Neuromodulation

1. Neuromodulation Modulation of synapses by amines and peptides

2. Aims • Review main cellular action of neuromodulators • actions through G-coupled receptors • role of NO • Describe the basic neural circuits for repetitive action • Describe effects of neuromodulation on neural systems • simple behaviour: molluscan swimming and feeding • complex behaviour: insect ecdysis

3. Neuromodulators • Amines and peptide • 5-HT, dopamine, Adrenaline, acetylcholine… • Oxytocin, vasopressin, CCAP • Steroids • ecdysone, oestrogen • Eicosanoids • leukotrienes, prostaglandins • NO

4. NO • Nitric oxide - a gas! • synthesised from L-arginine by NOS • neurons (nNOS, epithelium eNOS) • depends on Ca concentration COO- COO- COO- + O2 C H +H3N C H + NADPH NAD+ +H3N C H NO (CH2)3 (CH2)3 (CH2)3 NOS NOS NH NH NH + C NH2+ C N OH C H H2N H2N O NH2 Arginine N-w-Hydroxyarginine Citrulline

5. NO signalling • NO diffuses freely though cell membranes • but not very far! • half life from 3-5s • soluble guanylyl cyclase activated by NO • elevates cGMP • relaxes smooth muscle in blood vessels via PKG and an effect on IK(Ca) • important for heart-disease • nitrate (nitroglycerin) used to reduce angina

6. NO → cGMP

7. cGMP → relaxation K channels [Ca] cGMP normally broken down by phosphodiesterase type 5

8. Viagra • Sildenafil - best selling drug • termtadalafil [Cialis], vardenafil [Levitra]

9. Viagra • selective for phosphodiesterase - type 5 [of 11] • so maintains level of cGMP • type 6 PDE, • only in photoreceptors, • gives “blue flash” • affects penile, vaginal, clitoral smooth muscle

10. Multi hormone control vasoactive intestinal polypeptide P2Y receptors for ATP vaginal epithelial cell vaginal smooth muscle

11. Summary • NO – local transmission as gas; no vesicles

12. Modulation of single cells • Single cells can be rhythmic • R15 in Aplysia • sino-atrial node of vertebrate heart • Purkinje fibres of heart

13. vertebrate heart • single cell rhythm

14. Rhythm at sinoatrial node

15. Modulation of heart rate by If activation curve:100% of If channels open here • If – hyperpolarization activated Na+ current • ACh slows rhythm • Adrenaline accelerates iso = isoproterenol = isoprenaline

16. ivabradine • new heart drug • blocks If • (note difference from ACh) • safer than b-blockers

17. Summary • NO – local transmission as gas; no vesicles • heart: single cell rhythm • modulated in different ways to give same effect

18. Neural circuits • central pattern generation • role of reflexes (see 404)

19. Clione • Clione - a free swimming sea mollusc • swimming rhythm • alternation of up and down stroke of wings

20. 78 Clione - ii 78 • reciprocal inhibition • up (8) / down (7) • post inhibitory rebound 78

21. Faster with 5-HT • CPB1 is serotonergic heart down interneuron

22. Half centre model • Brown (1914) • evidence from tadpoles • I then E due to mixed synapse • probably at basis of most vertebrate locomotory systems

23. Molluscan feeding bg • Serotonin as modulator • local neural release (CGC) • hormonal signal in blood • What does it target? • How does it act? CG

24. Target 1 : muscles 5-HT on voltage clamped muscle fibers

25. Target 2 : motoneurons MCC is cerebral serotonergic cell in Aplysia; B21 is a buccal motoneuron

26. Target 3: sensory neurons sense organ in one bathganglion in anotherStretch evokes twitches add 5-HT to sense organ use low Ca to show this effect is not due to action on ganglion

27. Target 4: interneurons control + 5-HT fasterbigger EPSPquicker decline of EPSP B4 is a motoneuronB35 an interneuron in CPG

28. Most snail effects by cAMP

29. Summary • NO – local transmission as gas; no vesicles • heart: single cell rhythm • modulated in different ways to give same effect • Serotonin: • Action on all points of network • Coordinated effect • some cells inhibited • Similar data exist for dopamine, octopamine, myomodulin, FMRFamide…

30. Hard exoskeleton must be shed periodically Fundamental to growth and development 20-hydroxy-ecdysone juvenile hormone Manduca sexta ligature, extirpation, transplantation, injection, Insect ecdysis

31. Fly life cycle larva (3 instars) egg pupa adult

32. Drosophila • gene knockout • tissue/cell selective gene expression

33. Moulting • weakening of old cuticle • formation of new cuticle • emergence • separation of old /new by air bubble (pre-ecdysis) • peristaltic waves to move forward out of old cuticle (ecdysis) • expansion : compression, intake of air (post-ecdysis)

34. Main peptide hormones • ETH • EH • FMRFamide • CCAP • Bursicon

35. Ecdysis triggering hormone • ETH • 26 aa peptide in Manduca • 2 peptides in flies • secreted by Inka cells • in response to dropin ecdysone

36. ETH targets

37. Eclosion hormone (EH) • In Manduca, EH released from 2 cells in brain in response to ETH • positive feedback to Inka cells (which release more ETH …) • In Drosophila, EH thought to play lesser role; • ecdysis delayed by 4 min • similar role may be played by corazonin

38. FMRFamide • 4 aa peptide • secreted from Tv neurons • first cells to be activated by ETH • strengthen muscle contractions • Tv-KO is not lethal

39. CCAP • CCAP from 5 pairs of SOG cells and 2 pairs/segment in abdomen • In Manduca, CCAP turns off pre-ecdysis and starts ecdysis (abdominal waves) • In Drosophila, CCAP-KO do not start contractions or evert head

40. Bursicon • 140 aa (dimer with pBurs) • important in tanning • released from a subset of CCAP-cells Bursicon CCAP

41. Sequential response to ETH

42. Summary • NO – local transmission as gas; no vesicles • heart: single cell rhythm • modulated in different ways to give same effect • Serotonin: • Coordinated action on all points of network • Similar data exist for dopamine, octopamine, myomodulin, FMRFamide… • Ecdysis: Sequential program of hormone action