Opioid peptides and aging

Physical Activity to Prevent the Age-Related Decline of Endogenous Pain Modulation

As humans age, the capacity of the central nervous system to endogenously modulate pain significantly deteriorates, thereby increasing the risk for the development of chronic pain. Older adults are the least physically active cohort of all age groups. We hypothesize that a sedentary lifestyle and decreased physical activity may contribute to the decline of endogenous pain modulation associated with aging.

Sarcopenia: An Age-Related Multifactorial Disorder

Sarcopenia is an emerging clinical entity characterized by a gradual decline in skeletal muscle mass and strength that accompanies the normal aging process. It has been noted that sarcopenia is associated with various adverse health outcomes in the geriatric population like prolonged hospital admission, disability, poor quality of life, frailty, and mortality. Factors involved in the development of age-related sarcopenia include anorexia, alteration in the hormone levels, decreased neural innervation, low blood flow to the muscles, cytokine dysregulation, altered mitochondrial activity, genomic instability, intracellular proteolysis, and insulin resistance. Understanding the mechanism may help develop efficient preventive and therapeutic strategies which can improve the quality of life in elderly individuals. Thus, the objective of the present article is to review the literature regarding the mechanism involved in the development of sarcopenia in aged individuals.

Reduced Modulation of Pain in Older Adults After Isometric and Aerobic Exercise

Laboratory-based studies show that acute aerobic and isometric exercise reduces sensitivity to painful stimuli in young healthy individuals, indicative of a hypoalgesic response. However, little is known regarding the effect of aging on exercise-induced hypoalgesia (EIH). The purpose of this study was to examine age differences in EIH after submaximal isometric exercise and moderate and vigorous aerobic exercise. Healthy older and younger adults completed 1 training session and 4 testing sessions consisting of a submaximal isometric handgrip exercise, vigorous or moderate intensity stationary cycling, or quiet rest (control). The following measures were taken before and after exercise/quiet rest: 1) pressure pain thresholds, 2) suprathreshold pressure pain ratings, 3) pain ratings during 30 seconds of prolonged noxious heat stimulation, and 4) temporal summation of heat pain. The results revealed age differences in EIH after isometric and aerobic exercise, with younger adults experiencing greater EIH compared with older adults. The age differences in EIH varied across pain induction techniques and exercise type. These results provide evidence for abnormal pain modulation after acute exercise in older adults.

PERSPECTIVE

This article enhances our understanding of the influence of a single bout of exercise on pain sensitivity and perception in healthy older compared with younger adults. This knowledge could help clinicians optimize exercise as a method of pain management.

Mu opioid receptor availability in people with psychiatric disorders who died by suicide: a case control study

BACKGROUND

Mu opioid receptors have previously been shown to be altered in people with affective disorders who died as a result of suicide. We wished to determine whether these changes were more widespread and independent of psychiatric diagnoses.

METHODS

Mu receptor levels were determined using [3 H]DAMGO binding in BA24 from 51 control subjects; 38 people with schizophrenia (12 suicides); 20 people with major depressive disorder (15 suicides); 13 people with bipolar disorder (5 suicides) and 9 people who had no history of psychiatric disorders but who died as a result of suicide. Mu receptor levels were further determined in BA9 and caudate-putamen from 38 people with schizophrenia and 20 control subjects using [3 H]DAMGO binding and, in all three regions, using Western blots. Data was analysed using one-way ANOVAs with Bonferroni's Multiple Comparison Test or, where data either didn't approximate to a binomial distribution or the sample size was too small to determine distribution, a Kruskal-Wallis test with Dunn's Multiple Comparison Test.

RESULTS

[3 H]DAMGO binding density was lower in people who had died as a result of suicide (p<0.01). People with schizophrenia who had died as a result of suicide had lower binding than control subjects (p<0.001), whilst people with bipolar disorder (non- suicide) had higher levels of binding (p<0.05). [3 H]DAMGO binding densities, but not mu protein levels, were significantly decreased in BA9 from people with schizophrenia who died as a result of suicide (p<0.01).

CONCLUSIONS

Overall these data suggest that mu opioid receptor availability is decreased in the brains of people with schizophrenia who died as a result of suicide, which would be consistent with increased levels of endogenous ligands occupying these receptors.

