Catecholamines and attention. I: Animal and clinical studies

Pupillary dilations in a Target/Distractor visual task paradigm and attention deficit hyperactivity disorder (ADHD)

ADHD is a neurocognitive disorder characterized by attention difficulties, hyperactivity, and impulsivity, often persisting into adulthood with substantial personal and societal consequences. Despite the importance of neurophysiological assessment and treatment monitoring tests, their availability outside of research settings remains limited. Cognitive neuroscience investigations have identified distinct components associated with ADHD, including deficits in sustained attention, inefficient enhancement of attended Targets, and altered suppression of ignored Distractors. In this study, we examined pupil activity in control and ADHD subjects during a sustained visual attention task specifically designed to evaluate the mechanisms underlying Target enhancement and Distractor suppression. Our findings revealed some distinguishing factors between the two groups which we discuss in light of their neurobiological implications.

Pupil Size Tracks Attentional Performance In Attention-Deficit/Hyperactivity Disorder

Attention-deficit/hyperactivity disorder (ADHD) diagnosis is based on reported symptoms, which carries the potential risk of over- or under-diagnosis. A biological marker that helps to objectively define the disorder, providing information about its pathophysiology, is needed. A promising marker of cognitive states in humans is pupil size, which reflects the activity of an 'arousal' network, related to the norepinephrine system. We monitored pupil size from ADHD and control subjects, during a visuo-spatial working memory task. A sub group of ADHD children performed the task twice, with and without methylphenidate, a norepinephrine-dopamine reuptake inhibitor. Off-medication patients showed a decreased pupil diameter during the task. This difference was no longer present when patients were on-medication. Pupil size correlated with the subjects' performance and reaction time variability, two vastly studied indicators of attention. Furthermore, this effect was modulated by medication. Through pupil size, we provide evidence of an involvement of the noradrenergic system during an attentional task. Our results suggest that pupil size could serve as a biomarker in ADHD.

White matter integrity of the medial forebrain bundle and attention and working memory deficits following traumatic brain injury

BACKGROUND AND OBJECTIVE

The medial forebrain bundle (MFB) contains ascending catecholamine fibers that project to the prefrontal cortex (PFC). Damage to these fibers following traumatic brain injury (TBI) may alter extracellular catecholamine levels in the PFC and impede attention and working memory ability. This study investigated white matter microstructure of the medial MFB, specifically the supero-lateral branch (slMFB), following TBI, and its association with performance on attention and working memory tasks.

METHOD

Neuropsychological measures of attention and working memory were administered to 20 moderate-severe participants with TBI (posttraumatic amnesia M = 40.05 ± 37.10 days, median time since injury 10.48 months, range 3.72-87.49) and 20 healthy controls. Probabilistic tractography was used to obtain fractional anisotropy (FA) and mean diffusivity (MD) values for 17 participants with TBI and 20 healthy controls.

RESULTS

When compared to controls, participants with TBI were found to have significantly lower FA (p < .001) and higher MD (p < .001) slMFB values, and they were slower to complete tasks including Trail Making Task-A, Hayling, selective attention task, n-back, and Symbol Digit Modalities Test.

CONCLUSION

This study was the first to demonstrate microstructural white matter damage within the slMFB following TBI. However, no evidence was found for an association of alterations to this tract and performance on attentional tasks.

Effects of methylphenidate on attention in Wistar rats treated with the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4)

The aim of this study was to assess the effects of the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) on attention in rats as measured using the 5-choice-serial-reaction-time task (5CSRTT) and to investigate whether methylphenidate has effects on DSP4-treated rats. Methylphenidate is a noradrenaline and dopamine reuptake inhibitor and commonly used in the pharmacological treatment of individuals with attention deficit/hyperactivity disorder (ADHD). Wistar rats were trained in the 5CSRTT and treated with one of three doses of DSP4 or saline. Following the DSP4 treatment rats were injected with three doses of methylphenidate or saline and again tested in the 5CSRTT. The treatment with DSP4 caused a significant decline of performance in the number of correct responses and a decrease in response accuracy. A reduction in activity could also be observed. Whether or not the cognitive impairments are due to attention deficits or changes in explorative behaviour or activity remains to be investigated. The treatment with methylphenidate had no beneficial effect on the rats' performance regardless of the DSP4 treatment. In the group without DSP4 treatment, methylphenidate led to a reduction in response accuracy and bidirectional effects in regard to parameters related to attention. These findings support the role of noradrenaline in modulating attention and call for further investigations concerning the effects of methylphenidate on attentional processes in rats.

Computational Psychiatry of ADHD: Neural Gain Impairments across Marrian Levels of Analysis

Attention-deficit hyperactivity disorder (ADHD), one of the most common psychiatric disorders, is characterised by unstable response patterns across multiple cognitive domains. However, the neural mechanisms that explain these characteristic features remain unclear. Using a computational multilevel approach, we propose that ADHD is caused by impaired gain modulation in systems that generate this phenotypic increased behavioural variability. Using Marr's three levels of analysis as a heuristic framework, we focus on this variable behaviour, detail how it can be explained algorithmically, and how it might be implemented at a neural level through catecholamine influences on corticostriatal loops. This computational, multilevel, approach to ADHD provides a framework for bridging gaps between descriptions of neuronal activity and behaviour, and provides testable predictions about impaired mechanisms.

Lrp5/6 are required for cerebellar development and for suppressing TH expression in Purkinje cells via β-catenin

BACKGROUND

The cerebellum is responsible for coordinating motor functions and has a unique laminated architecture. Purkinje cells are inhibitory neurons and represent the only output from the cerebellar cortex. Tyrosine hydroxylase (TH) is the key enzyme for the synthesis of catecholamines, including dopamine and noradrenaline, and it is normally not expressed in cerebellar neurons.

RESULTS

We report here that the low-density lipoprotein receptors (Lrp) 5 and 6, Wnt co-receptors, are required for the development of the cerebellum and for suppressing ectopic TH expression in Purkinje cells. Simultaneous inactivation of Lrp 5 and 6 by Nestin-Cre results in defective lamination and foliation of the cerebellum during postnatal development. Surprisingly, TH is ectopically expressed by Purkinje cells, although they still keep its other neurochemical characteristics. These phenotypes are also observed in the cerebellum of GFAP-Cre;β-catenin(flox/flox) mice, and AAV2-Cre-mediated gene deletion leads to ectopic TH expression in Purkinje cells of β-catenin(flox/flox) mice as well.

CONCLUSIONS

Our results revealed a new role of the canonical Lrp5/6-β-catenin pathway in regulating the morphogenesis of the cerebellum during postnatal development.

Irrelevant stimulus processing in ADHD: catecholamine dynamics and attentional networks

A cardinal symptom of attention deficit and hyperactivity disorder (ADHD) is a general distractibility where children and adults shift their attentional focus to stimuli that are irrelevant to the ongoing behavior. This has been attributed to a deficit in dopaminergic signaling in cortico-striatal networks that regulate goal-directed behavior. Furthermore, recent imaging evidence points to an impairment of large scale, antagonistic brain networks that normally contribute to attentional engagement and disengagement, such as the task-positive networks and the default mode network (DMN). Related networks are the ventral attentional network (VAN) involved in attentional shifting, and the salience network (SN) related to task expectancy. Here we discuss the tonic-phasic dynamics of catecholaminergic signaling in the brain, and attempt to provide a link between this and the activities of the large-scale cortical networks that regulate behavior. More specifically, we propose that a disbalance of tonic catecholamine levels during task performance produces an emphasis of phasic signaling and increased excitability of the VAN, yielding distractibility symptoms. Likewise, immaturity of the SN may relate to abnormal tonic signaling and an incapacity to build up a proper executive system during task performance. We discuss different lines of evidence including pharmacology, brain imaging and electrophysiology, that are consistent with our proposal. Finally, restoring the pharmacodynamics of catecholaminergic signaling seems crucial to alleviate ADHD symptoms; however, the possibility is open to explore cognitive rehabilitation strategies to top-down modulate network dynamics compensating the pharmacological deficits.

