Rapid metabolic recovery following vigorous exercise in burrow-dwelling larval sea lampreys (Petromyzon marinus).

Although the majority of the sea lamprey's (Petromyzon marinus) life cycle is spent as a burrow-dwelling larva, or ammocoete, surprisingly little is known about intermediary metabolism in this stage of the lamprey's life history. In this study, larval sea lampreys (ammocoetes) were vigorously exercised for 5 min, and their patterns of metabolic fuel depletion and replenishment and oxygen consumption, along with measurements of net whole-body acid and ion movements, were followed during a 4-24-h postexercise recovery period. Exercise led to initial five- to sixfold increases in postexercise oxygen consumption, which remained significantly elevated by 1.5-2.0 times for the next 3 h. Exercise also led to initial 55% drops in whole-body phosphocreatine, which was restored by 0.5 h, but no significant changes in whole-body adenosine triphosphate were observed. Whole-body glycogen concentrations dropped by 70% immediately following exercise and were accompanied by a simultaneous ninefold increase in lactate. Glycogen and lactate were quickly restored to resting levels after 0.5 and 2.0 h, respectively. The presence of an associated metabolic acidosis was supported by very high rates of metabolic acid excretion, which approached 1,000 nmol g(-1) during the first 2 h of postexercise recovery. Exercise-induced ion imbalances were also rapidly alleviated, as initially high rates of net Na(+) and Cl(-) loss (-1,200 nmol g(-1) h(-1) and -1,800 nmol g(-1) h(-1), respectively) were corrected within 1-2 h. Although larval sea lampreys spend most of their time burrowed, they are adept at performing and recovering from vigorous anaerobic exercise. Such attributes could be important when these animals are vigorously swimming or burrowing as they evade predators or forage.

Repeated formaldehyde effects in an animal model for multiple chemical sensitivity.

Chemical intolerance is a phenomenon observed in multiple chemical sensitivity (MCS) syndrome, an ill-defined disorder in humans attributed to exposure to volatile organic compounds. Amplification of symptoms in individuals with MCS resembles the phenomenon of psychostimulant- and stress-induced sensitization in rodents. We have recently tested in rats the hypothesis that repeated chemical exposure produces sensitization of central nervous system (CNS) circuitry. A rat model of MCS in our laboratory has employed several endpoints of CNS function after repeated formaldehyde (Form) exposure (1 h/day x 5 days/week x 4 weeks). Repeated Form exposure produced behavioral sensitization to later cocaine injection, suggesting altered dopaminergic sensitivity in mesolimbic pathways. Rats given repeated Form also demonstrated increased fear conditioning to odor paired with footshock, implicating amplification of neural circuitry guiding fear responding to a conditioned odor cue. Recent studies examining the effects of repeated Form on locomotor activity during each daily exposure showed a decrease in rearing activity after 12-15 days of Form exposure compared to air-exposed controls. EEG recordings taken 1 week after withdrawal from daily Form revealed altered sleep architecture. Some of the differences in sleep disappeared after subsequent brief (15 min) challenge with Form the next day. Overall, the findings indicate that repeated low-level chemical exposure produces behavioral changes that may be akin to those observed in individuals with MCS, such as greater sensitivity to chemicals manifest as increased anxiety upon chemical exposure and altered sleep and/or fatigue. Study of the underlying CNS changes will provide a basis for mechanistically based animal models for MCS.

The glass ceiling is not fragile: A response to Odum (2000).

Odum (2000) criticized our recent conclusions about the participation of women in the experimental analysis of behavior (McSweeney & Swindell, 1998). We address her criticisms here. We argue against the need for statistical tests. We show that our conclusions still apply to all journals except the Journal of the Experimental Analysis of Behavior even when we include the senior editorial staff along with members of the editorial board. We argue that the data that Odum provides to show gender equity are limited, inconsistent with past findings, and hard to interpret in the absence of other data. Finally, we argue that Odum failed to address our most convincing argument for gender inequity and misinterpreted our suggestions for improvements.

Women in applied behavior analysis.

The status of women in applied behavior analysis was examined by comparing the participation of women in the Journal of Applied Behavior Analysis (JABA) to their participation in three similar journals. For all journals, the percentage of articles with at least one female author, the percentage of authors who are female, and the percentage of articles with a female first author increased from 1978 to 1997. Participation by women in JABA was equal to or greater than participation by women in the comparison journals. However, women appeared as authors on papers in special sections of Behavior Modification substantially more often when the editor was female than when the editor was male. In addition, female membership on the editorial boards of JABA, Behavior Modification, and Behaviour Research and Therapy failed to increase from 1978 to 1997. We conclude that a "glass ceiling" reduces the participation of women at the highest levels of applied behavior analysis and related fields.

Behavioral economics and within-session changes in responding.

