Exam 3 Flashcards
Costs of group living
- Ease of disease transmission
- Increased competition for resources
- Increased conspicuousness to predators
Benefits of group living
- Antipredator defense
- Elevated foraging efficiency
- Group defense of resources
- Increased mating opportunities
Hormones important in promoting affiliative behaviors thought to have been “co-opted from their roles in…
reproductive and parental behaviors
Nonapeptide hormones
- oxytocin and vasopressin
- Share common ancestry across vertebrates and invertebrates
- Originally evolved to regulate water, mineral balance, egg laying, parturition (mammals)
- Co-opted through evolution to regulate diverse social interactions (pair bonding in voles, flocking in birds)
Oxytocin receptors monogamous voles vs polygamous voles
Monogamous: more receptors in nucleus accumbens & prefrontal cortex
polygamous: less receptors in lateral septum
Vasopressin receptors monogamous voles vs polygamous voles
Monogamous: more receptors in ventral pallidum & amygdala
Polygamous: less receptors in lateral septum
Role of oxytocin in pair-bonding preference in female voles
- oxytocin facilitates pair-bonding
- partner preference reduced by blocking oxytocin receptors in nucleus accumbens and prefrontal cortex. NOT caudate putamen
Role of vasopressin in pair-bonding preference in male voles
- increases preference
- partner preference reduced by blocking vasopressin receptors in the ventral pallidum, but not the thalamus or amygdala
(If block vasopressin receptors in males, will spend less time with females)
Reward circuitry
nucleus accumbens, prefrontal cortex, and ventral pallidum
Vasopressin vs vasotocin
Vasopressin: not birds
vasotocin: birds
Oxytocin role in affiliate behavior
- can increase affiliate behavior across species
- Increasing oxytocin causes both dogs and humans to pay more attention to each other (social orientation and affiliation)
- Positive interactions with other dogs increases oxytocin release
- Mutual gaze: Some dogs look much longer at their owners than other dogs
- Gaze increases oxytocin levels in their owners —> increased affiliative behaviors towards dogs —> increasesdog oxytocin levels
Species-specific changes in c-FOS levels in AVT neurons in response to social interaction
- Highly social birds (zebra finch) increase
- Territorial birds (waxbills decrease)
When does c-FOS increase?
only following exposure to a positive affiliation-related stimulus
Male and female waxbills in response to pair-bonded partner
both increase AVT c-FOS
Social birds vs territorial birds AVT and oxytocin-like receptors
- social birds have more AVT neurons and AVT receptors
- social birds have more oxytocin-like receptors
Social bird and territorial bird example
Social: Zebra finches
Territorial: waxbills
Social birds oxytocin experiment
- Prefer to be near many familiar conspecifics
- Oxytocin antagonist reduced the time spent near familiar same-sex cage mates and reduced preferred group size
Same for male and female
Attachment
infant strives to maintain proximity to primary caregiver, highly motivated to reestablish contact after separation
How do young animals of some species respond to social isolation?
distress vocalization (babies cry when unattended)
Polygnous squirrel monkeys mothers attachment
Carry infants- separation of mother and infant greatly increases cortisol in both (until they are reunited)
Monogamous titi monkey fathers attachment
Carry their infants- separation of father and infant (but not mother and infant) increases cortisol in infant but not father or mother
How does cortisol affect voles?
- High corticosterone: increases partner preference in male voles
- Low corticosterone: increases partner preference in female voles
How does testosterone treatment affect voles?
- treatment of monogamous voles does NOT make them polygamous
- castration of polygamuos voles does NOT make them monogamous
- correlation, not causation!!!!!!!
What do opioid receptor antagonists do in animals?
- Reduce eye closing behavior in response to comfort in newly-hatched chickens
- Prevent contact comfort from mother from reducing distress vocalizations in rat pups (no effect on adult rat social interactions)
- Decrease maternal bonding and increase distress vocalization in infant monkeys
- Decrease social grooming in adult primates
How do opioids affect stress or fear of social contact?
