Characterization of Spindle Afferents in Rat Soleus Muscle Using Ramp-and-Hold and Sinusoidal Stretches

Abstract

Falempin. Characterization of spindle afferents in rat soleus muscle using ramp-and-hold and sinusoidal stretches. J Neurophysiol 89: 442-449, 2003; 10.1152/jn.00153.2002. The discharge properties of 51 afferents were studied in the rat soleus muscle spindles. Under deep anesthesia using a pentobarbital sodium solution (30 mg/kg), a laminectomy was performed and the right L 4 and L 5 dorsal and ventral roots were transected near their entry into the spinal cord. In situ, the minimal (L min ) muscle length [3 Ϯ 0.08 (SE) cm] of the soleus was measured at full ankle extension. Unitary potentials from the L 5 dorsal root were recorded in response to ramp-and-hold stretches applied at 3 mm (S3) and 4 mm (S4) amplitudes and four stretch velocities (6, 10, 15, and 30 mm/s), sinusoidal stretches performed at four amplitudes (0.12, 0.25, 0.5, and 1 mm) and six stretch frequencies (0.5, 1, 2, 3, 6, and 10 Hz), and vibrations applied at 50-, 100-, and 150-Hz frequencies. These two kinds of stretches were performed at three different muscle lengths (L minϩ10% , L minϩ15% , and L minϩ20% ), whereas vibrations were applied at L minϩ20% muscle length. Conduction velocity of the fibers was calculated but did not allow to discriminate different fiber types. However, the mean conduction velocity of the first fiber group (43.3 Ϯ 0.8 m/s) was significantly higher than that of the second fiber group (33.9 Ϯ 0.9 m/s). Three parameters allowed to differentiate the responses of primary and secondary endings: the dynamic index (DI), the discharge during the stretch release from the ramp-and-hold stretches, and the linear range and the vibration sensitivity from sinusoidal stretches. The slope histogram of the linear regression based on the DI and the stretch velocity was clearly bimodal. Therefore the responses were separated into two groups. During the stretch release at a velocity of 3 mm/s, the first response group (n ϭ 26) exhibited a pause, whereas the second (n ϭ 25) did not. The linear range of the second ending group (0.12-1 mm) was broader than that of the first (0.12-0.25 mm). The first ending group showed a higher sensitivity to high-vibration frequencies of small amplitude than the second. In comparison with the literature, we can assert that the first and the second ending groups corresponded to the primary and secondary endings, respectively. In conclusion, our study showed that in rat soleus muscle spindles, it was possible to immediately classify the discharge of Ia and II fibers by using some parameters measured under ramp-and-hold and sinusoidal stretches.

An index of spindle efficacy obtained by measuring electroneurographic activity and passive tension in the rat soleus muscle

“…By this fact, the normalization with regard to stretch amplitude, as proposed for cat (Boyd, 1981) or rat (De-Doncker et al, 2003a) afferents, leads to constant static spindle sensitivity index.…”

“…Spindle sensitivity is classically analyzed by the discharges of isolated afferents (primary or secondary) recorded during ramp-and-hold muscle stretches. The quantification of dynamic and static indices according to the method early proposed by Matthews (1963) or Crowe and Matthews (1964) has been often conducted to characterize the discharges of spindle afferents in the cat (see the review of Hunt, 1990) and in the rat (De-Doncker et al, 2003a). This characterization was used to attest the spindle sensitivities to muscle stretch, stretch velocity and even to stretch acceleration (Houk et al, 1992).…”

Morphometric analysis of the fiber populations of the rat sciatic nerve, its spinal roots, and its major branches

“…Calculated borders between the fiber populations compared with literature data. Borders are calculated according to Equation 2; corresponding conduction velocities (m/second) are estimated according to ABK equations; 1) Gokin, Philip, and Strichartz (2001); 2) Djouhri and Lawson (2004); 3) Doncker, Picquet, Petit, and Falempin (2003); 4) Lewin and McMahon (1991). sectional area, which can be used in further theoretical and experimental research of the peripheral nervous system.…”

Changes in the levels of activity of spinal neurons after long-lasting vibrational stimulation of the shin muscles in rats

“…The vibrator head (diameter 3 mm) was positioned on the tendon; the skin of the latter in the site of contact was anesthetized with lidocaine (2%, 0.1 ml). Sinusoidal high-frequency (100 sec -1) 30-sec-long intermittent stimulation (1-min-long periods of vibration and 1-min-long resting periods) was used; the amplitude of oscillations was 0.5 mm [10]. Vibration in the mode used evoked no noticeable movements of the limb.…”

“…Visualization of great numbers of Fos-immunopositive (Fos-ip) units localized mostly within the zones of localization of interneuronal pools confirms such a statement. Until now, sites of localization of populations of such units activated by influences from muscle spindles induced by stimulation of a muscle tendon (with leads to selective action on intrafusal spindle fibers) [8][9][10] have not been examined in detail.…”