Risperidone treatment increases CB1 receptor binding in rat brain.

BACKGROUND/AIMS: Body weight gain is a common side effect of treatment with antipsychotics, but the mechanisms underlying this weight gain are unknown. Several factors may be involved in antipsychotic-induced body weight gain including the cannabinoid receptor 1 (CB(1)), the serotonin receptor 2C, the ghrelin receptor, neuropeptide Y, adiponectin and proopiomelanocortin. We investigated whether the expression of these factors was affected in rats chronically treated with the antipsychotic risperidone. METHODS: Male Sprague-Dawley rats were treated with risperidone (1.0 mg/kg/day) or vehicle (20% hydroxypropyl beta-cyclodextrin) for 28 days. Expression of the aforementioned factors were examined together with plasma prolactin and ghrelin levels. RESULTS: No difference in body weight gained during treatment was observed between risperidone and vehicle treated rats, but plasma risperidone levels positively correlated with visceral fat mass. Risperidone treatment increased CB(1) receptor binding in the arcuate nucleus (40%), hippocampus (25-30%) and amygdala (35%) without concurrent alterations in the CB(1) receptor mRNA. Risperidone treatment increased adiponectin mRNA. CONCLUSION: The present study showed that risperidone treatment altered CB(1) receptor binding in the rat brain. Risperidone-induced adiposity and metabolic dysfunction in the clinic may be explained by increased CB(1) receptor density in brain regions involved in appetite and regulation of metabolic function.

Antipsychotic-like effect of retigabine [N-(2-Amino-4-(fluorobenzylamino)-phenyl)carbamic acid ester], a KCNQ potassium channel opener, via modulation of mesolimbic dopaminergic neurotransmission.

Dopaminergic (DAergic) neurons in the ventral tegmental area express both KCNQ2 and KCNQ4 channels, which opening is expected to decrease neuronal excitability via neuronal hyper-polarization. Because psychotic symptoms are believed to be associated with an increased excitability of dopamine (DA) cells in the mesencephalon, KCNQ channels might represent a new potential target for the treatment of psychosis. The aim of our study was to investigate the antipsychotic-like potential of KCNQ channel opening via modulation of neuronal activity within the mesolimbic DAergic system. We report that retigabine [N-(2-amino-4-(fluorobenzylamino)-phenyl)carbamic acid ester], a KCNQ opener, dose-dependently reduced basal DA firing rate and more potently suppressed burst firing activity in the ventral tegmental area, whereas XE-991 [10,10-bis(pyridinylmethyl)-9(10H)-anthracenone], a selective KCNQ blocker, induced opposite effects. In addition, retigabine prevented d-amphetamine-induced DA efflux in the nucleus accumbens and d-amphetamine-induced locomotor hyperactivity. In contrast, XE-991 potentiated both the locomotor hyperactivity and DA efflux evoked by d-amphetamine. These data strongly suggest that the activation of KCNQ channels attenuates DAergic neurotransmission in the mesolimbic system, particularly in conditions of excessive DAergic activity. In a model predictive of antipsychotic activity, the conditioned avoidance response paradigm, retigabine was found to inhibit avoidance responses, an effect blocked by coadministration of XE-991. Furthermore, retigabine was found to significantly inhibit the hyperlocomotor response to a phencyclidine (PCP) challenge in PCP-sensitized animals, considered as a disease model for schizophrenia. Taken together, our studies provide evidence that KCNQ channel openers represent a potential new class of antipsychotics.

Search for biological correlates of depression and mechanisms of action of antidepressant treatment modalities. Do neuropeptides play a role?

Dysregulation of the monoaminergic systems is likely a sufficient but not a necessary cause of depression. A wealth of data indicates that neuropeptides, e.g., NPY, CRH, somatostatin, tachykinins and CGRP play a role in affective disorders and alcohol use/abuse. This paper focuses on NPY in etiology and pathophysiology of depression. Decreased peptide and mRNA NPY were found in hippocampus of both the genetic, e.g., the FSL strain, and environmental rat models of depression, e.g., chronic mild stress and early life maternal separation paradigms. Rat models of alcoholism also show altered NPY. Furthermore, NPY is also reduced in CSF of depressed patients. Antidepressive treatments tested so far (lithium, topiramate, SSRIs, ECT and ECS, wheel running) increase NPY selectively in rat hippocampus and in human CSF. Moreover, NPY given icv to rat has antidepressive effects which are antagonized by NPY-Y1 blockers. The data support our hypothesis that the NPY system dysregulation constitutes one of the biological underpinnings of depression and that one common mechanism of action of antidepressive treatment modalities may be effects on NPY and its receptors. In a novel paradigm, early life maternal separation was superimposed on "depressed" FSL and control rats and behavioral and brain neurochemistry changes observed in adulthood. The consequences were more deleterious in genetically vulnerable FSL. Early antidepressive treatment modulated the adult sequelae. Consequently, if these data are confirmed, the ethical and medical question that will be asked is whether it is permissible and advisable to consider prophylactically treating persons at risk.

