Morphologic alteration of the olfactory bulb after acute ozone exposure in rats

PM2.5 exposure and olfactory functions

Growing evidence indicates that air pollution can negatively impact cognitive functions. The olfactory system is interesting in this context as it is directly exposed to pollutants and also associated with cognitive functions. The aim of this study was to investigate long- and short-term PM_2.5 exposure in association with olfactory functions. Scores from odor tests were obtained from the Betula project - a longitudinal cohort study. Estimates of annual mean PM_2.5 concentrations at the participants' residential address were obtained from a dispersion-model. Daily mean PM_2.5 concentrations were obtained from a measuring station close to the test location. We found a positive association between long-term PM_2.5 exposure and odor identification, i.e. exposure was associated with a better ability to identify odors. We also found an interaction effect between PM_2.5 and age on odor identification. We found no associations between any PM_2.5 exposure and odor detection or between short-term PM_2.5 exposure and olfactory functions.

Toxicity of environmental ozone exposure on mice olfactory bulbs, using Western blot technique

Environmental ozone (O₃) exposure has adverse effects on different body systems. This experimental work aimed to study the effect(s) of O₃ exposure on the olfactory bulbs (OB) of Swiss Webster and C57BL/6J mouse strains, using Western blot technique. Both mice strains were exposed to different O₃ doses for different number of exposures and durations. The results indicated that O₃ exposure caused a significant increase in the level of the proteins involved in the oxidative stress state such as 4-hydroxynonenal (4HNE) and Cytochrome P450, family 1, subfamily A, polypeptide 1 (CYP1A1), in addition to the total OB proteins in Swiss Webster mouse strain. However, this effect was not observed in C57BL/6J mouse strain. Furthermore, CYP1A1 was completely absent in the Green fluorescent protein (GFP) C57BL/6J O₃ exposed mice. Moreover, O₃ exposure caused a significant decrease in the body weight of the tested mice from the two strains.

An acute exposure to ozone impairs human olfactory functioning

INTRODUCTION

Ozone is a ubiquitous and irritant gas. We questioned whether an acute exposure to 0.2 ppm ozone impaired olfactory functioning.

METHODS

Healthy, normosmic subjects were exposed according to a parallel group design either to 0.2 ppm ozone (n = 15) or to sham (n = 13) in an exposure chamber for two hours. Possible irritating effects were assessed by questionnaire (range 0-5). The detection threshold of n-butanol was measured with the Sniffin' Sticks test before and after exposure. Olfactory thresholds were logarithmized and a two-way analysis of variance (ANOVA) with repeated measurements was carried out to test the effects of exposure (ozone vs. sham) and time (before vs. after exposure). Additionally, nasal secretions were taken at a preliminary examination and after exposure to determine interleukins 1ß and 8.

RESULTS

No irritating effects to the upper airways were observed. In the ozone group, the median score for cough increased from 0 to 2 at the end of exposure (sham group 0 and 0, respectively, p < 0.001). The ANOVA showed a main effect for ozone exposure (F (1, 26) = 27.6, p = 0.0002), indicating higher olfactory thresholds in the ozone group. Concentrations of interleukins in nasal secretions did not increase following ozone exposure.

CONCLUSIONS

This study shows a clear impairment of olfactory functioning following an acute exposure to 0.2 ppm ozone.

A ‘Best Practices’ Approach to Neuropathologic Assessment in Developmental Neurotoxicity Testing—for Today

A key trait of developmental neurotoxicants is their ability to cause structural lesions in the immature nervous system. Thus, neuropathologic assessment is an essential element of developmental neurotoxicity (DNT) studies that are designed to evaluate chemically-induced risk to neural substrates in young humans. The guidelines for conventional DNT assays have been established by regulatory agencies to provide a flexible scaffold for conducting such studies; recent experience has launched new efforts to update these recommendations. The present document was produced by an ad hoc subcommittee of the Society of Toxicologic Pathology (STP) tasked with examining conventional methods used in DNT neuropathology in order to define the ‘best practices’ for dealing with the diverse requirements of both national (EPA) and international (OECD) regulatory bodies. Recommendations (including citations for relevant neurobiological and technical references) address all aspects of the DNT neuropathology examination: study design; tissue fixation, collection, processing, and staining; qualitative and quantitative evaluation; statistical analysis; proper control materials; study documentation; and personnel training. If followed, these proposals will allow pathologists to meet the need for a sound risk assessment (balanced to address both regulatory issues and scientific considerations) in this field today while providing direction for the research needed to further refine DNT neuropathology ‘best practices’ in the future.

