Transcript Mitchell`s Seminar

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?
 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
Neuroanatomy
METHODS
1. Subjects: 65 femaleWistar rats
 Selection bias?
 The investigator aims to prove that the central organization of
the sympathetic nervous system in rats possess a
differentiation with respect to function
2. Anesthetics: 3 types used pentorbitone (pentorbital
sodium), urethane, and α-chloralose.
1.
Does this support or damage results?
1.
Results are supported because the effects of anesthesia
(confounding variable) can be eliminated
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
SPONTANEOUS ACTIVITY
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.
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
test to 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
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)
Arterial Baroreceptor Stimulation
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
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

T-Test
 MVC CR
 x bar1= 75; s1= 17; n1= 59
 CVC CR
 x bar2= 44; s2= 20; n2 =138
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 and n2
 Small sizes n1 and n2  Decreases | t |
 Larger p-value  Harder to reject Ho
 S.D. s1 and s2
 Small s.d. s1 and s2  Increases | t |
 Smaller p-value  Easier to reject Ho
CONCLUSION
MVC (muscle)
CVC (skin)
Strong (>60% CR)
Weak(40-60% CR)
Absent (<40% CR)
Mean =82±12%
n= 46 (78%)
Mean = 52 ±4%
n= 13 (22%)
n= 0 (0%)
Mean = 76±11%
n= 25 (18%)
Mean =51 ±6%
n= 46 (33%)
Mean = 28±8%
n= 67 (49%)
•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)
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