Proactive behavioral effects of theta-blocking septal stimulation in the rat

The induction of hippocampal theta rhythm using low-frequency septal stimulation has been shown to proactively (1) facilitate the acquisition and (2) increase resistance to extinction of a food-rewarded fixed-ratio (FR) bar-press response (Holt & Gray, Quarterly Journal of Experimental Psychology, 35B, 97-118, 1983). Both (1) and (2) are also seen after septal lesions. This suggests that Holt and Gray's (1983) results may have been due either to stimulation-produced theta waves (the "theta" hypothesis), or a small septal lesion produced by the stimulating current (the "lesion" hypothesis). Both hypotheses were tested in the present experiment using high-frequency septal stimulation. In one of two treatment conditions male Sprague-Dawley rats, chronically implanted with a bilateral septal stimulating electrode and a unilateral bipolar hippocampal recording electrode, received (1) trains of continuous pulses at 77 Hz which blocked the hippocampal theta rhythm, or (2) trains of pulses at 100 Hz interrupted by a 30-msec interval at a frequency of 7.7 Hz. Control animals were implanted but not stimulated. Acquisition of a discrete-trial bar-press response on a fixed ratio 5 reinforcement schedule immediately followed the treatment phase. After 15 days' acquisition all animals were extinguished over the subsequent 12 days. Results indicated that both types of septal stimulation reduced resistance to extinction of barpressing; theta-blocking stimulation produced the greater effect. Theta-blocking stimulation retarded the acquisition of bar-pressing in the early stages of training. These overall results are exactly opposite to those produced by low-frequency (7.7 Hz) theta-driving septal stimulation (Holt & Gray, 1983) and contrary to the predictions of the lesion hypothesis. Furthermore, these findings support the idea that long-term changes in behavior may depend on stimulation-produced changes in the hippocampal theta rhythm.     

Individual response patterns and the effects of different behavioral methods in the treatment of claustrophobia

The importance of individual response patterns in claustrophobic patients was examined in the present study. Thirty-four psychiatric outpatients with a phobia of enclosed spaces were assessed in a small test chamber. During the test their overt behavior was video-taped, heart-rate was measured continuously, and self-ratings of experienced anxiety were made at certain intervals. On the basis of their reactions in the test situation, the patients were divided into two groups showing different response patterns—behavioral and physiological reactors. Within each group the patients were randomly assigned to one behaviorally-focused method (exposure), one physiologically-focused method (applied relaxation) and a waiting-list control group. The patients were treated individually in eight sessions. The between-group comparisons showed that both exposure and applied relaxation were significantly better than the waiting-list condition. Furthermore, exposure yielded better results than applied relaxation for the behavioral reactors, while applied relaxation was better than exposure for the physiological reactors. The improvements were maintained at a follow-up assessment 14 months after the end of treatment. The results support the hypothesis that greater effects are achieved when the method used fits the patient's response pattern than when it does not.     

Individual response patterns and the effects of different behavioral methods in the treatment of agoraphobia

The importance of individual response patterns in agoraphobic patients was examined in the present study. Forty psychiatric outpatients with agoraphobia were assessed in individually relevant natural phobic situations. During this behavioral test their heart rates were measured continuously, and self-ratings of experienced anxiety were made at fixed intervals. On the basis of their reactions in the test situation, the patients were divided into two groups showing different response patterns—behavioral and physiological reactors. Within each group the patients were randomly assigned to one behaviorally-focused method (exposure in vivo, E) and one physiologically-focused method (applied relaxation, AR). The patients were treated individually for 12 sessions. Both treatments yielded significant improvements on most measures; 60% of the E group and 70% of the AR group patients were clinically improved after treatment. The between-group comparisons showed that both treatments did equally well both for behavioral and physiological reactors. Thus, the differential effects for these methods obtained in previous studies were not seen.     

Light reinforcement in the rat: The effects of continuous and discontinuous periods of apparatus familiarization

The effects of continuous and discontinuous periods of apparatus familiarization on light reinforcement in rats were examined. A previous finding that the light reinforcement effect is greater with longer pretest periods in the dark box was confirmed by comparing 270 min and 30 min periods in the box prior to testing 24 h later. A discontinuous period of 9 daily 30 min sessions, however, produced a bigger effect than the 270 min continuous period. It was concluded that the degree of familiarization with the apparatus is a more important factor than length of time per se in the dark in determining the effectiveness of light as a reinforcer.     

