Blast-related disinhibition and risk seeking in mice and combat Veterans: Potential role for dysfunctional phasic dopamine release

Mild traumatic brain injury (mTBI) caused by exposure to high explosives has been called the "signature injury" of the wars in Iraq and Afghanistan. There is a wide array of chronic neurological and behavioral symptoms associated with blast-induced mTBI. However, the underlying mechanisms are not well understood. Here we used a battlefield-relevant mouse model of blast-induced mTBI and in vivo fast-scan cyclic voltammetry (FSCV) to investigate whether the mesolimbic dopamine system contributes to the mechanisms underlying blast-induced behavioral dysfunction. In mice, blast exposure increased novelty seeking, a behavior closely associated with disinhibition and risk for subsequent maladaptive behaviors. In keeping with this, we found that veterans with blast-related mTBI reported greater disinhibition and risk taking on the Frontal Systems Behavior Scale (FrSBe). In addition, in mice we report that blast exposure causes potentiation of evoked phasic dopamine release in the nucleus accumbens. Taken together these findings suggest that blast-induced changes in the dopaminergic system may mediate aspects of the complex array of behavioral dysfunctions reported in blast-exposed veterans.

Lesioning noradrenergic neurons of the locus coeruleus in C57Bl/6 mice with unilateral 6-hydroxydopamine injection, to assess molecular, electrophysiological and biochemical changes in noradrenergic signaling

The locus coeruleus (LC) is the major loci of noradrenergic innervation to the forebrain. Due to the extensive central nervous system innervation of the LC noradrenergic system, a reduction in the number of LC neurons could result in significant changes in noradrenergic function in many forebrain regions. LC noradrenergic neurons were lesioned in adult male C57Bl/6 mice with the unilateral administration of 6-hydroxydopamine (6OHDA) (vehicle on the alternate side). Noradrenergic markers were measured 3 weeks later to determine the consequence of LC loss in the forebrain. Direct administration of 6OHDA into the LC results in the specific reduction of noradrenergic neurons in the LC (as measured by electrophysiology, immunoreactivity and in situ hybridization), the lateral tegmental neurons and dopaminergic neurons in the substantia nigra (SN) and ventral tegmental region were unaffected. The loss of LC noradrenergic neurons did not result in compensatory changes in the expression of mRNA for norepinephrine (NE)-synthesizing enzymes. The loss of LC noradrenergic neurons is associated with reduced NE tissue concentration and NE transporter (NET) binding sites in the frontal cortex and hippocampus, as well as other forebrain regions such as the amygdala and SN. Adrenoreceptor (AR) binding sites (α(1)- and α(2)-AR) were not significantly affected on the 6OHDA-treated side compared to the vehicle-treated side, although there is a reduction of AR binding sites on both the vehicle- and 6OHDA-treated side in specific forebrain regions. These studies indicate that unilateral stereotaxic injection of 6OHDA into mice reduces noradrenergic LC neurons and reduces noradrenergic innervation to many forebrain regions, including the contralateral side.

ABCB1 genotype and CSF beta-amyloid in Alzheimer disease

The ABCB1 gene, coding for the efflux transporter P-glycoprotein (PGP), is a candidate gene for Alzheimer disease (AD). P-glycoprotein is heavily expressed at the blood-brain barrier, where it mediates the efflux of β-amyloid (Aβ) from the brain. In this study, we investigated a possible association between 2 common ABCB1 polymorphisms, G2677T/A (Ala893Ser/Thr) and C3435T, AD, and cerebrospinal fluid (CSF) levels of Aβ. No strong evidence for association was found.

A comprehensive analysis of the effect of DSP4 on the locus coeruleus noradrenergic system in the rat

Degeneration of the noradrenergic neurons in the locus coeruleus (LC) is a major component of Alzheimer's (AD) and Parkinson's disease (PD), but the consequence of noradrenergic neuronal loss has different effects on the surviving neurons in the two disorders. Therefore, understanding the consequence of noradrenergic neuronal loss is important in determining the role of this neurotransmitter in these neurodegenerative disorders. The goal of the study was to determine if the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) could be used as a model for either (or both) AD or PD. Rats were administered DSP4 and sacrificed 3 days 2 weeks and 3 months later. DSP4-treatment resulted in a rapid, though transient reduction in norepinephrine (NE) and NE transporter (NET) in many brain regions receiving variable innervation from the LC. Alpha(1)-adrenoreceptors binding site concentrations were unchanged in all brain regions at all three time points. However, an increase in alpha(2)-AR was observed in many different brain regions 2 weeks and 3 months after DSP4. These changes observed in forebrain regions occurred without a loss in LC noradrenergic neurons. Expression of synthesizing enzymes or NET did not change in amount of expression/neuron despite the reduction in NE tissue content and NET binding site concentrations at early time points, suggesting no compensatory response. In addition, DSP4 did not affect basal activity of LC at any time point in anesthetized animals, but 2 weeks after DSP4 there is a significant increase in irregular firing of noradrenergic neurons. These data indicate that DSP4 is not a selective LC noradrenergic neurotoxin, but does affect noradrenergic neuron terminals locally, as evident by the changes in transmitter and markers at terminal regions. However, since DSP4 did not result in a loss of noradrenergic neurons, it is not considered an adequate model for noradrenergic neuronal loss observed in AD and PD.

Intranasal insulin improves cognition and modulates beta-amyloid in early AD

BACKGROUND

Reduced brain insulin signaling and low CSF-to-plasma insulin ratios have been observed in patients with Alzheimer disease (AD). Furthermore, intracerebroventricular or IV insulin administration improve memory, alter evoked potentials, and modulate neurotransmitters, possibly by augmenting low brain levels. After intranasal administration, insulin-like peptides follow extracellular pathways to the brain within 15 minutes.

OBJECTIVE

We tested the hypothesis that daily intranasal insulin treatment would facilitate cognition in patients with early AD or its prodrome, amnestic mild cognitive impairment (MCI). The proportion of verbal information retained after a delay period was the planned primary outcome measure. Secondary outcome measures included attention, caregiver rating of functional status, and plasma levels of insulin, glucose, beta-amyloid, and cortisol.

METHODS

Twenty-five participants were randomly assigned to receive either placebo (n = 12) or 20 IU BID intranasal insulin treatment (n = 13) using an electronic atomizer, and 24 participants completed the study. Participants, caregivers, and all clinical evaluators were blinded to treatment assignment. Cognitive measures and blood were obtained at baseline and after 21 days of treatment.

RESULTS

Fasting plasma glucose and insulin were unchanged with treatment. The insulin-treated group retained more verbal information after a delay compared with the placebo-assigned group (p = 0.0374). Insulin-treated subjects also showed improved attention (p = 0.0108) and functional status (p = 0.0410). Insulin treatment raised fasting plasma concentrations of the short form of the beta-amyloid peptide (A beta 40; p = 0.0471) without affecting the longer isoform (A beta 42), resulting in an increased A beta 40/42 ratio (p = 0.0207).

CONCLUSIONS

The results of this pilot study support further investigation of the benefits of intranasal insulin for patients with Alzheimer disease, and suggest that intranasal peptide administration may be a novel approach to the treatment of neurodegenerative disorders.

Temperament and response to the Trier Social Stress Test

OBJECTIVE

The personality characteristics behavioural inhibition and neuroticism have been associated with mood and anxiety disorders and, in some studies, hypothalamic-pituitary-adrenal (HPA) axis hyperactivity. We recently reported that low levels of Novelty Seeking were associated with elevated plasma cortisol responses to the dexamethasone/corticotropin-releasing hormone (Dex/CRH) test in healthy adults with no psychiatric disorder. The present study tested the association between temperament and HPA axis function in the same group of subjects using a standardized psychosocial neuroendocrine stress test.

METHOD

Subjects completed diagnostic interviews, questionnaires, and the Trier Social Stress Test (TSST).

RESULTS

Novelty Seeking was inversely associated with plasma cortisol concentrations at baseline and throughout the TSST, but was not related to adrenocorticotropic hormone (ACTH) levels.

CONCLUSION

Results of this study extend our previous finding in the Dex/CRH test to a psychosocial stress test. Future investigations are needed to replicate these findings and further elucidate how temperament and personality are linked to HPA function.

