Characterization of the K current mediated by 5-HT1A receptor in the acutely dissociated rat dorsal raphe neurons

The action of 5-hydroxytryptamine (5-HT) via the 5-HT_1A receptor on dissociated rat dorsal raphe neurons was characterized under the whole-cell mode by using the nystatin-perforated patch-clamp technique. Under voltage-clamp conditions, 5-HT induced an inwardly rectifying K⁺ current (I_5-HT) in a concentration-dependent manner. I_5-HT was mimicked by 8-OH-DPAT and buspirone, which are both 5-HT_1A receptor agonists. I_5-HT was reversibly blocked by such 5-HT_1A receptor antagonists as (S)-UH-301 and spiperone but not by ketanserin, a 5-HT₂ receptor antagonist, granisetron, a 5-HT₃ receptor antagonist, and GR-113808, a 5-HT₄ receptor antagonist. I_5-HT was antagonized concentration-dependently by such K⁺ channel blockers as quinine, Ba²⁺ and 4-aminopyridine but was relatively insensitive to both Cs⁺ and tetraethylammonium. When the neurons were loaded with guanosine 5′-O-3-thiotriphosphate through a patch pipette, the K⁺ current induced by 5-HT became irreversible. N-ethylmaleimide (NEM), a sulfhydryl alkylating agent, irreversibly blocked I_5-HT. The intracellular perfusion with 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA), a Ca²⁺ chelator, or neomycine, a phospholipase C inhibitor, never significantly affected the 5-HT-induced response. 12-Myristate 13-acetate diester (PMA), a protein kinase C (PKC) activator, had only a weak inhibitory effect on I_5-HT, and staurosporine, a PKC inhibitor, failed to significantly occlude I_5-HT. Therefore, the K⁺ conductance activated via the 5-HT_1A receptor of dorsal raphe neurons was thus characterized by the sensitivity to such K⁺ channel blockers as quinine, Ba²⁺ and 4-aminopyridine. Moreover, G protein, which is NEM-sensitive and can couple to the 5-HT_1A receptor, is thus considered to activate the inwardly rectifying K⁺ conductance without being mediated by such second messengers as Ca²⁺ and PKC.     

5-HT1A agonists induce hippocampal theta activity in freely moving cats: role of presynaptic 5-HT1A receptors

Electrical activity in the dorsal hippocampus was recorded in freely moving cats in response to intravenous administration of 5-HT_1A agonist and antagonist drugs. Administration of low doses of the selective 5-HT_1A agonists 8-OH-DPAT (5–20 μg/kg) and ipsapirone (20–100 μg/kg) produced rhythmic slow activity (theta) in the hippocampal EEG within 30 s. Similar effects were observed with BMY 7378 (20 and 100 μg/kg), which acts as an agonist at presynaptic (somatodendritic) 5-HT_1A receptors and as an antagonist at postsynaptic 5-HT_1A receptors. Power spectral analyses showed that all three compounds produced a dose-dependent increase in the EEG power occurring in the theta frequency band (3.5–8.0 Hz) as a proportion of total power from 0.25 to 30.0 Hz (relative theta power). The increase in relative theta power produced by 8-OH-DPAT (20 μg/kg) was greatly attenuated by spiperone (1 mg/kg), a highly effective 5-HT_1A autoreceptor antagonist. Administration of spiperone alone had no significant effect on relative theta power. These results are discussed in relationship to the effects of these drugs on serotonergic neuronal activity. Our results suggest that preferential activation of presynaptic 5-HT_1A receptors, and subsequent inhibition of serotonin neurotransmission, facilitates the appearance of hippocampal theta activity in awake cats.     

