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Biomedical subjects

C Casanova

Publications and source records attributed to C Casanova.

At least 73 records · Page 4Linked to original sources
PubMed1992

Contrast sensitivity in amblyopia: masking effects of noise.

Contrast sensitivities were determined for sinusoidal gratings of varying spatial frequencies with and without the presence of a random noise pattern superimposed on the gratings. Control subjects with normal binocular vision and observers with amblyopia were tested to determine the relative effects of noise on contrast sensitivity. For both amblyopes and normal subjects, contrast sensitivities are reduced by the presence of noise. Effects are maximal at 4 cycles/degree and are minimal at low and high spatial frequencies. Dichoptic presentation of noise and gratings to opposite eyes is equivalent to monoptic results for both amblyopes and normal subjects. Masking effects are eliminated if gratings are drifted while noise patterns are static. The contrast sensitivity of amblyopes is reduced by relatively similar amounts to that of normal subjects when noise is added to the stimulus. Overall, masking effects are virtually identical for amblyopes and for subjects with normal binocular vision.

Adult↗
PubMed1991

Long-term clinical follow-up of adult idiopathic pulmonary hemosiderosis and celiac disease.

A 22-year-old man with a history of repeated whole blood transfusions since the age of 7, was admitted to the hospital for dyspnea and blood-stained sputum. A complete blood cell count, a test for reticulin antibodies, an x-ray film of the chest, a transbronchial biopsy and a biopsy of the small bowel were performed and the results confirmed the diagnosis of IPH, associated with CD. The patient has been asymptomatic for four years on a gluten-free diet. In cases of IPH, it may be important to investigate the coexistence of CD because treatment of the latter could lead to a better prognosis.

Adult↗
PubMed1991

Responsiveness of reorganized primary somatosensory (SI) cortex after local inactivation of normal SI cortex in chronic spinal cats.

The cortical map of adult cats that sustained spinal cord transection at T12 when they were 2 weeks old is characterized by a clear duplication of the representation of the forelimb, rostral trunk, and neck. The novel representation is located in the cortical region that is, in nonoperated animals, normally devoted to the hindlimb representation. We have investigated the possibility that the reactivation of the deprived hindlimb cortex may be mediated by corticocortical projections from normal to reorganized cortex. The primary somatosensory (SI) cortex was initially mapped to determine the boundaries of the normal and reorganized cortical representations. Somatotopically corresponding regions in both normal and reorganized cortex representing the trunk, the web space, or the shoulder were more precisely mapped. Inactivation of normal cortex was achieved by the nanoinjection of a solution of lidocaine hydrochloride stained with Chicago sky blue. Two major findings are described. First, inactivation of a circumscribed region of normal cortex representing a given receptive field (RF) failed to reduce or inhibit the responsiveness of a somatotopically corresponding RF represented in reorganized cortex. Therefore, it is unlikely that intracortical connections between normal and reorganized cortex could account for the reorganizational processes observed in cats that sustained spinal cord transection at 2 weeks of age. Second, the chemical blockade of normal cortex provoked an increase of the responsiveness and of the size of the peripheral RFs represented in reorganized cortex. This finding suggests that there are corticocortical connections (possibly topographically organized) between normal and reorganized cortex, and that these connections are inhibitory.

Afferent Pathways↗
PubMed1991

[Pulvina-lateralis posterior nucleus complex of mammals and the visual function].

