we detected subtle phenotypes, which suggest that these animals compensate for the loss of DJ-1. First, we found a significant upregulation of mitochondrial respiratory enzyme activities, a mechanism known to protect against oxidative stress. Second, a close to significant increase in c-Jun N-terminal kinase 1 phosphorylation in old DJ-1-deficient mice hints at a differential activation of neuronal cell survival pathways. Third, as no change in the density of tyrosine hydroxylase (TH)-positive terminals in the striatum was observed, the remaining dopamine-producing neurons likely compensate by increasing axonal sprouting. In summary, the present data suggest that DJ-1 is implicated in major non-motor symptoms of PD appearing in the early phases of the disease-such as subtle impairments in motivated behaviour and cognition-and that under basal conditions the loss of DJ-1 is compensated.

Creatine improves health and survival of mice.

The supplementation of creatine (Cr) has a marked neuroprotective effect in mouse models of neurodegenerative diseases. This has been assigned to the known bioenergetic, anti-apoptotic, anti-excitotoxic, and anti-oxidant properties of Cr. As aging and neurodegeneration share pathophysiological pathways, we investigated the effect of oral Cr supplementation on aging in 162 aged C57Bl/6J mice. Outcome variables included "healthy" life span, neurobehavioral phenotyping, as well as morphology, biochemistry, and expression profiling from brain. The median healthy life span of Cr-fed mice was 9% higher than in control mice, and they performed significantly better in neurobehavioral tests. In brains of Cr-treated mice, there was a trend towards a reduction of reactive oxygen species and significantly lower accumulation of the "aging pigment" lipofuscin. Expression profiling showed an upregulation of genes implicated in neuronal growth, neuroprotection, and learning. These data show that Cr improves health and longevity in mice. Cr may be a promising food supplement to promote healthy human aging.

The onset of parvalbumin-expression in interneurons of the rat parietal cortex depends upon extrinsic factor(s).

Parvalbumin (PV) belongs to the large family of EF-hand calcium-binding proteins and is an excellent marker for a subpopulation of GABAergic neocortical interneurons. During cortical development, PV first appears on postnatal day (P)8, in the infragranular layers; after P14, it also becomes apparent within the supragranular layers. However, nothing is known about the factors controlling its expression, which could involve functional activity, neuronal connectivity and/or neurotrophic factors. It being difficult to manipulate these parameters in vivo, their role may be more readily assessed in organotypic cultures, which are deprived of their subcortical afferents and efferents, and hence of subcortically derived neurotrophic factors and extrinsic functional activity. We prepared slices of the rat brain on P3, P5, P7 and P9, maintained them in culture for 2-5 weeks, and compared the temporal and spatial distribution pattern of PV-immunoreactivity within these slices with the in vivo situation. We found, first, that during late postnatal in vivo development and ageing, the number of PV-immunoreactive neurons in the parietal cortex decreases significantly, and second, that the expression of PV-immunoreactivity in the parietal cortex was markedly influenced by the phase of postnatal development at which slice cultures were explanted. In those removed on P7 and P9, the number of PV-immunoreactive cells, as well as the temporal and spatial distribution pattern of PV-immunoreactivity corresponded to the in vivo situation, but in explants obtained on P3 or P5, PV-immunoreactivity remained confined to layer V of the cortex, reminiscent of the expression profile manifested at the end of the second postnatal week in vivo. Also, the number of PV-immunoreactive cells in these cultures was significantly lower than in explants at the later stages. Our results indicate that the onset of PV-expression in the parietal cortex depends upon extrinsic cortical factors subsisting prior to P7. Once the production of this protein has been initiated, such influences are no longer required.

Coupling of cAMP/PKA and MAPK signaling in neuronal cells is dependent on developmental stage.

Neurite formation, an essential feature of neuronal development, is believed to involve participation of the ras-mitogen-activated protein kinase (MAPK) and cAMP-dependent protein kinase A (cAMP/PKA)-mediated signaling pathways. These pathways have been studied extensively in the rat pheochromocytoma cell line PC12, and current hypotheses suggest a single effector mechanism resulting from the convergence of cAMP/PKA and MAPK signaling. However, based on observations using a central neuronal progenitor cell line, AS583-8, there also exists evidence that the two signaling pathways may act independently resulting in neurites with differing dynamic features. In the present study, the upstream components of cAMP/PKA signaling were examined in AS583-8 cells as well as possible interactions with the MAPK pathway. We found that activation of PKA is both necessary and sufficient for the elaboration of rapidly forming processes, typical of the cAMP response. In addition, blockade of the MAPK pathway has no effect on the cAMP response, suggesting that activation of the cAMP/PKA pathway can stimulate neurite formation independent of the MAPK pathway. In order to evaluate which cell line model, PC12 vs AS583-8, best reflects the signaling features of developing central neurons, we examined interactions between cAMP/PKA and MAPK signaling in primary neuronal cultures from several brain regions. In immature cultures (1-day-old), at a point where the initiation of neurite formation is maximal, no interaction was observed. In more mature cultures (7 days old), where synaptic contacts have been established, we found a weak but reproducible activation of MAPK following stimulation of the cAMP/PKA pathway. These results suggest that cAMP/PKA and MAPK signaling act independently at the initiation of neuritogenesis but become coupled during later stages of neuronal development. Therefore, the interaction of the two pathways may be cell stage (younger vs older) specific and may participate in cellular functions that take place after initial neurite formation.

Calretinin-immunoreactivity in organotypic cultures of the rat cerebral cortex: effects of serum deprivation.

