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Stimulation of brain cholinergic systems increases activity of both the sympathoneural (SN) and sympathoadrenomedullary (SAM) components of the peripheral sympathetic nervous system. Because presynaptic cholinergic neuron numbers are substantially reduced in Alzheimer's disease (AD), we predicted decreased responsiveness in AD of plasma norepinephrine (NE), an estimate of SN activity, and of epinephrine (EPI), an estimate of SAM activity, to central cholinergic stimulation by the cholinesterase inhibitor physostigmine (0.0125 mg/kg i.v.). Because previous studies have demonstrated that normal human aging increases SN activity but not SAM activity, we specifically hypothesized: (1) a smaller NE response to physostigmine in subjects with mild to moderate AD (n=11; age 72+/-2 yrs; mini-mental state exam [MMSE] scores of 19+/-2) than in healthy older subjects (n=20; age 71+/-1 yrs); and (2) a smaller EPI response in AD subjects than in either healthy older or healthy young subjects (n=9; age 27+/-2 yrs). Unexpectedly, the plasma NE increase following physostigmine only achieved significance in AD subjects and plasma EPI responses were greater in both AD and older subjects than in young subjects. Blood pressure responses to physostigmine were consistent with the catecholamine responses. These data suggest that the presence of mild to moderate AD increases the SN response to cholinergic stimulation and that both AD and normal aging increase the SAM response to cholinergic stimulation. As a result, plasma catecholamine responses to physostigmine do not appear to be useful peripheral neuroendocrine estimates of the severity of brain cholinergic deficits in mild to moderate AD.

Background: The effects of aging on sympathetic nervous system and adrenomedullary outflow were estimated by the measurement of plasma norepinephrine (NE) and epinephrine (EPI) responses to yohimbine and clonidine in healthy young and healthy older subjects., Methods: Yohimbine (0.65 mg/kg), clonidine (5 microg/kg), and placebo were administered on separate days in random order to 5 healthy older men (age 74 +/- 1 years) and 18 healthy young men (age 26 +/- 1 years). NE and EPI were measured by radioenzymatic assay in plasma samples obtained before and 30, 60, and 90 minutes after drug administration., Results: Plasma NE increases after yohimbine were greater in older men than in young men. but plasma NE decreases following clonidine did not differ between groups. Plasma NE and systolic blood pressure were higher in older men than in young men at baseline but no longer differed 90 minutes after clonidine. Plasma EPI increases after yohimbine and decreases after clonidine did not differ between groups., Conclusions: These results suggest increased sympathetic nervous system outflow in human aging that is not a function of reduced responsiveness of alpha-2 adrenoreceptor-mediated feedback inhibition.

Galanin (GAL) innervation is hypertrophied in the basal forebrain and cortex of patients with Alzheimer's disease (AD). Increased GAL could exacerbate the cognitive and behavioral deficits of AD because GAL acts as an inhibitory modulator of cholinergic and noradren-ergic neurotransmission. The locus ceruleus (LC) may be a source of increased GAL in AD because (a) GAL is coexpressed in a subset of LC neurons, (b) GAL expression is up-regulated with neuronal injury, and (c) the LC undergoes extensive degeneration in AD. Therefore, we have used in situ hybridization histochemistry to measure GAL gene expression in the LC of AD patients and sex- and age-matched nondemented controls. Despite the extensive loss of norepinephrine neurons with AD, GAL mRNA-expressing neurons in the LC did not differ between groups. This resulted in a significant increase in the percentage of neuromelanin-pigmented cells that coexpressed GAL in AD patients compared with controls. These findings raise the possibility that the increased incidence of GAL expression among remaining LC neurons contributes to the hyperinnervation of GAL fibers in AD. Furthermore, GAL may be neuroprotective in the LC.

Background: High cerebrospinal fluid (CSF) norepinephrine (NE) concentrations in aging and Alzheimer's disease (AD) could reflect decreased NE clearance from central nervous system (CNS) extracellular fluid or increased release of NE into CNS extracellular fluid. Measuring CSF concentrations of the intraneuronal NE metabolite dihydroxyphenylglycol (DHPG), an estimate of NE clearance, and the NE precursor dihydroxyphenylacetic acid (DOPA), an estimate of NE biosynthesis, can help differentiate these mechanisms., Methods: NE, DHPG, and DOPA were determined by HPLC in CSF and plasma obtained following yohimbine, clonidine, and placebo. Ten AD, 10 older, and 11 young subjects were studied., Results: CSF DOPA following yohimbine was higher in older and AD than in young subjects. CSF DHPG did not differ among groups. Plasma DOPA following yohimbine was higher in AD than in young subjects., Conclusions: During alpha-2 adrenoreceptor blockade in both aging and AD, there are increased responses of CNS NE biosynthesis and release with unchanged CNS NE clearance. This pattern is consistent with partial loss of CNS noradrenergic neurons with compensatory activation of remaining CNS noradrenergic neurons. Given the marked loss of locus coeruleus (LC) noradrenergic neurons in AD, achievement of high CSF NE suggests particularly prominent compensatory activation of remaining LC neurons in this 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.

