Gonadotropin-releasing hormone receptor in spinal cord neurons of embryos and adult rats

Mammalian gonadotropin-releasing hormone (GnRH) and its receptor have been found in the neuroendocrine reproductive axis. However, they can be localized in other extra-pituitary tissues as well including the central nervous system. The present study reports the expression of GnRH receptor and its mRNA in spinal cord neurons of rat embryos and adult rats, using immunohistochemistry and reverse transcriptase polymerase chain reaction (RT-PCR). Immunohistochemistry showed that the spinal cord neurons of rat embryos and adult rats expressed the GnRH receptor. The study of GnRH receptor mRNAs revealed that both cultured spinal cord neurons of rat embryos and adult rats expressed the GnRH receptor mRNA. Additional in vitro experiments showed that the expression of GnRH receptor mRNA was less in the spinal cord neurons exposed to GnRH compared to unexposed ones. These results raise the possibility that GnRH may play other roles independently from its participation in reproductive function.

Effect of the flavonoid quercetin on inflammation and lipid peroxidation induced by Helicobacter pylori in gastric mucosa of guinea pig

BACKGROUND

Helicobacter pylori infection induces an inflammatory response in the gastric mucosa. Activation of polymorphonuclear leukocytes can produce oxidative damage to gastric tissue through intermediary radicals of oxygen and nitrogen. Vegetable extracts containing polyphenols of the flavonoid family have antibacterial activity, and the flavonoid quercetin possesses anti-H. pylori activity in vitro. The aim of this study was to analyze the effect of oral administration of pure quercetin on inflammation and lipid peroxidation induced by H. pylori in the gastric mucosa of the guinea pig.

METHODS

Sixty days after oral infection with H. pylori guinea pigs received 200 mg/kg of quercetin daily by mouth for 15 days. The infiltration index of inflammatory cells and bacterial density in both the pyloric antrum and corpus were histologically determined by myeloperoxidase histochemistry, hematoxylin-eosin, and modified Giemsa stains. The lipid hydroperoxide content was assessed by the orange xylenol spectrophotometric method.

RESULTS

Quercetin significantly reduced the infiltration index of mononuclear cell and bacterial colonization in the pyloric antrum and corpus. In the antrum of infected quercetin-treated animals, a significant diminution of neutrophil leukocyte infiltration was observed compared with the infected nonquercetin-treated animals. In the antrum, the lipid hydroperoxide concentration was significantly decreased in infected animals treated with quercetin, whereas in the corpus no significant differences were observed.

CONCLUSIONS

Our results indicate that in vivo oral quercetin administration decreases H. pylori infection in the gastric mucosa and reduces both the inflammatory response and lipid peroxidation.

Allergen-sensitization increases mast-cell expression of the exocytotic proteins SNAP-23 and syntaxin 4, which are involved in histamine secretion

BACKGROUND

Activation of mast cells (MCs) via aggregation of immunoglobulin E (IgE) bound to its high affinity receptor (FcepsilonRI) results in release of inflammatory mediators from secretory granules. Histamine is one of the critical biological mediators released in the allergic response. Synaptosomal-associated protein of 23 kDa (SNAP-23) and syntaxin 4 are plasma membrane proteins that have been associated with exocytosis in MCs. Studies with monoclonal IgEs indicate that binding of IgE to FcepsilonRI induces molecular and biological changes in

OBJECTIVES

The aim of this study was to investigate changes in the expression of SNAP-23 and syntaxin 4 by MCs following rat sensitization with ovalbumin (OVA). In addition, we assessed whether these proteins were involved in histamine secretion.

METHODS

SNAP-23 and syntaxin 4 expression was analyzed by Western blot using MCs from control and sensitized animals. Successful sensitization was confirmed based on the passive cutaneous anaphylaxis reaction. To test the role of these exocytotic proteins in histamine secretion, permeabilized MCs were incubated with SNAP-23 and syntaxin 4 antibodies.

RESULTS

Expression of SNAP-23 and syntaxin 4 was significantly higher in MCs from OVA-sensitized rats than in cells from control animals. In addition, incubation of permabilized cells with antibodies to SNAP-23 and syntaxin 4 led to a marked reduction of histamine secretion in stimulated cells.

CONCLUSIONS

Sensitization with OVA increases the expression of SNAP-23 and syntaxin 4 in MCs. Furthermore, our data suggest that these exocytotic proteins participate in histamine secretion.

