Strain differences in the development of susceptibility to audiogenic seizures after acoustic priming but not after hearing loss

EXPERIMENTAL

Strain

NEUROLOGY

‘62,

Differences Audiogenic

4&2-488

(1978)

in the

Development

Seizures not

after

after

Departwed

of Biobehavioral Stows, Received

Acoustic

Hearing

STEPHEN

of Susceptibility Priming

to

but

Loss l

C. MAXSON

Sciences, The University Connecticut 06268 Jme

of Connecticut,

28,1978

Either exposure to an initial auditory stimulus (IAS) or external ear plugging (EEP) was used to produce susceptibility to audiogenic seizures in C57BL/6Bg and DBA/lBg-ras mice. After the IAS, increments in seizure susceptibility occurred by 5 h in C57BL/6Bg mice and by 24 h in DBA/lBg-rus mice, whereas after EEP, increments in seizure susceptibility occurred by 48 h in C57BL/6Bg and by 24 h in DBA/lBg-ras mice. Because both the IAS and EEP produce hearing loss, the strain differences in the effect of the IAS on the development of susceptibility and the strain similarities in the effect of the EEP on the development of susceptibility support the hypothesis that acoustic priming in the C57BL/6Bg at 19 days of age involves another mechanism in addition to that of hearing loss and disuse supersensitivity. It was suggested elsewhere that the other mechanism is mediated by a post-IAS decrease in the concentration of brain y-aminobutyric acid and requires brain protein synthesis for a brief period postIAS.

Maxson et al. (11) suggested, on the basis of findings from pharmacostudies of C57BL/6Bg and DBA/lBg-ras mice, that there are two developmental and neural mechanisms for the acoustic priming of susceptibility to audiogenic seizures. In one of these, the initial auditory stimulus (IAS), causesa partial deafness (5, 13), and the partial hearing

genetic

Abbreviations : IAS-initial auditory stimulus ; EEP-external ear plugging; GABA--y-aminobutyric acid. 1 This research was supported by grants from the William T. Grant Foundation, the University of Connecticut Research Foundation, and by Grant MH-28021 from the National Institute of Mental Health. 482 00144886/78/0622-0482$02.00/O Copyright All rights

@ 1978 by Academic Press, of reproduction in any form

Inc. reserved.

DEVELOPMENT

OF

AUDIOGENIC

SEIZURES

483

loss results in a disuse supersensitivity of the auditory brain stem (5, 7, 13). In the other mechanism, the effect of the IAS is mediated by a decrease in the brain concentration of y-aminobutyric acid (GABA) (10, 12), and during a brief interval after the IAS, it requires brain protein synthesis (9). Those pharmacogenetic studies also suggested that the mechanism involving GABA and requiring protein synthesis exists in C57BL/6 mice of the Bg and J substrains and that the mechanism involving hearing loss and disuse supersensitivity appears to occur in almost all mouse strains, including C57BL/6 and DBA/l-ras. This hypothesis suggests that there might be differences between C57BL/6 and DBA/l-ms mice in the development of susceptibility to audiogenic seizures after an IAS, but not after hearing loss due to treatment other than exposure to an IAS. Several investigators (3, 4, 7) showed that either plugging the external auditory canal (external ear plugging or EEP) or perforation of the tympanic membrane resulted in hearing loss and produced susceptibility to audiogenic seizures. The following study compares the effects of IAS and of EEP on the development of susceptibility to audiogenic seizures in C57BL/6Bg and DBA/IB~-?w mice. An approximately equal number of male or female C57BL/6Bg and DBA/lBg-ras mice were used. No sex differences have been found in acoustic priming with these strains and with our test conditions. DBA/lBgYUS mice were formerly identified as DBA/lBg-asv. The mice were obtained from our specific-pathogen-free colony, and as consequence, infectious otitis media could not contribute to seizure susceptibility in this study. The origin of the strains were described elsewhere (1 l), as were the conditions of rearing and maintenance (13). In the first experiment, the mice were exposed to the IAS at 19 days of age. The stimulus was applied in a chamber 38 x 48 X 4s cm. An Edwards-Lungen 7.6-cm electric doorbell provided a sound stimulus of 95-105 dB (re : 2 X 10e4 dyn/cm?) . The mouse was placed on the chamber floor and 60 s later the bell was activated for 90 s. Separate groups of mice were tested for susceptibility to audiogenic seizures at the following intervals after the stimulus: 0 h, 1 h, 5 h, 12 h, 18 h, 24 11, 48 h, and 9 days. The mice were tested for susceptibility to audiogenic seizures by being placed in the chamber and after a 60-s wait, the bell was activated 90 s or until the occurrence of a clonic-tonic seizure. The incidence of wild circling activity and of clonic-tonic seizures was recorded. The Npq test of significance between proportions was used to analyze the data (1). In the second experiment, the mice were rendered partially deaf by external ear plugging. For this, each external auditory canal was packed with cotton, and the cotton was secured in place with a clay plug. In

