Arterial hypertension - prevalence of risk factors and morbide associations that increase cardiovascular risk

Hypertension represents a serious problem in Romania, as there are over 3 million hypertensive people in our country. There is a high incidence of deaths caused by hypertension.WE PERFORMED AN ANALYTICAL PROSPECTIVE STUDY THAT AIMS TO DETERMINE: prevalence of arterial hypertension in a population from Cluj county, distribution on age and gender, arterial hypertension severity, association of hypertension with other cardiovascular risk factors. Our study included 2266 patients, age 14 years old up to over 90 years old, both masculine and feminine gender, known with hypertension and new-diagnosed ones. Each subject was submitted to an interview based on a questionnaire. Diagnosis of arterial hypertension was established according to ESH criteria that consider as hypertension: values over 140/90 mmHg. Out of all subjects submitted to the study 647 (29.74%) were diagnosed with arterial hypertension and, from these, 102 (15.13%) were new-diagnosed patients.We found out a predominance of arterial hypertension at the age of 51-60 and over 60, an increased involvement of feminine sex; an association of hypertension with other major cardiovascular risk factors: obesity, diabetes, dislypidemia.Arterial hypertension represents an important health problem in Romania due to an increased prevalence, major impact on morbidity and mortality by cardiovascular and cerebro-vascular disease. These facts accentuate the necessity of an early diagnosis, of making people aware of the severity of the disease and it's impact on their lifestyle.

Retinogeniculate EPSPs recorded intracellularly in the ferret lateral geniculate nucleus in vitro: Role of NMDA receptors

We used an in vitro preparation of the ferret lateral geniculate nucleus (LGN) to examine the role of the NMDA class of excitatory amino acid (EAA) receptors in retinogeniculate transmission. Intracellular recordings revealed that blockade of NMDA receptors both shortened the time course and reduced the amplitude of fast and slow components of excitatory postsynaptic potentials (EPSPs) evoked by optic tract stimulation. The amplitude and width of the EPSPs mediated by NMDA receptors increased as membrane potential was depolarized towards spike threshold. Individual LGN cells were influenced to varying extents by blockade of NMDA receptors; NMDA and non-NMDA receptor blockade together attenuated severely the entire retinogeniculate EPSP. The dependence of all components of retinogeniculate EPSPs (and action potentials) on NMDA receptor activation supports the hypothesis that the NMDA receptor participates in fast (<10 ms) synaptic events underlying conventional retinogeniculate transmission. The voltage dependence of the NMDA receptor-gated conductance suggests strongly that the transmission of retinal information through the LGN is subject to modulation by extraretinal inputs that affect the membrane potential of LGN neurons.

Comparison of parasite lactate dehydrogenase based immunochromatographic antigen detection assay (optimal) with microscopy for detection of malaria parasites

This study was done to compare the ability of a newly developed rapid malaria test OPtiMAL, an immunochromatographic antigen detection assay for the diagnosis of malaria using parasite lactate dehydrogenase, against standard microscopy. Blood samples were obtained from 232 patients suspected of having malaria. A total of 122 samples (52.5%) were positive by blood films while 118 (50.8%) were positive by OPtiMAL test. The blood film indicated that 21.4% (26 of 122) of the patients were positive for P. falciparum and 78.6% (96 of 122) were infected with P. vivax. OPtiMAL test showed that 21.2% (25 of 118) were positive for P. falciparum and 78.8% (93 of 118) were infected with P. vivax. This assay had sensitivities of 88.4% and 96.8% compared to traditional blood films for detection of P. falciparum and P. vivax malaria respectively. Thus OPtiMAL test can be used with or without traditional blood film examination for detection of both P. vivax and P. falciparum malaria and can be effectively used for the rapid diagnosis of malaria.

Intramedullary schistosomiasis

A case study of intramedullary schistosomiasis in a 10-year-old child is reported. The patient presented with a short history of ascending paraparesis with no sensory loss. Sphincter dysfunction was rapid. She had surgical exploration and removal of a conus medullaris mass. Schistosomiasis was confirmed histologically. Combined steroid and praziquantel therapy improved her sphincter function and paraparesis.

