The stress-induced hyperthermia paradigm as a physiological animal model for anxiety: A review of pharmacological and genetic studies in the mouse

This paper reviews the function, brain mechanisms and pharmacology of stress-induced hyperthermia (SIH) in a broad context. Hyperthermia itself is induced by all stressful stimuli and can be found across numerous species, including humans. As a model for anxiety, the process of insertion of a rectal probe increases temperature ranging from about 0.5-1.5 degrees C in 10-15min is called SIH. This temperature increase can be blocked by anxiolytic drugs. The methodological as well as pharmacological aspects of the group- (G-SIH) and singly housed (SIH) version of the paradigm are described in detail. Also, an overview is presented about studies using the SIH procedure in genetically modified mice together with the potential interference with immunological induction of a febrile response. The paper also presents data that highlight some of the limitations of the SIH procedure for use of drugs like nicotine, which contain particular characteristics such as short in vivo half-life, and/or disturbance of thermoregulation. The advantages and disadvantages of the SIH procedure as a physiological model of anxiety are discussed.

Oxytocin Involvement in SSRI-Induced Delayed Ejaculation: A Review of Animal Studies

INTRODUCTION

Selective serotonin reuptake inhibitors (SSRIs) differ in the severity of induced ejaculation delay. Various studies indicate that oxytocin is involved in sexual behavior.

AIM

To review and evaluate the involvement of oxytocin in SSRI-induced ejaculation delay.

MAIN OUTCOME MEASURES

Oxytocine release, 5-hydroxytryptamine (5-HT) neurotransmission, and desensitization of 5-HT(1A) receptors.

METHODS

A review and critical analysis of animal studies investigating the interaction of serotonergic and oxytocinergic neurotransmission in relation to the ejaculation process.

RESULTS

Although acute treatment with the SSRIs fluoxetine and paroxetine immediately causes increased serotonin levels, delayed ejaculation does not occur. The increased serotonin levels induce oxytocin release via activation of 5-HT(1A) receptors, and this might compensate for the inhibitory actions of serotonin on sexual behavior. Chronic treatment with fluoxetine and paroxetine desensitizes 5-HT(1A) receptors on oxytocin neurons, and that might in part determine the onset of delayed ejaculation. Desensitization of 5-HT(1A) receptors is less strong following chronic treatment with the SSRIs fluvoxamine or citalopram, which may attenuate the degree of delayed ejaculation.

CONCLUSIONS

Preliminary data suggest that the severity of chronic SSRI treatment-induced delayed ejaculation and the differences between the various SSRIs in inducing ejaculation delay is related to gradual desensitization of 5-HT(1A) receptors on oxytocin neurons.

A new animal welfare concept based on allostasis

Animal welfare is an increasing issue of public concern and debate. As a result, many countries are reconsidering the way animal welfare is embedded in the legislation and rules for housing and care of animals. This requires general agreement of what animal welfare is. Unfortunately, the current science of animal welfare is less scientific than what has been claimed. In our view, it is overly guided by anthropocentric thinking about how animals ought to be handled and neglects the latest concept of physiology: 'The Allostasis Concept'. Allostasis, which means stability through change, has the potential to replace homeostasis as the core model of physiological regulation. Not constancy or freedoms, but capacity to change is crucial to good physical and mental health and good animal welfare. Therefore, not homeostasis but allostasis is at the basis of our new animal welfare concept. This paper is aimed at a broader scientific discussion of animal welfare that includes knowledge from the latest scientific developments in neurobiology and behavioral physiology, and generates views that are extremely relevant for the animal welfare discussion.

