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Effects of monaural and binaural auditory deprivation on audiogenic seizure susceptibility in BALBc mice
EXPERIMENTAL
Effects
of Monaural
Audiogenic G.
38, 488-493 (1973)
NEUROLOGY
RICHARD
Dcpartmcnt
and
Seizure GATES,
Binaural Susceptibility
CHIA
SHOKG
of Psychology,
Auditory
Mot~ash Received
in BALB/c
CHEN,
AND
University,
September
Deprivation
Clayton,
GREGORY
Victoria,
on
Mice R.
BOCK’
Australia
18, 1972
Mice of the BALB/c strain were divided into three groups at 20 2 1 days of age. One group was deprived binaurally of auditory input by destroying the tympanic membrane bilaterally. A second group was monaurally deprived of auditory input by unilateral tympanic membrane destruction. The third group of control animals was sham-operated and the membranes were left intact. At 27 f 1 days of age, all three groups of mice were tested behaviorally for audiogenic seizures. On exposure to the loud sound, a majority of the auditory-deprived animals of both operative groups exhibited audiogenic seizure reactions, but none of the sham-operated controls showed seizure behavior. These findings lend support to the hypothesis that induction of seizure susceptibility is a result of auditory deprivation.
INTRODUCTION Several seizure-resistant strains of mice can be made susceptible to audiogenic seizures by exposure to intense acoustic stimulation during a sensitive period after birth (l-3, 8, 11). Until recently, the consequences of priming and the underlying physiological mechanisms of the sensitization process were poorly understood although there was some evidence suggesting that the effects of priming might reside in uncrossed auditory structures (9). Saunders, Bock, Chen, and Gates (14) studied the effects of acoustic priming on cochlear responses in BALB/c strain mice, and found that bell-primed mice exhibited a severe loss in cochlear sensitivity. This finding posed an interesting paradox. Audiogenic seizures which were partially deaf. A sensory deprivation
were occurring in mice hypothesis (14) was
proposed to account for this paradox. Essentially, this hypothesis suggested that the priming procedure caused damage to the peripheral auditory 1 This research was supported Committee
by Grants from the Australian 488
Copyright All rights
0 1973 by Academic Press, Inc. of reproduction in any form reserved.
Research Grants
receptor which in turn effectively reduced auditory input to the auditory system during a period of neural development critically dependent on auditory input for normal maturation. As a result of this deprivation, abnormal maturation of the system occurred such that on reesposure to a loud stimulus, the abnormal structures were exited and seizure reaction precipitated. If, in fact, auditory deprivation, rather than the sound of the bell, is responsible for this abnormal development, then auditory deprivation induced by means other than acoustic priming should be effective in producing seizure susceptibility. The present experiment was designed to test this hypothesis.
METHODS Subjects and Ex~erinzcntal Design. Ninety-eight BALB/c mice were used in this experiment. They were randomly assigned to one of three groups : a bilateral auditory-deprived group (TMB) , a unilateral auditorydeprived group (TMU), and a control group. In order to produce a condition of auditory deprivation in an ear by means other than bellpriming, the tympanic membrane was totally destroyed. This destruction is known to effectively reduce the sound energy reaching the oval window of the cochlea by approximately 40 db ( 13, 17). Procedure. At 20 * 1 days of age, all mice were briefly anesthetized with halothane and a small incision made in the ventral edge of the pinna near the opening of the auditory meatus to facilitate visual observation of the TM. In the TMB group, 44 mice had both membranes destroyed with a sharp probe. In the TMU group, 17 mice had either the left or right TM destroyed using the same method. The remaining 37 mice served as sham-operated controls ; their membranes were exposed and esamined but not destroyed. After recovery from the anesthetic, all animals were returned to their home cages. At 27 +1 days of age all mice except for two mice from the TMU group were exposed to the sound of a loud electric bell (108-110 db re. 0002 dyne/cm?) for 120 set or until convulsion occurred. Four behavioural measures were taken during this tekting: latency from bell onset to beginning of wild running ; latency from bell onset to beginning of clonic seizure ; seizure type; and incidence of death. Severity scores were assigned to each animal, 0 for no response, 1 for wild running not followed by seizure, 2 for clonic seizure, 3 for clonic seizure followed by tonic seizure, and 4 for death resulting from tonic seizure. After testing, these mice were killed with an overdose of anesthetic and their TM examined for signs of regeneration.