Objective: Although loss of noradrenergic neurons in the locus ceruleus has been consistently demonstrated postmortem in Alzheimer's disease, several small studies suggest that indices of central noradrenergic activity increase with the severity of Alzheimer's disease in living patients. The authors estimated the effect of Alzheimer's disease severity on central noradrenergic activity by comparing the CSF norepinephrine concentrations of subjects with Alzheimer's disease in earlier and advanced stages. The effect of normal aging on CSF norepinephrine also was determined., Method: Lumbar punctures were performed in 49 subjects with Alzheimer's disease of mild or moderate severity, 25 subjects with advanced Alzheimer's disease, 42 normal older subjects, and 54 normal young subjects. Advanced Alzheimer's disease was defined prospectively by a Mini-Mental State score of less than 12. Norepinephrine was measured by radioenzymatic assay., Results: CSF norepinephrine concentration was significantly higher in the patients with advanced Alzheimer's disease (mean = 279 pg/ml, SD = 122) than in those with mild to moderate severity (mean = 198 pg/ml, SD = 89), normal older subjects (mean = 219 pg/ml, SD = 88), or normal young subjects (mean = 154 pg/ml, SD = 53). CSF and plasma norepinephrine levels and mean arterial blood pressure all were higher in the older subjects than in the young subjects., Conclusions: Despite the loss of locus ceruleus neurons in Alzheimer's disease, the aging-associated high concentration of CSF norepinephrine is retained in the earlier stages of Alzheimer's disease and increases further as the disease progresses. Increased brain noradrenergic activity may contribute to the agitated behaviors or cognitive deficits of patients with advanced Alzheimer's disease.

Physostigmine is a cholinesterase inhibitor which enhances central and peripheral cholinergic activity. In this study, we explored in persons with Alzheimer's disease (AD) the effects of an acute dose of physostigmine in patients receiving chronic physostigmine treatment on the activity of the cholinergically regulated noradrenergic and arginine vasopressin (AVP) systems. Specifically, we estimated the effects of sustained release oral physostigmine on central and peripheral noradrenergic and AVP systems by measuring norepinephrine (NE) and AVP in cerebrospinal fluid (CSF) and plasma. Lumbar punctures were performed in both physostigmine and no drug treatment conditions. In some subjects the effects of physostigmine on the plasma AVP response to the osmolar stimulus of a hypertonic saline infusion also were measured. NE concentrations in both CSF and plasma were significantly lower in the physostigmine than in the no drug condition. AVP concentrations did not differ between conditions in either compartment, nor did physostigmine affect the AVP response to hypertonic saline. Physostigmine appears to decrease both central and peripheral noradrenergic activity in AD.

Background: The resting cerebrospinal fluid (CSF) norepinephrine concentration is unchanged or even increased in patients with Alzheimer's disease (AD). These in vivo findings appear to be inconsistent with the post-mortem locus ceruleus neuronal loss that is reported in patients with AD., Methods: The effects of AD and advanced age on central nervous system noradrenergic status were estimated by comparing CSF norepinephrine concentrations following the administration of yohimbine hydrochloride, clonidine hydrochloride, and placebo in outpatients with AD and older and young normal subjects. Levels of yohimbine, its metabolite 11-hydroxy-yohimbine, and clonidine were measured in CSF and plasma samples. Behavioral responses were quantified by rating the Tension, Excitement, and Anxiety items on the Brief Psychiatric Rating Scale., Results: Yohimbine-induced increases of CSF norepinephrine concentrations were greater in both patients with AD and normal older subjects than in normal young subjects. Clonidine-induced decreases of CSF norepinephrine concentrations did not differ among groups. Behavioral arousal following the administration of yohimbine was greater in patients with AD than in the other groups., Conclusions: Central nervous system noradrenergic responsiveness is enhanced in normal older subjects, and this age effect is retained in patients with AD. Behavioral sensitivity to increased central nervous system noradrenergic activity is enhanced in patients with AD.