Delay aversion: Effects of 7-OH-DPAT, 5-HT1A/1B-receptor stimulation and d-cycloserine

Impulsive individuals often display an aversion to waiting for rewards. Delay aversion can be quantified in rats in a delayed reward task, in which animals choose between an immediately available, small reward, and a large reward available after a delay. In previous research conducted at our laboratory and in literature, positive correlations between delay aversion and aggression, substance abuse and persistence during extinction of conditioned responses were found. The correlations suggest a possible shared pharmacology. Therefore, we tested drugs with known effects on these behaviors for possible effects on delay aversion: the dopamine D(3)-receptor agonist 7-OH-DPAT, the 5-HT(1A)-receptor agonist flesinoxan, the 5HT(1A/1B)-receptor agonist eltoprazine, and the NMDA-receptor agonist d-cycloserine. The results show that 7-OH-DPAT slightly decreased choice for the large reward. Flesinoxan disrupted task execution by lowering choice for the large reward even at a delay of 0 s. Eltoprazine slightly increased choice for the large reward, but the 5-HT(1B)-antagonist GR127935 had no effect. Administration of D-cycloserine also had no effect on choice behavior. The data suggest the dopamine D(3)-receptor and the 5-HT(1B)-receptor are interesting targets for treating delay aversion impulsivity. These targets were correctly predicted by the positive correlation between delay aversion and aggressive behavior and the intimate links between delay aversion and substance abuse disorders.

The impact of chronic pain patients' psychotropic drug knowledge and warning labels on the decision whether to drive a car or not

OBJECTIVE

The attitudes of patients towards driving a car while taking medication with psychotropic side effects is unclear. A growing number of patients use these psychotropic medicines on a daily basis, and this may interfere with their ability to drive a car.

METHODS

By means of a survey, we examined attitudes towards driving while using psychotropic medicinal drugs and the effect of warning labels on the decision whether to drive a car or not in patients with chronic pain.

RESULTS

Fifty-eight of 100 patients possessing a driver's license used psychotropic medication. Despite warning labels affixed on the packages that these drugs might impair driving ability, the majority (71%) of these patients continued driving a car. A point of concern is that 40% of these patients reported not to be more cautious in traffic after taking psychotropic drugs.

CONCLUSION

The results of this survey indicate that drug warning labels applied by Dutch pharmacies do not significantly change attitudes towards driving a car in patients taking medicinal drugs with psychotropic side effects. Future road-safety campaigns should pay more attention to the impairing effects of psychotropic drugs on driving.

Acute and subchronic effects of amitriptyline 25mg on actual driving in chronic neuropathic pain patients

The acute and subchronic effects of low doses nocturnally administered amitriptyline were compared to placebo in a double-blind crossover randomized study on driving ability and driving-related skills involving seven chronic neuropathic pain patients. Performance testing occurred at the first and last day of each 15-day drug administration period, which was preceded by a 6-day washout phase. A standardized method of measuring driving ability, the on-the-road driving test, was performed on all visits. Patients were instructed to drive with a steady lateral position while maintaining a constant speed of 95 km/h. The primary outcome of the driving test is the Standard Deviation of Lateral Position (SDLP, cm), which is an index of weaving of the car. At the first treatment day, driving performance was significantly impaired in patients after nocturnal administration of 25 mg amitriptyline compared to placebo. The increase in SDLP of 3 cm was higher than the increment generally observed with a blood alcohol concentration of 0.5 mg/ml or higher, the legal limit for driving in many countries. Also, reaction times on a memory test were significantly increased, indicating worse performance after acute treatment of amitriptyline compared to placebo. In contrast, after 2 weeks of treatment, no significant differences were found between amitriptyline and placebo, suggesting that tolerance had developed to the impairing effects of amitriptyline.

