Transcript Document

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
100 hz
Electromotoneuron
Natural
EO
100 hz
PN(f) = EOD (f)
Curare
Sine wave
Frequency varible
May or may not be
equal to PN(f)
EOD mimics elicit JAR
sine
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.
NO INTERNAL REFERENCE Uses the electrical field frequency
rather than internal frequency of the pacemaker nucleus
Frequency of the EOD mimic (Sine) was decreased to a
frequency 50 Hz below the frequency of the pacemaker nucleus
PN (f) = 300 hz, EOD mimic of self (Sine) = 250hz,
EOD mimic of neighbor (Sine) = 254hz
When confronted with neighbor’s EOD mimic it responded as
if this 50 Hz lower frequency was its own frequency.
Fish needs a mixture of its own signal and neighbor’s
Electroreceptor
signal to execute JAR
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
www.trilon.com/electricfish/
capacitor
Variation in mixing ratio
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
1:1
Under natural situation
electrical fields vary both in
frequency and geometry
VARIATION IN MIXING
RATIO-----JAR
1:0.5
How are the behavioral rules for execution of a correct JAR implemented at
the neural level?
ELL:
electrosensory
lateral line lobe
TS: torus
semicircularis
nE: nucleus
electrosensorius
PPn:
prepacemaker
nucleus
Pn: pacemaker
nucleus
Electric organ
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
Ampullary
Lateral
Centrolateral
Centromedial 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