Synaptic dynamics and long-term plasticity at synapses of Purkinje cells onto neighboring Purkinje cells of a mormyrid fish: a dual cell recording study

The input synapses of cerebellar Purkinje cells (PCs) have been extensively studied and much has been learned about their dynamics, plasticity and functionality. In contrast there is limited information available about PC output synapses. This study uses dual cell recording methods to investigate synaptic dynamics and plasticity at individual PC synapses onto neighboring PCs in in vitro preparations of the mormyrid cerebellum. This synaptic connectivity may be strong or weak. For strong connections, inhibitory postsynaptic potentials (IPSPs) or currents (IPSCs) are synchronized with the action potentials of the presynaptic cell. For weak connections, however, the pre- and postsynaptic potentials are no longer synchronized, and presynaptic burst firing at intraburst rates of ∼50 Hz or higher is required to reliably induce the postsynaptic inhibition. A depression of this postsynaptic inhibition was observed for both types of connectivity following repeated presynaptic bursts, which was subsequently largely reversed following pairings of the presynaptic burst-induced IPSPs/IPSCs with evoked burst firing of the postsynaptic cell. Moreover, the original postsynaptic depression was found to be either augmented or reversed depending on the temporal order of each pair of additional pre- and postsynaptic cell activations, hence demonstrating a reversible and spike timing-dependent plasticity (STDP) at this synapse.

Cerebellar globular cells receive monoaminergic excitation and monosynaptic inhibition from Purkinje cells

Inhibitory interneurons in the cerebellar granular layer are more heterogeneous than traditionally depicted. In contrast to Golgi cells, which are ubiquitously distributed in the granular layer, small fusiform Lugaro cells and globular cells are located underneath the Purkinje cell layer and small in number. Globular cells have not been characterized physiologically. Here, using cerebellar slices obtained from a strain of gene-manipulated mice expressing GFP specifically in GABAergic neurons, we morphologically identified globular cells, and compared their synaptic activity and monoaminergic influence of their electrical activity with those of small Golgi cells and small fusiform Lugaro cells. Globular cells were characterized by prominent IPSCs together with monosynaptic inputs from the axon collaterals of Purkinje cells, whereas small Golgi cells or small fusiform Lugaro cells displayed fewer and smaller spontaneous IPSCs. Globular cells were silent at rest and fired spike discharges in response to application of either serotonin (5-HT) or noradrenaline. The two monoamines also facilitated small Golgi cell firing, but only 5-HT elicited firing in small fusiform Lugaro cells. Furthermore, globular cells likely received excitatory monosynaptic inputs through mossy fibers. Because globular cells project their axons long in the transversal direction, the neuronal circuit that includes interplay between Purkinje cells and globular cells could regulate Purkinje cell activity in different microzones under the influence of monoamines and mossy fiber inputs, suggesting that globular cells likely play a unique modulatory role in cerebellar motor control.

A hybrid nanofiber matrix to control the survival and maturation of brain neurons

Scaffold design plays a crucial role in developing graft-based regenerative strategies, especially when intended to be used in a highly ordered nerve tissue. Here we describe a hybrid matrix approach, which combines the structural properties of collagen (type I) with the epitope-presenting ability of peptide amphiphile (PA) nanofibers. Self-assembly of PA and collagen molecules results in a nanofibrous scaffold with homogeneous fiber diameter of 20-30 nm, where the number of laminin epitopes IKVAV and YIGSR can be varied by changing the PA concentrations over a broad range of 0.125-2 mg/ml. Granule cells (GC) and Purkinje cells (PC), two major neuronal subtypes of cerebellar cortex, demonstrate distinct response to this change of epitope concentration. On IKVAV hybrid constructs, GC density increases three-fold compared with the control collagen substrate at a PA concentration of ≥0.25 mg/ml, while PC density reaches a maximum (five-fold vs. control) at 0.25 mg/ml of PA and rapidly decreases at higher PA concentrations. In addition, adjustment of the epitope number allowed us to achieve fine control over PC dendrite and axon growth. Due to the ability to modulate neuron survival and maturation by easy manipulation of epitope density, our design offers a versatile test bed to study the extracellular matrix (ECM) contribution in neuron development and the design of optimal neuronal scaffold biomaterials.

