Chronic administration of risperidone in a rat model of schizophrenia: A behavioural, morphological and molecular study

In the present work we analyzed the effect of the chronic administration of risperidone (2mg/kg over 65 days) on behavioural, morphological and molecular aspects in an experimental model of schizophrenia obtained by bilateral injection of ibotenic acid into the ventral hippocampus of new-born rats. Our results show that during their adult lives the animals with hippocampal lesions exhibit different alterations, mainly at behavioural level and in the gene expression of dopamine D2 and 5-HT2A receptors. However, at morphological level the study performed on the prefrontal cortex did not reveal any alterations in either the thickness or the number of cells immunoreactive for c-Fos, GFAP, CBP or PV. Overall, risperidone administration elicited a trend towards the recovery of the values previously altered by the hippocampal lesion, approaching the values seen in the animals without lesions. It may be concluded that the administration of risperidone in the schizophrenia model employed helps to improve the altered functions, with no significant negative effects. © 2013.

Interação entre as vias de sinalização de receptores serotoninérgicos e Β-adrenérgicos em artéria femoral de ratos

Fundamento: A doença coronária tem sido amplamente estudada em pesquisas cardiovasculares. No entanto, pacientes com doença arterial periférica (DAP) têm piores resultados em comparação àqueles com doença arterial coronariana. Portanto, os estudos farmacológicos com artéria femoral são altamente relevantes para a melhor compreensão das respostas clínicas e fisiopatológicas da DAP. Objetivo: Avaliar as propriedades farmacológicas dos agentes contráteis e relaxantes na artéria femoral de ratos. Métodos: As curvas de resposta de concentração à fenilefrina contrátil (FC) e à serotonina (5-HT) e os agentes relaxantes isoproterenol (ISO) e forskolina foram obtidos na artéria femoral de ratos isolada. Para as respostas ao relaxamento, os tecidos foram contraídos com FC ou 5-HT. Resultados: A potência de classificação na artéria femoral foi de 5-HT > FC para as respostas contráteis. Em tecidos contraídos com 5-HT, as respostas de relaxamento ao isoproterenol foram praticamente abolidas em comparação aos tecidos contraídos com FC. A forskolina, um estimulante da adenilil ciclase, restaurou parcialmente a resposta de relaxamento ao ISO em tecidos contraídos com 5-HT. Conclusão: Ocorre uma interação entre as vias de sinalização dos receptores β-adrenérgicos e serotoninérgicos na artéria femoral. Além disso, esta pesquisa fornece um novo modelo para estudar as vias de sinalização serotoninérgicas em condições normais e patológicas que podem ajudar a compreender os resultados clínicos na DAP.

Central, but not basolateral, amygdala involvement in the anxiolytic-like effects of midazolam in rats in the elevated plus maze

The role of the amygdala in the mediation of fear and anxiety has been extensively investigated. However, how the amygdala functions during the organization of the anxiety-like behaviors generated in the elevated plus maze (EPM) is still under investigation. The basolateral (BLA) and the central (CeA) nuclei are the main input and output stations of the amygdala. In the present study, we ethopharmacologically analyzed the behavior of rats subjected to the EPM and the tissue content of the monoamines dopamine (DA) and serotonin (5-HT) and their metabolites in the nucleus accumbens (NAc), dorsal hippocampus (DH), and dorsal striatum (DS) of animals injected with saline or midazolam (20 and 30 nmol/0.2 mu L) into the BLA or CeA. Injections of midazolam into the CeA, but not BLA, caused clear anxiolytic-like effects in the EPM. These treatments did not cause significant changes in 5-HT or DA contents in the NAc, DH, or DS of animals tested in the EPM. The data suggest that the anxiolytic-like effects of midazolam in the EPM also appear to rely on GABA-benzodiazepine mechanisms in the CeA, but not BLA, and do not appear to depend on 5-HT and DA mechanisms prevalent in limbic structures.

