Ontogeny of amphetamine anorexia in rats: A behavioral analysis.

Conducted 4 experiments with 246 Sprague-Dawley rats to ascertain the effects of dextroamphetamine (DAM; 1 or 2 mg/kg) on the behaviors associated with feeding in weanling and preweanling rats. The 1st 2 experiments produced the following results: (a) In 5-day-old Ss, DAM increased speed of approach to an anesthetized mother; (b) at 15 days of age, DAM increased speed of approach to the mother and produced marked weight loss (relative to the weight of controls), slowed or reduced frequency of attachment to the nipple, and decreased time spent nursing; and (c) at 25 days of age, DAM disrupted all aspects of the feeding process except initial approach. Weight gain, time spent in contact with the mother, time spent nursing, and time attached to the nipple were all reduced by the drug. In Exps III and IV, milk was delivered to Ss at 5, 15, and 25 days of age through tongue cannulas, which allowed ingestion without suckling. Under these circumstances, DAM produced clear-cut anorexia in Ss of all 3 ages. It is concluded that in early development, the anorectic effects of DAM are overridden by the strong suckling response that is not disrupted by the drug. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tolerance to amphetamine: Contingent suppression of stereotypy mediates recovery of feeding.

In this article, the effect of chronic injections of amphetamine on feeding and behavioral activation was analyzed. Rats were given milk either through an intraoral cannula or in a standard drinking tube, and the level of their behavioral activation was monitored before, during, and after access to the milk. Cannula- and bottle-fed rats given saline showed similar patterns of intake and activity. Bottle-fed rats given amphetamine (2 mg/kg) showed substantially greater suppression of intake than did cannula-fed rats, but recovered more rapidly, confirming earlier findings (Salisbury & Wolgin, 1985). Such recovery was accompanied by a suppression of stereotyped head scanning movements during access to milk, but not before and after milk access. In contrast, cannula-fed rats given amphetamine showed stereotyped head scans throughout the session for the duration of the experiment. These results suggest that tolerance to the suppression of intake by amphetamine involves learning to suppress stereotyped head movements. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amphetamine tolerance and body weight set point: A dose–response analysis.

Evaluated the theory that amphetamine anorexia and tolerance reflect the lowering of a set point for body-weight regulation. In Exp I, 18 male Long-Evans hooded rats given either 2 or 4 mg/kg dextro-amphetamine and access to milk ultimately achieved comparable levels of tolerance and maintained their weight at 94–96% of control levels. Thus, the level of maintained body weight was not dose-dependent. Increasing the doses resulted in renewed anorexia and weight loss and the appearance of behavioral stereotypies (Exp II). Whereas mean intake then recovered, body weight remained at 79–82% of control levels. However, milk intake for individual Ss was extremely variable. Such variability is inconsistent with the notion that body weight was actively regulated by caloric intake. Drug withdrawal had little further effect on intake, and it led to weight rebound in only 1 group. When subsequently retested with the original doses, both groups were again anorexic and showed more intense stereotypy. This finding suggested that drug withdrawal caused a general increase in sensitivity to amphetamine rather than a set-point-related change in feeding. Results do not support the set-point theory of amphetamine tolerance. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tolerance to amphetamine hypophagia: A miscrostructural analysis of licking behavior in the rat.

The development of tolerance to amphetamine-induced hypophagia was assessed by recording changes in lick parameters in rats given chronic administration of the drug (2 mg/kg) and access to sweetened milk. Although licking and milk intake gradually recovered, the volume of milk ingested per lick remained suppressed. Amphetamine had no effect on the interlick interval or the force per lick. In contrast, the drug caused a sustained increase in the number of lick bursts (defined by pause criteria of 0.5-2.0 s) and a decrease in the number of licks per burst (but only at pause criteria of 0.5 and 1.0 s). These results suggest that tolerant rats frequently interrupt licking, resulting in less efficient capture of milk. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Serotonin transporter gene-linked polymorphic region: allele distributions in relationship to body weight and in anorexia nervosa

Several lines of evidence implicate a role for the serotonergic system in body weight regulation and eating disorders. The magnitude and duration of postsynaptic responses to serotonin (5-HT) is directed by the transport into and release from the presynaptic neuron. Recently, a common polymorphism of a repetitive element in the region of the serotonin transporter (5-HTT) gene-linked polymorphic region (5-HTTLPR) was identified that results in a system of two common alleles. The activity of the 5-HTT, as measured in in vitro assays and in human lymphoblastoid cell lines, is dependent on the respective genotype. We thus hypothesized that this polymorphism is relevant for weight regulation in general and is possibly involved in the etiology of anorexia nervosa (AN). Allele frequencies and genotypes were determined in a total of 385 unrelated obese children, adolescents and adults, 112 underweight subjects and 96 patients with AN. Furthermore, both parents of 98 obese children and adolescents and of 55 patients with AN, respectively, were genotyped, thus allowing to test for both association and linkage. The comparison of allele frequencies between obese and underweight probands provided no evidence for a major role of the 5-HTTLPR in weight regulation. Patients with AN had allele frequencies not significantly different to those observed for obese and underweight individuals.     

