Behavioural consequences of manipulating GABA neurotransmission in the superior colliculus.
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Animals↗
Biomedical subjects
P Dean
Publications and source records attributed to P Dean.
Use of a distracting task to obtain defensive head movements to looming visual stimuli by human adults in a laboratory setting.
Defensive responses to looming visual stimuli have been obtained in a wide variety of species, including human infants as young as one week. This phenomenon has not, however, been formally demonstrated for adults under laboratory conditions. In this paper it is reported that similar responses, namely avoidance movements of the head, can be obtained in most human adults provided that they are suitably distracted by playing a computer tracking game. Such behaviours were not obtained when subjects were not so distracted. The use of control conditions also ruled out the possibility that simple movement cues from stimuli presented on a noncollision trajectory are sufficient stimulus to obtain defensive responses. It is of interest to note that latencies for avoidance movements were significantly shorter than those for orienting movements in the same situation, but were no different from the latencies for orienting movements when subjects were not distracted. It is argued that these findings are consistent with the proposition that defensive head movements to looming stimuli, like orienting movements to novel peripheral stimuli, represent a basic visual competence that is normally suppressed (or subsumed) by higher competences. The decision to avoid is probably based on the computation of time to contact, and may reflect the operation of a subcortical system for elementary analysis of optic flow.
Adult↗
Epilepsy surgery in childhood. A report of 79 patients.
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Adolescent↗
Renal needle biopsy of the transplant kidney: vascular and urologic complications.
The authors reviewed the complications of 114 needle biopsies performed in 103 transplant kidneys. The diagnostic and therapeutic approach has changed markedly as a result of the introduction of Doppler ultrasound and the possibility of selectively embolizing fistula tracts. Macroscopic haematuria was the most frequent complication (5%); in one case it appeared 1 week after biopsy and was complicated with obstructive anuria due to a pyeloureteric clot. The incidence of arteriovenous fistulae was fairly low (0.9%); a selective renal angiography was performed, confirming the vascular lesion and allowing its selective embolization. Perirenal blood collections were also rare and the amounts were small.
Adult↗
Saccade control in a simulated robot camera-head system: neural net architectures for efficient learning of inverse kinematics.
The high speed of saccades means that they cannot be guided by visual feedback, so that any saccadic control system must know in advance the correct output signals to fixate a particular retinal position. To investigate neural-net architectures for learning this inverse-kinematics problem we simulated a 4 deg-of-freedom robot camera-head system, in which the head could pan and tilt and the cameras pan and verge. The main findings were: (1) Linear nets, multilayer perceptrons (MLPs) trained by backpropagation, and cerebellar model arithmetic computers (CMACs) all learnt rapidly to 5-10% accuracy when given perfect error feedback. (2) For additional accuracy (down to 2%) two-layer nets learnt much faster than a single MLP or CMAC: the best combination tried was to have a CMAC learn the errors of a trained linear net. (3) Imperfect error signals were provided by a crude controller whose output was simply proportional to retinal input in the relevant axis, thereby providing a mechanism for (a) controlling the camera-head system when the feedforward neural net controller was wrong or inoperative, and (b) converting sensory error signals into motor error signals as required in supervised learning. It proved possible to train neural-net controllers using these imperfect error signals over a range of learning rates and crude-controller gains. These results suggest that appropriate neural-net architectures can provide practical, accurate and robust adaptive control for saccadic movements. In addition, the arrangement of a crude controller teaching a sophisticated one may be similar to that used by the primate saccadic system, with brainstem circuitry teaching the cerebellum.
Brain Stem↗
Tectal induction of cortical arousal: evidence implicating multiple output pathways.
The rodent superior colliculus mediates a wide range of physiological and behavioural responses to sudden stimuli, including desynchronisation of the cortical electroencephalogram (EEG). To investigate how this desynchronisation is produced, one of two powerful excitatory agents, sodium L-glutamate (200 nl, 10 nmol) or bicuculline methiodide (200 nl, 40 pmol), was injected into the dorsal midbrain of sleeping rats. Microinjections at sites widely distributed throughout all layers of the superior colliculus were able to desynchronise the cortical EEG. i) In the superficial layers, bicuculline was effective at more sites than glutamate, whereas the reverse was true for the deep layers. ii) At some sites EEG desynchronisation occurred together with the defensive or orienting movements that are obtained from collicular stimulation in awake animals. At other sites cortical arousal occurred without such movements. iii) Comparison with a previous study suggested that urethane selectively blocks cortical arousal to glutamate injections in the superficial and intermediate grey layers. This evidence suggests that multiple collicular output pathways can desynchronise the cortical EEG, perhaps reflecting multiple functions for EEG desynchronisation.
