Behavioral Neuroscience, lecture on C start, startle responses in fish
USD Department of Biology
Behavioral Neuroscience
C-Start Behavior
Fundamentals of Neurocircuitry
Senstory Stimulus for Startle
Mauthner Cells - Response Gating
Mauthner Efferent output
Neuromuscular Function
Integration of C-Start Circuitry and Behavior
text:Kandel pages 180
Transmitter Figures
Figures of C-Start Behavior
C-Start Circuitry
end   Acronyms/Abbreviations
Escape Behavior
IV. Sensory Stimulus for Startle 	

	A. Startle response stimulated by acute vibratory movement of H2O
		1. as would happen with a sudden attack
		2. can be simulated by a falling golf ball
			a. lifting the test tank
			b. acoustic stimulation (sound)
		3. Mauthner cell inputs from vestibular, auditory & lateral line systems
	B. 1o sensory input from vestibular hair cells 
Lateral line vestibular neurons
		1. Fish hair cells s single Kinocilium

			a. at the apical  surface  

				i. does not regress as in mammals

		2. with numerous sterocilia

			a. embedded in a jelly-like protrusion: the cupula 
		3. hair cell is depolarized when sterocilia move toward the kinocilium

			a. hyperpolarized when sterocilia lean away from the kinocilium

		4. \ they detect water movements around the body

		5. signal travels via VIIIth cranial nerve

	C. axons synapse onto Club Endings of Mauthner Cells
		1. ipsilateral monosynaptic connection

			a.  and onto inhibitory interneurons
				i. decussates to contralateral Mauthner cell
		2. Club Endings: lateral dendrite area of Mauthner Cell 

			a. mixed Synapse: chemical and electrical
				i. rapid, but modifiable transduction of action potential
	D. Electrical Synapses
		1. Mechanical/electrically conductive link between neurons
			a. narrow gap 3.5 nm between presynaptic and postsynaptic cells
				i. 20-40 nm for chemical synapse
			b. Gap Junctions = channels made from connexins 

				i. contiguous cytoplasm
				ii. ions/current move directly between neurons
				iii. voltage of presynaptic cell depolarizes
				     the postsynaptic cell
					(1) no neurotransmitter release/
					     receptor transduction
					(2) \ 10X more rapid - 0.2 ms
						(a) chemical synapse 2 ms

    E. Chemical synapses = Glu (glutamatergic)

		1. Receptors: AMPA/Kainate, NMDA 
			a. subunits: GluR2/3/GluR5, NR1

		2. AMPA-NMDA coupling at synapes via postsyaptic density proteins
			a. NMDA current often depends on AMPA depolarization
			b. NMDA current augments postsynaptic potentials
			c. AMPA up-regulation/trafficking increases NMDA activation
				i. makes silent synapses active
	F. Mixed synapses - mixed EPSP (excitatory post synaptic potential)
		1. rapid depolarization (EPSP) due to 24,000-106,000 gap junction channels
			a. central portion of the terminal
			b. electrical synapses are bidirectional - do not rectify
				i. retrograde spread of dendritic depolarization
					(1) to presynaptic club endings
						(a) influences excitability
				ii. enhances synaptic potential evoked (see c. iii. (1))
			c. peripherally surrounding the termimal - chemical release - Glu
				i. may be chemically silent
				ii. more transmitter release at higher stimulus strengths
					(1) electrical cooperativity (see b. ii.)
		2. rapid initial current augmented by Glu stimulated EPSP
			a. initial depolarization may free NMDA-R of Mg++ blockage
			b. AMPA-R and Kainate-R also present
				i. also activate NMDA
			c. doubly potent chemical component to EPSP
		3. Increased stimulus strength increases active terminals
			a. 15-20% of total gap channels open usually
			b. High frequency stimulation of pVIIIth nerve can evoke LTP
				i. includes chemical and electrical component of EPSP
				ii. repetitive: 4-6 pulses at 500Hz, every 2 s, for 4 mins
					(1) Auditory stimuli in range of 200-800 Hz

		4. DA dependent Plasticity of dual synaptic potentials

			a. DA release near club ending terminals modulates
			    1o sensory input to Mauthner cells
			b. binds D1 receptors on Mauther cells
				i. activates cAMP dependent phosphoylation pathway
				ii. phosphoylates Glu receptors, gap junction proteins,
				    and/or their regulatory molecules
			c. Leads to enhancement of mixed EPSP
	G. Commissural Inhibitory Interneurons
		1. Excitation paired with inhibition of cells on the opposite side
		2. Inhibitions mediated by interneurons coupled to the Mauthner axon

V. Glutamate (Glu)- Excitatory Neurotransmission

VI. Dopamine (DA)

VII. Response Gating - Mauthner Cells