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BS2077 - Neuro & Animal Behaviour > Straub > Flashcards

Straub Flashcards

1
Q

Describe a reflex with example

A 
Example: Knee jerk reflex
General features:
involuntary, unconscious 
triggered by specific stimulus
stereotypic fixed response
polysynaptic reflex
monosynaptic reflex
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2
Q

Give an example of specific stimuli and complex behaviour

A

Example: Egg retrieval in geese and gulls

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3
Q

Describe other fixed action patterns (FABs) eg.

A
  • many courtship behaviours

- gaping and pecking responses in young birds

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4
Q

Describe FABs

A
  • study of FAPs is particularly linked to work by von Holst, Lorenz and Tinbergen,which can be considered founders of field of neuroethology
  • study is based on observation of animal behaviour
  • FAPs are innate and species typical
  • FAPs are triggered by sign stimulus/releaser – a stimulus that triggers FAP once triggered FAPs are carried out to completion
  • today, the term ‘FAP’ has been widely replaced by the term ‘behavioural act’ or ‘behavioural pattern’
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5
Q

Who discovered universal FAPs in humans and what were they?

A

Eibl-Eibesfeldt observed many different cultures – found evidence for universal FAPs in humans:

  • ‘eyebrow flash’ – universal greeting
  • emotions in deaf-blind children
  • coyness behaviour
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6
Q

Describe the two hypothesis for control of FAPs

A

Hypothesis 1: FAPs are generated by a sequence of reflexes –> Reflex chainAlso known as the peripheral control hypothesis
Hypothesis 2:The central control hypothesis –a central pattern generator generates sequence of motor behaviours

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7
Q

What arguments exist in central vs peripheral control

A

Egg retrieval: behaviour carries on after stimulus is removed – suggests that behavioural sequence is generated centrally and not by a reflex chain

FAPs like egg retrieval are too complex for study of neuronal network that controls behaviour

Organisation of basic locomotion is less complex, e.g.

  • walking: limbs move forward and backwards
  • flying: wings move up and down
  • general: locomotion involves rhythmic flexion and extension of muscle groups
  • -> highly repetitive, good for experimental analysis
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8
Q

Describe the pacemaker model for central pattern generators (CPG)

A
  • intrinsic oscillator / pacemaker
  • imposes activity (rhythm) on network
  • To achieve two opposing phases of activity, neuron(s) that are active whilst pacemaker is inactive require mechanism that drives their activity, e.g.:
  • Post-inhibitory rebound (PIR)
  • Spontaneously active
  • Receives constant excitation
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9
Q

Describe the network oscillator model for central pattern generators (CPG)

A

How to build network oscillator?
Suggestion: Two neurons coupled by excitatory synapse
Problem: Positive feedback – circuit is very unstable!

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10
Q

Describe half centre model for central pattern generators (CPG)

A
  • Two neurons coupled by inhibitory synapses – produces stable oscillation (rhythm)
  • requires a mechanism that progressively reduces inhibitory effect: ‘fatigue’, adaptation, progressive self-inhibition
  • Post-inhibitory rebound (PIR) can sustain oscillation without constant drive
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11
Q

Describe the sea angel Clione limacina

A
  • Wings are modified foot of snail
  • swimming consists of two alternating phases:
    dorsal flexion (D-phase)
    ventral flexion (V-phase)
  • Clione CNS
    few thousand neurons
    clustered in a small number of central ganglia
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12
Q

Describe the ID of Clione swimming neurons

A
  • backfilling makes it possible to identify neurons with axons in a specific nerve
    place cut end of nerve into dye
    dye is taken up by axon and migrates to cell body
  • mapped neurons can be impaled with intracellular electrodes to record their activity
- ~40 motoneurons in total including
2 large neurons:
1A: innervates dorsal wing side
2A: innervates ventral wing side
smaller motoneurons innervate only certain areas of wing
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13
Q

What did experiments tell us about the generation of swim pattern in Clione

A
  • inactivation of individual motoneurons does not affect overall swim rhythm
  • in simultaneous recording from two swim motoneurons
    hyperpolarisation of D-phase motoneuron (red box) has no effect on V-phase motoneuron
  • even photoinactivation of all motoneurons does not interrupt basic rhythm
  • m motoneurons are not involved in generation of swim rhythm!
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14
Q

