Pleomorphic xanthoastrocytoma within the medulla oblongata of a young dog.

A 13-week-old male intact Poodle mix dog developed an acute onset of vestibular ataxia, tetraparesis, and vomiting. The patient presented ambulatory, tetraparetic, and ataxic with a head tilt to the left and a disconjugate nystagmus (rotary nystagmus with fast phase to the right in right eye and vertical nystagmus in left eye). There were absent postural reactions in the left pelvic and left thoracic limbs and decreased right-sided postural reactions. Magnetic resonance imaging demonstrated an intra-axial mass within the left midcaudal medulla oblongata. On gross dissection, there was a left-sided neoplasm in the medulla oblongata with surrounding hemorrhage. The histologic findings indicated that the mass was a pleomorphic xanthoastrocytoma. This tumor, an uncommon variant of an astrocytoma most often seen in children and young adult humans, has yet to be described in dogs.

Different pathways of molecular pathophysiology underlie cognitive and motor tauopathy phenotypes in transgenic models for Alzheimer's disease and frontotemporal lobar degeneration.

A poorly understood feature of the tauopathies is their very different clinical presentations. The frontotemporal lobar degeneration (FTLD) spectrum is dominated by motor and emotional/psychiatric abnormalities, whereas cognitive and memory deficits are prominent in the early stages of Alzheimer's disease (AD). We report two novel mouse models overexpressing different human tau protein constructs. One is a full-length tau carrying a double mutation [P301S/G335D; line 66 (L66)] and the second is a truncated 3-repeat tau fragment which constitutes the bulk of the PHF core in AD corresponding to residues 296-390 fused with a signal sequence targeting it to the endoplasmic reticulum membrane (line 1; L1). L66 has abundant tau pathology widely distributed throughout the brain, with particularly high counts of affected neurons in hippocampus and entorhinal cortex. The pathology is neuroanatomically static and declines with age. Behaviourally, the model is devoid of a higher cognitive phenotype but presents with sensorimotor impairments and motor learning phenotypes. L1 displays a much weaker histopathological phenotype, but shows evidence of neuroanatomical spread and amplification with age that resembles the Braak staging of AD. Behaviourally, the model has minimal motor deficits but shows severe cognitive impairments affecting particularly the rodent equivalent of episodic memory which progresses with advancing age. In both models, tau aggregation can be dissociated from abnormal phosphorylation. The two models make possible the demonstration of two distinct but nevertheless convergent pathways of tau molecular pathogenesis. L1 appears to be useful for modelling the cognitive impairment of AD, whereas L66 appears to be more useful for modelling the motor features of the FTLD spectrum. Differences in clinical presentation of AD-like and FTLD syndromes are therefore likely to be inherent to the respective underlying tauopathy, and are not dependent on presence or absence of concomitant APP pathology.

Clinicopathologic features of intracranial central neurocytomas in 2 dogs.

BACKGROUND: In humans, central neurocytomas are rare and typically benign intracranial tumors found within the lateral ventricles, although extraventricular variants have been reported. Intracranial central neurocytomas have not been previously recognized in domestic animals. OBJECTIVES: To describe the clinicopathologic features of canine intracranial central neurocytomas. ANIMALS: Two dogs with spontaneous intracranial and intraventricular neoplasms. RESULTS: Both dogs experienced seizures, rapid neurological deterioration, and death from tumor-associated complications within 5 days of the onset of clinical signs, and had neoplastic masses within the lateral ventricles. A brain MRI was performed in 1 dog, which revealed a T1-isointense, heterogeneously T2 and FLAIR hyperintense, and markedly and heterogeneously contrast-enhancing mass lesions within both lateral ventricles. Histologically, the neoplasms resembled oligodendrogliomas. The diagnosis of central neurocytoma was supported by documenting expression of multiple neuronal markers, including neuron-specific enolase, synaptophysin, neural-cell adhesion molecule, and neuronal nuclear antigen within the tumors, and ultrastructural evidence of neuronal differentiation of neoplastic cells. CONCLUSIONS AND CLINICAL IMPORTANCE: Central neurocytoma should be a differential diagnosis for dogs with intraventricular brain masses. Morphologic differentiation of central neurocytoma from other intraventricular neoplasms, such as ependymoma or oligdendroglioma, can be difficult, and definitive diagnosis often requires immunohistochemical or ultrastructural confirmation of the neural origin of the neoplasm.

