Hostaflon TF coating of tungsten sensory micro-needles

Microneurography: how it started and how it works

In the first section, this historical review describes endeavors to develop the method for recording normal nerve impulse traffic in humans, designated microneurography. The method was developed at the Department of Clinical Neurophysiology of the Academic Hospital in Uppsala, Sweden. Microneurography involves the impalement of a peripheral nerve with a tungsten needle electrode. Electrode position is adjusted by hand until the activity of interest is discriminated. Nothing similar had previously been tried in animal preparations, and thus the large number of preceding studies that recorded afferent activity in other mammals did not offer pertinent methodological guidance. For 2 years, the two scientists involved in the research impaled their own nerves with electrodes to test various kinds of needles and explore different neural systems, all the while carefully watching for signs of nerve damage. Temporary paresthesiae were common, whereas enduring sequelae never followed. Single-unit impulse trains could be discriminated, even those originating from unmyelinated fibers. An explanation for the discrimination of unitary impulses using a coarse electrode is inferred based on the electrical characteristics of the electrode placed in the flesh and the impulse shapes, as discussed in the second section of this paper. Microneurography and the microstimulation of single afferents, combined with psychophysical methods and behavioral tests, have generated new knowledge particularly regarding four neural systems, namely the proprioceptive system, the cutaneous mechanoreceptive system, the cutaneous nociceptive system, and the sympathetic efferent system to skin structures and muscular blood vessels. Examples of achievements based on microneurography are presented in the final section.

Properties of a microcoaxial electrode designed for unit recording from human peripheral nerves

A new microcoaxial electrode is presented, which has been used successfully for recording single- and multiunit activity from myelinated and unmyelinated human nerve fibres. The main advantages (as compared with conventional needle electrodes) are electrical stability, mechanical durability, capability of being re-used and an insulation not easily scraped off, resulting in a low leakage capacitance. The AC polarization impedance and the potential transducing properties of the microelectrode have also been studied.

Anatomical and physiological properties of ipsilaterally projecting spinothalamic neurons in the second cervical segment of the cat's spinal cord

Anatomical and electrophysiological methods were used to investigate the projections and response properties of neurons in the second cervical (C2) spinal segment of the cat giving origin to a previously undescribed projection to the ipsilateral thalamus. The method of retrograde axonal transport of horseradish peroxidase (HRP) was used to identify neurons in C2 giving rise to thalamic projections. Following large (3.0 microliter) thalamic HRP injections, a large number of labeled neurons was observed in lateral laminae VII-VIII of C2 ipsilateral to the injections. They occurred as small clusters of cells along the longitudinal axis of C2. Labeled neurons were also observed contralaterally in the lateral cervical nucleus, dorsal horn (especially medial lamina VI), and loosely distributed in the ventral horn. The ipsilaterally projecting neurons were also labeled following small (0.2--0.5 microliter) HRP injections restricted to individual spinothalamic terminal zones (intralaminar nuclei, ventrobasal complex-nucleus ventralis lateralis border zone, medial division of the posterior nuclei), indicating that as a group they project widely throughout the thalamus. Single unit recording methods were used to obtain complementary information on the functional properties of these neurons. The antidromic stimulation method was applied to identify units in C2 projecting to the ipsilateral thalamus in anesthetized, paralyzed cats. Three categories of ipsilaterally projecting C2 units were identified: (1) units not driven by any type of natural stimulation; (2) units having large cutaneous receptive fields (RFs) and wide dynamic response ranges ("widefield"), and (3) units with smaller RFs and varied properties ("other"). Widefield units with bilaterally symmetrical and asymmetrical RFs were observed. Co-stimulation of different portions of an excitatory RF produced summation of the unit response. Inhibitory RF components were identified in one-third of the widefield units. Unit recordings after spinal tract lesions revealed that the afferent input passed via the ipsilateral lateral and/or ventral funiculi. Widefield unit responses to somatosensory stimuli could be inhibited by dorsal column conditioning stimulation. Several "other" units resembled widefield units, while a second group had small RFs restricted to the C2 dermatome. Possible functional roles of the projecting C2 neurons in somatosensory and non-specific systems are discussed.

The dynamic response of warm units in human skin nerves

Electrophysiological recordings were made from 12 specific warm receptors in the sensory nerves of human hairy skin. In all cases examined, single warm fibers were spontaneously active at normal skin temperature from about 32 degrees C upwards, while touch, stretching, vibration or pricking the skin did not elicit any response within the receptive fields of warm units. Moderate warming of the skin using linear temperature rates from 0.5 degrees C/s to 1.5 degrees C/s caused a transient overshoot in the frequency of discharge with peak frequencies depending on the rate of change of temperature (dT/dt), the magnitude of thermal increment (deltaT) and the adapting temperature (TA). Cooling the skin caused a transient inhibition of discharge.

Response of rapidly and slowly adapting mechanoreceptors and vibratory sensitivity in human hairy skin

Single unit activity was recorded percutaneously with microelectrodes from 38 rapidly adapting (RA) mechanoreceptors of the dorsal surface of the hand in 49 awake human subjects. Tuning characteristics were determined for 28 RA-fibers at various frequencies between 5 and 100 cps of sinusoidal mechanical stimulation. In separate experiments human thresholds of vibration perception were studied under comparable conditions. Several RA-mechanoreceptive fibers were broadly tuned, showing no clearly defined best frequency in the range between 5 and 20 cps. Other RA-fibers had a minimum of sensitivity between 20 and 40 cps. For either lower or higher frequencies, stronger stimuli were required to elicit one nerve impulse per stimulus cycle. These RA-receptors may be related to the perception of low frequency oscillation (flutter). They cannot account for human vibration sensitivity in the higher frequency range, since tuning of the receptors required considerably higher amplitudes than perception. Sixteen slowly adapting (SA) mechanoreceptors of Type I and II showed a frequency modulation in phase with low frequency mechanical oscillations of stimulus amplitudes far below human thresholds for perception of movement.