Anxiety-like behaviour and c-fos expression in rats that inhaled vetiver essential oil.

Vetiver essential oil (VEO) has been used in aromatherapy for relaxation. This study aimed to investigate the effects of VEO on an anxiety-related behavioural model (the elevated plus-maze, EPM) and immediate-early gene c-fos in amygdala, known to be involved in anxiety. Male Wistar rats were administered diazepam (1 mg/kg i.p.) for 30 min or inhalated with VEO (1%, 2.5% or 5% w/w) for 7 min prior to exposure to the EPM. Then, the effects of 2.5% VEO, the anxiolytic dose, on c-fos expression in amygdala were investigated. The rats given either 2.5% VEO or diazepam exhibited an anxiolytic-like profile in the EPM. VEO and diazepam significantly increased c-fos expression in the lateral division of the central amygdaloid nucleus (CeL). Therefore, the anxiolytic properties of VEO might be associated with altering neuronal activation in CeL. However, future studies are needed to investigate the precise mechanism of action of VEO.

Lentiviral delivery of a vesicular glutamate transporter 1 (VGLUT1)-targeting short hairpin RNA vector into the mouse hippocampus impairs cognition.

Glutamate is the principle excitatory neurotransmitter in the mammalian brain, and dysregulation of glutamatergic neurotransmission is implicated in the pathophysiology of several psychiatric and neurological diseases. This study utilized novel lentiviral short hairpin RNA (shRNA) vectors to target expression of the vesicular glutamate transporter 1 (VGLUT1) following injection into the dorsal hippocampus of adult mice, as partial reductions in VGLUT1 expression should attenuate glutamatergic signaling and similar reductions have been reported in schizophrenia. The VGLUT1-targeting vector attenuated tonic glutamate release in the dorsal hippocampus without affecting GABA, and selectively impaired novel object discrimination (NOD) and retention (but not acquisition) in the Morris water maze, without influencing contextual fear-motivated learning or causing any adverse locomotor or central immune effects. This pattern of cognitive impairment is consistent with the accumulating evidence for functional differentiation along the dorsoventral axis of the hippocampus, and supports the involvement of dorsal hippocampal glutamatergic neurotransmission in both spatial and nonspatial memory. Future use of this nonpharmacological VGLUT1 knockdown mouse model could improve our understanding of glutamatergic neurobiology and aid assessment of novel therapies for cognitive deficits such as those seen in schizophrenia.

How do we re-engage the pharmaceutical industry in research on serotonin and psychiatric disorders?

The Serotonin Club celebrated its silver jubilee in 2012 with a meeting in Montpellier, France. During the past 25 years, great advances have been made in our understanding of the pharmacology of serotonin receptors and the roles of this neurotransmitter in psychiatric disorders. Most of these advances have involved effective collaborations between academic and industrial scientists. In recent years, however, this picture has changed, as many of the major pharmaceutical companies have pulled out of in-house psychopharmacology research into the major psychiatric disorders, despite an increasing worldwide burden of these disorders and a clear need for improved treatment, particularly in terms of improved efficacy. This Viewpoint investigates the reasons for the decline in industrial involvement and makes proposals as to how future academic research on serotonin function in the brain might reawaken industry interest in serotonin-based research. Briefly, academic preclinical scientists need to alter their experimental approach to research into the psychiatric disorders. This will require a move from a single-target approach to understanding the complex neuronal pathways the cause diverse functional and behavioral outputs, using novel technological advances and the development of animal models with enhanced translational values. It is hoped that such an approach will reveal novel drug targets and thus re-engage the pharmaceutical industry in research that will result in improved human health and social well-being.

Sensory gating, cannabinoids and schizophrenia.

Sensory gating, a mandatory process in early information processing, has been found to be defective in neuropsychiatric diseases such as schizophrenia. Understanding the neurobiology of sensory gating may provide insight into unravelling the neurobiology of information processing and to yet unanswered queries on the pathophysiology of disabling neuropsychiatric diseases. The endocannabinoid system has been linked to the pathophysiology of schizophrenia. Furthermore, cannabinoids disrupt sensory gating in animals and humans which supports the hypothesis that the disruption of sensory gating by alterations in the endocannabinoid system is a significant factor in the etiology of schizophrenia. Based on the above hypothesis this article reviews the sensory gating process in relation to the auditory conditioning-test paradigm with an emphasis on its association with the endocannabinoid system and schizophrenia.

