Instrumental learning within the spinal cord: V. Evidence the behavioral deficit observed after noncontingent nociceptive stimulation reflects an intraspinal modification

Spinally transected rats given leg shock whenever one hindlimb is extended learn to maintain the leg in a flexed position, which minimizes net shock exposure. Yoked rats, that receive an equal amount of shock independent of leg position (noncontingent shock), do not exhibit an increase in flexion duration. Yoked rats also fail to learn when response contingent shock is applied to the previously shocked leg, a behavioral deficit that resembles learned helplessness. This deficit could reflect either a peripheral (e.g. muscle fatigue) or central effect. Experiment 1 showed that spinalized rats given noncontingent shock to one hind limb fail to learn when response-contingent shock is applied to the contralateral leg. Experiment 2 demonstrated that blocking the afferent input to the spinal cord, by cutting the sciatic nerve, blocked the development of the deficit. Experiment 3 found that intrathecal lidocaine has a protective effect and prevents the deficit. These findings suggest that noncontingent nociceptive stimulation induces an intraspinal modification that undermines behavioral potential.

Instrumental learning within the spinal cord: IV. Induction and retention of the behavioral deficit observed after noncontingent shock

Spinalized rats given shock whenever 1 hind leg is extended learn to maintain that leg in a flexed position, a simple form of instrumental learning. Rats given shock independent of leg position do not exhibit an increase in flexion duration. Experiment 1 showed that 6 min of intermittent legshock can produce this deficit. Intermittent tailshock undermines learning (Experiments 2-3), and this effect lasts at least 2 days (Experiment 4). Exposure to continuous shock did not induce a deficit (Experiment 5) but did induce antinociception (Experiment 6). Intermittent shock did not induce antinociception (Experiment 6). Experiment 7 addressed an alternative interpretation of the results, and Experiment 8 showed that presenting a continuous tailshock while intermittent legshock is applied can prevent the deficit.

Instrumental learning within the spinal cord: IV. Induction and retention of the behavioral deficit observed after noncontingent shock

Spinalized rats given shock whenever 1 hind leg is extended learn to maintain that leg in a flexed position, a simple form of instrumental learning. Rats given shock independent of leg position do not exhibit an increase in flexion duration. Experiment 1 showed that 6 min of intermittent legshock can produce this deficit. Intermittent tailshock undermines learning (Experiments 2-3), and this effect lasts at least 2 days (Experiment 4). Exposure to continuous shock did not induce a deficit (Experiment 5) but did induce antinociception (Experiment 6). Intermittent shock did not induce antinociception (Experiment 6). Experiment 7 addressed an alternative interpretation of the results, and Experiment 8 showed that presenting a continuous tailshock while intermittent legshock is applied can prevent the deficit.

Instrumental learning within the spinal cord. II. Evidence for central mediation

Rats spinally transected at the second thoracic vertebra can learn to maintain their leg in a flexed position if they receive legshock for extending the limb. These rats display an increase in the duration of a flexion response that minimizes net shock exposure. The current set of experiments was designed to determine whether the acquisition of this behavioral response is mediated by the neurons of the spinal cord (i.e., is centrally mediated) or reflects a peripheral modification (e.g., a change in muscle tension). Experiment 1 found that preventing information from reaching the spinal cord by severing the sciatic nerve blocked the acquisition of this behavioral response. Spinalized rats also failed to learn if the spinal cord was anesthetized with lidocaine during exposure to response-contingent shock (Experiment 2). Experiment 3 demonstrated that prior exposure to response-contingent shock on one hindleg facilitated acquisition of the response when subjects were later tested on the opposite leg. These findings suggest that acquisition of the instrumental response depends on neurons within the spinal cord.

