Virulence and antimicrobial resistance profiles of Salmonella enterica isolated from foods, humans, and the environment in Mexico.

Salmonella enterica genotypic and phenotypic characteristics play an important role in its pathogenesis, which could be influenced by its origin. This study evaluated the association among the antimicrobial resistance, virulence, and origin of circulating S. enterica strains in Mexico, isolated from foods, humans, and the environment. The antimicrobial susceptibility to fourteen antibiotics by the Kirby-Bauer method (n = 117), and the presence of thirteen virulence genes by multiplex PCR (n = 153) and by sequence alignments (n = 2963) were evaluated. In addition, a set of S. enterica isolates from Mexico (n = 344) previously characterized according to their genotypic and phenotypic print was included to increase the coverage of the association analysis. Strains with the presence of sopE and strains with the absence of sspH1 were significantly associated with multidrug-resistant (MDR) phenotypes (p < 0.05). The origin of the strains had significant associations with the antimicrobial profiles and some virulence genes (hilA, orgA, sifA, ssaQ, sseL, sspH1, pefA, and spvC) (p < 0.05). Animal-origin food isolates showed the highest frequency of MDR (57.2 %), followed by human isolates (30.0 %). Also, sspH1, pefA, and spvC were found in major frequency in human (32.4 %, 31.0 %, 31.7 %) and animal-origin foods (41.6 %, 10.6 %, 10.6 %) isolates. The findings highlighted that antimicrobial profiles and specific virulence genes of S. enterica strains are related to their origin. Similar genotypic and phenotypic characteristics between human and animal-origin foods isolates were found, suggesting that animal-origin foods isolates are the most responsible for human cases. The revealed associations can be used to improve risk estimation assessments in national food safety surveillance programs.

[Evaluation of two immunocromatographic tests for the detection of antibodies against SARS-CoV-2]. / Valoración de dos pruebas inmunocromatográficas para la detección de anticuerpos frente a SARS-CoV-2.

OBJECTIVE: Serological tests have been a valuable tool during the SARS-CoV-2 pandemic, supporting molecular methods for detection, and monitoring the immune response, caused by vaccination or by natural infection. Within all these techniques, rapid tests are interesting due to their ease of use, rapid response and low cost. METHODS: Two different immunological techniques were evaluated: Realy Tech and Mikrogen Diagnostik recomLine SARS-CoV-2 IgG. SARS-CoV-2 IgG II Quant antibody test and SARS-CoV-IgG assay, both from Abbott Diagnostics, were used as reference techniques. RESULTS: Mikrogen Diagnostik recomLine SARS-CoV-2 IgG shows the best results (S=0.985; E=0.839). Three techniques offered good positive predictive values, but Realy Tech and Healgen negative predictive values left to be desired. CONCLUSIONS: Mikrogen Diagnostik recomLine SARS-CoV-2 IgG showed good results in the detection of antibodies against SARS-CoV-2 and could be used as an alternative to automated techniques.

High fructose-containing drinking water-induced steatohepatitis in rats is prevented by the nicotinamide-mediated modulation of redox homeostasis and NADPH-producing enzymes.

An imbalance in the redox state, increased levels of lipid precursors and overactivation of de novo lipogenesis determine the development of fibrosis during nonalcoholic steatohepatitis (NASH). We evaluated the modulation of NADPH-producing enzymes associated with the antifibrotic, antioxidant and antilipemic effects of nicotinamide (NAM) in a model of NASH induced by excess fructose consumption. Male rats were provided drinking water containing 40% fructose for 16 weeks. During the last 12 weeks of fructose administration, water containing NAM was provided to some of the rats for 5 h/day. The biochemical profiles and the ghrelin, leptin, lipoperoxidation and TNF-α levels in serum and the glucose-6-phosphate dehydrogenase (G6PD), malic enzyme (ME) and NADP+-dependent isocitric dehydrogenase (IDP) levels, the reduced/oxidized glutathione (GSH/GSSG) and reduced/oxidized nicotinamide adenine dinucleotide (phosphate) (NAD(P)H/NAD(P)+) ratios, and the levels of various lipogenic and fibrotic markers in the liver were evaluated. The results showed that hepatic fibrosis induced by fructose consumption was associated with weight gain, hunger-satiety system dysregulation, hyperinsulinemia, dyslipidemia, lipoperoxidation and inflammation. Moreover, increased levels of hepatic G6PD and ME activity and expression, the NAD(P)H/NAD(P)+ ratios, and GSSG concentration and increased expression of lipogenic and fibrotic markers were detected, and these alterations were attenuated by NAM administration. Specifically, NAM diminished the activity and expression of G6PD and ME, and this effect was associated with a decrease in the NADPH/NADP+ ratios, increased GSH levels and decreased lipoperoxidation and inflammation, ameliorating fibrosis and NASH development. NAM reduces liver steatosis and fibrosis by regulating redox homeostasis through a G6PD- and ME-dependent mechanism.

