D1 dopamine receptors in prefrontal cortex: involvement in working memory

Effects of antipsychotics on cognitive behaviour in rats using the delayed non-match to position paradigm

The acute effects of the dopamine D1 receptor antagonist SCH 23390 [(R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepi n-7-ol d hemimaleat, the dopamine D2 receptor antagonists raclopride and haloperidol, the compounds with mixed receptor profiles clozapine, risperidone and sertindole, the alpha 1-adrenoceptor antagonist prazosin and scopolamine were investigated in a delay-response task, a test for working memory, for rats. SCH 23390 induced a delay-dependent impairment of the performance. Raclopride, haloperidol, clozapine, and risperidone induced a delay-independent impairment. Sertindole was without effect. The specific (delay-dependent) and unspecific (delay-independent) effects on working memory of the dopamine D1 and D2 receptor antagonists, respectively, were associated with the dominance of dopamine D1 receptors in the prefrontal cortex and of dopamine D2 receptors in the basal structures of the brain. Prazosin did not affect working memory; however, a reduction in intertrial responses was found. Scopolamine induced a delay-independent impairment. It is concluded that the compounds have different activity profiles in this cognitive task. This finding may have important implications for the development of antipsychotics with a lower propensity for cognitive side effects.

Cortical maldevelopment, anti-psychotic drugs, and schizophrenia: a search for common ground

Two of the favorite hypotheses of schizophrenia research-maldevelopment of cerebral cortex and malfunction of brain dopamine systems-have often seemed difficult to reconcile. This article reviews recent research that suggests a heuristically useful reconciliation centered on the functional neuroanatomical concept of prefrontal-temporolimbic cortical connectivity. Anatomical findings from postmortem studies and neuropsychological and neuroimaging studies of brain function in patients with schizophrenia have implicated a developmental 'dysconnection' of temporolimbic-prefrontal cortices. The possibility that such dysconnection can account for the principal phenomenology of the illness, including its delayed onset and its treatment, is suggested by neurologic disease analogies such as metachromatic leukodystrophy and by recent studies in animals with developmental cortical lesions. Studies mapping neuronal gene expression indicate that all antipsychotic drugs modulate DNA transcription in a region of the nucleus accumbens that receives converging inputs from prefrontal and temporolimbic cortices, suggesting that indirect compensation for dysfunctional communication between prefrontal and temporolimbic cortices is a therapeutic mechanism of these drugs. Treatments aimed at direct cortical compensation may be more effective.

Postnatal maturation of the dopaminergic innervation of monkey prefrontal and motor cortices: a tyrosine hydroxylase immunohistochemical analysis

The mature functional architecture of the primate prefrontal cortex arises during a protracted period of postnatal development. Although catecholaminergic afferents arrive in the primate cortex quite early during fetal development, several lines of evidence suggest that substantial changes in the dopaminergic innervation of prefrontal cortex may occur during postnatal development. In this study, we used immunocytochemical techniques and antibodies against tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, to examine the precise time course from birth to adulthood of the maturational changes of tyrosine hydroxylase-labeled axons in prefrontal cortical areas 9 and 46 and primary motor cortex (area 4) of rhesus monkeys. In area 9, the densities of tyrosine hydroxylase-labeled axons and varicosities in the superficial and deep cortical layers remained relatively constant during postnatal development. In contrast, marked developmental changes in innervation density occurred in the middle cortical layers. For example, in deep layer III, the density of tyrosine hydroxylase-positive varicosities was relatively low and uniform in animals under 1 month of age but then increased by a factor of three in animals 2-3 months of age. The density of labeled varicosities continued to increase, reaching a peak (sixfold greater than in the youngest animals) in animals 2-3 years of age before declining to stable adult levels. Similar laminar-specific patterns of change also occurred in areas 46 and 4, although regional differences were present in the magnitude and precise time course of these developmental changes. These findings demonstrate that the innervation of monkey frontal cortex by tyrosine hydroxylase-immunoreactive axons undergoes a protracted, laminar-specific pattern of change during postnatal development that continues through adolescence and into early adulthood. These developmental refinements may interact with other modifications of cortical circuitry that underlie the functional maturation of these regions.

Distribution of messenger RNAs for D1 dopamine receptors and DARPP-32 in striatum and cerebral cortex of the cynomolgus monkey: relationship to D1 dopamine receptors

Messenger RNAs for the D1 dopamine receptor and dopamine- and cyclic AMP-regulated phosphoprotein of relative mass 32,000 (DARPP-32) were examined by in situ hybridization in the cynomolgus monkey brain. The messenger RNA distribution was compared to the distribution of D1 dopamine receptors using [3H]SCH 23390 autoradiography. In the caudate nucleus and putamen, D1 dopamine receptor messenger RNA-positive cells were unevenly distributed. Clusters of cells with an approximately three-fold higher intensity of labeling, as compared to surrounding regions, were found. Some of these D1 dopamine receptor messenger RNA intensive cell clusters in the caudate nucleus appeared to some extent to be matched to regions of higher intensity of [3H]SCH 23390 binding. The distribution of cells expressing DARPP-32 messenger RNA in the caudate nucleus and putamen was found to be non-clustered. In neocortical regions, cells of different sizes expressing D1 dopamine receptor messenger RNA were present in layers II-VI. D1 dopamine receptor messenger RNA-positive cells were most abundant in layer V. Unexpectedly, no DARPP-32 messenger RNA signal was detected in neocortex. Chronic SCH 23390 administration did not change the relative levels of messenger RNAs for the D1 dopamine receptor and DARPP-32 or [3H]SCH 23390 binding as measured by quantitative image analysis. The clustered distribution of D1 dopamine receptor messenger RNA is in contrast to that of DARPP-32 messenger RNA. This suggests that D1 dopamine receptors may play a more significant role in regulating DARPP-32 function in patch regions as compared to matrix regions. D1 dopamine receptor messenger RNA-expressing cells could also be visualized in several layers of the primate neocortex, implying that dopamine acts through D1 dopamine receptors within functionally different neuronal circuits of the neocortex.

