Improving clinical processes: one dialysis facility's experiences.

Northeast Louisiana Dialysis Center implemented continuous quality improvement (CQI) to improve the quality of care delivered to end stage renal disease (ESRD) patients treated by hemodialysis in their facility. The unit chose to address normalization of calcium and phosphorus and parathyroid hormone (PTH), anemia, nutrition, adequacy of dialysis and dialyzer reuse as well as performance benchmarks by the Health Care Financing Administration (HCFA) core indicators. This article presents the results obtained and the methodology used in this improvement effort. The article also presents nine principles the authors believe necessary for a successful CQI program.

Effects of eye position on auditory localization and neural representation of space in superior colliculus of cats.

The maps of visual and auditory space within the superior colliculus are in approximate register both with each other and with the underlying motor maps associated with orienting responses. The fact that eyes and ears can move independently poses a problem for the sensorimotor organization of these two modalities. By monitoring eye and pinna positions in alert, head-fixed cats, we showed that the accuracy of saccadic eye movements to auditory targets was little affected by eye eccentricity (range +/- 15 deg) at the onset of the sound. A possible neural basis for this behavioral compensation was suggested by recordings from superior colliculus neurons. The preferred sound directions of some neurons in the deep layers of this midbrain nucleus exhibited a shift with the direction of gaze, while in others the response throughout the auditory receptive field was either increased or decreased, suggesting that changes in eye position alter the gain of the auditory response.

Biomechanical study of C1-C2 posterior arthrodesis techniques.

Fifteen cervical spines from cadavers were used to compare the rotational and translational stability of the Brooks fusion, a fusion construct using Halifax interlaminar clamps, and the Gallie fusion. The Brooks and Halifax clamp constructs exhibited significantly greater rotational and translational stiffness than the Gallie construct (P < 0.001). The Halifax clamp construct exhibited greater rotational stiffness and equal translational stiffness when compared with the Brooks construct (P < 0.05). The Brooks and Halifax fixation constructs provided superior fixation but presented technical challenges. The Gallie construct is less technically demanding but provides less stable fixation.

Effects of multiple stimuli on ocular orientation by cats.

We investigated the characteristics of saccades made by cats in response to single and double stimuli. Stimuli were either visual, auditory, or bimodal. We initially trained cats to look toward the location of briefly presented single visual or single auditory targets that were extinguished before the initiation of eye movements. Following training, we monitored eye movements during and after the presentation of double targets, either two visual, two auditory, or bimodal, that were at disparate spatial locations. Cats made saccadic eye movements to positions that ranged between the location of the two targets. If the eye position at the start of a saccade was near the mid point of the targets, cats were less likely to initiate a saccade, and saccadic latencies were longer, compared to when starting eye position was at a distance from this location. These behavioral results are consistent with the hypothesis that the neural representations of briefly presented targets are combined and treated as a unitary, low resolution stimulus from which an orienting motor program is derived. The similarity of responses to double visual, double auditory, and bimodal stimuli suggests that a common sensorimotor mechanism applies within and between these sensory modalities.

A tecto-rotundo-telencephalic pathway in the rattlesnake: evidence for a forebrain representation of the infrared sense.

Rattlesnakes possess a sensory system specialized for the detection of infrared (IR) radiation. IR signals ascend as far as the optic tectum, where they generate a spatiotopic map. It is unknown if such signals reach the forebrain, but the existence of prominent tectothalamic pathways in other vertebrates makes this a distinct possibility. In nonmammalian forms, the major target of ascending tectal visual signals is nucleus rotundus, a thalamic nucleus that projects in turn to the subpallial telencephalon. We sought to determine whether a tecto-rotundo-telencephalic system exists in rattlesnakes and, if so, whether it carries IR as well as visual information. We have identified a thalamic nucleus in the rattlesnake Crotalus viridis that matches the n. rotundus of other reptiles in its topographic location, cytoarchitecture, and connections. Using anterograde and retrograde transport of HRP, we have demonstrated a strong ipsilateral and weaker contralateral tectorotundal projection. Tectorotundal cells lay primarily in the deeper tectal layers, which receive input from the IR system, but also in the superficial, visual layers. In n. rotundus, single units recorded extracellularly invariably responded to visual stimuli, but many were also sensitive to unimodal IR stimuli. IR and visual receptive fields were very large and often bilateral. Some rotundal units appeared sensitive to substrate vibration. Most habituated rapidly. Nucleus rotundus was found to project to a sector of the ipsilateral anterior dorsal ventricular ridge (ADVR) of the telencephalon. Single units in this region of the ADVR resembled those in rotundus, responding to visual, IR, and/or vibrational stimuli and possessing large, often bilateral receptive fields. These findings demonstrate the existence of a tecto-rotundo-telencephalic pathway in rattlesnakes and suggest that this system conveys IR as well as visual information to the forebrain. Ascending tectofugal pathways have been implicated in the discrimination of form. Thus, pattern recognition may have to be added to orientation as a proper function of the IR system of pit vipers.

