Loss of the cortisol response to naltrexone in Alzheimer's disease

Intact circadian rhythm despite cortisol hypersecretion in Alzheimer's disease: A meta-analysis

Hypersecretion of the glucocorticoid steroid hormone cortisol by individuals with Alzheimer's disease (AD) has been suspected for several decades, during which time dozens of examinations of this phenomenon have been conducted and published. The goals of this investigation were to summarize this sizeable body of literature, test whether participant and methodological characteristics modify the magnitude of the AD-associated basal cortisol hypersecretion, and examine whether cortisol circadian rhythmicity is maintained among individuals with AD. To this end, the present meta-analysis and systematic review examined over 300 comparisons of indices of basal HPA-axis functioning between individuals with AD and cognitively normal older adults. AD was associated with basal cortisol elevations (g = 0.45) but the magnitude of the effect was not systematically impacted by any of the participant characteristics considered or the time-of-day of the cortisol sampling. Further, there was no evidence of group differences among direct indices of circadian rhythmicity such as the cortisol awakening response or the diurnal cortisol slope. These results suggest that basal hypersecretion of cortisol, but not circadian dysrhythmia, is characteristic of individuals with AD. Mechanistically, the observed hypersecretion is consistent with the theorized AD-driven deterioration of the hippocampus and subsequent reduction in hypothalamic-pituitary-adrenal axis inhibition. Further investigation is warranted to elucidate the role and timing of cortisol elevations in the progression of AD.

Parallels between major depressive disorder and Alzheimer's disease: role of oxidative stress and genetic vulnerability

The thesis of this review is that oxidative stress is the central factor in major depressive disorder (MDD) and Alzheimer's disease (AD). The major elements involved are inflammatory cytokines, the hypothalamic-pituitary axis, the hypothalamic-pituitary gonadal, and arginine vasopressin systems, which induce glucocorticoid and "oxidopamatergic" cascades when triggered by psychosocial stress, severe life-threatening events, and mental-affective and somatic diseases. In individuals with a genomic vulnerability to depression, these cascades may result in chronic depression-anxiety-stress spectra, resulting in MDD and other known depressive syndromes. In contrast, in subjects with genomic vulnerability to AD, oxidative stress-induced brain damage triggers specific antioxidant defenses, i.e., increased levels of amyloid-β (Aβ) and aggregation of hyper-phosphorylated tau, resulting in paired helical filaments and impaired functions related to the ApoEε4 isoform, leading to complex pathological cascades culminating in AD. Surprisingly, all the AD-associated molecular pathways mentioned in this review have been shown to be similar or analogous to those found in depression, including structural damage, i.e., hippocampal and frontal cortex atrophy. Other interacting molecular signals, i.e., GSK-3β, convergent survival factors (brain-derived neurotrophic factor and heat shock proteins), and transition redox metals are also mentioned to emphasize the vast array of intermediates that could interact via comparable mechanisms in both MDD and AD.

Physiologic and neuroendocrine responses to intravenous naloxone in subjects with Alzheimer's disease and age-matched controls

BACKGROUND

Prior work showed that administration of naloxone HCl had different behavioral effects in patients with Alzheimer's disease (AD) than controls. The aim of the present study was to contrast the physiologic and neuroendocrine responses to administration of a wide range of doses of intravenous naloxone of patients with probable Alzheimer's disease to aged-matched controls.

METHODS

This was a double-blind, placebo-controlled, study of 12 patients with probable Alzheimer's disease and 8 age-matched normal controls who each received intravenous infusions of naloxone HCl on 3 different days in doses of 0.1 mg/kg and 2.0 mg/kg preceded by test doses of 0.5 mcg/kg. Order of treatment condition was randomized. Vital signs and plasma cortisol and prolactin were obtained at regular intervals.

RESULTS

Both groups showed increased cortisol after naloxone 0.1 mg/kg and 2.0 mg/kg (p < .0001), but the increase was significantly greater and longer lived in controls than in patients. Patients, but not controls, also experienced a significant hypothermic response after naloxone 2.0 mg/kg (p < .05). Prolactin, heart rate, and blood pressure did not change following naloxone and did not differ between groups.

CONCLUSIONS

These findings support a growing body evidence that HPA axis activity is increased in AD, and further suggest that at least part of this may be due to decreased opiatergic tonic inhibition.

Placebo-controlled acute dosage naltrexone study in young autistic children

In a double-blind, placebo-controlled crossover trial 23 autistic children were treated with a single 40-mg dose of the opiate antagonist naltrexone. Drug effects were monitored by detailed playroom observations, actometers, and parents' checklist ratings (Aberrant Behavior Checklist, social items and target behaviors). Naltrexone treatment failed to produce significant changes in social behavior, but it did reduce irritability and target scores on behavior checklists. The playroom data indicated that naltrexone significantly affected indices of activity and attention.

