Effects of peripheral hormones on memory and ingestive behaviors

The Influence of Fat Co-administration on the Glucose Memory Facilitation Effect

Memory for a list of 20 words can be enhanced when learning is preceded by consumption of 25 g of glucose, compared with consumption of an equally sweet aspartame solution. The present study examined whether memory performance is also enhanced when glucose is administered in conjunction with another food constituent, in particular fat. Four groups of healthy young participants were tested under one of four conditions: (a) glucose + full-fat yoghurt; (b) glucose + fat-free yoghurt; (c) aspartame + full-fat yoghurt; (d) aspartame + fat-free yoghurt. The groups were compared on measures of blood glucose and cognitive performance. Participants receiving a glucose drink in conjunction with a fat-free yoghurt displayed higher blood glucose levels (BGL) and better performance on short- and long-delay recall of the word list compared with (a) individuals who consumed the glucose drink in conjunction with a full-fat yoghurt and (b) individuals who consumed the aspartame drink. The glycaemic data indicated that the presence of fat slows down glucose absorption. The findings suggest that only foods with a relatively fast glucose absorption rate are able to significantly enhance the encoding and long-term retention of novel memory materials in healthy young adults.

Regular breakfast consumption is associated with increased IQ in kindergarten children

BACKGROUND

Studies have documented a positive relationship between regular breakfast consumption and cognitive outcomes in youth. However, most of these studies have emphasized specific measures of cognition rather than cognitive performance as a broad construct (e.g., IQ test scores) and have been limited to Western samples of school-age children and adolescents. This study aims to extend the literature on breakfast consumption and cognition by examining these constructs in a sample of Chinese kindergarten-age children.

METHODS

This cross-sectional study consisted of a sample of 1269 children (697 boys and 572 girls) aged 6 years from the Chinese city of Jintan. Cognition was assessed with the Chinese version of the Wechsler preschool and primary scale of intelligence-revised. Breakfast habits were assessed through parental questionnaire. Analyses of variance and linear regression models were used to analyze the association between breakfast habits and IQ. Socioeconomic and parental psychosocial variables related to intelligence were controlled for.

RESULTS

Findings showed that children who regularly have breakfast on a near-daily basis had significantly higher full scale, verbal, and performance IQ test scores (all p<0.001) compared to children who "sometimes" have breakfast. This relationship persisted for VIQ (verbal IQ) and FIQ (full IQ) even after adjusting for gender, current living location, parental education, parental occupation, and primary child caregiver.

CONCLUSION

Findings may reflect nutritional as well as social benefits of regular breakfast consumption on cognition, and regular breakfast consumption should be encouraged among young children.

Signaling proteins that influence energy intake may affect unintentional weight loss in elderly persons

After age 70 to 75 years, average body weight decreases both in ailing and healthy people because of a loss of appetite that results in reduced energy intake and the loss of body fat and lean muscle tissue. This so-called anorexia of aging predisposes elderly people to continued pathologic weight loss and malnutrition-major causes of morbidity and mortality. Health care professionals must understand the many factors involved in the anorexia of aging to help older adults prevent unintentional weight loss. Psychological, social, and cultural factors are important effectors; however, physiological factors are emphasized here because they are not thoroughly understood and they make it inherently difficult for most people to alter their body weight. Monoamines, steroid hormones (glucocorticoids and mineralocorticoids), endocannabinoids, and proteins all influence body weight. This review is an analysis of proteins from the brain, pancreas, adipose tissue, and gastrointestinal tract that are known to affect energy intake and energy balance, with an attempt to identify those factors that may change with aging. The articles included in this review were obtained by a PubMed database search using the keywords mouse OR rat OR human AND aged OR aging OR older OR elderly AND adult AND anorexia OR "unintentional weight loss," and each of the individual proteins discussed, as well as from the reference lists of those articles. The results reveal that some proteins may be important in the development of unintentional weight loss in elderly persons, whereas others may not have a significant role. However, many of the proteins that could conceivably have a role in unintentional weight loss have not yet been studied with that question in mind. Preventing unintentional weight loss in older adults is an important goal and further research on the role of proteins important for the maintenance of energy balance and the development of unintentional weight loss in elderly persons is warranted.