Preliminary study on sarcoglycan sub-complex in rat cerebral and cerebellar cortex

The sarcoglycan sub-complex is a protein system which plays a key role in sarcolemma stabilization during muscle activity. Although numerous studies have been conducted on this system, there are few data about its localization in non-muscular tissues. On this basis we carried out an indirect immunofluorescence study on normal rat cerebral and cerebellar cortex. In particular, we carried out single localization reactions to analyze if these proteins are present in brain and double localization reactions between sarcoglycans and either SMI-32 or GFAP to verify if they are expressed both in neurons and glial cells. We found that all tested sarcoglycans are present both in cerebral and cerebellar cortex and that they are expressed both in neurons and glial cells. The typical staining pattern of all sarcoglycans is represented by "spot-like" fluorescence, with spots of 0.5-2 microm average diameter laid out mainly around the soma of the cells. The main difference about sarcoglycans expression between cerebral and cerebellar cortex is that in the cerebellar cortex the sarcoglycans positivity is detectable only in an area which is likely to correspond to Purkinje cells layer. The presence of sarcoglycans in cerebral and cerebellar cortex and their disposition mainly around the soma of the cells suggest a role of these proteins in cellular signalling and in regulating postsynaptic receptor assembly mainly in axo-somatic synapses.

Age-related Purkinje cell death is steroid dependent: RORα haplo-insufficiency impairs plasma and cerebellar steroids and Purkinje cell survival

A major problem of ageing is progressive impairment of neuronal function and ultimately cell death. Since sex steroids are neuroprotective, their decrease with age may underlie age-related neuronal degeneration. To test this, we examined Purkinje cell numbers, plasma sex steroids and cerebellar neurosteroid concentrations during normal ageing (wild-type mice, WT), in our model of precocious ageing (Rora(+/sg), heterozygous staggerer mice in which expression of the neuroprotective factor RORα is disrupted) and after long-term hormone insufficiency (WT post-gonadectomy). During normal ageing (WT), circulating sex steroids declined prior to or in parallel with Purkinje cell loss, which began at 18 months of age. Although Purkinje cell death was advanced in WT long-term steroid deficiency, this premature neuronal loss did not begin until 9 months, indicating that vulnerability to sex steroid deficiency is a phenomenon of ageing Purkinje neurons. In precocious ageing (Rora(+/sg)), circulating sex steroids decreased prematurely, in conjunction with marked Purkinje cell death from 9 months. Although Rora(+/sg) Purkinje cells are vulnerable through their RORα haplo-insufficiency, it is only as they age (after 9 months) that sex steroid failure becomes critical. Finally, cerebellar neurosteroids did not decrease with age in either genotype or gender; but were profoundly reduced by 3 months in male Rora(+/sg) cerebella, which may contribute to the fragility of their Purkinje neurons. These data suggest that ageing Purkinje cells are maintained by circulating sex steroids, rather than local neurosteroids, and that in Rora(+/sg) their age-related death is advanced by premature sex steroid loss induced by RORα haplo-insufficiency.

Induction of excitatory and inhibitory presynaptic differentiation by GluD1

The δ subfamily of ionotropic glutamate receptor subunits consists of GluD1 and GluD2. GluD2, which is selectively expressed in cerebellar Purkinje neurons, has been shown to contribute to the formation of synapses between granule neurons and Purkinje neurons through interaction with Cbln1 (cerebellin precursor protein1) and presynaptic Neurexin. On the other hand, the synaptogenic activity of GluD1, which is expressed not in the cerebellum but in the hippocampus, remains to be characterized. Here, we report that GluD1 expressed in non-neuronal HEK cells, induced presynaptic differentiation of granule neurons through its N-terminal domain in co-cultures with cerebellar neurons, similarly to GluD2. We also show that GluD1 rescued the defect of synapse formation in GluD2-knockout Purkinje neurons, indicating the functional similarity of GluD1 and GluD2. In contrast, GluD1 expression alone did not induce presynaptic differentiation in co-cultures of HEK cells with hippocampal neurons. However, when Cbln1 was exogenously added to the culture medium, GluD1 induced presynaptic differentiation of not only glutamatergic presynaptic terminals but also GABAergic ones. Cbln1 is not expressed in hippocampal neurons but is expressed in entorhinal cortical neurons projecting to the hippocampus. In co-cultures of HEK cells expressing GluD1 and entorhinal cortical neurons, both glutamatergic and GABAergic presynaptic terminals were formed on the HEK cells without exogenous application of Cbln1. These results suggest that GluD1 might contribute to the formation of specific synapses in the hippocampus such as those formed by the projecting neurons of the entorhinal cortex.

