Muscarinic antagonists are anxiogenic in rats tested in the black-white box

Molecular mechanisms that regulate scopolamine effects on inducible fish antipredation responses in Daphnia magna

Daphnia's antipredator responses are regulated largely by the nervous system, making these responses particularly susceptible to compounds that impact neurodevelopmental or neurofunctional processes. This study aimed to determine the molecular pathways involved in modulating the effects of scopolamine on inducible antipredation responses triggered by fish kairomones. We used two clones showing two contrasting responses. The positive phototactic clone 85 responds strongly to fish kairomones showing a marked negative phototactism and higher developmental rates. Consistently, the negative phototactic clone F shows the opposite behavior to the same stimuli. Adults of both clones were exposed to fish kairomones, scopolamine alone and a mixture of both. Scopolamine is a muscarine antagonist able to mimic fish kairomones inducible behavioral responses in both clones, while affecting differently morphological and life-history traits. Whole transcriptomic Illumina analyses indicated a greater number of de-regulated genes of the fish kairomone sensitive clone 85 (1650) compared to the F one (1138), which were grouped in four clusters (two per clone). The mixture of scopolamine and fish kairomone treatments on gene transcription was additive in both clones, indicating similar modes of action. Most enriched metabolic routes were related with neurological pathways and regulation of cell proliferation/differentiation. Our results indicate that fish kairomones and scopolamine deregulate not only neurological signaling pathways but also cell differentiation and proliferation pathways, which are linked to the observed behavioral responses as well as the developmental, morphological, and reproductive effects.

The deer mouse (Peromyscus maniculatus bairdii) as a model organism to explore the naturalistic psychobiological mechanisms contributing to compulsive-like rigidity: A narrative overview of advances and opportunities

Deer mice (Peromyscus maniculatus bairdii), a wildtype species native to North America, have been investigated for their spontaneous compulsive-like behaviour. The repetitive and persistence nature of three unique compulsive-like phenotypes in deer mice, i.e., high stereotypy (HS), large nesting behaviour (LNB) and high marble burying (HMB), are characterized by behavioural and cognitive rigidity. In this narrative review, we summarize key advances in the model's application to study obsessive-compulsive disorder (OCD), emphasizing how it may be used to investigate neurobiological and neurocognitive aspects of rigidity. Indeed, deer mice provide the field with a unique naturalistic and spontaneous model system of behavioural and cognitive rigidity that is useful for investigating the psychobiological mechanisms that underpin a range of compulsive-like phenotypes. Throughout the review, we highlight new opportunities for future research.

Ndufs4 KO mice: A model to study comorbid mood disorders associated with mitochondrial dysfunction

The Ndufs4 knockout (KO) mouse is a validated and robust preclinical model of mitochondrial diseases (specifically Leigh syndrome), that displays a narrow window of relative phenotypical normality, despite its inherent mitochondrial complex I dysfunction and severe phenotype. Preclinical observations related to psychiatric comorbidities that arise in patients with mitochondrial diseases and indeed in Leigh syndrome are, however, yet to be investigated in this model. Strengthening this narrative is the fact that major depression and bipolar disorder are known to present with deficits in mitochondrial function. We therefore screened the behavioural profile of male and female Ndufs4 KO mice (relative to heterozygous; HET and wildtype; WT mice) between postnatal days 28 and 35 for locomotor, depressive- and anxiety-like alterations and linked it with selected brain biomarkers, viz. serotonin, kynurenine, and redox status in brain areas relevant to psychiatric pathologies (i.e., prefrontal cortex, hippocampus, and striatum). The Ndufs4 KO mice initially displayed depressive-like behaviour in the tail suspension test on PND31 but not on PND35 in the forced swim test. In the mirror box test, increased risk resilience was observed. Serotonin levels of KO mice, compared to HET controls, were increased on PND36, together with increased tryptophan to serotonin and kynurenine turnover. Kynurenine to kynurenic acid turnover was however decreased, while reduced versus oxidized glutathione ratio (GSH/GSSG) was increased. When considering the comorbid psychiatric traits of patients with mitochondrial disorders, this work elaborates on the neuropsychiatric profile of the Ndufs KO mouse. Secondly, despite locomotor differences, Ndufs4 KO mice present with a behavioural profile not unlike rodent models of bipolar disorder, namely variable mood states and risk-taking behaviour. The model may elucidate the bio-energetic mechanisms underlying mood disorders, especially in the presence of mitochondrial disease. Studies are however required to further validate the model's translational relevance.

Dose-Dependent Beneficial Effect of Ketone Supplement-Evoked Ketosis on Anxiety Level in Female WAG/Rij Rats: Sometimes Less Is More

While one-third of the population can be affected by anxiety disorders during their lifetime, our knowledge of the pathophysiology of these disorders is far from complete. Previously, it has been demonstrated in male animals that exogenous ketone supplement-evoked ketosis can decrease anxiety levels in preclinical rodent models, such as Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats. Thus, in this study, we investigated whether intragastric gavage of the exogenous ketone supplement KEMCT (mix of 1,3-butanediol-acetoacetate diester/ketone ester/KE and medium-chain triglyceride/MCT oil in 1:1 ratio) for 7 days can alter the anxiety levels of female WAG/Rij rats using the light-dark box (LDB) test. We demonstrated that a lower dose of KEMCT (3 g/kg/day) increased blood R-βHB (R-β-hydroxybutyrate) levels and significantly decreased anxiety levels (e.g., increased the time spent in the light compartment) in female WAG/Rij rats on the seventh day of administration. Although the higher KEMCT dose (5 g/kg/day) increased blood R-βHB levels more effectively, compared with the lower KEMCT dose, anxiety levels did not improve significantly. We conclude that ketone supplementation might be an effective strategy to induce anxiolytic effects not only in male but also in female WAG/Rij rats. However, these results suggest that the optimal level may be moderately, not highly, elevated blood R-βHB levels when the goal is to alleviate symptoms of anxiety. More studies are needed to understand the exact mechanism of action of ketone supplementation on anxiety levels and to investigate their use in other animal models and humans for the treatment of anxiety disorders and other mental health conditions.

Investigation of the protective effect of long-term exercise on molecular pathways and behaviours in scopolamine induced alzheimer's disease-like condition

Despite research, the role of exercise in treatment and prevention of neurodegenerative diseases remains unclear. Our study, investigated that protective effect of treadmill exercise on molecular pathways and cognitive behaviours in a scopolamine-induced model of Alzheimer's disease. For that purpose, male Balb/c mice subjected to exercise for 12 weeks. During the last 4 weeks of exercise, mice were given an injection of scopolamine (2 mg/kg). Following injection, open field test and Morris water maze test were used to assess emotional-cognitive behaviour. Hippocampus and prefrontal cortex of mice were isolated, and levels of BDNF, TrkB, and p-GSK3ßSer389 were assessed by western blotting, and levels of APP and Aß-40 were analysed by immunohistochemistry. In our study, scopolamine administration increased anxiety-like behaviour in open field test, while negatively affecting spatial learning and memory in Morris water maze test. We found that exercise had a protective effect against cognitive and emotional decline. Scopolamine decreased levels of p-GSK3ßSer389, BDNF in hippocampus and prefrontal cortex.Whereas TrkB decreased in hippocampus and increased in prefrontal cortex. There was an increase in p-GSK3ßSer389, BDNF, TrkB in the hippocampus, and p-GSK3ßSer389, BDNF in the prefrontal cortex in the exercise + scopolamine group. Immunohistochemical analysis showed that scopolamine administration increased APP and Aß-40 in hippocampus and prefrontal cortex in neuronal and perineuronal areas whereas Aß-40 and APP were reduced in exercise + scopolamine groups. In conclusion, long-term exercise may have a protective effect against scopolamine-induced impairments in cognitive-emotional behaviour. It can be suggested that this protective effect is mediated by increased BDNF levels and GSK3ßSer389 phosphorylation.

