[Effect of injection of enkephalin and bestatin in caudate-putamen on operant conditioning in rats].
Female Wistar rats were trained in a Skinner-box, 30 trials per day in a dark room to establish operant defence conditioning. Training started with a light (15 s), then combined with footshock for further 8 s. When the rats learned to press the key to avoid footshock within 15 s, conditioned response was considered established. After the rats reached a conditioning rate (CR) above 80% for 5 days, cannulae were implanted into caudate-putamen. Two to three days later, Met-enkephalin (MEK) or bestatin (an aminopeptidase inhibitor) was injected bilaterally into caudate-putamen. 30 min, 2 h, 24 h and 48 h after injection, conditioning tests were conducted, with each session consisting of 30 trials. Control experiments were done when 0.9% NaCl (NS) was injected. After injection of NS, CR maintained above 80% in all 4 test sessions. MEK (60 ng/rat) or bestatin (10 micrograms/rat) significantly lowered the CR during the 30 min and 2 h test session. In the latter case, the latency (L) was also prolonged. However both CR and L returned to the control level in the 24 h and 48 h test sessions. Naloxone (2 mg/kg, i.p.) blocked the conditioning-depression effect of bestatin. No significant alteration was seen in locomotor activity after MEK or bestatin injection. The results suggest that enkephalin in caudate-putamen may be involved in the regulation of retrieval of conditioning. Bestatin mimics the effect of MEK on conditioning reflex probably by increasing production of endogenous enkephalin.
Zhang
S Y
SY
Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Beijing.
Zhang
Y P
YP
Zhang
M L
ML
Qi
H X
HX
Wang
B
B
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology; D002421:Caudate Nucleus / Q000502:physiology*; D003216:Conditioning, Operant / Q000187:drug effects* / Q000502:physiology; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D005260:Female; D007930:Leucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D008845:Microinjections; D009043:Motor Activity / Q000187:drug effects; D011699:Putamen / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects
D004744:Enkephalin, Methionine; D007930:Leucine; C012211:ubenimex