Interactions of prefrontal cortex during eyeblink conditioning as a function of age.

Changes in regional cerebral blood flow (rCBF) in eleven elderly subjects during pairings of tone and air puff were compared to rCBF changes during pairings in young subjects. Although all subjects reported being aware of the relationship between tone and air puff, elderly subjects did not condition as well as young subjects and their rCBF measures were attenuated. Covarying the performance differences between young and old subjects did not change this conclusion suggesting that differences in neural activation during learning are related to binding of CS-US information prior to the impact of the association on performance. Both groups showed learning-specific rCBF changes in cerebellum, inferior right prefrontal cortex and posterior cingulate. However, only in young subjects were there learning-specific changes in rCBF in left temporal cortex, midbrain, caudate, and inferior left prefrontal cortex. Analysis of learning-dependent patterns of functional connectivity of inferior left prefrontal cortex showed only young subjects had a strong left prefrontal functional connectivity with cerebellum, hippocampus, thalamus and temporal cortex. Thus, beyond changes in regional activity, these data also suggest that age may alter the operations of functional networks underlying learning and memory.

The effects of scopolamine on changes in regional cerebral blood flow during classical conditioning of the human eyeblink response.

We examined the effects of scopolamine on the functional anatomy of classical conditioning of the human eyeblink response. Ten healthy young normal female volunteers (mean age +/- SEM: 26.7 +/- 0.9 years) were administered 0.4 mg scopolamine intravenously 1 h before regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) and H215O. Scans occurred during three sequential phases: (1) explicitly unpaired presentations of the unconditioned stimulus (airpuff to the right eye) and conditioned stimulus (binaural tone), (2) paired presentations of the two stimuli (associative learning) and (3) explicitly unpaired presentation of the stimuli (extinction phase). Scopolamine impaired acquisition of the conditioned eyeblink response (54.7 +/- 4.9%) relative to 18 untreated subjects from two previous PET studies. Regions that showed significant relative increases in rCBF during conditioning included the right lateral occipital cortex, the right inferior occipital cortex, the right lateral temporo-occipital cortex, the left medial temporo-occipital cortex, the posterior cingulate, the right cerebellum/brain stem area and the medial cerebellum. Significant relative decreases in rCBF were measured in the thalamus, the left putamen/insula area, the right putamen and the left and middle cerebellar cortex. The data partially replicate previous findings in unmedicated young volunteers of conditioning-specific rCBF changes in the cingulate cortex, the cerebellar cortex, the insula and the lateral temporo-occipital cortex. Our finding of decreased rCBF in the thalamus and increased rCBF in the occipital cortex may be attributable to effects of scopolamine per se rather than conditioning. Our data lend further support to the notion that classical conditioning involves distributed changes in multiple systems within the central nervous system.

Penetration of tacrine into cerebrospinal fluid in patients with Alzheimer's disease.

Tacrine is widely used for the treatment of Alzheimer's disease, but data are limited regarding cerebrospinal fluid (CSF) concentrations at steady state. To evaluate CSF penetration, seven patients with Alzheimer's disease who were receiving tacrine at doses of 40 to 140 mg/day as a part of a double-blind trial were studied. After 6 weeks of tacrine therapy, concomitant plasma and CSF samples were collected 30 minutes after the morning dose of tacrine. Although this time point is before the peak oral absorption in most patients, the critical issue for this study is that the plasma and CSF samples were collected concomitantly so that a percentage of tacrine penetration could be derived. The morning dose of tacrine ranged from 10 to 40 mg, which was given in the fasting state. Mean (+/-SD) plasma levels of tacrine were 8.01+/-7.07 ng/mL, whereas mean (+/-SD) CSF levels of tacrine were 5.21+/-6.00 ng/mL. The mean (+/-SD) ratio of CSF to plasma tacrine concentration was 0.50+/-0.45, with wide interindividual variability. No relationship between dose and percentage of penetration was observed. Plasma concentrations ranged from 0.99 to 22.6 ng/mL and were unrelated to dose, suggesting erratic oral absorption and/or rapid metabolism. CSF concentrations ranged from not detectable to 15.92 ng/mL. The authors support that penetration of tacrine into CSF is highly variable in patients with Alzheimer's disease and that disparity in tacrine concentrations at the site of action may be one reason for conflicting results from studies of the efficacy of tacrine in Alzheimer's disease.

Lateralization and behavioral correlation of changes in regional cerebral blood flow with classical conditioning of the human eyeblink response.

