Showing papers by "Harvey J. Grill published in 1988"

Cholecystokinin decreases sucrose intake in chronic decerebrate rats

Abstract: The capacity of chronic decerebrate rats to reduce their intake of an orally infused sucrose solution in response to peripherally administered cholecystokinin octapeptide (CCK-8) was investigated. The sucrose intake of both 24-h food-deprived chronic decerebrate rats and pair-fed control rats was reduced by CCK-8 relative to the intake after desulfated CCK-8. The intake-reducing effect of CCK-8 in the chronic decerebrate rat provides compelling evidence that the caudal brain stem is of sufficient neural complexity to mediate this response. Although others have hypothesized that connections between the caudal brain stem and forebrain are required to mediate this effect(s) of CCK-8, our results demonstrate that these pathways are not necessary.

Taste reactivity as a dependent measure of the rapid formation of conditioned taste aversion: a tool for the neural analysis of taste-visceral associations.

Abstract: Several explanations may account for deficits in the ability of animals to form taste aversions following neural manipulations. These encompass impairments in conditioned stimulus (CS) and unconditioned stimulus (US) processing, conditioned response (CR) measurement, and expression, memory, and taste-visceral integration. A behavioral procedure that aids in the distinction between some of these possibilities is presented. In Experiment 1, 10 rats received seven intraoral (IO) infusions of sucrose (30 s, 0.55 ml) spaced every 5 min starting immediately after the injection of 3.0 mEq/kg of lithium chloride (LiCl). Control rats (n = 12) were treated identically except that they were injected with sodium chloride (NaCl). Oromotor and somatic taste reactivity behaviors were videotaped and analyzed. Lithium-injected rats systematically decreased their ingestive taste reactivity behavior over time, whereas aversive behavior increased. Control rats maintained high and stable levels of ingestive responding and demonstrated virtually no aversive behavior over the 30-min period following sodium injection. Rats were tested several days later for the presence of a conditioned taste aversion (CTA). Rats previously injected with lithium during sucrose infusions demonstrated significantly more aversive behavior than the control group, which demonstrated none. There were no differences in the level of ingestive behavior displayed by the two groups on the CTA test. Experiment 3 revealed that when similarly treated rats were tested for a CTA while in a lithium-induced state, a difference in the ingestive behavior between the two groups was observed. In Experiment 2, naive rats were injected with either NaCl or LiCl but did not receive their first sucrose infusion until 20 min later. These rats also received sucrose infusions at 25 and 30 min postinjection. There were no differences in the taste reactivity behavior displayed by lithium- or sodium-injected rats during any of the sucrose infusions. Collectively, these findings indicate that rats dramatically change their oromotor responses to sucrose during the period following LiCl administration, provided that the infusions start immediately after injection. Furthermore, this time-related behavioral change is predominantly attributable to associative processes. This paradigm can be useful in distinguishing between neural manipulations that affect the establishment of taste-visceral associations from others that affect the animal's ability to retain such associations over the commonly employed 24-hr conditioning-test interval.

Intraoral intake and taste reactivity responses elicited by sucrose and sodium chloride in chronic decerebrate rats.

Abstract: The oral stimulating effects of sucrose and sodium chloride (NaCl) were assessed in chronic decerebrate and pair-fed intact control rats by measuring both oral motor taste-reactivity responses and intraoral intake volume. Taste-reactivity responses were videotaped during the first minute of the intraoral taste infusion. The infusion continued until the taste solution was rejected from the mouth, and the intake volume was computed accordingly. The number of ingestive taste-reactivity responses and the volume of intraoral intake consumed by pair-fed control and decerebrate rats increased with increasing sucrose concentration. Sucrose intake increased as concentration increased to 0.1 M, then plateaued between 0.3, 1.3, and 2.0 M sucrose for both groups. For control rats, intraoral NaCl elicited an inverted U-shaped function for both taste-reactivity responses and intake. Taste-reactivity responses of chronic decerebrate rats varied with NaCl concentration. In contrast to control rats, intake of NaCl did not differ from that of water for decerebrate rats. These data indicate that caudal brain-stem mechanisms are sufficient to control sucrose intake but are not adequate for the concentration dependent intake of NaCl. Second, these data also indicate that it is possible for taste-elicited oral motor responses to be dissociated from intake. The different roles of taste and postingestive factors in sucrose and NaCl intake are discussed.