Update in Infectious Diseases 2019.

The IX Course of Antimicrobials and Infectious Diseases update included a review of the main issues in clinical microbiology, epidemiology and clinical aspects for a current approach of infectious pathology. The present introduction summarizes about the most important meetings related to infectious diseases during 2018 (ECCMID, IAS, ASM and ID Week). In addition, the course provides a practical information to focus on nosocomial infection models, with immunosuppressed patients or complex multidrug-resistant pathogens. The closing lecture of this year reviewed the infection during donation process.

Brainstem leukoaraiosis independently predicts poor outcome after ischemic stroke.

BACKGROUND AND PURPOSE: Increased supratentorial white matter hyperintensities volume (S-WMHV) has been reported to be a predictor of worse outcome in patients with acute ischemic stroke (AIS). However, few studies have focused on less common locations, such as brainstem white matter hyperintensities (B-WMH), and their relationship to S-WMHV. This study aimed to examine whether B-WMH affect clinical outcome after AIS or transient ischemic attack (TIA). METHODS: Based on magnetic resonance imaging evidence, B-WMH were evaluated in 313 prospectively identified patients with AIS/TIA and registered as absent or present. Standardized S-WMHV was quantified using a validated volumetric image analysis and natural log-transformed (Log_S-WMHV). Poor outcome was defined as a modified Rankin Scale score of 3-6 at 3 months after the index event. RESULTS: Brainstem white matter hyperintensities were detected in 57 (18.2%) patients. In unadjusted analyses for outcome, the presence of B-WMH was associated with worse outcome, compared with patients without B-WMH (P = 0.034). In multivariate analysis controlling for age, atrial fibrillation, stroke severity, reperfusion therapies and Log_S-WMHV, only B-WMH [odds ratio (OR), 2.46; P = 0.021] and stroke severity (OR, 1.23; P < 0.001) remained independently associated with unfavourable 90-day modified Rankin Scale score. Patients with B-WMH were older (OR, 1.06; P < 0.001) and tended to have more hyperlipidaemia (OR, 2.21; P = 0.023) and peripheral arterial disease (OR, 2.57; P = 0.031). CONCLUSIONS: Brainstem white matter hyperintensities are an independent predictor of poor outcome after AIS/TIA and this relationship persists after adjustment for important prognostic factors. Our results also show that leukoaraiosis in this location identifies patients with a specific risk factor profile, suggesting differences in the underlying pathogenesis.

Simultaneous and individual quantitative estimation of Salmonella, Shigella and Listeria monocytogenes on inoculated Roma tomatoes (Lycopersicon esculentum var. Pyriforme) and Serrano peppers (Capsicum annuum) using an MPN technique.

Simultaneous and individual enumeration of Salmonella, Shigella and Listeria monocytogenes was compared on inoculated Roma tomatoes and Serrano peppers using an Most Probable Number (MPN) technique. Samples consisting of tomatoes (4 units) or peppers (8 units) were individually inoculated with a cocktail of three strains of Salmonella, Shigella or L. monocytogenes, or by simultaneous inoculation of three strains of each pathogen, at low (1.2-1.7 log CFU/sample) and high (2.2-2.7 log CFU/sample) inocula. Samples were analyzed by an MPN technique using universal pre-enrichment (UP) broth at 35 °C for 24 ±â€¯2 h. The UP tubes from each MPN series were transferred to enrichment and plating media following adequate conventional methods for isolating each pathogen. Data were analyzed using multifactorial analysis of variance (p < 0.05) and LSD multiple rang test. There were differences (p < 0.05) in recovery of simultaneous and individual bacteria inoculated (individual > simultaneous), type of bacteria (Salmonella > Shigella and L. monocytogenes), type of sample (UP broth > pepper and tomato), and inoculum level (high > low). The MPN technique was effective for Salmonella on both commodities. Shigella counts were higher on tomatoes compared to peppers, (p < 0.05), and for L. monocytogenes on peppers (p < 0.05).

