A temporal threshold for induction of persistent alcohol preference: behavioral evidence in a rat model of intermittent intoxication

OBJECTIVE

Development of alcohol dependence is gradual, requires prolonged exposure to alcohol and reflects neuroadaptive processes in the brain. An understanding of these neuroadaptive processes can lead to novel treatment targets. We recently showed that 7 weeks of intermittent alcohol vapor exposure in rats induces a long-lasting increase of voluntary ethanol consumption, accompanied by changes in gene expression patterns in cingulate cortex and amygdala. These findings prompt the question of whether underlying adaptive processes develop gradually over time or whether a temporal threshold exists for this phenotype conversion to occur. We addressed this question by examining the functional consequences of different exposure durations.

METHOD

Male Wistar rats (N = 43) were exposed to alcohol according to the previously published protocol for 2, 4 or 7 weeks. Following 3 weeks of abstinence to eliminate effects of acute withdrawal, subjects were introduced to voluntary alcohol self-administration in a two-bottle free-choice paradigm with continuous access.

RESULTS

Rats exposed to alcohol vapor for 7 weeks displayed a marked increase in voluntary ethanol consumption and a dramatic increase in ethanol preference. In rats exposed for shorter periods (2 and 4 weeks), neither ethanol self-administration nor ethanol preference were increased at any time point.

CONCLUSIONS

These observations support the existence of a temporal threshold for induction of long-lasting changes in voluntary alcohol consumption. The search for underlying molecular processes should be carried out in this context.

Persistent behavioral and autonomic supersensitivity to stress following prenatal stress exposure in rats

Prenatal restraint stress (PS) has been suggested as an attractive chronic model of anxiety. Here, we characterized the behavioral and autonomic responsivity to acute stress exposure in adult PS subjects. In Wistar rats, locomotor activity, as well as spontaneous behavior in an established animal model of anxiety, the elevated plus-maze, was unaffected by PS. However, the anxiogenic-like response normally seen on the plus-maze following a restraint stress was markedly potentiated in adult PS subjects, despite indistinguishable corticosterone responses. In addition, we assessed the tail skin temperature response to a mild social stressor, transient social mixing. The diazepam-sensitive, late phase of the temperature response was markedly potentiated in adult PS subjects. In summary, PS induces a persistent phenotype of increased behavioral and autonomic sensitivity to stress. This paradigm might serve as an attractive screening model for anti-anxiety compounds.

Gene expression in brain: a window on ethanol dependence, neuroadaptation, and preference

This article represents the proceedings of a symposium at the 2002 joint RSA/ISBRA Conference in San Francisco, California. The organizer was Paula L. Hoffman and the co-chairs were Paula L. Hoffman and Michael Miles. The presentations were (1) Introduction and overview of the use of DNA microarrays, by Michael Miles; (2) DNA microarray analysis of gene expression in brains of P and NP rats, by Howard J. Edenberg; (3) Gene expression patterns in brain regions of AA and ANA rats, by Wolfgang Sommer; (4) Patterns of gene expression in brains of selected lines of mice that differ in ethanol tolerance, by Boris Tabakoff; (5) Gene expression profiling related to initial sensitivity and tolerance in gamma-protein kinase C mutants, by Jeanne Wehner; and (6) Gene expression patterns in human alcoholic brain: from microarrays to protein profiles, by Joanne Lewohl.

Effects of tiagabine and diazepam on operant ethanol self-administration in the rat

OBJECTIVE

Benzodiazepines (BDZ) are widely used in the treatment of anxiety and ethanol withdrawal. It has been suggested that this class of compounds may increase the reinforcing value of ethanol; however, the literature is scarce. Tiagabine has recently been introduced into clinical use as an anti-epileptic drug. It acts through inhibiting gamma-aminobutyric acid (GABA) reuptake, and thus represents a pharmacodynamically novel principle for potentiating GABAergic transmission. The objective of the present study was to examine whether these two manners of modulating GABAergic transmission would affect ethanol self-administration in rats.

METHOD

Rats were trained on an operant oral ethanol self-administration task in a two-lever free-choice paradigm. When trained, subjects were treated with tiagabine (2, 6 and 18 mg/kg, intraperitoneally [i.p.]) or diazepam (0.5, 1.5 and 4.5 mg/kg, i.p.). Postsession blood alcohol concentrations and locomotor activity measures also were obtained.

RESULTS

At nonsedating doses, neither tiagabine nor diazepam affected operant ethanol self-administration. At the highest doses (18 and 4.5 mg/kg, respectively), both drugs suppressed ethanol self-administration but also induced significant suppression of locomotion, indicative of sedation.

CONCLUSIONS

Systemic administration of either the GABA-uptake blocker, tiagabine, or the GABA/BDZ agonist, diazepam, at nonsedating doses does not seem to affect oral ethanol self-administration.

Long-lasting increase in voluntary ethanol consumption and transcriptional regulation in the rat brain after intermittent exposure to alcohol

Prolonged exposure of the brain to ethanol is a prerequisite for developing ethanol dependence, but the underlying neural adaptations are unknown. Here we demonstrate that rats subjected to repeated cycles of intoxication and withdrawal develop a marked and long-lasting increase in voluntary ethanol intake. Exposure-induced but not spontaneous alcohol intake is antagonized by acamprosate, a compound clinically effective in human alcoholism. Expression analysis of cingulate cortex and amygdala reveals a set of long-term up-regulated transcripts in this model. These include members of pathways previously implicated in alcohol dependence (glutamatergic, endocannabinoid, and monoaminergic neurotransmission), as well as pathways not previously thought to be involved in this disorder (e.g., members of the mitogen-activated protein kinase pathway). Thus, alternating periods of ethanol intoxication and withdrawal are sufficient to induce an altered functional brain state, which is likely to be encoded by long-term changes in gene expression. These observations may have important implications for how alcoholism is managed clinically. Novel clinically effective treatments may be possible to develop by targeting the products of genes found to be regulated in our model.

