Reorganization of the rat cerebellar cortex during postnatal development following cisplatin treatment

Pax3 induces target-specific reinnervation through axon collateral expression of PSA-NCAM

Damaged or dysfunctional neural circuits can be replaced after a lesion by axon sprouting and collateral growth from undamaged neurons. Unfortunately, these new connections are often disorganized and rarely produce clinical improvement. Here we investigate how to promote post-lesion axonal collateral growth, while retaining correct cellular targeting. In the mouse olivocerebellar path, brain-derived neurotrophic factor (BDNF) induces correctly-targeted post-lesion cerebellar reinnervation by remaining intact inferior olivary axons (climbing fibers). In this study we identified cellular processes through which BDNF induces this repair. BDNF injection into the denervated cerebellum upregulates the transcription factor Pax3 in inferior olivary neurons and induces rapid climbing fiber sprouting. Pax3 in turn increases polysialic acid-neural cell adhesion molecule (PSA-NCAM) in the sprouting climbing fiber path, facilitating collateral outgrowth and pathfinding to reinnervate the correct targets, cerebellar Purkinje cells. BDNF-induced reinnervation can be reproduced by olivary Pax3 overexpression, and abolished by olivary Pax3 knockdown, suggesting that Pax3 promotes axon growth and guidance through upregulating PSA-NCAM, probably on the axon's growth cone. These data indicate that restricting growth-promotion to potential reinnervating afferent neurons, as opposed to stimulating the whole circuit or the injury site, allows axon growth and appropriate guidance, thus accurately rebuilding a neural circuit.

Neuroprotective Potential of Intranasally Delivered Sulforaphane-Loaded Iron Oxide Nanoparticles Against Cisplatin-Induced Neurotoxicity

Cisplatin (CIS) is a platinum-based chemotherapeutic drug that is widely used to treat cancer. However, its therapeutic efficiency is limited due to its potential to provoke neurotoxicity. Sulforaphane (SF) is a natural phytochemical that demonstrated several protective activities. Iron oxide nanoparticles (Fe₃O₄-NPs) could be used as drug carriers. This study aimed to explore the nanotoxic influence of SF-loaded within Fe₃O₄-NPs (N.SF), and to compare the neuroprotective potential of both N.SF and SF against CIS-induced neurotoxicity. N.SF or SF was administrated intranasally for 5 days before and 3 days after a single dose of CIS (12 mg/kg/week, i.p.) on the 6^th day. Neuromuscular coordination was assessed using hanging wire and tail-flick tests. Acetylcholinesterase (AChE) activities and markers of oxidative stress were measured in the brain. In addition, the brain iron (Fe) content was estimated. CIS significantly induced a significant increase in AChE activities and lipid peroxides, and a significant decrement in glutathione (GSH) and nitric oxide (NO) contents. CIS elicited impaired neuromuscular function and thermal hyperalgesia. CIS-induced brains displayed a significant reduction in Fe content. Histopathological examination of different brain regions supported the biochemical and behavioral results. Contradict, treatment of CIS-rats with either N.SF or SF significantly decreased AChE activity, mitigated oxidative stress, and ameliorated the behavioral outcome. The histopathological features supported our results. Collectively, N.SF demonstrated superior neuroprotective activities on the behavioral, biochemical, and histopathological (striatum and cerebral cortex) aspects. N.SF could be regarded as a promising “pre-clinical” neuroprotective agent. Furthermore, this study confirmed the safe toxicological profile of Fe₃O₄-NPs.

Chemotherapy and the pediatric brain

Survival rates of children with cancer are steadily increasing. This urges our attention to neurocognitive and psychiatric outcomes, as these can markedly influence the quality of life of these children. Neurobehavioral morbidity in childhood cancer survivors affects diverse aspects of cognitive function, which can include attention, memory, processing speed, intellect, academic achievement, and emotional health. Reasons for neurobehavioral morbidity are multiple with one major contributor being chemotherapy-induced central nervous system (CNS) toxicity. Clinical studies investigating the effects of chemotherapy on the CNS in children with cancer have reported causative associations with the development of leukoencephalopathies as well as smaller regional grey and white matter volumes, which have been found to correlate with neurocognitive deficits.Preclinical work has provided compelling evidence that chemotherapy drugs are potent neuro- and gliotoxins in vitro and in vivo and can cause brain injury via excitotoxic and apoptotic mechanisms. Furthermore, chemotherapy triggers DNA (deoxyribonucleic acid) damage directly or through increased oxidative stress. It can shorten telomeres and accelerate cell aging, cause cytokine deregulation, inhibit hippocampal neurogenesis, and reduce brain vascularization and blood flow. These mechanisms, when allowed to operate on the developing brain of a child, have high potential to not only cause brain injury, but also alter crucial developmental events, such as myelination, synaptogenesis, neurogenesis, cortical thinning, and formation of neuronal networks.This short review summarizes key publications describing neurotoxicity of chemotherapy in pediatric cancers and potential underlying pathomechanisms.