Opposing effects of 5,7-DHT lesions to the core and shell of the nucleus accumbens on the processing of irrelevant stimuli.

There is good evidence that forebrain serotonergic systems modulate cognitive flexibility. Latent inhibition (LI) is a cross-species phenomenon which manifests as poor conditioning to a stimulus that has previously been experienced without consequence and is widely considered an index of the ability to ignore irrelevant stimuli. While much research has focused on dopaminergic mechanisms underlying LI, there is also considerable evidence of serotonergic modulation. However, the neuroanatomical locus of these effects remains poorly understood. Previous work has identified the nucleus accumbens (NAc) as a key component of the neural circuit underpinning LI and furthermore, this work has shown that the core and shell subregions of the NAc contribute differentially to the expression of LI. To examine the role of the serotonergic input to NAc in LI, we tested animals with 5,7-dihydroxytryptamine (5,7-DHT) lesions to the core and shell subregions on LI assessed under experimental conditions that produce LI in shams and subsequently with weak stimulus pre-exposure designed to prevent the emergence of LI in shams. We found that serotonergic deafferentation of the core disrupted LI whereas 5,7-DHT lesions to the shell produced the opposite effect and potentiated LI.

Blockade of dopamine D3 but not D2 receptors reverses the novel object discrimination impairment produced by post-weaning social isolation: implications for schizophrenia and its treatment.

Dopamine D3 receptors are densely expressed in mesolimbic projection areas, and selective antagonists enhance cognition, consistent with their potential therapeutic use in the treatment of schizophrenia. This study examines the effect of dopamine D3 vs. D2 receptor antagonists on the cognitive impairment and hyperactivity produced by social isolation of rat pups, in a neurodevelopmental model of certain deficits of schizophrenia. Three separate groups of male Lister hooded rats were group-housed or isolation-reared from weaning. Six weeks later rats received either vehicle or the dopamine D3 selective antagonist, S33084 (0.04 and 0.16 mg/kg), the preferential D3 antagonist, S33138 (0.16 and 0.63 mg/kg) or the preferential D2 antagonist, L-741,626 (0.63 mg/kg) s.c. 30 min prior to recording; horizontal locomotor activity in a novel arena for 60 min and, the following day, novel object discrimination using a 2-h inter-trial interval. Isolation rearing induced locomotor hyperactivity in a novel arena and impaired novel object discrimination compared to that in group-housed littermates. Both S33084 and S33138 restored novel object discrimination deficits in isolation-reared rats without affecting discrimination in group-housed controls. By contrast, L-741,626 impaired novel object discrimination in group-housed rats, without affecting impairment in isolates. S33084 (0.16 mg/kg), S33138 and, less markedly, L741,626 reduced the locomotor hyperactivity in isolates without attenuating activity in group-housed controls. Selective blockade of dopamine D3 receptors reverses the visual recognition memory deficit and hyperactivity produced by isolation rearing. These data support further investigation of the potential use of dopamine D3 receptor antagonists to treat schizophrenia.

The effects of chronic administration of tranylcypromine and rimonabant on behaviour and protein expression in brain regions of the rat.

