Localization of synapsin-I and PSD-95 in developing postnatal rat cerebellar cortex

Postnatal development of the relaxin-3 innervation of the rat medial septum

Introduction

The septal area provides a rich innervation to the hippocampus regulating hippocampal excitability to different behavioral states and modulating theta rhythmogenesis. However, little is known about the neurodevelopmental consequences of its alterations during postnatal development. The activity of the septohippocampal system is driven and/or modulated by ascending inputs, including those arising from the nucleus incertus (NI), many of which contain the neuropeptide, relaxin-3 (RLN3).

Methods

We examined at the molecular and cellular level the ontogeny of RLN3 innervation of the septal area in postnatal rat brains.

Results

Up until P13-15 there were only scattered fibers in the septal area, but a dense plexus had appeared by P17 that was extended and consolidated throughout the septal complex by P20. There was a decrease in the level of colocalization of RLN3 and synaptophysin between P15 and P20 that was reversed between P20 and adulthood. Biotinylated 3-kD dextran amine injections into the septum, revealed retrograde labeling present in the brainstem at P10-P13, but a decrease in anterograde fibers in the NI between P10-20. Simultaneously, a differentiation process began during P10-17, resulting in fewer NI neurons double-labeled for serotonin and RLN3.

Discussion

The onset of the RLN3 innervation of the septum complex between P17-20 is correlated with the onset of hippocampal theta rhythm and several learning processes associated with hippocampal function. Together, these data highlight the relevance and need for further analysis of this stage for normal and pathological septohippocampal development.

Deep cerebellar stimulation enhances cognitive recovery after prefrontal traumatic brain injury in rodent

Functional outcome following traumatic brain injury (TBI) varies greatly, with approximately half of those who survive suffering long-term motor and cognitive deficits despite contemporary rehabilitation efforts. We have previously shown that deep brain stimulation (DBS) of the lateral cerebellar nucleus (LCN) enhances rehabilitation of motor deficits that result from brain injury. The objective of the present study was to evaluate the efficacy of LCN DBS on recovery from rodent TBI that uniquely models the injury location, chronicity and resultant cognitive symptoms observed in most human TBI patients. We used controlled cortical impact (CCI) to produce an injury that targeted the medial prefrontal cortex (mPFC-CCI) bilaterally, resulting in cognitive deficits. Unilateral LCN DBS electrode implantation was performed 6 weeks post-injury. Electrical stimulation started at week eight post-injury and continued for an additional 4 weeks. Cognition was evaluated using baited Y-maze, novel object recognition task and Barnes maze. Post-mortem analyses, including Western Blot and immunohistochemistry, were conducted to elucidate the cellular and molecular mechanisms of recovery. We found that mPFC-CCI produced significant cognitive deficits compared to pre-injury and naïve animals. Moreover, LCN DBS treatment significantly enhanced the long-term memory process and executive functions of applying strategy. Analyses of post-mortem tissues showed significantly greater expression of CaMKIIα, BDNF and p75NTR across perilesional cortex and higher expression of postsynaptic formations in LCN DBS-treated animals compared to untreated. Overall, these data suggest that LCN DBS is an effective treatment of cognitive deficits that result from TBI, possibly by activation of ascending, glutamatergic projections to thalamus and subsequent upregulation of thalamocortical activity that engages neuroplastic mechanisms for facilitation of functional re-organization. These results support a role for cerebellar output neuromodulation as a novel therapeutic approach to enhance rehabilitation for patients with chronic, post-TBI cognitive deficits that are unresponsive to traditional rehabilitative efforts.

