Parkinson's disease and dopaminergic therapy--differential effects on movement, reward and cognition

Cognitive deficits are very common in Parkinson's disease particularly for ‘executive functions’ associated with frontal cortico-striatal networks. Previous work has identified deficits in tasks that require attentional control like task-switching, and reward-based tasks like gambling or reversal learning. However, there is a complex relationship between the specific cognitive problems faced by an individual patient, their stage of disease and dopaminergic treatment. We used a bimodality continuous performance task during fMRI to examine how patients with Parkinson's disease represent the prospect of reward and switch between competing task rules accordingly. The task-switch was not separately cued but was based on the implicit reward relevance of spatial and verbal dimensions of successive compound stimuli. Nineteen patients were studied in relative ‘on’ and ‘off’ states, induced by dopaminergic medication withdrawal (Hoehn and Yahr stages 1–4). Patients were able to successfully complete the task and establish a bias to one or other dimension in order to gain reward. However the lateral prefrontal cortex and caudate nucleus showed a non-linear U-shape relationship between motor disease severity and regional brain activation. Dopaminergic treatment led to a shift in this U-shape function, supporting the hypothesis of differential neurodegeneration in separate motor and cognitive cortico–striato–thalamo–cortical circuits. In addition, anterior cingulate activation associated with reward expectation declined with more severe disease, whereas activation following actual rewards increased with more severe disease. This may facilitate a change in goal-directed behaviours from deferred predicted rewards to immediate actual rewards, particularly when on dopaminergic treatment. We discuss the implications for investigation and optimal treatment of this common condition at different stages of disease.

Rapid, high fidelity analysis of simple sequence repeats on an electronically active DNA microchip

We describe a method for the discrimination of short tandem repeat (STR) alleles based on active microarray hybridization. An essential factor in this method is electronic hybridization of the target DNA, at high stringency, in <5 min. High stringency is critical to avoid slippage of hybrids along repeat tracts at allele-specific test sites in the array. These conditions are attainable only with hybridization kinetics realized by electronic concentration of DNA. A sandwich hybrid is assembled, in which proper base stacking of juxtaposed terminal nucleotides results in a thermodynamically favored complex. The increased stability of this complex relative to non-stacked termini and/or base pair mismatches is used to determine the identification of STR alleles. This method is capable of simultaneous and precise identification of alleles containing different numbers of repeats, as well as mutations within these repeats. Given the throughput capabilities of microarrays our system has the potential to enhance the use of microsatellites in forensic criminology, diagnostics and genetic mapping.

Personality dimensions in panic disorder and generalized anxiety disorder

To make a dimensional assessment of personality in individuals with pathological anxiety, the Tridimensional Personality Questionnaire (TPQ) was administered to 32 patients with panic disorder (PD) and 49 patients with generalized anxiety disorder (GAD). The most striking findings were a substantially increased score on the harm avoidance dimension in both groups of patients, and a lack of significant differences between the TPQ scores in patients with PD and GAD. The former finding suggests that higher levels of harm avoidance may be common to (although not necessarily specific for) various types of anxiety disorders. The latter finding is in agreement with the findings that PD and GAD do not differ significantly with respect to the associated personality disorder diagnoses, which may further cast a doubt on the validity of the distinction between PD and GAD.

Ventilation of the deep Southern Ocean and deglacial CO2 rise

Past glacial-interglacial increases in the concentration of atmospheric carbon dioxide (CO2) are thought to arise from the rapid release of CO2 sequestered in the deep sea, primarily via the Southern Ocean. Here, we present radiocarbon evidence from the Atlantic sector of the Southern Ocean that strongly supports this hypothesis. We show that during the last glacial period, deep water circulating around Antarctica was more than two times older than today relative to the atmosphere. During deglaciation, the dissipation of this old and presumably CO2-enriched deep water played an important role in the pulsed rise of atmospheric CO2 through its variable influence on the upwelling branch of the Antarctic overturning circulation.

