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Biomedical subjects

K A Manning

Publications and source records attributed to K A Manning.

14 recordsLinked to original sources
PubMed1991

Spermidine acetylation in response to a variety of stresses in Escherichia coli.

Heat shock, cold shock, ethanol, and alkaline shift, but not hydrogen peroxide, stimulate the accumulation of monoacetylspermidine in Escherichia coli. Acetylation occurs with nearly equal frequencies at both the N1 and N8 positions of this ubiquitous polycation. Spermidine acetylation does not appear to be associated with known stress regulons, such as htpR, oxyR, and SOS. E. coli, capable of acetylating spermidine, constitutively express a spermidine acetyltransferase activity during all phases of growth, and this activity is unaffected by cold shock. A mutant strain, incapable of acetylating spermidine, does not express this enzyme activity but grows at an identical rate as the parent strain at 37 degrees C. These results demonstrate that the monoacetylation of spermidine in E. coli is regulated by some mechanism other than a stress-inducible acetyltransferase and is not essential for growth of these cells. They suggest that polyamine acetylation is involved in the responses of these organisms to a variety of chemical and physical stresses.

Acetylation↗
PubMed1991

Eyelid movements in facial paralysis.

We studied the eyelid movements of six patients with unilateral, isolated, facial paralysis using the magnetic search coil. The most significant abnormality consisted of a reduction in the magnitude of the orbicularis oculi contraction with slowing of the peak velocity of the closing phase of the blink. The closing phase blink velocity, which normally increases linearly as a function of amplitude (main sequence), in our patients displayed a relationship characterized by a slow saturating power function that fell off the main sequence. The contralateral normal lid in some cases can show adaptive signs of hyperactivity during the closing phase of the blink. Lid saccades showed a small but consistent decrease in amplitude and velocity compared with the contralateral unaffected eyelid. Unlike the closing phase of the blink, peak velocities of lid saccades stayed on the main sequence. In this study, we discuss how the eyelid executes downward lid saccades based purely on a passive mechanism.

Adult↗
PubMed1991

Eyelid movements. Mechanisms and normal data.

This study provides a comprehensive description of upper eyelid movement in normal human subjects. Using the magnetic search coil technique to monitor lid position and modified skin electrodes to record orbicularis oculi electromyographic (EMG) activity, the authors found that the basic eyelid movements, blinks, and saccadic lid movements, can be uniquely and reliably characterized by their amplitude-maximum velocity relationships. The data show that similar increases in levator palpebrae activity produce the upward lid movements that accompany upward saccadic eye movements as well as the upward phase of a blink. The lid movements that accompany downward saccadic eye movements arise almost exclusively from the passive downward forces and relaxation of the levator palpebrae muscle. In contrast, active orbicularis oculi contraction and the passive downward forces act together to generate lid closure with a blink. These normative data and techniques provide the basis for the clinical analysis of lid motility by which abnormal lid movements can be compared with normal lid kinematics.

Adult↗
PubMed1990

Eyelid movements before and after botulinum therapy in patients with lid spasm.

Quantitative analysis of lid motility is presented for 4 individuals with hemifacial spasm and 1 with Meige's syndrome. The data were obtained, by means of a magnetic search coil technique, prior to and 1 week after injection of botulinum toxin into the orbicularis oculi muscle. Before treatment, the peak velocity of blink-related lid lowering and lid raising was slower than normal, yet lid saccades were normal. After botulinum treatment, significant decreases occurred in (1) the amplitude of blinks and lid saccades, and (2) the peak velocity of the blink down-phase. Botulinum treatment significantly alters blink lid-lowering kinematics, while saccadic lid-lowering kinematics are normal, providing further evidence that the orbicularis oculi muscle does not play a primary role in downward lid saccades.

Aged↗
PubMed1990

Retrograde transneuronal transport properties of fragment C of tetanus toxin.

The atoxic fragment C of tetanus toxin reliably undergoes retrograde direct and transneuronal transport, but the full extent of its transport capabilities has not been examined. The primary visual pathways provide an excellent system for investigating, for the first time, the possibility of anterograde direct and transneuronal transport of fragment C. Following injection into the eye of the rat and rabbit, fragment C, localized with a monoclonal antibody, underwent anterograde direct transport to all retinorecipient areas. From these areas, fragment C exhibited retrograde transneuronal transport, strongly and reliably labeling regions that project to retinorecipient areas, including layers V and VI of visual cortex, the parabigeminal nucleus, the suprageniculate nucleus, and the reticular thalamus. In contrast, the absence of fragment C in regions receiving only input from, but not projecting to, retinorecipient areas, most notably layer IV of visual cortex, provides strong evidence for the lack of anterograde transneuronal transport. Thus, while fragment C can be induced to undergo anterograde direct transport by injection into the eye, it exhibits only retrograde transneuronal transport. These characteristics suggest that fragment C of tetanus toxin is a consistent and reliable retrograde transneuronal marker for the elucidation of central nervous pathways.

Animals↗
PubMed1988

The effects of tobacco smoking on smooth pursuit eye movements.

It has recently been shown that tobacco smoking in normal human subjects induces a transient primary-position upbeat nystagmus. We studied the effects of tobacco smoking on smooth pursuit eye movements and found defects in both vertical and horizontal tracking during the first 5 minutes after smoking one cigarette. The smooth pursuit defect consisted of a reduction in upward tracking velocity and the superposition of saccadic square-wave jerks on both vertical and horizontal tracking eye movements. The degree of impairment in upward smooth pursuit correlated with the intensity of tobacco-induced nystagmus present when recording in darkness. We suggest that these alterations are due to summation of nystagmus on normal tracking eye movements rather than primary defects in the smooth pursuit system.

