Control of food delivery in food-deprived rats mediates analgesia.
An experiment was carried out to investigate the effects of control of food delivery, in food-deprived rats, on analgesia. Tail flick latency was used as an index of pain sensitivity and naloxone reversibility of analgesia was used as the criterion for opioid involvement. Food-deprived rats were submitted to one of two schedules of food delivery. The 'contingent' group could control the delivery of food by lever-pressing. The 'non-contingent' group received the same number of food pellets but delivery of food was independent of lever-pressing behaviour. Animals in the 'control' group were placed in the test chamber but did not receive any pellets. Subjects were tested on 6 consecutive days, each test session being of 10 min duration. Half of the animals in each group received an intraperitoneal injection of saline (0.5 ml) prior to each test session, the other half received an intraperitoneal injection of naloxone (5 mg/kg in 0.5 ml saline) prior to each session. Both contingent and non-contingent food delivery resulted in a significant post-test analgesia. The analgesia was noticeably greater when food delivery was non-contingent and this analgesia was reversible by naloxone. The findings suggest that non-contingent food delivery, in food-deprived rats, elicits an opioid analgesia, whilst contingent food delivery elicits a non-opioid analgesia.
Hodgson
D M
DM
Macquarie University, N.S.W., Australia.
Bond
N W
NW
D000698:Analgesia / Q000523:psychology*; D000818:Animals; D003216:Conditioning, Operant / Q000502:physiology; D004723:Endorphins / Q000502:physiology; D005502:Food; D005508:Food Deprivation / Q000502:physiology*; D007274:Injections, Intraperitoneal; D008297:Male; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology; D010147:Pain Measurement; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000502:physiology; D012055:Reinforcement Schedule
D004723:Endorphins; D009270:Naloxone