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9 - Question: How do animals modify their behaviour to depend on circumstances? Longer term modulation of behaviour - tadpoles - crayfish - leeches
Terms in this set (34)
So far looked at the way sensory info and central mechanisms interact in a ? ? ? way
moment by moment
Now looking at interactions that work over ? periods of time
in Xenopus - A conventional neurotransmitter = ? produces a ? ? effect - an example of what we call ? inhibition
Stopping pathway reminder in XenopusL pressing cement gland excites sensory neurons that excite inhibitory neurons in hindbrain that turn off swimming --- these hindbrain neurons release?
At the Xenopus hatchling stage in development - these animals spend ?% of their time attached to a substrate using ? ? ? ? - when they are attached the sustained pressure on cement gland slowly continues to excite the ? ? ? which continue to slowly excite inhibitory ? neurons = slow background release of ? ---> PRODUCES LONG LASTING / TONIC ?
Mucus secreting cement gland
Trigeminal sensory neurons
What does tonic inhibition from GABA from hindbrain neurons do?
suppresses responsiveness to sensory stimuli
Can block the effect of GABA / tonic inhibition by?
using gabosine or bicuculine = GABA blockers.
By blocking GABA what happens to the tadpole?
spends more time moving - swimming - and are more predated if put in presence of a predator. So tonic inhibition makes them less likely to move around and be predated. A real functional context.
Another example of tonic inhibition in an invertebrate?
CRAYFISH ESCAPE RESPONSE: tail flip, in which the abdomen quickly flexes to flip crayfish backwards away from a stimulus.
Kranse showed this response is also subject to tonic inhibition mediated by GABA - again neurons response lie in the brain and project down onto ventral nerve cord and release GABA -
what is the effect of tonic inhibition of the escape response in the crayfish -- functional context?
effect = if animal is feeding then tonic inhibition reduces likelihood of a tail flip by up to 50%.
A different kind of release that can also have a long lasting effect on behaviour?
NEUROMODULATION = like transmitters but have more:
- long lasting
Example of a neuromodulater?
in vertebrate examples, what are the two general effects of serotonin?
1. turns down strength of sensory pathways
2. turns up strength of motor pathways
example of how serotonin turns up motor pathways
often interacts with glutamate pathways in turning on motor responses like LOCOMOTION.
example of how serotonin tends to turn down sensory pathways?
serotonin released in spinal cord tends to turn down sensory pathways associated with PAIN RECEPTION
invertebrate example: what does serotonin do in molluscs?
Giant serotonin releasing neurons - some particularly involved in turning up strength of FEEDING behaviour.
Leech (Hirudo) - when hungry will move into the ? of freshwater and stick its head (sucker) at ? of water to detect ? which serve as a stimulus for an animal suitable for the leech to take a blood meal from.
Leech swims towards source of those vibrations by ? and ? ? of the body.
If sucker makes contact with substrate the leech ? swimming and starts to ?. ? is a stimulus for biting and is detected by mouths and lips. If relatively high, typical of a warm blooded animal, they will ? to draw blood.
Likelihood of biting ? with temperature, if it falls within the high 30s - then decreases past 40 degrees.
? starts to pump blood into the ?. Whole body shows pulsing ? movements as blood is pumped into body. Leech will release ? with an ? to stop clotting.
Feeding is stopped when leech reaches ? original weight then detaches from animal.
UP and DOWN UNDULATIONS
STOPS .. CRAWL
There is a clear sequence of sensory and motor events in the leech involved during approach to possible food and in the feeding process itself.
How was the role of serotonin first investigated in these processes? ---- 2 approaches
1. Bathed leeches in serotonin - found that generally EXCITED activity
- Reduced latency to swim toward vibratory source
- Increased biting frequency
- Took larger blood meals
2. PHYSIOLOGICAL PREPARATION:
- Isolated head with nerve cord attached and applied 1 µM serotonin to isolated head and NS
FOUND: increased activity related to swimming and feeding - increased pharynx peristalsis - increased saliva secretion. It also increased responses that tend to be produced by warming the mouth/lips so increased jaw movements and movement of the crop that takes in and stores the blood.
Both of the 2 early experiments on effects of serotonin show it is involved in controlling feeding and swimming but both were relatively crude - next step in studying its effect?
IMMUNOCYTOCHEMISTRY: bound antibodies to serotonin (same kind of technique used to look at inhibitory cells of stopping pathway) to show where the serotonin was --- found contained in neurons in rostral part of ventral nerve cord in....
RETZIUS CELLS = contain serotonin
How did researchers test whether Retzius cells (neurons) were involved in controlling swimming and feeding
1. Recorded from Retzius cells with microelectrode to examine input -- what stimuli made them active
= Retzius cells are excited by vibration to body wall picked up by sensilla at body surface = what initiates swimming AND by increased temperature to mouth or lips = so Retizius cells are excited by the same stimuli that initiate swimming or feeding
2. Stimulated individual Retzius cells via microelectrode to make them fire impulses
= mimicked effects of applying serotonin - so increased saliva secretion - increased probability of swimming responses and also decreased the tension of muscles to allow body to swell up, also increased peristalsis of pharynx.
