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Reflex Patterns in Postganglionic Neurons Supplying Skin and Skeletal Muscle of the Rat Hindlimb

Reflex Patterns in Postganglionic Neurons Supplying Skin and Skeletal Muscle of the Rat Hindlimb. Stat 1000: Seminar 29 Mitchell Thompson III. Overview. Goal: To determine if the MVC (muscle)and CVC (skin)neurons can be distinguished functionally based on their reflex patterns?

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Reflex Patterns in Postganglionic Neurons Supplying Skin and Skeletal Muscle of the Rat Hindlimb

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  1. Reflex Patterns in Postganglionic Neurons Supplying Skin and Skeletal Muscle of the Rat Hindlimb Stat 1000: Seminar 29 Mitchell Thompson III

  2. Overview • Goal: To determine if the MVC (muscle)and CVC (skin)neurons can be distinguished functionally based on their reflex patterns? • Reflex analysis of postganglionic Vasoconstrictor neurons to Muscle (MVC) and skin (CVC) elicited through multiple stimuli. • Terms: MVC and CVC classified as postganglionic neurons that innervate blood vessels and are vasoconstrictor in function • Muscle • Cutaneous

  3. Neuroanatomy

  4. Methods • Subjects: 65 femaleWistar rats • Selection bias? • The investigator aims to prove that the central organization of the sympathetic nervous system in ratspossess a differentiation with respect to function • Anesthetics: 3 types used pentorbitone (pentorbital sodium), urethane, and α-chloralose. • Does this support or damage results? • Results are supported because the effects of anesthesia (confounding variable) can be eliminated

  5. Subjects • 65 femaleWistar rats • 59 preparations of spontaneously active MVC (skeletal) neurons • 138 preperations of spontaneously active CVC (skin) neurons • What is/are sample size(s)? • n1 = 59 n2= 138

  6. Spontaneous Activity

  7. U and Pooling • A non-parametric test for assessing whether two samples of observations come from the same distribution • The U test (Wilcoxon rank-sum test) is useful in the same situations as the independent samples Student’s t-test • For distributions sufficiently far from normal • Because the spontaneous activity of neurons under the different anesthetics had a similar distribution (P>0.05) all samples were pooled.

  8. Students’ Distribution • A test of the null hypothesis that the means of two normally distributed populations are equal. • Given two data sets, each characterized by its mean, standard deviation and number of data points, we can use two sample t testto determine whether the means are distinct, provided that the underlying distributions can be assumed to be normal. • All such tests are usually called Student's t tests, though strictly speaking that name should only be used if the variances of the two populations are also assumed to be equal

  9. Reflexes elicited by stimulation of the arterial baroreceptors • Arterial baroreceptors: Stimulation of arterial baroreceptors leads to inhibition of activity in vasoconstrictor neurons innervating resistance vessels. • Quantification of Neural responses: A 20% change of neural activity during the first 30s after stimulation compared with control activity during the 50s preceding stimulation was considered as a response. • Paired vs. Two-sample • Paired (comparison within sample nx)

  10. Arterial Baroreceptor Stimulation

  11. Two Sample T-Test • Equivalent to student’s distribution? • Because variances are assumed to be equal • s.d.1 ≈ s.d.2 • Categorical/ Quantitative Variable • Neuron Type (Categorical) • MVC (n1= 59) vs. CVC (n2= 138) • % Cardiac Rhythmicity (Quantitative) • Requirements • Unknown population σ • Difference between means not mean of differences • Sample means normally distributed • Independent samples • N ≥ 10n

  12. Hypothesis • Null Hypothesis: Ho • (a) μ1 – μ2 = 0 • (b) μ1 = μ2 • (c)μ1 = -μ2 • Alternative Hypothesis: Ha • (a) μ1 – μ2 ≠ 0 • (b) μ1 = μ2 • (c)μ1 > μ2

  13. T-Test • MVC CR • x bar1= 75; s1= 17; n1= 59 • CVC CR • x bar2= 44; s2= 20; n2 =138

  14. T-Statistic • Factors that affect t-statistic • Difference between x bar1 and x bar2 • Large difference  Increases | t | • Smaller p-value  Easier to reject Ho • Sample Sizes n1 andn2 • Small sizes n1 andn2  Decreases | t | • Larger p-value  Harder to reject Ho • S.D. s1 ands2 • Small s.d. s1 ands2 Increases | t | • Smaller p-value  Easier to reject Ho

  15. Conclusion • T-statistic large? • 11.1…. Big yes! • P-value small? • P< 0.001 …..Another Big Yes! • Reject Ho: μ1 – μ2 = 0? • I think you get the picture • Cardiac Rythmicity is greater in MVC Neurons than CVC neurons; Although CR is less prominent in CVC it is still inhibited by an increase in blood pressure (arterial baroreceptor stimulation)

  16. Reflections • Study Design • Test male rats and compare to females to determine if a significant difference of results exists • Paired vs. two-sample t-test • Two-sample • Subjects • No attempt was made to study neurons w/o spontaneous activity…recruitment of silent neurons within multiunit preparations… can not be ruled out • Type I vs. Type II Error? • Sample size would appear larger than it’s actual value • Statistic would appear larger (p-value smaller): Type I

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