Distribution of calcium-binding proteins in the cerebellum

Pattern of calbindin-D28k and calretinin immunoreactivity in the brain of Xenopus laevis during embryonic and larval development

The present study represents a detailed spatiotemporal analysis of the localization of calbindin-D28k (CB) and calretinin (CR) immunoreactive structures in the brain of Xenopus laevis throughout development, conducted with the aim to correlate the onset of the immunoreactivity with the development of compartmentalization of distinct subdivisions recently identified in the brain of adult amphibians and primarily highlighted when analyzed within a segmental paradigm. CR and CB are expressed early in the brain and showed a progressively increasing expression throughout development, although transient expression in some neuronal subpopulations was also noted. Common and distinct characteristics in Xenopus, as compared with reported features during development in the brain of mammals, were observed. The development of specific regions in the forebrain such as the olfactory bulbs, the components of the basal ganglia and the amygdaloid complex, the alar and basal hypothalamic regions, and the distinct diencephalic neuromeres could be analyzed on the basis of the distinct expression of CB and CR in subregions. Similarly, the compartments of the mesencephalon and the main rhombencephalic regions, including the cerebellum, were differently highlighted by their specific content in CB and CR throughout development. Our results show the usefulness of the analysis of the distribution of these proteins as a tool in neuroanatomy to interpret developmental aspects of many brain regions.

Ascending and descending propriospinal pathways between lumbar and cervical segments in the rat: evidence for a substantial ascending excitatory pathway

Precise mechanisms are required to coordinate the locomotor activity of fore- and hind-limbs in quadrupeds and similar mechanisms persist to coordinate movement of arms and legs in humans. Propriospinal neurons (PSNs) are major components of the networks that coordinate these mechanisms. The b subunit of cholera toxin (CTb) was injected unilaterally into either L1 or L3 segments in order to label ascending and descending propriospinal pathways. Labelled cells were examined with light or confocal microscopy. Cells projecting to lumbar segments were evenly distributed, bilaterally throughout all cervical segments. However many more cells were labelled from L1 injections than L3 injections. Roughly 15% of cells in both sides of the C2 segment was found to be immunoreactive for calretinin and a small number (4%) was immunoreactive for calbindin. Axons projecting from L1 to cervical segments formed predominant ipsilateral projections to the cervical intermediate grey matter and ventral horn. Very large numbers of terminals were concentrated within the ventrolateral motor (VLM) nuclei of C7-8 segments but there was sparse innervation of the contralateral nucleus. The vast majority (85%) of these axon terminals in the ipsilateral VML was immunoreactive for the vesicular glutamate transporter 2 (VGLUT2) and the remaining 15% was immunoreactive for the vesicular GABA transporter (VGAT); many of these contained GABA and/or glycine. Inhibitory and excitatory terminals were also found in the contralateral VLM. Most of the terminals in the VLM made contacts with motoneurons. The major finding of this study is the existence of a substantial excitatory propriospinal pathway that projects specifically to the VLM. Motoneurons in the VLM supply muscles of the axilla therefore this pathway is likely to have a profound influence on the activity of the shoulder joint. This pathway may synchronise lumbar and cervical pattern generators and hence the coordination of locomotor activity in the fore- and hind limbs.

Spatio-temporal characterization of the pleiotrophinergic system in mouse cerebellum: evidence for its key role during ontogenesis

The development of the central nervous system requires an appropriate micro-environment that is conditioned by a combination of various extracellular components. Most of the known signaling factors, such as neurotransmitters or neuropeptides, are soluble and diffuse into the extracellular matrix. However, other secreted molecules like proteoglycans or glycosaminoglycans anchor in the extracellular matrix to influence cerebral ontogenesis. As such, pleiotrophin (PTN), which binds the proteoglycans syndecan-3 (SDC3) and protein tyrosine phosphatase zeta (PTPζ), has been described as a pro-migratory and a pro-differentiating secreted cytokine on cortical neurons. In rat cerebellum, PTN is highly expressed during the first postnatal week, suggesting that this cytokine could participate to the development of the cerebellar cortex. According to this hypothesis, our spatio-temporal cartography of PTN, PTPζ and SDC3 indicated that, in mouse, the PTNergic system was present in the cerebellum at least from the first postnatal day (P0). Until P12, PTN was mainly expressed by granule cell precursors and located in the extracellular matrix, while SDC3 was expressed by Purkinje cells, Golgi cells and granule cell precursors, and PTPζ was present on Purkinje cells and Bergmann fibers. In vitro studies confirmed the presence of SDC3 on immature granule cells and demonstrated that PTN could stimulate directly their velocity in culture. In contrast, subarachnoidal injection of PTN in the cerebellum significantly reduced the rate of migration of granule cells, exacerbated their apoptosis and induced an atrophy of the Purkinje cell dendritic tree. Since differentiated granule cells did not express SDC3 or PTPζ, the PTN effect observed on migration and apoptosis may be indirectly mediated by Purkinje and/or Bergmann cells. From P21 to adulthood, the distribution of PTN, SDC3 and PTPζ changed and their expression dramatically decreased even if they were still detectable. PTN and SDC3 immunolabeling was restricted around Purkinje cell bodies and Golgi cells, whereas PTPζ was located around interneurons. These data suggested that, in the cerebellum of adult mice, PTN participates to the perineuronal nets that control neuronal plasticity. To conclude, the present work represents the first spatio-temporal characterization of the PTNergic system in the mouse cerebellum and indicates that PTN may contribute to cerebellum ontogenesis during the postnatal development as well as to neuronal plasticity at adulthood.

Type 2 K+ -Cl- cotransporter is preferentially recruited to climbing fiber synapses during development and the stellate cell-targeting dendritic zone at adulthood in cerebellar Purkinje cells

Postnatal expression of the type 2 K(+) -Cl(-) cotransporter (KCC2) in neurons lowers the Cl(-) equilibrium potential to values that are more negative than the resting potential, thereby converting the action of Cl(-) -permeable GABA(A) and glycine receptors from excitatory to inhibitory. In the present study, we investigated the spatiotemporal expression of KCC2 in mouse cerebella, particularly focusing on Purkinje cells (PCs). First, we confirmed the fundamental expression profiles of KCC2 in the cerebellum, i.e. neuron-specific expression, somatodendritic distribution, and postnatal upregulation. We also found preferential recruitment to climbing fiber (CF) synapses during the second and third postnatal weeks, when perisomatic innervation in PCs switches from CFs to basket cell axons (BAs) and also when single winner CFs translocate from somata to dendrites. In parallel with this synaptic recruitment, the intracellular distribution shifted from a diffuse cytoplasmic to a predominantly cell surface pattern. In adult PCs, CF synapse-associated accumulation was obscured. Instead, significantly high expression was noted on the surface of PC dendrites in the superficial two-thirds of the molecular layer, in which stellate cells reside and project axons to innervate PC dendrites. Thus, the somatodendritic distribution in PCs is regulated in relation to particular inputs or input zones. During development, timed recruitment of KCC2 to CF synapses will augment inhibitory GABAergic actions by incoming BAs, promoting the CF-to-BA switchover in perisomatic PC innervation. In adulthood, enriched KCC2 expression at the stellate cell-targeting territory of PC dendrites might help in maintaining intracellular Cl(-) homeostasis and the polarity of GABA(A) receptor-mediated responses upon sustained activity of this interneuron.