Strain differences in taste reactivity to NaCl

Abstract: The taste reactivity test was used to determine whether strain differences in response to NaCl revealed by preference tests were attributable to taste or postoral factors. Taste reactivity data revealed significant differences between sodium-replete Fischer 344 (F-344) and Wistar strains in response to NaCl for both aversive and ingestive oral motor behaviors. Because the taste reactivity test analyzed the immediate response to orally applied chemical stimuli, these data support a strain difference based on taste factors. Taste reactivity data also indicate strain differences in ingestive but not aversive scores to other normally ingested chemical stimuli, water, and two sucrose concentrations. In response to normally avoided quinine, F-344 and Wistar strains did not differ in either ingestive or aversive score. To investigate whether strain differences revealed when rats were tested while sodium replete would persist in the sodium-deficient state, both strains were treated with the diuretic furosemide. Taste reactivity tests revealed that in response to sodium deficiency both F-344 and Wistar strains shift their oral motor response profile to NaCl; strains did not differ in either ingestive or aversive score when sodium deficient. NaCl intake and preference measures also support the fact that both strains demonstrate a sodium appetite. Interpretive limitations based on ceiling and floor effects within taste reactivity and preference data were discussed.

Comparison of the interoceptive sensory consequences of CCK, LiCl, and satiety in rats.

Abstract: In three experiments we assessed the degree to which ad lib feeding, injection of cholecystokinin (CCK), and injection of lithium chloride (LiCl) produce states with similar sensory consequences. In each experiment, two groups of rats were trained to use cues arising from food deprivation and satiation as discriminative signals for shock. One group was shocked when deprived but not when nondeprived. The other group received the reversed discrimination. Testing began when incidence of freezing was greater under the shocked deprivation than under the nonshocked deprivation condition. In Experiment 1, the rats were tested under 24-hr food deprivation after injections of CCK, LiCl, and saline (in counterbalanced order). We reasoned that if either CCK or LiCl induce satiety-like states, they should promote patterns of responding different from those produced by saline but similar to those produced by ad lib feeding. The effects of CCK on freezing did not differ from those of saline, whereas both CCK and LiCl had effects that were different from ad lib feeding. This pattern of results was also obtained when deprivation level during training and testing was reduced to 8 hr (Experiment 1A) and also when rats received small amounts of food in conjunction with CCK (Experiment 2). The intubation of a high-calorie stomach load (Experiment 1A) produced a response profile like that observed after free feeding. Freezing after LiCl treatment differed from that observed after free feeding and from that found after injection of CCK. The results indicate that rats can differentiate between the sensory consequences of the states produced by CCK, by LiCl, and by ad lib feeding.

Effects of concentration presentation order and intraoral delivery on sucrose intake.

Abstract: In this article, intraoral intake of an ascending concentration series of sucrose was found to plateau between concentrations of 0.3 M and 2.0 M, and thus failed to show the typical inverted U-shaped intake function found in standard intake tests. Two experiments were conducted to explain this result. In Experiment 1, intraoral and standard 30-min, 1-bottle intake of ascending sucrose concentrations (0.03, 0.1, 0.3, 1.0, 1.3, and 2.0 M) were compared. Sucrose intake was similar for both delivery methods. In a second experiment we examined the effect of the order of sucrose concentration presentation on the 1-bottle 30-min intake of nondeprived intact rats. An ascending concentration order of the solutions produced a significantly greater intake of concentrated sucrose solutions than did a random order. This result strongly suggests that the standard decline in sucrose intake at higher concentrations is determined not only by postoral factors but also by experiential factors (i.e., order of presentation).