Who Did What and When? Using Word- and Clause-Level ERPs to Monitor Working Memory Usage in Reading

ERPs were recorded from 24 undergraduates as they read sentences known to differ in syntactic complexity and working memory requirements, namely Object and Subject Relative sentences. Both the single-word and multiword analyses revealed significant differences due to sentence type, while multiword ERPs also showed that sentence type effects differed for Good and Poor comprehenders. At the single-word level, ERPs to both verbs in Object Relative sentences showed a left anterior negativity between 300 and 500 msec postword-onset relative to those to Subject Relative verbs. At the multiword level, a slow frontal positivity characterized Subject Relative sentences, but was absent for Object Relatives. This slow positivity appears to index ease of processing or integration. and was more robust in Good than in Poor comprehenders.

Asymmetrical visual-spatial attentional performance in ADHD: evidence for a right hemispheric deficit

This study was designed to confirm the presence of a lateralizing deficit in visual-spatial attention in children with ADHD, to further characterize the nature of this deficit and to specify the likely hemispheric locus of dysfunction. Two versions of the covert orienting of attention procedure which evaluated separately endogenous and exogenous cuing effects were administered to 20 unmedicated children aged 9-12 with ADHD and 20 matched controls. Both groups also underwent thorough psychiatric assessment and testing using the TOVA and the Wisconsin Card Sorting Task (WCST). Children with ADHD showed an asymmetrical performance deficit characterized by a loss of costs on controlled (endogenous) attentional orienting to invalidly cured left visual field targets. The degree of cost asymmetry correlated negatively with the number of categories sorted on the WCST. It was concluded that unmedicated children with ADHD show an asymmetrical performance deficit on the covert orienting procedure characterized by a disruption of right hemispheric attentional mechanisms. This deficit may be related to diminished right hemispheric frontal-striatal catecholamine activity.

D1 and D2 receptor gene expression in the rat frontal cortex: cellular localization in different classes of efferent neurons

The dopaminergic input to the frontal cortex has an important role in motor and cognitive functions. These effects are mediated by dopamine receptors both of type D1 and of type D2, although the neural circuits involved are not completely understood. We used in situ hybridization to determine the cellular localization of D1 and D2 receptor mRNAs in the rat frontal cortex. Retrograde tracing was used in the same animals to identify the main cortical efferent populations. Fluorogold was injected into the different cortical targets of the frontal cortex and sections were hybridized with D1 and D2 35S-labelled cRNA probes. D1 and D2 mRNA-containing neurons were present in all the cortical areas investigated, with greater expression in the medial prefrontal, insular and cingulate cortexes and lower expression in the motor and parietal cortexes. Neurons containing D1 mRNA were most abundant in layer VIb; they were also present in layers VIa and V of all cortical layers and in layer II of the medial prefrontal, cingulate and insular areas. Double labelling with fluorogold demonstrated that D1 mRNA was present in corticocortical, corticothalamic and corticostriatal neurons. Neurons containing D2 mRNA were essentially restricted to layer V, but only in corticostriatal and corticocortical neurons. Neither D1 nor D2 mRNA was found in corticospinal or corticopontine neurons. The present results demonstrate that D1 and D2 receptor genes are expressed in efferent cortical populations, with higher expression for D1. In spite of an overlap in some cortical layers, the expression of D1 and D2 receptor genes is specific for different categories of pyramidal neurons.

Saccadic abnormalities in psychotic patients. II. The role of neuroleptic treatment

The effects of dopamine-antagonistic neuroleptic (NL) medication on saccadic eye movements were compared in matched groups of 40 NL-treated and 18 NL-free schizophrenic patients and in 18 NL-treated and 14 NL-free bipolar affective patients. Manipulation of the saccadic paradigm yielded data on four types of saccade: those reflexively elicited by novel stimuli (REFLEX saccades), those directed towards the remembered location of a target now extinguished (REM) or towards the location where a predictably alternating target is expected to appear (PRED), or ANTI saccades, directed away from the stimulus to the mirror image location. Extensive psychiatric, neurological and neuropsychological assessments were also carried out on all subjects. The saccades of NL-treated patients, regardless of diagnosis, were less spatially accurate than those of NL-free patients, with a greater tendency to fall short of the target when generated towards the locus of a mentally represented target. This effect was greatest with a predictably alternating target, especially during periods when target visibility was withdrawn, only a temporal cue remaining. This pattern of impairment which is also found in early stages of Parkinson's disease is likely to be due to deficiency of striatal dopamine. Its best clinical predictors were disease duration, and Webster-Parkinsonism scores. Failure to suppress reflexive saccades to the stimulus in the REM and ANTI paradigms were more closely associated with schizophrenia than with NL treatment and were best predicted by negative symptoms and Wisconsin perseverative errors, both of which are widely regarded as indicators of frontal lobe dysfunction.

Characterization of subtype-specific antibodies to the human D5 dopamine receptor: studies in primate brain and transfected mammalian cells

To achieve a better understanding of how D5 dopamine receptors mediate the actions of dopamine in brain, we have developed antibodies specific for the D5 receptor. D5 antibodies reacted with recombinant baculovirus-infected Sf9 cells expressing the D5 receptor but not with the D1 receptor or a variety of other catecholaminergic and muscarinic receptors. Epitope-tagged D5 receptors expressed in mammalian cells were reactive with both D5 antibodies and an epitope-specific probe. A mixture of N-linked glycosylated polypeptides and higher molecular-mass species was detected on immunoblots of membrane fractions of D5-transfected cells and also of primate brain. D5 receptor antibodies intensely labeled pyramidal neurons in the prefrontal cortex, whereas spiny medium-sized neurons and aspiny large interneurons of the caudate nucleus were relatively lightly labeled. Antibodies to the D5 dopamine receptor should prove important in experimentally determining specific roles for the D5 and D1 receptors in cortical processes and diseases.