Post-oral and perioral stimulations during nursing enhance appetitive olfactory memory in neonatal rabbits

Nursing-suckling interactions facilitate olfactory learning in newborns as long as suckling and the olfactory stimulus temporally overlap. We tested the hypothesis that olfactory preferences would develop even with a long delay between odor presentation and nursing. Thyme was presented to 2-day-old rabbit pups by placing an odorized plate 2 cm above their nest box. Duration and time of nursing were controlled and occurred before, during, or after odor presentation. Controls were not nursed. When exposed to the odor for 15 min, control pups preferred thyme to a novel odor in a 2-choice test immediately after exposure but not 3 and 22 h later. When pups were nursed immediately before thyme exposure or during exposure, they preferred the familiar odorant until 22 h later. Identically, when nursing occurred 30 min before odor exposure, a preference for thyme was maintained up to 22 h. This was not observed when nursing occurred 60 min before odor presentation. We concluded that enhancement of olfactory memory occurs in neonates during nursing but also after post-oral stimulation by postprandial internal state.

Characterization of mice lacking the gene for cholecystokinin

CCK acts peripherally as a satiating peptide released during meals in response to lipid feeding and centrally functions in the modulation of feeding, exploratory, and memory activities. The present study determined metabolic parameters, food intake, anxiety-like behaviors, and cognitive function in mice lacking the CCK gene. We studied intestinal fat absorption, body composition, and food intake of CCK knockout (CCK-KO) mice by using the noninvasive measurement of intestinal fat absorption along with quantitative magnetic resonance (QMR) imaging and the DietMax system, respectively. Additionally, exploratory and memory capacities were assessed by monitoring running wheel activity and conducting elevated plus-maze and Morris water-maze tests with these mice. Compared with wild-type (WT) littermate controls, CCK-KO mice had normal food intake, fat absorption, body weight, and body mass. CCK-KO mice ate more food than control animals during the light period and less food during the dark period. Energy expenditure was unchanged between the genotypes; however, CCK-KO mice displayed greater fatty acid oxidation. CCK-KO mice were as active as WT animals in the running wheel test. CCK-KO mice spent more time in the closed arms of an elevated plus-maze, indicative of increased anxiety. Additionally, CCK-KO mice exhibited attenuated performance in a passive avoidance task and impaired spatial memory in the Morris water maze test. We conclude that CCK is involved in metabolic rate and is important for memory and exploration. CCK is intimately involved in multiple processes related to cognitive function and food intake regulation.

Central nervous system and other effects

Amylin enhanced the uptake of certain amino acids, crossed the blood-brain barrier, and increased body temperature. The physiological significance of these responses is currently unclear. An effect of peripherally injected amylin to enhance weakly trained memory fitted with similar effects of other gastrointestinal peptide hormones. Centrally administered amylin reduced locomotor and exploratory behavior. Amylin administered alone was analgesic when administered peripherally, via a non-opiate pathway. When administered in combination with opiates, there was an opiate-sparing synergy.

A typical feeding enhances memory for spoken words in healthy 2- to 3-day-old newborns

OBJECTIVE

The objective of this study was to determine whether healthy 2- to 3-day-old newborns have better memory of a spoken word after a typical feeding (breast milk or formula) than before a feeding and, if so, whether memory is related to blood glucose.

METHODS

A naturalistic study was conducted in which delayed recognition memory of a spoken word was examined in 60 healthy 2- to 3-day-old newborns either 120 minutes after their previous feeding (preprandial) or 30 minutes after their last feeding (postprandial). In this procedure, infants initially turn their head toward a novel word (orientation) and with repeated presentations cease turning toward it (habituation). Mean number of trials to reach orientation and habituation criteria provides measures of attention and rate of learning, respectively. After a 100-second delay, the word is presented again. Infants either turn toward it, indicating that they have forgotten it, or remain habituated, indicating that they remembered the word. Percentage of trials with head turns toward the word after the delay is the principal dependent measure.

RESULTS

The postprandial group was split at the median for blood glucose to define high- and low-glucose groups. All 3 groups showed similar rates of orientation and habituation. On reexposure to the word during postdelay trials, the preprandial group displayed less retention than the postprandial high and low groups. No correlation was found between memory and blood glucose levels. The postprandial high blood glucose level differed statistically from the preprandial level, whereas the postprandial low level did not.