Laterality of changes in regional cerebral blood flow (rCBF) during classical conditioning of the human eyeblink response was studied and changes in rCBF were correlated with conditioned responses. In 10 normal volunteers, rCBF was mapped with positron emission tomography and H2(15)O during pairings of a binaural tone conditioned stimulus and an air puff unconditioned stimulus to the left eye. Control conditions consisted of explicitly unpaired presentations of the tone and air puff before (control) and after (extinction) pairings. During pairings, rCBF increased significantly in right primary auditory cortex (contralateral to air puff) and decreased significantly in left and right cerebellar cortex. There were also increases in rCBF in right auditory association cortex and left temporoccipital cortex. Decreases in rCBF were noted bilaterally in the temporal poles and in the left prefrontal cortex. Positive correlations between changes in rCBF and percent conditioned responses were located in middle cerebellum, right superior temporal cortex, left dorsal premotor cortex, right middle cingulate, and right superior temporal cortex. There were negative correlations in left inferior prefrontal cortex, left middle prefrontal cortex, and right inferior parietal cortex. The data replicate our previous findings of lateralized changes in rCBF following presentations of a binaural tone and air puff to the right eye and indicate that there are pairing-specific changes in primary auditory cortex and cerebellum that are not unique to the left or right hemisphere but are a function of the side of training. The commonalities as well as differences in regional involvement in our present and previous experiment as well as in other eyeblink studies illustrate the advantage of functional neuroimaging to quantify different strategies used by the brain to perform seemingly similar functions. Indeed, the data support the notion that learning-related changes can be detected in a number of specific, but not necessarily invariant, brain regions, and that the involvement of any one region is dependent on the characteristics of the particular learning situation.

Pharmacologic challenges in Alzheimer disease and normal controls: cognitive modeling in humans.

Alzheimer disease (AD) is a progressive disorder characterized by cognitive and behavioral dysfunction, central to which are deficits in the cholinergic and other neurotransmitter systems. These results in the essential symptoms of dementia, including impairment of memory, judgment, and abstract thinking. The pharmacologic relationships among the various neurotransmitters (e.g., cholinergic, serotonergic, nicotinic, and dopaminergic) are highly complex and are still being investigated. Information on the pharmacologic basis of cognitive and behavioral dysfunction in AD has applications to drug therapy. One method of obtaining this information is by pharmacomodeling, using individual or combined drugs. Joint cholinergic antagonism with both muscarinic and nicotinic blockade combines to produce short-term memory impairment, which approximates to mild AD in normal elderly people. This effect is better than that achieved with either agent alone. Mixed cholinergic and serotonergic antagonism has an effect on the cognitive function of AD patients and on depression-related behavior. Dopaminergic dysfunction is linked with the development of hallucinatory and psychotic symptoms and may also be involved in dysfunction of verbal fluency. Combination pharmacomodeling allows the various behavioral and cognitive deficits in AD to be studied and allows models for drug trials to be developed.

Cognitive and behavioral effects of cholinergic, dopaminergic, and serotonergic blockade in humans.

The purpose of this study was to investigate the cognitive and behavioral effects of anticholinergic, antidopaminergic, and antiserotonergic agents given alone and in combination to normal volunteers. Twelve young male volunteers took part in this double-blind, randomized, placebo-controlled, crossover study of six drug conditions, each administered on separate days [haloperidol (2 mg p.o.) +/-scopolamine (0.5 mg i.v.), metergoline (4 mg p.o.) +/-scopolamine (0.5 mg i.v.), placebo, and scopolamine alone (0.5 mg i.v.)]. Scopolamine-induced sedation (p < .01), slowed information processing (p < .01) and impaired new learning and memory (p < .01), but did not affect attention or retrieval from semantic memory. Given alone, haloperidol selectively impaired the ability to rapidly switch cognitive sets (p < .05), and metergoline decreased pupil size (p < .01) but did not induce cognitive deficits. In combination with scopolamine, neither haloperidol nor metergoline produced a worsening of the subjects' cognitive performance above and beyond that seen with scopolamine alone. On the contrary, a trend (p < .10) for haloperidol to reverse some of the scopolamine-induced exacerbation of verbal short-term forgetting was observed. The data indicate that scopolamine and haloperidol can independently and selectively affect cognition and that at the doses tested in this study no synergistic exacerbation of cognitive functioning was found when cholinergic blockage was coupled with dopaminergic or serotonergic blockade.

Minimal effects of dextroamphetamine on scopolamine-induced cognitive impairments in humans.