Chronic cortisol suppresses pituitary and hypothalamic peptide message expression in pigtailed macaques

The effects of chronic elevations in circulating glucocorticoids on the expression of peptides and peptide receptors of the hypothalamic-pituitary-adrenal (HPA) axis have been studied extensively in rodents, but they have not been examined in primates. To determine the responses of the HPA axis in primates to elevated cortisol, hypothalamic and pituitary tissue from normal older pigtailed macaques (Macaca nemestrina) that had received daily oral administration of cortisol or placebo for 1 year were studied. Pro-opiomelanocortin in the anterior pituitary and corticotropin-releasing factor (CRF) mRNA expression in the hypothalamic paraventricular nucleus (PVN) were significantly reduced in cortisol-treated monkeys in comparison with controls. CRF receptor 1 (CRF-R1) expression in the anterior pituitary and arginine vasopressin mRNA expression in the PVN were unchanged by chronic cortisol administration. Sustained elevation of circulating glucocorticoids results in suppression of HPA peptide and peptide receptor expression in the PVN and anterior pituitary similar to those found in rodents. Chronic therapeutic administration of glucocorticoids in humans may have unintended consequences for hypothalamic and pituitary function.

Effects of repetitive hypoglycemia on neuroendocrine response and brain tyrosine hydroxylase activity in the rat

Hypoglycemia-associated autonomic failure (HAAF) is a syndrome of acute adaptation to a metabolic stressor, in which neuroendocrine responses to repetitive hypoglycemic bouts are blunted. The CNS mechanisms that contribute to HAAF are unknown. In the present study, we modeled HAAF in the rat and measured the activity of tyrosine hydroxylase (TH) as an index of acute noradrenergic activation, to test the hypothesis that noradrenergic activation of the hypothalamus might be impaired. In association with a significant counter-regulatory response to a single bout of hypoglycemia (elevated corticosterone, catecholamines, and glucagon), TH activity was elevated overall in brainstem NE cell body areas and hypothalamus. With multiple hypoglycemic episodes in a 24 h period, the counter-regulatory response was blunted, and hypothalamic TH activity was comparable to that of saline-infused controls. In a similar paradigm, multiple bouts of CNS neuroglucopenia did not blunt the hyperglycemic or corticosterone responses, and were required for elevation of TH activity. This alternate response pattern suggests that insulin-induced hypoglycemia and cerebral neuroglucopenia represent somewhat different metabolic stressors at the CNS.

Acute modulation of aged human memory by pharmacological manipulation of glucocorticoids

In a previous longitudinal study of basal cortisol levels and cognitive function in humans, we showed that elderly humans with 4- to 7-yr cumulative exposure to high levels of cortisol present memory impairments, compared with elderly humans with moderate cortisol levels over years. Here, we measured whether memory performance in two groups of elderly humans separated on the basis of their cortisol history over a 5-yr period could be modulated by a hormone-replacement protocol in which we inhibited cortisol secretion by the administration of metyrapone and then restored baseline cortisol levels by infusion of hydrocortisone. We showed that in elderly subjects with a 5-yr history of moderate cortisol levels (n = 8), metyrapone treatment significantly impaired memory performance, a deficit that was reversed following hydrocortisone replacement. In the elderly subjects with a 5-yr history of high cortisol levels and current memory deficits (n = 9), metyrapone treatment did not have any significant effect on memory performance, but hydrocortisone treatment significantly decreased delayed memory. These results suggest that memory function in elderly humans can be intensely modulated by pharmacological manipulation of glucocorticoids, although the direction of these effects depends on the cortisol history of each individual.

PVN activation is suppressed by repeated hypoglycemia but not antecedent corticosterone in the rat

The mechanism(s) underlying hypoglycemia-associated autonomic failure (HAAF) are unknown. To test the hypothesis that the activation of brain regions involved in the counterregulatory response to hypoglycemia is blunted with HAAF, rats were studied in a 2-day protocol. Neuroendocrine responses and brain activation (c-Fos immunoreactivity) were measured during day 2 insulin-induced hypoglycemia (0.5 U insulin x 100 g body x wt(-1) x h(-1) iv for 2 h) after day 1 hypoglycemia (Hypo-Hypo) or vehicle. Hypo-Hypo animals demonstrated HAAF with blunted epinephrine, glucagon, and corticosterone (Cort) responses and decreased activation of the medial hypothalamus [the paraventricular (PVN), dorsomedial (DMH), and arcuate (Arc) nuclei]. To evaluate whether increases in day 1 Cort were responsible for the decreased hypothalamic activation, Cort was infused intracerebroventricularly (72 microg) on day 1 and the response to day 2 hypoglycemia was measured. Intracerebroventricular Cort infusion failed to alter the neuroendocrine response to day 2 hypoglycemia, despite elevating both central nervous system and peripheral Cort levels. However, day 1 Cort blunted responses in two of the same hypothalamic regions as Hypo-Hypo (the DMH and Arc) but not in the PVN. These results suggest that decreased activation of the PVN may be important in the development of HAAF and that antecedent exposure to elevated levels of Cort is not always sufficient to produce HAAF.

Glucocorticoid feedback sensitivity and adrenocortical responsiveness in posttraumatic stress disorder

BACKGROUND

Decreased basal cortisol levels have been reported in individuals with posttraumatic stress disorder (PTSD). There is evidence for enhanced negative feedback sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis in PTSD, which could account for this, but other possible mechanisms have not been ruled out. We examined the HPA axis employing a metyrapone-cortisol infusion protocol designed to study negative feedback sensitivity.

METHODS

Vietnam combat trauma-exposed subjects met DSM-IV criteria for PTSD. Exclusion criteria included substance abuse and most medications. Endogenous feedback inhibition was removed by blocking cortisol synthesis with oral metyrapone and reintroduced by intravenous infusion of cortisol. In a placebo condition, subjects received oral placebo and normal saline infusion. Serial blood samples drawn over 4 hours were assayed for adrenocorticotrophic hormone (ACTH), cortisol, and 11-deoxycortisol. Selected samples were assayed for cortisol binding globulin (CBG) and dehydroepiandrosterone (DHEA).

RESULTS

Basal plasma cortisol was significantly decreased in PTSD subjects (n = 13) compared with control subjects (n = 16). No significant difference in the ACTH response to cortisol infusion following metyrapone was observed; however 11-deoxycortisol was significantly decreased in PTSD subjects. In addition, CBG was significantly increased in PTSD subjects, and DHEA was significantly decreased in both PTSD and combat-exposed control subjects.

CONCLUSIONS

These observations suggest decreased adrenocortical responsiveness may be an additional or alternative mechanism accounting for low cortisol in PTSD.

Glucocorticoid induction of the glaucoma gene MYOC in human and monkey trabecular meshwork cells and tissues

PURPOSE

To examine the intracellular and extracellular expression of myocilin in the human and primate trabecular meshwork (TM) in the presence and absence of glucocorticoids.

METHODS

Myocilin expression was examined in cultured human TM cells by Northern blot analysis and myocilin antibody-mediated immunoprecipitation. Myocilin expression was quantified using high-resolution two-dimensional polyacrylamide gel electrophoresis of radiolabeled proteins from human TM cells, TM tissue explants, and perfused human anterior segments cultured with and without dexamethasone (DEX) for 14 to 21 days, as well as TM tissue from pigtailed monkeys treated orally for 1 year with cortisone acetate. Immunofluorescence with anti-myocilin antibodies was used to localize cellular and extracellular expression of myocilin in cultured human TM cells.

RESULTS

Glucocorticoid treatment caused a significant induction of myocilin mRNA, a tetrad of cell-associated proteins, and 8 to 20 secreted proteins (molecular mass [M(r)] 56 and 59 kDa and isoelectric point [pI] 5.2 and 5.3) in some, but not all the cultured human TM cells and explanted tissues. Western immunoblot analysis using anti-myocilin peptide antibodies identified these proteins as encoded by the MYOC gene. There was significant induction of the myocilin proteins in three perfusion-cultured human eyes, in which DEX-induced elevated intraocular pressure developed. Monkeys treated 1 year with cortisol acetate showed steroid glaucoma-like morphologic changes in the TM that correlated with the induction of myocilin in the TM. Immunofluorescence analysis of cultured TM cells localized myocilin intracellularly in discrete perinuclear and cytoplasmic vesicular deposits as well as extracellularly on the cell surface associated with the extracellular matrix. In several DEX-treated TM cell lines, there were significant levels of myocilin secreted into the media. Enzymatic deglycosylation of proteins in the TM media converted the higher molecular weight isoforms of myocilin (approximately 57 kDa) to the lower molecular weight isoforms ( approximately 55 kDa).