Open-field behavior in two models of genetic hypertension and the behavioral effects of salt excess

In order to assess the relationship of behavior to blood pressure and salt intake, open-field behavior was studied in 123 rats of the spontaneously hypertensive (SHR), Wistar-Kyoto (WKY), Sprague-Dawley (SD), and Dahl resistant (DR) and sensitive (DS) strains. DS rats become hypertensive upon exposure to either high dietary salt or psychogenic stress, while DR rats remain normotensive. A circular photobeam open field was used under full room illumination. Three 5-min trials were given on consecutive days. Rats were tested with or without 5 days of an 8% NaCl diet. We found that DS rats were less active than DR rats, regardless of diet. In contrast, SHR rats were more active than WKY rats. However, DS and SHR rats were equally active. Thus, behavioral differences between these two models of hypertension are expressed by the normotensive control strains. The relative ranking of activity levels between strains was DR = SD greater than SHR = DS greater than WKY. High-salt-enhanced intertrial habituation, defined as the decrease in activity across trials (DS, 100%; SD, 82%; SHR, 90%; WKY, 1350%; but DR, -50%) as well as intratrial habituation, defined as the decrease from the first to the second half of the trial (14%, all subjects). Defecation was increased with high salt (DS, 975%; SD, 59%; SHR, 267%; WKY, 89%; but DR, 40%). These effects of high salt may reflect an increase in an emotionality factor. DR rats were largely resistant to the behavioral effects of salt. Total activity was positively correlated with blood pressure in hypertensive rats, r(42) = 0.33, p less than .01, but negatively correlated in normotensive rats, r(81) = -0.34, p less than .01. The proportion of total activity occurring in the first half of the trial for the initial test day was correlated with blood pressure in normotensive rats r(81) = 0.44, p less than .01. Dietary salt excess has behavioral as well as cardiovascular consequences.     

Complementary nature of heat production and heat intake during behavioral thermoregulation in the rat

Rats were trained to work for radiant heat in a cold environment in an apparatus that permitted the simultaneous measurement of metabolic heat production. Reductions in behavioral efficacy produced either by a decrease in reward duration or intensity or by an increase in response effort resulted in a reduction in behavioral heat intake, an increase in metabolic heat production, and no change in body temperature. Thus, autonomic and behavioral temperature regulation interact to produce a constant body temperature.     

Early-life stress affects extinction during critical periods of development: An analysis of the effects of maternal separation on extinction in adolescent rats

Adolescence is a period of heightened susceptibility to anxiety disorders, yet we have little experimental evidence on what factors may lead to psychopathology in adolescence. Preclinical models of extinction are commonly used to study the treatment of anxiety symptoms. Interestingly, recent research has shown that there are fundamental changes in the process of extinction across development, which may have implications for our understanding of psychopathology across the lifespan. Specifically, this research shows that the process of extinction parallels the nonlinear function of prefrontal cortex development, such that extinction behaviour is similar in juvenile and adult rats, but involves different processes in infancy and adolescence (periods of rapid growth and pruning, respectively). Our previous studies have shown that early-life stress accelerates the transition between infant and juvenile extinction systems. In the current series of experiments, we examined whether the same early-life stress, maternal separation (MS), would lead to an earlier transition between the juvenile and adolescent extinction systems, and between the adolescent and adult extinction systems. We show that MS adolescent rats exhibit more adult-like extinction behaviour, and that adolescent-like extinction emerges earlier in development (i.e. in pre-adolescent rats). These results may have important implications for the understanding and treatment of anxiety symptoms in adolescent populations.     

Individual response patterns and the effects of different behavioral methods in the treatment of social phobia

The importance of individual response patterns in the treatment of phobic patients was examined in the present study. Forty psychiatric outpatients with social phobia were assessed with a social interaction test which was videotaped. Heart rate was continuously monitored during the test. On the basis of their reactions in the test situation, the patients were divided into two groups showing different response patterns; behavioral and physiological reactors. Within each group half of the patients were randomly assigned to a behaviorally focused method (social skills training) while the other half received a physiologically focused method (applied relaxation). The patients were treated individually in 10 sessions. The within-group comparisons showed that both treatments yielded significant improvements on most measures. The between-group comparisons showed that for the behavioral reactors, social skills training was significantly better than applied relaxation on six out of ten measures, and for the physiological reactors applied relaxation was significantly better than social skills training on three of the measures. The results support the hypothesis that greater effects are achieved when the method used fits the patient's response pattern.     

Individual response patterns and the effects of different behavioral methods in the treatment of dental phobia

The present study investigated the importance of individual response patterns in the treatment of dental phobia. Thirty-seven outpatients with dental phobia were assessed during a behavioral test in the form of dental examination. Heart rate was continuously monitored both in the waiting-room and during the examination. The patient's cognitions during the test were assessed through a self-report scale. On the basis of these reactions the patients were divided into two groups: cognitive and physiological reactors. Within these groups the patients were randomly assigned to either a cognitively focused method (self-instructional training) or a physiologically focused method (applied relaxation). The patients were treated in groups of 4 for 9 sessions. The within-group comparisons showed that both treatments yielded significant improvements on almost all measures. The between-group comparisons did not show differential results, except for one measure in the physiological reactors. The results did not support the hypothesis that greater effects are achieved when the method used fits the patient's response pattern.     

Opiate receptor binding in the brain of rat during stress

Two types of opioid receptors were studied in the brain of rats: Delta (for endogenous opiate) and mu (for exogenous opiates).³H derivates: D-Ala²-enkephalin and Naloxone were used as labeled ligands. The results obtained were calculated by computer program for automatic estimation of the data using approximation equations. An increase of binding delta receptors is observed in both types of stress (2–8 times), while to the mu receptors the binding is less effective mainly after irradiation. These data suggest that a close interaction exists between sympathoadrenal system and opioid mechanisms during stress.