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Visual Abstract, Grid cells in layer II of the medial entorhinal cortex (MEC LII) generate multiple regular firing fields in response to the position and speed of an individual within the environment. They exhibit a protracted postnatal development and, in the adult, show activity differences along the dorsoventral axis (DVA). Evidence suggests parvalbumin-positive (PV+) interneurons, most of which are perisomatic-targeting cells, play a crucial role in generation of the hexagonal grid cell activity pattern. We therefore hypothesized that the development and organization of PV+ perisomatic terminals in MEC LII reflect the postnatal emergence of the hexagonal firing pattern and dorsoventral differences seen in grid cell activity. We used immuno-electron microscopy to examine the development of PV+ perisomatic terminals and their target somata within dorsal and ventral MEC LII in rats of postnatal day (P)10, P15, and P30. We demonstrate that in dorsal and ventral MEC LII, the cross-sectional area of somata and number and density of perisomatic PV+ terminals increase between P10 and P15. A simultaneous decrease was observed in cross-sectional area of PV+ terminals. Between P15 and P30, both MEC regions showed an increase in PV+ terminal size and percentage of PV+ terminals containing mitochondria, which may enable grid cell activity to emerge and stabilize. We also report that dorsal somata are larger and apposed by more PV+ terminals than ventral somata at all stages, suggesting a protracted maturation in the ventral portion and a possible gradient in soma size and PV+ basket innervation along the DVA in the adult.

Contains fulltext : 87819.pdf (Publisher’s version ) (Closed access) Structural neuronal plasticity is present in the nucleus para-retroambiguus (NPRA) and the commissural nucleus of the solitary tract/A2 group (NTScom/A2) in female hamsters. Both brainstem nuclei play a role in estrous cycle related autonomic adaptations. We investigated how aging affects the capillary condition in these adaptive brainstem regions. Senescent female hamsters (+/-95 weeks) were tested weekly for their 4-day estrous cycle. Subsequently morphological changes of NPRA and NTScom/A2 were compared with those of young (+/-20 weeks) females in an ultrastructural study. The medial tegmental field served as control area. In 841 capillaries (n=319 capillaries, young females (N=3); n=522 capillaries, aged females (N=4)) vascular aberrations were classified into 3 categories: endothelial and tight junction, basement membrane and pericyte aberrations. In old animals, capillaries showed marked endothelial changes, disrupted tight junctions, and thickening and splitting of basement membranes. Aberrations were found in 40-60% of all capillaries. About 70% of the pericytes contained degenerative inclusions. Despite this generalized vascular degeneration, the reproductive cycle of female hamsters was unaffected by vascular senescence. Perivascular fibrosis as reported in aging rats was never observed, which suggests the existence of species differences. 01 augustus 2010

In vivo, homozygous staggerer (Rora(sg/sg)) Purkinje cells (PCs) remain in an early stage of development with rudimentary spineless dendrites, associated with a lack of parallel fiber (PF) input and the persistence of multiple climbing fibers (CFs). In this immunocytochemical study we used cerebellar organotypic cultures to monitor the development of Rora(sg/sg) PF-PC synapses in the absence of CF innervation. Ex vivo the vesicular glutamate transporters VGluT1 and VGluT2 reactivity was preferentially localized around the Rora(sg/sg) PC soma and proximal dendrites, which are typically CF domains. The shift from VGluT2 to VGluT1 in PF terminals during development was delayed in Rora(sg/sg) slices. The postsynaptic receptors mGluR1 and GluR52 were differently distributed on Rorasglsg PCs. mGluR1 reactivity was evenly distributed in PC soma and dendrites, whereas GluRS2 reactivity, normally restricted at PF synapses, was dense in Rora(sg/sg) PC somata. The presynaptic distribution of VGluT1 and VGluT2 on Rora'glsg PCs matched the postsynaptic distribution of the glutamate receptor GluR82, but not mGluR1. J. Comp. Neurol. 512: 467-477,2009. (c) 2008 Wiley-Liss, Inc.

