NEUR 303 - lecture 11

How common is biparental care in mammals?

Biparental care occurs in only ~5–10% of mammalian species, making it relatively rare.

Why is paternal care rare in mammals?

Because fertilisation is internal, which guarantees maternity but not paternity, and because females provide lactation, reducing the evolutionary pressure for male care.

Which mammal groups most commonly show biparental care?

Some rodents (e.g., mice), primates, and carnivores.

What behaviours can paternal care include?

Pup transporting, defending, warming, grooming, playing, socialising, and providing food/shelter/resources.

What is paternal behaviour in mice like before mating?

Adult male mice are often infanticidal, meaning they may attack and kill pups.

When does paternal behaviour emerge in male mice after mating?

Around 20 days after mating.

What percentage of male mice show paternal behaviour after mating?

About 80%.

Why is the timing of paternal behaviour emergence significant in mice?

Mouse gestation is ~21 days, so paternal behaviour appears right when the male’s offspring are likely to be born.

Why is paternal behaviour described as “transient” in male mice?

After about 50–60 days, males often revert back to infanticidal or non-paternal behaviour, matching the time pups are usually weaned.

What sensory system is critical for pup-related signalling in males?

The olfactory system, including both the main olfactory bulb (OB) and accessory olfactory bulb (AOB).

What is the main pup-avoidance circuit activated in virgin males?

OB/AOB → medial amygdala (mAMY) → AH/VMH → PAG.

What is the function of the pup-avoidance circuit (AH/VMH/PAG pathway)?

It promotes defensive and avoidance behaviour, contributing to pup-directed aggression/infanticide.

What does cFos evidence show about the pup-avoidance pathway in fathers vs virgins?

cFos activation is high in virgin males but low in fathers, suggesting avoidance circuits are suppressed in fathers.

What experiment supports the importance of pheromonal signalling in suppressing paternal behaviour?

Ablation of the vomeronasal organ can induce paternal behaviour in virgin males.

What does vomeronasal organ ablation suggest about paternal behaviour?

Paternal behaviour requires suppression of pup-avoidance signalling, particularly pheromonal inputs.

What motivational/reward pathway is activated in fathers to promote pup care?

mAMY → MPOA → VTA → nucleus accumbens (NAc) → ventral pallidum (VP).

Why is the MPOA important for paternal behaviour?

The MPOA integrates pup signals and shifts behaviour from avoidance to approach; lesions disrupt paternal behaviour.

What does increased cFos in the MPOA indicate in father males?

Fathers show higher MPOA activation, supporting its role in paternal behaviour.

What are GRAB sensors?

GPCR-activation based sensors that detect neurotransmitter release in real time using receptor-linked fluorescence.

How does the dopamine GRAB sensor (GRAB-DA) work?

A modified human dopamine receptor is fused to GFP; dopamine binding causes a conformational change that increases fluorescence.

What do GRAB sensors measure: synaptic signalling or extracellular neurotransmitter availability?

They measure extrasynaptic extracellular neurotransmitter availability, not intracellular signalling.

How are GRAB sensors delivered to the brain?

They are packaged into AAV viruses and expressed in targeted brain regions (e.g., nucleus accumbens).

What does fibre photometry with GRAB-DA show in father vs virgin male mice?

Fathers show strong sustained dopamine release in the NAc during pup approach, while aggressive virgins do not.

What does dopamine release in the NAc suggest about paternal behaviour?

Paternal behaviour involves activation of reward/motivation circuitry.

What type of MPOA neurons are strongly linked to paternal behaviour?

Galanin neurons in the MPOA.

What happens when MPOA galanin neurons are ablated?

Fathers show reduced crouching, grooming, nest building, and overall pup interactions.

What does GCaMP fibre photometry show about MPOA galanin neurons?

Their activity increases specifically during pup-directed behaviour, not unrelated behaviours like eating.

What is channelrhodopsin (ChR2) and how is it used?

A blue-light activated cation channel; stimulation depolarises neurons and can artificially activate galanin neurons.