Functional integration of calcium regulatory mechanisms at Purkinje neuron synapses

Cerebellar Purkinje neurons receive synaptic inputs from three different sources: the excitatory parallel fibre and climbing fibre synapses as well as the inhibitory synapses from molecular layer stellate and basket cells. These three synaptic systems use distinct mechanisms in order to generate Ca(2+) signals that are specialized for specific modes of neurotransmitter release and post-synaptic signal integration. In this review, we first describe the repertoire of Ca(2+) regulatory mechanisms that generate and regulate the amplitude and timing of Ca(2+) fluxes during synaptic transmission and then explore how these mechanisms interact to generate the unique functional properties of each of the Purkinje neuron synapses.

Models of calcium dynamics in cerebellar granule cells

Intracellular calcium dynamics is critical for many functions of cerebellar granule cells (GrCs) including membrane excitability, synaptic plasticity, apoptosis, and regulation of gene transcription. Recent measurements of calcium responses in GrCs to depolarization and synaptic stimulation reveal spatial compartmentalization and heterogeneity within dendrites of these cells. However, the main determinants of local calcium dynamics in GrCs are still poorly understood. One reason is that there have been few published studies of calcium dynamics in intact GrCs in their native environment. In the absence of complete information, biophysically realistic models are useful for testing whether specific Ca(2+) handling mechanisms may account for existing experimental observations. Simulation results can be used to identify critical measurements that would discriminate between different models. In this review, we briefly describe experimental studies and phenomenological models of Ca(2+) signaling in GrC, and then discuss a particular biophysical model, with a special emphasis on an approach for obtaining information regarding the distribution of Ca(2+) handling systems under conditions of incomplete experimental data. Use of this approach suggests that Ca(2+) channels and fixed endogenous Ca(2+) buffers are highly heterogeneously distributed in GrCs. Research avenues for investigating calcium dynamics in GrCs by a combination of experimental and modeling studies are proposed.

Effects of calretinin on Ca2+ signals in cerebellar granule cells: implications of cooperative Ca2+ binding

Calretinin is thought to be the main endogenous calcium buffer in cerebellar granule cells (GrCs). However, little is known about the impact of cooperative Ca(2+) binding to calretinin on highly localized and more global (regional) Ca(2+) signals in these cells. Using numerical simulations, we show that an essential property of calretinin is a delayed equilibration with Ca(2+). Therefore, the amount of Ca(2+), which calretinin can accumulate with respect to equilibrium levels, depends on stimulus conditions. Based on our simulations of buffered Ca(2+) diffusion near a single Ca(2+) channel or a large cluster of Ca(2+) channels and previous experimental findings that 150 μM 1,2-bis(o-aminophenoxy) ethane-N, N, N', N'-tetraacetic acid (BAPTA) and endogenous calretinin have similar effects on GrC excitability, we estimated the concentration of mobile calretinin in GrCs in the range of 0.7-1.2 mM. Our results suggest that this estimate can provide a starting point for further analysis. We find that calretinin prominently reduces the action potential associated increase in cytosolic free Ca(2+) concentration ([Ca(2+)]( i )) even at a distance of 30 nm from a single Ca(2+) channel. In spite of a buildup of residual Ca(2+), it maintains almost constant maximal [Ca(2+)]( i ) levels during repetitive channel openings with a frequency less than 80 Hz. This occurs because of accelerated Ca(2+) binding as calretinin binds more Ca(2+). Unlike the buffering of high Ca(2+) levels within Ca(2+) nano/microdomains sensed by large conductance Ca(2+)-activated K(+) channels, the buffering of regional Ca(2+) signals by calretinin can never be mimicked by certain concentration of BAPTA under all different experimental conditions.

Cell population-specific expression analysis of human cerebellum

Background

Interpreting gene expression profiles obtained from heterogeneous samples can be difficult because bulk gene expression measures are not resolved to individual cell populations. We have recently devised Population-Specific Expression Analysis (PSEA), a statistical method that identifies individual cell types expressing genes of interest and achieves quantitative estimates of cell type-specific expression levels. This procedure makes use of marker gene expression and circumvents the need for additional experimental information like tissue composition.

Results

To systematically assess the performance of statistical deconvolution, we applied PSEA to gene expression profiles from cerebellum tissue samples and compared with parallel, experimental separation methods. Owing to the particular histological organization of the cerebellum, we could obtain cellular expression data from in situ hybridization and laser-capture microdissection experiments and successfully validated computational predictions made with PSEA. Upon statistical deconvolution of whole tissue samples, we identified a set of transcripts showing age-related expression changes in the astrocyte population.

Conclusions

PSEA can predict cell-type specific expression levels from tissues homogenates on a genome-wide scale. It thus represents a computational alternative to experimental separation methods and allowed us to identify age-related expression changes in the astrocytes of the cerebellum. These molecular changes might underlie important physiological modifications previously observed in the aging brain.

Proliferative enteropathy (PE)-induced changes in the calbindin-immunoreactive (CB-IR) neurons of inferior mesenteric ganglion supplying the descending colon in the pig

A subpopulation of the pig inferior mesenteric ganglia (IMG) neurons projecting to the colon exhibit calbindin-like immunoreactivity. It is not known if there are any changes in the chemical coding patterns of these neurons during porcine proliferative enteropathy (PE). To answer this question, juvenile Large White Polish pigs with clinically diagnosed Lawsonia intracellularis infection (PE; n = 3) and a group of uninfected controls (C; n = 3) were compared. The retrograde tracer fast blue (FB) was injected into the descending colons of all animals and then tissue comprising IMGs from both groups was processed for double-labeling immunofluorescence with calbindin-D28k (CB) in combination with either tyrosine hydroxylase (TH), neuropeptide Y (NPY), somatostatin (SOM), vasoactive intestinal polypeptide (VIP), nitric oxide synthase, Leu-enkephalin, substance P, vesicular acetylcholine transporter, galanin, or pituitary adenylate cyclase-activating polypeptide. Immunohistochemistry revealed changes in the chemical coding pattern of calbindin-immunoreactive neurons in the inferior mesenteric ganglia of the pig. In control animals, FB/CB-positive neurons were immunoreactive to TH, NPY, SOM, and VIP. In the experimental group, TH-expressing neurons were unaffected, NPY-expressing neurons were increased, whereas the number of neurons immunoreactive to SOM or VIP was reduced. Changes in chemical coding of CB neurons during PE may play an important role in adaptation of these IMG cells under pathological conditions.

Changes induced by natural scrapie in the calretinin-immunopositive cells and fibres of the sheep cerebellar cortex

Calretinin (CR)-immunopositive cells and fibres in the cerebellar cortex (vermal archicerebellum and neocerebellum) of scrapie-affected, ARQ/ARQ, Rasa Aragonesa breed sheep were studied in comparison with healthy, young and aged, ARQ/ARQ, Rasa Aragonesa animals and with Manchega breed sheep. The scrapie-affected sheep showed signs of both cellular involution and hypertrophic/hyperimmunoreactive responses in all neuronal subtypes; the distribution of the neuronal subtypes in the archi- and neocerebellum, however, did not change compared with controls. The results suggest that the different CR expression and/or CR content of cerebellar cortical neurons in scrapie-affected sheep are more related to their specific functions than any neuroprotective response. The reduction in the cell density of some CR-immunopositive neuronal subsets (i.e. unipolar brush cells) is contradictory to the supposed neuroprotective role of the calcium binding protein CR. However, the hyperimmunoreactivity of many CR-immunopositive neuronal subsets (e.g. the Purkinje cells) suggests the involvement of an over-expression of CR (transitory or restricted to selected neurons) as an adaptative mechanism to fight against the neurodegeneration caused by this prion disease. The changes in the number of immunopositive cells and the hypertrophic/hyperimmunoreactive response seen in scrapie-affected and aged sheep suggests that some different and some similar mechanisms are at work in this disease and aging.