- may blunt
- aversive responses!!!
Aggression
- overt behavior with the intention of inflicting damage or other unpleasantness on another individual
- not the exact opposite of affiliation though
When is there possibility for aggressive behavior?
whenever the interests of two or more individuals are in conflict (territory, food, mates, etc.)
Agonistic behavior
The entire behavioral repertoire of both aggressive and submissive interactions within the context of a social interaction involving a conflict of interest
Aggression and submission may represent a ………..
single behavioral continuum, or may be independent (but interacting) dimensions of behavior
Evidence that androgens mediate aggressive behavior across species
- High correlation between seasonal variation in testosterone and seasonal variation in aggression (ex: red deer male testosterone, antler size, aggression peak near mating season)
- Aggressive behaviors increase at puberty
- Males are generally more aggressive than females
- Castration typically reduces aggression; testosterone therapy restores aggression to pre castration levels
What happens to male rodents that do not undergo seasonal castration?
- have higher testosterone and higher levels of aggression
- Prevents them from benefiting from communal huddling behavior during the winter to stay warm
- Low circulating testosterone reduces aggressive behaviors in most, but not all, rodents
What affects aggression in winter hamsters if not testosterone?
- Hamsters increase aggressive behaviors under short days (“winter”) even though their testosterone levels decrease (seasonal castration)
- Melatonin increases aggression in male and female hamsters
- Melatonin enhances secretion of DHEA (androgen) from adrenal glands during “winter” (from gonads during “summer”
How does estrogen affect aggression in mice in the “summer” and “winter”?
summer: estrogen inhibits aggression in mice
winter: estrogen increases aggression
- Estrogen injection increases aggression in “winter” mice within 15 min, but no short-term effect in “summer” mice
- Switch from genomic effects of estrogen in “summer” that inhibit aggression to non-genomic effects of estrogen in “winter” that increase aggression
Genomic vs nongenomic
Genomic: changes in gene expression
non-genomic: regulate neurotransmitter release, phosphorylation
How do song sparrows differ in breeding vs non-breeding season after a territorial aggression?
breeding: long-lasting territorial aggression after a territorial intrusion
non-breeding: behave aggressively after intrusion but rapidly stop –> Estrogen rapidly increases aggression during the non-breeding season but aromatase inhibitors reduce aggresion
Rapid, non-genomic effects of estrogen during non-breeding season
Hamster aggression and puberty
- Prior to puberty: play fighting (attacks to face and cheeks)
- During puberty: actual fighting (attacks to flanks, underbelly)
- Attack frequency decreases as hamsters become older
- Repeated exposure during puberty to aggressive adults (social stress) hastens the onset of aggression and slows the decrease in attack frequency with age
- Castration (testosterone) does not affect the transition from play to actual fighting
- Correlates with the development of the hypothalamic-pituitary-adrenal axis and adult glucocorticoid production
Rodent aggresion during puberty
- increased around puberty in male rodents (voles, hamsters)
- Many rodents disperse around puberty and encroach on other males’ territories
- Peripubertal aggression enhances the survival of dispersing males
- Androgens both enhance aggression and are necessary to elicit dispersal in most (but not all) rodents
- Relationship between high population density, high androgens, and high aggression in rodent groups
What is dispersal?
- “leaving home”
- a robust sexually dimorphic trait in many species
- behavior organized by androgens early in development (but not activated by them)
- Castration around puberty has no effect on dispersal
Bird dispersal
Female birds are more likely to disperse from their natal nesting area than male birds
Squirrel dispersal
- Males: much more likely to disperse from their natal nesting area than females
- Females: injected with testosterone shortly after birth greatly increase their likelihood of dispersal
What happens when beagle mothers are treated with testosterone during gestation and injecting testosterone after birth
female beagles are masculinized
How are dog hierarchies determined?
a bone is thrown into a group of dogs, the one that gets the bone is the dominant one; that dog is removed and the test is repeated to see the second most dominant, etc.