Hydroxyurea Exposure and Development of the Cerebellar External Granular Layer: Effects on Granule Cell Precursors, Bergmann Glial and Microglial Cells

The current paper presents a histological analysis of the cell death in the cerebellar external granular layer (EGL) following the treatment with a single dose (2 mg/g) of hydroxyurea (HU). The rats were examined at postnatal days (P) 5, 10, and 15, and sacrificed at appropriate times ranging from 6 to 48 h after treatment administration. Studies were done in each cortical lobe (anterior, central, posterior, and inferior). The quantification of several parameters, such as density of 5-bromo-2'-deoxyuridine, TUNEL, vimentin, and tomato lectin-stained cells, revealed that HU compromises the viability of EGL cells. Our results indicate that P10 is a time of high vulnerability to injury. We also show here that the anterior and central lobes are the cortical regions most susceptible to the action of the HU. Additionally, our data also indicate that from 6 to 24 h after HU-exposure is a time-window of high sensibility to this agent. On the other hand, our ultrastructural analysis confirmed that HU administration produces the activation of apoptotic cellular events in the EGL, resulting in a substantial number of dying cells. Different stages of apoptosis can be observed in all cortical lobes at all investigated postnatal ages and survival times. Moreover, we observed that dying neuroblasts were covered by laminar processes of Bergmann glia, and that these unipolar astrocytes presented cytological features of phagocytes engulfing apoptotic bodies and cell debris. The electron microscopy study also revealed the participation of ameboid microglial cells in the phagocytosis of apoptotic cells in the regions of the EGL with extensive cell death.

In vitro Magnetic Stimulation: A Simple Stimulation Device to Deliver Defined Low Intensity Electromagnetic Fields

Non-invasive brain stimulation (NIBS) by electromagnetic fields appears to benefit human neurological and psychiatric conditions, although the optimal stimulation parameters and underlying mechanisms remain unclear. Although, in vitro studies have begun to elucidate cellular mechanisms, stimulation is delivered by a range of coils (from commercially available human stimulation coils to laboratory-built circuits) so that the electromagnetic fields induced within the tissue to produce the reported effects are ill-defined. Here, we develop a simple in vitro stimulation device with plug-and-play features that allow delivery of a range of stimulation parameters. We chose to test low intensity repetitive magnetic stimulation (LI-rMS) delivered at three frequencies to hindbrain explant cultures containing the olivocerebellar pathway. We used computational modeling to define the parameters of a stimulation circuit and coil that deliver a unidirectional homogeneous magnetic field of known intensity and direction, and therefore a predictable electric field, to the target. We built the coil to be compatible with culture requirements: stimulation within an incubator; a flat surface allowing consistent position and magnetic field direction; location outside the culture plate to maintain sterility and no heating or vibration. Measurements at the explant confirmed the induced magnetic field was homogenous and matched the simulation results. To validate our system we investigated biological effects following LI-rMS at 1 Hz, 10 Hz and biomimetic high frequency, which we have previously shown induces neural circuit reorganization. We found that gene expression was modified by LI-rMS in a frequency-related manner. Four hours after a single 10-min stimulation session, the number of c-fos positive cells increased, indicating that our stimulation activated the tissue. Also, after 14 days of LI-rMS, the expression of genes normally present in the tissue was differentially modified according to the stimulation delivered. Thus we describe a simple magnetic stimulation device that delivers defined stimulation parameters to different neural systems in vitro. Such devices are essential to further understanding of the fundamental effects of magnetic stimulation on biological tissue and optimize therapeutic application of human NIBS.

Chemotherapy-induced neurotoxicity in pediatric solid non-CNS tumor patients: An update on current state of research and recommended future directions

Neurocognitive sequelae are known to be induced by cranial radiotherapy and central-nervous-system-directed chemotherapy in childhood Acute Lymphoblastic Leukemia (ALL) and brain tumor patients. However, less evidence exists for solid non-CNS-tumor patients. To get a better understanding of the potential neurotoxic mechanisms of non-CNS-directed chemotherapy during childhood, we performed a comprehensive literature review of this topic. Here, we provide an overview of preclinical and clinical studies investigating neurotoxicity associated with chemotherapy in the treatment of pediatric solid non-CNS tumors. Research to date suggests that chemotherapy has deleterious biological and psychological effects, with animal studies demonstrating histological evidence for neurotoxic effects of specific agents and human studies demonstrating acute neurotoxicity. Although the existing literature suggests potential neurotoxicity throughout neurodevelopment, research into the long-term neurocognitive sequelae in survivors of non-CNS cancers remains limited. Therefore, we stress the critical need for neurodevelopmental focused research in children who are treated for solid non-CNS tumors, since they are at risk for potential neurocognitive impairment.