In this study the effects of hypergravity were analyzed on cerebellar Purkinje cells during early development in rats. The cerebellum is a key structure in the control and the adaptation of posture and anti-gravity activities. This holds particularly when external conditions are modified. Three groups of rats were conceived, born and reared in hypergravity (2 g). At postnatal day 5 (P5), P10 or P15, they were exposed to normal gravity and at P40, the cerebella were investigated on the expression of calbindin-D28k and inositol-3-phosphate (IP3) in Purkinje cells. Control animals were bred in the same conditions but at I g. Immunoreactivity of Purkinje cells was studied in lobules III and IX of the vermis. Lobule IX of the vermis is one of the targets of primary otolithic vestibular projections, and lobule III served as a control, being much less related with vestibular inputs. The results show that hypergravity induces a decrease in calbindin and IP3 labeling in 20% of Purkinje cells of lobule IX without any change in lobule III. Animals transferred from 2g to 1 g at P5 or PI 0 showed the most pronounced effects and much less at P15. This study demonstrates that early development of the cerebellum is highly sensitive to changes in gravity. Ages until P10 are critical for the development of vestibulo-cerebellar connections, and in particularly the calcium signaling in Purkinje cells. (c) 2005 Published by Elsevier Ireland Ltd.

Urocortin belongs to the family of corticotropin-releasing factor (CRF)-like peptides, which play an important role in sensorimotor coordination. CRF induces locomotor activity, and urocortin has an inhibitory effect. Here, we document the regional and subcellular localization of urocortin in the developing rat cerebellum to compare it with CRF. During the first postnatal week, urocortin immunoreactivity (UCN-ir), within the white matter and cerebellar cortex, was strongest in vermal lobules I, II, IX, and X, closely followed by lobules IV, V, and VIII; lobules VI and VII showed the weakest labeling. Cortical immunoreactivity was in the form of puncta that encircled Purkinje cell somata. By postnatal day (PD) 12, UCN-ir had increased appreciably in all lobules. In Purkinje cells, labeling was spread throughout their somata and proximal dendrites. By PD 15, labeling in lobules I-TV appeared to wane, yet still prevailed in the central and posterior lobules. This anterior-to-posterior gradient persisted through to adulthood. The study shows that urocortin and CRF have similar regional distribution profiles during development, suggesting synergistic roles within the vestibulocerebellum. The onset of the adult distributional pattern of urocortin at the stage when rats are capable of fluent walking patterns further strengthens the correlation between CRF-like peptides and postural control. An important difference between urocortin and CRF is the localization of urocortin, and not CRF, within Purkinje cells, implying that urocortin probably has an additional role in modulating the signals emanating from the cerebellar cortex to the deep cerebellar nuclei. (C) 2004 Wiley-Liss, Inc.

The nucleus pararetroambiguus (NPRA) and the commissural nucleus of the solitary tract (NTScom) show estrogen nuclear receptor-alpha immunoreactivity (nuclear ER-alpha-IR). Both cell groups are involved in estrous cycle related adaptations. We examined in normally cycling aged hamsters the occurrence/amount/frequency of age-related degenerative changes in NPRA and NTScom during estrus and diestrus. In 2640 electron microscopy photomicrographs plasticity reflected in the ratio of axon terminal surface/dendrite surface (t/d) was morpho-metrically analyzed. Medial tegmental field (mtf, nuclear ER-alpha-IR poor), served as control. In aged animals, irrespective of nuclear ER-alpha-IR+ or nuclear ER-alpha-IR- related cell groups, extensive diffuse degenerative structural aberrations were observed. The hormonal state had a strong influence on t/d ratios in NPRA and NTScom, but not in mtf. In NPRA and NTScom, diestrous hamsters had significantly smaller t/d ratios (NPRA, 0.750 +/- 0.050; NTScom, 0.900 +/- 0.039) than the estrous hamsters (NPRA, 1.083 +/- 0.075; NTScom, 1.204 +/- 0.076). Aging affected axodendritic ratios only in mtf (p

