Meal-engendered circadian-ensuing activity in rats

The role of the dorsal striatum in a mouse model for fragile X syndrome: Behavioral and dendritic spine assessment

Fragile X syndrome (FXS), a leading monogenic cause of autism spectrum disorders (ASDs), typically occurs as the result of a mutation silencing the Fmr1 gene, preventing production of the fragile X messenger ribonucleoprotein (FMRP). FXS is characterized, in part, by hyperactivity, impaired behavioral flexibility, and the development of repetitive, or stereotyped, behaviors. While these phenotypes are influenced by striatal activity, few studies have examined FXS or FMRP in the context of striatal function. Here, we report enhanced repetitive behaviors in Fmr1 knockout (KO) compared to wild type (WT) mice according to multiple measures, including quantity and intensity of stereotypic behaviors in an open field and nose poking activity in an unbaited hole board test. However, using a baited version of the hole board assay, we see that KO mice do show some behavioral flexibility in that they make changes in their nose poking behavior following familiarization with an appetitive bait. By contrast, repeated exposure to cocaine (15 mg/kg) promotes repetitive behavior in both WT and KO mice, in a manner mostly independent of genotype. Branch length alterations in medium spiny neurons (MSNs) of the dorsolateral striatum (DLS) are similar between WT cocaine-treated and KO saline-treated mice, possibly suggesting shared synaptic mechanisms. Overall, we suggest that scoring open field behavior is a sensitive measure for repetitive sensory-motor behaviors in Fmr1 KO mice. In addition, our findings show that synaptic contacts onto MSNs in the DLS should be examined in conjunction with measures of stereotypical behavior.

Appetitive search behaviors and stereotypies in polar bears (Ursus maritimus)

Stereotypies in captive animals have been defined as repetitive, largely invariant patterns of behavior that serve no obvious goal or function. Stereotypies are commonly attributed to boredom or stress and are typically treated by enriching captivity with distracting, appealing stimuli. These stimuli often include food presented at times other than regular feedings, and as a result, engage species-typical foraging behaviors that reduce stereotypies. The present work on captive polar bears is based on the view that stereotypies are due in part to inadequate support for the expression of species-typical foraging "loops" and can be reduced by increasing support for a more complete expression of foraging responses. We tested this view through 4 experiments that presented small samples of food and scents on several schedules, examining their effects prior to, during, and after the schedule. Most schedules reduced stereotypies and increased general activity prior to and during the schedule. These data support three conclusions: (1) individual stereotypies appear related to incomplete, repeating loops of foraging behavior; (2) providing stimuli supporting a more complete sequence of search behaviors reduces stereotypies and increases non-stereotypic activity; and (3) a descriptive, analytic approach based on how foraging behaviors relate to the captive feeding procedures can facilitate understanding of stereotypies and suggest methods to reduce them.

Circadian entrainment by food and drugs of abuse

Circadian rhythms organize behavior and physiological processes to be appropriate to the predictable cycle of daily events. These rhythms are entrained by stimuli that provide time of day cues (zeitgebers), such as light, which regulates the sleep-wake cycle and associated rhythms. But other events, including meals, social cues, and bouts of locomotor activity, can act as zeitgebers. Recent evidence shows that most organs and tissues contain cells that are capable of some degree of independent circadian cycling, suggesting the circadian system is broadly and diffusely distributed. Within laboratory studies of behavior, circadian rhythms tend to be treated as a complication to be minimized, but they offer a useful model of predictable shifts in behavioral tendencies. In the present review, we summarize the evidence that formed the basis for a hypothesis that drugs of abuse can entrain circadian rhythms and describe the outcome of a series of experiments designed to test that hypothesis. We propose that such drug-entrained rhythms may contribute to demonstrated daily variations in drug metabolism, tolerance, and sensitivity to drug reward. Of particular importance, these rhythms may be evoked by a single episode of drug taking, strengthen with repeated episodes, and re-emerge after long periods of abstinence, thereby contributing to drug abuse, addiction, and relapse.

