RESUMEN

Network oscillations are essential for all cognitive functions. Oscillatory deficits are well established in psychiatric diseases and are recapitulated in animal models. They are significantly and specifically affected by pharmacological interventions using psychoactive compounds. Dopamine D4 receptor (D4R) activation was shown to enhance gamma rhythm in freely moving rats and to specifically affect slow delta and theta oscillations in the urethane-anesthetized rat model. The goal of this study was to test the effect of D4R activation on slow network oscillations at delta and theta frequencies during wake states, potentially supporting enhanced functional connectivity during dopamine-induced attention and cognitive processing. Network activity was recorded in the prefrontal cortex (PFC), hippocampus (HC) and nucleus reuniens (RE) in control conditions and after injecting the D4R agonist A-412997 (3 and 5 mg/kg; systemic administration). We found that A-412997 elicited a lasting (~40 min) wake state and drastically enhanced narrow-band delta oscillations in the PFC and RE in a dose-dependent manner. It also preferentially enhanced delta synchrony over theta coupling within the PFC-RE-HC circuit, strongly strengthening PFC-RE coupling. Thus, our findings indicate that the D4R may contribute to cognitive processes, at least in part, through acting on wake delta oscillations and that the RE, providing an essential link between the PFC and HC, plays a prominent role in this mechanism.

Asunto(s)

Agonistas de Dopamina , Receptores de Dopamina D4 , Animales , Ratas , Agonistas de Dopamina/farmacología , Hipocampo/metabolismo , Núcleos Talámicos de la Línea Media/metabolismo , Corteza Prefrontal/metabolismo

RESUMEN

There is some weak evidence that the black hole merger named GW190521 had a non-zero eccentricity1,2. In addition, the masses of the component black holes exceeded the limit predicted by stellar evolution3. The large masses can be explained by successive mergers4,5, which may be efficient in gas disks surrounding active galactic nuclei, but it is difficult to maintain an eccentric orbit all the way to the merger, as basic physics would argue for circularization6. Here we show that active galactic nuclei disk environments can lead to an excess of eccentric mergers, if the interactions between single and binary black holes are frequent5 and occur with mutual inclinations of less than a few degrees. We further illustrate that this eccentric population has a different distribution of the inclination between the spin vectors of the black holes and their orbital angular momentum at merger7, referred to as the spin-orbit tilt, compared with the remaining circular mergers.

RESUMEN

The origins of the stellar-mass black hole mergers discovered by LIGO/Virgo are still unknown. Here we show that if migration traps develop in the accretion disks of active galactic nuclei (AGNs) and promote the mergers of their captive black holes, the majority of black holes within disks will undergo hierarchical mergers-with one of the black holes being the remnant of a previous merger. 40% of AGN-assisted mergers detected by LIGO/Virgo will include a black hole with mass ≳50M_{⊙}, the mass limit from stellar core collapse. Hierarchical mergers at traps in AGNs will exhibit black hole spins (anti)aligned with the binary's orbital axis, a distinct property from other hierarchical channels. Our results suggest, although not definitively (with odds ratio of ∼1), that LIGO's heaviest merger so far, GW170729, could have originated from this channel.

RESUMEN

Treatment of lower respiratory tract infection poses as an ongoing challenge among respiratory tract diseases. Bacterial infections are causes of acute exacerbations in chronic bronchitis and indications for antibacterial therapy. Several antibiotics were applied to treat bacterial infections in chronic bronchitis, among them fluoroquinolones are considered potent, broad-spectrum agents with excellent tissue penetration. This monograph focuses on zabofloxacin, a novel fluoroquinolone agent recently approved and launched in South Korea, and summarizes the drug's antibacterial efficacy, pharmacokinetic properties and toxicity. Recent advances concerning fluoroquinolones in chronic bronchitis will be discussed, along with a comparison between zabofloxacin and moxifloxacin. Zabofloxacin has proved to be noninferior to moxifloxacin against major community-acquired Gram-positive and Gram-negative respiratory tract pathogens and found to be well tolerated in both oral and parenteral administrations. These features can make it a potential antimicrobial agent in therapy of chronic bronchitis and other lower respiratory tract infections.

