Effects of volatile anesthetics on the kinetics of inhibitory postsynaptic currents in cultured rat hippocampal neurons

1. The effects of the volatile anesthetics enflurane, halothane, and isoflurane on gamma-aminobutyric acid (GABA) receptor-mediated inhibitory postsynaptic currents (IPSCs) were studied in cultured rat hippocampal neurons. The experimental concentrations of anesthetics were measured directly using gas chromatography. All three anesthetics increased the overall duration of IPSCs, measured as the time to half-decay (T1/2). Clinically effective concentrations of anesthetics [between 0.5 and 1.5 times MAC (minimum alveolar concentration)] produced between 100 and 400% increases in T1/2. These effects were fully reversible, and did not involve alterations in the reversal potential for the IPSC (EIPSC). 2. The decay of the IPSC was fitted as a sum of two exponential functions, yielding a fast component (tau fast = 20 ms), and a slow component (tau slow = 77 ms), such that the fast component accounted for 79% of the IPSC amplitude and 52% of the total charge transfer. All three anesthetics produced concentration-related increases in the amplitude and charge transfer of the slow component, while simultaneously decreasing the amplitude and charge transfer of the fast component. Thus T1/2 approximated tau fast under control conditions, but approximated tau slow in the presence of the anesthetics. 3. Varying the calcium chelating agents in the recording pipettes had no effect on the quality or magnitude of alterations in IPSC kinetics produced by halothane, suggesting that variations in intracellular calcium levels are not required for the effect of halothane on the time course of the IPSC. 4. The (+)-stereoisomer of isoflurane produced greater increases in the duration of the IPSC than the (-)-isomer when applied at approximately equal concentrations, suggesting that there is a structurally selective site of interaction for isoflurane that modulates the GABAA receptor. 5. These results suggest that the previously shown abilities of volatile anesthetics to potentiate responses to exogenously applied GABA and to prolong the duration of GABA-mediated synaptic inhibition may be due to an alteration in the gating kinetics of the GABAA receptor/channel complex. Prolongation of synaptic inhibition in the CNS is consistent with the physiological effects that accompany anesthesia and may contribute to the mechanism of anesthetic action.     

The location and tracking of swallowed dental appliances: the role of radiology

BACKGROUND: The effects of beta 2 adrenergic agonists on chemoreceptors remain controversial. This study was designed to examine whether fenoterol, a beta 2 adrenergic agonist, increases the ventilatory responses to hypercapnia (HCVR) and hypoxia (HVR) in normal subjects. METHODS: HCVR was tested with a rebreathing method and HVR was examined with a progressive isocapnic hypoxic method in 11 normal subjects. Both HCVR and HVR were assessed by the slope of occlusion pressure (P0.1) or ventilation (VE) plotted against end tidal carbon dioxide pressure and arterial oxygen saturation, respectively. Respiratory muscle strength, spirometric values and lung volume were measured. After a single oral administration of 5 mg fenoterol or placebo HCVR and HVR were evaluated. RESULTS: Fenoterol treatment did not change the specific airway conductance or forced expiratory volume in one second. Respiratory muscle strength did not change. Fenoterol increased the slope of the HCVR of both P0.1 (from 0.251 (0.116) to 0.386 (0.206) kPa/kPa, average increase 71%) and VE (from 10.7 (3.4) to 15.1 (4.2) l/min/kPa, average increase 52%), and shifted the response curves to higher values. For the HVR fenoterol increased the slopes of both P0.1 and VE (from -4.06 (2.00) x 10(-3) to -7.99 (4.29) x 10(-3) kPa/%, an average increase of 83%, and from -0.221 (0.070) to -0.313 (0.112) l/min/%, a 44.5% increase, respectively), and shifted the response curves to higher values. CONCLUSION: Acute administration of fenoterol increases the ventilatory responses to both hypercapnia and hypoxia in normal subjects.     

Human papillomavirus investigation of patients with cervical intraepithelial neoplasia 3, some of whom progressed to invasive cancer