[Combination of new electrophysiological and imaging techniques in the study of primary visual cortex function]

INTRODUCTION

This work summarizes current research focused on explaining orientation selectivity of primary visual cortex (V1), and describes the electrophysiological and imaging techniques than are being used.

DEVELOPMENT

The study of orientation selectivity in V1 is key to understanding the cortical mechanisms implicated in the processing of sensory information, but this enterprise has proved more challenging than previously thought and there is no consensus about the best model to explain V1 neurons activity. Ongoing research is focused on determining the importance of the different inputs that a cortical cell receives (thalamic and lateral cortical inputs), and their link to cortical architecture. To achieve that, current research is combining optical imaging techniques with intracellular recordings of V1 neurons. Recent findings have found differences in the synaptic integration performed by neurons located in the iso orientation domains vs orientation centers of the functional V1 map.

CONCLUSIONS

Data describing synaptic activity combined with the cortical functional structure are yielding new clues about V1 computation, suggesting that there is more than one mechanism capable of generating orientation selectivity.

Stability of cortical responses and the statistics of natural scenes

The primary visual cortex (V1) of higher mammals contains maps of stimulus features; how these maps influence vision remains unknown. We have examined the functional significance of an asymmetry in the orientation map in cat V1, i.e., the fact that a larger area of V1 is preferentially activated by vertical and horizontal contours than by contours at oblique orientations. Despite the fact that neurons tuned to cardinal and oblique orientations have indistinguishable tuning characteristics, cardinal neurons remain more stable in their response properties after selective perturbation induced by adaptation. Similarly, human observers report different adaptation-induced changes in orientation tuning between cardinal and oblique axes. We suggest that the larger cortical area devoted to cardinal orientations imposes stability on the processing of cardinal contours during visual perception, by retaining invariant cortical responses along cardinal axes.

Enhanced plasticity of retinothalamic projections in an ephrin-A2/A5 double mutant

Ascending sensory information reaches primary sensory cortical areas via thalamic relay neurons that are organized into modality-specific compartments or nuclei. Although the sensory relay nuclei of the thalamus show consistent modality-specific segregation of afferents, we now show in a wild-type mouse strain that the visual pathway can be surgically "rewired" so as to induce permanent retinal innervation of auditory thalamic cell groups. Applying the same rewiring paradigm to a transgenic mouse lacking the EphA receptor family ligands ephrin-A2 and ephrin-A5 results in more extensive rewiring than in the wild-type strain. We also show for the first time that ephrin-A2 and ephrin-A5 define a distinct border between visual and auditory thalamus. In the absence of this ephrin-A2/A5 border and after rewiring surgery, retinal afferents are better able to invade and innervate the deafferented auditory thalamus. These data suggest that signals that induce retinal axons to innervate the denervated auditory thalamus may compete with barriers, such as the ephrins, that serve to contain them within the normal target. The present findings thus show that the targeting of retinothalamic projections can be surgically manipulated in the mouse and that such plasticity can be controlled by proteins known to regulate topographic mapping.

Disruption of retinogeniculate pattern formation by inhibition of soluble guanylyl cyclase

During development of the visual system of the ferret, the terminals of retinal ganglion cell axons first segregate to form eye-specific layers and subsequently On-center and Off-center sublayers within the dorsal lateral geniculate nucleus (dLGN). Sublamination requires the activity of the afferent fibers, NMDA receptors, and nitric oxide synthase (NOS). We here report that soluble guanylyl cyclase (sGC), which in turn produces cGMP, is critically involved in the process of sublamination. cGMP expression is upregulated in both retinal terminals and postsynaptic dLGN cells during sublamination, and this expression is controlled by the activity of both NMDA receptors and NOS. Furthermore, the infusion of specific inhibitors of sGC or protein kinase G (PKG), a target of cGMP, prevents sublamination in vivo. We conclude that the sGC-cGMP-PKG pathway acts downstream of NMDA receptors and nitric oxide as an effector of the activity-dependent refinement of connections at this level of the mammalian visual system.