The central anticholinergic drug scopolamine has been used to model aspects of the memory impairment that occurs in Alzheimer's disease and in aging. To determine whether nonspecific stimulant effects can attenuate the cognitive impairment induced by scopolamine, we studied the effects of scopolamine and the stimulant dextroamphetamine in 17 young normal volunteers. After a baseline day of cognitive testing, subjects participated in two study days, in which they received dextroamphetamine (d-AMP) (0.25 mg/kg p.o.) + scopolamine (0.5 mg i.v.) and placebo + scopolamine, in randomized order under double-blind conditions. There were no statistically significant differences in cognitive test performance between the two drug conditions with the exception of one of the category retrieval tasks. Stimulant effects were documented to occur by other measures. We conclude that d-AMP at the dose used does not attenuate the memory impairment induced by scopolamine.

The effects of scopolamine, lorazepam, and glycopyrrolate on classical conditioning of the human eyeblink response.

Human eyeblink conditioning, a relatively simple form of learning and memory, has previously been shown to be impaired by the central and peripheral anticholinergic scopolamine. The present study compared the behavioral effects of scopolamine with the benzodiazepine lorazepam and a peripherally active anticholinergic, glycopyrrolate. Thirty-six healthy normal volunteers (mean age: 23.7 years) were studied with 12 assigned double-blind to each of three drug conditions (0.5 mg scopolamine IV, 2 mg lorazepam PO, or 0.2 mg glycopyrrolate IV). Subjects underwent classical conditioning of the eyeblink response in which the conditioned stimulus was an 80 dB binaural tone, and the unconditioned stimulus was a 2 psi airpuff to the right eye. Ten trials of unpaired stimulus presentations were followed by 60 paired trials and finally by an extinction period of five tone-alone presentations. An eyeblink response that occurred during the tone but before the airpuff was scored as a conditioned response (CR). Subjects treated with lorazepam (43% mean CRs) and scopolamine (51% mean CRs) exhibited a significantly lower asymptotic level of conditioning than those treated with glycopyrrolate (85% mean CRs; P < 0.01). However, during extinction, lorazepam-treated subjects (35% CRs) showed a lower overall level of responding to the tone than either scopolamine (60% CRs) or glycopyrrolate (62% CRs) treated subjects (P < 0.05). It seems unlikely that these differences could be accounted for by drug-induced alterations in motor responses because there were no significant differences between the three drug conditions in the frequency, latency, or amplitude of unconditioned responses to the airpuff. Overall, our data indicate that scopolamine and lorazepam impair eyeblink conditioning and suggest that some of the effects of benzodiazepines and anticholinergics on learning and memory can be differentiated using this paradigm.

Differential cholinergic regulation in Alzheimer's patients compared to controls following chronic blockade with scopolamine: a SPECT study.

The effects of low-dose chronic scopolamine on measures of cerebral perfusion and muscarinic receptors were tested in eight Alzheimer's disease (AD) subjects and eight elderly controls. Single photon emission computed tomography (SPECT) scans using technetium-labelled hexamethypropylene amine oxide (99mTc-HMPAO) to measure cerebral perfusion before and after chronic scopolamine revealed a significant 12% increase in the normal controls (P < 0.01) while the AD subjects showed no significant change. In contrast, the controls showed decreased muscarinic binding as evidenced by 123I-quinuclidinyl-4-iodobenzilate (123I-QNB) labelling after chronic drug (-10%, P < 0.01) whereas the AD subjects showed increased 123I-QNB labelling (+8%, P < 0.05). The difference between AD and control subjects was even more marked when the ratio of I-QNB to HMPAO uptake was compared, pointing to a double dissociation in the SPECT results. These data cannot be explained by group differences in cerebral perfusion alone and suggest a differential sensitivity between AD and elderly controls to chronic cholinergic blockade.

Serotonergic modulation of anticholinergic effects on cognition and behavior in elderly humans.

Cholinergic neurotransmission is thought to be modulated by serotonin as documented in animal and human studies. We examined the effects of the muscarinic antagonist scopolamine (0.4 mg IV) given alone or together with the serotonin mixed agonist/antagonist m-chlorophenylpiperazine (m-CPP, 0.08 mg/kg IV), and the selective 5-HT3 receptor antagonist ondansetron (0.15 mg/kg IV). Ten normal elderly volunteers each received five separate pharmacologic challenges (placebo, ondansetron, scopolamine, scopolamine+ondansetron, and scopolamine+m-CPP). Cognitive, behavioral, and physiologic variables were analyzed using repeated measures analysis of variance. The acute effects of scopolamine in certain cognitive, behavioral, and physiological measures were significantly exaggerated by the addition of m-CPP. Scopolamine's cognitive effects were unaffected by ondansetron at the dose tested, nor did ondansetron given alone affect basal cognitive performance. This pilot study suggests that the serotonin mixed agonist/antagonist m-CPP may influence cholinergic neurotransmission. The changes associated with the combination of scopolamine and m-CPP do not appear to be secondary to simple pharmacokinetic alterations and suggest a complex interaction between the cholinergic and serotonergic systems centrally.

