Migration and Dependency: Mexican Countryside Proletarianization and the Seasonal Agricultural Worker Program.

This article addresses the Seasonal Agricultural Worker Program (SAWP) between Mexico and Canada by examining the forms of disposability and job insecurity of Mexicans employed in Canadian agribusiness. We argue that the Seasonal Agricultural Worker Program has exacerbated the precarity and disposability of Mexican workers by restructuring family dynamics and care chains. This article represents a critique of the SAWP as a model of regulated labor migration, serving as a basis for analyzing the consequences of the proletarianization of the Mexican peasantry and its use as disposable labor for export.

Estudio de la actividad antimicrobiana de una crema dental en gel con EDS frente a Streptococcus mutans y Actinobacillus actinomycetemcomitans / A study of the antimicrobial activity of a EDS-containing dental gel against Streptococcus mutans and Actinobacillus actinomycetemcomitans

Determinar la actividad antimicrobiana de la pasta en gel de dientes contra dos microorganismos: mutans Streptococccus y Actinobacillus actinomycetemcomitans...

Proline modulates the effect of bisphosphonate on calcium levels and adenosine triphosphate production in cell lines derived from bovine Echinococcus granulosus protoscoleces.

Bisphosphonates have been proposed as pharmacological agents against parasite and cancer cell growth. The effect of these compounds on helminthic cell viability and acellular compartment morphology, however, has not yet been studied. The effects of different types of bisphosphonates, namely etidronate (EHDP), pamidronate (APD), alendronate (ABP), ibandronate (IB) and olpadronate (OPD), and their interaction with amiloride, 1,25-dihydroxycholecalciferol (D3) and proline were evaluated on a cell line derived from bovine Echinococcus granulousus protoscoleces (EGPE) that forms cystic colonies in agarose. The EGPE cell line allowed testing the effect of bisphosphonates alone and in association with other compounds that could modulate calcium apposition/deposition, and were useful in measuring the impact of these compounds on cell growth, cystic colony formation and calcium storage. Decreased cell growth and cystic colony formation were found with EHDP, IB and OPD, and increased calcium storage with EHDP only. Calcium storage in EGPE cells appeared to be sensitive to the effect of amiloride, D3 and proline. Proline decreased calcium storage and increased colony formation. Changes in calcium storage may be associated with degenerative changes of the cysts, as shown in the in vitro colony model and linked to an adenosine triphosphate (ATP) decrease. In conclusion, bisphosphonates could be suitable tempering drugs to treat cestode infections.

Mineralization- and remodeling-unrelated improvement of the post-yield properties of rat cortical bone by high doses of olpadronate.

Some pharmacologic effects on bone modeling may not be evident in studies of remodeling skeletons. This study analyzes some effects of olpadronate on cortical bone modeling and post-yield properties in femurs diaphyses (virtually only-modeling bones) of young rats by mid-diaphyseal pQCT scans and bending tests. We studied 20/22 male/female animals traetad orally with olpadronate (45-90 mg/kg/d, 3 months) and 8/9 untreated controls. Both OPD doses enhanced diaphyseal cross-sectional moments of inertia (CSMI) with no change in cortical vBMD and elastic modulus. Yield stiffness and strength were mildly increased. Post-yield strength, deflection and energy absorption were strikingly enhanced. Ultimate strength was enhanced mainly because of effects on bone mass/geometry and post-yield properties. The large improvement of post-yield properties could be explained by improvements in bone geometry. Improvements in bone mass/geometry over weight-bearing needs suggest an enhanced modeling-related response to mechanical stimuli. Effects on tissue microstructural factors (not measured) could not be excluded. Results reveal novel olpadronate effects on bone strength and toughness unrelated to tissue mineralization and stiffness, even at high doses. Further studies could establish whether this could also occur in modeling-remodeling skeletons. If so, they could counteract the negative impact of anti-remodeling effects of bisphosphonates on bone strength.

Levonorgestrel antagonism on estrogen-induced pituitary tumors is mediated by progesterone receptors.