Perioral somatosensory but not visual inputs to the flank of the mouse superior colliculus.

An electrophysiological and anatomical study identified the sensory inputs to the "flank" of the mouse's superior colliculus, a large, ventrolateral extension of layer IV (stratum griseum intermediate) that has no overlying visual layers (II and III). Electrophysiological recordings with subsequent histological localization showed that the flank receives predominantly somatosensory projections from the perioral region but not visual input. In its caudal parts, the flank also has limb and trunk somatosensory inputs and auditory inputs. The perioral somatosensory projections to the flank are ordered somatotopically. The flank is considered part of the superior colliculus since the perioral inputs are adjacent to inputs from mystacial vibrissae in the more medial parts of the superior colliculus, hence forming a single continuous map. The finding that no visual responses occur above the flank (due to the absence of superficial layers) or within it is in accord with the concept of an intermodality "spatial register". Since flank neurons have somatosensory receptive fields in non-visible parts of the body and they lack visual responses, the flank may be involved more in tactile-dependent rather than in vision-dependent orienting behaviors. Thus, the superior colliculus may, in parallel, carry out sensorimotor transformations related to (1) shift of gaze and (2) tactile-dependent behaviors not involving vision.

2-Deoxyglucose labelling of the infrared sensory system in the rattlesnake, Crotalus viridis.

Infrared (IR) responsive nuclei in the rattlesnake Crotalus viridis were identified by using 14C-2-deoxyglucose (2DG) and autoradiography. Following 2DG intracardial injection, the IR-sensitive pit organ was stimulated periodically with an IR stimulus for 5 hours. The nucleus of the lateral descending trigeminal tract (LTTD, the primary IR sensory nucleus) was labelled heavily with 2DG. Labelling was bilateral, but somewhat heavier ipsilateral to the stimulated pit organ. The nucleus reticularis caloris (RC, the secondary nucleus of the IR system) was lightly labelled ipsilaterally. The middle laminae of the contralateral optic tectum (which contain IR-responsive units) were distinctly labelled; the corresponding layers of the ipsilateral tectum were lightly labelled. A subcerebellar nucleus not known to be part of the IR system was heavily labelled bilaterally. No consistent labelling was found in the diencephalon or telencephalon. Since units in the LTTD do not respond to stimulation of the contralateral pit yet the LTTD is labelled with 2DG when there is contralateral pit stimulation, several controls were carried out. Unilateral injection of 3H-proline into LTTD revealed no projection to the contralateral LTTD. In a monocularly, visually stimulated animal with both pits occluded, the LTTD still showed heavy but equal 2DG labelling bilaterally. In addition, the outer layers of the contralateral optic tectum were heavily labelled. No 2DG labelling of the LTTD was obtained when branches of the trigeminal nerve innervating the LTTD were previously cut. These results suggest that much of the 2DG labelling in the LTTD is due to spontaneous ongoing activity from the pit organ rather than from IR evoked activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Spatial and temporal integration in primary trigeminal nucleus of rattlesnake infrared system.