Dendritic calcium signaling in cerebellar Purkinje cell

The Purkinje cells in the cerebellum are unique neurons that generate local and global Ca(2+) signals in response to two types of excitatory inputs, parallel fiber and climbing fiber, respectively. The spatiotemporal distribution and interaction of these synaptic inputs produce complex patterns of Ca(2+) dynamics in the Purkinje cell dendrites. The Ca(2+) signals originate from Ca(2+) influx through voltage-gated Ca(2+) channels and Ca(2+) release from intracellular stores that are mediated by the metabotropic glutamate receptor signaling pathway. These Ca(2+) signals are essential for the induction of various forms of synaptic plasticity and for controlling the input-output relationship of Purkinje cells. In this article we review Ca(2+) signaling in Purkinje cell dendrites.

Location, location, location: genetic regulation of neural sex differences

Sex differences in many behaviors such as cognition, mood, and motor skills are well-documented in animals and humans and are regulated by many neural circuits. Sexual dimorphisms within cell populations in these circuits play critical roles in the production of these behavioral dichotomies. Here we focus on three proteins that have well described sexual dimorphisms; calbindin-D28k, a calcium binding protein, tyrosine hydroxylase, the rate limiting enzyme involved in dopamine synthesis and vasopressin, a neuropeptide with central and peripheral sites of action. We describe the sex differences in subpopulations of these proteins, with particular emphasis on laboratory mice. Our thrust is to examine genetic bases of sex differences and how the use of genetically modified models has advanced our understanding of this topic. Regional sex differences in the expression of these three proteins are driven by sex chromosome complement, steroid receptors or in some instances both. While studies of sex differences attributable to sex chromosome genes are still few in number it is exciting to note that this variable factors into expression differences for all three of these proteins. Different genetic mechanisms, which elaborate sex differences, may be employed stochastically in different cell populations. Alternately, general patterns involving the timing of differentiation of the sex differences, relative to the "critical period" in hormonal differences between males and female neonates may emerge. In conclusion, future directions in this area should include examination of the importance of location, timing, steroidal receptor/sex chromosome gene synergy and epigenetics in molding neural sex differences.

Heterochronic protein expression patterns in the developing embryonic chick cerebellum

The advantages of the embryonic chick as a model for studying neural development range from the relatively low cost of fertilized eggs to the rapid rate of development. We investigated in ovo cerebellar development in the chick, which has a nearly identical embryonic period as the mouse (19-22 days). We focused on three antigens: Calbindin (CB), Zebrin II (ZII), and Calretinin (CR), and our results demonstrate asynchronous expression patterns during cerebellar development. Presumptive CB+ Purkinje cells are first observed at embryonic day (E)10 in clusters in posterior cerebellum. At E12, corresponding with global expression of CB across the cerebellum, Purkinje cells began to express ZII. By E14-E16, Purkinje cells disperse into a monolayer and develop a pattern of alternating immunopositive and immunonegative ZII stripes. CR is initially expressed by clusters of presumptive Purkinje cells in the nodular zone at E8. However, this expression is transient and at later stages, CR is largely confined to the granule and molecular layers. Before hatch (E18-E20), Purkinje cells adopt a morphologically mature phenotype with complex dendritic arborizations. Comparing this data to that seen in mice, we found that the sequence of Purkinje cell formation, protein expression, and development is similar in both species, but these events consistently begin ∼5-7 days earlier in the precocial chick cerebellum, suggesting an important role for heterochrony in neurodevelopment.

Regional distribution of calretinin and calbindin-D28k expression in the brain of the urodele amphibian Pleurodeles waltl during embryonic and larval development

The sequence of appearance of calretinin and calbindin-D28k immunoreactive (CRir and CBir, respectively) cells and fibers has been studied in the brain of the urodele amphibian Pleurodeles waltl. Embryonic, larval and juvenile stages were studied. The early expression and the dynamics of the distribution of CBir and CRir structures have been used as markers for developmental aspects of distinct neuronal populations, highlighting the accurate extent of many regions in the developing brain, not observed on the basis of cytoarchitecture alone. CR and, to a lesser extent, CB are expressed early in the central nervous system and show a progressively increasing expression from the embryonic stages throughout the larval life and, in general, the labeled structures in the developing brain retain their ability to express these proteins in the adult brain. The onset of CRir cells primarily served to follow the development of the olfactory bulbs, subpallium, thalamus, alar hypothalamus, mesencephalic tegmentum, and distinct cell populations in the rhombencephalic reticular formation. CBir cells highlighted the development of, among others, the pallidum, hypothalamus, dorsal habenula, midbrain tegmentum, cerebellum, and central gray of the rostral rhombencephalon. However, it was the relative and mostly segregated distribution of both proteins in distinct cell populations which evidenced the developing regionalization of the brain. The results have shown the usefulness in neuroanatomy of the analysis during development of the onset of CBir and CRir structures, but the comparison with previous data has shown extensive variability across vertebrate classes. Therefore, one should be cautious when comparing possible homologue structures across species only on the basis of the expression of these proteins, due to the variation of the content of calcium-binding proteins observed in well-established homologous regions in the brain of different vertebrates.

Pinceau organization in the cerebellum requires distinct functions of neurofascin in Purkinje and basket neurons during postnatal development

Basket axon collaterals synapse onto the Purkinje soma/axon initial segment (AIS) area to form specialized structures, the pinceau, which are critical for normal cerebellar function. Mechanistic details of how the pinceau become organized during cerebellar development are poorly understood. Loss of cytoskeletal adaptor protein Ankyrin G (AnkG) results in mislocalization of the cell adhesion molecule Neurofascin (Nfasc) at the Purkinje AIS and abnormal organization of the pinceau. Loss of Nfasc in adult Purkinje neurons leads to slow disorganization of the Purkinje AIS and pinceau morphology. Here, we used mouse conditional knock-out techniques to show that selective loss of Nfasc, specifically in Purkinje neurons during early development, prevented maturation of the AIS and resulted in loss of Purkinje neuron spontaneous activity and pinceau disorganization. Loss of Nfasc in both Purkinje and basket neurons caused abnormal basket axon collateral branching and targeting to Purkinje soma/AIS, leading to extensive pinceau disorganization, Purkinje neuron degeneration, and severe ataxia. Our studies reveal that the Purkinje Nfasc is required for AIS maturation and for maintaining stable contacts between basket axon terminals and the Purkinje AIS during pinceau organization, while the basket neuron Nfasc in combination with Purkinje Nfasc is required for proper basket axon collateral outgrowth and targeting to Purkinje soma/AIS. Thus, cerebellar pinceau organization requires coordinated mechanisms involving specific Nfasc functions in both Purkinje and basket neurons.

