203
injection of pancuronium bromide (0.1–0.4 mg in toadfish saline, dependent on fish
size) in the tail musculature prevented swimming movements of the tail, but the
opercula moved and aerated the gills normally. Opercular movements did not interfere with the recording of auditory afferent activity, but could modulate the activity
of lateral line cells in the medulla or bimodal cells (lateral line and auditory
responses) in the midbrain. Water temperature and oxygen levels were maintained
by replacing half of the water in the cylinder at 2 h intervals.
The shaker system produced movement of the entire dish in nanometer amounts,
simulating particle motion stimulation at biologically relevant levels. The attachment of the head-holder to the dish ensured that the fish moved with the dish, and
no water movement was induced around the fish by the stimuli. Thus, there was no
hydrodynamic flow around the fish and the lateral line system was not stimulated
unless we produced water movement around the fish using a glass pipette (to test for
lateral line responsiveness, see Edds-Walton and Fay 2005a).
The experiments that will be summarized in this chapter included physiological
recordings from (1) primary afferents as they exited the saccule, cells in (2) the
descending octaval nucleus (DON) and (3) the magnocellular octaval nucleus
(MON) in the medulla, and cells in (4) the auditory nucleus centralis (and the lateral
line nucleus ventrolateralis (NVL)) in the torus semicircularis of the midbrain (Fig.
2b, c). Although the surgical approach varied somewhat for each recording site, the
surgical procedures included the same initial steps. The dorsal skin and musculature
were removed and the dorsal braincase was scraped with dental tools until thin
enough to remove without damaging the underlying tissues or blood supply. The
required region of the otic capsule or the brain was exposed carefully and fluids
around the ear and brain were replaced by a clear, inert fluorocarbon (FC-77). Pulled
glass electrodes were mounted on a 3D micromanipulator and lowered into a branch
of the VIIIth cranial nerve, an octaval nucleus of the medulla, or the midbrain (based
on surface landmarks and confirmed by neurobiotin injections at recording sites).
For more details about the methods, please see the original papers (e.g., EddsWalton et al. 1999; Edds-Walton and Fay 2005b; Edds-Walton and Fay 2008).
3 Anatomy and Physiology of the Toadfish Auditory System
As noted earlier, the insights into auditory processing by oyster toadfish were
obtained over more than 20 years. The work that is summarized here is organized
anatomically from the periphery to the medulla to the midbrain. The peripheral
investigations were limited to the saccule, whose inputs to auditory processing sites
in the medulla had been confirmed anatomically by Highstein et al. (1992) and
Edds-Walton (1998a, b). Systematic investigations of auditory responsiveness were
not conducted on the utricle or the relatively small lagena due to technical difficulties in reaching their afferents consistently without altering their normal orientations in the otic capsule or encountering afferents from the semicircular canal cristae
that are also associated with those branches of VIII (see Fig. 3 in Edds-Walton
What the Toadfish Ear Tells the Toadfish Brain About Sound
injection of pancuronium bromide (0.1–0.4 mg in toadfish saline, dependent on fish
size) in the tail musculature prevented swimming movements of the tail, but the
opercula moved and aerated the gills normally. Opercular movements did not interfere with the recording of auditory afferent activity, but could modulate the activity
of lateral line cells in the medulla or bimodal cells (lateral line and auditory
responses) in the midbrain. Water temperature and oxygen levels were maintained
by replacing half of the water in the cylinder at 2 h intervals.
The shaker system produced movement of the entire dish in nanometer amounts,
simulating particle motion stimulation at biologically relevant levels. The attachment of the head-holder to the dish ensured that the fish moved with the dish, and
no water movement was induced around the fish by the stimuli. Thus, there was no
hydrodynamic flow around the fish and the lateral line system was not stimulated
unless we produced water movement around the fish using a glass pipette (to test for
lateral line responsiveness, see Edds-Walton and Fay 2005a).
The experiments that will be summarized in this chapter included physiological
recordings from (1) primary afferents as they exited the saccule, cells in (2) the
descending octaval nucleus (DON) and (3) the magnocellular octaval nucleus
(MON) in the medulla, and cells in (4) the auditory nucleus centralis (and the lateral
line nucleus ventrolateralis (NVL)) in the torus semicircularis of the midbrain (Fig.
2b, c). Although the surgical approach varied somewhat for each recording site, the
surgical procedures included the same initial steps. The dorsal skin and musculature
were removed and the dorsal braincase was scraped with dental tools until thin
enough to remove without damaging the underlying tissues or blood supply. The
required region of the otic capsule or the brain was exposed carefully and fluids
around the ear and brain were replaced by a clear, inert fluorocarbon (FC-77). Pulled
glass electrodes were mounted on a 3D micromanipulator and lowered into a branch
of the VIIIth cranial nerve, an octaval nucleus of the medulla, or the midbrain (based
on surface landmarks and confirmed by neurobiotin injections at recording sites).
For more details about the methods, please see the original papers (e.g., EddsWalton et al. 1999; Edds-Walton and Fay 2005b; Edds-Walton and Fay 2008).
3 Anatomy and Physiology of the Toadfish Auditory System
As noted earlier, the insights into auditory processing by oyster toadfish were
obtained over more than 20 years. The work that is summarized here is organized
anatomically from the periphery to the medulla to the midbrain. The peripheral
investigations were limited to the saccule, whose inputs to auditory processing sites
in the medulla had been confirmed anatomically by Highstein et al. (1992) and
Edds-Walton (1998a, b). Systematic investigations of auditory responsiveness were
not conducted on the utricle or the relatively small lagena due to technical difficulties in reaching their afferents consistently without altering their normal orientations in the otic capsule or encountering afferents from the semicircular canal cristae
that are also associated with those branches of VIII (see Fig. 3 in Edds-Walton
What the Toadfish Ear Tells the Toadfish Brain About Sound