The male bias in the number of Purkinje cells and the size of the murine cerebellum may require Müllerian inhibiting substance/anti-Müllerian hormone

There is a male bias in the size of the cerebellum, with males, on average, having more Purkinje cells than females. The critical periods in cerebellum development occur when the immature testes secrete Müllerian inhibiting substance (MIS; synonym anti-Müllerian hormone) but only trace levels of testosterone. This suggests that the male bias in the cerebellum is generated by a different mechanism to the testosterone-sensitive reproductive nuclei. Consistent with this, in the present study, we report that Purkinje cells and other cerebella neurones express receptors for MIS, and that MIS(-/-) male mice have female-like numbers of Purkinje cells and a female-like size to other parts of their cerebellum. The size of the cell bodies of Purkinje cells was also dimorphic, although only a minority of this was a result of MIS. This suggests that MIS induces the initial male bias in the cerebellum, which is then refined by pubescent testosterone and/or other sex-specific factors.

Remodeling of monoplanar Purkinje cell dendrites during cerebellar circuit formation

Dendrite arborization patterns are critical determinants of neuronal connectivity and integration. Planar and highly branched dendrites of the cerebellar Purkinje cell receive specific topographical projections from two major afferent pathways; a single climbing fiber axon from the inferior olive that extend along Purkinje dendrites, and parallel fiber axons of granule cells that contact vertically to the plane of dendrites. It has been believed that murine Purkinje cell dendrites extend in a single parasagittal plane in the molecular layer after the cell polarity is determined during the early postnatal development. By three-dimensional confocal analysis of growing Purkinje cells, we observed that mouse Purkinje cells underwent dynamic dendritic remodeling during circuit maturation in the third postnatal week. After dendrites were polarized and flattened in the early second postnatal week, dendritic arbors gradually expanded in multiple sagittal planes in the molecular layer by intensive growth and branching by the third postnatal week. Dendrites then became confined to a single plane in the fourth postnatal week. Multiplanar Purkinje cells in the third week were often associated by ectopic climbing fibers innervating nearby Purkinje cells in distinct sagittal planes. The mature monoplanar arborization was disrupted in mutant mice with abnormal Purkinje cell connectivity and motor discoordination. The dendrite remodeling was also impaired by pharmacological disruption of normal afferent activity during the second or third postnatal week. Our results suggest that the monoplanar arborization of Purkinje cells is coupled with functional development of the cerebellar circuitry.

A deficiency of ceramide biosynthesis causes cerebellar purkinje cell neurodegeneration and lipofuscin accumulation

Sphingolipids, lipids with a common sphingoid base (also termed long chain base) backbone, play essential cellular structural and signaling functions. Alterations of sphingolipid levels have been implicated in many diseases, including neurodegenerative disorders. However, it remains largely unclear whether sphingolipid changes in these diseases are pathological events or homeostatic responses. Furthermore, how changes in sphingolipid homeostasis shape the progression of aging and neurodegeneration remains to be clarified. We identified two mouse strains, flincher (fln) and toppler (to), with spontaneous recessive mutations that cause cerebellar ataxia and Purkinje cell degeneration. Positional cloning demonstrated that these mutations reside in the Lass1 gene. Lass1 encodes (dihydro)ceramide synthase 1 (CerS1), which is highly expressed in neurons. Both fln and to mutations caused complete loss of CerS1 catalytic activity, which resulted in a reduction in sphingolipid biosynthesis in the brain and dramatic changes in steady-state levels of sphingolipids and sphingoid bases. In addition to Purkinje cell death, deficiency of CerS1 function also induced accumulation of lipofuscin with ubiquitylated proteins in many brain regions. Our results demonstrate clearly that ceramide biosynthesis deficiency can cause neurodegeneration and suggest a novel mechanism of lipofuscin formation, a common phenomenon that occurs during normal aging and in some neurodegenerative diseases.