Escitalopram and lorazepam differentially affect nesting and open field behaviour in deer mice exposed to an anxiogenic environment

Large nest building behaviour (LNB), as expressed by a subpopulation of laboratory housed deer mice (Peromyscus maniculatus bairdii), is persistent and repetitive. However, the response of LNB to an anxiogenic environment has not yet been investigated. Here, we employed LNB and normal nesting (NNB) expressing mice, subdivided into three drug-exposed groups per cohort, i.e. water (28 days), escitalopram (50 mg/kg/day, 28 days) and lorazepam (2 mg/kg/day; 4 days) to investigate this theme. During the last 4 days of drug exposure, mice were placed inside anxiogenic open field arenas which contained a separate enclosed and dark area for 4 consecutive nights during which open field and/or nest building assessments were performed. We show that LNB behaviour in deer mice is stable, irrespective of the anxiety-related context in which it is assessed, and that LNB mice find an open field arena to be less aversive compared to NNB mice. Escitalopram and lorazepam differentially affected the nesting and open field behaviour of LNB expressing mice, confirming deer mouse LNB as a repetitive behavioural phenotype that is related to a compulsive-like process which is regulated by the serotonergic system.

Muscarinic regulation of self-grooming behavior and ultrasonic vocalizations in the context of open-field habituation in rats

Laboratory rats repeatedly exposed to an open field (OF) apparatus display increasingly high levels of grooming -especially that characterized by long and complex sequences- which has been taken as an additional index of novelty habituation. We hypothesized that disrupting such a learning process by administering an amnesic drug as the antimuscarinic scopolamine (SCP) could delay the appearance of more complex grooming subtypes. Thus, rats were pretreated either with SCP (15 mg/kg or 30 mg/kg) or vehicle (VEH) upon four one-day apart OF (OF1-4). On a fifth assessment, all rats received VEH to analyze the likely carry-over effect of SCP. Finally, we measured 50-kHz and 22-kHz ultrasonic vocalizations (USVs) as reliable markers of positive and negative emotionality, respectively. We found that SCP increased locomotion during OF1 and reduced rearing on OF1-OF4, causing no disruption in habituation over tests. SCP prevented the increase of total grooming time by inhibiting complex grooming subtypes and promoting short cephalic sequences. Despite the SCP-induced alterations on grooming agreed with our hypotheses, those changes may have resulted from a motor impairment that could have also affected rearing behavior. Additionally, SCP suppressed 50-kHz USVs while marginally increased 22-kHz calls. Once SCP was withdrawn, rearing, grooming, and some 50-kHz USVs subtypes returned to VEH levels, suggesting that novelty habituation occurred despite the SCP administration. Altogether, that mixed profile of SCP-induced behavioral changes may derive from the complex interplay between the contrasting action of SCP on different brain regions and the doses here used.

Central Administration of Ampelopsin A Isolated from Vitis vinifera Ameliorates Cognitive and Memory Function in a Scopolamine-Induced Dementia Model

Neurodegenerative diseases are characterized by the progressive degeneration of the function of the central nervous system or peripheral nervous system and the decline of cognition and memory abilities. The dysfunctions of the cognitive and memory battery are closely related to inhibitions of neurotrophic factor (BDNF) and brain-derived cAMP response element-binding protein (CREB) to associate with the cholinergic system and long-term potentiation. Vitis vinifera, the common grapevine, is viewed as the important dietary source of stilbenoids, particularly the widely-studied monomeric resveratrol to be used as a natural compound with wide-ranging therapeutic benefits on neurodegenerative diseases. Here we found that ampelopsin A is a major compound in V. vinifera and it has neuroprotective effects on experimental animals. Bath application of ampelopsin A (10 ng/µL) restores the long-term potentiation (LTP) impairment induced by scopolamine (100 μM) in hippocampal CA3-CA1 synapses. Based on these results, we administered the ampelopsin A (10 ng/µL, three times a week) into the third ventricle of the brain in C57BL/6 mice for a month. Chronic administration of ampelopsin A into the brain ameliorated cognitive memory-behaviors in mice given scopolamine (0.8 mg/kg, i.p.). Studies of mice’s hippocampi showed that the response of ampelopsin A was responsible for the restoration of the cholinergic deficits and molecular signal cascades via BDNF/CREB pathways. In conclusion, the central administration of ampelopsin A contributes to increasing neurocognitive and neuroprotective effects on intrinsic neuronal excitability and behaviors, partly through elevated BDNF/CREB-related signaling.

The Pharmacology of Visual Hallucinations in Synucleinopathies

Visual hallucinations (VH) are commonly found in the course of synucleinopathies like Parkinson's disease and dementia with Lewy bodies. The incidence of VH in these conditions is so high that the absence of VH in the course of the disease should raise questions about the diagnosis. VH may take the form of early and simple phenomena or appear with late and complex presentations that include hallucinatory production and delusions. VH are an unmet treatment need. The review analyzes the past and recent hypotheses that are related to the underlying mechanisms of VH and then discusses their pharmacological modulation. Recent models for VH have been centered on the role played by the decoupling of the default mode network (DMN) when is released from the control of the fronto-parietal and salience networks. According to the proposed model, the process results in the perception of priors that are stored in the unconscious memory and the uncontrolled emergence of intrinsic narrative produced by the DMN. This DMN activity is triggered by the altered functioning of the thalamus and involves the dysregulated activity of the brain neurotransmitters. Historically, dopamine has been indicated as a major driver for the production of VH in synucleinopathies. In that context, nigrostriatal dysfunctions have been associated with the VH onset. The efficacy of antipsychotic compounds in VH treatment has further supported the notion of major involvement of dopamine in the production of the hallucinatory phenomena. However, more recent studies and growing evidence are also pointing toward an important role played by serotonergic and cholinergic dysfunctions. In that respect, in vivo and post-mortem studies have now proved that serotonergic impairment is often an early event in synucleinopathies. The prominent cholinergic impairment in DLB is also well established. Finally, glutamatergic and gamma aminobutyric acid (GABA)ergic modulations and changes in the overall balance between excitatory and inhibitory signaling are also contributing factors. The review provides an extensive overview of the pharmacology of VH and offers an up to date analysis of treatment options.

DARK Classics in Chemical Neuroscience: Atropine, Scopolamine, and Other Anticholinergic Deliriant Hallucinogens

Anticholinergic drugs based on tropane alkaloids, including atropine, scopolamine, and hyoscyamine, have been used for various medicinal and toxic purposes for millennia. These drugs are competitive antagonists of acetylcholine muscarinic (M-) receptors that potently modulate the central nervous system (CNS). Currently used clinically to treat vomiting, nausea, and bradycardia, as well as alongside other anesthetics to avoid vagal inhibition, these drugs also evoke potent psychotropic effects, including characteristic delirium-like states with hallucinations, altered mood, and cognitive deficits. Given the growing clinical importance of anti-M deliriant hallucinogens, here we discuss their use and abuse, clinical importance, and the growing value in preclinical (experimental) animal models relevant to modeling CNS functions and dysfunctions.