In vitro studies in hypothalamic-pituitary explants in the rat have suggested cholinergic mediation of arginine vasopressin (AVP) osmoregulation. In this study we attempted to demonstrate, in humans, cholinergic mediation of AVP osmoregulation. Specifically, we tested the hypothesis that the plasma AVP response to an osmolar stimulus would be attenuated by pharmacologic blockade of central nervous system muscarinic or nicotinic receptors in humans. We also evaluated the effects of cholinergic blockade on the norepinephrine (NE) response to an osmolar stimulus. Young normal males underwent hypertonic saline infusion following administration of the centrally active muscarinic antagonist scopolamine or the centrally active nicotinic antagonist mecamylamine. Neither mecamylamine nor scopolamine affected the AVP response to hypertonic saline infusion. Mecamylamine reduced NE concentrations in a dose-dependent manner, but did not affect the slope of the NE increase during hypertonic saline infusion. In a second experiment, we evaluated the effects of scopolamine and mecamylamine on the AVP and NE responses to physostigmine, a cholinesterase inhibitor which stimulates AVP release into plasma through a non-osmolar central nervous system cholinergic mechanism. Scopolamine eliminated the AVP response to physostigmine. Mecamylamine reduced NE concentrations both before and after scopolamine administration but did not affect the slope of the AVP response. These results fail to support cholinergic regulation of the AVP response to osmolar stimulation in humans.

Background: To determine whether elevations of plasma norepinephrine (NE) in major depression represent increased sympathetic nervous system (SNS) activity and to assess the effects of desipramine hydrochloride on sympathetic function., Methods: SNS activity was assessed in depressed patients and controls by an isotope-dilution, plasma NE kinetic technique using mathematical modeling and compartmental analysis. This approach provided estimates of the rate of NE appearance into an extravascular compartment, which is the site of endogenous NE release from SNS nerves, the corresponding rate of NE appearance into plasma, and the rate of NE clearance from plasma., Results: Norepinephrine appearance into the extravascular and vascular compartments was significantly elevated in 17 depressed patients compared with that in 36 controls. The rate of NE clearance from plasma was similar in both groups. This is compatible with increased SNS activity in major depression. Desipramine, given for 2 days, significantly reduced the concentration of NE in plasma of patients and controls by markedly suppressing the rates of extravascular and vascular NE appearance, compatible with a short-term reduction in SNS activity. Desipramine prolonged the rate of NE clearance from plasma, consistent with a blockade of NE re-uptake into SNS nerve terminals. The initial suppression of SNS activity by desipramine was reversed by long-term (28 days) treatment of patients, with extravascular and vascular NE appearance rates returning to approximately basal levels. An associated rise in plasma NE concentrations compared with the baseline was attributable to a progressive reduction in plasma NE clearance., Conclusion: Sympathetic nervous system activity is elevated in major depression and is suppressed by short-term desipramine administration. The demonstration of SNS reactivation occurring with prolonged desipramine treatment is compatible with the theory that long-term treatment desensitizes CNS alpha 2-adrenergic receptors and emphasizes the value of examining the temporal course of responses to pharmacological challenges of neuroendocrine systems. Previously reported elevations of plasma NE during prolonged administration of tricyclic antidepressants are probably the result of a reduction in plasma NE clearance, not an increase in SNS activity.

Abnormalities of neurochemical systems in Alzheimer disease, which are potentially relevant to the pathophysiology of such noncognitive problems as agitation and depression, have been demonstrated. However, the role of these abnormalities in the etiology of noncognitive problem behaviors remains poorly understood. Such abnormalities in brain noradrenergic and serotonergic systems are of particular interest because of their apparent involvement in normal regulation of mood, arousal, and aggressive behavior. The nature of the noradrenergic abnormalities in Alzheimer disease is particularly complex, with evidence suggesting both structural damage and compensatory increased norepinephrine release from remaining noradrenergic neurons. Currently available drugs that alter brain noradrenergic or serotonergic activity should be evaluated for efficacy in the management of noncognitive behavioral disorders complicating Alzheimer disease.

We recently demonstrated in patients with panic disorder that hypertonic saline infusion induces acute panic with the same frequency and intensity as the standard hypertonic sodium lactate infusion. We now report the effects in normal men of hypertonic saline infusion on neuroendocrine systems possibly relevant to panic and anxiety. We administered a 150-min infusion of hypertonic saline (5% sodium chloride) which increased plasma osmolality from 288 +/- 1 to 303 +/- 2 mOsm/kg and produced the appropriate increase of plasma arginine vasopressin (AVP). Plasma norepinephrine (NE) increased substantially during hypertonic saline infusion compared to a normal saline infusion of equal volume and duration. Mean arterial pressure (MAP) also increased and there were significant positive correlations between MAP and NE, but not between MAP and AVP during hypertonic saline infusion. Plasma epinephrine and cortisol did not differ between conditions. Although the pattern of plasma adrenocorticotrophic hormone (ACTH) response differed between hypertonic saline and normal saline conditions, ACTH concentrations did not increase compared to baseline in either condition. These data suggest that hypertonic saline infusion increases sympathetic nervous system activity in normal men.

