Further Experiments with Deplanted and Deranged Nerve Centers in Amphibians. ∗

Abstract

A previous communication 1 has described the appearance of rhythmic spontaneous (=endogenous) activity, and later of reflexes, in fragments of spinal cord transplanted (“deplanted”) to the dorsal fin of amphibian larvæ and provided with grafted limbs as effectors. A continuation of these studies has brought the following results.

A large section of spinal cord was deplanted to the fin and made to innervate 2 limbs, one grafted anteriorly and the other posteriorly. After re-innervation, prolonged seizures of spontaneous activity appeared in both limb grafts. During all major fits the beats of the 2 limbs occurred synchronously and with approximately proportional strength. This proves that in all actions, except very weak ones, the whole neurone pool of the grafted center discharges in unison. Reflexes likewise spread through the whole grafted center without localization.

Some limbs were deplanted along with their own spinal ganglia and cord segments, with all peripheral nerve connections being left intact. During the days following the operation this isolated reflex preparation gave orderly reflex responses. Gradually, however, the response deteriorated, assuming undifferentiated mass character with prolonged after-discharges, while at the same time spontaneous rhythmic seizures began to appear. This result demonstrates the direct relation between endogenous activity and central disorganization.

In order to intensify the structural break-down normally occurring in the deplanted centers, fragments were mutilated in various ways prior to their transplantation (slashing; sucking through pipettes too small in diameter; mincing). Such grafts behaved in the same way as undisrupted ones: spontaneous seizures and reflexes appeared within a few weeks.

Spontaneous activity has also been obtained from deplanted fragments of the spinal cord of adult animals; it is not, therefore, restricted to the larval stage in which the previous observations were made.