- Email: [email protected]
Properties and distribution of anterior VIIIth nerve excitatory inputs to the goldfish Mauthner cell
Brain Research, 174 (1979) 319-323 © Elsevier/North-Holland Biomedical Press
319
Properties and distribution of anterior Vlllth nerve excitatory inputs to the goldfish Mauthner cell
STEVEN J. ZOTTOLI and DONALD S. FABER Division of Neurobiology, Department of" Physiology, State University of New York, Buffalo, N.Y. 14214 and Research Institute on Alcoholism, Buffalo, N. Y. 14203 (U.S.A.)
(Accepted June 14th, 1979)
Key words: Mauthner cell - - VIllth nerve - - synaptic localization - - vestibular
system - - auditory system
The goldfish Mauthner cell (M-cell) is known to initiate a rapid startle response to auditory stimulation~, 9,15. The presumed pathway for this activation is from the sacculus and lagena by way of the posterior branch (VIIIp) of the VIllth nerve. On gross stimulation of this ramus, Furshpan 6 was able to localize a powerful electrotonic component of the compound excitatory postsynaptic potential (EPSP) to the distal lateral dendrite. He further concluded that this input originated from the segregated projection of large myelinated club endings to this area 1°,11,13. However, there is little comparable morphological or electrophysiological evidence on the projections from the anterior branch (VllIa) to the M-celV4,16. As these two nerve branches are thought to transmit functionally distinct sensory information, we have compared the properties and distribution of their excitatory inputs to the M-cell. The results demonstrate that VIIIa input is predominantly chemically mediated and localized on the soma and proximal lateral dendrite. Electrophysiological experiments were conducted on common goldfish, 12-18 cm in total length, using standard surgical and recording techniques v. Intracellular recordings were obtained with glass microelectrodes filled with either 2.7 M KCI or 0.6 M K2SO4. Stimulating electrodes, placed on VIIIa and VIIIp for orthodromic activation of the M-cell, were equidistant from the entry of these nerves into the brain (approximately 1.5 ram). The M-cell was first located by its large antidromically activated extracellular spike recorded in the axon cap (Fig. IA, B). Subsequent intracellular penetrations were made at the M-cell soma and lateral dendrite as far as 450 #m lateral to the axon cap. Records from one such penetration, 158/~m lateral, are shown in Fig. I. The antidromic spike (Fig. IC) is about 30 mV, which is consistent with its passive electrotonic conduction distal to the axon hillock~, 7.
320
c
'
°°,
I} lmsec
>
lmsec
Fig. 1. Monosynaptic PSPs recorded in the M-cell following stimulation of the anterior VIIIth nerve. A: schematic diagram of the goldfish M-cell, its axon cap (dashed lines) and the recording and stimulation arrangement. The placement of separate stimulation electrodes on different VIIIth nerve rami is not shown. B: the axon cap was located by maximizing the extracellular antidromic M-spike amplitude. The sites of subsequent M-cell penetrations were then measured relative to this focus. C-F: intracellular M-cell responses taken from a single experiment. C: the passively propagated antidromic impulse. D and E: upper traces are EPSPs evoked by stimulation of the anterior (VIIIa) and posterior (VIIIp) branches of the VIIIth nerve, respectively. Note that the VIlIp EPSP consists of two main peaks (arrows), due to electrotonic and chemical excitatory inputs. Lower traces are the corresponding fields recorded just extracellular to the M-cell. F: the responses of D and E are superiml~osed in order to emphasize the marked difference in the electrotonic inputs from the two branches. EPSPs evoked by stimulation of V I I I a (Fig. 1D) had a monosynaptic latency (0.56 msec 4- 0.15, mean 4- S.D.; n = 15), which is significantly longer than that of the early electrotonic c o m p o n e n t following V I I I p stimulation ( < 0.25 msec, e.g. Fig. 1E). The V i l l a EPSP recorded proximally was occasionally preceded by a small electrotonic PSP no more than 1 0 - 1 5 ~ the amplitude of the d o m i n a n t chemical c o m p o n e n t (e.g. Fig. 2A2) and might have been due to spread of the stimulating current to the posterior branch. In contrast, at comparable recording sites, the electrotonic and chemical PSPs followir~g V I I I p stimulation were generally o f equal amplitude, although the former could even be dominant, as in Fig. 1E. Superimposed traces in Fig. 1F clearly demonstrate the difference in the waveforms of the responses to the two nerve branches. It was difficult to directly compare the latencies of the presumed chemical components since that evoked by V I I I p stimulation is partially masked by the preceding electrotonic PSP; their peak times relative to stimulus onset were essentially the same (Villa: 0.89 4- 0.19 msec, n = 15; V I l I p : 0.91 4- 0.08 msec, n = 15). Spatial distributions of the V I I I a EPSPs are illustrated for a typical experiment in the recordings and graphs of Fig. 2. In this case the M-cell was penetrated successively at 6 sites lateral to the axon cap. EPSP amplitudes at two stimulus strengths, maximal (voltage required to give the largest EPSP; Fig. 2A1-D and halfmaximal, were normalized with respect to the largest response obtained at a given strength. These values, along with the antidromic spike amplitude normalized relative to its value in the soma, are plotted in Fig. 2B. N o t e that the EPSP amplitudes were
321
A1
A2
A3
A4 III
611
C
B
As lmsec
1.0.