LSD and structural analogs: pharmacological evaluation at D1 dopamine receptors

The hallucinogenic effects of lysergic acid diethylamide (LSD) have been attributed primarily to actions at serotonin receptors. A number of studies conducted in the 1970s indicated that LSD also has activity at dopamine (DA) receptors. These latter studies are difficult to interpret, however, because they were completed before the recognition of two pharmacologically distinct DA receptor subtypes, D1 and D2. The availability of subtype-selective ligands (e.g., the D1 antagonist SCH23390) and clonal cell lines expressing a homogeneous receptor population now permits an assessment of the contributions of DA receptor subtypes to the DA-mediated effects of LSD. The present study investigated the binding and functional properties of LSD and several lysergamide and analogs at dopamine D1 and D2 receptors. Several of these compounds have been reported previously to bind with high affinity to serotonin 5HT2 (i.e., 3H-ketanserin) sites in the rat frontal cortex (K0.5 5-30 nM). All tested compounds also competed for both D1-like (3H-SCH 23390) and D2-like (3H-spiperone plus unlabeled ketanserin) DA receptors in rat striatum, with profiles indicative of agonists (nH < 1.0). The affinity of LSD and analogs for D2 like receptors was similar to their affinity for 5HT2 sites. The affinity for D1 like receptors was slightly lower (2- to 3-fold), although LSD and several analogs bound to D1 receptors with affinity similar to the prototypical D1 partial agonist SKF38393 (K0.5 ca. 25 nM). A second series of experiments tested the binding and functional properties of LSD and selected analogs in C-6 glioma cells expressing the rhesus macaque D1A receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

D1/D5 receptor agonists induce a protein synthesis-dependent late potentiation in the CA1 region of the hippocampus

Agonists of the dopamine D1/D5 receptors that are positively coupled to adenylyl cyclase specifically induce a slowly developing long-lasting potentiation of the field excitatory postsynaptic potential in the CA1 region of the hippocampus that lasts for > 6 hr. This potentiation is blocked by the specific D1/D5 receptor antagonist SCH 23390 and is occluded by the potentiation induced by cAMP agonists. An agonist of the D2 receptor, which is negatively coupled to adenylyl cyclase through G alpha i, did not induce potentiation. Although this slow D1/D5 agonist-induced potentiation is partially independent of N-methyl-D-aspartate receptors, it seems to share some steps with and is occluded by the late phase of long-term potentiation (LTP) produced by three repeated trains of nerve stimuli applied to the Schaffer collateral pathway. Similarly, the D1/D5 antagonist SCH 23390 attenuates the late phase of the LTP induced by repeated trains, and the D1/D5 agonist-induced potentiation is blocked by the protein synthesis inhibitor anisomycin. These results suggest that the D1/D5 receptor may be involved in the late, protein synthesis-dependent component of LTP in the hippocampal CA1 region, either as an ancillary component or as a mediator directly contributing to the late phase.

Verbal working memory dysfunction in schizophrenia: use of a Brown-Peterson paradigm

Recent studies of schizophrenia have implicated deficits in processes related to working memory, but the cognitive features of these deficits have been incompletely characterized. We used a modified Brown-Peterson paradigm to compare working memory in patients with schizophrenia and in normal control subjects. Distractor conditions differed in processing demand, increasing in complexity from no distractor to counting backwards (serial threes). We found significant effects of group, of distractor condition, and of a group x distractor condition interaction. The significant interaction was the result of a more rapid decline in the performance of schizophrenic patients with concurrent articulation. In addition, the schizophrenic group also made significantly more intrusion errors. The study suggests that schizophrenic patients exhibit dysfunction of the verbal working memory system due to a diminution in its overall processing resources.

The role of the medial prefrontal cortex of rats in short-term memory functioning: further support for involvement of cholinergic, rather than dopaminergic mechanisms

The putative involvement of the dopaminergic innervation of the medial part of the prefrontal cortex (PFC) in short-term memory functioning was investigated by evaluating the effects of local infusions of dopaminergic drugs into the ventral part of the medial PFC of rats in an operant delayed-matching-to-position (DMTP) task. Two separate groups of rats were tested after bilateral microinfusion of several doses of either the dopamine receptor agonist apomorphine (APO) or the dopamine receptor antagonist cis-flupenthixol (FLU) into the ventromedial PFC. In addition, all animals were tested after infusion of several doses of the muscarinic receptor antagonist scopolamine (SCO) and the dopamine DI receptor antagonist SCH-23390 (SCH). The drugs tested affected DMTP performance differentially. APO had no effect on response accuracy, although it dose-dependently affected nose poke activity and response latencies. FLU and SCH both induced a dose-dependent, but delay-independent deterioration of response accuracy that was paralleled by increases in response latencies and decreases in nose poke frequencies, causing some animals to stop responding after infusion of the highest doses of both drugs. In contrast, SCO infusions into the ventromedial PFC induced a dose- and delay-dependent deterioration of response accuracy, that was accompanied by an increase in response latencies only. Taken together, these results provide additional support for the involvement of cholinergic, rather than dopaminergic mechanisms in short-term memory supported by the medial PFC of the rat, and they are not in favor of a functional dissociation between the dorsomedial PFC and the ventromedial PFC in the role.

PET imaging of neocortical monoaminergic terminals in Parkinson's disease

Post-mortem neurochemical studies in Parkinson's disease (PD) have shown that, in addition to the typical nigro-striatal dopamine denervation, there exists a concomitant neocortical monoamine fibre deafferentation (of variable severity) whose role in motor, and especially in associated cognitive and affective impairment, remains elusive. We have extensively examined whether PET imaging with 11C-S-Nomifensine (11C-NMF), a radioligand of the dopamine and norepinephrine presynaptic reuptake sites which has been used so far to investigate the striatum, could provide a method for assessing in vivo the neocortical monoamine terminal loss in PD; previously, this has been a little addressed and controversial issue. To this end, we prospectively selected a highly homogeneous sample of nine non-demented, non-depressed idiopathic PD patients with mild to marked side-to-side asymmetry in motor impairment. In addition to recovering the previously-reported correlations with putaminal 11C-NMF specific uptake asymmetries, the clinical motor asymmetries also significantly correlated in the clinically expected direction to neocortical (especially frontal) 11C-NMF asymmetries, suggesting the monoamine neocortical denervation might play a direct role in motor impairment in PD. These results demonstrate that it is possible to assess in vivo the neocortical monoamine terminal loss, and to elucidate its potential role in the complex cognitive and affective impairment, in both PD and atypical degenerative parkinsonism.