Shock-induced hyperalgesia: IV. Generality

Brief-moderate shock (3, 0.75 s, 1.0 mA) has opposite effects on different measures of pain, inducing antinociception on the tail-flick test while lowering vocalization thresholds to shock and heat (hyperalgesia) and enhancing fear conditioned by a gridshock unconditioned stimulus (US). This study examined the generality of shock-induced hyperalgesia under a range of conditions and explored parallels to sensitized startle. Reduced vocalization thresholds to shock and antinociception emerged at a similar shock intensity. Severe shocks (3, 25 s, 1.0 mA or 3, 2 s, 3.0 mA) lowered vocalization threshold to shock but increased vocalization and motor thresholds to heat and undermined fear conditioned by a gridshock or a startling tone US. All shock schedules facilitated startle, but only brief-moderate shock inflated fear conditioning. The findings suggest that brief-moderate shock enhances the affective impact of aversive stimuli, whereas severe shocks attenuate pain.

Pain and negative affect: evidence the inverse benzodiazepine agonist DMCM inhibits pain and learning in rats

RATIONALE

The anxiogenic DMCM, an inverse benzodiazepine agonist, was used to explore the relationship between negative affective states and pain. Past work suggests that the outcome obtained may depend on both the intensity of the affective state and the way in which pain is inferred.

OBJECTIVES

The present study was designed to test the impact of relatively low doses of DMCM on multiple measures of pain reactivity and learning.

METHODS

In experiment 1, systemic injections of 0.00, 0.015, 0.06, and 0.25 mg/kg DMCM were administered before vocalization and tail movements were assessed in response to a gradually incremented shock and radiant heat stimulus. Experiment 2 tested the effects of DMCM on Pavlovian conditioning. DMCM-treated subjects experienced a context paired with an aversive unconditioned stimulus (US) and conditioned freezing was assessed the next day.

RESULTS

Experiment 1 showed that DMCM inhibits both a spinal nociceptive reflex (tail-flick to heat) and a supraspinal measure of pain (vocalization to shock). Because these inhibitory effects could reflect a disruption in motor function, experiment 2 employed a remote test based on Pavlovian conditioning. A moderate dose of DMCM undermined learning, implying that the drug decreased the affective impact of the aversive US.

CONCLUSIONS

DMCM induces hypoalgesia on a wide range of assays. Furthermore, pharmacologically inducing a negative affective state blocks Pavlovian fear conditioning. It is suggested that DMCM induces a state of panic and that this state inhibits pain.

Effects of positive and negative music on performance of a karate drill

Although athletes frequently report using music while training or before an event, laboratory studies have not detected a beneficial effect, so the influence of positive and negative music on performance of a selected karate drill was investigated in this double-blind study using 14 volunteers from two Shotokan karate schools. Each subject performed a preselected drill three times following positive and negative music and white noise in a random order. Performance of the drill was rated on a 7-item, 5-point scale by 2 rates. Differences among conditions were assessed via a with-in-subject t test for paired scores. The subjects' self-evaluation of their performance was also examined. Enhancement of performance for both types of music over white noise was significant.

Purification and properties of an inhibitor of the tryptophan-synthase-inactivating enzymes in yeast

An inhibitor of the tryptophan‐synthase‐inactivating enzymes has been isolated from bakers' yeast and purified 27‐fold on a protein basis, by heat treatment, precipitation by trichloroacetic acid, ethanol fractionation and acid precipitation. The inhibitory activity of the purified material is not affected by incubation with RNAase, DNAase, or muramidase, but is destroyed by incubation with pronase or trypsin. Inhibitory activity depends, therefore, on the protein content of the material.

The extent to which the inactivating enzymes are inhibited is proportional to inhibitor concentration. Tryptophan‐synthase inactivases I and II are both inhibited. The inhibitor appears to be specific in its action: it is much more effective than soybean trypsin inhibitor in inhibiting the inactivases, but has comparatively little effect on the esterolytic activity of trypsin.

Inhibitory activity was measured in crude extracts of Saccharomyces cerevisiae growing in batch culture. In the exponential growth phase, the inhibitor was barely detectable, but its levels subsequently rose at the end of the exponential phase and in the stationary phase. The possible biological significance of these observations is discussed.