Purkinje Cell Heterotopy With Cerebellar Hypoplasia in Two Free-Living American Kestrels (Falco sparverius)

Two wild fledgling kestrels exhibited lack of motor coordination, postural reaction deficits, and abnormal propioception. At necropsy, the cerebellum and brainstem were markedly underdeveloped. Microscopically, there was Purkinje cells heterotopy, abnormal circuitry, and hypoplasia with defective foliation. Heterotopic neurons were identified as immature Purkinje cells by their size, location, immunoreactivity for calbindin D-28 K, and ultrastructural features. The authors suggest that this cerebellar abnormality was likely due to a disruption of molecular mechanisms that dictate Purkinje cell migration, placement, and maturation in early embryonic development. The etiology of this condition remains undetermined. Congenital central nervous system disorders have rarely been reported in birds.

The genesis of cerebellar GABAergic neurons: fate potential and specification mechanisms

All cerebellar neurons derive from progenitors that proliferate in two germinal neuroepithelia: the ventricular zone (VZ) generates GABAergic neurons, whereas the rhombic lip is the origin of glutamatergic types. Among VZ-derivatives, GABAergic projection neurons, and interneurons are generated according to distinct strategies. Projection neurons (Purkinje cells and nucleo-olivary neurons) are produced at the onset of cerebellar neurogenesis by discrete progenitor pools located in distinct VZ microdomains. These cells are specified within the VZ and acquire mature phenotypes according to cell-autonomous developmental programs. On the other hand, the different categories of inhibitory interneurons derive from a single population of Pax-2-positive precursors that delaminate into the prospective white matter (PWM), where they continue to divide up to postnatal development. Heterotopic/heterochronic transplantation experiments indicate that interneuron progenitors maintain full developmental potentialities up to the end of cerebellar development and acquire mature phenotypes under the influence of environmental cues present in the PWM. Furthermore, the final fate choice occurs in postmitotic cells, rather than dividing progenitors. Extracerebellar cells grafted to the prospective cerebellar white matter are not responsive to local neurogenic cues and fail to adopt clear cerebellar identities. Conversely, cerebellar cells grafted to extracerebellar regions retain typical phenotypes of cerebellar GABAergic interneurons, but acquire type-specific traits under the influence of local cues. These findings indicate that interneuron progenitors are multipotent and sensitive to spatio-temporally patterned environmental signals that regulate the genesis of different categories of interneurons, in precise quantities and at defined times and places.

Immunocytochemical localization of calretinin-containing neurons in the rat periaqueductal gray and colocalization with enzymes producing nitric oxide: a double, double-labeling study

The pattern of distribution and colocalization of the calcium-binding protein calretinin (Cal) and of enzymes producing nitric oxide (NO) was examined in the rat periaqueductal gray matter (PAG) using two different experimental approaches, by combining Cal immunocytochemistry with NADPH-diaphorase (NADPH-d) histochemistry and with NOS immunocytochemistry, respectively. Cal-immunopositive neurons were found throughout the rostrocaudal extension of both dorsolateral (PAG-dl) and ventrolateral PAG (PAG-vl). Double-labeled neurons were found only in PAG-dl. The first experimental approach indicated that 33-41% of the NADPH-d-positive (Nadph+) cells were immunoreactive for Cal, whereas NADPH-d activity appeared in 19-26% of the Cal-immunopositive (Cal(IP) ) neurons. Two-color immunofluorescence revealed that ∼39-43% of NOS-immunoreactive (NOS(IR) ) neurons were double-labeled with Cal and ∼23% of Cal(IP) neurons expressed NOS immunoreactivity. Measurement in semithin sections of the size of the three neuronal populations found in PAG-dl, showed that Cal(IP) neurons had a cross-sectional area of 94.7 μm², whereas Nadph+ neurons and double-labeled neurons were slightly smaller, having a cross-sectional area of 90.5 and 91.4 μm², respectively. On electron microscopy, Cal(IP) axon terminals formed either symmetric or asymmetric synapses; although the latter synapses were more numerous, both types contacted preferentially Cal(IP) dendrites. These experiments suggest that PAG-dl is characterized by a high degree of heterogeneity.

Copper is toxic to PrP-ablated mice and exacerbates disease in a mouse model of E200K genetic prion disease

The pathogenesis of the diverse forms of prion disease was attributed solely to the accumulation of the misfolded PrP forms, and not to the potential loss of normal PrP(C) function during disease propagation. In this respect, it was also not established whether mutant PrPs linked to genetic prion diseases, as is the case for E200K PrP, preserve the function of PrP(C). We now show that fibroblasts generated from both PrP-ablated mice and TgMHu2ME199K, a transgenic mouse line mimicking E200KCJD, were significantly more sensitive to copper toxicity than wt fibroblasts. Long-term administration of copper significantly accelerated the onset and progression of spontaneous prion disease in TgMHu2ME199K mice and caused marked irritability and cerebellar associated tip-toe walking in PrP(0/0) mice, while wt mice were not affected. Our results are consistent with the hypothesis that a functional PrP(C) is required to protect cells from high levels of copper, and that its substitution for a nonfunctional mutant PrP may accelerate the onset of genetic prion disease during oxidative insults.

PCP4 (PEP19) overexpression induces premature neuronal differentiation associated with Ca(2+) /calmodulin-dependent kinase II-δ activation in mouse models of Down syndrome

Pcp4/pep19 is a modulator of Ca(2+) -CaM, a key molecule for calcium signaling, expressed in postmitotic neuroectoderm cells during mouse embryogenesis. The PCP4 gene is located on human chromosome 21 and is present in three copies in Down syndrome (DS). To evaluate the consequences of three copies of this gene on the development of these cells in the nervous system, we constructed a transgenic (TgPCP4) mouse model, with one copy of human PCP4, and investigated the effects in this model and in the Ts1Cje, a mouse model of DS. During embryogenesis, we analyzed 1) the level of pcp4 transcript and protein in the two models; 2) the extent of colabeling for markers of neuronal differentiation (βIII-tubulin, Map2c, calbindin, and calretinin) and pcp4 by immunofluorescence analysis and overall protein levels of these markers by Western blotting; and 3) the rate of activation of CaMKII, a Ca(2+) -CaM target, to evaluate the impact of pcp4 overexpression on the Ca(2+) -CaM signaling pathway. We showed that three copies of the pcp4 gene induced the overexpression of transcripts and proteins during embryogenesis. Pcp4 overexpression 1) induced precocious neuronal differentiation, as shown by the distribution and levels of early neuronal markers; and 2) was associated with an increase in CaMKIIδ activation, confirming involvement in neuronal differentiation in vivo via a Pcp4-Ca(2+) -CaM pathway. TgPCP4 and Ts1Cje mice developed similar modifications, demonstrating that these mechanisms may account for abnormal neuronal development in DS.

A novel mouse model of Niemann-Pick type C disease carrying a D1005G-Npc1 mutation comparable to commonly observed human mutations

We have identified a point mutation in Npc1 that creates a novel mouse model (Npc1(nmf164)) of Niemann-Pick type C1 (NPC) disease: a single nucleotide change (A to G at cDNA bp 3163) that results in an aspartate to glycine change at position 1005 (D1005G). This change is in the cysteine-rich luminal loop of the NPC1 protein and is highly similar to commonly occurring human mutations. Genetic and molecular biological analyses, including sequencing the Npc1(spm) allele and identifying a truncating mutation, confirm that the mutation in Npc1(nmf164) mice is distinct from those in other existing mouse models of NPC disease (Npc1(nih), Npc1(spm)). Analyses of lifespan, body and spleen weight, gait and other motor activities, as well as acoustic startle responses all reveal a more slowly developing phenotype in Npc1(nmf164) mutant mice than in mice with the null mutations (Npc1(nih), Npc1(spm)). Although Npc1 mRNA levels appear relatively normal, Npc1(nmf164) brain and liver display dramatic reductions in Npc1 protein, as well as abnormal cholesterol metabolism and altered glycolipid expression. Furthermore, histological analyses of liver, spleen, hippocampus, cortex and cerebellum reveal abnormal cholesterol accumulation, glial activation and Purkinje cell loss at a slower rate than in the Npc1(nih) mouse model. Magnetic resonance imaging studies also reveal significantly less demyelination/dysmyelination than in the null alleles. Thus, although prior mouse models may correspond to the severe infantile onset forms of NPC disease, Npc1(nmf164) mice offer many advantages as a model for the late-onset, more slowly progressing forms of NPC disease that comprise the large majority of human cases.

