The Neuromuscular Transform between Heart Motor Neurons and the Heart in Leeches Open Access

Chang, Rimi (2015)

Permanent URL: https://etd.library.emory.edu/concern/etds/rb68xc55p?locale=en
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Abstract

Central pattern generators (CPGs) produce motor patterns that control motor outputs. The Calabrese laboratory studies a variety of aspects of the leech heartbeat system, particularly researching how the CPG activity is ultimately translated to heart contractions. The left half of a single mid-body segment in a reduced preparation was electrically stimulated extracellularly in order to observe the effects of the stimulus protocol on the heart contractions. Variation in the duration and frequency of stimulus was reflected in the motor performance of the heart. To quantify the beat pattern, the Clampfit analysis program and the Excel program were used to calculate the peak heart contraction, the contraction force integral (area for the heart contractions), and the latencies to the onset of heart contraction and to the peak heart contraction from the onset of stimulus. These 4 parameters were used to study the neuromuscular transform in the leech, which was the goal of this project.

I measured the peak amplitude and the contraction force integral to assess the force of the heart contraction. Additionally, two latencies to the onset of the heart contraction and to the peak contraction amplitude from the onset of the stimulus were measured to assess the responsiveness of heart contraction. The data from a total of 9 experiments showed that usually longer stimulus durations at higher frequencies yield stronger correlations among the data values for the peak heart amplitude and the force integral. Moreover, only 2 s stimulus or longer showed a statistically strong negative correlation for latency to peak amplitude as frequency increased. All together, the results from this project will aid in comprehending how stimulus changes the heart contraction patterns. Additionally, these data can be used as a control in comparison with future experiments.

Table of Contents

Table of Contents
I. Introduction.....................................................................................................1

II. Materials and Methods......................................................................................4

a. Equipment.......................................................................................................4

b. Preparation.....................................................................................................5

c. Heart contraction recording................................................................................6

d. Extracellular recording and stimulation from the anterior segmental nerve.................6

e. Stimulus protocol.............................................................................................8

f. Data digitization and acquisition..........................................................................8

g. Data analysis...................................................................................................9

h. Plots and statistics..........................................................................................10

III. Results........................................................................................................10

a. Peak contraction amplitude...............................................................................11

b. Contraction force integral.................................................................................12

c. Latency to the onset of the heart contraction and to the peak contraction

amplitude from the onset of the stimulus................................................................12
IV. Discussion....................................................................................................13

a. Assessing the force of heart contraction..............................................................13

b. Assessing the latencies of heart contraction.........................................................14

c. Importance of reduced preparation....................................................................15

d. Importance of the data for future research..........................................................16

e. Presence of mini-contractions...........................................................................17

f. Potential pitfalls..............................................................................................17

V. Figures.........................................................................................................19

VI. References...................................................................................................35

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