Anxiogenic-like action of centrally administered glucagon-like peptide-1 in a punished drinking test

A role for glucagon-like peptide-1 (GLP-1) has been postulated in the regulation of blood glucose and satiety. In addition, intracerebroventricular administration of GLP-1 has been shown to suppress locomotor activity, and produce a neuronal activation in the amygdala, a structure involved in mechanisms of fear and anxiety. Adult male Sprague-Dawley rats were prepared with chronic intracerebroventricular cannulae. Measures of experimental anxiety were assessed by the Vogel conflict test and the elevated plus maze. Central GLP-1 (fragment 7-36) administration produces a proconflict effect in the punished drinking test, while leaving measures of activity and nociception unaffected. GLP-1 may participate in the control of fear-induced suppression of behavior, probably via action in the amygdala.

Influences of presentation mode and time pressure on the utilisation of advance information in response preparation

An important approach to the investigation of movement selection and preparation is the precuing paradigm where preliminary information about a multidimensional response leads to reaction time benefits which are positively related to the amount of precue information. This so-called precuing effect is commonly attributed to data-limited preparatory motoric processes performed in advance of the response signal. By means of recording the lateralised readiness potential (LRP), the present experiments investigated whether the precuing effect could be explained also by variables that affect strategic utilisation of stimulus-conveyed information. Experiment 1 presented fully and partially informative precues either in mixed or blocked mode. Experiment 2 exerted various degrees of time pressure to the different precue conditions. In both experiments, the precuing effect on reaction times and the LRP was fully preserved, refuting the notion that the sensitivity of the LRP to the amount of preliminary information merely reflects differential precue utilisation. As a major finding, time pressure increased the LRP amplitude during response preparation which is consistent with the view that response strategies generally influence movement preparation on a motoric level.

Differential expression of NPY and its receptors in alcohol-preferring AA and alcohol-avoiding ANA rats

BACKGROUND

Central neuropeptide Y (NPY) is known to control feeding and stress responses. Recently, it has been suggested that NPY also has a role in regulation of alcohol consumption.

METHODS

NPY and NPY receptor expression in genetically selected alcohol-preferring (AA), alcohol-nonpreferring (ANA), and Wistar rats were investigated. Expression was assessed using in situ hybridization histochemistry with riboprobes specific for preproNPY, Y1, and Y2 receptors. Effects of central NPY administration on ethanol self-administration were also examined in AA, ANA, and Wistar rats by using oral operant self-administration.

RESULTS

NPY mRNA expression was higher in ANA than in both AA and Wistar rats in the hippocampal CA region and dentate gyrus, whereas AA and Wistar did not differ from each other. No differences in NPY expression were found in the other regions analyzed: cingulate cortex, medial nucleus of the amygdala, arcuate, and paraventricular nuclei of the hypothalamus. Y1 receptor mRNA expression did not differ between the three lines. Y2 expression was higher in the dentate gyrus of both AA and ANA rats than in Wistar subjects. In the medial amygdala, Y2 mRNA was reduced in the AA line, compared to both ANA and Wistar rats. NPY injected intracerebroventricularly (1.5-3.0 nmol) did not affect operant ethanol self-administration in any of the three lines examined.

CONCLUSION

The NPY system seems to differ in several respects between rat lines with different levels of alcohol preference. Differences observed within the hippocampus could be related to behavioral traits other than alcohol intake but it is also possible that elevated hippocampal expression of NPY in the ANA rats contributes to the low alcohol intake of this line. Aberrant NPY expression and/function within the amygdala complex could contribute to alcohol preference and constitute an anatomic substrate of the effects of NPY expression on alcohol intake observed previously in genetically modified animals.

Site-specific administration of antisense oligonucleotides using biodegradable polymer microspheres provides sustained delivery and improved subcellular biodistribution in the neostriatum of the rat brain

Antisense oligonucleotides (ODNs) are being increasingly used in the central nervous system as biological tools, as drug-target validation agents and as potential therapeutic agents. Although the local delivery of naked ODNs to the brain can result in the desired biological effects, the duration of efficacy is relatively short lived due to the combined effects of rapid ODN degradation and elimination half-lives in vivo. In this study, we have examined the use of biodegradable polymer microspheres as a site-specific delivery system for targeting ODNs to the neostriatum of the rat brain. Model phosphorothioate backbone-modified ODNs were entrapped within poly(D,L-lactide-co-glycolide) (PLAGA) microspheres using a double emulsion-deposition method and the formulations characterised in terms of particle size, surface morphology, percent encapsulation efficiency, ODN loading and in vitro release profiles. For in vivo evaluation, PLAGA microspheres containing fluorescently-labelled ODNs were stereo-taxically administered to the neostriatum of the rat brain and biodistribution of ODNs monitored after 48 h. Administration of free fluorescently-labelled ODNs to the neostriatum resulted in a punctate cellular distribution of ODNs after 24 h with little or no ODN remaining in the neostriatum after 48 h. In comparison, fluorescently-labelled ODNs delivered using polymer microspheres were intensely visible in cells after 48 h post-administration and the fluorescence appeared to be diffuse covering both cytosolic and nuclear regions. Dual-label immunohistochemical analyses suggested that ODNs were mainly distributed to neuronal cells. These data indicate that site-specific administration of ODNs using biodegradable polymer microspheres will not only provide sustained delivery of nucleic acids but can also improve the cellular distribution of ODNs to brain cells. Sustained or controlled-release biodegradable polymer formulations, therefore, represent an attractive strategy for improved local delivery of ODNs to the CNS.