~.0-
O.
:v,,,,: N
o__o
0.~
=
~0.2-
• AD Spike
~•_•
O
Maximal and 1/2Maximal
05
Z
~0
| 250 | ' 4i0 ~um lateral to Axon Cap
50
II 250 a 4~0 ~m lateral to Axon Cap
Fig. 2. Spatial distribution of excitatory VlIIa inputs to the M-cell. VIlIa EPSPs were recorded at 71, 212,250, 320 and 447/gin lateral to the axon cap in A1-As, respectively. Uneven distances are due to the necessity of making compensating posterior moves when the electrode is displaced laterally. In all records at least two responses are superimposed. Note that the cell fires once in A2. B : EPSP and antidromic spike amplitudes plotted as functions of distance lateral to the axon cap. EPSP amplitudes were normalized with respect to the largest response recorded following stimulation at a given strength, and spike amplitude was normalized relative to its value at the soma. Note that for both stimulation strengths (defined in text) the location of maximal EPSP amplitudes indicates a proximal lateral dendrite input. The decrement in spike height laterally is due to the passive cable properties of this dendrite, C: a plot of the normalized amplitude difference between VlIla EPSPs evoked by maximal and half-maximal stimulus strengths, indicating that increasing stimulus strength recruited a distinct fiber population projecting to a localized dendritic region.
largest 200-250 /~m lateral to the axon cap and decremented distally while the a n t i d r o m i c spike height decayed lateral to the soma. The V I I I a excitatory inputs in this experiment were thus distributed p r i m a r i l y on the p r o x i m a l lateral dendrite. In 5 a d d i t i o n a l experiments V I I I a i n p u t was also distributed over the s o m a a n d p r o x i m a l lateral dendrite with there being no suggestion o f a significant distal projection m o r e t h a n 2 7 0 / ~ m lateral to the axon cap. In 3 cases, there was a shift in the potential profiles when V I I l a stimulus strength was increased from h a l f - m a x i m a l to maximal. The distributions o f the incremental responses showed a sharp p e a k in the region o f 180-255 # m lateral to the axon cap, indicating recruitment o f a distinct fiber p o p u l a t i o n projecting to this specific region. This is illustrated in Fig. 2C, which is a plot o f the incremental profile from the experiment o f Fig. 2A, B. This discrete focus is found j u s t p r o x i m a l to the medial limit o f the large m y e l i n a t e d club ending projection 2,l°,16 and therefore provides evidence for a second input t h a t is m o r p h o logically segregated on the lateral dendrite. It is n o t clear whether this t e r m i n a t i o n p a t t e r n represents a localization o f fibers which originate from one division o f the labyrinth (e.g. otolithic m a c u l a e or semicircular canal cristae) or which are r a t h e r from functionally c o r r e s p o n d i n g parts o f m o r e than one o f these areas.