Involvement of dopamine-dependent and -independent mechanisms in the rewarding effects mediated by δ opioid receptor subtypes in mice

The rewarding effects of the δ₁ opioid receptor agonist [D-Pen², Pen⁵]enkephalin (DPDPE) and the δ₂ opioid receptor agonist [D-Ala²]deltorphin II (DELT) on the activity of mesolimbic and nigrostriatal dopamine (DA) neurons were examined in mice. Both DPDPE (15 nmol, i.c.v.) and DELT (5 nmol, i.c.v.) produced a significant place preference in mice. The DPDPE (15 nmol, i.c.v.)-induced place preference was abolished by 7-benzylidenenaltrexone (BNTX; 0.5 mg/kg, s.c.), a δ₁ opioid receptor antagonist, but not by naltriben (NTB; 0.5 mg/kg, s.c.), a δ₂ opioid receptor antagonist. In contrast, the DELT (5 nmol, i.c.v.)-induced place preference was antagonized by NTB, but not BNTX. I.c.v. injection of DPDPE, but not DELT, at a dose that produced a significant place preference produced a significant elevation of DA turnover in the mouse limbic forebrain, and this effect of DPDPE was antagonized by BNTX but not by NTB. In addition, i.c.v. injection of DPDPE or DELT did not affect DA turnover in the mouse striatum. These results suggest that the rewarding effects produced by the activation of central δ₁, but not δ₂, opioid receptors may be caused through the enhancement of the mesolimbic DA neurotransmission, and confirm our previous hypothesis that the DA-dependent and -independent mechanisms may exist in the rewarding effects produced by the activation of central δ opioid receptor subtypes.     

Divergent regulatory mechanisms governing BDNF mRNA expression in cerebral cortex and substantia nigra in response to striatal target ablation

We have studied the regulation of BDNF mRNA expression in the corticostriatal and nigrostriatal systems following neurotoxin ablation of striatal targets induced by quinolinic acid (QA) or 2S:2'R:3'R:-2-(2'3'-dicarboxycyclopropyl)glycine (DCG-IV) injections. Striatal lesions were verified by quantifying the loss of glutamic acid decarboxylase (GAD) mRNA expression. Levels of BDNF mRNA were analyzed at 6, 12, and 24 h postlesion. Both lesions paradigms highly induced BDNF mRNA in the ipsilateral cerebral cortex at 6 and 12 h postlesion to drop to control levels at 24 h postlesion. These inductions were mostly restricted to cortical layers II/III and V and ipsilateral insular and piriform cortices, which provide the main cortical inputs to the striatum. Analysis of neuronal activation on these areas demonstrated high levels of cFos mRNA in response to the excitotoxic striatal lesions. Dual labeling of cFos and BDNF mRNAs demonstrated a positive correlation between cortical neuronal activation and expression of BDNF mRNA. Consequently, expression of BDNF in cortical areas projecting to striatum is dependent on both target integrity and neuronal activity. Regulation of BNDF mRNA in substantia nigra, the second major source of BDNF to striatal cells, highly differed from that seen in cerebral cortex. Analysis of cellular expression alone or in combination of BDNF, cFos, tyrosine hydroxylase and GAD mRNAs demonstrated that expression of BDNF in substantia nigra is dependent on target integrity and independent of neuronal activity. In addition, we have studied regulatory mechanisms of BDNF mRNA in the subthalamic nucleus.     

The response of neurons in the bed nucleus of the stria terminalis to serotonin: Implications for anxiety

Substantial evidence has suggested that the activity of the bed nucleus of the stria terminalis (BNST) mediates many forms of anxiety-like behavior in human and non-human animals. These data have led many investigators to suggest that abnormal processing within this nucleus may underlie anxiety disorders in humans, and effective anxiety treatments may restore normal BNST functioning. Currently some of the most effective treatments for anxiety disorders are drugs that modulate serotonin (5-HT) systems, and several decades of research have suggested that the activation of 5-HT can modulate anxiety-like behavior. Despite these facts, relatively few studies have examined how activity within the BNST is modulated by 5-HT. Here we review our own investigations using in vitro whole-cell patch-clamp electrophysiological methods on brain sections containing the BNST to determine the response of BNST neurons to exogenous 5-HT application. Our data suggest that the response of BNST neurons to 5-HT is complex, displaying both inhibitory and excitatory components, which are mediated by 5-HT_1A, 5-HT_2A, 5-HT_2C and 5-HT₇ receptors. Moreover, we have shown that the selective activation of the inhibitory response to 5-HT reduces anxiety-like behavior, and we describe data suggesting that the activation of the excitatory response to 5-HT may be anxiogenic. We propose that in the normal state, the function of 5-HT is to dampen activity within the BNST (and consequent anxiety-like behavior) during exposure to threatening stimuli; however, we suggest that changes in the balance of the function of BNST 5-HT receptor subtypes could alter the response of BNST neurons to favor excitation and produce a pathological state of increased anxiety.     