Regional cerebral glucose metabolism in autopsy-confirmed Creutzfeldt-Jakob disease.

Regional cerebral glucose metabolism was measured in a 72-year-old man, with Creutzfeldt-Jakob disease (CJD), by positron emission tomography using [18F]-2-fluoro-2-deoxy-D-glucose as the tracer. The diagnosis of CJD, a rare neurodegenerative disorder, was confirmed at autopsy 13 months later. Compared with five unaffected elderly men, the patient had reduced metabolism heterogeneously distributed throughout the brain. The hypometabolism was most evident in the right hemisphere, particularly in the posterior frontal, parietal, Sylvian, and temporal regions. This left-right asymmetry is more extensive than that previously reported in Alzheimer's disease, and may provide a useful metabolic marker for early diagnosis of CJD.

A functional anatomical study of associative learning in humans.

The purpose of the study was to map the functional neuroanatomy of simple associative learning in humans. Eyeblink conditioning was studied in eight normal volunteers using positron emission tomography and H215O. Regional cerebral blood flow was assessed during three sequential phases: (i) explicitly unpaired presentations of the unconditioned stimulus (air puff to the right eye) and conditioned stimulus (binaural tone), (ii) paired presentations of the two stimuli (associative learning), and (iii) presentation of the conditioned stimulus alone. During associative learning, relative to the unpaired phase, blood flow was significantly increased in primary auditory and left posterior cingulate cortices and significantly decreased in areas of the right cerebellar, right prefrontal, right parietal, and insular cortices and right neostriatum. The lateralization of the changes may relate to the functional organization of memory and learning processes in the brain. The activation in primary auditory cortex is an example, using a neuroimaging technique, of a learning-related change in primary sensory cortex in humans. The changes in areas such as the cerebellum, prefrontal cortex, and neostriatum provide support for their roles in associative learning as proposed by animal models. Moreover, these findings show that in humans, even simple classical conditioning involves distributed changes in multiple neural systems.

High-dose selegiline in treatment-resistant older depressive patients.

BACKGROUND: We examined the effect of high-dose selegiline in 16 treatment-resistant older depressive patients. We hypothesized that selegiline, at a dosage of 60 mg/d, would be at least partially effective but that the higher doses would not maintain the monoamine oxidase B selectivity observed with the lower doses of selegiline. METHODS: Sixteen treatment-resistant subjects (mean [+/- SD] age, 65.6 +/- 9.3 years) entered a double-blind, randomized, crossover study of placebo vs 3 weeks of selegiline at a dosage of 60 mg/d. Objective measures of mood and behavior were obtained in all subjects, and 10 of the subjects underwent repeated lumbar punctures for analysis of monoamine metabolites in the cerebrospinal fluid. RESULTS: Objective measures of mood and behavior revealed significant improvement in the Hamilton Depression Rating Scale score (37.4% decrease), the Global Depression score (22.7% decrease), and the Brief Psychiatric Rating Scale score (19.3% decrease); subjective behavioral measures, however, did not show significant improvement during the 3-week medication trial. Cerebrospinal fluid values revealed a statistically significant drop in 3-methoxy-4-hydroxyphenylglycol (51%) and 5-hydroxyindoleacetic acid (17%) levels, and there was a significant lowering of systolic blood pressure on standing (15%), but these changes were not accompanied by clinical side effects. CONCLUSIONS: Our results suggest that high-dose selegiline can be an effective antidepressant in treatment-resistant older depressive patients. While the selegiline dose required has nonselective monoamine oxidase effects and thus would not be free of possible tyramine interactions, other advantages suggest that further investigations with selegiline are warranted in this population.

A double FDG/PET study of the effects of scopolamine in older adults.