The spatial and temporal characteristics of the infrared responses of single neurons in the nucleus of the lateral descending trigeminal tract (LTTD) of the rattlesnake were investigated. The LTTD is the sole projection site of trigeminal neurons that innervate the thermoreceptive pit organ. In contrast to the responses of the primary infrared neurons, which have phasic and tonic components, the neurons in the LTTD respond strictly phasically to a sustained infrared stimulus. During an excitatory stimulus, the transient burst is followed by suppression of firing or by reduction of the new rate below the rate that would have occurred in the absence of stimulation. The phasic character of the responses may enable these neurons to encode more accurately changes in the pattern of infrared stimuli. Neurons in the LTTD show adaptation within limited regions of their receptive fields, while responses in other regions remain undiminished. This indicates that each LTTD neuron receives input from a population of primary infrared neurons. LTTD neurons respond to infrared stimuli of intensity less than 0.01 mW/cm2, which is below the threshold reported for primary afferent neurons; this also suggests convergence of a number of primary infrared afferents onto each LTTD neuron. LTTD neurons have smaller excitatory receptive fields than do the primary afferent neurons in the infrared system, indicating that spatial sharpening also occurs in this nucleus. Receptive fields of LTTD neurons may have inhibitory areas flanking the excitatory area. Introduction of a stimulus into the inhibitory area results in depression of the background discharge; thus, the inhibition is due to an active process, not to rebound from excitation. Inhibition can also be demonstrated by simultaneous stimulation of the excitatory and inhibitory receptive-field areas, resulting in a decreased excitatory response. We suggest that convergence of antagonistic excitatory and inhibitory inputs can explain the time course of LTTD responses to infrared stimulation and the architecture of LTTD receptive fields. Such excitatory and inhibitory interaction, similar to that postulated for the responses of some vertebrate retinal ganglion cells, could function to provide the basis for directional selectivity, motion sensitivity, and border enhancement in the infrared system. Unlike the visual system, however, in the infrared system excitatory-inhibitory interactions allow the construction of small excitatory receptive fields in the LTTD from the larger receptive fields of the primary afferent neurons, resulting in a highly evolved trigeminal system with visionlike function.

Presynaptic uptake blockade hypothesis for LSD action at the lateral inhibitory synapse in Limulus.

We investigated the action of LSD at the putative indoleaminergic lateral inhibitory synapse in the lateral eye of Limulus polyphemus. We recorded extracellular and intracellular voltage responses from eccentric cells while producing inhibition either by light or by antidromic stimulation of the optic nerve in the presence of LSD, serotonin (5-HT), chlorimipramine, or a bathing medium whose high Mg++ and low Ca++ concentrations partially or completely blocked synaptic transmission. We found (a) light-evoked and antidromically stimulated lateral inhibition is enhanced during superfusion of low (1-5 microM) concentrations of LSD and suppressed by higher (5-20 microM) concentrations; (b) these actions of LSD are markedly reduced by bathing the retina in a medium high in Mg++ and low in Ca++; (c) very low concentrations of chlorimipramine, a putative uptake blocker of serotonin, appear to mimic actions of LSD both on eccentric cell firing rate and on lateral inhibition; (d) superfused 5-HT depresses lateral inhibition at all superthreshold concentrations (0.1-25 microM). These results suggest that LSD's action may require an intact inhibitory transmitter release and postsynaptic response mechanism, whereas serotonin exerts a direct postsynaptic effect. We propose that LSD blocks presynaptic uptake of transmitter at the lateral inhibitory synapse. The concentration dependence of LSD's action can be accounted for as follows: low concentrations partially restrict transmitter reuptake, thereby prolonging the lifetime of the transmitter in the synaptic cleft and thus increasing the magnitude and duration of postsynaptic inhibition. Higher concentrations cause more presynaptic uptake sites to be blocked; this causes accumulation of transmitter in the synaptic cleft, which causes a functional blockade of the synapse because of postsynaptic desensitization. As an alternative, we propose a hypothesis based on LSD action at presynaptic autoreceptors. Similar hypotheses can account for many aspects of LSD's action in mammalian brain.

The ascending projection of the nucleus of the lateral descending trigeminal tract: a nucleus in the infrared system of the rattlesnake, Crotalus viridis.

