Lecture 23 : Extra senses

1. Lecture 23 : Extra senses Fain chapter 10 11/23/09

2. Presentations • Talk length • 3 minutes • 3-4 slides • Organization - Same as written material • Intro - Why important - interesting • (Methods - If you did analyses) • Results - what was learned • Discussion • Practice helps make a smooth presentation • Especially important to keep us on time

3. Topics • Thermoreception • Electroreception • Magnetoreception

4. Skin sensors

5. Diversity of skin receptors • Neural termini come from different sources • Trunk - Dorsal root ganglia • Head - trigeminal ganglia • Free dermal endings involved in temperature sensation • Difficult to dissect out for single cell recordings

6. Thermoreceptors • More cold than warm receptors • Nose: 8-10 cold receptors / cm2 • 1 warm receptor / cm2 • Structure • Cold - myelinated axons terminate in epithelium • Warm - unmyelinated axons deeper in skin

7. Warm temperature response • Extracellular recording in nerves from dorsal root ganglia • Warmth increases firing rate of “warm” receptors Fig 10.1a

8. Cold temperature response • Cold sensitive receptors respond to temperature drop • Increase firing rate for larger temp drops • Bursts • More action potentials per burst with colder temp

9. Nociception • Response to pain • Can be response to chemicals or temperature • Chemical response can be to capsaicin • Causes influx of cations • Not sure if it is modification of cell membrane or actual binding to receptor

10. Adaptation • Over time, pain response decreases in response to capsaicin • Can use it as an analgesic!! • Results from desensitization • Also find destruction of nociceptors

11. Heat receptor identified

12. Method Make cDNA library from dorsal root ganglion Pool 16,000 clones and express in HEK cells Screen pools for capsaicin sensitivity by Ca+2 imaging Continue until single clone - sequence Subdivide pools

13. Response to capsaicin - cell culture • Screen pools • Break down to identify individual clone • Identify response by calcium fluorescing dye

14. Cells expressing VR-1 respond • Capsaicin turns on response • Even more sensitive to resinferatoxin • Capsazepine and RR block response Patch clamp response

15. Response to different peppers

16. Capsaicin kills cells!

17. Structure and pore region

18. Expressed exclusively in sensory neurons

19. Also responds to heat • Increase in Temp • Inward current • Opening of nonselective channel (K+ Na+ Ca+2) • Ionotropic • Response to heat requires VR1 expression • Heat response is blocked by capsaicin antagonist

20. Vanilloid receptor - TrpV1 Expressed in small diameter neurons in sensory ganglia

21. Cold receptor is TRP channel

22. Method Make cDNA library from trigeminal cell culture Pool 10,000 clones and express in HEK cells Screen pools for menthol sensitivity by Ca+2 imaging Continue until single clone - sequence Subdivide pools

23. Identify neurons responsive to menthol and cold - Ca2+ imaging If warm, menthol sensitivity can be overridden

24. Cold channels • Decrease in Temp • Inward current • Opening of nonselective channel (K+ Na+ Ca+2) • Ionotropic • Express in Xenopus oocytes

25. Identify receptor - test response • Express in Xenopus oocytes • Determine sensitivity to different compounds

26. Also responds to cold • Decrease in Temp • Inward current • Opening of nonselective channel (K+ Na+ Ca+2) • Menthol and temp add together to increase response

27. Expressed in sensory neurons

30. Diversity of TRP channels - mechanosensation and temperature Cold <23C T < 17 C T > 43 C T > 52C T > 33 T > 25

31. IR detection by snakes

32. IR pit organ • Bare nerve endings from trigeminal nerve (6000-7000 neurons) • Respond to heat by increased action potentials Sensitive to 0.003ºC changes Fig 10.5 Fig 10.5

33. IR sensing pit vipers

34. Pit organ • Acts like pin hole camera • Constrained input angle provides directional information

35. Effect of background temperature on imagingEffect of acceptance angle on resolution

36. Detecting objects of interest 2 mice Along pit axis In front of snake

37. Detecting objects of interestMouse hole under a bushBird in a tree against night sky

38. IR detection • What is the receptor? • TRP channel??

39. Electro-communication • Some species can detect electrical signals • Navigation • Prey detection • Some species can generate electrical signals • Probe environment • Communication • Stun prey

40. Electroreception • Electric field detection • Sharks and rays; teleosts; • Some salamanders • Platypus • Huge sensitivity to electrical gradient • Skate can detect 0.01 V/cm • Same as 9V battery over 1000 km

41. Salt water skates • Skates detect electric field gradient from ampullary organ -canal with openings • Use hair cells modified from lateral line • Receptor??

42. Response in freshwater fish ampullae

43. Electrolocation • Sharks use to sense nerve activity from gill or muscles • Detect flatfish buried in sand

44. Electrocommunication • Some organisms detect E field • Others can also generate E • Strongly electric - eels • Weakly electric - electric fish

45. Generating discharge • Discharge frequency set by pacemaker nucleus • Shape of discharge set by action potentials of electrocytes

46. Field perturbed by insulators but not conductors Fig 10.13 Use field to detect surroundings and navigate in dark

47. Electrocyte discharge • Electrocyte is innervated by neuron • When receives signal, cell depolarizes = change in voltage K+ Na+ -80 mV Na+ K+ +50 mV

48. Stacks of electrocytes add in series to increase total voltage in discharge 130 mV 520 mV Up to 700 V …

49. Electric discharge organs • Different organs create different pulses

50. Electric discharge organs • Gymnotids and mormyrids • Skates and eels • Wide variety of signals can be generated