D1 dopamine receptors in prefrontal cortex: involvement in working memory

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.

Neuronal colocalization of mRNAs for neurotrophins and their receptors in the developing central nervous system suggests a potential for autocrine interactions

Development and survival of neurons in the central nervous system are dependent on the activity of a variety of endogenous neurotrophic agents. Using combined isotopic and nonisotopic in situ hybridization histochemistry, we have found that subsets of neurons within the developing forebrain coexpress the mRNAs for both neurotrophins (nerve growth factor, brain-derived neurotrophic factor, and neurotrophin 3) and their receptors (p75NGFR, TrkA, and TrkB). The colocalization of mRNA for neurotrophin receptors and their ligands in presumptive neurotrophin target neurons suggests the potential for autocrine and paracrine mechanisms of action during development. Such mechanisms may ensure the onset of differentiation and survival of specific subsets of neurons prior to and following target innervation.

Cortical plasticity and memory

The roles of extrinsically modulated, plastic Hebb-like synapses and dynamic cortical cell assemblies underlying cortical plasticity in learning and memory operations are described. From our understanding of the distributed form of representation of learned behaviors in somatosensory and auditory cortical fields, and given new findings about the nature and distribution of responses representing learned and remembered stimuli in the inferior temporal cortex, a hypothetical picture of the cortical engram representing learned behaviors and memories is posited.

In vivo assessment of basal and drug-induced dopamine release in cortical and subcortical regions of the anesthetized primate

There is an acute interest in studying the functional characteristics of dopamine systems in the cortex of primates. In particular, the prefrontal cortical dopamine projections have received a great deal of attention. This system is essential for proper functioning of the prefrontal cortex, and dysfunction within the system may be involved in some psychiatric and neurological illnesses. In vivo assessments of cortical dopamine in the primate have been scarce. This has been due, in part, to technical difficulties associated with these studies and with quantifying the relatively low levels of dopamine found in cortical regions. In the present study, intracerebral microdialysis was utilized to assess the extracellular concentration of dopamine in cortical and subcortical areas of the pentobarbital-anesthetized rhesus monkey. Basal extracellular dopamine levels were consistently detected in the medial prefrontal cortex, premotor cortex, and caudate-putamen. The basal extracellular concentration of dopamine in the dorsolateral prefrontal cortex was reliably detected in 1 of 4 animals. Intravenous administration of amphetamine (1 mg/kg) enhanced extracellular dopamine levels in the caudate-putamen area by more than 20-fold. In cortical areas, amphetamine's effect was less profound: An increase of 400-500 percent over basal extracellular dopamine levels was observed in each region. These studies demonstrate the feasibility of microdialysis for detecting extracellular fluxes of dopamine in the cortex of nonhuman primates. They further provide direct evidence that the dopamine released within the prefrontal cortex and the premotor cortex of nonhuman primates responds to pharmacological manipulation.

Topography and collateralization of the dopaminergic projections to motor and lateral prefrontal cortex in owl monkeys

The sources and histochemical characteristics of dopaminergic projections to motor and premotor areas of cortex were investigated in owl monkeys in which information from related studies was used to subdivide cortex into motor fields. Brainstem projections to frontal cortex were identified by injections of different fluorescent dyes in the primary motor cortex (M1) and the supplementary motor area (SMA), first identified by microstimulation. Injections were also placed in dorsal premotor cortex and lateral prefrontal cortex. The distribution of retrogradely labeled neurons was related to the location of tyrosine hydroxylase immunolabeled neurons on the same or alternate brain sections to identify the dopamine (DA) neurons. All DA cortically projecting neurons were located in the A8-A10 complex, largely in its dorsal components, including the parabrachial pigmented n. of the ventral tegmental area (VTA), pars gamma of the substantia nigra compacta, and the dorsal part of the retrorubral area (A8). Fewer cells were in the midline groups of VTA (n. linearis rostralis and caudalis) and in the n. paranigralis. DA neurons projecting to M1, SMA, and prefrontal cortex were largely intermixed, and some of these neurons were double or triple labeled by the fluorescent dyes, indicating collateralization to two or three fields; DA cells projecting to M1 were more numerous than to the other locations. The dorsal components of the A8-A10 complex from which arose the DA mesocortical projection were also characterized by the presence of calbindin-immunoreactive neurons and by a dense neurotensin and noradrenergic terminal innervation. Compared to rodents or felines, the DA neurons projecting to the lateral frontal lobe of primates appear to be shifted dorsally and laterally in the nigral complex. The topographic overlap, partial collateralization, and common histochemical characteristics of the DA mesocortical neurons projecting to different fields of the lateral frontal lobe suggest that some degree of functional unity exists within this projection.