Changes in GABA and glutamate concentrations during memory tasks in patients with Parkinson's disease undergoing DBS surgery

Until now direct neurochemical measurements during memory tasks have not been accomplished in the human basal ganglia. It has been proposed, based on both functional imaging studies and psychometric testing in normal subjects and in patients with Parkinson’s disease (PD), that the basal ganglia is responsible for the performance of feedback-contingent implicit memory tasks. To measure neurotransmitters, we used in vivo microdialysis during deep brain stimulation (DBS) surgery. We show in the right subthalamic nucleus (STN) of patients with PD a task-dependent change in the concentrations of glutamate and GABA during an implicit memory task relative to baseline, while no difference was found between declarative memory tasks. The five patients studied had a significant decrease in the percent concentration of GABA and glutamate during the performance of the weather prediction task (WPT). We hypothesize, based on current models of basal ganglia function, that this decrease in the concentration is consistent with expected dysfunction in basal ganglia networks in patients with PD.

Evidence of dopaminergic processing of executive inhibition

Inhibition of unwanted response is an important function of the executive system. Since the inhibitory system is impaired in patients with dysregulated dopamine system, we examined dopamine neurotransmission in the human brain during processing of a task of executive inhibition. The experiment used a recently developed dynamic molecular imaging technique to detect and map dopamine released during performance of a modified Eriksen's flanker task. In this study, young healthy volunteers received an intravenous injection of a dopamine receptor ligand ((11)C-raclopride) after they were positioned in the PET camera. After the injection, volunteers performed the flanker task under Congruent and Incongruent conditions in a single scan session. They were required to inhibit competing options to select an appropriate response in the Incongruent but not in the Congruent condition. The PET data were dynamically acquired during the experiment and analyzed using two variants of the simplified reference region model. The analysis included estimation of a number of receptor kinetic parameters before and after initiation of the Incongruent condition. We found increase in the rate of ligand displacement (from receptor sites) and decrease in the ligand binding potential in the Incongruent condition, suggesting dopamine release during task performance. These changes were observed in small areas of the putamen and caudate bilaterally but were most significant on the dorsal aspect of the body of left caudate. The results provide evidence of dopaminergic processing of executive inhibition and demonstrate that neurochemical changes associated with cognitive processing can be detected and mapped in a single scan session using dynamic molecular imaging.

Spatial inhibition and the visual cortex: a magnetic resonance spectroscopy imaging study

INTRODUCTION

Deficits in processing spatial information have been observed in clinical populations who have abnormalities within the dopamine (DA) system. As psychostimulants such as methamphetamine (MA) are particularly neurotoxic to the dopaminergic system it was of interest to examine the performance of MA-dependent individuals on a task of spatial attention.

METHOD

51 MA-dependent subjects and 22 age-matched non-substance abusing control subjects were tested on a Spatial Stroop attention test. MR Spectroscopy (MRS) imaging data were analyzed from 32 MA abusers and 13 controls.

RESULTS

No group differences in response time or accuracy emerged on the behavioral task with both groups exhibiting equivalent slowing when the word meaning and the spatial location of the word were in conflict. MRS imaging data from the MA abusers revealed a strong inverse correlation between NAA/Cr ratios in the Primary Visual Cortex (PVC) and spatial interference (p=0.0001). Moderate inverse correlations were also seen in the Anterior Cingulate Cortex (ACC) (p=0.02). No significant correlations were observed in the controls, perhaps due to the small sample of imaging data available (n=13).

DISCUSSION

The strong correlation between spatial conflict suppression and NAA/Cr levels within the PVC in the MA-dependent individuals suggests that preserved neuronal integrity within the PVC of stimulant abusers may modulate cognitive mechanisms that process implicit spatial information.

What is remembered? Role of attention on the encoding and retrieval of hippocampal representations

The hippocampus is critically involved in storing explicit memory such as memory for space. A defining feature of explicit memory storage is that it requires attention both for encoding and retrieval. Whereas, a great deal is now known about the mechanisms of storage, the mechanisms whereby attention modulates the encoding and retrieval of space and other hippocampus-dependent memory representations are not known. In this review we discuss recent studies, including our own, which show on the cellular level that attention is critical for the stabilization of spatial and reward-associated odour representations. Our findings support the view that in the hippocampus attention selects the reference frame for task-relevant information. This mechanism is in part mediated by dopamine acting through D1/D5 receptors and involves an increase in neuronal synchronization in the gamma band frequency. We propose that synchronous activity leads to enhancements in synaptic strength that mediate the stabilization of hippocampal representations.

Paradoxical sleep deprivation: neurochemical, hormonal and behavioral alterations. Evidence from 30 years of research

Sleep comprises approximately one-third of a person's lifetime, but its impact on health and medical conditions remains partially unrecognized. The prevalence of sleep disorders is increasing in modern societies, with significant repercussions on people's well-being. This article reviews past and current literature on the paradoxical sleep deprivation method as well as data on its consequences to animals, ranging from behavioral changes to alterations in the gene expression. More specifically, we highlight relevant experimental studies and our group's contribution over the last three decades.

Clinical and experimental approaches to varieties of memory

Memory is described as a complex aspect of cognitive functioning. Memory is dependent upon input from the sensory modalities; it relies upon the passage of time; and it requires intervening processes for initial acquisition and subsequent access. Based upon questions posed concerning the relationship between clinical and experimental advances in memory and memory disorders, an example is given to illustrate the influence of research upon techniques for diagnosis and rehabilitation. Suggestions are provided about how to approach answering other related questions in neuropsychology. An integrated program is suggested with the aim of bringing together findings from neuroanatomy, neurochemistry, and neurobehavior. Emphasis is placed upon integrating results of research based upon human and nonhuman models of disordered memory and other cognitive functions. Neuroanatomical systems important for performing delayed-reaction tasks are reviewed, as are results of delayed response and delayed alternation testing in several human populations with neurological dysfunction suggestive of frontal lobe damage.

Information Processing Bias in Post-traumatic Stress Disorder

This review considers theory and evidence for abnormal information processing in post-traumatic stress disorder (PTSD). Cognitive studies have indicated sensitivity in PTSD for traumatic information, more so than general emotional information. These findings were supported by neuroimaging studies that identify increased brain activity during traumatic cognition, especially in affective networks (including the amygdala, orbitofrontal and anterior cingulate cortex). In theory, it is proposed that traumatic cognition may interfere with neutral cognition and there is evidence of abnormal neutral stimulus processing in PTSD. Firstly, PTSD patients perform poorly on a variety of neuropsychology tasks that involve attention and memory for neutral information. The evidence from event-related potentials and functional neuroimaging also indicates abnormal results in PTSD during neutral stimulus processing. The research evidence generally provides support for theories of trauma sensitivity and abnormal neutral stimulus processing in PTSD. However, there is only tentative evidence that trauma cognition concurrently interferes with neutral cognition. There is even some evidence that traumatic or novelty arousal processes can increase the capacity for attentive processing, thereby enhancing cognition for neutral stimulus information. Research on this topic has not yet fully explored the mechanisms of interaction between traumatic and neutral content in the cognitive dynamics of PTSD.