CONCLUSIONS

Although the function of myocilin is unknown, induction of these TM proteins was found in eyes in which glucocorticoid-induced ocular hypertension developed. Therefore, myocilin may play an important pathogenic role in ocular hypertension in addition to its role in certain forms of POAG.

Increased CSF cortisol in AD is a function of APOE genotype

BACKGROUND

Increased hypothalamic-pituitary-adrenal (HPA) axis activity manifested by elevated cortisol levels is observed in AD and may contribute to AD by lowering the threshold for neuronal degeneration. Presence of the APOE-epsilon4 allele increases risk for AD. Increased cortisol concentrations in apoE-deficient mice suggest that APOE genotype may influence cortisol concentrations in AD.

METHODS

The authors measured cortisol levels in CSF and determined APOE genotypes for 64 subjects with AD and 34 nondemented older control subjects.

RESULTS

CSF cortisol was significantly higher in AD than in control subjects. CSF cortisol concentrations differed with respect to APOE genotype in both subjects with AD (epsilon4/epsilon4 > epsilon3/4epsilon > epsilon3/epsilon3) and normal older control subjects (epsilon3/epsilon4 > epsilon3/epsilon3 > epsilon2/epsilon3). Comparison of CSF cortisol concentrations within the epsilon3/epsilon4 and epsilon3/epsilon3 genotypes revealed no differences between AD and control subject groups.

CONCLUSIONS

Higher CSF cortisol concentrations were associated with increased frequency of the APOE-epsilon4 allele and decreased frequency of the APOE-epsilon2 allele in AD subjects relative to control subjects. This effect of APOE genotype on HPA axis activity may be related to the increased risk for AD in persons carrying the APOE-epsilon4 allele and decreased risk for AD in persons carrying the APOE-epsilon2 allele.

Gender differences in age-related changes in HPA axis reactivity

Possible differences between men and women in age-related patterns of hypothalamic-pituitary-adrenal (HPA) axis response to challenge were examined to test the hypothesis that women show greater age-related increase in HPA axis reactivity to challenge. Twenty-six younger subjects, 9 men and 17 women, ages 22-26 and 14 older subjects, 7 men and 7 women, ages 67-88 participated in the study. Patterns of change in salivary "free" cortisol were measured in response to a standardized, 30-minute cognitive challenge, administered individually to each subject beginning at 1600 h. Consistent with previous research, there was a significant main effect for age with respect to baseline cortisol: older age was associated with higher baseline cortisol (P = <0.001). Results also provide support for the hypothesized age-by-gender interaction with respect to patterns of response to challenge. There was a significant interaction with respect to maximum percentage increase over baseline (P < 0.002): among younger adults, the men exhibited greater increases whereas among the older adults, the women exhibited greater increases. A similar, though only marginally significant pattern was seen for total area under the response curve (P = 0.07). Repeated measures ANOVA confirmed the gender-by-age differences in the patterns of response (P = 0.01 for time*age*gender interaction).

Human glucocorticoid feedback inhibition is reduced in older individuals: evening study

We have previously shown that when tested in the morning, older men and women, pretreated with metyrapone to block endogenous cortisol synthesis, exhibit delayed suppression of plasma ACTH in response to cortisol infusion. To confirm this finding and to determine whether aging-related changes in feedback responsiveness are exaggerated near the time of the circadian nadir in adrenocortical secretion, we performed a similar study in the evening. Healthy young (20-35 yr, n = 22) and old (>65 yr, n = 21) men and women were administered metyrapone orally (750 mg) at 1600 and 1900 h, followed by a cortisol infusion of 0.06 mg/kg/h for 150 min. Blood samples were taken at 15-min intervals for 4 h following infusion onset for measurement of plasma ACTH, cortisol, 11-deoxycortisol, and corticosteroid binding globulin. When corrections were made for differences in circulating cortisol concentrations achieved among age and gender subgroups, feedback inhibition of ACTH was found to be significantly greater in young than in old subjects of both genders. Our studies support the hypothesis that glucocorticoid responses to stress in aging individuals are likely to be prolonged due to blunted and delayed inhibition of ACTH secretion, thus increasing the total exposure to glucocorticoids.

Violence prevention at work. A business perspective

INTRODUCTION

The risk of workplace violence varies depending on the type and location of the business. Business managers should assess violence risk and develop a program based on the level of risk faced by their employees.

DISCUSSION

This assessment should include: (1) a review of workplace security and identification of positions with increased risk of exposure to violence, (2) risk reduction through environmental design and employee training, (3) development of a plan and identification of professional resources to respond to incidents should they occur, and (4) communication of the employer's commitment to providing a safe work environment for employees.

CONCLUSIONS

For most businesses, threat assessment and management comprise the cornerstone of a workplace violence-prevention program. Planning and preparation are key to workplace violence prevention.

Chronic daily ethanol and withdrawal: 1. Long-term changes in the hypothalamo-pituitary-adrenal axis

BACKGROUND

Hypothalamo-pituitary-adrenal (HPA) function has been demonstrated to be compromised for weeks and even months after alcoholics cease ethanol consumption. Because nonalcoholic subjects with family history-associated increased risk for alcoholism also exhibit compromised HPA function, it is not clear whether defects in the HPA axis of abstinent alcoholics reflect a preexisting condition that may be responsible for increased risk for alcohol abuse versus a persisting adaptational change in response to prolonged alcohol abuse. Consequently, we investigated whether chronic daily ethanol consumption and withdrawal by male Sprague Dawley rats would induce persistent HPA changes consistent with those demonstrated in abstinent alcoholics.

METHODS AND RESULTS

In an initial experiment in which ethanol (5%, w/v) was incrementally introduced to liquid diet over a 1 week period followed by 4 weeks of chronic ethanol consumption, not only ethanol-treated rats but also pair-fed control rats exhibited decreased (p < 0.05 vs. ad-libitum-fed controls) anterior pituitary pro-opiomelanocortin (POMC) mRNA concentrations and associated decreases in plasma corticosterone and adrenocorticotropin (ACTH) levels for at least 3 weeks after gradual withdrawal of ethanol from the diet. Pair-feeding-induced decreases (p < 0.05) in thymus and spleen weights suggested that the pair-fed controls were likely stressed in this model, probably in response to the marked and irregular suppression of liquid diet consumption immediately after introduction of ethanol. Consequently, a second model was developed in which ethanol was introduced to the liquid diet much more gradually (i.e., over 3 weeks). In contrast with the rapid ethanol-introduction model, this more prolonged ethanol introduction followed by 4 weeks of chronic daily ethanol consumption increased plasma corticosterone levels (p < 0.05), increased adrenal gland weight (p < 0.05), and decreased thymus and spleen weights (both p < 0.01) without altering any of these parameters in the pair-fed controls. Three weeks after gradual withdrawal of ethanol from the diet, anterior pituitary POMC mRNA concentrations were suppressed (p < 0.05) and thymus and spleen weights were increased (p < 0.05) versus both pair-fed and ad-libitum-fed controls, accompanied by trends for decreased basal plasma corticosterone and adrenal weights.

CONCLUSIONS

Chronic daily ethanol treatment induced changes in the HPA axis that persisted for at least 3 weeks after complete cessation of ethanol consumption. These persistent alterations in the HPA axis are similar to the aberrant HPA regulation of abstinent alcoholics, sons of alcoholics, Lewis rats, and individuals who suffer from posttraumatic stress disorder and some types of depression, that is, categories of individuals who all exhibit increased risk for high ethanol consumption. Thus, these chronic daily ethanol-induced persistent changes in the HPA axis may have significant roles in alcohol abstinence syndrome and may increase vulnerability to relapse.