Two consecutive positron emission scans were done in one session using a double injection method of [18F]2-fluoro-2-deoxyglucose administration to examine the effects of the antimuscarinic drug scopolamine on cerebral glucose metabolism in ten older adults. Scopolamine causes temporary memory impairment, and its effects have been used to model aspects of the cognitive impairment that occur in Alzheimer's disease (AD). Cortical metabolic rates of patients with AD have been reported to be depressed, especially in parietal, temporal, and frontal association areas. After scopolamine administration to the elderly volunteers, absolute and normalized glucose metabolic rates were depressed in prefrontal and occipital regions and increased in parietal-occipital cortical regions and a left middle temporal region. These changes in the older volunteers are generally not consistent with changes seen in AD. We conclude that deficits in muscarinic system function may contribute to some but not all of the hypometabolic changes seen in AD patients.

Scopolamine effects on the pressor response to thyrotropin-releasing hormone in humans.

Thyrotropin-releasing hormone (TRH) produces a marked pressor effect, which may be mediated by central cholinergic neurons, which in turn enhance sympathetic nervous system activity. In this study, 22 subjects (10 patients with Alzheimer's disease and 12 elderly controls) were administered IV scopolamine or placebo prior to administration of IV high-dose TRH (0.5 mg/kg). Systolic blood pressure was less on the day scopolamine was administered prior to TRH administration, as compared with placebo (F[1,20] = 6.12, p < 0.02). Results indicate that the pressor effect of TRH is attenuated by scopolamine, indicating a role of the cholinergic system in this response in humans.

Effects of chronic lithium treatment on platelet PKC isozymes in Alzheimer's and elderly control subjects.

Patients with Alzheimer's disease (AD) have been reported to have abnormalities in peripheral cells similar to some of those found in the brain, including decreased levels of protein kinase C (PKC) in fibroblasts. Since increasing evidence suggests that lithium affects PKC function, we investigated the effects of 3 weeks of lithium administration on the immunolabeling of 4 PKC isozymes (alpha, beta, epsilon, and zeta) in particulate and soluble fractions from platelets of 7 patients with probable AD and 6 age-matched controls. AD patients had significantly less particulate or membrane-associated PKC zeta than normals during the placebo phase (P < 0.003). After 3 weeks of lithium treatment, AD patients had significantly less membrane-associated PKC alpha (P < 0.002), epsilon (P < 0.003), and zeta (P < 0.001) than normals. This is the first report of a difference in PKC in blood cells between AD and control subjects. These findings appear to indicate that some PKC isozymes may be differentially regulated in AD versus elderly controls, at least as evidenced in this peripheral cellular system.

Autonomic dysfunction in patients with dementia of the Alzheimer type.

Abnormalities of the noradrenergic system have been documented in the central nervous system of patients with dementia of the Alzheimer's type (DAT). To evaluate the autonomic sympathetic system in DAT, we measured lying and standing blood pressure (BP), pulse, and plasma epinephrine (E) and norepinephrine (NE) in 60 DAT patients (mean age +/- SD = 65 +/- 8 years), and 20 normal elderly controls. DAT patients had normal baseline findings (BP, pulse, NE, and E). Upon standing, plasma NE and E significantly increased in both DAT patients and controls, without group differences. However, the systolic BP response to standing was reduced in DAT patients compared with the normal controls (repeated measures ANOVA, p < 0.01). This impaired response of the systolic BP on standing was particularly evident in DAT patients with symptoms of depression. Severely impaired DAT patients did not differ in E, NE, BP, pulse, or in orthostatic changes from mild-to-moderately impaired patients. These results suggest that the sympathetic response to the stress of standing is functionally impaired in DAT. This deficit was especially evident when DAT was accompanied by depression, consistent with prior studies in non-demented depressed patients.

CSF somatostatin in Alzheimer's disease and major depression: relationship to hypothalamic-pituitary-adrenal axis and clinical measures.

Patients with Alzheimer's disease (AD) and major depression have been shown to have overlapping clinical symptoms and biological markers, including decreased concentrations of cerebrospinal fluid (CSF) somatostatin-like immunoreactivity (SLI), which may be related to alterations in the hypothalamic-pituitary-adrenal axis activity. As in prior studies, we found that CSF SLI was significantly decreased in a group of AD patients (N = 49) and a group of elderly patients with major depression (N = 18), as compared with 13 age-matched controls (F[2, 77] = 12.9, p < .001). In the present study, CSF SLI and CSF corticotropin-releasing factor correlated significantly within the group of AD patients (r = 0.49, p < .0004) and almost attained significance in the depressed patients (r = 0.47, p < .07). CSF SLI correlated significantly with urinary free cortisol within each patient group (r = -0.51, p < .03). Clinical measures of dementia severity and depression did not consistently correlate with CSF SLI in either patient group.