Ultrastructural analysis and identification of membrane proteins in the free-living amoeba Difflugia corona

Syntaxin-1 and 25-kDa Synaptosome-associated Protein (SNAP-25) are present in the plasma membrane of several different secretory cell types and are involved in the exocytosis process. In this work, the free-living amoeba Difflugia corona was studied in relation to ultrastructure, structural membrane proteins, and proteins such as Syntaxin-1 and SNAP-25. Our results obtained by scanning electron microscopy in the amoeba without its theca, showed many membrane projections and several pore-like structures. Using immunocytochemistry, we found structural proteins Syntaxin-1 and SNAP-25.

Cancer prevalence in kidney transplant recipients in two general hospitals from Peru

21155

Background: Malignancy following kidney transplantation is an important medical problem during long-term follow-up. The accrual risk is approximately 100 times greater than the general population. We report some features of the cancers developed in our patient population Methods: We retrospectively reviewed records of 1050 kidney transplant recipients who received both unrelated or related allograft transplants from January 1972 to April 2006 and recorded the incidence of de novo malignancies that developed in this cohort. The study was carried out in two centers in Peru. The statistical method was descriptive and parametrical. Survival was calculated using the Kaplan-Meier method. Results: Forty-six cancer were diagnosed in 42 recipients (4.3%). Twenty six were men and 16 women, mean age was 46.0 years old (range:17–67). Malignancy was diagnosed between 2 to 240 months after transplantation. The tumors included Kaposi's sarcoma (KS) in ten patients, squamous cell carcinoma (SCC) in seven, basal cell carcinoma (BCC) in six, cervix cancer in four, colon and breast cancer in three and hepatocarcinoma in two. Also they were reported one case of small intestine cancer, osteosarcoma, pancreatic cancer, lung cancer, bladder cancer, schwanoma, melanoma, tongue cancer, postransplant lymphoproliferative disease, pelvis renal cancer and carcinomatosis from unknown primary. Thus, KS was the most common malignancy encountered in our series, with a prevalence of 0.95%, followed by SCC observed in 0.66% and BCC found in 0.57% of the patients. The average latency period between transplantation and development of malignancy was 25 months for KS, 72.0 months for SCC and 36.0 months for BCC. KS occurred earlier compared with the other cancers ( P < 0.05); We failed to demonstrate any correlation between age/sex and specific type of cancer. The 10 year - survival was 71%. Conclusions: The prevalence of cancer in our renal transplant recipients was 4.3%. KS and non melanoma skin cancer were the most frequent cancer. Low incidence of postransplant lymphoproliferative disease was found.

No significant financial relationships to disclose.

Prolactin-like hormone in the nematode Trichinella spiralis larvae

Expression of prolactin (PRL) or prolactin-like hormone has been reported in invertebrates. We investigated the larval phase of Trichinella spiralis: (a) to express 23 kDa PRL, (b) to define its localization and (c) to test its possible biological activity. Immunostaining in isolated larvae demonstrated positive material to 23 kDa PRL by all along the stichosome, specifically in the stichocytes. Homogenized immunoblot larvae showed a 23 kDa protein band. To assess PRL release and its biological activity, larvae were incubated in culture medium and the excretory/secretory products were analyzed by the Nb2 cells bioassay. A cellular growth equivalent until 10 nM PRL and using antibody against 23 kDa PRL, the growth was blocked. In conclusion our result provides evidence that PRL-like hormone is expressed and secreted by the larvae of T. spiralis.

Identification of exocytotic membrane proteins, syntaxin-1 and SNAP-25, in Entamoeba histolytica from hamster liver

Entamoeba histolytica is a protozoan parasite causing dysentery and in some cases liver abscesses. These effects have been attributed to cytolytic substances released by exocytosis. In this study, the presence of the proteins syntaxin-1 and SNAP-25, which are assumed to be involved in exocytosis, were examined by immunohistochemistry, immunoelectron microscopy and western blot analysis. Syntaxin-1 and SNAP-25 were expressed in the vesicular, vacuolar and plasma membranes of E. histolytica trophozoites. It can be concluded that these proteins might be involved in exocytosis processes.