Fentanyl, but not haloperidol, entrains persisting circadian activity episodes when administered at 24- and 31-h intervals

Administration of several drugs of abuse on a 24-h schedule has been shown to entrain both pre-drug (anticipatory) and post-drug (evoked) circadian activity episodes that persist for several days when the drug is withheld. The present study tested the entrainment effects of fentanyl, an opioid agonist with a noted abuse liability, and haloperidol, an anti-psychotic dopamine antagonist without apparent abuse liability. Adult female Sprague-Dawley rats housed under constant light in cages with attached running wheels received repeated low, medium, or high doses of either fentanyl or haloperidol on a 24-h administration schedule followed by a 31-h schedule (Experiment 1) or solely on a 31-h schedule (Experiment 2). The results showed that all three doses of fentanyl entrained both pre-drug and post-drug episodes of wheel running when administered every 24h, and the combined pre- and post-fentanyl activity episodes persisted for at least 3 days when the drug was withheld during test days. On the 31-h schedule, fentanyl produced an "ensuing" activity episode approximately 24h post-administration, but failed to produce an anticipatory episode 29-31h post-administration. In contrast, haloperidol injections failed to produce both pre-drug episodes on the 24-h schedule and circadian ensuing episodes on the 31-h schedule, and post-haloperidol suppression of activity appeared to mask the free-running activity rhythm. Taken together, these results provide additional evidence that drugs of abuse share a common ability to entrain circadian activity episodes.

Theoretical and conceptual issues in time-place discrimination

The need to discover resources that are available under specific environmental constraints represents a fundamental environmental pressure on the evolution of behavior. Time-place discrimination refers to the ability to secure resources when they are available under specific temporal and spatial contingencies. This article reviews a number of examples of time-place discrimination. The review highlights theoretical and conceptual issues that are needed to behaviorally identify the mechanisms responsible for time-place performance. Next, limitations on time-place performance that may be imposed by a circadian system are described. Finally, a number of lines of research that broaden these limitations are discussed. These lines of research include studies that suggest that (i) a broad range of long intervals (outside the limited range of circadian entrainment) are timed, (ii) at least some long intervals (16-21 h) are timed with an endogenous self-sustaining oscillator, (iii) short intervals (in the range of 1-3 min) are timed with an endogenous self-sustaining oscillator, and (iv) memory for specific unique events (including when and where they occurred) is based on a circadian representation of time. It is concluded that a unified theory of timing that can retain the times of occurrence of individual events is needed. The time of occurrence of an event may be encoded not only with respect to a circadian oscillator but also with respect to other oscillators in the long-interval and short-interval ranges.

From Malthus to motive: how the HPA axis engineers the phenotype, yoking needs to wants

The hypothalamo-pituitary-adrenal (HPA) axis is the critical mediator of the vertebrate stress response system, responding to environmental stressors by maintaining internal homeostasis and coupling the needs of the body to the wants of the mind. The HPA axis has numerous complex drivers and highly flexible operating characterisitics. Major drivers include two circadian drivers, two extra-hypothalamic networks controlling top-down (psychogenic) and bottom-up (systemic) threats, and two intra-hypothalamic networks coordinating behavioral, autonomic, and neuroendocrine outflows. These various networks jointly and flexibly control HPA axis output of periodic (oscillatory) functions and a range of adventitious systemic or psychological threats, including predictable daily cycles of energy flow, actual metabolic deficits over many time scales, predicted metabolic deficits, and the state-dependent management of post-prandial responses to feeding. Evidence is provided that reparation of metabolic derangement by either food or glucocorticoids results in a metabolic signal that inhibits HPA activity. In short, the HPA axis is intimately involved in managing and remodeling peripheral energy fluxes, which appear to provide an unidentified metabolic inhibitory feedback signal to the HPA axis via glucocorticoids. In a complementary and perhaps a less appreciated role, adrenocortical hormones also act on brain to provide not only feedback, but feedforward control over the HPA axis itself and its various drivers, as well as coordinating behavioral and autonomic outflows, and mounting central incentive and memorial networks that are adaptive in both appetitive and aversive motivational modes. By centrally remodeling the phenotype, the HPA axis provides ballistic and predictive control over motor outflows relevant to the type of stressor. Evidence is examined concerning the global hypothesis that the HPA axis comprehensively induces integrative phenotypic plasticity, thus remodeling the body and its governor, the brain, to yoke the needs of the body to the wants of the mind. Adverse side effects of this yoking under conditions of glucocorticoid excess are discussed.