Asunto(s)

Bronquitis Crónica/tratamiento farmacológico , Fluoroquinolonas , Bacterias Gramnegativas/efectos de los fármacos , Bacterias Grampositivas/efectos de los fármacos , Infecciones del Sistema Respiratorio , Antiinfecciosos/administración & dosificación , Antiinfecciosos/química , Antiinfecciosos/farmacocinética , Bronquitis Crónica/etiología , Bronquitis Crónica/fisiopatología , Estudios Clínicos como Asunto , Vías de Administración de Medicamentos , Evaluación Preclínica de Medicamentos , Fluoroquinolonas/administración & dosificación , Fluoroquinolonas/química , Fluoroquinolonas/farmacocinética , Humanos , Moxifloxacino , Infecciones del Sistema Respiratorio/tratamiento farmacológico , Infecciones del Sistema Respiratorio/microbiología , Resultado del Tratamiento

RESUMEN

Medial septum (MS) plays a critical role in controlling the electrical activity of the hippocampus (HIPP). In particular, theta-rhythmic burst firing of MS neurons is thought to drive lasting HIPP theta oscillations in rats during waking motor activity and REM sleep. Less is known about MS-HIPP interactions in nontheta states such as non-REM sleep, in which HIPP theta oscillations are absent but theta-rhythmic burst firing in subsets of MS neurons is preserved. The present study used Granger causality (GC) to examine the interaction patterns between MS and HIPP in slow-wave sleep (SWS, a nontheta state) and during its short interruptions called microarousals (a transient theta state). We found that during SWS, while GC revealed a unidirectional MS→HIPP influence over a wide frequency band (2-12 Hz, maximum: ∼8 Hz), there was no theta peak in the hippocampal power spectra, indicating a lack of theta activity in HIPP. In contrast, during microarousals, theta peaks were seen in both MS and HIPP power spectra and were accompanied by bidirectional GC with MS→HIPP and HIPP→MS theta drives being of equal magnitude. Thus GC in a nontheta state (SWS) vs. a theta state (microarousal) primarily differed in the level of HIPP→MS. The present findings suggest a modification of our understanding of the role of MS as the theta generator in two regards. First, a MS→HIPP theta drive does not necessarily induce theta field oscillations in the hippocampus, as found in SWS. Second, HIPP theta oscillations entail bidirectional theta-rhythmic interactions between MS and HIPP.

Asunto(s)

Nivel de Alerta , Hipocampo/fisiología , Neuronas/fisiología , Núcleos Septales/fisiología , Sueño , Ritmo Teta , Potenciales de Acción , Animales , Interpretación Estadística de Datos , Electroencefalografía , Electromiografía , Masculino , Vías Nerviosas/fisiología , Ratas , Ratas Sprague-Dawley , Procesamiento de Señales Asistido por Computador

RESUMEN

Lowered fitness cost associated with resistance to fluoroquinolones was recently demonstrated to influence the clonal dynamics of methicillin-resistant Staphylococcus aureus (MRSA) in the health care setting. We investigated whether or not a similar mechanism impacts Klebsiella pneumoniae. The fitness of K. pneumoniae isolates from major international hospital clones (ST11, ST15, ST147) already showing high-level resistance to fluoroquinolones and of strains from three minor clones (ST25, ST274, ST1028) in which fluoroquinolone resistance was induced in vitro was tested in a propagation assay. Strains from major clones showed significantly less fitness cost than three of four fluoroquinolone-resistant derivatives of minor clone isolates. In addition, plasmids with CTX-M-15 type extended-spectrum ß-lactamase (ESBL) genes were all retained in both major and minor clone isolates, irrespective of the strains' level of fluoroquinolone resistance, while each plasmid harboring SHV-type ESBLs had been lost during the induction of resistance. Major clone K. pneumoniae strains harbored more amino acid substitutions in the quinolone resistance determining regions (QRDRs) of the gyrA and parC genes than minor clone isolates. The presence of an active efflux system could be demonstrated in all fluoroquinolone-resistant derivatives of originally SHV-producing minor clone isolates but not in any CTX-M-15-producing strain. Further investigations are needed to expand and confirm our findings on a larger sample. In addition, a long-term observation of our ciprofloxacin-resistant minor clone isolates is required in order to elucidate whether or not they are capable of restoring their fitness while concomitantly retaining high minimum inhibitory concentration (MIC) values.