Relationship of delay aversion and response inhibition to extinction learning, aggression, and sexual behaviour

Impulsivity is an important symptom of many psychiatric disorders, and can be divided into two subtypes: response inhibition deficits and delay aversion. In the present study, we investigated the relationship between delay aversion and response inhibition, both to each other and to locomotion, extinction of conditioned responses, sexual behaviour, and aggressive behaviour. To that end, we quantified the behaviour of 24 rats in several tests. To measure response inhibition, rats were trained in a stop-signal task. In this operant task, rats were rewarded food if they inhibited execution of a response after presentation of an audible stop-signal. Delay aversion was measured in an operant task in which rats made a choice between a small, immediately available reward and a large reward available after a delay. The results showed that delay aversion and response inhibition were independent. Responses during extinction and various measures of aggressive behaviour were positively correlated to delay aversion. The speed of go-trials in the stop-task was correlated to non-aggressive behaviour. We conclude that the role of response inhibition in various behaviours is small, but delay aversion in particular contributes to several other behaviours, such as aggressive behaviour and extinction.

Akt1 deficiency affects neuronal morphology and predisposes to abnormalities in prefrontal cortex functioning

There is accumulating evidence that AKT signaling plays a role in the pathogenesis of schizophrenia. We asked whether Akt1 deficiency in mice results in structural and functional abnormalities in prefrontal cortex (PFC). Exploratory transcriptional profiling revealed concerted alterations in the expression of PFC genes controlling synaptic function, neuronal development, myelination, and actin polymerization, and follow-up ultrastructural analysis identified consistent changes in the dendritic architecture of pyramidal neurons. Behavioral analysis indicated that Akt1-mutant mice have normal acquisition of a PFC-dependent cognitive task but abnormal working memory retention under neurochemical challenge of three distinct neurotransmitter systems. Thus, Akt1 deficiency creates a context permissive for gene-gene and gene-environment interactions that modulate PFC functioning and contribute to the disease risk associated with this locus, the severity of the clinical syndrome, or both.

Effects of genetic background and null mutation of 5-HT1A receptors on basal and stress-induced body temperature: modulation by serotonergic and GABAA-ergic drugs

The stress-induced hyperthermia procedure, in which effects of drugs on basal (T(1)) and stress-induced body temperature (T(2)) are measured, predicts anxiolytic drug effect. Serotonergic drugs alter these responses and here, we studied the role of 5-HT(1A) receptors in stress-induced hyperthermia by using 5-HT(1A) receptor knockout mice. Three strains (129/Sv, Swiss Webster and C57Bl6) were used because genetic background can significantly modulate the null phenotype. We found that GABA-ergic drugs with an anxiolytic profile and stimulate alpha(2) subunit containing GABA(A) receptors, including diazepam and L838,417, result in reduced DeltaT (DeltaT=T(2)-T(1)). The alpha(1) subunit containing GABA(A) receptor was found to be primarily involved in regulation of basal body temperature T(1) and its stimulation can induce hypothermia. In addition, stimulation of 5-HT(1A) receptors by buspirone results in a reduced DeltaT, while stimulation of 5-HT(7) receptors primarily results in hypothermia. The null mutation of 5-HT(1A) receptors resulted in differences in drug-sensitivity that was further modulated by the genetic background. In particular, the null mutation on the SW and C57Bl6 backgrounds resulted in differential diazepam/L838,417 and 5-CT responses respectively. This indicates an interaction between the 5-HT(1A) receptor and genetic background and demonstrates the importance of selecting the background strain in a receptor knockout model.

Psychopharmacology of male rat sexual behavior: modeling human sexual dysfunctions?

Most of our current understanding of the neurobiology, neuroanatomy and psychopharmacology of sexual behavior and ejaculatory function has been derived from preclinical studies in the rat. When a large population of male rats is tested on sexual activity during a number of successive tests, over time individual rats display a very stable sexual behavior that is either slow, normal or fast as characterized by the number of ejaculations performed. These sexual endophenotypes are postulated as rat counterparts of premature (fast rats) or retarded ejaculation (slow rats). Psychopharmacology in these endophenotypes helps to delineate the underlying mechanisms and pathology. This is illustrated by the effects of serotonergic antidepressants and serotonergic compounds on sexual and ejaculatory behavior of rats. These preclinical studies and models contribute to a better understanding of the neurobiology of ejaculation and boost the development of novel drug targets to treat ejaculatory disorders such as premature and retarded ejaculation.

