Descending pathways to the cutaneous trunci muscle motoneuronal cell group in the cat

1. The cutaneus trunci muscle (CTM) is a thin broad sheet of skeletal muscle just beneath the skin. It does not contain muscle spindles and receives its afferents from the overlying skin. Contraction of the muscle can easily be triggered by pinching the skin or, in the cat, by gentle displacement of the fur (CTM reflex). The afferent information of this reflex is conveyed via the cutaneous nerves, which are segmentally organized. In the cat, the CTM motoneurons are located in a circumscribed cell group in the ventrolateral part of the ventral horn of the C8 and T1 spinal segments. The CTM motor nucleus corresponds with "nucleus X" of Giovanelli Barilari and Kuypers and with "ventral motor nucleus" of Matsushita and Ueyama. 2. Relatively long ascending propriospinal pathways, originating in the thoracolumbar cord, exist between the cutaneous afferents and the CTM motor nucleus. Such pathways have been described physiologically, as well as anatomically. Our results, based on anterograde autoradiographic experiments with [3H]leucine injections in the C1, C2, C6, and C8 segments, suggest that propriospinal pathways to the CTM motor nucleus originating in the cervical cord do not exist, although these propriospinal projections are very strong to all other motoneuronal cell groups surrounding the CTM motor nucleus. 3. The present results also demonstrate specific supraspinal projections to the CTM motor nucleus originating in 1) the contralateral nucleus retroambiguous (NRA) and 2) the ipsilateral dorsolateral pontine tegmentum. These projections suggest that the CTM motor nucleus is not only involved in spinal reflexes, but also in other functions such as abdominal straining.(ABSTRACT TRUNCATED AT 250 WORDS)