Acute dehydroepiandrosterone treatment exerts different effects on dopamine and serotonin turnover ratios in the rat corpus striatum and nucleus accumbens

It has been shown that the steroid dehydroepiandrosterone (DHEA) interacts with dopamine (DA) and serotonin (5-HT) neurotransmitter systems, which are involved in the pathophysiology of neurological and psychiatric diseases such as Parkinson's disease as well as mood and psychotic disorders. To explore if DHEA modulates DA and 5-HT metabolism we analyzed the content of both neurotransmitters and their metabolites in the rat corpus striatum (CS) and nucleus accumbens (NAc) 2 h after steroid administration (30, 60 and 120 mg/kg i.p.). DHEA treatment significantly reduced DA turnover (up to 33%) in the CS, but increased 5-HT turnover (up to 76%) in both regions. Those effects could be relevant to mood and neurodegenerative disorders.     

Specific personality traits and dopamine, serotonin genes in anxiety-depressive alcoholism among Han Chinese in Taiwan

BACKGROUND: Cloninger [Cloninger CR. 1987. Neurogenetic adaptive mechanisms in alcoholism. Science 236: 410-416.] had proposed a psychobiological model suggesting that three main personality dimensions distinguish the alcoholism into two subtypes (type I and type II). However, the classification was equivocal for clinical diagnosis. Recently, anxiety-depressive alcohol dependence (ANX/DEP ALC) has been posited as a genetically specific subtype of alcoholism. Its clinical characteristics were similar to individuals with type I alcoholism [Cloninger, C.R. 1987. Neurogenetic adaptive mechanisms in alcoholism. Science 236: 410-6.] such as having a high comorbidity with mood disorder, late-onset and more anxious/depressed traits. We attempted to investigate whether the dopamine D2 receptor (DRD2) and the serotonin transporter promoter region (5-HTTLPR) genes were involved in Novelty Seeking (NS) and Harm Avoidance (HA) of ANX/DEP ALC. METHODS: We recruited 46 pure alcohol dependents (Pure ALC) and 87 anxiety-depression alcohol dependents (ANX/DEP ALC). All participants were diagnosed by DSM-IV criteria, genotyped by the PCR method and assessed with Tridimensional Personality Questionnaire (TPQ). RESULTS: Both NS and HA were high in ANX/DEP ALC (p = 0.021; p = 0.001, respectively). The association between NS and ANX/DEP ALC only existed in subjects with DRD2 TaqI A1(+) allele (A1/A1 or A1/A2 genotypes) (p = 0.004) and in those with S/S genotype of 5-HTTLPR (p = 0.005). With the stratification of DRD2 TaqI A1(+) allele, high NS of ANX/DEP ALC existed only in carriers of 5-HTTLPR S/S genotype (p=0.001). Moreover, ANX/DEP ALC was related to high HA only in samples carrying 5-HTTLPR S/L or L/L genotype (p = 0.02). CONCLUSIONS: These findings provided the empirical genetic characterization of the specific personality traits in ANX/DEP ALC among Han Chinese population in Taiwan.     

Clozapine, haloperidol, and the D4 antagonist PNU-101387G: in vivo effects on mesocortical, mesolimbic, and nigrostriatal dopamine and serotonin release