Sensitization to the psychomotor stimulant effects of amphetamine: Modulation by associative learning.

The authors investigated the influence of associative pairing of contextual stimuli with amphetamine administration on the expression of psychomotor sensitization. Animals received d-amphetamine or saline in group-specific environments. Amphetamine produced robust behavioral sensitization in all environments, but when an amphetamine challenge was given in a test environment that was novel for some groups but not others, the expression of sensitization was completely context specific. An injection of saline in the amphetamine-paired environment produced a conditional response (CR), but this was quite small compared to the magnitude of the sensitized response, and sensitization remained completely context specific following extinction of the CR. Results are discussed in relation to 3 models of how context may modulate the expression of sensitization: an excitatory conditioning model, an inhibitory conditioning model, and an occasion-setting model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Insulin and glucagon as determinants of body weight set point and microregulation in rats.

Seven adult male Long-Evans rats were observed for body weight and microregulation (feeding, drinking, and running patterns) after manipulation of insulin and glucagon levels. They received 3 injections/day for 3 days/wk of 3 U of protamine zinc insulin, .25 mg of zinc glucagon, 50 μg of protamine zinc somatostatin (SRIF), or protamine zinc vehicle. Diabetes was then induced with an iv injection of streptozotocin (65 mg/kg), and the injection schedule was repeated after the full diabetic syndrome emerged. In all Ss whose insulin levels were increased relative to glucagon levels, body weight increased; in those whose glucagon levels were increased relative to insulin levels, body weight decreased. All injections except vehicle reduced meal sizes in both normal and diabetic rats, but only insulin increased the frequency of feeding. These effects could be predicted by the glucostatic theory of food intake regulation and are thus interpreted as supporting this theory. Results also support the hypothesis that the relative concentration of insulin to glucagon is a regulator of body weight set point. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some aspects of the relationship between body weight and sexual behaviour with particular reference to massive obesity and anorexia nervosa

There is some evidence for the existence of a precise weight/fat threshold for puberty. Following puberty, body weight and shape take on important new psycho-social significances for both males and females. Adolescent females usually strive to reduce their 'fatness' even it is not excessive from a biological standpoint. Super-obesity and anorexia nervosa are two human disorders of weight and fatness, more common in women, and importantly related to disturbances of sexual behavior, metabolic, social and experiential. These latter aspects sometimes at least reflect the presence of several factors which have contributed to the development of the disorders. Anorexia nervosa in particular reflects the adaptive psychosocial needs of the person concerned. Attention to this aspect during treatment will often allow the patient to tolerate the major weight gain required for recovery, thereby at the same time providing a paradigm for aspects of the pubertal process which can then be studied. The results of some such investigations together with related studies of the super-obese are reported here.     

Ibogaine interferes with the establishment of amphetamine place preference learning.

The ability of ibogaine, injected 24 hr before amphetamine, to modify the establishment of amphetamine-induced place preference learning was assessed. A single injection of ibogaine blocked the establishment of amphetamine place preference after 1 or 2 conditioning trials, but it was less effective after 4 trials. The reduced effectiveness of ibogaine across multiple conditioning trials appears to be the result of the development of tolerance to ibogaine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Equivalence of body image disturbances in anorexia and bulimia nervosa.

A silhouette method, the Body Image Assessment, was used to measure self-evaluation of current and ideal body size in 3 groups: Ss with anorexia nervosa (n?=?37), Ss with bulimia nervosa (n?=?59), and normal control Ss (n?=?95). Current and ideal body size measures were contrasted across the 3 groups using body mass index as a covariate to control for the Ss' actual body size. Both eating disorder groups judged current body size to be larger and ideal body size to be thinner relative to control Ss. When actual body size was not statistically controlled, Ss with anorexia nervosa judged current body size to be thinner than did control Ss and Ss with bulimia nervosa. Data illustrate the importance of controlling for actual body size when investigating the self-evaluation of body size. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Restraint, weight loss, and variability of body weight.