Effects of maternal separation on neuropeptide Y and calcitonin gene-related peptide in "depressed" Flinders Sensitive Line rats: a study of gene-environment interactions.

Interactions between genetic vulnerability to stress/depression and early life experience may play a crucial role in the pathogenesis of mood disorders. Here we explore this hypothesis by superimposing early life trauma in the form of maternal deprivation for 180 min per day from postnatal day 2 to 14 onto a genetic model of depression/susceptibility to depression, Flinders Sensitive Line (FSL) and their controls, Flinders Resistant Line (FRL) rats. We investigate effects on neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP) like immunoreactivity (LI) in 10 brain regions as these neuropeptides are affected by antidepressants and are altered in cerebrospinal fluid of depressed patients. NPY-LI was reduced while CGRP-LI was elevated in hippocampus and frontal cortex of "genetically depressed" FSL rats. The two peptides displayed a significant negative correlation in these regions that was strongest in the FSL strain. Maternal deprivation exacerbated the strain difference in hippocampal CGRP-LI, while it was without effect on NPY-LI. FSL rats had higher tissue concentration of both neuropeptides in periaqueductal grey and higher NPY-LI in caudate/putamen. Maternal deprivation selectively raised CGRP-LI in amygdala of the FRL control stain. Thus, in two brain regions implicated in the neurobiology of depression, hippocampus and frontal cortex, changes in CGRP-LI and NPY-LI were in opposite direction, and CGRP-LI appears to be more responsive to adverse experience. Our findings thus support the hypothesis that genetic disposition and developmental stress may contribute to the susceptibility to depression by exerting selective neuropeptide- and brain region-specific effects on adult neurobiology.

Gene-environment interactions in a rat model of depression. Maternal separation affects neurotensin in selected brain regions.

Although the etiology of major psychiatric disorders has not been elucidated, accumulating evidence indicates that both genetic and early environmental factors play a role. We have previously demonstrated behavioral and neurochemical changes both in non-manipulated genetic rat models of depression, such as Flinders Sensitive Line (FSL) and Fawn Hooded (FH), and in normal rats following maternal separation (MS). The aim of the present study was to extend this work by exploring whether neurotensin (NT), a peptide implicated in several psychiatric disorders, is altered in a new animal model based on gene - environment interactions. More specifically, we used the FSL rats as a genetic model of depression and the Flinders Resistant Line (FRL) as controls and subjected them to MS. Pups randomly assigned to the MS procedure were separated from the dam as a litter for 180min daily between postnatal day 2 to 14. On postnatal day 90, rats were weighed and sacrificed by a two second high energy focused microwave irradiation and several brain regions were obtained by micropuncture. Neurotensin-like immunoreactivity (NT-LI) was measured by radioimmunoassay (RIA). The results showed that the FSL rats compared to the FRL rats have higher baseline NT-LI concentrations in the temporal cortex and periaqueductal gray and a markedly different response to maternal separation. The only observed change following maternal separation in the FRL rats was an NT-LI increase in the periaqueductal gray. In contrast, in the FSL significant increases were found in the nucleus accumbens, hippocampus, and entorhinal cortex and a decrease was seen in the temporal cortex after MS. The present study revealed baseline regional differences in NT-LI concentrations between the FSL and FRL strains and demonstrated that early MD differentially affects the two strains. The relevance of these alterations for depression as well as possible mechanisms underlying this gene-environment interaction are discussed.

Maternal separation affects male rat copulatory behaviour and hypothalamic corticotropin releasing factor in concert.

Maternal separation (MS) is an animal model of early adverse experience, which is known to affect hypothalamic-pituitary-adrenal (HPA) axis function and various aspects of emotional behaviour. Sexual dysfunction is a prominent symptom in depression and in the present study we investigated the effects of maternal separation on copulatory behaviour and partner preference in adult male rats and paced mating in adult female rats. It has been suggested that corticotropin releasing factor (CRF) inhibits copulatory behaviour in male rats and we therefore examined if changes in male sexual behaviour were accompanied by changes in hypothalamic corticotropin releasing factor protein content. We found changed copulatory behaviour reflected in decreased mount latency, intromission latency, and post-ejaculatory interval in rats subjected to 180 min daily separation compared to handled rats, separated for 15 min daily on postnatal days (PNDs) 2-14. Ejaculation latency was not affected and there were no changes in partner preference in male rats. Paced mating behaviour of adult maternally separated female rats was unaffected. The concentration of corticotropin releasing factor-like immunoreactivity was lower in the hypothalamus of male rats separated for 180 min compared to male handled rats. We therefore suggest that 180 min of maternal separation generates a male phenotype with increased sexual motivation possibly due to inadequate levels of corticotropin releasing factor in the hypothalamus.

