Journal of Comparative and Physiological Psychology 1976, Vol. 90, No. 8, 765-772
Selection for Spontaneous or Priming-Induced Audiogenic Seizure Susceptibility in Mice Chia-Shong Chen Monash University Clayton, Victoria, Australia
John L. Fuller Stale University of New York at Binghampton
Four lines of mice were selectively bred from a heterogeneous foundation stock for audiogenic seizure prone (SP), priming prone (PP), moderately priming prone (MPP), and seizure resistant (SR). Significant changes in proportions of animals showing the desired phenotypes were found after two generations of selection, indicating involvement of genetic components in these behavioral characteristics. Although response to selection for spontaneous seizure proneness was rapid, the results do not support a view that initial seizure risk is controlled by a single recessive gene. The effects of tympanic membrane perforation on development of seizure susceptibility in these four selected lines were investigated in Experiment 2. Results indicate that the method is highly effective in inducing seizure susceptibility in the PP mice and the SR mice, but not so effective for the SP and the MPP lines. These results suggest that spontaneous and priming-induced seizure susceptibility could be due to development of hyperreactivity in centripetal auditory structures brought about by reduction of auditory input. They also suggest that the phenotypic difference between the PP and the SR lines could be due to differences in their cochlear susceptibility to stimulation damage but that a qualitatively different mechanism is involved in the MPP line.
ing from a heterogeneous stock of mice. If spontaneous audiogenic seizure risk is indeed indicative of the presence of a single recessive gene, the seizure risk of the first selected generation of a seizure-prone line should approximate unity. Since Henry (1967) demonstrated that audiogenic seizure susceptibility could be induced in normally seizure-resistant C57BL/6J mice by a priming procedure, similar results have been obtained in other "resistant" strains of mice (Fuller & Collins, 1968; Boggan, Freedman, & Lovell, 1971; Chen, 1973a, 1973b; Henry & Bowman, 1969, 1970; Iturrian & Fink, 1968). Nevertheless, difficulties in obtaining the priming effect in certain lines of mice have been reported (Chen, 1973a, 1973b; Schlesinger, Note 1), suggesting that a genetic factor is important in priming. In view of This study was conducted at State University of this possibility, selection for differential New York at Binghamton when the first author was on sabbatical leave from the Monash Uni- vulnerability to priming was also included versity. It was supported by Grant B041424 from in this project. The exact mechanism of genetic transmission of audiogenic seizure susceptibility in mice is still not fully understood. Data supporting a single dominant gene (Witt & Hall, 1949), double factors (Ginsberg & Miller, 1963), or multiple factors (Fuller, Easier, & Smith, 1950; Schlesinger, Elston, &. Boggan, 1966) have been reported. Suspecting that these discrepancies might be due to the action of a confounding factor, namely priming-induced seizure risk, Collins and Fuller (1968) conducted a properly controlled experiment and found that the difference in spontaneous seizure risk between strains C57BL/6J and DBA/2J was due to a single recessive gene, asp (audiogenic seizure prone). The aim of the present experiment was to test the generality of this hypothesis by selective breed-
the National Science Foundation. Part of the study was reported at the Fourth Annual Meeting of Behavior Genetics Association (1974). Requests for reprints should be sent to ChiaShong Chen, Psychology Department, Monash University, Clayton, Victoria 3168, Australia.