Establishing zebrafish as a model to study the anxiolytic effects of scopolamine

Scopolamine (hyoscine) is a muscarinic acetylcholine receptor antagonist that has traditionally been used to treat motion sickness in humans. However, studies investigating depressed and bipolar populations have found that scopolamine is also effective at reducing depression and anxiety symptoms. The potential anxiety-reducing (anxiolytic) effects of scopolamine could have great clinical implications for humans; however, rats and mice administered scopolamine showed increased anxiety in standard behavioural tests. This is in direct contrast to findings in humans, and complicates studies to elucidate the specific mechanisms of scopolamine action. The aim of this study was to assess the suitability of zebrafish as a model system to test anxiety-like compounds using scopolamine. Similar to humans, scopolamine acted as an anxiolytic in individual behavioural tests (novel approach test and novel tank diving test). The anxiolytic effect of scopolamine was dose dependent and biphasic, reaching maximum effect at 800 µM. Scopolamine (800 µM) also had an anxiolytic effect in a group behavioural test, as it significantly decreased their tendency to shoal. These results establish zebrafish as a model organism for studying the anxiolytic effects of scopolamine, its mechanisms of action and side effects.

High Resolution UHPLC-MS Metabolomics and Sedative-Anxiolytic Effects of Latua pubiflora: A Mystic Plant used by Mapuche Amerindians

Latua pubiflora (Griseb) Phil. Is a native shrub of the Solanaceae family that grows freely in southern Chile and is employed among Mapuche aboriginals to induce sedative effects and hallucinations in religious or medicine rituals since prehispanic times. In this work, the pentobarbital-induced sleeping test and the elevated plus maze test were employed to test the behavioral effects of extracts of this plant in mice. The psychopharmacological evaluation of L. pubiflora extracts in mice determined that both alkaloid-enriched as well as the non-alkaloid extracts produced an increase of sleeping time and alteration of motor activity in mice at 150 mg/Kg. The alkaloid extract exhibited anxiolytic effects in the elevated plus maze test, which was counteracted by flumazenil. In addition, the alkaloid extract from L. pubiflora decreased [³H]-flunitrazepam binding on rat cortical membranes. In this study we have identified 18 tropane alkaloids (peaks 1-4, 8-13, 15-18, 21, 23, 24, and 28), 8 phenolic acids and related compounds (peaks 5-7, 14, 19, 20, 22, and 29) and 7 flavonoids (peaks 25-27 and 30-33) in extracts of L. pubiflora by UHPLC-PDA-MS which are responsible for the biological activity. This study assessed for the first time the sedative-anxiolytic effects of L. pubiflora in rats besides the high resolution metabolomics analysis including the finding of pharmacologically important tropane alkaloids and glycosylated flavonoids.

Estrogen levels modify scopolamine-induced amnesia in gonadally intact rats

Previous studies suggested that estrogen plays a role in cognitive function by modulating the cholinergic transmission. However, most of the studies dealing with this subject have been conducted using ovariectomized rats. In the present study we evaluated the effects of physiological and supra-physiological variation of estrogen levels on scopolamine-induced amnesia in gonadally intact female rats. We used the plus-maze discriminative avoidance task (PMDAT) in order to evaluate anxiety levels and motor activity concomitantly to the memory performance. In experiment 1, female Wistar rats in each estrous cycle phase received scopolamine (1 mg/kg) or saline i.p. 20 min before the training session in the PMDAT. In experiment 2, rats in diestrus received estradiol valerate (1 mg/kg) or sesame oil i.m., and scopolamine (1 mg/kg) or saline i.p., 45 min and 20 min before the training, respectively. In experiment 3, rats in diestrus received scopolamine (1 mg/kg) or saline i.p. 20 min before the training, and estradiol valerate (1 mg/kg) or sesame oil i.m. immediately after the training session. In all experiments, a test session was performed 24 h later. The main results showed that: (1) scopolamine impaired retrieval and induced anxiolytic and hyperlocomotor effects in all experiments; (2) this cholinergic antagonist impaired acquisition only in animals in diestrus; (3) acute administration of estradiol valerate prevented the learning impairment induced by scopolamine and (4) interfered with memory consolidation process. The results suggest that endogenous variations in estrogen levels across the estrous cycle modulate some aspects of memory mediated by the cholinergic system. Indeed, specifically in diestrus, a stage with low estrogen levels, the impairment produced by scopolamine on the acquisition was counteracted by exogenous administration of the hormone, whereas the posttraining treatment potentiated the negative effects of scopolamine during the consolidation phase of memory.

Insular muscarinic signaling regulates anxiety-like behaviors in rats on the elevated plus-maze

Anxiety is one of the most prevalent neuropsychiatric disorders, and little is known about its pathogenesis. In order to investigate the neural mechanisms of this mental disorder, we used rat behavior in the elevated plus-maze as an animal model of anxiety and the insular cortex (insula) as a brain target. The microinjection of non-selective and selective M1 and M4 muscarinic acetylcholine receptor (mAChR) agonists or antagonists was used to explore whether the insular muscarinic receptor and its subtypes regulate levels of anxiety. The results showed that both non-selective and selective M1 and M4 mAChR agonists increased the time spent on exploring in the open arms, whereas antagonists decreased exploration. Our results indicate that activation of insular mAChRs could produce anxiolytic effects, whereas inhibition of insular mAChRs could increase anxiety. We concluded that the insular muscarinic system plays a role in the modulation of anxiety, and dysfunction of mAChR signaling may be involved in the mechanism of anxiogenesis.

Anxiety status affects nicotine- and baclofen-induced locomotor activity, anxiety, and single-trial conditioned place preference in male adolescent rats

Adolescents have an increased vulnerability to nicotine and anxiety may play a role in the development of nicotine abuse. One possible treatment for anxiety disorders and substance abuse is the GABAB agonist, baclofen. The aim of the present study was to determine the effect of anxiety-like behavior on single-trial nicotine conditioned place preference in adolescent rats, and to assess the action of baclofen. Baclofen was shown to have effects on locomotor and anxiety-like behavior in rats divided into high-anxiety and low-anxiety groups. Baclofen decreased locomotor behavior in high-anxiety rats. Baclofen alone failed to produce differences in anxiety-like behavior, but nicotine and baclofen + nicotine administration were anxiolytic. High- and low-anxiety groups also showed differences in single-trial nicotine-induced place preference. Only high-anxiety rats formed place preference to nicotine, while rats in the low-anxiety group formed no conditioned place preference. These results suggest that among adolescents, high-anxiety individuals are more likely to show preference for nicotine than low-anxiety individuals.

