Self-administration of neurokinin substance P into the ventromedial caudate-putamen in rats.
There is evidence that the neurokinin substance P plays a role in learning and reinforcement processes. Reinforcing effects of substance P were found upon injection into several parts of the brain. The aim of the present study was to gauge possible reinforcing effects of microinjections of substance P into the ventromedial caudate-putamen in rats. Two different behavioral paradigms were employed. In the first experiment a two-compartment choice procedure was used and the rats could trigger substance P injections (500 pg per 5 nl injection volume) into the ventromedial caudate-putamen by entering one distinctive compartment. During the injection period, substance P-injected animals spent significantly more time in the drug-paired compartment than vehicle-injected controls. In the second experiment, nose-poking through a hole in one wall of the cage was used as the operant. Rats that could self-administer substance P (100 pg per 5 nl injection volume) into the ventromedial caudate-putamen emitted a significantly higher rate of operant responding on the first day of testing and a significantly lower rate on the third day compared to vehicle-injected animals. The experiments provide evidence that the administration of substance P into the ventromedial part of the caudate-putamen can have positive reinforcing effects, but that repeated injections can have aversive properties. These effects are discussed, firstly, with regard to the possible mechanisms of intrastriatal substance P on striatonigral and striatopallidal output systems and, secondly, with respect to their possible relevance in the study of the basal forebrain reinforcement system.
Krappmann
P
P
Institute of Physiological Psychology I, Heinrich-Heine-University of Düsseldorf, Germany.
Hasenöhrl
R U
RU
Frisch
C
C
Huston
J P
JP
D000818:Animals; D002421:Caudate Nucleus / Q000187:drug effects / Q000502:physiology*; D002755:Choice Behavior; D003216:Conditioning, Operant; D008297:Male; D008845:Microinjections; D011699:Putamen / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D012054:Reinforcement, Psychology; D012646:Self Administration; D013373:Substance P / Q000008:administration & dosage* / Q000494:pharmacology
D013373:Substance P