Asunto(s)

Antibacterianos/farmacología , Farmacorresistencia Bacteriana , Metabolismo Energético , Fluoroquinolonas/farmacología , Klebsiella pneumoniae/crecimiento & desarrollo , Klebsiella pneumoniae/metabolismo , beta-Lactamasas/metabolismo , Genotipo , Humanos , Infecciones por Klebsiella/microbiología , Klebsiella pneumoniae/efectos de los fármacos , Klebsiella pneumoniae/enzimología , Pruebas de Sensibilidad Microbiana , Tipificación Molecular , Plásmidos/análisis , Selección Genética

RESUMEN

Polymyxins are polypeptide antibiotics, with a primary effect of membrane damaging due to their selective binding to the lipopolysaccharide of Gram-negative bacteria. Their nephro- and neurotoxic side effects limited their use, however, in the last decade the emergence of multidrug-resistant Gram-negative bacteria led to the reintroduction of polymyxins into clinical practice. This review provides an overview about the history and the latest developments of polymyxins. We describe the antimicrobial effects, pharmacodynamics, pharmacokinetics and different routes of administration. We highlight natural classic polymyxins, namely polymyxin B and E, the non-classic agents polymyxin M, S and T. Novel polymyxin chemical structure derivatives will be listed including NAB739, NAB740, NAB741 and NAB7061, that can have important therapeutical role in the future.

Asunto(s)

Descubrimiento de Drogas , Antibacterianos/química , Antibacterianos/farmacología , Proteínas de la Membrana Bacteriana Externa/efectos de los fármacos , Descubrimiento de Drogas/tendencias , Humanos , Pruebas de Sensibilidad Microbiana , Polimixinas/administración & dosificación , Polimixinas/química , Polimixinas/farmacología

RESUMEN

We investigated the prevalence of plasmid-mediated quinolone resistance genes in 756 clinical isolates of Enterobacteriaceae originating from Microbiology Diagnostic Laboratories of North-East Italy. Five point zero two percent of isolates carried a qnr determinant while the aac(6')-Ib-cr determinant was detected in 9·25% of isolates. We also investigated the association between the plasmid-mediated quinolone resistance and the beta-lactamase genes, and characterized the plasmids carrying these determinants of resistance.

Asunto(s)

Antibacterianos/farmacología , Enterobacteriaceae/genética , Fluoroquinolonas/farmacología , Plásmidos/genética , Farmacorresistencia Bacteriana , Enterobacteriaceae/efectos de los fármacos , Enterobacteriaceae/enzimología , Enterobacteriaceae/aislamiento & purificación , Infecciones por Enterobacteriaceae/tratamiento farmacológico , Infecciones por Enterobacteriaceae/microbiología , Proteínas de Escherichia coli/genética , Humanos , Italia , Pruebas de Sensibilidad Microbiana , Prevalencia , beta-Lactamasas/genética

RESUMEN

We investigated the presence of qnrC and qnrD among 756 non-replicate Enterobacteriaceae isolated in Italy, selected for being non-susceptible to fluoroquinolones and/or resistant to third-generation cephalosporins. Four Proteus mirabilis and one Morganella morganii (0.66% of the total) presented a qnrD gene, located in a 2687-base-pair plasmid that was entirely sequenced. The plasmid is un-typable, and contains no known coding region other than qnrD. That the qnrD gene was found in four unrelated P. mirabilis and in one M. morganii isolate might suggest a frequent association of this gene with the tribe Proteeae.