484

STEPHEN

C.

TABLE Audiogenic between

were

of Interval Stimulusa

Wild circling activity (70)

Clonic-tonic seizures (70)

N

0 8 30 42 29 65 53 91

0 0 7 17 21 45 3.5 85

20 49 43 41 38 47 58 67

Oh lh 5h 12 h 18 h 24 h 48 h 9 days mice

1

Seizures in C57BL/6Bg Mice as a Function Initial Auditory Stimulus (IAS) and Test

Interval

a C57BL/6 as indicated.

MAXSON

exposed

to the IAS on Day

19 and tested

at different

intervals

addition, each pinna was then folded over and clamped with a wound clip. This external ear plugging attenuates hearing by 40 dB and induces susceptibility to audiogenic seizures (7). Separate groups of mice were tested for susceptibility to audiogenic seizures at the following intervals after the placement of the plugs: 0 h, 5 h, 18 h, 24 h, 48 h, and 9 days. Plugs were removed just prior to testing. Susceptibility to audiogenic seizures was determined as in the first experiment. For C57BL/6 mice, after the IAS there was an increase in the incidence of wild circling activity at 5 h (P < 0.01, Table 1) and of clonic-tonic seizures at 12 h (P < 0.01, Table 1). Also, their incidence continued to increase to as long as 9 days after the IAS. The incidence of circling was significantly different between the 5-h and g-day groups (P < 0.01, Table l), and the incidence of clonic-tonic seizures was significantly different between the 12-h and 9-day groups (P < 0.01, Table 1). In contrast to the developmental pattern observed for C57BL/6Bg mice, there was no increase in the incidence of either symptom in the DBA/lBg-ras mice until 24 h after the IAS (P < 0.01, Table 2). In addition, the incidence of wild circling did not continue to increase between 24 h and 9 days after the IAS. However, there was an increment in the incidence of clonic-tonic seizures between 24 h and 9 days, after the IAS (P = 0.02, Table 2). Consequently, it appeared that the pattern of development for seizure susceptibility after an IAS was different for C57BL/6Bg and DBA/lBgras mice. After EEP, for C57BL/6Bg mice there was an increase in the incidence of wild circling activity at 48 h (P < 0.01, Table 3), and for DBA/lBgYU~, an increase in the incidence of circling at 24 h (P = 0.02, Table 4).

DEVELOPMENT

OF

AUDIOGENIC

TABLE

SEIZURES

2

Audiogenic Seizures in DBA/lBg-ras Mice as a Function of Interval between Initial Auditory Stimulus (IAS) and Test Stimulus0 Interval

Wild circling activity (70)

Oh 1 11 5h 12 h 18 h 24 h 48 h 9 days

Clonic-tonic seizures (%)

0 7 0 0 0

N

20 23 23 47 33

73

0 0 0 0 0 54

81

69

89

80

16 3.5

37

a DBA/l-ras mice were exposed to the IAS at 19 days of age and tested at the different intervals as indicated.