Summary. With in vivo microvoltammetry, the dopamine (DA) receptor antagonists, clozapine (D₄/D₂), haloperidol (D₂) and the selective D₄ antagonist, PNU-101387G, were evaluated for their effects on DA and serotonin (5-HT) release within A₁₀ neuronal terminal fields [mesocortical, prefrontal cortex (PFC), mesolimbic, nucleus accumbens, (NAcc)] and within A₉ neuronal terminal fields [nigrostriatal, caudate putamen (CPU)], in chloral hydrate anesthetized rats. Clozapine, which also has 5-HT₂ receptor antagonist properties, significantly (p < 0.001) increased DA release within A₁₀ terminal fields, PFC and NAcc; DA release was not increased by clozapine within A₉ terminals, CPU. Serotonin release was significantly (p < 0.001) increased by clozapine within A₁₀ and A₉ terminal fields. Haloperidol significantly (p < 0.001) increased DA release within PFC, dramatically and significantly (p < 0.001) increased DA release within CPU, but not within NAcc; haloperidol had a small but statistically significant (p < 0.05) increase on 5-HT release within PFC [only at the highest dose studied (2.5 mg/kg)] and within CPU [only at the lowest dose studied 1.0 mg/kg) (p < 0.05)]. The selective D₄ antagonist, PNU-101387G dramatically and significantly (p < 0.001) increased DA release within PFC, modestly, but significantly (p < 0.001) increased DA release within CPU, did not alter DA release within NAcc at the lowest dose studied (1.0 mg/kg) and significantly (p < 0.05) decreased DA release within NAcc at the highest dose studied (1.0 mg/kg). The selective D₄ antagonist did not affect 5-HT release within either A₁₀ or A₉ terminal fields. The present data are discussed in terms of the neurochemistry, antipsychotic activity, and side effect profiles of clozapine and haloperidol, in order to provide comparative profiles for a selective D₄ antagonist, PNU-101387G. Received January 13, 1998; accepted April 27, 1998     

Involvement of endocannabinoids in antidepressant and anti-compulsive effect of fluoxetine in mice

Endocannabinoid analogues exhibit antidepressant and anti-compulsive like effects similar to that of serotonin selective reuptake inhibitors (SSRIs) indicating a parallelism between the effects of serotonin and endocannabinoids. Therefore, the present study was designed to investigate the role of endocannabinoids in the antidepressant and anti-compulsive like effect of fluoxetine using mice model of forced swim test (FST) and marble-burying behavior (MBB). The results revealed that intracerebroventricular injections of endocannabinoid analogues, anandamide, a CB₁ agonist (AEA: 1-20 μg/mouse); AM404, an anandamide transport inhibitor (0.1-10 μg/mouse); and URB597, a fatty acid amide hydrolase inhibitor (0.05-10 μg/mouse) produced antidepressant-like effect dose-dependently, whereas influenced the MBB in a biphasic manner (produced a U-shaped dose-response curve). Fluoxetine (2.5-20 mg/kg, i.p.) dose dependently decreased the immobility time as well as burying behavior. Co-administration of sub-effective dose of fluoxetine (2.5 mg/kg, i.p.) potentiated the effect of sub-effective dose of AEA (0.5 μg/mouse, i.c.v.), AM404 (0.05 μg/mouse, i.c.v) or URB597 (0.01 μg/mouse, i.c.v) in both the paradigms. Interestingly, pretreatment with AM251, a CB₁ antagonist, blocked the effect of fluoxetine in FST and MBB at a dose (1 μg/mouse, i.c.v) that per se had no effect on either parameter. Similar effects were obtained with endocannabinoid analogues in AM251 pretreated mice. However, AM251 increased the burying behavior in MBB at a highest dose tested (5 μg/mouse). None of the treatments had any influence on locomotor activity. Thus, the study indicates an interaction between endocannabinoid and serotonergic system in regulation of depressive and compulsive-like behavior.     

Acute stress differentially affects corticotropin-releasing hormone mRNA expression in the central amygdala of the "depressed" flinders sensitive line and the control flinders resistant line rats

