1. The responses of the brachioradialis and biceps brachii muscles to non-invasive magnetic and electrical stimulation of the human motor cortex have been investigated during performance of different tasks. 2. Both muscles were simultaneously active during elbow flexor isometric torque, or forearm flexion lifting a weight (shortening contraction), or extension breaking the fall of the weight (lengthening contraction). The forearm extensor triceps brachii muscle was not engaged in any task. By using different weights, comparable levels of EMG activity were obtained in the same muscle across tasks.3. Both magnetic (7 subjects) and electrical (3 subjects) brain stimulation (at about 1P5 times the motor threshold) produced larger responses during shortening, and smaller responses during lengthening, in the brachioradialis muscle with respect to isometric contractions, in spite of equal background EMG levels. Responses evoked in the biceps brachii by either stimulation mode were smaller during lengthening but not significantly enhanced during shortening. No consistent differences in the task-related modulation of the responses were present between electrical or magnetic stimulations. No significant changes in the evoked responses occurred during passive elbow flexion or extension. 4. In three subjects, the H reflex was evoked in the brachioradialis by stimulation of the radial nerve during performance of the same tasks. The pattern of task-related modulation of the reflex amplitude paralleled that obtained for brain stimulation. 5. The opposite modulation induced by the shortening and lengthening tasks both in magnetically and electrically evoked motor responses, and in the H reflex, suggests that task-related changes in excitability of the cortical neurones play a minor role. The cortical control of the two different tasks might be exerted by an appropriate 'setting' action on the excitability of the spinal circuit, or by a change in the excitability profile of the motoneuronal pool.

Results of our study indicate that it is possible to record NWR in conscious standing horses, to define a reflex threshold, and to measure reflexes in response to increasing stimulus intensity.

We documented NWRs evoked from the forelimb and hind limb and their recruitment with stimuli of increasing intensity in horses. These results provide a basis for use of NWRs in studies on nociceptive modulation in horses.

Temporal summation obtained by repeated stimulations of subthreshold intensity appears to represent a new tool for investigating nociceptive pathophysiologic processes in horses; this experimental model may be useful to examine the mode of action and efficacy of analgesic and anesthetic interventions and possibly to assess sensory dysfunction in clinical settings.

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Results confirm antinociceptive activity of romifidine and may represent an objective demonstration of the well-known hypersensitivity to tactile stimuli observed in horses receiving alpha2-adrenoreceptor agonists in clinical practice. Romifidine can be included in analgesic and anesthetic protocols to provide additional analgesia in horses.

Amacrine cells of the goldfish retina were characterized electrophysiologically and subsequently labelled by intracellular injection of horseradish peroxidase. An attempt was made to broaden the electrophysiological classification of the cells. Light-evoked sustained amacrine cell responses were divided into two subtypes depending on colour opponency. Colour-coded responses (red/depolarizing and green/hyperpolarizing) were found to arise in amacrine cells possessing highly polarized dendritic fields; the dendrites were monostratified in the proximal half (sublamina b) of the inner plexiform layer. Non-colour-opponent sustained responses also arose in monostratified units, but the level of dendritic ramification was in sublamina a or b (hyperpolarizing or depolarizing units, respectively). Transient (ON-OFF) responses were associated mainly with bi- or multi-stratified or diffuse amacrine cells. Some variability was observed in the sizes of the dendritic fields in different sublaminae. There was a tendency for units with brisk components of responses to be narrowly stratified in the inner plexiform layer. Some units possessed "distant" dendrites. Several aspects of structure-function correlation in amacrine cells are discussed.