Neurotoxic Effects of Platinum Compounds: Studies in vivo on Intracellular Calcium Homeostasis in the Immature Central Nervous System

Platinum compounds cause significant clinical neurotoxicity. Several studies highlight neurological complications especially in paediatric oncology patients with Central Nervous System (CNS) and non-CNS malignancies. To understand the toxicity mechanisms of platinum drugs at cellular and molecular levels in the immature brain, which appears more vulnerable to injury than in the adult one, we compared the effects in vivo of the most used platinum compounds, i.e., cisdichlorodiammineplatinum (cisplatin, cisPt), and the new [Pt(O,O′-acac)(γ-acac)(DMS)] (PtAcacDMS). As models of developing brain areas, we have chosen the cerebellum and hippocampus dentate gyrus. Both areas show the neurogenesis events, from proliferation to differentiation and synaptogenesis, and therefore allow comparing the action of platinum compounds with DNA and non-DNA targets. Here, we focused on the changes in the intracellular calcium homeostasis within CNS architecture, using two immunohistochemical markers, the calcium buffer protein Calbindin and Plasma Membrane Calcium ATPase. From the comparison of the cisPt and PtAcacDMS effects, it emerges how essential the equilibrium and synergy between CB and PMCA1 is or how important the presence of at least one of them is to warrant the morphology and function of nervous tissue and limit neuroarchitecture damages, depending on the peculiar and intrinsic properties of the developing CNS areas.

Pistachio supplementation attenuates motor and cognition impairments induced by cisplatin or vincristine in rats

Background:

A large number of natural products and dietary components have been evaluated as potential chemoprotective agents. In the present investigation we report the effects of treatment with the dietary antioxidant, pistachio, on cisplatin- or vincristine-induced neurotoxicity in male Wistar rats.

Materials and Methods:

Dietary pistachio (10%) was assessed for its neuroprotective effects through the alteration in performance of hippocampus- and cerebellum-related behaviors following chronic cisplatin (5 mg/kg) or vincristine (0.2 mg/kg) treatment in male rats. We also evaluated the effects of cisplatin, vincristine, and pistachio administration on nociception. Six behavioral tasks were used: open field, rotarod, grasping, Morris water maze (MWM), hot plate, and motor nerve conductive velocity (MNCV).

Results:

We showed that the exposure of adolescent rats to cisplatin or vincristine resulted in a significant decrease in explorative behaviors and memory retention. Pistachio consumption somewhat improved memory and motor abilities in cisplatin- or vincristine-treated rats, while pistachio alone did not show any significant changes in these abilities compared to saline. Cisplatin and vincristine increased the latency of response to nociception, and pistachio did not reverse this effect.

Conclusion:

We conclude that pistachio in the diet following anticancer drugs such as cisplatin and vincristine might have a protective effect against anticancer drug-induced disruptions in motor and cognitive function. However, further studies are needed to elucidate the exact mechanisms of this protective effect of pistachio.

Cerebellum neurotransmission during postnatal development: [Pt(O,O'-acac)(γ-acac)(DMS)] vs cisplatin and neurotoxicity

Several chemotherapeutic drugs are known to cause neurotoxicity. Platinum-based agents in use or in clinical trials display neurotoxic potential accompanied by neurological complications; recent studies have identified a large number of behavioural issues in paediatric oncology patients. To understand the toxicity of platinum drugs at the molecular and cellular levels, this study compares the possible cytotoxic effects of an older platinum compound, cisplatin and a new platinum compound, [Pt(O,O'-acac)(γ-acac)(DMS)], on the CNS of postnatally developing rats, which is much more vulnerable to injury than the CNS of adult rats. Since several drugs interact with neurotransmitters during neuronal maturation, we performed immunostainings with antibodies raised against markers of glutamate and GABA, the major neurotransmitters in the cerebellum. After a single injection of cisplatin at postnatal day 10 (PD10), the labelling of Purkinje cells with the neurotransmitter markers evidenced alterations between PD11 and PD30, i.e. atrophy of the dendrite tree, changes in the distribution of synaptic contacts of parallel and climbing fibres, delay in the elimination of transient synapses on cell soma and severely impaired pinceau formation at the axon hillock. After treatment with [Pt(O,O'-acac)(γ-acac)(DMS)], the sole relevant change concerned the timing of climbing fibres elimination; the transient synapses disappearance on the Purkinje cell soma was delayed in some cells; instead, the growth of Purkinje cell dendrite tree was normal as was the formation of inhibitory synaptic contacts on these neurons. These findings add new evidence not only on the lower neurotoxicity of [Pt(O,O'-acac)(γ-acac)(DMS)] vs cisplatin but also on the involvement of neurotransmitters and relative synaptic connections in the maturation of central nerve tissue.

