Physiology of locomotion of Blatta orientalis L. III. Importance of the thoracic ganglion system

Abstract

As a continuation to other papers (R. csp. Fisiol. 7, 1951) the authors investigate in the coakroach Blatta oricntalis (L) the importance of the «thoracic ganglionie system» in the coordination of walking of inseets.

By means of experiments sectioning the longitudinal interganglionic connectives, amputation of legs, decapitation, preparation of two, one or half an isolated thoracic segments and electric stimulation of connectives, the following conclusions are come to :

1. Each thoracic ganglion is a motor and reflex center of the corres- ponding leg, conditioning even the typical form of movement of the apendix.

2. The pair of ganglia determines tliat the movements of the two depending legs be alternate.

3. The nomal coordination is independent of the upper ganglia. These latter only exercise influences on the spontaneity, reflex inhibition, inhibitory tonus and other features. But the connection of the three pairs of thoracic ganglia is necessary.

4. The conduction of impulses related to locomotion, by fibres running through a single connective, can take place also, when the latter is sectioned, through the remainder ways that substitute saíne functionally in a high degree, without alteration of the normal coordination.

5. When two connectives of distinct segments are cut, the fibre traets of transversal commissures become already insufficient for the functional substitution of the former. If they are homolateral, the middle leg of the same side becomes slower ; if heterolateral, co-ordination is rarely observed. The cross way passing through the transversal fibre traets suposses a delay in the conduction, making coordination impossible if, by section of the connectives, becomes the necessary and exclusive passway.

6. In the insect with six legs, the system composed of only four thora­cic ganglia, which are isolated from the other two by section of the connectives, leads at the most to a «croswise coordination» (synchronism of oppossite legs of distinct segments) of the four corresponding legs, independently of the activity of the other pair, therefore the same as if the latter were latter were amputated. Such a crossvise co-ordination is cons- tant only in the case of the four associated ganglia being the first and seccond pairs, maintaining the connections with the upper ones. Only cccasionally can there be a transitory nonnal co-ordination among the six legs by influence of the mechanical factors (rough substrate).

7. The upper ganglia have influence on the first pair of thoracic gan­glia facilitating the active movements of the first pair of legs, whenever a pair of thoracic ganglions has been isolated froni the rest.

8. The crosswise coordination (with only four legs) requires the con­nections of the six thoracic ganglia. However the first two pairs are sufficient if there be a connection with the upper ganglia. The preparation of two isolated segments with their, four legs shows no coordination in crosswise walking.

9. Coordination, although central, is dependent on the peripherical sensitiveness, there being necessari kinaesthetic impulses starting fromproprioceptors, which reach the corresponding ganglia and influence on the «thoracic ganglionic system». The reciprocal inhibition determines the alternate movements of legs in the same pair. The lack of the kinaesthetic impulses starting from two legs after amputation, anaesthesia, fixing or immobilization by curarization what determines the new mode of coordination in crosswise walking.

10. By electric excitation of any connective movements of all the legs may be provoked, although distinct intensities are necessary, the legs responding in a certain order as the strength of stimulus is increased, depending on the point stimulated. Stimulation is in general more effective on the legs situated behind the point excitated.

11. The partial suppression of ways between ganglia by svetion of the connectives does not prevent the response of the legs ; although considering lengthening the ways, with the corresponding increase of synap- sis, the conduction is delayed and such a way can even come to be blocked to the impulse, if it does not reach maximum intensities. This explains the great difficulty of coordination observed when several con­nectives are sectioned

12. Normal walking coordination with six legs results thus from the functional integration in the six thoracic ganglia of fthe kinaesthetic im­ pulses starting from proprioceptors of the appendages, requiring sufficient ganglionic interrelation through longitudinal and transversal fibres.

If kinaesthetic sensitiveness of two legs is suppressed, while keaping up the connections between the six ganglia, crosswise walking coordina­ tion is adopted; but if the munber of thoracic ganglia mutually connected is reduced, such a coordination is not possible, excepting when those are the two first pairs and retain the conectives with the upper ganglia.

13. In consequence, the conclusion is come to that coordination of walking is determined according to the nature of the «ganglionic system» of the insect, it thereby being understood os «the physiological unity obtained by thhe association of the ganglia that maintain sufficient connec­tions among each other». Besides with the same «ganglionic system» there are differences of behaviour according to the degree of kinaesthetic sensitiveness from the appendages and according to the number of the latter which may have influence on the ganglia through the impulses starting from their proprioceptors.