How do unmasculinized females react?
yield to (allow them to get the bone) males and masculinized females without aggressive behavior
How do masculinized females react?
did not yield to males but males behaved as if they expected the female to let them get the bone (aggressive: each attacking the other if they got the bone first)
What are dog social signals about dominance status affected by?
organizational effects of androgens
Evidence for sex differences in play behavior
- Sex difference in aggression in non-human primates (males > females) evident early in development
- Young male primates exhibit more rough and tumble play than females
Play behavior androgen exposure vs castration
- prenatal androgens treatment increases play behavior in female offspring
- castration has no effect on play behavior
Rough and tumble play behavior requires organizational, but not activational effects of androgens
How did aggressive and not aggresive mice react to castration?
all became docile
How did mice react after they were supplemented with equal amounts of testosterone?
previously aggressive: became aggressive again
previously nonaggressive: did not become aggressive even
Testosterone is ……….. for aggressive behavior in mice
- necessary but not sufficient
- receptor sensitivity to androgens?
What happened to mice castrated after an aggressive experince?
typically remain aggressive for much longer after castration
Castration and testosterone supplement effect on high and low-ranking dogs/monkeys
no effect on dominance hierarchy
What happens to androgen levels in male mice, hamsters, rhesus monkeys, and humans if they lose and win a fight?
- lose: Androgen levels decrease and remain low for several days
- winners: increased androgen levels
How did receiving a dose of testosterone immediately after winning a fight affect California mice?
increased their chances of winning a future fight in their home cage
Associated with upregulation of androgen receptors in reward areas of the brain (ventral tegmental area, nucleus accumbens)
How did receiving a dose of testosterone affect white-footed mice?
no effect of winning a fight in home cage nor future win chances
Pairing winning with testosterone greatly increases future win chances in white-footed mice!
Conditioned defeat definition and effect in male rodents
- after losing an aggressive encounter, more likely to lose in future encounters
- rodents: after defeat in their own territory, will fail to defend their territory in the future even if new intruder is a non-aggressive male
losing in HOME TERRITORY affects circuitry and lasts for a long time.
Mice social defeat stress experiment: stress response
increased: ACTH, endorphin, glucocorticoids
decreased: testosterone and prolactin
Mice social defeat stress experiment: hormones and physiological/behavioral consequences
- Hormonal changes present even when the new intruder is behind a barrier: psychological stressor, not the pain of combat itself
- Physiological and behavioral consequences of conditioned defeat persist for over a month
Female conditioned defeat
rare and only persists for a very short time
Birds’ first week vs. second week of establishing territory
first: high-ranking birds are highly aggressive and have high levels of testosterone
second: high-ranking birds remain aggressive but testosterone no longer higher than low- ranking birds
When are social rank, aggression, and testosterone correlated?
when social status is being actively challenged but can be maintained without hormones
Challenge hypothesis
- Androgens mediate aggression in birds only during establushment of other territories or whenver males are highly competitive
- ex: In breeding season, testosterone elevated when sparrows are setting up territory and guarding their first brood (eggs) –> Testosterone maintained at lower levels during the rest of the breeding season, declines during non-breeding season
Evidence that it is hard to correlate hormones and aggressive behavior
sparrows breed multiple times throughout breeding season but behaviors are not synchronized
What can be seen when hormones are plotted against the stages of the breeding cycle?
- LH and testosterone are high when aggression is high (sexual stage)
- low during parental stage
Evidence that testosterone and aggression vary by species
- Starlings increase testosterone and aggression before each egg-laying period
- Gulls have little intermale competition, form pair bonds, and have almost no change in testosterone during the breeding season
How does testosterone promote aggression in adult males?
