Viable dark matter via radiative symmetry breaking in a scalar singlet Higgs portal extension of the standard model.

We consider the generation of dark matter mass via radiative electroweak symmetry breaking in an extension of the conformal standard model containing a singlet scalar field with a Higgs portal interaction. Generating the mass from a sequential process of radiative electroweak symmetry breaking followed by a conventional Higgs mechanism can account for less than 35% of the cosmological dark matter abundance for dark matter mass M(s)>80 GeV. However, in a dynamical approach where both Higgs and scalar singlet masses are generated via radiative electroweak symmetry breaking, we obtain much higher levels of dark matter abundance. At one-loop level we find abundances of 10%-100% with 106 GeV80 GeV detection region of the next generation XENON experiment.

Silver nanoparticles modified ZnO nanocatalysts for effective degradation of ceftiofur sodium under UV-vis light illumination.

Light-induced photocatalytic degradation of ceftiofur sodium (CFS) has been assessed in the presence of plasmonic zinc oxide nanostructures (ZnONSTs), like, ZnO nanoparticles, ZnO nanorods (ZnONRs) and ZnO nanoflowers (ZnONFs). Silver nanoparticles (Ag NPs) loaded ZnO nanostructures (Ag-ZnONSTs) are obtained through seed-assisted chemical reaction followed by chemical reduction of silver. The surface modification of ZnO nanostructures by Ag NPs effectually altered their optical properties. Further, the surface plasmonic effect of Ag NPs facilitates visible light absorption by ZnONSTs and improved the photogenerated electron and hole separation, which makes the ZnONSTs a more active photocatalyst than TiO2 (P25) nanoparticles. Especially, Ag-ZnONRs showed higher CFS oxidation rate constant (k' = 4.6 × 10-4 s-1) when compared to Ag-ZnONFs (k' = 2.8 × 10-4 s-1) and Ag-ZnONPs (k' = 2.5 × 10-4 s-1), owing to their high aspect ratio (60:1). The unidirectional transport of photogenerated charge carriers on the Ag-ZnONRs may be accountable for the observed high photocatalytic oxidation of CFS. The photocatalytic oxidation of CFS mainly proceeds through •OH radicals generated on the Ag-ZnONRs surface under light illumination. In addition, heterogeneous activation of peroxymonosulfate by Ag-ZnONRs accelerates the rate of photocatalytic mineralization of CFS. The quantification of oxidative radicals supports the proposed CFS oxidation mechanism. Stability studies of plasmonic Ag-ZnONSTs strongly suggests that it could be useful to clean large volume of pharmaceutical wastewater under direct solar light irradiation.

The Sda/GM2-glycan is a carbohydrate marker of porcine primordial germ cells and of a subpopulation of spermatogonia in cattle, pigs, horses and llama.

Spermatogonia are a potential source of adult pluripotent stem cells and can be used for testis germ cell transplantation. Markers for the isolation of these cells are of great importance for biomedical applications. Primordial germ cells and prepubertal spermatogonia in many species can be identified by their binding of Dolichos biflorus agglutinin (DBA). This lectin binds to two different types of glycans, which are α-linked N-acetylgalactosamine (GalNac) and ß-linked GalNac, if this is part of the Sda or GM2 glycotopes. We used the MAB CT1, which is specific for the trisaccharides motif NeuAcα2-3(GalNAcß1-4)Galß1-, which is common to both Sda and GM2 glycotopes, to further define the glycosylation of DBA binding germ cells. In porcine embryos, CT1 bound to migratory germ cells and gonocytes. CT1/DBA double staining showed that the mesonephros was CT1 negative but contained DBA-positive cells. Gonocytes in the female gonad became CT1 negative, while male gonocytes remained CT1 positive. In immunohistological double staining of cattle, pig, horse and llama testis, DBA and CT1 staining was generally colocalised in a subpopulation of spermatogonia. These spermatogonia were mainly single, sometimes paired or formed chains of up to four cells. Our data show that the Sda/GM2 glycotope is present in developing germ cells and spermatogonia in several species. Owing to the narrower specificity of the CT1 antibody, compared with DBA, the former is likely to be a useful tool for labelling and isolation of these cells.

New insights in the dihydroxybenzenes-driven Fenton reaction: electrochemical study of interaction between dihydroxybenzenes and Fe(III).