Preventive Electroacupuncture Ameliorates D-Galactose-Induced Alzheimer's Disease-Like Pathology and Memory Deficits Probably via Inhibition of GSK3β/mTOR Signaling Pathway

Acupuncture has been practiced to treat neuropsychiatric disorders for a thousand years in China. Prevention of disease by acupuncture and moxibustion treatment, guided by the theory of Chinese acupuncture, gradually draws growing attention nowadays and has been investigated in the role of the prevention and treatment of mental disorders such as AD. Despite its well-documented efficacy, its biological action remains greatly invalidated. Here, we sought to observe whether preventive electroacupuncture during the aging process could alleviate learning and memory deficits in D-galactose-induced aged rats. We found that preventive electroacupuncture at GV20-BL23 acupoints during aging attenuated the hippocampal loss of dendritic spines, ameliorated neuronal microtubule injuries, and increased the expressions of postsynaptic PSD95 and presynaptic SYN, two important synapse-associated proteins involved in synaptic plasticity. Furthermore, we observed an inhibition of GSK3β/mTOR pathway activity accompanied by a decrease in tau phosphorylation level and prompted autophagy activity induced by preventive electroacupuncture. Our results suggested that preventive electroacupuncture can prevent and alleviate memory deficits and ameliorate synapse and neuronal microtubule damage in aging rats, which was probably via the inhibition of GSK3β/mTOR signaling pathway. It may provide new insights for the identification of prevention strategies of AD.

Gene replacement ameliorates deficits in mouse and human models of cyclin-dependent kinase-like 5 disorder

Cyclin-dependent kinase-like 5 disorder is a severe neurodevelopmental disorder caused by mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene. It predominantly affects females who typically present with severe early epileptic encephalopathy, global developmental delay, motor dysfunction, autistic features and sleep disturbances. To develop a gene replacement therapy, we initially characterized the human CDKL5 transcript isoforms expressed in the brain, neuroblastoma cell lines, primary astrocytes and embryonic stem cell-derived cortical interneurons. We found that the isoform 1 and to a lesser extent the isoform 2 were expressed in human brain, and both neuronal and glial cell types. These isoforms were subsequently cloned into recombinant adeno-associated viral (AAV) vector genome and high-titre viral vectors were produced. Intrajugular delivery of green fluorescence protein via AAV vector serotype PHP.B in adult wild-type male mice transduced neurons and astrocytes throughout the brain more efficiently than serotype 9. Cdkl5 knockout male mice treated with isoform 1 via intrajugular injection at age 28–30 days exhibited significant behavioural improvements compared to green fluorescence protein-treated controls (1012 vg per animal, n = 10 per group) with PHP.B vectors. Brain expression of the isoform 1 transgene was more abundant in hindbrain than forebrain and midbrain. Transgene brain expression was sporadic at the cellular level and most prominent in hippocampal neurons and cerebellar Purkinje cells. Correction of postsynaptic density protein 95 cerebellar misexpression, a major fine cerebellar structural abnormality in Cdkl5 knockout mice, was found in regions of high transgene expression within the cerebellum. AAV vector serotype DJ efficiently transduced CDKL5-mutant human induced pluripotent stem cell-derived neural progenitors, which were subsequently differentiated into mature neurons. When treating CDKL5-mutant neurons, isoform 1 expression led to an increased density of synaptic puncta, while isoform 2 ameliorated the calcium signalling defect compared to green fluorescence protein control, implying distinct functions of these isoforms in neurons. This study provides the first evidence that gene therapy mediated by AAV vectors can be used for treating CDKL5 disorder.

Exploratory study of the effects of intra-uterine growth retardation and neonatal energy supplementation of low birth-weight piglets on their post-weaning cognitive abilities

The present study investigated the effects of intra-uterine growth retardation (IUGR, score 0-3; i.e., "normal" to "severe") level at birth, and the effects of neonatal energy supplementation (dosed with 2 ml of coconut oil, commercial product or water, or sham-dosed), on post-weaning cognitive abilities of low birth-weight piglets (< 1.1 kg). In total, 184 piglets were recruited at weaning (27 ± 0.1 days) for habituation to the test procedures, and were either tested for spatial learning and memory in a T-maze (n = 42; 37 ± 0.5 days) or for short-term memory in a spontaneous object recognition task (SORT; n = 47; 41 ± 0.3 days). Neonatal supplementation did not affect performances of pigs in the T-maze task or SORT. IUGR3 pigs tended to be faster to enter the reward arm and to obtain the reward in the reversal step of the T-Maze task, suggesting a better learning flexibility, compared to IUGR1 (entry t72.8=2.9, P = 0.024; reward t80 = 3.28, P = 0.008) and IUGR2 (entry t70.3=2.5, P = 0.068; reward t73.9 = 2.77, P = 0.034) pigs. However, a higher percentage of IUGR1 pigs tended to approach the novel object first (DSCF-value = 3.07; P = 0.076) and to interact with it more (t40 = 2.19, P = 0.085), relative to IGUR3 pigs. IUGR1 pigs showed a strong preference for the novel object, as they had a greater percentage time difference interacting with the objects when the novel object was presented (t81 = - 3.41, P = 0.013). In conclusion, some low birth-weight piglets are able to perform a spatial task and an object recognition test, but performances in these tests may be modulated by IUGR level.