- Androgen-responsive pathway (responds to testosterone and dihydrotestosterone: 5a-reductased testosterone)
- Estrogen-responsive pathway (responds to estrogen: aromatized testosterone): most common!
- Combined/synergistic pathway: Responds to estrogen and dihydrotestosterone
- Direct testosterone-mediated pathway: only responds to testosterone
Effects of estrogen receptor knockout mice when castrated and implanted with testosterone
no aggressive behavior even when castrated and implanted with testosterone
Effects of monkeys on diets high in estrogens over a long period of time (>1 year)
more aggressive
Effects of vasopressin injection into the anterior hypothalamic area in males and females
Voles and hamsters
males: increases offensive aggression
females: decreases
How are vasopressin neuron activation and vasopressin release correlated in rats, mice, hamsters, and voles?
positively correlated with aggression in male hamsters and voles
negatively correlated in male mice, rats
Effects of AVT and AVT antagonist in birds
- promotes aggression in presence of potential mate, but decreases territorial aggression
- Antagonist increases aggression in less aggressive males
What neurotransmitter is the major regulator of aggression? and evidence
- serotonin
- Low serotonin levels/ low serotonin receptor activation associated with high aggression (and vice versa)
- Depleting serotonin in brain increases offensive & defensive aggression
- Elevated serotonin levels (like with SSRIs) suppresses aggression in many species: mice, cats, monkeys, humans, lobsters
How do sex steroids affect aggression?
- by influencing serotonin signaling in brain areas associated with aggression (amygdala, BNST, VMH)
- they can change serotonin receptor gene expression, serotonin synthesis, serotonin reuptake on target neurons
Male mice typically attack another mouse unless……
estrous female promotes mating
WHen are VMH neurons more and less active?
- more active during aggression
- less active during mating
Stimulating VMH in presence of male vs estrous female
increases aggression/ causes attacks
fMRI results of male rats in presence of unfamiliar male
amygdala, cortex, hippocampus increased activity
How did vasopressin antagonist and serotonin antagonist before exposure to unfamiliar male affect results of male rats?
each reduced the activity in amygdala, cortex, hippocampus
Homeostasis
- maintenance of a “steady state” within an organism by means of physiological or behavioral feedback control mechanisms
- largely regulated by hormones; can be an entirely physiological process or combined behavioral & physiological processes
What are animals motivated to maintain?
a relatively constant internal environment (body temperature, sodium, water, other nutrients, pH)
Adrenalectomized rat
- no longer produces aldosterone
- cannot physiologically retain sodium and dies, but can behaviorally compensate by ingesting increased amounts of sodium
What happens when physiological homeostatic processes fail?
behavioral homeostatic processes are engaged to get back to homeostasis
Set point
a reference value for a regulated (physiological) variable
Things required for a system in homeostasis
- Reference value: set point for regulated variable
- Detection mechanism: to identify deviations from reference value
- Mobilization: be induced to make changes to return the regulated to the set point
- Negative feedback: to recognize when desired change occurs and shut down mobilization
Thirst definition and types
motivation to seek and ingest water; a psychological construct, so must be inferred from behavior
1. Osmotic: motivation to consume water caused by increased osmolality (concentration of salts) in the brain
2. Hypovolemic: motivation to consume water caused by lack of blood plasma volume (hemorrhage, diarrhea, excessive sweating)
Evidence that thirst is a psychological construct
Must be inferred from behavior –> Animals will work harder to receive water as duration of water deprivation increases
How can thirst in water deprived humans be measured?
using a rating scale: thirst sensations improved almost immediately after drinking
Hypovolemia
- low plasma volume
- causes the brain to signal the kidneys to produce renin
What does renin do?
converts angiotensinogen (in blood) into angiotensin (hormone)
What does angiotensin do?