It has been reported that the dihydroxybenzene (DHB) driven Fenton reaction is more efficient to degrade recalcitrant substrates than the simple Fenton reaction. The enhanced reactivity of the DHB driven Fenton reaction is not clear, but it could be explained by the formation of oxidant species different from the ones formed by classical Fenton reaction or by the shift of the redox potential of the complex formed by DHB and Fe(III). The redox reaction between Fe(III) and the DHBs 1,2-dihydroxybenzene (catechol, CAT), 2,3-dihydroxybenzoic acid (2,3-DHBA), 3,4-dihydroxybenzoic acid (3,4-DHBA), and 1,2-dihydroxy-3,5-benzenedisulfonate (TIRON) was studied by cyclic voltammetry to better understand the enhanced reactivity of the DHB driven Fenton reaction. It was determined that the amount of Fe(II) produced by the redox reaction between Fe(III) and DHBs was insufficient to explain the enhanced reactivity. Cyclic voltammograms (CV) of the DHBs/Fe(III) systems show a quasi-reversible or irreversible behavior and also shifting and splitting the anodic peaks. This effect can be related to DHBs oxidation by Fe(III), but not to a real interaction.

N-methyl-d-aspartic acid receptor antagonist-induced frequency oscillations in mice recreate pattern of electrophysiological deficits in schizophrenia.

INTRODUCTION: Electrophysiological responses to auditory stimuli have provided a useful means of elucidating mechanisms and evaluating treatments in psychiatric disorders. Deficits in gating during paired-click tasks and lack of mismatch negativity following deviant stimuli have been well characterized in patients with schizophrenia. Recently, analyses of basal, induced, and evoked frequency oscillations have gained support as additional measures of cognitive processing in patients and animal models. The purpose of this study is to examine frequency oscillations in mice across the theta (4-7.5 Hz) and gamma (31-61 Hz) bands in the context of N-methyl-d-aspartic acid receptor (NMDAR) hypofunction and dopaminergic hyperactivity, both of which are thought to serve as pharmacological models of schizophrenia. EXPERIMENTAL PROCEDURES: Electroencephalograms (EEG) were recorded from mice in five treatment groups that consisted of haloperidol, risperidone, amphetamine, ketamine, or ketamine plus haloperidol during an auditory task. Basal, induced and evoked powers in both frequencies were calculated. RESULTS: Ketamine increased basal power in the gamma band and decreased the evoked power in the theta band. The increase in basal gamma was not blocked by treatment with a conventional antipsychotic. No other treatment group was able to fully reproduce this pattern in the mice. CONCLUSIONS: Ketamine-induced alterations in EEG power spectra are consistent with abnormalities in the theta and gamma frequency ranges reported in patients with schizophrenia. Our findings support the hypothesis that NMDAR hypofunction contributes to the deficits in schizophrenia and that the dopaminergic pathways alone may not account for these changes.

Control of spatiotemporal coherence of a thalamic oscillation by corticothalamic feedback.

The mammalian thalamus is the gateway to the cortex for most sensory modalities. Nearly all thalamic nuclei also receive massive feedback projections from the cortical region to which they project. In this study, the spatiotemporal properties of synchronized thalamic spindle oscillations (7 to 14 hertz) were investigated in barbiturate-anesthetized cats, before and after removal of the cortex. After complete ipsilateral decortication, the long-range synchronization of thalamic spindles in the intact cortex hemisphere changed into disorganized patterns with low spatiotemporal coherence. Local thalamic synchrony was still present, as demonstrated by dual intracellular recordings from nearby neurons. In the cortex, synchrony was insensitive to the disruption of horizontal intracortical connections. These results indicate that the global coherence of thalamic oscillations is determined by corticothalamic projections.

A system to evaluate the quality of frozen embryos through short-term culture.

The aim of the present study was to evaluate a culture system as a non-invasive approach intended for assessing the viability of recently thawed embryos prior to transfer. Embryos (n=51) were collected seven days after insemination out of 20 cows that had been treated to synchronize estrus and induce superovulation. Embryos were classified as good, fair, and poor and frozen. All embryos were cultured in McCoy medium. Morphology was monitored for a period of 24h to register the development stage every 30 min for the first 2h, and every hour thereafter. A sample of four embryos of each classification was separated at 4h, another four at 12h, and the remaining seven at 24h and the degree of apoptosis was determined for all the embryos using the TUNEL technique. Embryos of good and fair quality did not undergo major detrimental changes in development even after 7h of incubation, whereas poor quality embryos experienced changes as early as 2h after incubation. Good quality embryos invariably had fewer numbers of apoptotic cells than those of fair and poor quality suggesting that embryo culture can be a useful method to assess viability and to confirm the quality of thawed embryos previously stored in liquid nitrogen prior to transfer.