Preclinical and clinical evidence suggests that neuropeptides play a role in the pathophysiology of mood disorders. In the present study, we investigated the involvement of the peptides corticotropin-releasing hormone (CRH), neuropeptide Y (NPY) and nociceptin/orphanin FQ (N/OFQ) and of their receptors in the regulation of emotional behaviours. In situ hybridization experiments were performed in order to evaluate the mRNA expression levels of these neuropeptidergic systems in limbic and limbic-related brain regions of the Flinders Sensitive Line (FSL) rats, a putative genetic animal model of depression. The FSL and their controls, the Flinders Resistant Line (FRL) rats, were subjected to one hour acute restraint and the effects of the stress exposure, including possible strain specific changes on these neuropeptidergic systems, were studied. In basal conditions, no significant differences between FSL and FRL rats in the CRH mRNA expression were found, however an upregulation of the CRH mRNA hybridization signal was detected in the central amygdala of the stressed FRL, compared to the non stressed FRL rats, but not in the FSL, suggesting a hypoactive mechanism of response to stressful stimuli in the "depressed" FSL rats. Baseline levels of NPY and N/OFQ mRNA were lower in the FSL rats compared to the FRL in the dentate gyrus of hippocampus and in the medial amygdala, respectively. However, the exposure to stress induced a significant upregulation of the N/OFQ mRNA levels in the paraventricular thalamic nucleus, while in the same nucleus the N/OFQ receptor mRNA expression was higher in the FSL rats. In conclusion, selective alterations of the NPY and N/OFQ mRNA in limbic and limbic-related regions of the FSL rats, a putative animal model of depression, provide further support for the involvement of these neuropeptides in depressive disorders. Moreover, the lack of CRH activation following stress in the "depressed" FSL rats suggests a form of allostatic load, that could alter their interpretation of environmental stimuli and influence their behavioural response to stressful situations.     

DNA microarray analysis of striatal gene expression in symptomatic transgenic Huntington's mice (R6/2) reveals neuroinflammation and insulin associations

Huntington's disease (HD) is an inherited, progressive neurodegenerative disorder caused by CAG repeat expansion in the gene that codes for the protein huntingtin. The underlying neuropathological events leading to the selectivity of striatal neuronal loss are unknown. However, the huntingtin mutation interferes at several levels of normal cell function. The complexity of this disease makes microarray analysis an appealing technique to begin the identification of common pathways that may contribute to the pathology. In this study, striatal tissue was extracted for gene expression profiling from wild-type and symptomatic transgenic Huntington mice (R6/2) expressing part of the human Huntington's disease gene. We interrogated a 15 K high-density mouse EST array not previously used for HD and identified 170 significantly differentially expressed ESTs in symptomatic R6/2 mice. Of the 80 genes with known function, 9 genes had previously been identified as altered in HD. 71 known genes were associated with HD for the first time. The data obtained from this study confirm and extend previous observations using DNA microarray techniques on genetic models for HD, revealing novel changes in expression in a number of genes not previously associated with HD. Further bioinformatic analysis, using software to construct biological association maps, focused attention on proteins such as insulin and TH1-mediated cytokines, suggesting that they may be important regulators of affected genes. These results may provide insight into the regulation and interaction of genes that contribute to adaptive and pathological processes involved in HD.     

Altered levels of POMC, AgRP and MC4-R mRNA expression in the hypothalamus and other parts of the limbic system of mice prone or resistant to chronic high-energy diet-induced obesity

The melanocortinergic system plays an important role in promoting negative energy balance and preventing excessive fat deposition. This study has investigated the levels of mRNA expression of proopiomelanocortin (POMC), agouti-related protein (AgRP) and the melanocortin-4 receptor (MC4-R) in diet-induced obese (DIO) and diet-resistant (DR) mice. Thirty C57 mice were used in this study. Twenty-four mice were fed with a high-fat diet (HF: 40% of calories from fat, 20% from saturated fat) for 4 weeks and then classified as DIO and DR according to their body weight gain. Six mice were placed on a low-fat diet (LF: 10% of calories from fat, 1% from saturated fat) and were used as controls. After 22 weeks of feeding, visceral fat deposits were more than twice as heavy in the DIO mice as in the DR and LF mice, while the latter two groups had no significant difference. Using quantitative in situ hybridization techniques, this study found that the DIO mice had a significantly lower level of Arc POMC (-29%) and AgRP (-31%) mRNA expression than the DR and LF mice, respectively. The mice on high-fat diets had higher levels of AgRP mRNA expression in the bed nucleus of stria terminalis (BST), and ventral part of the lateral septal nucleus (LSV) than the LF mice. Furthermore, the DIO mice had a 40% higher level of MC4-R mRNA expression in the ventromedial hypothalamic nucleus (VMH) and posterodorsal part of the medial amygdaloid nucleus (MePD) than the LF mice. In conclusion, this study has demonstrated that differential expression of POMC, AgRP and MC4-R mRNA levels exists in DIO, DR and LF mice. These differences were shown to occur in the specific nuclei of the hypothalamus and other parts of the limbic system. These findings may assist in understanding the involvement of the melanocortinergic system in the regulation of body weight via the autonomic and limbic systems.     