Animals↗
[Renal angiomyolipoma: diagnostic approach and therapeutic up-date; report of 11 clinical cases].
Eleven cases of renal angiomyolipoma are reported. In all cases a correct preoperative diagnosis was made, using standards x-radiography, ultrasonography and computerized tomography. Small size AML do not generally require any surgery, while surgical procedures for larger AML vary depending on the size, associated diseases, other complicating factors. As a general rule, surgical treatment should be as conservative as possible.
Adolescent↗
Proposed standard for image cytometry data files.
A number of different types of computers running a variety of operating systems are presently used for the collection and analysis of image cytometry data. In order to facilitate the development of sharable data analysis programs, to allow for the transport of image cytometry data from one installation to another, and to provide a uniform and controlled means for including textual information in data files, this document describes a data storage format that is proposed as a standard for use in image cytometry. In this standard, data from an image measurement are stored in a minimum of two files. One file is written in ASCII to include information about the way the image data are written and optionally, information about the sample, experiment, equipment, etc. The image data are written separately into a binary file. This standard is proposed with the intention that it will be used internationally for the storage and handling of biomedical image cytometry data. The method of data storage described in this paper is similar to those methods published in American Association of Physicists in Medicine (AAPM) Report Number 10 and in ACR-NEMA Standards Publication Number 300-1985.
Electronic Data Processing↗
Prostanoids and leukotrienes in experimental feline cholecystitis.
Current information suggests that arachidonic acid metabolites are involved in the development of cholecystitis. The purpose of this study was to evaluate eicosanoid formation during the development of experimental cholecystitis in cats. Lysophosphatidylcholine is found in the gallbladders of patients with cholecystitis and is known to be a cytolytic, membrane-damaging substance. Anesthetized cats underwent gallbladder perfusion with and without 1.5 mmol/L lysophosphatidylcholine. Additional experiments were performed when calcium ionophore were added to the perfusates and experiments were performed when cats were treated with indomethacin and underwent perfusion with lysophosphatidylcholine. Changes in the gallbladder were determined by evaluating mucosal water transport as measured by determining the changes in concentration in a nonabsorbable marker, by protein secretion and by beta-glucuronidase accumulation in gallbladder tissue as an index of inflammation. Eicosanoid formation was evaluated by measuring perfusate concentrations and gallbladder homogenate concentrations by radioimmunoassay of prostaglandin E, 6 keto prostaglandin F1 alpha, leukotriene B4 and leukotriene C4. Lysophosphatidylcholine perfusion reversed the control patterns of absorption and produced water exsorption, produced an efflux of protein into the perfusate and increased beta-glucuronidase activity. These changes were accompanied by increased production of prostaglandin E and 6 keto prostaglandin F1 alpha in gallbladder perfusate and homogenate. The concentration of leukotriene C4 in gallbladder effusate was increased by lysophosphatidylcholine when compared with control values. Indomethacin inhibited the protein efflux, decreased beta-glucuronidase levels and decreased prostaglandin E and 6 keto prostaglandin F1 alpha formation when compared with values produced by lysophosphatidylcholine alone. Cyclooxygenase inhibition did not alter the secretion of water into the gallbladder or perfusate leukotriene C4 concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
N-methyl D-aspartate (NMDA) evoked changes in blood pressure and heart rate from the rat superior colliculus.
Electrical stimulation and microinjections of the GABA antagonist bicuculline methiodide into the superior colliculus (SC) of the anaesthetized rat can evoke changes in blood pressure and heart rate. The long latency of bicuculline evoked responses, however, raises the possibility that they may have been produced by the diffusion of bicuculline to surrounding tissue, in particular, the periaqueductal gray. Thus, the purpose of the present study was to investigate whether such changes could have been produced by the activation of extracollicular neural elements. This was achieved by assessing the relative regional sensitivity of the SC and underlying structures (periaqueductal gray and dorsal tegmentum) with microinjections of the excitatory amino acid N-methyl D-aspartate (NMDA) for the production of short latency pressor responses. Dorsal midbrain injections of NMDA (200 nl of 100 mM) in the Saffan anaesthetized rat evoked clear short latency (single or double phase) increases in blood pressure accompanied in most cases by a longer latency increase in heart rate and respiration. Two regions within the dorsal midbrain contained significantly higher proportions of active sites compared with surrounding tissue: i) the superficial and intermediate layers of rostromedial SC, and ii) the caudal periaqueductal gray. The distribution of active sites indicated that pressor responses elicited from the rostromedial SC could not be explained by the diffusion of NMDA to underlying tissue. The question of whether the rostromedial SC might represent an early link in the circuitry responsible for organizing defensive movements and appropriate physiological changes to potentially dangerous overhead stimuli is considered.