322
A
B
¢
1reset 1reset
Fig. 3. Excitatory nature of the VIIIa input. A-C: intracellular recordings obtained from the M-cell soma. Subthreshold EPSPs were elicited by stimulation of VIIIp in A and VIlla in B. C: when the two stimuli in A and B were combined, the resultant PSP evoked an orthodromic impulse (arrow) in the M-cell. Upper and lower traces : high-gain AC and low-gain DC records, resl~ectively.In all records at least two responses are superimposed. The maximal V I I I a EPSP was generally too small to bring the M-cell to threshold (Fig. 3B; but see Fig. 2A2). However, its excitatory nature could be demonstrated by pairing it with a subthreshold response to V H I p stimulation (Fig. 3A). Under these conditions, the two summated and evoked an orthodromic spike (arrow in Fig. 3C). Timing of the two stimuli was critical, as V I I l a stimulation also produces a polysynaptic inhibition of the M-cell (unpublished observations) which can block orthodromic activation of the neuron. To ensure that the synaptic potentials recorded were not a result of current spread to neighboring cranial nerves 16 recordings were obtained before and after cutting the V I I I a branch. This procedure eliminated the V i l l a EPSP but did not alter that from the posterior branch. Therefore, current spread to other nerves was not a major source of the inputs attributed to VIIIa. Goldfish display a rapid M-cell initiated startle response to sounda,9, la. The sacculus and lagena of cyprinids contain primarily auditory receptorsl,4,sA2; these otolithic organs are innervated by the posterior branch of the VIIIth nerve. O n the other hand, the utriculus is involved in the maintenance of equilibrium 5 (see ref. 8 for review), with its afferents confined to the anterior ramus. The combined behavioral and morphological evidence is therefore consistent with the observed functional and physiological differences between anterior and posterior VIIIth nerve inputs to the Mcell. Although input activity in both might be expected to modulate M-cell excitability, synchronous activity in the latter is more likely to produce the rapid excitation of the M-cell which underlies the startle response. Finally, evidence for discretely localized projections of anterior VIIIth nerve fiber populations provides a basis for further investigation of the functional specification of afferent connections to the M-cell. We t h a n k K. Davis and J. Lakatos for help with the figures and J. Jordan for secretarial assistance. This research was supported in part by N I H Postdoctoral Fellowship F 32
323 N S 5 2 8 2 t o D r . S t e v e n J. Z o t t o l i a n d b y P H S
Grant
NS
12132 t o D r . D o n a l d
S.
Faber.
1 Bigelow, H. B., The sense of hearing in the goldfish, Cara.~ius auratus L, 4mer. Nat., 38 (1904) 275-284. 2 Diamond, J., The activation and distribution of GABA and L-glutamate receptors on goldfish Mauthner neurones: an analysis of dendritic remote inhibition, J. Physiol. (Lond.), 194 (1968) 669-723. 3 Eaton, R. C., Bombardieri, R. A. and Meyer, D. L., The Mauthner-initiated startle response in teleost fish, J. exp. Biol., 66 (1977) 65-81. 4 Fay, R. R. and Olsho, L. W., Discharge patterns of lagenar and saccular neurones of the goldfish eighth nerve: displacement sensitivity and directional characteristics, Comp. Biochem. Physiol., 62A (1979) 377-386. 5 Frisch, K., von, The sense of hearing in fish, Nature (Lond.), 141 (1938) 8-11. 6 Furshpan, E. J., 'Electrical transmission' at an excitatory synapse in a vertebrate brain, Science, 144 (1964) 878 880. 7 Furshpan, E. J. and Furukawa, T., Intracellular and extracellular response of the several regions of the Mauthner cell of the goldfish, J. NeurophysioL, 25 (1962) 732-771. 8 Lowenstein, O., The labyrinth. In W. S. Hoar and D. J. Randall (Eds.), Fish Physiology, Academic Press, New York, 1971, pp. 207-263. 9 Mueller, T. J., Factors modulating the occurence and direction of the startle response in goldfish, Neurosci. Abstr., 4 (1978) 363. 10 Nakajima, Y., Fine structure of the synaptic endings on the Mauthner cell of the goldfish, J. camp. Neurol., 156 (1974) 375~-02. 11 Nakajima, Y. and Kohno, K., Fine structure of the Mauthner cell: synaptic topography and comparative study. In D. S. Faber and H. Korn (Eds.), Neurobiology afthe Mauthner cell, Raven Press, New York, 1978, pp. 133-166. 12 Popper, A. and Fay, R. R., Sound detection and processing by teleost fishes: a critical review, J. aeoust. Soc. Amer., 53 (1973) 1515-1529. 13 Robertson, J. D., Bodenheimer, T. S. and Stage, D. E., The ultrastructure of Mauthner cell synapses and nodes in goldfish brains, J. Cell Biol., 19 (1963) 159-199. 14 Zottoli, S. J., Comparison of anterior and posterior Vlllth nerve input to the goldfish Mauthner cell, Neurosci. Abstr., 3 (1977) 547. 15 Zottoli, S. J., Correlation of the startle reflex and Mauthner cell auditory responses in unrestrained goldfish, J. exp. Biol., 66 (1977) 243 254. 16 Zottoli, S. J., Comparative morphology of the Mauthner cell in fish and amphibians. In D. S. Faber and H. Korn (Eds.), Neurobiology of the Mauthner Cell, Raven Press, New York, 1978, pp. 13-45.
