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Behavioral Neuroscience 2 Homeoestasis & Thermoregulation (Thirst two…
Behavioral Neuroscience 2
Homeoestasis & Thermoregulation
Thirst
two kinds
2 kinds
Osmometric thirst
--> interstitial fluid = hypertonic
--> caused by: sweat, salty meal
--> relieved by: water intake
Osmoreceptors
--> mechanoreceptor
--> converts volume of fluid in cell into membrane potential, thus firing rate !!
lamina terminalis
--> anterior / rostral portion of ventral thrid ventricle (one around thalamus)
--> contains circumventricular organs (OVLT, SFO)
circumventricular organs = always outside blood brain barrier
OVLT (organum vasculosum of lamina terminales)
--> converts volume of fluid in cell into membrane potential, thus changes firing rate !!
stimulates magnocellular neurons paraventricular + supraoptic nucleus in lateral hypothalamus
synapse on blood vessel in posterior pituitary
vasopressine release!!
--> kidneys water retention
--> blood vessel constriction
SFO (subfornical organ)
--> ventral to commisure of fornix
--> converts volume of fluid in cell into membrane potential, thus firing rate !!
Brain activity if osmotic thirst
OVLT (bodily need for water)
ACC (conscious perception of thirst)
fMRI study (saline injection) OVLT and ACC lit up
participants reported thirst, drank --> ACC activity ceased
OVLT activity persisted (takes 20 minutes for water to be fully absorbed) mehh sounds bs lol
----> ACC = conscious perception of thirst
stops perception of thirst cause mechanoreceptors detect tension in stomach + osmoreceptors detect fluid (hypotension)
------> stops vasopressin production
Hypovolemic thirst
--> caused by: blood loss (hypovolemia), vomiting, too much urinating
--> occurs naturally with osmometric thirst (evaporation)
--> INDEPENDET OF OSMOMETRIC THIRST, BLOOD LOSS LOSES BOTH SOLUBLE AND WATER HENCE OSMOTIC PRESSURE SAME!!
-----> hence relieved by water and sodium intake together !! BOTH NEEDED!!
Kidneys
--> detect drop in blood pressure via barometric receptors
--> Renin is secreted
renin catalizes angiotensinogen into
Angiotensine I
--> (hormone)
Angiotensine II
--> hormone
---> stimulates aldosterone release in adrenal cortex kidneys (sodium retention)
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SFO (Subfornical organ below commisure of fornix)
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median preoptic nucleus
--> also receives input form OVLT
----> so integrates thirst info from SFO AND OVLT!! :D!!
--> leads to drinking
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Angiotenise II (peptide)
--> transformed from hormone to peptide by SFO
1 more item...
Heart
--> baroreceptors
vagus nerve
medulla
--> nucleus of solitary tract
hypothalamus
--> magno paraventricular + supraoptical
vasopressin
Diabetes insipitus
--> no vasopressine --> no water retention
--> constantly urinating and drinking water
drink too much when vasopressine levels high or lots of water retention can makes cells temporalily swell but meh BS lol
fluid balance
only two important for thirst
intracellular
intervascular
Intracelluar fluid
--> fluid inside the cells 67%
--> IMPORTANT FOR OSMOMETRIC THIRST!!
--> depends on solute concentration of interstitital fluid
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extracelluar fluid
--> fluids outside the cells
interstitital fluid
--> fluid surrounding and between the cells 26%
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--> mediates intracelluar fluid based on solute concentration
intervascular fluid
--> blood plasma 7%
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--> IMPORTANT FOR VOLUMETRIC THIRST
cerebrospinal fluid
--> fluid in ventricles and around brain, less than 1%
Osmosis
Hypertonic
--> higher sodium concentration in one fluid than another
--> draws water out of cell with less sodium concentration
Water lost through evaporation or salty meal
decreases water in interstitial fluid
increases salt concentration there cause now same amount of sodium in less liquid
draws water out of surrounding cells (intracellular fluids)
---> if too little water cells shrivel, less chemical reaction, cell death trying to achive isotonic state
Hypotonic
--> less sodium concentration in one fluid than another
--> draws water from less sodium concentration into higher sodium concentration fluid
Water gained through drinking or IV (intravenous administration)
Increases water in Interstitial fluid
decreases salt concentration there cause now same sodium but in more liquid
draws water into the surrounding cells cause now the sodium concentration in them is higher than the on in interstitial fluid
---> if too much water cells can rupture trying to reach isotonic state
Isotonic
--> same solute concentration on either side of membrane
--> equilibrium
Homeoestatis
set point
--> point of ideal functioning (not for food cause why so many ppl fat then?!)