Presence of SNAP-23 and syntaxin 4 in mouse and hamster peritoneal mast cells

Mast cells (MCs) play a crucial role in inflammatory reactions. Their presence and number in the peritoneal cavity is important to overcome and enhance resistance to peritoneal infection. When MCs are activated they release a variety of biological mediators from their granules, such as histamine, that contribute to the appropriate and rapid local immune response. Granular content is released using a process of compound exocytosis, also termed degranulation. SNAP-23 and syntaxin 4 are plasma membrane proteins involved in degranulation of rat MCs. Their presence, however, has not been studied in MCs of other rodent species. The aim of the present study was to investigate using immunocytochemistry whether SNAP-23 and syntaxin 4 are present in peritoneal MCs of the mouse and hamster. In addition, the diameter, percentage and histamine content of these cells were also analyzed. Our results demonstrate that SNAP-23 and syntaxin 4 are present in the mouse and hamster peritoneal MCs, suggesting that proteins involved in the secretory process in MCs are conserved among species. Likewise, we conclude that peritoneal MCs of mouse and hamster are heterogeneous in size, percentage and histamine content.

Expression of gonadotropin-releasing hormone receptor in cerebral cortical neurons of embryos and adult rats

Mammalian gonadotropin-releasing hormone (GnRH) was initially isolated from hypothalamus and its receptor from anterior pituitary, although extrapituitary GnRH receptors have been reported. The aim of the present study was to investigate whether GnRH receptor and its mRNA are expressed in cerebral cortical neurons of rat embryos and adult rats using immunohistochemical and reverse transcriptase polymerase chain reaction (RT-PCR) techniques. The immunohistochemistry and RT-PCR analysis showed expression of GnRH receptor and presence of its mRNA, in both cerebral cortical neurons of rat embryos and cerebral cortical tissues of adult rats. Additional experiments showed a decrease in the receptor mRNA expression when cultured neurons of rat embryos were treated with GnRH. It is possible that the presence of GnRH receptors in cortical neurons of rat may be involved in other physiological roles such as neurohormone or neuromodulator.

Urban dust fecal pollution in Mexico City: Antibiotic resistance and virulence factors of Escherichia coli

Fecal pollution of settled dust samples from indoor and outdoor urban environments, was measured and characterized by the presence of fecal coliforms (FC), and by the characterization of Escherichia coli virulence genes, adherence and antibiotic resistance traits as markers. There were more FC indoors than outdoors (mean values 1089 and 435MPN/g). Among indoor samples, there were more FC in houses with carpets and/or pets. Using a PCR-based assay for six enteropathogenicity genes (belonging to the EAEC, EHEC and EPEC pathotypes) on randomly selected E. coli isolates, there was no significant difference between isolates from indoors and outdoors (60% and 72% positive to at least one gene). The serotypes commonly associated with pathogenic strains, such as O86 and O28, were found in the indoor isolates; whereas O4, O66 and O9 were found amongst outdoor isolates. However, there were significantly more outdoor isolates resistant to at least one antibiotic (73% vs. 45% from indoors) among the strains positive for virulence factors, and outdoor isolates were more commonly multiresistant. There was no relationship between the presence of virulence genes and resistance traits. These results indicate that outdoor fecal bacteria were more likely from human sources, and those found indoors were related to pets and maintained in carpets. This study illustrates the risk posed by fecal bacteria from human sources, usually bearing virulence and resistance traits. Furthermore, the high prevalence of strains carrying genes associated to EAEC or EHEC pathotypes, in both indoor and outdoor environments, adds to the health risk.