Describe swim interneurons

A
  • swim interneurons have no peripheral processes – can not be identified by backfilling
  • can only be identified by systematic search using intracellular electrodes – look for neurons that are active in phase with swim motoneurons
  • inactivation of swim interneuron by hyperpolarisation (red box) stops swim rhythm
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15
Q

Describe how swim interneurons are involved with pattern generation in Clione

A
  • Clione has two groups of swim interneurons called 7 and 8
    swim interneurons 7 are active during D-phase
    swim interneurons 8 are active during V-phase
  • interneurons 7 and 8 are connected by inhibitory synapses
  • interneurons in the same group are electrically coupled
  • swim interneurons fire on rebound from inhibition ( post-inhibitory rebound)
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16
Q

Describe the Clione CPG as a half centre oscillator with a twist

A
  • Clione swim CPG has all the elements of a half-centre oscillator
  • rhythm generation can be fully explained by connections between different interneuron types
  • Swim interneurons possess intrinsic bursting property!
  • Swim rhythm generation is result of the combination of intrinsic cellular properties and network properties
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17
Q

SUMMARY FAP, MODELS, CLIONE

A
  • Fixed action patterns are innate behaviours triggered by a sign stimulus/releaser
  • Fixed action patterns are centrally controlled
  • Various models have been proposed for the central control of rhythmic behaviours including:
    pacemaker neurons
    half-centre oscillators
    closed-loop rhythm generators
  • Swim rhythm in the marine snail Clione is generated by a central pattern generator with all the features of a half-centre oscillator
  • In addition, the interneurons of the Clione swim pattern generator also have intrinsic bursting properties  so, they have the potential to function as pacemaker neurons
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18
Q

Describe the neuroanatomy of the tadpole

A
  • Hatchling tadpole
    Spinal cord: ~100 mm diameter
- Eight types of spinal neurons including:
motoneurons:
commissural interneurons
descending interneurons
dorsolateral interneurons
dorsolateral commissural interneurons
Rohon-Beard neurons
  • Spinal neurons form longitudinal columns of 100-300 cells on each side of CNS
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19
Q

Describe tadpole swim motor neuron

A
  • motoneurons show rhythmic activity in response to brief tail stimulus —> swim episode
  • activity of left and right motoneurons alternates (like pattern of laying bricks)
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20
Q

Describe tadpole swim CPG

A
  • Three neuron types are sufficient to generate basic swimming pattern
  • All three types show similar activity pattern:
    fire single AP during fictive swimming
    are tonically excited
    receive mid-cycle inhibition
  • Neurons form half-centre oscillator
21
Q

Describe what was found in Roberts, Soffe, Perrins (1998) in Neurons, Networks, and Motor Behavior (SUMMARY)

A
  • Commissural interneurons project to opposite site where their axon branches and projects both rostrally and caudally
  • Commissural interneurons are responsible for mid-cycle inhibition (Glycine)
  • Some have also ipsilateral axons, presumably responsible for recurrent on-cycle inhibition of sensory decussating interneurons (dlc), etc.
  • Descending interneurons project caudally on the same side of the cord
  • Provide fast AMPA excitation to more caudal neurons and slow NMDA excitation that sustains next cycle
  • Motoneurons have peripheral axons, but also descending longitudinal axons that make central synapses (ACh)
  • PIR plays a role in pattern generation
  • Tonic drive is provided by cycle-by-cycle feedback due to slow NMDA excitation
  • Other mechanisms might also play a role
22
Q

Describe the activation of swim CPG

A
  • Rohon-Beard neurons innervate trunk skin
  • RB neurons have longidutinal axons in dorsal spinal cord
  • Excite dorsolateral (dl) and dorsolateral commissural (dlc) sensory interneurons
  • Trigger activity in swim CPG
23
Q

How does motoneuron activity propagate?