Sequence-sensitive subcomponents of P300: topographical analyses and dipole source localization

P300 amplitude and reaction time (RT) are strongly affected by the sequence of events preceding the eliciting stimulus. Sommer, Leuthold and Soetens (1999) found that robust sequential effects in P300 amplitude could be dissociated from more variable sequential effects in RTs. However, global changes in P300 amplitude and topography gave rise to the suggestion that sequential effects are specific for a subcomponent of P300 that is separate from and anterior to the classical parietal P300. Here, confirming evidence for dissociable subcomponents of P300 is reported from two experiments. Independent component analysis separated a centrally distributed sequence-sensitive subcomponent from a more parietal subcomponent. Subsequent dipole source analysis indicated a deep mesial source for the sequence-sensitive subcomponent. Overlap with reafferent somatosensory activity appears to be responsible for an apparent lateralization of this component towards the hemisphere ipsilateral to the responding hand.

Local 5,7-dihydroxytryptamine lesions of rat amygdala: release of punished drinking, unaffected plus-maze behavior and ethanol consumption

Several serotonergic drugs are effective for anxiety disorders, but underlying mechanisms are unclear, and findings in experimental animals are difficult to reconcile with human data. It has been proposed that differential effects of serotonin within specific anatomical systems may account for these difficulties, and the amygdala has been suggested as one of the structures involved. To examine this hypothesis, the neurotoxin 5,7-dihydroxytryptamine was administered locally in rat amygdala. Within the amygdala, serotonin was depleted by approximately 80%, with other transmitters unaffected, and serotonin transporter labelling was decreased by approximately 85%. Cortical areas near the lesion site were also affected, although to a lesser degree. Other forebrain areas were unaffected. Lesions resulted in a specific anti-conflict effect in a punished drinking test, but did not influence elevated plus-maze behavior (under baseline conditions and after restraint stress), locomotor activity or ethanol intake. These data suggest that the punished drinking test and the elevated plus-maze may activate different components of fear circuitry, and that the serotonergic input to the amygdala specifically participates in fear-related behavioral suppression mediated by this structure.

Multiple bottlenecks in information processing? An electrophysiological examination

When two stimuli are to be processed in rapid succession, reaction time (RT) to the second stimulus is delayed. The slowing of RT has been attributed to a single processing bottleneck at response selection (RS) or to a central bottleneck following the initiation of the first response. The hypothesis of a response initiation bottleneck is mainly based on reports of underadditive interactions between stimulus onset asynchrony (SOA) and the number of stimulus-response alternatives (simple vs. two-choice response). The present study tested the hypothesis of a response initiation bottleneck by recording the lateralized readiness potential (LRP), a brain wave, emerging during or immediately following RS. The LRP findings were consistent with a central bottleneck but did not support the late bottleneck hypothesis. Instead, the LRP provided direct evidence that the underadditive interaction of number of alternatives and SOA is due to an increase of response anticipations in the simple response condition.

Induction of hippocampal glial cells expressing basic fibroblast growth factor RNA by corticosterone

A transcriptional regulation of bFGF expression via both gluco- and mineralocorticoid receptors is known to exist. In the present study the glial nuclear fraction of bFGF transcripts was studied in sham-operated (SHAM), adrenalectomized (ADX), and corticosterone-treated ADX rats in subregions of the dorsal hippocampal formation. A substantial increase was observed in the population of bFGF RNA-expressing glial cells after acute corticosterone treatment (10 mg/kg, s.c.) in subregions of the CA1 area and the dentate gyrus but no changes were observed after adrenalectomy. The levels of glial nuclear bFGF transcripts were similar in all the experimental groups. These data suggest that in a subpopulation of hippocampal glial cells corticosterone regulates bFGF gene expression transcriptionally in an on/off manner.

Differential expression of diacylglycerol kinase iota and L18A mRNAs in the brains of alcohol-preferring AA and alcohol-avoiding ANA rats

Ethanol preference and behavioral disinhibition in AA (alcohol accepting) animals is a behavioral constellation similar to that seen in human type II alcoholism, for which considerable genetic loading has been shown. In search of novel neural substrates for this phenotype, we compared gene expression in the cerebral cortex of the AA rat with two groups of control animals, the ANA (alcohol non-accepting) line and heterogeneous Wistar animals, by differential display RT-PCR. We identified two transcripts, ribosomal protein L18a mRNA and diacyglycerol kinase iota mRNA, which are differentially expressed between AA and ANA rats. Ribosomal protein L18A mRNA is evenly expressed throughout the brain, but strongly reduced in cortex of AA rats vs controls. Diacylglycerol kinase iota is exclusively found in the brain, and expressed in a distinct regional pattern. Its cortical expression is about 25% higher in AA than ANA rats. Differential display RT-PCR seems to provide a feasible strategy to identify previously unknown genes whose differential expression correlates with behavioral phenotypes related to dependence.