Neuroprotective effects of modafinil in a marmoset Parkinson model: behavioral and neurochemical aspects

The vigilance-enhancing agent modafinil has neuroprotective properties: it prevents striatal ischemic injury, nigrostriatal pathway deterioration after partial transsection and intoxication with 1-methyl-1,2,3,6-tetrahydropyridine. The present study determines the protective effects of modafinil in the marmoset 1-methyl-1,2,3,6-tetrahydropyridine Parkinson model on behavior and on monoamine levels. Twelve marmoset monkeys were treated with a total dose of 6 mg/kg 1-methyl-1,2,3,6-tetrahydropyridine. Simultaneously, six animals received a daily oral dose of modafinil (100 mg/kg) and six animals received vehicle for 27 days. Behavior was observed daily and the locomotor activity, hand-eye coordination, small fast movements, anxiety-related behavior and startle response of the animals were tested twice a week for 3 weeks. Modafinil largely prevented the 1-methyl-1,2,3,6-tetrahydropyridine-induced change in observed behavior, locomotor activity, hand-eye coordination and small fast movements, whereas the vehicle could not prevent the devastating effects of 1-methyl-1,2,3,6-tetrahydropyridine. Dopamine levels in the striatum of the vehicle+1-methyl-1,2,3,6-tetrahydropyridine-treated animals were reduced to 5% of control levels, whereas the dopamine levels of the modafinil+1-methyl-1,2,3,6-tetrahydropyridine-treated animals were reduced to 41% of control levels. The present data suggest that modafinil prevents decrease of movement-related behavior and dopamine levels after 1-methyl-1,2,3,6-tetrahydropyridine intoxication and can be an efficaceous pharmacological intervention in the treatment of Parkinson's disease.

Stress and hypothermia in mice in a nose-only cigarette smoke exposure system

In nose-only exposure systems, animals need to be restrained inside a tube, which leads to stress. Stress is known to cause hyperthermia in rodents. Chronically repeated episodes of hyperthermia could be detrimental to animal health and influence results of nose-only exposure studies. Therefore we investigated whether hyperthermia occurred in male C57BL/6J mice that were restrained for increasing lengths of time, using nosepieces held at room temperature, preheated at 37 degrees C, or thermostat controlled at different temperatures, with and without exposure to different concentrations of cigarette smoke. Body temperature, body weight, plasma corticosterone levels, and adrenal weights were recorded. Restraint using nosepieces at room temperature caused a time-dependent decrease in body temperature, which could be reversed by preheating the nosepieces to 37 degrees C. Cigarette smoke dose-dependently caused an additional decrease, which was counteracted by controlling nosepiece temperature at 38 degrees C. During 3 mo of exposure using heated nosepieces, Delta body temperature remained constant. Body weight gain did not differ between smoke-exposed and room air-breathing animals exposed using either heated or room-temperature nosepieces, but both groups gained significantly less weight, while adrenal weights were significantly and similarly increased, when compared to unrestrained littermates. Plasma corticosterone levels did not differ between the three groups. In conclusion, during restraint in nose-only exposure tubes with room temperature metal nosepieces, mice suffer a pronounced hypothermia. Preventing this by heating the nosepieces does not reduce the stress experienced by the animals.

Pharmacotherapy for the treatment of aggressive behavior in general adult psychiatry: A systematic review

OBJECTIVE

To systematically review the evidence for pharmacologic management of outwardly directed aggressive behavior in general adult psychiatry.

DATA SOURCES

Literature searches in PubMed, EMBASE, PsycINFO, and Cochrane libraries from 1966 through March 2005 were used to identify relevant studies. The keywords aggression, violence, anger, and hostility combined with drug therapy, psychotropic drugs, adrenergic beta-antagonists, anticonvulsants, anti-depressants, antipsychotic agents, benzodiazepines, and lithium were searched. Furthermore, the retrieved publications were searched for additional references.