Using both IN VITRO and IN VIVO approaches, we studied the antagonism exerted by the synthetic progestin levonorgestrel on estrogen-induced prolactinomas, considering that levonorgestrel shows partial androgenic properties and that androgens inhibit estrogen-induced prolactin synthesis and secretion. In the tumors, binding of estrogens to their receptors was competed neither by progesterone receptor ligands nor by androgen receptor ligands, ruling out direct inhibitory effects of these drugs on tumor development. Progestin binding was competed by the progesterone receptor agonists progesterone and levonorgestrel, by the antagonist mifepristone, and also by the androgen dihydrotestosterone, whereas the androgen receptor antagonist hydroxyflutamide was a weak competitor. In addition, both progesterone receptor and androgen receptor ligands competed for binding to androgen receptors. In primary cultures of pituitary tumors, levonorgestrel decreased prolactin secretion, an effect that was blocked by mifepristone but not by hydroxyflutamide. IN VIVO results indicated that levonorgestrel inhibition of both estrogen-induced pituitary weight increment and hyperprolactinemia was reduced by mifepristone, whereas flutamide was unable to block levonorgestrel effects. Our results suggest that even when an interaction of levonorgestrel with androgen receptors in the tumors is possible, the antagonistic effects of levonorgestrel on tumor development and functionality are mediated by progesterone receptors.

Ictal non-forced grasping behaviour.

Our aim was to investigate whether patients with epileptiform foci in the frontal lobe, as revealed by video EEG (VEEG) analysis, exhibit non-forced grasping behaviour and manipulatory movements during seizures. We retrospectively reviewed ictal videotapes of 30 consecutive patients with frontal and 30 with temporal lobe epilepsy undergoing VEEG for the presence and type of grasping and manipulatory movements. Four of the 30 patients with frontal lobe epilepsy (13%) showed unilateral grasping behaviour, three of whom had whole hand prehension (one with manipulation movements as well) and one pinching movements. In all patients, arm abduction and elevation resembling reaching invariably preceded grasping hand movements. The epileptogenic focus was located in the contralateral and ipsilateral frontocentral region in two and one patient, respectively, and in the ipsilateral orbitofrontal region in another. However, none of the patients with temporal lobe epilepsy showed grasping behaviour. Patients with frontal lobe epilepsy may show non-forced grasping with or without manipulatory finger movements as part of ictal phenomena.

Effect of pentoxifylline on levels of pro-inflammatory cytokines during chronic hepatitis C.

The cellular and humoral natural immune response induced by hepatitis C virus (HCV) is commonly unable to eradicate the virus. HCV is a highly mutable, hepatotropic RNA virus that causes acute and chronic hepatitis, an infection that involves the production of various cytokines. The aim of the study is to analyse the expression of pro-inflammatory cytokines IL-1beta, TNF-alpha, IFN-gamma and the chemokine CXCL8 (IL-8) in liver tissue and their expression and secretion in PBMC of patients with chronic hepatitis C (CHC), in response to pentoxyfilline (PTX). We studied six CHC patients, naive to treatment. Patients received PTX 400 mg twice a day/8 weeks. Pentoxyfilline resulted in decreased expression of mRNA of liver IL-1beta, TNF-alpha and IFN-gamma: 144.2 versus 83.5 molecules of IL-1beta (P < 0.05), TNF-alpha 194.3 versus 17.6 molecules (P = 0.03) and IFN-gamma 26.1 versus 0.5 molecules (P = 0.04). Following PTX, PBMC exhibited a decrease in IFN-gamma mRNA 12.2 versus 1.5 molecules (P = 0.028) and CXCL8 4.2 versus 2.5 molecules (P = 0.027). In PBMC, only the secretion of TNF-alpha was decreased 1109 versus 933.5 pg/ml, P = 0.046. Production of cytokines both locally (within the liver) and systemically (PBMC) may serve as biomarkers of the infection with hepatitis C. PTX inhibits the expression of several pro-inflammatory cytokines in the liver. These results indicate that it is worth exploring PTX in hepatitis in future clinical trials in nonresponders to antiviral treatment.

Biomechanical background for a noninvasive assessment of bone strength and muscle-bone interactions.