CONCLUSIONS

Memory for spoken words in newborns is better after a typical milk feeding than before a feeding. This feeding effect is specific to memory and does not include attention or rate of learning. Also, it is not necessarily associated with increased blood glucose. It remains to be seen whether feeding enhances memory for other types of stimuli and what implications this may have for development.

Electrophysiological responses of nucleus tractus solitarius neurons to CCK and gastric distension in newborn lambs

The effect of cervical vagus nerve stimulation, gastric distension and CCK-8S administration was studied on the activity of 120 neurons located in the nucleus tractus solitarius (NTS) of anesthetized newborn lambs. One hundred cells responded to the three different inputs. The distribution of the cells in the NTS was from 3 mm rostral to 3 mm caudal to the obex, the major responsive cells being located at the level of the obex. Neurons were either excited or inhibited by gastric distension and CCK-8S, and the responses to these two stimuli were always in the same direction. A small number of cells responded to gastric distension and CCK-8S but not to vagus nerve stimulation. Injection of the CCK-A receptor antagonist 2-NAP abolished both the responses to CCK-8S and to gastric distension. The results are consistent with the idea that CCK-8S acts directly on vagal mechanoreceptive endings in the gastric corpus close to duodenum. These results from lambs may reflect the pathway by which gastric distension and peripheral CCK-8S modulate NTS cells activity during colostrum ingestion, which could in turn activate structures related to learning and memory processes involved in the development of mother preference.

Inhibition of food intake

Over 100 publications, principally from five groups, describe an effect of amylin and amylin analogs in inhibition of food intake in animals and humans. The major groups contributing to this area are those of the following: Chance and Balasubramaniam (Balasubramaniam et al., 1991a,b; Chance et al., 1991a,b, 1992a,b, 1993). Morley, Flood, and Edwards (Edwards and Morley, 1992; Flood and Morley, 1992; Macintosh et al., 2000; Morley and Flood, 1991, 1994; Morley et al., 1992, 1993, 1994, 1995, 1996, 1997). Lutz, Geary, and others (Barth et al., 2003; Del Prete et al., 2002; Lutz et al., 1994, 1995a,b, 1996a,b, 1997a,b, 1998a,b,c, 2000a,b, 2001a,b,c, 2003; Mollet et al., 2001, 2003a,b, 2004; Riediger et al., 2002, 2004; Rushing et al., 2000a,b, 2001, 2002). Workers at Amylin Pharmaceuticals Inc., or their collaborators (Bhavsar et al., 1995, 1996, 1997a, 1998; Birkemo et al., 1995; Chapman et al., 2004a,b; Edwards et al., 1998; Feinle et al., 2002; Mack et al., 2003; Riediger et al., 1999; Roth et al., 2004; Watkins et al., 1996; Weyer et al., 2004; Young, 1997; Young and Bhavsar, 1996). Arnelo, Reidelberger, and others (Arnelo et al., 1996a,b, 1997a,b, 1998, 2000; Fruin et al., 1997; Granqvist et al., 1997; Reidelberger et al., 2001, 2002, 2004). The magnitude of amylin inhibition of food intake, and its potency for this effect when delivered peripherally, suggests a physiological role in satiogenesis. Increases in food intake following disruption of amylin signal-signaling (e.g., with amylin receptor blockade, or with amylin gene knock-out mice) further support a role of endogenous amylin to tonically restrict nutrient intake. In addition, synergies with other endogenous satiety agents may be present, and convey greater physiological importance than is conveyed by single signals. The anorectic effect of amylin is consistent with a classic amylin pharmacology. The anorectic effect of peripheral amylin appears principally due to a direct action at the area postrema/nucleus tractus solitarius, and is not merely a consequence of gastric fullness, for example. Circulating amylin appears to physiologically inhibit secretion of ghrelin, an orexigenic peptide from the stomach. In contrast to the actions of many other anorexigens, amylin appears to stimulate drinking. This disposgenic effect is likely mediated via amylin-sensitive neurones in the subfornical organ, a circumventricular structure, that like the area postrema does not present a blood-brain barrier. Amylin's dipsogenic effect may explain prandial drinking, which has heretofore been regarded as a learned behavior.