NMDA and D1 receptors mediate induction of c-fos and junB genes in striatum following morphine administration: implications for studies of memory

The c-fos and junB immediate early genes (IEGs) were induced in neurons of the medial and ventral striatum following administration of morphine. The striatal induction of c-fos and junB mRNA and Fos protein was blocked by naloxone, the D1 dopamine (DA) receptor antagonists, SCH23390 and SCH39166, and the N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, MK801. SCH23390 and MK801 did not block morphine induction of c-fos and junB in septum. Since the pattern of the morphine induction of c-fos and junB in striatum and nucleus accumbens was similar to that observed with cocaine and amphetamine [2,18,45,51], these data support current concepts that limbic striatum and nucleus accumbens are among the brain regions that mediate drug abuse [9,10,23,27,49]. If it is true that D1 receptors activate the CRE (cyclase response element) and NMDA receptors activate the SRE (serum response element) in the c-fos promoter [1], then this data suggests that serial activation of mu opiate, NMDA and D1 receptors on different neurons is required to induce Fos in striatal neurons with D1 Moreover, concurrent activation of NMDA and D1 receptors is required for Fos induction in striatal neurons. The Fos induced by this simultaneous activation of NMDA and D1 receptors should lead to long-term changes of gene expression that might also be involved in changes of brain circuits that could form the basis for 'memories' relating to prior exposure to addictive drugs.

Topographically specific hippocampal projections target functionally distinct prefrontal areas in the rhesus monkey

The sources of ipsilateral projections from the hippocampal formation, the presubiculum, area 29a-c, and parasubiculum to medial, orbital, and lateral prefrontal cortices were studied with retrograde tracers in 27 rhesus monkeys. Labeled neurons within the hippocampal formation (CA1, CA1', prosubiculum, and subiculum) were found rostrally, although some were noted throughout the entire rostrocaudal extent of the hippocampal formation. Most labeled neurons in the hippocampal formation projected to medial prefrontal cortices, followed by orbital areas. In addition, there were differences in the topography of afferent neurons projecting to medial when compared with orbital cortices. Labeled neurons innervating medial cortices were found mainly in the CA1' and CA1 fields rostrally, but originated in the subicular fields caudally. In contrast, labeled neurons which innervated orbital cortices were considerably more focal, emanating from the same relative position within a field throughout the rostrocaudal extent of the hippocampal formation. In marked contrast to the pattern of projection to medial and orbital prefrontal cortices, lateral prefrontal areas received projections from only a few labeled neurons found mostly in the subicular fields. Lateral prefrontal cortices received the most robust projections from the presubiculum and the supracallosal area 29a-c. Orbital, and to a lesser extent medial, prefrontal areas received projections from a smaller but significant number of neurons from the presubiculum and area 29a-c. Only a few labeled neurons were found in the parasubiculum, and most projected to medial prefrontal areas. The results suggest that functionally distinct prefrontal cortices receive projections from different components of the hippocampal region. Medial and orbital prefrontal cortices may have a role in long-term mnemonic processes similar to those associated with the hippocampal formation with which they are linked. Moreover, the preponderance of projection neurons from the hippocampal formation innervating medial when compared with orbital prefrontal areas followed the opposite trend from what we had observed previously for the amygdala (Barbas and De Olmos [1990] (J Comp Neurol 301:1-23). Thus, the hippocampal formation, associated with mnemonic processes, targets predominantly medial prefrontal cortices, whereas the amygdala, associated with emotional aspects of memory, issues robust projections to orbital limbic cortices. Lateral prefrontal cortices receive robust projections from the presubiculum and area 29a-c and sparse projections from the hippocampal formation. These findings are consistent with the idea that the role of lateral prefrontal cortices in memory is distinct from that of either medial or orbital cortices. The results suggest that signals from functionally distinct limbic structures to some extent follow parallel pathways to functionally distinct prefrontal cortices.

The perception of head rotation in Parkinson's disease

The accuracy in detecting angular displacements of the head and the neck was investigated in 14 patients with idiopathic Parkinson's disease (PD) and 16 age matched normal controls by the technique of vestibular and cervical "remembered" saccades. It was found that although the remembered saccades in PD patients were multiple-step and showed low initial saccadic gain, the final eye position of the eyes matched the rotational stimulus as accurately as in normals. This indicates that perception of head/neck rotation is normal in PD which is inconsistent with views that vestibulo/proprioceptive dysfunction contributes to the postural disorder in PD. The presence of multiple-step remembered vestibular and cervical saccades agrees with reported abnormalities in visual remembered saccades in PD and indicates that the difficulty in generating saccadic movements based on memorized sensory information is not confined to visual-memory.

Adrenergic and serotonergic receptors in aged monkey neocortex

Autoradiography was employed to compare the distribution and density of adrenergic (alpha 1, alpha 2, and beta) and serotonergic (5-HT1 and 5-HT2) receptors in the neocortex of young adult (3 to 10 years of age) and aged (> 20 years of age) rhesus monkeys. The age-related changes in the density of adrenergic and serotonergic sites were area and layer specific. A decrease in the density of alpha 1 receptors occurred only in the superficial layers of the somatosensory cortex, whereas the density of alpha 2 receptors declined in layer I of the prefrontal cortex and in most layers of the motor and somatosensory regions. The increase in beta receptors was largely confined to the deep layers of the motor and somatosensory areas. The density of 5-HT1 sites decreased in most layers of the somatosensory cortex, while 5-HT2 receptors declined in the deep layers of the motor cortex and middle strata of the visual cortex. Overall, adrenergic and serotonergic receptors were least affected in the prefrontal cortex and most compromised in the motor and somatosensory cortex of aged primates.