New concepts and methods of study in bone biomechanics defy the prevailing idea that bone strength is determined by a systemically-controlled "mineralized mass" which grows until reaching a peak and then is lost at individually-specific rates. In case of bones, "mass" represents actually the substratum of a structure, the stiffness of which does not depend on the mass, but on the intrinsic stiffness and the spatial distribution of the mineralized material. A feed-back system called "bone mechanostat" seems to orient the osteoblastic and osteoclastic processes of bone, modeling and remodeling, according to the sensing by osteocytes of strains caused in the structure by mechanical usage of the skeleton, in specific directions as determined principally by the customary contractions of regional muscles and impact forces. The endocrine-metabolic systems, crucial for the normal skeletal development, modulate the work of osteocytes, blasts and clasts in a systemic way (i.e., not related to a specific direction of the stimuli). Therefore, they tend actually to interact with, rather than contribute to, the biomechanical control of bone structure. Furthermore, no feed-back loop enabling a cybernetic relationship of those systems with bone is known. Instead of passively letting hormones regulate their "mass" in order to optimize their strength, bones would actively self-regulate their architecture following an anisotropic pattern in order to optimize their stiffness (the only known variable to be ever controlled in the skeleton) and strength "despite of" the endocrine systems. Three practical questions derive from those ideas: 1. Osteoporoses are not "intense osteopenias" but "osteopenic fragilities". 2. The diagnosis of osteopenia could be solved densitometrically; but that of bone fragility is a biomechanical problem which requires auxiliary resources for evaluating the stiffness and the spatial distribution of the mineralized material. 3. Osteopenias and osteoporoses should be on time evaluated as related to the mass or strength of the regional muscles, respectively, in order to differentiate between the "primary" (intrinsic lesion of the mechanostat) or "secondary" (systemic) etiologies and the biomechanical origin (disuse) in each case, with important therapeutic implications.

Modulation of cytosolic calcium levels in osteoblast-like osteosarcoma cells by olpadronate and its amino-derivative IG-9402.

The molecular mechanisms as well as the structure/activity relationships involved in the antiresorptive actions of bisphosphonates on bone cells are still not clear. Replacement of the R1-hydroxyl by an NH2 group in olpadronate (OPD) abolishes its antiresorptive activity. We show here that in the rat osteosarcoma-derived osteoblast-like ROS 17/2.8 cell line, OPD and IG-9402 (NH2-OPD; [3-(N,N-dimethylamine)-1-aminopropylidene bisphosphonate]), similar to 1,25(OH)2-vitamin D3, rapidly modulate cytosolic calcium levels ([Ca2+]i). As for the steroid hormone, the osteosarcoma cell Ca2+i response to OPD was rapid (30 sec) and sustained (>5 min), exhibiting a biphasic profile. The response to IG-9402 was also fast but smaller than that of OPD and 1,25(OH)2D3, and rapidly declined to levels near basal. The effect of these bisphosphonates on [Ca2+]i was dose-dependent, being maximal at 10(-8) M and was not observed in non-bone cellular systems, e.g., skeletal muscle and breast cells. Pretreatment of the ROS 17/2.8 cells with the Ca2+ channel blockers nifedipine and verapamil markedly reduced (>70%) the influx phase of the response to OPD and almost completely inhibited that of IG-9402, indicating the participation of voltage-dependent Ca2+ channels in the action of both compounds. Moreover, preincubation with the phospholipase C inhibitors U73122 and neomycin or depletion of inner stores with thapsigargin completely blocked the response to either olpadronate or its amino-derivative. Both OPD and IG-9402 significantly increased osteocalcin release into the culture medium of osteosarcoma cells. The results support the involvement of the Ca2+ signaling pathway as part of the mechanism by which bisphosphonates induce bone cellular responses.

GABA(B) receptors in anterior pituitary cells. Mechanism of action coupled to endocrine effects.