Ameliorative role of antioxidant supplementation on sodium-arsenite induced adverse effects on the developing rat cerebellum

Background

Arsenic is an environmental contaminant of global concern. Consumption of ground water contaminated with inorganic arsenic (iAs) continues to be the major source of its exposure. The developing nervous system is especially vulnerable to environmental insults due to its higher rate of oxygen consumption and provision of weaker antioxidant (AOX) machinery.

Objective

Since oxidative stress has been reported as one of the major factors underlying iAs induced toxicity, the aim of the present study is to study the effect of two AOXs i.e., Alpha Lipoic Acid (ALA) and Curcumin (Cur) in developing cerebellum of rats exposed to arsenic during postnatal period.

Materials and Methods

The study was carried out on mother reared neonatal rat pups grouped as normal (Ia) and sham (vehicle) controls (Ib,c,d), while the experimental groups IIa/ IIb received sodium arsenite (NaAsO2) [(1.5/2.5 mg/kg body weight (bw)] alone or along with ALA (70 mg/kg bw)- IIIa/ IIIb or along with Cur (150 mg/kg bw)- IVa/ IVb. Behavioural, biochemical and immunohistochemical procedures were carried out to understand the underlying mechanisms.

Results

The observations indicated deficits in locomotor function, accumulation of iAs, increased levels of oxidative stress markers along with downregulation of the expression of proteins closely associated with synaptic functioning (Synaptophysin and Postsynaptic density protein95) in the cerebellum of iAs treated animals. Substantial recovery in all these parameters was observed in AOX co-treated groups.

Conclusion

Our results support the potential of ALA and Cur in amelioration of iAs induced developmental neurotoxicity. ALA and Cur can be proposed as dietary adjuvants amongst populations inhabiting areas with high iAs contamination as a safe and cost effective antidotes.

Platelets mediate protective neuroinflammation and promote neuronal plasticity at the site of neuronal injury

It is generally accepted that inflammation within the CNS contributes to neurodegeneration after traumatic brain injury (TBI), but it is not clear how inflammation is initiated in the absence of infection and whether this neuroinflammation is predominantly beneficial or detrimental. We have previously found that brain-enriched glycosphingolipids within neuronal lipid rafts (NLR) induced platelet degranulation and secretion of neurotransmitters and pro-inflammatory factors. In the present study, we compared TBI-induced inflammation and neurodegeneration in wild-type vs. St3gal5 deficient (ST3^-/-) mice that lack major CNS-specific glycosphingolipids. After TBI, microglial activation and CNS macrophage infiltration were substantially reduced in ST3^-/- animals. However, ST3^-/- mice had a larger area of CNS damage with marked neuronal/axonal loss. The interaction of platelets with NLR stimulated neurite growth, increased the number of PSD95-positive dendritic spines, and intensified neuronal activity. Adoptive transfer and blocking experiments provide further that platelet-derived serotonin and platelet activating factor plays a key role in the regulation of sterile neuroinflammation, hemorrhage and neuronal plasticity after TBI.

DiI tracing of the hypothalamic projection systems during perinatal development

The hypothalamus is the higher neuroendocrine center of the brain and therefore possesses numerous intrinsic axonal connections and is connected by afferent and efferent fiber systems with other brain structures. These projection systems have been described in detail in the adult but data on their early development is sparse. Here I review studies of the time schedule and features of the development of the major hypothalamic axonal systems. In general, anterograde tracing experiments have been used to analyze short distance projections from the arcuate and anteroventral periventricular nuclei (Pe), while hypothalamic projections to the posterior and intermediate pituitary lobes (IL) and median eminence, mammillary body tracts and reciprocal septohypothalamic connections have been described with retrograde tracing. The available data demonstrate that hypothalamic connections develop with a high degree of spatial and temporal specificity, innervating each target with a unique developmental schedule which in many cases can be correlated with the functional maturity of the projection system.