Gluco- and mineralocorticoid receptor-mediated regulation of neurotrophic factor gene expression in the dorsal hippocampus and the neocortex of the rat

Gluco- and mineralocorticoid receptors (GR and MR) act via common promoter elements but may exert different effects on gene regulation in various regions of the forebrain. In order to separately analyse the role of GR and MR in the regulation of neurotrophic factor genes and their receptors, we used adrenalectomy and subsequent hormone injections in the rat as a model system. Twenty-four hours after adrenalectomy rats were injected with a single dose of corticosterone (2 and 10 mg/kg), aldosterone (0.5 mg/kg) or the synthetic glucocorticoid agonist RU 28362 (4 mg/kg). Gene expression of basic fibroblast growth factor (bFGF) and its high-affinity receptors [fibroblast growth factor receptor subtypes 1-3 (FGF-R1, FGF-R2, FGF-R3)], as well as brain-derived growth factor (BDNF) and neurotrophin-3 (NT-3) was analysed at 4 h after the hormone injection in CA1-CA4 (cornus of Ammon areas of the hippocampus) and dentate gyrus of the dorsal hippocampus and in neocortex by means of in situ hybridization. We found that bFGF is regulated in CA2, CA3 and dentate gyrus by GR and MR together, and in CA1, CA4 and neocortex by GR alone. FGF-R2 expression in the hippocampus seems to be regulated only by MR, while BDNF expression appears to depend on both receptors. FGF-R1, FGF-R3 and NT-3 were only moderately affected by the hormone activation of GR and MR acting in concert or alone in the various regions. Thus, the present findings suggest that the adrenal cortical system through GR and MR participate in the control of neurotrophic factor signalling in a highly subregion- and cellular-dependent manner.

[Education of patients with inflammatory bowel diseases]

Patients with chronic inflammatory bowel disease were interviewed about their degree of satisfaction with the medical information provided by the professional staff and the reasons for their satisfaction. 30 patients, suffering from ulcerative colitis or Crohn's disease, underwent semistandardized interviews with the result that professional education about their disease was provided either in a single concluding session or in several consecutive sessions. The patients were informed about the diagnosis, the assumed etiology and medical treatment, yet much less frequently were they told about the course of their disease or its possible consequences. On the average the clarifying sessions did not take more than 10 to 15 minutes. Only 50% of the patients were able to fully understand the information they received. 40% were dissatisfied. Greater patient satisfaction was related to more time, more detailed explanation, and emotional support by the physician. These facts should be seriously considered during medical training.

Anxiogenic-like action of galanin after intra-amygdala administration in the rat

The neuropeptide galanin is expressed in brain structures implicated in regulation of emotionality. The amygdala is known to play a central role in mechanisms of fear and anxiety. We therefore examined the effects of galanin (0.2 and 0.6 nmol/side) on experimental anxiety upon microinjection into the amygdala. Two established animal models of anxiety were used: a punished drinking test, and the elevated plus-maze. Punished responding was dose dependently suppressed by intra-amygdala galanin, whereas unpunished responding, drinking motivation, locomotor activity, and shock thresholds were unaffected. No effects on experimental anxiety were seen in the plus-maze following galanin injection. When injected into parietal cortex, no anxiety promoting properties of galanin were detected. These data suggest that activation of galanin receptors in amygdala modulates neurotransmission involved in fear and experimental anxiety.

Covert signs of expectancy in serial reaction time tasks revealed by event-related potentials

Choice reaction time is strongly determined by the sequence of preceding stimuli. With long response-stimulus intervals (RSIs), a cost-benefit pattern is observed, which has been related to expectancy, whereas with short RSIs a benefit-only pattern emerges, possibly because of automatic facilitation. In the present study, event-related potentials were recorded while subjects performed serial choice responses to visual and auditory stimuli at long and short RSIs. As expected, reaction times displayed cost-benefit and benefit-only patterns at long and short RSIs, respectively. In contrast, sequential effects in event-related potential amplitudes displayed a cost-benefit pattern, unaffected by the RSI. The results demonstrate that an expectancy-like mechanism is always active in serial tasks but appears to influence performance only when the RSI is long.

ERP correlates of error processing in spatial S-R compatibility tasks

When participants in reaction time (RT) tasks commit errors, the event-related brain potential (ERP) has been reported to show a negative-going deflection, the so-called error negativity (NE), followed by a positive-going component (PE). To examine the locus of NE within information processing and in order to test whether two successive P300 components are elicited in error trials, we manipulated the duration of perception- and response-related processing stages in visual and auditory spatial S-R compatibility tasks. Our results suggest that NE is closely coupled to motoric processes and elicited when information about the incorrectly executed response is available. The latency of the subsequent PE was influenced by perceptual as well as by response-related variables. Its scalp topography was not different from that of the P300 in correct trials and from a preceding positivity in incorrect trials. Therefore, we concluded that an additional error-related P300 is elicited by error events presumably relating to error recognition and the updating of the error context.

[Antisense oligonucleotides are clinically tested. They inhibit the expression of disease-related genes]

Recent advances in molecular biology have improved our understanding of basic pathophysiological mechanisms, and indicated possible strategies for their manipulation. The use of oligonucleotides occupies a prominent position among the emerging strategies, and has given rise to a new generation of pharmaceutical preparations now entering clinical usage. Antisense oligonucleotides are capable of blocking the expression of specific genes, thus permitting highly precise intervention in pathophysiology at the molecular level. Several clinical trials have recently produced highly promising results. The most likely applications of antisense agents are viral infections, malignancies, and chronic inflammatory disease. The article consists in a presentation of the antisense principle, discussion of its advantages and limitations, and a review of recent clinical developments and future prospects.

