Triphenyl Phosphite and Diisopropylphosphorofluoridate Produce Separate and Distinct Axonal Degeneration Patterns in the Central Nervous System of the Rat

This study compared the neurotoxic effects of triphenyl phosphite(TPP) in the rat with those seen after exposure to diisopropylphosphorofluoridate(DFP), a compound known to produce organophosphorus-induceddelayed neurotoxicity (OPIDN). Animals received either threesubcutaneous injections of TPP (1184 mg/kg body wt each dose)administered at 3-day intervals or a single subcutaneous injectionof DFP (4 mg/kg body wt). TPP-induced clinical signs were initiallyobserved 2 to 18 days after the last injection and includedataxia, flaccid paresis, stereotyped alternating side-to-sidemovements, and circling behavior. Axonal and terminal degenerationwere present in the cerebellum, vestibular nuclear complex,cochlear nuclei, and superior and inferior colliculi. The subthalamicnucleus, substantia nigra, septal region, hypothalamus, thalamus,hippocampus, and cerebral cortex also contained degeneratingaxons and terminals. Degeneration was particularly evident inthe sensorimotor cerebral cortex, mediodorsal, ventromedial,and medial geniculate thalamic nuclei and in the magnocellularpreoptic and medial mammillary nuclei of the hypothalamus. Verylight degeneration was present in the gracile fasciculus andnucleus. In contrast, rats injected with DFP showed moderatedegeneration in the gracile fasciculus and nucleus but did notdisplay degeneration in any other brain region. Injections ofDFP did not produce delayed onset clinical signs. The resultsindicate that in the rat, different central nervous system cellgroups are affected by these two organophosphorus compoundsand that TPP affects nuclei and tracts at all levels of theneuraxis, including those associated with higher-order processingand cognitive functions. In addition, the distinct degenerationpatterns produced by these two compounds support the view thatTPP-induced neurotoxicity should not be considered as a typeof OPIDN, but rather as a separate category of organophosphorus-inducedneurotoxicity.     

Storage of feature conjunction in transient auditor memory

The purpose of this study was to determine whether feature conjunction are stored in transient auditory memory. The mismatch negativity (MMN), an event-related potential that is elicited by stimuli that differ from a series of preceding stimuli was used in this endeavour. A tone that differed from the preceding series of stimuli in the conjunction of tow of its features, both present in preceding stimuli but in different combination, was found to elicit the MMN, the data are interpreted to indicate that information about the conjunction of feature is stored in the memory.     

Giant thrombosed aneurysm associated with an arteriovenous malformation: Case report and review of the literature

The association of cerebral arteriovenous malformations and intracranial aneurysms has been well documented. Among these are a subset of giant aneurysms in association with arteriovenous malformations which are relatively rare. We present a case report and a brief review of the literature regarding this entity.     

MRI in ankle tuberculosis: Review of 14 cases

We reviewed the MR imaging features of ankle tuberculosis and determined the role of MR in its diagnosis. A retrospective analysis of 14 cases of ankle tuberculosis imaged with MRI was performed. Plain radiographs were also reviewed where available, and the imaging characteristics were noted. We also reviewed the medical records in order to assess the impact of the imaging findings on management of these patients. Magnetic resonance imaging is extremely helpful for detection, mapping the extent and resolution of the disease. It can identify cases, enables early institution of antituberculous chemotherapy and might obviate the need for surgery.     

Evaluation of the Interaction of Three Genotoxic Agents in Eliciting Sister-Chromatid Exchanges Using Response Surface Methodology

Chinese hamster cells (V79) were treated with ethylnitrosourea(ENU), bischloroethylnitrosourea (BCNU), and cis-diamminedichloroplatinum(II)(DDP) alone and in combination. Sister chromatid exchanges (SCEs)were quantitated as measures of genotoxicity of the three agents.The combination experiment employed a factorial design in whichcells were treated, in various concentration combinations, withall agents simultaneously. Response surface methodology usinga polynomial model in treatment variables to approximate themean the distribution of SCE events was employed for analysisof the interactions of the three genotoxic agents. Due to unequalvariances of the number of SCEs in the various treatment groups,a weighted leastsquares analysis was used to estimate the parametersof the dose-response relationship. The single-agent resultssuggest that the DDP concentration-response curve has a muchsteeper slope than the ENU and BCNU curves, and is concave downwardas compared to the relatively linear concentration-responsecurves of ENU and BCNU. The combination results suggest thatENU and DDP are involved in a negative interaction. The BCNTJ/DDPinteraction, the ENU/BCNU interaction, and the three-factorinteraction are not statistically significant. The analysisof these data demonstrates the usefulness of a statistical procedurefor evaluating the biological effects resulting from exposureto multiple cytotoxic agents. The methodology can be used withmany other types of endpoints and is not limited by the numberof treatment agents.