Asunto(s)

Antibacterianos/farmacología , Farmacorresistencia Bacteriana , Fluoroquinolonas/farmacología , Morganella morganii/genética , Plásmidos , Proteus mirabilis/genética , Cefalosporinas/farmacología , ADN Bacteriano/química , ADN Bacteriano/genética , Infecciones por Enterobacteriaceae/microbiología , Genes Bacterianos , Humanos , Italia , Datos de Secuencia Molecular , Morganella morganii/aislamiento & purificación , Proteus mirabilis/aislamiento & purificación , Análisis de Secuencia de ADN

RESUMEN

Binding of fluorescein isothiocyanate-labeled concanavalin A to a series of molecular species of lipopolysaccharide (LPS), purified from pathogenic bacteria, was studied via agarose gel precipitation experiments and the results were compared with available structural data.The LPS species could be divided into ConA-reactive and non-reactive ones. Reactivity resided in the O-specific chain of LPS, and binding to the lipid A or core moieties of LPS could not be demonstrated by the present methods. The α-D-glucose or α-D-mannose residues of the repeating O-specific oligosaccharide units appeared to be recognized by ConA, except when blocked by steric hindrance. Specificity of the reaction was verified by inhibition with 2% D-glucose. Binding by bacterium-specific sugar-residues could not be demonstrated.For precipitation to occur, polyvalency was required both for LPS and ConA, and the resulting precipitation appeared to be promoted by hydrophobic interactions between the lipid A moieties of LPS molecules. The LPS species were differently retained by the agarose gel, which can be explained by differences in their micellar structure in aqueous solution. E. coli O83 LPS did not readily diffused in 1% agarose gel, but its precipitation with ConA could be demonstrated either at elevated temperature or mixing it previously with molten agarose (Mancini's arrangement).

Asunto(s)

Concanavalina A/metabolismo , Interacciones Hidrofóbicas e Hidrofílicas , Lipopolisacáridos/metabolismo , Escherichia coli/metabolismo , Glucosa/análisis , Glucosa/metabolismo , Lípido A/metabolismo , Lipopolisacáridos/aislamiento & purificación , Manosa/análisis , Manosa/metabolismo , Salmonella enterica/metabolismo , Shigella flexneri/metabolismo

RESUMEN

Osteomyelitis continues to be a severe problem worldwide, causing plenty of hospital admissions and entailing vast expenses. Previously, we developed a low-cost polymethyl-methacrylate (PMMA)-sorbitol based capsule system for local long-term drug delivery. In the present study we aimed to test the in vitro release of clindamycin capsules by high performance liquid chromatography. By the end of the clinically relevant period (42 days), the capsules released 70-100% of their load. Furthermore, the release kinetics suggested that an effective antimicrobial concentration may be maintained within the target area. Our findings indicate that these newly developed capsules may be a versatile device for local clindamycin delivery by providing efficient release and reducing financial burdens.

Asunto(s)

Antibacterianos/química , Clindamicina/química , Sistemas de Liberación de Medicamentos , Osteomielitis/tratamiento farmacológico , Antibacterianos/administración & dosificación , Antibacterianos/efectos adversos , Antibacterianos/economía , Cápsulas , Cromatografía Líquida de Alta Presión , Enfermedad Crónica , Clindamicina/administración & dosificación , Clindamicina/efectos adversos , Clindamicina/economía , Preparaciones de Acción Retardada/economía , Composición de Medicamentos , Sistemas de Liberación de Medicamentos/economía , Costos de la Atención en Salud , Cinética , Osteomielitis/economía , Polimetil Metacrilato/química , Solubilidad , Sorbitol/química

