Behavioral Neuroscience Summers

Rhythmicity & Behavior Sensory input for Rhythmicity Afferent path to the SCN Figures of Rhythmicity Retina-RGC-SCN

Circadian Rhythms Efferent SCN output Integration of Rhythms into Behavior Molecular SCN end  Acronyms/Abbreviations   Syllabus

Glu VIP AVP GABA 5-HT

BIOLOGICAL RHYTHMS
I. Behavior of Rhythmicity 			

	A. Behavioral and Physiological responses exhibit predictable
	   changes over time
	   
	   	1. Rhythmically repeating responses 
		
			a. oscillations with periods from milliseconds to years
			
			b. complement environmentally salient events
			
				i. e.g. seasons, daybreak, high tide
			
			c. merge physiological functions
			
				i. e.g. HPA (stress hormone) acrophase and wakefulness
				
				ii. e.g. activity and body temperature
		
		2. Biologically adaptive


	B. Increased efficiency - Energy Management

		1. most animals and plants follow a pattern of either
		   diurnally or nocturnally increased metabolic activity

		2. Advantages:

			a. decreased
			
				i. total energy expenditure, predator presence

			b. increased 

			   	i. availability of moisture (dew), photosynthesis
				   metabolic turnover for poikilotherms,
				   prey availability

			c. hibernation/migration
			

	C. Periodicity

		1. Yearly/Seasonally
		
			a. even multiple years

		2. Monthly/lunar cycle

		3. two weeks

		4. daily, Diurnal or Nycthemeral

		5. shorter than one day
		
			a. a variety


	D. Origin of Rhythmicity

		1. exogenous rhythms

			a. passive reaction to peroidic input from the environment


		2. enodogenous rhythms

			a. internally driven

				i. oscillator(s)

					(1) biological clock(s)
					

			b. Entrainable

				i. can be made to match current env. pattern

					(1) setting or resetting biological clocks 

				ii. zeitgeiber = time giver

					(1) often light (always in birds)(solar & lunar)

					(2) also temperature, moisture, water pressure,
					    sound, food availability, greeness, magnatism,
						gravity, others?


				iii. window(s) for clock setting sensitivity

					(1) night sensitivity greatest
					
						(a) morning sensitivity also high

					(2) resetting jet-lag easiest going from east to west


			c. free running period

				i. length of cycle without zeitgeibers

					(1) varies from species to species

					(2) varies between individuals


				ii. Circannual Rhythms       about a year

				iii. Circalunar              28 days

				v. Circatidal

					(1) Spring/Neap           13-14 days

					(2) Daily High/Low        12 - 13 h

				vi. Circadian Rhythms         23 to 28 h

				vii. Ultradian rhythms        shorter than 24 h

					(1) pulsatile             seconds/minutes/ 1 hour


	E. Oscillators

		1. Most cells have a free-running periodicity

		2. suprachiasmatic nucleus (SCN)

			a. primary oscillator
			
				i. master clock
				
					(1) organizes other oscillators
					
					(2) synchronizes other oscillators

				ii. located just above the optic chiasm in the
				    hypothalamus
					
					(1) core and shell regions


		3. other oscillators: retina, pineal, habenula,
		   other hypothalamic nuclei


		4. Frequency and Phase 

			a. frequency = period = length of one cycle


			b. phase = instantaneous state of an oscillation

				i. acrophase = peak in the cycle

					(1) nadir = low point 

				ii. phase shifting

					(1) acrophase may change to another time of day

				iii. altering the frequency automatically
				     shifts the phase
				
				iv. phase angle = difference in phase between 
				    2 oscillations


		4. Multiple vs Single oscillator systems

			a. variable rhythm periodicity within an organism

				i. circa: annual, lunar, tidal, dian

			b. phase synchronization

				i. two or more rhythms with the same or complementary frequency and phase

				ii. desynchronization: rhythms may be phase
				    shifted under strong zeitgeiber influence

				iii. yearly patterns may be related to circadian patterns
				     with different frequencies or different zeitgeibers
					 that come into phase once a year

			c. split rhythms

				i. bimodal patterns


	F. Examples

		1. Circannual: reproduction, migration, hibernation,
		   molting, antler growth, rut, courting, nesting,
		   parental behavior, dispersal

		2. Circalunar: gruion feeding, rectal temperatures,
		   menstrual cycles

		3. Circatidal: oysters opening shell valves,
		   crab feeding/locomotion

		4. Circadian: sleeping/wakefulness, HPA axis, activity,
		   body temperature

		5. Ultradian: pulsatile hormone release - GnRH, LH, FSH, CRH,
		   ACTH, B