Membrane bistability in olfactory bulb mitral cells

Whole-cell patch-clamp recordings were used to investigate the electrophysiological properties of mitral cells in rat main olfactory bulb brain slice preparations. The majority of mitral cells are bistable. These cells spontaneously alternate between two membrane potentials, separated by approximately 10 mV: a relatively depolarized potential (upstate), which is perithreshold for spike generation, and a relatively hyperpolarized potential (downstate), in which spikes do not occur. Bistability occurs spontaneously in the absence of ionotropic excitatory or inhibitory synaptic inputs. Bistability is voltage dependent; transition from the downstate to the upstate is a regenerative event activated by brief depolarization. A brief hyperpolarization can switch the membrane potential from the upstate to the downstate. In response to olfactory nerve (ON) stimulation, mitral cells in the upstate are more likely to fire an action potential than are those in the downstate. ON stimulation can switch the membrane potential from the downstate to the upstate, producing a prolonged and amplified depolarization in response to a brief synaptic input. We conclude that bistability is an intrinsic property of mitral cells that is a major determinant of their responses to ON input.

Image analysis quantification of the Miles assay

The Miles assay for vascular permeability has high intra- and interassay coefficients of variation (CVs). Quantification, usually by dye extraction and spectrophotometry, is time consuming. In this study, quantification by this means was compared with image analysis using the Olympus CUE-2 Image Analyzer (version 4). The test substance was recombinant human vascular permeability factor (rhVPF). The quantification process took approximately 10 min with image analysis. Formamide extraction and spectrophotometry required 1 hr of preparation, 4-6 days of incubation, and 1 hr for filtration and spectrophotometry. Between assay CVs ranged from 0 to 30% for spectrophotometry, but were all < 10% for image analysis. The sensitivity (2SD above the negative control mean) of the image analysis approach was 64 +/- 25 ng/mL, whereas for spectrophotometry it was 65 +/- 29 ng/mL. Interanimal CVs for rhVPF at 200 and 1000 ng/mL were 15% and 26% when assessed by spectrophotometry and 7% and 22%, respectively, by image analysis. The R2 value for the correlation of image analysis with spectrophotometry was 81.4%. Test substances injected close to the spine evoked a greater permeability response than those injected laterally: at 200 ng/mL p = 0.005, at 1000 ng/mL p = 0.1 (unpaired t tests).

Voltage-dependent potassium currents in ovine somatotrophs and their function in growth hormone secretion

Sheep somatotroph-enriched cultures were obtained by means of enzyme dissociation and Percoll gradient separation. Nystatin-perforated-whole-cell recordings were performed on post-recording-identified somatotrophs after 4-14 days in vitro. Using Ca(2+)-free, tetrodotoxin-containing (1 microM) bath solution and K+ electrode solution, three types of voltage-dependent K+ currents were recorded as inward rectifying, outward transient and outward delayed rectifying K+ currents. The inward rectifying K+ current was very small at physiological extracellular K+ concentrations (5 mM) and enhanced by increasing the K+ concentration in the bath to 55 mM; it was blocked by tetraethylammonium (2 mM) but not by 4-aminopyridine (5 mM). A transient outward K+ current appeared at -50 mV and was selectively diminished by 4-aminopyridine (2 or 4 mM). A delayed rectifying outward K+ current was observed when the membrane potential was depolarized to -20 mV and was blocked by tetraethylammonium (2 mM) but not 4-aminopyridine (4 mM). Application of 4-aminopyridine but not tetraethylammonium (up to 5 mM) depolarized the cell membrane potential recorded under current clamp conditions and triggered action potentials when the bath solution contained Ca2+ (2 mM) but not tetrodotoxin. The intracellular Ca2+ concentration was increased by 4-aminopyridine as was growth hormone release. Therefore, the 4-aminopyridine-sensitive transient outward K+ current appears to be important in the determining the resting potential of ovine somatotrophs and plays a major role in regulating basal intracellular Ca2+ concentration and growth hormone secretion.

Ethanol-induced inhibition of the drinking response to hypertonic saline in the rat

The effects of ethanol, in doses of 0.05, 0.1 and 0.2 ml/100 g, on the drinking responses of rats to subcutaneous injection of hypertonic saline (1 mEq/100 g) were examined. Rats were also studied for the effects of ethanol (0.1 ml/100 g) on drinking responses to intraperitoneal injection of dextran (20% w/v, 1.5 ml/100 g). After injection of hypertonic saline, rats given ethanol drank less than those administered water or isocalorific glucose. Ethanol inhibited the drinking responses to hypertonic saline dose-dependently with higher doses having a greater inhibitory effect. Ethanol administration had no effect on water consumption stimulated by intraperitoneal injection of dextran. It is concluded that administration of ethanol to rats has a dose-dependent inhibitory effect on thirst and fluid consumption stimulated by injection of hypertonic saline but is without effect on thirst and drinking stimulated by intraperitoneal injection of dextran.