Blockade of muscarinic receptors impairs the retrieval of well-trained memory

Acetylcholine (ACh) is known to play an important role in memory functions, and its deficit has been proposed to cause the cognitive decline associated with advanced age and Alzheimer's disease (the cholinergic hypothesis). Although many studies have tested the cholinergic hypothesis for recently acquired memory, only a few have investigated the role of ACh in the retrieval process of well-trained cognitive memory, which describes the memory established from repetition and daily routine. To examine this point, we trained rats to perform a two-alternative forced-choice visual detection task. Each trial was started by having the rats pull upward a central-lever, which triggered the presentation of a visual stimulus to the right or left side of the display monitor, and then pulling upward a stimulus-relevant choice-lever located on both sides. Rats learned the task within 10 days, and the task training was continued for a month. Task performance was measured with or without systemic administration of a muscarinic ACh receptor (mAChR) antagonist, scopolamine (SCOP), prior to the test. After 30 min of SCOP administration, rats stopped manipulating any lever even though they explored the lever and surrounding environment, suggesting a loss of the task-related associative memory. Three hours later, rats were recovered to complete the trial, but the rats selected the levers irrespective of the visual stimulus, suggesting they remembered a series of lever-manipulations in association with a reward, but not association between the reward and visual stimulation. Furthermore, an m1-AChR, but not nicotinic AChR antagonist caused a similar deficit in the task execution. SCOP neither interfered with locomotor activity nor drinking behavior, while it influenced anxiety. These results suggest that the activation of mAChRs at basal ACh levels is essential for the recall of well-trained cognitive memory.

Cholinergic blockade reduces theta-gamma phase amplitude coupling and speed modulation of theta frequency consistent with behavioral effects on encoding

Large-scale neural activation dynamics in the hippocampal-entorhinal circuit local field potential, observable as theta and gamma rhythms and coupling between these rhythms, is predictive of encoding success. Behavioral studies show that systemic administration of muscarinic acetylcholine receptor antagonists selectively impairs encoding, suggesting that they may also disrupt the coupling between the theta and gamma bands. Here, we tested the hypothesis that muscarinic antagonists selectively disrupt coupling between theta and gamma. Specifically, we characterized the effects of systemically administered scopolamine on movement-induced theta and gamma rhythms recorded in the superficial layers of the medial entorhinal cortex (MEC) of freely moving rats. We report the novel result that gamma power at the peak of theta was most reduced following muscarinic blockade, significantly shifting the phase of maximal gamma power to occur at later phases of theta. We also characterize the existence of multiple distinct gamma bands in the superficial layers of the MEC. Further, we observed that theta frequency was significantly less modulated by movement speed following muscarinic blockade. Finally, the slope relating speed to theta frequency, a correlate of familiarity with a testing enclosure, increased significantly less between the preinjection and recovery trials when scopolamine was administered during the intervening injection session than when saline was administered, suggesting that scopolamine reduced encoding of the testing enclosure. These data are consistent with computational models suggesting that encoding and retrieval occur during the peak and trough of theta, respectively, and support the theory that acetylcholine regulates the balance between encoding versus retrieval.

Roles of p75(NTR), long-term depression, and cholinergic transmission in anxiety and acute stress coping

BACKGROUND

Stress is causally associated with anxiety. Although the underlying cellular mechanisms are not well understood, the basal forebrain cholinergic neurons have been implicated in stress response. p75(NTR) is a panneurotrophin receptor expressed almost exclusively in basal forebrain cholinergic neurons in adult brain. This study investigated whether and how p75(NTR), via regulation of the cholinergic system and hippocampal synaptic plasticity, influences stress-related behaviors.

METHODS

We used a combination of slice electrophysiology, behavioral analyses, pharmacology, in vivo microdialysis, and neuronal activity mapping to assess the role of p75(NTR) in mood and stress-related behaviors and its underlying cellular and molecular mechanisms.

RESULTS

We show that acute stress enables hippocampal long-term depression (LTD) in adult wild-type mice but not in mice lacking p75(NTR). The p75(NTR) mutant mice also exhibit two distinct behavioral impairments: baseline anxiety-like behavior and a deficit in coping with and recovering from stressful situations. Blockade of stress-enabled LTD with a GluA2-derived peptide impaired stress recovery without affecting baseline anxiety. Pharmacological manipulations of cholinergic transmission mimicked the p75(NTR) perturbation in both baseline anxiety and responses to acute stress. Finally, we show evidence of misregulated cholinergic signaling in animals with p75(NTR) deletion.

CONCLUSIONS

Our results suggest that loss of p75(NTR) leads to changes in hippocampal cholinergic signaling, which may be involved in regulation of stress-enabled hippocampal LTD and in modulating behaviors related to stress and anxiety.

Altered temporal patterns of anxiety in aged and amyloid precursor protein (APP) transgenic mice

Both normal aging and dementia are associated with dysregulation of the biological clock, which contributes to disrupted circadian organization of physiology and behavior. Diminished circadian organization in conjunction with the loss of cholinergic input to the cortex likely contributes to impaired cognition and behavior. One especially notable and relatively common circadian disturbance among the aged is "sundowning syndrome," which is characterized by exacerbated anxiety, agitation, locomotor activity, and delirium during the hours before bedtime. Sundowning has been reported in both dementia patients and cognitively intact elderly individuals living in institutions; however, little is known about temporal patterns in anxiety and agitation, and the neurobiological basis of these rhythms remains unspecified. In the present study, we explored the diurnal pattern of anxiety-like behavior in aged and amyloid precursor protein (APP) transgenic mice. We then attempted to treat the observed behavioral disturbances in the aged mice using chronic nightly melatonin treatment. Finally, we tested the hypothesis that time-of-day differences in acetylcholinesterase and choline acetyltransferase expression and general neuronal activation (i.e., c-Fos expression) coincide with the behavioral symptoms. Our results show a temporal pattern of anxiety-like behavior that emerges in elderly mice. This behavioral pattern coincides with elevated locomotor activity relative to adult mice near the end of the dark phase, and with time-dependent changes in basal forebrain acetylcholinesterase expression. Transgenic APP mice show a similar behavioral phenomenon that is not observed among age-matched wild-type mice. These results may have useful applications to the study and treatment of age- and dementia-related circadian behavioral disturbances, namely, sundowning syndrome.

Cholinergic receptor subtypes and their role in cognition, emotion, and vigilance control: an overview of preclinical and clinical findings

RATIONALE

The cholinergic system has long been linked to cognitive processes. Two main classes of acetylcholine (ACh) receptors exist in the human brain, namely muscarinic and nicotinic receptors, of which several subtypes occur.

OBJECTIVES

This review seeks to provide an overview of previous findings on the influence of cholinergic receptor manipulations on cognition in animals and humans, with particular emphasis on the role of selected cholinergic receptor subtypes. Furthermore, the involvement of these receptor subtypes in the regulation of emotion and brain electrical activity as measured by electroencephalography (EEG) shall be addressed since these domains are considered to be important modulators of cognitive functioning.

RESULTS

In regard to cognition, the muscarinic receptor subtypes have been implicated mainly in memory functions, but have also been linked to attentional processes. The nicotinic α7 receptor subtype is involved in working memory, whereas the α4β2* subtype has been linked to tests of attention. Both muscarinic and nicotinic cholinergic mechanisms play a role in modulating brain electrical activity. Nicotinic receptors have been strongly associated with the modulation of depression and anxiety.

CONCLUSIONS

Cholinergic receptor manipulations have an effect on cognition, emotion, and brain electrical activity as measured by EEG. Changes in cognition can result from direct cholinergic receptor manipulation or from cholinergically induced changes in vigilance or affective state.