Ascl1 genetics reveals insights into cerebellum local circuit assembly

Two recently generated targeted mouse alleles of the neurogenic gene Ascl1 were used to characterize cerebellum circuit formation. First, genetic inducible fate mapping (GIFM) with an Ascl1(CreER) allele was found to specifically mark all glial and neuron cell types that arise from the ventricular zone (vz). Moreover, each cell type has a unique temporal profile of marking with Ascl1(CreER) GIFM. Of great utility, Purkinje cells (Pcs), an early cohort of Bergmann glia, and four classes of GABAergic interneurons can be genetically birth dated during embryogenesis using Ascl1(CreER) GIFM. Astrocytes and oligodendrocytes, in contrast, express Ascl1(CreER) throughout their proliferative phase in the white matter. Interestingly, the final position each neuron type acquires differs depending on when it expresses Ascl1. Interneurons (including candelabrum) attain a more outside position the later they express Ascl1, whereas Pcs have distinct settling patterns each day they express Ascl1. Second, using a conditional Ascl1 allele, we discovered that Ascl1 is differentially required for generation of most vz-derived cells. Mice lacking Ascl1 in the cerebellum have a major decrease in three types of interneurons with a tendency toward a loss of later-born interneurons, as well as an imbalance of oligodendrocytes and astrocytes. Double-mutant analysis indicates that a related helix-loop-helix protein, Ptf1a, functions with Ascl1 in generating interneurons and Pcs. By fate mapping vz-derived cells in Ascl1 mutants, we further discovered that Ascl1 plays a specific role during the time period when Pcs are generated in restricting vz progenitors from becoming rhombic lip progenitors.

Sources of calretinin inputs to motoneurons of extraocular muscles involved in upgaze

Recent monkey studies showed that motoneurons of the oculomotor nucleus involved in upward eye movements receive a selective input from afferents containing calretinin (CR). Here, we investigated the sources of these CR-positive afferents. After injections of tract-tracers into the oculomotor nucleus (nIII) of two monkeys, the retrograde labeling was combined with CR-immunofluorescence in frozen brainstem sections. Three sources of CR inputs to nIII were found: the rostral interstitial nucleus of the medial longitudinal fascicle (RIMLF), the interstitial nucleus of Cajal, and the y-group. CR is not present in all premotor upward-moving pathways. The excitatory secondary vestibulo-ocular neurons in the magnocellular part of the medial vestibular nuclei contained nonphosphorylated neurofilaments, but no CR, and they received a strong supply of large CR-positive boutons. In conclusion, the present study presents evidence that only specific premotor pathways for upward eye movements--excitatory upgaze pathways--contain CR, but not the up vestibulo-ocular reflex pathways. This property may help to differentiate between premotor up- and downgaze pathways in correlative clinico-anatomical studies in humans.

Modulation of cell-cycle dynamics is required to regulate the number of cerebellar GABAergic interneurons and their rhythm of maturation

The progenitors of cerebellar GABAergic interneurons proliferate up to postnatal development in the prospective white matter, where they give rise to different neuronal subtypes, in defined quantities and according to precise spatiotemporal sequences. To investigate the mechanisms that regulate the specification of distinct interneuron phenotypes, we examined mice lacking the G1 phase-active cyclin D2. It has been reported that these mice show severe reduction of stellate cells, the last generated interneuron subtype. We found that loss of cyclin D2 actually impairs the whole process of interneuron genesis. In the mutant cerebella, progenitors of the prospective white matter show reduced proliferation rates and enhanced tendency to leave the cycle, whereas young postmitotic interneurons undergo severe delay of their maturation and migration. As a consequence, the progenitor pool is precociously exhausted and the number of interneurons is significantly reduced, although molecular layer interneurons are more affected than those of granular layer or deep nuclei. The characteristic inside-out sequence of interneuron placement in the cortical layers is also reversed, so that later born cells occupy deeper positions than earlier generated ones. Transplantation experiments show that the abnormalities of cyclin D2(-/-) interneurons are largely caused by cell-autonomous mechanisms. Therefore, cyclin D2 is not required for the specification of particular interneuron subtypes. Loss of this protein, however, disrupts regulatory mechanisms of cell cycle dynamics that are required to determine the numbers of interneurons of different types and impairs their rhythm of maturation and integration in the cerebellar circuitry.

Zac1 plays a key role in the development of specific neuronal subsets in the mouse cerebellum

BACKGROUND

The cerebellum is composed of a diverse array of neuronal subtypes. Here we have used a candidate approach to identify Zac1, a tumor suppressor gene encoding a zinc finger transcription factor, as a new player in the transcriptional network required for the development of a specific subset of cerebellar nuclei and a population of Golgi cells in the cerebellar cortex.

RESULTS

We found that Zac1 has a complex expression profile in the developing cerebellum, including in two proliferating progenitor populations; the cerebellar ventricular zone and the external granular layer overlying posterior cerebellar lobules IX and X. Zac1 is also expressed in some postmitotic cerebellar neurons, including a subset of GABAergic interneurons in the medial cerebellar nuclei. Notably, GABAergic interneurons in the cerebellar nuclei are derived from the cerebellar ventricular zone, where Zac1 is also expressed, consistent with a lineage relationship between these two Zac1+ populations. Zac1 is also expressed in a small subset of cells in the posterior vermis, including some neurogranin-immunoreactive (NG+) Golgi cells, which, based on short-term birthdating, are derived from the EGL, where Zac1 is also expressed. However, Zac1+ cells and NG+ Golgi cells in the cerebellar cortex also display unique properties, as they are generated within different, albeit overlapping, time windows. Finally, consistent with the expression profile of Zac1, two conspicuous abnormalities were found in the cerebellum of Zac1 null mice: the medial cerebellar nuclei, and not the others, were significantly reduced in size; and the number of Golgi cells in cerebellar lobule IX was reduced by approximately 60% compared to wild-type littermates.

CONCLUSIONS

The data presented here indicate that the tumor suppressor gene Zac1 is expressed in a complex fashion in the developing cerebellum, including in two dividing progenitor populations and in specific subsets of postmitotic neurons, including Golgi cells and GABAergic neurons in the medial nuclei, which require Zac1 for their differentiation. We thus conclude that Zac1 is a critical regulator of normal cerebellar development, adding a new transcriptional regulator to the growing list of factors involved in generating neuronal diversity in the developing cerebellum.

Zac1 plays a key role in the development of specific neuronal subsets in the mouse cerebellum

Background

The cerebellum is composed of a diverse array of neuronal subtypes. Here we have used a candidate approach to identify Zac1, a tumor suppressor gene encoding a zinc finger transcription factor, as a new player in the transcriptional network required for the development of a specific subset of cerebellar nuclei and a population of Golgi cells in the cerebellar cortex.