Foci of orientation plasticity in visual cortex

Cortical areas are generally assumed to be uniform in their capacity for adaptive changes or plasticity. Here we demonstrate, however, that neurons in the cat striate cortex (V1) show pronounced adaptation-induced short-term plasticity of orientation tuning primarily at specific foci. V1 neurons are clustered according to their orientation preference in iso-orientation domains that converge at singularities or pinwheel centres. Although neurons in pinwheel centres have similar orientation tuning and responses to those in iso-orientation domains, we find that they differ markedly in their capacity for adaptive changes. Adaptation with an oriented drifting grating stimulus alters responses of neurons located at and near pinwheel centres to a broad range of orientations, causing repulsive shifts in orientation preference and changes in response magnitude. In contrast, neurons located in iso-orientation domains show minimal changes in their tuning properties after adaptation. The anisotropy of adaptation-induced orientation plasticity is probably mediated by inhomogeneities in local intracortical interactions that are overlaid on the map of orientation preference in V1.

Development and plasticity of cortical areas and networks

The development of cortical layers, areas and networks is mediated by a combination of factors that are present in the cortex and are influenced by thalamic input. Electrical activity of thalamocortical afferents has a progressive role in shaping cortex. For early thalamic innervation and patterning, the presence of activity might be sufficient; for features that develop later, such as intracortical networks that mediate emergent responses of cortex, the spatiotemporal pattern of activity often has an instructive role. Experiments that route projections from the retina to the auditory pathway alter the pattern of activity in auditory thalamocortical afferents at a very early stage and reveal the progressive influence of activity on cortical development. Thus, cortical features such as layers and thalamocortical innervation are unaffected, whereas features that develop later, such as intracortical connections, are affected significantly. Surprisingly, the behavioural role of 'rewired' cortex is also influenced profoundly, indicating the importance of patterned activity for this key aspect of cortical function.

Specific roles of NMDA and AMPA receptors in direction-selective and spatial phase-selective responses in visual cortex

Cells in the superficial layers of primary visual cortex (area 17) are distinguished by feedforward input from thalamic-recipient layers and by massive recurrent excitatory connections between neighboring cells. The connections use glutamate as transmitter, and the postsynaptic cells contain both NMDA and AMPA receptors. The possible role of these receptor types in generating emergent responses of neurons in the superficial cortical layers is unknown. Here, we show that NMDA and AMPA receptors are both involved in the generation of direction-selective responses in layer 2/3 cells of area 17 in cats. NMDA receptors contribute prominently to responses in the preferred direction, and their contribution to responses in the nonpreferred direction is reduced significantly by GABAergic inhibition. AMPA receptors decrease spatial phase-selective simple cell responses and generate phase-invariant complex cell responses.

Investigation of human papillomavirus in transitional cell carcinomas of the urinary bladder in South Africa

AIM

To investigate the prevalence of human papillomavirus in transitional cell carcinoma of the urinary bladder in South Africa.

METHODS

Ninety-one archival samples of bladder transitional cell carcinoma were subjected to polymerase chain reaction (PCR) and non-isotopic in situ hybridisation (NISH) for the detection of human papillomavirus 6, 11, 16, 18, 31, and 33 genotypes.

RESULTS

HPV was detected in only one case with PCR. HPV was not detected in any of the cases subjected to the NISH system.

CONCLUSION

This study shows that although HPV has been shown to be associated with uterine cervical and esophageal squamous cell carcinomas in South Africa, this virus is not present in the transitional cell carcinoma of the urinary bladder in this geographical location. It is suggested that other factors, including nitrosamine exposure, p53 mutation, and additional unknown chromosomal events, may play a role in the carcinogenesis of this neoplasm in the bladder.