STUDY SELECTION

All randomized controlled trials addressing pharmacotherapy for aggression or aggression-related symptoms were included, except studies addressing the "emergency situation" and studies conducted in specialized psychiatric or non-psychiatric settings.

DATA EXTRACTION

Evidence synthesis was performed using the "best-evidence principle." Two authors independently adjudicated methodological quality and generalizability to daily clinical practice.

DATA SYNTHESIS

Thirty-five randomized controlled trials met the inclusion criteria and were evaluated. On the basis of a best-evidence synthesis model, weak evidence for antiaggressive effects of antipsychotics, anti-depressants, anticonvulsants, and beta-adrenergic-blocking drugs was found. Atypical antipsychotics appeared superior to typical antipsychotics. The use of various outcome measures and insufficient data reporting in the individual studies hampered the quantitative assessment of efficacy across studies. Further limitations of the available randomized controlled trials included small sample sizes, short study duration, and poor generalizability to daily clinical practice setting.

CONCLUSIONS

Whereas pharmacotherapy is frequently applied in aggressive patients, only weak evidence of efficacy of various drug classes was found. Consensus about the use of aggression measurement scales in clinical trials is necessary for future research. Furthermore, large-scale trials with more naturalistic designs, as opposed to classical randomized controlled trials with strict inclusion and exclusion criteria, may be advisable in order to obtain results that are more generalizable to daily clinical practice.

Behavioral effects of modafinil in marmoset monkeys

RATIONALE

Modafinil is increasingly used in sleep disturbances in general and in neurodegenerative diseases and is recently being used in healthy people for attention control. However, the application of modafinil is possibly not only restricted to alertness enhancing effects. More insight in this compound may lead to new applications. Not all behavioral aspects have been studied sufficiently; therefore, more detailed investigations on modafinil's positive and aversive behavioral effects are addressed in this paper.

OBJECTIVES

Determination of effects of modafinil in marmoset monkeys with observational methods and with behavioral tests measuring locomotor activity, hand-eye coordination, response to a threat situation and startle response.

MATERIALS AND METHODS

Two hours after oral administration of modafinil in doses of 50, 100, 150, and 225 mg/kg, animals were observed and tested in the behavioral test systems.

RESULTS

Locomotor activity was increased after 100 mg/kg modafinil in the Bungalow test and after 100, 150, and 225 mg/kg, as found in the movement parameters of the human threat test. Moreover, modafinil showed anxiolytic-like effects in the human threat test. No other side effects were observed, nor were the hand-eye coordination and startle response affected.

CONCLUSIONS

Besides psychostimulation, modafinil has no aversive effects in the doses used in the domains measured. The potential anxiolytic-like effects of modafinil may create new possibilities for the therapeutic use of modafinil.

Pain and attention: attentional disruption or distraction?

The effect of pain processing on attention capacity during visual search was examined in 2 experiments. In the first experiment, we investigated whether pain draws on the same limited resources as attentional task performance. It was hypothesized that pain would negatively affect task performance under different load manipulations. Low and high load conditions of a visual search task were presented in a mixed design combined with a painfully cold or neutral cold pressor test. Performance was not affected by pain. In experiment 2, low and high load conditions were separated in different blocks to study whether pain perception was affected when task load could be anticipated. Again, pain did not significantly affect task performance. In contrast, subjective pain intensity scores were significantly lower after performing the high load compared with the low load condition. Simultaneous recordings of event-related potentials indicated an increased negativity during the pain compared with the control condition. Also, in the early (350 to 450 msec) interval of event-related potentials, an increase in negativity was found for the high load compared with the low load condition. Topographic distributions suggested that pain and task load are mediated by qualitatively different resources.

PERSPECTIVE

Our findings indicate that highly demanding attentional task performance and pain processing interfere as a result of difficulties in allocating attention. The clinical relevance of this finding is that performing a highly demanding task might distract attention from pain.