490
GATES,
CHEN,
u Median severity score behavior, 1 for wild running,
BOCK
\\.ild running
Clonic seizure
Tonic seizure
Death
37 44
0 33
0 26
0 12
0 2
0 2.3
1.5
12
8
0
0
2.0
NO.
of mice Sham-operated Bilateral tympanic Membrane destroyed Unilateral tympanic Membrane destroyed
AND
Severit) scorea
calculated for each group by assigning 0 for no seizure 2 for clonic seizure, 3 for tonic seizure and 4 for death.
In order to determine the actual transmission loss across the middle ear of mice in which the tympanic membrane had been destroyed, two TMU mice were anesthetized and prepared for round window recording of a-c cochlear potentials using the same procedure’ previously described by Saunders et al. (14). A l-pv threshold curve for the cochlear microphonic was recorded from the round window using pure tone stimuli at selected frequencies between 5 kHz and 20 kHz. A comparison was then made between the threshold curve from TM-destroyed ears and that obtained from the cochlea of mice with normal TM-intact ears. RESULTS Table 1 shows incidence of successive stages of audiogenic seizure behavior and median severity scores for all three groups of mice. The sham-operated mice showed no seizure behavior whereas 75% of TMB mice and 80% of TMU mice showed wild running while 60% of TMB, and 53% of TMU mice convulsed. (X-square tests indicate significant differences among the three groups for wild running (x’ = 53.23, df = 2, P < 0.0001) and incidence of clonic seizure (x” = 33.18, df = 2, P < 0.0001). A Kruskal-Wallis test on median severity scores (7) indicates that the groups differ significantly in their respective severity scores
(H = 53.23, df = 2, P < 0.0001). Median latency to wild-running and clonic seizure for both TMB and TMU groups are shown in Table 2. These medians are based on latencies for those mice in each group which exhibited this behavior in response to the test stimulus. A Mann-Whitney U test (two-tailed) indicates that latency to wild running is not significantly different between groups (U = 153, P > 0.05) ; 1lowever, median latency to clonic seizure for TMB
SEIZURE
491
SUSCEPTIIHLITY
and TMU mice did differ significantly (U = 37, P < 0.007), TMB reaching clonic seizure before TMU mice. Post mortem examination of the ears of TM-damaged animals showed that all mice had achieved at least partial regrowth of the TM while most showed complete regrowth ; however, this regeneration did not present a normal appearance. The usually translucent TM had an opaque granular appearance and was considerably thicker than that found in normal mice. Comparison of the 1-pv threshold curves obtained from the damaged ears of two mice with those from normal ears (14) showed that across the frequencies examined, TM-damaged ears exhibited less sensitive thresholds. For example, in the most sensitive region of the mouse audiogram at 17 kHz, M3 showd a 1-pv threshold 38 db above the normal curve and M4 exhibited a similar 4.2 db loss in sensitivity. At all other frequencies, similar losses in threshold sensitivity were found. DISCUSSION The results clearly demonstrate that susceptibility to audiogenic seizures in normally nonsusceptible BALB/c mice (2, 10) can be induced by means other than acoustic priming. This finding lends support to the sensory deprivation hypothesis ; namely, that susceptibility to audiogenic seizure develops as a result of lack of auditory input to auditory structures during maturation. According to this hypothesis, auditory deprivation results in abnormal neural maturation which may possibly take the form of the wellknown denervation condition of “supersensitivity” (16), a condition of neural over-reactivity to normal stimulation. On subsequent exposure to intense acoustic stimulation, these over-reactive neural elements are stimulated and seizure behavior is triggered. TABLE LATENCY AND
TO WILD BILATERAL
RUNNING
AND
TYMPANIC
2 CLONIC
MEMBRANE
SEIZURES DESTROYED
IN
UNILATERAL MICE
Latency to wild runninga
Bilateral tympanic membrane destroyed Unilateral tympanic membrane destroyed a Measured
in seconds.