Spine formation and maturation in the developing rat auditory cortex

The rat auditory cortex is organized as a tonotopic map of sound frequency. This map is broadly tuned at birth and is refined during the first 3 weeks postnatal. The structural correlates underlying tonotopic map maturation and reorganization during development are poorly understood. We employed fluorescent dye ballistic labeling ("DiOlistics") alone, or in conjunction with immunohistochemistry, to quantify synaptogenesis in the auditory cortex of normal hearing rats. We show that the developmental appearance of dendritic protrusions, which include both immature filopodia and mature spines, on layers 2/3, 4, and 5 pyramidal and layer 4 spiny nonpyramidal neurons occurs in three phases: slow addition of dendritic protrusions from postnatal day 4 (P4) to P9, rapid addition of dendritic protrusions from P9 to P19, and a final phase where mature protrusion density is achieved (>P21). Next, we combined DiOlistics with immunohistochemical labeling of bassoon, a presynaptic scaffolding protein, as a novel method to categorize dendritic protrusions as either filopodia or mature spines in cortex fixed in vivo. Using this method we observed an increase in the spine-to-filopodium ratio from P9-P16, indicating a period of rapid spine maturation. Previous studies report mature spines as being shorter in length compared to filopodia. We similarly observed a reduction in protrusion length between P9 and P16, corroborating our immunohistochemical spine maturation data. These studies show that dendritic protrusion formation and spine maturation occur rapidly at a time previously shown to correspond to auditory cortical tonotopic map refinement (P11-P14), providing a structural correlate of physiological maturation.

Neuronal expression, cytosolic localization, and developmental regulation of the organic solute carrier partner 1 in the mouse brain

Organic solute carrier partner 1 (OSCP1) is a mammalian, transporter-related protein that is able to facilitate the uptake of structurally diverse organic compounds into the cell when expressed in Xenopus laevis oocytes. This protein has been implicated in testicular handling of organic solutes because its mRNA expression is almost exclusive in the testis. However, in this study, we demonstrated significant expression of OSCP1 protein in mouse brain, the level of which was rather higher than that in the testis, although the corresponding mRNA expression was one-tenth of the testicular level. Immunohistochemistry revealed that OSCP1 was broadly distributed throughout the brain, and various neuronal cells were immunostained, including pyramidal cells in the cerebral cortex and hippocampus. However, there was no evidence of OSCP1 expression in glia. In primary cultures of cerebral cortical neurons, double-labeling immunofluorescence localized OSCP1 to the cytosol throughout the cell body and neurites including peri-synaptic regions. This was consistent with the subcellular fractionation of brain homogenates, in which OSCP1 was mainly recovered after centrifugation both in the cytosolic fraction and the particulate fraction containing synaptosomes. Immunoelectron microscopy of brain sections also demonstrated OSCP1 in the cytosol near synapses. In addition, it was revealed that changes in the expression level of OSCP1 correlated with neuronal maturation during postnatal development of mouse brain. These results indicate that OSCP1 may have a role in the brain indirectly mediating substrate uptake into the neurons in adult animals.