- stimulates drinking behavior in rats
- Stimulates aldosterone from the adrenal gland
What does aldosterone release do?
retains sodium in the kidneys –> increases reabsorbed water and decreases excreted water –> BP increases
What does blocking angiotensin receptors do?
decreases drinking behavior
- What do SFO neurons mediate?
- Optogenetic activation of neurons in the SFO
- SFO neurons mediate thirst for water, not other ingestive behaviors
2.
* Triggers immediate drinking behavior
* Drives selective drinking, not feeding
* Drives selective drinking of water, not other fluids (mineral oil, glycerol, polyethylene glycol, honey)
Evidence that optogenetic drive to consume water is independent of the internal state of the animal
Reliably evoked even in fully water- satiated (not thirsty) mice
What happens when SFO neuron stimulation stops?
Drinking behavior quickly stops within a few seconds
What happens to SFO neurons when mouse is given increasing concentraions of saline?
What happens when it is given water?
- SFO neurons increase their activity dose-dependently given
- can sense osmolarity (through OVLT signaling)
- Water: OVLT and SFO neurons gradually decrease their activity
Detection vs. preference vs. aversion threshold of rat fluid balance
Detection: concentration at which a rat can tell the difference between water and saline
Preference: lowest concentration at which a rat prefers saline over water
Aversion: concentration at which a rat’s preference changes from saline to water
Intact vs adrenalectomized rats NaCl preference
Adrenalectomized rats
* exhibit same detection threshold as intact rats
* reduced preference threshold
* No aversion threshold (Strongly prefer saline because missing aldosterone and can’t normally conserve sodium)
How do estrogen and progesterone affect plasma volume?
evidence
- Estrogen increases plasma volume
- progesterone decreases plasma volume
- Estrogen birth control pills decreased the threshold for vasopressin release and drinking behavior in women that were dehydrated or infused with hypertonic saline
- estrogen receptors present in PVN and SON
Estrogen and progesterone modulate neural circuits that regulate thirst, water, and sodium intake
Why is food availability not constant?
seasonal and daily cycles in food availability
Dynamic relationship between energy acquisition and energy expenditure:
Food consumed > energy required > energy stored in adipose tissue
Behavioral and physiological homeostatic mechanisms exist to:
- Ensure there is a continuous supply of metabolic
- Promote long-term energy balance (keep body mass relatively fixed over time)
- Regulate short-term energy balance (switch on and off feeding behavior)
Evience that endocrine signals can stop feeding behavior
- Transplanting an extra stomach into a rat and feeding the transplanted stomach –> rat reduces its feeding behavior, even though its actual stomach is empty and the transplanted stomach has no neural connections
- Rats that receive a blood transfusion from rats that have been recently fed –> reduce eating behavior
- Sea slugs constantly eat anything smaller than themselves: their own eggs would normally be considered food, but the hormone that stimulates egg laying in sea slugs inhibits feeding behavior
- Injections of egg-laying hormone almost immediately stop feeding behavior and induce egg laying behavior
Leptin
- Produced by adipose cells
- Blood levels of leptin fall when stored fat is being metabolized, conveys information about fat levels to hypothalamus
- “Starvation” signal not “satiety” signal: stimulates food intake when leptin falls, decrease food intake when leptin increases
Insulin
- Produced by the pancreas
- Signals brain about peripheral levels of metabolic fuel (fat, carbohydrates)
- Infusion reduces food intake; directly (feeding behavior) and indirectly (effects on metabolic fuel availability, physiology)
Ghrelin
- Gut-derived hormone produced by the stomach
- only gut-derived hormone that increases food intake and body mass (all other gut- derived hormones reduce food intake and body mass)
- Ghrelin works in opposition to leptin/insulin: they exert opposite effects on brain
Cholecystokinin (CCK)
- made by the intestines
- “Satiety signal:” CCK receptors bind to nerve that projects from gut to dorsal hindbrain to stop feeding behavior; hunger experienced again when CCK binding stops
- Decreases food intake in hungry animals, but may be aversive/nauseating: increases learned aversion to saccharine in some rodent studies
Glucagon-like peptide-1 (GLP-1)
- Gut-derived hormone produced by the intestines
- Reduces food intake by affecting physiology: slows gastric emptying, inhibits glucagon release, stimulates insulin release
- Reduces food intake by affecting behavior: binds to GLP-1 receptors on nerve that projects from gut to dorsal hindbrain to stop feeding behavior
- GLP-1 analogs including semaglutide (Ozempic, Wegovy) are prescribed for type 2 diabetes and obesity
- 1 in 8 adults have taken GLP-1 analogs, over 4 in 10 adults with diabetes!