Immune tolerance induction to enzyme-replacement therapy by co-administration of short-term, low-dose methotrexate in a murine Pompe disease model.

Clinical investigations of recombinant human acid alpha-glucosidase for the treatment of Pompe disease often reveal the appearance of therapy-specific antibodies. These antibodies could potentially interfere with recombinant human acid alpha-glucosidase efficacy and induce immunological consequences. Several immunosuppressive agents, including methotrexate, mycophenolate mofetil and cyclosporin A with azathioprine, were evaluated for their potential to induce immune tolerance to recombinant human acid alpha-glucosidase. Methotrexate was the only agent that reduced recombinant human acid alpha-glucosidase-specific antibody responses in acid alpha-glucosidase knock-out mice. A 3-week, low-dose methotrexate regimen controlled recombinant human acid alpha-glucosidase-specific antibody levels throughout 8 months of weekly recombinant human acid alpha-glucosidase treatment. The success of this methotrexate regimen appears to require methotrexate administration within the first 24 h of recombinant human acid alpha-glucosidase treatment. In an attempt to understand the benefit of methotrexate within the first day of recombinant human acid alpha-glucosidase administration, the immune response 24 h following intravenous recombinant human acid alpha-glucosidase treatment was investigated. A consistent expansion of peritoneal B1 B cells was observed. Control over this B1 B cell response may be part of the complex mechanism of action of methotrexate-induced immune tolerance.

Use of stool collection kits delivered to patients can improve confirmation of etiology in foodborne disease outbreaks.

BACKGROUND: In 68% of foodborne disease outbreaks, no etiologic pathogen is identified. In two-thirds of outbreaks with no identified etiology, no stool specimens are submitted for testing. METHODS: From April 2001 to March 2003, we pilot-tested use of prepackaged, self-contained stool specimen collection kits in 3 states, delivered to and from patients by courier or mail, to improve rates of specimen collection in the outbreak setting. Specimens were tested for bacterial and viral pathogens at health department laboratories, and results were correlated with epidemiological investigation data. RESULTS: Specimens were returned by > or =1 person in 52 (96%) of 54 outbreaks in which kits were deployed; in total, 263 (76%) of 347 persons who received kits returned specimens. Resolution of symptoms was the most commonly cited reason for nonsubmission of kits. An etiology was confirmed in 37 (71%) of 52 outbreaks with specimens returned; 28 (76%) were attributable to norovirus, and 9 (24%) were attributed to bacterial pathogens. Stool kits were well received and cost an average of approximately 43 dollars per specimen returned. CONCLUSIONS: In two-thirds of foodborne disease outbreaks in which delivered stool collection kits were successfully deployed, an etiologic organism was identified. Delivery of kits to and from patients to improve rates of stool collection in outbreaks in which specimens might otherwise not be submitted could substantially reduce the number of outbreaks with an unknown etiology.

Methotrexate reduces antibody responses to recombinant human alpha-galactosidase A therapy in a mouse model of Fabry disease.

Therapeutic enzymes are often recognized as foreign by the immune system of patients undergoing enzyme replacement therapy. The antibodies that develop may alter pharmacokinetics and biodistribution of the therapeutic protein, may be able to neutralize the activity of the enzyme, or may cause immune reactions in certain patients. We have explored treatment regimens to reduce the antibody response to human alpha-galactosidase A (r-halphaGAL) in Fabry (alphaGAL knock-out) and normal BALB/c mice. A wide variety of treatment modalities were tested, including high dose tolerance induction, increased frequency of therapeutic doses and immunosuppressive drugs in combination with administration of enzyme. The most substantial effects were observed in mice injected intravenously with r-halphaGAL in combination with methotrexate (MTX), which significantly lowered r-halphaGAL-specific serum antibody levels. A short course of treatment with MTX was able to reduce antibody and spleen cell proliferative responses to long-term r-halphaGAL treatment. MTX was able to suppress the development of r-halphaGAL-specific IgG in antigen-primed mice. However, MTX was not effective in dampening robust ongoing antibody responses. These experiments provide a framework for the design of clinical protocols to prevent the drug-specific antibody responses of patients undergoing enzyme replacement therapy.