Latency to clonic seizure0
Median
Range
Median
Range
10.2
3.1-50.9
47.2
12.4-77.0
11.85
2.8-65.0
60.05
51.8-115.2
402
GATES,
CHEN,
AND
BOCK
Although we have no direct evidence showing that auditory deprivation results in abnormal anatomical changes in the auditory system of the mouse, the anatomical studies by Gyllensten, Malmfors and Norrlin (6) and Gyllensten (S), showing that visual deprivation causes gross changes in the visual and auditory systems of the mouse, suggest that similar anatomical changes might occur in the auditory system as a result of auditory deprivation. Additionally, the evoked-response study of Saunders, Bock, James, and Chen ( 15) demonstrating that click-evoked responses obtained from the cochlear nucleus and inferior colliculus of bell-primed mice at high intensities are approximately twice the amplitude of those obtained from normal mice, provides direct evidence for the notion that auditory deprivation results in abnormal nervous system development. From the I-pv threshold results of the TM-destroyed animals it would appear that TM destruction is an effective method for achieving a condition of auditory deprivation. Although it might be argued that in the process of TM destruction some damage was caused to the cochlea, this seems highly unlikely as only a d-c shift in the fluids of the cochlea would have occurred in response to the pressure applied to the TM by the probe during destruction. Moreover, consideration of the frequency content of the transient TM movement involved in this procedure suggests that little energy would be transmitted to the basilar membrane. Ideally, induction of auditory deprivation by means other than middle ear damage may help to answer this question; a possibility which we are currently exploring. In the case of unilateral priming effects, Fuller and Collins (4) and Henry (9) have suggested that the effects of bell-priming are confined to the uncrossed auditory structures of the auditory pathway. Although our experiment provides no direct evidence for this suggestion, the significant difference in latency to clonic seizure between the TMB and TMU groups of mice suggests that bilateral deprivation produces an additive neural effect in the higher crossed structures which results in seizure threshold being reached more quickly than it is for unilaterally deprived mice which only have the uncrossed auditory structures of one side affected by deprivation. It is also worth noting that Fuller and Collins (4) suggested that the same anatomical locus may be involved in the development of susceptibility for both nonsusceptible and genetically susceptible strains of mice. The cochlear threshold studies of Saunders et al. (14) on primed, nonsusceptible mice and Niaussat (12) on genetically, seizure-prone RB mice confirm a deficit in cochlear sensitivity indicative of a severe hearing loss. This implies that genetically susceptible mice as well as nonsusceptible mice depend on the same mechanism for induction of seizure susceptibility : auditory deprivation.
SEIZURE
SUSCEPTIBILITY
493
Perhaps one of the most important implications of the present study is that the bell or loud sound has been removed as the critical factor in induction of seizure susceptibility. The loud bell appears to be important only as an agent for producing damage to the cochlea and for stimulating neural structures at test. Auditory deprivation, not the bell per se would appear to be the critical factor for the development of seizure susceptibility. REFERENCES 1. BOGGAN, W. O., D. X. FREEDMAN, and R. A. LOVELL. 1971. Studies in Audiogenic seizure susceptibility. Psycho~harlllacologia 20: 48-56. 2. CHEN, C. S. 1972. Sensitization for audiogenic seizures in two strains of mice and their F, hybrids. Develop. PsycltoDiol. (in press). 3. FULLER, J. L., AND R. L. COLLINS. 1968. Temporal parameters of sensitization for audiogenic seizures in SJL/J mice. Dcvclop. Psychobiol. 1: 185-188. 4. FULLER, J. L., AND R. L. COLLINS. 1968. Mice unilaterally sensitized for audiogenie seizures. Science 162: 1295. 5. GYLLENSTEN, L. 1966. Growth alteration in the auditory cortex of visually deprived mice. J. Cowzp. Neural. 