Effects of methylphenidate in ADHD adults on target evaluation processing reflected by event-related potentials

Attention deficit/hyperactivity disorder (ADHD) is a widely examined disease in childhood. There is evidence that the disease responds well to medication with methylphenidate (MPH). The effect of MPH in adults with ADHD is a question that is often raised, because many adults request such therapy today. As yet, there is a lack of studies on event-related potentials (ERPs) and MPH in ADHD adults. In the present study we examined 10 adults diagnosed with ADHD, with and without MPH medication (30 mg daily), by means of ERP in a visual Go/NoGo experiment to gain information about target evaluation processing in these patients and about the effects on these attentional processes during medication with MPH. Visually, there seem to be differences in the frontal electrodes for the N2 and in the parietal electrodes for the P300. But these differences do not achieve statistical significance. There are also no statistically relevant differences for the N1 or the slow wave. MPH does not seem to have an effect on target evaluation processing, when comparing the ERPs of non-medicated and medicated ADHD adults. Especially the P3 does not appear to be modulated by medication with MPH in these ADHD adults, in contrast to findings in ADHD children.

Attentional processing in adults with ADHD as reflected by event-related potentials

Attention deficit/hyperactivity disorder (ADHD) is a well known childhood disease and well researched via event-related potentials (ERPs), but unfortunately there is little information on this illness in adults in ERPs. In the present study, 12 adults diagnosed with ADHD and 12 healthy control adults were examined with respect to ERPs in a visual Go/NoGo-experiment to gain information about target evaluation processing in these patients. Two attention-related ERP-components, the N1 and N2 were significantly increased for the ADHD adults compared to the healthy control adults. These findings were illustrated using source analysis results: In the time frame corresponding to the N1, significant increases of activity were found in the medial frontal gyrus and during the N2 time frame significant increases were detected in the lingual gyrus. The P300 showed a tendency towards decreased activity in the patient group, however, only a subsequent slow wave activity indicated significant differences. Neuronal activity related to early attentional mechanisms (N1 and N2) appears to be enhanced in ADHD patients. Together with the finding of a reduction in the P300, the data suggest that ADHD adults have learned to gather their attention more strongly than healthy adults in order to achieve the same results and compensate for their impairment. This is supported by the source analysis results which show activity in additional brain areas.

Prenatal cocaine exposure alters alpha2 receptor expression in adolescent rats

BACKGROUND

Prenatal cocaine exposure produces attentional deficits which to persist through early childhood. Given the role of norepinephrine (NE) in attentional processes, we examined the forebrain NE systems from prenatal cocaine exposed rats. Cocaine was administered during pregnancy via the clinically relevant intravenous route of administration. Specifically, we measured alpha2-adrenergic receptor (alpha2-AR) density in adolescent (35-days-old) rats, using [3H]RX821002 (5 nM).

RESULTS

Sex-specific alterations of alpha2-AR were found in the hippocampus and amygdala of the cocaine-exposed animals, as well as an upregulation of alpha2-AR in parietal cortex.

CONCLUSION

These data suggest that prenatal cocaine exposure results in a persistent alteration in forebrain NE systems as indicated by alterations in receptor density. These neurochemical changes may underlie behavioral abnormalities observed in offspring attentional processes following prenatal exposure to cocaine.

Prenatal intravenous cocaine and the heart rate-orienting response: a dose-response study

Attentional dysfunction is a persistent behavioral abnormality that is emerging as one of the cardinal features in the investigations of the teratogenic effects of cocaine in humans and rodents. The present study sought to extend this work by using a dose-response design with an alternate strain of rat. Virgin Long-Evans female rats, implanted with an IV access port prior to breeding were administered saline, 0.5, 1.0, or 3.0 mg/kg of cocaine HCl from gestational day (GD) GD8-21 (1x per day-GD8-14, 2x per day-GD15-21). Cocaine had no significant effect on maternal or litter parameters. At 14-15 days of age, 1 male and 1 female from each litter were tested to evaluate the heart rate orienting response (HR-OR). Following 20 min for acclimation, pups were presented an olfactory stimulus for 20s per trial, across four trials, and with an intertrial interval of 2 min. The initial baseline HR was not significantly different across the treatment groups, although cocaine did alter the stability of the QRS complex duration. The magnitude of the HR-OR averaged across trials increased as a linear function of dosage of cocaine. A more complex (quadratic) interaction between cocaine dose and sex of the offspring was also noted. When examined across trials, the controls failed to display any significant within-session variation in the HR-OR; in contrast all of the prenatal cocaine treated groups displayed either sensitization (low and high dose) or habituation of the response (middle dose). Analysis of the peak HR-OR confirmed that the controls were indeed displaying the response on at least one trial of the session, albeit not consistently on any specific trial. The more vigorous HR-OR of the prenatal cocaine groups, relative to vehicle controls, most likely reflects an alteration in development of the neural basis of response; as previously shown, the most vigorous response to the olfactory stimulus is seen early (12 days of age) and progressively decreases across the preweaning period. In sum, prenatal exposure to cocaine, at least when administered by the IV route, provides reproducible alterations in attentional processes, as indexed by the noradrenergically-mediated HR-OR. The documentation of a linear dose-response function suggests that there is likely no threshold for the drug-induced alteration. Moreover, the sex of the animal also appears to play some role in the nature of the expression of the altered HR-OR.

Reduction in acetylcholine release in the hippocampus of dopamine D5 receptor-deficient mice

Activation of the dopamine D1-like receptor stimulates acetylcholine (ACh) release in the hippocampus, apparently through the molecularly defined d5 receptor. In the present study, we used a transgenic mouse completely deprived of functional d5 receptor (d5-/-) to confirm the role and elucidate the possible function of the d5 receptor subtype on hippocampal cholinergic neurotransmission. ACh release was measured using in vivo microdialysis in the mouse dorsal hippocampus of 4 months old homozygous (d5-/-), heterozygous (d5+/-), and the wild-type (d5+/+) littermates. Using the no net flux technique, a significant reduction in basal hippocampal ACh level was found in the d5-/- compared to d5+/- and d5+/+ mice. Moreover, the administration of SKF 38393, a D1-like receptor agonist, systemically (2.0 and 10.0 mg/kg ip), or locally through the dialysis probe (10 and 50 microM), produced a dose-dependent enhancement of ACh release in the d5+/+, a moderate stimulation in the d5+/- but had no effect in the d5-/- mice. Quantitative receptor autoradiography revealed significant increases in M1-like but not in M2-like muscarinic receptor binding sites in the hippocampal formation. These results confirm and extend the role of the d5 receptor in the modulation of hippocampal ACh release and provide evidence for long-term alteration of hippocampal cholinergic neurotransmission resulting from the absence of the d5 receptors including chronically reduced ACh release and change in M1-like receptor levels.