Changes in cerebral neurotransmitters and metabolites induced by acute donepezil and memantine administrations: A microdialysis study

Cholinesterase inhibitors including donepezil, rivastigmine, and galantamine and the N-methyl-D-aspartate (NMDA) antagonist, memantine are the medications currently approved for the treatment of Alzheimer's disease (AD). In addition to their beneficial effects on cognitive and functional domains typically disrupted in AD, these agents have also been shown to slow down the emergence of behavioral and psychotic symptoms associated with this disease. However, the underlying mechanisms for these therapeutic effects remain poorly understood and could involve effects of these medications on non-cholinergic or non-glutamatergic neurotransmitter systems respectively. These considerations prompted us to initiate a series of investigations to examine the acute and chronic effects of donepezil (Aricept (+/-)-2,3-dihydro-5,6-dimethoxy-2-[[1-(phenylmethyl)-4-piperidinyl]methyl]-1H-inden-1-1 hydrochloride and memantine (1-amino-3,5-dimethyladamantane hydrochloride C12H21N.HCl)). The present study focuses on the acute effects of donepezil and memantine on brain extracellular levels of acetylcholine, dopamine, serotonin, norepinephrine and their metabolites. We assayed changes in the ventral and dorsal hippocampus and the prefrontal and medial temporal cortex by microdialysis. Memantine resulted in significant increases in extracellular dopamine (DA), norepinephrine (NE), and their metabolites, in the cortical regions, and in a reduction of DA in the hippocampus. Donepezil produced an increase in extracellular DA in the cortex and in the dorsal hippocampus. Norepinephrine increased in the cortex; with donepezil it increased in the dorsal hippocampus and the medial temporal cortex, and decreased in the ventral hippocampus. Interestingly both compounds decreased extracellular serotonin (5HT) levels. The metabolites of the neurotransmitters were increased in most areas. We also found an increase in extracellular acetylcholine (ACh) by memantine in the nucleus accumbens and the ventral tegmental area. Our results suggest both region and drug specific neurotransmitter effects of these agents as well as some similarities. We conclude that drugs influencing cognitive mechanisms induce changes in a number of neurotransmitters with the changes being both region and drug specific. Release and metabolism are altered and extracellular neurotransmitter levels can be increased or decreased by the drugs. Other studies are in progress to determine the pharmacological effects associated with chronic treatment with these compounds, which may be more pertinent to the clinical situation in which patients take these medications for months or years.

Experimental approaches towards interpreting dolphin-stimulated bioluminescence

Flow-induced bioluminescence provides a unique opportunity for visualizing the flow field around a swimming dolphin. Unfortunately, previous descriptions of dolphin-stimulated bioluminescence have been largely anecdotal and often conflicting. Most references in the scientific literature report an absence of bioluminescence on the dolphin body, which has been invariably assumed to be indicative of laminar flow. However, hydrodynamicists have yet to find compelling evidence that the flow remains laminar over most of the body. The present study integrates laboratory, computational and field approaches to begin to assess the utility of using bioluminescence as a method for flow visualization by relating fundamental characteristics of the flow to the stimulation of naturally occurring luminescent plankton. Laboratory experiments using fully developed pipe flow revealed that the bioluminescent organisms identified in the field studies can be stimulated in both laminar and turbulent flow when shear stress values exceed approximately 0.1 N m-2. Computational studies of an idealized hydrodynamic representation of a dolphin (modeled as a 6:1 ellipsoid), gliding at a speed of 2 m s-1, predicted suprathreshold surface shear stress values everywhere on the model, regardless of whether the boundary layer flow was laminar or turbulent. Laboratory flow visualization of a sphere demonstrated that the intensity of bioluminescence decreased with increasing flow speed due to the thinning of the boundary layer, while flow separation caused a dramatic increase in intensity due to the significantly greater volume of stimulating flow in the wake. Intensified video recordings of dolphins gliding at speeds of approximately 2 m s-1 confirmed that brilliant displays of bioluminescence occurred on the body of the dolphin. The distribution and intensity of bioluminescence suggest that the flow remained attached over most of the body. A conspicuous lack of bioluminescence was often observed on the dolphin rostrum and melon and on the leading edge of the dorsal and pectoral fins, where the boundary layer is thought to be thinnest. To differentiate between effects related to the thickness of the stimulatory boundary layer and those due to the latency of the bioluminescence response and the upstream depletion of bioluminescence, laboratory and dolphin studies of forced separation and laminar-to-turbulent transition were conducted. The observed pattern of stimulated bioluminescence is consistent with the hypothesis that bioluminescent intensity is directly related to the thickness of the boundary layer.