Skin irritation, basal epithelial cell proliferation, and carcinogenicity evaluations of a representative specialty acrylate and methacrylate.

Specialty acrylates and methacrylates (SAM) comprise a large family of industrial monomers. In the late 1980s, the United States EPA and the industry SAM Panel collaborated to evaluate the potential effects, particularly carcinogenesis, of this family of chemicals. As part of this arrangement, the SAM Panel, with EPA input and approval, conducted four studies with a representative acrylate, triethyleneglycol diacrylate (TREGDA), and methacrylate, triethyleneglycol dimethacrylate (TREGDMA). All studies used unoccluded skin application to male mice as follows: Study 1, evaluation of skin irritation compared to cell proliferation in the basal epithelium (BE) following 7 or 14 days of treatment; Study 2, 14-day dose range-finding study; Study 3, 90-day subchronic toxicity study; and Study 4, chronic bioassays employing the EPAs draft guidelines for dermal chronic bioassays. BE cell proliferation was determined in subchronic and carcinogenicity studies (Studies 1, 3, and 4). Organ weight changes (Studies 3 and 4) and increased mortality (Study 4) were observed for the highest dose of TREGDMA. However, there was no related histopathology. Both chemicals induced cell proliferation (7 days through 78 weeks) that correlated with acute and chronic inflammation of the skin. No skin tumors were observed in this study. TREGDA resulted in skin lesions at doses approximately 20-fold lower than TREGDMA. Most of the skin lesions showed similar patterns of microscopic cutaneous alteration suggestive of nonspecific irritation for both chemicals. However, the high concentration TREGDA group in the 78-week study also had evidence of epidermal cell necrosis. In contrast to earlier studies with acrylates, dose selection was based on careful examination of skin irritation and cell proliferation to avoid excessive skin damage. Under these conditions, TREGDA and TREGDMA were not carcinogenic.

The Alzheimer's Disease Assessment Scale: evaluation of psychometric properties and patterns of cognitive decline in multicenter clinical trials of mild to moderate Alzheimer's disease.

PURPOSE: To evaluate the psychometric properties and patterns of decline on the total score and item scores of the cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-Cog) in patients with Alzheimer Disease (AD). METHODS: We analyzed data from 536 AD outpatients randomized to the placebo group in two identical 26-week multicenter drug trials. RESULTS: Mean deterioration at week 26 on the ADAS-Cog total score for subjects with moderate dementia was 84% greater than that for those with milder severity ( p < 0.001). After adjusting for this effect, age ( p = 0.015) and educational level ( p = 0.01) also predicted cognitive decline. In a model, absolute change for most individual ADAS items was less than 10% of the possible change, and it was generally smaller than one-third of the standard deviation of the measure. Measurement error variability was greatest for word recognition and the "placebo" effect was greatest for word recall. Variability increased with trial duration in a model. CONCLUSIONS: There is a relationship between baseline severity and magnitude of cognitive decline. In 6-month trials, measurement error makes a substantial contribution to the variance in ADAS-Cog change scores. Sensitivity to intervention effects will therefore depend both on the variability and magnitude of change. Such data must be considered when designing future trials to minimize measurement error variability and increase sensitivity for specific populations.

Evaluation of Binax NOW, an assay for the detection of pneumococcal antigen in urine samples, performed among pediatric patients.

In our evaluation of a new assay for the detection of pneumococcal antigen in urine (Binax NOW; Binax), the test result was no more likely to be positive among 88 children with radiographically confirmed pneumonia than among 198 control subjects; however, it was significantly more likely to be positive among children who were nasopharyngeal carriers of pneumococci. This test is not likely to be useful for distinguishing children with pneumococcal pneumonia from those who are merely colonized.

Methods to identify and characterize developmental neurotoxicity for human health risk assessment. II: neuropathology.

Neuropathologic assessment of chemically induced developmental alterations in the nervous system for regulatory purposes is a multifactorial, complex process. This calls for careful qualitative and quantitative morphologic study of numerous brains at several developmental stages in rats. Quantitative evaluation may include such basic methods as determination of brain weight and dimensions as well as the progressively more complex approaches of linear, areal, or stereologic measurement of brain sections. Histologic evaluation employs routine stains (such as hematoxylin and eosin), which can be complemented by a variety of special and immunohistochemical procedures. These brain studies are augmented by morphologic assessment of selected peripheral nervous system structures. Studies of this nature require a high level of technical skill as well as special training on the part of the pathologist. The pathologist should have knowledge of normal microscopic neuroanatomy/neuronal circuitry and an understanding of basic principles of developmental neurobiology, such as familiarity with the patterns of physiologic or programmed cell de

Delayed, spontaneous hypothermia reduces neuronal damage after asphyxial cardiac arrest in rats.