The activation of pituitary GABA(B) receptors by the specific agonist baclofen inhibits pituitary hormone secretion in vitro. Here we studied the mechanism of action of GABA(B) receptors in rat adenohypophysis. Anterior pituitary cells were obtained by trypsinization and were either plated for hormonal studies and cAMP determination or incubated in FURA 2AM for calcium measurements. Baclofen (BACL: 1 x 10(-5) M) significantly inhibited basal and thyrotropic releasing hormone (TRH)-stimulated (1 x 10(-7) M) PRL secretion in anterior pituitary cells from proestrous rats. In the presence of pertussis toxin (PTX: 150 ng/ml, 20 h), which leads to the uncoupling of the G(i/o)-protein from the receptor, both effects of BACL were abolished while the effect of dopamine (DA: 1 x 10(-8) M), used as an inhibitory control, was reduced from 70 to 25%. PTX also reversed BACL-induced inhibition of gonadotropin-releasing hormone (GnRH)-elicited luteinizing hormone (LH) secretion in anterior pituitary cells from 15-day-old female rats. In addition, though working in a pituitary mixed cell population, in which only some cell types possess GABA(B) receptors, BACL (1 x 10(-5) M) attenuated the forskolin-induced (0.5 microM) increase in cAMP. This effect was prevented by co-incubation with the antagonist 2 hydroxysaclofen and by preincubation with PTX. BACL (5 x 10(-5) M) and DA (5 x 10(-7) M) inhibited basal intracellular calcium concentrations ([Ca(2+)](i)) in pituitary cells and the effect of the latter was significantly stronger. The effect of BACL on [Ca(2+)](i) was abolished after preincubation with PTX. In the presence of the potassium channel blocking agents barium (200 microM and 1 mM) and tetraethylammonium (10 mM), BACL was still able to inhibit [Ca(2+)](i). Blockade of voltage-sensitive calcium channels (VSCC) with either verapamil (5 x 10(-6) M) or nifedipine (1 x 10(-6) M) completely abolished the effect of BACL on [Ca(2+)](i). In the presence of 12.5 mM potassium concentration baclofen significantly inhibited [Ca(2+)](i). In conclusion, our results describe the negative coupling of adenohypophyseal GABA(B) receptors to VSCC through PTX-sensitive G-proteins. These characteristics suggest a resemblance of these receptors to the typical presynaptic GABA(B) sites described in the central nervous system.

Postmenopausal changes in the distribution of the volumetric BMD of cortical bone. A pQCT study of the human leg.

Three different regions of interest (ROIs) were defined in pQCT scans (XCT-3000 machine, Stratec, Germany) taken at the tibial mid-diaphyses of 12 pre-menopausal (pre-MP) and 12 post-menopausal (post-MP) women who were otherwise normal, according to the volumetric bone mineral density (vBMD) value of their corresponding pixels (voxels) as assessed by their respective attenuation values. They were classified as "low-vBMD" (LD-ROI, with a vBMD of 200-400 mg/cm(3)), corresponding chiefly to trabecular-subcortical bone; "medium-vBMD" (MD-ROI, vBMD = 400-800 mg/cm(3)), corresponding mainly to porous cortical bone or cortical-subcortical bone, and "high-vBMD" (HD-ROI, vBMD higher than 800 mg/cm(3)), corresponding to dense cortical bone. The fraction of the total cross-sectional bone area covered by the HD-ROI was 16% higher, and that covered by the MD-ROI 20% lower, in pre-MP than post-MP women. No differences concerning the LDROIs were found. A close, linearly negative relationship was found between the MD- and HD-ROI fractions in all the women together, with no inter-group differences in slope. The Stress-Strain Index (an indicator of the torsional stiffness and strength of the whole bones that involved both the vBMD and the spatial disposition of the HD bone in the cross-section - torsional moment of inertia -) correlated linearly and positively with the cross-sectional area of the HD-ROI, with a higher slope for pre-MP than post-MP women. Qualitatively, a. post-MP women showed a significantly more prevalent discontinuity of the voxels in the HD-ROI than pre-MP women, and b. the tendency of LD-ROIs to accumulate along the mechanically lesseffective (antero-posterior) axis of the image - a characteristic of pre-MP bones - was visually less evident in post-MP bones. These features describe non-invasively some changes induced by menopause in the human tibia that may be critical for defining the skeletal condition and to monitor the effects of treatments addressed either to protect or to improve mechanically the bone structure, beyond the possibilities of standard densitometry.