Long-interval timing is based on a self-sustaining endogenous oscillator

The mechanism of anticipating long-intervals (16-21 h) was investigated. Rats earned food by interrupting a photobeam in a food trough during 3- or 4-h meals. Intermeal intervals were 16, 21, and 24 h (offset to offset) for independent groups of rats (n=8 per group). After approximately a month of experience with the intermeal intervals, the meals were discontinued. The rate of visiting the food trough increased as a function of time before the meal. When meals were discontinued, visits continued to be periodic. The periodicity was approximately 21 h after 16- and 21-h intermeal intervals and approximately 28 h after 24-h intermeal intervals. These data suggest that long-interval timing is based on a self-sustaining, endogenous oscillator.

An activity indicator of acute withdrawal depends on amphetamine dose in rats

A moderate dose of amphetamine (AMPH) produces hypoactivity around 20 h post-administration. This hypoactivity may be an indicator of an acute withdrawal state. The purpose was to see how AMPH doses affected the expression of this hypoactivity and, by inference, AMPH-induced acute withdrawal. Rats were housed in individual open fields, with free access to food and water. Light-dark cycles were scheduled such that drug-elicited patterns could be readily detected. Animals first received a series of eight control treatments, and then a series of 10 experimental treatments spaced at 33-h intervals. Different experimental treatment groups received saline, 1.0 mg/kg, 2.0 mg/kg, or 4.0 mg/kg AMPH. The effects of these treatments on 33-h patterns of locomotor activity were observed. Control treatments produced no systematic time-dependent changes in activity beyond the first hour post-treatment. All doses of AMPH produced typical short-term effects: They markedly increased locomotion and/or stereotypy during the first 3 to 6 h post-treatment. Acute and chronic administrations of the 2.0 and 4.0 mg/kg doses also produced similar changes in longer term activity patterns: They produced hypoactivity 20 h later, followed by a recovery of activity around hour 25 post-treatment. The timing of amphetamine-induced hypoactivity and acute withdrawal may be independent of dose over a wide range of doses. Time-dependent changes in AMPH-induced state may influence motivation and drug-related assessments. The methodology described here may provide an easy and rapid way to investigate the determinants of AMPH-induced hypoactivity and acute withdrawal.

Circadian pattern of spontaneous behavior in monarthritic rats: a novel global approach to evaluation of chronic pain and treatment effectiveness

OBJECTIVE

Preclinical evaluation is an essential step in the assessment of new antiinflammatory or analgesic drugs. This study was undertaken to develop a new mode of evaluation of drug effectiveness based on behavior indicating well-being in a rat model of chronic inflammatory pain. We chose to examine the circadian pattern of spontaneous behavior.

METHODS

The work was performed with a model of chronic monarthritis induced by Freund's complete adjuvant. Variations in behavioral patterns during the time course of arthritis were analyzed. In a second phase, the impact of acetaminophen and 2 nonsteroidal antiinflammatory drugs (aspirin and celecoxib), which are currently used in clinical practice to treat chronic inflammation, was studied after 7 days of treatment.

RESULTS

The nocturnal pattern of activity of healthy rats comprised 3 main bursts. Chronic painful monarthritis altered this spontaneous pattern of nocturnal behavior (normal period of activity). Monarthritic rats showed a decrease in the total time spent in activity during the night, and lost their pattern of activity. These behavioral disturbances were reversed after long-term treatment with acetaminophen or celecoxib, with celecoxib appearing to be more effective. Aspirin was ineffective.

CONCLUSION

These results enabled us to test this new procedure as a means of assessing well-being or ill- being during stages of chronic inflammatory pain in rats, and the effectiveness of repeated pharmacologic treatments.