Effect of cytosine arabinoside on cerebellar neurofilaments during development: A sexual dimorphism

Previous reports suggest that the resistance of neuronal cytoskeleton to drug toxicity may vary with age and gender. The aim of the present study was to assess the impact of cytosine arabinoside (AraC) treatment on neurofilament (NF) levels and phosphorylation status in the developing cerebellum of male, female and testosterone propionate (1.25 mg/rat)-androgenized female rats. AraC (200 mg/kg bw) was administered from postnatal day (PND) 14–16 and changes in the level and phosphorylation of NFs were detected at PND 16 by Western blot analysis. The drug had no effect in male pups, while it increased the non-phosphorylated NF subunits of medium and low molecular weight in females. Androgenization of females prevented the AraC-induced increase in NF subunits. The levels of estrogen receptor beta (ER-β), known to mediate neuroprotective actions of estrogens in the brain, were significantly higher in the developing female cerebellum, as compared to males and androgenized females.

These data show that the neurofilament cytoskeleton in the developing rat cerebellum exhibits resistance to AraC that appears sexually dimorphic. In young males the resistance is exemplified by a lack of responsiveness, whereas in juvenile females it is presented by an androgenization-sensitive NF upregulation.

Evaluation of destructive effects of exposure to cisplatin during developmental stage: no profound evidence for sex differences in impaired motor and memory performance

We have elucidated the alteration in hippocampal and cerebellum function following chronic cisplatin treatment in male and female rats. Hippocampus and cerebellum related behavioral dysfunction in cisplatin-treated [intraperitoneally, 5 mg/(kg/week) for 5 weeks from 23-day-old] rats were analyzed using explorative, motor function, learning, and memory tasks (grasping, rotarod, open field, and Morris water maze tests). Exposure to cisplatin impaired the motor coordination in male and female rats. Exposure to cisplatin was reflected by a decrease in grasping time compared to vehicle-treated controls (saline) only in male rat while there were not any differences in female rats. When the rearing frequency, total distance moved and velocity of their recorded in open fieldtest, both males and females were dramatically affected by exposure to cisplatin. Compared to the saline, male and female rats trained 5 weeks after cisplatin injection showed significant memory deficits in the Morris water maze test. However, hippocampal and cerebellum functions of male and female rats were profoundly affected by exposure to cisplatin while no sex differences in the most variable were evident.

Developing central nervous system and vulnerability to platinum compounds

Comparative studies on the effects of the platinum complexes in use or in clinical trials are carried out in order to discover differences in the neurotoxic potential and the reversibility of neurotoxicity. In this paper, we summarized the current literature on neurotoxicity and chemoresistance of cisplatin (cisPt) and discussed our recent efforts on the interference of cisPt and a new platinum compound [Pt(O,O′-acac)(γ-acac)(DMS)] (PtAcacDMS), with high specific reactivity with sulphur ligands instead of nucleobases as cisPt, on some crucial events of rat postnatal cerebellum development. The acute effects of drug treatments on cell proliferation and death in the external granular layer and granule cell migration and the late effects on the dendrite growth of Purkinje cells were evaluated. Together with the demonstrated antineoplastic effectiveness in vitro, compared with cisPt, data suggest a lower neurotoxicity of PtAcacDMS, in spite of its presence in the brain that involves considerations on the blood brain barrier permeability.

The developmental neurotoxicity study of platinum compounds. Effects of cisplatin versus a novel Pt(II) complex on rat cerebellum

