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Comparison of the effects of morphine on hypothalamic and medial frontal cortex self-stimulation in the rat

Comparison of the effects of morphine on hypothalamic and medial frontal cortex self-stimulation... 213 48 48 2 2 Stanley A. Lorens Department of Pharmacology University of Bergen MFH-Bygget N-5000 Bergen Norway Abstract The effect of morphine (3.75, 7.5, and 15.0 mg/kg. s.c.) on medial frontal cortex (MF) and hypothalamic self-stimulation (SS) was determined 1, 3, 5, and 7 h after injection for 5 consecutive days. Morphine suppressed or enhanced SS responding as a function of dose, time after injection, and the site stimulated. The MF SS groups were less sensitive to the toxic effects of morphine, and evidenced elevated rates of responding earlier after injection than the hypothalamic animals. The dose-response relationship of the MF rats, thus, clearly differed from that of the hypothalamic rats. With repeated administration, tolerance was rapidly (3–4 days) developed to the suppressive effect while the excitatory effect appeared earlier and tended to be enhanced, peaking 1 and 3 h after injection in the MF and hypothalamic groups, respectively. These data provide additional evidence against the hypothesis that the effect of morphine on SS behavior is non-specific. It it were, the time course and degree of effects should be similar, regardless of the electrode site tested. Furthermore, an inhibitory effect was not observed in the groups receiving 3.75 mg/kg although both showed a significant increase in responding 1 and/or 3 h after injection. This observation indicates that the excitatory effect is not dependent on the depressant effect and, therefore, probably is not a rebound phenomenon. It also suggests that the toxic effects of morphine can either mask or delay the appearance of its facilitatory action on SS responding. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Psychopharmacology Springer Journals

Comparison of the effects of morphine on hypothalamic and medial frontal cortex self-stimulation in the rat

Psychopharmacology , Volume 48 (2) – Jan 1, 1976

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References (16)

Publisher
Springer Journals
Copyright
Copyright © 1976 by Springer-Verlag
Subject
Biomedicine; Pharmacology/Toxicology; Psychiatry
ISSN
0033-3158
eISSN
1432-2072
DOI
10.1007/BF00423264
Publisher site
See Article on Publisher Site

Abstract

213 48 48 2 2 Stanley A. Lorens Department of Pharmacology University of Bergen MFH-Bygget N-5000 Bergen Norway Abstract The effect of morphine (3.75, 7.5, and 15.0 mg/kg. s.c.) on medial frontal cortex (MF) and hypothalamic self-stimulation (SS) was determined 1, 3, 5, and 7 h after injection for 5 consecutive days. Morphine suppressed or enhanced SS responding as a function of dose, time after injection, and the site stimulated. The MF SS groups were less sensitive to the toxic effects of morphine, and evidenced elevated rates of responding earlier after injection than the hypothalamic animals. The dose-response relationship of the MF rats, thus, clearly differed from that of the hypothalamic rats. With repeated administration, tolerance was rapidly (3–4 days) developed to the suppressive effect while the excitatory effect appeared earlier and tended to be enhanced, peaking 1 and 3 h after injection in the MF and hypothalamic groups, respectively. These data provide additional evidence against the hypothesis that the effect of morphine on SS behavior is non-specific. It it were, the time course and degree of effects should be similar, regardless of the electrode site tested. Furthermore, an inhibitory effect was not observed in the groups receiving 3.75 mg/kg although both showed a significant increase in responding 1 and/or 3 h after injection. This observation indicates that the excitatory effect is not dependent on the depressant effect and, therefore, probably is not a rebound phenomenon. It also suggests that the toxic effects of morphine can either mask or delay the appearance of its facilitatory action on SS responding.

Journal

PsychopharmacologySpringer Journals

Published: Jan 1, 1976

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