Early life stress changes concentrations of neuropeptide Y and corticotropin-releasing hormone in adult rat brain. Lithium treatment modifies these changes.

Experiences of early life stress are more prevalent among depressed patients than healthy controls. Neuropeptide Y (NPY) was suggested to play a role in the pathophysiology of depression. Consequently, we investigated in adult rats the effects of maternal deprivation for 3 h/day during postnatal days (PND) 2-14 and of dietary lithium during PND 50-83 on brain levels of NPY-like immunoreactivity (LI). Brain levels of corticotropin-releasing hormone (CRH) and serum corticosterone were also measured. Maternal deprivation reduced NPY-LI levels in the hippocampus and the striatum but increased NPY-LI and CRH-LI levels in the hypothalamus. Lithium treatment counteracted the effect of maternal deprivation in the hippocampus and striatum by increasing NPY-LI levels. In the hypothalamus, lithium tended to decrease CRH-LI but further increased levels of NPY-LI; it also increased serum corticosterone levels. The results suggest that early life stress has long-term effects on brain NPY with implications for the development of depression/vulnerability to stress, and that one therapeutic mechanism of action of lithium is to increase brain NPY.

Topiramate normalizes hippocampal NPY-LI in flinders sensitive line 'depressed' rats and upregulates NPY, galanin, and CRH-LI in the hypothalamus: implications for mood-stabilizing and weight loss-inducing effects.

Topiramate is currently used in the treatment of epilepsy, but this anticonvulsant drug has also been reported to exert mood-stabilizing effects and induce weight loss in patients. Neuropeptide Y (NPY) is abundantly and widely distributed in the mammalian central nervous system and centrally administered NPY markedly reduces pharmacologically induced seizures and induces antidepressant-like activity as well as feeding behavior. Two other peptides, galanin and corticotropin-releasing hormone (CRH), have also been proposed to play a modulatory role in mood, appetite, and seizure regulation. Consequently, we investigated the effects of single and repeated topiramate (10 days, once daily: 40 mg/kg i.p.) or vehicle treatment in 'depressed' flinders sensitive line (FSL) and control Flinders resistant line (FRL) rats on brain regional peptide concentrations of NPY, galanin, and CRH. The handling associated with repeated injections reduced hippocampal levels of NPY- and galanin-like immunoreactivities (LI) while NPY- and CRH-LI levels were increased in the hypothalamus, regardless of strain or treatment. In the hippocampus, concentrations of NPY-LI, galanin-LI, and CRH-LI were lower in FSL than FRL animals. Repeated topiramate treatment selectively normalized NPY-LI in this region in the FSL animals. In the hypothalamus, galanin-LI was reduced in FSL compared to FRL animals. Topiramate elevated the hypothalamic concentrations of NPY-LI, CRH-LI, and galanin-LI in both strains. Furthermore, topiramate elevated serum leptin but not corticosterone levels. The present findings show that topiramate has distinct effects on abnormal hippocampal levels of NPY, with possible implications for its anticonvulsant and mood-stabilizing effects. Furthermore, stimulating hypothalamic NPY-LI, CRH-LI and galanin-LI as well as serum leptin levels may be associated with the weight loss-inducing effects of topiramate.

Neuropeptide Y Y5 receptors suppress in vitro spontaneous epileptiform bursting in the rat hippocampus.

Neuropeptide Y (NPY) has been implicated in antiepileptic action in different in vivo and in vitro epilepsy models in rats and mice. Both Y2 and Y5 receptors could mediate the seizure-suppressant effect of NPY. However, lack of selective ligands precluded previous studies from conclusively evaluating the role of Y5 receptors in anti-epileptiform action of NPY. In the present study, using the new highly selective Y5 receptor antagonist, CGP71683A, and agonist, [cPP]hPP, we show that the Y5 receptor subtype is centrally involved in NPY-induced suppression of spontaneous epileptiform (interictaform) bursting in the CA3 area of rat hippocampal slices. This novel finding underscores the importance of Y5 receptors as a potential target for future antiepileptic therapy, particularly, for interictal components of temporal lobe epilepsy.