Methylthioninium chloride reverses cognitive deficits induced by scopolamine: comparison with rivastigmine

RATIONALE

The cholinergic system is involved in cognition as well as in age-related cognitive decline and Alzheimer disease (AD). Cholinergic enhancers ameliorate AD symptoms and represent the main current therapy for AD. MTC (Methylthioninium chloride), an antioxidant with metabolism-enhancing properties may be a novel candidate with pro-cognitive capacities.

OBJECTIVES

This study was performed: (1) to assess the pro-cognitive efficacy of MTC and establish its dose-response; (2) to compare the efficacy of MTC with rivastigmine and (3) to determine the potential for combination therapy by co-administration of MTC and rivastigmine.

METHODS

Spatial cognition of female NMRI mice was tested in a reference memory water maze task. Subjects received intra-peritoneal injections of scopolamine (0.5 mg/kg) followed by vehicle, and/or MTC and/or rivastigmine (0.15-4 mg/kg MTC; 0.1-0.5 mg/kg rivastigmine) in mono or combination treatment.

RESULTS

Scopolamine treatment prevented spatial learning in NMRI female mice and the deficit was reversed by both rivastigmine and MTC in a dose-dependent manner. Mono-therapy with high doses of rivastigmine (>0.5 mg/kg) caused severe side effects but MTC was safe up to 4 mg/kg. Co-administration of sub-effective doses of both drugs acted synergistically in reversing learning deficits and scopolamine-induced memory impairments.

CONCLUSIONS

In our model, MTC reversed the spatial learning impairment. When combined with the ChEI rivastigmine, the effect of MTC appeared to be amplified indicating that combination therapy could potentially improve not only symptoms but also contribute beneficially to neuronal metabolism by minimising side effects at lower doses.

Self-reported motivation to smoke in schizophrenia is related to antipsychotic drug treatment

PURPOSE

The prevalence of smoking in schizophrenia has reliably been reported as being higher than for any other psychiatric disorder. While a number of theories have been proposed to account for such high rates of smoking, little is known about the subjective motivation for why schizophrenia patients smoke in comparison with those without the disease.

OBJECTIVES

The aim of the present study was to evaluate and compare smoking motivation in control subjects and schizophrenia patients, and determine if factors such as type of medication or access to cigarettes could contribute to self-reported motivation for smoking.

METHODS

We assessed motivation to smoke in 61 schizophrenia inpatients and 33 non-psychiatric health worker controls at a tertiary care psychiatric facility in a cross-sectional study. Nicotine dependency and smoking behavior were evaluated using the Fagerstrom Test for Nicotine Dependence and a validated questionnaire that assesses motivation for smoking along seven different dimensions.

RESULTS

Schizophrenia patients reported a stronger motivation to smoke than controls for reasons related to pleasure from the act of smoking, as well as a need for psychomotor stimulation. Scores on both these factors were significantly associated with daily antipsychotic drug dose. The sedative and anxiolytic effects of smoking were related to anticholinergic load of psychiatric medications.

CONCLUSION

The findings highlight important differences in self-reported motivation to smoke between schizophrenia patients and normals. Antipsychotic drugs may also influence aspects of motivation to smoke.

Comparisons between anxiety tests for selection of anxious and non anxious mice

Male Swiss albinos mice were submitted to two behavioural tests intended to determine their anxiety level: the elevated plus-maze test as well as the black and white compartments test. In addition they were submitted to the hole-board test. It was observed: (i) that the correlation between scores in the two first tests was weak, suggesting that they explore different components of anxiety; (ii) that the score on the latter test was better correlated with the response in the elevated plus-maze test than in the black and white compartments test. From these data three groups of animals were constituted, considered, respectively, as anxious, non anxious and intermediates. It was observed that both horizontal and vertical locomotion in an unfamiliar environment differed between groups, with higher activity in non anxious than in anxious. In the hole-board test, only animals classified as anxious displayed an obvious response to the anxiolytic drug diazepam (0.5mg/kg). Finally in the forced-swimming test, the three groups demonstrated a similar immobility time, suggesting that the operated segregation was not depending on a helpless component. It is proposed that the selection of mice from a combination of either elevated plus-maze and black and white compartments tests or a combination of hole-board test and black and white compartments test, allows to distinguish high or low anxiety animals among a population of mice.

Comparison of anxiety-like behavior in adolescent and adult Sprague-Dawley rats

The conditions under which age differences in anxiety are observed in rodents are unclear. These studies explored the influence of test condition on anxiety-like behavior in adolescent and adult rats using the light-dark box. Behavior was assessed under different illumination levels (30 or 60 lux) and after brief stress (restraint or bright light). Anxiety-like behavior did not differ in the 30-lux test but was increased in adolescents in the 60-lux test. Restraint increased anxiety-like behavior in adolescents, resulting in elevated anxiety-like behavior relative to adults. Bright light decreased anxiety-like behavior, possibly because of negative contrast or novelty-induced anxiolysis. These studies demonstrate that adolescents display increased anxiety-like behavior when test conditions are more aversive and following exposure to stress.

Enhanced prepulse inhibition following adolescent ethanol exposure in Sprague-Dawley rats

OBJECTIVES

Recent studies have demonstrated that ethanol exposure differentially affects adolescents and adults. The current studies were designed to compare the effects of 2-week exposure to ethanol during adolescence or adulthood on the acoustic startle response (ASR) and prepulse inhibition (PPI) METHODS: Male Sprague-Dawley rats were exposed to ethanol vapor 12 hr/d (on from 6 pm to 6 am) for 14 days during adolescence or adulthood. Six days after the cessation of ethanol vapor exposure, the ASR and PPI were assessed.

RESULTS

During ethanol treatment, overall blood alcohol levels averaged 230 to 250 mg/dl in the adolescent and adult treatment groups. Assessment of the ASR revealed that latency to startle was more rapid in adolescents than in adults, but ASR latency was not altered by ethanol exposure. In addition, ASR magnitude was lower in adolescents and was decreased in ethanol-exposed rats on startle trials. Ethanol exposure significantly enhanced PPI, but only after adolescent exposure

CONCLUSIONS

These data further demonstrate a differential sensitivity of adolescents and adults to the effects of ethanol exposure. Specifically, a 2-week period of ethanol exposure during adolescence selectively enhanced PPI, a neurobehavioral index of sensorimotor gating. However, ASR magnitude was decreased by ethanol exposure regardless of age. On the basis of previous studies, the effects of ethanol exposure on PPI data could indicate that adolescent rats exposed to ethanol are more likely to exhibit behavioral inflexibility and that ethanol exposure acts as a more potent physical stressor in adolescent rats.

Behavioral effects and ChE measures after acute and repeated administration of malathion in rats

Organophosphorus compounds such as malathion are environmental contaminants that may evoke neurobehavioral responses including anxiety and depression. In this study, after a functional observational battery, rats were tested in an open field and temperature test to better define doses used in subsequent experiments. Then, we investigated the effects of acute and repeated treatment with malathion on elevated plus-maze and forced-swim test, which are validated animal models to observe for anxiety- and depressive-related behaviors, respectively. We found that both acute and repeated malathion administration induced anxiogenic and depressive-like responses at doses that affected neither locomotion nor systemic temperature. Biochemical assays demonstrated inhibition of cholinesterase activity by these effective doses.