RESUMEN

Antimicrobial resistance is an emerging worldwide concern in light of the widespread antimicrobial drug use in humans, livestock and companion animals. The treatment of life-threatening infections is especially problematic because clinical strains rapidly acquire multiple-drug resistance. Antimicrobial peptides have long been considered to be viable alternatives to small molecule antibiotics. However, the peptides' parenteral use is frequently hampered by inadequate safety margins and rapid renal clearance leaving them suitable only for topical applications. The proline-rich peptide A3-APO represents a family of a new class of synthetic dimers that kill bacteria by a dual mode of action and carry domains for interaction with both the bacterial membrane and an intracellular target. From a series of designer antibacterial peptides, A3-APO emerged as a viable preclinical candidate by virtue of its superior ability to disintegrate the bacterial membrane, inhibit the 70-kDa heat shock protein DnaK alone or in synergy with small molecule antibiotics, lack of eukaryotic toxicity and withstand proteolytic degradation in body fluids. As many other proline-rich peptides, A3-APO binds to the C-terminal helical lid of bacterial DnaK and inhibits chaperone-assisted protein folding in bacteria but not in mammalian Hsp70. In this review, the structure, pharmacokinetic properties, antimicrobial spectrum of peptide A3-APO and its in vivo metabolite are summarized and the in vitro and in vivo antimicrobial effects (antimicrobial susceptibilities, postantibiotic effects, resistance induction) are discussed in detail.

Asunto(s)

Antibacterianos/química , Antibacterianos/farmacología , Péptidos/química , Péptidos/farmacología , Secuencia de Aminoácidos , Animales , Diseño de Fármacos , Pruebas de Sensibilidad Microbiana , Modelos Moleculares , Datos de Secuencia Molecular , Prolina/química , Prolina/farmacología

RESUMEN

Preclinical findings demonstrate procognitive actions of histamine 3 (H3) receptor antagonists/inverse agonists. Since a prominent role of neuronal network oscillations of the hippocampus, such as theta band oscillation, has been recognized in numerous cognitive functions, in the present study, the potential involvement of H3 receptors in modulation of hippocampal theta activity has been investigated using various recording paradigms. Systemic administration of the selective H3 receptor antagonists/inverse agonists, thioperamide and ciproxifan (0.1 mg/kg to 1 mg/kg i.v.), dose dependently increased hippocampal theta power, similarly to methylphenidate (0.1-1 mg/kg i.v.), in chloral hydrate anesthetized rats. When hippocampal theta oscillation was elicited by electrical brainstem (nucleus pontis oralis) stimulation, ciproxifan (1 mg/kg i.v.) augmented the power of stimulation-induced theta. In contrast, systemic administration of methylphenidate (1 mg/kg i.v.) did not modify elicited theta. To analyze the role of H3 receptors on stage- and behavior-dependent hippocampal theta activity, polysomnographic recordings were carried out together with field potential recordings at the hippocampal fissure in freely moving rats for 8 h during the light phase of the circadian cycle. Systemic administration of ciproxifan (3.0 mg/kg, i.p.) promoted wakefulness with a concomitant reduction in cortical delta power and augmented novelty-induced hippocampal theta activity. These findings provide evidence that H3 receptors play an important role in regulation of hippocampal theta oscillation, representing one of the probable mechanisms involved in histamine-induced modulation of higher brain functions, such as attention and learning.

Asunto(s)

Hipocampo/efectos de los fármacos , Antagonistas de los Receptores Histamínicos H3/farmacología , Imidazoles/farmacología , Piperidinas/farmacología , Receptores Histamínicos H3/fisiología , Ritmo Teta/efectos de los fármacos , Anestésicos , Animales , Estimulantes del Sistema Nervioso Central/farmacología , Hidrato de Cloral , Electroencefalografía/efectos de los fármacos , Electromiografía/efectos de los fármacos , Hipocampo/fisiología , Masculino , Metilfenidato/farmacología , Músculo Esquelético/fisiología , Cuello , Ratas , Ratas Sprague-Dawley , Uretano