126: 463-470. 6. GYLLENSTEN, L., T. MALMFORS, and M. NORRLIN. 1965. Effects of visual deprivation on the optic centers of growing and adult mice. J. camp. Nczlrol. 124: 148160. 7. HAY, W. L. 1963. “Statistics for Psychologists.” Holt, Rinehart and Winston, New York. 8. HENRY, K. R. 1967. Audiogenic seizure susceptibility induced in C57BL/6J mice by prior auditory exposure. Science 158: 938-940. 9. HENRY, K. R. 1972. Pinna Reflex Thresholds and Audiogenic Seizures: Developmental Changes After Acoustic Priming. J. Conlp. Physiol. Psychol. 79: 77-81. 10. HENRY, K. R., and R. E. BOWMAN. 1969. Effects of acoustic priming in audiogenic, electroconvulsive and chemoconvulsive seizures. J. Camp. Physiol. Psychol. 67 : 401-406. 11. ITURRIAN, W. B., and G. B. FINI<. 1968. Effect of age and condition test interval (days) on an audio-conditioned convulsive response in CF-1 mice. Dezdop. Psyckobiol. 1: 230-235. 12. NIAUSSAT, MARIE-M., and J.-P. LECOUIX. 1967. Anaomalies des responses microphoniques cochleaires dans une lignee de souris presentant des crises convulsives au son. C.R. ,&ad. Sci. Paris. 264: 103-105. 13. PAYNE, M. C., and F. J. GITHLER. 1951. Effects of perforations of the tympanic membrane on cochlear potentials. Arch. Otolaryngol. 54: 666-674. 14. SAUNDERS, J. C., G. R. BOCK, C. S. CHEN, and G. R. GATES. 1972. The Effects of Priming for Audiogenic Seizures on Cochlear and Behavioural Responses in BALB/c Mice. .%p. Nerlrol. 36: 426-436. 15. SAUNDERS, J. C., G. R. BOCK, R. JAMES, and C. S. CHEN. 1972. Effects of priming for audiogenic seizure on auditory evoked responses in the cochlear nucleus and inferior colliculus of BALB/c mice. Exp. Nezrrol. 37 : 388-394. 16. STAVRAKY, G. W. 1961. “Supersensitivity Following Lesions of the Nervous System.” University of Toronto Press, Toronto. 17. TONNWRF, J., and S. M. KHANNA. 1970. The Role of the Tympanic Membrane in Middle Ear Transmission. Ann. Otol. Rhino/. Laryngol. 79: 743-753.
Effects
of Monaural
Audiogenic G.
38, 488-493 (1973)
NEUROLOGY
RICHARD
Dcpartmcnt
and
Seizure GATES,
Binaural Susceptibility
CHIA
SHOKG
of Psychology,
Auditory
Mot~ash Received
in BALB/c
CHEN,
AND
University,
September
Deprivation
Clayton,
GREGORY
Victoria,
on
Mice R.
BOCK’
Australia
18, 1972
Mice of the BALB/c strain were divided into three groups at 20 2 1 days of age. One group was deprived binaurally of auditory input by destroying the tympanic membrane bilaterally. A second group was monaurally deprived of auditory input by unilateral tympanic membrane destruction. The third group of control animals was sham-operated and the membranes were left intact. At 27 f 1 days of age, all three groups of mice were tested behaviorally for audiogenic seizures. On exposure to the loud sound, a majority of the auditory-deprived animals of both operative groups exhibited audiogenic seizure reactions, but none of the sham-operated controls showed seizure behavior. These findings lend support to the hypothesis that induction of seizure susceptibility is a result of auditory deprivation.
INTRODUCTION Several seizure-resistant strains of mice can be made susceptible to audiogenic seizures by exposure to intense acoustic stimulation during a sensitive period after birth (l-3, 8, 11). Until recently, the consequences of priming and the underlying physiological mechanisms of the sensitization process were poorly understood although there was some evidence suggesting that the effects of priming might reside in uncrossed auditory structures (9). Saunders, Bock, Chen, and Gates (14) studied the effects of acoustic priming on cochlear responses in BALB/c strain mice, and found that bell-primed mice exhibited a severe loss in cochlear sensitivity. This finding posed an interesting paradox. Audiogenic seizures which were partially deaf. A sensory deprivation
were occurring in mice hypothesis (14) was
proposed to account for this paradox. Essentially, this hypothesis suggested that the priming procedure caused damage to the peripheral auditory 1 This research was supported Committee
by Grants from the Australian 488
Copyright All rights
0 1973 by Academic Press, Inc. of reproduction in any form reserved.