319
Properties and distribution of anterior Vlllth nerve excitatory inputs to the goldfish Mauthner cell
STEVEN J. ZOTTOLI and DONALD S. FABER Division of Neurobiology, Department of" Physiology, State University of New York, Buffalo, N.Y. 14214 and Research Institute on Alcoholism, Buffalo, N. Y. 14203 (U.S.A.)
(Accepted June 14th, 1979)
Key words: Mauthner cell - - VIllth nerve - - synaptic localization - - vestibular
system - - auditory system
The goldfish Mauthner cell (M-cell) is known to initiate a rapid startle response to auditory stimulation~, 9,15. The presumed pathway for this activation is from the sacculus and lagena by way of the posterior branch (VIIIp) of the VIllth nerve. On gross stimulation of this ramus, Furshpan 6 was able to localize a powerful electrotonic component of the compound excitatory postsynaptic potential (EPSP) to the distal lateral dendrite. He further concluded that this input originated from the segregated projection of large myelinated club endings to this area 1°,11,13. However, there is little comparable morphological or electrophysiological evidence on the projections from the anterior branch (VllIa) to the M-celV4,16. As these two nerve branches are thought to transmit functionally distinct sensory information, we have compared the properties and distribution of their excitatory inputs to the M-cell. The results demonstrate that VIIIa input is predominantly chemically mediated and localized on the soma and proximal lateral dendrite. Electrophysiological experiments were conducted on common goldfish, 12-18 cm in total length, using standard surgical and recording techniques v. Intracellular recordings were obtained with glass microelectrodes filled with either 2.7 M KCI or 0.6 M K2SO4. Stimulating electrodes, placed on VIIIa and VIIIp for orthodromic activation of the M-cell, were equidistant from the entry of these nerves into the brain (approximately 1.5 ram). The M-cell was first located by its large antidromically activated extracellular spike recorded in the axon cap (Fig. IA, B). Subsequent intracellular penetrations were made at the M-cell soma and lateral dendrite as far as 450 #m lateral to the axon cap. Records from one such penetration, 158/~m lateral, are shown in Fig. I. The antidromic spike (Fig. IC) is about 30 mV, which is consistent with its passive electrotonic conduction distal to the axon hillock~, 7.
320
c
'
°°,
I} lmsec
>
lmsec
Fig. 1. Monosynaptic PSPs recorded in the M-cell following stimulation of the anterior VIIIth nerve. A: schematic diagram of the goldfish M-cell, its axon cap (dashed lines) and the recording and stimulation arrangement. The placement of separate stimulation electrodes on different VIIIth nerve rami is not shown. B: the axon cap was located by maximizing the extracellular antidromic M-spike amplitude. The sites of subsequent M-cell penetrations were then measured relative to this focus. C-F: intracellular M-cell responses taken from a single experiment. C: the passively propagated antidromic impulse. D and E: upper traces are EPSPs evoked by stimulation of the anterior (VIIIa) and posterior (VIIIp) branches of the VIIIth nerve, respectively. Note that the VIlIp EPSP consists of two main peaks (arrows), due to electrotonic and chemical excitatory inputs. Lower traces are the corresponding fields recorded just extracellular to the M-cell. F: the responses of D and E are superiml~osed in order to emphasize the marked difference in the electrotonic inputs from the two branches. EPSPs evoked by stimulation of V I I I a (Fig. 1D) had a monosynaptic latency (0.56 msec 4- 0.15, mean 4- S.D.; n = 15), which is significantly longer than that of the early electrotonic c o m p o n e n t following V I I I p stimulation ( < 0.25 msec, e.g. Fig. 1E). The V i l l a EPSP recorded proximally was occasionally preceded by a small electrotonic PSP no more than 1 0 - 1 5 ~ the amplitude of the d o m i n a n t chemical c o m p o n e n t (e.g. Fig. 2A2) and might have been due to spread of the stimulating current to the posterior branch. In contrast, at comparable recording sites, the electrotonic and chemical PSPs followir~g V I I I p stimulation were generally o f equal amplitude, although the former could even be dominant, as in Fig. 1E. Superimposed traces in Fig. 1F clearly demonstrate the difference in the waveforms of the responses to the two nerve branches. It was difficult to directly compare the latencies of the presumed chemical components since that evoked by V I I I p stimulation is partially masked by the preceding electrotonic PSP; their peak times relative to stimulus onset were essentially the same (Villa: 0.89 4- 0.19 msec, n = 15; V I l I p : 0.91 4- 0.08 msec, n = 15). Spatial distributions of the V I I I a EPSPs are illustrated for a typical experiment in the recordings and graphs of Fig. 2. In this case the M-cell was penetrated successively at 6 sites lateral to the axon cap. EPSP amplitudes at two stimulus strengths, maximal (voltage required to give the largest EPSP; Fig. 2A1-D and halfmaximal, were normalized with respect to the largest response obtained at a given strength. These values, along with the antidromic spike amplitude normalized relative to its value in the soma, are plotted in Fig. 2B. N o t e that the EPSP amplitudes were
321
A1
A2
A3
A4 III
611
C
B
As lmsec
1.0.