A
  • from head to tail
  • During swimming, waves of bending pass from the head to the tail
  • Progression can also be seen in motoneuron activity in isolated spinal cord
24
Q

What are the two hypothesis for how a wave of activity is propagated

A

Hypothesis 1:
- single oscillator – variable delays:signal takes longer to reach caudal segments than rostral segments

  • Unlikely because:
    CPG elements are distributed along the whole length of spinal cord
    stretches of spinal cord can be isolated and show rhythmic activity —> CPG is distributed along the spinal cord

Hypothesis 2:
- tadpole spinal cord represent a chain of unitary oscillators

  • leading oscillator hypothesis:
    each CPG generates rhythm
    CPG with fastest rhythm sets overall frequency and co-ordinates activity in other CPGs
  • rostral-caudal wave propagation requires gradient from head to tail that ensures more rostral CPGs oscillate faster than more caudal CPGs
25
Q

How is activity in unitary oscillators coordinators

A
  • spinal cord shows rostral-caudal gradient of excitability:
    rostral motoneurons are more depolarised during swimming than caudal motoneurons
    rostral motoneurons also receive larger midcycle inhibition
  • prediction:changing excitability of caudal segments changes rostral-caudal delay
26
Q

How is excitability manipulated in caudal segments and what does it change

A
  • glutamate is excitatory neurotransmitter involved in swimming
  • NMDA application (glutamate receptor agonist) to caudal segments increases excitability in these segments and shortens or even reverses rostral-caudal delay
  • AP5 application (glutamate receptor antagonist) to caudal segments decreases excitability and increases rostral-caudal delay
27
Q

Describe longitudinal gradients in exon distribution

A
  • highest number of axons originating from dorsolateral commissural interneurons (dlc), dorsolateral ascending interneurons (dca) and descending interneurons (dIN) are found at rostral end of spinal cord
  • could be morphological basis for longitudinal gradient in excitability
28
Q

Describe lamprey swim CPG

A
  • could be morphological basis for longitudinal gradient in excitability
29
Q

What is the leading oscillator hypothesis in lamprey

A
  • as in tadpole, glutamate is excitatory neurotransmitter involved in swimming
  • separating the spinal cord into three pools and applying different concentrations of the glutamate agonist NMDA alters wave propagation:
  • same concentration in all pools —> rostral-caudal wave (forward swim)
  • high concentration in caudal pool —-> caudal-rostral wave (backward swim)
  • high concentration in middle pool —-> two waves propagating rostrally and caudally
30
Q

SUMMARY: TADPOLE AND LAMPREY

A
  • Swimming in tadpole and lamprey consists of undulatory body movements that progress as a rostral-caudal wave
  • Rhythms are generated by CPG with characteristics of a half-centre oscillator
  • Spinal cord can be considered as a chain of unitary oscillators/CPGs
  • Segment with fastest frequency leads wave, other segments follow with a specific phase lag  generation of a propagating wave
31
Q

Describe kinematic analysis of walking

A
  • Eadweard Muybridge looked at horses running by taking pictures along a track
  • step cycle consists of two phases:
    stance (support) phase:
    ~ anterior extreme position —> posterior extreme position
    ~ limb moves backward relative to body
    ~ limb is loaded by part of body weight and also develops propulsive force
  • swing (transfer) phase:
    ~ posterior extreme position —> anterior extreme position
  • three joints:
    ~ hip, knee, ankle
    ~ perform flexion and extension movements
  • hip joint: single cycle of flexion and extension per step
  • knee and ankle joint: two peaks of flexion and extension per step
32
Q

How are the two step phases affected by changes in speed

A

speed changes mainly due to change in duration of stance phase, smaller changes in swing phase

33
Q

How is locomotor pattern changed with speed

A
  • changes interlimb coordination

- sequence of foot contacts in quadruped animals:

34
Q

Describe the sequence and phase of walking

A
  • sequence:LHLFRHRF

- all four limbs out of phase

35
Q

Describe the sequence and phase of trotting

A
  • sequence:LH/RFLF/RH

- diagonal limbs in phase with each other

36
Q

Describe the sequence and phase of pacing

A
  • sequence:LH/LFRH/RF

- limbs on one body side in phase with each other

37
Q

Describe the sequence and phase of galloping

A
  • sequence:LH/RHLF/RF

- pair of limbs in phase with each other

38
Q

Describe neuronal control of walking

A
  • Each limb is controlled by its own controller
    ~ First proposed by von Holst in 1938
    ~ Evidence:
    Stepping rhythm in different limbs can differ from each other; e.g. animals and humans walking on a treadmill with split belt
  • Various gaits are controlled by a single neuronal network
    Evidence:
    ~ Temporal characteristics of step cycle change gradually over wide range
    ~ Basic pattern of joint movements and muscle activity persists at various speeds/gaits
    ~ Changes in gait patterns can be achieved by changing single parameter  the phase relationship between individual limb controllers
39
Q