Hypothalamic melanin-concentrating hormone and estrogen-induced weight loss

Melanin-concentrating hormone (MCH) is an orexigenic neuropeptide produced by neurons of the lateral hypothalamic area (LHA). Because genetic MCH deficiency induces hypophagia and loss of body fat, we hypothesized that MCH neurons may represent a specific LHA pathway that, when inhibited, contributes to the pathogenesis of certain anorexia syndromes. To test this hypothesis, we measured behavioral, hormonal, and hypothalamic neuropeptide responses in two models of hyperestrogenemia in male rats, a highly reproducible anorexia paradigm. Whereas estrogen-induced weight loss engaged multiple systems that normally favor recovery of lost weight, the expected increase of MCH mRNA expression induced by energy restriction was selectively and completely abolished. These findings identify MCH neurons as specific targets of estrogen action and suggest that inhibition of these neurons may contribute to the hypophagic effect of estrogen.

Effect of intracerebroventricular alpha-MSH on food intake, adiposity, c-Fos induction, and neuropeptide expression

alpha-Melanocyte-stimulating hormone (alpha-MSH) is a hypothalamic neuropeptide proposed to play a key role in energy homeostasis. To investigate the behavioral, metabolic, and hypothalamic responses to chronic central alpha-MSH administration, alpha-MSH was infused continuously into the third cerebral ventricle of rats for 6 days. Chronic alpha-MSH infusion reduced cumulative food intake by 10.7% (P < 0.05 vs. saline) and body weight by 4.3% (P < 0.01 vs. saline), which in turn lowered plasma insulin levels by 29.3% (P < 0.05 vs. saline). However, alpha-MSH did not cause adipose-specific wasting nor did it alter hypothalamic neuropeptide mRNA levels. Central alpha-MSH infusion acutely activated neurons in forebrain areas such as the hypothalamic paraventricular nucleus, as measured by a 254% increase in c-Fos-like immunoreactivity (P < 0.01 vs. saline), as well as satiety pathways in the hindbrain. Our findings suggest that, although an increase of central melanocortin receptor signaling acutely reduces food intake and body weight, its anorectic potency wanes during chronic infusion and causes only a modest decrease of body weight.

Hypothalamic pituitary adrenocortical and sympathetic nervous system responses to the cold pressor test in Alzheimer's disease

BACKGROUND

Increased basal activity of the hypothalamic-pituitary-adrenocortical (HPA) axis has been repeatedly demonstrated in Alzheimer's disease (AD), and some studies suggest increased basal activity of the sympathetic nervous system (SNS) in this disorder; however, the effects of AD on HPA axis or SNS responses to a standardized aversive stressor have not been examined. The neuroendocrine response to aversive stress may be relevant to the pathophysiology of AD.

METHODS

Plasma adrenocorticotropic hormone (ACTH), cortisol, norepinephrine (NE), and epinephrine responses to a 1-min cold pressor test (CPT) were measured in nine medically healthy AD outpatients (age 76 +/- 2 years) and nine age- and gender-matched medically healthy cognitively normal older subjects (age 76 +/- 1 year).

RESULTS

The cortisol response to CPT was increased in the AD group but the ACTH response did not differ between groups. Basal NE concentrations were higher in the AD group. Although NE responses to CPT did not differ between groups, the blood pressure response to CPT was higher in the AD subjects.

CONCLUSIONS

These results suggest increased HPA axis responsiveness to CPT at the level of the adrenal cortex in AD. The results also suggest increased basal sympathoneural activity and increased cardiovascular responsiveness to sympathoneural stimulation in AD under the conditions of this experimental protocol. Increased SNS stimulatory modulation of the adrenal cortex is a possible mechanism contributing to the observed enhanced cortisol response to CPT in these AD subjects.

Daily melatonin administration to middle-aged male rats suppresses body weight, intraabdominal adiposity, and plasma leptin and insulin independent of food intake and total body fat

Pineal melatonin secretion declines with aging, whereas visceral fat, plasma insulin, and plasma leptin tend to increase. We have previously demonstrated that daily melatonin administration at middle age suppressed male rat intraabdominal visceral fat, plasma leptin, and plasma insulin to youthful levels; the current study was designed to begin investigating mechanisms that mediate these responses. Melatonin (0.4 microg/ml) or vehicle was administered in the drinking water of 10-month-old male Sprague Dawley rats (18/treatment) for 12 weeks. Half (9/treatment) were then killed, and the other half were submitted to cross-over treatment for an additional 12 weeks. Twelve weeks of melatonin treatment decreased (P<0.05) body weight (BW; by 7% relative to controls), relative intraabdominal adiposity (by 16%), plasma leptin (by 33%), and plasma insulin (by 25%) while increasing (P<0.05) locomotor activity (by 19%), core body temperature (by 0.5 C), and morning plasma corticosterone (by 154%), restoring each of these parameters toward more youthful levels. Food intake and total body fat were not changed by melatonin treatment. Melatonin-treated rats that were then crossed over to control treatment for a further 12 weeks gained BW, whereas control rats that were crossed to melatonin treatment lost BW, but food intake did not change in either group. Feed efficiency (grams of BW change per g cumulative food intake), a measure of metabolic function, was negative in melatonin-treated rats and positive in control rats before cross-over (P<0.001); this relationship was reversed after cross-over (P<0.001). Thus, melatonin treatment in middle age decreased BW, intraabdominal adiposity, plasma insulin, and plasma leptin, without altering food intake or total adiposity. These results suggest that the decrease in endogenous melatonin with aging may alter metabolism and physical activity, resulting in increased BW, visceral adiposity, and associated detrimental metabolic consequences.

Enhancement of memory in Alzheimer disease with insulin and somatostatin, but not glucose

BACKGROUND

Increasing plasma glucose levels improves memory in patients with Alzheimer disease (AD). Increasing plasma glucose levels also increases endogenous insulin levels, raising the question of whether memory improvement is due to changes in insulin, independent of hyperglycemia. We address this question by examining memory and counterregulatory hormone response during hyperglycemia when endogenous insulin was suppressed by concomitant infusion of the somatostatin analogue octreotide (Sandostatin).

METHODS

Twenty-three patients with AD and 14 similarly aged healthy adults participated in 4 metabolic conditions on separate days: (1) hyperinsulinemia (538 pmol/L) with fasting glucose (5.6 mmol/L [100 mg/dL]), achieved by insulin and variable dextrose infusion; (2) hyperglycemia (12.5 mmol/L [225 mg/dL]) with fasting insulin (57 pmol/L), achieved by dextrose and somatostatin (octreotide) infusion (150 mg/h); (3) placebo with isotonic sodium chloride solution (saline) infusion (fasting insulin and glucose); and (4) an active control condition in which somatostatin alone was infused (150 mg/h). Declarative memory (story recall) and selective attention (Stroop interference test) were measured during steady metabolic states.

RESULTS

Patients with AD showed improved memory during hyperinsulinemia relative to placebo (P = .05) and relative to hyperglycemia (P<.005). Memory did not improve during hyperglycemia when insulin was suppressed. Somatostatin analogue infusion alone also improved memory for patients with AD (P<.05). Hyperinsulinemia increased cortisol levels in subjects with AD, whereas somatostatin alone lowered cortisol concentrations.

CONCLUSIONS

These results confirm that elevated insulin without hyperglycemia enhances memory in adults with AD, and indicate that insulin is essential for hyperglycemic memory facilitation. These results also suggest a potential therapeutic role for somatostatin in AD.

Plasma lipid concentrations during episodic occupational stress

The possibility that stress affects plasma lipid concentrations has been the subject of recent investigation, but the findings are equivocal in nonlaboratory settings. To determine whether psychological stress contributes to variability in plasma lipid concentrations and concomitant changes in health behaviors, the effect of increased work load on plasma lipids and apolipoproteins was examined in 173 lawyers. Plasma cholesterol, triglyceride, and apolipoprotein concentrations were studied during periods of high work load (corresponding to impending tax deadlines) and during periods of usual work load. Self-reports of stress, work load, and time pressure, and cortisol, blood pressure, and heart rate were measured to verify that impending deadlines were associated with increased stress levels. Health behaviors which may affect plasma lipoprotein concentrations, including dietary intake and exercise, were also examined. High work load was accompanied by increases in self-reported work load among lawyers most directly affected by the impending deadlines. Plasma apolipoprotein B and triglycerides increased during periods of high work load (M = 1.9 mg/dL, SD = 10.1 and M = 5.3, SD = 34.4, respectively). No changes in dietary intake and exercise were observed. Psychological stress (high work load) is associated with potentially atherogenic changes in plasma lipid concentrations. While the lipoprotein effect of this short-term work stress is small, the effects of longer-term stress on multiple rise factors including triglycerides and apolipoprotein B could have significance for the development of coronary artery disease.

