Plasma corticosterone and immune reactivity in restrained female C3H mice

Psychological stressors are known to stimulate the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system resulting in the release of corticosterone and catecholamines respectively. They have also been reported to induce cytokine production. All these molecules affect various immune parameters and can alter overall immune competence of the individual. The purpose of this investigation was to study the regulation of the production of corticosterone during stress and its possible effects on immune reactivity. In a first series of experiments, the possible regulation of corticosterone production by interleukin (IL)-1beta and peripheral catecholamines during restraint was assessed using a pharmacological approach in mice. Plasma IL-1beta concentrations remained at basal after 1-h restraint and the stress-induced increase of plasma corticosterone was not modified by a peripheral injection of an IL-1 receptor antagonist (IL-1ra). By contrast, chemical sympathectomy potentiated the restraint-induced increase in plasma corticosterone concentration, this potentiation being reversed by IL-1ra. In a second series of experiments, the role of corticosterone in stress-immune relationships was studied in adrenalectomized mice subjected to restraint and immunized with sheep erythrocytes. Non-specific immunity, i.e. proliferation of splenocytes and thymocytes and plasma levels of IL-1beta, as well as specific immunity, i.e. antibody production and delayed hypersensitivity, were not altered after 2-h restraint. Adrenalectomy failed to induce immune effects in stressed animals, except that delayed hypersensitivity was stronger in adrenalectomized animals, revealing that the high levels of corticosterone produced during stress have an anti-inflammatory activity. The present data show that the stress-induced production of corticosterone was modulated by both peripheral catecholamines and IL-1beta. However, this production of corticosterone was unable to modulate immune reactivity except delayed hypersensitivity.     

Intra-habenular injection of 6-hydroxydopamine produces impaired acquisition of DRL operant behavior

The anatomical connections of the habenula complex indicate it provides a relay between limbic forebrain and midbrain. Somewhat paradoxically, consequences of nonspecific lesion of the habenula are ambiguous with little change in basic response evident within simple behavioral paradigms. However, the potential functional importance for this relay has more recently been indicated by the demonstration of deficits in the ability of lesioned animals to alter behavior appropriate to both internal and external stimuli in more demanding behavioral tasks. Doubts concerning the importance of the habenula remain because of the large number of descending fibers of passage through the habenula. To provide more substantive evidence, 6-hydroxydopamine was injected into the habenula of rats to provide more limited lesion of catecholaminergic terminals. Animals were subsequently trained on an operant DRL 20-s schedule for which deficits have been reported following nonspecific lesion of the habenula. Lesioned animals showed a tendency to overrespond and were significantly less efficient on the schedule with decreased number of reinforcements received relative to controls. While the neurotoxic lesion procedure used does not differentiate noradrenergic and dopaminergic damage, the importance of intact catecholaminergic systems within the habenula for effective DRL acquisition is consistent with the suggested importance of the habenula for feedback regulation of dopamine within the ventral tegmental area through ascending dopamine fibers to the habenula.     

Increased stress-induced intra-hippocampus corticosterone rise associated with memory impairments in middle-aged mice

The present study investigates the relationships between hippocampal corticosterone concentrations and memory retrieval performance in stress and non-stress conditions, in both young (6 month-old) and middle-aged (16 month-old) mice. For this purpose, the time-course evolution of stress-induced corticosterone rise in the dorsal hippocampus (dHPC) was investigated in both young and middle-aged mice. In parallel, the evolution of memory retrieval patterns was assessed using a contextual serial discrimination task (CSD). Finally, metyrapone (corticosterone synthesis inhibitor) was administered in order to evaluate the stress-induced impact of corticosterone rise on contextual memory retrieval in middle-aged animals.Results showed that: (i) non-stressed middle-aged mice exhibited a memory retrieval pattern opposite to that of non-stressed young animals, but similar to that of stressed young mice; (ii) the impact of stress on memory performance was transient (90 min) in young, as compared to middle-aged mice (120 min); (iii) dHPC basal (non-stress) corticosterone level was significantly increased by ageing; (iv) acute stress induced a rapid (15 min) and transient (90 min) dHPC corticosterone rise in young mice, while exhibiting greater magnitude and duration (120 min) in middle-aged animals; and (v) both the stress-induced endocrinal and memory effects were blocked by metyrapone in young and middle-aged mice.Finally, to our knowledge, the present work is the first study to directly measure the corticosterone rise in the hippocampus following exposure to stress and to directly correlate the corticosterone changes in the hippocampus with memory performance in both young and middle-aged mice.     

Behavioral reactivity and approach-withdrawal bias in infancy

Seven hundred seventy-nine infants were screened at 4 months of age for motor and emotional reactivity. At age 9 months, infants who showed extreme patterns of motor and negative (n = 75) or motor and positive (n = 73) reactivity and an unselected control group (n = 86) were administered the Laboratory Temperament Assessment Battery, and baseline electroencephalogram data were collected. Negatively reactive infants showed significantly more avoidance than positively reactive infants and displayed a pattern of right frontal electroencephalogram asymmetry. Positively reactive infants exhibited significantly more approach behavior than controls and exhibited a pattern of left frontal asymmetry. Results support the notion that approach-withdrawal bias underlies reactivity in infancy.     

