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Neurobiology > Neural basis of sex-specific behaviours > Flashcards

Neural basis of sex-specific behaviours Flashcards

1
Q

Why are sex-specific behaviours needed?

A

To allow survival and propagation of the species.

They allow individuals to identify each other, breed and to care for their progeny.

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2
Q

Give 3 examples of sex-specific behaviours

A
  • Parental behaviour
  • Aggression
  • Mate attraction and selection: courtship dances & songs
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3
Q

What causes sex-specific behaviours?

A

Differences in the nervous system.

These are innate to the organism.

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4
Q

How are neurons arranged in order to control behaviour?

A

Neurons are organised into circuits which process a specific type of information.
Each circuit controls a certain behaviour.

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5
Q

What are the 3 types of neurons and what are their functions?

A
  • Sensory neurons: detect stimuli and transmit info to the CNS.
  • Interneurons: In the CNS. These receive and process information from sensory neurons and pass on this information to motor neurons.
  • Motor neurons: These transmit information to muscles and glands to give a response.
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6
Q

What components of neural circuits are shared between sexes?

A
  • Sensory neurons
  • Interneurons
  • Motor neurons

They can be shared in different compositions, e.g. all, or just sensory neurons.

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7
Q

Give examples of different neural circuit wirings in sex-specific neurons which can occur?

A
  1. The whole circuit is sex specific.
  2. Sensory neurons are sex specific, and the inteneurons & motor neurons are shared.
  3. Motor neurons are sex specific, and the sensory and interneurons are shared.
  4. Interneurons are sex specific. Sensory and motor neurons are shared.
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8
Q

Which neurons initiate male courtship in Drosophila?

A

P1 neurons.

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9
Q

What are sexually-dimorphic neurons?

A

These are neurons which are present in both males and females. They cause sex-specific behaviours.

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10
Q

How do sexually-dimorphic neurons differ between sexes?

A
  • Differ in structure: number of cells, their projections and their connectivity.
  • Differ in physiological properties: neurochemical composition, dormancy, ease of excitation.
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11
Q

What sexually dimorphic neurons can be wired differently? Explain

A

Sensory neurons, motor neurons and interneurons can be wired differently, so the same neuron can be present in both sexes, but they may differ in number, so are sexually dimorphically different.

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12
Q

How can dimophic behaviours arise from different wiring?

A

They can appear together in different combinations, as they are not mutually exclusive.

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13
Q

What is the difference between sex-specific neurons and sexually-dimorphic neurons?

A

Sex-specific neurons:
- The entire circuit is present in one sex but not the other.

Sexually-dimorphic neurons:
- The neurons are shared between sexes but each sex has differences in structure/molecular/cellular properties.

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14
Q

Why are invertebrate model organisms used to look at sex-specific differences?

A
  • Humans and mammals have billions/millions of neurons, which makes it difficult to study neurons in these animals.
  • Invertebrates are easy to manipulate at a high level of detail.
  • They can also be used to look at genetic markers and regulatory factors.
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15
Q

Give examples of behaviours which use neural circuits that are common to both sexes.

A

Locomotion and jaw movement activities:

  • Maternal retrieval of its child.
  • Biting during fights.
  • Feeding.
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16
Q

Why are C.elegans used to study brain function and behaviour?

A
  • They are transparent.
  • The number of somatic cells are known.
  • They are simple (hundreds of neurons).
  • Mapping of cell lineages, including has been done.
  • They display primitive and complex behaviour.
  • There are tools available which can be used to tweak the neural function.
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17
Q

What are the 2 sexes in C.elegans and their chromosomes?

A
  • Hermafrodites = XX

- Males = XO

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18
Q

Describe the experiment which was used for sexual conditioning in C.elegans.

A
  1. Conditioning
    - The worms are put in a chamber under starvation conditions for 2 hours.
    - Salt is added, and all the worms migrate to the area of high salt concentration.
  2. Associative learning
    - The worms are put in a chamber which contains salt, but they are under starvation conditions.
    - The worms associate salt with starvation so now repel the salt.
  3. Sexual conditioning
    - The worms are put in a chamber under starvation conditions, with salt and mates.
    - The male worms now associate salt with mates, and are now attracted to the salt.
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19
Q

Why do only males undergo sexual conditioning?

A

Only males go and find mates, so only they become attracted to salt when it is associated with mates.

20
Q

Which neurons are involved in sexual conditioning and how was this proved?

A

MCM neurons. When these neurons were switched off in males, it was seen that sexual conditioning was lost, as the males were no longer attracted to salt.

21
Q

What are MCM neurons and their properties?

A
  • They are male specific interneurons.
  • They appear as a bilateral pair, and are found in the head of male worms.
  • They arise from glia during sexual maturation.
  • They are incorporated into neural circuits, so are found in both male specific and sex shared circuits. This allows for remodelling of circuits.
22
Q

How do MCM neurons allow for mate finding?