Physostigmine challenge before and after chronic cholinergic blockade in elderly volunteers

BACKGROUND

As a test of possible muscarinic up-regulation, the cortisol response to intravenous (i.v.) physostigmine (an anticholinesterase) was measured in 9 elderly volunteers before and after chronic cholinergic blockade with the muscarinic cholinergic antagonist scopolamine.

METHODS

Each of the 9 elderly control subjects was given two physostigmine (0.5 mg i.v.) infusions separated by 21 doses of nightly scopolamine (1.2 mg p.o.). No scopolamine was administered the night before infusions, and glycopyrrolate (0.2 mg i.v.) was administered prior to physostigmine, to block its peripheral effects. Vital signs were monitored and blood samples were collected at six time points surrounding the physostigmine infusion (-10, +10, +20, +30, +50, and +70 min). Behavioral measures and cognitive tests were administered prior to and 30 min after the physostigmine.

RESULTS

The cortisol response to physostigmine was greater after the second (post-chronic scopolamine) infusion study compared to the first (p < .05) as measured by an area under the curve analysis of all time points. When individual time points were compared, the mean cortisol response was significantly increased after the second physostigmine infusion at the +50- and +70-min time points (p < .05). There were no significant changes in behavioral rating scales, cognitive tests, or vital signs between the two physostigmine infusion study days.

CONCLUSIONS

This study demonstrates increased hypothalamic-pituitary-adrenocortical axis responsivity to a central nervous system cholinergic stimulus after chronic muscarinic blockade in 9 elderly control subjects. It also gives further evidence to support previous suggestions of muscarinic plasticity, specifically postsynaptic up-regulation, in the aging brain following exposure to chronic anticholinergic treatment.

Low plasma leptin levels contribute to diabetic hyperphagia in rats

The adipocyte hormone leptin reduces food intake in normal animals. During uncontrolled type 1 diabetes, plasma leptin levels fall, whereas food intake increases. To test the hypothesis that low leptin levels contribute to diabetic hyperphagia, we investigated the effect on food intake of replacement of leptin at basal plasma concentrations for 7 days in Long-Evans rats with uncontrolled diabetes induced by streptozotocin (STZ). One group of STZ diabetic rats received saline (STZ + Sal) (n = 11), while the other group (STZ + Lep) (n = 15) received a subcutaneous infusion of recombinant rat leptin (100 microg x kg(-1) x day(-1)) via osmotic minipumps. A nondiabetic control group (Con) (n = 11) received saline only. In the STZ + Sal group, plasma leptin levels decreased by 75% (P < 0.05) from 2.4+/-0.5 on the day before STZ/citrate buffer vehicle (Veh) injection (day 0) to 0.6+/-0.2 ng/ml on day 7. In contrast, plasma leptin levels on days 3-7 were comparable to pretreatment values in both the STZ + Lep group (day 0: 2.6+/-0.4 vs. day 7: 2.5+/-0.3 ng/ml, NS) and the Con group (day 0: 3.8+/-0.4 vs. day 7: 2.9+/-1.0 ng/ml, NS). In the STZ + Sal group, daily food intake increased gradually to values 43% above basal by day 7 (day 0: 24+/-2 to day 7: 33+/-3 g, P < 0.05), whereas food intake did not increase in either the STZ + Lep group (day 0: 24+/-1 vs. day 7: 21+/-2 g, NS), or the Con group (day 0: 23+/-1 vs. day 7: 23+/-2 g). Plasma glucose levels exceeded nondiabetic control values (7.7+/-0.2 mmol/l) in both diabetic groups, but were lower in the STZ + Lep group (17.2+/-1.8 mmol/l) than in the STZ + Sal group (24.3+/-1.1 mmol/l, P < 0.05). To determine if sensitivity to leptin-induced anorexia was affected by STZ treatment, a second experiment was performed in which the effect of intracerebroventricular leptin injection (at doses of 0.35, 1.0, or 3.5 microg) on food intake was measured 10 days after STZ or Veh treatment. Leptin suppressed both 4- and 24-h food intake in the two groups to an equal extent at every dose (by 15, 22, and 35%, respectively). These findings support the hypothesis that the effect of uncontrolled diabetes to lower leptin levels contributes to diabetic hyperphagia and that this effect is not due to altered leptin sensitivity.

Effects of Alzheimer's disease and gender on the hypothalamic-pituitary-adrenal axis response to lumbar puncture stress

Differences in hypothalamic-pituitary-adrenal (HPA) axis responsiveness to lumbar puncture (LP) stress were studied in normal elderly subjects and Alzheimer's disease (AD) patients of both genders. Elderly normal subjects had larger peak cortisol and ACTH responses than AD patients. These results contrast with some previous reports of increased HPA-axis responsivity associated with AD and suggest that AD-related changes in HPA responsiveness depend on the type of stressor involved and are mediated 'upstream' to the final common pathway to ACTH secretion. HPA-axis responsiveness also differed by gender, with higher peaks and prolonged elevations in elderly female subjects than in elderly males.

Metabolic, gastrointestinal, and CNS neuropeptide effects of brain leptin administration in the rat

To investigate whether brain leptin involves neuropeptidergic pathways influencing ingestion, metabolism, and gastrointestinal functioning, leptin (3.5 micrograms) was infused daily into the third cerebral ventricular of rats for 3 days. To distinguish between direct leptin effects and those secondary to leptin-induced anorexia, we studied vehicle-infused rats with food available ad libitum and those that were pair-fed to leptin-treated animals. Although body weight was comparably reduced (-8%) and plasma glycerol was comparably increased (142 and 17%, respectively) in leptin-treated and pair-fed animals relative to controls, increases in plasma fatty acids and ketones were only detected (132 and 234%, respectively) in pair-fed rats. Resting energy expenditure (-15%) and gastrointestinal fill (-50%) were reduced by pair-feeding relative to the ad libitum group, but they were not reduced by leptin treatment. Relative to controls, leptin increased hypothalamic mRNA for corticotropin-releasing hormone (CRH; 61%) and for proopiomelanocortin (POMC; 31%) but did not reduce mRNA for neuropeptide Y. These results suggest that CNS leptin prevents metabolic/gastrointestinal responses to caloric restriction by activating hypothalamic CRH- and POMC-containing pathways and raise the possibility that these peripheral responses to CNS leptin administration contribute to leptin's anorexigenic action.

Effect of chronic high-dose exogenous cortisol on hippocampal neuronal number in aged nonhuman primates

Chronic exposure to increased glucocorticoid concentrations appears to lower the threshold for hippocampal neuronal degeneration in the old rat. It has been proposed that increased brain exposure to glucocorticoids may lower the threshold for hippocampal neuronal degeneration in human aging and Alzheimer's disease. Here, we asked whether chronic administration of high-dose cortisol to older nonhuman primates decreases hippocampal neuronal number as assessed by unbiased stereological counting methodology. Sixteen Macaca nemestrina (pigtailed macaques) from 18 to 29 years of age were age-, sex-, and weight-matched into pairs and randomized to receive either high-dose oral hydrocortisone (cortisol) acetate (4-6 mg/kg/d) or placebo in twice daily palatable treats for 12 months. Hypothalamic-pituitary-adrenal activity was monitored by measuring plasma adrenocorticotropin and cortisol, 24 hr urinary cortisol, and CSF cortisol. Urinary, plasma, and CSF cortisol were elevated, and plasma adrenocorticotropin was reduced in the active treatment group. Total hippocampal volume, subfield volumes, subfield neuronal density, and subfield total neuronal number did not differ between the experimental groups. These findings suggest that chronically elevated cortisol concentrations, in the absence of stress, do not produce hippocampal neuronal loss in nonhuman primates.

