Exteroceptive suppression of temporalis and masseter muscle activity is enhanced in offspring of hypertensives

Exteroceptive suppression of temporalis and masseter muscle activity was examined in young men with and without a parental history of hypertension. Recent clinical studies suggest that the second exteroceptive suppression period is attenuated in several chronic pain disorders and that this brainstem reflex may serve as a noninvasive index of endogenous pain control. In the present study, offspring of hypertensives exhibited a significant protraction of the late exteroceptive suppression period for both muscle sites, suggesting that the decreased pain sensitivity previously observed in individuals at risk for hypertension may be related to enhanced central pain modulation.     

Respiratory sinus arrhythmia: Autonomic origins, physiological mechanisms, and psychophysiological implications

Respiratory sinus arrhythmia (RSA) is being used increasingly in psychophysiological studies as an index of vagal control of the heart and may be among the most selective noninvasive indices of parasympathetic control of cardiac functions. A comprehensive understanding of RSA, however, requires an appreciation of its multiple autonomic and physiological origins. We review the physiological bases of RSA and show that RSA arises from multiple tonic and phasic processes of both central and peripheral origin. These underlying mechanisms are at least partially differentiated, have distinct dynamics and consequences, and may be differentially sensitive to behavioral and cognitive events. These multiple mechanisms are relevant for psychophysiological studies of RSA, and a thorough understanding of RSA can only be achieved through an appreciation of the dynamics of its underlying origins. There is a distinction between the psychophysiological and neurophysiological domains, and conceptual and empirical bridges between these domains are needed.     

新生儿B组链球菌感染的预防

B组链球菌也称为无乳链球菌,是导致新生儿患病和死亡的重要原因之一,可导致败血症、肺炎和脑膜炎。过去十年间,针对B组链球菌主要是预防早发感染,所谓早发感染是指发生于出生后1周内的新生儿感染。采取的预防措施是给感染B组链球菌的孕妇和新生儿选择性地服用抗生素,以减少或消除B组链球菌的垂直传播。目前,尚没有其他办法能完全预防新生儿B组链球菌败血症的发生,在分娩期内对母亲的预防或者结合分娩后对新生儿的预防,可分别使新生儿早发疾病的发病率减少80%和95%。1病因和危险因素已经证实,高达30%的女性阴道和直肠、肛门携带B组链球菌,…     

Autonomic cardiac control. I. Estimation and validation from pharmacological blockades

Pharmacological blockades have been used to estimate the relative contributions of the autonomic branches to cardiac chronotropic control. Systematic biases in these estimates, however, can arise from both methodological and physiological factors. Selective blockades can be interpreted by two inferential models, and a single blockade condition can yield estimates of autonomic control for both autonomic branches. The residual autonomic control of the heart after blockade of a single division provides an index of the functional contribution of the unblocked branch. In contrast, the change in chronotropic state of the heart after blockade of the same division reflects the subtractive loss of that branch and thus provides an index of the normal contribution of the blocked branch. We demonstrate that the systematic biases that can arise in blockade studies introduce distortions of the subtractive and residual estimates that are of equal magnitude but opposite sign. Consequently, the discrepancy between the subtractive and residual-model estimates provides a measure of bias in blockade studies and permits the derivation of validity indices that can facilitate interpretations of blockade data.     

The influence of the site of parasite inoculation on the development of Th1 and Th2 type immune responses in (BALB/c × C57BL/6) F1 mice infected with Leishmania major

Although inbred strains of mice are classified as genetically resistant or susceptible to Leishmania major based upon their ability to control infection, other factors such as the strain, dose, and site of parasite inoculation can also affect the outcome of the disease. Here we used the Fl progeny of BALB/c (susceptible) and C57BL/6 (resistant) mice (designated CB6F1) to investigate whether mice or intermediate susceptibility to infection differed from the parental strains in their ability to control infections at different cutaneous sites. CB6F1 mice developed progressive disease when inoculated in the dorsal skin, but healed infections in the footpad. Consistent with these observations, mice inoculated in the footpad ultimately developed Th1 responses, known to be required for healing, while Th2 responses developed in mice inoculated in the dorsal skin. However, IL-4 and IFN-γ production during the first few weeks of infection was similar in CB6F1 mice inoculated at either site, suggesting that factors in addition to the relative levels of these cytokines produced early in infection may influence the nature of the antileishmanial immune response, and the eventual disease outcome. Infection in CB6F1 mice provides a model for the study of immunity to L. major in genetically identical animals, in which a prolonged mixed Thl/Th2 cytokine pattern initially develops, but ultimately diverges into more defined Th1 and Thl type responses.     

Subchronic Inhalation Toxicity of 1,1,1,3-Tetrachloropropane in Rats

The purpose of this study was to evaluate the inhalation toxicityof 1,1,1,3-tetrachloropropane (TCP), an intermediate in productionof chlorinated silicone fluids. Male and female Sprague- Dawleyrats were exposed 6 hr/day, 5 days/week, for days to TCP atconcentrations of 0, 25, 75, or 225 ppm (Phase study) and to0, 1, 5, or 10 ppm (Phase II study). Phase II of study was conductedbecause a no-observed-effect level was not achieved in PhaseI. No animals died during the study. Clinical signs of toxicityincluded oral, nasal, and/or ocular discharge. No statisticallysignificant differences were observed in either body weightsor food consumption between exposed and control animals. Clinicalpathology did not indicate any treatment related effects. Absoluteand relative liver and kidney weights were increased in maleand female rats exposed to 225 ppm TCP, and heart weights wereincreased in male rats exposed to 225 ppm TCP. The liver andheart weight changes were supported by the findings of microscopiclesions in these organs. These lesions consisted of multifocal/focalmyofiber degeneration necrosis with adjacent chronic myocarditisin the heart and multifocal single-cell necrosis in the liverparenchyma. The liver lesions had essentially resolved at theend of a 28-day recovery period but the heart lesions were stillpresent in male rats in the recovery group exposed to 225 ppmTCP. No treatment-related effects were observed in animals exposedto 1, 5, or 10 ppm TCP. The data of this study showed that theno-observable-effect level for TCP was 10 ppm in male and femaleCD rats.     

Toxicokinetics of Intravenous Methanol in the Female Rat

The toxicokinetics of intravenously administered methanol wereexamined in female Sprague-Dawley rats. Animals received a singleadministration of 100, 500, or 2500 mg methanol/kg; the twolower doses were administered as a bolus, while the high dosewas administered over 1.5 min. A small (approximately 3%) butstatistically insignificant (p>0.1) degree of transpulmonarymethanol extraction, expressed as the fractional arterial-venousdifference in concentration, was observed after administrationof 250 mg methanol/kg. The elimination of methanol from thesystemic circulation was markedly nonlinear, suggestive of asignificant capacity-limited route of elimination. A singleset of kinetic parameters (apparent distributional volume ofthe central compartment [V_c], intercompartmental transfer rateconstants [k₁₂ and k₂₁], and V_max and K_m for elimination) describedthe blood methanol concentration-time data from rats receivingthe 100 and 500 mg/kg doses. Blood methanol concentrations declinedmuch more rapidly in animals receiving the 2500 mg/kg dose thanwould be predicted from the kinetic parameters derived fromthe other two experimental groups. The data from the 2500 mg/kggroup could be described adequately by a kinetic model incorporatingparallel first-order and saturable elimination processes. Aportion of this apparent linear elimination pathway was dueto renal excretion of the unchanged alcohol. The presence ofboth linear and nonlinear elimination pathways for methanolmay have implications regarding high-dose to low-dose toxicologicextrapolations.