alpha 1d Adrenoceptor signaling is required for stimulus induced locomotor activity

alpha 1 Adrenergic receptors mediate a variety of physiological responses and have been well studied in the cardiovascular and peripheral nervous system. However, their role in the central nervous system remains ill defined because of the lack of highly specific ligands to the alpha1 receptor subtypes. Here, we have employed gene targeting to elucidate the role of alpha 1d receptors in vivo. In addition to disrupting function, the insertion of the lacZ gene into the alpha 1d receptor locus enabled the specific identification of cells expressing the alpha 1d gene. These cells are localized in the cortex, hippocampus, olfactory bulb, dorsal geniculate and ventral posterolateral nuclei of the thalamus. Behaviorally, the alpha 1d(-/-) mice show normal locomotor activity during the subjective day, or resting phase of their cycle. However, during subjective night, or active phase, wheel-running activity is significantly reduced in mutant mice. Furthermore, these mice show a reduction in exploratory rearing behavior in a novel cage environment. Lastly, alpha 1d(-/-) mice show reduced hyperlocomotion after acute amphetamine administration. Together, these data reveal the functional importance of alpha 1d adrenoceptors in mediating a variety of stimulus-induced changes in locomotor behaviors. While the sensitivity of noradrenergic neurons to environmental stimuli has been well documented, our data demonstrate that at least some of these post-synaptic responses are mediated by alpha 1d adrenergic receptors.

The locus coeruleus-noradrenergic system: modulation of behavioral state and state-dependent cognitive processes

Through a widespread efferent projection system, the locus coeruleus-noradrenergic system supplies norepinephrine throughout the central nervous system. Initial studies provided critical insight into the basic organization and properties of this system. More recent work identifies a complicated array of behavioral and electrophysiological actions that have in common the facilitation of processing of relevant, or salient, information. This involves two basic levels of action. First, the system contributes to the initiation and maintenance of behavioral and forebrain neuronal activity states appropriate for the collection of sensory information (e.g. waking). Second, within the waking state, this system modulates the collection and processing of salient sensory information through a diversity of concentration-dependent actions within cortical and subcortical sensory, attention, and memory circuits. Norepinephrine-dependent modulation of long-term alterations in synaptic strength, gene transcription and other processes suggest a potentially critical role of this neurotransmitter system in experience-dependent alterations in neural function and behavior. The ability of a given stimulus to increase locus coeruleus discharge activity appears independent of affective valence (appetitive vs. aversive). Combined, these observations suggest that the locus coeruleus-noradrenergic system is a critical component of the neural architecture supporting interaction with, and navigation through, a complex world. These observations further suggest that dysregulation of locus coeruleus-noradrenergic neurotransmission may contribute to cognitive and/or arousal dysfunction associated with a variety of psychiatric disorders, including attention-deficit hyperactivity disorder, sleep and arousal disorders, as well as certain affective disorders, including post-traumatic stress disorder. Independent of an etiological role in these disorders, the locus coeruleus-noradrenergic system represents an appropriate target for pharmacological treatment of specific attention, memory and/or arousal dysfunction associated with a variety of behavioral/cognitive disorders.

Acute cholecystokinin effects on event-related potentials in healthy volunteers

This study investigated the effects of a continuous slow infusion of cholecystokinin tetrapeptide (CCK-4), a neuropeptide with panicogenic properties, on brain event-related potentials (ERPs) in healthy adults. Twenty-four volunteers, 15 females and 9 males, were assigned to infusion with either placebo or CCK-4 in a randomized, double-blind, parallel group design. ERPs, elicited within a standard auditory odd-ball paradigm requiring the counting of rare (20%) occurring 'deviant' tones interspersed among more frequent (80%) occurring 'standard' tones, were assessed once before infusion, and at 10 min and 40 min after the onset of infusion. Compared with the placebo, CCK-4 delayed the latencies of N100 and P200 components elicited by 'deviant' stimuli. No significant treatment differences were observed with respect to N200, P300b, mood or adverse symptoms. These preliminary findings suggest that CCK-4 may interfere with information processing relating to the selection of significant stimuli and as such, may be of relevance to mechanisms underlying panic disorder.

Prenatal cocaine exposure alters sensitivity to the effects of idazoxan in a distraction task

The present study was designed to test whether prenatal cocaine (COC) exposure alters sensitivity to the attentional effects of idazoxan (IDZ), an alpha-2 adrenergic antagonist that increases coeruleocortical NE activity. The task assessed subjects' ability to selectively attend to an unpredictable light cue and disregard olfactory distractors. IDZ increased commission errors specifically under conditions of distraction, an effect that was similar in the COC and control groups. In contrast, COC animals were significantly more sensitive than controls to the effects of IDZ on omission errors and nontrials. The pattern of effects suggests that the differential treatment response to IDZ on these latter measures resulted from an alteration in norepinephrine (NE)-modulated dopamine release in the COC animals, reflecting lasting changes in dopaminergic and/or noradrenergic systems as a result of the early cocaine exposure. Based on the behavioral measures that showed a differential response to IDZ in the COC animals, it seems likely that these changes may contribute to the alterations in sustained attention and arousal regulation that have been reported in both animals and humans exposed to cocaine in utero.

Biologic models of traumatic memories and post-traumatic stress disorder. The role of neural networks

Neural networks and their behavior provide an information-processing model for initiation and maintenance of the biologic aspects of post-traumatic stress disorder (PTSD). The repeated replaying of the intrusive and distressing recollections that follow a trauma modifies the structure of the neural networks involved in the processing of traumatic memories. The hypothesis is proposed that this repetition instigates the mechanisms of iterative learning, top-down activation and pruning. The development of the symptoms of PTSD can be explained by current knowledge about modeling disturbances of parallel distributing processing. The noradrenergic neurons play a central role in coordinating the interaction of multiple cortical regions, which is an essential aspect of parallel distributed processing. Disturbances of this system in PTSD are likely to be manifest as a dysfunctional modulation of working memory and involuntary traumatic recollection. Modifications of neural networks have a secondary effect of kindling in the hippocampus that further moderates the individual's sensitivity to a range of stressors. Therefore, a neural network model of PTSD provides a method for conceptualizing the onset of PTSD symptoms and their subsequent modification with the passage of time.

Sexually conditioned incentives: attenuation of motivational impact during dopamine receptor antagonism

The motivational impact of sexually conditioned incentives was examined in two experiments. In Experiment 1, male Long-Evans rats copulated to ejaculation in the presence of one of two scents (orange or almond extract) on five separate occasions. On alternating days, subjects spent an equal amount of time in social isolation with the opposing scent. Following the 10-day conditioning regimen, subjects ran more rapidly down an operant runway toward a goalbox containing the sex-paired scent (CS+) compared to trials on which the isolation-paired scent (CS-) or no scent was provided. In Experiment 2, comparably conditioned male rats were first given a baseline runway trial with an unscented goalbox. The following day, subjects were pretreated with one of four doses of haloperidol (0.0, 0.075, 0.15, or 0.30 mg/kg i.p.) 45 min prior to being tested in the runway for their motivation to approach either the CS+ or CS- scents. Control subjects given vehicle injections performed comparably to subjects from Experiment 1, taking significantly less time to approach the CS+ than an unscented goalbox. This decrease in run latency was not observed in subjects within the 0.075 and 0.15 mg/kg haloperidol groups. Subjects in the 0.30 mg/kg haloperidol groups took significantly more time to approach both the CS+ and CS- compared to their baseline run times. These data reveal that an olfactory cue associated with sexual reward becomes a conditioned incentive capable of eliciting approach behavior, and that dopamine receptor antagonism (at moderate but not high doses) selectively attenuates this cue-induced motivation.