Daily melatonin administration at middle age suppresses male rat visceral fat, plasma leptin, and plasma insulin to youthful levels

Human and rat pineal melatonin secretion decline with aging, whereas visceral fat and plasma insulin levels increase. Melatonin modulates fat metabolism in some mammalian species, so these aging-associated melatonin, fat and insulin changes could be functionally related. Accordingly, we investigated the effects of daily melatonin supplementation to male Sprague-Dawley rats, starting at middle age (10 months) and continuing into old age (22 months). Melatonin was added to the drinking water (92% of which was consumed at night) at a dosage (4 microg/ml) previously reported to attenuate the aging-associated decrease in survival rate in male rats, as well as at a 10-fold lower dosage. The higher dosage produced nocturnal plasma melatonin levels in middle-aged rats which were 15-fold higher than in young (4 months) rats; nocturnal plasma melatonin levels in middle-aged rats receiving the lower dosage were not significantly different from young or middle-aged controls. Relative (% of body wt) retroperitoneal and epididymal fat, as well as plasma insulin and leptin levels, were all significantly increased at middle age when compared to young rats. All were restored within 10 weeks to youthful (4 month) levels in response to both dosages of melatonin. Continued treatment until old age maintained suppression of visceral (retroperitoneal + epididymal) fat levels. Plasma corticosterone and total thyroxine (T4) levels were not significantly altered by aging or melatonin treatment. Plasma testosterone, insulin-like growth factor I (IGF-I) and total triiodothyronine (T3) decreased by middle age; these aging-associated decreases were not significantly altered by melatonin treatment. Thus, visceral fat, insulin and leptin responses to melatonin administration may be independent of marked changes in gonadal, thyroid, adrenal or somatotropin regulation. Since increased visceral fat is associated with increased insulin resistance, diabetes, and cardiovascular disease, these results suggest that appropriate melatonin supplementation may potentially provide prophylaxis or therapy for some prominent pathologies associated with aging.

Sodium lactate and hypertonic sodium chloride induce equivalent panic incidence, panic symptoms, and hypernatremia in panic disorder

BACKGROUND

Although experimental induction of panic by infusion of 0.5 mol/L sodium lactate in persons with panic disorder was described three decades ago, the mechanism underlying this observation remains unclear. Here we asked if the rapid administration of the large sodium load contained in the 0.5-mol/L sodium lactate infusion might be involved in panic induction.

METHODS

We compared in panic disorder and healthy subjects behavioral, electrolyte, endocrine, and acid-base responses to three double-blind randomly ordered equal volume 20-min infusions: 0.5 mol/L sodium lactate, hypertonic saline (3% sodium chloride), and normal saline placebo.

RESULTS

Sodium lactate (0.5 mol/L) and hypertonic saline produced the same high incidence of panic and equivalent increases in panic symptoms, serum sodium, and plasma vasopressin in the panic disorder subjects. Neither hypertonic infusion increased cortisol or adrenocorticotropin. No normal subject experienced panic in any condition. The 0.5-mol/L sodium lactate infusion induced alkalosis, whereas hypertonic saline and normal saline induced a mild acidosis.

CONCLUSIONS

Hypertonic sodium solution containing either chloride or lactate anion induces panic in panic disorder. The large sodium loads delivered by hypertonic saline and 0.5 mol/L sodium lactate may be involved in the mechanism of panic induction.

NPY-induced overfeeding suppresses hypothalamic NPY mRNA expression: potential roles of plasma insulin and leptin

To test the hypothesis that NPY-induced overfeeding activates compensatory responses that inhibit hypothalamic NPY gene expression, we investigated the effect of chronically administered neuropeptide Y (NPY) on plasma hormones involved in energy balance and on the level of mRNA for hypothalamic neuropeptides. After cannulation of the third cerebral ventricle, male Long-Evans rats received a 4.5-day intracerebroventricular (i.c.v.) infusion of either human NPY (12 microg per day), or synthetic cerebrospinal fluid (CSF). NPY-treated animals were either allowed ad libitum access to food or were pairfed to the intake of CSF-treated controls. In rats fed ad libitum, i.c.v. NPY induced significant increases in food intake (75%), body weight (9%), plasma insulin (150%) and plasma leptin levels (300%) as compared to the i.c.v. CSF group. Levels of plasma leptin, but not insulin, remained elevated in NPY-treated rats that were pairfed to the intake of the CSF group. NPY mRNA levels in the midregion of the arcuate nucleus (ARC) were reduced by 50% in NPY-treated rats that were allowed to overeat, but not in the pairfed group, as determined by in situ hybridization. In contrast, mRNA for corticotropin-releasing hormone (CRH) in the paraventricular nucleus (PVN) and proopiomelanocortin (POMC) in the rostral ARC were not significantly different among groups. These findings indicate that NPY-induced overfeeding suppresses ARC NPY mRNA expression, and that this effect unlikely to be mediated by a direct action of NPY, since it was abolished by limiting food intake in NPY-treated animals to that observed in controls. NPY-induced overfeeding was also associated with elevated plasma levels of leptin and insulin. The effect of these hormones to inhibit NPY gene expression may therefore have contributed to the decrease of NPY mRNA.

Acute alcohol effects on opiomelanocortinergic regulation

To assess acute effects of alcohol on forebrain and pituitary opiomelanocortinergic regulation, a model was developed in which "experienced" (previously introduced to ethanol administration, so the subjective response was not a novel stimulus) male Sprague-Dawley rats received pulsatile intragastric ethanol infusions during the dark (active) photophase to produce and sustain (for 3 hr) behaviorally relevant (0, 40 to 70, 80 to 110, or 120 to 150 mg/dl) plasma ethanol levels. The effects of alcohol on hypothalamo-pituitary-adrenal (H-P-A) axis function were biphasic with respect to dosage (inhibition with low dosage and stimulation with higher dosages) and time (initial stimulation with higher dosages was followed by rapid return to control levels even though elevated plasma ethanol levels were maintained). The effects of alcohol on H-P-A activation were also inconsistent; some of the animals did not appear to respond even though elevated (i.e., >100 mg/dl) plasma ethanol levels were produced. Induction of moderate (80 to 110 mg/dl) plasma ethanol levels acutely (within 30 min) increased immunoreactive (i) beta-endorphin concentrations in the ventral tegmental area of the brain; higher (120 to 150 mg/dl) plasma ethanol levels increased i beta-endorphin concentrations in both the ventral tegmental area and the nucleus accumbens, whereas i beta3-endorphin concentrations were not significantly altered in other brain areas. High (120 to 150 mg/dl) plasma ethanol levels also increased mediobasohypothalamic pro-opiomelanocortin (biosynthetic precursor of forebrain beta-endorphin) mRNA concentrations at 3 and 6 hr after initiation of ethanol infusions. Results demonstrate that atraumatic induction of physiologically meaningful plasma alcohol levels by gastric ethanol infusion activates the forebrain opiomelanocortinergic opioid system and exerts complex effects on the interrelated H-P-A system, consistent with evidence that these systems may interact to mediate or modulate some responses to alcohol ingestion.

Central leptin stimulates corticosterone secretion at the onset of the dark phase

Leptin, a hormone secreted by adipose tissue in proportion to body adiposity, is proposed to be involved in the central nervous regulation of food intake and body weight. In addition, evidence is emerging that leptin regulates neuroendocrine and metabolic functions as well, presumably via its action in the central nervous system (CNS). To investigate this regulatory effect of leptin, we infused 3.5 microg of human leptin directly into the third cerebral ventricle (i3vt) of lean male Long-Evans rats, 90 min before the onset of their dark phase. Before and after infusion, blood samples were withdrawn through indwelling catheters for assessment of hormonal (plasma corticosterone, insulin, leptin), autonomic (plasma norepinephrine, epinephrine), and metabolic (plasma glucose) parameters. I3vt leptin caused an increase in plasma corticosterone and plasma leptin levels relative to the control condition. The effects of i3vt leptin on corticosterone secretion became particularly apparent after the onset of the dark phase. The results of the present study indicate that i3vt leptin stimulates the hypothalamo-pituitary-adrenal (HPA) axis, particularly when rats normally encounter their largest meals. These results are consistent with the possibility that high circulating leptin levels may underlie the increased activity of the HPA axis that is generally characteristic of human obesity and most animal models of obesity.

Adrenalectomy increases sensitivity to central insulin

When infused into the third ventricle of rats, insulin dose-dependently reduces food intake and body weight, with doses of 1 mU/day and lower being ineffective. Because corticosterone functionally antagonizes many of insulin's peripheral actions, and because corticosterone acts in the brain to enable hyperphagia under some conditions, a subthreshold dose of insulin (1 mU/day), or its saline vehicle, was infused into the third ventricle of adrenalectomized (ADX) and sham-ADX male Long-Evans rats. Sham-ADX rats that received insulin or saline had no significant change of food intake or body weight over a 2-week interval. Likewise, saline-infused ADX were unaffected. In contrast, ADX rats receiving insulin had a significant reduction of food intake and body weight. These results suggest that the absence of circulating glucocorticoids increases the brain's sensitivity to insulin, and that insulin in the brain acts to lower food intake and body weight via a glucocorticoid-sensitive mechanism.