Metabolic hypothesis
- sensory system monitors metabolic fuel oxidation (changes in [ATP]) and changes food intake, energy expenditure, body fat storage to maintain a constant supply of metabolic fuel
- Integration of metabolic sensory systems and hormonal signals that control ingestive behavior
Energy balance circuit
- Leptin and insulin secreted in proportion to level of stored fat
- High levels of leptin and insulin inhibit feeding stimulatory circuit, activate feeding inhibitory circuit; low levels do the opposite
- Feeding circuits influence food intake and energy expenditure, which influences energy balance (and fat storage)
Optogenetic activation and inhibition of AgRP neurons
- happens in arcuate nucleus
- activation: triggers immediate feeding behavior even in well-fed mice
- inhibition: stops feeding behavior (triggers hypophagia) even in hungry mice
AgRP neural recording results
- AgRP neurons inhibited by food (they’re super active when hungry but once presented with food, they stop)
- POMC neurons are activated by food (they aren’t very active when you’re hungry but become active when you start eating)
AgRP and POMC neural recording depends on how hungry the animal is and the “hedonic value” of the food
- AgRP and POMC neurons barely respond to chow (regular food) when animal is full
- AgRP and POMC neurons respond more strongly to peanut butter than chow when the animal is hungry
- AgRP and POMC neurons strongly respond to peanut butter even when the animal is full
How do opioids affect food intake?
- regulate the hedonic (rewarding) aspects of eating
- modulate the mesolimbic dopaminergic reward pathway (ventral tegmental area, nucleus accumbens)
Opioid agonist injection into mesolimbic dopaminergic reward pathway
elicits feeding in completely satiated (full) animals
What do ingested sugars and fats release?
large amounts of endorphins (endogenous opioids)
Endorphin knockout mice characteristics
hyperphagic (eat a lot) and obese
What does Naloxone do?
- acts as opioid antagonist
- Reduces food intake in rodents and humans
- Reduces the hedonic value of food –> consumption less rewarding
- Treatment followed by ghrelin treatment still increases food intake: hedonic aspects of eating not essential compared to “hunger” aspects of eating
How does the liver generate signals for satiety?
can monitor changes in the concentration of insulin and metabolic fuel
Evidence that gonadal steroids influence feeding behavior
- Ovariectomy quickly increases food intake and body mass in rats; increases fat deposition and decreases locomotor activity
- Estrogen receptor knockout mice are hyperphagic (eat a lot) and obese
…………… is catabolic (increases energy expenditure, weight loss) but catabolic effects are blocked by ………….
- estrogen is catabolic
- blocked by progesterone
Why do mechanisms that control appetite for food influence reproductive behavior
to optimize reproductive success in environments with fluctuating energy availability
Ovariectomy + estrogen=
ovariectomy + progesterone
ovariectomy + estrogen+progesterone=
Ovariectomy + estrogen=
reverses obesity
the rest dont
What causes obesity in intact rats?
progesterone
Evidence: Ovarian steroids cycle with estrous cycles and seasonal reproductive cycles: correlated changes with eating and body weight
- Rats: high estrogen during proestrus reduces body mass and eating behavior; low estrogen during diestrus increases body mass and eating behavior
- Primates (monkeys, humans): food intake is higher during luteal phase (high progesterone)
- Hamsters, squirrels: increase their body mass in winter when estrogen is low, decrease their body mass in summer when estrogen is high
- Ensure that females give priority to eating when estrogen is low and give priority to mating when estrogen is high (most fertile)
What happens to ovariectomized rats when they are fed exactly the same amount as an intact rat or an ovariectomized + estrogen treated rat?