Exploring the possible link between MeCP2 and oxidative stress in Rett syndrome

Rett syndrome (RTT, MIM 312750) is a rare and orphan progressive neurodevelopmental disorder affecting girls almost exclusively, with a frequency of 1/15,000 live births of girls. The disease is characterized by a period of 6 to 18 months of apparently normal neurodevelopment, followed by early neurological regression, with a progressive loss of acquired cognitive, social, and motor skills. RTT is known to be caused in 95% of the cases by sporadic de novo loss-of-function mutations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene encoding methyl-CpG binding protein 2 (MeCP2), a nuclear protein able to regulate gene expression. Despite almost two decades of research into the functions and role of MeCP2, little is known about the mechanisms leading from MECP2 mutation to the disease. Oxidative stress (OS) is involved in the pathogenic mechanisms of several neurodevelopmental and neurodegenerative disorders, although in many cases it is not clear whether OS is a cause or a consequence of the pathology. Fairly recently, the presence of a systemic OS has been demonstrated in RTT patients with a strong correlation with the patients' clinical status. The link between MECP2 mutation and the redox imbalance found in RTT is not clear. Animal studies have suggested a possible direct correlation between Mecp2 mutation and increased OS levels. In addition, the restoration of Mecp2 function in astrocytes significantly improves the developmental outcome of Mecp2-null mice and reexpression of Mecp2 gene in the brain of null mice restored oxidative damage, suggesting that Mecp2 loss of function can be involved in oxidative brain damage. Starting from the evidence that oxidative damage in the brain of Mecp2-null mice precedes the onset of symptoms, we evaluated whether, based on the current literature, the dysfunctions described in RTT could be a consequence or, in contrast, could be caused by OS. We also analyzed whether therapies that at least partially treated some RTT symptoms can play a role in defense against OS. At this stage we can propose that OS could be one of the main causes of the dysfunctions observed in RTT. In addition, the major part of the therapies recommended to alleviate RTT symptoms have been shown to interfere with oxidative homeostasis, suggesting that MeCP2 could somehow be involved in the protection of the brain from OS.

Oxidative stress-dependent changes in immune responses and cell death in the substantia nigra after ozone exposure in rat

Parkinson's disease has been associated with the selective loss of neurons in the substantia nigra pars compacta. Increasing evidence suggests that oxidative stress plays a major role. The resulting increase in reactive oxygen species triggers a sequence of events that leads to cell damage, activation of microglia cells and neuroinflammatory responses. Our objective was to study whether chronic exposure to low doses of ozone, which produces oxidative stress itself, induces progressive cell death in conjunction with glial alterations in the substantia nigra. Animals were exposed to an ozone-free air stream (control) or to low doses of ozone for 7, 15, 30, 60, or 90 days. Each group underwent (1) spectrophotometric analysis for protein oxidation; (2) western blot testing for microglia reactivity and nuclear factor kappa B expression levels; and (3) immunohistochemistry for cytochrome c, GFAP, Iba-1, NFkB, and COX-2. Our results indicate that ozone induces an increase in protein oxidation levels, changes in activated astrocytes and microglia, and cell death. NFkB and cytochrome c showed an increase until 30 days of exposure, while cyclooxygenase 2 in the substantia nigra increased from 7 days up to 90 days of repetitive ozone exposure. These results suggest that oxidative stress caused by ozone exposure induces changes in inflammatory responses and progressive cell death in the substantia nigra in rats, which could also be occurring in Parkinson's disease.