The clinical significance of gastrointestinal changes with aging

PURPOSE OF REVIEW

With the graying of the world's population, there is an increased interest in the physiological effects of aging. This review examines the physiological changes of the gut with aging and their clinical significance.

RECENT FINDINGS

Changes with aging in the gastrointestinal tract are variable, but in some cases they are responsible for a variety of symptoms. Thus, alterations in taste and smell, gastric motility, intestinal overgrowth and changes in gastrointestinal hormone release are the basis of the physiological anorexia of aging. Alterations in swallowing lead to silent aspiration. Changes in gastric emptying play a role in postprandial hypotension. Changes in gastrointestinal function can lead to constipation and fecal incontinence. Weakening of the colonic muscular wall produces diverticula. Achlorhydria is associated with malabsorption of some forms of iron and calcium. Vitamin D malabsorption aggravates the hypovitaminosis D that is so common in older persons. Changes in probiotics can lead to diarrhea and altered immune system. In the liver, aging is associated with delayed drug metabolism.

SUMMARY

Changes in the physiology of the gut play a role in the anorexia of aging, aspiration pneumonia, postprandial hypotension, constipation and fecal incontinence.

Cognitive impairment

As populations continue to age, the prevalence of dementia is expected to increase. AD is by far the most common cause of dementia. The clinical course of dementia represents the challenges that this disease presents. There are no truly effective therapies for treating dementia, and the cost effectiveness of ChEIs has been challenged; however, there has been an explosion of information about AD. Evidence-based practice parameters for diagnosis and management of dementia have been developed. There has been an increased interest in the possible prodromal states of dementia, such as MCI. The concept of MCI has risen in prominence in recent years; it is speculated that initiation of therapies early in the course of disease may be needed for them to be effective. Considering the enormous burdens that AD places on individuals and society, disease-modifying treatments for AD are needed desperately. There are promising avenues for the development of potentially disease-modifying therapies for this devastating disease.

Age-related changes in brain proDynorphin gene expression in the rat

Dynorphin has a well-established role in feeding and gustation. Alterations in taste perception and feeding behavior are common with age. We hypothesized that proDynorphin gene expression in brain areas involved in taste and feeding declines with age. Male Sprague-Dawley rats were housed individually with ad libitum access to food and water. Brain punches of the selected regions were dissected out in groups of rats aged 4-6, 12-14 and 18-21 months. ProDynorphin mRNA (measured using a cDNA probe) decreased significantly with age in arcuate nucleus and amygdala; increased significantly with age in hippocampus; and was not significantly affected in nucleus of the solitary tract, cortex, caudate putamen or hypothalamic paraventricular nucleus. These data suggest an age-related decrease in the synthesis of dynorphin in two brain regions strongly associated with feeding behavior, and an increase in dynorphin synthesis in a brain region associated with learning and memory.

Functional opioid pathways are necessary for hypocretin-1 (orexin-A)-induced feeding

We investigated the interaction of the orexigenic neuropeptide, hypocretin-1 (Hcrt-1, also known as orexin-A), with endogenous opioids (also orexigenic neuropeptides). Rats were injected with naltrexone (NTX, nonspecific opioid antagonist) i.p., i.c.v., in the lateral hypothalamus (LH), and in the accumbens shell (AcbSh), and naloxone methiodide (nonspecific opioid antagonist unable to cross the blood brain barrier) was injected i.p. Rats were then injected with Hcrt-1 in the LH. Food intake was measured for up to 4h thereafter. Rats were also pretreated with NTX in the LH, with Hcrt-1 injected in the AcbSh. NTX suppressed Hcrt-1-induced feeding only when injected i.p., i.c.v., and in the AcbSh. These studies reveal the necessity for functional central opioidergic pathways involving the AcbSh, but not the LH in Hcrt-1-induced feeding.

Decreased food intake with aging

There is a physiological decline in food intake with aging. The reasons for the decline in food intake are multifactorial and involve both peripheral and central mechanisms. Altered hedonic qualities of food occur due to alterations in taste and, more particularly, smell with aging. A decline in adaptive relaxation of the fundus of the stomach and an increased rate of antral filling appear to play a role in the early satiation seen in many older persons. Cholecystokinin levels are increased with aging and older persons are more sensitive to the satiating effects of this gut hormone. The decline in testosterone levels in older males leads to increased leptin levels and this may explain the greater decline in food intake with aging in the male. Within the hypothalamus, decreased activity of both the dynorphin (kappa opioid) and neuropeptide Y systems occurs in aging rodents. Cytokines are potent anorectic agents. Many older persons have mild inflammatory disorders that lead to anorexia. Exercise may increase food intake in older persons.