Photocatalyzed degradation of flumequine by doped TiO2 and simulated solar light.

Titanium dioxide was obtained in its pure form (TiO2) and in the presence of urea (u-TiO2) and thiourea (t-TiO2) using the sol-gel technique. The obtained powders were characterized by BET surface area analysis, Infrared Spectroscopy, Diffuse Reflectance Spectroscopy and the Rietveld refinement of XRD measurements. All the prepared catalysts show high anatase content (>99%). The a and b-cell parameters of anatase increase in the order TiO2u-TiO2>TiO2. The photocatalytic activities of the samples were determined on flumequine under solar-simulated irradiation. The most active catalysts were u-TiO2 and t-TiO2, reaching values over 90% of flumequine degradation after 15 min irradiation, compared with values of 55% for the pure TiO2 catalyst. Changing simultaneously the catalyst amount (t-TiO2) and pH, multivariate analysis using the response surface methodology was used to determine the roughly optimal conditions for flumequine degradation. The optimized conditions found were pH below 7 and a catalyst amount of 1.6 g L(-1).

[Relation between some techniques of hypospadias repair and complications: Universitary San Vicente de Paul Hospital 1986-2005]. / Relación entre algunas técnicas de reparación de hipospadias y complicaciones en el Hospital Universitario San Vicente de Paul 1986-2005.

OBJECTIVE: The incidence of hypospadias has been increasing in the last decades. Successful hypospadias repair depends on patient factors and surgical technique, a factor closely related to the surgeon's experience. The aim of this descriptive, retrospective study was to determine the preferred technique and its association with postoperative complications. METHODS: Charts of 207 patients who had had hypospadias repair performed between January 1986 and December 2005, in the San Vicente de Paul University Hospital, were reviewed. RESULTS: Hypospadias repair was performed in patients between 1 and 14 years of age. Duckett technique was performed in 38.7%, Mathiew technique in 30% MAGPI technique in 11.6%, Snodgrass in 6.3% and other techniques in 14% of the patients. Postoperative complications included hemorrhagic complications (1.9%), infectious complications (1.9%), urethral diverticular dilatation (3.9%), residual ventral chordee (5.8%), failure of urethroplasty, (8.7%), strictures (23%), and fistulas (41%). Strictures was the most important risk factor for postoperative fistulas (p>0.05). Patients with hypospadias repair with PDS sutures had a lower incidence of postoperative fistulas (p<0.05). Tissue layer over the suture line, age of patient, and number of days with urethral stent was not related to the presence of postoperative complications. CONCLUSION: The importance of known and accepted protective factors in hypospadias repair, like tissue layer over the suture line, age of patient and more or less days with urethral stent, in terms of avoidance of postoperative complications after hypospadias repair, may have to be re-evaluated.

[Adult attention-deficit/hyperactivity disorder: descriptive study in a Memory Unit]. / Trastorno por déficit de atención/hiperactividad del adulto: estudio descriptivo en una Unidad de Memoria.

INTRODUCTION: Attention-deficit/hyperactivity disorder (ADHD) is the main neurological diagnosis in Chilean children. Its profile and evolution in adults has not been appropriately studied, despise its personal and social impact. AIM: To describe the characteristics of adults with ADHD evaluated in a memory unit, verifying the existence of differences depending on gender. PATIENTS AND METHODS: A demographic and symptomatic evaluation protocol was applied to all patients diagnosed with ADHD who consulted at the Memory Unit of the Pontificia Universidad Católica de Chile, during the year 2004. RESULTS: Eighty six patients were included. Average age was 37, being 53% male. Most patients were diagnosed for the first time in adulthood, corresponding to an ADHD of combined type. The main patients' complaints were forgetfulness and distraction. A stressing factor capable of worsening the symptoms was identified in 59% of patients. Depression was the principal comorbidity, with a significantly higher incidence in women. CONCLUSIONS: The limitations of ADHD diagnostic criteria available for adult patients are discussed. Differences depending on gender were analyzed, describing a predominantly disruptive profile in men and depressive profile in women. There is a clear under-diagnosis of female children with ADHD, with a potential negative impact on their neuropsychological development. The differential diagnosis with mild cognitive impairment, in patients complaining of recent memory decline is discussed.