Functional and morphological olfactory bulb modifications in mice after vanadium inhalation

Neurodegenerative disorders, such as Parkinson's and Alzheimer's diseases, have olfaction impairment. These pathologies have also been linked to environmental pollutants. Vanadium is a pollutant, and its toxic mechanisms are related to the production of oxidative stress. In this study, we evaluated the effects of inhaled vanadium on olfaction, the olfactory bulb antioxidant, through histological and ultrastructural changes in granule cells. Mice in control group were made to inhale saline; the experimental group inhaled 0.02-M vanadium pentoxide (V2O5) for 1 hr twice a week for 4 weeks. Animals were sacrificed at 1, 2, 3, and 4 weeks after inhalation. Olfactory function was evaluated by the odorant test. The activity of glutathione peroxidase (GPx) and glutathione reductase (GR) was assayed in olfactory bulbs and processed for rapid Golgi method and ultrastructural analysis. Results show that olfactory function decreased at 4-week vanadium exposure; granule cells showed a decrease in dendritic spine density and increased lipofuscin, Golgi apparatus vacuolation, apoptosis, and necrosis. The activity of GPx and GR in the olfactory bulb was increased compared to that of the controls. Our results demonstrate that vanadium inhalation disturbs olfaction, histology, and the ultrastructure of the granule cells that might be associated with oxidative stress, a risk factor in neurodegenerative diseases.

Subsite awareness in neuropathology evaluation of National Toxicology Program (NTP) studies: a review of select neuroanatomical structures with their functional significance in rodents

This review article is designed to serve as an introductory guide in neuroanatomy for toxicologic pathologists evaluating general toxicity studies. The article provides an overview of approximately 50 neuroanatomical subsites and their functional significance across 7 transverse sections of the brain. Also reviewed are 3 sections of the spinal cord, cranial and peripheral nerves (trigeminal and sciatic, respectively), and intestinal autonomic ganglia. The review is limited to the evaluation of hematoxylin and eosin-stained tissue sections, as light microscopic evaluation of these sections is an integral part of the first-tier toxicity screening of environmental chemicals, drugs, and other agents. Prominent neuroanatomical sites associated with major neurological disorders are noted. This guide, when used in conjunction with detailed neuroanatomic atlases, may aid in an understanding of the significance of functional neuroanatomy, thereby improving the characterization of neurotoxicity in general toxicity and safety evaluation studies.

Air pollution and newly diagnostic autism spectrum disorders: a population-based cohort study in Taiwan

There is limited evidence that long-term exposure to ambient air pollution increases the risk of childhood autism spectrum disorder (ASD). The objective of the study was to investigate the associations between long-term exposure to air pollution and newly diagnostic ASD in Taiwan. We conducted a population-based cohort of 49,073 children age less than 3 years in 2000 that were retrieved from Taiwan National Insurance Research Database and followed up from 2000 through 2010. Inverse distance weighting method was used to form exposure parameter for ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and particles with aerodynamic diameter less than 10 µm (PM10). Time-dependent Cox proportional hazards (PH) model was performed to evaluate the relationship between yearly average exposure air pollutants of preceding years and newly diagnostic ASD. The risk of newly diagnostic ASD increased according to increasing O3, CO, NO2, and SO2 levels. The effect estimate indicating an approximately 59% risk increase per 10 ppb increase in O3 level (95% CI 1.42–1.79), 37% risk increase per 100 ppb in CO (95% CI 1.31–1.44), 340% risk increase per 10 ppb increase in NO2 level (95% CI 3.31–5.85), and 17% risk increase per 1 ppb in SO2 level (95% CI 1.09–1.27) was stable with different combinations of air pollutants in the multi-pollutant models. Our results provide evident that children exposure to O3, CO, NO2, and SO2 in the preceding 1 year to 4 years may increase the risk of ASD diagnosis.

STP position paper: Recommended practices for sampling and processing the nervous system (brain, spinal cord, nerve, and eye) during nonclinical general toxicity studies

The Society of Toxicologic Pathology charged a Nervous System Sampling Working Group with devising recommended practices to routinely screen the central nervous system (CNS) and peripheral nervous system (PNS) in Good Laboratory Practice-type nonclinical general toxicity studies. Brains should be weighed and trimmed similarly for all animals in a study. Certain structures should be sampled regularly: caudate/putamen, cerebellum, cerebral cortex, choroid plexus, eye (with optic nerve), hippocampus, hypothalamus, medulla oblongata, midbrain, nerve, olfactory bulb (rodents only), pons, spinal cord, and thalamus. Brain regions may be sampled bilaterally in rodents using 6 to 7 coronal sections, and unilaterally in nonrodents with 6 to 7 coronal hemisections. Spinal cord and nerves should be examined in transverse and longitudinal (or oblique) orientations. Most Working Group members considered immersion fixation in formalin (for CNS or PNS) or a solution containing acetic acid (for eye), paraffin embedding, and initial evaluation limited to hematoxylin and eosin (H&E)-stained sections to be acceptable for routine microscopic evaluation during general toxicity studies; other neurohistological methods may be undertaken if needed to better characterize H&E findings. Initial microscopic analyses should be qualitative and done with foreknowledge of treatments and doses (i.e., "unblinded"). The pathology report should clearly communicate structures that were assessed and methodological details. Since neuropathologic assessment is only one aspect of general toxicity studies, institutions should retain flexibility in customizing their sampling, processing, analytical, and reporting procedures as long as major neural targets are evaluated systematically.