Motor programming of response force and movement direction

Effects of movement advance information were assessed on the prestimulus amplitude of the lateralized readiness potential (LRP), on the contingent negative variation (CNV), and on reaction time (RT). In a precuing paradigm with movement parameters hand, direction, and force, partial precues provided advance information about either hand alone, hand plus force, or hand plus direction, and the full precue specified all response parameters. The full precue produced the shortest RTs and the largest CNV amplitude, precuing hand and force or hand and movement direction produced somewhat slower RTs and a somewhat smaller CNV amplitude, and precuing only hand yielded slowest RTs and the smallest CNV amplitude. In contrast, the LRP amplitude was largest for the full precue and was the same for the remaining precues. The CNV appears to index the central assembling of a motor program, and the LRP represents the implementation of the program at more peripheral levels.

Suppressed neuropeptide Y (NPY) mRNA in rat amygdala following restraint stress

We have previously demonstrated that NPY produces anxiolytic-like effects through actions in the amygdala, and that anxiogenic-like effects of restraint stress are mediated through this structure. Here, we examined the effects of restraint stress on NPY mRNA levels in amygdala and several other brain regions. A sensitive solution hybridization-RNase protection assay (RPA) was developed, employing a combination of internal and external standards, which allowed absolute quantitation of NPY mRNA in tissue-samples of less than 10 mg. NPY mRNA levels were determined, following a 1-h restraint stress, in homogenates of tissue from the amygdala, neocortex, striatum and hypothalamus, and the time course of these effects was examined. A highly significant decrease in NPY-mRNA levels was seen in the amygdala at 1 h and 2 h following restraint, with levels returning to normal within 10 h. A similar effect was seen in the neocortex, but was less pronounced and slower in onset. Striatal and hypothalamic NPY expression was not significantly affected. Tissue levels of NPY-peptide were modestly decreased in the amygdala at 1 h following restraint and had returned to normal within 4 h. The present findings support the hypothesis that anxiety related behavioral effects of stress may in part be mediated through modulation of NPY function in the amygdala.

Existence of striatal nerve cells coexpressing CCK(B) and D2 receptor mRNAs

Co-localization of CCK(B) and D2 receptor mRNAs was analysed in adjacent sections of nucleus caudate putamen of the rat by means of in situ hybridization. A distinct subpopulation of D2 mRNA containing striatal nerve cells (in the order of 10%) was shown to co-express CCK(B) and D2 receptor mRNAs. All the CCK(B) receptor mRNA-positive nerve cells were co-localized with D2 receptor mRNA. These results give one morphological substrate to the previously demonstrated CCK(B)/D2 receptor interactions in the striatum.

The spread and uptake pattern of intracerebrally administered oligonucleotides in nerve and glial cell populations of the rat brain

The fate of 15-mer phosphorothioate-modified antisense oligonucleotides to c-fos was followed after their microinjection into rat brain. Using radiolabeled oligonucleotides, it was demonstrated that the bulk of the material stays in the injected region but that a minor part is transported with the projection pathways to regions far away from the site of injection. Using tetramethylrhodamine-isothiocyanate (TRITC) labeling as well as fluorescein isothiocyanate (FITC) labeling, it was found that the oligonucleotides were taken up by a great number of cells within 30 minutes after the injection. A diffuse cytoplasmic staining and also nuclear staining were observed in these cells, which could be identified exclusively as neurons by double labeling for the neuron-specific protein NeuN. At later times (6, 24, and 48 hours), the appearance of the oligonucleotides changed gradually to a punctate cytoplasmic staining, which by electron microscopic analysis was shown to be caused by the presence of the oligonucleotides in intracellular vesicles. The pattern of intracellular fluorescence was changed when the oligonucleotides were injected together with the cationic lipid 1,2-bis(oleoyloxy)-3-(trimethylammonio)propane (DOTAP). A small number of astrocytes and microglial cells were found to be labeled by the oligonucleotides, but only at later times after the injection and exclusively in a punctate cytoplasmic manner. Thus, the uptake of oligonucleotides in the nerve and glial cell populations of the brain might involve different mechanisms, the one in the neurons appearing to be very rapid and potent.

Specificity of face recognition: recognition of exemplars of non-face objects in prosopagnosia

We investigated whether the recognition deficits of two patients with long-standing prosopagnosia would also extend to exemplars within visually homogeneous object categories other than faces. Categorical object recognition was unimpaired in both patients. One patient was impaired in recognizing exemplars within both "living" and "nonliving" object categories. In contrast, the other patient performed at normal levels in exemplar recognition. These results provide further evidence that prosopagnosia does not necessarily reflect a general disorder in exemplar recognition, but can be a face-specific deficit.

[llocalization of grouping effect in overlapping tasks]

In certain kinds of overlapping tasks subjects have to respond to two stimuli (S1 and S2), presented in close succession with variable onset asynchrony (SOA), carrying out two different responses (R1 and R2). When responding to S1 is given priority over S2 processing, reaction time (RT) to the first stimulus is unaffected by SOA. However, sometimes subjects adopt, either spontaneously or because of instruction, a different processing strategy called grouping. In this case R1 is postponed until R2 has been determined too. The present study addresses the localization of the postponed processing stage by means of the lateralized readiness potential (LRP). One group of subjects was instructed to group responses and a second group was to give priority to S1 processing. The adherence to instructions was verified by subjects' reaction times. In case of grouping the interval between LRP onset and overt reaction increased proportionally to the postponement caused by SOA. In contrast, the interval between stimulus and LRP onset was unaffected by SOA. These findings speak against assumptions that grouping causes response activation postponement; rather, the corresponding reaction is already selected and activated prior to postponement.