Suppression of operant behavior and schedule-induced licking in rats

The first experiment studied the effects of punishment on rats' lever pressing maintained by a fixed-interval schedule of food reinforcement and on the associated schedule-induced licking. When licking was followed by shock, licking was suppressed but lever pressing was largely unaffected. When lever pressing was followed by shock, lever pressing was suppressed but licking was unaffected. In both cases, the punished behavior recovered its previous unpunished level when the shocks were discontinued. In a second experiment, the rats' lever pressing was maintained by a variable-interval schedule of food reinforcement under which polydipsic licking also developed. Both lever pressing and licking were partially suppressed during a stimulus correlated with occasional unavoidable electric shocks. With a higher shock intensity, both behaviors were suppressed further. Both lever pressing and licking recovered their previous levels when shocks were discontinued. These results show that schedule-induced licking, which has been described as adjunctive behavior, can be suppressed by procedures that suppress reinforced lever pressing, an operant behavior.     

Development and function of consequence classes in operant behavior

The term class has been discussed extensively in the behavioral literature for groups of stimuli or responses that share a common function. In contrast, the concept of consequence class, including its definition, its formation, and other relevant characteristics, has not been the topic of much attention in the literature. Issues pertaining to consequence classes are discussed to provide a more thorough analysis of the units of operant and discriminated operant functional relations. The concept of class for consequences provides a means to integrate data and theory from the behavior-analytic literature.     

Ontogeny and adult behavior of mice with congenital neural tube defects

Effects of abnormal neural tube development were studied in immature and adult mice. The behavior of affected adult mice was found to resemble that of mice that exhibit the "waltzer syndrome." Behavioral ontogenetic studies indicate that effected mice are deficient in labyrinthine responses as shown by the late development or lack of negative geotaxic behaviors and the delayed loss of pivoting behavior. Retarded maturation of neural responses was indicated by a delay in the appearance of the startle response. Evidence that circling behavior in adult mice of the "waltzer syndrome" may be a result of central nervous system disorders alone, or in concert with abnormalities of the inner ear, was provided by the fact that open field activity was increased in affected mice that exhibit circling behavior as adults.     

The temporal structure of goal-directed and habitual operant behavior

Operant behavior can reflect the influence of goal-directed and habitual processes. These can be distinguished by changes to response rate following devaluation of the reinforcing outcome. Whether a response is goal directed or habitual depends on whether devaluation affects response rate. Response rate can be decomposed into frequencies of bouts and pauses by analyzing the distribution of interresponse times. This study sought to characterize goal-directed and habitual behaviors in terms of bout-initiation rate, within-bout response rate, bout length, and bout duration. Data were taken from three published studies that compared sensitivity to devaluation following brief and extended training with variable-interval schedules. Analyses focused on goal-directed and habitual responding, a comparison of a habitual response to a similarly trained response that had been converted back to goal-directed status after a surprising event, and a demonstration of contextual control of habit and goal direction in the same subjects. Across experiments and despite responses being clearly distinguished as goal directed and habitual by total response rate, analyses of bout-initiation rate, within-bout rate, bout length, and bout duration did not reveal a pattern that distinguished goal-directed from habitual responding.     

Signaled alternative reinforcement and the persistence of operant behavior

Differential reinforcement of alternative behavior (DRA) is a treatment designed to eliminate problem behavior by reinforcing an alternative behavior at a higher rate. Availability of alternative reinforcement may be signaled, as with Functional Communication Training, or unsignaled. Whether or not alternative reinforcement is signaled could influence both the rate and persistence of problem behavior. The present study investigated whether signaling the availability of alternative reinforcement affects the rate and persistence of a concurrently available target response with pigeons. Three components of a multiple concurrent schedule arranged equal reinforcement rates for target responding. Two of the components also arranged equal reinforcement rates for an alternative response. In one DRA component, a discrete stimulus signaled the availability of response‐contingent alternative reinforcement by changing the keylight color upon reinforcement availability. In the other DRA component, availability of alternative reinforcement was not signaled. Target responding was most persistent in the unsignaled DRA component when disrupted by satiation, free food presented between components, and extinction, relative to the signaled DRA and control components. These findings suggest the discrete stimulus functionally separated the availability of alternative reinforcement from the discriminative stimuli governing target responding. These findings provide a novel avenue to explore in translational research assessing whether signaling the availability of alternative reinforcement with DRA treatments reduces the persistence of problem behavior.     

Response cost and the aversive control of human operant behavior

The effects of cost (point-loss per response) upon human avoidance, escape, and avoidance-escape behavior maintained by PLPs (point-loss periods) were investigated. Cost had a marked but differentially suppressive effect upon responding under all schedules. The greatest number of PLPs taken under cost occurred on the escape schedule. In most instances PLPs were more frequent on the avoidance-escape schedule than on the avoidance schedule under cost. Inferior avoidance performance appeared only under cost conditions. Under no-cost, all subjects (Ss) successfully avoided all PLPs after the first hour of conditioning. These results indicate that the development and maintenance of human avoidance and escape behavior may, in part, be dependent upon response cost conditions. Aversive control of human operant behavior may be limited without an adequate specification of response-cost conditions.