Pentylenetetrazole-induced inhibition of recombinant gamma-aminobutyric acid type A (GABA(A)) receptors: mechanism and site of action

Pentylenetetrazole (PTZ) is a central nervous system convulsant that is thought, based on binding studies, to act at the picrotoxin (PTX) site of the gamma-aminobutyric acid type A (GABA(A)) receptor. In the present study, we have investigated the mechanism and site of action of PTZ in recombinant GABA(A) receptors. In rat alpha 1 beta 2 gamma 2 receptors, PTZ inhibited GABA-activated Cl(-) current in a concentration-dependent, voltage-independent manner, with an IC(50) of 0.62 +/- 0.13 mM. The mechanism of inhibition appeared competitive with respect to GABA in both rat and human alpha 1 beta 2 gamma 2 receptors. Varying subunit configuration (change or lack of alpha subunit isoform or lack of gamma 2 subunit) had modest effects on PTZ-induced inhibition, as evidenced by comparable IC(50) values (0.6-2.2 mM) in all receptor configurations tested. This contrasts with PTX and other PTX-site ligands, which have greater affinity in receptors lacking an alpha subunit. Using a one-site model for PTZ interaction with alpha 1 beta 2 gamma 2 receptors, the association rate (k(+1)) was found to be 1.14 x 10(3) M(-1) s(-1) and the dissociation rate (k(-1)) was 0.476 s(-1), producing a functional k(d) of 0.418 mM. PTZ could only gain access to its binding site extracellularly. Single-channel recordings demonstrated that PTZ decreased open probability by increasing the duration of closed states but had no effect on single-channel conductance or open state duration. alpha-Isopropyl-alpha-methyl-gamma-butyrolactone, a compound known to antagonize effects of PTX, also diminished the effects of PTZ. Taken together, our results indicate that pentylenetetrazole and picrotoxin interact with overlapping but distinct domains of the GABA(A) receptor.     

Recent progress in understanding,diagnosing, and treating hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the few cancers in which a continued increase in incidence has been observed over several years. As such, there has been a focus on safe and accurate diagnosis and the development of treatment algorithms that take into consideration the unique complexities of this patient population. In the past decade, there have been improvements in nonsurgical treatment platforms and better standardization with respect to the diagnosis and patient eligibility for liver transplant. How to navigate patients through the challenges of treatment is difficult and depends on several factors: 1) patient‐related variables such as comorbid conditions that influence treatment eligibility; 2) liver‐related variables such as Child‐Pugh score; and 3) tumor‐related variables such as size, number, pattern of spread within the liver, and vascular involvement. The objectives of this review are to put into perspective the current treatment options for patients with HCC, the unique advantages and disadvantages of each treatment approach, and the evidence that supports the introduction of sorafenib into the multidisciplinary management of HCC. CA Cancer J Clin 2012;. © 2012 American Cancer Society.     

DSM criteria for tobacco use disorder and tobacco withdrawal: a critique and proposed revisions for DSM-5

Aims This paper aims to identify appropriate criteria for tobacco dependence assessment, evaluate relevant research and suggest revisions that may be incorporated into DSM‐5. Methods Desirable conceptual and psychometric features of tobacco dependence assessments were identified, including the types of outcomes against which such assessment should be validated. DSM‐IV criteria were matched against these criteria and compared with other dependence measures. Results DSM‐IV criteria were found to be ambiguous, little used in tobacco research, and have relatively low predictive validity. Other dependence measures were found to have greater validity in the prediction of important dependence features such as relapse likelihood. Strength of urges to smoke on typical smoking days and during abstinence, markers of nicotine intake or frequency of smoking and latency to smoke soon after waking were found to be useful dependence measures. Conclusion The use and utility of DSM‐5 will be enhanced by eliminating most DSM‐IV criteria and adding new ones based on smoking pattern, smoking heaviness, and the severity of craving during periods of smoking and withdrawal.     

Hepatic leptin signalling and subdiaphragmatic vagal efferents are not required for leptin-induced increases of plasma IGF binding protein-2 (IGFBP-2) in <Emphasis Type="Italic">ob/ob</Emphasis> mice

Aims/hypothesis  

The fat-derived hormone leptin plays a crucial role in the maintenance of normal body weight and energy expenditure as well as in glucose homeostasis. Recently, it was reported that the liver-derived protein, insulin-like growth factor binding protein-2 (IGFBP-2), is responsible for at least some of the glucose-normalising effects of leptin. However, the exact mechanism by which leptin upregulates IGFBP-2 production is unknown. Since it is believed that circulating IGFBP-2 is predominantly derived from the liver and leptin has been shown to have both direct and indirect actions on the liver, we hypothesised that leptin signalling in hepatocytes or via brain–liver vagal efferents may mediate leptin control of IGFBP-2 production.     

Hypoxic effects on the anterior eye of high-Dk soft contact lens wearers are negligible.