Variations of maternal care differentially influence 'fear' reactivity and regional patterns of cFos immunoreactivity in response to the shock-probe burying test

Natural variations in maternal care in the rat influence the development of neuronal systems that regulate endocrine and behavioral responses to stress. Thus, as adults, rats that received higher levels of maternal licking/grooming (LG) in infancy are less 'fearful' in response to novelty, compared with adult offspring of Low LG mothers. The present study examined the influence of maternal care on behavioral and neuronal responses to a more specific, localizable form of threat using an electrified probe in the shock-probe burying test. Even under these conditions, adult offspring of High LG mothers displayed lower levels of fear reactivity (i.e. less shock-induced freezing and probe burying) throughout the test than did offspring of Low LG mothers. These differences in fearfulness were associated with differential patterns of cFos immunoreactivity (cFos-IR), 120 min following test exposure. Relative to control rats exposed to a non-electrified probe, cFos-IR was increased in the offspring of High LG mothers exposed to an electrified probe in the dentate gyrus, ventral subiculum, lateral and medial septum, nucleus accumbens and the dorsal periaqueductal gray. Shock-exposed offspring of Low LG dams displayed a very different pattern of neuronal activation characterized by both increases (area CA1 of the ventral hippocampus and the inferior colliculus) and decreases (paraventricular nucleus of the hypothalamus and the ventrolateral periaqueductal gray) in cFos-IR compared with the no-shock controls. Together these results suggest that maternal care serves to 'program' neuronal circuits that modulate fear-related responding in the rat resulting in qualitatively different neuronal responses to stress.

Disruption of mice sleep stages induced by low doses of organophosphorus compound soman

We have explored during 7 days, EEG spectral response and sleep pattern of mice after a mild intoxication with soman. Using an automatic staging method, we have quantified the sleep stage of the mice to identify disruptions of the sleep pattern. The 50 microg/kg dose of soman produced several effects during several time windows after intoxication. A first decrease followed by an increase of theta energy, a disturbance of slow wave sleep during 5 days and an increase of the REM sleep during the first and second day after intoxication. During the first 6h, we have observed some effects which were not consistent with a muscarinic activation and might have involved GABA-ergic system. After this early period, the observed effects were in accordance with a muscarinic activation. We observed an increase of energy in the EEG theta band during 3 days after soman injection and an increase of slow wave sleep during the second to the fifth day after soman injection.

Addictive and non-addictive drugs induce distinct and specific patterns of ERK activation in mouse brain

A major goal of research on addiction is to identify the molecular mechanisms of long-lasting behavioural alterations induced by drugs of abuse. Cocaine and delta-9-tetrahydrocannabinol (THC) activate extracellular signal-regulated kinase (ERK) in the striatum and blockade of the ERK pathway prevents establishment of conditioned place preference to these drugs. However, it is not known whether activation of ERK in the striatum is specific for these two drugs and/or this brain region. We studied the appearance of phospho-ERK immunoreactive neurons in CD-1 mouse brain following acute administration of drugs commonly abused by humans, cocaine, morphine, nicotine and THC, or of other psychoactive compounds including caffeine, scopolamine, antidepressants and antipsychotics. Each drug generated a distinct regional pattern of ERK activation. All drugs of abuse increased ERK phosphorylation in nucleus accumbens, lateral bed nucleus of the stria terminalis, central amygdala and deep layers of prefrontal cortex, through a dopamine D1 receptor-dependent mechanism. Although some non-addictive drugs moderately activated ERK in a few of these areas, they never induced this combined pattern of strong activation. Antidepressants and caffeine activated ERK in hippocampus and cerebral cortex. Typical antipsychotics mildly activated ERK in dorsal striatum and superficial prefrontal cortex, whereas clozapine had no effect in the striatum, but more widespread effects in cortex and amygdala. Our results outline a subset of structures in which ERK activation might specifically contribute to the long-term effects of drugs of abuse, and suggest mapping ERK activation in brain as a way to identify potential sites of action of psychoactive drugs.

The chick separation stress paradigm: a validation study

To expand the generalizability of the chick separation stress paradigm as a high-throughput anxiolytic screen, six positive drug probes (doses in mg/kg: meprobamate 15-120, pentobarbital 2.5-20.0, chlordiazepoxide 2.5-15.0, buspirone 2.5-10.0, imipramine 1-15, and clonidine 0.10-0.25) and five negative drug probes (amphetamine 0.5-4.0, scopolamine 0.2-1.6, caffeine 5-20, chlorpromazine 1-30, and haloperidol 0.03-1.00) were evaluated in the test. Seven-day-old chicks received intramuscular injections of either vehicle or drug probe 15 min prior to tests in either a mirror (low-stress) or a no-mirror (high-stress) condition for a 3-min observation period. The dependent measures were distress vocalizations to index separation stress and sleep onset latency to index sedation. All positive drug probes attenuated distress vocalizations in a dose-dependent manner, except buspirone. All positive drug probes affected sleep onset latency in a dose-dependent manner, except buspirone and imipramine. In all cases, the anxiolytic-like effect of positive drug probes was greater than its sedative effect. None of the negative drug probes affected either distress vocalizations or sleep onset latency, except for the highest dose of amphetamine, which caused pronounced stereotypy. These findings demonstrate that this anxiolytic screen is sensitive to a wide range of positive pharmacological probes and insensitive to a wide range of negative pharmacological probes.

Dorsal and ventral hippocampal cholinergic systems modulate anxiety in the plus-maze and shock-probe tests

There is emerging evidence that increased acetylcholine levels in brain reduce anxiety. More specifically there is evidence that some of these anxiolytic effects of acetylcholine are modulated by the hippocampus. In the present study we examined the roles of the cholinergic systems in the dorsal and ventral hippocampus in two animal models of anxiety: the elevated plus-maze and the shock-probe burying tests. We found that microinfusions (10 microg/0.5 microl) of the acetylcholinesterase inhibitor physostigmine in either the dorsal or the ventral hippocampus increased rats' open arm exploration in the plus-maze test, and decreased burying behavior in the shock-probe test. Interestingly, infusions in the ventral, but not the dorsal hippocampus also increased the number of contacts rats made with the shock-probe. Overall, the results suggest that cholinergic stimulation in the dorsal and ventral hippocampus modulate anxiety, but that only the ventral hippocampal cholinergic system is involved in the passive avoidance of painful stimuli.

Effects of excitotoxic median raphe lesion on working memory deficits produced by the dorsal hippocampal muscarinic receptor blockade in the inhibitory avoidance in rats

The experiments investigated the interactions between median raphe nucleus (MRN) serotonergic and septo-hippocampal muscarinic cholinergic systems in the modulation of forming and storing performances of working memory. Rats with ibotenic acid-induced MRN-lesion bilaterally received scopolamine (2-4 microg/each side) infusion into the dentate gyrus of the dorsal hippocampus and were tested in a single trial step-through inhibitory avoidance. Initial preference to the dark compartment (escape latency) was taken as the measure of non-mnemonic behaviours and response latency to enter the dark compartment immediately after the foot-shock was used to measure working memory. The high-dose scopolamine infusion 10 min before the training decreased escape latencies in the sham-lesioned rats, whereas had no effect in the MRN-lesioned rats. Although MRN lesion per se did not alter response latency, it alleviated pre-training scopolamine-induced decrease, but aggravated post-training scopolamine-induced reduction in this parameter. These results suggest that the antagonistic interactive processes between MRN-serotonergic and hippocampal cholinergic systems modulate non-mnemonic component of working memory formation, whereas the storing performance of working memory is modulated by the synergistic interactions between these systems in the hippocampus, mainly in the dentate gyrus.

