Arabidopsis thaliana LUP1 converts oxidosqualene to multiple triterpene alcohols and a triterpene diol.

The Arabidopsis thaliana LUP1 gene encodes an enzyme that converts oxidosqualene to pentacyclic triterpenes. Lupeol and beta-amyrin were previously reported as LUP1 products. Further investigation described here uncovered the additional products germanicol, taraxasterol, psi-taraxasterol, and 3,20-dihydroxylupane. These results suggest that the 80 known C(30)H(50)O compounds that are structurally consistent with being oxidosqualene cyclase products may be derived from fewer than 80 enzymes and that some C(30)H(52)O(2) compounds may be direct cyclization products of oxidosqualene.

Functional cloning of an Arabidopsis thaliana cDNA encoding cycloeucalenol cycloisomerase.

Plants and certain protists use cycloeucalenol cycloisomerase (EC ) to convert pentacyclic cyclopropyl sterols to conventional tetracyclic sterols. We used a novel complementation strategy to clone a cycloeucalenol cycloisomerase cDNA. Expressing an Arabidopsis thaliana cycloartenol synthase cDNA in a yeast lanosterol synthase mutant provided a sterol auxotroph that could be genetically complemented with the isomerase. We transformed this yeast strain with an Arabidopsis yeast expression library and selected sterol prototrophs to obtain a strain that accumulated biosynthetic ergosterol. The novel phenotype was conferred by an Arabidopsis cDNA that potentially encodes a 36-kDa protein. We expressed this cDNA (CPI1) in Escherichia coli and showed by gas chromatography-mass spectrometry that extracts from this strain isomerized cycloeucalenol to obtusifoliol in vitro. The cDNA will be useful for obtaining heterologously expressed protein for catalytic studies and elucidating the in vivo roles of cyclopropyl sterols.

Cerebral tumor-like American trypanosomiasis in acquired immunodeficiency syndrome.

Cerebral tumor-like American trypanosomiasis (CTLAT) is an uncommon complication of Chagas' disease, observed only in immunosuppressed patients. We assessed 10 human immunodeficiency virus-positive patients with Chagas' disease who presented with CTLAT. All patients had neurological involvement and 6 developed intracranial hypertension. Neuroimaging studies showed supratentorial lesions in 9 patients, being single in 8. One case had infratentorial and supratentorial lesions. Low CD4+ cell counts were observed in all the cases and in 6 of them CTLAT was the first manifestation of acquired immunodeficiency syndrome. Serological tests for Chagas' disease were positive in 6 of 8 patients. Trypanosoma cruzi was identified in all brain specimens and in three cerebrospinal fluid samples. CTLAT should be considered in the differential diagnosis of intracranial mass lesions in human immunodeficiency virus-positive patients and should be added to the list of acquired immunodeficiency syndrome-defining illnesses.

Motor activation time in Parkinson's disease.

Motor activation time (MAT), considered in the present work as the actual intracerebral processing delay during a reaction time (RT) task, was assessed in 17 patients with Parkinson's disease (PD) and in 7 age-matched healthy volunteers. MAT was calculated by subtracting from the premotor RT the afferent and efferent times obtained by sensory and motor evoked potentials. When compared with healthy volunteers, patients exhibited significantly (p < 0.02) prolonged MATs. In a smaller group of 9 PD patients MAT and the auditory P3 event related potential were assessed while on antiparkinsonian treatment and after a 12-hour withdrawal period. During the off medication condition patients showed a significant slowing (p < 0.01) of MAT values without any remarkable change in P3 latency or amplitude. These results suggest that MAT slowing indicates an abnormal function of the dopaminergic mechanism involved in the initiation of movement which is not related to changes in the arousal or cognitive state.

Motor activation time in Parkinsons disease.

Motor activation time (MAT), considered in the present work as the actual intracerebral processing delay during a reaction time (RT) task, was assessed in 17 patients with Parkinsons disease (PD) and in 7 age-matched healthy volunteers. MAT was calculated by subtracting from the premotor RT the afferent and efferent times obtained by sensory and motor evoked potentials. When compared with healthy volunteers, patients exhibited significantly (p < 0.02) prolonged MATs. In a smaller group of 9 PD patients MAT and the auditory P3 event related potential were assessed while on antiparkinsonian treatment and after a 12-hour withdrawal period. During the off medication condition patients showed a significant slowing (p < 0.01) of MAT values without any remarkable change in P3 latency or amplitude. These results suggest that MAT slowing indicates an abnormal function of the dopaminergic mechanism involved in the initiation of movement which is not related to changes in the arousal or cognitive state.

Multiple sclerosis: assessment of lesional levels by means of transcranial stimulation.

Conduction in the Pyramidal Tracts (PTs) was studied in 30 healthy volunteers and 17 patients with definite Multiple Sclerosis. Central motor conduction time (CMCT) was assessed employing unipolar electrical transcranial stimulation and studies of the peripheral conduction time. Fourteen out of the seventeen studied patients showed CMCT abnormalities. No significative correlation was found between the intensity of muscle weakness and the slowness of conduction in the corresponding PTs. Subclinical abnormalities were detected in more than half of the studied patients. CMCT slowness showed a good correlation with the time course of the disease in the cortico-cervical (CCT) but not in the cortico-lumbar (CLT) tracts. Evidence favoring the existence of two different lesional levels along the PSs was found in 9 out of the 14 patients studied with recordings in the hand and leg muscles. Two patterns of abnormalities gave support to this conclusion. The first consisted of slowed conduction or inexcitability in both the CCT and CLT at one side, while only one of the contralateral PTs was impaired. In the second one, the 4 explored PTs showed a slowed conduction, but in addition, CMCT difference between the CLT and CCT was longer than normal. Both patterns suggest that one lesional level could be situated between the internal capsula and the lower cervical cord and the other in the spine below the 8th cervical methamera or in the corona radiata.

