NeuromodulationModulation of synapses by amines and peptides

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

Neuromodulators

Amines and peptide 5-HT, dopamine, Adrenaline,

acetylcholine… Oxytocin, vasopressin, CCAP

Steroids ecdysone, oestrogen

Eicosanoids leukotrienes, prostaglandins

NO

NO Nitric oxide - a gas! synthesised from L-arginine by NOS

neurons (nNOS, epithelium eNOS) depends on Ca concentration

COO-

C

(CH2)3

NH

C

H2N

H

NH2+

Arginine

NOS

NADPH

+ O2

NAD+

COO-

C

(CH2)3

NH

C

H+H3N

N+

H2NH

OH

N-w-Hydroxyarginine

COO-

C

(CH2)3

NH

H+H3N + NO

NOS

C

O NH2

Citrulline

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

NO → cGMP

cGMP → relaxationK channels

[Ca]

cGMP normally broken down by phosphodiesterase type 5

Viagra

Sildenafil - best selling drug

termtadalafil [Cialis], vardenafil [Levitra]

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

Multi hormone control

vaginal smooth muscle vaginal epithelial

cell

vasoactive intestinal polypeptide

P2Y receptors for ATP

Summary

NO – local transmission as gas; no vesicles

Modulation of single cells

Single cells can be rhythmic R15 in Aplysia sino-atrial node of vertebrate heart Purkinje fibres of heart

vertebrate heart

single cell rhythm

Rhythm at sinoatrial node

Modulation of heart rate by If

If – hyperpolarization activated Na+ current ACh slows rhythm Adrenaline accelerates

activation curve:100% of If channels open here

iso = isoproterenol = isoprenaline

ivabradine

new heart drug blocks If (note difference

from ACh) safer than -blockers

Summary

NO – local transmission as gas; no vesicles

heart: single cell rhythm modulated in different ways to give same

effect

Neural circuits

central pattern generation role of reflexes (see 404)

Clione

Clione - a free swimming sea mollusc

swimming rhythm

alternation of up and down stroke of wings

Clione - ii

reciprocal inhibition up (8) / down (7)

post inhibitory rebound

78

78

78

Faster with 5-HT

CPB1 is serotonergic

heart

down interneuron

Half centre model

Brown (1914) evidence from tadpoles

I then E due to mixed synapse probably at basis of most vertebrate

locomotory systems

Molluscan feeding

Serotonin as modulator local neural release (CGC) hormonal signal in blood

What does it target? How does it act?

CG

bg

Target 1 : muscles

5-HT on voltage clamped muscle fibers

Target 2 : motoneurons

MCC is cerebral serotonergic cell in Aplysia; B21 is a buccal motoneuron

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

Target 4: interneurons

B4 is a motoneuronB35 an interneuron in CPG

control + 5-HT

fasterbigger EPSPquicker decline of EPSP

Most snail effects by cAMP

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…

Insect ecdysis

Hard exoskeleton must be shed periodically

Fundamental to growth and development 20-hydroxy-ecdysone juvenile hormone

Manduca sexta ligature, extirpation,

transplantation, injection,

Fly life cycle

larva (3 instars)

adult

pupaegg

Drosophila

gene knockout tissue/cell selective gene expression

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)

Main peptide hormones

ETH EH FMRFamide CCAP Bursicon

Ecdysis triggering hormone

ETH 26 aa peptide in Manduca 2 peptides in flies secreted by Inka cells in response to drop

in ecdysone

ETH targets

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

FMRFamide

4 aa peptide secreted from Tv

neurons first cells to be

activated by ETH strengthen muscle

contractions Tv-KO is not lethal

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

Bursicon

140 aa (dimer with pBurs)

important in tanning released from a subset

of CCAP-cells

Bursicon CCAP

Sequential response to ETH

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