OBJECTIVE: Core temperature is reduced spontaneously after asphyxial cardiac arrest in rats. To determine whether spontaneous hypothermia influences neurologic damage after asphyxial arrest, we compared neurologic outcome in rats permitted to develop spontaneous hypothermia vs. rats managed with controlled normothermia. INTERVENTIONS: Male Sprague-Dawley rats were asphyxiated for 8 mins and resuscitated. After extubation, a cohort of rats was managed with controlled normothermia (CN) by placement in a servo-controlled incubator set to maintain rectal temperature at 37.4 degrees C for 48 hrs. CN rats were compared with permissive hypothermia (PH) rats that were returned to an ambient temperature environment after extubation. Rats were killed at either 72 hrs (PH72hr, n = 14; CN72hr, n = 9) or 6 wks (PH6wk, n = 6, CN6wk, n = 6) after resuscitation. PH72 rats were historic controls for the CN72 rats, whereas PH6 and CN6 rats were randomized and studied contemporaneously. MEASUREMENTS: A clinical neurodeficit score (NDS) was determined daily. A pathologist blinded to group scored 40 hematoxylin and eosin -stained brain regions for damage by using a 5-point scale (0 = none, 5 = severe). Quantitative analysis of CA1 hippocampus injury was performed by counting normal-appearing neurons in a defined subsection of CA1. MAIN RESULTS: Mean rectal temperatures measured in the PH6wk rats (n = 6) were 36.9, 34.8, 35.5, 36.7, and 37.4 degrees C at 2, 8, 12, 24, and 36 hrs, respectively. Mortality rate (before termination) was lower in PH compared with CN (0/20 vs. 7/15; p < .005). PH demonstrated a more favorable progression of NDS (p = .04) and less weight loss (p < .005) compared with CN. Median histopathology scores were lower (less damage) in PH72hr vs. CN72hr for temporal cortex (0 vs. 2.5), parietal cortex (0 vs. 2), thalamus (0 vs. 3), CA1 hippocampus (1.5 vs. 4.5), CA2 hippocampus (0 vs. 3.5), subiculum (0 vs. 4), and cerebellar Purkinje cell layer (2 vs. 4) (all p < .05). There was almost complete loss of normal-appearing CA1 neurons in CN72hr rats (6 +/- 2 [mean +/- SD] normal neurons compared with 109 +/- 12 in naïve controls). In contrast, PH72hr rats demonstrated marked protection (97 +/- 23 normal-appearing neurons) that was still evident, although attenuated, at 6 wks (42 +/- 24 normal-appearing neurons, PH6wk). CONCLUSION: Rats resuscitated from asphyxial cardiac arrest develop delayed, mild to moderate, prolonged hypothermia that is neuroprotective.

Phenytoin, midazolam, and naloxone protect against fentanyl-induced brain damage in rats.

UNLABELLED: In previous studies, large-dose fentanyl produced electrographic seizure activity and histologically evident brain damage. We assessed whether fentanyl-induced brain damage is attenuated by using anticonvulsant drugs. Using halothane/nitrous oxide anesthesia, 40 Sprague-Dawley rats underwent tracheal intubation, arterial and venous cannulation, and insertion of biparietal electroencephalogram electrodes and a rectal temperature probe. Halothane was discontinued. The dose of IV fentanyl shown previously to cause maximal brain damage was given to all animals and N(2)O was discontinued. Control rats were given fentanyl only. Rats in the three study groups also received midazolam, phenytoin, or N(2)O/naloxone. After characteristic seizure activity began with fentanyl loading the study drug was started. After a 2-h infusion, wounds were closed, and animals recovered overnight and underwent cerebral perfusion-fixation. Neuropathologic alterations were ranked on a scale of 0-5 for both neuronal death (0 = normal, 5 = more than 75% neuronal death) and for malacia. Significantly fewer rats in the N(2)O/Naloxone, Phenytoin, and Midazolam Groups sustained any brain damage compared with controls. Protection against opioid neurotoxicity is achieved with midazolam, naloxone, and phenytoin. If opioid neurotoxicity is clinically relevant, a small change in anesthetic practice might reduce any potential neurologic morbidity. IMPLICATIONS: Narcotics in large doses can cause brain damage in rats. This brain damage is attenuated by a narcotic antagonist, a sedative, and an antiepileptic drug.