Extracellular levels of NPY in the dorsal hippocampus of freely moving rats are markedly elevated following a single electroconvulsive stimulation, irrespective of anticonvulsive Y1 receptor blockade.

Neuropeptide Y (NPY) has been proposed to play a role in the pathophysiology of depression and also to act as an endogenous anticonvulsant. Repeated administration of electroconvulsive stimulations (ECS) has been shown to induce a long-term increase in hippocampal NPY neurotransmission, while the effects of single ECS are largely unexplored. In this study, we assessed extracellular levels of NPY in the dorsal hippocampus of freely moving rats following a single ECS. We also studied the effect of locally administered BIBP3226, a selective NPY Y1 receptor antagonist with reported anticonvulsant properties, on the duration of the ECS-induced seizure and NPY release in freely moving animals. Our data demonstrate that a single ECS increases extracellular NPY-like immunoreactivity (LI) levels in the dorsal hippocampus, reaching statistical significance 2h following the treatment. KCl transiently and calcium-dependently increased extracellular levels of NPY, suggesting that the measured NPY-LI is derived from functional neurons. Local BIBP3226 perfusion essentially abolished the ECS-induced seizure but had no effect on the basal NPY-LI outflow or on the ECS-induced rise in extracellular NPY levels. Our data are in line with the hypothesis that one mechanism of action of ECS is to release NPY in the hippocampus and suggest that the increase is in itself not associated with anticonvulsant activity but may represent other properties of NPY.

Addiction-related effects of DOV 216,303 and cocaine: A comparative study in the mouse.

DOV 216,303, an inhibitor of serotonin, noradrenaline and dopamine reuptake, belongs to a new line of drugs called 'triple reuptake inhibitors' that have been proposed for treatment of depression. The addictive drug cocaine has similar mechanism of action and exerts rewarding effects by blocking reuptake of dopamine, leading to increased extracellular concentrations of dopamine in the nucleus accumbens. Thus, DOV 216,303 and other triple reuptake inhibitors might be speculated to exhibit abuse potential, limiting their future therapeutic use. To further elucidate potential addictive properties of DOV 216,303, we conducted a comparative study of addiction-related effects of DOV 216,303 and cocaine in mice using acute self-administration, conditioned place preference (CPP) and drug-induced hyperlocomotion. Effects on accumbal extracellular dopamine levels were determined using microdialysis, and we measured monoamine receptor occupancy as well as brain and plasma exposure. DOV 216,303 was self-administered acutely in the same dose range as cocaine. However, in the CPP model, DOV 216,303 did not induce place preference at doses where cocaine caused place preference. Higher doses of DOV 216,303 than cocaine were needed to induce hyperlocomotion and increase extracellular accumbal dopamine with effective doses being higher than effective doses used in depression models. Moreover, DOV 216,303 displayed a pharmacokinetic profile with lower potential for addiction than cocaine. Thus, high levels of DAT occupancy were reached slower and decayed more slowly after DOV 216,303 than cocaine administration. The present study shows that acute administration of DOV 216,303 displays some addictive-like properties in mice, but these were less pronounced than cocaine, most likely due to different pharmacokinetic profiles.

Antimanic efficacy of retigabine in a proposed mouse model of bipolar disorder.

Retigabine is a novel compound with anticonvulsant efficacy. Preclinical studies have indicated that the compound, like other anticonvulsants may also have antimanic efficacy. Bipolar disorder is characterized by episodes of depression and mania, which show a progressively faster recurrence and an increase in severity with time. Recurrence of episodes in bipolar disorders is suggested to reflect a process of sensitization. Repeated intermittent administration of amphetamine in rodents gives rise to a behavioral sensitization phenomena argued to have similarities to the sensitization found in humans. The aims were therefore to explore the predictive validity of the amphetamine sensitization model as a behavioral model of mania by testing the effect of a range of antimanic drugs and to evaluate the effect of retigabine on the sensitized amphetamine response. Furthermore, since withdrawal from prolonged use of amphetamine in humans can result in depression symptoms it was explored if a state of anhedonia could be assessed by testing saccharine preference before and during the withdrawal period of the model. The tested antimanic drugs (lithium, valproate, carbamazepine and lamotrigine) all attenuated the sensitized locomotor activity induced and with the exception of valproate the found effects seemed not to be due to sedation. Interestingly, retigabine also attenuated the induced locomotor activity with a lowest effective dose at 1.0mg/kg, whereas basal locomotor activity was only reduced at 8.0mg/kg, suggesting a genuine calming and antimanic-like efficacy of the compound. In addition, saccharine preference data suggest that withdrawal from the d-amphetamine pre-treatment regimen may induce depression-like behavior indicating that both manic and depression-like behavior is expressed in this mouse model.