Describe location of neuronal network for walking

A
  • transection experiments:
    ~ transection at level of superior colliculus (SC) just posterior to corpus mammilary CM creates mesencephalic cat:
    recovers ability to stand and walk
    walking is very machine-like
    ~ transection at more caudal levels:
    no recovery of spontaneous walking
    -basic neuronal network for locomotion located in spinal cord, posterior brainstem and cerebellum
  • Identification of Mesencephalic Locomotor Region (MLR)
40
Q

Describe walking in mesencephalic cat

A
  • set-up enables recording of cellular activity during walking
  • walking in mesencephalic cat can be triggered by electrical stimulation of mesencephalic locomotor region (MLR)
  • but, destruction of MLR does not abolish cats ability to walk
41
Q

Describe 2 experiments to do with function of MLR

A

Experiment 1:

  • MLR stimulated at constant level, speed of treadmill was gradually decreased
  • decrease in step cycle frequency, MLR does not control cycle frequency

Experiment 2:

  • MLR stimulated at increasing levels, speed of treadmill was kept constant
  • increase in forcechange in gait pattern/phase-relationship between legs

Conclusion:

  • MLR activity determines intensity of muscle contraction
  • MLR activity affects muscle force and limb co-ordination
42
Q

Describe the role of the spinal cord in walking

A
  • low spinal cats: transection of spinal cord in thoracic region
    ~ can perform stepping movements when placed on treadmill and body weight is supported
  • movements are weak and not-well coordinated
  • strength and coordination can be improved by application of clonidine (a2-noradrenergic receptor agonist)
  • Conclusion
    limb controller present in spinal cord
    weak movements due to insufficient excitatory drive
43
Q

Is limb stepping controlled by CPG?

A
  • removal of sensory feedback by:
    ~ paralysing preparation using muscle relexant
    ~ deafferentation (cutting dorsal roots that carries sensory inputs)
     spinal cord does not rely on sensory feedback to create rhythmic activity
44
Q

How do we know one rhythm has multiple CPGs

A
  • cooling blocks neuronal activity in affected areas
  • cooling of L5 does not affect rhythm activity in L4
  • cooling of L5 blocks rhythmic activity in more caudal spinal cord segments
    So… CPG exists in L2-L4
  • destruction of grey matter in L3/L4
    ~ rhythm generation in L5 and more caudal segments remains unchanged
    ~CPG also exists in L5-L7
  • destruction of grey matter in L3/L4+ L6/L7  L5 still able to generate rhythm, i.e. contains CPG

Conclusions

  • stepping is controlled by local oscillatory networks
  • individual oscillators are coordinated into one single rhythm generator
45
Q

Describe neuronal elements of limb CPG

A
  • Identification by:
    Activity-dependent labelling
    Genetic approaches
    Electrophysiology

Only about 0.1% of spinal cord neurons appear to be part of CPG

46
Q

Describe models for limb CPG

A 
Unit burst model:
- Individual CPGs for each joint
- Coupled to generate overall limb movement pattern
Two level CPG model:
- Rhythm generation
- Pattern generation
47
Q

Describe contribution from endogenous bursters

A
  • Hb9 interneurons possess endogenous bursting properties
  • Membrane potential oscillations can be induced by low extracellular calcium and/or a combination of N-methyl-aspartate (NMA), serotonin (5-HT) and dopamine
  • Membrane potential oscillations persist in presence of TTX (i.e. do not require APs and synaptic activity)
48
Q

SUMMARY STEPPING CPG LOCOMOTION

A
  • stepping involves alternate activity in limb extensor and flexor muscles
  • speed changes is mainly due to shortening/lengthening of stance phase
  • speed changes lead to changes in interlimb coordination (walk, trot, gallop)
  • stepping CPG is located in spinal cord, additional elements in lower brain stem (control strength and coordination)
  • stepping is controlled by multiple CPGs that are unified in one locomotion controller
  • actual stepping CPG has not been identified

BS2077 - Neuro & Animal Behaviour (7 decks)

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