The acoustic startle response and disruption of aiming: II. Modulation by forewarning and preliminary stimuli

Four experiments examined the disruption of rifle aim by intense noise bursts. In Experiment 1 a trigger pull was followed occasionally by a noise burst. Aiming was disrupted for 1-2 s, an effect that habituated within days and recovered between days. Expected stimuli were less disruptive than were unexpected stimuli. Experiment 2 demonstrated that weak auditory prestimuli 100 ms before unexpected intense sounds also reduced noise-produced errors. Experiment 3 showed that the intratympanic reflex had not played a protective role in this effect. Experiment 4 showed that a weak tactile prestimulus increased both a muscular measure of the acoustic startle reaction and the perturbing effect of the noise burst on motor performance. In general, conditions that affect the amplitude of the acoustic startle reflex similarly influence the disruptive effect of a noise burst on motor performance, but the two measures are not correlated in the detail necessary to suggest a causative relationship.     

Visual function measured by reflex modification in rats with inherited retinal dystrophy.

Two experiments, with 16 Ss, examined developmental changes in visual function in the Royal College of Surgeons (RCS) rat with inherited retinal degeneration (retinal dystrophy) by studying the inhibition of acoustic startle reflexes by visual prestimuli. Compared with a congenic strain of nondystrophic rat, RCS Ss showed an increase in the interstimulus interval between the inhibitory prestimulus and the eliciting stimulus that produced maximal inhibition, a result suggesting a decrease in the speed of processing. The amount of inhibition also decreased over time, which suggests a progressive loss of visual function. Simultaneous presentation of auditory and visual prestimuli was used to demonstrate that the changes in inhibition were related to alterations in visual function and that auditory function was not impaired. Results show that reflex modification is a suitable test for evaluating visual dysfunction in rats. ( 27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation and inhibition of the human startle blink reflexes by stimulus anticipation.

The cutaneous eyeblink has 2 electromyographic components, 1 unilateral and early (R1) and 1 bilateral and late (R2), which are served by different neural pathways. These 2 reactions were measured when the eliciting stimulus was expected or relatively surprising. Forewarning was varied in 3 ways: Subjects received notice that the stimulus was about to occur on some trials (Experiment 1); delivered the stimulus to themselves on some trials (Experiments 2 & 3); or experienced a series of trials in which a tone was paired with the eliciting stimulus, followed by tone-alone trials interspersed with test trials (Experiment 4). In each case, forewarning enhanced R1 amplitudes while depressing R2 but reduced the latency of both components. This mixed pattern of effects reveals that the preparatory state provoked by forewarning focuses excitatory and inhibitory processes simultaneously on different reflex pathways: inhibition central and excitation peripheral. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Activation of complement by mannose-binding lectin on isogenic mutants of Neisseria meningitidis serogroup B

Mannose-binding lectin (MBL) is a serum protein that has been demonstrated to activate the classical complement pathway and to function directly as an opsonin. Although MBL deficiency is associated with a common opsonic defect and a predisposition to infection, the role of the protein in bacterial infection remains unclear. We have investigated MBL binding to Neisseria meningitidis serogroup B1940 and three isogenic mutants, and the subsequent activation of the two major isoforms of C4 (C4A and C4B) by an associated serine protease, MASP. The mutants lacked expression of the capsular polysaccharide (siaD-), the lipo-oligosaccharide (LOS) outer core that prevented LOS sialylation (cpsD-), or both capsule and LOS outer core (cps-). Using flow cytometry, it was possible to detect strong MBL binding to the cps- and cpsD- mutants over a wide range of concentrations. In contrast, minimal or no MBL binding was detected on the parent organism, with binding to siaD- only at higher MBL concentrations. C4 was activated and bound by mutants that had previously bound MBL/MASP, but there was no significant difference in the amounts of C4A and C4B bound. When sialic acid residues were removed from the parent organism by neuraminidase treatment, the binding of both MBL and C4 increased significantly. Our results suggest that MBL may bind to and activate complement on these encapsulated organisms, and the major determinants of these effects are the LOS structure and sialylation.     

Reflex modification in the domain of startle: II. The anomalous history of a robust and ubiquitous phenomenon.