Analgesic agents. Pharmacology and application in critical care

Evaluation of analgesic agents is multifactorial. The authors know of no direct comparisons among the choices in analgesic agents that suggest one therapy over another in global outcomes such as mortality or morbidity. Therefore, until further outcome differentiation between agents is proved, understanding the primary difference of delivery routes, mechanisms of action, pharmacokinetics, and adverse effects serves as the best guide for selecting the appropriate agent for each patient.

Anorexia, sarcopenia, and aging

Food intake declines throughout the life span. This physiologic anorexia of aging is caused in part by alterations of stomach-fundus compliance and release and activity of cholecystokinin. In addition, the decline in testosterone in males results in elevated leptin levels that increase the anorexia. There is also evidence that cytokines play a role in the pathogenesis of anorexia and sarcopenia, thus accelerating the development of frailty in older persons. Numerous treatable causes of anorexia and weight loss exist. Depression is the most commonly diagnosed cause of pathologic weight loss in older persons.

Androgens and aging

This review supports the conclusion that the use of testosterone replacement therapy for the treatment of the symptoms of androgen deficiency in aging males (ADAM) may be appropriate if undertaken with due caution. The best safety data exists for using oral therapy with testosterone undeconoate. Less data exists for the treatment of postmenopausal women with testosterone. Tibolone (an estrogen--prostagen--testosterone) compound, may make the need for testosterone being added to estrogen in women unnecessary. Less data is available to support the use of DHEA or its sulfate or pregnenolone. Further studies are clearly necessary in all these areas. However, it may be tentatively concluded that we are at the dawning of the age of androgens.

Effects of a 6-week hypocaloric diet on changes in body composition, hunger, and subsequent weight regain in healthy young and older adults

Recent studies have suggested a short-term impairment in the regulation of food intake in older adults, but further studies are needed to determine if a longer-term impairment exists and to identify underlying causes. Changes in body weight and composition were measured over a 6-week underfeeding study and a 6-month follow-up period in healthy young (n = 23) and older (OLD, n = 18) men and women. The young adults were either normal weight (YNW, n = 12) or overweight (YOW, n = 11). Energy intakes during underfeeding were 896 +/- 18 (SEM) kcal less than weight-maintenance energy requirements determined prior to underfeeding. In addition, changes in perceived hunger during underfeeding were monitored in a subgroup (n = 19). OLD and YOW subjects lost significantly more weight during underfeeding than did YNW subjects (p = .025 and .000, respectively), and they did not gain back significant weight in the 6-month follow-up. In addition, OLD subjects reported a significantly lower frequency of hunger during underfeeding (p = .05). There was no significant difference among groups in the relationship between weight lost and fat-free mass lost. Healthy OLD adults have an impaired ability to regulate food intake over at least 6 months following underfeeding compared with YNW adults, and a reduction in their perceived frequency of hunger may be a contributing factor.

Management of nutritional problems in subacute care

Poor nutritional status is one of the major factors associated with functional decline and mortality in older persons. Older persons are at increased risk for malnutrition because of the physiologic anorexia of aging. During a stay in a subacute care facility, attention to nutrition is a major component of the rehabilitative process. The pathophysiology of malnutrition, diagnostic techniques available to diagnose malnutrition, causes and management of protein energy malnutrition, specific nutritional problems caused by vitamin and trace element deficiency, and nutritional management of specific diseases (e.g., hip fracture and diabetes mellitus) are reviewed.

A review of age-related changes in energy regulation and suggested mechanisms

This review discusses recent studies on possible causes of weight loss in older individuals. Studies of the regulation of food intake suggest that aging is associated with an impairment in the regulation of food intake that inhibits appropriate short-term and long-term compensation for imposed alterations in energy intake. The combination of a reduced ability to regulate energy intake, decreased sensory specific satiety, and adverse social factors such as functional limitations, social isolation and depression, increases the risk of negative energy balance leading to weight loss in older individuals.