Nicotinic receptor agonists facilitate retention of avoidance training: participation of dopaminergic mechanisms

The effect of nicotinic receptor agonists on retention of the inhibitory avoidance (IA) response were investigated in mice. Animals received intraperitoneal drug injections before training, and retention was evaluated 24 h later. Nicotine and cytisine, but not lobeline, significantly increased retention of the IA training. Cotinine, the main metabolite of nicotine, was inactive in the same test. Retention was not affected by the injection of the D1-D2 receptor antagonist cis-flupentixol, but the preadministration of cis-flupentixol significantly blocked the facilitatory effect of nicotine and cytisine on memory. These results demonstrate that the nicotinic receptor agonists nicotine and cytisine facilitate the retention of avoidance responses and suggest that this effect is mediated through central dopaminergic pathways.

Immunohistochemical localization of the D1 dopamine receptor in rat brain reveals its axonal transport, pre- and postsynaptic localization, and prevalence in the basal ganglia, limbic system, and thalamic reticular nucleus

D1 dopamine receptor localization was examined by immunohistochemistry using a polyclonal anti-peptide antibody which (i) immunoprecipitated a protein fragment encoded by a D1 receptor cDNA and (ii) on Western blots of solubilized striatal and hippocampal membranes recognized two proteins of approximately 50 kDa and 75 kDa, corresponding to reported sizes of D1 receptor proteins. Immunoreactivity overlapped with dopamine-containing pathways, patterns of D1 receptor binding, and mRNA expression. Staining was concentrated in prefrontal, cingulate, parietal, piriform, entorhinal, and hippocampal cortical areas and subcortically in the basal ganglia, amygdala, septal area, substantia inominata, thalamus, hypothalamus, and neurohypophysis. Prominent labeling was seen in the thalamic reticular nucleus, a region known to integrate ascending basal forebrain inputs with thalamocortical and corticothalamic pathways and in fiber bundles interconnecting limbic areas. In striatal neuropil, staining appeared in spines (heads and necks), at postsynaptic sites in dendrites, and in axon terminals; in the pars reticulata of the substantia nigra, labeling was prevalent in myelinated and unmyelinated axons and dendrites. These data provide direct evidence for the regional and subcellular distribution of D1 receptor protein in the brain and for its pre- and postsynaptic localization in the basal ganglia. The prominent immunoreactivity seen in the limbic system and thalamic reticular nucleus supports an important role for this receptor subtype in mediating integrative processes involved with learning, memory, and cognition.

Dopaminergic drugs reverse the impairment of radial-arm maze performance caused by lesions involving the cholinergic medial pathway

Pharmacological studies have shown that both cholinergic and dopaminergic transmitter systems are crucial for optimal choice accuracy in the radial-arm maze and that these systems interact in a complex fashion. Lesion studies have provided evidence that the basal nuclear complex of the forebrain, the origin of cholinergic projections to the cerebral mantle, may be critical for the cholinergic modulation of learning and memory. We have shown that knife-cut lesions of the medial cholinergic pathway significantly impair radial-arm maze choice accuracy performance. The current study examined the effectiveness of D1 and D2 ligands in counteracting this lesion-induced deficit. The adverse effects of medial cholinergic pathway lesions were diminished or reversed by daily treatment with a D1 agonist (SKF 38393), a D2 agonist (LY 171555) or a D1 antagonist (SCH 23390), but were not affected by treatment with a D2 antagonist (raclopride). The three beneficial treatments have previously been found to attenuate the adverse effects of nictonic or muscarinic blockade on choice accuracy performance in the radial-arm maze. The finding that these dopaminergic drugs ameliorate the memory deficit caused by lesions involving the cholinergic medial pathway suggests the importance of interactions between cholinergic and dopaminergic systems in radial-arm maze performance. These results may provide leads for the development of novel therapeutic approaches for treating human disorders thought to result from cholinergic hypofunction.

Characterization of gene organization and promoter region of the rat dopamine D1 receptor gene

Genomic and cDNA clones encoding the rat D1 receptor were isolated and sequenced. Comparison of the D1 receptor cDNA and genomic sequences revealed that the rat D1 receptor gene is organized into two exons separated by a small intron in the 5' untranslated region of its mRNA. The transcription start site is located 864 bp upstream from the translational initiation site. The 5'-flanking sequences of the D1 receptor gene do not contain TATA and CAAT canonical sequences, but have a high G+C content, potential cyclic AMP and glucocorticoid response element sequences, and binding sites for transcription factors such as Sp1, Ap1, and Ap2. Transfection studies using the D1 5'-flanking sequence and CAT gene fusion constructs have demonstrated that (1) the D1 promoter is active in D1-expressing neuroblastoma NS20Y cells, but inactive in D1-deficient glioma C6 and kidney 293 cells, (2) the information contained within 735 bp of 5'-flanking sequence of the D1 gene appears to be sufficient to confer its cell-specific expression, and (3) the D1 gene promoter responds to cyclic AMP induction, suggesting the existence of an auto-regulation mechanism by which the stimulation of D1 receptor exerts a positive feedback on its own gene expression.