Partially Dehulled Sunflower Seeds in Diets for Grazing Chickens: Effect in Meat Quality

The effect of including partially dehulled sunflower seeds in the diet of grazing chickens in meat quality was evaluated. Two hundred and forty, one-day-old, Ross 308 chickens were used, randomly distributed into four treatments with six replicates of 10 birds each. Seventy-two birds were slaughtered at seven weeks of age, 18 per treatment, extracting the Pectoralis major muscle to analyze meat quality. The treatments were completely randomized in a 2x2 factorial arrangement, where type of rearing (confinement or grazing) and diet (base diet or base diet substituting 10% soybean meal for partially dehulled sunflower seeds) were the independent variables. The grazing chickens spent 8 hours a day in a white clover (Trifolium repens) paddock. Including sunflower seeds improved (p<0.05) the color and crude protein (CP) in breast meat (p<0.05), while grazing increased (p<0.05) CP, dry mater (DM), and shear force (SF), and the percentage of breast fat decreased (p<0.05) by up to 50%. Additionally, grazing increased (p<0.05) saturated fatty acids (SFA) and reduced (p<0.05) lipid oxidation by up to 50%. Partially replacing soybean meal with partially dehulled sunflower seeds in the diet of grazing chickens with white clover improves the physicochemical characteristics and nutritional quality of the breast meat; it also decreases lipid oxidation, extending the shelf life of the meat.(AU)

Synchronized sleep oscillations and their paroxysmal developments.

The state of resting sleep is associated with a series of oscillations generated in cortical and thalamic networks. A newly discovered rhythm groups the spindle and delta sleep oscillations within slowly recurring (< 1 Hz) sequences. Multi-site, extra- and intracellular recordings provide evidence for synchronization of various classes of cell in the neocortex and thalamus during sleep oscillations that might reach paroxysmal levels similar to epileptic states. Sleep oscillations and the underlying synchronizing processes are disrupted during transition to brain arousal.

[Intramuscular midazolam in the initial treatment of status epilepticus]. / Midazolam intramuscular en el tratamiento inicial del estado epiléptico.

INTRODUCTION: The status epilepticus a serious complication of the epileptic syndrome with high rates of morbidity and mortality. Treatment is aimed to a fast control of the crisis. AIM: To evaluate the efficacy and security of intramuscular (IM) midazolam in the initial treatment of status epilepticus. PATIENTS AND METHODS: A prospective open clinical trial that included 43 status epilepticus in 38 adult patients. All of the cases received an initial dose of 15 mg IM of midazolam, with a simultaneous oral dose of phenytoin (15 to 20 mg/kg) or carbamazepine (15 mg/kg). If there was immediate control of the seizure but recurrence occurred during the next hours, 15 mg im of midazolam every 8 hours were given, for 24 hours. If there was immediate failure intravenous (IV) midazolam was given. RESULTS: 36 of the 43 status epilepticus were controlled: 30 with only one dose, 3 required additional IM doses, and 3 needed administration of IV midazolam, no patient had neither cardiovascular, respiratory or local complications. The only adverse effect was drowsiness in a variable grade. CONCLUSIONS: The use of IM midazolam is suggested as the initial treatment in status epilepticus in adults, especially in a low complexity setting, due to its effectiveness, quick action and security.

Voltage-sensitive dye imaging of neocortical spatiotemporal dynamics to afferent activation frequency.

The spatial and temporal patterns of neocortex activation are determined not only by the dynamic character of the input but also by the intrinsic dynamics of the cortical circuitry. To study the role of afferent input frequency on cortical activation dynamics, the electrical activity of in vitro neocortex slices was imaged during white-matter electrical stimulation. High-speed optical imaging was implemented using voltage-sensitive dyes in guinea pig visual and somatosensory cortex slices concomitantly with intracellular recordings. Single white-matter electrical stimuli activated well-defined cortical sites with a radially oriented columnar configuration. This configuration was followed, over the next few milliseconds, by a lateral spread of excitation through cortical layers 5 and 6 and layers 2 and 3. Much of the optical response was eliminated in low extracellular calcium, indicating that it was primarily synaptically mediated. Repetitive stimuli at 10 Hz reproduced the spatiotemporal pattern observed for single stimuli. In contrast, repetitive stimulation in the gamma frequency range ( approximately 40 Hz) rapidly restrained the area of excitation to a small columnar site directly above the stimulating electrode. Intracellular recordings from cells lateral to the activated column revealed increased inhibitory synaptic activity and/or decreased excitatory responses during the train at 40 Hz, but not during a 10 Hz stimulation. Localized microinjections of GABA(A) antagonist produced a reorganization of the geometrical activity pattern that was dependent on the position of the microinjection site. These findings indicate that the frequency-dependent spatial organization of neocortex activation is determined by inhibitory sculpting attributable to local network dynamics.

