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 PN(f) = EOD (f) Frequency varible May or may not be equal 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 behavior Lowers its pacemaker frequency if DF=(+)ve Raises 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 chamber Pectoral region sealed No EOD could be detected by head region Jamming stimulus presented to the head No JAR JAR elicited when EOD leaked into head chamber Jamming signal entered the tail chamber Fish needs a mixture of its own signal and neighbor’s signal to execute JAR Electroreceptor capacitor

A Mimics of two EODs (Sine) were added and presented. Electrical fields had different Frequency, but identical geometry NO VARIATION IN MIXING RATIO OVER BODY SURFACE----NO JAR Under natural situation electrical fields vary both in frequency and geometry VARIATION 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 unit Firing of P unit

Electrosensory processing II: Electrosensory lateral line lobe (hind brain) Tuberous Lateral Centrolateral Centromedial 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 synapse Ptype receptors form excitatory synapse onto basilar pyramidal cells and inhibitory synapse onto nonbasilar pyramidal cells (via exciting the granule cells) Excitation of basilar pyramidal cells reflect rise in stimulus amplitude Inhibition of non basilar pyramidal cells reflect rise in stimulus amplitude Excitation of non basilar pyramidal cells reflect fall of stimulus amplitude

Electrosensory processing III: Torus semicercularis (midbrain) Divided into laminae Sperical cells project onto laminae 6 Encodes phase differences Basilar and non basilar pyramidal cells project onto various laminae Encodes phase and amplitude information Convergence 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--- nE Cells of ventral part of nE lowers the EOD frequency---nE Lglutamate – stimulate dorsal cluster -- raises EOD frequency Lglutamate – 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 nucleus SPPn 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