Spatiotemporal expression of PSD-95 in Fmr1 knockout mice brain

To investigate and compare the spatial and temporal expression of post-synaptic density-95 (PSD-95) in Fmr1 knockout mice (the animal model of fragile X syndrome, FXS) and wild-type mice brain, on postnatal day 7 (P7), P14, P21, P28 and P90, mice from each group were decapitated, and three principal brain regions (cerebral cortex, hippocampus and cerebellum) were obtained and stored for later experiments. PSD-95 mRNA in the three brain areas was analyzed with quantitative RT-PCR. PSD-95 protein was measured by immunohistochemical staining and Western blot. In the three principal brain areas of Fmr1 knockout mice and wild-type mice, the expression of PSD-95 mRNA and protein were detected at the lowest levels on P7, and then significantly increased on P14, reaching the peak levels in adolescents or adults. Moreover, it was found that PSD-95 mRNA and protein in the hippocampus were significantly decreased in Fmr1 knockout mice during the developmental period (P7, P14, P21 and P28) as well as at adulthood (P90) (P < 0.05, and P < 0.01, respectively). However, there was no significant difference of expression of PSD-95 in the cortex and cerebellum between Fmr1 knockout and wild mice. The expression of PSD-95 in the hippocampus might be regulated by fragile X mental retardation protein (FMRP) during mice early developmental and adult periods. It is suggested that impairment of PSD-95 is possibly involved in hippocampal-dependent learning defects, which are common in people with FXS.

Clostridium perfringens epsilon toxin targets granule cells in the mouse cerebellum and stimulates glutamate release

Epsilon toxin (ET) produced by C. perfringens types B and D is a highly potent pore-forming toxin. ET-intoxicated animals express severe neurological disorders that are thought to result from the formation of vasogenic brain edemas and indirect neuronal excitotoxicity. The cerebellum is a predilection site for ET damage. ET has been proposed to bind to glial cells such as astrocytes and oligodendrocytes. However, the possibility that ET binds and attacks the neurons remains an open question. Using specific anti-ET mouse polyclonal antibodies and mouse brain slices preincubated with ET, we found that several brain structures were labeled, the cerebellum being a prominent one. In cerebellar slices, we analyzed the co-staining of ET with specific cell markers, and found that ET binds to the cell body of granule cells, oligodendrocytes, but not astrocytes or nerve endings. Identification of granule cells as neuronal ET targets was confirmed by the observation that ET induced intracellular Ca(2+) rises and glutamate release in primary cultures of granule cells. In cultured cerebellar slices, whole cell patch-clamp recordings of synaptic currents in Purkinje cells revealed that ET greatly stimulates both spontaneous excitatory and inhibitory activities. However, pharmacological dissection of these effects indicated that they were only a result of an increased granule cell firing activity and did not involve a direct action of the toxin on glutamatergic nerve terminals or inhibitory interneurons. Patch-clamp recordings of granule cell somata showed that ET causes a decrease in neuronal membrane resistance associated with pore-opening and depolarization of the neuronal membrane, which subsequently lead to the firing of the neuronal network and stimulation of glutamate release. This work demonstrates that a subset of neurons can be directly targeted by ET, suggesting that part of ET-induced neuronal damage observed in neuronal tissue is due to a direct effect of ET on neurons.

Neuronal MHC class I molecules are involved in excitatory synaptic transmission at the hippocampal mossy fiber synapses of marmoset monkeys

Several recent studies suggested a role for neuronal major histocompatibility complex class I (MHCI) molecules in certain forms of synaptic plasticity in the hippocampus of rodents. Here, we report for the first time on the expression pattern and functional properties of MHCI molecules in the hippocampus of a nonhuman primate, the common marmoset monkey (Callithrix jacchus). We detected a presynaptic, mossy fiber-specific localization of MHCI proteins within the marmoset hippocampus. MHCI molecules were present in the large, VGlut1-positive, mossy fiber terminals, which provide input to CA3 pyramidal neurons. Furthermore, whole-cell recordings of CA3 pyramidal neurons in acute hippocampal slices of the common marmoset demonstrated that application of antibodies which specifically block MHCI proteins caused a significant decrease in the frequency, and a transient increase in the amplitude, of spontaneous excitatory postsynaptic currents (sEPSCs) in CA3 pyramidal neurons. These findings add to previous studies on neuronal MHCI molecules by describing their expression and localization in the primate hippocampus and by implicating them in plasticity-related processes at the mossy fiber-CA3 synapses. In addition, our results suggest significant interspecies differences in the localization of neuronal MHCI molecules in the hippocampus of mice and marmosets, as well as in their potential function in these species.