Effects of molsidomine on scopolamine-induced amnesia and hypermotility in the rat

Nitric oxide (NO) is hypothesized to be a novel intracellular messenger in the central nervous system. Recently, NO involvement in learning and memory processes has been proposed. Compounds that inhibit nitric oxide synthase, the key synthesizing enzyme, may block cognition, while NO donors may facilitate it. The aim of this study was to assess in the rat the effects of the NO donor molsidomine (2 and 4 mg/kg, i.p.) on memory deficits caused by scopolamine. For this purpose, the object recognition task and the step-through passive avoidance procedure were chosen. In addition, the effects of molsidomine in antagonizing the scopolamine-induced hypermotility were also examined. Scopolamine at 0.2 mg/kg (object recognition) and 0.75 mg/kg (passive avoidance) disrupted acquisition in both the tasks and induced locomotor hyperactivity at the dose of 0.2 mg/kg. Molsidomine at either dose reversed the scopolamine-induced deficits in the object recognition paradigm but did not counteract the hypermotility and the deficits occurred in the passive avoidance test. These results suggest that to some extent, the NO donor molsidomine is involved in memory processing.

Hyperactivity and intact hippocampus-dependent learning in mice lacking the M1 muscarinic acetylcholine receptor

Members of the muscarinic acetylcholine receptor family are thought to play key roles in the regulation of a large number of important functions of the CNS. However, the precise roles of the individual muscarinic receptor subtypes in modulating these processes are not well understood at present, primarily because of the lack of ligands with sufficient receptor subtype selectivity. To investigate the behavioral significance of the M(1) muscarinic receptor (M(1)R), which is abundantly expressed in the forebrain, we subjected M(1) receptor-deficient mice (M(1)R(-/-) mice) to a battery of behavioral tests. M(1)R(-/-) mice showed no significant impairments in neurological reflexes, motor coordination, pain sensitivity, and prepulse inhibition. Strikingly, however, M(1)R(-/-) mice consistently exhibited a pronounced increase in locomotor activity in various tests, including open field, elevated plus maze, and light/dark transition tests. Moreover, M(1)R(-/-) mice showed reduced immobilization in the Porsolt forced swim test and reduced levels of freezing after inescapable footshocks, suggesting that M(1)R(-/-) mice are hyperactive under stressful conditions as well. An increased number of social contacts was observed in a social interaction test. Surprisingly, M(1)R(-/-) mice displayed no significant cognitive impairments in the Morris water maze and in contextual fear conditioning. M(1)R(-/-) mice showed slight performance deficits in auditory-cued fear conditioning and in an eight-arm radial maze, most likely because of the hyperactivity phenotype displayed by the M(1)R(-/-) mice. Our results indicate that M(1) muscarinic receptors play an important role in the regulation of locomotor activity but appear to be less critical for cognitive processes, as generally assumed.

Interaction between the cholinergic system and CRH in the modulation of spatial discrimination learning in mice

Both cholinergic and CRH systems have been linked to cognitive processes such as learning and memory, and neuroanatomical as well as neurochemical evidence suggests important interactions between these two systems. Moreover, recent reports of pro-mnestic effects of CRH open the possibility that CRH could have beneficial effects in animals with cholinergic dysfunction. In a first experiment, spatial discrimination of C57BL/6 mice treated with various doses of scopolamine (0.5--2.0 mg/kg IP) was tested in a two-choice water maze task. Scopolamine, but not methylscopolamine, impaired accuracy and decreased responsivity. In contrast, similar doses of the nicotinic antagonist mecamylamine had no effect on choice accuracy but altered responsivity, as indicated by increased errors of omission and a reduction in swim speed during early experimental stages. ICV CRH (0.5--1.0 microg) also failed to significantly affect accuracy, but a strong tendency was observed to impair percentage correct responses. Measures of responsivity, such as errors of omission, choice latency and distance traveled, and of thigmotaxis were not significantly affected by CRH. However, initial swim speed was reduced by the peptide. Combined treatment with scopolamine (0.5 mg/kg IP) and CRH (0.5 microg ICV) had only mild, and primarily independent, effects, but overall suggested that concomitant blockade of muscarinic receptors and activation of the CRH system would rather act synergistically to disrupt spatial discrimination learning. Synergistic effects were also observed when animals receiving a combination of mecamylamine (2.0 mg/kg IP) and CRH (0.5 microg ICV) were tested, both in terms of responsivity and thigmotaxis, and there was limited evidence that part of these effects were potentiating. Thus, the cholinergic and CRH systems interact in the modulation of learning, but CRH, contrary to prediction, worsens the impairment caused by cholinergic blockade.

Corticosteroids in relation to fear, anxiety and psychopathology

Corticosteroids play extremely important roles in fear and anxiety. The mechanisms by which corticosteroids exert their effects on behavior are often indirect, because, although corticosteroids do not regulate behavior, they induce chemical changes in particular sets of neurons making certain behavioral outcomes more likely in certain contexts as a result of the strengthening or weakening of particular neural pathways. The timing of corticosteroid increase (before, during or after exposure to a stressor) determines whether and how behavior is affected. The present review shows that different aspects of fear and anxiety are affected differentially by the occupation of the mineralocorticoid receptor (MR) or glucocorticoid receptor (GR) at different phases of the stress response. Corticosteroids, at low circulating levels, exert a permissive action via brain MRs on the mediation of acute freezing behavior and acute fear-related plus-maze behavior. Corticosteroids, at high circulating levels, enhance acquisition, conditioning and consolidation of an inescapable stressful experience via GR-mechanisms. Brain GR-occupation also promotes processes underlying fear potentiation. Fear potentiation can be seen as an adjustment in anticipation of changing demands. However, such feed-forward regulation may be particularly vulnerable to dysfunction. MR and/or GR mechanisms are involved in fear extinction. Brain MRs may be involved in the extinction of passive avoidance, and GRs may be involved in mediating the extinction of active avoidance. In the developing brain, corticosteroids play a facilitatory role in the ontogeny of freezing behavior, probably via GRs in the dorsal hippocampus, and their influence on the development of the septo-hippocampal cholinergic system. Corticosteroids can exert maladaptive rather than adaptive effects when their actions via MRs and GRs are chronically unbalanced due to chronic stress. Both mental health of humans and animal welfare is likely to be seriously threatened after psychosocial stress, prolonged stress, prenatal stress or postnatal stress, especially when maternal care or social support is absent, because these can chronically dysregulate the central MR/GR balance. In such circumstances the normally adaptive corticosteroid responses can become maladaptive.