~.0-
O.
:v,,,,: N
o__o
0.~
=
~0.2-
• AD Spike
~•_•
O
Maximal and 1/2Maximal
05
Z
~0
| 250 | ' 4i0 ~um lateral to Axon Cap
50
II 250 a 4~0 ~m lateral to Axon Cap
Fig. 2. Spatial distribution of excitatory VlIIa inputs to the M-cell. VIlIa EPSPs were recorded at 71, 212,250, 320 and 447/gin lateral to the axon cap in A1-As, respectively. Uneven distances are due to the necessity of making compensating posterior moves when the electrode is displaced laterally. In all records at least two responses are superimposed. Note that the cell fires once in A2. B : EPSP and antidromic spike amplitudes plotted as functions of distance lateral to the axon cap. EPSP amplitudes were normalized with respect to the largest response recorded following stimulation at a given strength, and spike amplitude was normalized relative to its value at the soma. Note that for both stimulation strengths (defined in text) the location of maximal EPSP amplitudes indicates a proximal lateral dendrite input. The decrement in spike height laterally is due to the passive cable properties of this dendrite, C: a plot of the normalized amplitude difference between VlIla EPSPs evoked by maximal and half-maximal stimulus strengths, indicating that increasing stimulus strength recruited a distinct fiber population projecting to a localized dendritic region.
largest 200-250 /~m lateral to the axon cap and decremented distally while the a n t i d r o m i c spike height decayed lateral to the soma. The V I I I a excitatory inputs in this experiment were thus distributed p r i m a r i l y on the p r o x i m a l lateral dendrite. In 5 a d d i t i o n a l experiments V I I I a i n p u t was also distributed over the s o m a a n d p r o x i m a l lateral dendrite with there being no suggestion o f a significant distal projection m o r e t h a n 2 7 0 / ~ m lateral to the axon cap. In 3 cases, there was a shift in the potential profiles when V I I l a stimulus strength was increased from h a l f - m a x i m a l to maximal. The distributions o f the incremental responses showed a sharp p e a k in the region o f 180-255 # m lateral to the axon cap, indicating recruitment o f a distinct fiber p o p u l a t i o n projecting to this specific region. This is illustrated in Fig. 2C, which is a plot o f the incremental profile from the experiment o f Fig. 2A, B. This discrete focus is found j u s t p r o x i m a l to the medial limit o f the large m y e l i n a t e d club ending projection 2,l°,16 and therefore provides evidence for a second input t h a t is m o r p h o logically segregated on the lateral dendrite. It is n o t clear whether this t e r m i n a t i o n p a t t e r n represents a localization o f fibers which originate from one division o f the labyrinth (e.g. otolithic m a c u l a e or semicircular canal cristae) or which are r a t h e r from functionally c o r r e s p o n d i n g parts o f m o r e than one o f these areas.