Animals↗
Output pathways from the rat superior colliculus mediating approach and avoidance have different sensory properties.
Neuroanatomical studies have demonstrated that the two major descending pathways from the superior colliculus arise from regionally segregated, distinct, cells of origin. Stimulation and lesion studies have implicated the crossed descending tecto-reticulo-spinal projection in approach movements towards novel stimuli whereas the ipsilateral pathway appears to be involved in the control of avoidance and escape-like behaviours. The present electrophysiological study attempted to characterise the sensory properties of antidromically identified cells of origin of these pathways in anaesthetised rats. We found that the contralaterally projecting predorsal bundle (PDB) efferents were primarily somatosensory while the ipsilateral cuneiform (CNF) projection was primarily visual. PDB cells, mainly found in the intermediate layers, responded principally to vibrissal stimulation with their overlying visual fields optimally stimulated by small dark moving objects in the lower rostral and lateral field. In contrast, most CNF cells were located rostromedially, with the greatest contribution from visual cells responsive to stimuli in the upper rostral field. A significant proportion of these showed no response to small moving dark discs but fired vigorously to 'looming' stimuli. Ethological considerations suggest that these are appropriate stimulus characteristics for a system controlling approach and avoidance behaviour in an animal such as the rat where predators generally appear from above and prey is found on the ground.
Afferent Pathways↗
Results of internal thoracic artery grafting over 15 years: single versus double grafts.
One hundred consecutive patients who had coronary artery bypass grafting using both internal thoracic arteries (ITAs) and saphenous veins, operated on during a 3-year period between 1972 and 1975, have been compared retrospectively with a series of 100 patients operated on during the same period who had one ITA graft along with saphenous vein grafts. The two groups were similar with respect to age, sex, risk factors for coronary artery disease, angina class, extent of coronary artery disease, left ventricular function, number of coronary bypass grafts performed, and completeness of revascularization. Single ITA operative mortality was 2% and double ITA, 9% (p = NS). The mean follow-up of hospital survivors was 14.4 +/- 2.7 years; all but 7 patients had follow-up for at least 10 years. At 13 years, the actuarial patency of the right ITA was 85% and the left ITA, 82%. These data strongly suggest a survival benefit for patients with double ITA grafts among hospital survivors (74% versus 59%; p = 0.05). Patients receiving two ITA grafts had a significant freedom from subsequent myocardial infarction (75% versus 59%, p less than 0.025), recurrent angina pectoris (36% versus 27%, p less than 0.025), and subsequent total ischemic events (32% versus 18%, p less than 0.01). These data also suggest improved freedom from coronary artery interventional therapy (percutaneous transluminal coronary angioplasty and reoperation) when two ITA grafts were used. These results support the use of bilateral internal thoracic artery grafting in selected patients.
Actuarial Analysis↗
Organization of the crossed tecto-reticulo-spinal projection in rat--I. Anatomical evidence for separate output channels to the periabducens area and caudal medulla.
The superior colliculus has been used to study principles of sensorimotor transformation underlying the guidance of orienting movements by multimodal sensory stimuli. We have previously suggested that there may be two different classes of mechanism which can produce orienting-like movements towards a novel event; one that locates a stimulus on the basis of remembered position, and another which uses continuous feedback relating to target velocity. The crossed descending pathway of the superior colliculus is widely considered the projection most likely to relay signals associated with the production of orienting movements. However, if different neural mechanisms are used to produce functionally distinct types of orienting, we might expect this pathway to have separate anatomical components related to function. The purpose of the present experiment was to see if collicular fibres innervating two important pre-motor targets of the crossed descending pathway, the periabducens area and the caudal medulla-spinal cord, come from the same population of tectal cells. One of the retrogradely transported fluorescent tracers (Diamidino Yellow) was injected into the periabducens area, and another (True Blue or Fast Blue) was injected into tectospinal fibres at the level of the ventromedial caudal medulla. Under these conditions we found: (i) less than 10% of labelled cells within the superior colliculus contained both tracers; (ii) the bulk of singly labelled cells projecting to the periabducens area or the caudal medulla were concentrated at different locations within the colliculus, (iii) in regions of the superior colliculus where there was overlap of singly labelled cells, neurons projecting to the periabducens area or the caudal medulla could be distinguished morphologically. These data provide three classes of evidence which indicate that the crossed descending projection in rat can be subdivided into at least two relatively independent anatomical components. This conclusion may, in part, provide an anatomical substrate for the functional dissociations proposed for orienting movements.
Amidines↗
Organization of the crossed tecto-reticulo-spinal projection in rat--II. Electrophysiological evidence for separate output channels to the periabducens area and caudal medulla.