Methamphetamine effects on cognitive processing during extended wakefulness

We examined the effects of both 5- and 10-mg/7O kg body weight of d-methamphetamine HCl on high event rate vigilance and tracking performance in a 13.5-hr sustained-performance session during one night of sleep loss. At 0116 hours participants were administered either a 5 mg/70 kg oral dose of d-methamphetamine (n=10), 10 mg/70 kg d-methamphetamine (n=10), or a placebo (n=10) using standard double-blind procedures. Performance on all measures degraded markedly during the night in the placebo group. Both the 5- and 10-mg methamphetamines treatment reversed an initial decline in d', and reversed increases in nonresponses (lapses) and tracking error within approximately 3 hr of administration. No evidence that amphetamine treatment increased impulsive responding (fast guesses) was observed. The magnitude of the performance effects of the methamphetamine treatments was similar at 3 hr postadministration. However, the effects of the 5-mg dose were shorter-lived, disappearing by the last testing session (6.5 hr postadministration), whereas effects of the 10-mg dose tended to remain throughout testing. Both amphetamine treatments decreased subjective sleepiness during the night and tended to increase subjective sleep latencies during a post-testing sleep period.

Consciousness and the brainstem

In the first part of this article we summarize a theoretical framework and a set of hypotheses aimed at accounting for consciousness in neurobiological terms. The basic form of consciousness, core consciousness is placed in the context of life regulation; it is seen as yet another level of biological processing aimed at ensuring the homeostatic balance of a living organism; and the representation of the current organism state within somato-sensing structures is seen as critical to its development. Core consciousness is conceived as the imaged relationship of the interaction between an object and the changed organism state it causes. In the second part of the article we discuss the functional neuroanatomy of nuclei in the brainstem reticular formation because they constitute the basic set of somato-sensing structures necessary for core consciousness and its core self to emerge. The close relationship between the mechanisms underlying cortical activation and the bioregulatory mechanisms outlined here is entirely compatible with the classical idea that the reticular formation modulates the electrophysiological activity of the cerebral cortex. However, in the perspective presented here, that modulation is placed in the setting of the organism's homeostatic regulation.

Comparative effects of alpha-2 receptor agents and THA on the performance of adult and aged rats in the delayed non-matching to position task

The present study investigated the effects of dexmedetomidine (an alpha-2 adrenoceptor agonist), atipamezole (an alpha-2 adrenoceptor antagonist) and tacrine (an inhibitor of acetylcholinesterase) on the performance of adult and aged rats in a delayed non-matching to position task assessing spatial short-term memory. Most of the aged rats were impaired in the pretraining phases and in the acquisition of the non-delayed version of the task. After a substantial training period of the delayed version of the task, both adult and aged rats reached their asymptotic level of performance. Both adult and aged rats showed a decline in the percent correct responses at the longest delays in this task, and a delay independent decrease in the percent correct responses across the delays (0-30 s) was found in the group of aged rats (25-month-old) as compared to the adults (10-month-old). Dexmedetomidine (0.3, 1.0 or 3.0 micrograms/kg), atipamezole (0.03, 0.3 or 3.0 mg/kg) and tacrine (1.0 or 3.0 mg/kg) did not increase the percent correct responses in adult or aged rats. The highest doses of dexmedetomidine and tacrine decreased behavioural activity of rats during this short-term memory testing. Atipamezole (0.03 mg/kg) increased behavioural activity of rats. The results suggest that acute, systemic administrations of alpha-2 drugs or an anticholinesterase do not improve short-term memory in rats.

Decreased exploratory activity and impaired passive avoidance behaviour in mice deficient for the alpha(1b)-adrenoceptor

There is growing evidence that a dysfunction of central noradrenergic neurotransmission is involved in age-related impairments of cognitive performance and the pathophysiology of Alzheimer's disease (AD). A reduction of density of central alpha(1)-adrenergic receptors (alpha(1)-AR) has been shown in aging and AD brains. Three alpha(1)-AR subtypes (alpha(1a), alpha(1b) and alpha(1d)) have been identified by molecular cloning. However, very little is known about the functional role of distinct alpha(1)-AR subtypes in the brain. This problem was specifically addressed using a model of knockout mouse deficient in alpha(1b)-AR (alpha(1B)-/-) because these animals show a 40% reduction of alpha(1)-AR density in the brain as already reported. In comparison to the wild-type mice (alpha(1B)+/+), alpha(1B)-/- mice showed significantly reduced square entries and a reduced rearing behaviour was observed over all sessions in the open field. In passive avoidance procedures, alpha(1B)-/- mice showed a tendency towards decreased short-term-latency and a significant decline in long-term-latency. The present results indicate that mutation of a single member of the alpha(1)-AR gene family creates a distinct phenotype and provide evidence that alpha(1B)-AR is possibly involved in modulation of memory consolidation and fear-motivated exploratory activity. Furthermore, this model of knockout mice may be useful in elucidating the role of alpha(1B)-AR in dementias involving deficits of the noradrenergic system.

Dopamine D4 receptor (DRD4) gene polymorphism is associated with attachment disorganization in infants

About 15% of one-year-old infants in non-clinical, low-risk and up to 80% in high-risk (eg maltreated) populations show extensive disorganized attachment behavior(1,2) in the Strange Situation Test.(3) It has also been reported that disorganization of early attachment is a major risk factor for the development of childhood behavior problems.(4) The collapse of organized attachment strategy has been explained primarily by inappropriate caregiving, but recently, the contribution of child factors such as neurological impairments and neonatal behavioral organization(6) has also been suggested. Here we report an association between the DRD4 III exon 48-bp repeat polymorphism and attachment disorganization. Attachment behavior of 90 infants was tested in the Strange Situation and they were independently genotyped for the number of the 48-bp repeats by polymerase chain reaction (PCR). The 7-repeat allele was represented with a significantly higher frequency in infants classified as disorganized compared to non-disorganized infants: 12 of 17 (71%) vs 21 of 73 (29%) had at least one 7-repeat allele (chi2 = 8.66, df = 1, P < 0.005). The estimated relative risk for disorganized attachment among children carrying the 7-repeat allele was 4.15. We suggest that, in non-clinical, low-social-risk populations, having a 7-repeat allele predisposes infants to attachment disorganization.

Haloperidol challenge during copulation prevents subsequent increase in male sexual motivation

Male rats manifest an increase in sexual motivation following sexual experience. The current experiment was devised to investigate the role of dopamine in this process by assessing whether sexual behavior occurring in the presence of the dopamine receptor antagonist, haloperidol, would continue to alter the subjects' subsequent sexual motivation. Four groups of male Long-Evans rats (total N=34) traversed an operant runway once per day for one of two goalbox targets: a nonestrous or estrous female. Following establishment of baseline run times (10 trials), all males received one ejaculation with a receptive female in a separate testing environment. Subjects were pretreated with vehicle or one of three doses of haloperidol (0.05, 0.075, 0.10 mg/kg) 45 min prior to being paired with the receptive female. All subjects successfully achieved ejaculation under these conditions. Subjects were then re-tested within the runway for their motivation to approach the two types of female targets (10 trials). Vehicle-treated subjects expressed the expected increase in sexual motivation following sexual experience, while haloperidol treatment dose-dependently attenuated this effect. Subjects that received the highest haloperidol dose subsequently manifested increased run times and intra-runway "retreat" behaviors, suggesting that female cues may have become associated with an aversive sexual experience. These results are consistent with the view that dopamine systems play a role in the rewarding or reinforcing consequences of male sexual behavior.