Activity-dependent patterning of retinogeniculate axons proceeds with a constant contribution from AMPA and NMDA receptors

Neural activity is critical for the refinement of neural circuitry during development, although the mechanisms involved in stabilizing appropriate connectivity remain unclear. It has been proposed that the insertion of AMPA receptors at synapses with only NMDA receptors ("silent synapses") mediates this stabilization, leading to an increasing contribution from AMPA receptors as development proceeds. Here we show in a mammalian system known to undergo activity-dependent development [the segregation of retinal afferents into ON/OFF sublaminae in the ferret lateral geniculate nucleus (LGN)] that the refinement of the neural circuitry occurs in the presence of a constant functional contribution from AMPA and NMDA receptors. Although we detected a small number of silent synapses on LGN cells, their proportion did not decrease with age. The size and kinetics of NMDA-mediated spontaneous EPSCs (sEPSCs) were also stable over this period. Together with previous results reporting the stability of unitary AMPA-mediated EPSCs, the constancy of NMDA-mediated sEPSCs indicates an unchanging AMPA/NMDA contribution. Additionally, the CNQX-sensitivity did not increase for either sEPSCs or optic tract-evoked EPSCs. Likewise, the anatomical AMPA/NMDA ratio, as assayed by quantifying the colocalized expression of AMPA and NMDA receptor subunits, was fixed throughout ON/OFF sublamination. In particular, the colocalization of AMPA receptor subunits (GluR1 or GluR4) and NMDA receptor subunit NR1 opposite identified retinogeniculate terminals was stable during this period. These results add to the view of the population of retinogeniculate synapses as robustly stable or normalized during a period when retinogeniculate axons are undergoing dramatic activity-dependent refinement.

Adaptation-induced plasticity of orientation tuning in adult visual cortex

A key emergent property of the primary visual cortex (V1) is the orientation selectivity of its neurons. The extent to which adult visual cortical neurons can exhibit changes in orientation selectivity is unknown. Here we use single-unit recording and intrinsic signal imaging in V1 of adult cats to demonstrate systematic repulsive shifts in orientation preference following short-term exposure (adaptation) to one stimulus orientation. In contrast to the common view of adaptation as a passive process by which responses around the adapting orientation are reduced, we show that changes in orientation tuning also occur due to response increases at orientations away from the adapting stimulus. Adaptation-induced orientation plasticity is thus an active time-dependent process that involves network interactions and includes both response depression and enhancement.

Visual behaviour mediated by retinal projections directed to the auditory pathway

An unresolved issue in cortical development concerns the relative contributions of intrinsic and extrinsic factors to the functional specification of different cortical areas. Ferrets in which retinal projections are redirected neonatally to the auditory thalamus have visually responsive cells in auditory thalamus and cortex, form a retinotopic map in auditory cortex and have visual receptive field properties in auditory cortex that are typical of cells in visual cortex. Here we report that this cross-modal projection and its representation in auditory cortex can mediate visual behaviour. When light stimuli are presented in the portion of the visual field that is 'seen' only by this projection, 'rewired' ferrets respond as though they perceive the stimuli to be visual rather than auditory. Thus the perceptual modality of a neocortical region is instructed to a significant extent by its extrinsic inputs. In addition, gratings of different spatial frequencies can be discriminated by the rewired pathway, although the grating acuity is lower than that of the normal visual pathway.

Induction of visual orientation modules in auditory cortex

Modules of neurons sharing a common property are a basic organizational feature of mammalian sensory cortex. Primary visual cortex (V1) is characterized by orientation modules--groups of cells that share a preferred stimulus orientation--which are organized into a highly ordered orientation map. Here we show that in ferrets in which retinal projections are routed into the auditory pathway, visually responsive neurons in 'rewired' primary auditory cortex are also organized into orientation modules. The orientation tuning of neurons within these modules is comparable to the tuning of cells in V1 but the orientation map is less orderly. Horizontal connections in rewired cortex are more patchy and periodic than connections in normal auditory cortex, but less so than connections in V1. These data show that afferent activity has a profound influence on diverse components of cortical circuitry, including thalamocortical and local intracortical connections, which are involved in the generation of orientation tuning, and long-range horizontal connections, which are important in creating an orientation map.