The previous paper (Redgrave et al., Neuroscience 37, 571-584, 1990) presented anatomical evidence indicating there are at least two largely segregated components of the crossed tecto-reticulo-spinal pathway which project to the periabducens area and caudal medulla. An immediate question arising from this finding is whether tectal cells which project either to the periabducens area or to the caudal medulla have different electrophysiological response properties. An answer to this question would be relevant to the issue of whether different components of the tecto-reticulo-spinal system are specialized for the production of different classes of orienting movement. Accordingly, extracellularly recorded units in the superior colliculus of urethane anaesthetized rats were tested for antidromic activity following electrical stimulation of the periabducens area or the caudal medulla. When antidromic potentials were successfully recorded the sensory properties of the units were tested with a range of unimodal visual, somatosensory and auditory stimuli. The following results were obtained. (i) Tectal cells antidromically activated by stimulation of the caudal medulla were preferentially sensitive to somatosensory stimuli from the perioral region, while cells activated from the periabducens area were more frequently responsive to auditory stimuli. (ii) Tectal fibres activated by stimulation of the caudal medulla had significantly higher conduction velocities than the fibres activated by electrodes in the periabducens region. (iii) More than 90% of antidromically activated cells were located in stratum album intermediale or dorsal stratum profundum. These electrophysiological findings confirm and extend previous anatomical observations which indicate that components of the crossed descending projection of the colliculus may be functionally specialized for the production of different classes of orienting movements.
Acoustic Stimulation↗
Long-term outcome of reversal of small intestinal bypass operations.
Between 1976 and 1987, 43 patients underwent reversal of jejunoileal bypass operations because of metabolic complications of the operation. Electrolyte imbalance, malnutrition, and diarrhea (16 patients); cirrhosis (9); nephrolithiasis (9); arthritis (7); and pathologic fractures (1) were the primary indications for reconstruction. Many patients had multiple complications of the jejunoileal bypass operation. Twenty-nine patients underwent gastroplasty at the time of reversal and 14 did not. Seventy three +/- 5 months after reversal, patients with a gastroplasty weighed significantly less than patients without a gastroplasty. Patients with electrolyte imbalance, malnutrition, and diarrhea were all improved after reconstruction. Two patients with cirrhosis died of liver failure after reconstruction; the distinguishing preoperative characteristic was ascites. Postoperative interval liver biopsies indicated improvement in histologic appearance in four patients and no change in three. Nephrolithiasis improved or disappeared in all patients after reconstruction, whereas arthritis improved in 5 of 7 patients. Gastroplasty produced no benefit in alleviation of metabolic complications of jejunoileal bypass operations. Although the survival rate in these patients at last follow-up was 95 percent, 28 percent were incapacitated. Simultaneous gastroplasty performed at the time of reversal significantly decreases body weight when compared with patients undergoing reversal without a gastroplasty.
Arthritis↗
Anticonvulsant action of GABA receptor blockade in the nigrotectal target region.
Anticonvulsant activity in a wide variety of experimental seizure models can be obtained by enhancing gamma-aminobutyric acid (GABA) transmission within the pars reticulata of substantia nigra. Recent evidence indicates that the nigrotectal projection may mediate some of the nigra-evoked anticonvulsant effects. The action of GABA within substantia nigra would, by inhibiting the GABAergic nigrotectal projections, cause disinhibition of target neurons in the superior colliculus. This hypothesis predicts that administration of GABA antagonists into the region of the superior colliculus that receives nigrotectal terminals should also have anticonvulsant actions. We therefore examined the effects of injections of bicuculline methiodide aimed at rostrolateral superior colliculus upon maximal electroshock convulsions. The incidence and duration of tonic hindlimb extension was substantially reduced by these injections, a result consistent with the hypothesis that the nigrotectal GABAergic pathway may mediate the anticonvulsant actions of GABA transmission in the substantia nigra.
Animals↗
Event or emergency? Two response systems in the mammalian superior colliculus.
Recent studies of the effects of stimulating the superior colliculus (SC) in rodents suggest that this structure mediates at least two classes of response to novel sensory stimuli. One class contains the familiar orienting response, together with movements resembling tracking or pursuit, and appears appropriate for undefined sensory 'events'. The second class contains defensive movements such as avoidance or flight, together with cardiovascular changes, that would be appropriate for a sudden emergency such as the appearance of a predator, or of an object on collision course. The two response systems appear to depend on separate output projections, and are probably subject to different sensory and forebrain influences. These findings (1) suggest an explanation for the complex anatomical organization of the SC, with multiple output pathways differentially accessed by a very wide variety of inputs, (2) emphasize the similarities between the SC and the optic tectum in non-mammalian species, and (3) suggest that the SC may be useful as a model for studying both the sensory control of defensive responses, and how intelligent decisions can be taken about relatively simple sensory inputs.
Animals↗