Tobacco smoke modulates ozone-induced toxicity in rat lungs and central nervous system

Adult Sprague-Dawley (SD) male rats were exposed for a single 3 h period to air, ozone (O₃) or O₃) followed by tobacco smoke (O₃/TS). For pulmonary effects, bronchoalveolar lavage (BAL) cells and fluid were analyzed. Data revealed a significant increase in polymorphonuclear leukocytes (PMN), total protein and albumin concentrations in the O₃ group, reflecting inflammatory and toxic responses. A subsequent exposure to TS attenuated PMN infiltration into the airspaces and their recovery in the BAL. A similar reduction was observed for BAL protein and albumin in the O₃/TS group, but it was not statistically significant. We also observed a significant increase in BAL total antioxidant capacity following O₃ exposure, suggesting development of protective mechanisms for oxidative stress damage from O₃. Exposure to TS attenuated the levels of total antioxidant capacity. Lung tissue protein analysis showed a significant reduction of extracellular superoxide dismutase (EC-SOD) in the O₃ or O₃/TS group and catalase in the O₃/TS group. TS further altered O₃-induced EC-SOD and catalase protein expression, but the reductions were not significant. For effects in the central nervous system (CNS), we measured striatal dopamine levels by HPLC with electrochemical detection. O₃ exposure produced a nonsignificant decrease in the striatal dopamine content. The effect was partially reversed in the O₃/TS group. Overall, the results show that the toxicity of O₃ in the lung is modulated by TS exposure, and the attenuating trend, though nonsignificant in many cases, is contrary to the synergistic toxicity predicted for TS and O₃, suggesting limited cross-tolerance following such exposures.

Toxic effects of inhaled manganese on the olfactory bulb: an ultrastructural approach in mice

Olfactory dysfunction is a common symptom reported by patients with neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Despite the knowledge gathered about the pathology of these diseases, little information has been generated regarding the ultrastructure modifications of the granule cells that regulate the information for odor identification. Swollen organelles and nuclear invaginations identified the exposed mice. Necrosis was evidenced at 4th week of exposure, whereas apoptosis arose at 8th week of exposure. A ruffled electron-dense membrane changes were also found. The changes observed could be explained by the reactive oxygen species generated by manganese and its effects on the membrane's structure and on the cytoskeleton's function. This study contributes to correlate metal air pollution and neurodegenerative changes with olfactory affection.

Ozone modulates the effects of imipramine on immobility in the forced swim test, and nonspecific parameters of hippocampal oxidative stress in the rat

Depression has been associated with oxidative stress. There is increased awareness of the role of environmental toxins in the development of mood disorders. Ozone, a pro-oxidant and environmental pollutant, has been noted to have central nervous system effects. We investigated the effects of acute and chronic ozone inhalation on the response of imipramine in the forced-swim test (FST) and on biomarkers of oxidative stress in rat hippocampus. Sprague Dawley rats were exposed to 0, 0.25 or 0.7 ppm ozone per inhalation 4 h daily for either 30 days (chronic) or once (acute). Animals were then injected intraperitoneally with imipramine (10 mg/kg) or saline 24, 5 and 1 h before the forced-swim test. Hippocampal superoxide accumulation and lipid peroxidation were measured. Imipramine evoked an antidepressant-like effect independent of acute or chronic ozone exposure. However, 0.7 ppm acute ozone and 0.25 ppm chronic ozone attenuated the antidepressant-like effects of imipramine. The ozone exposures also elevated hippocampal superoxide accumulation and lipid peroxidation. Importantly, imipramine reversed the lipid peroxidation induced by chronic ozone, thereby preventing cellular damage induced by oxidative stress. Ozone exposure presents a feasible model with etiological validity to investigate oxidative stress in depression and antidepressant action.