It is now well established that the lateral posterior-pulvinar (LP-P) complex of mammals is involved in visual processing. However, the actual function of these large nuclei of the thalamus remains unknown. In contrast to the nearby lateral geniculate nucleus, the LP-P complex does not receive any substantial direct projections from the retina. Its main visual inputs come from the mesencephalon and the neocortex. Most cells in the LP-P complex behave like cortical units. They are tuned to the orientation, direction, spatial and temporal frequencies of the visual stimulus. In addition, most units are binocular and sensitive to relative retinal disparity. Despite their multiple inputs, the LP-P complex cells form an homogeneous population and their overall properties do not reflect those of a given cortical or subcortical area. On the basis of its afferent and efferent connectivity, it has been proposed that the LP-P complex may serve as a relay of an extrageniculate ascendant pathway which originates from the superior colliculus, and/or provide another route for the geniculo-striate input to reach the extrastriate areas. Despite the fact that there is some electro-physiological evidence of such functions, it is now often suggested that the LP-P complex may integrate its multiple inputs and be involved in functions which go beyond those of a simple thalamic relay. Recent findings suggest that the LP-P complex might play a role in visual spatial attention.

Animals↗
PubMed1990

Influence of the superior colliculus on visual responses of cells in the rabbit's lateral posterior nucleus.

The lateral posterior-pulvinar (LP-P) complex of mammals receives a major input from the superior colliculus (SC). We have studied the response properties of LP cells and investigated the effects of reversible inactivation of the colliculus on the visual responses of LP units in anesthetized and paralyzed rabbits. Cells in LP had large receptive fields responsive to either stationary or moving stimuli. One third of the motion-sensitive cells were direction selective. The size of the receptive fields increased with eccentricity and there was a retinotopic organization along the dorso-ventral axis. Comparison of the LP and superior colliculus properties revealed substantial differences in visual response characteristics of these two structures such as the size of the receptive fields and the number of direction-selective cells. Electrical stimulation of the LP evoked antidromic action potentials in tectal cells that were motion sensitive. We found a dorsoventral gradient in the projections of collicular cells. Units located more dorsally in the colliculus sent their axons to LP while cells lying more ventrally sent axons toward the region lying posterior to LP. A micropipette filled with lidocaine hydrochloride was lowered into the superficial layers of the superior colliculus in order to reversibly inactivate a small population of collicular cells. Rendering the superior colliculus inactive produced a sharp attenuation of visual responses in the majority of LP cells. Some neurons ceased all stimulus-driven activity after collicular blockade while a few cells exhibited increased excitability following collicular inactivation. These experiments also indicate that the tecto-LP path is topographically organized. An injection in the colliculus failed to influence the thalamic response when it was not in retinotopic register with the LP cells being recorded. Our results demonstrate that the superior colliculus input to LP is mainly excitatory in nature.

Animals↗
PubMed1990

Diarrhea in diabetics: the role of sorbitol.

Diabetics often consume dietetic foods with sorbitol as the sweetener. Sorbitol, in amounts as little as 10 g. may produce diarrhea in healthy individuals. Sorbitol intolerance was studied in 12 diabetics and 23 nondiabetics. Similar numbers of diabetics (n = 10, 83.3%) and nondiabetics (n = 18, 78.3%) were found intolerant as judged by a greater than or equal to 20 ppm rise in postprandial breath hydrogen levels. Six diabetics (50%) and 13 nondiabetics (56.5%) developed abdominal symptoms after sorbitol ingestion. Subsequently, 100 diabetics and 100 nondiabetics were interviewed to determine the relationship between regular sorbitol consumption and abdominal symptoms. The interview revealed that (1) most individuals consuming sorbitol were unaware of its presence in their diet and (2) diarrhea was significantly (p less than 0.001) more prevalent in diabetics consuming sorbitol than diabetics not consuming it. We conclude that (1) many diabetics are intolerant to sorbitol and (2) regular sorbitol consumption may explain the "idiopathic" diarrhea in some diabetics.

Abdominal Pain↗
PubMed1990

The action of botulinum toxin on cholinergic nerve terminals isolated from the electric organ of Torpedo marmorata. Detection of a putative toxin receptor.