Results

We found that Zac1 has a complex expression profile in the developing cerebellum, including in two proliferating progenitor populations; the cerebellar ventricular zone and the external granular layer overlying posterior cerebellar lobules IX and X. Zac1 is also expressed in some postmitotic cerebellar neurons, including a subset of GABAergic interneurons in the medial cerebellar nuclei. Notably, GABAergic interneurons in the cerebellar nuclei are derived from the cerebellar ventricular zone, where Zac1 is also expressed, consistent with a lineage relationship between these two Zac1⁺ populations. Zac1 is also expressed in a small subset of cells in the posterior vermis, including some neurogranin-immunoreactive (NG⁺) Golgi cells, which, based on short-term birthdating, are derived from the EGL, where Zac1 is also expressed. However, Zac1⁺ cells and NG⁺ Golgi cells in the cerebellar cortex also display unique properties, as they are generated within different, albeit overlapping, time windows. Finally, consistent with the expression profile of Zac1, two conspicuous abnormalities were found in the cerebellum of Zac1 null mice: the medial cerebellar nuclei, and not the others, were significantly reduced in size; and the number of Golgi cells in cerebellar lobule IX was reduced by approximately 60% compared to wild-type littermates.

Conclusions

The data presented here indicate that the tumor suppressor gene Zac1 is expressed in a complex fashion in the developing cerebellum, including in two dividing progenitor populations and in specific subsets of postmitotic neurons, including Golgi cells and GABAergic neurons in the medial nuclei, which require Zac1 for their differentiation. We thus conclude that Zac1 is a critical regulator of normal cerebellar development, adding a new transcriptional regulator to the growing list of factors involved in generating neuronal diversity in the developing cerebellum.

Arginine-rich cell-penetrating peptide dramatically enhances AMO-mediated ATM aberrant splicing correction and enables delivery to brain and cerebellum

Antisense morpholino oligonucleotides (AMOs) can reprogram pre-mRNA splicing by complementary binding to a target site and regulating splice site selection, thereby offering a potential therapeutic tool for genetic disorders. However, the application of this technology into a clinical scenario has been limited by the low correction efficiency in vivo and inability of AMOs to efficiently cross the blood brain barrier and target brain cells when applied to neurogenetic disorders such as ataxia-telangiecatasia (A-T). We previously used AMOs to correct subtypes of ATM splicing mutations in A-T cells; AMOs restored up to 20% of the ATM protein and corrected the A-T cellular phenotype. In this study, we demonstrate that an arginine-rich cell-penetrating peptide, (RXRRBR)(2)XB, dramatically improved ATM splicing correction efficiency when conjugated with AMOs, and almost fully corrected aberrant splicing. The restored ATM protein was close to normal levels in cells with homozygous splicing mutations, and a gene dose effect was observed in cells with heterozygous mutations. A significant amount of the ATM protein was still detected 21 days after a single 5 µm treatment. Systemic administration of an fluorescein isothiocyanate-labeled (RXRRBR)(2)XB-AMO in mice showed efficient uptake in the brain. Fluorescence was evident in Purkinje cells after a single intravenous injection of 60 mg/kg. Furthermore, multiple injections significantly increased uptake in all areas of the brain, notably in cerebellum and Purkinje cells, and showed no apparent signs of toxicity. Taken together, these results highlight the therapeutic potential of (RXRRBR)(2)XB-AMOs in A-T and other neurogenetic disorders.

Disruption of metabotropic glutamate receptor signalling is a major defect at cerebellar parallel fibre-Purkinje cell synapses in staggerer mutant mice

Staggerer mutant mice have functional loss of a transcription factor, retinoid-related orphan receptor α (RORα), which is abundantly expressed in Purkinje cells (PCs) of the cerebellum.Homozygous staggerer (sg/sg)mice show cerebellar hypoplasia and congenital ataxia. Sg/sg mice serve as an important extreme mouse model of the hereditary spinocerebellar ataxia type 1 (SCA1), since it has been shown that RORα dysfunction is strongly correlated with SCA1 pathogenesis. However, synaptic abnormalities, especially at parallel fibre (PF)-PC synapses, in SCA1-related sg/sg mice have not been examined in detail electrophysiologically. In this study, we report that PFs can still establish functional synapses onto PCs in sg/sg mice in spite of reduction in the number of PF-PC synapses. Compared with PF-evoked EPSCs in the wild-type or heterozygotes, the success rate of the EPSC recordings in sg/sg was quite low (∼40%) and the EPSCs showed faster kinetics and slightly decreased paired pulse facilitation at short intervals. The prominent synaptic dysfunction is that sg/sg mice lack metabotropic glutamate receptor (mGluR)-mediated slow EPSCs completely. Neither intense PF stimulation nor an exogenously applied mGluR agonist, DHPG, could elicit mGluR-mediated responses.Western blot analysis in the sg/sg cerebellum revealed low-level expression of mGluR1 and TRPC3, both of which underlie mGluR-mediated slow currents in PCs. Immunohistochemical data demonstrated marked mislocalization of mGluR1 on sg/sg PCs.We found that mGluR-mediated retrograde suppression of PF-PC EPSCs by endocannabinoid is also impaired completely in sg/sg mice. These results suggest that disruption of mGluR signalling at PF-PC synapses is one of the major synaptic defects in sg/sg mice and may manifest itself in SCA1 pathology.

Apoptosis inducing factor deficiency causes reduced mitofusion 1 expression and patterned Purkinje cell degeneration

Alteration in mitochondrial dynamics has been implicated in many neurodegenerative diseases. Mitochondrial apoptosis inducing factor (AIF) plays a key role in multiple cellular and disease processes. Using immunoblotting and flow cytometry analysis with Harlequin mutant mice that have a proviral insertion in the AIF gene, we first revealed that mitofusion 1 (Mfn1), a key mitochondrial fusion protein, is significantly diminished in Purkinje cells of the Harlequin cerebellum. Next, we investigated the cerebellar pathology of Harlequin mice in an age-dependent fashion, and identified a striking process of progressive and patterned Purkinje cell degeneration. Using immunohistochemistry with zebrin II, the most studied compartmentalization marker in the cerebellum, we found that zebrin II-negative Purkinje cells first started to degenerate at 7 months of age. By 11 months of age, almost half of the Purkinje cells were degenerated. Subsequently, most of the Purkinje cells disappeared in the Harlequin cerebellum. The surviving Purkinje cells were concentrated in cerebellar lobules IX and X, where these cells were positive for heat shock protein 25 and resistant to degeneration. We further showed that the patterned Purkinje cell degeneration was dependent on caspase but not poly(ADP-ribose) polymerase-1 (PARP-1) activation, and confirmed the marked decrease of Mfn1 in the Harlequin cerebellum. Our results identified a previously unrecognized role of AIF in Purkinje cell degeneration, and revealed that AIF deficiency leads to altered mitochondrial fusion and caspase-dependent cerebellar Purkinje cell loss in Harlequin mice. This study is the first to link AIF and mitochondrial fusion, both of which might play important roles in neurodegeneration.