MORPHOLOGICAL RECOVERY OF THE GRANULE CELLS FROM THE OLFACTORY BULB AFTER THE CESSATION OF ACUTE OZONE EXPOSURE

The purpose of this study was to analyze the possible morphological recovery of the granule cells in the olfactory bulb as a consequence of oxidative stress after an acute ozone exposure. Rats were divided in two groups: Control (air exposed) and experimental group, exposed 4 h, to 1 ppm ozone and divided into 4 subgroups, which were sacrificed at 2 and 24 h, 10 and 15 days, respectively. Olfactory bulbs were processed with the rapid Golgi method and for transmission electron microscopy. The granule cells of the olfactory bulb disclosed less dendritic spine density at 2, 24 h, and 10 days after the exposure compared with controls. At 15 days, the number of spines increased to values similar to those found in controls. The granule cells ultrastructure demonstrated an increment in lipofucsin granules, as well as swollen organelles, changes that decreased overtime. This change decline might be related to a partial recovery of the associative granule cells function.

“Current Pathology Techniques” Symposium Review: Advances and Issues in Neuropathology

Our understanding of the mechanisms that incite neurological diseases has progressed rapidly in recent years, mainly owing to the advent of new research instruments and our increasingly facile ability to assemble large, complex data sets acquired across several disciplines into an integrated representation of neural function at the molecular, cellular, and systemic levels. This mini-review has been designed to communicate the principal technical advances and current issues of importance in neuropathology research today in the context of our traditional neuropathology practices. Specific topics briefly addressed in this paper include correlative biology of the many facets of the nervous system; conventional and novel methods for investigating neural structure and function; theoretical and technical issues associated with investigating neuropathology end points in emerging areas of concern (developmental neurotoxicity, neurodegenerative conditions); and challenges and opportunities that will face pathologists in this field in the foreseeable future. We have organized this information in a manner that we hope will be of interest not only to professionals with a career focus in neuropathology, but also to general pathologists who occasionally face neuropathology questions.

Effect of growth hormone on Cyclooxygenase-2 expression in the hippocampus of rats chronically exposed to ozone

The aim of this study was to determine GH-effects on Cyclooxygenase-2 (COX-2) expression on hippocampus alterations caused by ozone exposure. Seventy male rats were divided into: (1) control; (2) exposed to ozone for 7, 15, and 30 days; (3) exposed to ozone and treated with GH, for 7, 15, and 30 days. Results showed that lipoperoxidation levels and number of COX-2-positive cells increased in all groups exposed to ozone compared to control. In the groups treated with GH, COX-2 immunoreactive cell number decreased with respect to the ozone group. Therefore, GH could provide protection against damage induced by oxidative stress.

Organization of olfactory glomeruli in neonatally undernourished rats

Newborn rats maintain mother-litter bonds by using olfactory signals. At birth, units in the olfactory glomeruli (OG) are immature and vulnerable to noxious epigenetic factors like undernutrition. Because little is known about the effects of neonatal undernutrition upon the OG morphological organization, different OG parameters were studied in undernourished Wistar rats at 7, 14 and 21 days of age. The issue was addressed by analyzing the olfactory bulb (OB) cross sectional area, the total number and area of OGs in the OB coronal sections, and the distribution of OG area in dorsal and ventral quadrants. Reductions in the OB and OG cross sectional areas were detected at 7 and 14 days posnatally. OG area comparisons by OB quadrants were reduced along the study in quadrants, with larger effects in medial than in lateral OB quadrants. Current OG cytoarchitectonic modifications may affect the newborn capabilities for odour discrimination by disrupting early mother-litter interactions.

Hippocampal cell alterations induced by the inhalation of vanadium pentoxide (V(2)O(5)) promote memory deterioration

Spatial memory may be severely impaired as a consequence of ageing and neurodegenerative diseases, conditions that include neuronal damage. Vanadium (V) is a metalloid widely distributed in the environment and exerts severe toxic effects on a wide variety of biological systems. Reports about V inhalation toxicity on the CNS are limited, thus the purpose of this study is to determine the effects of Vanadium pentoxide (V(2)O(5)) inhalation (0.02M) on the memory and its correlation with the cytology of the hippocampus CA1. Forty eight CD-1 male mice were trained in spatial memory tasks and inhaled 1h twice a week; after each inhalation animals were evaluated and sacrificed from 1 to 4 weeks, perfused and processed for Golgi method and for ultrastructure evaluation. The cytological analysis consisted in counting the number of dendritic spines of 20 pyramidal neurons of hippocampus CA1, as well as ultrastructural characteristics. Results show that V inhalation produces a time dependent loss of dendritic spines, necrotic-like cell death, and notorious alterations of the hippocampus CA1 neuropile, which correlate with spatial memory impairment. Our data suggest that V induces important cellular and functional alterations, fact that deserves special attention since the concentration's trend of this element in the atmosphere is increasing.