Research Grants
receptor which in turn effectively reduced auditory input to the auditory system during a period of neural development critically dependent on auditory input for normal maturation. As a result of this deprivation, abnormal maturation of the system occurred such that on reesposure to a loud stimulus, the abnormal structures were exited and seizure reaction precipitated. If, in fact, auditory deprivation, rather than the sound of the bell, is responsible for this abnormal development, then auditory deprivation induced by means other than acoustic priming should be effective in producing seizure susceptibility. The present experiment was designed to test this hypothesis.
METHODS Subjects and Ex~erinzcntal Design. Ninety-eight BALB/c mice were used in this experiment. They were randomly assigned to one of three groups : a bilateral auditory-deprived group (TMB) , a unilateral auditorydeprived group (TMU), and a control group. In order to produce a condition of auditory deprivation in an ear by means other than bellpriming, the tympanic membrane was totally destroyed. This destruction is known to effectively reduce the sound energy reaching the oval window of the cochlea by approximately 40 db ( 13, 17). Procedure. At 20 * 1 days of age, all mice were briefly anesthetized with halothane and a small incision made in the ventral edge of the pinna near the opening of the auditory meatus to facilitate visual observation of the TM. In the TMB group, 44 mice had both membranes destroyed with a sharp probe. In the TMU group, 17 mice had either the left or right TM destroyed using the same method. The remaining 37 mice served as sham-operated controls ; their membranes were exposed and esamined but not destroyed. After recovery from the anesthetic, all animals were returned to their home cages. At 27 +1 days of age all mice except for two mice from the TMU group were exposed to the sound of a loud electric bell (108-110 db re. 0002 dyne/cm?) for 120 set or until convulsion occurred. Four behavioural measures were taken during this tekting: latency from bell onset to beginning of wild running ; latency from bell onset to beginning of clonic seizure ; seizure type; and incidence of death. Severity scores were assigned to each animal, 0 for no response, 1 for wild running not followed by seizure, 2 for clonic seizure, 3 for clonic seizure followed by tonic seizure, and 4 for death resulting from tonic seizure. After testing, these mice were killed with an overdose of anesthetic and their TM examined for signs of regeneration.
490
GATES,
CHEN,
u Median severity score behavior, 1 for wild running,
BOCK
\\.ild running
Clonic seizure
Tonic seizure
Death
37 44
0 33
0 26
0 12
0 2
0 2.3
1.5
12
8
0
0
2.0
NO.
of mice Sham-operated Bilateral tympanic Membrane destroyed Unilateral tympanic Membrane destroyed
AND
Severit) scorea
calculated for each group by assigning 0 for no seizure 2 for clonic seizure, 3 for tonic seizure and 4 for death.
In order to determine the actual transmission loss across the middle ear of mice in which the tympanic membrane had been destroyed, two TMU mice were anesthetized and prepared for round window recording of a-c cochlear potentials using the same procedure’ previously described by Saunders et al. (14). A l-pv threshold curve for the cochlear microphonic was recorded from the round window using pure tone stimuli at selected frequencies between 5 kHz and 20 kHz. A comparison was then made between the threshold curve from TM-destroyed ears and that obtained from the cochlea of mice with normal TM-intact ears. RESULTS Table 1 shows incidence of successive stages of audiogenic seizure behavior and median severity scores for all three groups of mice. The sham-operated mice showed no seizure behavior whereas 75% of TMB mice and 80% of TMU mice showed wild running while 60% of TMB, and 53% of TMU mice convulsed. (X-square tests indicate significant differences among the three groups for wild running (x’ = 53.23, df = 2, P < 0.0001) and incidence of clonic seizure (x” = 33.18, df = 2, P < 0.0001). A Kruskal-Wallis test on median severity scores (7) indicates that the groups differ significantly in their respective severity scores
(H = 53.23, df = 2, P < 0.0001). Median latency to wild-running and clonic seizure for both TMB and TMU groups are shown in Table 2. These medians are based on latencies for those mice in each group which exhibited this behavior in response to the test stimulus. A Mann-Whitney U test (two-tailed) indicates that latency to wild running is not significantly different between groups (U = 153, P > 0.05) ; 1lowever, median latency to clonic seizure for TMB
SEIZURE
491
SUSCEPTIIHLITY
