Frog Hindlimb Research Articles

Efficacy of sympathetic influences as related to initial vascular tonicity.

The efficacy of vasoconstrictor influences as dependent on the initial vascular tone (initial rate of perfusion) and perfusion pressure was investigated in rat and frog hindlimb preparations perfused with saline solution. Efficacy was determined as the ratio of the preparation resistance (R) induced by sympathetic stimulation to the initial resistance R0. At a pressure normal for the experimental animal, the relationship between R/R0 and flow is expressed by a dome-shaped curve. At a pressure twice the normal, it is low at all points; at a pressure half the normal, different responses were obtained from the two species used in the experiment: in rats elevation of vascular tone induced by sympathetic stimulation resulted in a complete cessation of flow, whereas in frogs the initial high efficacy diminished with increasing vascular tone. A mathematical model devised to study the dependence of the efficacy of sympathetic stimulation on initial tonicity is described. The good consistency of experimental and calculated results is regarded as evidence that the prerequisites stipulated in the model, i.e., the capacity of closure and the heterogeneity of arterioles, in regard to the effort developed by their smooth muscle, are actually inherent in the vascular system of organs.

An analysis of muscle weight variations in the hindlimbs of Rana esculenta.

Dry weights of 24 muscles of the left and of the right hindlimbs in 63 frogs (Rana esculenta) are determined. By means of factor analysis is calculated which part of the variance in a muscle's weight can be accounted for by common factors and which part by the characteristics of the muscle itself. The main results are: 1. Body size (factor 1) accounts for more than 90% of the variance in all the heavier muscles and more than 64% in the eight lighter muscles. 2. Since only one single common factor is found, no separate groups of highly correlated muscle weights are present in the frog's hindlimb. 3. A decrease in the number of fibers is coupled with an increase in the residual variance of a muscle. 4. Left and right identic muscles follow the same variation-pattern. Two models for muscle development are discussed: 1. A model in which the innervation of the muscle determines the number of fibers. 2. A model in which clumping play an important role.

The anatomical organization of hindlimb motoneurons in the lumbar spinal cord of the frog, Rana catesbiana.

AbstractThe precise location of lumbar spinal motoneurons was studied in the bullfrog by observing the retrograde reaction following injury to nerves which innervate different hindlimb muscles. The results were confirmed and their usefulness for physiological studies was demonstrated by iontophoretically injecting dye through an intracellular recording micropipette into motoneurons which were identified by antidromic spike invasion. The effects of plexus variation upon the location of motoneuron pools was considered in order to standardize the results and make possible comparisons between different frogs.New determinations were made of frog hindlimb muscle function with reference to jumping in order to assess the possible functional significance of motoneuron organization. In general, motoneurons acting upon proximal joints are located rostrally to motoneurons acting upon distal joints and flexor motoneurons are located rostrally to extensors.The somatotopic significance of motoneuron organization was also assessed and it was found that within the lateral motoneuron column there are three groups of cells, each of which innervates different, but somatotopically related groups of muscles. This organization is quite similar to that found in cats. The developmental and functional implications of this similarity are considered.

SUPPRESSION OF MOTOR RESPONSE IN MAN

In 1876 Ferrier 1 stated: There is no reason to suppose that one part of the brain is excitable and another not. The question is, how the stimulation manifests itself. As one is prone to look for active responses, one may fail to observe other manifestations elicited by electrical stimulation of nerve tissue. In 1845, biologic inhibition was first experimentally demonstrated by the Weber brothers, 2 who showed that vagal stimulation slowed the heart. For their studies a background of cardiac activity was necessary. Similarly, a background of activity is necessary for any studies of inhibition, whether central or peripheral. Setschenow 3 (1863) employed the withdrawal response of the frog's hindlimb as the background of activity for his attempts to localize inhibition within the central nervous system. Bubnoff and Heidenhain 4 (1881) showed that inhibition of a muscular contraction may be brought about through tactile stimulation of an ipsilateral member.