Pro-inflammatory cytokines and treatment response to escitalopram in major depressive disorder

Alterations in the immune system may have importance for the pathophysiology of depression. Several studies have linked increased production of pro-inflammatory cytokines to depression and depressive symptoms. There is growing evidence that antidepressive treatment may influence the production of pro-and anti-inflammatory cytokines. In the present study we aimed to find associations between the levels of soluble interleukin-2 receptor (sIL-2R), interleukin-8 (IL-8) and tumor necrosis factor alpha (TNF-alpha) and the response to antidepressant treatment in patients with major depression. Our study group consisted of 100 patients (35 males and 65 females) who were treated with escitalopram 10-20 mg/day for 12 weeks. Responders and non-responders were identified according to Montgomery-Asberg's Depression Rating Scale (MADRS) scores. The levels of cytokines were measured at baseline and at 4th and 12th week of the treatment and compared to cytokine concentrations in healthy volunteers (n=45; 19 males and 26 females). Our data indicated that a higher level of TNF-alpha might predict a non-response to treatment with escitalopram and that changes in concentrations of sIL-2R during the treatment were different in responders and non-responders.     

Protein expression and mRNA cellular distribution of the NKCC1 cotransporter in the dorsal root and trigeminal ganglia of the rat

Primary afferent neurons maintain depolarizing responses to GABA into adulthood. The molecular basis for this GABAergic response appears to be the Na+K+2Cl- cotransporter NKCC1 that contributes to the maintenance of a high intracellular chloride concentration. Recently, a role for NKCC1 has been proposed in nociceptive processing which makes it timely to gain a better understanding of the distribution of NKCC1 in sensory ganglia. Here, we describe that, in the rat, NKCC1 mRNA is predominately expressed by small and medium diameter dorsal root (DRG) and trigeminal (TG) ganglion neurons. The colocalization of NKCC1 mRNA with sensory neuron population markers was assessed. In the DRG, many NKCC1 mRNA-expressing neurons colocalized peripherin (57.0+/-2.5%), calcitonin-gene-related peptide (CGRP, 39.2+/-4.4%) or TRPV1 immunoreactivity (50.0+/-1.9%) whereas only 8.7+/-1.2% were co-labeled with a marker for large diameter afferents (N52). Similarly, in the TG, NKCC1 mRNA-expressing neurons frequently colocalized peripherin (50.0+/-3.0%), CGRP (35.4+/-2.6%) or TRPV1 immunoreactivity (44.7+/-1.2%) while 14.8+/-1.3% were co-labeled with the N52 antibody. NKCC1 mRNA was also detected in satellite glial (SGCs) in both the DRG and TG. Colocalization of NKCC1 protein with the SGC marker NG2 confirmed the phenotype of these NKCC1-expressing glial cells. In contrast to in situ hybridization experiments, we did not observe NKCC1 immunoreactivity in primary afferent somata. These findings suggest that NKCC1 is expressed in anatomically appropriate cells in order to modulate GABAergic responses in nociceptive neurons. Moreover, these results suggest the possibility of a functional role of NKCC1 in the glial cells closely apposed to primary sensory afferents.     