Thyroid-stimulating hormone assessments in a Dutch cohort of 620 men with lifelong premature ejaculation without erectile dysfunction

INTRODUCTION

Apart from the involvement of central serotonergic neurotransmission on lifelong premature ejaculation, interference of thyroid function has been speculated.

AIM

To study thyroid function in a large group of men with lifelong premature ejaculation (LPE).

METHODS

Lifelong premature ejaculation was defined as an intravaginal ejaculation latency time (IELT) of less than 1 minute. Any consecutive man with LPE and no erectile dysfunction assessed by medical history and the International Index of Erectile Function (IIEF-5) was eligible for the study. Apart from the assessment of thyroid-stimulating hormone (TSH) also free thyroxin (f T4) was determined in case of a TSH of <0.3 mU/L or TSH of >4.0 mU/L (being the lower and upper limits of normal values, respectively). Blood samples were drawn throughout the day within office hours.

MAIN OUTCOME MEASURES

Thyroid-stimulating hormone and f T4.

RESULTS

Included were 620 men; age (mean+/-SD) was 39.9+/-9.4 years (range 19-65). TSH concentrations from morning, early and late afternoon samples did not differ. The geometrical mean TSH concentration was 0.85 mU/L (95% confidence intervals: 0.82-0.90) with a coefficient of variation of 57.9%. Fourteen men had a TSH of <0.3 mU/L (2.2%), while five men (0.8%) of >4.0 mU/L. All men with an abnormal TSH had a normal f T4 (between 10 and 20 pmol/L). No relationship was found between age and TSH concentrations.

CONCLUSION

Thyroid-stimulating hormone distribution was analyzed in a cohort of Dutch men with lifelong premature ejaculation and no erectile dysfunction. According to statistical analysis, there appeared to be no interaction between this ejaculatory complaint and the prevalence of thyroidal dysfunction. However, further studies are needed to gain more insight into the role of thyroid dysfunction and regulation of ejaculation time.

Spontaneously hypertensive rats do not predict symptoms of attention-deficit hyperactivity disorder

The validity of the Spontaneously Hypertensive rat (SHR) as a model for Attention Deficit Hyperactivity Disorder (ADHD) is explored by comparing the SHR with Wistar-Kyoto (WKY) and Wistar rats in a number of different tests. In the open field, SHR are hyperactive compared to both Wistar and WKY, but only at specific ages. At those ages, methylphenidate (1mg/kg) did not attenuate hyperactivity. Subsequently, a dose response study of methylphenidate (0.1-10mg/kg) was conducted in the Differential Reinforcement of Low-rate responding (DRL)-72s and five-choice serial reaction time tests (5-CSRTT). Compared to WKY but not Wistar rats, SHR performed worse on the DRL-72s. Performance was not improved by methylphenidate (0.1-1.0mg/kg). In the 5-CSRTT, attentional performance was similar for all rat strains, but Wistar rats made more impulsive responses than both the SHR and the WKY. Methylphenidate only attenuated impulsivity in Wistar rats. Because SHR do not consistently display symptoms of ADHD across the different tests, and methylphenidate effects were observed in both WKY and Wistar rats, but not in SHR, we conclude that SHR is not a representative animal model for ADHD.