Dynamic properties of recurrent inhibition in primary visual cortex: contrast and orientation dependence of contextual effects

A fundamental feature of neural circuitry in the primary visual cortex (V1) is the existence of recurrent excitatory connections between spiny neurons, recurrent inhibitory connections between smooth neurons, and local connections between excitatory and inhibitory neurons. We modeled the dynamic behavior of intermixed excitatory and inhibitory populations of cells in V1 that receive input from the classical receptive field (the receptive field center) through feedforward thalamocortical afferents, as well as input from outside the classical receptive field (the receptive field surround) via long-range intracortical connections. A counterintuitive result is that the response of oriented cells can be facilitated beyond optimal levels when the surround stimulus is cross-oriented with respect to the center and suppressed when the surround stimulus is iso-oriented. This effect is primarily due to changes in recurrent inhibition within a local circuit. Cross-oriented surround stimulation leads to a reduction of presynaptic inhibition and a supraoptimal response, whereas iso-oriented surround stimulation has the opposite effect. This mechanism is used to explain the orientation and contrast dependence of contextual interactions in primary visual cortex: responses to a center stimulus can be both strongly suppressed and supraoptimally facilitated as a function of surround orientation, and these effects diminish as stimulus contrast decreases.

Dynamics of neuronal processing in rat somatosensory cortex

Recently, the study of sensory cortex has focused on the context-dependent evolution of receptive fields and cortical maps over millisecond to second time-scales. This article reviews advances in our understanding of these processes in the rat primary somatosensory cortex (SI). Subthreshold input to individual rat SI neurons is extensive, spanning several vibrissae from the center of the receptive field, and arrives within 25 ms of vibrissa deflection. These large subthreshold receptive fields provide a broad substrate for rapid excitatory and inhibitory multi-vibrissa interactions. The 'whisking' behavior, an approximately 8 Hz ellipsoid movement of the vibrissae, introduces a context-dependent change in the pattern of vibrissa movement during tactile exploration. Stimulation of vibrissae over this frequency range modulates the pattern of activity in thalamic and cortical neurons, and, at the level of the cortical map, focuses the extent of the vibrissa representation relative to lower frequency stimulation (1 Hz). These findings suggest that one function of whisking is to reset cortical organization to improve tactile discrimination. Recent discoveries in primary visual cortex (VI) demonstrate parallel non-linearities in center-surround interactions in rat SI and VI, and provide a model for the rapid integration of multi-vibrissa input. The studies discussed in this article suggest that, despite its original conception as a uniquely segregated cortex, rat SI has a wide array of dynamic interactions, and that the study of this region will provide insight into the general mechanisms of cortical dynamics engaged by sensory systems.

Erratum

Hahm J-O, Cramer KS, Sur M. 1999. Pattern formation by retinal afferents in the ferret lateral geniculate nucleus: developmental segregation and the role of N-methyl-D-aspartate receptors. J Comp Neurol 411:327-345. Due to a printer's error, Figures 6 and 12 were transposed after the proofs of the article had been approved by the author. The correct figures and legends are reprinted on the following pages. The publisher regrets the error.

Development and plasticity of the cerebral cortex: from molecules to maps

The role played by environmental influences in the development of the nervous system has been subject to intense study for the last three decades. Many laboratories are currently engaged in characterizing the exact contributions of activity-dependent or -independent processes to the development of the mammalian neocortex. Here we introduce a special issue devoted to the topic and briefly review recent progress in this exciting field. At the systems level, many investigators are now distinguishing between an "establishment" phase of cortical connections, where activity-dependent and independent mechanisms could operate, and a later "maintenance" phase, which appears to be controlled by neuronal activity. A particularly interesting recent example of the role of top-down vs. bottom-up influences in the development of cortical connections is the emergence of orientation selectivity in visual cortex: we propose a synthetic view highlighting the role of the thalamo-cortical reciprocal projection in this process. Finally, at the cellular level, NMDA receptors, neurotrophins and many other molecules contribute to activity-dependent rearrangement of cortical connections during appropriate critical periods of development.

