Conduction properties of identified neural pathways in the central nervous system of mice in vivo

Abstract

Various lines of transgenic or knockout mice are now available that have abnormalities in neuron, glial cells or neuron-glial interaction. However, the techniques for quantitative analysis of their pathophysiological functions are still limited. We established an experimental model system to measure the properties of nerve conduction of identified neural pathways in the CNS using anesthetized and immobilized mice. Dorsal column (DC), vestibulospinal/reticulospinal tracts (VRST) and pyramidal tract (PT) were stimulated by inserting stimulating electrodes into the dorsal column nuclei, medial longitudinal fasciculus, and the medullary pyramid, respectively. Volleys were recorded at various segments in the cervical spinal cord with surface electrodes, and their conduction velocities (CVs) and relative refractory periods (RRPs) were measured. The CVs of the DC, VRST and PT were 26.25 +/- 4.96 m/s (n = 7), 51.55 +/- 4.65 m/s (n = 7), 8.89 +/- 1.81 m/s (n = 7), respectively. Data from paired stimulation indicated that the median values of RRPs of the DC, VRST and PT were 10, 2 and 4 ms, respectively, which suggested marked difference among individual tracts. This is the first attempt to measure the conduction properties of the central tracts in mice in vivo. This experimental procedure will give us a physiological measure of CNS functions in normal and genetically manipulated mice and contribute to clarifying the molecular mechanisms and pathophysiology of neurodegenerative diseases such as multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS).

In Vivo Recordings of Bulbospinal Excitation in Adult Mouse Forelimb Motoneurons

“…In contrast to the rat (Alstermark et al 2004), the volley remained rather synchronized in the caudal segments C 5 -C 7 , which indicates that the corticospinal fibers are fairly homogenous with respect to size. The conduction velocity was 8.7 Ϯ 2.4 (SD) m/s (n ϭ 10); similar velocity was recently found by Tanaka et al (2004), which is similar to the slow component in the rat (Alstermark et al 2004). As shown in Fig.…”

“…As shown in Fig. 1C (bottom) stimulation in the MLF evoked a descending volley (shown with faster time base), which remained virtually unchanged in amplitude from C 2 to C 7 and had a conduction velocity of ϳ50 m/s (as recently found by Tanaka et al 2004). Figure 1D shows the latency of the corticospinal (Pyr; solid line and filled circles) and MLF (dotted line and open circles) volleys as a function of conduction distance in the different cervical segments.…”

Histological and electrophysiological analysis of the corticospinal pathway to forelimb motoneurons in common marmosets

“…The protocol for electrophysiological analysis of the corticospinal effects on the spinal circuits was based on that of previous studies (Alstermark et al, 2004;Tanaka et al, 2004;Umeda et al, 2010) and is summarized below. Tungsten electrodes (impedance: 100 k , uninsulated tip diameter: 10 m) were inserted to stimulate the CST, the reticulospinal tract (RST), and the ascending fibers in the dorsal column (DC) terminating at the cuneate nucleus, all at the medullary level.…”

“…The initial positive peak was regarded as the timing of impulse arrival via the fastest conducting fibers, measured as the latency (Illert et al, 1976). CV was estimated from Q5 regression analysis and electrode distances (Tanaka et al, 2004). The measurements of the distance were made in situ.…”

Electrophysiological abnormalities precede apparent histological demyelination in the central nervous system of mice overexpressing proteolipid protein

“…The method for measuring CVs of the spinal ascending and descending tracts is described in detail in previous papers (Alstermark and Ogawa, 2004; Tanaka et al,2004). Figure 1A schematically illustrates the experimental arrangement.…”