Recent findings indicate that CB1 receptor blockade might be relevant to the action of antidepressant drugs as inhibition of endocannabinoid function can increase synaptic availability of neurotransmitters; an effect also seen with chronic antidepressant drug treatment. Chronic treatments with established antidepressants also lead to raised brain BDNF levels. The aim of this study was to compare the effects of rimonabant (an inverse agonist/antagonist of CB1 receptors) with those of the antidepressant tranylcypromine (TCP), on behaviour and expression of BDNF/CREB signalling pathways in rat brain. Daily (i.p.) injections of vehicle or TCP (10 mg/kg) or rimonabant (2 mg/kg) were given for 14 days. Locomotor activity (LMA) and a conditional emotional response (CER) were measured in addition to levels of BDNF and CREB/phospho-CREB, using immunoblotting, in the frontal cortex, hippocampus, striatum and cerebellum. The velocity of movement was increased significantly on the 3rd, but not 9th, day of TCP treatment versus vehicle-treated rats (p<0.05) while rimonabant had no effect. There were no significant changes in grooming or freezing behaviours after rimonabant or TCP compared to vehicle-treated rats. Rearing was significantly reduced by TCP treatment on the 3rd, but not 9th, day of treatment (p<0.001) while rimonabant had no effect. BDNF levels were significantly increased in the frontal cortex after TCP (p<0.05) but not by rimonabant. Neither TCP nor rimonabant significantly affected CREB or p-CREB expression. In conclusion, chronic administration of TCP to rats increased BDNF expression in the frontal cortex but no similar effect was observed with rimonabant indicating that rimonabant does not show antidepressant drug-like responses after chronic treatment.

Selective blockade of dopamine D3 receptors enhances while D2 receptor antagonism impairs social novelty discrimination and novel object recognition in rats: a key role for the prefrontal cortex.

Dopamine D(3) receptor antagonists exert pro-cognitive effects in both rodents and primates. Accordingly, this study compared the roles of dopamine D(3) vs D(2) receptors in social novelty discrimination (SND), which relies on olfactory cues, and novel object recognition (NOR), a visual-recognition task. The dopamine D(3) receptor antagonist, S33084 (0.04-0.63 mg/kg), caused a dose-related reversal of delay-dependent impairment in both SND and NOR procedures in adult rats. Furthermore, mice genetically deficient in dopamine D(3) receptors displayed enhanced discrimination in the SND task compared with wild-type controls. In contrast, acute treatment with the preferential dopamine D(2) receptor antagonist, L741,626 (0.16-5.0 mg/kg), or with the dopamine D(3) agonist, PD128,907 (0.63-40 µg/kg), caused a dose-related impairment in performance in rats in both tasks after a short inter-trial delay. Bilateral microinjection of S33084 (2.5 µg/side) into the prefrontal cortex (PFC) of rats increased SND and caused a dose-related (0.63-2.5 µg/side) improvement in NOR, while intra-striatal injection (2.5 µg/side) had no effect on either. In contrast, bilateral microinjection of L741,626 into the PFC (but not striatum) caused a dose-related (0.63-2.5 µg/side) impairment of NOR. These observations suggest that blockade of dopamine D(3) receptors enhances both SND and NOR, whereas D(3) receptor activation or antagonism of dopamine D(2) receptor impairs cognition in these paradigms. Furthermore, these actions are mediated, at least partly, by the PFC. These data have important implications for exploitation of dopaminergic mechanisms in the treatment of schizophrenia and other CNS disorders, and support the potential therapeutic utility of dopamine D(3) receptor antagonism.

The effect of catecholaminergic depletion within the prelimbic and infralimbic medial prefrontal cortex on recognition memory for recency, location, and objects.

There is good evidence that the medial prefrontal cortex (mPFC) is involved in different aspects of recognition memory. However, the mPFC is a heterogeneous structure, and the contribution of the prelimbic (PL) and infralimbic (IL) cortices to recognition memory has not been investigated. Similarly, the role of different neuromodulators within the mPFC in these processes is poorly understood. To this end, we tested animals with 6-hydroxydopamine (6-OHDA) lesions of the PL and IL mPFC on three tests of object recognition memory that required judgments about recency, object location, and object identity. In the recency task, lesions to both PL and IL severely impaired animals' ability to differentiate between old (earlier presented) and recently presented familiar objects. Relative to sham and PL animals, the IL lesion also disrupted performance on the object location task. However, both lesions left novel object recognition intact. These data confirm previous reports that the mPFC is not required for discriminations based on the relative familiarity of individual objects. However, these results demonstrate that catecholamines within the PL cortex are crucial for relative recency judgments and suggest a possible role for neural processing within the IL in the integration of information about object location.

Depolarizing and calcium-mobilizing stimuli fail to enhance synthesis and release of endocannabinoids from rat brain cerebral cortex slices.