Influence of cholinergic system on motor learning during aging in mice

Three, 12- and 20-month-old C57Bl6 mice, reared in standard conditions or in an enriched environment, were administered subcutaneously either scopolamine hydrobromide (SIGMA), 0.6 and 1.2 mg kg(-1), or physiological saline 15 min before testing their motor skills (muscular strength, dynamic equilibrium and motor coordination) and motor learning abilities (number of trials needed to reach a learning criterion on a rotorod rotating at 27 revolutions per min). The results demonstrated a lack of correlation between motor skill scores and between motor skill and motor learning scores, suggesting that the rotorod training procedure measures motor learning and not motor skills or is insensitive to changes in motor skills. They also demonstrated that motor skills decreased with age but were insensitive to environmental rearing and to scopolamine. In contrast, the learning scores, which also decreased with age, were very sensitive to scopolamine, particularly in the oldest mice. These results are discussed according to the role of cholinergic system in motor learning during aging.

Unconditioned anxiety and social behaviour in two rat lines selectively bred for high and low anxiety-related behaviour

Individuals of high anxiety-related behaviour (HAB) and low anxiety-related behaviour (LAB) rat lines were selectively bred for differences in anxiety-related behaviour on the elevated plus-maze. The goal of this study was to investigate whether this behavioural difference is restricted to the test used as the selection criterion or whether it is a stable and robust trait also in other conflict or non-conflict situations. Therefore, behaviour of male and female HAB and LAB rats was examined in two further tests of unconditioned anxiety: the black-white box and the social interaction test. Furthermore, behaviour of group-housed male HAB and LAB rats was studied in their home cages. In addition to standard statistics, discriminant analyses were performed. The difference in anxiety-related behaviour between the two lines was highly consistent in all tests of unconditioned anxiety. There were also differences in home cage behaviour, LAB rats being more active than HAB rats; this is likely to be a consequence of the LAB rats displaying a higher aggressiveness in social behaviour, compared to HAB rats. In all tests used HAB and LAB rats were clearly distinguished by discriminant analysis. However, while in the elevated plus-maze and the black-white box test the most important parameters for discrimination between the two lines were mainly those generally seen as closely related to anxiety, the discrimination in the social interaction paradigm was primarily due to differences in locomotor activity.

Effects of diazepam on the behaviour of weaned pigs in three putative models of anxiety

The present study examined the effects of diazepam (a widely used anxiolytic benzodiazepine) on the behavioural response of pigs to three novel experimental situations used to measure anxiety-related behaviour in rodents. Twelve weaned pigs (two pairs from each of the three litters) were tested in an elevated plus-maze at the age of 6 weeks, a light/dark test at the age of 7 weeks and an open-field test at the age of 8 weeks. Six of the pigs were pre-treated with diazepam (valium) and the other six with saline (control). In the elevated plus-maze, diazepam-treated pigs had a higher number of entries into open arms (P=0.04), spent more time on open arms (P=0.07), and had a higher number of total arm entries (P=0.05) than pigs from the control group. However, diazepam had no significant effects on behaviour in the light/dark test (i.e., latency to enter lit compartment, number of entries into lit compartment and the time spent in lit compartment) or the open-field test (i.e., number of lines crossed, number of entries into centre). In summary, the anxiolytic effects of diazepam on the pigs' behaviour were only demonstrated in the elevated plus-maze, where the time spent on open arms and the number of entries into open arms could be interpreted as measures of anxiety in pigs.

Anxiogenic effects of nicotine in the dorsal hippocampus are mediated by 5-HT1A and not by muscarinic M1 receptors

After direct administration into the dorsal hippocampus nicotine decreased the time spent in social interaction, without changing locomotor activity, indicating an anxiogenic effect. The possibility that post-synaptic M1 muscarinic receptors mediated this effect was examined by determining whether dorsal hippocampal administration of a specific M1 receptor agonist (McN-A-343) had anxiogenic effects, and whether the anxiogenic effect of nicotine could be reversed by co-administration of the M1 receptor antagonist, pirenzepine. McN-A-343 (0.3, 1.6, 3.2, 15.8 nmol) was without effect on social interaction, and pirenzepine (0.7 and 2.4 nmol) injection into the dorsal hippocampus failed to reverse the decrease in social interaction caused by nicotine (6.3 nmol) injection into this area. However, the decrease in social interaction after nicotine (50 nmol) was completely reversed by the specific 5-HT1A receptor antagonist, WAY 100635 (0.4 nmol) after co-administration of both drugs into the dorsal hippocampus. Thus, the anxiogenic effect of nicotine in this brain region seems to be mediated by 5-HT1A, but not M1, receptors. In contrast to the effect of nicotine in naive animals, those retested after a second injection of 50 nmol did not show a significant anxiogenic effect. The theoretical implications of this are discussed and from a practical point of view this suggests caution in the retesting of animals after central injections.

Injections of tacrine and scopolamine into the nucleus accumbens: opposing effects of immediate vs delayed posttrial treatment on memory of an open field

Using the paradigm of habituation learning in the open field, we tested the effects of microinjections of the nonspecific acetylcholine-esterase inhibitor tacrine (0.1, 1.0, 10.0 micrograms), and the muscarinic receptor antagonist scopolamine (0.1, 1.0, 10.0 micrograms) into the core of the nucleus accumbens. When injected immediately after the first exposure to the open field (posttrial), tacrine dose-dependently enhanced habituation of rearing behavior during the test on the following day, indicating a facilitation of memory. In contrast, scopolamine impaired habituation of rearing behavior at the two lower doses, but not at the highest dose. When scopolamine or tacrine (10.0 micrograms) was injected with a delay of 5 h after the learning trial, both drugs impaired habituation of rearing on the following day. The effects on locomotor activity differed from those on rearing behavior. Here, habituation on Day 2 was observed only in those animals which had received posttrial injections of vehicle or 10 micrograms of tacrine on the day before, whereas in animals which had received the two lower doses of tacrine, locomotor activity on Day 2 was not significantly decreased. In animals with posttrial treatment of scopolamine, locomotor activity on Day 2 was even enhanced, especially with the lower doses. No such effects were observed when scopolamine or tacrine (10.0 micrograms each) was injected with a delay of 5 h after the learning trial. These results show that cholinergic manipulations aimed at the nucleus accumbens can have substantial effects in this posttrial memory paradigm, which depend on drug, dose, and time of injection, and the specific kind of behavioral measure analyzed. Among others, the findings are discussed with respect to the role of muscarinic and nicotinergic cholinergic mechanisms in the nucleus accumbens on cognitive functions. They may be relevant, for example, for understanding the psychopathology of Alzheimer's disease, since the nucleus accumbens is one of the sites where cholinergic neurons are lost in this neurodegenerative disease.

Stimulation of nicotinic receptors in the lateral septal nucleus increases anxiety

The present study investigated the role of nicotinic receptors in the lateral septum in the modulation of anxiety. The effects of direct injections of nicotine into the lateral septum were first investigated in two tests of anxiety, social interaction and elevated plus-maze tests. Intra-septal injection of nicotine (1 and 4 microgram) induced consistent anxiogenic effects in both tests. The reversal of nicotinic effects with mecamylamine was then studied in the social interaction test. Intra-septal injection of mecamylamine at a low dose (15 ng) induced an anxiolytic effect, suggesting the presence of intrinsic cholinergic tone increasing anxiety. At higher doses (30-50 ng), mecamylamine was without effect in the social interaction test, but blocked the anxiogenic effects of nicotine (4 microgram). These findings provide further evidence for the role of the lateral septum in the modulation of anxiety and suggest that cholinergic projections to this brain area facilitate anxiety through nicotinic receptors.