and TMU mice did differ significantly (U = 37, P < 0.007), TMB reaching clonic seizure before TMU mice. Post mortem examination of the ears of TM-damaged animals showed that all mice had achieved at least partial regrowth of the TM while most showed complete regrowth ; however, this regeneration did not present a normal appearance. The usually translucent TM had an opaque granular appearance and was considerably thicker than that found in normal mice. Comparison of the 1-pv threshold curves obtained from the damaged ears of two mice with those from normal ears (14) showed that across the frequencies examined, TM-damaged ears exhibited less sensitive thresholds. For example, in the most sensitive region of the mouse audiogram at 17 kHz, M3 showd a 1-pv threshold 38 db above the normal curve and M4 exhibited a similar 4.2 db loss in sensitivity. At all other frequencies, similar losses in threshold sensitivity were found. DISCUSSION The results clearly demonstrate that susceptibility to audiogenic seizures in normally nonsusceptible BALB/c mice (2, 10) can be induced by means other than acoustic priming. This finding lends support to the sensory deprivation hypothesis ; namely, that susceptibility to audiogenic seizure develops as a result of lack of auditory input to auditory structures during maturation. According to this hypothesis, auditory deprivation results in abnormal neural maturation which may possibly take the form of the wellknown denervation condition of “supersensitivity” (16), a condition of neural over-reactivity to normal stimulation. On subsequent exposure to intense acoustic stimulation, these over-reactive neural elements are stimulated and seizure behavior is triggered. TABLE LATENCY AND
TO WILD BILATERAL
RUNNING
AND
TYMPANIC
2 CLONIC
MEMBRANE
SEIZURES DESTROYED
IN
UNILATERAL MICE
Latency to wild runninga
Bilateral tympanic membrane destroyed Unilateral tympanic membrane destroyed a Measured
in seconds.
Latency to clonic seizure0
Median
Range
Median
Range
10.2
3.1-50.9
47.2
12.4-77.0
11.85
2.8-65.0
60.05
51.8-115.2
402
GATES,
CHEN,
AND
BOCK
Although we have no direct evidence showing that auditory deprivation results in abnormal anatomical changes in the auditory system of the mouse, the anatomical studies by Gyllensten, Malmfors and Norrlin (6) and Gyllensten (S), showing that visual deprivation causes gross changes in the visual and auditory systems of the mouse, suggest that similar anatomical changes might occur in the auditory system as a result of auditory deprivation. Additionally, the evoked-response study of Saunders, Bock, James, and Chen ( 15) demonstrating that click-evoked responses obtained from the cochlear nucleus and inferior colliculus of bell-primed mice at high intensities are approximately twice the amplitude of those obtained from normal mice, provides direct evidence for the notion that auditory deprivation results in abnormal nervous system development. From the I-pv threshold results of the TM-destroyed animals it would appear that TM destruction is an effective method for achieving a condition of auditory deprivation. Although it might be argued that in the process of TM destruction some damage was caused to the cochlea, this seems highly unlikely as only a d-c shift in the fluids of the cochlea would have occurred in response to the pressure applied to the TM by the probe during destruction. Moreover, consideration of the frequency content of the transient TM movement involved in this procedure suggests that little energy would be transmitted to the basilar membrane. Ideally, induction of auditory deprivation by means other than middle ear damage may help to answer this question; a possibility which we are currently exploring. In the case of unilateral priming effects, Fuller and Collins (4) and Henry (9) have suggested that the effects of bell-priming are confined to the uncrossed auditory structures of the auditory pathway. Although our experiment provides no direct evidence for this suggestion, the significant difference in latency to clonic seizure between the TMB and TMU groups of mice suggests that bilateral deprivation produces an additive neural effect in the higher crossed structures which results in seizure threshold being reached more quickly than it is for unilaterally deprived mice which only have the uncrossed auditory structures of one side affected by deprivation. It is also worth noting that Fuller and Collins (4) suggested that the same anatomical locus may be involved in the development of susceptibility for both nonsusceptible and genetically susceptible strains of mice. The cochlear threshold studies of Saunders et al. (14) on primed, nonsusceptible mice and Niaussat (12) on genetically, seizure-prone RB mice confirm a deficit in cochlear sensitivity indicative of a severe hearing loss. This implies that genetically susceptible mice as well as nonsusceptible mice depend on the same mechanism for induction of seizure susceptibility : auditory deprivation.
