Abstract
The positively-reinforcing effect of acute morphine sulfate (MS) administration was assessed by concurrent rate-dependent and rate-independent measures of brain stimulation reward in male rats. An acute 4 mg/kg MS injection produced a rapid, statistically-significant decrease in reward threshold of 28.5%, when compared with saline control values, 45 min after injection. Response rates for brain stimulation delivery decreased by 60.6%, when compared with saline values during the period of maximum threshold change. Other animals, injected with an acute 1 mg/kg MS dose, exhibited significant threshold decreases (21.5%), relative to changes in saline values that occurred in a prior session, and response-rate increases of 23.1%, relative to saline-session changes, when the data were recorded 40 min after injection. The findings reported here demonstrate that the decreases in reward threshold produced by acute morphine administration are independent of the response-rate changes that occur and also support the idea that morphine's rewarding effect may be independent of the behavioral inhibition or activation that can result from the effects of different morphine doses.
Similar content being viewed by others
References
Esposito RU, Kornetsky C (1977) Morphine lowering of self-stimulation thresholds: lack of tolerance with long-term administration. Science 195:189–191
Esposito RU, Kornetsky C (1978) Opioids and rewarding brain stimulation. Neurosci Biobehav Rev 2:115–122
Fog R (1970) Behavioural effects in rats of morphine and amphetamine and of a combination of the two drugs. Psychopharmacologia 16:305–312
Glick SD, Rapaport G (1974) Tolerance to the facilitatory effect of morphine on self-stimulation of the medial forebrain bundle in rats. Res Commun Chem Pathol Pharmacol 9:647–652
Izenwasser SF, Kornetsky C (1987) Pharmacological effects of morphine on brain stimulation reward. Psychopharmacology 93:136–137
Liebman JM (1983) Discriminating between reward and performance: a critical review of intracranial self-stimulation methodology. Neurosci Biobehav Rev 7:45–72
Lorens SA, Mitchell CL (1973) Influence of morphine on lateral hypothalamic self-stimulation in the rat. Psychopharmacologia 32:271–277
Marcus R, Kornetsky C (1974) Negative and positive intracranial reinforcement thresholds: effects of morphine. Psychopharmacologia 38:1–13
Nazzaro JM, Seeger TF, Gardner EL (1981) Morphine differentially affects ventral tegmental and substantia nigra brain reward thresholds. Pharmacol Biochem Behav 14:325–331
O'Callaghan JP, Holtzman SG (1975) Quantification of the analgesic activity of narcotic antagonists by a modified hot-plate procedure. J Pharmacol Exp Ther 192:497–505
Paxinos G, Watson C (1986) The rat brain in stereotaxic coordinates, 2nd edn. Academic Press, New York
Schaefer GJ, Michael RP (1986) Changes in response rates and reinforcement thresholds for intracranial self-stimulation during morphine withdrawal. Pharmacol Biochem Behav 25:1263–1269
Stein L, Ray OS (1960) Brain stimulation reward “thresholds” self-determined in rats. Psychopharmacologia 1:751–756
van Wolfswinkel L, Seifert WF, van Ree JM (1985) Long-term changes in self-stimulation threshold by repeated morphine and naloxone treatment. Life Sci 37:169–176
Vasko MR, Domino EF (1978) Tolerance development to the biphasic effects of morphine on locomotor activity and brain acetylcholine in the rat. J Pharmacol Exp Ther 207:848–858
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Hine, B., Lopez, M. Acute morphine lowers brain stimulation reward thresholds in rats with depressed or elevated response rates. Psychopharmacology 102, 309–311 (1990). https://doi.org/10.1007/BF02244095
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF02244095