Pigeons and rats responded on fixed-ratio schedules with requirements ranging from 5 to 120 responses. Consistent with past results from several schedules and procedures, responding usually changed systematically within experimental sessions. The within-session changes were usually larger and were less symmetrical around the middle of the session for schedules that provided higher, rather than lower, rates of reinforcement. These results suggest that similar variables contribute to within-session changes in responding under different schedules. When an economic demand function was fit to the data, the intensity and elasticity of demand for food and the percentage of the variance accounted for decreased within sessions, although the trend for elasticity did not reach statistical significance for pigeons. These results suggest that relatively short sessions should be used to study economic demand in open economies and that demand may differ at different times in a session and in sessions of different lengths. Within-session changes in intensity, but not necessarily elasticity, of demand are consistent with behavioral economic theories.

Women in the experimental analysis of behavior.

We examined the status of women in the experimental analysis of behavior by comparing authorship by women in the Journal of the Experimental Analysis of Behavior (JEAB) to authorship by women in three similar journals. For all journals, the percentage of articles with at least one female author, the percentage of authors who are female, and the percentage of articles with a female first author increased from 1978 to 1997. However, the participation by women in JEAB lagged behind participation in the other journals on each measure. Female membership on the editorial board of JEAB also failed to increase from 1978 to 1997. Suggestions are made that may increase the participation of women in the experimental analysis of behavior.

Exposure to context may contribute to within-session changes in responding.

Rats and pigeons responded on multiple variable interval 30-s variable interval 30-s and multiple variable interval 60-s variable interval 60-s schedules. The 60-min sessions began 0, 5, 10, 15 or 30 min after the subject was placed in the experimental enclosure, determined randomly. Early-session response rates were usually higher, and the early-session increases in responding were usually smaller, when the beginning of the session was delayed than when it was immediate. These results show that factors related to reinforcement (e.g. satiation, sensitization-habituation to the reinforcers) do not provide a complete explanation for within-session changes in operant responding. Instead, an additional factor, possibly arousal or sensitization to the experimental context, also contributes. The results suggest an explanation for the spontaneous recovery of extinguished behavior.

Behavioral contrast using different reinforcers: effect of baseline rate of reinforcement.

The present study determined whether behavioral contrast would occur when different reinforcers were delivered in the different components and whether its size would vary at different baseline rates of reinforcement. Pigeons pecked keys on a multiple variable-interval schedule. Mixed grain was the reinforcer in one component and wheat was the reinforcer in the other component. In contrast conditions, the rate of wheat reinforcement was increased or decreased, from the baseline delivery rate, by a factor of four. Contrast was studied at four different baseline rates of reinforcement. Contrast was usually observed and its size almost always varied directly with the programmed baseline rate of reinforcement. The present results indicate that changes in the condition of reinforcement of a different reinforcer can produce contrast. They also broaden the potential implications of behavioral contrast.

Previous- and following-component contrast effects using a three-component multiple schedule.

Behavioral contrast can be defined as an inverse relation between the rate of behavior in one component of a multiple schedule of reinforcement and the conditions of reinforcement in another component. In the present experiment, four pigeons pecked a key for mixed-grain reinforcers delivered by a three-component multiple schedule. During baseline conditions, the same variable-interval schedule was in effect during each component. In contrast conditions, the rate of reinforcement in the second component was increased or decreased. Behavioral contrast was usually observed in both the first and third components. Across-component contrast effects were neither larger nor more reliable when the change in reinforcement occurred in the following component than when it occurred in the previous component. Furthermore, in both the first and third components, the size of contrast was almost always largest early in the component and decreased as the component progressed. Both across- and within-component data were analyzed using the model proposed by Williams and Wixted (1986). The results question the adequacy of the model. The results also pose difficulties for several existing theories of contrast.

Within-session patterns of responding with changes in the variability and probability of food delivery.

The present study was an attempt to determine the factors to which subjects sensitize and/or habituate within experimental sessions. Rats pressed a lever and pigeons pecked a key for food reinforcers delivered during a 60 min session. In experiment 1, subjects initially responded on a simple variable-interval 30 s schedule that consisted of 25 intervals. In subsequent conditions, the number of intervals in the series was decreased until subjects responded on a simple fixed-interval 30 s schedule. In experiment 2, subjects always responded on a variable-interval 15 s schedule that resulted in a stimulus change. The probability that a food reinforcer would accompany the stimulus change varied across conditions. Results showed that within-session patterns of responding did not change for either species with changes in the temporal pattern of reinforcer delivery (experiment 1). The within-session response patterns generally became flatter with decreases in the probability of food delivery for both species (experiment 2). The present results indicate that subjects are sensitizing and/or habituating to the reinforcer itself and/or to some aspect of its delivery. They also help to highlight the strength of sensitization-habituation as an explanation for within-session changes in responding.

Behavioral contrast with changes in duration and rate of reinforcement.