NE/DA interactions in prefrontal cortex and their possible roles as neuromodulators in schizophrenia

The monoaminergic innervation of the rat prefrontal cortex arises from well-defined mesencephalic nuclei, with noradrenergic (NE) neurons located in the locus coeruleus, dopaminergic (DA) neurons located in the ventral tegmental area, and serotonergic (5-HT) neurons originating in the raphe nuclei. Specific destruction of the NE bundle was found to induce morphological (i.e., sprouting) as well as metabolic (i.e., changes in rate of DA utilization) modifications of mesocortical DA neurons, suggesting that these two catecholaminergic systems have functional interactions within the prefrontal cortex. This was substantiated by experiments showing that DA afferents modulate the sensitivity of cortical post-synaptic beta-adrenergic receptors and that, reciprocally, NE neurons control the sensitivity of cortical D1 receptors. Behavioural and pharmacological data have further indicated that the stimulation of cortical alpha-1 adrenergic receptors inhibits cortical DA transmission at D1 receptors. Secondly, we have attempted to analyze how such interactions between neuromodulatory systems may be related to the development of mental diseases such as schizophrenia. On the basis of studies in the literature describing the effects produced by the ingestion of hallucinogenic drugs or data collected regarding REM sleep, it is postulated that two modes of brain functioning exist: analogical and cognitive. Each mode is characterized by differences in the relative activities of NE, DA and 5-HT neurons. At birth, during REM sleep, and following the ingestion of hallucinogens, the mode of brain functioning is essentially analogical; in contrast, both analogic and cognitive modes are postulated to coexist in the awake state. Oscillations between these two modes are under the control of monoaminergic systems on which an increase in cortical DA release favours the cognitive processing mode, whereas intermittent activations of NE neurons would switch the brain into the analogical mode of processing. It is proposed that schizophrenic patients with "positive" symptoms suffer from an abnormal preponderance of the analogical mode while awake, whereas "negative" symptoms are due to the excessive presence of the cognitive mode. Although pure biological deficits cannot be excluded, these dysfunctions could be related to the absence of particular environmental variables early in the development of these patients. This condition is probably required to establish normal regulatory control of monoaminergic neuronal activity.

Differential modulation by dopamine of responses evoked by excitatory amino acids in human cortex

The responses of human neocortical neurons to iontophoretic application of excitatory amino acids and their modulation by dopamine (DA) were studied in vitro. Brain slices were obtained from children undergoing surgery for intractable epilepsy. Application of N-methyl-D-aspartate (NMDA) to the slices induced slow depolarizations accompanied by decreased input conductances and sustained action potentials in cortical neurons. Glutamate produced rapid depolarizations and firing with few changes in input conductances. Quisqualate also induced depolarization and firing, but input conductances increased during the rising phase of the membrane depolarization. Iontophoretic application of DA alone produced no change in membrane potential or input conductance. However, when DA was applied in conjunction with the excitatory amino acids, it produced contrasting effects. With either bath application of DA or when iontophoresis of DA preceded application of NMDA, the amplitude of the membrane depolarizations and the number of action potentials were increased, whereas the latency of these responses decreased. In contrast, DA decreased the amplitude of the depolarizations and the number of action potentials evoked by glutamate or quisqualate. The fact that DA affects responses to NMDA and glutamate or quisqualate in opposite directions is of considerable importance to the understanding of cellular mechanisms of neuromodulation and the role of DA in cognitive processing and in epilepsy.

Measuring the neuromodulatory effects of drugs in man with positron emission tomography

Cognitive activation in conjunction with pharmacological challenge was used to demonstrate neuromodulation in man. Using positron emission tomography (PET), measurements of regional cerebral blood flow were made during the performance of memory tasks, before and after the administration of apomorphine (dopamine agonist), buspirone (5-HT1A partial agonist) or placebo. Drug effects on memory-induced increases in regional cerebral blood flow were assessed, on a voxel-by-voxel basis, using statistical parametric mapping. Increases of regional cerebral blood flow in response to the memory challenge were attenuated by apomorphine in the dorsolateral prefrontal cortex and augmented in the retrosplenial region of the posterior cingulate. Conversely, buspirone attenuated blood flow increases in the retrosplenial region. These interactions between drugs and a cognitive challenge can best be interpreted as neuromodulatory effects.