Nav2 hypomorphic mutant mice are ataxic and exhibit abnormalities in cerebellar development

Development of the cerebellum involves a coordinated program of neuronal process outgrowth and migration resulting in a foliated structure that plays a key role in motor function. Neuron navigator 2 (Nav2) is a cytoskeletal-interacting protein that functions in neurite outgrowth and axonal elongation. Herein we show that hypomorphic mutant mice lacking the full-length Nav2 transcript exhibit ataxia and defects in cerebellar development. At embryonic day (E)17.5, the mutant cerebellum is reduced in size and exhibits defects in vermal foliation. Reduction in cell proliferation at early times (E12.5 and E14.5) may contribute to this size reduction. The full-length Nav2 transcript is expressed in the premigratory zone of the external granule layer (EGL). Granule cells in the germinal zone of the EGL appear to proliferate normally, however, due to the reduction in cerebellar circumference there are fewer total BrdU-labeled granule cells in the mutants, and these fail to migrate normally toward the interior of the cerebellum. In Nav2 hypomorphs, fewer granule cells migrate out of cerebellar EGL explants and neurite outgrowth from both explants and isolated external granule cell cultures is reduced. This suggests that the formation of parallel axon fibers and neuronal migration is disrupted in Nav2 mutants. This work supports an essential role for full-length Nav2 in cerebellar development, including axonal elongation and migration of the EGL neurons.

In vivo analysis of inhibitory synaptic inputs and rebounds in deep cerebellar nuclear neurons

Neuronal function depends on the properties of the synaptic inputs the neuron receive and on its intrinsic responsive properties. However, the conditions for synaptic integration and activation of intrinsic responses may to a large extent depend on the level of background synaptic input. In this respect, the deep cerebellar nuclear (DCN) neurons are of particular interest: they feature a massive background synaptic input and an intrinsic, postinhibitory rebound depolarization with profound effects on the synaptic integration. Using in vivo whole cell patch clamp recordings from DCN cells in the cat, we find that the background of Purkinje cell input provides a tonic inhibitory synaptic noise in the DCN cell. Under these conditions, individual Purkinje cells appear to have a near negligible influence on the DCN cell and clear-cut rebounds are difficult to induce. Peripheral input that drives the simple spike output of the afferent PCs to the DCN cell generates a relatively strong DCN cell inhibition, but do not induce rebounds. In contrast, synchronized climbing fiber activation, which leads to a synchronized input from a large number of Purkinje cells, can induce profound rebound responses. In light of what is known about climbing fiber activation under behaviour, the present findings suggest that DCN cell rebound responses may be an unusual event. Our results also suggest that cortical modulation of DCN cell output require a substantial co-modulation of a large proportion of the PCs that innervate the cell, which is a possible rationale for the existence of the cerebellar microcomplex.

Electrophysiological characteristics of cells in the anterior caudal lobe of the mormyrid cerebellum