A

MCM neurons detect mating pheremones and they relay this information into circuits which are involved in regulating sex differences.

23
Q

Why are Drosophila good model organisms for studying neurobiology?

A
  • They have a simple brain consisting of 100,000 neurons.
  • They show complex behaviours: sleep, aggression, courtship and learning.
  • 75% of their processes are conserved with humans.
  • There are genetic tools which allow for neural function to be tweaked.
24
Q

How can the whole Drosophila brain be visualised by its synapses?

A

Using high-throughput EM.

25
Q

Why is courtship in Drosophila observed?

A
  • It is an innate behaviour.
  • It is robust and easy to quantify.
  • It is a sex-specific behaviour.
26
Q

Describe the 6 stages of courtship in Drosophila.

A
  1. Following
    - Visual and olfactory cues are exchanged. - The male follows the female.
  2. Tapping
    - The male taps the female abdomen with its forelegs.
    - This detects pheremones to see if they are the same species.
  3. Wing extension
    - The male extends his wing to initiate a courtship song.
    - Louder males are preferred..
  4. Licking
    - The male licks the female genitalia.
  5. Attempted copulation
    - The male tries to copulate. If the female rejects, it is usually robust, and includes kicking.
  6. Copulation.
27
Q

What type of nervous system do sex-specific behaviours rely on?

A

Sexually dimorphic nervous systems.

28
Q

What regions of the nervous system were found to be important in male courtship behaviour in Drosophila?

A
  • The brain

- The ventral nerve cord (equivalent to the spinal cord)

29
Q

What parts of courtship does the brain induce?

A
  • Initiation
  • Following
  • Tapping
  • Wing extension
  • Licking
30
Q

What parts of courtship does the VNC induce?

A
  • Licking (top of VNC)
  • Wing vibration (middle of VNC)
  • Attempted copulation (bottom of VNC)
  • Copulation (bottom of VNC)
31
Q

How were these regions determined to be important in inducing male courtship behaviour?

A

Male tissue patches were made and these were overlaid with the female nervous system.
Mosaics were made and tested for courtship behaviour.

32
Q

What are the limitations of only looking at regions of the nervous system which control courtship behaviour?

A
  • Neurons and circuits aren’t determined.
  • Neural structures aren’t tested.
  • Sex-specific neurons and circuits aren’t tested.
33
Q

Which genes were found to be involved in sex-specific behaviours?

A
  • Fruitless (fru)

- Doublesex (dsx)

34
Q

What do the genes fru and dsx do, and where are they expressed?

A

They are transcription factors and they are expressed in every neuron.

35
Q

How is sex determined in Drosophila?

A

Via the sex determination pathway.
Each cell undergoes a cell fate decision to be either female or male.
Sex determination and differentiation are cell autonomous.

36
Q

How is the number of X chromosomes important in sex determination?

A

If XX is present, the gene Sxl (sex lethal) is activated.

This activates the sex-determination cascade.

37
Q

What is the sex determination cascade?

Female pathway

A
  1. XX activates Sxl.
  2. Sxl splices Tra-2+Tra (transformers).
  3. Tra splices dsx and fru to give dsx(f) and fru(m).
  4. dsx(f) directs the cell to female differentiation, by causing female specific neurons to differentiate.
38
Q

What is the sex determination cascade?

Male pathway

A
  1. XO silences Sxl.
  2. Transformers are not spliced.
  3. dsx(m) and fru(m) remain.
  4. Both fru(m) and dsx(m) directs the cell to male differentiation, by causing male specific neurons to differentiate.
39
Q

How do fru and dsx determine sex-specific behaviour?

A

They determine sex-specific neural circuitry.

40
Q

How can we test the effect of fru and dsx on behaviour?

A

By making fru and dsx mutants and looking at courtship behaviours.

41
Q

What was found during courtship in fru and dsx mutants?

A

Male fru mutants:

  • Show male-male courtship.
  • Chaining occurs.
  • Defective courtship with females.

dsx mutants:

  • Show intersexual courtship.
  • Courtship is reduced.
42
Q

Where are fru and dsx proteins found?

A
  • fru(m) is found only in the male nervous system.
  • dsx proteins are found in the nervous system and non-neural tissues.
  • > dsx(m) is found in the male nervous system.
  • > dsx(f) is found in the female nervous system.
43
Q

Which transcription factor (fru/dsx) shows a sexually dimorphic expression?

A

dsx

44
Q

What does the presence of fru(m) in females cause?

A

Causes these females to behave like males, as they try to induce courtship.

45
Q

What needs to be expressed for a female to show full male courtship?

A

fru(m) and dsx(m)

Neurobiology (15 decks)

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