In both strains, there were no further increments in the incidence of circling to as long as 9 days after the EEP (P > 0.05, Tables 3, 4). Also, in the C57BL/6Bg strain, there were no further significant increments

in the incidence

of clonic-tonic

seizures

for any additional

interval

between the EEP and testing (P > 0.05, Table 3). In the DBA/lBg-ras, there

may have

been a slight

increment

in the incidence

of clonic-tonic

seizures at 9 days after the EEP (P = 0.05, Table 4). Thus, it appeared that the development of susceptibility following EEP is virtually identical for C57BL/6Bg and DBA/lBg-rus mice. As was predicted by the two-mechanism hypothesis of acoustic priming

TABLE Audiogenic Interval Oh 5h 18 h 24 h 48 h 9 days

3

Seizures in C57BL/6Bg Mice as a Function of the Interval between external Ear Plugging and Test Stimulusa Wild circling activity (ye)

Clonic-tonic seizures (%)

0

0

2 13

14

2 3 2

33 52

9

5

N

20

41 46 43 42 23

a C57BL/6 mice had both external auditory canals plugged (EEP) at 19 days of age, and the plugs were removed after different intervals as indicated prior to testing.

486

STEI’IIEN

C.

TABLE Audiogenic

4

Seizures in DBA/lBg-ras Mice as a Function of Interval between External Ear Plugging and Test Stimulusa

Interval

Wild circling activity (ye)

Oh Sh 18 h 24 h 48 h 9 days a DBA/lBg-ras and the plugs

MASSON

were

Clonic-tonic seizures (ye)

0 0 6 24 32 36 mice had removed

both after

external different

0 0 0 5 9 17 auditory intervals

N

20 30 31 42 34 36

canals plugged at 19 days of age, as indicated prior to testing.

and by the finding of pharmacogenetic differences in acoustic priming of C57BL/6Bg and DBA/lBg-ras mice, there are strain differences in the development of audiogenic seizures following an initial auditory stimulus, but not after external ear plugging. Because both conditions result in attenuation of hearing (5, 7, 14), it seems reasonable to conclude that the strain differences in the development of susceptibility after acoustic priming must involve a mechanism in addition to that of IAS-produced hearing loss. Maxson et al. (11) suggestedthat this additional mechanism is mediated by a post-IAS decrease in the concentration of brain GABA and that for a brief period post-IA& this mechanism requires brain protein synthesis. This study also shows that this direct and central neurochemical mechanism produces increased susceptibility to audiogenic seizures within 5 h after exposure to the IAS and that the other mechanism involving peripheral hearing loss and central disuse supersensitivity requires as much as 24 h for it to cause increased seizure susceptibility. Evidence of the latter effect is seen in both the IAS-produced susceptibility of DBA/lBgras and the EEP-produced susceptibility of C57BL/6Bg and DBAJlBgras mice. The findings reported for the effects of the IAS on the development of susceptibility of C57BL/6 are consistent with those described by Boggan et al. (2), but not by Henry (5) and McGinn and Henry (8). Boggan et al. (2) found that C57BL/6 mice were susceptible by 1 h post-IAS, whereas Henry and his colleagues (5, 8) reported that C57BL/6 mice were not susceptible until 48 h after exposure to the IAS. Interestingly, in our studies and in those of Boggan et al. (2), the mice were exposed to the IAS at 19 days of age, whereas in those of Henry and hk associates (5, S), the mice were exposed to the IAS at 16 days of age. One plausible