We have examined the basic electrophysiology and pharmacology of cells in the anterior caudal lobe (CLa) of the mormyrid cerebellum. Intracellular recordings were performed in an in vitro slice preparation using the whole-cell patch recording method. The responses of cells to parallel fiber (PF) and climbing fiber (CF) stimulation and to somatic current injection were recorded, and then characterized by bath application of receptor and ion channel blockers. Using biocytin or neurobiotin, these cells were also morphologically identified after recording to ensure their classification. Efferent cells and two subtypes of Purkinje cells were identified on the basis of their physiology and morphology. While the majority of Purkinje cells fire a single type of spike that is mediated by Na(+), some fire a large broad spike mediated by Ca(2+) and a narrow spike mediated by Na(+) at resting potential levels. By patching one recording electrode to the soma and another to one of the proximal dendrites of the same cell simultaneously, it was found that the Na(+) spike has an axonal origin and the Ca(2+) spike is generated in the soma-dendritic region of Purkinje cells. Efferent cells fire a single type of Na(+) spike only. Despite variations in their physiology and morphology, all cell types responded to PF stimulation with graded excitatory postsynaptic potentials (EPSPs) mediated by AMPA receptors. However, none of the efferent cells and only some of the Purkinje cells responded to CF activation with a large, AMPA receptor-mediated all-or-none EPSPs. We conclude that the functional circuitry of the CLa resembles that of other regions of the mormyrid cerebellum and is largely similar to that of the mammalian cerebellum.

Visualizing the distribution of synapses from individual neurons in the mouse brain

Background

Proper function of the mammalian brain relies on the establishment of highly specific synaptic connections among billions of neurons. To understand how complex neural circuits function, it is crucial to precisely describe neuronal connectivity and the distributions of synapses to and from individual neurons.

Methods and Findings

In this study, we present a new genetic synaptic labeling method that relies on expression of a presynaptic marker, synaptophysin-GFP (Syp-GFP) in individual neurons in vivo. We assess the reliability of this method and use it to analyze the spatial patterning of synapses in developing and mature cerebellar granule cells (GCs). In immature GCs, Syp-GFP is distributed in both axonal and dendritic regions. Upon maturation, it becomes strongly enriched in axons. In mature GCs, we analyzed synapses along their ascending segments and parallel fibers. We observe no differences in presynaptic distribution between GCs born at different developmental time points and thus having varied depths of projections in the molecular layer. We found that the mean densities of synapses along the parallel fiber and the ascending segment above the Purkinje cell (PC) layer are statistically indistinguishable, and higher than previous estimates. Interestingly, presynaptic terminals were also found in the ascending segments of GCs below and within the PC layer, with the mean densities two-fold lower than that above the PC layer. The difference in the density of synapses in these parts of the ascending segment likely reflects the regional differences in postsynaptic target cells of GCs.

Conclusions

The ability to visualize synapses of single neurons in vivo is valuable for studying synaptogenesis and synaptic plasticity within individual neurons as well as information flow in neural circuits.

Alternating array of tyrosine hydroxylase and heat shock protein 25 immunopositive Purkinje cell stripes in zebrin II-defined transverse zone of the cerebellum of rolling mouse Nagoya

The present study examined the spatial organization of tyrosine hydroxylase (TH) immunopositive Purkinje cells in the cerebellum of rolling mouse Nagoya with reference to the distribution pattern of the cerebellar compartmentation antigen, heat shock protein 25 (HSP25). Whole-mount immunostaining revealed a striking pattern of parasagittal stripes of TH staining in the rolling mouse cerebellum but not in the control cerebellum. Although the TH stripes resembled the zebrin II stripes in the rolling cerebellum, these two distributions did not completely overlap. The TH stripes were present in the lobules VI and VII (central zone), the lobule X (nodular zone), and the paraflocculus, where zebrin II immunostaining was uniformly expressed. Double immunostaining revealed that TH stripes were aligned in an alternative fashion with HSP25 stripes within the caudal half of lobule VIb, lobules IXb and X, and paraflocculus. Some, but not all, TH stripes shared boundaries with HSP25 stripes. These results revealed an alternating array of TH immunopositive Purkinje cell subsets with HSP25 immunopositive Purkinje cells in the zebrin II-defined transverse zone of the rolling mouse cerebellum. The constitutive expression of HSP25 may prevent the ectopic expression of TH in zebrin II immunopositive Purkinje cell subsets.

Distinct modes of neuritic growth in purkinje neurons at different developmental stages: axonal morphogenesis and cellular regulatory mechanisms

Background

During development, neurons modify their axon growth mode switching from an elongating phase, in which the main axon stem reaches the target territory through growth cone-driven extension, to an arborising phase, when the terminal arbour is formed to establish synaptic connections. To investigate the relative contribution of cell-autonomous factors and environmental signals in the control of these distinct axon growth patterns, we examined the neuritogenesis of Purkinje neurons in cerebellar cultures prepared at elongating (embryonic day 17) or arborising (postnatal day zero) stages of Purkinje axon maturation.

