Fine structure of the pecten oculi of the barred owl (Strix varia)

Relapse prevention in abstinent cocaine addicts remains a major focus of drug addiction therapy. We used a rat model of cocaine addiction that focused on cocaine-seeking behavior elicited interoceptively and by conditioned stimuli. Each of 18 rats could self-administer a maximum of 20 intravenous cocaine injections (1.5 mg/kg) per session per day. To prevent initiation of responding by cocaine itself priming injections were never administered. Although cocaine was available beginning every session the rats displayed a self-imposed period of abstinence followed by a period of rapid consumption. The abstinence period was variable among rats but consistent for individual rats. In experiment 1 we studied the contribution of a CS+ (stimulus light and lever retraction) to the motivation to initiate and maintain a cocaine self-administration episode. We compared the number of responses the rats emitted to receive the first and subsequent injections of the day between a group responding on a fixed-ratio (FR) schedule (n = 6) and a group responding on a second-order (SO) schedule (n = 5) of reinforcement. For all rats the number of responses per injection was raised daily until a rat failed to consume more than four injections. The SO group was able to emit approximately four times as many responses as the FR group to obtain their first and subsequent injections. In experiment 2 (n = 7) responses during extinction were counted with and without the CS+. Responding was greater in the presence of the CS+ than in its absence. The present model demonstrates that the motivation to self-administer cocaine is variable and greatly enhanced by conditioned stimuli.     

Reconstitution of a functional interleukin (IL)-7 receptor demonstrates that the IL-2 receptor gamma chain is required for IL-7 signal transduction

The interleukin (IL)-2 receptor gamma chain has recently been shown to be a component of the IL-7 and IL-4 receptors. Using a transient transfection assay and the trans-activation of reporter gene constructs which are under the control of cytokine-responsive promoter elements, we have studied signal transduction through the IL-7 receptor (IL-7R). The reporter gene expression was not stimulated by receptors that contained the cytoplasmic domain of the IL-7R, either as intact IL-7R or as part of a chimeric receptor. However, co-expression of the IL-7R with the IL-2 receptor gamma chain was able to stimulate gene activation. For maximal stimulation the intact cytoplasmic domains of each chain was required.     

Acetylcholine activates an alpha-bungarotoxin-sensitive nicotinic current in rat hippocampal interneurons, but not pyramidal cells

The effects of acetylcholine on both pyramidal neurons and interneurons in the area CA1 of the rat hippocampus were examined, using intracellular recording techniques in an in vitro slice preparation. In current-clamp mode, fast local application of acetylcholine (ACh) to the soma of inhibitory interneurons in stratum radiatum resulted in depolarization and rapid firing of action potentials. Under voltage-clamp, ACh produced fast, rapidly desensitizing inward currents that were insensitive to atropine but that were blocked by nanomolar concentrations of the nicotinic alpha7 receptor-selective antagonists alpha-bungarotoxin (alphaBgTx) and methyllycaconitine. Nicotinic receptor antagonists that are not selective for alpha7-containing receptors had little (mecamylamine) or no effect (dihydro-beta-erythroidine) on the ACh-induced currents. Glutamate receptor antagonists had no effect on the ACh-evoked response, indicating that the current was not mediated by presynaptic facilitation of glutamate release. However, the current could be desensitized almost completely by bath superfusion with 100 nM nicotine. In contrast to those actions on interneurons, application of ACh to the soma of CA1 pyramidal cells did not produce a detectable current. Radioligand-binding experiments with [125I]-alphaBgTx demonstrated that stratum radiatum interneurons express alpha7-containing nAChRs, and in situ hybridization revealed significant amounts of alpha7 mRNA. CA1 pyramidal cells did not show specific binding of [125I]-alphaBgTx and only low levels of alpha7 mRNA. These results suggest that, in addition to their proposed presynaptic role in modulating transmitter release, alpha7-containing nAChRs also may play a postsynaptic role in the excitation of hippocampal interneurons. By desensitizing these receptors, nicotine may disrupt this action and indirectly excite pyramidal neurons by reducing GABAergic inhibition.     

Impact of noise and nonlinear distortion due to clipping on the BERperformance of a 64-QAM signal in hybrid AM-VSB/QAM optical fibertransmission system

Experimental BER measurements of a 64-QAM signal in a hybrid AM-VSB/QAM optical fiber transmission system are shown to be in good agreement with a corrected and reinterpreted theory of impulsive and Gaussian noise based on Middleton's class B impulsive noise model. Fiber dispersion induced distortion of the chirped laser output is also shown to adversely affect the QAM signal     

Low-temperature behavior of alkali halides doped with hydroxyl

The low-temperature dielectric dispersions of LiF, NaCl, KCl, and KBr have been measured for different concentrations of OH^?. With decreasing tunnel splitting of the OH^? levels, and with increasing dipolar interaction, a behavior is observed below ～1 K similar to that found in amorphous materials and attributed to two-level states (TLS). Differences between OH^? and TLS are noted, the main difference being that the broad spectrum of energy levels associated with the OH^? in alkali halides arises from dipolar interactions rather than an atomically disordered environment. It is argued that an electric dipole analog of the magnetic spin-glass state does not occur in the OH^? systems.