Altered neuroligin expression is involved in social deficits in a mouse model of the fragile X syndrome

The fragile X syndrome (FXS) is the most common form of inherited mental retardation. Caused by a transcriptional silencing of the fragile X mental retardation protein (FMRP), a mRNA binding protein itself, misregulated translation is thought to be the leading cause of the fragile X syndrome. Interestingly, recent results indicated several neuroligin interacting proteins to be affected by this misregulation, including neurexin1 and PSD95, which have also been implicated in autism spectrum disorders. Using co-immunoprecipitation assays and RT-PCR, FMRP is shown to interact with neuroligin1- and 2-mRNA, while no interaction with neuroligin3-mRNA is observed. In line with FMRP's role in translation regulation, Western blot as well as immunohistochemistry analysis reveal changes in protein expression levels suggesting impaired synaptic function. As increasing evidence indicates neuroligin expression to be critical for synapse maturation and function, consequences of impaired neuroligin1 expression in FXS are assessed by overexpressing HA-neuroligin1 in FMR1-/- mice, a model for FXS. Behavioural assessments demonstrate that enhanced neuroligin1 expression improves social behaviour in FMR1-/- mice, whereas no positive effect on learning and memory is seen. These results provide for the first time evidence for an involvement of a neuroligin-neurexin protein network in core symptoms of FXS.

Evidence for oxidative stress in the developing cerebellum of the rat after chronic mild carbon monoxide exposure (0.0025% in air)

BACKGROUND

The present study was designed to test the hypothesis that chronic very mild prenatal carbon monoxide (CO) exposure (25 parts per million) subverts the normal development of the rat cerebellar cortex. Studies at this chronic low CO exposure over the earliest periods of mammalian development have not been performed to date. Pregnant rats were exposed chronically to CO from gestational day E5 to E20. In the postnatal period, rat pups were grouped as follows: Group A: prenatal exposure to CO only; group B: prenatal exposure to CO then exposed to CO from postnatal day 5 (P5) to P20; group C: postnatal exposure only, from P5 to P20, and group D, controls (air without CO). At P20, immunocytochemical analyses of oxidative stress markers, and structural and functional proteins were assessed in the cerebellar cortex of the four groups. Quantitative real time PCR assays were performed for inducible (iNOS), neuronal (nNOS), and endothelial (eNOS) nitric oxide synthases.

RESULTS

Superoxide dismutase-1 (SOD1), SOD2, and hemeoxygenase-1 (HO-1) immunoreactivity increased in cells of the cerebellar cortex of CO-exposed pups. INOS and nitrotyrosine immunoreactivity also increased in blood vessels and Purkinje cells (PCs) of pups from group-A, B and C. By contrast, nNOS immunoreactivity decreased in PCs from group-B. Endothelial NOS immunoreactivity showed no changes in any CO-exposed group. The mRNA levels for iNOS were significantly up-regulated in the cerebellum of rats from group B; however, mRNA levels for nNOS and eNOS remained relatively unchanged in groups A, B and C. Ferritin-H immunoreactivity increased in group-B. Immunocytochemistry for neurofilaments (structural protein), synapsin-1 (functional protein), and glutamic acid decarboxylase (the enzyme responsible for the synthesis of the inhibitory neurotransmitter GABA), were decreased in groups A and B. Immunoreactivity for two calcium binding proteins, parvalbumin and calbindin, remained unchanged. The immunoreactivity of the astrocytic marker GFAP increased after prenatal exposure.

CONCLUSION

We conclude that exogenously supplied CO during the prenatal period promotes oxidative stress as indicated by the up-regulation of SOD-1, SOD-2, HO-1, Ferritin-H, and iNOS with increased nitrotyrosine in the rat cerebella suggesting that deleterious and protective mechanisms were activated. These changes correlate with reductions of proteins important to cerebellar function: pre-synaptic terminals proteins (synapsin-1), proteins for the maintenance of neuronal size, shape and axonal quality (neurofilaments) and protein involved in GABAergic neurotransmission (GAD). Increased GFAP immunoreactivity after prenatal CO-exposure suggests a glial mediated response to the constant presence of CO. There were differential responses to prenatal vs. postnatal CO exposure: Prenatal exposure seems to be more damaging; a feature exemplified by the persistence of markers indicating oxidative stress in pups at P20, following prenatal only CO-exposure. The continuation of this cellular environment up to day 20 after CO exposure suggests the condition is chronic. Postnatal exposure without prenatal exposure shows the least impact, whereas prenatal followed by postnatal exposure exhibits the most pronounced outcome among the groups.