Opioidergic, GABAergic and serotonergic neurotransmission in the dorsal raphe nucleus modulates tonic immobility in guinea pigs

Tonic immobility (TI) is an innate defensive behavior that can be elicited by physical restriction and postural inversion and is characterized by a profound and temporary state of akinesis. Our previous studies demonstrated that the stimulation of serotonin receptors in the dorsal raphe nucleus (DRN) appears to be biphasic during TI responses in guinea pigs (Cavia porcellus). Serotonin released by the DRN modulates behavioral responses and its release can occur through the action of different neurotransmitter systems, including the opioidergic and GABAergic systems. This study examines the role of opioidergic, GABAergic and serotonergic signaling in the DRN in TI defensive behavioral responses in guinea pigs. Microinjection of morphine (1.1 nmol) or bicuculline (0.5 nmol) into the DRN increased the duration of TI. The effect of morphine (1.1 nmol) was antagonized by pretreatment with naloxone (0.7 nmol), suggesting that the activation of pi opioid receptors in the DRN facilitates the TI response. By contrast, microinjection of muscimol (0.5 nmol) into the DRN decreased the duration of TI. However, a dose of muscimol (0.26 nmol) that alone did not affect TI, was sufficient to inhibit the effect of morphine (1.1 nmol) on TI, indicating that GABAergic and enkephalinergic neurons interact in the DRN. Microinjection of alpha-methyl-5-HT (1.6 nmol), a 5-HT2 agonist, into the DRN also increased TI. This effect was inhibited by the prior administration of naloxone (0.7 nmol). Microinjection of 8-OH-DPAT (1.3 nmol) also blocked the increase of TI promoted by morphine (1.1 nmol). Our results indicate that the opioidergic, GABAergic and serotonergic systems in the DRN are important for modulation of defensive behavioral responses of TI. Therefore, we suggest that opioid inhibition of GABAergic neurons results in disinhibition of serotonergic neurons and this is the mechanism by which opioids could enhance TI. Conversely, a decrease in TI could occur through the activation of GABAergic interneurons. (C) 2012 Elsevier Inc. All rights reserved.

Studio elettrofisiologico di modificazioni a lungo termine della forza della trasmissione sinaptica nel sistema nervoso centrale

Il nucleo accumbens (NAc), il maggior componente del sistema mesocorticolimbico, è coinvolto nella mediazione delle proprietà di rinforzo e nella dipendenza da diverse sostanze d’abuso. Le sinapsi glutammatergiche del NAc possono esprimere plasticità, tra cui una forma di depressione a lungo termine (LTD) dipendente dagli endocannabinoidi (eCB). Recenti studi hanno dimostrato un’interazione tra le vie di segnalazione del sistema eCB e quelle di altri sistemi recettoriali, compreso quello serotoninergico (5-HT); la vasta colocalizzazione di recettori serotoninergici e CB1 nel NAc suggerisce la possibilità di un’interazione tra questi due sistemi. In questo studio abbiamo riscontrato che una stimolazione a 4 Hz per 20 minuti (LFS-4Hz) delle afferenze glutammatergiche in fettine cerebrali di ratto, induce una nuova forma di eCB-LTD nel core del NAc, che richiede l’attivazione dei recettori CB1 e 5-HT2 e l’apertura dei canali del Ca2+ voltaggio-dipendenti di tipo L. Inoltre abbiamo valutato che l’applicazione esogena di 5-HT (5 M, 20 min) induce una LTD analoga (5-HT-LTD) a livello delle stesse sinapsi, che richiede l’attivazione dei medesimi recettori e l’apertura degli stessi canali del Ca2+; LFS-4Hz-LTD e 5-HT-LTD sono reciprocamente saturanti. Questi risultati suggeriscono che la LFS-4Hz induce il rilascio di 5-HT, che si lega ai recettori 5-HT2 a livello postsinaptico incrementando l’influsso di Ca2+ attraverso i canali voltaggio-dipendenti di tipo L e la produzione e il rilascio di 2-arachidonoilglicerolo; l’eCB viaggia a ritroso e si lega al recettore CB1 a livello presinaptico, causando una diminuzione duratura del rilascio di glutammato, che risulta in una LTD. Queste osservazioni possono essere utili per comprendere i meccanismi neurofisiologici che sono alla base della dipendenza da sostanze d’abuso, della depressione maggiore e di altre malattie psichiatriche caratterizzate dalla disfunzione della neurotrasmissione di 5-HT nel NAc.