Bombesin/gastrin-releasing peptide receptors in the basolateral amygdala regulate memory consolidation

Several receptor and intracellular signalling systems in the basolateral amygdala (BLA) regulate memory formation. In the present study, we show that bombesin/gastrin-releasing peptide (GRP) receptors in the BLA are involved in the consolidation of affectively motivated memory. Adult male rats were trained in a single-trial step-down inhibitory avoidance task and tested for retention 24 h later. Post-training systemic injection of the bombesin/GRP receptor antagonist (D-Tpi6, Leu13 psi[CH2NH]-Leu14) bombesin (6-14) (RC-3095) impaired memory retention. In rats implanted under thionembutal anaesthesia with guide cannulae aimed at the BLA, post-training bilateral infusion of RC-3095 into the BLA dose-dependently impaired retention. Pre-training unilateral muscimol inactivation of the BLA blocked the memory-impairing effect of post-training systemic administration of RC-3095. The results suggest that bombesin/GRP receptors in the BLA are involved in the consolidation of aversive memory, and the BLA mediates the memory-impairing effect of systemic bombesin/GRP receptor blockade.

Intrahippocampal infusion of the bombesin/gastrin-releasing peptide antagonist RC-3095 impairs inhibitory avoidance retention

Bombesin (BN)-like peptides regulate cell proliferation and cancer growth as well as neuroendocrine and neural functions. We evaluated the effects of the BN/gastrin-releasing peptide (GRP) antagonist RC-3095 on memory formation. Male Wistar rats were given a bilateral infusion of saline or RC-3095 (0.2, 1.0 or 5.0 microg) into the dorsal hippocampus either immediately or 2 h after training in an inhibitory avoidance (IA) task. Retention test trials were carried out 1.5 h (short-term memory) and 24 h (long-term memory) after training. RC-3095 impaired both short- and long-term retention only when given immediately after training. The results suggest that the hippocampal BN/GRP receptor system modulates IA memory formation.

The delivery rate of dietary carbohydrates affects cognitive performance in both rats and humans

RATIONALE

Glucose is the main metabolic fuel of the brain. The rate of glucose delivery from food to the bloodstream depends on the nature of carbohydrates in the diet, which can be summarized as the glycaemic index (GI).

OBJECTIVES

To assess the benefit of a low versus high GI breakfast on cognitive performances within the following 4 h.

METHODS

The influence of the GI of the breakfast on verbal memory of young adults was measured throughout the morning in parallel to the assessment of blood glucose levels. The learning abilities of rats performing an operant-conditioning test 3 h after a breakfast-like meal of various GI was also examined.

RESULTS

A low GI rather than high GI diet improved memory in humans, especially in the late morning (150 and 210 min after breakfast). Similarly, rats displayed better learning performance 180 min after they were fed with a low rather than high GI diet.

CONCLUSION

Although performances appeared to be only remotely related to blood glucose, our data provide evidence that a low GI breakfast allows better cognitive performances later in the morning.

Effect of central and peripheral administrations of cholecystokinin-tetrapeptide on panic-like reactions induced by stimulation of the dorsal periaqueductal grey area in the rat

Administration of cholecystokinin-tetrapeptide (CCK-4) triggers panic attacks in humans, but it is not known whether CCK-4 acts in the brain to produce this effect. Panic-like reactions (flight and tachycardia) induced in rats by injecting D, L-homocysteic acid (DLH) into the dorsal periaqueductal grey area (DPAG), were used as an animal model to investigate this issue. CCK-4 (2 micrograms) infused into the DPAG did not change these panic-like reactions. The DLH-induced tachycardia was prolonged by intracerebroventricular injection of CCK-4 (40 or 4 micrograms); however, the DLH-induced flight behavior was not changed by similar central injections of CCK-4 (40, 4, or 0.4 micrograms). Peripheral injection of t-butoxycarbonyl (BOC)-CCK-4 (40 micrograms) potentiated the flight behavior, but did not alter the tachycardia response. It was concluded that CCK tetrapeptide potentiates panic-like behaviors by acting on a peripheral target or on a circumventricular area of the brain. In contrast, increased brain CCK-4 prolongs tachycardia by acting in the brain at a level distinct from the DPAG.