Molecular interactions of the plasma membrane calcium ATPase 2 at pre- and post-synaptic sites in rat cerebellum

The plasma membrane calcium extrusion mechanism, PMCA (plasma membrane calcium ATPase) isoform 2 is richly expressed in the brain and particularly the cerebellum. Whilst PMCA2 is known to interact with a variety of proteins to participate in important signalling events [Strehler EE, Filoteo AG, Penniston JT, Caride AJ (2007) Plasma-membrane Ca(2+) pumps: structural diversity as the basis for functional versatility. Biochem Soc Trans 35 (Pt 5):919-922], its molecular interactions in brain synapse tissue are not well understood. An initial proteomics screen and a biochemical fractionation approach identified PMCA2 and potential partners at both pre- and post-synaptic sites in synapse-enriched brain tissue from rat. Reciprocal immunoprecipitation and GST pull-down approaches confirmed that PMCA2 interacts with the post-synaptic proteins PSD95 and the NMDA glutamate receptor subunits NR1 and NR2a, via its C-terminal PDZ (PSD95/Dlg/ZO-1) binding domain. Since PSD95 is a well-known partner for the NMDA receptor this raises the exciting possibility that all three interactions occur within the same post-synaptic signalling complex. At the pre-synapse, where PMCA2 was present in the pre-synapse web, reciprocal immunoprecipitation and GST pull-down approaches identified the pre-synaptic membrane protein syntaxin-1A, a member of the SNARE complex, as a potential partner for PMCA2. Both PSD95-PMCA2 and syntaxin-1A-PMCA2 interactions were also detected in the molecular and granule cell layers of rat cerebellar sagittal slices by immunohistochemistry. These specific molecular interactions at cerebellar synapses may allow PMCA2 to closely control local calcium dynamics as part of pre- and post-synaptic signalling complexes.

Perinatal development of the mammillothalamic tract and innervation of the anterior thalamic nuclei

Axonal projections originating from the mammillary bodies represent important pathways that are essential for spatial information processing. Mammillothalamic tract is one of the main efferent projection systems of the mammillary body belonging to the limbic "Papez circuit". This study was aimed to describe the schedule of the mammillothalamic tract development in the rat using carbocyanine dye tracing. It was shown for the first time that fibers of the mammillothalamic tract being the collaterals of the mammillotegmental tract axons start bifurcating from the mammillotegmental tract on E17. The axons of the mammillothalamic tract grow simultaneously and reach the ventral region of the anterior thalamus where they form first terminal arborizations on E20-E21. Ipsilateral projections from the medial mammillary nucleus to the anteromedial and anteroventral thalamic nuclei develop from E20 to P6. Bilateral projections from the lateral mammillary nucleus to the anterodorsal thalamic nuclei develop later, on P3-P6, after the formation of the thalamic decussation of the mammillary body axons. Unique spatial and temporal pattern of the perinatal development of ascending mammillary body projections to the anterior thalamic nuclei may reflect the importance of these connections within the limbic circuitry.

Analysis of phosphatidylinositol-4,5-bisphosphate signaling in cerebellar Purkinje spines

A 3D model was developed and used to explore dynamics of phosphatidylinositol-4,5-bisphosphate (PIP2) signaling in cerebellar Purkinje neurons. Long-term depression in Purkinje neurons depends on coincidence detection of climbing fiber stimulus evoking extracellular calcium flux into the cell and parallel fiber stimulus evoking inositol-1,4,5-trisphosphate (IP3)-meditated calcium release from the endoplasmic reticulum. Experimental evidence shows that large concentrations of IP3 are required for calcium release. This study uses computational analysis to explore how the Purkinje cell provides sufficient PIP2 to produce large amounts of IP3. Results indicate that baseline PIP2 concentration levels in the plasma membrane are inadequate, even if the model allows for PIP2 replenishment by lateral diffusion from neighboring dendrite membrane. Lateral diffusion analysis indicates apparent anomalous diffusion of PIP2 in the spiny dendrite membrane, due to restricted diffusion through spine necks. Stimulated PIP2 synthesis and elevated spine PIP2 mediated by a local sequestering protein were explored as candidate mechanisms to supply sufficient PIP2. Stimulated synthesis can indeed lead to high IP3 amplitude of long duration; local sequestration produces high IP3 amplitude, but of short duration. Simulation results indicate that local sequestration could explain the experimentally observed finely tuned timing between parallel fiber and climbing fiber activation.