Central motor conduction in human chronic Chagas' disease.

The possible involvement of spinal alpha motor neurons, dorsal root ganglia and sensory fibers in human chronic Chagas' disease was previously demonstrated. More recently neuropsychological and sensory evoked potentials studies suggest the existence of central nervous system abnormalities in these patients. We assessed the state of central motor pathways in 46 patients with chronic Chagas' disease and 30 healthy volunteers by means of percutaneous cortical and spinal electrical stimulation. No significative slowness in pyramidal tracts (PT) conduction was found when comparing both groups. Neither any individual patient exhibited abnormally delayed PT conduction values beyond the upper normal limit of the healthy volunteers. These results suggest that, in contrast with other neural systems, the large myelinated PT fibers are usually spared in human chronic Chagas' disease.

Central motor conduction in human chronic Chagas' disease

Estudios previos han demostrado que la enfermedad de Chagas cronica (ECHC) humana puede comprometer las motoneuronas espinales alfa, el ganglio de la raiz dorsal y las fibras sensitivas perifericas. Mas recientemente otras investigaciones han senalado que algunos de estos pacientes presentan anomalias en pruebas cognitivas y de potenciales evocados sensoriales, sugiriendo tambien la existencia de compromiso central en 46 pacientes con ECHC en 30 voluntarios sanos. Para ello se emplearon tecnicas de estimulación electrica cortical transcraneana y espinal percutanea. No se encontro un enlentecimiento significativo en la conducción piramidal del grupo con ECHC comparado con los voluntarios sanos. Considerados individualmente, en ningun paciente con ECHC la conducción corticoespinal presento valores que excedieran el limite superior normal del grupo control. Estos resultados sugieren que a diferencia de lo que ocurre con otros sistemas neurales, las fibras piramidales mielinizadas de grueso calibre se encuentran usualmente indemnes en pacientes con ECHC

Electrophysiological assessment of spinal cord lesions by means of transcranial cortical stimulation.

Central Motor Conduction Time (CMCT) was assessed in 30 healthy volunteers and 22 patients with spinal cord lesions due to compressive, degenerative and demyelinating disease. To obtain the CMCT, electrical Transcranial Stimulation and Percutaneous Spinal Stimulation or F wave calculations were employed. Pyramidal Tract (PT) conduction was always abnormal in the clinically impaired corticospinal tracts of all the studied patients. This results correlated with the degree of muscle weakness specially in those having compressive lesions. Subclinical evidence of pyramidal damage was also observed in two patients with Multiple Sclerosis. As opposed to the other groups, patients with degenerative spinal disease, showed essentially symmetric abnormalities. An important overlap of CMCT slowness was seen among the three studied groups, suggesting that this isolated clue is not valuable enough for aetiological suspicion. Double muscle responses due to single TCS were obtained, during rest, in some patients from each group, but never in controls. This pathological feature, not reported by others, could represent the excitation of indirect corticospinal connections, partially responsible for the residual motor function after PT damage.

Percutaneous cervical stimulation: effects on intraspinal structures.

Changes in the amplitude of motor evoked potentials (MEPs) from percutaneous cervical stimulation (PCS) obtained at rest in the thenar muscles, and smaller than 0.8 mV, were studied under 3 different experimental conditions. A significant enhancement was observed mainly with a conditioning subthreshold transcranial stimulus and when MEPs were obtained in coincidence with weak voluntary contraction of the target muscle. Subthreshold stimulation of Ia fibers of the median nerve seemed to have a smaller facilitatory effect. It is generally accepted that PCS excites the spinal motoneuron (SMN) axons at the spinal nerve. However, our results show that other SMNs, usually not recruited, may be triggered by PCS when they receive excitatory postsynaptic potentials from the pyramidal tract (PT) or Ia fibers. This behavior suggests that low intensity PCS also exerts subthreshold excitation of the PT fibers and, perhaps, of the incoming spindle afferents, which adds its effects to the conditioning stimuli.

Central motor conduction in ischaemic and hemorrhagic cerebral lesions.

Electrical Transcranial Cortical Stimulation was performed in 20 healthy volunteers and 14 patients having supra- or infratentorial vascular lesions. Central Conduction Time (CCT) in the Pyramidal Tract (PT) was calculated by subtraction of the Peripheral Conduction Time and the spinal synaptic delay to the Motor Evoked Potential (MEP) latency. Twelve out of fourteen patients showed prolonged MEP latencies or CCTs in the affected corporal segments. Only in 3 cases, 2 with subcortical hematoma and other with bilateral ischaemic lesions, the PT was inexcitable. Two patients, one with a discrete cortical lesion and the other with an hemispheric cerebellar infarct showed no abnormalities in pyramidal conduction. Electrophysiological results showed a good correspondence with the degree of clinical impairment.