Methodology/Principal Findings

When placed in vitro, Purkinje cells of both ages undergo an initial phase of neurite elongation followed by the development of terminal ramifications. Nevertheless, elongation of the main axon stem prevails in embryonic Purkinje axons, and many of these neurons are totally unable to form terminal branches. On the contrary, all postnatal neurites switch to arbour growth within a few days in culture and spread extensive terminal trees. Regardless of their elongating or arborising pattern, defined growth features (e.g. growth rate and tree extension) of embryonic Purkinje axons remain distinct from those of postnatal neurites. Thus, Purkinje neurons of different ages are endowed with intrinsic stage-specific competence for neuritic growth. Such competence, however, can be modified by environmental cues. Indeed, while exposure to the postnatal environment stimulates the growth of embryonic axons without modifying their phenotype, contact-mediated signals derived from granule cells specifically induce arborising growth and modulate the dynamics of neuritic elongation.

Conclusions/Significance

Cultured Purkinje cells recapitulate an intrinsically coded neuritogenic program, involving initial navigation of the axon towards the target field and subsequent expansion of the terminal arborisation. The execution of this program is regulated by environmental signals that modify the growth competence of Purkinje cells, so to adapt their endogenous properties to the different phases of neuritic morphogenesis.

Immunohistochemistry of GluR1 subunits of AMPA receptors of rat cerebellar nerve cells

The localization of GluR1 subunits of ionotropic glutamate receptors in the glial cells and inhibitory neurons of cerebellar cortex and their association with the climbing and parallel fibers, and basket cell axons were studied. Samples of P14 and P21 rat cerebellar cortex were exposed to a specific antibody against GluR1 subunit(s) ofAMPA receptors and were examined with confocal laser scanning microscopy. GluR1 strong immunoreactivity was confined to Purkinje cell and the molecular layer. Weak GluR1 immunoreactivity was observed surrounding some Golgi cells in the granule cell layer. Intense GluR1 immunoreactivity was localized around Purkinje, basket, and stellate cells. Purkinje cells expressed strong GluR1 immunoreactivity surrounding the cell body, primary dendritic trunk and secondary and tertiary spiny dendritic branches. Marked immunofluorescent staining was also detected in the Bergmann glial fibers at the level of middle and outer third molecular layer. Positive immunofluorescence staining was also observed surrounding basket and stellate cells, and in the capillary wall. These findings suggest the specific localization of GluR1 subunits ofAMPA receptors in Bergmann glial cells, inhibitory cerebellar neurons, and the associated excitatory glutamatergic circuits formed by climbing and parallel fibers, and by the inhibitory basket cell axons.

Insulin-like growth factor-I prevents the accumulation of autophagic vesicles and cell death in Purkinje neurons by increasing the rate of autophagosome-to-lysosome fusion and degradation

Continuous macroautophagic activity is critical for the maintenance of neuronal homeostasis; however, unchecked or dysregulated autophagy can lead to cell death. Cultured Purkinje neurons die by an autophagy-associated cell death mechanism when deprived of trophic support. Here, we report that insulin-like growth factor-I (IGF-I) completely blocked the autophagy-associated cell death of Purkinje neurons. To examine the mechanism by which IGF-I influences autophagy, neurons were infected with adeno-RFP-LC3 and subjected to trophic factor withdrawal, and the size and number of autophagosomes were analyzed by live-cell fluorescence imaging. In control neurons, autophagy occurred at a constitutive low level with most autophagosomes measuring less than 0.75 microm. Trophic factor withdrawal increased the number and size of autophagosomes with most autophagosomes ranging between 0.75 and 1.5 microm and some reaching 1.5-2.25 microm. IGF-I added at the time of trophic factor withdrawal prevented the accumulation of the larger autophagosomes; however, it had no effect on the conversion of LC3, an indicator of autophagy induction. Instead, the rate of autophagosome-to-lysosome fusion measured by colocalization of RFP-LC3 and LysoSensor Green was accelerated by IGF-I. Treating the neurons with bafilomycin A(1) in the presence of IGF-I led to the accumulation of autophagosomes even larger than those induced by trophic factor withdrawal alone, indicating that IGF-I regulates autophagic vesicle turnover. Finally, the effect of IGF-I on autophagy was mediated by an Akt/mTOR-de pend ent and an ERK-independent pathway. These data suggest a novel role for IGF-I in protecting Purkinje neurons from autophagy-associated cell death by increasing autophagy efficiency downstream of autophagy induction.