Describes the discovery and rediscoveries of the phenomenon of the reflex modification of the startle reaction. The startle reaction is elicited in animals by abrupt stimuli in diverse modalities. Weak stimuli can modify the reflex. This phenomenon of reflex modification has been discovered on at least 4 separate occasions since the mid-19th century, beginning with I. M. Sechenov in 1862. The empirical and theoretical climate at the time of each discovery and each period of neglect are described. The authors conclude that reflex modification has been repeatedly discovered because it is a powerful and ubiquitous effect that finds expression in a wide variety of species and circumstances. It has suffered neglect because (a) it failed to be incorporated by the central theoretical conceptions of the times, (b) its procedures were sometimes confused with those of classical Pavlovian conditioning, and (c) too little attention was paid to the assessment of basic behavioral phenomena that might yield to direct empirical investigation in psychology's search for general theory. (66 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reflex-inhibiting stimuli and the refractory period of the acoustic startle reflex in the rat.

Previous studies show that if acoustic startle stimuli are presented in pairs, then the reaction to the 2nd stimulus (S2) is reduced, with the size of the refractory decrement determined by the interstimulus interval and the relative intensity of the 1st stimulus (S1). If a neutral stimulus (p) is presented just prior to S1, then the reaction to S1 is similarly inhibited, revealing the phenomenon of prestimulus inhibition. In 2 experiments with male albino Holtzman rats (N = 24) it was found that suppression of the reflex to S2 by S1 was unaffected by prestimulus inhibition of S1 (i.e., reflex amplitudes associated with S2 were identical in pS1-S2 series and S1-S2 series). In contrast, a reduction in the intensity of S1 relative to S2 did reduce the effect of S1 on S2. These data indicate that prestimulus inhibition of the reflex to S1 does not result because the preliminary stimulus attenuates the sensory impact of S1. The inhibitory process may be presumed to have a central locus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus-produced reflex inhibition in the rat during induction of and recovery from barbiturate anesthesia.

Reported 3 experiments which show that the inhibitory effect of a preliminary stimulus on the acoustic startle reflex was disrupted during the induction of sodium pentobarbital (40 mg/kg) in a total of 50 male Holtzman rats. In Exp I (n = 35) and II (n = 8), Ss were injected with the barbiturate, and a startle stimulus was presented either alone or preceded by a white noise burst. Results show that (a) stimulus inhibition was present immediately after injection, (b) was lost during a phase of hyperreactivity which accompanied induction of the anesthesia, and (c) recovered as reactivity diminished in the anesthetic state. Exp III showed that inhibition recovered during an intervening stage prior to complete areflexia and that this recovery revealed that the earlier and later inhibitory failure cannot be ascribed to a drug-dependent degradation in a hypothetical inhibitory system. It was suggested that the expression of reflex inhibition depends on the balanced interplay of excitatory and inhibitory processes which are differentially sensitive to drug intake. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Molecular typing of Neisseria gonorrhoeae causing repeated infections: evolution of porin during passage within a community

Thirty-three Neisseria gonorrhoeae isolates from 15 persons infected multiple times with the same serovar were compared using por gene sequencing, opa-typing, and arbitrarily primed-polymerase chain reaction. All three molecular techniques were more discriminatory than serotyping and identified differences between some isolates belonging to the same serovar. Although there were differences among Por sequences within some serovars, 10 of 15 subjects became reinfected with gonococci expressing identical Por proteins. Sequence analysis of por genes revealed evidence of horizontal genetic exchange and point mutations in potential surface-exposed regions during passage in the community.     

The acoustic startle response and disruption of aiming: I. Effect of stimulus repetition, intensity, and intensity changes

Three experiments examined the disruption of perceptual motor performance by intense noise bursts. Subjects aimed a rifle at a fixed target for 15-s periods separated by 15 s of rest. This cycle was repeated 30 times in each of two series separated by a 15-min rest, each series containing five noise bursts. The noise bursts disrupted aiming for 1-2 s, an effect that increased with sound pressure level for 110, 120, and 130 dB stimuli. There was no difference between stimuli with energy centered on 250 Hz as opposed to 800 Hz. The effect diminished over the five bursts within the first series (but not to zero) and did not recover in the 15-min rest period. Some subjects received three days of testing; in these cases the effect of the noise bursts partially recovered after rest intervals of 24 hrs and then seven days. Other subjects received 15 trials with 110-dB stimuli, then five more trials with 130-dB stimuli. The disruption of aiming by 130 dB stimuli was not reduced by prior exposure to 110-dB stimuli.