Opioid neurotoxicity: role of neurotransmitter systems.

We hypothesized that blockade of synthesis or release of several categories of neurotransmitters would ameliorate opioid neurotoxicity. Rats were randomly assigned to one of six groups in two sequential protocols: vesamicol (VES, n = 10), alpha-fluoromethylhistidine (FMH, n = 10), reserpine (RES, n = 10), BW1003C87 (BW, n = 7), lamotrigine (LAM, n = 10), or one of two control groups (CON, n = 19). Physiologically controlled rats received fentanyl (fen) i.v., loading dose 800 micrograms kg-1 followed by maintenance dose 32 micrograms kg-1 min-1 for 2 h. Drug dosing: CON, isovolemic (between rats) 0.9% saline i.v.; BW, 20 mg kg-1 i.v. 15 min pre-fen; LAM, 16 mg kg-1 i.v. 30 min pre-fen; VES, 2.5 mg kg-1 i.p. 60 min and 30 min pre-fen then infused 3.75 mg kg-1 during fen; FMH, 20 mg kg-1 i.p. 2 h pre-fen; RES, 0.75 mg kg-1 i.p. 18 h pre-fen. Seven days later all rats underwent cerebral perfusion fixation, followed by histologic grading (0-5, 0 = normal). Pathological data was analyzed by Wilcoxen's Signed rank test (two-tailed) for pathologic scores summated across all brain areas (overall severity score) and for scores of areas previously associated with opioid neurotoxicity. Compared to CON, overall severity was decreased by RES (p = 0.05) with an effect suggested by VES (p = 0.10). Compared to CON, lesions were decreased: (a) in the amygdala with VES (p = 0.03) and RES (p = 0.05) with a trend suggested by BW (p = 0.06); (b) in the subiculum by VES (p = 0.02) and RES (p = 0.008) with a trend suggested by FMH (p = 0.06); and (c) in the entorhinal cortex by VES (p = 0.004) and RES (p = 0.008) with a trend suggested by FMH (p = 0.07). The data indicate that brain acetylcholine and catecholamines contribute to opioid neurotoxicity, and suggest a possible role of glutamate and histamine in opioid neurotoxicity.

Subchronic and developmental toxicity studies of n-butyl propionate vapor in rats.

Two inhalation studies were conducted to evaluate the possible subchronic and developmental toxic effects of n-butyl propionate. In the subchronic study, Sprague-Dawley rats (15/sex/group) were exposed to 0, 250, 750, or 1500 ppm vapor for 6 h/d, 5 d/wk for 13 wk. Five of the rats per sex per group were held after the final exposure for an 8-wk recovery period. Standard parameters of subchronic toxicity were measured throughout the study, and at the end of exposure and recovery periods, necropsies were performed, organs weighed, and tissues processed for microscopic examination. Exposure did not produce marked treatment-related deaths or adversely affect clinical signs, hematology, clinical chemistries, organ weights, or the histology of major visceral organs. The only systemic toxic effects were significant decreases in body weight, body weight gain, and feed consumption that occurred in 1500 ppm group rats. Morphologic changes were limited to the nasal cavity as evidenced by a concentration-related increased incidence and severity of olfactory epithelium degeneration in rats of the 750 and 1500 ppm groups. These degenerative microscopic alterations were primarily confined to the olfactory epithelium within the dorsal portion of the medial meatus, with lesser involvement of the olfactory mucosae overlying the tips of some of the adjacent ethmoturbinates. Both the systemic and nasal cavity effects appeared reversible after exposure ceased. In the developmental toxicity study, pregnant Sprague-Dawley rats (24/group) were exposed to 0, 500, 1000, or 2000 ppm vapor for 6 h/d on gestation d 6-15 and sacrificed on gestation d 20. All treatment-group dams exhibited significant reductions in body weight, body weight gain, and feed consumption. Gestational parameters were equivalent across all groups and there were no treatment-related developmental or teratogenic effects. The no-observed-adverse effects levels (NOAELs) determined for nbutyl propionate were 250 ppm for subchronic toxicity (based on the olfactory epithelium degeneration) and 22000 ppm for developmental toxicity (no developmental effects at top dose tested). Under the conditions of this study, a NOAEL was not determined for maternal toxicity.

