Slow saccades in spinocerebellar degeneration

Two patients with spinocerebellar degeneration made abnormally slow horizontal refixations. One patient produced quick phases of nystagmus with identical maximum velocities, suggesting her refixations were abnormal saccades and not voluntary pursuit movements. In response to double target jumps, neither patient showed an obligatory refractory period after each saccade; they responded to every target movement after one reaction time. Their slow refixations were not preprogrammed since they could be modified in flight. To reconcile these observations with normal saccadic behavior, we hypothesized a neural network that made saccades by driving the eyes to an orbital position rather than preprogramming a distance for movement. Computer simulation of this model produced both realistically appearing normal saccades and, when appropriately "lesioned" to simulate a loss of saccadic "burst" neurons in the pontine reticular formation, slow saccades that could be modified in flight.

A quantitative analysis of extraocular muscle cooperation and squint

The mechanical properties of human extraocular muscles have recently been described. This allows one to use the force-balance equation of mechanics to solve for the complete mechanical state of all six extraocular muscles and the passive orbital tissues in any eye position. This includes each muscle's force, length, innervation, and unit action vector, which describes how its force is distributed to act horizontally, vertically, and in torsion. Most important, this calculation method allows one to predict the tropias that occur in an eye subject to any imaginable form of peripheral pathology. It also permitts, by calculation, an estimation of the correction that might be expected from any sort of muscle surgery. The tight lateral rectus syndrome is used to illustrate the application of the method in diagnosis and surgery. It also offers, for the first time, a quantitative estimate of the multitude of ways in which muscles can interact and interfere with each other when they hold the globe. Two of the results are interesting: because muscles have different lengths and sizes, their innervational participation in a movement can appear to be quite different than their mechanical participation. From an innervational standpoint, the vertical recti and obliques participate equally in vertical gaze. Muscles interfere with each other a good deal and necessitate changes of innervation to counteract these cross-couplings. This causes unexpected dependencies of innervation on eye position and leads, for example, to the fact that the superior rectus innervation in up gaze is just as large in adduction as in abduction.

The irreversible binding of acetylcholine mustard to muscarinic receptors in intestinal smooth muscle of the guinea-pig

1. Acetylcholine mustard (N-2-chloroethyl-N-methyl-2-acetoxyethylamine), a potent muscarinic agonist, binds virtually irreversibly to muscarinic receptors in longitudinal muscle strips from guinea-pig small intesting, as shown by the inhibition of the binding of E13-H]-propylbenzilycholine mustard ([3-H-PrBCM), an affinity label for the muscarinin receptor. 2. A value for the apparent binding affinity of acetylcholine mustard and a value for the rate constant for the receptor alkylation reaction have been deduced from the rate of onset of the inhibition of [3-H]-PrBCM binding. 3. The kinetic constants obtained may refer largely to the interaction between acetylcholine mustard and the desensitized receptor. 4. At high concentrations acetylcholine mustard practically abolishes the contractile response to carbachol. At the concentrations acetylcholine mustard appears to have multiple actions on the tissue.