The efferent projections of the nucleus of the lateral descending trigeminal tract (LTTD) in the rattlesnake (Crotalus viridis) were studied by anterograde tracing techniques. The LTTD, a brainstem trigeminal nucleus, is the sole projection site of the infrared-sensitive trigeminal fibers that innervate the pit organs in these snakes. The efferent fibers exit from the ventromedial edge of the LTTD and course medially and caudally toward the central grey area of the medulla. Upon reaching the central region of the medulla these fibers turn and move laterally and rostrally, eventually forming a tract on the ventrolateral surface of the brainstem. Embedded in this tract and slightly overlapping the LTTD in the rostrocaudal axis, is a population of large (20-45 micrometer) multipolar neurons that forms the nucleus reticularis caloris. Heavy terminal and preterminal degeneration in this area indicates that many of the efferent fibers of the LTTD terminate in this nucleus. A small bundle of degenerating fibers turn dorsally from the ventrolateral tract and ascend to terminate in a nucleus associated with the cerebellum, the lateral tegmental nucleus. No projection was found to any other nuclei or areas in the brain. This study demonstrates that the infrared-sensitive snakes, along with developing peripheral specializations (the pit organs), have developed specialized nuclei to handle this additional sensory information. The direct projection from the LTTD to the nucleus reticularis caloris provides a pathway linking the infrared-sensitive neurons of the LTTD with neurons of the same modality in the optic tectum. The second LTTD projection, to the lateral tegmental nucleus, suggests a connection between the infrared system and the cerebellum in these animals.

Integration of visual and infrared information in bimodal neurons in the rattlesnake optic tectum.

Bimodal neurons in the rattlesnake tectum, which receive sensory input from the retina and from the infrared-sensing pit organ, exhibit novel, highly nonlinear cross-modality interactions. Some units respond only to simultaneous bimodal stimulation. Others respond to only one of the two modalities, but show greatly enhanced or depressed responses when stimulated simultaneously in the second modality. These cross-modality interactions may play an important role in recognizing and orienting toward biologically important objects.

The infrared trigemino-tectal pathway in the rattlesnake and in the python.

We have studied the infrared trigemino-tectal pathway of the rattlesnake (Crotalus viridis) and the python (P. reticulatus). In the rattlesnake, horseradish perosidase (HRP) injections into the nucleus reticularis caloris (RC) result in retrograde filling of cells in the ipsilateral nucleus of the lateral descending trigeminal tract (LTTD) and in the anterograde labelling of terminal fields in the contralateral optic tectum, confirming our previous finding of an RC-tectal projection. The primary projection of the pit organ of the rattlesnake was traced by injecting cobalt chloride into the pit, demonstrating that the pit organ projects exclusively to the ipsilateral LTTD. Electrophysiological recording from single units in the RC shows that these cells respond to infrared stimulation. Taken together, these results demonstrate that the infrared pathway in the rattlesnake proceeds from the pit organ to the LTTD, to the RC, to the contralateral tectum. In contrast, HRP injection into the tectum of the python results in the retrograde filling of the large cells of the contralateral LTTD. Thus, a direct LTTD-tectal projection occurs in the python. The cells of the rattlesnake RC and the larger cells of the python LTTD stain heavily for acetylcholinesterase activity and have a similar multipolar appearance, suggesting that the tectal-projecting cells in the two species may have a common origin.

Spatial sharpening by second-order trigeminal neurons in crotaline infrared system.

Neural responses in the nucleus of the lateral descending tract of the trigeminal nerve (LTTD) of the rattlesnake Crotalus viridis were recorded. Neurons in the LTTD respond phasically to infrared stimulation of the pit organ, in contrast to the tonic responses that have been reported for the primary afferents. The receptive field dimensions of LTTD neurons are smaller than those of the primary afferents; some LTTD neurons have inhibitory regions within their receptive fields. The smaller receptive fields of neurons in the LTTD, as well as the phasic responses of these cells, might be a result of this inhibition. This is an instance of spatial sharpening and possibly enhancement of responses to time-changing stimuli due to excitatory and inhibitory neural interactions in a primary trigeminal nucleus.