Prenatal intravenous cocaine adversely affects attentional processing in preweanling rats

Perhaps the sole, clinically reported, deficit in infants of women that abused cocaine (COC) during pregnancy that persists through early childhood is that of an attentional disorder. Using the heart rate orienting response (HR-OR), a putative valid and reliable measure of attention, we examined the offspring of rats exposed to COC in utero via the clinically relevant intravenous (IV) route. Sprague-Dawley females, implanted with IV access ports prior to breeding, were administered saline or 3 mg/kg COC HC1, 1X/day on gestational day (GD) 8-14 and 2X/day on GD15-21. No significant effects of prenatal COC were apparent for maternal or litter parameters. Six pups/litter were tested: one of each sex on postnatal day (PD) 12, PD16, and PD21. Following 20 min of adaptation, pups were exposed to a novel odor (20 s amyl acetate) for a set of four acquisition trials; after a 4-h retention interval, the same procedure was again employed. At PD12, both prenatal COC and control pups demonstrated a significant HR-OR on the acquisition trials and both groups showed significant within-session habituation. Across the 4-h retention interval, prenatal COC-exposed pups showed habituation whereas control pups did not. At PD16, the magnitude of the HR-OR was significantly greater in prenatal COC-exposed pups relative to control pups. Within-session habituation also characterized the HR-OR of the COC, but not control, pups. For the retention data, within-subject and regression analyses suggested the COC-exposed pups displayed greater between and within-session habituation, respectively. At PD21, the prenatal COC-treated pups displayed an HR-OR that did not habituate across acquisition trials; the control pups displayed a significant HR-OR only during the initial 5 s of the first two trials. During the retention trials, regression analyses again suggested the COC-exposed pups displayed greater evidence of within-session habituation. Collectively, these data demonstrate that prenatal exposure to COC alters attention throughout the preweanling period of development. Given the putative role of norepinephrine, but not dopamine or serotonin, in central mediation of the HR-OR of preweanling rats, the effects of prenatal IV COC exposure in this task are consistent with a noradrenergically based attentional disorder.

Psychomotor performance and monoamine function in bipolar and unipolar affective disorders

BACKGROUND

Affective disorders are associated with prominent psychomotor abnormalities that may be related to changes in arousal or motivation due to altered catecholamine function.

METHODS

We investigated relationships between performance on psychomotor tests of motor speed (reaction time and tapping speed) and visual tracking (trail making and dot placement) and catecholamine system function including cerebrospinal fluid (CSF) or urinary concentrations of catecholamines or their metabolites. Subjects were medicine-free inpatients with unipolar depression or with manic, depressive, or mixed episodes of bipolar disorder, and healthy controls matched by gender and stratified by age.

RESULTS

Unipolar and bipolar depressed patients were impaired in motor speed, dexterity, and visual tracking, whereas manic and mixed patients did not differ from controls. Tapping speed correlated positively with CSF 3-methoxy-4-hydroxyphenylglycol in healthy controls and with CSF homovanillic acid in bipolar depressed subjects. Increased catecholamine function correlated with slowing in all other measures for patients with bipolar disorder. Relationships between catecholamines and psychomotor function were weaker in unipolar depressed subjects. Psychomotor function was related to severity of depression in bipolar, but not in unipolar, patients.

CONCLUSIONS

These data suggest that catecholamine systems are associated with increased arousal and psychomotor impairment in patients with bipolar disorder. Similar behavioral changes have different neurotransmitter relationships in unipolar disorder.

Cerebellar and spinal projections of the coeruleus complex in the duck: a fluorescent retrograde double-labeling study

The double fluorescent retrograde tracing technique was used to identify, within the coeruleus complex (Co complex) of the duck, the nerve cells projecting to the cerebellar cortex and to the spinal cord. This technique was also used to investigate the possibility that the cerebellar and spinal projections of the Co complex are collaterals of the same axons. In the same animal, nuclear Diamidino yellow dihydrochloride (DY) fluorescent tracer was placed into the cerebellar cortex of folia V-VII, and cytoplasmic fluorescent Fast blue (FB) dye was injected into C3-C4 spinal cord segments. FB labeled multipolar somata and DY fluorescent nuclei were intermingled within the dorsal caudal region of the locus coeruleus (LCo) and within the dorsal division of the nucleus subcoeruleus (dSCo). Moreover, in the LCo, a low proportion of double-labeled neurons (about 3-4% of labelings) was evidenced among single-labeled neurons. In the ventral division of the nucleus subcoeruleus (vSCo), occasional DY labeled nuclei were found, whereas FB-labeled cells were frequently present. The present findings reveal the location of the coeruleocerebellar and coeruleospinal projecting neurons within the Co complex of the duck. They are intermingled in the caudal portion of the LCo and along the rostrocaudal extent of the subjacent dSco. The LCo and the dSCo are the major source of the projections to the folia V-VII, whereas the vSCo contributes very slightly to the innervation of the cerebellar injected areas. Moreover, the double-labeling study demonstrates that in the duck a low percentage of neurons within the ventrolateral portion of the caudal region of the LCo projects both to the cerebellar cortex of folia V-VII and to C3-C4 spinal cord segments via collaterals. Therefore, these neurons simultaneously influence the cerebellar cortex and spinal cord. The possibility that the projections studied are noradrenergic and that they play a role in feeding is discussed.

Computational models of neuromodulation

Computational modeling of neural substrates provides an excellent theoretical framework for the understanding of the computational roles of neuromodulation. In this review, we illustrate, with a large number of modeling studies, the specific computations performed by neuromodulation in the context of various neural models of invertebrate and vertebrate preparations. We base our characterization of neuromodulations on their computational and functional roles rather than on anatomical or chemical criteria. We review the main framework in which neuromodulation has been studied theoretically (central pattern generation and oscillations, sensory processing, memory and information integration). Finally, we present a detailed mathematical overview of how neuromodulation has been implemented at the single cell and network levels in modeling studies. Overall, neuromodulation is found to increase and control computational complexity.

Catecholaminergic involvement in the control of aggression: hormones, the peripheral sympathetic, and central noradrenergic systems

Noradrenaline is involved in many different functions, which all are known to affect behaviour profoundly. In the present review we argue that noradrenaline affects aggression on three different levels: the hormonal level, the sympathetic autonomous nervous system, and the central nervous system (CNS), in different, but functionally synergistic ways. Part of these effects may arise in indirect ways that are by no means specific to aggressive behaviour, however, they are functionally relevant to it. Other effects may affect brain mechanisms specifically involved in aggression. Hormonal catecholamines (adrenaline and noradrenaline) appear to be involved in metabolic preparations for the prospective fight; the sympathetic system ensures appropriate cardiovascular reaction, while the CNS noradrenergic system prepares the animal for the prospective fight. Indirect CNS effects include: the shift of attention towards socially relevant stimuli; the enhancement of olfaction (a major source of information in rodents); the decrease in pain sensitivity; and the enhancement of memory (an aggressive encounter is very relevant for the future of the animal). Concerning more aggression-specific effects one may notice that a slight activation of the central noradrenergic system stimulates aggression, while a strong activation decreases fight readiness. This biphasic effect may allow the animal to engage or to avoid the conflict, depending on the strength of social challenge. A hypothesis is presented regarding the relevance of different adrenoceptors in controlling aggression. It appears that neurons bearing postsynaptic alpha2-adrenoceptors are responsible for the start and maintenance of aggression, while a situation-dependent fine-tuning is realised through neurons equipped with beta-adrenoceptors. The latter phenomenon may be dependent on a noradrenaline-induced corticosterone secretion. It appears that by activating very different mechanisms the systems working with adrenaline and/or noradrenaline prepare the animal in a very complex way to answer the demands imposed by, and to endure the effects caused by, fights. It is a challenge for future research to elucidate how precisely these mechanisms interact to contribute to functionally relevant and adaptive aggressive behaviour.