Phenylalanine levels of 6-10 mg/dl may not be as benign as once thought

Results of a longitudinal study of children treated early and continuously for phenylketonuria (PKU) indicated that those children whose plasma phenylalanine (Phe) levels were approximately 3-5 times normal (6-10 mg/dl; levels previously considered safe in the US) were impaired in cognitive functions dependent on prefrontal cortex. In particular, the children had difficulty when required to hold information in the mind and, at the same time, exercise inhibitory control to resist doing what might be their first inclination. The deficits were evident in relation to each of several comparison groups and at all three age ranges (infants, toddlers and young children). The deficits appeared to be selective in that the same children who were impaired on the prefrontal cortex tests performed normally on the control tests. Since most of the control tasks tap functions dependent on parietal cortex or the medial temporal lobe, these results suggest that those functions are spared. To investigate the biological mechanism causing these cognitive deficits, we created an animal model of early-treated PKU. The results indicated that rats whose plasma Phe levels were mildly, but chronically, elevated had cognitive deficits (impaired performance on a behavioral task dependent on frontal cortex (delayed alternation)) and neurochemical changes (most notably, reduced dopamine metabolism in frontal cortex).

Role of dopamine in the plasticity of glutamic acid decarboxylase messenger RNA in the rat frontal cortex and the nucleus accumbens

The modulatory role of dopamine (DA) on the expression of mRNA encoding the large isoform of glutamic acid decarboxylase (GAD67), the biosynthesis enzyme of gamma aminobutyric acid (GABA), was examined in GABA neurons of two structures innervated by DA neurons originating from the ventral tegmental area (VTA): the medial frontal cortex (MFC) and the nucleus accumbens (NAcc). A bilateral electrolytic lesion of VTA was performed in rats to produce a DA denervation of both the MFC and NAcc. The efficacy of VTA lesions was verified by measurement of locomotor activity and by immunohistochemical detection of tyrosine hydroxylase in the mesencephalon. GAD67 mRNA was detected by in situ hybridization histochemistry using a 35S-labelled cDNA probe. Densitometric analysis of GAD67 mRNA hybridization signals revealed in VTA-lesioned rats a significant decrease (-24%) in GAD67 mRNA levels in the prelimbic area of the MFC and no significant effect in the anterior cingulate area or the frontoparietal cortex. Single cell analyses by computer-assisted grain counting showed that the decrease in GAD67 mRNA levels in prelimbic MFC was due to a change in GAD67 mRNA expression in a subpopulation of GABA interneurons located in the deep cortical layers (V-VI). By contrast, in the NAcc of VTA-lesioned rats, GAD67 mRNA levels were significantly increased in the anterior part and in the core but were unchanged in the shell part. These results suggest that in two target structures of VTA DA neurons, GAD67 mRNA expression is, in normal conditions, under a tonic stimulatory and a tonic inhibitory DA control in the MFC and the NAcc respectively. A schematic diagram is proposed for functional interactions between these structures.

Biologic factors in schizotypal personal disorders

New studies of the boundaries of schizophrenia suggest that schizotypal personality disorder is biologically and genetically related to schizophrenia with alterations in brain structure/function related to deficit-like symptoms and increased dopaminergic function to psychotic-like symptoms.

Working memory and prefrontal cortex

Several different types of memory have recently been proposed, some of which are believed to operate within specific areas in the brain. In this article, we will discuss the relationship between the prefrontal cortex and working memory, which is a recently proposed type of short-term memory. The tight relationship between the prefrontal cortex and working memory has been supported by recent human and animal studies. This relationship provides good evidence that a particular type of memory is related to a particular brain structure, and can be used as an important model for understanding the neuronal mechanisms of memory. In this article, we will present a modular model based on recent neurophysiological results and discuss for spatial working memory processes in the prefrontal cortex.

The therapeutic potential of bromocriptine in neuropsychological rehabilitation of patients with acquired brain damage

1. Activation of neuropsychological rehabilitation by pharmacological agents is a promising therapeutic strategy. 2. Reports of single cases and case series claim improvement of akinetic mutism, non-fluent aphasia, apathy, attentional and other neuropsychiatric disturbances after treatment with bromocriptine, a D2 dopamine receptor agonist. 3. A critical review of published reports and own experiences discusses the results in the light of pharmacological and neurobiological considerations. 4. Dopaminergic stimulation after certain kinds of brain damage might influence neuronal recovery and/or substitute dopaminergical linked functions after destruction of the corresponding neurons. 5. Although controlled clinical studies are very difficult to design and such evidence is still lacking, preliminary recommendations are given with regard to differential indications, drug regime and evaluation criteria.

Dopamine D1 receptor mechanisms in the cognitive performance of young adult and aged monkeys

Dopamine (DA) D1 receptor compounds were examined in monkeys for effects on the working memory functions of the prefrontal cortex and on the fine motor abilities of the primary motor cortex. The D1 antagonist, SCH23390, the partial D1 agonist, SKF38393, and the full D1 agonist, dihydrexidine, were characterized in young control monkeys, and in aged monkeys with naturally occurring catecholamine depletion. In addition, SKF38393 was tested in young monkeys experimentally depleted of catecholamines with chronic reserpine treatment. Injections of SCH23390 significantly impaired the memory performance of young control monkeys, but did not impair aged monkeys with presumed catecholamine depletion. Conversely, the partial agonist, SKF38393, improved the depleted monkeys (aged or reserpine-treated) but did not improve young control animals. The full agonist, dihydrexidine, did improve memory performance in young control monkeys as well as in a subset of aged monkeys. Consistent with D1 receptor mechanisms, agonist-induced improvements were blocked by SCH23390. Drug effects on memory performance occurred independently of effects on fine motor performance. These results underscore the importance of DA D1 mechanisms in cognitive function, and provide functional evidence of DA system degeneration in aged monkeys. Finally, high doses of D1 agonists impaired memory performance in aged monkeys, suggesting that excessive D1 stimulation may be deleterious to cognitive function.

