The effect of apomorphine on blink kinematics in subhuman primates with and without facial nerve palsy. (65/564)

PURPOSE: The purpose of this study was to document the effect of acutely delivered apomorphine, a dopamine receptor agonist with both D1 and D2 properties, on blink rate and the amplitude-velocity characteristics of eyelid kinematics in a group of nonhuman primates. METHODS: Three cynomolgus and two rhesus macaques underwent baseline recordings for eyelid kinematics, using the Robinson search coil technique. Next, each animal received a 0.15-mg/kg subcutaneous injection of apomorphine. Recordings were taken at 45 and 90 minutes, respectively, after injection. Blink rates per minute were obtained, and main sequence relationships were calculated for every animal. The data were pooled for each eyelid, excluding one monkey who was affected by facial nerve palsy and was analyzed separately. RESULTS: Monkeys with normal facial musculature and normal baseline blink rates showed consistently longer, faster blinks after apomorphine. The main sequence relationship, although tending to be lower, was not statistically different from baseline. One monkey, with prior facial nerve palsy and a very steep amplitude versus peak velocity relationship, showed normalization of the main sequence slope after apomorphine at both 45 and 90 minutes after injection. CONCLUSIONS: Apomorphine consistently lowers blink rate and changed blink metrics in normal monkeys and, more dramatically, in a monkey with facial nerve palsy. These findings add credence to models in which dopamine deficiency plays a role in the modulation of blink kinematics.  (+info)

Effects of voluntary blinks on saccades, vergence eye movements, and saccade-vergence interactions in humans. (66/564)

Blinks are known to change the kinematic properties of horizontal saccades, probably by influencing the saccadic premotor circuit. The neuronal basis of this effect could be explained by changes in the activity of omnipause neurons in the nucleus raphe interpositus or in the saccade-related burst neurons of the superior colliculus. Omnipause neurons cease discharge during both saccades and vergence movements. Because eyelid blinks can influence both sets of neurons, we hypothesized that blinks would influence the kinematic parameters of saccades in all directions, vergence, and saccade-vergence interactions. To test this hypothesis, we investigated binocular eye and lid movements in five normal healthy subjects with the magnetic search coil technique. The subjects performed conjugate horizontal and vertical saccades from gaze straight ahead to targets at 20 degrees up, down, right, or left while either attempting not to blink or voluntarily blinking. While following the same blink instruction, subjects made horizontal vergence eye movements of 7 degrees and combined saccade-vergence movements with a version amplitude of 20 degrees. The movements were performed back and forth from two targets simultaneously presented nearby (38 cm) and more distant (145 cm). Small vertical saccades accompanied most vergence movements. These results show that blinks change the kinematics (saccade duration, peak velocity, peak acceleration, peak deceleration) of not only horizontal but also of vertical saccades, of horizontal vergence eye movements, and of combined saccade-vergence eye movements. Peak velocity, acceleration, and deceleration of eye movements were decreased on the average by 30%, and their duration increased by 43% on the average when they were accompanied by blinks. The blink effect was time dependent with respect to saccade and vergence onset: the greatest effect occurred 100 ms prior to saccade onset, whereas there was no effect when the blink started after saccade onset. The effects of blinks on saccades and vergence, which are tightly coupled to latency, support the hypothesis that blinks cause profound spatiotemporal perturbations of the eye movements by interfering with the normal saccade/vergence premotor circuits. However, the measured effect may to a certain degree but not exclusively be explained by mechanical interference.  (+info)

Synapse formation is associated with memory storage in the cerebellum. (67/564)

The idea that memory is encoded by means of synaptic growth is not new. However, this idea has been difficult to demonstrate in the mammalian brain because of both the complexity of mammalian behavior and the neural circuitry by which it is supported. Here we examine how eyeblink classical conditioning affects synapse number within the cerebellum; the brain region essential for long-term retention of the conditioned response. Results showed eyeblink-conditioned rats to have significantly more synapses per neuron within the cerebellar interpositus nucleus than both explicitly unpaired and untrained controls. Further analysis showed that the increase was caused by the addition of excitatory rather than inhibitory synapses. Thus, development of the conditioned eyeblink response is associated with a strengthening of inputs from precerebellar nuclei rather than from cerebellar cortex. These results demonstrate that the modifications of specific neural pathways by means of synaptogenesis contributes to formation of a specific memory within the mammalian brain.  (+info)

Blink reflex: comparison of latency measurements in different human races. (68/564)

The blink reflex latencies and cephalometric indexes were analysed in 30 male volunteers from three different races, 10 white, 10 black, and 10 Oriental. Ages ranged from 15 to 59 years, height from 1,60 to 1,80 m, and weight from 60 to 80 kg. Blink reflexes were obtained after unilateral electric stimulation of the supraorbital nerve for quantitative analysis of 3 responses, early ipsilateral (R1), late ipsilateral (R2i) and late contralateral (R2c), obtained from the orbicularis oculi muscle. Cephalometric indexes were calculated by multiplying the ratio between the longer transverse and the longer saggital head diameters by 100. The R1, R2i and R2c latencies were consistent with other published papers revealing no differences between the different racial groups. The mean of the cephalometric indexes of each group were consistent with respective racial characteristics. This study revealed that there are no differences between R1, R2i and R2c latencies in the 3 different studied races.  (+info)

The punctal apposition syndrome: a new surgical approach. (69/564)