Advances in the pharmacotherapy of Alzheimer's disease

The authors reviewed the literature on the agents proposed for the treatment of Alzheimer's disease (AD). Different classes of drugs have been tested for this indication including psychostimulants, anticoagulants, vasodilators, hyperbaric oxygen, hormones, nootropics, cholinomimetics, monoaminergics and neuropeptides without conclusive evidence of being beneficial for the treatment of this condition. Among the cholinomimetics recent research data seems to indicate that they might produce modest benefits in mild-to-moderate AD patients. Recently, other drugs have also been proposed including neurotrophic factors, phosphatidylserine, angiotension [corrected] converting enzyme (ACE) inhibitors, calcium channel blockers, acetyl-L-carnitine, xanthine derivatives, anti-inflammatory agents, aluminum chelate agents, and D-cycloserine. Of these new strategies few hold promise of more substantial benefits for AD, with the possibility of altering the course of the disease, but these drugs await confirmatory trials.

A novel biochemical model linking dysfunctions in brain melatonin, proopiomelanocortin peptides, and serotonin in autism

A novel biochemical model for autism is presented, which proposes that a subgroup of autistic individuals may have a hypersecretion of pineal melatonin that produces a cascade of biochemical effects including a corresponding hyposecretion of pituitary proopiomelanocortin (POMC) peptides and a hypersecretion of hypothalamic opioid peptides and serotonin (5-HT). The model is reviewed, and supporting animal and clinical research, is summarized. The first arm of the model suggests that increases in pineal melatonin results in hypersecretion of 5-HT in hypothalamus and blood. The second arm of the model indicates that hypersecretion of melatonin also inhibits the release of hypothalamic corticotrophin-releasing hormone (CRH). Hyposecretion of CRH may result in decreased release of both pituitary B-endorphin (B-E) and adrenocorticotrophin hormone (ACTH); this, in turn, may result in decreased plasma concentrations of B-E, ACTH, and cortisol. In autism, a genetically determined hypersecretion of hypothalamic B-E may further contribute to an inhibition of pituitary B-E because of negative feedback inhibition. Therefore, autism may reflect a dysfunction in the pineal-hypothalamic-pituitary-adrenal axis which, modulates POMC and 5-HT systems of the brain. This model is consistent with numerous clinical investigations implicating hypersecretion of brain 5-HT and opioid peptides in autism. The model may have heuristic importance in guiding future research in the biochemistry of autism.

A possible role of proopiomelanocortin peptides in self-injurious behavior

1. The hypothesis that opioids may be involved in self-injurious behavior is supported by fifteen years of basic animal research suggesting that opioid peptides of the brain and spinal cord participate in the modulation of antinociception in animals, and research of animal models for self-injurious behavior utilizing exogenously administered opiate agonists. 2. Clinical biochemical and pharmacological research conducted over the past five years has also suggested the possibility that opioid peptides may play an important etiological role in the elaboration of self-injurious behavior in some individuals. 3. An opioid overactivity self-injurious hypothesis is supported by results of one study indicating elevated Fraction II opioids (enkephalins) in the lumbar-thecal cerebrospinal fluid of self-injurious children compared to controls, and by the five out of six published studies demonstrating statistically significant decreases in the frequency of self-injurious behavior with the opiate antagonist, naltrexone. 4. A very recent investigation has suggested that some self-injurious individuals show abnormalities in their plasma proopiomelanocortin peptide response to naltrexone, thereby indicating a possible dysfunction in the responsitivity of the proopiomelanocortin system of the hypothalamic-pituitary-adrenal axis of these individuals. 5. These data and results of other investigations have resulted in the elaboration of the original opioid hypothesis to a more comprehensive biochemical model that focuses on this proopiomelanocortin dysregulation. 6. Because of biochemical and functional interrelationships between proopiomelanocortin peptides and certain other neurochemical systems in the brain, it is proposed that pineal melatonin and serotonin may also be involved in this dysregulation. Further basic and clinical research will be needed to test the proposed biochemical model for self-injurious behavior.

Endogenous opiates: 1988

This paper is the eleventh installment in our annual review of the research during the past year involving the endogenous opiate system. It is concerned with nonanalgesic and behavioral studies of the opiate peptides that were published during 1988. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic functions; mental illness; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical activity; locomotor activity; sex, pregnancy, and development; immunology and cancer; and other behavior.