Adult↗
PubMed1988

A model system for motor learning: adaptive gain control of the blink reflex.

An important aspect of the control of movement is how the nervous system produces adaptive gain modification. To investigate this problem in a simple motor system, we studied lid movement and orbicularis oculis muscle activity in human and rabbit subjects during adaptation of reflex eye blinks. The gain of the reflex could be increased or decreased, depending upon the nature of the adaptive stimulus. Since these gain changes could persist upon removal of the adapting stimulus, adaptation appears to result from a modification of the neural program subserving the blink reflex. The orbicularis oculis electromyogram revealed that the neural modifications producing adaptive gain changes predominantly altered the longer latency components of the reflex, while the short latency components remained unchanged. Moreover, in two other paradigms that modulate the gain of reflexes, habituation and reflex modification, similar changes also occurred primarily in the longer latency components of the blink reflex. This result suggests that modification of neurons in longer latency, indirect pathways, may underlie different forms of motor learning.

Adaptation, Physiological↗
PubMed1988

A pharmacological distinction between the long and short latency pathways of the human blink reflex revealed with tobacco.

In three, normal, human subjects, tobacco smoking was used as a pharmacological probe to modify differentially the direct and indirect pathways underlying the blink reflex. The latency of the indirect R2 component of the orbicularis oculis electromyogram evoked by electrical stimulation of the trigeminal supraorbital nerve transiently increased 20-80% after smoking, while the latency of the shorter latency, direct R1 component remained constant. The magnitude of both components of the blink reflex transiently decreased. The data demonstrate that tobacco smoking can differentially alter the long and short latency components of the blink reflex, and suggest that these effects result from modifications of central pathways sensitive to nicotine.

Adult↗
PubMed1987

Tobacco-induced primary-position upbeat nystagmus.

The effects of tobacco smoking on the eye movements of normal human subjects were studied using direct current electrooculography and the magnetic search coil technique. Tobacco induced a transient primary-position upbeat nystagmus in the dark, which was suppressed by visual fixation. It obeyed Alexander's law and was associated with oblique upward fast phases that alternated from side to side. Tobacco-induced nystagmus exhibited a latency of onset at 40 to 90 seconds, a duration of 10 to 20 minutes, and maximum slow-phase velocities at 2 to 3 minutes. We suggest that tobacco induces primary-position upbeat nystagmus through the excitatory effects of nicotine on the central vestibular pathways.

Adult↗
PubMed1986

Different forms of blinks and their two-stage control.

The purpose of this paper is to examine blink kinematics and the neural basis of blinks evoked reflexively by different kinds of stimuli. The kinematics of the upper lid movement and the electromyographic response of lid muscles levator palpebrae and orbicularis oculi were recorded in the rabbit during trigeminally and visually-evoked blinks. We find that there is a basic, kinematic difference between blinks. A blink in response to an airpuff is more rapidly accomplished and achieves a higher velocity than does an equal amplitude blink in response to a flash of light. The two forms of the reflex blink result from differences in the nature and timing of activity in antagonistic lid muscle motoneurons. Nevertheless, most characteristics of blink neural control are common to both reflex blinks. Most importantly, it appears that blinks are produced by two-stage neural control, an early component that is preprogrammed and a late component that is under stimulus control.

Animals↗
PubMed1986

Eye-movement-dependent loss in vision and its time course during vergence.

The attenuation of vision that has long been known to accompany saccadic eye movement has a significant component that is not attributable to visual masking or image smear, and this suppression of vision is now associated with nonsaccadic movement. The purpose of the present experiment was to determine the time course of visual suppression during a vergence eye movement. Suppression was evaluated psychophysically in human observers by measuring their loss of sensitivity to a brief, full-field decrement of light during 6 degrees-9 degrees convergence. Vergence-related suppression was similar in total duration and amplitude to saccadic and blink-related suppression. Since these other forms of oculomotor activity are vastly different in speed and total duration, it is unlikely that suppression results directly from the activity itself. Instead, these results support the hypothesis that a common, more centrally originating, suppression of vision occurs during eye movements, including saccades, eyeblinks, and vergence. Thus, while vision during eye movements can often be reduced through masking and smearing effects, the movement-dependent visual suppression measured in these experiments is a more generally occurring event.

Convergence, Ocular↗
PubMed1979

Infant vision testing by a behavioral method.

A behavioral method of screening binocular infant vision called forced choice preferential looking (FPL) has been developed. Clinical trials of the FPL test for young infants are reported here. The test aids nonspecialized personnel in early identification of bilateral ocular abnormalities and anomalies of binocular cooperation (strabismus). It is not possible to screen for monocular eye disease or amblyopia with this test. Modifications of the FPL test may offer new ways of assessing other aspects of visual function early in life.

Age Factors↗
PubMed1978

A behavioral method for efficient screening of visual acuity in young infants. II. Clinical application.

Visual performance in 130 infants was assessed in a clinical setting with the forced-choice preferential looking (FPL) method described by Dobson et al.5 Over 90% of infants completed testing. Testing usually required less than 10 min. One group of infants tested also underwent complete ophthalmic examination. The second, larger group was screened with handlight examinations and FPL testing; any abnormalities detected were evaluated by full ophthalmic examination. Results so far indicate that the FPL test accurately identifies babies with binocular visual problems and that, when coupled with a handlight examination, it provides efficient screening for ocular problems in infants 0 through 16 weeks of age (postterm).

Age Factors↗