Calretinin, a calcium-binding protein, is expressed in a specific set of interneurons in the adult rat cortex. Although its role in development is not known with any degree of certainty, evidence in support of a neuroprotective function has been forthcoming. To test this hypothesis, we submitted organotypic cultures (interphase technique) of 4- to 6-day-old rat brain slices to nutritive stress by serum deprivation for 1-3 weeks. Cultures were immunolabelled either with an antiserum against calretinin or with an antibody against MAP2 (the latter being used to assess neuronal cell number). In control (serum-enriched) cultures, the pattern of development of calretinin immunoreactivity mimicked that evinced in vivo with respect to layer- and cell-type specificity, but the maturation process was retarded by about 1 week. In the experimental group, cultures were incubated for 1 week in the presence of serum and then transferred to serum-free medium for an additional 2 weeks. Tissue was characterized by necrotic foci, a marked decrease in neuronal cell number and a further retardation in the course of development of the calretinin immunoreactivity pattern. The proportion of calretinin-immunoreactive cells to total number of viable neurons was 16% in serum-free cultures as against 9% in serum-enriched ones, suggesting that cells expressing the calcium-binding protein exhibit a greater tenacity for survival under conditions of nutritive stress, and thereby supporting the contention that calretinin acts in a neuroprotective capacity.

Expression of neurochondrin in the developing and adult mouse brain.

Here we describe a detailed analysis of the expression of neurochondrin ( ncdn) in the developing and adult mouse brain. Ncdn is first expressed in the hindbrain and spinal cord at embryonic day 10.5 (E10.5) followed by expression in the midbrain at E11.5. By E18 ncdn is also expressed in the diencephalon and telencephalon. However, strongest expression is still observed in the hindbrain. In adults, the expression in the forebrain is as strong as in the hindbrain. Ncdn is highly expressed in the hippocampus, piriform cortex, septum, amygdaloid complex, medial geniculate nucleus, inferior colliculus, cerebellar nuclei and the nuclei of the Vth, VIIth, and XIIth cranial nerves.

Beta-adrenergic and fibroblast growth factor receptors induce neuronal process outgrowth through different mechanisms.

The mechanisms that initiate and direct neuronal process formation remain poorly understood. We have recently described a neuronal progenitor cell line, AS583-8.E4.22 (AS583-8) which undergoes neurite formation in response to beta2-adrenergic and basic fibroblast growth factor (bFGF) receptor activation [Kwon, J.H. et al., (1996) Eur. J. Neurosci., 8, 2042-2055]. In the present study, a comparison of these responses revealed that isoproterenol (ISO), a beta-adrenergic receptor agonist, induces multiple, highly branched processes within 30 min while bFGF induces fewer, unbranched processes within 24 h. In contrast to the ISO response, bFGF induces mitogen-activated protein kinase activation and c-fos expression in the cell line and results in neurite outgrowth that is dependent on new mRNA and protein synthesis. Two-dimensional isoelectric focusing-sodium dodecyl sulphate-polyacrylamide gel electrophoresis of cytoskeletal preparations revealed different patterns following ISO vs. bFGF exposure suggesting selective changes in protein expression and/or post-translational modifications. Immunoblot analysis of these preparations for beta-tubulin, tyrosinated alpha-tubulin and acetylated alpha-tubulin also revealed different patterns following each type of treatment. Follow-up confocal microscopy revealed that following ISO, the distribution of tyrosinated tubulin extends to the distal ends of processes whereas acetylated alpha-tubulin is diminished within distal ends. This pattern has been reported to be associated with enhanced microtubule dynamics, a state in which process outgrowth is facilitated. In contrast, following bFGF treatment the distributions of tyrosinated and acetylated alpha-tubulin were identical, a state associated with a diminution of microtubule dynamics. These results, a different time course of neurite formation, dependency on new gene expression and differential expression and cellular distribution of major cytoskeleton proteins suggest that neurite outgrowth induced by ISO vs. bFGF is mediated by two distinct intracellular effector mechanisms in AS583-8 cells. In addition, studies, using the differential distribution of post-translational modified alpha-tubulins in neurites of primary neuronal cultures as marker for the two distinct processes of neurite formation suggest, that similar mechanisms are present in vivo. Therefore, the AS583-8 cell line provides a useful model to study these signalling mechanisms that couple neurotransmitter and growth factor receptor activation to the cytoskeletal changes that mediate neurite formation.

Calretinin-immunoreactivity during postnatal development of the rat isocortex: a qualitative and quantitative study.

Postnatal development of the rat cortex is characterized by the gradual development of many calcium-dependent processes which demand a precise control of the intracellular levels of this cation; when the balance is disturbed, neuronal death ultimately ensues. Calretinin (CR), a calcium-binding protein, has been postulated to have neuroprotective capacity by buffering intracellular calcium. This putative relationship between CR and neuroprotection is still, however, a controversial issue. With a view to shedding further light on this subject, we studied the temporal and spatial distribution of CR in five different regions (the frontal- sensorimotor-, parietal-, temporal- and occipital region) of the rat cortex during postnatal development. Qualitative and quantitative immunocytochemistry of newborn, 5-, 10-, 15-, 20- and 30-day-old and adult rats revealed a profound increase in the density of the CR-positive neurons during the first two postnatal weeks in all regions examined. At the end of this period, CR-immunoreactive cells decreased sharply to adult levels. Cell classes exhibiting transient CR-immunoreactivity during the first two postnatal weeks included cells in layer I (amongst which were Cajal-Retzius cells), the subplate and pyramidal-like cells in the upper portion of layer V, most of them in the motor cortices. The above-described dynamics of CR expression were reflected also in the biochemical analysis performed (immunoblotting, ELISA). The temporal and spatial correlation with calcium-dependent events such as synaptogenesis, neurite elongation and remodelling in further support the contention that CR may play a neuroprotective role during postnatal development of the rat cortex.