Selection of Yeast Strains for Tequila Fermentation Based on Growth Dynamics in Combined Fructose and Ethanol Media.

The high concentration of fructose in agave juice has been associated with reduced ethanol tolerance of commercial yeasts used for tequila production and low fermentation yields. The selection of autochthonous strains, which are better adapted to agave juice, could improve the process. In this study, a 2-step selection process of yeasts isolated from spontaneous fermentations for tequila production was carried out based on analysis of the growth dynamics in combined conditions of high fructose and ethanol. First, yeast isolates (605) were screened to identify strains tolerant to high fructose (20%) and to ethanol (10%), yielding 89 isolates able to grow in both conditions. From the 89 isolates, the growth curves under 8 treatments of combined fructose (from 20% to 5%) and ethanol (from 0% to 10%) were obtained, and the kinetic parameters were analyzed with principal component analysis and k-means clustering. The resulting yeast strain groups corresponded to the fast, medium and slow growers. A second clustering of only the fast growers led to the selection of 3 Saccharomyces strains (199, 230, 231) that were able to grow rapidly in 4 out of the 8 conditions evaluated. This methodology differentiated strains phenotypically and could be further used for strain selection in other processes. PRACTICAL APPLICATION: A method to select yeast strains for fermentation taking into account the natural differences of yeast isolates. This methodology is based on the cell exposition to combinations of sugar and ethanol, which are the most important stress factors in fermentation. This strategy will help to identify the most tolerant strain that could improve ethanol yield and reduce fermentation time.

Results of a multicenter survey showing interindividual variability among neurosurgeons when deciding on the radicality of surgical resection in glioblastoma highlight the need for more objective guidelines

Purpose. We assessed agreement among neurosurgeons on surgical approaches to individual glioblastoma patients and between their approach and those recommended by the topographical staging system described by Shinoda. Methods. Five neurosurgeons were provided with pre-surgical MRIs of 76 patients. They selected the surgical approach [biopsy, partial resection, or gross total resection (GTR)] that they would recommend for each patient. They were blinded to each other’s response and they were told that patients were younger than 50 years old and without symptoms. Three neuroradiologists classified each case according to the Shinoda staging system. Results. Biopsy was recommended in 35.5-82.9%, partial resection in 6.6-32.9%, and GTR in 3.9-31.6% of cases. Agreement among their responses was fair (global kappa = 0.28). Nineteen patients were classified as stage I, 14 as stage II, and 43 as stage III. Agreement between the neurosurgeons and the recommendations of the staging system was poor for stage I (kappa = 0.14) and stage II (kappa = 0.02) and fair for stage III patients (kappa = 0.29). An individual analysis revealed that in contrast to the Shinoda system, neurosurgeons took into account T2/FLAIR sequences and gave greater weight to the involvement of eloquent areas. Conclusions. The surgical approach to glioblastoma is highly variable. A staging system could be used to examine the impact of extent of resection, monitor post-operative complications, and stratify patients in clinical trials. Our findings suggest that the Shinoda staging system could be improved by including T2/FLAIR sequences and a more adequate weighting of eloquent areas (AU)

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Results of a multicenter survey showing interindividual variability among neurosurgeons when deciding on the radicality of surgical resection in glioblastoma highlight the need for more objective guidelines.

PURPOSE: We assessed agreement among neurosurgeons on surgical approaches to individual glioblastoma patients and between their approach and those recommended by the topographical staging system described by Shinoda. METHODS: Five neurosurgeons were provided with pre-surgical MRIs of 76 patients. They selected the surgical approach [biopsy, partial resection, or gross total resection (GTR)] that they would recommend for each patient. They were blinded to each other's response and they were told that patients were younger than 50 years old and without symptoms. Three neuroradiologists classified each case according to the Shinoda staging system. RESULTS: Biopsy was recommended in 35.5-82.9%, partial resection in 6.6-32.9%, and GTR in 3.9-31.6% of cases. Agreement among their responses was fair (global kappa = 0.28). Nineteen patients were classified as stage I, 14 as stage II, and 43 as stage III. Agreement between the neurosurgeons and the recommendations of the staging system was poor for stage I (kappa = 0.14) and stage II (kappa = 0.02) and fair for stage III patients (kappa = 0.29). An individual analysis revealed that in contrast to the Shinoda system, neurosurgeons took into account T2/FLAIR sequences and gave greater weight to the involvement of eloquent areas. CONCLUSIONS: The surgical approach to glioblastoma is highly variable. A staging system could be used to examine the impact of extent of resection, monitor post-operative complications, and stratify patients in clinical trials. Our findings suggest that the Shinoda staging system could be improved by including T2/FLAIR sequences and a more adequate weighting of eloquent areas.

