Distribution of motoneurons supplying dorsal and ventral suboccipital muscles in the feline neck

Abstract

A combination of retrograde tracers was used to compare the relative distributions of motoneurons supplying the ventral and lateral suboccipital muscles, rectus capitis anterior (RCA), and rectus capitis lateralis (RCL), with those supplying dorsal muscles, including rectus capitis posterior muscles (RCP), complexus (CM), and the medial head of obliquus capitis superior (OCS). Three of the tracers, horseradish peroxidase, fluororuby, and fluorescein-conjugated dextran, were applied to cut nerve ends. Fast blue was applied by intramuscular injection, and fluorogold was delivered both by injection and by cut nerve exposure. Motoneurons supplying RCA and RCL were clustered on the medial wall of the ventral horn in a restricted region defined previously as the commissural nucleus. Labelled cells supplying RCL were confined to the C1 segment, but those supplying RCA were distributed from C1 to rostral C4. Motoneurons supplying RCA tended to lie more dorsomedially than those supplying RCL, but there was substantial overlap between the two populations. Motoneurons supplying dorsal muscles had a separate, more ventral distribution. RCP motoneurons were located primarily in the ventromedial nucleus, but a small proportion of cells was found in the white matter of the ventral funiculus or the gray matter surrounding the central canal. Motoneurons supplying CM and OCS were located dorsomedially to the RCP cell population. These results suggest that neck motoneurons are arranged according to a "musculotopic" pattern in which dorsal muscles have the most ventral locations, and progressively more lateral and then ventral muscles are layered dorsomedially along the medial wall of the ventral horn.

Projections from the lateral vestibular nucleus to the upper cervical spinal cord of the cat: A correlative light and electron microscopic study of axon terminals stained with PHA‐L

“…This result is consistent with electrophysiological studies that reported monosynaptic connections between neurons in the LVN and premotor commissural interneurons and neck motoneurons (Wilson and Yoshida, 1969;Wilson and Maeda, 1974;Isu et al, 1988Isu et al, , 1990Uchino et al, 1988;Shinoda et al, 1994Shinoda et al, , 1997Sugiuchi et al, 1995). The somata and dendrites of these interneurons and motoneurons are located in areas of the ventral horn that are coincident with the termination zones of LVN neurons (Rose and Keirstead, 1988;Gordon and Richmond, 1991;Kitamura and Richmond, 1994;Suguichi et al, 1995). In addition, sparse projections were found ipsilaterally, in laminae IV to VII, and contralaterally, from lamina IV to IX (Holstege and Kuypers, 1982;Holstege, 1988;Rose et al, 1992).…”

“…Some of these terminals may contact motoneurons innervating suboccipital flexor muscles, such as rectis capitis anterior major. These motoneurons are found on the medial wall of the ventral horn (Kitamura and Richmond, 1994) and stimulation of the utricular nerve evokes disynaptic EPSPs in these motoneurons (Ikegami et al, 1994). Other terminals of LVST axons in this region probably synapse on commissural and unidentified interneurons (Bolton et al, 1991;Sugiuchi et al, 1992Sugiuchi et al, , 1995Isu et al, 1996).…”

Distribution of motoneurons supplying feline neck muscles taking origin from the shoulder girdle

“…Perhaps it is unwise to propose any specific functional rationale to explain the motoneuronal distributions reported here and elsewhere (for further discussion, see Kitamura and Richmond, 1994). The identification of motoneuronal location, however, is a significant first step in the analysis of connectivity.…”

“…The motoneuron nuclei identified in the present study are compared with the motor nuclei identified in previous studies on the cervical cord. Distributions of motor nuclei of deep neck muscles in C1 come from Kitamura and Richmond (1994). Descriptions of motor nuclei in C4 and C6 are based on drawings from Sterling and Kuypers (1967), Richmond et al (1978), and Hentona (1993). cord.…”

“…To label RH motoneurons in the same experiments, we then coated the LS muscle with a thick wax layer through which only the nerves supplying RH were allowed to penetrate. The nerves were cut close to their points of muscle entry, and the proximal cut ends were laid into reservoirs carved in the wax (Gordon and Richmond, 1990;Kitamura and Richmond, 1994). Each cut nerve was soaked in distilled water for 10 minutes.…”