The concentrations of the endocannabinoids 2-arachidonoylglycerol (2-AG) and N-arachidonylethanolamine (anandamide) were examined in rat brain cerebral cortex slices and surrounding medium. Basal concentrations of endocannabinoids were similar to those identified previously in rat brain, with anandamide content being much lower (19 pmol/g) than that of 2-AG (7300 pmol/g). In contrast, basal concentrations in the surrounding medium were proportionally much lower for 2-arachidonoylglycerol (16 pmol/mL) compared to anandamide (0.6 pmol/mL). Incubation of slices with glutamate receptor agonists, depolarizing concentrations of KCl, or ionomycin failed to alter tissue concentrations of endocannabinoids, while endocannabinoids in the medium were unaltered by elevated KCl. Cyclohexyl carbamic acid 3'-carbamoyl-biphenyl-3-yl ester, an inhibitor of fatty acid amide hydrolase, significantly enhanced tissue concentrations of anandamide (and related N-acylethanolamines), without altering 2-AG, while evoking proportional elevations of anandamide in the medium. Removal of extracellular calcium ions failed to alter tissue concentrations of anandamide, but significantly reduced 2-AG in the tissue by 90% and levels in the medium to below the detection limit. Supplementation of the medium with 50 µM N-oleoylethanolamine only raised tissue concentrations of N-oleoylethanolamine in the presence of cyclohexyl carbamic acid 3'-carbamoyl-biphenyl-3-yl ester and failed to alter either tissue or medium anandamide or 2-AG concentrations. These results highlight the ongoing turnover of endocannabinoids, and the importance of calcium ions in maintaining 2-AG concentrations in this tissue.

Influence of social isolation in the rat on serotonergic function and memory--relevance to models of schizophrenia and the role of 5-HT6 receptors.

There is increasing awareness of the importance that early environmental factors have on brain development and their role in the neurobiology of neurodevelopmental disorders including schizophrenia. The isolation reared rat attempts to model adverse effects that human social isolation (absence of social contact) can have on normal brain development. The isolation reared rat also models aspects of schizophrenia including the development of persistent learning and memory deficits. This short review concentrates on the effects of isolation rearing on cognition, including deficits in novel object discrimination, and the neural mechanisms that may underlie this impairment. There is evidence that a key effect of social isolation may be loss of neuronal plasticity combined with change in the functional state of various cortical and hippocampal neurotransmitters, including glutamate and serotonin. Reduced glutamate function may underlie the deficits in novel object discrimination, which can be reversed by administration of a 5-HT(6) receptor antagonist. This suggests that the 5-HT(6) antagonists may act by reducing 5-HT(6) receptor mediated activation of GABA, resulting in glutamate disinhibition. Thus drugs acting at 5-HT(6) receptors may offer a novel approach to treat neurodevelopmental cognitive symptoms, including those seen in schizophrenia.

Acute effects of bergamot oil on anxiety-related behaviour and corticosterone level in rats.

Bergamot essential oil (BEO), Citrus aurantium subsp. bergamia (Risso) Wright & Arn. (Rutaceae), is used widely in aromatherapy to reduce stress and anxiety despite limited scientific evidence. A previous study showed that BEO significantly increased gamma-aminobutyric acid levels in rat hippocampus, suggesting potential anxiolytic properties. The aim of this study was to investigate the effect of BEO (1.0%, 2.5% and 5.0% w/w) administered to rats on both anxiety-related behaviours (the elevated plus-maze (EPM) and hole-board tests) and stress-induced levels of plasma corticosterone in comparison with the effects of diazepam. Inhalation of BEO (1% and 2.5%) and injection of diazepam (1 mg/kg, i.p.) significantly increased the percentage of open arm entries on the EPM. The percentage time spent in the open arms was also significantly enhanced following administration of either BEO (2.5% and 5%) or diazepam. Total arm entries were significantly increased with the highest dose (5%), suggesting an increase in locomotor activity. In the hole-board test, 2.5% BEO and diazepam significantly increased the number of head dips. 2.5% BEO and diazepam attenuated the corticosterone response to acute stress caused by exposure to the EPM. In conclusion, both BEO and diazepam exhibited anxiolytic-like behaviours and attenuated HPA axis activity by reducing the corticosterone response to stress.

