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Biomedical subjects

J Wallman

Publications and source records attributed to J Wallman.

67 records · Page 4Linked to original sources
PubMed1982

Avian vestibuloocular reflex: adaptive plasticity and developmental changes.

1. This study demonstrates plasticity of the vestibuloocular reflex (VOR) in chickens and compares it to that of other species and to that of newly hatched chicks. Adaptive changes in the VOR were induced by subjecting the animals to combinations of visual and vestibular stimuli that simulated the effect of the VOR being either too low in gain or reversed in phase. 2. The VOR of chickens resembles that of mammals, but the curve of phase lead versus frequency seems shifted toward higher frequencies. The VOR of newly hatched chicks has extremely low gain (less than 0.1). 3. In both the older and newly hatched animals, the VOR gain increased substantially after 2 h in an environment in which the imposed en bloc rotations produced increased retinal image slip in the normal directions. Similarly, 2 h of reversed retinal image slip produced decreased VOR gain and, in some cases, reversal fo the phase of the VOR. The gain changes were largest at the "training" frequency. The phase changes were in the direction of increased phase lead. Changes in the gains of the optokinetic responses and of the combination of VOR and optokinetic responses were also seen, especially in the newly hatched animals. 4. The newly hatched birds showed the largest VOR changes in the increased-gain situation, whereas the older birds showed the largest changes in the reversed-phase situation, as assessed by the changes in the average retinal slip velocity experienced. These results may well not be a consequence of differences in age, per se, but of differences in average retinal slip experienced in the two experimental situations at the start of the trial because of the lower VOR gain of the newly hatched animals. There seems to be no dramatic difference in VOR plasticity between newly hatched and older birds. 5. Our results with reversed visual motion are substantially different from those obtained in similar studies on rabbits, suggesting that these two species use different error signals to control the adaptive adjustment of the VOR.

Adaptation, Physiological↗
PubMed1981

Relation of single unit properties to the oculomotor function of the nucleus of the basal optic root (accessory optic system) in chickens.

Single unit recordings in the nucleus of the basal optic root (nBOR) of the accessory optic system in chickens suggest that it has a role in vertical stabilizing eye movements. Cells have unusually large receptive fields and never respond to small stationary stimuli. They respond best to large richly patterned stimuli moving slowly (2-4 degrees/s) in vertical directions. Cells responsive to upward movement tend to be located in the dorsal portion of nBOR, which projects to motor areas producing upward eye movement, whereas cells responsive to downward movement tend to be located in the ventral portion of nBOR, which projects to motor areas producing downward eye movement; this suggests that these synapses onto oculomotor neurons are excitatory. In many nBOR units, the preferred and null directions are not opposite to each other. These directional asymmetries seem to be correlated with other properties of the units in a manner that supports the idea that the accessory optic system is arranged according to a vestibular coordinate system. This finding complements the abundant anatomical and physiological evidence linking the accessory optic system to the vestibular system.

Animals↗
PubMed1981

The eyes of young chickens grow toward emmetropia.

The distribution of refractive errors was followed in chicks from hatching to 8 weeks of age. A dramatic progressive decrease in the variability of refractions was observed over this period. In addition, there appeared to be a parallel decline in hyperopia, even when the artifactual hyperopia of retinoscopy was taken into account. These results are evidence for a postnatal development regulatory mechanisms, most likely dependent on vision, which directs growth of the eye toward emmetropia.

Animals↗
PubMed1978

Extreme myopia produced by modest change in early visual experience.

Chicks whose vision was restricted to the frontal visual field became extremely myopic (mean, -10 diopters; maximum, -24 diopters) and had eyes of increased axial length. Animals restricted to lateral field vision did not differ from normal animals. Monocular deprivation of form vision also produced myopia and eye enlargement and, in addition, produced increased anterior chamber depth.

Animals↗
PubMed1977

Antinociceptive effects of vaginal stimulation in rats: neurophysiological and behavioral studies.

The present studies extend previous findings that probing the vaginal cervix of rats blocks withdrawal reflexes and induces immobilization44. In the present studies, we report that this effect is apparently not due to an action on the final motor pathway, for limb or facial movement induced by electrical stimulation of the pyramidal tract was not suppressed by the probing. In contrast, the sensory response of neurons in the ventrobasal complex of the thalamus to noxious pinch stimulation was markedly attenuated by probing the vaginal cervix. However, the response of these neurons to gentle tactile stimulation was not attenuated, indicating a selective antinociceptive effect of the probing. The antinociceptive effect was not necessarily related to changes in arousal. These findings were supported by behavioral studies in which probing the vaginal cervix blocked vocalization in response to tail shock, and elevated the current threshold for eliciting vocalization in response to tail shock. Furthermore, during the probing, the rats were found to be capable of vocalizing in response to presumably non-noxious (lifting) stimulation, even though their vocalization response to noxious tail shock was suppresed. These studies suggest that probing the vaginal cervix rats exerts an analgesic action.

Animals↗
PubMedDate not supplied

Covalent disulfide binding of human IL-1 beta to alpha 2-macroglobulin: inhibition by D-penicillamine.