Mouse strain differences in autonomic responses to stress

In humans, anxiety disorders are often accompanied by an overactive autonomic nervous system, reflected in increased body temperature (BT) and heart rate (HR). In rodents, comparable effects are found after exposure to stress. These autonomic parameters can give important information on stress and anxiety responses in mice. In the present experiments, stress reactivity of three frequently used mouse strains [129 Sv/Ev, Swiss Webster (SW) and C57 BL/6] was assessed using their autonomic stress responses. BT, HR and activity were telemetrically measured. Undisturbed circadian rhythms already showed clear differences between the mouse strains. Hereafter, autonomic responses to stressors with increasing intensity were measured. Strain differences were found in magnitude and duration of the stress responses, especially after high-intensity stressors. Generally, C57BL/6 mice showed the largest autonomic response, SW the lowest and the 129Sv/Ev the intermediate response. Interestingly, the observed ranking in autonomic stress response does not match the behavioral stress responsivity of these strains. Finally, sensitivity to the anxiolytic diazepam (0, 1, 2, 4 and 8 mg/kg) was tested using the stress-induced hyperthermia paradigm. Pharmacological sensitivity to diazepam differed between the strains with the 129Sv/Ev being most sensitive. These studies show that simultaneous measurement of behavioral and autonomic parameters under stressful conditions contributes considerably to a better interpretation of anxiety and stress levels in mice.

Effect of chronic nonmalignant pain on highway driving performance

Most pain patients are treated in an outpatient setting and are engaged in daily activities including driving. Since several studies showed that cognitive functioning may be impaired in chronic nonmalignant pain, the question arises whether or not chronic nonmalignant pain affects driving performance. Therefore, the objective of the present study was to determine the effects of chronic nonmalignant pain on actual highway driving performance during normal traffic. Fourteen patients with chronic nonmalignant pain and 14 healthy controls, matched on age, educational level, and driving experience, participated in the study. Participants performed a standardized on-the-road driving test during normal traffic, on a primary highway. The primary parameter of the driving test is the Standard Deviation of Lateral Position (SDLP). In addition, driving-related skills (tracking, divided attention, and memory) were examined in the laboratory. Subjective assessments, such as pain intensity, and subjective driving quality, were rated on visual analogue scales. The results demonstrated that a subset of chronic nonmalignant pain patients had SDLPs that were higher than the matched healthy controls, indicating worse highway driving performance. Overall, there was a statistically significant difference in highway driving performance between the groups. Further, chronic nonmalignant pain patients rated their subjective driving quality to be normal, although their ratings were significantly lower than those of the healthy controls. No significant effects were found on the laboratory tests.

Processing capacity in chronic pain patients: a visual event-related potentials study

Chronic pain may impair performance on attentional processing capacity tasks. In the present study, event-related potentials were recorded to examine whether pain patients show performance decrements on attentional processing capacity tasks due to shared resources by pain and attention or, alternatively, due to deficits in allocating attentional resources during pain. Fourteen chronic pain patients and thirty age and education matched healthy controls were investigated. An attentional capacity probe task was used in which the difficulty level was manipulated, resulting in an easy and a difficult condition, while task-irrelevant visual probes were presented. These probe-elicited P3 amplitudes were assumed to provide the most pure estimate of processing capacity since they are relatively free from target-related processes. Event-related potentials were recorded from the midline electrodes Fz, Cz, Pz, and Oz. For the behavioral measures, it was found that pain patients maintained a different speed-accuracy tradeoff. Pain patients showed faster reaction time responses and higher error rates compared to controls. No significant differences were found between pain patients and controls on the primary task. Pain patients differed from controls with respect to amplitudes elicited by task-irrelevant probe stimuli. For healthy controls, the expected decreased amplitude was found for probe stimuli in the difficult compared to the easy task. In contrast, the pain patients did not show decreased probe amplitudes with increasing task load. The data may imply that allocation of attentional resources is deficient in pain patients, instead of attentional capacity.

Animal models of ejaculatory behavior

Premature ejaculation is generally regarded the most frequent male ejaculatory complaint and has been considered a psychosexual disorder with psychogenic aetiology. The efficacy of various antidepressants, however, to delay ejaculation in men and to pharmacologically treat premature ejaculation suggests a strong neurobiological involvement. Most of our current understanding of the neurobiology and neuroanatomy of sexual behavior and ejaculatory function has been derived from preclinical studies using several laboratory species. In the present paper we will review the various animal models that have been developed to further study ejaculatory function in the laboratory rat. In addition, we will briefly review the effects of serotonergic antidepressants and serotonergic compounds on sexual and ejaculatory behavior. Together, these preclinical studies may contribute to a better understanding of the neurobiology of ejaculation and help the development of novel drug targets to treat ejaculatory disorders such as premature ejaculation.

