An operant determination of the behavioral mechanism of benzodiazepine enhancement of food intake.

RATIONALE: A recent review paper by Cooper (Appetite 44:133-150, 2005) has pointed out that a role for benzodiazepines as appetite stimulants has been largely overlooked. Cooper's review cited several studies that suggested the putative mechanism of enhancement of food intake after benzodiazepine administration might involve increasing the perceived pleasantness of food (palatability). OBJECTIVES: The present study examined the behavioral mechanism of increased food intake after benzodiazepine administration. MATERIALS AND METHODS: The cyclic-ratio operant schedule has been proposed as a useful behavioral assay for differentiating palatability from regulatory effects on food intake (Ettinger and Staddon, Physiol Behav 29:455-458, 1982 and Behav Neurosci 97:639-653, 1983). The current study employed the cyclic-ratio schedule to determine whether the effects on food intake of chlordiazepoxide (CDP) (5.0 mg/kg), sodium pentobarbital (5.0 mg/kg), and picrotoxin (1.0 mg/kg) were mediated through palatability or regulatory processes. RESULTS: The results of this study show that both the benzodiazepine CDP and the barbiturate sodium pentobarbital increased food intake in a manner similar to increasing the palatability of the ingestant, and picrotoxin decreased food intake in a manner similar to decreasing the palatability of the ingestant. CONCLUSIONS: These results suggest that the food intake enhancement properties of benzodiazepines are mediated through a mechanism affecting perceived palatability.

Viewing behaviour of spider phobics and non-phobics in the presence of threat and safety stimuli.

OBJECTIVES: To determine whether spider phobics and spider non-phobics differ in attending to threat and safety stimuli in close proximity, or spatially separated. METHOD: A sample group of 16 spider-phobic and 16 spider-non-phobic volunteers were drawn from a student population on the basis of their scores on Watts and Sharrock's Spider Phobia Questionnaire. Attention was assessed by way of participants' viewing behaviour using an ASL 501 head-mounted eye-tracking system. In a control condition, participants viewed a neutral stimulus (a TV video) in the absence of the threat stimulus. In two experimental conditions, the threat stimulus (a live Chilean rose tarantula) was introduced (a) immediately beside the safety stimulus (the only exit of the experimental room), or (b) away from the safety stimulus. RESULTS: In the experimental conditions, phobics reduced their viewing of the TV and increased their viewing of the tarantula and of the exit; the biggest changes occurred when tarantula and exit were together. Phobics also made more eye motions across the experimental room. CONCLUSION: Our results are consistent with previous research employing reaction time to a neutral stimulus as dependent measure. In addition, our results suggest that phobics scan the environment as part of safety behaviour. We suggest that exposure treatments to reduce spider phobia may be facilitated by encouraging patients to stop environmental scanning.

Behavioral and neurochemical mechanisms of the action of mild stress in the enhancement of feeding.

Rats were trained to respond under a cyclic-ratio schedule of reinforcement composed of an ascending, followed by a descending, sequence of ratio values. Subjects were trained while exposed to 70 dB white noise, then tested while exposed to 70 or 90 dB white noise. Exposure to 90 dB white noise elevated the response function (p<.02). Naloxone was then administered intraperitoneally at 0.3. 1.0. and 3.0 mg/kg under 70 dB and 90 dB white noise. Naloxone administration (1.0 and 3.0 mg/kg) significantly depressed the response function obtained under 90 dB white noise (ps<.01) but did not affect the function obtained under 70 dB white noise. These findings suggest that mild stress increases food intake through a mechanism affecting palatability enhanced by the release of endogenous opioids.

Controversy and consensus in disaster mental health research.

Controversies regarding the mental health consequences of disasters are rooted both in disciplinary orientations and in the widely varied research strategies that have been employed in disaster mental health studies. However, despite a history of dissensus, there are also key issues on which researchers agree. Disasters constitute stressful and traumatic experiences. However, vulnerability to such experiences, as well as to more chronic stressors, is socially structured, reflecting the influence of socio-economic status and other axes of stratification, including gender, race, and ethnicity. Disaster events differ in the extent to which they generate stress for victims. A holistic perspective on disaster mental health would take into account not only disaster event characteristics, but also social-systemic sources of both acute and chronic stress, secondary and cumulative stressors, and victims internal and external coping capacities.

Utilization of a novel model of food reinforced behavior involving neuropeptide Y, insulin, 2-deoxy-d-glucose and naloxone.

The cyclic-ratio schedule methodology exposes animals to an ascending followed by a descending sequence of ratio values over six consecutive cycles. The response functions, obtained by plotting response rates against reinforcement rates at each schedule value, are argued to provide features useful in the evaluation of drug effects on feeding behavior. In the present study the effects of s.c. insulin (5.0IU/kg), i.c.v. neuropeptide Y (NPY) (5.0µg/5.0µl), i.c.v. insulin (0.5mU/5.0µl), i.c.v. 2-deoxyglucose (2-DG) (10.0µg/5.0µl), i.c.v. naloxone (NLX) (50.0µg/5.0µl) in conjunction with i.c.v. NPY (5.0µg/5.0µl), and i.c.v. NLX alone (50.0µg/5.0µl) were assessed, i.c.v. NPY, insulin and 2-DG caused an elevation of the response function obtained by plotting response rates against reinforcement rates but did not affect the slope of the function. This elevation was similar to that observed after increasing the incentive value of the reinforcer (i.e., similar to increasing a 5.0% sucrose concentration reinforcer to 10.0%, and to substituting 45mg sweet food pellets for 45mg grain pellets). S.c. insulin produced no shift in the function from baseline, and i.c.v. NLX blocked the effect of i.c.v. NPY. I.c.v. NLX given alone reduced the slope of the response function, by selectively reducing response rates at the higher schedule values, a shift in the function similar to that observed following an increase in body weight. Since the literature on NPY and insulin would suggest that their effects are mediated through mechanisms associated with internal regulation, these findings were not predicted.