Unstable expansion of the CTG repeats in the 3' untranslated region encoding a member of the protein kinase family in the q13.3 band on chromosome 19 is a mutation specific for myotonic dystrophy. To examine the correlation between clinical expression and CTG trinucleotide repeat length, we carried out Southern blot analysis in a family with myotonic dystrophy. In this pedigree, the expanded CTG repeats were transmitted maternally. The mother had three female children. The mother had about 200 CTG repeats, and the number of repeats for each child was about 800, 1500 and 1600 in birth order. The mother and the patient with 800 repeats were unaware of muscle weakness or myotonia. Symptoms were present from age 3 years in the patient with 1500 repeats and from birth in the one with 1600 repeats. Although the mother menstruated regularly, the patients with 800 and 1500 repeats both menstruated irregularly, and the one with 1600 repeats has never menstruated. The age of onset and severity of the disease were correlated with the size of the expanded repeats. Endocrinological studies revealed that the basal levels of the gonadotropins, PRL and E2 were within normal range, and a pituitary response to LHRH was observed. These data suggest that the amenorrhea and menstrual irregularities were caused by a suprahypophyseal dysfunction. When expanded CTG repeats are transmitted maternally, abnormal products resulting from the metabolic disturbance in the affected mother may harm the fetus in utero. A heterozygous fetus, who has more CTG repeats, may be unable to metabolize the pathologic products sufficiently and therefore may become more severely affected. This may explain the exclusive maternal transmission of congenital myotonic dystrophy.     

Evidence for the involvement of protein kinase C isoforms in alpha-1 adrenergic activation of phospholipase A2 in FRTL-5 thyroid cells

BACKGROUND: FRTL-5 thyroid cells are a cell line extensively used for the investigation of thyroid functions. Activation of alpha-1 adrenergic receptors stimulates both arachidonic acid (AA) release and cytosolic Ca2+ increase in this cell line. Cytosolic Ca2+ and arachidonic acid are known to be important second messengers regulating a variety of thyroid functions. The generation of these messengers is regulated primarily by two different types of phospholipases, phospholipase C (PLC) and phospholipase A2 (PLA2). METHODS: Norepinephrine (NE, 10 mumol/L) was used as an alpha-1 adrenergic activator, and cytosolic-free Ca2+ concentration ([Ca2+]i) was determined using the fluorescent dye indo-1. Arachidonic acid release was measured as an indicator of PLA2 activation, and protein kinase C (PKC) activity determination and isoforms identification were performed using commercial kits. RESULTS: Norepinephrine increased [Ca2+]i and AA release. Prevention of NE-induced cytosolic Ca2+ influx, either by removal of extracellular Ca2+ or by use of Ca2+ channel blockers, NiCl2 or CoCl2, inhibited AA generation entirely. Inhibition of NE-induced increase in [Ca2+]i by the Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), also significantly suppressed NE-induced AA release. Inhibition of PKC activity by PKC inhibitors (H-7 or staurosporine) or downregulation induced by prolonged treatment with phorbol 12-myristate 13-acetate (PMA) or thyleametoxin (TX) significantly blocked the NE-induced AA release, which indicates PKC is involved in mediating NE-induced AA release. Protein kinase C activity measurement indicated that NE induced an activation of PKC in 5 minutes. To further characterize the role of PKC or Ca2+ in regulation of AA release, we identified PKC isoforms by immunoblotting with specific antibodies against 8 different Protein kinase C isoforms. PKC-alpha, -beta I, -beta II, -gamma, delta, -epsilon, -zeta, and -eta isoforms were identified. Norepinephrine induced translocation of PKC-alpha, -beta I, -beta II, -gamma, -delta, and -epsilon isoforms but not -zeta and -eta from cytosol to membrane. Chelation of intracellular Ca2+, prevention of Ca2+ influx, or prolonged treatment with thymeleatoxin (TX) completely blocked the NE-induced translocation of PKC-alpha. CONCLUSIONS: These results, taken together with data obtained from AA experiments, suggest that PKC plays a critical role in alpha-1 adrenergic receptor mediated PLA2 activation and subsequent AA release. Extracellular Ca2+ influx is a prerequisite for both PKC-alpha translocation and AA release. Whether Ca2+ acts directly upon the PLA2, or via PKC-alpha, to regulate AA generation is an intriguing question that remains to be clarified.     

Dynamic elastic-plastic buckling phenomena in a rod due to axial impact

Dynamic elastic-plastic buckling phenomena which might develop in a rod from an axial impact loading are studied in order to identify the conditions for quasi-static behaviour. A discrete model for dynamic elastic-plastic buckling, which retains the axial and the lateral inertia forces, is proposed, and the relationship between the model parameters and the characteristics of an actual structure is given. Examples of different external loadings and boundary conditions are considered in order to clarify the influence of elastic-plastic axial wave propagation on the buckling process. The critical time for the initiation of buckling is obtained and the post-buckling behaviour of the model is analysed. Particular attention is paid to the role of the striking mass on the characteristics of the buckling process and on the development of the buckling shape. The numerical study reveals that the inertia of the striking mass affects considerably the development of the buckling shape causing different patterns of axial strain distributions at the initiation of buckling. The comparisons which are made between the model predictions and some previously published experimental data show that the buckling process is governed by the impact velocity as well as by the external loading history provided by the experimental technique.