New quantitative, qualitative, and confirmatory media for rapid analysis of food for Clostridium perfringens

A selective and differential medium, Shahidi-Ferguson Perfringens agar (SFP agar), and a confirmatory medium, lactose-motility agar (LM agar), were developed for the enumeration and identification of Clostridium perfringens in foods. These media provide a rapid, specific, and direct diagnosis of C. perfringens. SFP agar contains sodium metabisulfite and ferric ammonium citrate to demonstrate H(2)S production and egg yolk to demonstrate lecithinase production by C. perfringens. On SFP agar, C. perfringens produces black colonies, 2 to 3 mm in diameter, surrounded by zones of opaque precipitate. The typical colonies are confirmed on LM agar. Enumeration and identification are completed within 48 hr. All of the ingredients of SFP agar are stable to heat and storage conditions. SFP agar also contains two antibiotics, kanamycin and polymyxin B, which are inhibitory to many bacteria commonly occurring in foods. A comparative study of SFP agar and noninhibitory media showed that SFP agar did not inhibit any of the 16 strains of C. perfringens tested. Recovery of C. perfringens added to foods averaged 90.6% for SFP agar as compared with 69.8% for sulfite polymyxin-sulfadiazine (SPS) agar (BBL) and 60.2% for SPS agar (Difco). The colonies on the SFP agar, were much larger and were consistently black. Of 464 food samples tested, C. perfringens was found in 27 samples with SFP agar and in 5 samples with SPS agar (Difco), with a recovery ratio considerably higher on SFP agar. SFP agar is a more specific presumptive medium for the enumeration of C. perfringens and in conjunction with LM agar should save considerable time, effort, and materials toward the final identification of the species.

Nitrogen metabolism of Spirodela oligorrhiza : III. Amino acids and the utilization of nitrate

Wheras ammonium inhibited almost completely utilization of nitrate (NO3) by Spirodela oligorrhiza, asparagine, aspartate, glutamine, and glutamate had only a sparing effect. Asparagine and glutamine were used more rapidly than NO3; aspartate and glutamate at about the same rate. These differences in utilization of NO3 were not determined by differences in the levels of nitrate reductase.

The nitrogen metabolism of Spirodela oligorrhiza : II. Control of the enzymes of nitrate assimilation

Nitrate reductase (NO3R) in Spirodela oligorrhiza has a specific requirement for NAD, and no activity could be detected when reduced NADP was supplied as a cofactor. NO3R and nitrite reductase (NO2R) are adaptive enzymes, being present only when the plant is supplied with NO3 or NO2. There is significant correlation between the concentration of NO3 in plants, and the levels of NO3R that they contain. When plants not containing NO3R or NO2R are supplied with NO3, there was a rapid increase in the levels of the two enzymes and in the concentration of NO3 in the plants. These increases were retarded but not prevented by NH4 in the medium. When NO3-grown plants were depleted of N, there was a rapid decrease in the levels of NO3R and NO2R.The utilization of NH4 prevented the assimilation of NO3 even by plants that contained high levels of NO3R and NO2R. It was therefore concluded that NH4, or the processes or products of its assimilation must inhibit the activity of NO3R. NH4, arginine, asparagine or glutamine, tested separately or together, had little effect on the in vitro activity of NO3R.

Nitrogen metabolism of Spirodela oligorrhiza : I. Utilization of ammonium, nitrate and nitrite

Spirodela oligorrhiza grown in axenic culture was able to use either ammonium, nitrate, or nitrite as sole source of nitrogen, although the morphology of the plants was affected. Plants utilizing ammonium contained higher levels of NH4, arginine, asparagine and glutamine than did those utilizing NO3, whereas concentrations of other amino acids were similar.The utilization of NH4 inhibited that of NO3 by inhibiting, at least partially, NO3 uptake, and by inhibiting almost completely the reduction of NO3 to NO2. NO2 also inhibited the utilization of NO3. NH4 and NO2 were taken up and assimilated simultaneously when they were supplied together in the medium.