Secreted human IL-1 beta is known to have two free SH groups due to unpaired cysteines (positions 8 and 71). Alpha 2-Macroglobulin (alpha 2-M) has internal thioester bonds between cysteine and glutamate residues. Free SH groups may be generated at these alpha 2M residues through the action of proteinases, amines such as methylamine, or at a slow rate, by H2O ("aging" of alpha 2M). Thus, the possibility that IL-1 beta forms a disulfide bond with alpha 2M was investigated. 125I-labeled human rIL-1 beta (15 kDa) was incubated with fresh normal human serum or with purified alpha 2M, treated or not with methylamine. The mixtures were submitted to nondenaturing and denaturing polyacrylamide gel electrophoresis (PAGE) followed by autoradiography. IL-1 beta bound to commercially purified "aged" alpha 2M and to alpha 2M in methylamine-treated serum but not to native serum alpha 2M. It did not bind detectably to any other serum proteins. The addition of D-penicillamine (D-pen) during the reaction of [125I]rIL-1 beta with serum or purified alpha 2M blocked the covalent binding of rIL-1 beta to alpha 2M. [125I]rIL-1 beta was removed from alpha 2M by 2-mercaptoethanol in SDS. Thus, disulfide bonds were formed between the free SH groups on [125I]rIL-1 beta and those resulting from the cleavage of the internal thioester bonds of alpha 2M. "Cold" rIL-1 beta and a Cys71----Ser71 rIL-1 beta mutant effectively competed with [125I]rIL.1 beta for binding sites on alpha 2M. When complexes of rIL-1 beta or the mutant rIL-1 beta and alpha 2M were subjected to nonreducing SDS-PAGE and subsequent Western blot analysis, the rIL-1 beta molecules were found to be present in the alpha 2M bands in a dose-dependent manner. rIL-1 beta attached to alpha 2M in the presence or absence of D-pen showed similar biological activity in the mouse thymocyte-assay. Thus, rIL-1 beta attached noncovalently to alpha 2M is biologically active. The lack of inhibition of rIL-1 beta activity by binding to methylamine-treated alpha 2M in the absence of D-pen suggests, but does not prove, that the covalently bound rIL-1 beta is also active. We concluded that human rIL-1 beta binds to alpha 2M through the Cys at position 8 and that D-pen inhibits this binding. We speculate that this inhibitory effect may contribute to the therapeutic benefits of D-pen in patients with rheumatoid arthritis.

Animals↗
PubMedDate not supplied

The retinal targets of centrifugal neurons and the retinal neurons projecting to the accessory optic system.

In birds, neurons of the isthmo-optic nucleus (ION), as well as "ectopic" neurons, send axons to the retina, where they synapse on cells in the inner nuclear layer (INL). Previous work has shown that centrifugal axons can be divided into two anatomically distinct types depending on their model of termination: either "convergent" or "divergent" (Ramon y Cajal, 1889; Maturana & Frenk, 1965). We show that cytochrome-oxidase histochemistry specifically labels "convergent" centrifugal axons and target neurons which appear to be amacrine cells, as well as three "types" of ganglion cells: two types found in the INL (displaced ganglion cells) and one in the ganglion cell layer. Labeled target amacrine cells have distinct darkly labeled "nests" of boutons enveloping the somas, are associated with labeled centrifugal fibers, and are confined to central retina. Lesions of the isthmo-optic tract abolish the cytochrome-oxidase labeling in the centrifugal axons and in the target amacrine cells but not in the ganglion cells. Cytochrome-oxidase-labeled ganglion cells in the INL are large; one type is oval and similar to the classical displaced ganglion cells of Dogiel, which have been reported to receive centrifugal input; the other type is rounder. Rhodamine beads injected into the accessory optic system results in retrograde label in both types of cells, showing that two distinct types of displaced ganglion cells project to the accessory optic system in chickens. The ganglion cells in the ganglion cell layer that label for cytochrome oxidase also project to the accessory optic system. These have proximal dendrites that ramify in the outer inner plexiform layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Sonographic appearance of callosal agenesis: correlation with radiologic and pathologic findings.

Sonographic features are described in six infants in whom total or partial agenesis of the corpus callosum was confirmed by either computed tomographic or pathologic examination. The six patients demonstrated a range of abnormalities involving the neuraxis as well as other systems, notably cardiovascular, gastrointestinal, and genitourinary. Chromosomal abnormalities were present in two patients. The sonographic features of callosal agenesis seen in these patients included: lack of characteristic acoustic interfaces to define the corpus callosum on both coronal and sagittal sonograms; increased separation and parallelism of the bodies of the lateral ventricles; loss of the characteristic convexity of the medial border of the anterior horns of the lateral ventricles; variable prominence of the occipital horns of the lateral ventricles; variable degree of superior extension of the third ventricle; alteration or absence of the cavum septi pellucidi; and radial arrangement of cerebral sulci about the prominent third ventricle. Cases of partial agenesis may show the dysplastic features found in complete agenesis. However, only some of the callosal echoes are present. The sonographic features of partial agenesis in one infant had not been described before.

Agenesis of Corpus Callosum↗