Endogenous opiates and stress-induced eating.

Maickel, G. K. W. Yim, Life Sci. 26, 2113 (1980)] and failed to observe their reported decrease ofTP eating after naloxone. We have also used greater numbers of TP trials with the same negative results [N. L. Ostrowski, N. Rowland, T. L. Foley, J. L. Nelson, L. D. Reid, PharmacQl. Biochem. Behav. 14, 549 (1981)]. In each case we measured the amount consumed, amount spilled, and duration of food-directed oral behavior. 5. G. Curzon, P. H. Hutson, P. J. Knott, Br. J. Pharmacol. 66, 127P (1979). 6. J. Feigenbaum, B. Moon, H. Klawans, in Neuro-Psychopharmacology, B. Saletu, P. Berner, L. Hollister, Eds, (Pergamon, New York, 1979), p. 541; P. M. Adams, R. Beauchamp, C. Alston, Life Sci. 28, 629 (1981). 7. S. M. Antelman, A. J. Eichler, C. A. Black, D. Kocan, Science 207, 329 (1980). 8. D. E. McMillan, Psychopharmacologia 19, 128 (1971). 9. Haloperidol (0.2 mg/kg) was injected intraperitoneally I hour before the start offour 2-minute TP trials, and naloxone (10 mg/kg, subcutaneously) was given 15 minutes before the test (N = 8 to 9 per group). A positive trial was defined as more than 10 seconds of eating or gnawing. As before, rats injected with naloxone alone showed TP behavior on 97 percent of the trials. Rats given haloperidol showed oral behaviors on 84 percent of the trials, while those receiving both haloperidol and naloxone ate on only 55 percent of the trials (P < .05 compared to haloperidol; P < .005 compared to naloxone). The amounts consumed closely paralleled the trials data. 10. J. C. Schwartz et al., Adv. Biochem. Psychopharmacol. 18, 245 (1978). II. J. Sawynok, C. Pinsky, F. S. LaBella, Life Sci. 25, 1621 (1979). 12. We used less total time of TP than Morley and Levine: five 2-minute trials per day for 10 days, including subgroups with and without food present during TP. Additional rats were made dependent on morphine (two daily injections of 10 to 30 mg/kg for I week). On the test day, rats received saline, and were observed for 15 minutes, then were given naloxone subcutaneously (I mg/kg), and observed for another 15 minutes. Not one truly vigorous withdrawal response (as opposed to normal "twitching") was recorded in any of the TP rats in either period. 13. Morley and Levine cite Antelman et al. [reference 5 in (2)] as evidence for a parallel between TP and schizophrenia, yet we later specifically pointed out the differences [Antelman and Caggiula in (1)]. 14. Morley and Levine report that diazepam did not decrease TP eating, yet do not refer to any one of three previous descriptions of facilitation of TP eating after anxiolytics [S. M. Antelman, N. E. Rowland, A. E. Fisher, Physiol. Behav. 17, 743 (1976); T. W. Robbins, A. G. Phillips, B. J. Sahakian, Pharmacol. Biochem. Behav. 6, 297 (1977); M. B. Wallach, M. Dawber, C. McMahon, C. Rogers, ibid., p. 529]. The data from their experiments with diazepam, cholecystokinin, and haloperidol (none of which are new) are given in their table 1, yet this table is cited only once in their text in relation to a saline-injected group. Their text also reads as if we (1) used the high dose of 2.5 mg/kg haloperidol; this is at least six times the highest dose that we typically use. 15. Supported by NIH grants MH32306 and RSDA00238 (S.M.A.) and AM26231 (N.R.). We thank Donna Kocan for help with the experiments.