Sex differences in the cerebellum and frontal cortex: roles of estrogen receptor alpha and sex chromosome genes

Most neurobehavioral diseases are sexually dimorphic in their incidence, and sex differences in the brain may be key for understanding and treating these diseases. Calbindin (Calb) D28K is used as a biomarker for the well-studied sexually dimorphic nucleus, a hypothalamic structure that is larger in males than in females. In the current study weanling C56BL/6J mice were used to examine sex differences in the Calb protein and message focusing on regions outside of the hypothalamus. A robust sex difference was found in Calb in the frontal cortex (FC) and cerebellum (CB; specifically in Purkinje cells); mRNA and protein were higher in females than in males. Using 2 mouse lines, i.e. one with a complete deletion of estrogen receptor alpha (ERα) and the other with uncoupled gonads and sex chromosomes, we probed the mechanisms that underlie sexual dimorphisms. In the FC, deletion of ERα reduced Calb1 mRNA in females compared to males. In addition, females with XY sex chromosomes had levels of Calb1 equal to those of males. Thus, both ERα and the sex chromosome complement regulate Calb1 in the FC. In the CB, ERα knockout mice of both sexes had reduced Calb1 mRNA, yet sex differences were retained. However, the sex chromosome complement, regardless of gonadal sex, dictated Calb1 mRNA levels. Mice with XX chromosomes had significantly greater Calb1 than did XY mice. This is the first study demonstrating that sex chromosome genes are a driving force producing sex differences in the CB and FC, which are neuoranatomical regions involved in many normal functions and in neurobehavioral diseases.

Evidence for tangential migration disturbances in human lissencephaly resulting from a defect in LIS1, DCX and ARX genes

During corticogenesis, neurons adopt different migration pathways to reach their final position. The precursors of pyramidal neurons migrate radially, whereas most of the GABA-containing interneurons are generated in the ventral telencephalon and migrate tangentially into the neocortex. Then, they use a radial migration mode to establish themselves in an inside-out manner in the neocortex, similarly to pyramidal neurons. In humans, the most severe defects in radial migration result in lissencephaly. Lately, a few studies suggested that lissencephaly was also associated with tangential neuronal migration deficits. In the present report, we investigated potential anomalies of this migration mode in three agyric/pachygyric syndromes due to defects in the LIS1, DCX and ARX genes. Immunohistochemistry was performed on paraffin-embedded supra- and infratentorial structures using calretinin, calbindin and parvalbumin antisera. The results were compared with age-matched control brain tissue. In the Miller-Dieker syndrome, GABAergic neurons were found both in upper layers of the cortex and in heterotopic positions in the intermediate zone and in ganglionic eminences. In the DCX mutant brain, few interneurons were dispersed in the cortical plate, with a massive accumulation in the intermediate zone and subventricular zone as well as in the ganglionic eminences. In the ARX-mutated brain, the cortical plate contained almost exclusively pyramidal cells and was devoid of interneurons. The ganglionic eminences and basal ganglia were poorly cellular, suggesting an interneuron production and/or differentiation defect. These data argue for different mechanisms of telencephalic tangential migration impairment in these three agyric/pachygyric syndromes.

Organization and neurochemical properties of intersegmental interneurons in the lumbar enlargement of the adult rat

Intersegmental interneurons with relatively short axons perform an important role in the coordination of limb movement but surprisingly little is known about their organization and how they contribute to neuronal networks in the adult rat. We undertook a series of anatomical tract-tracing studies to label cell bodies and axons of intersegmental neurons in the lumbar cord and characterized their neurochemical properties by using immunocytochemistry. The b-subunit of cholera toxin was injected into L1 or L3 segments of seven rats in the vicinity of lateral or medial motor nuclei. In L5 lumbar segments, cells were found to be concentrated in contralateral lamina VIII, and in ipsilateral lamina VII and laminae V-VI following injections into the lateral and medial motor nuclei respectively. About 25% of labelled cells contained calbindin or calretinin or a combination of both. Calbindin positive cells were mainly distributed within the ipsilateral side of the L5 segment, especially within the ipsilateral dorsal horn whereas there was a concentration of calretinin cells in contralateral lamina VIII. A small population of cells around the central canal were cholinergic. We also examined axon terminals that projected from L1/3 to the L5 contralateral lateral motor nucleus. The majority of these axons were excitatory (75%) and made direct contacts with motoneurons. However, most inhibitory axons in L5 contained a mixture of GABA and glycine (20%) and about 22% of the total population of axons contained calbindin. In contrast, 19% of all intra-segmental axons in the L3 contralateral lateral motor nucleus were found to be purely glycinergic and 17% contained a mixture of GABA and glycine. This study shows that short range interneurons form extensive ipsi- and contralateral projections within the lumbar enlargement and that many of them contain calcium binding proteins. Those projecting contralaterally to motor nuclei are predominantly excitatory.

Calcium-binding protein immunoreactivity characterizes the auditory system of Gekko gecko

Geckos use vocalizations for intraspecific communication, but little is known about the organization of their central auditory system. We therefore used antibodies against the calcium-binding proteins calretinin (CR), parvalbumin (PV), and calbindin-D28k (CB) to characterize the gecko auditory system. We also examined expression of both glutamic acid decarboxlase (GAD) and synaptic vesicle protein (SV2). Western blots showed that these antibodies are specific to gecko brain. All three calcium-binding proteins were expressed in the auditory nerve, and CR immunoreactivity labeled the first-order nuclei and delineated the terminal fields associated with the ascending projections from the first-order auditory nuclei. PV expression characterized the superior olivary nuclei, whereas GAD immunoreactivity characterized many neurons in the nucleus of the lateral lemniscus and some neurons in the torus semicircularis. In the auditory midbrain, the distribution of CR, PV, and CB characterized divisions within the central nucleus of the torus semicircularis. All three calcium-binding proteins were expressed in nucleus medialis of the thalamus. These expression patterns are similar to those described for other vertebrates.

Immunohistochemical localization of calbindin D28-k, parvalbumin, and calretinin in the cerebellar cortex of the circling mouse

The spontaneous mutant circling mouse has an autosomal recessive pattern of inheritance and is an animal model for deafness, which is characterized by circling, head tossing, and hyperactivity. Since the main pathology in circling mice lies in the organ of Corti, most studies on deaf mice have focused on auditory brain stem nuclei. No studies regarding behavior-related CNS changes in circling mice have been reported. The major center of sensory input for modulation of motor activity is best-studied in the cerebellum. Considering the importance of calcium homeostasis in numerous processes, calcium-binding proteins (CaBPs), such as calbindin D-28k (CB), parvalbumin (PV), and calretinin (CR), may play crucial roles in preserving cerebellar coordinated motor function. Thus, the distribution of CB, PV, and CR was determined in the cerebellum using immunohistochemical methods to compare immunoreactivity (IR) of CaBPs between wild-type (+/+), heterozygous (+/cir), and homozygous (cir/cir) mice. The IR of CB and PV was predominantly observed in the Purkinje cell layer of all three genotypes. Compared with the +/+ genotype, the relative mean density of CB and PV IR in the Purkinje cell layer and CR IR in the granular layer was significantly decreased in the cir/cir genotype. Changes in calcium homeostasis in parallel fiber/Purkinje cell synapses could diminish cerebellar control of motor coordination. A number of deficiencies among the CaBPs lead to distinct alterations in brain physiology, which may affect normal behavior.