Successful 6-month endurance training does not alter insulin-like growth factor-I in healthy older men and women

BACKGROUND

Lean body mass, strength, and endurance decline with advancing age, changes paralleled by declines in anabolic hormones, including growth hormone (GH) and insulin-like growth factor-I (IGF-I). Acute exercise has been shown to stimulate the GH/IGF-I axis, and long-term exercise increases GH. This study examined the effect of endurance training on IGF-I in healthy older men and women.

METHODS

Thirty-one healthy older men (66.9 +/- 1.0 yrs, mean +/- SEM) and 21 healthy older women (67.1 +/- 1.7 yrs) were randomized to either 3d/wk, 6-month endurance (ET3) or stretching/flexibility (SF3) protocols. Another group of 15 healthy older men (69.0 +/- 1.3 yrs) participated in a more intensive 5d/wk, 6-month endurance protocol (ET5). Before and after training, subjects were weight stabilized and participated in maximal exercise tolerance testing, body composition assessment, and fasting blood sampling.

RESULTS

ET3 training resulted in a significant increase (14%) in maximal aerobic power (VO2max), significant decreases in body weight (BW), fat mass (FM), and waist/hip ratio (WHR), and a significant increase in fat-free mass (FFM). No significant VO2max or body composition changes were observed in the SF3 group. For the ET5 group, a significant increase (22%) in VO2max and significant decrease in BW, FM, and WHR were observed. No significant changes in IGF-I were observed for any of the three groups. Pre- versus post-training IGF-I values were very stable (r = .86, p < .001) across subjects.

CONCLUSIONS

Within-subject basal levels of IGF-I in healthy seniors were extremely stable between pre- and post-training assessments. Two endurance training protocols of magnitudes sufficient to significantly increase aerobic capacity and decrease measures of body adiposity did not significantly increase basal levels of IGF-I in healthy older men and women.

Protein changes during aging and the effects of long-term cortisol treatment in macaque monkey lens

Macaca nemestrina pig-tail macaques were administered daily oral doses of 3.85 or 5.78 mg/kg of cortisol for 1 year. The ages of the macaques were from 19 to 29 years. After 1 year, lenses were observed using a slitlamp ophthalmoscope and the stage of cataract was classified in each eye. Enucleated lenses were analyzed for content of soluble and insoluble proteins. Lens proteins were analyzed using SDS polyacrylamide gel electrophoresis (SDS-PAGE) and the changes in lens proteins were quantified using densitometry of the individual gels. Untreated control lenses were obtained over the range of 4 to 29 years of age and the proteins were analyzed. A slow progressive increase in the cataract stage and in the proportion of insoluble protein aggregates corresponded with the animal age, not the cortisol treatment. The observed changes in the protein components may suggest an important role for cytoskeletal proteins in lens transparency during aging. Exposure to high doses of oral steroids over a period of 1 year did not result in detectable modification of crystallin or cytoskeletal proteins. Even at high doses, longer exposure may be necessary to produce the cataract associated with steroid administration.

Behavioral and neuroendocrine responses to sodium lactate infusion in subjects with posttraumatic stress disorder

OBJECTIVE

Sodium lactate infusion has induced flashbacks accompanied by panic attacks in male combat veterans with posttraumatic stress disorder (PTSD) and concurrent panic disorder. This study addressed whether sodium lactate induces flashbacks or other intrusive PTSD symptoms in PTSD patients free of concurrent panic disorder.

METHOD

Behavioral, cardiovascular, catecholamine, and cortisol responses to infusion of 0.5 M sodium lactate were compared among seven subjects with PTSD without panic disorder, seven subjects with panic disorder only, and seven healthy subjects.

RESULTS

Six of the seven PTSD subjects but no panic disorder or healthy subjects reported flashbacks or other intrusive PTSD symptoms during lactate infusion. Flashbacks were accompanied by substantial anxiety symptoms. Cortisol levels were low in the PTSD subjects.

CONCLUSIONS

Sodium lactate induces flashbacks in persons with PTSD without comorbid panic disorder. The relationship between anxiety responses accompanying a PTSD flashback and those in a panic attack remains unclear.

Decreased hypothalamic-pituitary-adrenal axis sensitivity to cortisol feedback inhibition in human aging

Aging-related reduction in the sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis to glucocorticoid feedback inhibition has been demonstrated in rodents, but aging effects on glucocorticoid feedback inhibition in humans are unclear. This study assessed the influence of aging on the sensitivity of the human HPA axis to feedback inhibition induced by cortisol. Endogenous cortisol feedback inhibition was removed by treatment with metyrapone, which reduces cortisol synthesis by inhibiting 11 beta-hydroxylase. Feedback inhibition was then reintroduced by infusing exogenous cortisol. Sixteen young (26 +/- 1 years old) and 16 older (70 +/- 2 years old) subjects underwent three study conditions in random order. In the two cortisol infusion conditions, oral metyrapone treatment was followed by intravenous infusion of 0.03 mg/kg/h (83 nmol/kg/h) or 0.06 mg/kg/h (166 nmol/kg/h) cortisol for 150 min. Feedback sensitivity was estimated by the latency to and extent of decline of plasma ACTH concentration during and following the cortisol infusion. In a placebo condition, placebo tablets were substituted for metyrapone and normal saline infusion was substituted for cortisol. Blood samples were drawn twice prior to and at 15-min intervals for 4 h following the onset of the infusions, and plasma was assayed for 11-deoxycortisol, cortisol and ACTH. Plasma cortisol suppression and ACTH and 11-deoxycortisol elevations did not differ between age groups after metyrapone. Older subjects exhibited delayed and blunted ACTH responses to infused cortisol. Within older subjects, the ACTH response to the higher dose cortisol infusion was blunted in older women compared to older men. These data provide direct evidence for reduced responsiveness to glucocorticoid feedback inhibition in human aging.

Learned tolerance to the corticosterone-increasing action of ethanol in rats

Ethanol administration stimulates the hypothalamic-pituitary-adrenal (HPA) axis, resulting in increased plasma levels of corticosterone. As occurs with many other effects of ethanol, tolerance develops with repeated administration such that plasma corticosterone levels become less effected by subsequent ethanol administration. The present experiment explored the possibility that the environmental cues associated with the administration of ethanol can control the expression of tolerance to ethanol's corticosterone-elevating effects. Male Long-Evans rats received intragastric administrations of ethanol (3.2 g/ kg) in association with one set of environmental cues and intragastric saline in association with a different set of environmental cues. Plasma corticosterone levels were elevated after the first ethanol administration, but after the tenth ethanol administration, corticosterone levels failed to increase significantly above control values. After demonstrating tolerance, rats were administered ethanol in the saline-paired environment and plasma corticosterone levels were higher than in the ethanol-paired environment. This environmental specificity suggests that tolerance to the neuroendocrine effects of ethanol is not simply the result of long-term alterations in sensitivity of the HPA axis but is, at least in part, mediated by learned responses to cues that predict the effects of ethanol.

Variations in plasma lipid concentration during examination stress

The effect of psychological stress on plasma lipids was studied in 40 law students (20 men and 20 women). Plasma cholesterol, triglyceride, and apolipoprotein concentrations were examined at the beginning of the quarter and during the week before final examinations. Cortisol, blood pressure, and heart rate, and self-reports of stress and workload were also measured to verify that examinations were associated with increased stress levels. Perceived stress, perceived workload, and cortisol increased before examinations. Low density lipoprotein cholesterol (LDL-C) increased 5.8 +/- 13.9 mg/dL, and apolipoprotein B (apo B) increased 2.9 +/- 4.0 mg/dL. High density lipoprotein cholesterol decreased in women only. These changes were not due to changes in dietary intake or indexes of plasma volume. However, changes in cortisol and changes in LDL-C and apo B were associated, suggesting a neuroendocrine component to the effects. These results suggest that episodic, stressful situations may lead to potentially atherogenic changes in lipid and lipoprotein concentrations.