Spatiotemporal analysis of local field potentials and unit discharges in cat cerebral cortex during natural wake and sleep states.

The electroencephalogram displays various oscillation patterns during wake and sleep states, but their spatiotemporal distribution is not completely known. Local field potentials (LFPs) and multiunits were recorded simultaneously in the cerebral cortex (areas 5-7) of naturally sleeping and awake cats. Slow-wave sleep (SWS) was characterized by oscillations in the slow (<1 Hz) and delta (1-4 Hz) frequency range. The high-amplitude slow-wave complexes consisted in a positivity of depth LFP, associated with neuronal silence, followed by a sharp LFP negativity, correlated with an increase of firing. This pattern was of remarkable spatiotemporal coherence, because silences and increased firing occurred simultaneously in units recorded within a 7 mm distance in the cortex. During wake and rapid-eye-movement (REM) sleep, single units fired tonically, whereas LFPs displayed low-amplitude fast activities with increased power in fast frequencies (15-75 Hz). In contrast with the widespread synchronization during SWS, fast oscillations during REM and wake periods were synchronized only within neighboring electrodes and small time windows (100-500 msec). This local synchrony occurred in an apparent irregular manner, both spatially and temporally. Brief periods (<1 sec) of fast oscillations were also present during SWS in between slow-wave complexes. During these brief periods, the spatial and temporal coherence, as well as the relation between units and LFPs, was identical to that of fast oscillations of wake or REM sleep. These results show that natural SWS in cats is characterized by slow-wave complexes, synchronized over large cortical territories, interleaved with brief periods of fast oscillations, characterized by local synchrony, and of characteristics similar to that of the sustained fast oscillations of activated states.

Impaired fast-spiking, suppressed cortical inhibition, and increased susceptibility to seizures in mice lacking Kv3.2 K+ channel proteins.

Voltage-gated K(+) channels of the Kv3 subfamily have unusual electrophysiological properties, including activation at very depolarized voltages (positive to -10 mV) and very fast deactivation rates, suggesting special roles in neuronal excitability. In the brain, Kv3 channels are prominently expressed in select neuronal populations, which include fast-spiking (FS) GABAergic interneurons of the neocortex, hippocampus, and caudate, as well as other high-frequency firing neurons. Although evidence points to a key role in high-frequency firing, a definitive understanding of the function of these channels has been hampered by a lack of selective pharmacological tools. We therefore generated mouse lines in which one of the Kv3 genes, Kv3.2, was disrupted by gene-targeting methods. Whole-cell electrophysiological recording showed that the ability to fire spikes at high frequencies was impaired in immunocytochemically identified FS interneurons of deep cortical layers (5-6) in which Kv3.2 proteins are normally prominent. No such impairment was found for FS neurons of superficial layers (2-4) in which Kv3.2 proteins are normally only weakly expressed. These data directly support the hypothesis that Kv3 channels are necessary for high-frequency firing. Moreover, we found that Kv3.2 -/- mice showed specific alterations in their cortical EEG patterns and an increased susceptibility to epileptic seizures consistent with an impairment of cortical inhibitory mechanisms. This implies that, rather than producing hyperexcitability of the inhibitory interneurons, Kv3.2 channel elimination suppresses their activity. These data suggest that normal cortical operations depend on the ability of inhibitory interneurons to generate high-frequency firing.

[Vitreous surgery in paediatric population. Visual and anatomic outcomes]. / Cirugía vítreo-retiniana en pacientes pediátricos. Resultados anatómicos y visuales.

PURPOSE: To determine the anatomic and visual outcome of children that had undergone vitreoretinal surgery. METHOD: 229 clinical files where analyzed at our center, were included 73 patients, 77 eyes. We considered those who were 18 years old or younger and had undergone retinal surgery, retinopathy of prematurity (ROP) was excluded. RESULTS: The mean age was 10 years; the main indication for surgery was retinal detachment. Trauma and congenital and developmental abnormalities where found in 80% of the ocular pathology involved. 90.9% of the patients had an initial visual acuity of light perception to counting fingers. Final visual acuity ranged from counting fingers to 1.0 in 41.6%. There was no statistical significance between initial visual acuity and the final (p = 0.782) neither was the time of surgery and the final visual acuity (p = 0.454). 12.5% presented total retinal detachment and the macula was involved in 63.6% of all patients. Vitrectomy and retinopexy was the preferred surgery. Silicon oil was used in 58.4%. Retinal attachment was achieved in 63% of the patients after 6 months. CONCLUSION: In this kind of patients the ocular characteristics of the vitreous, made the surgery a very difficult procedure, and the final success include the visual rehabilitation.