Postperceptual effects and P300 latency

P300 latency is commonly thought to provide a chronometric index of the duration of perceptual processing. Because the evidence in favor of this assumption is controversial, we examined whether P300 latency is influenced by perceptual processes, response selection, and by motoric processes in two experiments using a two-choice spatial stimulus-response compatibility (SRC) task. Both experiments revealed additive effects of perceptual difficulty with spatial SRC in reaction time and P300 latency. In addition, Experiment 2 showed that P300 latency measured in average waveforms is insensitive to motoric processes. The influence of spatial SRC on P300 latency disagrees with the view that P300 latency is sensitive only to stimulus evaluation processes. However, P300 latency may be used to discriminate between influences on premotoric and motoric processing stages. A response conflict account for the SRC effect on P300 latency is suggested.

On the role of c-fos expression in striatal transmission. The antisense oligonucleotide approach

The antisense oligonucleotide approach has been established as a tool to analyse the functional role of c-fos gene expression in the striatum. Studies on the distribution and cellular localization of microinjected oligonucleotides, as well as their effect on gene expression, demonstrate that the action of the c-fos oligonucleotides can be used to evaluate the role of c-fos gene expression selectively in neuronal function. Antisense oligonucleotides to c-fos inhibit both basal and stimulated c-fos expression in the striatum, which leads to characteristic changes in behavioural and biochemical parameters, as evaluated by analysis of rotational behaviour and dual probe in vivo microdialysis for the neurotransmitter GABA, respectively. These observations could be explained by a postulated D1/NMDA receptor interaction in the striatonigral GABA pathway controlled by the immediate early gene c-fos. We concluded that c-fos might be involved not only in the control of long-term changes in the cellular phenotype but also in control of firing rate.

The phonological loop model of working memory: an ERP study of irrelevant speech and phonological similarity effects

The phonological loop model for retention of auditory verbal material in working memory, developed by Baddeley, assumes that irrelevant speech and phonological similarity influence only one and the same element of the system--that is, the phonological short-term store. We tested this idea by recording event-related potentials (ERPs) to auditorily presented letters that were phonologically similar or dissimilar and were to be memorized in the presence of more or less disturbing irrelevant speech. Irrelevant speech and phonological similarity caused ERP effects with clearly different scalp topographies, indicating that these factors influence different brain systems and hence probably different cognitive elements. Moreover, ERPs indicated that the phonological similarity effect might involve processes at the level of phonological analysis. Our data also support recent suggestions that the irrelevant speech effect is not based on the phonological similarity between relevant and irrelevant material, but on the phonological variability within the irrelevant stream.

Decreased experimental anxiety and voluntary ethanol consumption in rats following central but not basolateral amygdala lesions

A long-debated 'tension reduction' hypothesis postulates anti-anxiety effects to be important for ethanol reward, and states that elevated anxiety levels might predispose for ethanol consumption and addiction. Human data are contradictory, possibly due to heterogeneity of patient samples. In rats, baseline levels of experimental anxiety have been reported to correlate with voluntary ethanol consumption. Here, we addressed the possibility that mechanisms underlying experimental anxiety might be causally related to regulation of voluntary ethanol intake. Rats were bilaterally lesioned in central amygdala using microinjections of ibotenic acid. This resulted in a robust release of punished drinking in a modified Vogel conflict test, an effect typically seen with anxiety reducing drugs. This effect was specific, as unpunished drinking was unaffected by the lesion. On the elevated plus-maze, central amygdala lesions did not affect behaviour under baseline conditions, but attenuated the anxiogenic effect of restraint stress. Measures of locomotor activity were not affected. Voluntary ethanol consumption was examined in a two-bottle, free choice paradigm. Ethanol intake was markedly decreased in the lesion group. Total fluid intake was not affected. Basolateral amygdala lesions, which did not affect conflict behaviour, also left ethanol intake unaffected. These results are consistent with previous reports of an important role for central amygdala in anxiety related behaviours, and suggest that cell bodies located in central amygdala might be important in this context. Further, our results support a relation between experimental anxiety and voluntary ethanol consumption.

Recognizing famous voices: influence of stimulus duration and different types of retrieval cues

The current investigation measured the effects of increasing stimulus duration on listeners' ability to recognize famous voices. In addition, the investigation studied the influence of different types of cues on the naming of voices that could not be named before. Participants were presented with samples of famous and unfamiliar voices and were asked to decide whether or not the samples were spoken by a famous person. The duration of each sample increased in seven steps from 0.25 s up to a maximum of 2 s. Voice recognition improvements with stimulus duration were with a growth function. Gains were most rapid within the first second and less pronounced thereafter. When participants were unable to name a famous voice, they were cued with either a second voice sample, the occupation, or the initials of the celebrity. Initials were most effective in eliciting the name only when semantic information about the speaker had been accessed prior to cue presentation. Paralleling previous research on face naming, this may indicate that voice naming is contingent on previous activation of person-specific semantic information.

Differential localization of brain systems subserving memory for names and faces in normal subjects with event-related potentials

Evidence from brain-damaged patients suggests different memory systems for verbal and nonverbal stimuli which also have different neuroanatomical substrates. We explored whether the scalp topographies of event-related potentials (ERPs) might confirm the dissociability of these systems. Unfamiliar faces and names were presented in separate conditions, study blocks alternating with recognition blocks. During recognition the familiarity of each stimulus was rated on a 4-point scale. The amplitudes of the ERPs to the study items were monotonically related in size to the mean subsequent familiarity ratings. Memory-related ERP differences (Dm) were calculated by subtracting ERPs recorded during the study phase to items with low subsequent familiarity ratings from items with high familiarity ratings. The Dm for faces and names showed stimulus-specific scalp topographies between 400 and 800 ms. These findings confirm that memory for names and faces is mediated by at least partially different brain systems.