Ontogenic expression of anterior pituitary GABA(B) receptor subunits.

gamma-Aminobutyric acid (GABA) is involved in the neuroendocrine control of hypophyseal secretion, acting both in the central nervous system and directly at the pituitary. We have characterized the properties of anterior pituitary GABA(B) receptors. In this work the ontogeny of rat anterior pituitary GABA(B) receptors and the pattern of subunit expression in rats of both sexes were determined. Western blot analysis showed a temporal decrease in GABA(B) subunits GABA(B(1a)) and GABA(B(1b)) expression in female anterior pituitary membranes from day 4 to adulthood, with GABA(B(1a)) being significantly more abundant than GABA(B(1b)) at early stages of development; the GABA(B(2)) subunit was barely detectable. In the male, GABA(B(1a)) followed a similar pattern and appeared to be significantly less abundant than in 4- and 12-day-old females; GABA(B(1b)) and GABA(B(2)) expression in the male was barely detectable. Scatchard plot analysis showed a temporal decrease in binding sites in female anterior pituitary membranes, in agreement with the western blot results. The number of binding sites was significantly higher in female than in male 4-day-old membranes. Dissociation constant values were similar for both sexes at all ages studied. This study reports for the first time the ontogeny of anterior pituitary GABA(B) receptors, showing a particular developmental pattern of subunit expression and a clear sexual dimorphism.

Densitometric and tomographic analyses of musculoskeletal interactions in humans.

Previous studies with standard densitometry (DXA) have suggested that the bone mass is strongly dependent on the muscle mass in the species, following a similar relationship at any age and sex hormones or related factors potentiate that relationship. Studies with pQCT indicated that the surplus bone mass per unit of muscle mass previously observed in premenopausal women would be stored in skeletal regions with relatively little mechanical relevance, thus avoiding remotion through mechanically oriented remodelling by the bone mechanostat. Scanning the distal radius with pQCT has also showed a highly significant, linear relationship between SSI of the distal radius and the dynamometric maximal bending moment of the forearm in normal men and women. In order to investigate similar relationships in regions that are inaccessible to pQCT, we used spinal radiographs and axial QCT. This study affords additional evidence to the previous references concerning the direct, significant impact of the regional muscle strength on the determination of the tomographic indicators of bone mechanical quality and their indirect repercussion of the skeletal condition (curvature of the spine).

Development of an experimental ovarian tumor over a year in the rat.

Tumor growth, possible malignant transformation or metastatic propagation and hormonal patterns were evaluated over a year in luteoma induced by introducing an ovary into the spleen of ovariectomized 60 day-old rats. Sham castrated animals had a piece of muscle inserted into the spleen. Jugular blood samples were taken monthly. After a year animals were cycled and decapitated. Troncal blood was collected, autopsies were performed and luteoma were measured and fixed in 10% buffered formalin. Serum LH, FSH, PRL, estradiol and progesterone were measured. Serum inhibin content was determined in one month-old tumors-bearing animals and estrous rats as controls. After one year no external changes in tumor-bearing rats were observed, nor differences in body weight or mortality rates compared to Sham animals. Metastatic propagation was absent. Routine histological examination showed two types of tumors according to either granulosa or luteal cell predomination, tumor type did not determine hormonal patterns. However, a clear relationship between gonadotropin levels and tumor size was established. Low gonadotropins: Small tumors, 18.7% of cases and high gonadotropins: Large tumors, 81.3%. In Sham animals gonadotropins attained castrate levels and remained elevated until the end of the experiment. In the Small group no increases in gonadotropins or estradiol were detected, progesterone and PRL fluctuated. In the Large tumor group LH increased to Sham titers until month 7, then fell to initial levels, FSH augmented significantly as from month three and remained high up to month 5. No variations in either estradiol, progesterone or PRL were observed. Serum inhibin of one month-old tumor-bearing rats was significantly elevated, justifying the lack of FSH increase at this time point. We conclude that these luteoma do not suffer malignant transformation or induce metastases. They appear in two histological types. Tumor size depends on hormonal patterns. The delay in the initial increase and the sharp decrease observed in FSH in animals bearing Large tumors suggest a possible role for inhibin in this regulation.