What happens when MPOA galanin neurons are optogenetically stimulated in father mice?

It rapidly induces pup retrieval and speeds up pup gathering and nest-building.

What does optogenetic stimulation of MPOA galanin neurons demonstrate?

Galanin neurons can actively drive paternal behaviour, not just correlate with it.

What environmental cue is important for inducing paternal behaviour in males?

Cohabitation with a pregnant female.

What does cohabitation with a pregnant female do to male behaviour?

It suppresses infanticide and helps induce paternal responses, likely via chemical cues.

In some species, what is sufficient to induce paternal behaviour even without cohabitation?

Copulation/mating alone, suggesting hormonal priming can be enough.

Which hormone is strongly associated with paternal behaviour in biparental species?

Prolactin

What evidence from hamster species supports prolactin’s role in paternal care?

Paternal species (Phodopus campbelli) have higher prolactin levels than non-paternal species (Phodopus sungorus).

What prolactin event occurs after mating?

A post-ejaculatory prolactin surge.

How do prolactin levels compare between paternal mice and non-paternal rats?

Father mice have significantly higher circulating prolactin than father rats.

What is pSTAT5 and why is it important in paternal behaviour studies?

pSTAT5 is a marker of activated prolactin receptors, showing where prolactin signalling is occurring.

What does pSTAT5 immunohistochemistry show in male mice vs rats?

Male mice show higher prolactin receptor activation in the MPOA than rats.

What happens when prolactin receptors are deleted specifically in the MPOA of adult males?

Pup retrieval is impaired in father mice, showing MPOA prolactin signalling is necessary for retrieval behaviour.

Does deleting prolactin receptors in the MPOA disrupt all paternal behaviours equally?

No, the strongest effect is on pup retrieval, suggesting selective control of pup-directed motivation.

What neurons control prolactin secretion from the pituitary?

Tuberoinfundibular dopaminergic (TIDA) neurons in the arcuate nucleus.

Where do TIDA neurons project and what do they release?

They project to the median eminence and release dopamine into portal blood.

What is dopamine’s effect on prolactin secretion?

Dopamine inhibits prolactin release from the anterior pituitary.

What feedback loop regulates prolactin secretion?

Prolactin activates TIDA neurons → dopamine release increases → prolactin secretion is suppressed (negative feedback).

What are the rapid prolactin feedback mechanisms acting on TIDA neurons?

(1) Increased TIDA neuronal firing → dopamine release
(2) Phosphorylation of tyrosine hydroxylase (TH) → increased dopamine synthesis

What is tyrosine hydroxylase (TH)?

The rate-limiting enzyme in dopamine synthesis.

What is the slow mechanism of prolactin feedback on TIDA neurons?

JAK/STAT signalling → STAT5 activation → increased TH gene transcription, sustaining dopamine synthesis long-term

What species difference was discovered in TIDA neuron activity?

Rats have slower oscillations, while mice have faster oscillations.

What optogenetic tool was used to manipulate TIDA neurons in paternal behaviour studies?

Halorhodopsin, a yellow-light activated chloride pump that inhibits neurons.

What happens when mouse TIDA neurons are driven at rat-like frequency (0.2 Hz)?

Dopamine output increases, prolactin decreases, and paternal pup retrieval is disrupted.

What happens when mouse TIDA neurons are driven at mouse-like frequency (0.4 Hz)?

Prolactin levels remain normal and paternal pup retrieval is unaffected.

What does the 0.2 Hz result suggest about prolactin regulation?

Rat-like TIDA oscillation frequency may maximize dopamine inhibition of prolactin, preventing prolactin-dependent paternal behaviour.

What overall model links TIDA neurons to paternal behaviour?

TIDA oscillation frequency → dopamine inhibition strength → prolactin levels → MPOA prolactin receptor activation → paternal pup retrieval.

What is the overall conclusion about prolactin in paternal behaviour?

Prolactin signalling through MPOA prolactin receptors supports paternal care in biparental species, and species differences in prolactin regulation may explain why paternal behaviour varies across mammals.