Working memory performance and cholinergic effects in the ventral tegmental area and substantia nigra

The nicotinic antagonist mecamylamine has been found to impair working memory performance in the radial-arm maze (RAM) after s.c. or i.c.v. administration. Mecamylamine has important interactions with dopaminergic (DA) systems. Mecamylamine-induced memory deficits in the RAM are potentiated by the D2 antagonist raclopride and reversed by the D2 agonist quinpirole. The nicotinic agonist nicotine has been found to improve working memory performance in the RAM after s.c. or i.c.v. administration. Nicotine-induced memory improvement in the RAM is potentiated by the D2 agonist quinpirole. The midbrain DA nuclei, the substantia nigra (SN) and the ventral tegmental area (VTA) have relatively dense concentrations of nicotinic receptors which may be critical sites of action for mecamylamine and nicotine. In the current study, the effects of mecamylamine (1, 3.3 and 10 micrograms/side) infusions into the SN (n = 12) and VTA (n = 13) on working memory in the radial-arm maze were examined in adult female Sprague-Dawley rats. The 10-micrograms/side dose of mecamylamine significantly impaired radial-arm maze working memory performance when infused into either the SN or VTA. No significant effects of mecamylamine on response latency were seen. The nicotinic agonists cytisine (0.1, 0.33 and 1.0 microgram/side) and nicotine (0.3, 1.0 and 3.3 micrograms/side) were administered in a counterbalanced order. The high dose of cytisine (1 microgram/side) nearly caused a significant deficit in choice accuracy. Nicotine slightly depressed choice accuracy but not significantly in this study. The interaction of nicotine and mecamylamine was then studied. A dose of 1.0 microgram/side of nicotine caused a significant decrease in choice accuracy. Interestingly, this was significantly reversed by a 3.3-micrograms/side dose of mecamylamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of pharmacologic catecholamine manipulation on smooth pursuit eye movements in normals

The pathophysiology of schizophrenia may be related directly or indirectly to abnormal dopaminergic activity. Both subcortical excess and frontal cortical deficiency of dopamine have been suggested, and primary or downstream failures of dopamine activation to the prefrontal cortex has been posited to explain some of the cognitive deficiencies in schizophrenia patients. Although the prefrontal cortex may also be a site for the disruption of smooth pursuit eye movements (SPEM), the most substantially described psychophysiological marker for schizophrenia vulnerability, no relationship of SPEM to dopaminergic activity has been demonstrated. In this study we explored the effect of altered dopamine function on SPEM quality through pharmacological manipulation of catecholamine tone in 11 healthy subjects. The subjects had SPEM measured at baseline, and under challenge conditions including amphetamine (0.3 mg/kg), haloperidol (2 mg), placebo, and combined amphetamine with haloperidol. Changes in the profile of mood scale (POMS) confirmed the expected subjective central nervous system effects the agents. Placebo and amphetamine had no effect on qualitative ratings of SPEM, but haloperidol, alone and in combination with amphetamine, disrupted eye tracking, producing a pattern of small saccadic intrusions characteristic of patients with schizophrenia. These findings link dopaminergic blockade with SPEM disruption in normal subjects.

A pathophysiological approach to saccadic eye movements in neurological and psychiatric disease

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Effects of local application of dopaminergic drugs into the dorsal part of the medial prefrontal cortex of rats in a delayed matching to position task: comparison with local cholinergic blockade

Lesions of the medial prefrontal cortex (mPFC) disrupt performance in a variety of delay tasks, which suggests that the mPFC supports short-term memory processes. The putative involvement of the dopaminergic innervation of the mPFC in these mnemonic processes was investigated by evaluating the effects of local infusions of dopaminergic drugs into the mPFC of rats in an operant delayed-matching-to-position (DMTP) task. Trained animals were provided with bilateral guide cannulae aimed at the dorsal part of the mPFC. Two separate groups of rats were tested after microinfusion of several doses of either the dopamine agonist apomorphine (APO) or the dopamine antagonist cis-flupenthixol (FLU). In addition, all animals were tested after infusion of several doses of the muscarinic antagonist scopolamine (SCO). Animals were tested 0 and 135 min after each infusion. At the 0 min interval, neither APO nor FLU affected accuracy of DMTP performance, while both drugs dose-dependently increased response latencies and decreased nosepoke frequencies. At the 135 min interval, APO had almost no effect, whereas the effects of FLU were very prominent. A number of animals no longer responded after infusion of the highest doses of FLU and those that did showed a delay-independent decrease in response accuracy. In contrast, SCO infusions into the mPFC induced a dose- and delay-dependent deterioration of DMTP performance. Taken together, these results support a direct involvement of the rat mPFC in short-term memory processes, although they implicate cholinergic rather than dopaminergic mechanisms in this function.

Activation of regional cerebral blood flow by a memorization task in early Parkinson's disease patients and normal subjects

Task-induced changes in regional cerebral blood flow (rCBF) during memory activation were compared in 18 right-handed patients with early Parkinson's disease (PD) and 20 normal volunteers using the same activation paradigm. We used single-photon emission computed tomography and 133Xe in 21 regions of interest during rest, passive listening of a work list, and memorization of another word list, which was followed by a free recall test immediately after completion of the rCBF measurement. The average performance on free recall was not significantly lower in PD patients than in controls. In normal subjects, five left-sided regions (anterior middle frontal, posterior inferior frontal, superior middle temporal, thalamic, and lenticular) showed a significant increase in memorizing compared to passive listening. This pattern of activation suggests the existence of a verbal rehearsal strategy during the memorization task in normals. In PD patients, increases in these regions did not reach significance, whereas significant activations were noted in superior prefrontal regions. Such alterations in the pattern of activation in PD patients, despite a memory performance similar to that of controls are viewed as a consequence of an early dysfunction of the articulatory loop system and of compensatory mechanisms in other parts of the frontal lobe emerging in the early stages of the disease.