Acute concomitant effects of MDMA binge dosing on extracellular 5-HT, locomotion and body temperature and the long-term effect on novel object discrimination in rats.

RATIONALE: 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) produces an acute release of 5-HT in the brain, together with increased locomotion and hyperthermia. OBJECTIVE: This study examined whether the acute functional changes of locomotor activity and body temperature are related to enhanced 5-HT release induced by MDMA. METHODS: We concomitantly measured changes in extraneuronal 5-HT by in vivo brain microdialysis and used radiotelemetry to measure locomotion and body temperature to establish whether any positive correlations occur between these three parameters. 'Binge-type' repeated administration of low doses of MDMA (3 and 6 mg/kg given at 2-h intervals three times) were given to provide drug exposure similar to that experienced by recreational drug users. RESULTS: MDMA induced acute hyperactivity, changes in core body temperature (both hypothermia and hyperthermia) and elevation of hippocampal 5-HT overflow, all of which were dependent on the dose of MDMA administered. The change in locomotor activity and the magnitude of the hyperthermia appeared to be unrelated both to each other and to the magnitude of MDMA-induced 5-HT release. The study also found evidence of long-term disruption of novel object discrimination 2 weeks following "binge-type" repeated MDMA administration. CONCLUSIONS: MDMA-induced 5-HT release in the brain was not responsible for either the hyperthermia or increased locomotor activity that occurred. Since neither dose schedule of MDMA induced a neurotoxic loss of brain 5-HT 2 weeks after its administration, the impairment of recognition memory found in novel object discrimination probably results from other long-term changes yet to be established.

Dissociable roles of dopamine within the core and medial shell of the nucleus accumbens in memory for objects and place.

There is increasing focus on the role of the nucleus accumbens (NAc) in learning and memory, but there is little consensus as to how the core and medial shell subregions of the NAc contribute to these processes. In the current experiments, we used spontaneous object recognition to test rats with 6-hydroxydopamine lesions targeted at the core or medial shell of the NAc on a familiarity discrimination task and a location discrimination task. In the object recognition variant, control animals were able to discriminate the novel object at both 24-hr and 5-min delay. However, in the lesion groups, performance was systematically related to dopamine (DA) levels in the core but not the shell. In the location recognition task, sham-operated animals readily detected the object displacement at test. In the lesion groups, performance impairment was systematically related to DA levels in the shell but not the core. These results suggest that dopamine function within distinct subregions of the NAc plays dissociable roles in the modulation of memory for objects and place.

Novel cage stress alters remote contextual fear extinction and regional T2 magnetic resonance relaxation times in TASTPM mice overexpressing amyloid.

We have previously shown that repeated exposure to mild novel cage stress prevents the onset of recent contextual fear memory deficits and attenuated amyloid deposition in the TASTPM mouse model of Alzheimer's disease. Here, we extended this investigation to remote contextual fear memory and extinction. TASTPM and wild-type mice acquired contextual fear at 4 months of age. Retention and extinction of contextual fear were assessed at 5.5 months prior to in vivo MRI assessment of regional T2 relaxation times and brain volumes followed by immunostaining to determine amyloid plaque load. Remote contextual fear memory was preserved in TASTPM mice regardless of the stress condition. Stress impaired extinction in wild-type mice but facilitated this process in TASTPM mice. Genotype-dependent effects of stress were observed on regional T2 times which were prolonged in the subiculum and thalamus of stressed TASTPM, possibly reflecting reduced amyloid pathology. Amyloid plaque load was particularly decreased in the retrosplenial cortex of stressed TASTPM mice, which also showed an overall reduction in the number of diffuse plaques. These findings support the hypothesis that repeated mild levels of stress induced by novel activities can delay the progression of pathological changes relevant to Alzheimer's disease.

Mapping the central effects of methylphenidate in the rat using pharmacological MRI BOLD contrast.