Botulinum neurotoxin type A (BoNTx) inhibits the release of acetylcholine (ACh) from Torpedo electric organ synaptosomes. We have studied several biochemical and morphological aspects in order to characterize the molecular interactions of BoNTx intoxication in our preparation. 1. We are describing for the first time an electrophoretic band from cholinergic presynaptic plasma membrane (PSPM) that is recognized by 125I-BoNTx as a putative BoNTx receptor. 2. Furthermore we describe direct interaction of botulinum toxin-gold complexes with synaptic vesicles through the three-step model of the BoNTx intoxication.

Animals↗
PubMed1989

Optic nerve blockade influences the retinal responses to flash in rabbits.

The presence of retinopetal fibers in mammals has been debated many times in the past two decades. Do rabbits have a retinopetal system? This question is addressed with the present investigations. In anesthetized and paralysed rabbits the b-wave and the oscillatory potentials (OP) are recorded at the cornea. The optic nerve is isolated retrobulbarly and is gently hooked to a curved injecting capillary. Through the latter lidocaine hydrochloride is pressure injected. This drug interrupts the neuronal flow travelling along the nerve. A steel electrode is positioned in the optic chiasm allowing us to monitor the evoked field potentials from the tested and untested eyes. The optic nerve blockade produces the following observations: (1) the amplitude of the b-wave is not significantly altered; and (2) the amplitudes of the long latency OP are significantly increased. The retinal capacity to respond to a second flash after the application of an initial light pulse was evaluated by varying the interval between the two flashes. After optic nerve blockade the recovery of the retinal responsiveness is considerably slower. Fourier analysis indicated that the highest power increases occurred around 200 Hz. It is difficult to escape the suggestion that rabbits possess retinopetal fibers.

Animals↗
PubMed1989

Monocular and binocular response properties of cells in the striate-recipient zone of the cat's lateral posterior-pulvinar complex.

1. We have studied response properties of single cells in the striate-recipient zone of the cat's lateral posterior-pulvinar (LP-P) complex. This zone is in the lateral section of the lateral posterior nucleus (LP1). Our purpose was to determine basic response characteristics of these cells and to investigate the possibility that the LP-P complex is a center of integration that is dominated by input from visual cortex. 2. The majority (72%) of cells in the striate-recipient zone respond to drifting sinusoidal gratings with unmodulated discharge. 3. Cells in the LP1 are selective to the orientation of gratings, and tuning functions have a mean bandwidth of 31 degrees. More than one-half of these units are direction-selective. The preferred orientation and the tuning widths for the two eyes are generally well matched. However, a few cells exhibited the interesting property of opposite preferred directions for the two eyes. Orientation tuning for a small group of cells was different for the mean discharge and first harmonic components, suggesting a convergence from different inputs to these cells. 4. Two-thirds of LP1 cells are tuned to low spatial frequencies (less than 0.5 c/deg). The tuning is broad with a mean bandwidth of 2.2 octaves. The remaining one-third of the units are low-pass because they show no attenuation of their responses to low spatial frequencies. Both eyes exhibit the same spatial frequency preference and the same spatial frequency tuning. There is a high correlation between spatial frequency and orientation selectivities. 5. All cells tested are tuned for temporal frequency with a sharp attenuation for low frequencies. The optimal values range between 4 and 8 Hz, and the mean bandwidth is 2.2 octaves. 6. Cells in LP1 are mostly binocular. When monocular, cells are almost always contralaterally driven. Dichoptic presentation of gratings reveals the presence of strong binocular interaction. In almost all cases, these interactions are phase specific. The cell's discharge is facilitated at particular phases and inhibited at phases 180 degrees away. These binocular interactions are orientation dependent. 7. Twenty-five percent of the cells with phase-specific binocular facilitation appear to be monocular when each eye is tested separately. For three cells, we observed a non-phase-specific inhibitory effect of the silent eye. 8. Our findings indicate that LP1 cells form a relatively homogeneous group, suggesting a high degree of integration of multiple cortical inputs.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

[Contrast sensitivity is not only an additional complementary test].