RESUMEN

AIMS: Routine procedures for monitoring viruses in water samples have not been drawn up for the water-microbiology screening panel. Enteric viruses, including astroviruses, are able to persist under environmental conditions and may cause public health problems by contaminating natural and drinking water resources. The aim of this study was to detect human astroviruses (HAstVs) from raw wastewater samples. METHODS AND RESULTS: To obtain data on whether human astroviruses are shed in the environment, 35 raw sewage samples from 22 sewage plants in different regions of Baranya County, Hungary were tested for astrovirus using a polyethylene glycol method for concentration and a guanidinium thiocyanate-silica procedure for extraction of viral RNA. Reverse transcription-polymerase chain reaction (RT-PCR) with HAstV-specific primer pairs was used for amplification and the specificity of amplicons was confirmed by nucleotide sequencing and phylogenetic analysis. Among the 35 raw sewage samples, 15 (43%) contained HAstV and by sequence analysis, 10 genotype HAstV-1 and one genotype HAstV-2 were identified. CONCLUSIONS: The high detection rate of astroviruses we encountered in this study provide convincing evidence that HAstVs circulate at a relatively high frequency in the Hungarian population. No correlation between the standard indicators of faecal pollution and the presence of HAstVs was found. SIGNIFICANCE AND IMPACT OF THE STUDY: Our study is the first report on detection of HAstV in sewage in Hungary and suggests that HAstV might be potent indicators of viral pollution in environmental specimens.

Asunto(s)

Mamastrovirus/aislamiento & purificación , Aguas del Alcantarillado/virología , Microbiología del Agua , Monitoreo del Ambiente/métodos , Humanos , Hungría , Mamastrovirus/genética , Filogenia , ARN Viral/aislamiento & purificación , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa/métodos

RESUMEN

Debye-like screening by edge dislocations of some externally given stress is studied by means of a variational approach to coarse grained field theory. Explicitly given are the force field and the induced geometrically necessary dislocation (GND) distribution, in the special case of a single glide axis in 2D, for (i) a single edge dislocation and (ii) a dislocation wall. Numerical simulation demonstrates that the correlation in relaxed dislocation configurations is in good agreement with the induced GND in case (i). Furthermore, the result (ii) well predicts the experimentally observed decay length for the GND developing close to grain boundaries.

RESUMEN

In the septohippocampal formation alpha7 nicotinic receptors (alpha7 nAChRs) are predominantly expressed by neurons well positioned to modulate hippocampal theta oscillation, such as GABAergic interneurons in the hippocampus, and by both GABAergic and cholinergic septal neurons. In the present experiments, we evaluated the efficacy of the recently developed selective alpha7 nAChR agonist PNU-282987 on hippocampal theta oscillation in anaesthetized rats. This compound shows high affinity for the rat alpha7 nAChRs (Ki = 26 nM) but a negligible activity at other nAChRs. Systemic administration of PNU-282987 significantly enhanced the power (by 40%) of hippocampal theta oscillation induced by electrical stimulation of the brainstem reticular formation. In contrast, the amnesic and muscarinic receptor antagonist scopolamine significantly decreased the power (by 68%) of the stimulation-induced theta oscillation. Given the connection between hippocampal theta oscillation and cognitive processes, it is proposed that precognitive actions of alpha7 nAChR agonists could be mediated, at least in part, by modulation of hippocampal oscillatory activity.

Asunto(s)

Hipocampo/fisiología , Receptores Nicotínicos/fisiología , Ritmo Teta , Animales , Benzamidas/administración & dosificación , Tronco Encefálico/fisiología , Tronco Encefálico/efectos de la radiación , Compuestos Bicíclicos con Puentes/administración & dosificación , Agonistas Colinérgicos/administración & dosificación , Estimulación Eléctrica/métodos , Hipocampo/efectos de los fármacos , Masculino , Antagonistas Muscarínicos/farmacología , Ratas , Ratas Sprague-Dawley , Escopolamina/farmacología , Ritmo Teta/efectos de los fármacos , Ritmo Teta/efectos de la radiación , Receptor Nicotínico de Acetilcolina alfa 7

Asunto(s)

Arginina/análogos & derivados , Arginina/sangre , Catalasa/genética , Diabetes Mellitus Tipo 2/sangre , Glutatión Peroxidasa/genética , Polimorfismo Genético , Anciano , Diabetes Mellitus Tipo 2/genética , Femenino , Humanos , Hungría , Masculino , Persona de Mediana Edad