EXPERIMENT 1 Method The foundation stock (128 mice) for this selection program was from the 19th generation of a
765
766
CHIA-SHONG CHEN AND JOHN L. FULLER
heterogeneous stock (Binghamton-HET) maintained by one of us (J. L. Fuller). The original heterogeneous stock was produced by an eightway cross of eight inbred strains: LP/J, BALB/cJ, MA/J, SM/J, C57BL/6J, LG/J, 129/J, and DBA/ 2J. The DBA/2J, LP/J and 129/J strains are known to be highly seizure prone, whereas CS7BL/ 6J and BALB/cJ are regarded as seizure resistant (Fuller & Sjursen, 1967). The plan of the selection program was to select five lines of mice differing in types and degrees of seizure susceptibility. Selection for a highly seizure-prone (SP) line was based on the phenotype of at least clonic seizure on the first exposure to an intense bell sound at 18 days of age. Selection of a moderately seizure-prone line was based on the phenotype of wild running only or longlatency clonic seizure (longer than 30 sec after onset of the bell sound) on first exposure; however, this line was later dropped from the program because of lack of subjects. Selection for a primingprone (PP) line was based on the phenotype of no seizure responses on the first test at 18 days of age but at least a clonic seizure on the second test at 20 days of age. Selection for a moderately priming-prone (MPP) line was based on the phenotype of no seizure responses on the first test, with only wild running or long-latency seizure (>30 sec) on the second test at 20 days of age. The seizure-resistant line (SR) was selected for not seizing on both tests. At 18 days of age, all mice in the selection experiment were exposed to the sound of an electric bell (108-110 dB re 20 M N/m 2 ) for 60 sec or until seizure occurred. Animals that failed to seize on the first test were reexposed 2 days later to the same test stimulus for 60 sec or until seizure occurred. Thus, the first test could be regarded as the priming treatment. Unpublished data (Fuller, 1972) indicated that 18 days of age and a 2-day prime-test interval were the optimal temporal parameters for obtaining seizure responses in the heterogeneous line. The incidence of wild running, clonic-tonic seizures, and death, and the latencies to wild running and clonic seizure were recorded. All tests were carried out in the afternoon to minimize the effects of circadian variation of seizure susceptibility. Results and Discussion The results shown in Figure 1 clearly indicate that the response to selection was very rapid. Significant change from the foundation stock in the proportions of animals showing wild running (WR) and clonic seizure (CL) on the first trial was obtained in the first generation of selection (SP line:
WR,
2
X
(l) = 5.47; CL,
2
X
(D = 6.18; ps
< .02; non-seizure-prone mice, the combined PP, MPP, and the SR lines: WR, X 2 (D = 52.24; CL, x »(l) = 64.42, ps < .01). These changes were further accel-
100
N-107
90 Ul
a:
80
UJ C/l
70
• o
Selection for Spontaneous or Priming-Induced Audiogenic Seizure Susceptibility in Mice Chia-Shong Chen Monash University Clayton, Victoria, Australia
John L. Fuller Stale University of New York at Binghampton
Four lines of mice were selectively bred from a heterogeneous foundation stock for audiogenic seizure prone (SP), priming prone (PP), moderately priming prone (MPP), and seizure resistant (SR). Significant changes in proportions of animals showing the desired phenotypes were found after two generations of selection, indicating involvement of genetic components in these behavioral characteristics. Although response to selection for spontaneous seizure proneness was rapid, the results do not support a view that initial seizure risk is controlled by a single recessive gene. The effects of tympanic membrane perforation on development of seizure susceptibility in these four selected lines were investigated in Experiment 2. Results indicate that the method is highly effective in inducing seizure susceptibility in the PP mice and the SR mice, but not so effective for the SP and the MPP lines. These results suggest that spontaneous and priming-induced seizure susceptibility could be due to development of hyperreactivity in centripetal auditory structures brought about by reduction of auditory input. They also suggest that the phenotypic difference between the PP and the SR lines could be due to differences in their cochlear susceptibility to stimulation damage but that a qualitatively different mechanism is involved in the MPP line.