Lipofuscin accumulation is a characteristic feature of senescent postmitotic neuronal cells but estrogen may have protecting effects by inhibiting its formation. In the present ultrastructural study, lipofuscin accumulation was studied in 2 estrogen-alpha-receptive brainstem areas: nucleus pararetroambiguus (NPRA) and the commissural part of the solitary tract nucleus/A2 catecholaminergic group (NTScom/A2) and compared with the estrogen-insensitive medial tegmental field (mtf), in young (23 weeks) and aged (95 weeks) female hamsters. In the aged animals, extensive intracytoplasmic lipofuscin accumulation was observed. A total number of 6450 neurons were classified in 4 categories. Levels were significantly elevated in each of the brain areas studied. Lipofuscin accumulation was strongest in the mtf, less in NPRA, and remarkably less in the area of NTScom/A2. In conclusion, the observed differences in lipofuscin accumulation suggest: (1) considerable regional differences in the degree of neuronal vulnerability; and (2) a possible neuroprotective role for estrogen, because the degree of accumulation is inversely related to the density of the estrogen receptors, varying from nonreceptive (mtf) to NPRA and NTScom/A2 (most receptive). (C) 2012 Elsevier Inc. All rights reserved.

We have studied the organization of gamma-aminobutyric acid (GABA)ergic profiles in the superior colliculus of the rabbit to determine whether the synaptic types found in cat and monkey also exist in a mammalian species whose visual system has a different organization. Ultrastructure of GABAergic profiles was examined by use of a polyclonal antibody to GABA and quantitative postembedding immunocytochemistry. Three distinct types of vesicle-containing profiles were labeled by the GABA antibody in the rabbit superior colliculus. One type was a putative presynaptic dendrite (PSD profile) that received synaptic input from other profiles and contained pleomorphic synaptic vesicles scattered throughout the profile. These PSD profiles frequently received retinal input and formed dendrodendritic synapses. A second type of profile was a large caliber dendrite, often horizontal in orientation (H profile), that had one or more discrete clusters of pleomorphic synaptic vesicles at sites of synaptic contact with conventional dendrites. These H profiles received few synaptic contacts. A third profile type was a putative axon terminal (F profile) with smaller, more flattened synaptic vesicles that densely and uniformly filled the profile. Quantitative analysis of gold particle density revealed that F profiles had a significantly higher gold particle density (14.3/microns 2) than did PSD or H profiles (10.4 and 10.2/microns 2), suggesting that GABAergic profile types contain different concentrations of GABA. The vesicle density of these profile types also differed, but no obvious relationship between vesicle and particle distributions was observed. We conclude that the profiles labeled by GABA in rabbit superior colliculus are similar to those in cat and monkey and must represent a phylogenetically conserved organization common to many mammals, and that particle density analysis of postembedding immunocytochemistry can distinguish different GABAergic profile types.