Contributions of the dopaminergic system to voluntary and automatic orienting of visuospatial attention

Visuospatial attention can be directed by voluntary or involuntary control independent of eye movement. The involvement of cortical and subcortical neural structures in this covert orienting mechanism has been studied using neuroimaging and electrophysiological techniques. This study was designed to investigate the role of the dopaminergic system in both voluntary and automatic orienting mechanisms of visuospatial attention. We recorded event-related evoked potentials (ERPs) and reaction time (RT) during a cued priming task in both patients with idiopathic Parkinson's disease (PD) and control subjects. Voluntary and automatic shifts in attention were studied by using central and peripheral cues, respectively. In the experiment using a central cue, the RT data showed that when the cue-target interval was long, PD patients' responses were delayed, and cue validity effects were reduced, whereas in the peripheral cue experiment the validity effects persisted across all trials. The ERPs demonstrated reduced sustained negativities preceding the imperative targets in both the central and peripheral cue experiments in PD patients. Furthermore, during the long cue-target interval in the central cue experiment, PD patients showed reduced attention shift-related negativities (ARNs) at the anterior scalp sites, whereas ARNs were generated widely in the peripheral cue experiment. The ERP findings were consistent with the RT data. These findings suggest that the dopaminergic system may contribute to voluntary and sustained control of visuospatial attention as well as to the neural system for response preparation, whereas automatic control of visuospatial attention is relatively independent of the dopamine system.

Neurochemical and neurobehavioral effects of neonatal administration of beta-N-methylamino-L-alanine and 3,3'-iminodipropionitrile

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that is characterized by a loss of motor neurons in the spinal cord, brain stem, and cortex. The present study examined the neurochemical and neurobehavioral consequences of the neonatal administration of IDPN and BMAA, two neurotoxins previously considered as experimental models of ALS. Sprague-Dawley rat pups (male and female) were injected SC with IDPN or BMAA. The following treatment groups (n = 5-14 per group) were studied; IDPN [100 mg/kg on postnatal days (PNDs) 2, 4, and 6], BMAA-A (500 mg/kg PND 5 only), BMAA-B (500 mg/kg PND 2 and 5), and BMAA-C (100 mg/kg PND 2 and 5). Neurobehavioral testing was performed and the rats were sacrificed at 101 days of age. Monoamine and amino acid content was measured by HPLC in brain regions and the spinal cord. IDPN treatment impaired the righting reflex and decreased forepaw suspension times. BMAA-A and BMAA-B males exhibited an increase in open field behavior. The hindlimb splay of BMAA-A females was increased. Other significant behavioral and endocrine effects were also seen with neonatal IDPN or BMAA treatment. IDPN females had increased spinal cord content of norepinephrine (NE), serotonin, and 5-hydroxyindoleacetic acid (5-HIAA). IDPN males had no alterations in spinal cord content of NE or Glu, but serotonin and 5-HIAA content were increased. BMAA-A and BMAA-B males also had elevated spinal cord 5-HIAA content whereas females were unaffected. Glu and Asp content in the spinal cord was elevated in the female BMAA-C group. Monoamines were also altered in the cerebellum, mediobasal hypothalamus, and hippocampus by IDPN and BMAA treatment. alpha 2-Adrenergic binding sites were increased in the spinal cord by IDPN and in the cerebellum by BMAA treatment. The results of this study clearly demonstrated that both IDPN and BMAA given neonatally can produce changes in motor function and spinal cord neurochemistry, although the pattern of the effects is both treatment and sex dependent. Neonatal exposure to either IDPN or BMAA resulted in permanent changes in adult neurochemistry that may be related to reorganizational effects induced by toxin-mediated neuroplasticity in developing neurons.

Lateralized attentional deficits in drug-free and medicated schizophrenic patients

Performance on a cued reaction time (RT) task, theoretically linked to posterior and anterior neuroanatomical systems in the brain (Posner, M. I. et al., Science, 1988, 210, 1627-1631; Archives of General Psychiatry, 1988, 15, 811-821), was used to assess sensory orienting and maintenance of attention. In schizophrenic patients, Posner et al. found a lateralized abnormality in RT (longer RTs to uncued targets in the right visual field than in the left visual field), as did Maruff et al. (Neuropsychologia, 1995, 33, 1205-1223), but Strauss et al. (Journal of Psychiatric Research, 1991, 37, 139-146), among others, did not replicate this effect. However, the subjects in these studies differed in the percentage of schizophrenic patients taking neuroleptic medication at the time of testing and in the chronicity of the illness. In the present study, we used two groups of schizophrenic subjects to control for the use of neuroleptic medication. The lateralized abnormality in RT was observed in the drug-free group of schizophrenic subjects, but not in the group of drug-treated schizophrenic subjects.

Fractal analysis of striatal dopamine re-uptake sites

Spatial variation in regional blood flow, metabolism and receptor density within the brain and in other organs is measurable even with a low spatial resolution technique such as emission tomography. It has been previously shown that the observed variance increases with increasing number of subregions in the organ/tissue studied. This resolution-dependent variance can be described by fractal analysis. We studied striatal dopamine re-uptake sites in 39 healthy volunteers with high-resolution single-photon emission tomography using iodine-123 labelled 2beta-carbomethoxy-3beta-(4-iodophenyl)tropane ([123I]beta-CIT). The mean fractal dimension was 1.15+/-0.07. The results indicate that regional striatal dopamine re-uptake sites involve considerable spatial heterogeneity which is higher than the uniform density (dimension=1.00) but much lower than complete randomness (dimension=1.50). There was a gender difference, with females having a higher heterogeneity in both the left and the right striatum. In addition, we found striatal asymmetry (left-to-right heterogeneity ratio of 1.19+/-0.15; P<0.001), suggesting functional hemispheric lateralization consistent with the control of motor behaviour and integrative functions.