Connections of the tectum of the rattlesnake Crotalus viridis: an HRP study.

We have studied the connections of the tectum of the rattlesnake by tectal application of horseradish peroxidase. The tectum receives bilateral input from nucleus lentiformis mesencephali, posterolateral tegmental nuclei, anterior tegmental nuclei and periventricular nuclei; ipsilateral input from nucleus geniculatus pretectalis, and lateral geniculate nucleus pars dorsalis; and contralateral input from dorso-lateral posterior tegmental nucleus and the previously undescribed nucleus reticularis caloris (RC). RC is located on the ventro-lateral surface of the medulla and consists of large cells 25--45 micrometer in diameter. Efferent projections from the tectum can be traced to the ipsilateral nucleus lentiformis mesencephali, the ipsilateral lateral geniculate region, anterior tegmental region and a wide bilateral area of the neuropil of the ventral tegmentum and ventral medualla. We have not found any direct tectal projections from the sensory trigeminal nuclei including the nucleus of the lateral descending trigeminal tract (LTTD). We suggest that in the rattlesnake, RC is the intermediate link connecting LTTD to the tectum.

Fourier analysis of spike train data.

A formal representation of nerve spike trains in the form of a sum of rectangular functions is proposed. This formal instantaneous frequency function can be Fourier analyzed. The resulting algorithm has the useful properties of spike by spike calculations and an insensitivity to the mean (carrier) spike rate. The technique is also useful for producing a smooth (filtered) reconstruction of a spike train.

Anatomical and physiological localization of visual and infrared cell layers in tectum of pit vipers.

Visual and infrared cell layers were identified in the tectum of the pit vipers Crotalus viridis and Sistrurus melitus. Histologic reconstructions of 48 lesions utilizing the Prussian Blue technique were correlated with micrometer depth readings for 251 visual, infrared and bimodal single unit recordings. The visual cell layer extends caudally from approximately the level of the habenula to the rostral border of the posterior corpora quadrigemina. Neurons responding to visual stimulation are generally contained within zones 7b-13, i.e., the superficial 600--700 micrometer of the optic tectum (stratum fibrosum et griseum superficiale and the superficial sublayer of stratum griesum centrale). The infrared cell group is found in layer 7 (a and b; stratum griseum centrale) throughout the optic tectum. Eighty percent of the infrared neurons are found within 500--1,200 micrometer of the surface. In layer 7b the visual and infrared cell groups are mixed; bimodal neurons that respond to a combination of visual and infrared input are located predominantly in this sublamina. The lamination pattern for visual and nonvisual cell groups in the rattlesnake tectum appears to more closely resemble the colubrid tectum and mammalian superior colliculus than the tecta of other reptiles.

Merging of modalities in the optic tectum: infrared and visual integration in rattlesnakes.

The optic tectum of pit vipers (Crotalinae) contains a layer of infrared-sensitive neurons subjacent to the visual layer; these indirectly receive input from the facial pit organs. They respond transiently to the appearance or motion of warm objects within their 25 degrees to 70 degrees excitatory receptive fields (some have inhibitory regions) and presumably allow the snake to orient or strike toward prey. The infrared and visual spatiotopic tectal maps have similar but not identical axes; the infrared magnification is greater than that for vision. Bimodal neurons have receptive fields for each modality that reflect the disparity of the two maps. This finding suggests that (i) during development the infrared and visual fibers spread out independently to fill available tectal sites and (ii) bimodal neurons form local connections without regard to establishing spatial correspondence between the two modalities.

Octopine as an end product of anaerobic glycolysis in the chambered nautilus.

The terminal step in the anaerobic glycolysis of muscle in the chambered nautilus, Nautilus pompilius, is not pyruvate reduction to lactate as in vertebrate muscle. Instead of lactate dehydrogenase, these organisms utilize octopine dehydrogenase (E.C. 1.5.1.11), catalyzing the reductive condensation of pyruvate and arginine, which is dependent on the reduced form of nicotinamide adenine dinucleotide, to form octopine and the oxidized form of the coenzyme. The kinetic properties of octopine dehydrogenase favor the production of octopine, which accumulates under a variety of conditions.