A combined electrophysiological and morphological investigation of the medial terminal nucleus (MTN) in the rat was undertaken, aimed at a better understanding of the relationship between structure and function in this nucleus. The locations of upward and downward direction selective units in the MTN were documented with extracellular electrophysiological recording. By means of tracer experiments, with Phaseolus vulgaris-leucoagglutinin, biocytin, and cholera toxin subunit B-horseradish peroxidase, the internal connections of the MTN, its retinal afferents, and the projection neurons to the inferior olive were visualized. Terminals originating from the retina and from internal connections were characterized at the ultrastructural level. Their termination pattern on cells in the MTN, including identified inferior olive projection neurons, were determined. Additionally, postembedding GABA immunocytochemistry was performed to identify GABAergic elements. From reconstructions of the positions of electrophsiologically recorded units in the MTN, a local segregation between upward and downward direction selective units was revealed. Upward direction selective units were found in the dorsal part and ventromedially, whereas downward direction selective units were found ventral and laterally in the MTN. The MTN receives optic fibers via two separate routes which, based on their trajectory, presumably terminate in different parts of the MTN: the inferior fascicle of the accessory optic tract in the dorsal part, and the posterior fiber bundle of the superior fascicle in the ventral part of the MTN. A correspondence has been found between the segregation of direction selective units and the areas in the MTN where the retinal fibers from the two pathways distribute. It is, therefore, proposed that the inferior fasciculus conveys upward direction selectivity and the posterior fiber bundle downward direction selectivity, and that the two fiber bundles terminate segregated in the MTN. After anterograde tracing from the eye, retinal terminals were found evenly distributed throughout the MTN. They are characterized as GABA negative R-type terminals. After retrograde tracing from the inferior olive, identified MTN-inferior olive projection neurons were found in the dorsal MTN and medially in the ventral MTN. Their location in the MTN suggests that MTN-inferior olive projection neurons are upward direction selective. MTN-inferior olive projection neurons are large non-GABAergic cells, with a variable form. A majority of both F- and R-type terminals were found to make synaptie contacts on the dendrites of MTN cells. MTN-inferior olive projection neurons did not differ from other neurons in this respect. A reciprocal projection between the ventral and dorsal MTN was revealed by anterograde tracing. These connections make F-type terminals which contain GABA. This indicates that the dorsally located upward direction selective neurons have reciprocal inhibitory connections with the ventrally located downward direction selective neurons. The presence of inhibitory intranuclear connections can explain the noncollinearity of the preferred and nonpreferred directions of MTN units. © 1993 Wiley-Liss, Inc.

The mammalian circadian pacemaker of the suprachiasmatic nucleus (SCN) is entrained to the environmental light-dark cycle via a retinal projection, the retinohypothalamic tract (RHT). Several studies suggest that an excitatory amino acid, possibly glutamate, is involved in photic entrainment. However, it has not yet been established whether glutamate is a transmitter of the RHT itself. We have now identified terminals of the RHT in the SCN of brown Norwegian rats by intravitreous injections of horse radish peroxidase conjugated to cholera toxin. To detect glutamate immunoreactivity (IR), post-embedding immunocytochemistry was performed with polyclonal antibodies which were visualized for electron microscopy with colloidal gold particles. Retinal terminals had a significantly 82% higher glutamate-IR than their post-synaptic dendrites and a significantly 76% higher glutamate-IR than non-retinal terminals. These observations provide ultrastructural evidence that glutamate is a transmitter of the RHT.

International audience; The geometric and subcellular organization of axon arbors distributes and regulates electrical signaling in neurons and networks, but the underlying mechanisms have remained elusive. In rodent cerebellar cortex, stellate interneurons elaborate characteristic axon arbors that selectively innervate Purkinje cell dendrites and likely regulate dendritic integration. We used GFP BAC transgenic reporter mice to examine the cellular processes and molecular mechanisms underlying the development of stellate cell axons and their innervation pattern. We show that stellate axons are organized and guided towards Purkinje cell dendrites by an intermediate scaffold of Bergmann glial (BG) fibers. The L1 family immunoglobulin protein Close Homologue of L1 (CHL1) is localized to apical BG fibers and stellate cells during the development of stellate axon arbors. In the absence of CHL1, stellate axons deviate from BG fibers and show aberrant branching and orientation. Furthermore, synapse formation between aberrant stellate axons and Purkinje dendrites is reduced and cannot be maintained, leading to progressive atrophy of axon terminals. These results establish BG fibers as a guiding scaffold and CHL1 a molecular signal in the organization of stellate axon arbors and in directing their dendritic innervation.