Primary cutaneous lymphomas in Peru

17566

Background: The clinicopathologic characteristics of malignant lymphomas vary according to geography. The aim of this study was to determine the relative frequency of cutaneous lymphomas and to examine the clinical relevance of the new WHO/EORTC classification in Peruvian cases of cutaneous lymphoma. Methods: We conducted a clinicopathologic retrospective study of a collection of 68 primary cutaneous lymphomas, diagnosed from 1997 to 2004 in a National General Hospital. The clinical records, haematoxylin & eosin-stained slides and immunohistochemical stains from 67 patients with malignant lymphomas of the skin were reviewed. HTLV-1 serology was made using ELISA and Western Blot methods. The statistical method was descriptive and survival was calculated using the Kaplan-Meier method. Results: Mean age at presentation was 62 years and the female/male ratio 1.5:1. T cell lymphomas were 88.6% and 11.4% were B-cell lymphomas. The most frequent cutaneous lymphoma was mycosis fungoides (MF) 30/67 (44.7%), Adult T-cell leukemia/lymphoma (ATLL) 13/67 (19.4%), unspecified peripheral T-cell lymphoma 4/67 (6%), lymphomatoid papulosis 2/67 (3%), leg-type diffuse large B-cell lymphoma 2/67 (3%), diffuse large B-cell lymphoma 2/67 (3%), subcutaneous panniculitis-like T-cell lymphoma 2/67 (3%), anaplastic large cell lymphoma 1/67 (1.4%), Sézary síndrome 1/67 (1.4%), nasal type extranodal NK/T-cell lymphoma 1/67 (1.4%), marginal zone B-cell lymphoma 1/67 (1.4%), follicle center lymphoma 1/67 (1.4%), intravascular lymphoma 1/67 (1.4%) and unclassifiable 5/67 ( 7.4%). Clinical stages of MF were: 60% stage I; 30% stage II; 3% stage III and 7% stage IV. 5-year survival was 77%. In ATLL group, 3 had smouldering type and 10 had cutaneous type. 5-year survival was 18%. Conclusions: In this retrospective analysis, cutaneous T cell lymphomas were prevalent; both MF and ATLL had the most frequency among primary cutaneous lymphomas in our hospital. ATLL had a poor 5-year survival.

No significant financial relationships to disclose.

Presence of SNAP-25 in rat mast cells

Mast cells participate in inflammation and allergies by releasing active mediators stored in numerous cytoplasmic granules. Degranulation implies compound exocytosis which involves a combination of granule-granule and granule-plasma membrane fusions. One of the most important proteins in the exocytotic process in neural and endocrine cells is the synaptosomal associated protein of 25 kDa (SNAP-25). In the present study, using a highly specific monoclonal antibody against SNAP-25, we have demonstrated by immunocytochemistry, western blot and immunoelectron microscopy the presence of SNAP-25 in rat peritoneal mast cells. Likewise we localized the protein mainly on the membrane of the secretory granules. Thus while the precise function of SNAP-25 in mast cells remains to be elucidated, it may be envolved in granule-granule fusion needed in degranulation.

Pituitary synaptic protein SNAP-25 sensitive to GnRH is necessary for LH release

OBJECTIVE

The protein SNAP-25 is located in the plasma membrane and is known to participate in hormone exocytosis process. In the present work we studied the role of SNAP-25 on LH secretion in permeabilized adenohypophyseal cultured cells. The question of whether GnRH regulates SNAP-25 expression in adenohypophyseal cultured cells and in the adenohypophyses in vivo was also investigated.

METHODS

In digitonin-permeabilized cells incubated with anti-SNAP-25, stimulated LH secretion with Ca2+ was analysed. The presence and expression of SNAP-25 in adenohypophyseal cultured cells incubated with GnRH and in adenohypophyses of orchidectomized rats with GnRH administration was studied by immunochemistry and immunoblotting.

RESULTS

Immunochemical study revealed that SNAP-25 was present in cultured adenohypophyseal cells and in adenohypophysis of orchidectomized rats both with GnRH treatment. We found that LH secretion can be blocked by antibodies raised against SNAP-25 in permeabilized cells. Likewise, GnRH administration induced a significant decrease of SNAP-25 expression in cultured adenohypophyseal cells and in adenohypophysis of orchidectomized rats.

CONCLUSION

Our study showed that SNAP-25 is present in adenohypophyses in vitro as well as in vivo and that is involved in LH release and that GnRH can modify its expression.

Detection of glial fibrillary acidic protein and neurofilaments in the cerebrospinal fluid of patients with neurocysticercosis

Neurocysticercosis (NCC) is an infection caused by Taenia solium larval metacestodes in the central nervous system. The glial fibrillary acidic protein (GFAP) and neurofilaments (NFs) can be used as markers of glial and neuronal damage, respectively. We studied the GFAP and NFs of 68, 160 and 200 kDa in the cerebrospinal fluid (CSF) of patients with NCC by Western blotting. Our results showed that patients with NCC had significantly elevated GFAP levels in the CSF compared with the control, whereas NFs of 68, 160 and 200 kDa were not detected in the CFS of NCC patients. We concluded that GFAP could be used as a marker of glial damage in the CFS of NCC patients.