SPECT de perfusión, SISCOM y PET 18F-FDG en la valoración del paciente epiléptico fármaco-resistente candidato a cirugía de epilepsia / Perfusion SPECT, SISCOM and PET 18F-FDG in the assessment of drug- refractory epilepsy patients candidates for epilepsy surgery

Objetivos. La SPECT de perfusión ictal-interictal, subtraction ictal SPECT coregistered to MRI (SISCOM) y 18F-FDG-PET (interictal), desempeñan un papel fundamental en la valoración prequirúrgica del paciente epiléptico fármaco-resistente. Los objetivos de este trabajo fueron establecer la reproducibilidad del análisis visual de la SPECT y SISCOM y la capacidad de la SPECT, SISCOM y PET en la identificación del foco epileptógeno. Material y métodos. Se realizó una SPECT 99mTc-HMPAO (ictal-interictal) y SISCOM (Analyze 7.0) en 47 pacientes epilépticos fármaco-resistentes (24 M, 19-60 años). En 13 pacientes se repitió el SISCOM utilizando el programa FocusDET. El análisis de las imágenes fue realizado por 2 observadores. Se valoró la reproducibilidad utilizando el índice Kappa. Los resultados conjuntos de la SPECT, SISCOM y PET, en 16 pacientes, fueron comparados con la localización del área resecada y el seguimiento clínico poscirugía (escala de Engel) o con la estereo-EEG. Resultados. Grado de acuerdo interobservador de la SPECT 91% índice Kappa 0,86. Grado de acuerdo interobservador SISCOM Analyze 7.0 82%, índice Kappa 0,80. El Analyze 7.0 mostró un elevado número de resultados no concluyentes, superior al del análisis visual. El SISCOM FocusDET mostró un grado de acuerdo interobservador 92% con un índice Kappa 0,87 y menor número de resultados no concluyentes que el Analyze. La valoración conjunta SPECT, SISCOM y PET permitió identificar 87% focos epileptógenos: 79% temporales, 26% parieto-temporales y 7% frontales. Conclusión. La SPECT ictal-interictal y el SISCOM mostraron una elevada reproducibilidad. La valoración conjunta de la SPECT ictal-interictal, SISCOM y PET permitió mejorar la rentabilidad diagnóstica de la valoración individualizada (AU)

Aims. Brain perfusion SPECT (ictal-interictal), SPECT images and subtraction ictal SPECT coregistered to MRI (SISCOM) and 18F-FDG-PET (interictal), play an important role in the pre-surgical diagnosis of patients with medically refractory epilepsy. This study aimed to establish: the reproducibility of visual ictal-interictal SPECT and SISCOM analysis altogether with the capacity of SPECT, SISCOM and PET to determine the epileptogenic zone. Material and methods. 99mTc-HMPAO SPECT ictal-interictal and SISCOM (Analyze 7.0) were performed on 47 refractory epilepsy patients (24 F, 19-60 yrs). In 13 patients, SISCOM was also performed using a new program (Focus DET). Ictal-interictal SPECT and SISCOM images were analysed independently by two nuclear medicine physicians (observer 1 and 2). Kappa concordance coefficient was used to evaluate the reproducibility. In sixteen patients, SPECT, SISCOM and PET findings were compared with the resected area during the surgery, and surgical outcome using Engel scale or with the stereo EEG-(SEEG). Results. The ictal-interictal SPECT interobserver agreement was 91%, Kappa index 0.86, SISCOM (Analyze 7.0) interobserver agreement percentage was 82%, Kappa index 0.80, Analyze 7.0 showed a higher inconclusive results than visual SPECT analysis. SISCOM FocusDET interobserver agreement was 92%, Kappa index 0.87, with lower inconclusive results than Analyze 7.0. SPECT, SISCOM and PET combined findings identified 87% seizure onset zone: 79% temporal, 26% parieto-temporal and 7% frontal. Conclusions. Ictal-interictal SPECT and SISCOM showed a high reproducibility in this sample of patients with drug-refractory epilepsy. SPECT,SISCOM and PET combined findings improved detection of epileptogenic zone in comparison with the individual assessment (AU)

Detection and Genotyping of Leuconostoc spp. in a Sausage Processing Plant.