CEREBELLAR PURKINJE CELL LOSS IN HETEROZYGOUSRORA+/−MICE: A LONGITUDINAL STUDY

The staggerer (sg) mutation is a spontaneous deletion in the Rora gene that prevents the translation of the ligand-binding domain (LBD), leading to the loss of RORalpha activity. The homozygous Rorasg/sg mutant mouse, whose most obvious phenotype is ataxia associated with cerebellar degeneration, also displays a variety of other phenotypes. The heterozygous Rora+/sg is able to develop a cerebellum that is qualitatively normal but which suffers a significant loss of cerebellar neuronal cells with advancing age. A truncated protein synthesized by the mutated allele may play a role both in Rorasg/sg and Rora+/sg. To determine the effects during life span of true haplo-insufficiency of the RORalpha protein, derived from the invalidation of the gene, we compared the evolution of Purkinje cell numbers in heterozygous Rora knock-out males (Rora+/-) and in their wild-type counterparts from 1 to 24 months of age. We also compared the evolution of Purkinje cell (PC) numbers in Rora+/- and Rora+/sg males from 1 to 9 months. The main finding is that in Rora+/- mice, for which only one-half the normal amount of protein is produced, the deficit was established as early as 1 month and did not change during the animals' adult lifespans. Thus, the effects of aging on PC number were apparent much earlier in Rora+/- than in Rora+/sg, although at 24 months of age the degrees of deficit were similar.

S100beta upregulation: a possible mechanism of deltamethrin toxicity and motor coordination deficits

Deltamethrin (DLT) is a type II synthetic pyrethroid with insecticidal properties. It has been considered safe to humans. Excessive exposure of DLT is being variously reported, recently, to cause potential neurotoxicity in adults, as characterized by ataxia, loss of coordination, hyperexcitability, convulsions and paralysis. However, limited information is available on its impact at lower/safe to human doses during development. The present study was designed to assess the postnatal (P) exposure of DLT (as low as 0.7 mg/kg, i.p.) on S-100beta expression in developing rat cerebellum and its impact on Purkinje cell morphogenesis and dendritogenesis, and subsequent spontaneous motor activity (SMA) deficits. Wistar rat pups born to healthy mothers were injected with DLT (Sigma) at a dosage of 0.7 mg/kg body wt., i.p. dissolved in DMSO (Sigma) during P0-7th (DLT-I) and P9-13th day (DLT-II). The control pups were injected with equivalent volumes of DMSO. The pups of both the groups were used to assess the spontaneous motor activity P21 onwards. The cryocut sections (30 microm) of the cerebella were used for anti-S-100beta antibody labeling using streptavidin biotin HRP method. An upregulation of S-100beta expression in Bergmann glial fibers was recorded at P12 and P15 day preparations in both DLT-I and DLT-II treated groups. However, such upregulation of S-100beta was more prominent in DLT-II treated group animals with a large number of strongly S-100beta immunopositive astrocytes flanking around the Purkinje neurons. In Golgi preparation the Purkinje neurons in DLT treated groups had reduced dendritic arbor with short primary dendrites and much reduced dendritic branches which appeared stumpy and hypertrophied. The granule cell proliferation and migration as well as Purkinje cell morphogenesis and dendritogenesis are affected following DLT exposure in the present investigation. This may also affect the mossy fiber-granule cell-parallel pathway formation which in turn may decrease the firing of Purkinje cells (GABAergic inhibitory projections) and thus an increase in the output of the neurons in the deep cerebellar nuclei neurons and disturbed motor coordination.