Restrained and unrestrained Ss (n?=?24) were weighed daily for a 6-wk period and again 6 mo later in order to determine whether dietary restraint or relative body weight is the better predictor of weight variability. Restraint was a significantly better predictor of naturally occurring weight fluctuations than was relative body weight. Furthermore, the 2 factors of the Restraint Scale, Concern for Dieting and Weight Fluctuations, were both significant predictors of weight variability. We propose that exaggerated weight fluctuations are not a natural concomitant of higher body weight but possibly the consequence of a cycle of dieting and overeating, which seems to preclude actual weight loss. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of instrumental learning in tolerance to cathinone hypophagia.

The effects of dl-cathinone on milk intake and motor activity were investigated in bottle- and cannula-fed rats. Acute injections of cathinone produced dose-dependent increases in activity in both groups but only produced decreased intake in bottle-fed rats. With chronic injections, tolerance to the suppression of intake developed in the bottle-fed group, accompanied by decreased activity. After the tolerance phase, switching from bottle to cannula feeding produced further increases in intake, whereas switching from cannula to bottle feeding produced decreased intakes. These results suggest that (a) cathinone suppresses intake by inducing locomotion and stereotypy, which interfere with the appetitive phase of feeding, and (b) tolerance to drug-induced hypophagia involves learning to suppress such movements, as proposed by the instrumental learning model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Implicit and explicit memory for shape, body weight, and food-related words in patients with anorexia nervosa and nondieting controls.

Twelve patients with anorexia nervosa and 12 control participants watched a series of 64 words. There were 4 word types: anorexia related, positive, negative, and neutral. The last 3 types were anorexia unrelated. Anorexia-related words had the same affective valence as the neutral control words. Next, the participants completed an explicit memory test ( cued recall ) and an implicit memory test (word stem completion). Results showed a strong explicit memory bias for anorexia-related words for patients with anorexia nervosa but not for nondieting controls. There was no evidence for a similar bias in implicit memory. Results are discussed in the context of cognitive biases in psychopathology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Individual differences in learning: Visual versus auditory presentation.

Investigated the possible interaction of individual differences in learning with mode of presentation. Ss were college students; data analyses were replicated by conducting separate analyses for 2 groups of 77 and 83 Ss, respectively. Each S learned 4 test lists of 20 words each, 2 under auditory and 2 under visual presentation. The main analyses indicated that individual differences in learning were reliable and that individual differences were just as predictable across as within modalities. A complementary analysis showed that Ss could not be reliably classified in terms of auditory–visual preference scores. The findings give no support to the contention that Ss can be classified as auditory learners or visual learners. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adrenal responses to reinforcement and extinction: Role of expectancy versus instrumental responding.

Measured plasma corticosterone levels during operant conditioning to determine the effect of reinforced and nonreinforced responding (extinction) on adrenal activation; Ss were 44 male Long-Evans rats. The influence of instrumental responding was assessed by comparing trained Ss with yoked Ss that received a matched reward schedule in the absence of an operant task. Reinforcement sessions resulted in a significant decrease in adrenal secretion at 20 min but not at 5 min, whereas extinction caused a rapid increase in corticosterone levels at 5 min and an even greater elevation at 20 min. Comparison of the operant and yoked Ss showed that this effect of reinforcement and extinction was not dependent on instrumental responding, but rather on the receipt or withdrawal of the expected reward. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social learning family therapy versus parent training: Inconclusive.

Comments that methodological and interpretive issues raised by a study of a behavioral therapy program for aggressive behavior in elementary-school boys by T. V. Sayger et al (see record 1989-12762-001) limit conclusions about the effectiveness of the treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of memory in concept learning.

Studies manipulating variables in the attempt to produce different memory requirements in concept learning are reviewed. Many of them have tested Underwood's theoretical position of response contiguity. Performance is generally improved by increasing the availability of previous stimulus information. The degree to which instances of the same concept occur contiguously directly affects acquisition of the concept. Attempts to demonstrate inferior performance with spaced practice have not been successful, although procedural problems make any conclusion tentative. There is some suggestion that memory effects could be classified as proactive and retroactive inhibition. A basic problem concerns the indirect type of question posed by investigators. (36 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of attention in implicit learning.

Previous research has shown that implicit learning of a serial pattern in a reaction time (RT) task is eliminated or reduced when the task is performed concurrently with a tone-counting task. These results led to the inference that implicit learning requires attentional capacity. Two experiments tested the alternative hypothesis that the tone-counting task disrupts learning by preventing consistent organization of the sequence. The tone-counting condition was compared with a condition with additional attentional demands, but no disruption of organization, and with a condition with no additional attentional demands, but disruption of organization. The results were consistent with the organizational hypothesis. It is argued that learning depends on practicing consistently organized runs of trials, that shifts of attention may determine how the runs are organized, and that the relation between attention and learning depends more on organization and intention than on capacity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)