Memory

The key interrelated issues in the neurobiology of memory are to identify the neural circuitries essential for memory formation, localize sites of memory storage and analyze mechanisms of memory formation, storage and retrieval. Several circuits have now been identified in vertebrates and researchers are investigating their properties, in particular the role of glutamate receptors and long-term potentiation, in memory formation. Invertebrate preparations continue to be of value and recent studies suggest that changes in gene expression and protein synthesis may be important in long-term sensitization.

The Drosophila learning and memory gene rutabaga encodes a Ca2+/Calmodulin-responsive adenylyl cyclase

Four putative adenylyl cyclase genes from Drosophila melanogaster were identified by virtue of their extensive sequence homology with mammalian cyclases. One corresponds to the learning and memory gene rutabaga and is most similar to the mammalian brain Ca2+/calmodulin (CaM)-responsive cyclase. In a mammalian expression system, rutabaga cyclase activity was stimulated approximately 5-fold by the presence of Ca2+/CaM. A point mutation, identified at this locus in rut1 mutant flies, resulted in loss of detectable adenylyl cyclase activity. New P element insertion-induced rutabaga mutations mapped to within 200 nucleotides of the 5' end of the rutabaga cDNA. These data confirm the identity of the rutabaga locus as the structural gene for the Ca2+/CaM-responsive adenylyl cyclase and show that the inactivation of this cyclase leads to a learning and memory defect.

Delayed-non-match-to-sample performance in the radial arm maze: effects of dopaminergic and gabaergic agents

Central dopaminergic transmission has been implicated in memory processes. The present experiments examined the effects of several direct acting dopaminergic agents on performance of a delayed-non-match-to-sample radial arm maze task. Preadministration of apomorphine (D1-D2 agonist; 0.25, 0.5, and 1.0 mg/kg), quinpirole (D2 agonist; 0.1 mg/kg), or SKF38393 (D1 agonist; 3 mg/kg) increased the latency of choices but did not affect any index of accuracy with a 1 h retention interval. Post-training administration of quinpirole (0.1, 0.2, 1.0, and 2.0 mg/kg), SKF38393 (0.3, 3.0, and 6.0 mg/kg), sulpiride (D2 antagonist; 3, 10, and 30 mg/kg), or SCH23390 (D1 antagonist; 0.01, 0.1, and 1.0 mg/kg) also did not affect accuracy, although quinpirole produced a dose-dependent increase in the latency of choices, assessed 10 h post-treatment. For comparison, pretraining and post-training administration of the benzodiazepine chlordiazepoxide (1, 3, 5 mg/kg) was also tested and produced dose-dependent impairments in mnemonic performance at either a 1 or 4 h retention interval. The effects of chlordiazepoxide are consistent with evidence indicating that GABAergic agents can influence memory processes. In contrast, the present findings indicate that (peripheral administration of dopaminergic agents IS) not sufficient to alter the mnemonic processes required for accurate performance of this DNMTS-RAM task.

The anatomy of dopamine in monkey and human prefrontal cortex

This chapter reviews recent evidence establishing the comparable organization of dopamine afferents and dopaminergic receptors in the human and monkey prefrontal cortex. Light microscopy using a dopamine-specific antibody reveals that the dopamine innervation in the human prefrontal cortex exhibits a distinct bilaminar distribution with dense bands of fibers in the upper and deeper strata of the cortex, closely resembling the patterning of dopamine fibers in the monkey prefrontal cortex. Also, EM-immunohistochemistry has now revealed identical synaptic complexes both in human and monkey. In both species, dopamine axons from symmetric synapses predominantly on the spines of pyramidal cells. In many cases, the same spine is apposed by an asymmetric, putatively excitatory synapse. Finally, both in human and monkey prefrontal cortex, the dopamine D1-specific ligand, 3H-SCH23390, and the D2-specific ligand, H3-raclopride, label binding sites in laminar positions which match the location of the densest dopamine innervation. These results indicate that the organization of the cortical dopamine system is essentially the same in macaque monkey and human and that the nonhuman primate is a suitable animal model for analysis of dopamine function in prefrontal cortex.