Insights on eukaryotic translation initiation factor 5A (eIF5A) in the brain and aging

Long-term memory, a persistent form of synaptic plasticity, requires translation of a subset of mRNA present in neuronal dendrites during a short and critical period through a mechanism not yet fully elucidated. Western blotting analysis revealed a high content of eukaryotic translation initiation factor 5A (eIF5A) in the brain of neonatal rats, a period of intense neurogenesis rate, differentiation and synaptic establishment, when compared to adult rats. Immunohistochemistry analysis revealed that eIF5A is present in the whole brain of adult rats showing a variable content among the cells from different areas (e.g. cortex, hippocampus and cerebellum). A high content of eIF5A in the soma and dendrites of Purkinje cells, key neurons in the control of motor long-term memory in the cerebellum, was observed. Detection of high eIF5A content was revealed in dendritic varicosities of Purkinje cells. Evidence is presented herein that a reduction of eIF5A content is associated to brain aging.

Developmental enhancement of alpha2-adrenoceptor-mediated suppression of inhibitory synaptic transmission onto mouse cerebellar Purkinje cells

Noradrenaline (NA) modulates glutamatergic and GABAergic transmission in various areas of the brain. It is reported that some alpha2-adrenoceptor subtypes are expressed in the cerebellar cortex and alpha2-adrenoceptors may play a role in motor coordination. Our previous study demonstrated that the selective alpha2-adrenoceptor agonist clonidine partially depresses spontaneous inhibitory postsynaptic currents (sIPSCs) in mouse cerebellar Purkinje cells (PCs). Here we found that the inhibitory effect of clonidine on sIPSCs was enhanced during postnatal development. The activation of alpha2-adrenoceptors by clonidine did not affect sIPSCs in PCs at postnatal days (P) 8-10, when PCs showed a few sIPSCs and interneurons in the molecular layer (MLIs) did not cause action potential (AP). In the second postnatal week, the frequency of sIPSCs increased temporarily and reached a plateau at P14. By contrast, MLIs began to fire at P11 with the firing rate gradually increasing thereafter and reaching a plateau at P21. In parallel with this rise in the rate of firing, the magnitude of the clonidine-mediated inhibition of sIPSCs increased during postnatal development. Furthermore, the magnitude of the clonidine-mediated firing suppression in MLIs, which seemed to be mediated by a reduction in amplitude of the hyperpolarization-activated nonselective cation current, I(h), was constant across development. Both alpha2A- and alpha2B-, but not alpha2C-, adrenoceptors were strongly expressed in MLIs at P13, and P31. Therefore, the developmental enhancement of the clonidine-mediated inhibition of sIPSCs is attributed to an age-dependent increase in AP-derived sIPSCs, which can be blocked by clonidine. Thus, presynaptic activation of alpha2-adrenoceptors inhibits cerebellar inhibitory synaptic transmission after the second postnatal week, leading to a restriction of NA signaling, which is mainly mediated by alpha1- and beta2-adrenoceptors in the adult cerebellar neuronal circuit.

Myeloid and lymphoid contribution to non-haematopoietic lineages through irradiation-induced heterotypic cell fusion

Recent studies have suggested that regeneration of non-haematopoietic cell lineages can occur through heterotypic cell fusion with haematopoietic cells of the myeloid lineage. Here we show that lymphocytes also form heterotypic-fusion hybrids with cardiomyocytes, skeletal muscle, hepatocytes and Purkinje neurons. However, through lineage fate-mapping we demonstrate that such in vivo fusion of lymphoid and myeloid blood cells does not occur to an appreciable extent in steady-state adult tissues or during normal development. Rather, fusion of blood cells with different non-haematopoietic cell types is induced by organ-specific injuries or whole-body irradiation, which has been used in previous studies to condition recipients of bone marrow transplants. Our findings demonstrate that blood cells of the lymphoid and myeloid lineages contribute to various non-haematopoietic tissues by forming rare fusion hybrids, but almost exclusively in response to injuries or inflammation.