Plasma membrane Ca2+-ATPases in the nervous system during development and ageing

Calcium signaling is used by neurons to control a variety of functions, including cellular differentiation, synaptic maturation, neurotransmitter release, intracellular signaling and cell death. This review focuses on one of the most important Ca²⁺ regulators in the cell, the plasma membrane Ca²⁺-ATPase (PMCA), which has a high affinity for Ca²⁺ and is widely expressed in brain. The ontogeny of PMCA isoforms, linked to specific requirements of Ca²⁺ during development of different brain areas, is addressed, as well as their function in the adult tissue. This is based on the high diversity of variants in the PMCA family in brain, which show particular kinetic differences possibly related to specific localizations and functions of the cell. Conversely, alterations in the activity of PMCAs could lead to changes in Ca²⁺ homeostasis and, consequently, to neural dysfunction. The involvement of PMCA isoforms in certain neuropathologies and in brain ageing is also discussed.

Perinatal copper deficiency alters rat cerebellar purkinje cell size and distribution

Copper is required for activity of several key enzymes and for optimal mammalian development, especially within the central nervous system. Copper-deficient (CuD) animals are visibly ataxic, and previous studies in rats have demonstrated impaired motor function through behavioral experiments consistent with altered cerebellar development. Perinatal copper deficiency was produced in Holtzman rat dams by restricting dietary copper during the last two thirds of gestation and lactation. Male offspring were evaluated at postnatal day 25. Compared to cerebella from copper-adequate pups, the CuD pups had larger Purkinje cell (PC) size and irregularities in the Purkinje cell monolayer. These results suggest that the ataxic behavioral phenotype of CuD rats may result from disrupted inhibitory pathways in the cerebellum. A similar PC phenotype is seen in Menkes disease and in mottled mouse mutants with genetic copper deficiency, suggesting that copper deficiency and not just specific loss of ATP7A function is responsible.

Of mice and rats: key species variations in the sexual differentiation of brain and behavior

Mice and rats are important mammalian models in biomedical research. In contrast to other biomedical fields, work on sexual differentiation of brain and behavior has traditionally utilized comparative animal models. As mice are gaining in popularity, it is essential to acknowledge the differences between these two rodents. Here we review neural and behavioral sexual dimorphisms in rats and mice, which highlight species differences and experimental gaps in the literature, that are needed for direct species comparisons. Moving forward, investigators must answer fundamental questions about their chosen organism, and attend to both species and strain differences as they select the optimal animal models for their research questions.

Local connection patterns of parvalbumin-positive inhibitory interneurons in rat primary auditory cortex

In the auditory cortex (AC), GABAergic neurons constitute approximately 15-25% of all neurons. GABAergic cells are present in all sensory modalities and essential for modulating sensory receptive fields. Parvalbumin (PV) positive cells represent the largest sub-group of the GABAergic population in auditory neocortex. We investigated the projection pattern of PV cells in rat primary auditory cortex (AI) with a retrograde tracer (wheat germ apo-HRP conjugated to gold [WAHG]) and immunocytochemistry for PV. All AC layers except layer I contained cells double-labeled for PV and WAHG. All co-localized PV+ cells were within 2 mm of the injection site, regardless of laminar origin. Most (ca. 90%) of the co-localized PV cells were within 500 μm of the injection site in both dorsal-ventral and rostral-caudal dimension of the auditory core region. WAHG-only cells declined less rapidly with distance and were found up to 6 mm from the deposit sites. WAHG-only labeled cells in the medial geniculate body were in ventral division loci compatible with an injection in AI. Differences in the range and direction of the distribution pattern of co-localized PV+ cells and WAHG-only cells in AI express distinct functional convergence patterns for the two cell populations.

Reduced size of the dendritic tree does not protect Purkinje cells from excitotoxic death

Purkinje cell loss by excitotoxic damage is a typical finding in many cerebellar diseases. One important aspect of this high sensitivity of Purkinje cells to excitotoxic death might be the enormous size of their dendritic tree, with a high load of excitatory glutamate receptors. We have studied whether reduction in the size of the dendritic tree might confer resistance against excitotoxic death to Purkinje cells. We have grown Purkinje cells in organotypic cerebellar slice cultures under chronic activation of metabotropic glutamate receptors or of protein kinase C. Both treatments strongly reduced dendritic tree size. After this treatment, cells were exposed to the glutamate receptor agonist AMPA, which has a strong excitotoxic effect on Purkinje cells. We found that Purkinje cells with small dendritic trees were as sensitive to AMPA exposure as untreated control cells with large dendritic trees. Immunostaining against vesicular glutamate transporter 1 revealed that the small dendritic trees were densely covered by glutamatergic terminals. Our results indicate that the expansion of the dendritic tree and the total number of AMPA receptors per neuron do not play a major role in determining the susceptibility of Purkinje cells to excitotoxic death.

Innervation of tracheal parasympathetic ganglia by esophageal cholinergic neurons: evidence from anatomic and functional studies in guinea pigs

In the present study, we describe a subset of nerve fibers, characterized by their immunoreactivity for the calcium-binding protein calretinin, that are densely and selectively associated with cholinergic postganglionic neurons in the guinea pig tracheal ganglia. Retrograde neuronal tracing with cholera toxin B, combined with immunohistochemical analyses, showed that these nerve fibers do not originate from sensory neurons in the nodose, jugular, or dorsal root ganglia or from motor neurons in the nucleus ambiguus, dorsal motor nucleus of the vagus nerve, spinal cord, stellate ganglia, or superior cervical ganglia. Calretinin-immunoreactive nerve fibers disappeared from tracheal segments after 48 h in organotypic culture, indicating that the fibers were of extrinsic origin. However, calretinin-positive nerve fibers persisted in tracheal ganglia when tracheae were cocultured with the adjacent esophagus intact. Immunohistochemical analysis of the esophagus revealed a population of cholinergic neurons in the esophageal myenteric plexus that coexpressed calretinin. In functional studies, electrical stimulation of the esophagus in vitro evoked measurable contractions of the trachea. These contractions were not altered by prior organotypic culture of the trachea and esophagus to remove the extrinsic innervation to the airways but were significantly (P < 0.05) inhibited by the ganglionic blocker hexamethonium or by physical disruption of the tissue connecting the trachea and esophagus. These data suggest that a subset of esophageal neurons, characterized by the expression of calretinin and acetylcholine, provide a previously unrecognized excitatory input to tracheal cholinergic ganglia in guinea pigs.

Calbindin D28k expression and the absence of apoptosis in the cerebellum of Solanum bonariense L-intoxicated bovines

Solanum bonariense intoxication is characterized by cerebellar neuronal vacuolation, degeneration, and necrosis. Cerebellar Purkinje cells seem especially susceptible, but more research is needed to determine the pathogenesis of neuronal necrosis and the mechanism of Purkinje cell susceptibility. Calbindin D28k (CbD28k) is highly expressed in Purkinje cells and has been used as a marker for normal and degenerative Purkinje cells. The goal of this study was to describe S bonariense-induced disease by ascertaining Purkinje cell-specific degenerative changes using CbD28k expression and to correlate this with apoptosis in Purkinje cells, as determined using TUNEL (transferase-mediated dUTP-biotin nick end-labeling) and ultrastructural changes. In all cases, an increase in both dose and duration of S bonariense intoxication resulted in a decrease in the number of Purkinje cells. CbD28k immunohistochemistry was an excellent marker for Purkinje cells because immunoreactivity did not change in normal or degenerative tissues. This finding suggests that excessive calcium excitatory stimulation does not induce rapid neuronal degeneration and death. As found in previous studies, TUNEL tests and electron microscopy suggest that Purkinje cell degeneration and death are not occurring via an apoptotic process. These findings suggest that S bonariense poisoning induces progressive Purkinje cell death that is not mediated by excitotoxicity or apoptotic activation.