Modulation of vigilance and behavioral activation by alpha-1 adrenoceptors in the rat

This study investigated the role of alpha-1 adrenergic receptors in the modulation of attention and behavioral activity by assessing the effects of alpha-1 adrenergic receptor stimulation or blockade on the performance of rats in tasks involving vigilance (sustained attention) and selective attention [five-choice serial reaction time (5-CSRT)]. Pretesting subcutaneous administration of St-587 (a putative alpha-1 agonist) at 100 micrograms/kg, but not at 300 or 1000 micrograms/kg, significantly improved the choice accuracy of rats in the 5-CSRT task (monitoring of visual stimuli), whereas prazosin (a prototype alpha-1 antagonist) at 300 micrograms/kg administered subcutaneously slightly impaired choice accuracy of the rats in this task. Prazosin at 100 micrograms/kg blocked the ability of St-587 at 100 micrograms/kg to improve choice accuracy. Furthermore, St-587 at 100 micrograms/kg significantly increased the number of trials completed and reduced the probability of premature responses, whereas prazosin at 300 micrograms/kg decreased the number of trials completed and the latency of animals to make correct responses in the task. Prazosin at 100 micrograms/kg blocked the effect of St-587 at 100 micrograms/kg in increasing the number of trials completed. However, prazosin at 100 micrograms/kg did not abolish the effect of St-587 in reducing the probability of premature responses. Because the effect of St-587 at 100 micrograms/kg in improving choice accuracy is rather modest, it is possible that when the 100- and 300-microgram/kg doses of St-587 were administered in a counterbalanced order, this effect could have been overlooked due to day-to-day variation. Thus, the present results suggest that stimulation of alpha-1 adrenergic receptors can facilitate vigilance.

Dexmedetomidine reduces response tendency, but not accuracy of rats in attention and short-term memory tasks

The present study investigated the role of alpha 2-adrenergic mechanisms in the performance of motor responses, attention and short-term memory in rats. A low dose (3.0 micrograms/kg, s.c.) of dexmedetomidine, an alpha 2-adrenoceptor agonist, reduced response tendency in an attentional task and a working memory task, but it did not affect the choice accuracy of rats. Atipamezole (300 micrograms/kg), an alpha 2-adrenoceptor antagonist, increased anticipatory responding. Although atipamezole did not affect the number of omissions, it reversed the effects of dexmedetomidine on that parameter. We also investigated the effects of dexmedetomidine in rats with partial destruction of noradrenergic nerves induced by the neurotoxin DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride). On its own, DSP-4 treatment did not affect choice accuracy or behavioural activity of rats in the attentional task. The effects of dexmedetomidine (0.3-3.0 micrograms/kg) on anticipatory responses did not differ between controls and DSP-4 group. Furthermore, the effect on omissions was not consistently diminished in DSP-4 treated rats. These results suggest that the activation of postsynaptic alpha 2-adrenoreceptors may be responsible for dexmedetomidine-induced reduction of response tendency while attention and short-term memory are not markedly affected.

Prazosin inhibits MK-801-induced hyperlocomotion and dopamine release in the nucleus accumbens

This study examined the putative inhibitory effect of the alpha 1-adrenoceptor antagonist prazosin (1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(2-furanylcarbonyl)pip erazine) on changes evoked by the psychotomimetic, non-competitive NMDA receptor antagonist, MK-801((+)-5-methyl-10,11-dihydroxy-5H-dibenzo-(a,d)cyclohepten-5, 10-imine), in locomotor activity and extracellular concentrations of dopamine and its metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the nucleus accumbens as assessed by microdialysis in freely moving rats. MK-801 (0.1 and 0.3 mg/kg, s.c.) induced a significant, dose-dependent increase in horizontal locomotor activity but did not affect rearing. Prazosin administration alone (1 mg/kg, s.c.) only slightly reduced horizontal activity during an initial 10 min measurement period, although it consistently reduced rearing. However, pretreatment with prazosin effectively suppressed the locomotor stimulation caused by either dose of MK-801 throughout the whole observation period, i.e. 40 min. Both doses of MK-801 significantly increased extracellular levels of dopamine in the nucleus accumbens up to approximately 90%. In addition, MK-801 dose dependently increased dopamine metabolite concentrations in the nucleus accumbens, but 5-HIAA was significantly increased only by the high dose of MK-801. When given alone, prazosin did not affect either dopamine, DOPAC, HVA or 5-HIAA levels. However, prazosin pretreatment effectively blocked MK-801-evoked increases in dialysate dopamine concentrations. Consequently, the potent and selective alpha 1-adrenoceptor antagonist prazosin was found to specifically suppress MK-801-evoked, but not basal dopamine release in the nucleus accumbens, while effectively blocking MK-801-evoked locomotor stimulation with only negligible effects on basal locomotor activity. Thus, alpha 1-adrenoceptor antagonism may act by reducing the sensitivity of the mesolimbic dopamine system to pharmacological or environmental challenge. Since most antipsychotic drugs exhibit both dopamine D2 receptor and alpha 1-adrenoceptor antagonistic properties, they may alleviate psychosis not only through blockade of postsynaptic dopamine receptors, but also presynaptically on the mesolimbic dopamine system, through their alpha 1-adrenoceptor antagonistic action. This latter action may contribute to reduce evoked dopamine hyperactivity, e.g. in response to stress.

Grammaticality judgments and sentence comprehension in Parkinson's disease: a comparison with Broca's aphasia

In order to test the hypothesis that significant linguistic deficits could be associated with predominantly subcortical dopaminergic pathways which projected to the frontal lobes (in patients with Parkinson's Disease-PD), we compared language performance in PD patients to that of Broca's aphasics with linguistic deficits. On tests of grammaticality judgements and sentence comprehension, performance by patients with Parkinson's Disease did not vary with different types of sentence structure (as was the case with the aphasics) and was instead, uniformly high (about 75% correct). Comprehension performance, however, did significantly decline in a subgroup of patients with PD who were tested when withdrawn from their dopaminergic medications. We conclude that patients with treated Parkinson's Disease evidence no selective linguistic dysfunction. When, however, they are withdrawn from dopaminergic medication language functions suffer.

Changes in monoamines and their metabolite concentrations in REM sleep-deprived rat forebrain nuclei

Rapid eye movement sleep deprivation (REMSD) is a potent stressor in rats. Behavioral abnormalities such as passive and active avoidance, locomotor activity, problem solving, sensory information processing, and the development of adaptive copping strategy in response to repeated stress are among the earliest obvious symptoms of REMSD, the mechanism for which remain largely unknown. The aim of this study was to determine whether 96 h of REMSD causes changes in monoamine neurotransmitters concentrations in rat forebrain regions (frontal cortex, FC; parietal cortex, PC, and striatum) that are involved in mediating higher brain functions such as attentional mechanisms, sensory information processing, and locomotor activity, which are severely affected in REMSD conditions. Rats were subjected to 96 h of REMSD using inverted flower pot water tank technique. To account for the stress associated with water tanks, a tank control group (TC) was included where the animals could reside comfortably on a large pedestal in the water tank. Regional brain concentrations of norepinephrine (NE), dopamine (DA), dihydroxyphenyacetic acid (DOPAC), L-3,4-dihydroxyphenylalanine (L-DOPA), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (HIAA) were determined by electrochemical detection using high-performance liquid chromatography. The concentrations of serotonin and its metabolite, HIAA, was reduced in the frontal and parietal cortexes of REMSD rats compared with TC or cage control (CC) group. NE, DA, DOPAC, and HVA concentrations in FC and PC of REMSD animals were remained unchanged compared with TC or CC rats. A significant increase in the concentrations of DA metabolites was observed in the striatum of REMSD rats when compared with CC and TC rats. There was a 29 and 31% increase in the concentration of striatal DA in REMSD group compared to the TC and CC groups, respectively; however, these percentages were not statistically different. Striatal NE, 5-HT, and HIAA concentrations were not significantly different among the three groups. These results suggest that 96 h of REMSD alters dopaminergic and serotonergic systems in different locations in rat brain. The effect of REMSD on the serotonergic systems are localized in the cerebral cortex, whereas dopaminergic metabolism is increased in the striatum.