Oxidative stress and the deleterious consequences to the rat cochlea after prenatal chronic mild exposure to carbon monoxide in air

Pregnant rats (starting on E5) were exposed chronically to carbon monoxide (CO) from gestational days 5-20. In the postnatal period, rat pups were grouped as follows: group A: prenatal exposure to CO only; group B: prenatal exposure to CO then exposed to CO from postnatal day (P) 5 to P20; group C, control (air without CO). Groups A and B showed similar deleterious effects after CO exposure. At P3, rat pup cochlea from group A showed a normal organization of the organ of Corti. There was no morphological deterioration, or loss of inner or outer hair cells. At P20, animals from group A and B showed vacuolization on the afferent terminals at the basal portion of the cochlea. We found synapsin-1 immunoreactivity (IR) to be decreased in efferent nerve terminals in CO-exposed pups at P3. From P12 to P20, synapsin-1-IR is low in efferent terminals. At P20, type I spiral ganglia neurons and afferent nerve fibers showed decreased neurofilament-IR in CO-exposed groups when compared with controls. Heme oxygenase-1 and superoxide dismutase-1-IR were elevated in the stria vascularis and blood vessels from CO-exposed rat pups at P12 and P20 in group B; in contrast group A showed a comparable expression to controls. Inducible nitric oxide synthase (iNOS) and nitrotyrosine-IR were increased in blood vessels of the cochlea in CO-exposed groups, from P3 to P20. iNOS up-regulation and the presence of nitrotyrosine in blood vessels of the cochlea indicated that CO exposure activates the production of nitric oxide via increased iNOS activity. Prenatal chronic CO exposure promotes oxidative stress in the cochlea blood vessels that in turn is reflected in damage to spiral ganglia neurons and inner hair cells, suggesting for the first time that prenatal exposure to CO at concentrations expected in poorly ventilated environments impairs the development of the inner ear.

Presynaptic plasma membrane Ca2+ ATPase isoform 2a regulates excitatory synaptic transmission in rat hippocampal CA3

Plasma membrane calcium ATPase isoforms (PMCAs) are expressed in a wide variety of tissues where cell-specific expression provides ample opportunity for functional diversity amongst these transporters. The PMCAs use energy derived from ATP to extrude submicromolar concentrations of intracellular Ca2+ ([Ca2+]i) out of the cell. Their high affinity for Ca2+ and the speed with which they remove [Ca2+]i depends upon splicing at their carboxy (C)-terminal site. Here we provide biochemical and functional evidence that a brain-specific, C-terminal truncated and therefore fast variant of PMCA2, PMCA2a, has a role at hippocampal CA3 synapses. PMCA2a was enriched in forebrain synaptosomes, and in hippocampal CA3 it colocalized with the presynaptic marker proteins synaptophysin and the vesicular glutamate transporter 1, but not with the postsynaptic density protein PSD-95. PMCA2a also did not colocalize with glutamic acid decarboxylase-65, a marker of GABA-ergic terminals, although it did localize to a small extent with parvalbumin-positive presumed inhibitory terminals. Pharmacological inhibition of PMCA increased the frequency but not the amplitude of mEPSCs with little effect on mIPSCs or paired-pulse depression of evoked IPSCs. However, inhibition of PMCA activity did enhance the amplitude and slowed the recovery of paired-pulse facilitation (PPF) of evoked EPSCs. These results indicated that fast PMCA2a-mediated clearance of [Ca2+]i from presynaptic excitatory terminals regulated excitatory synaptic transmission within hippocampal CA3.