322
A
B
¢
1reset 1reset
Fig. 3. Excitatory nature of the VIIIa input. A-C: intracellular recordings obtained from the M-cell soma. Subthreshold EPSPs were elicited by stimulation of VIIIp in A and VIlla in B. C: when the two stimuli in A and B were combined, the resultant PSP evoked an orthodromic impulse (arrow) in the M-cell. Upper and lower traces : high-gain AC and low-gain DC records, resl~ectively.In all records at least two responses are superimposed. The maximal V I I I a EPSP was generally too small to bring the M-cell to threshold (Fig. 3B; but see Fig. 2A2). However, its excitatory nature could be demonstrated by pairing it with a subthreshold response to V H I p stimulation (Fig. 3A). Under these conditions, the two summated and evoked an orthodromic spike (arrow in Fig. 3C). Timing of the two stimuli was critical, as V I I l a stimulation also produces a polysynaptic inhibition of the M-cell (unpublished observations) which can block orthodromic activation of the neuron. To ensure that the synaptic potentials recorded were not a result of current spread to neighboring cranial nerves 16 recordings were obtained before and after cutting the V I I I a branch. This procedure eliminated the V i l l a EPSP but did not alter that from the posterior branch. Therefore, current spread to other nerves was not a major source of the inputs attributed to VIIIa. Goldfish display a rapid M-cell initiated startle response to sounda,9, la. The sacculus and lagena of cyprinids contain primarily auditory receptorsl,4,sA2; these otolithic organs are innervated by the posterior branch of the VIIIth nerve. O n the other hand, the utriculus is involved in the maintenance of equilibrium 5 (see ref. 8 for review), with its afferents confined to the anterior ramus. The combined behavioral and morphological evidence is therefore consistent with the observed functional and physiological differences between anterior and posterior VIIIth nerve inputs to the Mcell. Although input activity in both might be expected to modulate M-cell excitability, synchronous activity in the latter is more likely to produce the rapid excitation of the M-cell which underlies the startle response. Finally, evidence for discretely localized projections of anterior VIIIth nerve fiber populations provides a basis for further investigation of the functional specification of afferent connections to the M-cell. We t h a n k K. Davis and J. Lakatos for help with the figures and J. Jordan for secretarial assistance. This research was supported in part by N I H Postdoctoral Fellowship F 32
323 N S 5 2 8 2 t o D r . S t e v e n J. Z o t t o l i a n d b y P H S
Grant
NS
12132 t o D r . D o n a l d
S.
Faber.
1 Bigelow, H. B., The sense of hearing in the goldfish, Cara.~ius auratus L, 4mer. Nat., 38 (1904) 275-284. 2 Diamond, J., The activation and distribution of GABA and L-glutamate receptors on goldfish Mauthner neurones: an analysis of dendritic remote inhibition, J. Physiol. (Lond.), 194 (1968) 669-723. 3 Eaton, R. C., Bombardieri, R. A. and Meyer, D. L., The Mauthner-initiated startle response in teleost fish, J. exp. Biol., 66 (1977) 65-81. 4 Fay, R. R. and Olsho, L. W., Discharge patterns of lagenar and saccular neurones of the goldfish eighth nerve: displacement sensitivity and directional characteristics, Comp. Biochem. Physiol., 62A (1979) 377-386. 5 Frisch, K., von, The sense of hearing in fish, Nature (Lond.), 141 (1938) 8-11. 6 Furshpan, E. J., 'Electrical transmission' at an excitatory synapse in a vertebrate brain, Science, 144 (1964) 878 880. 7 Furshpan, E. J. and Furukawa, T., Intracellular and extracellular response of the several regions of the Mauthner cell of the goldfish, J. NeurophysioL, 25 (1962) 732-771. 8 Lowenstein, O., The labyrinth. In W. S. Hoar and D. J. Randall (Eds.), Fish Physiology, Academic Press, New York, 1971, pp. 207-263. 9 Mueller, T. J., Factors modulating the occurence and direction of the startle response in goldfish, Neurosci. Abstr., 4 (1978) 363. 10 Nakajima, Y., Fine structure of the synaptic endings on the Mauthner cell of the goldfish, J. camp. Neurol., 156 (1974) 375~-02. 11 Nakajima, Y. and Kohno, K., Fine structure of the Mauthner cell: synaptic topography and comparative study. In D. S. Faber and H. Korn (Eds.), Neurobiology afthe Mauthner cell, Raven Press, New York, 1978, pp. 133-166. 12 Popper, A. and Fay, R. R., Sound detection and processing by teleost fishes: a critical review, J. aeoust. Soc. Amer., 53 (1973) 1515-1529. 13 Robertson, J. D., Bodenheimer, T. S. and Stage, D. E., The ultrastructure of Mauthner cell synapses and nodes in goldfish brains, J. Cell Biol., 19 (1963) 159-199. 14 Zottoli, S. J., Comparison of anterior and posterior Vlllth nerve input to the goldfish Mauthner cell, Neurosci. Abstr., 3 (1977) 547. 15 Zottoli, S. J., Correlation of the startle reflex and Mauthner cell auditory responses in unrestrained goldfish, J. exp. Biol., 66 (1977) 243 254. 16 Zottoli, S. J., Comparative morphology of the Mauthner cell in fish and amphibians. In D. S. Faber and H. Korn (Eds.), Neurobiology of the Mauthner Cell, Raven Press, New York, 1978, pp. 13-45.