Methylphenidate amplifies long-term potentiation in rat hippocampus CA1 area involving the insertion of AMPA receptors by activation of ß-adrenergic and D1/D5 receptors.

Methylphenidate (MPH, Ritalin©) is widely used in the treatment of Attention Deficit Hyperactivity Disorder and recently as a drug of abuse. Although the effect of MPH has been studied in brain regions such as striatum and prefrontal cortex (PFC), the hippocampus has received relatively little attention. It is known that MPH increases the TBS-dependent Long Term Potentiation (LTP) in the CA1 area. However, the cellular and molecular mechanisms involved in this process are still unknown. Using field potential recordings and western blot analysis in rat hippocampal slices of young rats, we found that acute application of MPH enhances LTP in CA3-CA1 synapses in a dose-dependent manner with an EC50 of 73.44±6.32 nM. Using specific antagonists and paired-pulse facilitation protocols, we observed that the MPH-dependent increase of LTP involves not only ß-adrenergic receptors activation but also post-synaptic D1/D5 dopamine receptors. The inhibition of PKA with PKI, suppressed the facilitation of LTP induced by MPH consistent with an involvement of the adenyl cyclase-cAMP-PKA dependent cascade downstream of the activation of D1/D5 receptors. In addition, samples of CA1 areas taken from slices potentiated with MPH presented an increase in the phosphorylation of the Ser845 residue of the GluA1 subunit of AMPA receptors compared to control slices. This effect was reverted by SCH23390, antagonist of D1/D5 receptors, and PKI. Moreover, we found an increase of surface-associated functional AMPA receptors. We propose that MPH increases TBS-dependent LTP in CA3-CA1 synapses through a polysynaptic mechanism involving activation of ß-adrenergic and D1/D5 dopaminergic receptors and promoting the trafficking and insertion of functional AMPA receptors to the plasma membrane.

Glucose-induced oscillations of intracellular Ca2+ concentration resembling bursting electrical activity in single mouse islets of Langerhans.

Intracellular Ca2+ levels were monitored in single, acutely isolated mouse islets of Langerhans by dual emission Indo-1 fluorometry. High-frequency (3.1 min-1) [Ca2+]i oscillations with a brief rising time (1-2 s) and 10 s half-width ('fast' oscillations) were detected in 11 mM glucose. Raising the glucose concentration to 16.7 mM increased the duration of these oscillations, which were otherwise absent in 5.5 mM glucose. [Ca2+]i waves of lower frequency (0.5 min-1) and longer rising time ('slow' oscillations) were also recorded. The data indicate that "fast" oscillations are directly related to beta-cell bursting electrical activity, and suggest the existence of extensive networks of electrically coupled cells in the islet.

Synchronization of low-frequency rhythms in corticothalamic networks.

We have investigated the degree of synchronization between cortical, thalamic reticular and thalamocortical neurons of cats during low-frequency (< 15 Hz) sleep-like oscillations, as they appear under anaesthesia. We have also studied the effects exerted by cortical stimulation on the synchronization among thalamic units. Parallel experiments [Steriade et al. (1996) J. Neurosci. 16, 392-417] in this laboratory have demonstrated the similarity between the slow oscillation (< 1 Hz) under ketamine-xylazine anaesthesia and that occurring during the natural state of resting sleep. Spontaneous activity was recorded simultaneously, with independent microelectrodes, from groups of two to five physiologically identified neurons. The rhythmicity of spontaneous activity and the temporal relations between cellular discharges were statistically evaluated by auto- and crosscorrelation techniques. We have found no topography in the distribution of synchronization between thalamic reticular and thalamocortical cells. Only the slow, cortical-generated oscillation (< 1 Hz) displayed a stable frequency and correlation among groups of cortical and thalamic cells. The other two sleep oscillations (thalamic-generated spindles at 7-14 Hz and clock-like delta at 1-4 Hz) fluctuated in frequency and the degree of correlation between neurons varied. Cortical volleys entrained and synchronized thalamic cells, and triggered synchronized spindling in the thalamus. These results extend for large populations of cortical and thalamic neurons the phase relations found in intracellular recordings.