Methylphenidate (Ritalin) is a selective dopamine reuptake inhibitor and an effective treatment for attention deficit hyperactivity disorder (ADHD) however the anatomical foci and neuronal circuits involved in these therapeutic benefits are unclear. This study determines the temporal pattern of brain regional activity change produced by systemic administration of a therapeutically relevant dose of methylphenidate in anaesthetised Sprague-Dawley rats using BOLD MRI and a 2.35T Bruker magnet. Following 60 min basal recording separate rats received saline (n = 9) or +/- methylphenidate hydrochloride (2 mg/kg, i.p., n = 9) and BOLD changes were recorded for 90 min using statistical parametric maps. Methylphenidate produced significant positive random BOLD effects in the nucleus accumbens, substantia nigra, entorhinal cortex and medial orbital cortex. Negative random BOLD effects were more widespread and intense, occurring in the motor and somatosensory cortices, caudate putamen, lateral globus pallidus and bed nucleus of the stria terminalis, without accompanying changes in blood pressure or respiratory rate. Methylphenidate-induced negative BOLD in the striatum, and other dopamine terminal areas, may reflect post-synaptic changes produced by blockade of the neuronal dopamine reuptake transporter. While increased positive BOLD in the medial orbital cortex may reflect altered dopamine and/or noradrenaline release indirectly altering striatal activity. The overall pattern of BOLD changes is comparable to that seen in previous studies using guanfacine, amphetamine and atomoxetine, and suggests that although these compounds operate through distinct pharmacological mechanisms the BOLD changes may represent a 'fingerprint pattern' predictive of therapeutic benefit in ADHD.

Early life programming of fear conditioning and extinction in adult male rats.

The early rearing environment programs corticolimbic function and neuroendocrine stress reactivity in adulthood. Although early environmental programming of innate fear has been previously examined, its impact on fear learning and memory later in life remains poorly understood. Here we examined the role of the early rearing environment in programming fear conditioning and extinction in adult male rats. Pups were subjected to maternal separation (MS; 360 min), brief handling (H; 15 min), or animal facility rearing (AFR) on post-natal days 2-14. As adults, animals were tested in a 3-day fear learning and memory paradigm which assessed the acquisition, expression and extinction of fear conditioning to an auditory cue; the recall of extinction was also assessed. In addition, contextual fear was assessed prior to cued extinction and its recall. We found that the acquisition of fear conditioning to the cue was modestly impaired by MS. However, no early rearing group differences were observed in cue-induced fear expression. In contrast, both the rate of extinction and extinction recall were attenuated by H. Finally, although contextual fear was reduced after extinction to the cue, no differences in context-induced fear were observed between the early rearing groups. These results add to a growing body of evidence supporting an important role for early environmental programming of fear conditioning and extinction. They also indicate that different early rearing conditions can program varying effects on distinct fear learning and memory processes in adulthood.

Effects of phencyclidine on auditory gating in the rat hippocampus and the medial prefrontal cortex.

Sensory gating can be assessed using an auditory conditioning (C)-test (T) paradigm which measures the reduction in the auditory-evoked response produced by a test stimulus following a conditioning stimulus. Schizophrenic patients demonstrate absence of gating while dysfunction in glutamatergic neurotransmission is implicated in the pathophysiology of schizophrenia. This study examined the effect of the glutamate receptor antagonist, phencyclidine (PCP) on auditory gating in the CA3 region and dentate gyrus (DG) of rat hippocampus and medial prefrontal cortex (mPFC). Local field potential (LFP) activity was recorded simultaneously from CA3, DG and mPFC in isoflurane anaesthetised Lister hooded rats using in vivo electrophysiology. Paired auditory stimuli were presented binaurally over 128 trials. The effect of PCP (1 mg/kg, i.p.) on gating of the N2 LFP wave was assessed as the test:conditioning response amplitude ratio (T/C ratio); a value of < or =50% was indicative of gating. Auditory gating of the N2 wave was observed in the CA3, DG and mPFC. PCP disrupted gating in all three areas with significant increases in test amplitudes (P<0.001). Clozapine (5 mg/kg i.p) prevented the auditory gating deficits induced by PCP in the CA3, DG and mPFC. This study shows that PCP disrupts sensory gating in the CA3, DG and mPFC in the isoflurane anaesthetised rat. Similar deficits are observed in schizophrenic patients and the current method may provide an animal model with good predictive validity, a view substantiated by the fact that clozapine prevented the sensory gating deficits induced by PCP.