Don W. Esplin

Effects of Tetanization on Transmitter Dynamics

This discussion has surveyed the phenomenon of posttetanic potentiation (PTP), has indicated studies concerned with basic intracellular mechanisms responsible for this process, and has discussed the presumed role of PTP in epilepsy in relation to the actions of some antiepileptic drugs.

Impairment of muscle stretch reflexes in tick paralysis.

Experiments with tick-paralyzed dogs and woodchucks have shown impairment of stretch reflexes in addition to partial paralysis at the neuromuscular junction. Stretch reflexes disappear very early during paralysis, whereas nociceptive reflexes do not appear to be directly affected. The early incoordination and the ascending nature of the paralysis may be related to impairment of stretch reflex pathways.

Spinal Reflexes and Seizure Patterns in the Two-Toed Sloth

In striking contrast to the seizure patterns of other animals, the electroshock seizure of the sloth consists of weak extension followed by tonic flexion and terminal clonus. A similar pattern is seen with direct spinal cord stimulation. Strychnine produces a pure flexor convulsion. In the spinal sloth, painful stimulation of one foot causes extension at some joints of that limb and strong flexion at all joints of the contralateral limb.

Postictal hyperexcitability in experimental convulsions.

Abstract In this study mice and hamsters were electroshocked at varied times in the postictal period. The purpose of the study was to elucidate the factors involved in what is customarily referred to as “postictal depression.” By means of paired electroshock stimuli it has been shown that flexor-extensor seizures can be elicited early in the postictal period prior to the time of maximal depression. Three measures of brain excitability, namely, ability to sustain a tonic extensor seizure, duration of flexion, and current required to elicit tonic extension, indicate that the time-course of postictal recovery is diphasic. The suggested explanation for this phenomenon is that postictal recovery is a composite of a brief phase of hyperexcitability and a long-lasting phase of depression. Increase in the electroshock stimulus, above that judged to be maximal on the basis of the motor pattern of the initial seizure, profoundly altered the patterns of subsequent seizures elicited during the postictal period. This suggests that the stereotyped “maximal” motor pattern may occur with submaximal brain discharge. Diphenylhydantoin, trimethadione, and especially phenobarbital were found to be much more effective in abolishing tonic extension in the second seizure than in the first. The experimental observations are discussed as they relate to status epilepticus.

Effects of Cortisone, Ascorbic Acid and Piromen on Phagocytosis in Mice.∗†

Summary Cortisone, ascorbic acid and Piromen were tested in mice for their effect upon macrophage activity as determined from the splenic uptake of colloidal ThO2 and upon the phagocytic activity of leukocytes in the peritoneal cavity against Micrococcus aureus. Cortisone in high doses (0.1 to 1 mg every 12 hours) significantly enhanced phagocytic activity of both macrophages and leukocytes. Ascorbic acid in doses as high as 1 mg every 12 hours had no effect on the activity of macrophages but this dose did significantly enhance the phagocytic ability of leukocytes in the peritoneal cavity. Piromen (0.1 μg every 12 hours) significantly increased the phagocytic activity of both types of cells. However, doses above or below this value were without significant effect in either type of experiment. The more potent auxophagocytic agents (cortisone and Piromen) were without salutary effect when tested singly and in combination in protection experiments in mice challenged with predetermined doses of Klebsiella pneumoniae.

A simple, inexpensive, continuously-variable infusion pump.

The instrument to be described was developed to fill the need for an infusion pump with which rate of delivery could be continuously varied over a wide range during injection. The present pump has met this need and has been employed for 9 months in experiments on small animals in which rate of injection has been critical. Details of construction and mode of operation of this pump will be apparent from Fig. 1 and 2. The motor (Bodine Electric Co., Chicago, 1/50 H.P., 1725 rpm, with gear reduction to 11.5 rpm) turns the first drive cone (A). The 4 identical drive cones are knurled cast aluminum. The conical portion is 4′′ long and the large and small diameters are 3′′ and .95′′ respectively. Cone A drives cone B by means of rubber ring (1/4′′ by 18′′ circumference) which provides contact between the 2 cones. The point of contact of the ring with the cones is adjustable by means of yoke K, rod L and setscrew M (Fig. 1). It can be seen that when the largest portion of cone A is driving B, B rotates 3.16 times as rapidly as A; conversely, when the smallest portion of A is driving B, A rotates at 3.16 times the speed of B. Thus, a 10-fold range of speed is achieved by the first pair of cones. Cone C is coupled to B and both turn at the same speed. Cone D, however, is driven by C through a mechanism identical to that linking cones A and B. Range of speed for the 2 pairs of drive cones is therefore 100-fold. To prevent slippage of the cones on the rubber rings it is necessary to have considerable tension on the 2 pairs of drive cones.