Strong evidence - retzius cells and their release of serotonin does indeed control strength of feeding and swimming.
3. One other experiment to test that:
Chemically lesioned the Retzius cells by using substance 5,7 dihydroxytrytamine.
= All animals stopped biting - stopped producing feeding movements. They could still swim a bit.
THEN injected serotonin and all treated animals showed restored feeding behaviour = feeding is enhanced by serotonin. +++++advantage of physiological experiments is that you can reverse them!
Series of experiments together gives good evidence that serotonin released from ? ? enhances ? behaviour and ? and over long period of time.
Next, looked at what happens whilst the animals are feeding and have had a blood meal
- metholdogical approaches?
Showed a further level of behavioural control by Retizus cells
Cannulated the crop = place tube into crop so could introduce saline to simulate animal having a blood meal -- could control stretching of the crop
= found this artificial extension of the crop would:
1. STOP leech feeding
2. STOP Retzius cells from firing
3. STOP Retzius cells responding to warming of moth which usually excites them
= Further level of control of Retzius cells that affects feeding and swimming
What has more recent worked looked at in the leech and the relationship between swimming and feeding?
Gauldry and Kristan:behavioural choice -- decision-making - different perspective on the system - animals made a choice between feeding or swimming
Gauldry and Kristan:
A hungry leech detectes prey - moves to prey - attaches - feeding now ? over swimming.
Once the leech has fed, the feeding itself is ? and the animals responsiveness is ? and remains this way for a long time = LONG TERM EFFECTS ON BEHAVIOUR
During feeding - they found that ? ? from the sensory neurons that would normally elicit ? was ? = made animal less likely to swim.
METHODS: Used a serotonin blocker = ? and found?
SWIMMING (by responding to stimuli to body wall and making animal swim)
serotonin blocker: MIANSERIN -- found that blocking serotonin blocked the feeding induced decreases in synaptic transmission -- so serotonin is responsible for decreasing the synaptic transmission from swimming sensory neurons during feeding
Second proposal from Gaudry and Kristan
That there are stretch receptors that detect the extension of the crop after feeding that gave long term suppression of responses --
METHODS to detect where the stretch receptors were (could be in body wall like lamprey or in wall of gut):
1. Stretched isolated nervous system by 4-5x normal length -- did not weaken swimming = receptors not in the CNS
2. Removed gut of leeches - so removing possible stretch receptors in gut. Then extended body wall and
= this did suppress swimming - so stretch receptors must be in body wall not in gut or CNS. These stretch receptors in body wall detect increase in distension and suppress feeding and swimming
While leech is feeding, get inhibition by ? of sensory synapses involved in triggering swimming.
Once animal has fed and has fully extended crop there is suppression of the swimming ? itself probably through ?.
Leeches rely on ? different decision-making networks to ensure a biologically important behaviour is not disrupted by other behaviours. One mechanism for producing these long term effects on motor activity involves ? while the other uses ?.
NEUROMODULATOR - serotonin
FINAL EXAMPLE of long term modulation of behaviour in leeches is based on ? ?
Work on simple learning in leeches involved putting leeches in a ? attached by their tail.
Stimulated ? every minute and used ? to monitor how quickly they started to swim.
Findings from experiments stimulating leech every minute?
Speed of response decreased with repeats -- response showed HABITUATION
Next part of simple learning experiment in leeches:
Brushed ? surface = a ? stimulus, for 10 seconds.
What did this show?
Brushed DORSAL surface = NOXIOUS stimulus
This removed habituation and increased speed of response = sensitised the response. Again through repeated stimulation - habituation would start to occur.
When did the leeches NOT show this sensitisation effect and removal of habituation from apply noxious stimulus (brush to dorsal surface)
April - June -- did not show removal of habituation (=dishabituation) -- instead they stayed habituated
What methodology did researchers use which showed dishabituation and sensitisation would occur any time of year?
If injected serotonin instead of brushing the animal -- always showed dishabituation and sensitisation following repeated exposure to stimulus ==== response recovered
Looked at serotonin concentration in leeches CNS over different times of year and found what?
there is an annual cycle in level of serotonin and is at its lowest during that May period and highest in January.
So concluded dishabituation involves release of serotonin and that can only happen when levels of serotonin are relatively high which means that it can't happen when its low between April and June.
This is incidently period of year when leeches would normally breed and feed less - ties in nicely with their being low levels of serotonin. (feeding requires serotonin to block synaptic transmission from sensory neurons involved in swimming)
So today: introduced idea of neuromodulators producing longer term effects of motor responses and latterly introduced idea of simple learning which is what we will be looking at next as a mechanism for much longer term modification of ? behaviour.
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