Important requirements for JAR:

1. Absolute value of the difference in frequency less than 20 Hz

2. Mixing of signals

3. Variation in mixing ratio

4. Modulation of phase and amplitude of the mixed signal

The regularity of the electric organ discharge is determined by an endogenous oscillator in medulla oblongata called the pacemaker nucleus (PN).

PN

EO

Electromotoneuron

Natural

Curare

Sine wave

100 hz

100 hz PN(f) = EOD (f)

Frequency varibleMay or may not beequal to PN(f)

EOD replaced by electric sine wave of similar amplitude and frequency

EOD mimic (Sine) of neighbor’s electric field

Result: Correct jamming avoidance behaviorLowers its pacemaker frequency if DF=(+)veRaises its pacemaker frequency if DF=(-)ve

Do not tell much about the behavioral mechanism involved in determining the sign of DF.

EOD mimics elicit JAR

sine

Frequency of the EOD mimic (Sine) was decreased to a frequency 50 Hz below the frequency of the pacemaker nucleus

When confronted with neighbor’s EOD mimic it responded as if this 50 Hz lower frequency was its own frequency.

NO INTERNAL REFERENCE Uses the electrical field frequency rather than internal frequency of the pacemaker nucleus

PN (f) = 300 hz, EOD mimic of self (Sine) = 250hz, EOD mimic of neighbor (Sine) = 254hz

Fish placed in two compartment chamberPectoral region sealedNo EOD could be detected by head regionJamming stimulus presented to the headNo JAR

JAR elicited when EOD leaked into head chamberJamming signal entered the tail chamber

Fish needs a mixture of its own signal and neighbor’s signal to execute JAR Electroreceptor

www.trilon.com/electricfish/

capacitor

AMimics of two EODs (Sine) were added and presented.Electrical fields had differentFrequency, but identical geometryNO VARIATION IN MIXINGRATIO OVER BODY SURFACE----NO JAR

Under natural situationelectrical fields vary both infrequency and geometryVARIATION IN MIXING RATIO-----JAR

Variation in mixing ratio

1:1

1:0.5

ELL: electrosensory lateral line lobe TS: torus semicircularis nE: nucleus electrosensorius PPn: prepacemaker nucleus Pn: pacemaker nucleus Electric organ

How are the behavioral rules for execution of a correct JAR implemented at the neural level?

Extraction of the sine of DF by electrosensory processing of phase and amplitude information

Translation of the determination of the sign of the DF into change of the motor output,that is of the pacemaker frequency

Electrosensory processing I: Electroreceptors

Ampullary receptors: Tuned to DC and low frequency AC signals of both biological and non biological sources.Used for ---- Prey detection Detection of earths magnetic field

Tuberous receptors: Tuned to AC signals with frequencies in the range of fish’s own EOD

P type: Fire intermittently and increase their rate of firing with rise in stimulus amplitude.T type: Fire one spike on each cycle of the stimulus.

Firing of T unitFiring of P unit

Electrosensory processing II:

Electrosensory lateral line lobe (hind brain)

Tuberous LateralCentrolateralCentromedial

Ampullary

Medial

Somatotopically ordered (preserves spatial order)Parallel processing (Ptype and Ttype information processed seperately)Inputs from several Ttype receptors are received by one sperical cell via electronic synapsePtype receptors form excitatory synapse onto basilar pyramidal cells and inhibitory synapseonto nonbasilar pyramidal cells (via exciting the granule cells)

Excitation of basilar pyramidal cells reflect rise in stimulus amplitudeInhibition of non basilar pyramidal cells reflect rise in stimulus amplitudeExcitation of non basilar pyramidal cells reflect fall of stimulus amplitude

Electrosensory processing III:

Torus semicercularis(midbrain)

Divided into laminaeSperical cells project onto laminae 6Encodes phase differences

Basilar and non basilar pyramidal cells project onto various laminaeEncodes phase and amplitude informationConvergence of amplitude and phase information is achieved by vertical connections between different layers

Electrosensory processing IV:Nucleus electrosensorius(Diencephalon)

Receives input from torus semicircularis

Somatotopic arrangement of the toral layers is lost in this area

Cells encode sign of DF

Cells of dorsal part of nE raises the EOD frequency--- nECells of ventral part of nE lowers the EOD frequency---nE

Lglutamate – stimulate dorsal cluster -- raises EOD frequencyLglutamate – stimulate ventral cluster -- lowers EOD frequency

Bilateral lesion of these two areas eliminate the frequency shift in the JAR.

Motor Control

nE innervates via excitatory synapses the CP/PPn-G in dorsal thalamus

PPn- prepacemaker nucleus is the dorsolateral portion of central posterior nucleus

CP/PPn-G innervates Pacemaker cells via AMPA type glutamate receptors

Lesion or CNQX application abolishes frequency rise due to –ve DF

CNQX- 6 cyano 7 nitroquinoxaline –2,3- dione

nE innervates via inhibitory synapses (GABA) the SPPn in mesencephalon

SPPn- sublemniscal prepacemaker nucleusSPPn innervates Relay cells via NMDA type glutamate receptors

Lesion or APV application abolishes lowering of frequency due to +ve DF

APV- 2 amino 5 phosphonovaleric acid

Final motor control achieved in the Pacemaker nucleus