Some Leuconostoc spp. have the ability to produce slime and undesirable compounds in cooked sausage. The objectives of this research were to identify Leuconostoc sources in a Vienna-type sausage processing plant and to evaluate the genetic diversity of the isolated strains. Three hundred and two samples of sausage batter, sausages during processing, spoiled sausage, equipment surfaces, chilling brine, workers' gloves and aprons, and used casings were collected (March to November 2008 and February to April 2010) from a sausage processing plant. Lactic acid bacteria (LAB) were quantified, and Leuconostoc were detected using PCR. Strains were isolated and identified in Leuconostoc-positive samples. Leuconostoc strains were genotyped using randomly amplified polymorphic DNA and pulsed-field gel electrophoresis. LAB content of nonspoiled and spoiled sausage ranged from <0.8 to 4.4 log CFU/g and from 4.9 to 8.3 log CFU/g, respectively. LAB levels on equipment surfaces ranged from <1.3 to 4.8 log CFU/100 cm(2). Leuconostoc was detected in 35% of the samples, and 88 Leuconostoc spp. strains were isolated and genotyped. The main Leuconostoc spp. isolated were L. mesenteroides (37 genotypes), L. fallax (29 genotypes), and L. lactis (6 genotypes). Some strains of Leuconostoc isolated from equipment surfaces and sausages showed the same genotype. One L. lactis genotype included strains isolated from spoiled sausages analyzed in April 2008 and March to April 2010. Equipment and conveyor belts constitute Leuconostoc contamination sources. Leuconostoc persistence in the sausage processing environment and in the final product suggests the existence of microbial reservoirs, possibly on equipment surfaces.

Perfusion SPECT, SISCOM and PET (18)F-FDG in the assessment of drug- refractory epilepsy patients candidates for epilepsy surgery.

AIMS: Brain perfusion SPECT (ictal-interictal), SPECT images and subtraction ictal SPECT coregistered to MRI (SISCOM) and (18)F-FDG-PET (interictal), play an important role in the pre-surgical diagnosis of patients with medically refractory epilepsy. This study aimed to establish: the reproducibility of visual ictal-interictal SPECT and SISCOM analysis altogether with the capacity of SPECT, SISCOM and PET to determine the epileptogenic zone. MATERIAL AND METHODS: (99m)Tc-HMPAO SPECT ictal-interictal and SISCOM (Analyze 7.0) were performed on 47 refractory epilepsy patients (24 F, 19-60 yrs). In 13 patients, SISCOM was also performed using a new program (Focus DET). Ictal-interictal SPECT and SISCOM images were analysed independently by two nuclear medicine physicians (observer 1 and 2). Kappa concordance coefficient was used to evaluate the reproducibility. In sixteen patients, SPECT, SISCOM and PET findings were compared with the resected area during the surgery, and surgical outcome using Engel scale or with the stereo EEG-(SEEG). RESULTS: The ictal-interictal SPECT interobserver agreement was 91%, Kappa index 0.86, SISCOM (Analyze 7.0) interobserver agreement percentage was 82%, Kappa index 0.80, Analyze 7.0 showed a higher inconclusive results than visual SPECT analysis. SISCOM FocusDET interobserver agreement was 92%, Kappa index 0.87, with lower inconclusive results than Analyze 7.0. SPECT, SISCOM and PET combined findings identified 87% seizure onset zone: 79% temporal, 26% parieto-temporal and 7% frontal. CONCLUSIONS: Ictal-interictal SPECT and SISCOM showed a high reproducibility in this sample of patients with drug-refractory epilepsy. SPECT,SISCOM and PET combined findings improved detection of epileptogenic zone in comparison with the individual assessment.

Simple fMRI postprocessing suffices for normal clinical practice.