[Pathophysiology of catabolism in undernurished elderly patients]

Malnutrition is a common finding amongst our elders. The causes of malnutrition are multifactorial and although they have been extensively studied, they are not entirely understood. Both physiological and pathological processes of aging put this population at a higher risk of being undernourished. These may be related to social, financial, psychological and/or physiological changes directly or indirectly associated to growing old. Age associated changes increase the risk of malnutrition in older individuals. These alterations range from problems in taste and smell perception, which were previously thought to be the main cause of anorexia in this population, to alterations in either the concentration or efficacy of the previously mentioned feeding modulators. Increased intestinal malabsorption together with an altered pancreatic exocrine response to different diets, further contributing to subclinical malabsorption in the elderly population aged and may account in part for the malnutrition observed in this group. Although not directly caused by the aging process, several conditions such as anorexia nervosa, cancer, infectious conditions, and inflammatory processes are associated with decreased food intake and weight loss. These conditions present with elevated levels of immunoregulatory substances known as cytokines. Each of these cytokines has multiple effects and play a leading role in the pathophysiology and maintainance of malnutrition in these situations.

Pharmacokinetic and pharmacodynamic changes in the elderly. Clinical implications

Age-related changes in pharmacokinetics principally affect drug absorption, distribution, metabolism and elimination. Changes in pharmacodynamics are primarily seen in the cardiovascular and neuroendocrine system. Age-dependent changes in the kinetics and dynamics of drugs acting on the cardiovascular system and central nervous system are common, and this review, while by no means exhaustive of the effects of drugs on all organ systems, is reflective of the principles and gives examples of the effects of age on these 2 major systems. While pharmacokinetic changes in the elderly are usually well characterised, pharmacodynamic changes are understood only in the most preliminary way. There has been relatively little research in this area of geriatric clinical pharmacology, and pharmacodynamic changes are still an area of investigation.

Refusal to eat in the elderly

Refusal to eat by the elderly, and subsequent malnutrition, occurs in both institutional and community settings. Causes include physiologic changes associated with aging, mental disorders such as dementia and depression, and medical, social, and environmental factors. Treatment approaches call for management of these causes while considering the roles that medicine, ethics, and culture play in the process.

Pain and its management

The management of pain in geriatric patients is a critical part of good veterinary care. The older patient poses unique issues in the selection of appropriate analgesic drugs due to altered drug absorption, metabolism and the frequent occurrence of underlying disease. Narcotics and NSAIDs are important analgesics that can be safely administered in geriatric patients provided that dosing amount and frequency are adjusted. Alternative analgesic techniques, such as nerve blocks, spinal analgesia and transcutaneous patches, offer a particularly useful source of analgesia in compromised geriatric patients.

Inhibition of feeding by a nitric oxide synthase inhibitor: effects of aging

Nitric oxide has been demonstrated to play a role in the modulation of food intake. With advancing age, there is a physiological decrease in food intake. The effect of the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) on food intake in C57BL/6Nnia mice aged 3, 12 and 24 months was studied. L-NAME was more effective at decreasing food intake in 12- and 24-month-old mice than in the 3-month-old mice. NO synthase levels in the hypothalamus were increased in 16- and 25-month-old mice compared to 6-month-old mice (P < 0.01). NO synthase mRNA increased in 16- compared to 6-month-old mice, but decreased in 25-month-old mice. Overall, these studies may suggest that nitric oxide may play an increasingly important role in the feeding drive with advancing age.

Neuroactive peptides: unique phases in research on mammalian brain over three decades