RESUMEN

Neuronal projections to the dorsal raphe nucleus (DRN) from the medial prefrontal cortex (mPFC) and lateral habenula nucleus (LHb) provide the two key routes by which information processed by mood regulatory, cortico-limbic-striatal circuits input into the 5-HT system. These two projections may converge as it appears that both activate local GABAergic neurons to inhibit 5-HT neurons in the DRN. Here we have tested this hypothesis by measuring the effect of stimulation of the mPFC and LHb on the activity of 5-HT and non-5-HT, putative gamma-amino butyric acid (GABA) neurons in the DRN using extracellular recordings in anaesthetized rats. A total of 119 5-HT neurons (regular, slow firing, broad spike width) and 21 non-5-HT, putative GABA neurons (fast-firing, narrow spike width) were tested. Electrical stimulation of the mPFC or LHb caused a poststimulus inhibition (30 ms latency) of 101/119 5-HT neurons, of which 61 (60%) were inhibited by both the mPFC and LHb. Electrical stimulation of the mPFC or LHb also caused a short latency (12-20 ms) poststimulus facilitation of 10/21 non-5-HT neurons, of which 5 (50%) were activated by both the mPFC and LHb. These data indicate that a significant number of 5-HT neurons and non-5-HT neurons in the DRN are influenced by both the mPFC and LHb. Moreover, the data are compatible with the hypothesis and that there is a convergence of mPFC and LHb inputs on local circuit GABAergic neurons in the DRN which in turn inhibit the activity of 5-HT neurons.

Asunto(s)

Mapeo Encefálico , Habénula/fisiología , Neuronas/fisiología , Corteza Prefrontal/fisiología , Núcleos del Rafe/fisiología , Animales , Estimulación Eléctrica , Electrofisiología , Masculino , Vías Nerviosas , Ratas , Ratas Sprague-Dawley , Serotonina/metabolismo , Ácido gamma-Aminobutírico/metabolismo

RESUMEN

The supramammillary neurons projecting directly to the hippocampus or indirectly via the septum participate in the regulation of hippocampal theta activity. Inputs to the supramammillary nucleus are only partly specified neurochemically. Glutamate appears to be an excitatory transmitter in this cell group, however, the origin of the glutamatergic afferents is unknown. The present investigations were devoted to study this question. The transmitter-selective [(3)H]D-aspartate retrograde transport method was used injecting the tracer into the lateral subregion of the nucleus. The radioactive tracer was visualized by autoradiography. Non-selective retrograde tracing experiments were also performed for reference injecting wheat germ agglutinin-conjugated colloidal gold into the same supramammillary region. Retrogradely radiolabelled neurons in various numbers were detected in several brain regions including medial septum-diagonal band complex, lateral septum, rostral part of medial and lateral preoptic areas, lateral habenula, ventral premammillary nucleus, apical subregion of interpeduncular nucleus, laterodorsal tegmental nucleus, and dorsal and median raphe nuclei. Radiolabelled neurons in the mentioned raphe nuclei were serotonin-immunonegative. In the non-selective retrograde tracing experiments combined with immunocytochemistry, about 50% of the retrogradely labelled neurons in the raphe nuclei was serotonin-immunonegative, showing that not only serotonergic raphe neurons project to the supramammillary nucleus. The findings indicate that a significant part of the afferents from telencephalic, diencephalic and brainstem regions to the supramammillary nucleus may contain glutamate/aspartate as neurotransmitter. The most important functional implications of these observations concern the role of the supramammillary nucleus in controlling the electrical activity of the hippocampus, and in particular the generation and maintenance of the theta rhythm.