BACKGROUND AND PURPOSE: Whereas fMRI postprocessing tools used in research are accurate but unwieldy, those used for clinical practice are user-friendly but are less accurate. We aimed to determine whether commercial software for fMRI postprocessing is accurate enough for clinical practice. METHODS: Ten volunteers underwent fMRI while performing motor and language tasks (hand, foot, and orolingual movements; verbal fluency; semantic judgment; and oral comprehension). We compared visual concordance, image quality (noise), voxel size, and radiologist preference for the activation maps obtained by using Neuro3D software (provided with our MR imaging scanner) and by using the SPM program commonly used in research. RESULTS: Maps obtained with the 2 methods were classified as "partially overlapping" for 70% for motor and 72% for language paradigm experiments and as "overlapping" in 30% of motor and in 15% of language paradigm experiments. CONCLUSIONS: fMRI is a helpful and robust tool in clinical practice for planning neurosurgery. Widely available commercial fMRI software can provide reliable information for therapeutic management, so sophisticated, less widely available software is unnecessary in most cases.

Two cases of hemorrhagic diarrhea caused by Cronobacter sakazakii in hospitalized nursing infants associated with the consumption of powdered infant formula.

Two cases of acute gastroenteritis occurred in 5-month-old infants hospitalized in a mother-and-child hospital in Queretaro, Mexico, on 24 January 2010. C. sakazakii was recovered from the powdered infant formula (PIF), rehydrated PIF (R-PIF) fed to infants, and their fecal samples. The microorganism was present at levels of 0.33 most probable number (MPN)/g and 24 MPN/ml in PIF and R-PIF, respectively. The total ingested dose for the day before the onset of the diarrheic syndrome ranged between 2,160 and 3,600 MPN/ml. All strains of C. sakazakii recovered from the three sources (R-PIF, PIF, and fecal matter) showed identical biotypes, adhesion and invasiveness factors, and pulsed-field gel electrophoresis profiles. No deaths were observed. Salmonella, Shigella, and enterotoxigenic Escherichia coli were not found in food or fecal samples.

Fístulas arteriovenosas renales como causa de hipertensión arterial refractaria / Renal arteriovenous fistulas as a cause of refractory hypertension

Las malformaciones arteriovenosas renales congénitas son una entidad de baja prevalencia y, por tanto, una causa muy poco frecuente de hipertensión arterial.Sin embargo, la potencial posibilidad de ofrecer un tratamiento curativo hace muy importante su diagnóstico, permitiendo modificar el curso natural de la patología hipertensiva refractaria a tratamiento farmacológico.Se presenta el caso de un paciente con fístulas arteriovenosas renales congénitas bilaterales que se trataron mediante 2 técnicas diferentes de embolización en función de la morfología de la fístula y la intensidad del flujo, que consiguió el control sintomatológico de la clínica hipertensiva derivada de dicha patología (AU)

The prevalence of congenital renal arteriovenous malformations is low; for this reason, they are a very uncommon cause of arterial hypertension.However, arterial hypertension due to congenital renal arteriovenous malformations is potentially curable; thus, it is important to reach the correct diagnosis so that the natural course of the hypertension refractory to drug therapy can be modified.We present a case of a patient with bilateral congenital renal arteriovenous fistulas that were treated with two different embolization techniques in function of the morphology of the fistula and the intensity of the flow; treatment achieved control of the clinical symptoms of hypertension (AU)

[Renal arteriovenous fistulas as a cause of refractory hypertension]. / Fístulas arteriovenosas renales como causa de hipertensión arterial refractaria.

The prevalence of congenital renal arteriovenous malformations is low; for this reason, they are a very uncommon cause of arterial hypertension. However, arterial hypertension due to congenital renal arteriovenous malformations is potentially curable; thus, it is important to reach the correct diagnosis so that the natural course of the hypertension refractory to drug therapy can be modified. We present a case of a patient with bilateral congenital renal arteriovenous fistulas that were treated with two different embolization techniques in function of the morphology of the fistula and the intensity of the flow; treatment achieved control of the clinical symptoms of hypertension.

Obstrucción intestinal en paciente en tratamiento con acenocumarol / Bowel obstruction in patients under treatment withacenocumarol

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On the ontogeny of the motor circadian rhythm in crayfish.

In this paper we attack the problem of understanding the localization of the main structures involved in the motor circadian rhythm of crayfish by analysing its ontogeny. We present experimental results giving the properties of this rhythm in young and adult crayfish. Then we construct a mathematical model (based on a previous one for the electroretinogram circadian rhythm in the same species) simulating those properties. In the process of constructing the model we clarified and made precise various hypotheses about the biological structures involved in them and about the characteristics of the oscillators present in those structures. We also formulate some hypotheses about the general properties of circadian rhythms. Finally, we propose some experiments suggested by the mathematical model.