Tectospinal and tectoreticular cells: their distribution and afferent connections.

Experiments on chloralose-anaesthetized cats have shown that cells in the superior colliculus may be antidromically activated either from the pontomedullary reticular formation or the ventral cervical spinal cord, or from both sites. In tests on 111 units this has provided a basis for differentiating between cells of origin of the tectospinal tract and the tectoreticular system within the superior colliculus. Tectospinal cells may be activated both by spinal and pontine stimulation; tectoreticular cells cannot be activated by spinal stimulation. Both tectoreticular and tectospinal cells respond to visual and muscle afferent stimulation. The afferent connections may be strongly inhibitory as afferent input to the superior colliculus ofter prevented subsequent antidromic invasion. This was more commonly seen in tectospinal cells than tectoreticular cells. The distribution of the two cell populations within the superior colliculus was also found to be dissimilar. Evidence has also been obtained to suggest that the tectoreticular system, in part, consists of collaterals of the tectospinal tract.