Cyclic-ratio schedule analysis of a serotonin agonist and depletor on consummatory behaviour.

Four male Wistar rats, 180 days old at the start of the experiment, at 85% of their free-feeding body weight were trained to respond on a geometric cyclic-ratio schedule comprised of the following ratio values: 2, 4, 8, 16, 32 and 64, for 0.1 ml of 5% sucrose reinforcement. The response functions (response rates plotted against reinforcement rates) were linear and of negative slope over the range of ratio values from 2 to 16. IP administration of 1.0 mg/kg 5-MeODMT reduced the x- and y-intercepts of the linear portion of the response function without altering the slope relative to 2.0 ml/kg 0.85% saline IP. This was interpreted as a perceived palatability effect. IP administration of 100 mg/kg pCPA elevated the reinforcement rate intercept but also decreased the slope of the response function. This finding was interpreted as an increase in the perceived palatability of the reinforcer, coupled with a decrease in motivation at higher schedule conditions, possibly due to peripheral effects of pCPA.

The effect of auditory stimulation on the consumption of soft drinks.

Three groups of five male and five female students were exposed to different levels of auditory stimulation (no music or music played at 70 dB or 90dB) under naturalistic conditions and were permitted to avail themselves freely of a supply of soft drinks. Increasing auditory stimulation produced an increase in total consumption. Reported prior frequencies of soft drink consumption and of exposure to loud music had no bearing on the result of the experimental manipulation, suggesting that the effect was not due to previous history.

Effects of rate and distance of procurement wheel-running on saccharin-and-sucrose solution drinking by non-deprived rats.

Four non-deprived rats received daily sessions of 20 min access to a saccharin-and-sucrose solution following various prior activities, in an attempt to disentangle the normally confounded roles of time spent, amount and rate of procurement responding in causing an increase in consumption once access is gained. After the normal rate of running (approx 35 m/min) was established, six conditions were run in random order, involving waiting zero and 2.5 min in an immobilised running-wheel, and running, with the wheel rotated by a motor, in four conditions formed by combining two speeds (12 and 30 m/min) with two distances (12 and 30 m), prior to access to the solution. Drinking increased with the speed of prior running, and to a lesser extent with the distance run, but was not related systematically to the time spent running. It is suggested that information from the animal's own behavior in gaining access to a commodity, particularly the rate of energy expenditure, may influence its utilisation of the commodity by affecting the rate of subsequent consummatory responding.

Effect of procurement cost on the drinking of a saccharin-sucrose solution by non-deprived rats.

Four non-deprived female rats were required to run in a wheel to obtain 20 min unconstrained access to a saccharin and sucrose solution. Each was run in a series of conditions in which the requirement was a proportion (0.25, 0.5, 1.0, 1.25 and 1.5) of the amount of running performed in a condition in which the wheel alone was available. A condition in which no running was required to gain access to the solution and one in which the subject was locked in the stationary wheel for the time taken to complete the highest requirement before being allowed access to the solution were also included. The results showed that as the requirement increased the amount of solution consumed also increased, and this relationship did not depend on the time taken to perform the requirement.

Effect of procurement wheel running on the rate of drinking in rats.

Four rats, 22.5 hr deprived of water, were tested in 3 conditions, in which they were required to run zero, 5 or 300 one-sixth revolutions in a wheel to gain 30 min access to water in a drinking tube. The number of licks performed in the 30 min increased monotonically with the procurement cost, and was 20% greater following the larger cost than when there was no cost. However, examination of the rates of drinking throughout the 30 min revealed that differences occurred between the conditions only at the beginning of the period. In the first 3 min there was a monotonic relationship between the proportion of time spent drinking and the procurement cost, but no effect of the cost on the rate could be detected after the first 6 min. The results are consistent with the hypothesis that the effect is mediated by a transient elevation of the subject's arousal level.

Effects of procurement cost on food consumption in rats.

Rats deprived of food for 23 hr were given unconstrained access to food for 1 hr following the completion of a lever-press requirement. Four experimental subjects were each tested for 7 sessions in each of a series of lever-press requirement conditions (1, 5, 10, 20, 50, 100, 150, 200) with a free access condition before and after this series, and with a final return to the 100 lever-press condition. To each experimental subject was yoked an equally deprived control subject which received access to food independently of its own responding, at the same time as its experimental partner. The food consumption of the experimental subjects, but not that of the controls, increased systematically as the lever-press requirement increased. It is argued that the results suggest that the way the procurement cost of food is related to both the frequency and size of meals is due to a direct but independent effect of the cost on both meal size and latency to initiate eating.