Oxidative damage in substantia nigra and striatum of rats chronically exposed to ozone

The purpose of this work was to study if chronic low-dose ozone exposure could per se induce oxidative damage to neurons of striatum and substantia nigra. Thirty male Wistar rats were divided into three groups--Group 1: exposed to an air stream free of ozone; Group 2: exposed for 15 days to ozone; Group 3: exposed for 30 days to ozone. Ozone exposure was carried out daily for 4 h at a 0.25 ppm dose. Each group was then tested for (1) motor activity, (2) quantification of lipid peroxidation levels, (3) Klüver-Barrera staining, and (4) immunohistochemistry for tyrosine hydroxylase (TH), dopamine and adenosine 3',5'-monophosphate-regulated phosphoprotein of 32 kD (DARPP-32), inducible nitric oxide synthase (iNOS), and superoxide dismutase (SOD), to study neuronal alterations in striatum and substantia nigra. Results indicate that ozone exposure causes a significant decrease in motor activity. Ozone produced lipid peroxidation, morphological alterations, loss of fibers and cell death of the dopaminergic neurons. The DARPP-32, iNOS and SOD expression increased with repetitive ozone exposure. These alterations suggest that ozone causes oxidative stress which induces oxidative damage to substantia nigra and striatum of the rat.

Prolonged prenatal exposure to low-level ozone affects aggressive behaviour as well as NGF and BDNF levels in the central nervous system of CD-1 mice

The long-term effects on isolation-induced aggressive behaviour and central NGF and BDNF levels of gestational exposures to ozone (O(3)) were evaluated in adult CD-1 mice. Females were exposed to O(3), at the dose of 0.0, 0.3 or 0.6 ppm from 30 days prior the formation of breeding pairs until gestational day 17. Litters were fostered at birth to untreated dams and, at adulthood, male offspring underwent five successive daily encounters (15 min each) with a standard opponent of the same strain, sex, weight and age. The encounters on day 1, 3 and 5 were videotaped and agonistic and non-agonistic behavioural items finely scored. O(3)-exposed mice showed a significant increase in freezing and defensive postures, a decrease in nose-sniffing behaviour and reduced progressively the aggressive behavioural profile displayed on day 1. Reduced NGF levels in the hippocampus and increased BDNF in the striatum were also found upon O(3) exposure.

Nigrostriatal modifications after vanadium inhalation: an immunocytochemical and cytological approach

Vanadium (V) has increased in the air as a component of suspended particles originated from fuel combustion. In this report, a model of inhaled V in mice was implemented to identify the effect that V has in the corpus striatum and substantia nigra, structures with high concentrations of dopamine and scarce antioxidants burden. Mice inhaled 0.02 M V2O5 1 h twice a week and were sacrificed at points from 1 to 8 weeks after inhalation, perfused, and processed for Golgi method and for tyroxine hidroxylase (TH) inmunocytochemistry. Cytological analysis consisted in counting the number of dendritic spines in 20 medium-size spiny neurons and the number of TH immunoreactive neurons in the substatia nigra pars compacta. Dendritic spine density decreased drastically after V exposure; the same was observed with the TH-positive neurons, which decreased in a time-dependent mode. No previous morphological studies about V and nervous system have been reported. The decrease in spine density and in TH-positive neurons might have functional repercussions that should be studied because the trend of this element in the atmosphere is to increase.

Dendritic spine pathology: cause or consequence of neurological disorders?