The Effects of Glutamate and GABA Receptor Antagonists on Nicotine-induced Neurotransmitter Changes in Cognitive Areas*

In the present study, we tested the effects of glutamate and GABA receptor antagonists on nicotine-induced neurotransmitter changes in the hippocampal (dorsal and ventral) and cortical (medial temporal and prefrontal) brain areas of conscious freely moving rats via microdialysis. Both the antagonists and nicotine were administered intracerebrally. The antagonists tested were NMDA, AMPA-kainate, and metabotropic glutamate receptor subtype antagonists (MK801, CNQX, and LY 341495, respectively) and GABA(A) and GABA(B) receptor subtype antagonists (bicuculline and hydroxysaclofen, respectively). We assayed nicotine-induced changes in dopamine (DA), norepinephrine (NE), serotonin (5-HT), and their metabolites. We found with the antagonists, both decreases and increases in nicotine-induced neurotransmitter responses. In the presence of nicotine all the antagonists (except LY 341495) caused a decrease in DA levels in the regions tested. NE levels were decreased in the cortex by all antagonists. In the hippocampus, GABA antagonists decreased NE levels, as did the metabotropic glutamate antagonist, LY 341495, while the other glutamate antagonists increased NE levels. The results of the 5-HT assay were more variable and dependent on the region and antagonist examined; increases were found slightly more often than decreases. The changes in metabolites were not often parallel with changes in their associated neurotransmitters, indicating that the antagonists also affect the metabolism of the neurotransmitters. The effect of the antagonists in the absence of nicotine was mostly to decrease the level of neurotransmitters, although increases were seen in a few cases. The results suggest that the excitatory glutamatergic- and inhibitory GABAergic-amino acid receptors are both involved in mediating nicotine-induced neurotransmitter responses, and their inhibitory or stimulatory effects are receptor subtype and brain region dependent.

Generalized anxiety disorder, worries about illness, and hypochondriacal fears and beliefs

In order to compare hypochondriacal phenomena in patients with generalized anxiety disorder (GAD) and panic disorder (PD), and in order to examine the relationship between worries about illness on one hand, and disease fears/phobias and hypochondriacal beliefs on the other, the authors administered the Illness Attitudes Scales to patients with both GAD and PD, and determined the spheres of worry in patients with GAD. Patients with GAD were significantly less hypochondriacal than PD patients. A specific relationship between GAD and hypochondriasis was not found because worries about illness, which characterize some GAD patients, were largely independent from disease fears/phobias and hypochondriacal beliefs, which are a hallmark of hypochondriasis.

Progressive changes in the acute dyskinetic syndrome as a function of repeated elicitation in squirrel monkeys

Various neuroleptic-induced motor disorders that appear in primates previously treated with neuroleptics are collectively designated the acute dyskinetic syndrome. The relative incidence of these motor disorders was examined as the syndrome was repeatedly elicited by haloperidol and other dopamine antagonists in individual monkeys. After several weekly or biweekly treatments with haloperidol (1.25 mg/kg orally), catalepsy began to appear, which was then accompanied by athetoid movements (writhing and limb extensions) as intermittent neuroleptic treatment continued. Other dyskinetic movements ('duck walk', oral dyskinesias, pushing of the head into a cage corner, and perseverative circling) that were suggestive of hyperkinesia subsequently began to be elicited by haloperidol and other neuroleptics after additional treatments with these drugs had intervened. As intermittent treatments continued, tolerance to the athetoid movements gradually developed and, eventually, only circling and pushing could be consistently elicited by haloperidol. In monkeys that had reached this phase, the athetoid movements were not again induced by higher doses of haloperidol (up to 5 mg/kg), chlorpromazine (3 mg/kg), or metoclopramide (3 mg/kg). In these tolerant monkeys, haloperidol impaired Sidman avoidance performance less and benztropine more than in drug-naive monkeys. Neither pharmacokinetic changes nor behavioral tolerance could readily account for these results. It is hypothesized that they reflect progressive functional alterations in dopaminergic or cholinergic neurotransmission.