Behavioral contrast can be defined as an inverse relation between rate of responding in one component of a multiple schedule and conditions of reinforcement in the other components. The present study was an attempt to produce contrast with changes in duration of reinforcement. Pigeons pecked a key for mixed grain delivered by a multiple variable-interval variable-interval schedule. In Experiment 1, the reinforcer duration in the second component was decreased or increased, for different subjects, by a factor of two, four, and six from that delivered during baseline. These changes usually produced contrast. In Experiment 2, rate, duration, or rate and duration of reinforcement varied in the second component. Contrast was usually observed when only one variable was manipulated. When both variables were manipulated in the same condition, but in opposite directions, responding in the constant component usually changed inversely with the change in rate of reinforcement, not the change in reinforcer duration. The results demonstrate that changes in duration of reinforcement can produce contrast. They also increase the empirical base for which a successful theoretical account of contrast must encompass and the generality of contrast, which increases its potential practical implications.

Within-Session Changes in Adjunctive and Instrumental Responding

Rats pressed levers for food delivered by several fixed interval schedules. A drinking spout or running wheel was also available during some conditions, but not during others. The rate of lever pressing, drinking and running often changed within experimental sessions. The within-session patterns of lever pressing did not differ when drinking or running was available and when it was not. The correlation between the amount of lever pressing and the amount of drinking or running at a particular time in the session was inconsistently positive or negative. Finding within-session changes in responding for adjunctive behaviors implies that the factors that produce these changes are present for both adjunctive and instrumental behavior. Finding inconsistent correlations between instrumental responding and adjunctive behaviors questions arousal and interference from adjunctive behaviors as explanations for within-session changes in instrumental responding.

Within-session changes in responding during concurrent schedules with different reinforcers in the components.

Rats and pigeons responded on several concurrent schedules that provided different reinforcers in the two components (food and water for rats, Experiment 1; wheat and mixed grain for pigeons, Experiment 2). The rate of responding and the time spent responding on each component usually changed within the session. The within-session changes in response rates and time spent responding usually followed different patterns for the two components of a concurrent schedule. For most subjects, the bias and sensitivity to reinforcement parameters of the generalized matching law, as well as the percentage of the variance accounted for, decreased within the session. Negative sensitivity parameters were sometimes found late in the session for the concurrent food-water schedules. These results imply that within-session changes in responding could cause problems for assessing the validity of quantitative theories of concurrent-schedule responding when the components provide different reinforcers. They question changes in a general motivational state, such as arousal, as a complete explanation for within-session changes in responding. The results are compatible with satiation for, or sensitization-habituation to, the reinforcers as explanations.

Genetic manipulation of the pathway for diacetyl metabolism in Lactococcus lactis.

Diacetyl is an important food flavor compound produced by certain strains of citrate-metabolizing lactic acid bacteria. Citrate is converted to pyruvate, from which diacetyl is produced via intermediate alpha-acetolactate. This paper reports the cloning and analysis of the gene (aldB) encoding alpha-acetolactate decarboxylase from Lactococcus lactis MG1363. Deletion of the MG1363 chromosomal aldB gene was achieved by double crossover homologous recombination. The mutant strain was found to produce diacetyl; alpha-acetolactate decarboxylase activity was eliminated. Overexpression of the cloned ilvBN genes (encoding an alpha-acetolactate synthase) in the aldB deletion strain produced even higher levels of alpha-acetolactate, acetoin, and diacetyl.

Reinforcer value may change within experimental sessions.

Large and systematic changes in response rates often occur within sessions during operant conditioning procedures. In the present experiment, we asked whether the value of the reinforcer that supports responding also changes within sessions. Pigeons pecked a key for mixed grain available throughout the session. Occasionally, wheat was also provided for pecking a second key. The ratio of the rates of responding for mixed grain and wheat, a frequently used measure of relative reinforcer value, changed significantly within sessions when mixed grain was provided at high, but not at low, rates. Habituation to the reinforcer provides the most likely explanation for these changes in reinforcer value. Eventually, habituation may provide a unified explanation for the within-session changes in behavior that occur when many species of subjects respond on a wide variety of tasks.

Within-session changes in responding during variable interval schedules.

Four rats and four pigeons responded for food delivered by variable interval schedules that provided programmed rates of reinforcement ranging from 15 to 480 reinforcers per hour. Rate of responding increased, decreased, or increased and then decreased within sessions. The within-session pattern of responding changed with changes in the programmed rate of reinforcement and with the species of subject. Finding within-session changes in responding during variable interval schedules extends the generality of these changes to another schedule. It implies that variable interval schedules should be used cautiously as baselines for assessing the effects of other variables, such as drugs. Finally, the results suggest that systematic pauses in responding during the session may contribute to the decreases in the average rates of responding with increases in the rates of reinforcement that are sometimes observed when subjects respond on variable interval schedules that deliver high rates of reinforcement.