Rewiring cortex: the role of patterned activity in development and plasticity of neocortical circuits

Visually driven activity is not required for the establishment of ocular dominance columns, orientation columns, and long-range horizontal connections in visual cortex, although spontaneous activity appears to be necessary. The role of activity may be instructive or simply permissive; evidence for an instructive role requires inquiry into the role of the pattern of activity in shaping cortical circuits. The few experiments that have probed the role of patterned activity include the effects of artificial strabismus, artificial stimulation of the optic nerve, and rewiring visual projections from the retina to the auditory thalamus and cortex. These experiments demonstrate that patterned activity is vital for the maintenance of thalamocortical, local intracortical, and long-range horizontal connections in cortex.

Pattern formation by retinal afferents in the ferret lateral geniculate nucleus: developmental segregation and the role of N-methyl-D-aspartate receptors

The projection from the retina to the lateral geniculate nucleus (LGN) in ferrets segregates during development into eye-specific layers and ON/OFF sublayers. The projection pattern and the morphology of single axons was examined at several postnatal ages. The axons progress from a simple, sparsely branched morphology at birth to crude arbors at postnatal day 7 (P7). At P14-P15, axons have terminal arbors that span one eye-specific layer. By P19-P21, retinal afferents in the A layers have segregated into inner and outer sublaminae that correspond to ON- and OFF-center cells. Sublaminae form mainly by directed growth of terminal arbors in appropriately positioned regions of the LGN, along with elimination of extraneous branches in inappropriate regions. From P28 to P35, the LGN assumes an adult-like shape, and retinogeniculate axons form terminal boutons on branch endings. During the period between P14 and P21, when retinogeniculate axons segregate into ON/OFF sublaminae, N-methyl-D-aspartate (NMDA) receptors were blocked with chronic infusion of specific antagonists into the LGN. NMDA receptor blockade prevents the retinal afferent segregation into ON/OFF sublaminae. Some individual retinogeniculate axons have arbors that are not restricted appropriately, and most are restricted in size but are located inappropriately within the eye-specific laminae. Thus, NMDA receptor blockade prevents the positioning of retinogeniculate arbors that lead to the formation of ON/OFF sublaminae in the LGN. These results indicate that the activity of postsynaptic cells, and the activation of NMDA receptors in particular, can influence significantly the patterning of inputs and the structure of presynaptic afferents during development.

The neuronal form of nitric oxide synthase is required for pattern formation by retinal afferents in the ferret lateral geniculate nucleus

The ferret retinogeniculate projection undergoes activity-dependent refinement of connections that become restricted to eye specific laminae and On/Off sublaminae in the lateral geniculate nucleus (LGN). We have previously shown that the developmental process by which On/Off sublaminae form requires N-methyl-D-aspartate (NMDA) receptors and nitric oxide (NO). In this study, we investigate the role of the neuronal form of NO synthase (nNOS) in sublaminar refinement. This isoform of NOS may be coupled with NMDA receptors at postsynaptic sites. We found that nNOS is present in the developing LGN, and that blocking nNOS during development disrupts the formation of On/Off sublaminae. Endothelial NOS (eNOS) is not expressed in the LGN until after sublaminae have formed. These results suggest that the nNOS isoform is the predominant contributor of NO during development, and support the hypothesis that NO acts downstream of NMDA receptor activation to mediate activity-dependent changes in the patterning of connections in the LGN.