Effect of hypothyroidism on synaptosomal-associated protein of 25 kDa and syntaxin-1 expression in adenohypophyses of rat

The aim of this study was to analyze the expression of SNAP-25 and syntaxin-1 in the adenohypophyses of hypothyroid rats. Rats were divided into: 1) controls; 2) thyroidectomized 40 days; and 3) thyroidectomized 40 days with replacement of T4 20 days after surgery. Adenohypophyses were studied by immunohistochemistry and immunoblot analysis using antibodies against SNAP-25, syntaxin-1 and TSH. By immunostaining, SNAP-25 and syntaxin-1 were conspicuous and were localized around cytoplasmic vacuoles of thyroidectomy cells. Immunoblot analysis shows that thyroidectomy increases adenohypophysial SNAP-25 expression and decreases syntaxin-1 levels. T4 administration for 20 days produces a recovery similar to control values. In conclusion, thyroidectomy produces changes in both expression and immunoreactivity of SNAP-25 and syntaxin-1 in adenohypophyses of rats and these effects can be reversed by T4 administration.

[Neural codes for perception]

OBJECTIVE

This article describes experiments designed to show the neural codes associated with the perception and processing of tactile information.

DEVELOPMENT

The results of these experiments have shown the neural activity correlated with tactile perception. The neurones of the primary somatosensory cortex (S1) represent the physical attributes of tactile perception. We found that these representations correlated with tactile perception. By means of intracortical microstimulation we demonstrated the causal relationship between S1 activity and tactile perception. In the motor areas of the frontal lobe is to be found the connection between sensorial and motor representation whilst decisions are being taken.

CONCLUSIONS

S1 generates neural representations of the somatosensory stimuli which seen to be sufficient for tactile perception. These neural representations are subsequently processed by central areas to S1 and seem useful in perception, memory and decision making.

Pattern of symptom improvement following treatment with venlafaxine XR in patients with generalized anxiety disorder

BACKGROUND

The efficacy of anxiolytic drugs in generalized anxiety disorder (GAD) is conventionally assessed by evaluating changes in the total score of psychometric scales such as the Hamilton Rating Scale for Anxiety (HAM-A). The purpose of this pooled analysis of data was to evaluate the efficacy of venlafaxine extended release (XR) on individual items of the HAM-A and the Brief Scale for Anxiety (BSA).

METHOD

Data were pooled from 5 studies of patients with GAD who were treated with either venlafaxine XR or placebo for 8 weeks (N = 2,021) and up to 6 months (N = 767). Individual items of the HAM-A and the BSA were examined. and, using the mean changes from baseline to endpoint, an effect size for each item was calculated by dividing the difference between baseline and endpoint values for each item by the standard deviation of this difference. The effect sizes determined for the venlafaxine group were compared with those for the placebo group. Items from each scale that are concordant with the DSM-IV diagnostic criteria for GAD were selected for further examination, and the specific effect sizes of each item were expressed after controlling for placebo effects.

RESULTS

The effect size of the majority of the 14 items of the HAM-A scale and the 10 items of the BSA scale associated with treatment with venlafaxine XR was greater than with placebo at both 8 weeks and 6 months. Furthermore, the effect sizes at 6 months were generally greater than at 8 weeks in venlafaxine XR-treated patients. Effect sizes associated with venlafaxine XR were greatest for the HAM-A items that were most closely related to diagnostic symptoms of GAD, namely anxious mood, tension, intellectual functioning, and behavior at interview at both 8 weeks and 6 months. Similarly, GAD-related BSA items of inner tension, worrying over trifles, hostile feelings, and muscular tension were associated with the greatest improvements with venlafaxine XR at both time-points.

CONCLUSION

The HAM-A and BSA items that most closely corresponded to DSM-IV diagnostic criteria for GAD showed the largest improvement during treatment with venlafaxine XR. This indicates that the specific symptoms of GAD can be treated effectively with venlafaxine XR, both in the short and longer term.

