Microneurography

Microneurography is a technique using metal electrodes to observe and record neural traffic of both myelinated and unmyelinated axons in efferent and afferent neurons of the skin and muscle. Therefore, it can provide information of the neurophysiology of nerve fibers (both afferent and efferent) in the face and peripheral nervous system. The technique was founded and developed in Sweden between 1965-1966. During that time, the primary aim was to record multiunit activity from the large spindle afferents. The results were to define the role of muscle spindles and the voluntary movement system.

Electrodes of various metals have been used in the past to increase the signal-to-noise ratio. Platinum-iridium was found to be too soft and steel was too brittle. Finally tungsten, which was hard and non-brittle was used and it was found that an electrode tip (5-10 µm) provided acceptable records of nerve activity. An epoxy-based varnish was also found to provide an acceptable electrode coating.

Microneurography applications include:

• Observing single action potentials from unmyelinated axons
• Studying neural control autonomic effector organs
• Understanding of receptive fields of mechanoreceptors

If the recording is done in nerve fasicles, the neuronal activity is directly related to the sensory afferents or motor efferents. Therefore, the firing rate of sensory afferents is directly from stimulation of receptors, either in muscles, tendons, or skin. Similarly, the muscle activation directly relate to efferent signals to skeletal muscle or smooth muscle.

It has been shown that microneurography appears to have little permanent detrimental affects to human subjects. However, symptoms such as abnormal sensations, deep muscle aches, muscle weakness, and loss of sensations can be observed after the study, but generally not during the study. Usually 95% of symptoms are resolved within 14 days. In animal studies, it has been shown that axonal damage does occur, but this axonal damage in animals does not translate into perceived damage or loss of function in human experiments.

Microneurography can be performed using the ADInstruments Neuro Amp EX together with a PowerLab data acquisition system. The Neuro Amp EX is a low noise and high gain amplifier which has a wide range of filters and a high signal to noise ratio and is supplied with the Neuro Amp EX headstage. The device is certified safe for human connection. The Neuro Amp EX is NOT suitable for intracellular recording and use with glass microelectrodes.

The Neuro Amp EX in conjunction with PowerLab, LabChart or Scope provides:

• Full electrical isolation from power-line (mains) circuitry to guarantee subject safety
• A low-noise, high-gain differential amplifier specifically designed for recording extracellular potentials
• Software-controlled low-pass, high-pass, notch and mains filters to remove unwanted Signal frequencies for particular uses
• Audio output to listen to neural signals

For more information see:

• Sympathetic Nerve Activity application page

LabChart
LabChart software (for Windows and Macintosh) combines the familiar simplicity of a traditional strip chart recorder with the powerful analysis features of a digital acquisition system. LabChart software and a PowerLab data acquisition unit provide data integrity, easy selection of hardware settings, powerful online and offline analysis, procedure automation, seamless extraction of experimental data and flexible display options. Acquisition and analysis capabilities can be further increased with LabChart Extensions and LabChart Modules. LabChart Modules are available as part of LabChart Pro and LabChart Extensions are free for download from the website for existing LabChart users.

Spike Histogram Module (Windows or Macintosh)
The MLS062/6 Spike Histogram Module for LabChart, in combination with ADInstruments hardware, provides the neuroscientist with the ability to record and analyze extracellular spike data in real time and offline. Typical features include:

• Provides easy to use spike discrimination and data analysis
• Automatically indicates and examines changes in neural firing rate
• Automatically determines the distribution of all interspike intervals
• Performs autocorrelograms and crosscorrelograms analysis (Mac only)
  

Scope
Scope software, supplied with PowerLab systems, provides powerful display, recording and analysis features to transform your computer into a two-channel storage oscilloscope, XY plotter or Power Spectrum (FFT) analyser. Scope is used commonly to measure any high-frequency signal that is time-locked to a stimulus such as action potentials and evoked responses. For analyzing Evoked Potentials, the Scope Software is recommended because it provides signal averaging functions that are necessary to extract the evoked response from background noise.

This software:

• Provides the ability to record, display and analyze any high frequency signal that is time-locked to a stimulus
• Synchronizes sweeps with recorded or built-in stimulation patterns
• Provides a range of real-time and offline analysis features
• Generates stimuli of differing intensities and waveform structures (i.e. single-pulse, multiple pulse, simple ramps) and control an external stimulator using the analog output on the front of the PowerLab.

GLP and 21 CFR Part 11
For those researchers working within a laboratory requiring GLP and 21 CFR Part 11 compliance the GLP Client and GLP Server are available for use with LabChart (Windows only) and PowerLab data acquisition systems. For more information, visit the Good Laboratory Practice application page or contact your nearest ADInstruments representative.

Neuro Amplifier
The ML185 Neuro Amp EX is a low noise and high gain device which makes it suitable for all recording environments requiring a wide bandpass (100 Hz – 5 kHz) and a high signal to noise ratio. It provides a gain of 100x with a 10Hz High Pass filter. The cable shielding is directly connected to the casing, limiting the need for additional shielding at the input terminals. The device is certified safe for human connection with the supplied MLT185 Neuro Amp EX headstage. Only a single Neuro Amp EX may be connected to a single PowerLab.

It is supplied:

• MLT185 Neuro Amp EX headstage
• Six male (6) Amphenol connectors for customization of microelectrode adapters (microelectrodes are not supplied)

Human and animal applications include:

• Extracellular recordings from single cells or groups of cells
• Single nerve fiber recordings (split-nerve preparation or human microneurography)

Sympathetic nerve activity in end-stage renal disease

M Hausberg, M Kosch, P Harmelink, M Barenbrock, H Hohage, K Kisters, K H Dietl and K H Rahn, Circulation, 1974-1979, 2002

Heart rate was measured continuously by an ECG. Blood pressure was measured using an automatic sphygmomanometer (Dinamap XL, Johnson & Johnson) during the last half of each minute. Calf blood flow (CBF) was measured by venous occlusion plethysmography using an air plethysmograph. Respiration was monitored by a strain gauge respiration transducer (Pneumotrace, UFI). Intraneural recording techniques were used to obtain multifiber recordings of postganglionic muscle sympathetic nerve activity (MSNA) from the peroneal nerve Tracings of sympathetic neurograms, electrocardiograms, respiration, and CBF were recorded with a MacLab data acquisition system (ADInstruments, Wisstech GmbH) on a Macintosh computer (Apple Inc).

Forearm neurovascular responses during mental stress and vestibular activation

J R Carter, W Cooke and C A Ray, American Journal of Physiology: Heart and Circulatory Physiology, H904-H907, 2005

In human subjects multifiber recordings of MSNA were measured directly by insertion of a tungsten microelectrode into the radial nerve of the left arm. A reference electrode was inserted subcutaneously 2–3 cm from the recording electrode. Both electrodes were connected to a differential preamplifier and then to an amplifier, where the nerve signal was band-pass filtered (700 –2,000 Hz), and integrated at a time constant of 0.1 s to obtain a mean voltage display of nerve activity. Satisfactory recordings of MSNA were defined by spontaneous, pulse-synchronous bursts that did not change during arousal or stroking of the skin. Sympathetic bursts were identified from inspection of mean voltage neurograms displayed by a computer program (Peaks, ADInstruments).