DEVELOl’RlENT

OF

AUl~IC)C;ENIC

4x7

Sl’IZURIZi

explanation for the discrepancy in the patterns for development of susceptibility after the IAS at 16 and 19 days would be that acoustic priming at 16 days involves only the IAS-produced hearing loss and does not involve the IAS-produced decrease in the concentration of brain GABA and that acoustic priming at 19 days is mediated by both mechanisms. In support of this hypothesis is the observation that it takes between 24 and 48 h for either an IAS or EEP to produce susceptibility in C57BL/6 mice acoustically primed at 16 days of age and DBA/lBg+us acoustically primed at 19 days of age, and for either C57BL/6 or DBA/lBg-ms mice with ears plugged at 19 days of age. Also consistent with this hypothesis are the findings that elevating brain concentrations of biogenic amines blocks acoustic priming in mice exposed to the IAS at Day 16 (6), but not in mice exposed to the IAS at Day 19 (2). Thus, there may not only be genetic but also developmental variation in the mechanism of acoustic priming for susceptibility to audiogenic seizures. REFERENCES 1. ARKIN, H., AND New York. 2. BOGGAN, W. O.,

3.

4.

5. 6. 7.

R. R. COLTON.

1970. Statistical

Methods.

Barnes and

Noble,

D. X. FREEDMAN, AND R. A. LOVELL. 1971. Studies in audiogenie seizure susceptibility. Psyclzoplzarmacologia 20 : 48-56. CHEN, C.-S., AND J. L. FULLER. 1976. Selection for spontaneous or priming induced audiogenic seizure susceptibility iu mice. J. co~tp. Physiol. Psyclrol. 90 : 765-772. GATES, G. R., C.-S. CHEN, AND G. R. BOCK. 1973. Effects of monaural and binaural auditory deprivation on audiogenic seizure susceptibility in BALB/c mice. Exp. Nrurol. 38 : 488-493. HENRY, K. R. 1972. Pinna reflex thresholds and audiogenic seizures : Developmental changes after acoustic priming. J. Cowp, Physiol. Psyclrol. 79: 77-81. KELLOCG, C. 1975. Audiogenic seizures: Relation to age and central monoaminergic mechanisms. Sot. Neurosci. .4&r. 1: 793. MCGINN, M. D., J. F. WILLOTT, AND K. R. HENRY. 1973. Effects of conductive hearing loss on auditory evoked potentials and audiogenic seizures in mice. Nature

(Loudon)

244 : 255-256.

8. MCGINN, M. D., AND K. R. HENRY. 1975. Acute versus chronic acoustic deprivation: Effects on auditory evoked potentials and seizures in mice. Dczf. PJJIC~Obiol. 8: 223-232. 9. MAXSON, S. C., A. C. TOWLE, AND P. Y. SZE. 1976. Macromolecules of the central nervous system and acoustic priming in C57BL/6Bg mice. BC/~UZI.Biol. 18: 111-122. 10. MAXSON, S. C., A. C. TOWLE, AND P. Y. SZE. 1977. Brain y-aminobutyric acid and acoustic priming in C57BL/6Bg mice. Psychopharmacology 53 : 217-222. 11. MAXSON,

S. C., J. S. COWEN,

in audiogenic Pharmacol.

seizure

Biochcm.

AND P. Y. SZE.

priming Bchazr.

1977.

of C57BL/6Bg

7 : 221-226.

Pharmacogenetic

and

DBA/lBg-asr

differences

mice.

488

STEPHEN

C.

MAXSON

12. SZE, P. Y. 1970. Neurochemical factors in auditory stimulation and development of susceptibility to audiogenic seizures. Pages 259-269 in B. L. WELCH AND A, S. WELCH, ECds., Physiological Effects of Noise. Plenum, New York. 13. SZE, P. Y., AND S. C. MAXSON. 1975. Involvement of corticosteroids in acoustic induction of audiogenic seizure susceptibility in mice. Ps_vchopkar~HocologiazocoZog~a 45 : 79-82. 14. WILLOTT, J. F., AND K. R. HENRY. 1974. Auditory evoked potentials: Developmental changes of threshold and amplitude following early acoustic trauma. J. Con@.

Physiol.

Psychol.

86:

1-7.