biological rhythms Flashcards
rhythm
any process that varies through time
-has a constant period
period
time interval
= length of time to complete one cycle
frequency
number of completed cycles per unit of time
cycle
repeating unit
phase
any point in a cycle
amplitude (strength/ intensity)
amount of change above or below the average value
exogenous
factors outside of the organism
endogenous
factors within the organism
circadian rhythm
period around 24 hours a day (ex: sleep wake cycle, body temperature)
ultradian rhythm
period less than 24 hours
ex: circatidal: 12.4 hours
infradian rhythms
period greater than 24 hours, less than 1 year
- circanular: moon phases
- ovulatory cycle
circannual rhythm
BR approximately 1 year
-ex: seasonal changes
Zeitberger
environmental time cue/temporal synchronizer
- something in the environment the cues internal rhythm to synchronize with external cue
- most primary zeitberger is light
free running
biological rhythms NOT synchronized by environmental cues
entrainment
synchronization of endogenous rhythms with periodic cue in the environment
reason for jet lag
MAJOR phase shift: quick adaptation of activity levels, but other rhythms/physiological rhythms/processes lead to a rapid phase shift
biological blocks
internal timing mechanisms that are responsible for generating rhythms and allowing entrainment to take place
arrhythmia
activity present but a lack of rhythm
-happens when SCN is lesioned
restoration of SCN rhythm
SCN tissue transplants–> restoration in circadian functioning in SCN lesioned recipient so that the period of the recipient’s rhythm matches that of the donor, regardless of the original rhythm
humoral output
diffusible signal responsible for LOCOMOTOR activity
- SCN transplant studies in hamsters
- SCN tissue transplanted into the brain of an arrhythmic, SCN lesioned hamster
- restored circadian rhythms but NOT endocrine function
- b/c no neural connectivity was re-established, hypothesized that rhythms in locomotor activity could be supported by diffusible SCN signal
- transplants sealed in semipermeable membrane
neural output
mediates ENDOCRINE function
eye pathway
light–> ganglion layer and inner retina to rods and cone photo receptors–> R’s and C’s send info to ganglion cells–> intrinsically photosensitive retinal ganglion cells contain melanospin–> encodes and transmits light information into the SCN via the RHT
SCN: central vs. peripheral oscillators
SCN acts a central oscillator and coordinates/acts as a master clock for the peripheral oscillators
-peripheral oscillators have different phase relationships and the SCN makes sure that these rhythms are properly synchronized
Estrogens and scalloping
on day of estrus, F hamsters in chronic dark conditions have an earlier onset of running behavior= phase advanced (rising levels of estrogens–> earlier onset of behavior)
scalloping can be eliminated via ovariectomy
but E replacement to OVX free running F rats–> decreased period of locomotor activity onset, suggesting direct effect of E on clock
Glucocorticoids CR
cortisol: highest in morning just when you wake (if nocturnal, highest post wake prior to activity onset)
corresponds with activity levels and locomotor activity
gonadotropins
LH
- patterns of LH release dependent on E feedback (+/-) and signals from SDN
- LH surge is a product of estradiol signals from the ovaries AND a circadian signal from the SCN
- SCN sends direct and indirect projections to GnRH system to appropriately time LH surge
Swann and Turek: Splitting
constant light–> split in activity levels so that there are 2 distinct LH pulses
- decreased period–> more LH pulses
- SDN controls activity of hormones, and when activity splits, you get a double hormone pattern
sex steroid hormones: estrogen and t CR
Estrogens: no CR
testosterone: CR of T in males that persists under constant conditions
Melatonin CR
=darkness hormone
- same pattern of release for diurnal and nocturnal animals: high at night, low in day
- light-dark cycle, NOT tied to activity levels
- secreted ONLY at night
- duration of melatonin secretion reflects lengths of photoperiod= day length
pathway of melatonin release
light–> melanospin expressing retinal ganglion cells–> RHT–> SCN–> PVN–> multi synaptic pathway–> pineal–>melatonin
enzymes that produce melatonin are inhibited when there is light
type 1 seasonal breeder
driven by endogenous and exogenous signals
ex: reproduction in Syrian golden hamsters
(breed in spring/summer, respond favorably to light (day=long) so when days get short, use that cue to shut down reproduction (b/c you don’t breed in winter b/c baby will be born in unfavorable conditions)
type 2 seasonal breeder
truly endogenous, driven by circannual clocks; without external cues, rhythm persists (ex: ground squirrel)
type 1 seasonal breeder syrian golden hamster example steps
- decrease in mating behavior is happening in the fall to the point where they are at reproductive quiescence (complete cessation of reproductive activity)
- photo refractory: will not respond to short day length–> increase in reproductive behaviors, happens end of winter/early spring
- photorefractoriness STOPS after exposure to long days
- photosensitivity: must be exposed to long days in order to show response to short days of fall and winter
SCN as a clock and calendar: melatonin example
clock: day vs. night pattern of melatonin
calendar: short day vs. long day pattern (seasonal)–> varies in duration
**SCN controls the rhythm of sexual activity and physiology b/c of DURATION of melatonin secretion determines the biological response
(gonads are smaller in the winter when melatonin duration is high, testes larger in summer when melatonin duration in low)
variations in breeding practices among short and long day breeders: interpretation of melatonin signals and relation to fertility
melatonin signal encoded differently by short and long day breeders (short day= sheep, long=hamster)
long days: eye–> RHT–> SCN–> pineal–> decrease M duration–> sheep will be anovulatory, hamster will be fertile
short days: sheep will be ovulatory, hamster will be infertile
hypothalamic interpretation of M will impact GnRH release, LH/FSH release, and release of ovarian/testicular hormones
if hypo interprets M as inhibitory
-lower GnRH–> lower FSH/LH–> lower sex hormones
if hypo interprets M as stimulatory
-higher GnRH–> higher FSH/LH–> higher sex hormones
short day breeder
-high duration of M–> enhance GnRH…
long day breeder
-low duration of M–> enhance GnRH…
estradiol, melatonin, long day and short day breeders, reproductive transitions
melatonin is altering estradiol feedback on AVPV and ARC
- seasonal reproductive transitions are a result of changes in ability of estradiol to inhibit GnRH
- Sheep: long days
- -estradiol–> inhibit GnRH–> decreased LH/FSH–> blocking ovulation (E has higher levels during long days)
Sheep during short days: estradiol concentrations go down, decreased negative feedback–> higher GnRH–> higher LH/FSH–> ovulation–> sex behavior
seasonal changes in ARC kisspeptin cells and GNRH neurons
- breeding season: increase in number of kiss1 cells in caudate
- and increase in % of GnRH cells with kiss 1 input