Tyrosine reverses a cold-induced working memory deficit in humans

Acute exposure to cold stress has been shown to impair short-term, or working, memory, which may be related to reduction in, or disruption of, sustained release of brain catecholamines. Administering a supplemental dose of the catecholamine precursor tyrosine may alleviate cold stress-induced memory impairments by preventing cold-induced deficits in brain catecholamine levels. The present experiment determined whether administration of tyrosine would prevent a cold-induced working memory deficit, using a computer-based delayed matching-to-sample (DMTS) memory task. Eight male volunteers performed the DMTS task for 30 min at an ambient temperature of either 4 degrees C (cold) or 22 degrees C following a 30-min preexposure period and 2 h after ingesting 150 mg/kg of L-tyrosine or placebo. Subjects demonstrated a decline in matching accuracy on the DMTS task as delay interval increased, such that matching accuracy following a 16-s delay between sample and comparison stimuli was lower than that following a delay of 2 or 8 s. Consistent with previous research, and relative to 22 degrees C exposure sessions, matching accuracy during 4 degrees C exposure sessions was reduced significantly following placebo administration, which is attributed to the effect of cold exposure on short-term, or working, memory. Administration of tyrosine significantly improved matching accuracy at the longest delay interval most affected by cold exposure, such that matching accuracy in the cold following tyrosine was at the same level as matching accuracy following placebo or tyrosine administration at 22 degrees C. Tyrosine administered prior to 22 degrees C exposure had no effect on DMTS performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequences of memory-guided saccades in Parkinson's disease

Sequences of ocular saccades were studied in 8 patients with Parkinson's disease, with (i.e., "on") and without (i.e., "off") levodopa treatment. The amplitude of single saccades was decreased and not improved by treatment. The chronology of saccades during sequences was impaired in patients in the "off" state, but significantly improved during the "on" period. These results are compatible with a decreased activation of the supplementary motor area, which can be reversed by levodopa.

Effects of amphetamine and medial septal lesions on acquisition and retention of radial maze learning in rats

Procholinergic drugs have failed to overcome the memory deficit induced by alterations of the cholinergic system because their neurochemical target in the brain is either lacking or disorganised. However, there are many reports on a relative involvement of the dopaminergic system in learning and memory that may compensate for the cholinergic deficit because of the interaction or balance between neurotransmitters and the redundancy of the brain. The aim of our experiments is to examine the activation of the dopaminergic system on the performance of normal and medial septal lesioned rats in the radial maze test involving continuous choices. In the first experiment different groups of normal rats were treated with either 0.5, 1.0 or 2.0 mg/kg of D-amphetamine and tested in the radial maze. In the second experiment, medial septal lesioned rats which had learnt pre-op the radial maze test were retested a month later. Amphetamine had no effect on the memory measures provided by the radial maze test in normal and lesioned rats, but non-memory measures were significantly affected: amphetamine decreased the sequential choice responses and the time taken by the rats to perform the test. The present results show that the activation of the dopaminergic system does not compensate for the alteration of the cholinergic activity inducing amnesia, however, they support the recent data on the improving effect of amphetamine on locomotor activity. The interpretation of drug/lesion interaction effects is discussed in this paper in relation to the literature on the effect of promnesic drugs.

Blockade of D-1 dopamine receptors in the medial prefrontal cortex produces delayed effects on pre- and postsynaptic indices of dopamine function in the nucleus accumbens

The present experiments assessed the acute and delayed effects of D-1 dopamine (DA) receptor blockade in the medial prefrontal cortex (mPFC) on pre- and postsynaptic indices of DA neurotransmission in the nucleus accumbens (N.Acc). Different groups of rats received intra-mPFC injections of saline (control animals) or the D-1 DA receptor antagonist SCH-23390 (0.25 microgram/side). Acutely, intra-mPFC injections of this antagonist did not affect spontaneous locomotion but significantly increased the locomotion induced by intra-N.Acc. amphetamine (1.5 micrograms/side), in agreement with our earlier findings [Vezina et al. (1991) Eur. J. Neurosci., 3:1001-1007]. When tested two days post-injection, however, mPFC-SCH-23390 preexposed animals showed lower levels of locomotor activity than Control animals in response to intra-N.Acc. injections of amphetamine. This effect was not observed in other animals preexposed two days earlier to mPFC injections of amphetamine (2.5 micrograms/side) or the D-2 DA receptor antagonist sulpiride (1.0 microgram/side). Animals preexposed two days earlier to mPFC SCH-23390 also showed higher levels of locomotor activity (+98%) when tested with intra-N.Acc. injections of the D-1 DA receptor agonist SKF-38393 (1.0 microgram/side) and a 36% increase in maximal DA-sensitive adenylate cyclase activity in comparison to Control animals. These effects were no longer observed in animals tested seven days following the mPFC SCH-23390 injections. These results demonstrate delayed actions resulting from cortical D-1 DA receptor blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissociation between delayed alternation and memory after pediatric head injury: relationship to MRI findings

This study investigated the usefulness of a delayed alternation task in characterizing the cognitive sequelae of closed head injury in children and adolescents. Verbal learning and memory (California Verbal Learning Test) were also studied for comparison. Sixty-two closed head injury patients (mean age, 9.6 years), who were studied after an average postinjury interval of 20 months, were divided according to both their lowest postresuscitation Glasgow Coma Scale score (3 to 8 versus 9 to 15) and age range (5 to 7 years versus 8 to 16 years) at the time of testing. Magnetic resonance imaging was performed to evaluate the relationship of focal brain lesions to cognitive and memory performance. Fifty-six neurologically normal children (mean age, 9.9 years) were tested on the same measures. The results disclosed no relationship between delayed alternation performance and severity of injury. In contrast, verbal memory was impaired in the severely-injured patients, relative to both controls and less severely-injured patients. Frontal lobe (but not extrafrontal) lesion size incremented the Glasgow Coma Scale score in predicting verbal memory, but there was no relationship between focal brain lesions and delayed alternation performance. In contrast to the tendency for more efficient delayed alternation performance in the 5- to 7-year-old subjects than in the 8- to 16-year-old subjects, verbal memory significantly improved with age in the closed head injury and control groups. Notwithstanding our essentially negative findings for delayed alternation, it is possible that this task may be useful for assessing frontal lobe injury in younger children or infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Association of working memory deficit and eye tracking dysfunction in schizophrenia