SEIZURE
SUSCEPTIBILITY
493
Perhaps one of the most important implications of the present study is that the bell or loud sound has been removed as the critical factor in induction of seizure susceptibility. The loud bell appears to be important only as an agent for producing damage to the cochlea and for stimulating neural structures at test. Auditory deprivation, not the bell per se would appear to be the critical factor for the development of seizure susceptibility. REFERENCES 1. BOGGAN, W. O., D. X. FREEDMAN, and R. A. LOVELL. 1971. Studies in Audiogenic seizure susceptibility. Psycho~harlllacologia 20: 48-56. 2. CHEN, C. S. 1972. Sensitization for audiogenic seizures in two strains of mice and their F, hybrids. Develop. PsycltoDiol. (in press). 3. FULLER, J. L., AND R. L. COLLINS. 1968. Temporal parameters of sensitization for audiogenic seizures in SJL/J mice. Dcvclop. Psychobiol. 1: 185-188. 4. FULLER, J. L., AND R. L. COLLINS. 1968. Mice unilaterally sensitized for audiogenie seizures. Science 162: 1295. 5. GYLLENSTEN, L. 1966. Growth alteration in the auditory cortex of visually deprived mice. J. Cowzp. Neural. 126: 463-470. 6. GYLLENSTEN, L., T. MALMFORS, and M. NORRLIN. 1965. Effects of visual deprivation on the optic centers of growing and adult mice. J. camp. Nczlrol. 124: 148160. 7. HAY, W. L. 1963. “Statistics for Psychologists.” Holt, Rinehart and Winston, New York. 8. HENRY, K. R. 1967. Audiogenic seizure susceptibility induced in C57BL/6J mice by prior auditory exposure. Science 158: 938-940. 9. HENRY, K. R. 1972. Pinna Reflex Thresholds and Audiogenic Seizures: Developmental Changes After Acoustic Priming. J. Conlp. Physiol. Psychol. 79: 77-81. 10. HENRY, K. R., and R. E. BOWMAN. 1969. Effects of acoustic priming in audiogenic, electroconvulsive and chemoconvulsive seizures. J. Camp. Physiol. Psychol. 67 : 401-406. 11. ITURRIAN, W. B., and G. B. FINI<. 1968. Effect of age and condition test interval (days) on an audio-conditioned convulsive response in CF-1 mice. Dezdop. Psyckobiol. 1: 230-235. 12. NIAUSSAT, MARIE-M., and J.-P. LECOUIX. 1967. Anaomalies des responses microphoniques cochleaires dans une lignee de souris presentant des crises convulsives au son. C.R. ,&ad. Sci. Paris. 264: 103-105. 13. PAYNE, M. C., and F. J. GITHLER. 1951. Effects of perforations of the tympanic membrane on cochlear potentials. Arch. Otolaryngol. 54: 666-674. 14. SAUNDERS, J. C., G. R. BOCK, C. S. CHEN, and G. R. GATES. 1972. The Effects of Priming for Audiogenic Seizures on Cochlear and Behavioural Responses in BALB/c Mice. .%p. Nerlrol. 36: 426-436. 15. SAUNDERS, J. C., G. R. BOCK, R. JAMES, and C. S. CHEN. 1972. Effects of priming for audiogenic seizure on auditory evoked responses in the cochlear nucleus and inferior colliculus of BALB/c mice. Exp. Nezrrol. 37 : 388-394. 16. STAVRAKY, G. W. 1961. “Supersensitivity Following Lesions of the Nervous System.” University of Toronto Press, Toronto. 17. TONNWRF, J., and S. M. KHANNA. 1970. The Role of the Tympanic Membrane in Middle Ear Transmission. Ann. Otol. Rhino/. Laryngol. 79: 743-753.