Cellular Neurobiology BIPN 140 Fall 2016 Problem Set #1

Transcription

1 Cellular Neurobiology BIPN 140 Fall 2016 Problem Set #1 1. (Antonia) You are studying a neuron with an arterial cuff under a microscope. However, you knock over a bunch of chemicals onto the plate because of your coffee jitters (you ve been caffeinating all night to keep up with BIPN 140 reading). Anxiously, you look at the neuron again and see a bulge forming on one side of the cuff, as shown in the figure below: a) Would you normally expect the bulge forming on only one side of the arterial cuff? Why? b) What type of axoplasmic transport can still be observed? c) At what rate can the functioning axoplasmic transport propagate? d) Which motor protein has most likely been damaged by the chemicals? 2. (Stephanie) For each of the following questions, decide which technique would be more suitable and provide a brief explanation. a) To compare the density of hippocampal neurons between a wild-type and Alzheimer s disease mouse model (Nissl vs. Golgi staining). b) To identify brain regions which project their axons to the substantia nigra (anterograde versus retrograde tracer). c) To study dopaminergic signaling during a reward task in humans (PET vs. fmri). d) To confirm that a knockout mouse model does not express the targeted protein (immunohistochemistry [antibody labeling] versus a reporter gene [GFP expression regulated by the promoter of the targeted protein]). 3) (Milad) Below are three figures showing an action potential profile measured using the recording methods discussed in class. Based on the depolarization/repolarization schemes determine which recording method was used: intracellular, extracellular, or neither. The +/- on the y-axis describe the voltage measured by the recording electrode relative to the reference electrode, while the x-axis is a measure of time. The reference electrode is placed at a reasonable distance away from the recording electrode. (For practice, justify each answer to see if the recording methods actually make sense to 1

2 you). 4) (Antonia) Fill in the missing blanks: Name Location (CNS/PNS) Function Functional fact PNS CNS Production of myelin around the axon of a neuron. Involved in the production of myelin around axons. Myelin helps propagate the action potentials at a higher speed. Multiple sclerosis is an immune disease that attacks the myelin sheets. Radial glial cells Neuronal migration is important for the formation of connections and differentiation of cells into either neurons or astrocytes. These cells act as immune responders to brain injuries and trauma. Very dynamic. Astrocytes The most numerous cells in the brain. Involved in the production of the cerebrospinal fluid. Cerebrospinal fluid provides proteins and nutrients to the brain and the spinal cord. 2

3 5) (Milad) You are studying the concept of frequency coding in the lab by injecting a strong stimulus into the axon of a neuron. You take three measurements: the control, a case when a drug (Drug X) is applied, and the case when the drug is washed off. Provided below are action potential profiles showing how the Vm is influenced in the three scenarios. Furthermore, the frequencies of action potentials were also provided for these three scenarios. You are using an intracellular recording to make your measurements, and Drug X completely blocks the pore of the type(s) of channel(s) it binds to. Also, you are using a 500 Hz frequency train of suprathreshold stimuli (threshold of neuron is always reached with these stimuli). The absolute refractory period is 2 msec while the relative refractory period is 4 msec for the untreated neuron. a) Why is Drug X causing this effect on the action potential and how does this effect decrease the frequency of action potentials? b)why don't the data from the wash match those of the control? c)you are given a list of 4 drugs that could rectify the effects of drug X. Which of these drugs will ameliorate the effects of Drug X and which will not? Drug A Effect Increases the translation and transport of voltage-gated Na+ channels to the membrane. 3

4 B C D Increases the translation and transport of voltage-gated K+ channels to the membrane. Increases the conductance of the unaffected channels the drug X normally binds to. Decreases the number of K+ leak channels. 6) (Stephanie) Recording and stimulating at the cell body of a neuron (approximated as a sphere), you would like to calculate values for the passive membrane properties of your neuron. You inject a rectangular pulse of current of magnitude I during interval x (see below). a) On the graph of voltage and time (below), which equation describes time interval y? b) Based on this equation and using your graph, how could you estimate the value of τ? c) When t is large relative to τ (i.e. when V is approximately V ), the capacitive current of the circuit will be negligible. Using this interval, how would you calculate the resistance of the cell in terms of Vo, V, and I (ignoring any resistance from the electrode itself)? How would you calculate the capacitance using your knowledge from part b? d) If you were determining these properties in a living, functional neuron, why might it be preferable to inject a hyperpolarizing current, as opposed to a depolarizing current? 7) (PeiXi) You are carrying out an experiment using an isolated piece of a sciatic nerve of a Hungarian frog, immersed in a solution resembling its native environment. a) By placing a cold block along this axon at some distance away from where battery-driven, above-threshold electrical stimulation of the axon takes place, what would the propagation of the action potentials look like before and after they reach the block? What about the electrical current (what would the extracellular recordings look like)? (Hint: what kind of effect is the cold block eliciting?) 4

5 b) Draw the action potentials before they reach the cold block. What happens when the block is removed? c) What is this experiment suggesting? 8) (PeiXi) a) An intracellular recording is used to measure the voltage across the membrane of a neuron. The membrane potential measured is 0 mv. What would be the concentration of extracellular K+ ions when the intracellular concentration of K+ ions is 50 mm, considering that the membrane is only permeable to K+ + ions, and the neuron is bathed at 20 o C? b) In lecture, the following graph was presented. Why is there a deviation of the curve from the line? What do the line and curve each represent? c) Determine the membrane potential of this neuron with the given data, assuming that it is bathed at a 20 o C environment. What would the membrane potential be when extracellular [Na] is lowered to 70 mm? Ion Intracellular (mm) Extracellular (mm) Permeability K Na Cl Ca Nernst Equation Resting Potential = (RT/zF) ln ([K+]o/[K+]i) = 58 log ([K+]o/[K+]i) R= gas constant T= temperature z= charge of ion/valence F= Farraday s constant (10^5 coulombs/mol) 5