Lack of selective developmental neurotoxicity in rat pups from dams treated by gavage with chlorpyrifos.

Pregnant Sprague-Dawley rats were given chlorpyrifos (O:, O-diethyl-O:-[3,5,6-trichloro-2-pyridinyl] phosphorothioate; CPF) in corn oil by gavage from gestation day 6 (GD 6) through lactation day 10 (LD 10) at dosages of 0, 0.3, 1, or 5 mg/kg/day in a developmental neurotoxicity study that conformed to U.S. Environmental Protection Agency 1991 guidelines. GD 0 was the day when evidence of mating was observed and postnatal day 0 (PND 0) was the day of birth. Toxicity was limited to the highest dosage level (5 mg/kg/day) and, in the dams, consisted of muscle fasciculation, hyperpnea, and hyperreactivity. A nonsignificant overall trend toward weight gain and feed consumption was also observed in the high-dosage dams, with a statistically significant Group x Time interaction for reduced weight gain in the 5-mg/kg/day group near the end of gestation. Although many developmental indices were normal, pups from high-dosage dams had increased mortality soon after birth, gained weight more slowly than controls, and had several indications of slightly delayed maturation. The early deaths and delayed maturation were attributed to maternal toxicity, though a possible contributing role of direct pup toxicity in delayed development cannot be eliminated. In spite of the apparent delay in physical development, high-dosage pups tested just after weaning had normal learning and memory as tested on a T-maze spatial delayed-alternation task. Habituation, a primitive form of learning, was tested in 2 tasks (motor activity and auditory startle) and was not affected. No overt effects were noted in either dams or pups at 1 or 0.3 mg/kg/day. Based on these data, chlorpyrifos produced maternal and developmental toxicity in the 5-mg/kg/day-dosage group. There was no evidence of selective developmental neurotoxicity following exposure to chlorpyrifos.

Haemophilus influenzae type b and Streptococcus pneumoniae as causes of pneumonia among children in Beijing, China.

To determine if Haemophilus influenzae type b (Hib) and Streptococcus pneumoniae could be identified more often from the nasopharynx of patients with pneumonia than from control patients, we obtained nasopharyngeal swab specimens from 96 patients with chest x-ray-confirmed pneumonia and 214 age-matched control patients with diarrhea or dermatitis from the outpatient department at Beijing Children's Hospital. Pneumonia patients were more likely to be colonized with Hib and S. pneumoniae than control patients, even after the data were adjusted for possible confounding factors such as day-care attendance, the presence of other children in the household, and recent antibiotic use. In China, where blood cultures from pneumonia patients are rarely positive, the results of these nasopharyngeal cultures provide supporting evidence for the role of Hib and S. pneumoniae as causes of childhood pneumonia.

Practical aspects of neuropathology: a technical guide for working with the nervous system.

Toxicologic pathologists are evaluating tissues from the central and peripheral nervous systems with increasing frequency. This change is being driven by recently established regulatory guidelines and intense interest in developing pharmaceutical compounds to treat various nervous system disorders. However, morphologic evaluation of the nervous system by light or electron microscopy requires special understanding and effort. Here, we review the general concepts of fixation for the nervous system, explain perfusion procedures for optimal preservation, and provide information on handling tissues to avoid artifacts. In general, fixation with aldehydes is recommended for nervous tissue (a combination of paraformaldehyde and glutaraldehyde is preferred). Electron microscopic studies require fixatives of the highest purity possible, typically paraformaldehyde prepared fresh from powder mixed with high-grade glutaraldehyde. The final osmolality of the solution should be slightly hypertonic, in the range of 400-600 mOsmol. Slight hypertonicity is very important and will facilitate maintenance of vascular distention during whole-body perfusion, which is the best method for producing high-quality tissue preparations. Special effort is necessary for handling nervous tissue in a way that minimizes artifacts because chemical fixation is not completed immediately following the perfusion. These technical details should help toxicologic pathologists in their efforts to work with the nervous system, thereby increasing their effectiveness in supporting safety characterization of new test materials undergoing toxicologic assessments.