Neuropathic pain and the endocannabinoid system in the dorsal raphe: pharmacological treatment and interactions with the serotonergic system

We used a model of neuropathic pain consisting of rats with chronic constriction injury (CCI) of the sciatic nerve, in order to investigate whether endocannabinoid levels are altered in the dorsal raphe (DR) and to assess the effect of repeated treatment with (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate, a synthetic cannabinoid agonist, or N-(4-hydroxyphenyl)-5Z,8Z,11Z,14Z-eicosatetraenamide (AM404), an inhibitor of endocannabinoid reuptake, on DR serotonergic neuronal activity and on behavioural hyperalgesia. CCI resulted in significantly elevated anandamide but not 2-arachidonoylglycerol levels in the DR. Furthermore, as well as thermal and mechanical hyperalgesia, CCI caused serotonergic hyperactivity (as shown by the increase of basal activity of serotonergic neurones, extracellular serotonin levels and expression of 5-HT1A receptor gene). Repeated treatment with either (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone mesylate or AM404 reverted the hyperalgesia and enhanced serotonergic activity induced by CCI in a way attenuated by N-piperidino-5-(4-chlorophenyl)-1-(2,4dichlorophenyl)-4-methyl-3-pyrazolecarboxamide, a selective cannabinoid subtype 1 (CB1) receptor antagonist. Despite the elevated levels of anandamide following CCI, N-piperidino-5-(4-chlorophenyl)-1-(2,4dichlorophenyl)-4-methyl-3-pyrazolecarboxamide did not produce hyperalgesia or any other effect on serotonergic neuronal activity when administered alone. Furthermore, the effects of AM404 were not accompanied by an increase in endocannabinoid levels in the DR. In conclusion, following CCI of the sciatic nerve, the endocannabinoid and serotonergic systems are activated in the DR, where repeated stimulation of CB1 receptors with exogenous compounds restores DR serotonergic activity, as well as thermal and mechanical nociceptive thresholds, to pre-surgery levels. However, an elevated level of endogenous anandamide in the DR does not necessarily contribute to the CB1-mediated tonic control of analgesia and serotonergic neuronal activity.     

Platelet PAR1 receptor density--correlation to platelet activation response and changes in exposure after platelet activation

INTRODUCTION: A polymorphism (-14 A/T) affecting PAR1 expression on the platelet surface has recently been identified. A two-fold variation in receptor density, which correlated with the platelet response to PAR1-activating peptide (PAR1-AP), has been reported. MATERIALS AND METHODS: We used flow cytometry to measure the correlation between the number of PAR1 receptors and platelet activation. We also measured the changes in receptor exposure after platelet activation with PAR1-AP, ADP, PAR4-AP or a collagen-related peptide (CRP). RESULTS: In our study, the PAR1 receptor number varied almost four-fold, from 547 to 2063 copies/platelet (mean+/-S.D. 1276+/-320, n=70). The number of PAR1 receptors on resting platelets correlated to platelet fibrinogen binding and P-selectin expression following platelet activation with PAR1-AP (r(2)=0.30, p<0.01 and r(2)=0.15, p<0.05, respectively, n=36). The correlation was not improved by exclusion of the ADP-component from the PAR1-AP-induced response. We found a trend, but no statistically significant differences in PAR1 receptor number and platelet reactivity between A/A individuals and T/A or T/T individuals. Ex vivo activation with PAR1-AP decreased PAR1 surface exposure to 71+/-19% of the exposure on resting platelets (mean+/-S.D., p<0.01, n=19), while activation by ADP, PAR4-AP or CRP significantly increased the exposure, to 151+/-27%, 120+/-21% and 138+/-25%, respectively (n=11, 11 and 10). CONCLUSIONS: This study shows a large variation in PAR1 receptor number in healthy individuals, a variation correlated to the platelet activation response. We found a significant reduction in PAR1 surface exposure after adding PAR1-AP, while activation with ADP, PAR4-AP or CRP increased the exposure.     

Animal models of depression and anxiety: What do they tell us about human condition?

While modern neurobiology methods are necessary they are not sufficient to elucidate etiology and pathophysiology of affective disorders and develop new treatments. Achievement of these goals is contingent on applying cutting edge methods on appropriate disease models. In this review, the authors present four rodent models with good face-, construct-, and predictive-validity: the Flinders Sensitive rat line (FSL); the genetically “anxious” High Anxiety-like Behavior (HAB) line; the serotonin transporter knockout 5-HTT^−/− rat and mouse lines; and the post-traumatic stress disorder (PTSD) model induced by exposure to predator scent, that they have employed to investigate the nature of depression and anxiety.     

