Article Figures & Data
Figures
- Figure 1.
Reactions to pain were suppressed during chocolate eating and ingestion of water and preferred fluids delivered intraorally. A, Withdrawal latencies (±SEM) were greater during chocolate eating (Choc) and infusion (Inf) of fluids in groups receiving water (W), sucrose (Suc), or saccharin (Sac) than during quiet wake (Qw). Salt and quinine (Q) infusions had no effect on withdrawal latencies, although chocolate-eating analgesia was present in the same animals (*p < 0.05 relative to Qw; †p < 0.05 relative to Inf; repeated-measures ANOVA followed by post hoc tests). B, A representative rat withdrew (PW), marked by an increase in EMG activity in the right biceps femoris, at a longer latency during chocolate eating (Chocolate; bottom) than during quiet wake (QW; top). Heat was applied in both conditions as marked by the line in the top. C, A representative rat withdrew (PW) at similar latencies during quiet wake (QW) and quinine infusion (Quinine). Conventions of B apply. D, E, The EMG patterns of anterior digastric muscle activity during ingestion of water (D) and rejection [gaping (G)] of quinine (E) were distinct.
- Figure 2.
Suppression of heat-evoked paw withdrawals (PW) during ingestion was attenuated by nausea, illness, and conditioned taste avoidance. A, Rats withdrew at longer latencies (±SEM) while eating chocolate (Choc) than during quiet wake (Qw). Previous infusions had no effect on withdrawal latency during chocolate eating (Choc Post-inf) for animals receiving water (Water) or salt (Salt). However, when animals ate chocolate after quinine (Quinine), a nauseating substance, withdrawal latencies were not different from those during chocolate eating without a preceding infusion or those during quiet wake. B, Saline-injected rats (Sal) withdrew at longer latencies during chocolate (Choc) or water ingestion than during quiet wake, 2–4 h after injection. In contrast, LPS-injected rats (LPS) withdrew at longer latencies only during water ingestion, withdrawing at similar latencies during chocolate eating and quiet wake. C, Exposure to a cue previously paired with illness disengaged ingestion analgesia. Unpaired rats (UP) showed analgesia during chocolate and water ingestion and a partial analgesia during sucrose ingestion: withdrawal latencies during sucrose ingestion (Suc) were intermediate between chocolate/water ingestion and quiet wake (Qw). Paired rats (P) showed ingestion analgesia to chocolate and water ingestion but not to sucrose, withdrawing at similar latencies during sucrose infusion and quiet wake. *p < 0.05 relative to Qw; †p < 0.05 relative to without a preceding infusion (A), chocolate eating (B), or sucrose infusion (C); repeated-measures ANOVA followed by post hoc tests.
- Figure 3.
Paw licks (PL) were suppressed during chocolate eating but not during intraoral infusions. A, Rats typically licked their heated paw during quiet wake but not when eating chocolate. During intraoral infusions of both palatable and unpalatable substances, rats licked their paws in response to a noxious heat stimulus. B–D, When eating chocolate during quinine-induced nausea (B), LPS illness (C), or conditioned taste aversion to sucrose (D), rats seldom licked their paw. Percentage of trials is outside the 95% confidence intervals for quiet wake (Qw; *) and infusion (Inf; †). Conventions as in Figures 1 and 2.
- Figure 4.
RM mediates the suppression of withdrawals associated with ingestion of intraorally infused water. A, After saline (Sal) microinjection into RM, rats withdrew at longer latencies (±SEM) during infusion (Inf) of water (Water) than during quiet wake (Qw). However, after muscimol (Mus) microinjection, the withdrawal latencies during water infusion and quiet wake were not different. Microinjection had no effect on withdrawal latencies during infusion of salt relative to during quiet wake. B, All microinjections were made into RM on the midline.
Tables
Total occurrencesof eating chow Total number ofchips retrieved (offered) Chips dropped(unretrieved) Average ± SEMchips eaten Total of offeredeaten (% eaten) Experiment 1: infusate Water (n = 16) 1.0 46.5 (46.5) 5.0 2.9 ± 0.2 Sucrose (n = 15) 1.0 43.0 (43.0) 1.0 2.9 ± 0.2 Saccharin (n = 12) 2.0 33.0 (33.0) 1.0 2.8 ± 0.3 Salt (n = 12) 0.0 35.0 (35.0) 1.0 2.9 ± 0.2 Quinine (n = 13) 1.0 38.5 (38.5) 3.0 3.0 ± 0.2 196.0 (100%) Experiment 2: nausea Water (n = 14) 2.0 71.5 (71.5) 3.0 5.1 ± 0.1 Salt (n = 16) 1.0 81.0 (81.0) 2.0 5.1 ± 0.1 Quinine (n = 16) 1.0 82.5 (82.5) 13.0 5.2 ± 0.2 235.0 (100%) Experiment 3: LPS LPS (n = 19) 2.0 162.0 (177.0) (15.0) 8.5 ± 0.8 162.0 (91.5%) Saline (n = 14) 6.0 141.0 (141.0) 0.0 10.1 ± 0.5 141.0 (100%) 303.0 (95.3%) Experiment 4: CTA Paired (conditioning, n = 19) 1.0 49.5 (49.5) 2.0 2.9 ± 0.2 Unpaired (conditioning, n = 14) 1.0 420.0 (42.0) 0.0 3.0 ± 0.1 Paired (test, n = 19) 4.0 46.0 (46.0) 0.0 2.7 ± 0.2 Unpaired (test, n = 14) 4.0 41.0 (41.0) 0.0 2.9 ± 0.1 178.5 (100%) Grand total 27.0 912.5 (927.5) 31.0 (15.0) 912.5 (98.4%) -
During testing, rats ate freely available chow infrequently but ate almost every chip offered. There were no significant differences in the number of chips eaten between groups in any of the experiments. Chips were dropped very rarely (chips dropped), but, when this occurred, rats always picked the chip back up and resumed eating. Although some LPS-injected rats were hypophagic (unretrieved), they still retrieved and ate >90% of chips offered. CTA, Conditioned taste aversion.
-