The ultrastructural organization of the pretecto-olivary projection neurons within the nucleus of the optic tract and dorsal terminal accessory optic nucleus of rabbits was studied by using anti-GABA immunolabelling and retrograde transport of WGA-HRP. GABA-like immunoreactivity was determined with a postembedding colloidal gold technique. WGA-HRP was injected in the dorsal cap of the inferior olive. The WGA-HRP-labelled neurons were incubated with gold-substituted silver peroxidase. Neurons projecting to the inferior olive had large to medium-sized cell bodies and were GABA negative. In the nucleus of the optic tract, projection neurons are found in the rostral parts, while the majority of the local GABAergic interneurons are mainly found in the caudal parts. In the dorsal terminal nucleus both types of neurons are intermingled. The projection neurons were frequently in synaptic contact by GABAergic terminals. These neurons also receive retinal afferents indicating the existence of a two-step synaptic connection from the retina to the inferior olive. It is suggested that this class of projection neurons forms the "direction-selective" neurons that can be antidromically stimulated from the inferior olive. The GABAergic terminals on the identified projection neurons are of axonal origin (F-terminals), whereas presynaptic dendrites of interneurons (P-terminals) were seldom observed to be in synaptic contact with retrogradely labelled profiles. The strong input of GABA on direction-selective neurons indicates that GABA is directly involved in modulating retinal signals to the inferior olive.

Disease-associated misfolded proteins or proteins damaged due to cellular stress are generally disposed via the cellular protein quality-control system. However, under saturating conditions, misfolded proteins will aggregate. In higher eukaryotes, these aggregates can be transported to accumulate in aggresomes at the microtubule organizing center. The fate of cells that contain aggresomes is currently unknown. Here we report that cells that have formed aggresomes can undergo normal mitosis. As a result, the aggregated proteins are asymmetrically distributed to one of the daughter cells, leaving the other daughter free of accumulated protein damage. Using both epithelial crypts of the small intestine of patients with a protein folding disease and Drosophila melanogaster neural precursor cells as models, we found that the inheritance of protein aggregates during mitosis occurs with a fixed polarity indicative of a mechanism to preserve the long-lived progeny., Human cells containing polyglutamine damage enter mitosis and complete cytokinesis. The association of aggresomes with one centrosome means that accumulated damage is asymmetrically inherited in only one daughter cell.

Corticotropin releasing factor receptor 2 (CRF-R2) is strongly expressed in the cerebellum and plays an important role in the development of the cerebellar circuitry, particularly in the development of the dendritic trees and afferent input to Purkinje cells. However, the mechanisms responsible for the distribution and stabilization of CRF-R2 in the cerebellum are not well understood. Here, we provide the first detailed analysis of the cellular localization of the full-length form of CRF-R2 in rat cerebellum during early postnatal development. We document unique and developmentally regulated subcellular distributions of CRF-R2 in cerebellar cell types, e.g. granule cells after postnatal day 15. The presence of one or both receptor isoforms in the same cell may provide a molecular basis for distinct developmental processes. The full-length form of CRF-R2 may be involved in the regulation of the first stage of dendritic growth and at later stages in the controlling of the structural arrangement of immature cerebellar circuits and in the autoregulatory pathway of the cerebellum.

The nucleus of the optic tract (NOT) and the medial terminal nucleus (MTN) are two primary visual nuclei that take part in circuits sustaining the optokinetic reflex, The morphology of rat NOT cells projecting to the inferior olive (NOT-IO neurons) and their terminal input, specifically terminals originating from the MTN, have been studied in the rat at the light and electron microscopical level. This has been done by means of combined retrograde tracing from the inferior olive and anterograde tracing from the MTN to the NOT. The area containing MTN terminal fibers and the area occupied by NOT-IO neurons has been found to match. This matched distribution provides a more detailed description of the NOT, with possible functional implications. Identified NOT-IO neurons demonstrate considerable variability in their dendritic branching pattern and have been found to include all neuronal cell types described for the NOT. The dendritic branching pattern of NOT-IO cells could be related to the orientation and distribution of the NOT's major afferent fiber systems. NOT-IO neurons receive a variable MTN and retinal input onto their somata, comparable to other cells in the NOT. With exception of the superficial part of the NOT, NOT-IO neurons with the most MTN terminals were found dorsally in areas containing large numbers of MTN terminals. In conclusion, although NOT-IO neurons are uniform with respect to their receptive field properties, they vary considerably with respect to the shape of the cell body, dendritic branching pattern, and terminal input. This means that morphological characteristics of NOT-IO neurons have no predictive value with regard to their receptive field properties. © 1992 Wiley-Liss, Inc.