Postsynaptic dopamine agonist properties of TL-99 are revealed by yohimbine co-treatment

The claim that TL-99 (6,7-dihydroxy-2-dimethylaminotetralin hydrobromide) is a selective dopamine autoreceptor agonist relies partly upon indirect behavioral evidence, particularly the absence of stereotyped behavior in treated rats. The possibility was examined that concurrent alpha 2-adrenoceptor agonist properties of TL-99 could have masked postsynaptic dopamine agonist activity. Co-administration of yohimbine or piperoxan with a high dose of TL-99 (30 mg/kg) dramatically increased motor activity in reserpinized rats, whereas each drug by itself had no effect. Contralateral rotational behavior in 6-hydroxydopamine-lesioned rats resulted from combined treatment with yohimbine and a high dose of TL-99 (30 mg/kg) but appeared to be suppressed by concurrent flaccidity if TL-99 was given by itself. Yohimbine failed to alter the effects of 3-PPP (N-n-propyl-3-(3-hydroxyphenyl)-piperidine), another putative dopamine autoreceptor agonist, in either model of postsynaptic dopamine agonism. It is concluded that a concurrent behaviorally depressant action of TL-99, possibly alpha 2-agonism, masks the stimulation of postsynaptic dopamine receptors by high doses of TL-99.

Acute dyskinesias in monkeys elicited by halopemide, mezilamine and the "antidyskinetic" drugs, oxiperomide and tiapride

Oxiperomide and tiapride are dopamine receptor antagonists claimed to have "antidyskinetic" properties in animal models and the clinic. Halopemide and mezilamine are other dopamine antagonists predicted to lack extrapyramidal side effects in man on the basis of animal studies. Acute dyskinesias, a neuroleptic-induced acute extrapyramidal syndrome, were elicited in squirrel monkeys by oxiperomide (1 mg/kg), tiapride (30 mg/kg), and halopemide (10 mg/kg). The dyskinesias were virtually indistinguishable from those caused by a standard behaviorally equivalent dose of haloperidol (1.25 mg/kg PO) in the same individual monkeys. Mezilamine (0.3 mg/kg) also induced dyskinesias, which appeared to be less pronounced than those following haloperidol. The antidyskinetic properties of oxiperomide and tiapride evidently do not confer protection against dyskinetic movements induced by dopamine antagonism.

The frequency and severity of generalized anxiety disorder symptoms. Toward a less cumbersome conceptualization

The frequency and severity of the symptoms of generalized anxiety disorder (GAD) were determined in a sample of 49 patients with the DSM-III-R diagnosis of GAD. The frequency of the symptoms was considered to meet the DSM-III-R requirement of "often" if the symptoms were present for at least 3 days in every week over a 6-month period. The severity of the symptoms was rated on a 5-point scale. Seven symptoms, all of which belong to the clusters of motor tension and vigilance and scanning, were identified as both frequent and at least moderate in terms of their intensity. They were provisionally designated as the "criterion symptoms" of GAD, in contrast to the symptoms of autonomic hyperactivity, which were found to be less frequent and, especially, less intense. A more simplified conceptualization of GAD was proposed on the basis of these findings.

Comorbidity rates do not support distinction between panic disorder and generalized anxiety disorder

Groups of patients with principal diagnosis of panic disorder (n = 54) and generalized anxiety disorder (n = 49) were compared on the basis of their comorbidity with other mental disorders. The rates and patterns of comorbidity were similar, except for comorbid simple phobia and past drug abuse. This finding was interpreted as failing to support a notion that there is essential distinction between panic disorder and generalized anxiety disorder.