Hypothalamic-pituitary-adrenocortical axis responses to physostigmine: effects of Alzheimer's disease and gender

We asked whether hypothalamic-pituitary-adrenocortical (HPA) axis responses to a cholinergic stimulus are blunted in patients with Alzheimer's disease (AD) of mild to moderate severity. Such a finding would be consistent with a central cholinergic deficiency early in the course of AD. To address this question, we measured the plasma adrenocorticotropic hormone (ACTH), beta-endorphin-like immunoreactivity (beta E-LI), and cortisol responses to the cholinesterase inhibitor physostigmine in 10 healthy normal older subjects (age = 71 +/- 2 years) and 11 outpatients with probable AD (age = 72 +/- 2 years; Mini Mental State Exam score = 19 +/- 2). Cortisol concentrations were higher in AD subjects throughout the study, but AD and normal older subjects had similar robust ACTH, beta E-LI, and cortisol responses to physostigmine. In all subjects combined, women had greater ACTH, beta E-LI, and cortisol responses to physostigmine than did men. Plasma physostigmine concentrations did not differ between groups. These results suggest that female gender enhances the magnitude of HPA axis responses to cholinergic stimulation in older humans; however, the HPA axis response to physostigmine does not appear to reflect central cholinergic deficiency in the early stages of AD.

A comparison of the effects of food deprivation and 2,5-anhydro-D-mannitol on metabolism and ingestion

Using respiratory quotient as an index of metabolic state, we compared the effects of administrations of the fructose analogue 2,5-anhydro-D-mannitol (2,5-AM) at a dose of 300 mg/kg with the effect of 10 h of food deprivation. We measured behavioral and physiological responses of the animals receiving the two treatments, including food intake, energy expenditure, rates of carbohydrate and fatty acid utilization, and plasma levels of glucose, insulin, corticosterone, epinephrine, and norepinephrine. A vehicle-treated control group was also included. Fasting produced a greater food intake than 2,5-AM administration. Although plasma glucose, insulin, and norepinephrine levels were similar between the two treatments, plasma corticosterone and epinephrine levels were significantly elevated in animals receiving 2,5-AM. We conclude that although 2,5-AM can produce a metabolic state similar to fasting, as measured by an index of whole body metabolic state (respiratory quotient), there remain factors that influence food intake that are not similar in the two conditions.

Glucocorticoid regulation of vasopressin V1a receptors in rat forebrain

Vasopressin V1a receptors (V1aRs) are expressed in the septum of the rat brain where they are thought to mediate several of the physiologic and behavioral effects of this neuropeptide. We have investigated the effects of adrenal steroids on forebrain V1aRs. Rats were bilaterally adrenalectomized (ADX) and hormone replaced with either corticosterone (CORT), dexamethasone (DEX) or aldosterone (ALDO) at different concentrations. V1aR mRNA was evaluated using in situ hybridization, and V1aR binding site density was quantified using a specific iodinated V1aR antagonist [125I]d(CH2)5Sar7-AVP (125I-SAVP). V1aR density in the dorsolateral septum and the bed nucleus of the stria terminalis (BNST) decreased significantly with adrenalectomy, and 5 micrograms/100 g b.wt. of DEX was able to restore V1aR binding to levels comparable to those of sham operated controls in both regions. ALDO replacement also elevated V1aR binding in the BNST but not in the septum. In ADX animals given corticosterone in their drinking water, V1aR mRNA levels detected by in situ hybridization increased significantly over the ADX rats given saline. In order to understand the molecular basis of this effect, a putative genomic clone encoding the rat V1aR was isolated, and sequence analysis of the 5' flanking region has revealed the presence of several putative glucocorticoid response elements (GREs). Gel retardation assays were performed using these putative GREs, and two appear to be active in protein binding in glucocorticoid receptor containing nuclear extracts. The glucocorticoid effects on V1aR mRNA and binding, and the presence of putative active GREs in the promoter of the V1aR gene strongly implicate a role for adrenal steroids in the regulation of V1a receptor gene expression in glucocorticoid receptor and/or mineralocorticoid receptor expressing tissues.

Evidence for glucocorticoid regulation of the rat vasopressin V1a receptor gene

WRK-1 cells express vasopressin V1a receptors. Twenty-four-hour treatment of these cells with dexamethasone (DEX) resulted in an increase in [3H]AVP binding that was maximal at 12 h, and could be blocked by addition of RU 38486. The increases in [3H]AVP binding were paralleled by increases in V1a receptor mRNA. The in vivo effects of glucocorticoids (GCs) on V1a receptor binding in hepatic tissue were also investigated in adrenalectomized and hormone-replaced rats given either DEX or aldosterone (ALDO). DEX effectively increased V1a receptor binding site density whereas ALDO had no effect. The DEX effects on V1a receptor mRNA and binding strongly implicate glucocorticoids in the regulation of V1a receptor gene expression.

The effects of normal aging on cortisol and adrenocorticotropin responses to hypertonic saline infusion

To assess the effects of aging on hypothalamic-pituitary-adrenal (HPA) axis responsivity, we compared the plasma cortisol and adrenocorticotropin (ACTH) responses to hypertonic saline infusion between normal older and young human volunteers. We administered a 90 min hypertonic saline infusion (5% sodium chloride at 0.06 ml/kg/min) and a 90 min placebo infusion (0.9% sodium chloride at 0.06 ml/kg/min) to normal young subjects (n = 13, age = 29 +/- 2 years) and normal older subjects (n = 8, age = 63 +/- 3 years). Plasma cortisol, ACTH, osmolality and arginine vasopressin (AVP) were measured before and at 30 min intervals during the infusions. The rate of increase in plasma osmolality and AVP induced by hypertonic saline infusion was similar between groups. The plasma cortisol increase during hypertonic saline infusion was greater in normal older subjects than in young subjects (p = .03), but a stimulatory effect of hypertonic saline infusion on plasma ACTH was not apparent in either older or young subjects. These results suggest increased sensitivity with human aging to stimulation of cortisol release by hypertonic saline infusion at the adrenocortical level of the HPA axis.

Cardiovascular and neuroendocrine responses to extended laboratory challenge

The purpose of this study was to examine the effects of a 2-hour laboratory challenge on heart rate, blood pressure, catecholamines, and cortisol; and investigate the contribution of the physical act of speaking on both neuroendocrine and cardiovascular measures. Using a within-subjects design, 14 subjects were tested individually during two separate laboratory sessions. During one session, subjects engaged in two cognitively demanding tasks for 2 hours. During the other session, subjects executed the verbal demands of the tasks for 2 hours, but cognitive demands were absent. During both sessions, blood pressure and heart rate were measured and arterialized blood samples were obtained for the measurement of epinephrine, norepinephrine, and cortisol. Subjects demonstrated significantly greater increases in systolic blood pressure diastolic blood pressure, heart rate, epinephrine, and cortisol during the cognitively challenging session than during the control session. It is concluded that sustained elevations in cardiovascular and neuroendocrine measures can be achieved in the laboratory, and that the effects of such tasks cannot be attributed solely to the physical demands of speaking. Implications for the measurement of circulating catecholamines and cortisol during laboratory studies are discussed.

Evidence for two differentially regulated populations of peripheral beta-endorphin-releasing cells in humans

In the current study we tested the hypothesis that human plasma beta-endorphin (beta E) is derived from at least two subpopulations of beta E-releasing cells: one sensitive to glucocorticoids as well as to dopamine (DA; regulated analogously to the corticotrophs of the rat pituitary), and one insensitive to glucocorticoids but sensitive to DA (regulated analogously to the melanotrophs of the rat pituitary). To test this hypothesis, human plasma levels of ACTH, cortisol, and beta E-like immunoreactivity were measured at baseline and after haloperidol treatment (0.05 mg/kg, i.v.) in two experimental groups, one pretreated with dexamethasone (1.5 mg) and one pretreated with placebo. Plasma PRL levels were also measured in both groups as an indicator of DA receptor blockade. Dexamethasone partially suppressed both baseline and haloperidol-stimulated levels of human plasma beta E-like immunoreactivity, whereas it completely suppressed both basal and haloperidol-stimulated levels of ACTH and cortisol and had no statistically significant effect on either basal or haloperidol-stimulated PRL levels. These data support a negative feedback effect of glucocorticoids on one DA-sensitive cell population that releases both ACTH and beta E (corticotroph like), but not on a second cell population that releases beta E but not ACTH.