Nitric oxide as a signaling molecule in visual system development

The lateral geniculate nucleus (LGN) of the ferret is characterized by the readily discernible anatomical patterning of afferent terminations from the retina into both eye-specific layers and On/Off sublaminae. The eye-specific layers form during the first post-natal week, and On/Off sublaminae become apparent during the third to fourth post-natal weeks. The post-natal appearance of these patterns thus provides an advantageous model for the study of the mechanisms of activity-dependent development. The second phase of pattern formation, the appearance of On/Off sublaminae, involves the elaboration of appropriately placed axonal terminals and the restriction (or retraction) of inappropriately placed terminals. Previous work has demonstrated that this process is dependent on the activation of NMDA-receptors. Other studies have provided strong evidence that nitric oxide, a diffusible gas which is produced downstream of NMDA-receptor activation, acts as a retrograde messenger molecule to induce changes in pre-synaptic structures. In this article we review the evidence that nitric oxide plays a role in activity-dependent synaptic plasticity in the developing retinogeniculate pathway. The role of nitric oxide in other aspects of visual system development is also discussed.

Stable properties of spontaneous EPSCs and miniature retinal EPSCs during the development of ON/OFF sublamination in the ferret lateral geniculate nucleus

Retinal projections to the lateral geniculate nucleus (LGN) in ferrets progressively segregate into eye-specific laminae and subsequently into sublaminae that receive inputs from either ON-center or OFF-center afferents. To study the development of synaptic efficacy during a period of activity-dependent growth and reorganization in the CNS, we recorded spontaneous EPSCs (sEPSCs) from cells of the LGN during ON/OFF sublamination. We also examined retinal inputs specifically by stimulating the optic tract in the presence of strontium and recording evoked miniature EPSCs (emEPSCs). The rise times, areas, half-widths, and decay times of sEPSCs and emEPSCs and interevent intervals of sEPSCs recorded at the beginning of ON/OFF sublamination were not different from those recorded after its completion. Typically EPSC areas were small (10-20 fC) but varied greatly both within and between neurons. The frequency of sEPSCs was also quite variable, ranging from 0.2 to 5 Hz. sEPSCs were equivalent to miniature EPSCs recorded in the presence of tetrodotoxin, and both sEPSCs and emEPSCs were CNQX-sensitive. No difference was observed between sEPSCs recorded at room temperature and those recorded at 34 degreesC, and strontium could be substituted for calcium with no effect on sEPSC shape. These data argue for a remarkable stability in the components of at least AMPA-mediated synaptic transmission during a period of major synaptic rearrangement in the LGN.

The role of the human papilloma virus in esophageal cancer

Esophageal squamous cell carcinoma (ESCC) demonstrates wide regional variation in incidence and causal associations. Human papillomavirus (HPV) has been implicated in ESCC, particularly the sub-types 16 and 18. Transforming proteins E6 and E7 from these high risk sub-types, interact with p53 protein and Rb protein respectively, leading to loss of function of these tumor suppressor gene products. These interactions further lead to inactivation of the growth suppressive effects of the p53 and Rb proteins, resulting in abnormal proliferative states. p53 protein expression has been found in both HPV-positive and -negative tumors, indicating that HPV and p53 protein expression are not mutually exclusive and can occur together in the same tumor. It has been observed that HPV plays a more significant role in esophageal carcinogenesis in geographic areas with a high prevalence of the disease. A variation in the association between HPV and ESCC worldwide may be due to environmental and geographic factors, or to genetic susceptibility to esophageal HPV infections. Variations in the sensitivity of techniques used in the detection of the virus and in the methodology for processing the tumor tissues, may also be responsible for global differences. Esophageal carcinogenesis is a complex multistep process with a multifactorial etiology. Infection with oncogenic HPV types may be an integral part in a multistep process that leads to ESCC.