Overexpression of gastrin-releasing peptide receptors in tumor-associated blood vessels of human ovarian neoplasms

BACKGROUND: Peptide receptors, overexpressed in specific cancers, represent new diagnostic and therapeutic targets. In this study, receptors for the gastrin-releasing peptide (GRP), and other members of the bombesin-family of peptides, were evaluated in ovarian neoplasms. METHODS: 75 primary, secondary and metastatic ovarian tumors were investigated for their bombesin-receptor subtype expression, incidence, localization and density using in vitro autoradiography on tissue sections with the universal radioligand (125)I-[D-Tyr(6), beta-Ala(11), Phe(13), Nle(14)]-bombesin(6-14) and the GRP-receptor subtype-preferring (125)I-[Tyr(4)]-bombesin. RESULTS: GRP-receptors were detected in 42/61 primary ovarian tumors; other bombesin-receptor subtypes (BB1, bb3) were rarely present (3/61). Two different tissue compartments expressed GRP-receptors: the tumoral vasculature was the predominant site of GRP-receptor expression (38/61), whereas neoplastic cells more rarely expressed GRP-receptors (14/61). GRP-receptor positive vessels were present in the various classes of ovarian tumors; generally, malignant tumors had a higher incidence of GRP-receptor positive vessels compared to their benign counterparts. The prevalence of such vessels was particularly high in ovarian carcinomas (16/19) and their metastases (5/5). The GRP-receptors were expressed in high density in the muscular vessel wall. Normal ovary (n=10) lacked GRP-receptors. CONCLUSIONS: The large amounts of GRP-receptors in ovarian tumor vessels suggest a role in tumoral vasculature and possibly angiogenesis. Further, these vessels might be targeted in vivo with bombesin analogs for diagnosis or for therapy.

Cellular and network mechanisms of rhythm generation in spinal cord circuits

The generation of rhythmic electrical activity is a prominent feature of spinal cord circuits that is used for locomotion and also for circuit refinement during development. The mechanisms involved in rhythm generation in spinal cord networks are not fully understood. It is for example not known whether spinal cord rhythms are driven by pacemaker neurons and if yes, which neurons are involved in this function. We studied the mechanisms involved in rhythm generation in slice cultures from fetal rats that were grown on multielectrode arrays (MEAs). We combined multisite extracellular recordings from the MEA electrodes with intracellular patch clamp recordings from single neurons. We found that spatially restricted oscillations of activity appeared in most of the cultures spontaneously. Such activity was based on intrinsic activity in a percentage of the neurons that could activate the spinal networks through recurrent excitation. The local oscillator networks critically involved NMDA, AMPA and GABA / glycine receptors at subsequent phases of the oscillation cycle. Intrinsic spiking in individual neurons (in the absence of functional synaptic coupling) was based on persistent sodium currents. Intrinsic firing as well as persistent sodium currents were increased by 5-HT through 5-HT2 receptors. Comparing neuronal activity to muscle activity in co-cultures of spinal cord slices with muscle fibers we found that a percentage of the intrinsically spiking neurons were motoneurons. These motoneurons were electrically coupled among each other and they could drive the spinal networks through cholinergic recurrent excitation. These findings open the possibility that during development rhythmic activity in motoneurons is not only involved in circuit refinement downstream at the neuromuscular endplates but also upstream at the level of spinal cord circuits.

TGF-beta1 in Aplysia: role in long-term changes in the excitability of sensory neurons and distribution of TbetaR-II-like immunoreactivity.

Exogenous recombinant human transforming growth factor beta-1 (TGF-beta1) induced long-term facilitation of Aplysia sensory-motor synapses. In addition, 5-HT-induced facilitation was blocked by application of a soluble fragment of the extracellular portion of the TGF-beta1 type II receptor (TbetaR-II), which presumably acted by scavenging an endogenous TGF-beta1-like molecule. Because TbetaR-II is essential for transmembrane signaling by TGF-beta, we sought to determine whether Aplysia tissues contained TbetaR-II and specifically, whether neurons expressed the receptor. Western blot analysis of Aplysia tissue extracts demonstrated the presence of a TbetaR-II-immunoreactive protein in several tissue types. The expression and distribution of TbetaR-II-immunoreactive proteins in the central nervous system was examined by immunohistochemistry to elucidate sites that may be responsive to TGF-beta1 and thus may play a role in synaptic plasticity. Sensory neurons in the ventral-caudal cluster of the pleural ganglion were immunoreactive for TbetaR-II, as well as many neurons in the pedal, abdominal, buccal, and cerebral ganglia. Sensory neurons cultured in isolation and cocultured sensory and motor neurons were also immunoreactive. TGF-beta1 affected the biophysical properties of cultured sensory neurons, inducing an increase of excitability that persisted for at least 48 hr. Furthermore, exposure to TGF-beta1 resulted in a reduction in the firing threshold of sensory neurons. These results provide further support for the hypothesis that TGF-beta1 plays a role in long-term synaptic plasticity in Aplysia.