The influence of food on pain perception in healthy human volunteers

The aim of this study was to investigate if food could reduce pain perception in a group of 16 healthy human volunteers (8 male and 8 female), and to explore the differential effects of macronutrient composition on the response to cold-induced pain. All subjects underwent the cold pressor test (CPT) on 3 occasions in a counterbalanced order, before and after administration of isoenergetic high-fat low-carbohydrate (CHO) and high-CHO low-fat meals, and when no meal was given. The CPT was carried out 4 times on each test day, once before the meal, and 0.5, 1.5, and 2.5 h after the meal, and at the equivalent times on the day when no food was given. Radial pulse and blood pressure measurements and visual analogue scales of mood/emotional state were carried out before and after each CPT. Mean pain scores were significantly reduced following both meals compared with the no-food condition. The maximum reduction in pain occurred 1.5 h after ingestion, and a significantly greater effect was exerted by the high-fat low-CHO meal compared with the high-CHO low-fat meal. These results demonstrate that food, particularly when rich in fat, significantly reduces the pain induced by the cold pressor stimulus in healthy human subjects.

Brain aging in a sample of normal Egyptians cognition, education, addiction and smoking

The impact of duration of education, cannabis addiction and smoking on cognition and brain aging is studied in 211 normal Egyptian volunteers with mean age 46.4+/-3.6 years (range: 20-76 years). Subjects were classified into two groups: Gr I (non-addicts) with 174 subjects, mean age 49.9+/-3.8 years (range 20-76 years), smokers and non-smokers, educated and non-educated and Gr II (cannabis addicts) with 37 subjects, mean age 43.6+/-2.6 years (range 20-72 years) all smokers, educated and non-educated. Outcome measures included the Paced Auditory Serial Addition test (PASAT) for testing attention and the Trailmaking test A, and B (TMa and TMb) for testing psychomotor performance. Age correlated positively with score of Trailmaking test (TMb) in the non-addict group and in the addict group (TMa and TMb). Years of education correlated negatively with scores of Trialmaking test (TMb) in the non-addict group (Gr I) but not the addict group (Gr II). However, in both groups mean scores of the Trailmaking test (TMa) were significantly lower in subjects with a primary level of education than those with higher levels of education. No significant difference was detected between male smokers and nonsmokers of Gr I (non-addicts) regarding any of the neuropsychological tests. Yet, smokers and the non-educated group had poorer attention compared to non-smokers of the same group. Cannabis addicts (Gr II) had significantly poorer attention than non-addict normal volunteers (Gr I). It is concluded that impairment of psychomotor performance is age related whether in normal non-addicts or in cannabis addicts. A decline in attention was detected in cannabis addicts and has been considered a feature of pathological aging. Education in early life as well as the duration of education are neuroprotectors for brain aging more so in the non-addict than addict group. Though cigarette smoking per se has no effect on cognitive abilities in normal aging, it becomes evident that its association with lack of education impairs attention.

Brain aging in normal Egyptians: neuropsychological, electrophysiological and cranial tomographic assessment

Eighty-eight normal Egyptian volunteers above the age of 40 years were studied for brain aging and subjected to neuropsychological (the Paced Auditory Serial Addition Test; the Trailmaking test A, B; the Digit Symbol Substitution Test; sensory and secondary memory tests), electrophysiological (computerized EEG, P300 and reaction time measures), and Computerized Cranial Tomography (CCT) assessment. A significant correlation was found between age and both perception (Digit Symbol Substitution Test (DDST) and psychomotor performance (Trailmaking B test (TMb)), reaction time (RT) and the size of the third ventricle. Whereas females were worse in attention (Paced Auditory Serial Addition Test (PASAT)), males had worse performance in secondary memory test. Elderly subjects with vascular risk factors did worse in psychomotor performance (TMa) than subjects with no risk factors. Non-educated subjects showed worse perception (DSST) than educated subjects. A significant decrease in upper and lower limit percent power of the alpha band was found in subjects above 60 years, males, and non-educated subjects. A significant increase in theta activity was found only in non-educated subjects. It is concluded that decline in specific cognitive functions occurs with advancing age. Vascular risk factors and lack of education early in life enhance these changes. Moreover, the EEG slowing in the elderly was linked to lack of education early in life.