In the field of experimental oncology, many efforts are being carried out to search new platinum-based drugs overcoming the CNS toxicity and drug resistance. One of the adopted strategies is the synthesis of platinum compounds able to form Pt-DNA adducts different from the cisplatin ones or to react with other subcellular targets. In this context a novel Pt(II) complex, [Pt(O,O'-acac)(γ-acac)(DMS)](PtAcacDMS), was synthesized which reacts preferentially with protein thiols or thioethers. In this work we investigated the in vivo effects of cisplatin and PtAcacDMS on normal development. Moreover, to verify the dose-dependence of the effects, different groups of animals were treated with 5 μg/g or 10 μg/g body weight of cisPt and PtAcacDMS. We have focused our attention on the cerebellum because it provides a useful model system to evaluate the outcomes of perinatal treatment with chemotherapeutic agents on key CNS developmental processes such as neural cells proliferation, migration and differentiation. We have demonstrated the ability of both cisPt and PtAcacDMS to reach the brain tissue once injected. The brain platinum content after PtAcacDMS treatment was notably higher (approximately 4-fold as much) than after cisPt. The platinum accumulation in the brain was still considerable 7 days after PtAcacDMS administration. However, compared with cisplatin, PtAcacDMS induces less severe changes on fundamental events of neuroarchitecture development, such as no high apoptotic events, less altered granule cell migration and Purkinje cell dendrite growth, suggesting a low neurotoxicity of this new Pt complex for normal CNS. The mild damages could be attributable to the different subcellular target of this compound as well as to a greater efficiency of the cell repair system to recognize the drug-target adducts and to repair them. Together with the previously demonstrated antineoplastic effectiveness in vitro, the findings here reported suggest PtAcacDMS as a potential alternative to cisplatin indicating, at the same time, that the choice of platinum compounds with new subcellular targets could be a strategy to prevent neurotoxicity induced by cisplatin and overcome drug resistance induced by mutations in the intrinsic apoptotic pathway.

Cell proliferation, apoptosis and mitochondrial damage in rat B50 neuronal cells after cisplatin treatment

OBJECTIVES

Cisplatin (cisPt) is used as a chemotherapeutic agent for the treatment of a variety of human tumours; more recently, it has been demonstrated that tumour cell exposure to cisPt ultimately results in apoptosis, but the mechanism by which nuclear cisPt/DNA generates the cytoplasmic cascade of events involved has not been clarified. We have investigated the effects of cisPt on proliferation in the neuronal cell line B50, with particular attention being given to understand whether mitochondria are a target of cisPt and their involvement in the apoptotic process.

MATERIALS AND METHODS

Rat neuronal B50 cells were used to investigate the mechanisms of cisPt-induced cytotoxicity; this line has been used as a model system for neurotoxicity in vivo.

RESULTS

Changes in proliferation, induction of apoptosis, activation of caspase-3 and DNA fragmentation were observed in the cells, as well as morphological and biochemical alterations of mithocondria. Activation of caspase-9 confirmed that mitochondria are a target of cisPt.

CONCLUSION

CisPt exerts cytotoxic effects in the neuronal B50 cell line via a caspase-dependent pathway with mitochondria being central relay stations.

Monoamine receptors and immature cerebellum cytoarchitecture after cisplatin injury

The experimental model of cisplatin treatment provides the opportunity to identify the precise function of the neurotransmitters in some crucial events of brain development, and their interactions or modulatory roles. The serotonin and noradrenaline monoamines influence the formation of the cerebellar cortex circuitry. In this study we found changes in the expression of the serotonin and noradrenaline receptors after a single injection of cisplatin in 10-day-old rats. The growth of Pc dendrites was early altered in lobules VI-VIII of cerebellum vermis. In these lobules, at postnatal day (PD) 17, the cisplatin-induced increase of the serotoninergic receptor 5-HT2AR, a factor that inhibits Pc dendrite growth by acting post-synaptically, occurred in all cerebellar layers, suggesting also alteration of granule cell proliferation and migration. The decreased labelling of beta l adrenergic receptor (beta1AR) in the soma of some Pc at PD11 can be correlated with the altered expression of glutamate receptors and GAD65 (glutamic acid decarboxylase) of and on Pc we have previously described [Pisu, M.B., Guioli, S., Conforti, E., Bernocchi, G., 2003. Signal molecules and receptors in the differential development of cerebellum lobules. Acute effects of cisplatin on nitric oxide and glutamate system in Purkinje cell population. Dev. Brain Res. 145, 229-240; Pisu, M.B., Roda, E., Avella, D., Bernocchi, G., 2004. Developmental plasticity of rat cerebellar cortex after cisplatin injury: inhibitory synapses and differentiating Purkinje neurons. Neuroscience 129, 655-664]. Moreover, beta1AR seems to be the key factor in the cerebellar reorganization between PD17 and PD30. The expression of this receptor was maintained in the molecular layer (ML), in particular in the inhibitory interneurons, despite their different distributions. The labelling of 5-HT1AR in the ML areas lacking Pc dendrite branches could contribute to the recovery phase of the cerebellar cytoarchitecture in cisplatin-treated rats. In general these findings should be taken into consideration in therapeutic interventions for developmental CNS disorders with a morphological basis.