TRH protection against memory retrieval deficits is independent of endocrine effects

An electrobrainshock (EBS)-induced memory retrieval deficit was produced in normal and hypophysectomized mice. In normal mice, thyrotropin-releasing hormone (TRH) (0.1 to 30 mg/kg) protected against this EBS disruption of memory after intraperitoneal but not oral (1.0 to 100 mg/kg) administration. In hypophysectomized mice, TRH (0.3 and 3.0 mg/kg) also protected against the retrieval deficit induced by EBS. The memory protection afforded by TRH was unrelated to its ability to elevate plasma levels of triiodothyronine (T3) and thyroxine (T4), nor was TRH's memory protection mediated through an anticonvulsive mechanism. These results support the notion that TRH may play an important role in memory modulation and may have therapeutic value in certain disease states in humans.

Responses of monkey midbrain dopamine neurons during delayed alternation performance

Cognitive deficits are important components of the parkinsonian syndrome. In order to investigate the role of dopamine (DA) neurons in cognitive functions, we recorded the electrical activity of midbrain DA neurons in a monkey performing in a spatial delayed alternation task. Triggered by a light, the animal reached toward one of two levers to receive a drop of liquid reward. The lever associated with reward was alternated after each correct movement. Of 88 DA neurons, 65% and 52% showed phasic responses to the trigger light and reward, respectively. By contrast, sustained delay-related activity described for striatum and frontal cortex was not observed, suggesting that the activity of DA neurons does not reflect mnemonic or preparatory representational task components. Rather, DA neurons respond to the salient attentional and motivating stimuli guiding task performance.

Maladaptive anticipatory saccades in schizophrenia

We compared the saccades made by 8 neuroleptic-treated and 7 drug-free schizophrenic inpatients with those made by 11 normal controls during two eye movement tasks. The first task was designed to elicit visually guided but not internally guided saccades. The second task was designed so that optimal performance required saccades be guided on the basis of an internal representation of target behavior. During the first task, schizophrenics made visually guided saccades that were as accurate as those made by control, but both drug-free and neuroleptic-treated schizophrenics made intrusive saccades at a significantly higher rate than control subjects. Most of these maladaptive saccades appeared to be premature attempts to anticipate target jump. During the second eye movement task, which for optimal performance required use of an internal representation to guide eye movements, most patients learned to anticipate target jump as well as controls. However, neuroleptic-treated patients made significantly smaller adaptive anticipatory saccades than either drug-free schizophrenic patients or normal subjects. These finding are discussed as they relate to the prefrontal cortex-basal ganglia circuits involved in the regulation of behavior by representational knowledge and the idea that the abnormal anticipatory saccades we observed represent a failure in the sensorimotor gating of information derived from internal representations.

Localization of D1 dopamine receptor mRNA in brain supports a role in cognitive, affective, and neuroendocrine aspects of dopaminergic neurotransmission

Expression of a D1 dopamine receptor was examined in the rat brain by using a combination of in situ hybridization and in vitro receptor autoradiography. Cells expressing D1 receptor mRNA were localized to many, but not all, brain regions receiving dopaminergic innervation. The highest levels of hybridization were detected in the caudate-putamen, nucleus accumbens, and olfactory tubercle. Cells expressing D1 receptor mRNA were also detected throughout the cerebral cortex, limbic system, hypothalamus, and thalamus. D1 receptor mRNA was differentially expressed in distinct regions of the hippocampal formation. Dentate granule cells were labeled in dorsal but not ventral regions, whereas the subicular complex was prominently labeled in ventral but not dorsal regions. Intermediate to high levels of D1 binding sites, but no hybridizing D1 receptor mRNA, were detected in the substantia nigra pars reticulata, globus pallidus, entopeduncular nucleus, and subthalamic nucleus. In these brain regions, which are involved in the efferent flow of information from the basal ganglia, D1 receptors may be localized on afferent nerve terminals originating in other brain regions. These results indicate that in addition to a role in control of motor function, the D1 receptor may also participate in the cognitive, affective, and neuroendocrine effects of dopaminergic neurotransmission.

The D1 receptor antagonist, SCH 23390, induces signs of parkinsonism in African green monkeys

Systemic administration of the selective D1 antagonist, SCH 23390, caused significant motor changes in healthy African green monkeys. The effects included the parkinsonian signs of motor freezing, incoordination, bradykinesia, poverty of movement, tremor and depressed blink rate. SCH 23390 administered to MPTP-treated monkeys increased existing parkinsonism. The results are of particular interest in light of recent data that demonstrate the effectiveness of dihydrexidine, a full D1 agonist, in alleviating parkinsonism in MPTP-treated monkeys. These data implicate D1 receptors in the functions impaired by Parkinson's disease and suggest the possibility of parkinsonian side effects in the clinical use of this or similar D1 antagonists as treatments for psychiatric disorders.