Effect of the new antiepileptic drug retigabine in a rodent model of mania.

Bipolar spectrum disorders are severe chronic mood disorders that are characterized by episodes of mania or hypomania and depression. Because patients with manic symptoms often experience clinical benefit from treatment with anticonvulsant drugs, it was hypothesized that retigabine, a novel compound with anticonvulsant efficacy, may also possess antimanic activity. The amphetamine (AMPH)+chlordiazepoxide (CDP)-induced hyperactivity model has been proposed as a suitable model for studying antimanic-like activity of novel compounds in mice and rats. The aims of the present study in rats were therefore (1) to confirm previous findings with lithium and lamotrigine, and (2) to evaluate the effect of the novel compound retigabine on AMPH+CDP-induced hyperactivity in rats. In all experiments, co-administration of AMPH and CDP induced a significant increase (191-295%) in locomotor activity. Lithium chloride (0.9 mg/kg) and lamotrigine (20 mg/kg), which are known to effectively stabilize mood in humans, both significantly decreased AMPH+CDP-induced locomotor activity without affecting basal locomotor activity. The results furthermore indicate that retigabine, like lithium and lamotrigine, significantly and dose-dependently attenuates the induced hyperactivity at a lowest effective dose of 1.0 mg/kg, whereas basal locomotor activity is reduced only at doses 4.0 mg/kg. In conclusion, retigabine was found to have an antimanic-like effect in the AMPH+CDP-induced hyperactivity model, suggesting a potential role for retigabine in the treatment of mania and possibly in the management of bipolar disorder.

Gene-environment interaction affects substance P and neurokinin A in the entorhinal cortex and periaqueductal grey in a genetic animal model of depression: implications for the pathophysiology of depression.

Evidence implies a role for corticotropin-releasing hormone (CRH) and tachykinins, e.g. substance P (SP) and neurokinin A (NKA) in the pathophysiology of depression. We have previously shown that SP- and NKA-like immunoreactivity (-LI) concentrations were altered in the frontal cortex and striatum of the congenitally 'depressed' Flinders Sensitive Line (FSL) compared to the Flinders Resistant Line (FRL) control rats. It is also known that environmental stress may affect brain levels of tachykinins. In view of these results we decided to superimpose maternal deprivation, an early life environmental stressor, onto the genetically predisposed 'depressed' FSL rats and the FRL control rats and use this paradigm as a model of gene-environment interaction. The adult animals were sacrificed, adrenal glands and brains dissected out and SP-, NKA- and CRH-LI levels were determined in ten discrete brain regions. Maternal deprivation led to a marked increase in SP-LI and NKA-LI levels in the periaqueductal grey (PAG) and entorhinal cortex of the 'depressed' FSL strain while it had no significant effect in the FRL controls. Furthermore, specific strain differences in peptide-LI content were confirmed. No difference was found in relative adrenal gland weight, which is consistent with the finding that CRH-LI levels in the hypothalamus were similar across strains, and insensitive to stress in either strain. Taken together, these data are in line with behavioural experiments showing ameliorating effects of NK1 and NK2 receptor antagonists against anxiety and depression-like symptoms in rodents, and therefore further implicate the tachykinin systems in the pathophysiology of depression and adult life psychopathology.

Differential suppression of seizures via Y2 and Y5 neuropeptide Y receptors.

Neuropeptide Y (NPY) prominently inhibits epileptic seizures in different animal models. The NPY receptors mediating this effect remain controversial partially due to lack of highly selective agonists and antagonists. To circumvent this problem, we used various NPY receptor knockout mice with the same genetic background and explored anti-epileptic action of NPY in vitro and in vivo. In Y2 (Y2-/-) and Y5 (Y5-/-) receptor knockouts, NPY partially inhibited 0 Mg2+-induced epileptiform activity in hippocampal slices. In contrast, in double knockouts (Y2Y5-/-), NPY had no effect, suggesting that in the hippocampus in vitro both receptors mediate anti-epileptiform action of NPY in an additive manner. Systemic kainate induced more severe seizures in Y5-/- and Y2Y5-/-, but not in Y2-/- mice, as compared to wild-type mice. Moreover, kainate seizures were aggravated by administration of the Y5 antagonist L-152,804 in wild-type mice. In Y5-/- mice, hippocampal kindling progressed faster, and afterdischarge durations were longer in amygdala, but not in hippocampus, as compared to wild-type controls. Taken together, these data suggest that, in mice, both Y2 and Y5 receptors regulate hippocampal seizures in vitro, while activation of Y5 receptors in extra-hippocampal regions reduces generalized seizures in vivo.