Gain modulation in the central nervous system: where behavior, neurophysiology, and computation meet

Gain modulation is a nonlinear way in which neurons combine information from two (or more) sources, which may be of sensory, motor, or cognitive origin. Gain modulation is revealed when one input, the modulatory one, affects the gain or the sensitivity of the neuron to the other input, without modifying its selectivity or receptive field properties. This type of modulatory interaction is important for two reasons. First, it is an extremely widespread integration mechanism; it is found in a plethora of cortical areas and in some subcortical structures as well, and as a consequence it seems to play an important role in a striking variety of functions, including eye and limb movements, navigation, spatial perception, attentional processing, and object recognition. Second, there is a theoretical foundation indicating that gain-modulated neurons may serve as a basis for a general class of computations, namely, coordinate transformations and the generation of invariant responses, which indeed may underlie all the brain functions just mentioned. This article describes the relationships between computational models, the physiological properties of a variety of gain-modulated neurons, and some of the behavioral consequences of damage to gain-modulated neural representations.

Touch and go: decision-making mechanisms in somatosensation

A complex sequence of neural events unfolds between sensory receptor activation and motor activity. To understand the underlying decision-making mechanisms linking somatic sensation and action, we ask what components of the neural activity evoked by a stimulus are directly related to psychophysical performance, and how are they related. We find that single-neuron responses in primary and secondary somatosensory cortices account for the observed performance of monkeys in vibrotactile discrimination tasks, and that neuronal and behavioral responses covary in single trials. This sensory activity, which provides input to memory and decision-making mechanisms, is modulated by attention and behavioral context, and microstimulation experiments indicate that it may trigger normal perceptual experiences. Responses recorded in motor areas seem to reflect the output of decision-making operations, which suggests that the ability to make decisions occurs at the sensory-motor interface.

Neurofilament expression in cultured rat adenohypophysial cells

The aim of the present work was to investigate in cultured rat adenohypophysial cells: a) the presence of neurofilaments of 200 kDa (NF-H), b) the effect of thyroid hormone (T(3)) and thyrotropin releasing hormone (TRH) on the expression of NF-H and c) the possible role of NF-H on thyrotropin (TSH) secretion. The presence of NF-H was observed by immunocytochemistry in cultured rat adenohypophysial cells. The exposure to T(3) for 12 h produced a significant increase in NF-H expression; whereas incubation with TRH or T(3)+TRH resulted in no change. The cells treated with T(3) or TRH or T(3)+TRH for 24 h showed no alteration. However, incubation for 48 h with TRH or T(3)+TRH caused significant decrease in NF-H expression. Incubation with NF-H antibodies produced a significant inhibition of calcium-induced TSH release in digitonin-permeabilized adenohypophysial cells. These results provide evidence that NF-H is present in cultured rat adenohypophysial cells, and that T(3) and TRH can modify NF-H expression. It can be suggested that in cultured adenohypophysial cells, NF-H may play a role in the secretory process.

Thyroidectomy induces neurofilament expression in adenohypophyses of rats

We studied the effect of thyroidectomy on neurofilament expression in adenohypophyses of rats. The question of whether thyroxine (T4) administration can reduce this effect was also investigated. Rats were divided into: 1. Euthyroid controls, 2. Thyroidectomized 20 d (Tx 20 d), 3. Thyroidectomized 20 d with replacement of T4 (Tx 20 d + T4 20 d), 4. Thyroidectomized 40 d (Tx 40 d), 5. Thyroidectomized 40 d with replacement of T4 20 d after surgery (Tx 40 d + T4 20 d). Adenohypophyses were studied by immunohistochemistry and Western blot analysis using antibodies against neurofilament 200 kDa (NF-H) and thyroid-stimulating hormone (TSH). The number of thyrotrophs with immunoreactivity for NF-H was increased in Tx 20 d and Tx 40 d rats, whereas T4 administration protected the effect of thyroidectomy. In the thyroidectomized animals, thyrotrophs showed eccentric nuclei and the cytoplasm was full of NF-H immunoreactivity, whereas in T4 treated rats, the thyrotrophs were similar to control. Western blot analysis showed that NF-H expression increased in rats thyroidectomized for 20 and 40 d. T4 given immediately or 20 d after thyroidectomy caused no changes in NF-H expression. We conclude that thyroidectomy induces NF-H expression in adenohypophyses of rats and administration of T4 decreases this effect.

Correlated neuronal activity and the flow of neural information

For years we have known that cortical neurons collectively have synchronous or oscillatory patterns of activity, the frequencies and temporal dynamics of which are associated with distinct behavioural states. Although the function of these oscillations has remained obscure, recent experimental and theoretical results indicate that correlated fluctuations might be important for cortical processes, such as attention, that control the flow of information in the brain.