--> deviation from set point triggers compensatory response (negative feedback loop)
motivation
--> positive incentive theory (sex, food, not so much temp and thirst)
temperature
variation
--> sleep
--> circadic rhythm
--> menstruation (for women)
--> Torpor
--> setpoint not fixed hence not really a set point lol !!
regulation
if too high:
--> less thyroid stimulating hormone
--> less vasopressin
detection by thermoreceptors
--> peripheal = TRPV1
--> central = pre optic area, anterior hypothalamus, spinal chord
endocrine response
parvocellualar neurons of hypothalamus
portal vein
anterior pituitary
LESS TSH (thyroid-stimulating hormone) = lower metabolism
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magnocelluar neurons of hypothalamus
--> (paraventricular nucleus + supraoptic nucleus)
synapse posterior pituitary bloodvessel
LESS vasopressine release = dilation of blood vessels
---> leads to cooling (mouse and tail that now conducts heat)
through more convection heat loss
---> lower blood pressure
.
behavioral change:
--> moving to cooler place, sweating, stretch out, lick fur
thermoreceptors
--> periphial and central
periphial
--> in skin and organs
--> TRP ion channel (transient receptor potentional)
TRPV1 = hot (capsin binds here, hence cillis = hot)
TRPM8 = cold (menthol binds here = cool)
central
--> receive input from peripheral thermoreceptors)
--> monitor local temp of blood
--> have hot and cold sensitive neurons that fire more strongly to preferred stimulus (hot/cold)**
pre-optic area (POA)
anterior hypothalamus (AH)
spinal chord
if too low:
--> same as above but:
periphial recepto = TRPM8
anterior pituitary = more TSH = higher metabolism
behavior = shivering,warmth seeking
posterior pituitary = MORE vasopressine = constriction of blood vessels = core body heat retention (no heat loss via extremities)
detection by thermoreceptors
--> peripheal = TRPM8
--> central = pre optic area, anterior hypothalamus, spinal chord
endocrine response
parvocellualar neurons of hypothalamus
portal vein
anterior pituitary
MORE TSH (thyroid-stimulating hormone) = higher metabolism
.
magnocelluar neurons of hypothalamus
--> (paraventricular nucleus + supraoptic nucleus)
synapse posterior pituitary bloodvessel
MORE vasopressine release = constriction of blood vessels
---> leads to core heat retention (no heat lost via extremities through convection ) (mouse no heat loss over tail)
---> higher blood pressure
.
behavioral change:
--> shivering, move to a warmer place huddle with others, be more active
Lesion in POA and AH
---> Autonomic and endocrine thermoregulation are disrupted, while behavioural thermoregulation is largely intact
Experiments:
Torpor
--> state of low body temp + low metabolism
--> less than 24 hours
--> gradual decrease in body temp until same as outside temp
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--> shows set point = adjustable so not really set point
Hibernation
---> multiple torpors for days (longer than 24 hours)
--> cells and dendrites retract (probs less energy so thats why)
---> --> instantly grow back when hibernation over :3 !!
Optogenetics
--> making ion channels light sensitive with CRISPR
implementation of SSFO [modified version of channelrhodopsin 2 (ChR2)] in heat preffering neurons in Pre-optic area (POA)
activation of heat sensitive POA area = increased firing rate of heat senitive neurons
lead to cool down response
--> strongly decreased adipose tissue heat production (LESS TSH thyroid = less metabolism)
--> strong blood vessel dilation (high vasopressine) thus heat loss via tail
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--> seeking cold area to cool down further
Stay cool live longer?
--> genetic mice
uncoupling protein 2
--> mitochondria produce heat instead of ATP!!
--> +0.6°C in hypothalamus
--> - 0.5°C body temp
--> lifespan higher 12 % males and 20% females
--> correlation not causation lol !!
Starvation = less body temp, cause less metabolism...
--> not good though !! epigenetics, starvation winter :P
ALSO DOESNT MEAN SHIT LOL !!!
so water and salt retention at this point :)!!