Because of the enormous growth over the last three decades of research on the role of peptides in the brain, the need became apparent to determine the status of these compounds in terms of their current research interest. Since 1965, over a quarter of a million research papers have been published on peptides that have since been classified as neuroactive. The present study was undertaken to analyze systematically the yearly trends of research emphasis in neuroactive peptides as reflected by their individual frequency of publication by year, beginning in 1966. A computer analysis of the publication characteristics was carried out using the Medline data base in which the citation search was limited to the topic brain crossed with the topic mammal. One criterion for the inclusion of a given peptide in the analysis was a frequency of 25 or more citations following its discovery, as related to the mammalian brain. The 42 peptides that met this criterion were: adrenocorticotropic hormone, angiotensin II, atrial natriuretic factor, bombesin, bradykinin, calcitonin, calcitonin gene-related peptide, carnosine, beta-casomorphin, cholecystokinin, corticotropin-releasing factor, delta sleep-inducing peptide, dynorphin, beta-endorphin, Leu-enkephalin, Met-enkephalin, galanin, gastrin, glucagon, growth hormone, growth hormone-releasing factor, insulin, kyotorphin, beta-lipotropin, luteinizing hormone-releasing factor, melanocyte-stimulating hormone release inhibitory factor-1, alpha-melanocyte-stimulating hormone, motilin, neurokinin A, neurokinin B, neuropeptide Y, neurotensin, oxytocin, pituitary adenylate cyclase activating polypeptide, peptide HI, prolactin, secretin, somatostatin, substance P, thyroid-releasing hormone, vasopressin, and vasoactive intestinal peptide. An overall analysis of the 298,105 papers published on these 42 peptides since 1965 revealed that the research activity of 24,742, or 8.30%, of the studies, focused on their neuroactive properties. Taken as a whole, the research on neuroactive peptides reached a peak in 1986, as reflected by the total of 1793 papers published during that year. Although the level of publication has fluctuated between 1548 and 1774 research papers over the last 6 years, it is now clear that the trend in research on neuroactive peptides has reached an asymptote today that shows no sign of deviation. A temporal analysis year by year of individual publication profiles revealed three distinct trends: 1) peptides showed a slow development in research interest and did not exceed more than 15-30 publications per year; 2) peptides exhibited a steady increase in research activity over the years that continues today; and 3) peptides displayed an initial, often intense, research emphasis that inexplicably declined, in some cases precipitously, in the mid 1980s.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain methionine- and leucine-enkephalin receptors in patients with dementia

Brain [3H]Met- and [3H]Leu-enkephalin binding was studied in patients with Alzheimer's disease (AD) and vascular dementia (VD), and in age-matched controls. Brain areas investigated were the internal and external globus pallidus, amygdala, hippocampus and temporal cortex. In AD, the binding of both enkephalins decreased in all brain areas examined, except in the external globus pallidus for both enkephalins and in the internal globus pallidus for leucine-enkephalin. Scatchard analysis of amygdaloid samples showed a decrease in the number of receptors (Bmax) without any change in their affinity (Kd). In patients with VD, no significant changes in enkephalin binding were seen. Thus, in AD, enkephalin binding (mainly reflecting delta opioid receptor subtype) is decreased, especially in limbic areas.

Human brain methionine- and leucine-enkephalins and their receptors during ageing

Brain Met- and Leu-enk levels were investigated with radioimmunoassay and their binding to enkephalin receptors was studied with [3H]Met- and [3H]Leu-enkephalin in 56 human subjects (4-93 yr). Of the brain areas investigated, the head of the caudate nucleus and pallidum showed an age-associated decline for both Met- and Leu-enk content. In the substantia nigra and in putamen, no significant age-effect was seen. Binding of the enkephalins, which was studied in the head of the caudate nucleus and hippocampus, did not show significant age dependency. In conclusion, ageing affects human brain enkephalin levels but not their receptor binding, at least in brain areas investigated in the present study.

Alcoholism and prescription drug abuse in the elderly: St. Louis University grand rounds

This Grand Rounds will review the problem of alcoholism and prescription drug abuse in the elderly. Several case vignettes will be presented. The pharmacology of alcohol and potentially addictive prescription medications will be reviewed. The clinical presentation of and psychiatric symptoms associated with these disorders will be discussed. The process of addiction and issues regarding the clinical evaluation of the elderly addict will be discussed. The medical complications of these disorders will be reviewed, followed by a discussion of guidelines for the appropriate use of these drugs in the elderly. The grand rounds will conclude with a discussion of the treatment of patients with these disorders.

Effects of peripheral hormones on memory and ingestive behaviors

This article explores the mechanisms by which peripheral gastrointestinal hormones produce central nervous system effects on memory and feeding. Cholecystokinin produces its satiety effects and memory-enhancing effects by stimulating ascending vagal fibers. Hyperglycemia has been demonstrated to be a cause of memory dysfunction in persons with diabetes mellitus. A number of other hormones, such as amylin and bombesin, modulate both memory processing and feeding. The causes of the anorexia of aging are briefly reviewed.