A silver impregnation technique for the study of steroid receptors in central nervous system tissue prepared for autoradiography

The commonly used silver stains were found to be unsatisfactory for nervous tissue processed for autoradiography. A silver impregnation procedure for central nervous system tissues prepared for the autoradiographic study of steroid receptors is described. The procedure is a combination of several silver and reticular strains made up in solutions containing dimethylsulfoxide. The technique clearly distinguishes perikarya of neurons, brain nuclei and fiber tracts without substantial loss of silver grains, and thus greatly facilitates the identification of steroid receptor nuclei at all levels of the central nervous system.     

Inhibition of nitrogen fixation in alfalfa by arsenate, heavy metals, fluoride, and simulated Acid rain

The acute effects of aqueous solutions of As, Cd, Cu, Pb, F, and Zn ions at concentrations from 0.01 to 100 micrograms per milliliter and solutions adjusted to pH 2 to 6 with nitric or sulfuric acid were studied with respect to acetylene reduction, net photosynthesis, respiration rate, and chlorophyll content in Vernal alfalfa (Medicago sativa L. cv. Vernal). The effects of the various treatments on acetylene reduction varied from no demonstrable effect by any concentration of F⁻ and 42% inhibition by 100 micrograms Pb²⁺ per milliliter, to 100% inhibition by 10 micrograms Cd²⁺ per milliliter and 100 micrograms per milliliter As, Cu²⁺, and Zn²⁺ ions. Zn²⁺ showed statistically significant inhibition of activity at 0.1 micrograms per milliliter. Acid treatments were not inhibitory above pH 2, at which pH nitric acid inhibited acetylene reduction activity more than did sulfuric acid. The inhibition of acetylene reduction by these ions was Zn²⁺ > Cd²⁺ > Cu²⁺ > AsO₃⁻ > Pb²⁺ > F⁻. The sensitivity of acetylene reduction to the ions was roughly equal to the sensitivity of photosynthesis, respiration, and chlorophyll content when Pb²⁺ was applied, but was 1,000 times more sensitive to Zn²⁺. The relationship of the data to field conditions and industrial pollution is discussed.     

The modes of action of gallamine

The action of gallamine, a classical competitive neuromuscular blocking agent, has been examined on voltage-clamped endplates of frog skeletal muscle fibres. Gallamine produces a parallel shift of the equilibrium log (concentration)--response curves in concentrations of up to about 40 microM. At a membrane potential of -70 mV the Schild plot of the dose ratios so measured has a gradient of slightly less than the theoretical value, for a competitive antagonist, of unity. The apparent equilibrium constant for 'competitive' block is about 2 microM, and is approximately independent of the membrane potential. Fluctuation analysis of the endplate current shows two components in the presence of gallamine. The results can be fitted, over the range tested, by a mechanism that involves block of open ion channels by gallamine in a manner similar to that by procaine or quaternary local anaesthetic analogues. The rate constants for this action are strongly dependent on the membrane potential. At -100 mV the association rate constant is about 4 x 10(7) M-1S-1, the dissociation rate constant is about 600 s-1, and the equilibrium constant about 15 microM. Other kinetic measurements (voltage-jump relaxation, and nerve-evoked endplate currents) give results consistent with this conclusion, but apparently these results are valid over a range of conditions narrower than that for fluctuation analysis.     

Role of voltage-sensitive receptors in nicotinic transmission.

This paper compares the conductance induced by bath-applied acetyl-choline (ACh) and by the same transmitter released from nerve terminals at Electrophorus electroplaques. For the former case, dose-response relations are characterized by the maximal agonist-induced conductance, rgamma (130 mmho/cm2), and by the concentration which induces half this conductance; this concentration is termed Kapp and equals 50 micron at -85 mV. For the latter case, neurally evoked postsynaptic currents (PSCs) are characterized by the peak conductance during strongly facilitated release, gPSC, and by the rate constant for decay, alpha. Since gPSC roughly equals rgamma, it is concluded that the PSC activates nearly all available receptor channels. These and other data agree with recent estimates that during the growth phase of the quantal response, (a) the ACh concentration is at least several hundred micromolar; and (b) most nearby channels are activated. However both alpha and Kapp increase during depolarization, at a rate of about e-fold per 86 mV. These observations on voltage sensitivity suggest that a suprathreshold synaptic event is rapidly terminated because the action potential abruptly releases ACh molecules from receptors.     

Fine structure of neurons of the arcuate nucleus and median eminence of the hypothalamus of the golden hamster following immobilization

Summary The fine structure of arcuate neurons of the arcuate nucleus, the ependymal tanycytes and the contact zone of the median eminence was examined following immobilization, an acute stress which significantly activated the hypothalamo-pituitary-adrenal (HPA) axis. Arcuate neurons of immobilized adult male hamsters displayed morphological indications of heightened activity; the number of lysosomes and dense core vesicles (80–120 nm) was increased. A markedly greater number of dense core vesicles was present in axon terminals of the contact zone of the mid-central median eminence and the ventral proximal stalk.Tanycytes of the median eminence exhibited an augmented number of electron dense bodies in both perikarya and end processes. These results indicate that the arcuate neurons, the axons of the contact zone, and the ependymal tanycytes of the hamster medial basal hypothalamus (MBH) may be involved in the response to immobilization.This work was supported by Program Project Grant #NS-11642     

TOXICITY OF BISULFITE TO PHOTOSYNTHESIS AND RESPIRATION1

Inhabition of photosynthesis in Chloroccoum sp by bisulfileion was the reciprocal of the light intensity curve. Respiration was least affected of the bisulfite after endogenous substrate was reduced by incubation in darkness. Maximum areduction in growth occurred with bisulfile treatment at or above optimal growth temperatures. Maximum phytotoxicity correlated with conditions resulting in maximum metabolic activity. The order of toxicity was –H₂SO₃HSO₃^?SO₃.     

A comparison of immunomagnetic and surface adhesion immunofluorescent techniques for the rapid detection of Listeria monocytogenes and Listeria innocua in meat

an immunomagnetic immunofluorescent method was investigated for the rapid detection of Listeria monocytogenes and Listeria innouca . This technique involved enrichment of the suspect sample at 30°C overnight. Listeria monocytogenes cells were isolated from the enriched sample using immunomagnetic separation and Listeria were subsequently visualized using an immunofluorescent microscopy technique. This technique was used in the detection of Listeria cells from pure culture, inoculated beef mince samples and naturally contaminated retail beef mince samples. A detection level of approximately 1×10³ cfu ml⁻¹ was achieved. When compared with traditional detection methods no false negatives or positives were recorded for L. monocytogenes or L. innocua . The immunomagnetic immunofluorescent technique had a detection level similar to a previously described surface adhesion immunofluorescent technique. Isolation of the Listeria cells by surface adhesion involved dipping a membrane attached to a microscope slide into the enriched sample for 10 min. This was quicker and simpler to perform than the immunomagnetic separation technique which took 2 h to carry out.