This study replicates our earlier findings that schizophrenic but not bipolar patients are impaired on oculomotor delayed response tasks, analogous to those used to assess spatial working memory functions of the dorsolateral prefrontal cortex (DLPFC) in monkeys (Park and Holzman, 1992). In addition, we examined the relation between working memory deficits and smooth pursuit eye movement (SPEM) dysfunction, since data from human neuropsychological and animal lesion studies implicate prefrontal pathology in both deficits. Schizophrenic patients showed marked deficits in the oculomotor memory task and the SPEM task relative to the control groups. However, they were not impaired on the oculomotor sensory task in which their responses were guided by external cues rather than by working memory. This result from outpatients replicates our earlier study which was conducted with inpatients. Within the schizophrenic group those patients with good eye tracking performed better than those with impaired pursuit on the oculomotor memory task but there was no correlation between SPEM and performance on the sensory task. These findings support the hypothesis that schizophrenics show a deficit in representational processes and add to the growing evidence for involvement of the dorsolateral prefrontal cortex in schizophrenic pathology.

Improvement in cognitive functions and psychiatric symptoms in treatment-refractory schizophrenic patients receiving clozapine

Cognitive functions and psychopathology were assessed in 36 treatment-refractory schizophrenic patients before initiation of clozapine, and at 6 weeks and 6 months, thereafter. Before treatment, cognitive impairment was found in each measure of memory, attention, and executive function as compared with 26 normal controls. After both 6 weeks and 6 months of treatment, significant improvement occurred in the Controlled Oral Word Association Test, a measure of retrieval from reference memory. Improvement was also noted at 6 months in the Category Instance Generation Test, another measure of retrieval from reference memory, and in some, but not all, tests of executive function, attention, and recall memory. Clozapine treatment also resulted in significant improvement in Brief Psychiatric Rating Scale (BPRS) Total and Positive symptom scores at both 6-week and 6-month assessment points. There was some evidence for a relationship between improvement in psychopathology and cognitive function. The improvement in cognitive function during clozapine treatment could have consequences for capacity to work and social function.

Cognitive impairment in schizophrenia: how experimental models using nonhuman primates may assist improved drug therapy for negative symptoms

Antipsychotic drugs provide effective relief from hallucinations but do not improve, and may even induce, other symptoms of schizophrenia. Tardive dyskinesia, which is often associated with intellectual impairment, is generally attributed to chronic therapy with antipsychotic drugs. However, the possible contribution of medication to cognitive impairment is not easily dissociated from the underlying progression of the disease. Recently evidence has accumulated from studies performed in patients and experimental monkeys that augmentation of catecholamine function may improve performance on certain cognitive tasks. Further investigation of the role of catecholamines in cognition is warranted in order to assist development of antipsychotic drugs with fewer undesirable effects and entirely new approaches to therapy for cognitive impairment in schizophrenia.

Effects of dopaminergic drugs on working and reference memory in rats

Changes in dopaminergic function have been associated with alterations in motor and cognitive function in man and in animals. This study was designed to assess the effects of dopaminergic drugs on these aspects of conditioned behavior in animals. Male Long-Evans rats were trained to perform an appetitive operant task that allowed daily quantification of working memory (accuracy of spatial delayed nonmatching-to-position), reference memory (accuracy of visual discrimination) and motor function [choice lever-press latency and nosepoke interresponse time (IRT) during delay]. The indirect dopamine agonist d-amphetamine (0.3-1.0 mg/kg) reduced nonmatching accuracy without significantly affecting discrimination accuracy, response latency, or nosepoke IRT. The D2/D3 agonist quinpirole (0.01-0.056 mg/kg) also decreased nonmatching accuracy without changing discrimination accuracy, but increased choice response latency and nosepoke IRT as well. The D1 agonist SKF 38393 (1.0-3.0 mg/kg) and the D1 antagonist SCH 23390 (0.01-0.03 mg/kg) only affected nosepoke IRT, at doses below those causing response failure. The D2 antagonist raclopride (0.056-0.177 mg/kg) exerted no significant effects at doses that did not suppress responding completely. The selective reduction of nonmatching accuracy by d-amphetamine and quinpirole indicates a mnemonic impairment specific to working memory (relative to reference memory). These results suggest further 1) that stimulation of D2/D3, but not D1, receptors may account for the d-amphetamine-induced deficit in working memory; 2) that stimulation of D2/D3 receptors alone by quinpirole may also impair spatial working memory, but only in conjunction with motor slowing; and 3) that antagonism of either receptor type (by SCH 23390 or raclopride) does not significantly affect memory at doses causing motor slowing and response failure.

Regional cerebral blood flow in depression measured by positron emission tomography: the relationship with clinical dimensions

We have previously reported focal abnormalities of regional cerebral blood flow (rCBF) in a group of 33 patients with major depression. This report, on an extended sample of 40 patients who demonstrated identical regional deficits to those previously described, examines the relationships between depressive symptoms and patterns of rCBF. Patients' symptom ratings were subjected to factor analysis, producing a three-factor solution. The scores for these three factors, which corresponded to recognizable dimensions of depressive illness, were then correlated with rCBF. The first factor had high loadings for anxiety and correlated positively with rCBF in the posterior cingulate cortex and inferior parietal lobule bilaterally. The second factor had high loadings for psychomotor retardation and depressed mood and correlated negatively with rCBF in the left dorsolateral prefrontal cortex and left angular gyrus. The third factor had a high loading for cognitive performance and correlated positively with rCBF in the left medial prefrontal cortex. These data indicate that symptomatic specificity may be ascribed to regional functional deficits in major depressive illness.