Distribution and expression of CRF receptor 1 and 2 mRNAs in the CRF over-expressing mouse brain

Corticotropin-releasing factor (CRF) acts through CRF 1 and CRF 2 receptors (CRF1, CRF2). To test the hypothesis that CRF controls the expression of these receptors in a brain site- and receptor-type specific manner, we studied CRF1 mRNA and CRF2 mRNA expressions in mice with central CRF over-expression (CRF-OE) and using in situ hybridization. CRF1 and CRF2 mRNAs appear to be differentially distributed across the brain. The brain structures expressing the receptors are the same in wild-type (WT) and in CRF-OE mice. We therefore conclude that chronically elevated CRF does not induce or inhibit expression of these receptors in structures that normally do not or do, respectively, show these receptors. However, from counting cell body profiles positive for CRF1 and CRF2 mRNAs, clear differences appear in receptor expression between CRF-OE and WT mice, in a brain-structure-specific fashion. Whereas some structures do not differ, CRF-OE mice exhibit remarkably lower numbers of CRF1 mRNA-positive profiles in the subthalamic nucleus (-38.6%), globus pallidus (-31.5%), dorsal part of the lateral septum (-23.5%), substantia nigra (-22,8%), primary somatosensory cortex (-18.9%) and principal sensory nucleus V (-18.4%). Furthermore, a higher number of CRF2 mRNA-positive profiles are observed in the dorsal raphe nucleus (+32.2%). These data strongly indicate that central CRF over-expression in the mouse brain is associated with down-regulation of CRF1 mRNA and up-regulation of CRF2 mRNA in a brain-structure-specific way. On the basis of these results and the fact that CRF-OE mice reveal a number of physiological and autonomic symptoms that may be related to chronic stress, we suggest that CRF1 in the basal nuclei may be involved in disturbed information processing and that CRF2 in the dorsal raphe nucleus may play a role in mediating stress-induced release of serotonin by CRF.

Acute and subchronic effects of amitriptyline on processing capacity in neuropathic pain patients using visual event-related potentials: preliminary findings

RATIONALE

Little is known about the effects of low doses of amitriptyline, prescribed in the treatment of neuropathic pain, on attentional processing capacity.

OBJECTIVES

Changes due to amitriptyline treatment on attentional processing capacity were investigated on behavioral measures and event-related brain potentials (ERPs) in six patients with neuropathic pain.

MATERIALS AND METHODS

Patients were treated for 15 consecutive days with 25 mg nocturnally administered amitriptyline or placebo in a double-blind crossover randomized design. Measurements were carried out on day 1 and day 15 of each treatment period. An attentional capacity probe task was used in which the difficulty level was manipulated, resulting in an easy and a hard condition, while task-irrelevant visual probes were presented. During task performance, ERPs were measured from the midline electrodes Fz, Cz, Pz, and Oz.

RESULTS

Amitriptyline increased reaction times (RTs) after acute but not after subchronic administration. ERP analyses showed that P3 amplitudes to the task stimuli were not affected by amitriptyline in either treatment phase. Moreover, P3 amplitudes to the probes were increased in the easy compared to the hard task condition after subchronic amitriptyline treatment, indicating beneficial effects of repeated amitriptyline administration. In contrast, acute amitriptyline administration did reduce an earlier visual evoked potential, N1, preceding the P3 component.

CONCLUSIONS

The results suggest that amitriptyline, even at low dosages of 25 mg, affects performance after acute administration in chronic neuropathic pain patients. After 2 weeks of treatment, performance appears to be unaffected. No deficits in processing capacity due to amitriptyline treatment were found.