Histopathology of nasal olfactory mucosa from selected inhalation toxicity studies conducted with volatile chemicals.

In recent years, histopathologic changes have been reported in the olfactory mucosa of rodents exposed, by inhalation, to a variety of volatile chemicals. In order to better characterize these lesions, a panel of experienced pathologists reviewed microscopic lesions of the olfactory epithelium of rats reported in 10 inhalation studies conducted with 8 different chemicals. The objectives were to determine if the olfactory epithelial lesions are morphologically similar or different for the chemicals of interest, to develop and recommend appropriate diagnostic criteria and nomenclature to characterize the morphology of these olfactory lesions, and to provide specific criteria for judging the degree of severity of the olfactory changes in these studies. The results indicated that the distribution and nature of the lesions were similar in all the examined studies in which olfactory changes were observed. Recommended standardized nomenclature and diagnostic criteria and a uniform method for scoring lesion severity based on the extent of distribution and severity of tissue damage are presented.

Chronic toxicity and carcinogenicity studies of ethylenediamine dihydrochloride by dietary incorporation in Fischer 344 rats.

Ethylenediamine dihydrochloride (EDA.2HCl) was incorporated into the diet and fed to Fischer 344 rats for 2 years at target doses of 0, 0.02, 0.10 or 0.35 g/kg/day (equivalent to 0.009, 0.045 and 0.158 g free EDA/kg/day). Two separate untreated control groups were used. Interim sacrifices were at 6, 12 and 18 months and the terminal sacrifice was at 24 months. Under the conditions of this study, EDA.2HCl was not carcinogenic in the Fischer 344 rat. Most toxic responses were observed at the 12-month sacrifice and thereafter. Reductions in mean body weight gain were observed in high dose group male rats throughout most of the study and in the high dose group of female rats after approximately 18 months. Conversely, there was a slight increase in the mean body weight gain for the medium level female rats from about day 21 until 21 months that was of equivocal biological significance. Increased mortality was observed in the high dose group of both sexes and the mid dose group of female rats. The cause of the decreased survival was unclear, but may have been related to the enhancement of background degenerative lesions such as chronic nephropathy. Throughout the study, male rats from the high dose group had decreased erythrocyte counts, haemoglobin concentration and haematocrit. The cause and biological significance of the haematological changes were unknown. Increased water consumption was observed in the high dose group of both sexes during the latter half of the study. Increased urine volume with concurrent decreased urine specific gravity was generally observed in the high dose group of both sexes in the last half of the study and suggested a possible alteration in kidney function. Altered urine volume and specific gravity persisted to termination in female rats only. Slight increases in absolute and relative kidney weights were also observed in the high dose group of female rats during the latter half of the study. Hepatocellular pleomorphism was observed in the high dose group of both sexes, especially the female rats, and may have contributed to increased mean liver weights observed primarily in female rats from the high dose group. Hepatocellular pleomorphism was first observed in female rats at 12 months but was not observed in male rats until the final sacrifice. Rhinitis and tracheitis were observed with greater frequency in the high dose group of male rats at 12, 18 and 24 months and in high dose group female rats at 18 months. At 24 months, rhinitis, but not tracheitis, persisted at a significantly greater frequency in high dose group female rats. The apparent no-observable-effect level (NOEL) of this study was at the lowest dose level, 0.02 g/kg/day (equivalent to 9 mg EDA/kg/day).

Subcutaneous administration of T-epitope sequences of the acetylcholine receptor prevents experimental myasthenia gravis.

Immunization with acetylcholine receptor (AChR) causes experimental myasthenia gravis (EMG). The s.c. administration to C57B1/6 mice of synthetic AChR CD4+ epitopes, before and during AChR immunization, reduced the epitope-specific CD4+ responses and the anti-AChR Ab synthesis, and prevented EMG. The s.c. administration of solubilized AChR had effects similar to those of peptide treatment. Sham-tolerized mice had only Th1 anti-AChR cells, whereas peptide-treated mice had also Th2 cells, and Th2-induced anti-peptide Ab. Established EMG was not affected by s.c. peptide treatment, whereas it worsened after s.c. administration of solubilized AChR.