AIMS: To assess the punctal apposition syndrome (PAS) and its response to lateral canthal tendon (LCT) repair. METHODS: In this retrospective, interventional case series, five patients (seven symptomatic eyes) with PAS were managed. Lateral canthal tendon repair was performed in all seven eyes. The main outcome measure was correction of watery eye symptomatology. RESULTS: All five patients achieved symptomatic resolution. Conjunctivochalasis and functional nasolacrimal duct obstruction were associated with the PAS. CONCLUSION: This new surgical approach to the PAS, using a LCT repair, was successful in all patients. Two patients (three eyes) required conjunctivochalasis excision.  (+info)

Neuronal premotor networks involved in eyelid responses: retrograde transneuronal tracing with rabies virus from the orbicularis oculi muscle in the rat. (70/564)

Retrograde transneuronal tracing with rabies virus from the right orbicularis oculi muscle was used to identify neural networks underlying spontaneous, reflex, and learned blinks. The kinetics of viral transfer was studied at sequential 12 hr intervals between 3 and 5 d after inoculation. Rabies virus immunolabeling was combined with the immunohistochemical detection of choline acetyltransferase expression in brainstem motoneurons or Fluoro-Ruby injections in the rubrospinal tract. Virus uptake involved exclusively orbicularis oculi motoneurons in the dorsolateral division of the facial nucleus. At 3-3.5 d, transneuronal transfer involved premotor interneurons of trigeminal, auditory, and vestibular reflex pathways (in medullary and pontine reticular formation, trigeminal nuclei, periolivary and ventral cochlear nuclei, and medial vestibular nuclei), motor pathways (dorsolateral quadrant of contralateral red nucleus and pararubral area), deep cerebellar nuclei (lateral portion of interpositus nucleus and dorsolateral hump ipsilaterally), limbic relays (parabrachial and Kolliker-Fuse nuclei), and oculomotor structures involved in eye-eyelid coordination (oculomotor nucleus, supraoculomotor area, and interstitial nucleus of Cajal). At 4 d, higher order neurons were revealed in trigeminal, auditory, vestibular, and deep cerebellar nuclei (medial, interpositus, and lateral), oculomotor and visual-related structures (Darkschewitsch, nucleus of the posterior commissure, deep layers of superior colliculus, and pretectal area), lateral hypothalamus, and cerebral cortex (particularly in parietal areas). At 4.5 and 5 d the labeling of higher order neurons occurred in hypothalamus, cerebral cortex, and blink-related areas of cerebellar cortex. These results provide a comprehensive picture of the premotor networks mediating reflex, voluntary, and limbic-related eyelid responses and highlight potential sites of motor learning in eyelid classical conditioning.  (+info)

Ocular torsion during voluntary blinks in humans. (71/564)

PURPOSE: Most studies on blink-induced eye movements have been restricted to rotations about the horizontal and vertical axes. By additionally measuring rotation about the torsional axis, the authors investigated whether the three-dimensional rotation of the eye during the early phase of eyelid closure could be assigned to the action of a single extraocular muscle. METHODS: In five healthy human subjects, eye movements about all principal axes of rotation (horizontal, vertical, and torsional) were recorded during voluntary blinks of different durations (as short as possible, 0.83 seconds, and 1.67 seconds) in straight-ahead gaze. Original dual search coils frequently rotate about the line of sight, because the upper eyelid touches the nasally exiting wire leads. Therefore, the search coils were modified so that the wires left the silicon annulus from its inner border at 6 o'clock. RESULTS: The earliest eye movement during blinks consisted of a pulselike trajectory in a direction that was always extorsional, downward, and inward, regardless of the duration of eyelid closure. The beginning of all three movement components preceded the beginning of eyelid movement; thus, a coil artifact is unlikely. On eyelid opening, a consistent pulselike movement in the intorsional, upward, and outward direction occurred. CONCLUSIONS: During the initial phase of voluntary eyelid closure, the eyes move in a three-dimensional direction that is consistent with a pulselike innervation of the inferior rectus muscle. To obtain reliable measurement of torsional eye movements with dual search coils during blinks, modification of the annulus is indispensable.  (+info)

Are women more sensitive than men to 2-propanol and m-xylene vapours? (72/564)

AIMS: To evaluate possible differences between men and women in acute health effects after controlled short term chamber exposure to vapours of two common organic solvents. METHODS: Fifty six healthy volunteers (28 per sex) were exposed to 150 ppm 2-propanol, 50 ppm m-xylene, and clean air for two hours at rest. The subjects rated symptoms on a visual analogue scale before, during, and after the exposure. Blinking frequency was measured continuously during exposure. Pulmonary function, nasal swelling, inflammatory markers (lysozyme, eosinophilic cationic protein, myeloperoxidase, albumin) in nasal lavage and colour vision (Lanthony D-15 desaturated panel) were measured before and at 0 and 3 hours after the exposure. RESULTS: There were no significant sex differences in response to solvent exposure with respect to blinking frequency, lung diffusing capacity, nasal area and volume, inflammatory markers in nasal lavage, and colour vision. Increased symptoms were rated by both sexes for nearly all 10 questions during exposure to 2-propanol or m-xylene, most increases being significant at one time point at least. The rating of "discomfort in the throat or airways" increased more in women during exposure to 2-propanol or m-xylene. During exposure to 2-propanol the rating of "fatigue" was more increased in men after one hour, but more increased in women after two hours of exposure. With regard to pulmonary function, women had small but significant decreases in FVC, FEV(1)/FVC, and FEF(75) three hours after exposure to m-xylene, but only the decrease in FVC was significantly different from that in men. CONCLUSION: Our results suggest that women are slightly more sensitive than men to the acute irritative effects of 2-propanol and m-xylene vapours.  (+info)