Altered dendritic spines are characteristic of traumatized or diseased brain. Two general categories of spine pathology can be distinguished: pathologies of distribution and pathologies of ultrastructure. Pathologies of spine distribution affect many spines along the dendrites of a neuron and include altered spine numbers, distorted spine shapes, and abnormal loci of spine origin on the neuron. Pathologies of spine ultrastructure involve distortion of subcellular organelles within dendritic spines. Spine distributions are altered on mature neurons following traumatic lesions, and in progressive neurodegeneration involving substantial neuronal loss such as in Alzheimer's disease and in Creutzfeldt-Jakob disease. Similarly, spine distributions are altered in the developing brain following malnutrition, alcohol or toxin exposure, infection, and in a large number of genetic disorders that result in mental retardation, such as Down's and fragile-X syndromes. An important question is whether altered dendritic spines are the intrinsic cause of the accompanying neurological disturbances. The data suggest that many categories of spine pathology may result not from intrinsic pathologies of the spiny neurons, but from a compensatory response of these neurons to the loss of excitatory input to dendritic spines. More detailed studies are needed to determine the cause of spine pathology in most disorders and relationship between spine pathology and cognitive deficits.

Differences between hippocampus and cerebral cortex in aged rats in an oxidative stress model

Ozone exposure increases the production of free radicals that causes oxidative stress (OS), a state that also occurs during aging and in neurodegenerative diseases. This study identified ultrastructural alterations produced by OS induced by acute ozone exposure in hippocampus and prefrontal cortex in aged compared with young rats. Animals were exposed to 0.70 ppm ozone for 4 h, and controls to flowing air. After the exposure, the tissues were processed for ultrastructural analysis. Results showed increased ultrastructural alterations in the hippocampus and prefrontal cortex in the aged exposed animals compared with controls. OS enhanced the modifications induced by the aging process in those areas related with learning and memory functions, which are the first where degenerative aging changes are observed.

Effects of different ozone doses on memory, motor activity and lipid peroxidation levels, in rats

Ozone is one of the main atmospheric pollutants. Its inhalation causes an increase in free radicals, when these free radicals are not compensated by antioxidants, it leads to an oxidative stress state. This oxidative stress state has been implicated in neurodegenerative processes. To determine the effects of oxidative stress caused by exposure to ozone on memory and motor activity, we used 120 male Wistar rats exposed to one of the following ozone doses, (0.0, 0.1, 0.4, 0.7, 1.1 and 1.5 ppm), for four hours. After ozone exposure, short and long term memory of a one trial passive avoidance test were measured, and motor activity was registered for five minutes, in 10 rats of each group. In 16 rats exposed to 0.0, 0.4, 0.7 or 1.1 ppm lipid peroxidation levels from frontal cortex, hippocampus, striatum and cerebellum, were measured. Results show that ozone, causes memory impairment from doses of 0.7 ppm, decrease in motor activity from doses of 1.1 ppm, and increase in lipid peroxidation levels from doses of 0.4 ppm. that increase with the dose.

Motor impairments in an oxidative stress model and its correlation with cytological changes on rat striatum and prefrontal cortex

Exposure to ozone results in an increased production of free radicals which causes oxidative stress. The purpose of this study was to determine the effects of ozone exposure on motor behavior and its correlation with the cytology of the striatum and prefrontal cortex. Twenty-four male Wistar rats were exposed to 1 p.p.m. (parts per million) ozone for 4 hrs in a closed chamber. Control group was exposed to flowing air. Twenty-four hours after ozone exposure, the motor behavior was measured. After that, the animals were perfused and the brains were placed in Golgi stain. The analysis consisted in counting the dendritic spines in 5 secondary and 5 tertiary dendrites of each of the 20 medium size spiny neurons of striatum and 20 pyramidal neurons of prefrontal cortex analyzed. Our results showed alterations in motor behavior and a significant reduction of dendritic spines, and provided evidence that the deterioration in motor behavior is probably due to the reduction in spine density in the neurons of striatum and prefrontal cortex.

'Sensitivity syndromes' related to radiation exposures

The primary health effects of radiation are traditionally believed to result from cellular genetic damage. These effects are believed to result in a statistically detectable increase in the induction of cancer in exposed populations. A significant number of residents of areas affected by the Chernobyl disaster and workers involved in the clean-up ('liquidators') have reported debilitating physical illnesses that cannot be easily explained by a genetic effect. This paper presents results of a literature search that strongly suggests that a previously unrecognized neural pathway may be responsible for the induction of these debilities. In addition, a common link between radiation and chemical sensitivity syndromes may now be identified.