Contrast sensitivity gives new insight on visual troubles encountered in ophthalmology. Indeed the measurement of this function yields some explanations on how vision is impaired by diseases frequently observed by clinicians. The deficits seen in strabismic amblyopes raise the possibility that the neural impairment in amblyopia is derived from a single continuum, varying in degree. The absence of stimulation of the size-selective detectors processing high spatial frequencies accounts for the shape of the contrast sensitivity curve in congenital nystagmus. Glaucomatous or multiple sclerosis patients show early deficits in medium range spatial frequencies where the sensitivity is the highest. These changes appear sometimes before any other investigation can detect them. When compared with physiological results using the same sinusoidal gradings as stimuli, contrast sensitivity gives reliable informations on how visual information is processed by the brain.

Amblyopia↗
PubMed1988

Influences of cortico-pretectal fibers on responses of rat pretectal neurons.

Responses of pretectal cells were studied following cortical excitation and inactivation in anesthetized rats. The visual cortex was excited electrically and by a topical application of strychnine while it was inactivated by a reversible cryoblockade. In a few experiments the superior colliculus was locally depressed by microinjections of lidocaine hydrochloride. Results showed a large spectrum of response latencies to electrical stimulations of the optic chiasm and visual cortex, and a significant correlation between responses to both sites of stimulation. It appears that pretectal cell responses strongly depend upon corticofugal impulses, as the disruption of the latter results in a profound decline of pretectal discharges. The suppressed-by-light cells were the most affected by a cryoblockade while the ON-tonic units were the least affected. The same types of cells were affected at the retinal level by cortical blockade.

Animals↗
PubMed1986

Influence of a local inactivation in the superior colliculus on lateral geniculate responses in rabbits.

The influence of the superficial layers of the superior colliculus (SC) on responses of the lateral geniculate nucleus was studied in anesthetized and paralyzed rabbits. Fifty to one hundred nanoliters of inactivating drugs were injected through a micropipette positioned in the SC in register with the geniculate cells. The latter were tested with discrete moving and stationary targets presented in random sequences. Results revealed that the SC exerted a dual facilitative (n = 19) and inhibitory (n = 25) influence. The latter segment of the response pattern was modified while the initial portion remained unchanged. In some cases differential effects were observed, that is, the responses to one particular stimulus were more affected than responses to other modalities. However, in the majority of cells it was the on-off responses which were most affected. These findings point toward complex influences of the SC upon geniculate responses in rabbits. This complexity is also supported by findings that in cats the colliculo-geniculate synapses are of various types.

Animals↗
PubMed1986

Modulations of the lateral geniculate nucleus cell responses by a second discrete conditioning stimulus: implications of the superior colliculus in rabbits.

This study analyzes the interactions between two discrete stimuli located in the visual field of the rabbit at the lateral geniculate level. Single unit recordings were carried out simultaneously from the superior colliculus (SC) and lateral geniculate nucleus (LGN) in anesthetized and paralyzed rabbits. A first conditioning stimulus (most often a moving target) was positioned in the receptive field of the collicular cell to ensure activation of the retino-collicular path. A second test stimulus was introduced into the receptive field of the LGN cell. The presentation of this latter stimulus was timed so as to fire the geniculate cell at various delays after the collicular neuron had responded to its own stimulus. The spontaneous firing of each cell was unaffected by the stimulus appropriate to the complementary unit. The conditioning collicular stimulus produced increases or decreases in geniculate responses. This modulation may eventually reduce the direction specificity of a geniculate unit. The fluctuations of the geniculate responses peaked 200 to 300 ms after collicular cells had responded. In a separate series of experiments the influence of the conditioning stimulus on geniculate responses was abolished when the SC was locally inactivated. These results suggest that the well documented colliculo-geniculate system mediates the interactions of several stimuli in the visual field. The outcome of this processing results in a modulation of geniculate responses.

Action Potentials↗