Structural requirements for 5-HT2A and 5-HT1A serotonin receptor potentiation by the biologically active lipid oleamide

Oleamide is an endogenous fatty acid primary amide that possesses sleep-inducing properties in animals and that has been shown to effect serotonergic receptor responses and block gap junction communication. Herein, the potentiation of the 5-HT1A receptor response is disclosed, and a study of the structural features of oleamide required for potentiation of the 5-HT2A and 5-HT1A response to serotonin (5-HT) is described. Of the naturally occurring fatty acids, the primary amide of oleic acid (oleamide) is the most effective at potentiating the 5-HT2A receptor response. The structural features required for activity were found to be highly selective. The presence, position, and stereochemistry of the Δ9-cis double bond is required, and even subtle structural variations reduce or eliminate activity. Secondary or tertiary amides may replace the primary amide but follow a well defined relationship requiring small amide substituents, suggesting that the carboxamide serves as a hydrogen bond acceptor but not donor. Alternative modifications at the carboxamide as well as modifications of the methyl terminus or the hydrocarbon region spanning the carboxamide and double bond typically eliminate activity. A less extensive study of the 5-HT1A potentiation revealed that it is more tolerant and accommodates a wider range of structural modifications. An interesting set of analogs was identified that inhibit rather than potentiate the 5-HT2A, but not the 5-HT1A, receptor response, further suggesting that such analogs may permit the selective modulation of serotonin receptor subtypes and even have opposing effects on the different subtypes.

Brain-derived neurotrophic factor-deficient mice develop aggressiveness and hyperphagia in conjunction with brain serotonergic abnormalities

Brain-derived neurotrophic factor (BDNF) has trophic effects on serotonergic (5-HT) neurons in the central nervous system. However, the role of endogenous BDNF in the development and function of these neurons has not been established in vivo because of the early postnatal lethality of BDNF null mice. In the present study, we use heterozygous BDNF+/− mice that have a normal life span and show that these animals develop enhanced intermale aggressiveness and hyperphagia accompanied by significant weight gain in early adulthood; these behavioral abnormalities are known to correlate with 5-HT dysfunction. Forebrain 5-HT levels and fiber density in BDNF+/− mice are normal at an early age but undergo premature age-associated decrements. However, young adult BDNF+/− mice show a blunted c-fos induction by the specific serotonin releaser-uptake inhibitor dexfenfluramine and alterations in the expression of several 5-HT receptors in the cortex, hippocampus, and hypothalamus. The heightened aggressiveness can be ameliorated by the selective serotonin reuptake inhibitor fluoxetine. Our results indicate that endogenous BDNF is critical for the normal development and function of central 5-HT neurons and for the elaboration of behaviors that depend on these nerve cells. Therefore, BDNF+/− mice may provide a useful model to study human psychiatric disorders attributed to dysfunction of serotonergic neurons.

Columnar distribution of serotonin-dependent plasticity within kitten striate cortex

Recent studies have identified the potential for an important role for serotonin (5-HT) receptors in the developmental plasticity of the kitten visual cortex. 5-HT2C receptors are transiently expressed in a patchy fashion in the visual cortex of kittens between 30–80 days of age complementary to patches demarcated by cytochrome oxidase staining. 5-HT, operating via 5-HT2C receptors, increases cortical synaptic plasticity as assessed both in brain slices and in vivo. Herein, we report that bath application of 5-HT substantially increases the probability of long-term potentiation within 5-HT2C receptor-rich zones of cortex, but this effect is not observed in the 5-HT2C receptor-poor zones. Instead, in these zones, 5-HT application increases the probability of long-term depression. These location-specific effects of 5-HT may promote the formation of compartment-specific cortical responses.