Brainstem inputs to the ferret medial geniculate nucleus and the effect of early deafferentation on novel retinal projections to the auditory thalamus

Following specific neonatal brain lesions in rodents and ferrets, retinal axons have been induced to innervate the medial geniculate nucleus (MGN). Previous studies have suggested that reduction of normal retinal targets along with deafferentation of the MGN are two concurrent factors required for the induction of novel retino-MGN projections. We have examined, in ferrets, the relative influence of these two factors on the extent of the novel retinal projection. We first characterized the inputs to the normal MGN, and the most effective combination of neonatal lesions to deafferent this nucleus, by injecting retrograde tracers into the MGN of normal and neonatally operated adult ferrets, respectively. In a second group of experiments, newborn ferrets received different combinations of lesions of normal retinal targets and MGN afferents. The resulting extent of retino-MGN projections was estimated for each case at adulthood, by using intraocular injections of anterograde tracers. We found that the extent of retino-MGN projections correlates well with the extent of MGN deafferentation, but not with extent of removal of normal retinal targets. Indeed, the presence of at least some normal retinal targets seems necessary for the formation of retino-MGN connections. The diameters of retino-MGN axons suggest that more than one type of retinal ganglion cells innervate the MGN under a lesion paradigm that spares the visual cortex and lateral geniculate nucleus. We also found that, after extensive deafferentation of MGN, other axonal systems in addition to retinal axons project ectopically to the MGN. These data are consistent with the idea that ectopic retino-MGN projections develop by sprouting of axon collaterals in response to signals arising from the deafferented nucleus, and that these axons compete with other sets of axons for terminal space in the MGN.

Specification of retinogeniculate X and Y axon arbors in cats: fundamental differences in developmental programs

Monocular enucleation at E36, followed by intracellular labeling of single, physiologically identified X and Y axons, demonstrates fundamental differences in their termination patterns within the lateral geniculate nucleus (LGN). X axons have arbors that appear normal in their dorsoventral extent, though some are located in inappropriate regions of the LGN. Y axons have arbors that are either abnormally tall, spanning the entire extent of the LGN, or of normal height but located in inappropriate regions of the LGN. These termination patterns resemble patterns seen after monocular enucleation at E44, and reinforce the conclusion that X and Y axons differ fundamentally in the cues that constrain the dorsoventral extents of their arbors.

A local circuit approach to understanding integration of long-range inputs in primary visual cortex

Integration of inputs by cortical neurons provides the basis for the complex information processing performed in the cerebral cortex. Here, we have examined how primary visual cortical neurons integrate classical and nonclassical receptive field inputs. The effect of nonclassical receptive field stimuli and, correspondingly, of long-range intracortical inputs is known to be context-dependent: the same long-range stimulus can either facilitate or suppress responses, depending on the level of local activation. By constructing a large-scale model of primary visual cortex, we demonstrate that this effect can be understood in terms of the local cortical circuitry. Each receptive field position contributes both excitatory and inhibitory inputs; however, the inhibitory inputs have greater influence when overall receptive field drive is greater. This mechanism also explains contrast-dependent modulations within the classical receptive field, which similarly switch between excitatory and inhibitory. In order to simplify analysis and to explain the fundamental mechanisms of the model, self-contained modules that capture nonlinear local circuit interactions are constructed. This work supports the notion that receptive field integration is the result of local processing within small groups of neurons rather than in single neurons.

Temporal modulation of spatial borders in rat barrel cortex

We examined the effects of varying vibrissa stimulation frequency on intrinsic signal and neuronal responses in rat barrel cortex. Optical imaging of intrinsic signals demonstrated that the region of cortex activated by deflection of a single vibrissa at 1 Hz is more diffuse and more widespread than the territory activated at 5 or 10 Hz. With the use of two different paradigms, constant time of stimulation and constant number of vibrissa deflections, we showed that the optically imaged spread of activity is more discrete at higher stimulation frequencies. We combined optical imaging with multiple electrode recording and confirmed that the neuronal response to individual vibrissa stimulation at the optically imaged center of activity is greater than the response away from the imaged center. Consistent with the imaging data, these recordings also showed no response to a second vibrissa deflection at 5 Hz at a peripheral recording site, though there was a significant response to a second vibrissa deflection at 1 Hz at the same peripheral site. These findings demonstrate that vibrissa stimulation at higher frequencies leads to more focused physiological responses in cortex. Thus the spread of activation in rat barrel cortex is modulated in a dynamic fashion by the frequency of vibrissa stimulation.