Intrastriatally injected c-fos antisense oligonucleotide interferes with striatonigral but not striatopallidal gamma-aminobutyric acid transmission in the conscious rat

Antisense c-fos oligonucleotides injected into the neostriatum of conscious rats selectively inhibited c-fos expression associated with compensatory increases in striatal c-fos mRNA levels and also with increased expression of junB and NGFI-A mRNA, probably as a result of regulatory phenomena. Dual probe in vivo microdialysis was used to investigate gamma-aminobutyric acid (GABA) release in the substantia nigra and the globus pallidus, which represent the terminal sites of the dopamine D1 receptor regulated striatonigral and the dopamine D2 receptor regulated striatopallidal GABA pathways, respectively. Intrastriatal infusion of the c-fos antisense oligonucleotide profoundly decreased dialysate GABA levels in the ipsilateral substantia nigra within 60 min but did not influence the dialysate GABA levels in the globus pallidus compared with the sham and control oligonucleotide treated groups. The site of action of the antisense oligonucleotides was mainly restricted to striatal neurons as shown by the distribution of locally injected fluoresceine isothiocyanate and radiolabeled oligonucleotides. The findings demonstrate a facilitatory role for c-fos mediated gene regulation in striatonigral GABA transmission and strengthen the evidence that the regulation of neurotransmission is different in the striatonigral and striatopallidal GABA pathways.

Partial advance information and response preparation: inferences from the lateralized readiness potential

Response speed to a signal is faster when advance information about the forthcoming movement is provided before signal onset. Although this precuing effect is well established, the location of this saving in reaction time (RT) in the information-processing system is controversial. Some authors have claimed that the precuing effect resides at a motoric level, whereas others have suggested a nonmotoric locus. The present experiments used onset latencies of the lateralized readiness potential (LRP) to locate the precuing effect. The results of 2 experiments with a highly compatible (Experiment 1) and with an incompatible (Experiment 2) stimulus-response mapping indicate that this effect resides, at least partially, in the motoric portion of RT. In addition, the LRP amplitude before signal appearance increased with the amount of advance information, supporting a muscle-specific preparation hypothesis.

Partial advance information and response preparation: inferences from the lateralized readiness potential

Response speed to a signal is faster when advance information about the forthcoming movement is provided before signal onset. Although this precuing effect is well established, the location of this saving in reaction time (RT) in the information-processing system is controversial. Some authors have claimed that the precuing effect resides at a motoric level, whereas others have suggested a nonmotoric locus. The present experiments used onset latencies of the lateralized readiness potential (LRP) to locate the precuing effect. The results of 2 experiments with a highly compatible (Experiment 1) and with an incompatible (Experiment 2) stimulus-response mapping indicate that this effect resides, at least partially, in the motoric portion of RT. In addition, the LRP amplitude before signal appearance increased with the amount of advance information, supporting a muscle-specific preparation hypothesis.

Covert face recognition in prosopagnosia: a dissociable function?

Covert face recognition was investigated in a patient with prosopagnosia without object agnosia. This patient performed well in various face processing tasks like expression analysis and feature processing and had relatively preserved semantic knowledge about persons, but was slightly impaired in the visual matching of unfamiliar faces. In face-name paired-associate relearning task, covert face recognition was demonstrated to be above-chance. However, as this task cannot be meaningfully applied to control subjects, results do not necessarily indicate that the degree of covert face recognition is normal. In fact, in contrast to control subjects, the patient showed significantly reduced associative priming of names by face primes as compared to name primes, suggesting a quantitative reduction of covert face recognition. It is argued that these results support the view that overt and covert face recognition are brought about by the same functional system (Farah, O'Reilly and Vecera, 1993).

Metamemory, distinctiveness, and event-related potentials in recognition memory for faces

A neglected topic in metamemory research is the ability of subjects to predict their own recognition performance for faces. We investigated whether subjects can make such judgments of learning (JOL) for unfamiliar faces and whether JOLs relate to facial distinctiveness, a powerful determinant of face recognition. One group of subjects made JOLs, and a second group rated the same faces for distinctiveness; subsequently, both groups tried to recognize these faces among new faces. There was significant prospective metamemory for faces that appeared to be based on facial distinctiveness. Both prospective metamemory and distinctiveness ratings related to long-lasting effects in event-related brain potentials (ERPs), closely resembling an ERP component that predicted face recognition. Therefore, the brain processes underlying JOLs, distinctiveness, and recognition memory for faces appear to be intimately related.

The lateralized readiness potential preceding brief isometric force pulses of different peak force and rate of force production

Previous studies have reported that the lateralization of the readiness potential is unaffected by force amplitude of brief unimanual responses. However, because those studies did not specify rate of force production, response force probably was mainly controlled by force unit duration rather than by recruitment of force units, which may explain this negative finding. To enforce recruitment control, we factorially combined peak force (10% or 50% of maximal voluntary finger force) and time to peak force (100 or 200 ms). A precue provided advance information about the responding index finger (left vs. right). After 1 s, the imperative stimulus followed, requiring a brisk isometric flexion of the specified index finger. Symmetric effects, maximal at the vertex, of both force and rate of force production were observed 200-100 ms before the imperative stimulus in stimulus-synchronized averages and 200-100 ms before response onset in response-synchronized averages. However, neither force nor rate of force production affected the lateralized readiness potential. We conclude that this measure does not reflect movement parameters but appears to indicate an abstract preparation of lateralized response channels.