Differential quantal release of histamine and 5-hydroxytryptamine from mast cells of vesicular monoamine transporter 2 knockout mice

The recent availability of mice lacking the neuronal form of the vesicular monoamine transporter 2 (VMAT2) affords the opportunity to study its roles in storage and release. Carbon fiber microelectrodes were used to measure individual secretory events of histamine and 5-hydroxytryptamine (5-HT) from VMAT2-expressing mast cells as a model system for quantal release. VMAT2 is indispensable for monoamine storage because mast cells from homozygous (VMAT2−/−) mice, while undergoing granule-cell fusion, do not release monoamines. Cells from heterozygous animals (VMAT2+/−) secrete lower amounts of monoamine per granule than cells from wild-type controls. Investigation of corelease of histamine and 5-HT from granules in VMAT2+/− cells revealed 5-HT quantal size was reduced more than that of histamine. Thus, although vesicular transport is the limiting factor determining quantal size of 5-HT and histamine release, intragranular association with the heparin matrix also plays a significant role.

Increased anxiety of mice lacking the serotonin1A receptor

Brain serotonin (5-HT) has been implicated in a number of physiological processes and pathological conditions. These effects are mediated by at least 14 different 5-HT receptors. We have inactivated the gene encoding the 5-HT1A receptor in mice and found that receptor-deficient animals have an increased tendency to avoid a novel and fearful environment and to escape a stressful situation, behaviors consistent with an increased anxiety and stress response. Based on the role of the 5-HT1A receptor in the feedback regulation of the 5-HT system, we hypothesize that an increased serotonergic neurotransmission is responsible for the anxiety-like behavior of receptor-deficient animals. This view is consistent with earlier studies showing that pharmacological activation of the 5-HT system is anxiogenic in animal models and also in humans.

Tonic nicotinic modulation of serotoninergic transmission in the spinal cord

The spinal serotoninergic projection from the raphe magnus has been shown to modulate nociceptive inputs, and activation of this projection mediates nicotine-elicited analgesia. Here, we investigate the interactions between cholinergic and serotoninergic systems in the spinal cord, by conducting serotonin [5-hydroxytryptamine (5-HT)] efflux experiments on mouse spinal slices. At least three spinal populations of nicotinic receptors are distinguished that affect 5-HT release. The first could be directly located on serotoninergic terminals, is insensitive to nanomolar concentrations of methyllicaconitine (MLA), and may be subjected to a basal (not maximal) cholinergic tone. The second is tonically and maximally activated by endogenous acetylcholine, insensitive to nanomolar concentrations of MLA, and present on inhibitory neurons. The last is also present on inhibitory neurons but is sensitive to nanomolar concentrations of MLA and not tonically activated by acetylcholine. Multiple nicotinic acetylcholine receptor populations thus differentially exert tonic or not tonic control on 5-HT transmission in the spinal cord. These receptors may be major targets for nicotine effects on antinociception. In addition, the presence of a tonic nicotinic modulation of 5-HT release indicates that endogenous acetylcholine plays a role in the physiological regulation of descending 5-HT pathways to the spinal cord.

Receptor stimulation causes slow inhibition of IRK1 inwardly rectifying K+ channels by direct protein kinase A-mediated phosphorylation.

Strongly rectifying IRK-type inwardly rectifying K+ channels are involved in the control of neuronal excitability in the mammalian brain. Whole-cell patch-clamp experiments show that cloned rat IRK1 (Kir 2.1) channels, when heterologously expressed in mammalian COS-7 cells, are inhibited following the activation of coexpressed serotonin (5-hydroxytryptamine) type 1A receptors by receptor agonists. Inhibition is mimicked by internal perfusion with GTP[gamma-S] and elevation of internal cAMP concentrations. Addition of the catalytic subunits of protein kinase A (PKA) to the internal recording solution causes complete inhibition of wild-type IRK1 channels, but not of mutant IRK1(S425N) channels in which a C-terminal PKA phosphorylation site has been removed. Our data suggest that in the nervous system serotonin may negatively control IRK1 channel activity by direct PKA-mediated phosphorylation.