Converging effects of acute stress on spatial and recognition memory in rodents: A review of recent behavioural and pharmacological findings

The heterogeneous effects of acute stress on learning and memory depend on numerous parameters related to the stressor, the time the stressor is experienced, and the nature of the stimuli or task examined. In the present review, we systematically summarize the rodent literature examining the effects of acute extrinsic stress on spatial and recognition memory. Converging evidence from a number of behavioural tasks suggests acute stress disrupts the retrieval of spatial and recognition memory regardless of whether the stress is experienced before or after learning. Few studies have attempted to discern whether these effects are due to specific failures in consolidation or retrieval of task relevant information. Recent studies demonstrate that diverse mechanisms related to activation of the hypothalamic-pituitary-adrenal axis and alterations in glutamatergic synaptic plasticity mediate the effects of acute stress on spatial and recognition memory. Taken together, these findings have significantly advanced our understanding of the neural mechanisms mediating learning and memory and may stimulate the search for novel therapeutics to treat stress-related psychiatric disorders.     

Cyclooxygenases and 5-lipoxygenase in Alzheimer's disease

Typically, cyclooxygenases (COXs) and 5-lipoxygenase (5-LOX), enzymes that generate biologically active lipid molecules termed eicosanoids, are considered inflammatory. Hence, their putative role in Alzheimer's disease (AD) has been explored in the framework of possible inflammatory mechanisms of AD pathobiology. More recent data indicate that these enzymes and the biologically active lipid molecules they generate could influence the functioning of the central nervous system and the pathobiology of neurodegenerative disorders such as AD via mechanisms different from classical inflammation. These mechanisms include the cell-specific localization of COXs and 5-LOX in the brain, the type of lipid molecules generated by the activity of these enzymes, the type and the localization of receptors selective for a type of lipid molecule, and the putative interactions of the COXs and 5-LOX pathways with intracellular components relevant for AD such as the gamma-secretase complex. Considering the importance of these multiple and not necessarily inflammatory mechanisms may help us delineate the exact nature of the involvement of the brain COXs and 5-LOX in AD and would reinvigorate the search for novel targets for AD therapy.     

AMPA receptor involvement in 5-hydroxytryptamine2A receptor-mediated pre-frontal cortical excitatory synaptic currents and DOI-induced head shakes

Glutamate plays an important role in the psychotomimetic effects of both channel blocking N-methyl D-aspartate (NMDA) receptor antagonists and hallucinogenic drugs which activate 5-hydroxytryptamine2A (5-HT2A) receptors. Previous work suggested that activation of non-NMDA ionotropic glutamate receptors mediates the effects of 5-HT-induced excitatory post-synaptic potentials/currents (EPSPs/EPSCs) when recording from layer V pyramidal cells in the rat medial pre-frontal cortex (mPFC). However, those effects are mediated by either alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) or kainate receptors of the iGluk5 subtype. To test whether activation of AMPA receptors is sufficient to mediate 5-HT-induced EPSCs, a 2,3-benzodiazepine that selectively blocks AMPA receptors was assessed. This selective AMPA receptor antagonist potently suppressed 5-HT-induced EPSCs. Since phenethylamine hallucinogens induce head shakes by activating 5-HT2A receptors in the mPFC and this action is modulated by glutamate, we also examined whether selective blockade of AMPA receptors would suppress DOI-induced head shakes. As predicted, we found that selective blockade of AMPA receptors suppressed DOI-induced head shakes. Given evidence that activation of AMPA receptors is an important downstream effect for both channel blocking NMDA receptor antagonists and phenethylamine hallucinogens, we also tested multiple doses of DOI with a sub-anesthetic dose of MK-801. Synergistic action between these two classes of psychotomimetic drugs was demonstrated by MK-801 enhancing DOI-induced head shakes and locomotor activity. These findings expand the dependence of both channel blocking NMDA receptor antagonists and phenethylamine hallucinogens on enhancing extracellular glutamate.