Lack of pharmacokinetic interaction between vinpocetine and oxazepam

The influence of multiple doses of vinpocetine (10 mg three times daily) on the steady state plasma concentrations of oxazepam (10 mg three times daily) was studied in 16 healthy subjects. The mean (+/- s.d.) AUC (ng ml-1h-1) of oxazepam over 24 h during combined treatment was 4716 +/- 2296 and for oxazepam treatment alone it was 4737 +/- 2448 (95% confidence intervals for ratio of means = 95.4-103.7%). The degree of plasma protein binding of oxazepam was 98.11 +/- 0.32% and was not affected by vinpocetine. Independent of vinpocentine treatment a significant diurnal change in the plasma binding of oxazepam was observed; the free drug fraction was 20% higher during the night than during the day. Cmax and AUC values based on total oxazepam in plasma were 10% lower during the night. The results indicate a lack of influence of vinpocetine on oxazepam kinetics. Diurnal changes in the plasma binding of oxazepam probably have no clinical consequences.

Event-related potentials and models of performance asymmetries in face and word recognition

Performance asymmetries in divided visual field studies may be ascribed either to hemispheric differences in processing efficiency or to the costs of interhemispheric transfer towards the superior hemisphere. In order to distinguish between these alternatives, event-related potentials (ERPs) were recorded while subjects had to recognize laterally presented faces or words. As expected, behavioural left- and right-field advantages were observed for faces and words, respectively. Regardless of stimulus type, the ERPs displayed a sustained temporo-parietal negativity over the hemisphere stimulated directly via the contralateral hemifield. Both this hemifield-dependent negativity (HDN) and the performance asymmetries diminished to insignificance when the same stimuli were presented but subjects simply made a left-right decision about stimulus location. We conclude that the HDN is no obligatory, stimulus-bound ERP component but depends on lateralized cognitive processing. The stimulus-unspecific and time-invariant topography of the HDN might indicate that it relates to the allocation of processing resources to the directly stimulated hemisphere. The findings suggest that both faces and words were processed predominantly in the directly stimulated hemisphere, supporting an efficiency explanation of the performance asymmetries.

Antisense oligonucleotide to c-fos induces ipsilateral rotational behaviour to d-amphetamine

The immediate-early genes, especially c-fos, have been suggested to have an important role in neuronal plasticity and memory. However, it has been difficult to determine if in fact c-fos can participate in control of behaviour. Here we can report that direct unilateral infusion into the rat neostriatum of an antisense phosphothioate oligodeoxynucleotide to c-fos mRNA leads to the rapid induction of ipsilateral rotational behaviour after d-amphetamine administration. This is associated with an elimination of the in vivo expression of Fos-like immunoreactivity within the infused region of neostriatum. Following infusion of these oligodeoxynucleotides labelled with fluorescein isothiocyanate they appear with a nuclear and cytoplasmic location in a large number of nerve cells, many of which are immunoreactive for dopamine and cyclic AMP regulated phosphoprotein. The present findings suggest that the immediate-early gene c-fos has a role also in control of behavioural activity, as illustrated in D1 receptor containing striatal neurones.

Stimulus presentation rate dissociates sequential effects in event-related potentials and reaction times

The present study explored the impact of the stimulus presentation rate on sequential effects in event-related potentials (ERPs) and reaction times (RTs). Random series of equiprobable tones were presented at interstimulus intervals (ISIs) of 1.3, 2.1, and 2.9 s. Fast and accurate choice responses to the tones were required. Although sequential effects in RTs were stable across all ISIs, the common first-order repetition effect in P300 amplitude was only observed at the 1.3-s ISI and not at the slower presentation rates. This dissociation between the first-order effects in RTs and ERPs speaks against an explanation of both effects by a common expectancy mechanism. In addition, sequential effects were observed as early as about 100 ms after stimulus onset in the lateralized readiness potential. Together with similar sequential effects in P300 latency, this finding supports a continuous flow model of information processing.

Covert effects of alcohol revealed by event-related potentials

Contradictory evidence as to the effects of alcohol on early information processing stages has been obtained from behavioral and psychophysiological investigations. In the present study, choice reaction times, error rates, and event-related potentials (ERPs) were recorded in a task in which variations in stimulus discriminability and of the (task irrelevant) correspondence between stimulus location and response location were orthogonally combined. Both discriminability and stimulus-response correspondence affected reaction time and electrophysiological chronometric measures as expected. However, no behavioral effects of alcohol were observed, possibly because of strategic adjustments. Psychophysiological chronometric measures indicated that alcohol leaves the initial flow of perceptual evidence to motor stages unimpaired, whereas it appears to increase the duration of stimulus evaluation. Interestingly, a number of alcohol effects appeared in the ERP amplitudes. Decrements in early ERP components indicate alcohol-induced impairments of involuntary visual attention and/or the automatic stimulus location-dependent activation of response channels. In contrast, a strong enhancement of a late slow-wave component under alcohol may reflect the investment of processing resources in order to maintain normal performance levels.

Reaction time improvements with practice in brain-damaged patients

This study investigated practice effects on reaction time (RT) in patients with unilateral brain damage and age-matched controls. Subjects performed a Sternberg-type stimulus recognition task. Both RT and RT variability decreased in all subjects from a short initial session to a second session, 1 to 3 days later. Within the second session, however, RT remained constant in the controls, whereas it was further reduced in the patients. These findings argue against the assumption that brain-damaged patients generally show smaller practice effects on RT than controls, and instead suggest that it may be essential to provide patients with sufficient practice opportunities. To locate the processing stage where practice is effective, analyses were performed also on the intercept and slope parameters of the RT function. It is argued that the differential practice effects were due to the speeding of perceptual and/or response-related stages, rather than gains in memory search speed.