ing from a heterogeneous stock of mice. If spontaneous audiogenic seizure risk is indeed indicative of the presence of a single recessive gene, the seizure risk of the first selected generation of a seizure-prone line should approximate unity. Since Henry (1967) demonstrated that audiogenic seizure susceptibility could be induced in normally seizure-resistant C57BL/6J mice by a priming procedure, similar results have been obtained in other "resistant" strains of mice (Fuller & Collins, 1968; Boggan, Freedman, & Lovell, 1971; Chen, 1973a, 1973b; Henry & Bowman, 1969, 1970; Iturrian & Fink, 1968). Nevertheless, difficulties in obtaining the priming effect in certain lines of mice have been reported (Chen, 1973a, 1973b; Schlesinger, Note 1), suggesting that a genetic factor is important in priming. In view of This study was conducted at State University of this possibility, selection for differential New York at Binghamton when the first author was on sabbatical leave from the Monash Uni- vulnerability to priming was also included versity. It was supported by Grant B041424 from in this project. The exact mechanism of genetic transmission of audiogenic seizure susceptibility in mice is still not fully understood. Data supporting a single dominant gene (Witt & Hall, 1949), double factors (Ginsberg & Miller, 1963), or multiple factors (Fuller, Easier, & Smith, 1950; Schlesinger, Elston, &. Boggan, 1966) have been reported. Suspecting that these discrepancies might be due to the action of a confounding factor, namely priming-induced seizure risk, Collins and Fuller (1968) conducted a properly controlled experiment and found that the difference in spontaneous seizure risk between strains C57BL/6J and DBA/2J was due to a single recessive gene, asp (audiogenic seizure prone). The aim of the present experiment was to test the generality of this hypothesis by selective breed-
the National Science Foundation. Part of the study was reported at the Fourth Annual Meeting of Behavior Genetics Association (1974). Requests for reprints should be sent to ChiaShong Chen, Psychology Department, Monash University, Clayton, Victoria 3168, Australia.
EXPERIMENT 1 Method The foundation stock (128 mice) for this selection program was from the 19th generation of a
765
766
CHIA-SHONG CHEN AND JOHN L. FULLER
heterogeneous stock (Binghamton-HET) maintained by one of us (J. L. Fuller). The original heterogeneous stock was produced by an eightway cross of eight inbred strains: LP/J, BALB/cJ, MA/J, SM/J, C57BL/6J, LG/J, 129/J, and DBA/ 2J. The DBA/2J, LP/J and 129/J strains are known to be highly seizure prone, whereas CS7BL/ 6J and BALB/cJ are regarded as seizure resistant (Fuller & Sjursen, 1967). The plan of the selection program was to select five lines of mice differing in types and degrees of seizure susceptibility. Selection for a highly seizure-prone (SP) line was based on the phenotype of at least clonic seizure on the first exposure to an intense bell sound at 18 days of age. Selection of a moderately seizure-prone line was based on the phenotype of wild running only or longlatency clonic seizure (longer than 30 sec after onset of the bell sound) on first exposure; however, this line was later dropped from the program because of lack of subjects. Selection for a primingprone (PP) line was based on the phenotype of no seizure responses on the first test at 18 days of age but at least a clonic seizure on the second test at 20 days of age. Selection for a moderately priming-prone (MPP) line was based on the phenotype of no seizure responses on the first test, with only wild running or long-latency seizure (>30 sec) on the second test at 20 days of age. The seizure-resistant line (SR) was selected for not seizing on both tests. At 18 days of age, all mice in the selection experiment were exposed to the sound of an electric bell (108-110 dB re 20 M N/m 2 ) for 60 sec or until seizure occurred. Animals that failed to seize on the first test were reexposed 2 days later to the same test stimulus for 60 sec or until seizure occurred. Thus, the first test could be regarded as the priming treatment. Unpublished data (Fuller, 1972) indicated that 18 days of age and a 2-day prime-test interval were the optimal temporal parameters for obtaining seizure responses in the heterogeneous line. The incidence of wild running, clonic-tonic seizures, and death, and the latencies to wild running and clonic seizure were recorded. All tests were carried out in the afternoon to minimize the effects of circadian variation of seizure susceptibility. Results and Discussion The results shown in Figure 1 clearly indicate that the response to selection was very rapid. Significant change from the foundation stock in the proportions of animals showing wild running (WR) and clonic seizure (CL) on the first trial was obtained in the first generation of selection (SP line:
WR,
2
X
(l) = 5.47; CL,
2
X
(D = 6.18; ps
< .02; non-seizure-prone mice, the combined PP, MPP, and the SR lines: WR, X 2 (D = 52.24; CL, x »(l) = 64.42, ps < .01). These changes were further accel-
100
N-107
90 Ul
a:
80
UJ C/l
70
• o
