Functional characteristics of the intraspinal spread of viscerosomatic activity

The functional characteristics of the intraspinal spread of the dual-component viscerosomatic reflex response were studied in chloralose-anaesthetized cats. In the region of the direct inputs of splanchnic afferents into the spinal cord, the initial part of the early (propriospinal) component is evoked by afflux from the extraspinal pathway in the sympathetic chain and has the shortest latent period. At segment Th8 to Th12 level this was 5.2--8.1 msec; cranially and caudally from this level it was longer. Activity spreading from the adjacent segments via intraspinal longitudinal systems also participates in the origin and course of the early component of the efferent discharge. The rate of ascending intraspinal irradiation in the thoracic region was 3.2--12 m/sec (6.6 +/- 2.4 m/sec). The rate of the descending spread of propriospinal activity in the thoracic region via intraspinal pathways was 3.6--18.3 m/sec (12.5 +/- 4.5 m/sec); in the lumbar region it was significantly lower -- 2.9--19.3 m/sec (7 +/- 4.5 m/sec). The latent period of the later component varied from 20 to 30 msec and displayed a cranio-caudal increase in length. The rate of the descending spread of the later component in the thoracic and lumbar cord did not differ significantly (20 +/- 10 m/sec and 22 +/- 13 m/sec respectively). The continuous splanchnic discharge in the lumbosacral region is correlated to the different rate of the intraspinal spread of the early and the late response and to their overlapping.