Circadian activity rhythms in high-alcohol-preferring and low-alcohol-preferring mice

The circadian periods of high-alcohol-preferring (HAP) and low-alcohol-preferring (LAP) selected lines of mice were compared. The mice were ethanol-naive. Circadian periods were calculated from records of running-wheel activity in constant dark. The number of daily wheel revolutions and body weights of the two lines of mice were also compared. The HAP line had a shorter period of wheel running than that of the LAP lines. The HAP mice also had a tendency to run more on wheels than did LAP mice. These findings support the suggestion that genes affecting ethanol consumption in mice have pleiotropic effects on circadian period.

Niche-related learning in laboratory paradigms: the case of maze behavior in Norway rats

The general hypothesis underlying this paper is that behavior in traditional paradigms of laboratory learning is based on niche-related mechanisms. The specific hypothesis is that the behavior of Norway rats in laboratory mazes is based on niche-related mechanisms related to trail following and navigating. I evaluate seven types of evidence for this hypothesis: (a) resemblance of maze behavior to behavior in unconstrained settings; (b) importance of experimenter tuning of apparatus and procedures; (c) overdetermination of laboratory behavior; (d) reverse-engineering of niche-related mechanisms from laboratory data; (e) prediction of laboratory results from ecological data; (f) contribution of specific relative to general mechanisms; and (g) phylogenetic conservation and ecologically-based convergence and divergence of maze mechanisms. I conclude there is strong evidence for the hypothesis that behavior of rats in laboratory mazes is based on niche-related mechanisms. I suggest that a niche-related approach to laboratory learning paradigms has conceptual generality and the potential to facilitate connections with the study of neurophysiology, genetics, and evolution.

The temporal organization of ingestive behaviour and its interaction with regulation of energy balance

Body weight of man and animals is under homeostatic control mediated by the adjustment of food intake. It is discussed in this review that besides signals reporting energy deficits, optimized programs of body clocks take part in feeding behaviour as well. Circadian light- and food-entrainable clocks determine anticipatory adaptive behavioural and physiological mechanisms, promoting or inhibiting food intake. In fact these clocks form the constraints within which the homeostatic regulation of feeding behaviour is operating. Therefore, a strong interaction between circadian and homeostatic regulation must occur. In this homeostatic control, a wide variety of regulatory negative feedback mechanisms, or satiety signals, play a dominant role. In this respect several gut hormones and body temperature function as 'short-term' satiety factors and determine meal sizes and intermeal intervals. Leptin, secreted by fat cells in proportion to the size of adipose tissue mass, is probably an important determinant of the 'long-term' regulation of feeding behaviour by setting the motivational background level for feeding behaviour. Thus, initiation or termination of meals at any particular point in time, depends on the resultant of all satiety signals and on constraints imposed by circadian light- and food-entrainable oscillators.

Integrating niche-related and general process approaches in the study of learning

For nearly a century the experimental analysis of learning in animals has been divided into niche-related and general-process approaches, each emphasizing different procedures and conceptual strategies. After considering several current forms of rapprochement, I outline evidence for the integrative hypothesis that niche-related learning provides the basis for results in traditional general-process learning paradigms. Although the full ramifications of this view are not developed here, its advantages include: a clearer relation between laboratory and field results; conceptual and pragmatic guidance in developing new paradigms, and applying old ones to different species and circumstances; clarification of the laws, limits, and anomalies in general-process paradigms; and a more efficient path for inter-relating the study of learning with neurophysiology, genetics, and evolution.

Effects of administering cocaine at the same versus varying times of day on circadian activity patterns and sensitization in rats

The effects of different schedules of cocaine administration on circadian activity patterns and locomotor sensitization were studied. Rats received intraperitoneal injections of either saline or 20 mg/kg cocaine at either 24- or 33-hr intervals for 8 cycles (development). After a 2-day withdrawal, they were given a cocaine challenge in a novel environment. Rats given cocaine at 24-hr intervals were hypoactive 4 to 9 hr postinjection during development and, during cocaine challenge, showed sensitization of locomotor activity. Rats given cocaine at 33-hr intervals did not show these effects. On the 33-hr-period schedule, activity was enhanced beginning 24 hr after drug receipt. Different intermittent schedules of cocaine receipt may alter the vulnerability to cocaine, and altered vulnerability may be more likely when a subsequent cocaine injection interacts with a distal state of sensitivity produced by a prior injection.