MK-801 Disrupts the expression but not the development of bromocriptine sensitization: A state-dependency interpretation
✍ Scribed by William A. Carlezon Jr.; Adrianna Mendrek; Roy A. Wise
- Publisher
- John Wiley and Sons
- Year
- 1995
- Tongue
- English
- Weight
- 974 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0887-4476
No coin nor oath required. For personal study only.
✦ Synopsis
Repeated administration of the D,-type agonist bromocriptine (5.0 mg/ kg, IP) caused progressive increases in the locomotor-stimulating effects of the drug in rats. Similar progressive increases in locomotor activity were observed in rats that received repeated coadministration of the NMDA receptor antagonist MK-801 (0.25 mg/ kg, IP) plus bromocriptine. However, when rats previously treated with the combination of drugs received either bromocriptine or MK-801 alone, their levels of activity were comparable to those of rats having no prior experience with either drug. A second group of rats was sensitized to the effects of bromocriptine alone; no evidence of bromocriptine sensitization was seen when MK-801 was subsequently coadministered with bromocriptine. Thus, either the presence or the absence of MK-801 could-depending upon the conditions of previous drug treatment-block the expression of bromocriptine sensitization. When a third group of rats was sensitized to the combination of MK-801 plus bromocriptine and subsequently tested following 2 or 6 drug-free weeks, evidence of sensitized responses was still present. Thus, at the very least, blockade of NMDA receptors with MK-801 fails to compromise the cellular changes associated with sensitization to the repeated combination of MK-801 plus bromocriptine. Bromocriptine sensitization may prove to be unique in this regard, but the present findings suggest a control condition that should be carefully explored in studies of the effects of MK-801 on sensitization involving other stimulant drugs. o 1995 WiIey-Liss, Inc.