Postmortem findings of decreased brain norepinephrine (NE) content and decreased locus ceruleus neuronal density have suggested a possible noradrenergic deficit in Alzheimer's disease (AD). We assessed CNS and peripheral noradrenergic function in patients with advanced AD, moderate AD, and age-matched normals by measuring NE and the NE metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) levels in CSF and plasma. Subjects were drug free for at least two weeks. Plasma and CSF NE and MHPG levels were significantly higher in patients with advanced AD than in either patients with moderate AD or normal controls, while values in the patients with moderate AD did not differ from those in normal controls. These findings do not support either a central or peripheral noradrenergic deficit in AD. Rather, they suggest increased CNS and peripheral noradrenergic activity in advanced stages of the disease.

Previous studies have demonstrated alpha 2-inhibitory regulation of central nervous system (CNS) noradrenergic and arginine vasopressinergic systems. We tested the hypothesis that alpha 2-inhibition of CNS noradrenergic and vasopressinergic systems is tonic in nature by measuring the response of cerebrospinal fluid (CSF) norepinephrine (NE) and arginine vasopressin (AVP) to the alpha 2-antagonist yohimbine in 7 young normal male human subjects. We also evaluated the tonic nature of alpha 2-inhibition of the sympathetic nervous system (SNS) and of AVP release into plasma by measuring the response of plasma NE and plasma AVP to yohimbine. CSF NE was significantly higher following yohimbine as compared to placebo. In contrast CSF AVP did not differ between yohimbine and placebo conditions. Similarly, plasma NE was significantly higher following yohimbine as compared to placebo, while plasma AVP was unchanged. These results support a tonic alpha 2-inhibitory regulatory mechanism for both CNS noradrenergic systems and sympathetic outflow. Such tonic alpha 2-inhibition could not be demonstrated for regulation of AVP levels in CSF or plasma in humans.

To evaluate the effect of advanced age on central nervous system noradrenergic activity, cerebrospinal fluid (CSF) and plasma norepinephrine (NE) concentrations were measured concurrently in 14 older [mean, 65 +/- 9 (+/- SD) yr] and 33 younger (25 +/- 2 yr) normal men. CSF NE was significantly higher in older men than in young men [214 +/- 75 (+/- SD) vs. 164 +/- 56 pg/mL (1.26 +/- 0.44 vs. 0.97 +/- 0.33 nmol/L); P less than 0.02] as was plasma NE [282 +/- 103 vs. 211 +/- 63 pg/mL (1.67 +/- 0.61 vs. 1.25 +/- 0.37 nmol/L); P less than 0.02]. Subgroups of young and older men underwent two lumbar punctures, one of which was performed 100 min after the administration of 5 micrograms/kg oral clonidine. The young (n = 7) and older (n = 7) men had similar plasma clonidine levels [1.0 +/- 0.1 vs. 0.8 +/- 0.1 ng/mL (4.35 +/- 0.43 vs. 3.48 +/- 0.78 nmol/L)] and CSF clonidine levels [0.18 +/- 0.02 vs. 0.22 +/- 0.03 ng/mL (0.78 +/- 0.09 vs. 0.96 +/- 0.13 nmol/L)]. The suppression of CSF NE by clonidine was significantly greater (P less than 0.015) in young men [189 +/- 44 to 104 +/- 26 pg/mL (1.12 +/- 0.26 to 0.62 +/- 0.15 nmol/L)] than in older men [190 +/- 49 to 164 +/- 58 pg/mL (1.12 +/- 0.29 to 0.97 +/- 0.34 nmol/L)]. In contrast, the suppression of plasma NE by clonidine did not significantly differ between young [242 +/- 72 to 93 +/- 24 pg/mL (1.43 +/- 0.43 to 0.55 +/- 0.14)] and older men [285 +/- 102 to 167 +/- 84 pg/mL (1.68 +/- 0.60 to 0.99 +/- 0.50 nmol/L)]. These data suggest that decreased sensitivity of alpha 2-adrenergic mechanisms regulating CNS noradrenergic activity may contribute to increased CNS noradrenergic activity with aging.

Despite a blood-brain barrier for norepinephrine, the concentration of norepinephrine in plasma and cerebrospinal fluid has been observed to be similar. This relationship between plasma and cerebrospinal fluid norepinephrine levels suggest that peripheral sympathetic neurons innervating blood vessels to brain and spinal cord may contribute significantly to cerebrospinal fluid norepinephrine levels, and questions the validity of cerebrospinal fluid norepinephrine as an index of central nervous system noradrenergic activity. We demonstrate that extensive destruction of the peripheral sympathetic nervous system and the adrenal medulla has no effect on rat cerebrospinal fluid norepinephrine. It is therefore unlikely that peripheral sources of norepinephrine contribute significantly to cerebrospinal fluid norepinephrine levels.