PURPOSE: To determine whether the eyes of high-Dk soft contact lens wearing subjects can be discriminated from non-contact lens wearing subjects. METHODS: This study was a prospective masked assessment of 32 subjects, 16 of whom wore experimental high-Dk soft contact lenses and 16 of whom did not wear contact lenses. Subjects wore high-Dk lenses on a 30-night replacement schedule for an average of 9 months. Tear film characteristics, staining and vascularization of the cornea, conjunctival staining, and the presence of microcysts in the corneal epithelium were assessed using slitlamp microscopy. The endothelium was examined for polymegethism. RESULTS: No differences were found between the two groups in any of the variables that were examined (p > 0.05) except that the high-Dk lens wearing group had about twofold more tear film debris and 2.5-fold more severe conjunctival staining (p < 0.05). CONCLUSIONS: Hypoxia-associated effects were not apparent in the eyes of subjects wearing experimental high-Dk soft contact lenses. Conjunctival staining can generally distinguish lens wearers from non-lens wearers and can be used to discriminate between high-Dk lens wearing subjects and non-lens wearing subjects.     

Porosity in manually and machine mixed resin-modified glass ionomer cements.

The powder and liquid components of resin-modified glass ionomer cements are available in manual and machine mixed forms. This study quantified the effect mixing methods have on the porosity and shear strength of a resin-modified glass ionomer cement (RMGIC). A RMGIC (Fuji II LC) was manually or machined mixed according to manufacturer's instructions. Thin, disc-shaped specimens (n = 5) were made by compressing the cement between glass platens to a thickness of approximately 76 microns. The specimens were light cured for 120 seconds. Digital images of the specimens were recorded using a measuring microscope and slide film scanner. Digital imaging software was used to determine the number and volume of the cement's pores. Shear test specimens of manual and machine mixed cements (n = 10) of each group (approximately 800 microns thickness) were made as previously described. Shear punch tests were conducted using a 3.75 mm diameter punch mounted on a universal testing machine. The mean number and total volume of pores in the manually mixed specimens was considerably greater than that of the machine mixed group (p < 0.05). The shear punch test results of the machine mixed group was significantly higher than the manual mixed group, (p < 0.05).     

Medial superior olive of the big brown bat: neuronal responses to pure tones, amplitude modulations, and pulse trains.

The structure and function of the medial superior olive (MSO) is highly variable among mammals. In species with large heads and low-frequency hearing, MSO is adapted for processing interaural time differences. In some species with small heads and high-frequency hearing, the MSO is greatly reduced in size; in others, including those echolocating bats that have been examined, the MSO is large. Moreover, the MSO of bats appears to have undergone different functional specializations depending on the type of echolocation call used. The echolocation call of the mustached bat contains a prominent CF component, and its MSO is predominantly monaural; the free-tailed bat uses pure frequency-modulated calls, and its MSO is predominantly binaural. To further explore the relation of call structure to MSO properties, we recorded extracellularly from 97 single neurons in the MSO of the big brown bat, Eptesicus fuscus, a species whose echolocation call is intermediate between that of the mustached bat and the free-tailed bat. The best frequencies of MSO neurons in the big brown bat ranged from 11 to 79 kHz, spanning most of the audible range. Half of the neurons were monaural, excited by sound at the contralateral ear, while the other half showed evidence of binaural interactions, supporting the idea that the binaural characteristics of MSO neurons in the big brown bat are midway between those of the mustached bat and the free-tailed bat. Within the population of binaural neurons, the majority were excited by sound at the contralateral ear and inhibited by sound at the ipsilateral ear; only 21% were excited by sound at either ear. Discharge patterns were characterized as transient ON (37%), primary-like (33%), or transient OFF (23%). When presented with sinusoidally amplitude modulated tones, most neurons had low-pass filter characteristics with cutoffs between 100 and 300 Hz modulation frequency. For comparison with the sinusoidally modulated sounds, we presented trains of tone pips in which the pulse duration and interstimulus interval were varied. The results of these experiments indicated that it is not the modulation frequency but rather the interstimulus interval that determines the low-pass filter characteristics of MSO neurons.     

Preclinical Pharmacokinetics Study of R- and S-Enantiomers of the Histone Deacetylase Inhibitor,AR-42 (NSC 731438), in Rodents

AR-42, a new orally bioavailable, potent, hydroxamate-tethered phenylbutyrate class I/IIB histone deacetylase inhibitor currently is under evaluation in phase 1 and 2 clinical trials and has demonstrated activity in both hematologic and solid tumor malignancies. This report focuses on the preclinical characterization of the pharmacokinetics of AR-42 in mice and rats. A high-performance liquid chromatography–tandem mass spectrometry assay has been developed and applied to the pharmacokinetic study of the more active stereoisomer, S-AR-42, when administered via intravenous and oral routes in rodents, including plasma, bone marrow, and spleen pharmacokinetics (PK) in CD2F1 mice and plasma PK in F344 rats. Oral bioavailability was estimated to be 26 and 100% in mice and rats, respectively. R-AR-42 was also evaluated intravenously in rats and was shown to display different pharmacokinetics with a much shorter terminal half-life compared to that of S-AR-42. Renal clearance was a minor elimination pathway for parental S-AR-42. Oral administration of S-AR-42 to tumor-bearing mice demonstrated high uptake and exposure of the parent drug in the lymphoid tissues, spleen, and bone marrow. This is the first report of the pharmacokinetics of this novel agent, which is now in early phase clinical trials.