- still gain weight
- Effect on brain: estrogen implanted into the PVN or VMH of ovariectomized rats reduce food intake and body weight
- Effect on metabolism: adipose tissue contains estrogen and progesterone receptors, cannot store fat when exposed to estrogen, store more fat when exposed to estrogen and progesterone
How does fat deposition change during pregnancy?
Whats the evolutionary basis?
- increases during the first two trimesters of pregnancy (increasing estrogen and progesterone)
- decreases during the third trimester (prolactin increase inhibits adipose tissue storage of fat in all tissues but mammary glands)
- Evolutionary basis: lactation is extremely energy demanding, increased fat storage during pregnancy
Exogenous rhythms
driven by something outside organism
Endogenous
driven by something inside organism
De Mairan’s experiment
plants isolated from sun continue to open and close their leaves in synchrony with the day-night cycle, first recorded observation that rhythms are endogenous
Proof De Mairan’s experiment wasn’t “subtle geophysical cues”
- Animals in outer space have biological rhythms
- Animals maintained in adjacent, but separate, cages have stable rhythms with slightly different periods
- Period and phase of biological rhythms can be transplanted from one organism to another
- Period and phase of biological rhythms are heritable and depend on certain genes
How can circadian rhythms be measured in small mammals?
using running wheels connected to a computer, in humans using activity watches (“scientific fitbits)
What is the most potent environmental time cue?
light
or zeitgeber in mammals
What happens if an animal is placed in constant conditions without a zeitgeber?
- locomotor activity begins to drift
- ex: waking up ~15 min earlier (mice) or later (hamsters) each day (remember circadian = about a day, not exactly 24 h)
Free-running rhythm
- endogenous rhythm that is not synchronized to environmental cues
- Precise (lab mice have a free running period of 23.7 hours exactly) but not 24 hours
What happens if the environmental light-dark cycle is “phase shifted”?
- animals adapt their activity rhythms to the new light-dark cycle in a few days, but rhythms in other physiological processes (hormone secretion, body temperature, etc.) may require longer to adapt to the shift: jet lag!
(Brain shifts quickly but brain takes longer to adapt)
Ultradian rhythms
- biological rhythms that have a period of less than 24 h (a frequency of more than 1x/day)
- Are common: 90 min cycles of REM sleep, pulsatile secretion of hormones, bursts of activity and metabolism in small mammals
Infradian rhythms
- biological rhythms that have a period of greater than 24 h but shorter than a (lunar) month (a frequency of less than 1x/ day) (between 24 hrs and 1 month)
- Are rare: mostly associated with estrous cycles (4-5 d in rats), menstrual cycle in humans (only coincidentally similar to lunar month)
Nearly every behavior and physiological process has …………..
a circadian rhythm
Circadian system matures: ……
rhythms generally stabilized by:…….
- progressively
- stabilized by ~3 months of age
Circadian rhythms are not driven by
increased/decreased activity (being awake or asleep) –> still observed in bedridden patients in constant conditions
When does peak daily cortisol occur?
just prior to awakening –> increases blood pressure and cardiac output prior to the active phase of the day
When does peak body temperature occur?