Asunto(s)

Ácido Aspártico/metabolismo , Ácido Glutámico/metabolismo , Tubérculos Mamilares/citología , Vías Nerviosas/citología , Neuronas/citología , Animales , Tronco Encefálico/citología , Tronco Encefálico/metabolismo , Recuento de Células , Banda Diagonal de Broca/citología , Banda Diagonal de Broca/metabolismo , Oro Coloide , Habénula/citología , Habénula/metabolismo , Inmunohistoquímica , Masculino , Tubérculos Mamilares/metabolismo , Vías Nerviosas/metabolismo , Neuronas/metabolismo , Área Preóptica/citología , Área Preóptica/metabolismo , Núcleos del Rafe/citología , Núcleos del Rafe/metabolismo , Ratas , Ratas Sprague-Dawley , Tabique del Cerebro/citología , Tabique del Cerebro/metabolismo , Serotonina/metabolismo , Distribución Tisular , Tritio , Aglutininas del Germen de Trigo

RESUMEN

Previous studies have shown that serotonergic neurons of the median raphe nucleus have a suppressive effect on theta synchronization in the hippocampus. Median raphe lesion, suppression of 5-HT neuronal activity by administration of GABA(A) receptor antagonist or by glutamate blockade or depletion produced long-lasting non-interrupted hippocampal theta in freely behaving rats independent of behavior and in rats anesthetized with urethane. Serotonergic neurons show a characteristic sleep-wake pattern of activity and there is evidence that GABAergic mechanisms play an important role in their regulation. In this study we analyzed the distribution and subcellular localization of GABA(B) receptors in the midbrain raphe complex using combined 5-HT/GABA(B) receptor immunohistochemistry at the light and electron microscopic levels and studied the effects of their pharmacological manipulation on hippocampal electroencephalographic activity in urethane-anesthetized rats. We found that sustained infusion of the GABA(B) receptor agonist baclofen into the median raphe nucleus, using the microdialysis technique, elicited lasting theta activity in the hippocampus. The effect was antagonized by selective GABA(B) receptor antagonists. The predominant localization of GABA(B) receptors in the median, as well as in dorsal raphe was found on serotonergic neurons which strongly indicates that the increase in theta occurrence after baclofen injection resulted from suppression of the serotonergic output originating from the median raphe. On the electron microscopic level, we found GABA(B) receptors located extrasynaptically indicating that these receptors are preferentially activated by strong inputs, i.e. when GABA released from the synaptic terminals is sufficient to spill over from the synaptic cleft. Such conditions might be satisfied during rapid eye movement sleep when GABAergic neurons in the raphe are firing at their highest rate and in rhythmic synchronized bursts. Our data indicate that midbrain raphe GABA(B) mechanisms play an important role in behavioral state control and in hippocampal activity, in particular.

Asunto(s)

Hipocampo/metabolismo , Vías Nerviosas/metabolismo , Neuronas/metabolismo , Puente/metabolismo , Núcleos del Rafe/metabolismo , Receptores de GABA-B/metabolismo , Serotonina/metabolismo , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/fisiología , Animales , Baclofeno/farmacología , Membrana Celular/metabolismo , Membrana Celular/ultraestructura , Dendritas/metabolismo , Dendritas/ultraestructura , Electroencefalografía/efectos de los fármacos , Fenclonina/farmacología , Agonistas del GABA/farmacología , Antagonistas del GABA/farmacología , Agonistas de Receptores GABA-B , Antagonistas de Receptores de GABA-B , Hipocampo/efectos de los fármacos , Hipocampo/ultraestructura , Inmunohistoquímica , Microscopía Electrónica , Vías Nerviosas/efectos de los fármacos , Vías Nerviosas/ultraestructura , Neuronas/efectos de los fármacos , Neuronas/ultraestructura , Puente/efectos de los fármacos , Puente/ultraestructura , Núcleos del Rafe/efectos de los fármacos , Núcleos del Rafe/ultraestructura , Ratas , Ratas Sprague-Dawley , Ratas Wistar , Formación Reticular/citología , Formación Reticular/efectos de los fármacos , Formación Reticular/metabolismo , Antagonistas de la Serotonina/farmacología , Sinapsis/metabolismo , Sinapsis/ultraestructura