FROG MUSCLE TWITCHES AND SHORT-TERM SYNAPTIC PLASTICITY
This confirms your Indiana Academy of Abstract Submission for the Event ‘130th Annual Academy Meeting’. Abstract submission is below:
Muscle Twitches from Frog Muscle Used to Study Short-Term Synaptic Plasticity from a Population Perspective
Authors and Institutions:
MANALIS, Richard S., Goshen College, Goshen, IN
Short-term synaptic plasticity was studied from a population perspective; the muscle twitch, recorded from the frog (Rana pipiens) sciatic nerve/gastrocnemius muscle preparation, was the population measurement. Muscle twitches are dependent on changes in the recruitment of muscle fibers; such changes result from synaptic plasticity changes. The high safety factor of neuromuscular transmission was reduced through the continuous stimulation of the sciatic nerve at a frequency of 0.25-0.45 Hz for 25-30 min. The muscle twitch was, thereby, reduced by 85-90%, leaving the majority of the synapses in a subthreshold state or subliminal fringe. A paired-pulse facilitation protocol in which 2 stimuli are applied to the nerve at a given interval was used to study facilitation. The nerve was stimulated with trains of 5 identical paired-pulses with 2 min rests between trains. In a given train, however, the 5 contractile responses were NOT IDENTICAL. There was a sharp decay of the twitches produced by the 1st stimulus in each of the 5 paired-pulses; this illustrated depression, which is attributed to a depletion of the readily releasable pool (RRP) of synaptic vesicles. The twitches produced by the 2nd stimulus either decayed at a slower rate or actually increased during the train; this illustrated facilitation. The RRP was replenished during the subsequent 2 min rest only to be depleted again with the next train. Facilitation occurs when muscle fibers transfer from the subliminal fringe into the excited state; this is indicated when the peak of the 2nd twitch > that of the1st. The level of facilitation is inversely proportional to the interval between the two stimuli. Facilitation is readily observed at intervals >> 20 ms, which is the duration of the endplate potential. Therefore, facilitation is primarily due to an increased transmitter release at long intervals. This is the first study in which synaptic plasticity has been studied using population responses rather than single-unit responses (endplate potentials).
Animal Physiology and Neuroscience
Students have the opportunity to learn physiology by performing experiments on living tissue, e.g., frog heart, frog nerve, and frog muscle.
MENTORING students in the BIOLOGY JUNIOR SEMINAR in 20014
I am willing to serve as a MENTOR for this program. My research pertains to an integrative physiological approach to the study of SHORT-TERM SYNAPTIC EFFICACY using the frog sciatic nerve/gastrocnemius preparation. The essence of my findings is illustrated in the following graph:
In the above graph, the sciatic nerve was stimulated five times with identical dual-pulses; each dual-pulse consisted of a conditioning stimulus followed 120 ms later by a test stimulus. The conditioning twitches decreased during the stimulus train; this is called depression. On the other hand, the test twitches increased during the train; this is called facilitation. Both depression and facilitation are important examples of changes in synaptic efficacy.
Here are some questions that might serve as the basis of a junior seminar research project:
1. Explain how the measurement of muscle twitches can provide meaningful information with respect to short-term synaptic efficacy.
2. Compare and contrast changes in synaptic efficacy measured from the frog sciatic nerve/gastrocnemius preparation with those measured from a hippocampus brain slice, which is the preparation in which LONG-TERM POTENTIATION is studied.
EXPERIMENTS ON SYNAPTIC EFFICACY IN FROG MUSCLE
August 20, 2012
I am attaching two charts which indicate the present status of my research on synaptic efficacy and which clearly show increases in synaptic efficacy. Such changes form the basis of learning and memory that occur in the mammalian brain. Data shown in Chart A (below) can be obtained by undergraduate students in the student laboratory.
Very briefly, chart A shows the contractile responses of frog muscle to the application of five paired-stimuli to its nerve. Each paired stimulus consists of a conditioning (C) stimulus and a test (T) stimulus (Chart B); the interval between the C & T stimuli is .3 s (300 ms). The BLUE line represents the CONTROL contractions, and the RED line the EXPERIMENTAL contractions, which are those measured in the presence of CURARE. Curare is an arrow poison, and it was the first muscle relaxant to be used clinically. Note: the experimental contractions are considerably smaller than are the control ones, but what is remarkable is that the TEST twitch in each of the five paired-contractions is, at first, smaller than its corresponding CONDITIONING twitch, but then it gradually increases relative to its corresponding C twitch (RED line, Chart A). This change is most pronounced in the fifth paired-contraction (RED line, far right); this is shown more clearly in Chart B.
The reason why the T twitch is greater than the C twitch in Chart B is because the C stimulus “sensitized” the synapses present in the frog muscle to release neurotransmitter more readily and this increased sensitization was still present 300 milliseconds later when the T stimulus arrived. The continued presence of this sensitization for 300 ms is a form of memory. Thus the T stimulus had a greater effect on the muscle than did the preceding C stimulus, resulting in a larger contraction – the T twitch. This is an example of an INCREASED SYNAPTIC EFFICACY. Such changes can last several hundred milliseconds in a frog nerve/muscle preparation but many decades in the human brain!
A summary of my current research on synaptic efficacy is given my my poster presented to the IAS in the spring of 2013: RichManalis_IN_PHYSIOL_SOC POSTER_pdf
A summary of my research on synaptic efficacy as of April 2014 appears in my poster presented at the IAS meeting of 2014: IAS poster March 2014 Manalis RS
My earlier work on synaptic efficacy in which the frog sartorius nerve/muscle preparation was used can be found here: Manalis RS (1992) SHORT-TERM MEMORY … TWITCHES
I am a fine art photographer. A sample of my images can be viewed here.