in the mid-afternoon
Locomotor activity of fiddler crabs exhibit circatidal rhythms
- In the wild, move on the beach during low tide and return to their burrows during high tide
- In aquariums in constant conditions will become active at approximately the same time that low tide occurs at their capture site
- Exhibit a free-running period: close, but not exactly, 12.4 h
circalunar rhythms
- Nocturnal predators increase their evening activities around the time of a full moon, decrease around the time of a new moon; prey species show the opposite pattern
- Antlions hunt by building a steep pit made of sand, buries itself in pit and waits for ant to fall in so it can eat it
- Circalunar rhythm in pit building: in the laboratory in constant conditions, antlions dig bigger pits every ~29.5 days, corresponding to the full moon
Circannual rhythms: Palolo worms
- swim to the surface to release sperm and eggs only at sunrise on the last day of the last quarter of the moon in October, November, and December
- humans apparently know this and eat the worms
Circannual rhythms: “Grunion runs” in California
during the spring, a few days after the full moon, after high tide, female grunion fish swim onto shore, dig nests, lay eggs, males curve around the buried grunion and fertilize eggs
* humans apparently know this and catch the fish
Circannual rhythms: bird and mammal examples
- migratory patterns of birds, hibernation in many mammalian species
- In lab in constant conditions, birds and mammals exhibit 10-12 month patterns of weight gain, reproductive competence; pre-migratory restlessness in birds, hibernation in mammals
Adaptive function of biological clocks
Coordinate essential activities both with the appropriate time of day and with other individuals
What does destroying the circadian clock in the brain in ground squirrels do?
greatly increased the likelihood of being killed by a predator (inappropriate timing of daily activity)
Carolus Linneaus’s flower clock
different clocks bloom at different times of day depending on their biological clocks
What does the rotation of the earth result in?
periodic exposure to solar radiation, which causes predictable changes in light, temperature, humidity, etc.
Characteristics of circadian biological clocks: period
- Inherited (length from cycle to cycle)
- Relatively independent of temperature, chemical influence, and behavioral feedback
- Want a reliable clock. Not influenced by outside behavioral feedback
- Can only be entrained (synchronized) to limited cycle lengths
Evidence that single cells have the “machinery” to produce circadian rhythms
cyanobacteria
neurons isolated from the snail eye
neurons isolated from the mammalian hypothalamus
Approaches to identify the molecular machinery for circadian rhythmicity
Forward genetics: phenotype (behavior) to genotype (gene), giving animal a drug that promotes gene mutations, screening to see which animals have abnormal circadian rhythms, identifying gene responsible
Reverse genetics: genotype (gene) to phenotype (behavior), mutating or knocking out a gene and observing its effects on circadian rhythms
Using these approaches, the “circadian molecular clock” has been identified in fruit flies, hamsters, mice, plants, humans (although some of the specific genes differ between species)
In mammals, what are circadian rhythms coordinated by?
SCN: a group of neurons at the bottom of the hypothalamus right above where the optic nerves cross in the optic chiasm
Why was SCN a possible location of the circadian clock?
Because circadian rhythms can be entrained to light, and because the SCN has no known role in visual perception
What do bilateral lesions of the SCN do?
eliminate circadian rhythms in behavior: hamster with intact SCN is entrained to the light dark cycle and free runs in constant darkness, hamster with lesioned SCN is arrhythmic in a light dark cycle and in constant darkness
Mutant tau hamsters have a short free running period (~20 h vs. wild-type ~24 h)
* Lesion the SCN (animal goes arrhythmic) and transplant a “donor” SCN, circadian rhythms are restored
* Lesion the SCN of a tau (20 h) hamster and transplant a donor wild-type (24 h) hamster SCN, circadian rhythms in the recipient hamster become 24 h
* Lesion the SCN of a wild-type (24 h) hamster and transplant a donor tau (20 h) hamster SCN, circadian rhythms in the recipient hamster become 20 h
“clock gene” Per
- can be linked to a luciferase (bioluminescence) reporter: as PER is transcribed, more photons are produced, as PER is degraded, less photons are produced
- Circadian rhythms of bioluminescence (i.e., molecular clock cycling!) can be recorded from the SCN in culture for almost 2 years
