275
The RECHABS consisted of a cylindrical habitat (12 cm internal diameter × 30 cm)
that opened onto an octagonal stage (16 cm per side), and served to receive the
telemetry signal and recharge the tag. Telemetry and recharging was possible whenever the fi sh was within the footprint of the RECHABS up to an elevation of approximately 15 cm above the stage. Magnetic induction fully powered the tag in less
than 30 s and provided telemetry for up to 20 min between charging. Alternatively,
the microwire electrodes were connected via a transdermal lead to a long, thin tether
(~2.0 m) that terminated into the head stage of the amplifi er outside of the tank.
Suffi cient slack remained in the cable to allow the toadfi sh to freely move around
the aquarium.
The electrodes were implanted chronically into the utricular or anterior lateral
line nerves. All implants were performed on anesthetized (MS-222) and paralyzed
(pancuronium bromide) toadfi sh. Extracellular potentials were differentially amplifi ed and monitored on a portable computer. The two recording channels that provided the highest fi delity signal were chosen for the experiments. Cyanoacrylate gel
was used to affi x the electrode to the skull and seal the craniotomy with the overlying tissue sutured to provide a watertight seal over the implant and around the transdermal electrode lead.
Immediately after surgery, the toadfi sh was placed in an opaque round fi berglass
tank (~1 m dia) with a water depth of 30 cm and left undisturbed for a minimum of
90 min, a time previously shown to eliminate any effects of anesthesia on neural
recordings (Palmer and Mensinger 2004 ). A University Sound UW-30 speaker (frequency response 80 Hz–10 kHz) was suspended vertically in the water column
approximately 80 cm from the fi sh, and a hydrophone was placed directly above the
toadfi sh head.
Pure tones and previously recorded male toadfi sh vocalizations were used as
auditory stimuli. The front of the RECHABS cylinder habitat was maintained 80 cm
from the speaker, and fi sh were only presented with sounds while in the habitat with
their head facing out near the opening. As the fi sh were free to move, small displacements inside the RECHABS of ±5 cm from the opening and/or ±5° left or right
were possible and allowed. However, if fi sh exited the habitat or retreated further
than 5 cm into the habitat, the experiment was suspended and the fi sh repositioned
in the cylinder. The habitats were rotated in 45° increments relative to the speaker
to test for directional sensitivity with the distance from the front of the habitat to the
speaker kept constant (i.e., the endorgans remained the same distance from the
speaker). For sound presentation to the lateral line, the habitat was removed to
streamline sound presentation and only the tether was used for recording.
Thresholds were determined for each test frequency along the axis of best directional sensitivity by starting with a supra-threshold intensity followed by decreasing
intensities until the afferent no longer responded to the stimulus. For the utricle
experiments, a calibrated hydrophone (Brüel and Kjær 8103 or High Tech HTI-94)
recorded the sound stimulus reaching the toadfi sh. Relative sound pressure levels
(SPL) were calculated for each frequency and intensity by measuring the root mean
square (rms) voltage at the position of the fi sh head and converted to SPL in dB rms
re: 1 μPa. For the lateral line experiments, the frequency response of the underwater
Multimodal Sensory Input in the Utricle and Lateral Line of the Toadfi sh, Opsanus…
The RECHABS consisted of a cylindrical habitat (12 cm internal diameter × 30 cm)
that opened onto an octagonal stage (16 cm per side), and served to receive the
telemetry signal and recharge the tag. Telemetry and recharging was possible whenever the fi sh was within the footprint of the RECHABS up to an elevation of approximately 15 cm above the stage. Magnetic induction fully powered the tag in less
than 30 s and provided telemetry for up to 20 min between charging. Alternatively,
the microwire electrodes were connected via a transdermal lead to a long, thin tether
(~2.0 m) that terminated into the head stage of the amplifi er outside of the tank.
Suffi cient slack remained in the cable to allow the toadfi sh to freely move around
the aquarium.
The electrodes were implanted chronically into the utricular or anterior lateral
line nerves. All implants were performed on anesthetized (MS-222) and paralyzed
(pancuronium bromide) toadfi sh. Extracellular potentials were differentially amplifi ed and monitored on a portable computer. The two recording channels that provided the highest fi delity signal were chosen for the experiments. Cyanoacrylate gel
was used to affi x the electrode to the skull and seal the craniotomy with the overlying tissue sutured to provide a watertight seal over the implant and around the transdermal electrode lead.
Immediately after surgery, the toadfi sh was placed in an opaque round fi berglass
tank (~1 m dia) with a water depth of 30 cm and left undisturbed for a minimum of
90 min, a time previously shown to eliminate any effects of anesthesia on neural
recordings (Palmer and Mensinger 2004 ). A University Sound UW-30 speaker (frequency response 80 Hz–10 kHz) was suspended vertically in the water column
approximately 80 cm from the fi sh, and a hydrophone was placed directly above the
toadfi sh head.
Pure tones and previously recorded male toadfi sh vocalizations were used as
auditory stimuli. The front of the RECHABS cylinder habitat was maintained 80 cm
from the speaker, and fi sh were only presented with sounds while in the habitat with
their head facing out near the opening. As the fi sh were free to move, small displacements inside the RECHABS of ±5 cm from the opening and/or ±5° left or right
were possible and allowed. However, if fi sh exited the habitat or retreated further
than 5 cm into the habitat, the experiment was suspended and the fi sh repositioned
in the cylinder. The habitats were rotated in 45° increments relative to the speaker
to test for directional sensitivity with the distance from the front of the habitat to the
speaker kept constant (i.e., the endorgans remained the same distance from the
speaker). For sound presentation to the lateral line, the habitat was removed to
streamline sound presentation and only the tether was used for recording.
Thresholds were determined for each test frequency along the axis of best directional sensitivity by starting with a supra-threshold intensity followed by decreasing
intensities until the afferent no longer responded to the stimulus. For the utricle
experiments, a calibrated hydrophone (Brüel and Kjær 8103 or High Tech HTI-94)
recorded the sound stimulus reaching the toadfi sh. Relative sound pressure levels
(SPL) were calculated for each frequency and intensity by measuring the root mean
square (rms) voltage at the position of the fi sh head and converted to SPL in dB rms
re: 1 μPa. For the lateral line experiments, the frequency response of the underwater
Multimodal Sensory Input in the Utricle and Lateral Line of the Toadfi sh, Opsanus…