0 1979 Gordon and Breach Science Publishers, Inc.
Intern. J . Neuroscience, 1979, Vol. 9, pp. 213-215 002@-7454/79/0904-02 13$04.50/0
Printed in Great Britain
OPIATE STIMULATION INCREASES EXPLORATION IN THE MOUSE RICHARD J. KATZ Mental Health Research Institute, University of Michigan Medical Center
Int J Neurosci Downloaded from informahealthcare.com by Osaka University on 10/28/14 For personal use only.
(Received February 2, 1979) Adult male Swiss-Webster mice were injected with a low dose of morphine sulfate or vehicle and placed in an apparatus which allowed the assessment of exploratory behavior. Two measures of exploration (rearing, nose poking) were recorded during a single brief exposure. Both exploratory behaviors increased after drug treatment. This suggests opiate involvement in behavioral arousal, and more specifically, in exploratory behavior.
METHODS
Based upon typical patterns of response in an open field (Katz, 1979a) behavioral reductions in several typically employed models of activation and exploration by narcotic antagonists (Katz et al., 1978; Katz & Gelbart, 1978; Katz, 1979b), and high correlations of exploration and opiate activation (Katz & Gelbart, 1978), we have argued that endogenous opiates (endorphins) may be involved in exploration. Several related experiments additionally support and extend these observations and hypothesis (Grevert & Goldstein, 1977; Berntson et al., 1978; Haber et al., 1979). If exploration, in fact, is partially mediated through opiate receptor activity, then receptor activation by pharmacological means should, at least in principle, also increase behaviors associated with exploration. The present experiment tested this hypothesis. Since naturally occurring opiates are short-acting and highly susceptible to catabolism, morphine was used as a more stable receptor agonist.
Subjects
Thirty-five adult male Swiss-Webster albino mice 3 0 4 0 g each were obtained locally (Charles River Farms, Portage, Michigan) and maintained in group housing 6 mice per cage. Food (Teklad 4.0% fat rodent diet S-0836) and tap water were continuously available, and normal daylnight cycles of 12 hours (lights on = 0800-2000 h) were maintained by automatic timers. Seventeen mice were used as the experimental group, and the remaining 18 mice served as controls.
Apparatus ond Behavioral Procedure
The apparatus has been described in detail elsewhere (Katz & Gelbart, 1978, experiment 1). Briefly it consisted of an 8 . 5 ~ 2 9 . 15 5 ~cm clear Plexiglas box which contained a black Plexiglas floor with two centrally located beveled holes, each of which was 1 cm in diameter. Approximately 10 to 15 min after injection the mouse was individually placed in the apparatus for a single 5 min recording period. Two behaviors were assessed: these were rearing and discrete nose pokes into the holes. Both behaviors have been established as exploratory in previous studies (e.g., File & Wardill, 1975; Mackintosh et al., 1977; Katz & Gelbart, 1978).
Supported in part by postdoctoral grant MH 07417 from the National Institute of Mental Health, through the Mental Health Research Institute. The technical assistance of E. Duff Bailey and editorial assistance of Linda Stevenson are ecknowledged with gratitude. I am also grateful to Dr. Huda Akil for her comments, and several conversations upon her own related findings. 213
R. J. KATZ
214
Drugs Morphine was injected as morphine sulfate 1.5 mg/kg. All injections were administered 10 ml/kg, and utilized 0.9% sodium chloride solution as the vehicle.
that the experimental treatment elevated both rearing and nose poking in comparison with control performance. Both changes were roughly equivalent in magnitude and represented 20-30 % increases above baseline. Respective U scores indicate that both changes are statistically significant (U = 49, 60 respectively; p
Intern. J . Neuroscience, 1979, Vol. 9, pp. 213-215 002@-7454/79/0904-02 13$04.50/0
Printed in Great Britain
OPIATE STIMULATION INCREASES EXPLORATION IN THE MOUSE RICHARD J. KATZ Mental Health Research Institute, University of Michigan Medical Center
Int J Neurosci Downloaded from informahealthcare.com by Osaka University on 10/28/14 For personal use only.
(Received February 2, 1979) Adult male Swiss-Webster mice were injected with a low dose of morphine sulfate or vehicle and placed in an apparatus which allowed the assessment of exploratory behavior. Two measures of exploration (rearing, nose poking) were recorded during a single brief exposure. Both exploratory behaviors increased after drug treatment. This suggests opiate involvement in behavioral arousal, and more specifically, in exploratory behavior.
METHODS
Based upon typical patterns of response in an open field (Katz, 1979a) behavioral reductions in several typically employed models of activation and exploration by narcotic antagonists (Katz et al., 1978; Katz & Gelbart, 1978; Katz, 1979b), and high correlations of exploration and opiate activation (Katz & Gelbart, 1978), we have argued that endogenous opiates (endorphins) may be involved in exploration. Several related experiments additionally support and extend these observations and hypothesis (Grevert & Goldstein, 1977; Berntson et al., 1978; Haber et al., 1979). If exploration, in fact, is partially mediated through opiate receptor activity, then receptor activation by pharmacological means should, at least in principle, also increase behaviors associated with exploration. The present experiment tested this hypothesis. Since naturally occurring opiates are short-acting and highly susceptible to catabolism, morphine was used as a more stable receptor agonist.
Subjects
Thirty-five adult male Swiss-Webster albino mice 3 0 4 0 g each were obtained locally (Charles River Farms, Portage, Michigan) and maintained in group housing 6 mice per cage. Food (Teklad 4.0% fat rodent diet S-0836) and tap water were continuously available, and normal daylnight cycles of 12 hours (lights on = 0800-2000 h) were maintained by automatic timers. Seventeen mice were used as the experimental group, and the remaining 18 mice served as controls.
Apparatus ond Behavioral Procedure
The apparatus has been described in detail elsewhere (Katz & Gelbart, 1978, experiment 1). Briefly it consisted of an 8 . 5 ~ 2 9 . 15 5 ~cm clear Plexiglas box which contained a black Plexiglas floor with two centrally located beveled holes, each of which was 1 cm in diameter. Approximately 10 to 15 min after injection the mouse was individually placed in the apparatus for a single 5 min recording period. Two behaviors were assessed: these were rearing and discrete nose pokes into the holes. Both behaviors have been established as exploratory in previous studies (e.g., File & Wardill, 1975; Mackintosh et al., 1977; Katz & Gelbart, 1978).
Supported in part by postdoctoral grant MH 07417 from the National Institute of Mental Health, through the Mental Health Research Institute. The technical assistance of E. Duff Bailey and editorial assistance of Linda Stevenson are ecknowledged with gratitude. I am also grateful to Dr. Huda Akil for her comments, and several conversations upon her own related findings. 213
R. J. KATZ
214
Drugs Morphine was injected as morphine sulfate 1.5 mg/kg. All injections were administered 10 ml/kg, and utilized 0.9% sodium chloride solution as the vehicle.
that the experimental treatment elevated both rearing and nose poking in comparison with control performance. Both changes were roughly equivalent in magnitude and represented 20-30 % increases above baseline. Respective U scores indicate that both changes are statistically significant (U = 49, 60 respectively; p
